Elements of success in cooperatives conformed by Maya women in the Yucatan Peninsula, Mexico

Directory of Open Access Journals (Sweden)

Maria Cristina Osorio Vázquez

2016-05-01

Full Text Available This paper describes different elements leading to the success of cooperatives formed by indigenous Maya women of the Yucatan Peninsula in Mexico. These elements have shown to facilitate the sustainability (permanence over time of the cooperatives and their presence in the market, while improving the work environment and enhancing the practice of honesty. All these elements have generated an increase in the number of clients and beneficiaries due to their trustable relationships. As can be appreciated in this study, indigenous Maya women living in the Yucatan Peninsula are demonstrating an innovative way to do business, which has resulted in greater social benefits and profitability through social capital, ethical leadership and monitoring of actions.

Modeling carbon stocks in a secondary tropical dry forest in the Yucatan Peninsula, Mexico

Science.gov (United States)

Zhaohua Dai; Richard A. Birdsey; Kristofer D. Johnson; Juan Manuel Dupuy; Jose Luis Hernandez-Stefanoni; Karen. Richardson

2014-01-01

The carbon balance of secondary dry tropical forests of Mexico’s Yucatan Peninsula is sensitive to human and natural disturbances and climate change. The spatially explicit process model Forest-DeNitrification-DeComposition (DNDC) was used to estimate forest carbon dynamics in this region, including the effects of disturbance on carbon stocks. Model evaluation using...

Local evolution of pyrethroid resistance offsets gene flow among Aedes aegypti collections in Yucatan State, Mexico.

Science.gov (United States)

Saavedra-Rodriguez, Karla; Beaty, Meaghan; Lozano-Fuentes, Saul; Denham, Steven; Garcia-Rejon, Julian; Reyes-Solis, Guadalupe; Machain-Williams, Carlos; Loroño-Pino, Maria Alba; Flores-Suarez, Adriana; Ponce-Garcia, Gustavo; Beaty, Barry; Eisen, Lars; Black, William C

2015-01-01

The mosquito Aedes aegypti is the major vector of the four serotypes of dengue virus (DENV1-4). Previous studies have shown that Ae. aegypti in Mexico have a high effective migration rate and that gene flow occurs among populations that are up to 150 km apart. Since 2000, pyrethroids have been widely used for suppression of Ae. aegypti in cities in Mexico. In Yucatan State in particular, pyrethroids have been applied in and around dengue case households creating an opportunity for local selection and evolution of resistance. Herein, we test for evidence of local adaptation by comparing patterns of variation among 27 Ae. aegypti collections at 13 single nucleotide polymorphisms (SNPs): two in the voltage-gated sodium channel gene para known to confer knockdown resistance, three in detoxification genes previously associated with pyrethroid resistance, and eight in putatively neutral loci. The SNPs in para varied greatly in frequency among collections, whereas SNPs at the remaining 11 loci showed little variation supporting previous evidence for extensive local gene flow. Among Ae. aegypti in Yucatan State, Mexico, local adaptation to pyrethroids appears to offset the homogenizing effects of gene flow. © The American Society of Tropical Medicine and Hygiene.

Contaminants in the coastal karst aquifer system along the Caribbean coast of the Yucatan Peninsula, Mexico

International Nuclear Information System (INIS)

Metcalfe, Chris D.; Beddows, Patricia A.; Bouchot, Gerardo Gold; Metcalfe, Tracy L.; Li Hongxia; Van Lavieren, Hanneke

2011-01-01

Intensive land development as a result of the rapidly growing tourism industry in the 'Riviera Maya' region of the Yucatan Peninsula, Mexico may result in contamination of groundwater resources that eventually discharge into Caribbean coastal ecosystems. We deployed two types of passive sampling devices into groundwater flowing through cave systems below two communities to evaluate concentrations of contaminants and to indicate the possible sources. Pharmaceuticals and personal care products accumulated in the samplers could only have originated from domestic sewage. PAHs indicated contamination by runoff from highways and other impermeable surfaces and chlorophenoxy herbicides accumulated in samplers deployed near a golf course indicated that pesticide applications to turf are a source of contamination. Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health, thus damaging the tourism-based economy of the region. - Research highlights: → Intensive land development as a result of the rapidly growing tourism industry in the 'Riviera Maya' region of the Yucatan Peninsula, Mexico is contaminating groundwater resources that discharge into Caribbean coastal ecosystems. → Passive sampling devices deployed in groundwater flowing through cave systems below two communities in the Riviera Maya accumulated: pharmaceuticals and personal care products originating from domestic sewage. → PAHs originating from runoff from highways and other impermeable surfaces; chlorophenoxy herbicides originating from pesticide applications to lawns and turf. → Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health in the region. - Contaminants accumulated in passive samplers deployed in flooded cave systems in the Yucatan Peninsula in Mexico indicate contamination by domestic sewage, runoff and applications of pesticides

Contaminants in the coastal karst aquifer system along the Caribbean coast of the Yucatan Peninsula, Mexico

Energy Technology Data Exchange (ETDEWEB)

Metcalfe, Chris D., E-mail: cmetcalfe@trentu.ca [Worsfold Water Quality Centre, Trent University, Peterborough, ON, K9J 7B8 (Canada); Beddows, Patricia A. [Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL (United States); Bouchot, Gerardo Gold [Departemento de Recursos del Mar, CINVESTAV Unidad Merida, Yucatan (Mexico); Metcalfe, Tracy L.; Li Hongxia [Worsfold Water Quality Centre, Trent University, Peterborough, ON, K9J 7B8 (Canada); Van Lavieren, Hanneke [UN University Institute for Water, Environment and Health (UNU-INWEH), Hamilton, ON (Canada)

2011-04-15

Intensive land development as a result of the rapidly growing tourism industry in the 'Riviera Maya' region of the Yucatan Peninsula, Mexico may result in contamination of groundwater resources that eventually discharge into Caribbean coastal ecosystems. We deployed two types of passive sampling devices into groundwater flowing through cave systems below two communities to evaluate concentrations of contaminants and to indicate the possible sources. Pharmaceuticals and personal care products accumulated in the samplers could only have originated from domestic sewage. PAHs indicated contamination by runoff from highways and other impermeable surfaces and chlorophenoxy herbicides accumulated in samplers deployed near a golf course indicated that pesticide applications to turf are a source of contamination. Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health, thus damaging the tourism-based economy of the region. - Research highlights: > Intensive land development as a result of the rapidly growing tourism industry in the 'Riviera Maya' region of the Yucatan Peninsula, Mexico is contaminating groundwater resources that discharge into Caribbean coastal ecosystems. > Passive sampling devices deployed in groundwater flowing through cave systems below two communities in the Riviera Maya accumulated: pharmaceuticals and personal care products originating from domestic sewage. > PAHs originating from runoff from highways and other impermeable surfaces; chlorophenoxy herbicides originating from pesticide applications to lawns and turf. > Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health in the region. - Contaminants accumulated in passive samplers deployed in flooded cave systems in the Yucatan Peninsula in Mexico indicate contamination by domestic sewage, runoff and applications of

CONTRIBUTION TO THE KNOWLEDGE OF THE ARACHNIDS IN THE YUCATAN PENINSULA, MEXICO (EXCLUDING ARANAE AND ACARI

Directory of Open Access Journals (Sweden)

Hugo Delfin Gonzalez

2017-08-01

Full Text Available The Chelicerata are the second group of arthropods with the highest diversity after insects and they can inhabit almost all types of environments. The most current classification recognizes 11 orders and estimates in the number of species vary from 52,000 to 100,000. We have made an extensive literature review on the diversity of arachnids in the Yucatan Peninsula (YP (excluding spiders and ticks. In Mexico there are 834 known species which represent 6% of the worldwide diversity. In the YP 63 records were found (58 species and 5 genera of arachnids, which represent 6.8% of the Mexican species. According to our research, 28 of the 58 species (48% in the YP were also record in other parts of Mexico, the continent and the world. Undoubtedly, the state of Yucatan is the best represented of the YP. In order to have a better understanding of the diversity of arachnid species is important to promote biological compendiums and sampling programs, which will improve the representation of this group and probably increasing the number of local species.

Validation of an indirect ELISA for the diagnosis of Babesia bovis in cattle in Yucatan, Mexico

International Nuclear Information System (INIS)

Dominguez, A.J.L.; Rodriguez, V.R.I.; Oura, C.; Cob, G.L.A.

1998-01-01

The ELISA kit provided by the FAO/IAEA for the diagnosis of Babesia bovis was validated. In order to determine the appropriate ELISA cut-off point that would serve as the threshold between positive and negative samples, 119 serum samples from a Mexican Babesia-free zone were analyzed. The optimal cut-off point chosen was at 12% of the reactivity of the high positive control serum sample (PP) which resulted in a specificity of 97%. One hundred and ninety-six cattle from Wisconsin, USA, were introduced into Yucatan, Mexico, of which 181 were vaccinated with an attenuated live Babesia bovis vaccine; 15 animals remained as unvaccinated controls. Before and after vaccination all animals were bled and tested by enzyme linked immunosorbent assay (ELISA) and indirect fluorescence antibody test (IFAT). Both tests showed a high degree of correlation in their results. To evaluate an immune response to vaccination the optimal cut-off point chosen was 12% PP resulting in a sensitivity 99% and a specificity 95%. We concluded that the ELISA test has proved to be useful in Yucatan, Mexico for serological surveys and monitoring the efficiency o vaccination programmes. (author)

Shaded Relief with Height as Color and Landsat, Yucatan Peninsula, Mexico

Science.gov (United States)

2003-01-01

The top picture is a shaded relief image of the northwest corner of Mexico's Yucatan Peninsula generated from Shuttle Radar Topography Mission (SRTM) data, and shows a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life on Earth. The pattern of the crater's rim is marked by a trough, the darker green semicircular line near the center of the picture. This trough is only about 3 to 5 meters (10 - 15 feet) deep and is about 5 km (3 miles) wide; so subtle that if you walked across it you probably would not notice it. It is the surface expression of the buried crater's outer boundary. Scientists believe the impact, which was centered just off the coast in the Caribbean, altered the subsurface rocks such that the overlying limestone sediments, which formed later and erode very easily, would preferentially erode along the crater rim. This formed the trough as well as numerous sinkholes (called cenotes) which are visible as small circular depressions.The bottom picture is the same area viewed by the Landsat satellite, and was made by displaying the Thematic Mapper's Band 7 (mid-infrared), Band 4 (near-infrared) and Band 2 (green) as red, green and blue. These colors were chosen to maximize the contrast between different vegetation and land cover types, with native vegetation and cultivated land showing as green, yellow and magenta, and urban areas as white. The circular white area near the center of the image is Merida, a city of about 720,000 population. Notice that in the SRTM image, which shows only topography, the city is not visible, while in the Landsat image, which does not show elevations, the trough is not visible.Two visualization methods were combined to produce the SRTM image: shading and color coding of topographic height. The shade

Tuluweckelia cernua, a new genus and species of stygobiont amphipod crustacean (Hadziidae) from anchialine caves on the Yucatan Peninsula in Mexico

NARCIS (Netherlands)

Holsinger, John R.

1990-01-01

Tuluweckelia cernua, a new genus and species of stygobiont amphipod is described from six anchialine caves near the northeastern coast of the state of Quintana Roo on the Yucatan Peninsula in Mexico. The new genus is closely allied morphologically with Mayaweckelia Holsinger, which is also recorded

Regional-scale airborne electromagnetic surveying of the Yucatan karst aquifer (Mexico): geological and hydrogeological interpretation

DEFF Research Database (Denmark)

Gondwe, Bibi Ruth Neuman; Ottowitz, David; Supper, Robert

2012-01-01

-spectral remote sensing imagery, shuttle radar topography data and frequency-domain airborne electromagnetic (AEM) survey data were used to map karst-aquifer structure on the Yucatan Peninsula, Mexico. Anomalous AEM responses correlated with topographic features and anomalous spectral reflectance of the terrain...... as ejecta from the Chicxulub impact (Cretaceous/Paleogene boundary), based on similar resistivity signatures found in borehole logs. Due to limited sensitivity of the AEM survey, the subsurface configuration beneath the low-resistivity layer could not be unambiguously determined. AEM measurements combined...

PES Impact and Leakages over Several Cohorts: The Case of PSA-H in Yucatan, Mexico

OpenAIRE

LE VELLY , Gwenole; Sauquet , Alexandre; CORTINA-VILLAR , Sergio

2015-01-01

We assess the impact of a payment for environmental services scheme implemented in Mexico, the PSA-H, over the 2005-2012 period. By studying several cohorts of program beneficiaries we are able to shed lights on the permanence of the program's impact. Based on the exploitation of 2.5 to 20m resolution SPOT images and ejido-surveys carried out in 76 ejidos located in the Cono Sur of Yucatan, we find that the program's effects are cancelled after communities choose to withdraw from the program,...

Detection of different Leishmania spp. and Trypanosoma cruzi antibodies in cats from the Yucatan Peninsula (Mexico) using an iron superoxide dismutase excreted as antigen.

Science.gov (United States)

Longoni, Silvia S; López-Cespedes, Angeles; Sánchez-Moreno, Manuel; Bolio-Gonzalez, Manuel E; Sauri-Arceo, Carlos H; Rodríguez-Vivas, Roger I; Marín, Clotilde

2012-09-01

Although human leishmaniasis has been reported in 20 states in Mexico, no case of leishmaniasis has been reported in cats to date. In the Yucatan Peninsula, it has been found that dogs may act as reservoirs for at least three Leishmania species (Leishmania mexicana, Leishmania braziliensis, and Leishmania panamensis). In this study we identified specific antibodies against these three Leishmania spp. and Trypanosoma cruzi in the sera from 95 cats from two States on the Yucatan Peninsula, namely Quintana Roo and Yucatan, by ELISA and Western blot techniques using whole extract and an iron superoxide dismutase excreted by the parasites as antigens. As well as demonstrating the presence of trypanosomatid antibodies in the feline population on the Yucatan Peninsula, we were also able to confirm the high sensitivity and specificity of the iron superoxide dismutase antigen secreted by them, which may prove to be very useful in epidemiological studies. Copyright © 2012 Elsevier Ltd. All rights reserved.

Impact ejecta and carbonate sequence in the eastern sector of the Chicxulub crater

Science.gov (United States)

Urrutia-Fucugauchi, Jaime; Chavez-Aguirre, Jose Maria; Pérez-Cruz, Ligia; De la Rosa, Jose Luis

2008-12-01

The Chicxulub 200 km diameter crater located in the Yucatan platform of the Gulf of Mexico formed 65 Myr ago and has since been covered by Tertiary post-impact carbonates. The sediment cover and absence of significant volcanic and tectonic activity in the carbonate platform have protected the crater from erosion and deformation, making Chicxulub the only large multi-ring crater in which ejecta is well preserved. Ejecta deposits have been studied by drilling/coring in the southern crater sector and at outcrops in Belize, Quintana Roo and Campeche; little information is available from other sectors. Here, we report on the drilling/coring of a section of ˜34 m of carbonate breccias at 250 m depth in the Valladolid area (120 km away from crater center), which are interpreted as Chicxulub proximal ejecta deposits. The Valladolid breccias correlate with the carbonate breccias cored in the Peto and Tekax boreholes to the south and at similar radial distance. This constitutes the first report of breccias in the eastern sector close to the crater rim. Thickness of the Valladolid breccias is less than that at the other sites, which may indicate erosion of the ejecta deposits before reestablishment of carbonate deposition. The region east of the crater rim appears different from regions to the south and west, characterized by high density and scattered distribution of sinkholes.

CONTRIBUTION TO THE KNOWLEDGE OF THE ARACHNIDS IN THE YUCATAN PENINSULA, MEXICO (EXCLUDING ARANAE AND ACARI)

OpenAIRE

Hugo Delfin Gonzalez; Virginia Meléndez-Ramírez; Pablo C. Manrique-Saide; Abdiel Martin-Park; Carlos Arisqueta-Chablé

2017-01-01

The Chelicerata are the second group of arthropods with the highest diversity after insects and they can inhabit almost all types of environments. The most current classification recognizes 11 orders and estimates in the number of species vary from 52,000 to 100,000. We have made an extensive literature review on the diversity of arachnids in the Yucatan Peninsula (YP) (excluding spiders and ticks). In Mexico there are 834 known species which represent 6% of the worldwide diversity. In the YP...

Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

Science.gov (United States)

Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

1995-09-01

Differing interpretations of the Bouguer gravity anomaly over the Chicxulub crater, Yucatan Peninsula, Mexico, have yielded diameter estimates of 170 to 320 km. Knowing the crater's size is necessary to quantify the lethal perturbations to the Cretaceous environment associated with its formation. The crater's size (and internal structure) is revealed by the horizontal gradient of the Bouguer gravity anomaly over the structure, and by mapping the karst features of the Yucatan region. To improve our resolution of the crater's gravity signature we collected additional gravity measurements primarily along radial profiles, but also to fill in previously unsurveyed areas. Horizontal gradient analysis of Bouguer gravity data objectively highlights the lateral density contrasts of the impact lithologies and suppresses regional anomalies which may obscure the gravity signature of the Chicxulub crater lithologies. This gradient technique yields a striking circular structure with at least 6 concentric gradient features between 25 and 85 km radius. These features are most distinct in the southwest probably because of denser sampling of the gravity field. Our detailed profiles detected an additional feature and steeper gradients (up to 5 mGal/km) than the original survey. We interpret the outer four gradient maxima to represent concentric faults in the crater's zone of slumping as is also revealed by seismic reflection data. The inner two probably represent the margin of the central uplift and the peak ring and or collapsed transient cavity. Radial gradients in the SW quadrant over the inferred ~40 km-diameter central uplift (4) may represent structural "puckering" as revealed at eroded terrestrial craters. Gradient features related to regional gravity highs and lows are visible outside the crater, but no concentric gradient features are apparent at distances > 90 km radius. The marginal gradient features may be modelled by slump faults as observed in large complex craters on

Antibodies to West Nile virus in asymptomatic mammals, birds, and reptiles in the Yucatan Peninsula of Mexico.

Science.gov (United States)

Farfán-Ale, José A; Blitvich, Bradley J; Marlenee, Nicole L; Loroño-Pino, María A; Puerto-Manzano, Fernando; García-Rejón, Julián E; Rosado-Paredes, Elsy P; Flores-Flores, Luis F; Ortega-Salazar, Andres; Chávez-Medina, Jaidy; Cremieux-Grimaldi, Juan C; Correa-Morales, Favián; Hernández-Gaona, Gerson; Méndez-Galván, Jorge F; Beaty, Barry J

2006-05-01

Surveillance for evidence of West Nile virus (WNV) infection in taxonomically diverse vertebrates was conducted in the Yucatan Peninsula of Mexico in 2003 and 2004. Sera from 144 horses on Cozumel Island, Quintana Roo State, 415 vertebrates (257 birds, 52 mammals, and 106 reptiles) belonging to 61 species from the Merida Zoo, Yucatan State, and 7 farmed crocodiles in Ciudad del Carmen, Campeche State were assayed for antibodies to flaviviruses. Ninety (62%) horses on Cozumel Island had epitope-blocking enzyme-linked immunosorbent assay (ELISA) antibodies to flaviviruses, of which 75 (52%) were seropositive for WNV by plaque reduction neutralization test (PRNT). Blocking ELISA antibodies to flaviviruses also were detected in 13 (3%) animals in the Merida Zoo, including 7 birds and 2 mammals (a jaguar and coyote) seropositive for WNV by PRNT. Six (86%) crocodiles in Campeche State had PRNT-confirmed WNV infections. All animals were healthy at the time of serum collections and none had a history of WNV-like illness.

Monogeneans of freshwater fishes from cenotes (sinkholes) of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Mendoza-Franco, E F; Scholz, T; Vivas-Rodríguez, C; Vargas-Vázquez, J

1999-01-01

During a survey of the parasites of freshwater fishes from cenotes (sinkholes) of the Yucatan Peninsula the following species of monogeneans were found on cichlid, pimelodid, characid and poeciliid fishes: Sciadicleithrum mexicanum Kritsky, Vidal-Martinez et Rodriguez-Canul, 1994 from Cichlasoma urophthalmus (Günther) (type host), Cichlasoma friedrichsthali (Heckel), Cichlasoma octofasciatum (Regan), and Cichlasoma synspilum Hubbs, all new host records; Sciadicleithrum meekii Mendoza-Franco, Scholz et Vidal-Martínez, 1997 from Cichlasoma meeki (Brind); Urocleidoides chavarriai (Price, 1938) and Urocleidoides travassosi (Price, 1938) from Rhamdia guatemalensis (Günther); Urocleidoides costaricensis (Price et Bussing, 1967), Urocleidoides heteroancistrium (Price et Bussing, 1968), Urocleidoides anops Kritsky et Thatcher, 1974, Anacanthocotyle anacanthocotyle Kritsky et Fritts, 1970, and Gyrodactylus neotropicalis Kritsky et Fritts, 1970 from Astyanax fasciatus; and Gyrodactylus sp. from Gambusia yucatana Regan. Urocleidoides chavarriai, U. travassosi, U. costaricensis, U. heteroancistrium, U. anops, Anacanthocotyle anacanthocotyle and Gyrodactylus neotropicalis are reported from North America (Mexico) for the first time. These findings support the idea about the dispersion of freshwater fishes and their monogenean parasites from South America through Central America to southeastern Mexico, following the emergence of the Panamanian isthmus between 2 and 5 million years ago.

Seasonal abundance of crustaceans associated with artisanal fishery of blue crab (Callinectes sapidus) in Sisal, Yucatan, Mexico

OpenAIRE

Celis-Sánchez, José Alfredo; Estrella-Canto, Arely de Jesús; Poot-López, Gaspar Román; González-Salas, Carlos; López-Rocha, Jorge Alberto

2014-01-01

Seasonal abundance and selectivity of the main crustacean species associated with blue crab fishing was studied at the port of Sisal, Yucatan, Mexico. For this purpose, 52 crab traps were used, which were divided into four parallel transects placed 100, 150, 200 and 250 m of the shoreline. Each transect consisted of 13 traps 20 m from each other. Traps were set at dusk and checked at dawn, standardizing the fishing effort to 17 hours/trap/day. A total of 832 organisms from eight species were ...

An epidemiological study of intestinal parasites of dogs from Yucatan, Mexico, and their risk to public health.

Science.gov (United States)

Rodríguez-Vivas, Roger Ivan; Gutierrez-Ruiz, Edwin; Bolio-González, Manuel Emilio; Ruiz-Piña, Hugo; Ortega-Pacheco, Antonio; Reyes-Novelo, Enrique; Manrique-Saide, Pablo; Aranda-Cirerol, Francisco; Lugo-Perez, J A

2011-08-01

The prevalence of intestinal parasites in dogs and factors associated were studied in a rural community of Yucatan (southern Mexico), with special attention to those gastrointestinal parasites potentially transmitted to man. One hundred thirty dogs from 91 households were studied. Fecal samples were processed by the centrifugation-flotation and the McMaster techniques. To determine factors associated with zoonotic parasites in dogs, univariate analysis was performed, using sex, age, and body condition as independent variables. Variables with p caninum, Thichuris vulpis, Toxocara canis, and Dipylidium caninum) and coccidian oocysts were detected. A. caninum was the most prevalent parasite (73.8%), followed by T. vulpis (25.4%), T. canis (6.2%), D. caninum (2.3%), and coccidian oocysts (2.3%). The majority of dogs were infected by only one species of parasite (70/130, 53.8%). Mixed infection caused by two or three zoonotic parasites were discovered in 21.3% (30/130) and 3.1% (4/130), respectively. A. caninum showed the highest egg output (42.3% of dogs had ≥ 500 eggs per gram). Factors associated with zoonotic parasites were age (<2 years old; odds ratio = 5.30, p = 0.029) and body condition (poor body condition; odds ratio = 6.69, p = 0.026). In conclusion, young dogs from rural Yucatan, Mexico, with poor body condition had a higher prevalence of intestinal zoonotic parasites as these factors were associated with a higher risk of becoming infected.

INFECTION BY Rickettsia felis IN OPOSSUMS (Didelphis sp.) FROM YUCATAN, MEXICO.

Science.gov (United States)

Peniche-Lara, Gaspar; Ruiz-Piña, Hugo A; Reyes-Novelo, Enrique; Dzul-Rosado, Karla; Zavala-Castro, Jorge

2016-01-01

Rickettsia felis is an emergent pathogen and the causative agent of a typhus-like rickettsiosis in the Americas. Its transmission cycle involves fleas as biological vectors (mainly Ctenocephalides felis) and multiple domestic and synanthropic mammal hosts. Nonetheless, the role of mammals in the cycle of R. felis is not well understood and many efforts are ongoing in different countries of America to clarify it. The present study describes for the first time in Mexico the infection of two species of opossum (Didelphis virginiana and D. marsupialis) by R. felis. A diagnosis was carried out from blood samples by molecular methods through the gltA and 17 kDa genes and sequence determination. Eighty-seven opossum samples were analyzed and 28 were found to be infected (32.1%) from five out of the six studied localities of Yucatan. These findings enable recognition of the potential epidemiological implications for public health of the presence of infected synanthropic Didelphis in households.

INFECTION BY Rickettsia felis IN OPOSSUMS (Didelphis sp. FROM YUCATAN, MEXICO

Directory of Open Access Journals (Sweden)

Gaspar PENICHE-LARA

2016-01-01

Full Text Available Rickettsia felis is an emergent pathogen and the causative agent of a typhus-like rickettsiosis in the Americas. Its transmission cycle involves fleas as biological vectors (mainly Ctenocephalides felis and multiple domestic and synanthropic mammal hosts. Nonetheless, the role of mammals in the cycle of R. felis is not well understood and many efforts are ongoing in different countries of America to clarify it. The present study describes for the first time in Mexico the infection of two species of opossum (Didelphis virginiana and D. marsupialis by R. felis. A diagnosis was carried out from blood samples by molecular methods through the gltAand 17 kDa genes and sequence determination. Eighty-seven opossum samples were analyzed and 28 were found to be infected (32.1% from five out of the six studied localities of Yucatan. These findings enable recognition of the potential epidemiological implications for public health of the presence of infected synanthropic Didelphis in households.

Early results from genetic trials on the growth of Spanish cedar and itssusceptibility to the shoot borer moth in the Yucatan Peninsula, Mexico.

Science.gov (United States)

Sheila E. Ward; Kevyn E. Wightman; Bartolo. Rodriguez Santiago

2008-01-01

Cedrela odorata (Spanish cedar) is a neotropical broadleaf tree species that is in high demand for furniture and interior fittings. In 1998, seed collections were made from Spanish cedar in the Yucatan Peninsula, Mexico, for genetic conservation and tree improvement projects. Progeny from these collections were established in genetic trials at Bacalar, Noh Bec, and Zoh...

Yucatan Subsurface Stratigraphy from Geophysical Data, Well Logs and Core Analyses in the Chicxulub Impact Crater and Implications for Target Heterogeneities

Science.gov (United States)

Canales, I.; Fucugauchi, J. U.; Perez-Cruz, L. L.; Camargo, A. Z.; Perez-Cruz, G.

2011-12-01

Asymmetries in the geophysical signature of Chicxulub crater are being evaluated to investigate on effects of impact angle and trajectory and pre-existing target structural controls for final crater form. Early studies interpreted asymmetries in the gravity anomaly in the offshore sector to propose oblique either northwest- and northeast-directed trajectories. An oblique impact was correlated to the global ejecta distribution and enhanced environmental disturbance. In contrast, recent studies using marine seismic data and computer modeling have shown that crater asymmetries correlate with pre-existing undulations of the Cretaceous continental shelf, suggesting a structural control of target heterogeneities. Documentation of Yucatan subsurface stratigraphy has been limited by lack of outcrops of pre-Paleogene rocks. The extensive cover of platform carbonate rocks has not been affected by faulting or deformation and with no rivers cutting the carbonates, information comes mainly from the drilling programs and geophysical surveys. Here we revisit the subsurface stratigraphy in the crater area from the well log data and cores retrieved in the drilling projects and marine seismic reflection profiles. Other source of information being exploited comes from the impact breccias, which contain a sampling of disrupted target sequences, including crystalline basement and Mesozoic sediments. We analyze gravity and seismic data from the various exploration surveys, including multiple Pemex profiles in the platform and the Chicxulub experiments. Analyses of well log data and seismic profiles identify contacts for Lower Cretaceous, Cretaceous/Jurassic and K/Pg boundaries. Results show that the Cretaceous continental shelf was shallower on the south and southwest than on the east, with emerged areas in Quintana Roo and Belize. Mesozoic and upper Paleozoic sediments show variable thickness, possibly reflecting the crystalline basement regional structure. Paleozoic and Precambrian

Application of Artificial Neural Networks for Dengue Fever Outbreak Predictions in the Northwest Coast of Yucatan, Mexico and San Juan, Puerto Rico

Directory of Open Access Journals (Sweden)

Abdiel E. Laureano-Rosario

2018-01-01

Full Text Available Modelling dengue fever in endemic areas is important to mitigate and improve vector-borne disease control to reduce outbreaks. This study applied artificial neural networks (ANNs to predict dengue fever outbreak occurrences in San Juan, Puerto Rico (USA, and in several coastal municipalities of the state of Yucatan, Mexico, based on specific thresholds. The models were trained with 19 years of dengue fever data for Puerto Rico and six years for Mexico. Environmental and demographic data included in the predictive models were sea surface temperature (SST, precipitation, air temperature (i.e., minimum, maximum, and average, humidity, previous dengue cases, and population size. Two models were applied for each study area. One predicted dengue incidence rates based on population at risk (i.e., numbers of people younger than 24 years, and the other on the size of the vulnerable population (i.e., number of people younger than five years and older than 65 years. The predictive power was above 70% for all four model runs. The ANNs were able to successfully model dengue fever outbreak occurrences in both study areas. The variables with the most influence on predicting dengue fever outbreak occurrences for San Juan, Puerto Rico, included population size, previous dengue cases, maximum air temperature, and date. In Yucatan, Mexico, the most important variables were population size, previous dengue cases, minimum air temperature, and date. These models have predictive skills and should help dengue fever mitigation and management to aid specific population segments in the Caribbean region and around the Gulf of Mexico.

Infection by Trypanosoma cruzi in mammals in Yucatan, Mexico: a serological and parasitological study Infecção pelo Trypanosoma cruzi em mamíferos em Yucatan, México: estudo sorológico e parasitológico

Directory of Open Access Journals (Sweden)

J Zavala-Velázquez

1996-08-01

Full Text Available In order to determine Trypanosoma cruzi infection among mammals in Yucatan, Mexico, 372 animals, both wild and synanthropic including carnivores, marsupials and rodents were studied. Serological studies by indirect haemagglutination (IHA were carried out to detect antibodies to T. cruzi and a parasitological study was also performed (blood smear and histopathology. Of all the animals tested 18.54% were serologically positive, with a significantly higher frequency among the wild ones (33.33% compared to the synanthropic ones (17.79%. To determine T. cruzi in positive animals, blood was inoculated into a white mouse (webster type to prove myocardium colonization. The serological and parasitological positivity of these animals, as well as their behavior in the environment, taken together with the socioeconomic and cultural characteristics of the population, suggest that in Yucatan, Mexico, Canis familiaris, Didelphis marsupialis and Rattus rattus act as a link with the wild cycle.Para determinar a infecção pelo Trypanosoma cruzi em mamíferos em Yucatan, México, foram estudados 372 animais selvagens e sinantrópicos incluindo carnívoros, marsupiais e roedores. Estudos sorológicos pela hemaglutinação indireta (IHA foram realizados para detectar anticorpos contra o T. cruzi e estudos parasitológicos (esfregaços de sangue e histopatologia. De todos os animais testados 18,54% foram sorologicamente positivos com freqüência significativamente maior entre os silvestres (33,3% em comparação com os sinantrópicos (11,79%. Para determinação do T. cruzi nos animais positivos, o sangue foi inoculado em camundongos brancos (tipo Webster para provar a colonização miocárdica. Através da sua positividade sorológica e parasitológica, bem como seu comportamento no meio ambiente acompanhado pelas características sociais, econômicas e culturais da população, deduz-se que em Yucatan, México, Canis familiaris, Didelphis marsupialis e Rattus

Chemical constraints of groundwater management in the Yucatan peninsula, Mexico

Science.gov (United States)

Back, W.; Lesser, J.M.

1981-01-01

Two critical objectives of water management in the Yucatan are: (1) to develop regional groundwater supplies for an expanding population and tourism based on the Mayan archeological sites and excellent beaches; and (2) to control groundwater pollution in a chemically sensitive system made vulnerable by geologic conditions. The Yucatan peninsula is a coastal plain underlain by permeable limestone and has an annual rainfall of more than 1000 mm. Such a setting should provide abundant supplies of water; however, factors of climate and hydrogeology have combined to form a hydrologic system with chemical boundaries that decrease the amount of available fresh water. Management of water resources has long had a major influence on the cultural and economic development of the Yucatan. The Mayan culture of the northern Yucatan developed by extensive use of groundwater. The religion was water-oriented and the Mayan priests prayed to Chac, the water god, for assistance in water management primarily to decrease the severity of droughts. The Spaniards arrived in 1517 and augmented the supplies by digging wells, which remained the common practice for more than 300 years. Many wells now have been abandoned because of serious problems of pollution resulting from the use of a sewage disposal well adjacent to each supply well. The modern phase of water management began in 1959 when the Secretari??a de Recursos Hidra??ulicos (S.R.H.) was charged with the responsibility for both scientific investigations and development programmes for water-supply and sewage-disposal systems for cities, villages and islands. ?? 1981.

Climate and cultural history of the Northeastern Yucatan Peninsula, Quintana Roo, Mexico

Energy Technology Data Exchange (ETDEWEB)

Hodell, D.A. [Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, FL 32611 (United States); Brenner, M.; Curtis, J.H. [Land Use and Environmental Change Institute (LUECI), University of Florida, Gainesville, FL (United States)

2007-07-15

We inferred the Holocene paleoclimate history of the northeastern Yucatan Peninsula, Mexico, by studying stratigraphic variations in stable isotopes (d 18O and d 13C) and lithologic properties (organic matter and carbonate content) in sediment cores taken in 6.3 and 16.2 m of water from Lake Punta Laguna. We present a simple model to explain the lithologic and isotopic variations, and discuss the inferred paleoclimate history in terms of its relation to ancient Maya cultural development. We find evidence for lower lake level and drier climate at about the same time as each major discontinuity in Maya cultural history: Preclassic Abandonment (150-250 A.D.), Maya Hiatus (534 to 593 A.D.), Terminal Classic Collapse (750-1050 A.D.), and Postclassic Abandonment (mid-fifteenth century). Although these broad temporal correlations suggest climate played a role in Maya cultural evolution, chronological uncertainties preclude a detailed analysis of climate changes and archaeologically documented cultural transformations.

Global Mercury Observatory System (GMOS): measurements of atmospheric mercury in Celestun, Yucatan, Mexico during 2012.

Science.gov (United States)

Velasco, Antonio; Arcega-Cabrera, Flor; Oceguera-Vargas, Ismael; Ramírez, Martha; Ortinez, Abraham; Umlauf, Gunther; Sena, Fabrizio

2016-09-01

Within the Global Mercury Observation System (GMOS) project, long-term continuous measurements of total gaseous mercury (TGM) were carried out by a monitoring station located at Celestun, Yucatan, Mexico, a coastal site along the Gulf of Mexico. The measurements covered the period from January 28th to October 17th, 2012. TGM data, at the Celestun site, were obtained using a high-resolution mercury vapor analyzer. TGM data show values from 0.50 to 2.82 ng/m(3) with an annual average concentration of 1.047 ± 0.271 ng/m(3). Multivariate analyses of TGM and meteorological variables suggest that TGM is correlated with the vertical air mass distribution in the atmosphere, which is influenced by diurnal variations in temperature and relative humidity. Diurnal variation is characterized by higher nighttime mercury concentrations, which might be influenced by convection currents between sea and land. The back trajectory analysis confirmed that local sources do not significantly influence TGM variations. This study shows that TGM monitoring at the Celestun site fulfills GMOS goals for a background site.

Pigging the unpiggable: a total integrated maintenance approach of the Progreso Process Pipelines in Yucatan, Mexico

Energy Technology Data Exchange (ETDEWEB)

Sanchez Graciano, Luis [PEMEX Refinacion, Mexico, MX (Mexico); Gonzalez, Oscar L. [NDT Systems and Services, Stutensee (Germany)

2009-07-01

Pemex Refinacion and NDT Systems and Services, executed a Total Integrated Maintenance Program of the Process Pipeline System in the Yucatan Peninsula in Mexico, in order to modernize, enhance and bring the pipeline system up to the best industry standards and ensure the integrity, reliability and safe operation of the system. This approach consisted in using multi-diameter ultrasonic inspection technology to determine the current status of the pipelines, repair every 'integrity diminishing' feature present on the system and establish a Certified Maintenance Program to ensure the future reliability and safety of the pipelines. Due to the complex nature of the pipeline construction, dated from 1984, several special modifications, integrations and solutions were necessary to improve the in line inspection survey as for all traditionally unpiggable systems. The Progreso Pipeline System consists in 3 major pipelines which transport diesel, jet fuel and gasoline respectively. The outside diameter of two pipelines varies along its length between 12 inches - 14 inches - 16 inches, making the inspection survey more difficult and particularly demanding an Inspection Tool solution. It is located on the coast of the Yucatan Peninsula, at the Mexican Caribbean, and its main purpose is to transport the product from the docked tanker ships to the Pemex Storage and Distribution Terminal. (author)

Hydrogeothermal Convective Circulation Model for the Formation of the Chicxulub Ring of Cenotes in the Yucatan Peninsula, Mexico.

Science.gov (United States)

Monroy-Rios, E.; Beddows, P. A.

2015-12-01

Despite being deeply buried, the topography and geophysical characteristics of the multi-ring Chicxulub impact structure are reflected on the now subaerial Yucatan Peninsula with aligned arcs of cenotes (sinkholes), forming the "Ring of Cenotes". A pending question is the determination of the geological, geochemical, structural features and associated processes that have led to void development, and the upwards propagation of the voids, cross cutting over 1000 m of super-deposited carbonate sequences. Drawing from the published literature on drill core and geophysical surveys undertaken by Pemex, UNAM, and IODP/ICDP, numerical modeling, and general carbonate platform hydrothermal reactive transport models, we provide a conceptual model for the genesis of the Ring of Cenotes. In horizontally bedded carbonate platforms, geothermal gradients will drive convective flow, with strong vertical components specifically in the platform center. In the Yucatan Platform, a high occurrence of anhydrite and dolomite at depth evokes early burial dolomitization and anhydritization, sourcing Mg from seawater. The Chicxulub impact near the center of the platform produced a low permeability and high thermal conductivity melt rock that arguably extends to the basement rock at 3.5 km below surface. Heat of impact enforced the pre-existing geothermal circulation pattern, and even with depletion of the heat of impact, the high thermal conductivity of the crystalline melt would lead to enhanced geothermal gradients in the center of the platform. The cenotes overlying the crater are deep (150+ m) vertical shafts with most (but not all) breaching the surface. The pit geomorphology suggests a bottom-up formation. Excess Si in the shallow groundwater points to a convective circulation with strong vertical components geochemically linking the granodioritic basement rock to the surface. Water temperature and conductivity profiles support ongoing vertical flux in some deep pit cenotes. Within

Wildlife uses and hunting patterns in rural communities of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Santos-Fita, Dídac; Naranjo, Eduardo J; Rangel-Salazar, José Luis

2012-10-02

Subsistence hunting is a traditional practice providing food and many other goods for households in the Yucatan Peninsula, southeast Mexico. Economic, demographic, and cultural change in this region drive wildlife habitat loss and local extinctions. Improving our understanding about current practices of wildlife use may support better management strategies for conserving game species and their habitat. We aimed to evaluate if wildlife use remained relevant for the subsistence of rural residents of the Yucatan Peninsula, as well as if local hunting practices were related to environmental, geographical, and cultural factors. Fieldwork was done between March 2010 and March 2011. Information was obtained through conversations, interviews, and participant observation. Record forms allowed recording animals hunted, biomass extracted, distance intervals to hunting sites, habitat types and seasonality of wildlife harvests. Data were analyzed using one-way Analysis of Variance, and Generalized Linear Models. Forty-six terrestrial vertebrate species were used for obtaining food, medicine, tools, adornments, pets, ritual objects, and for sale and mitigating damage. We recorded 968 animals taken in 664 successful hunting events. The Great Curassow, Ocellated Turkey, paca, white-tailed deer, and collared peccary were the top harvested species, providing 80.7% of biomass (10,190 kg). The numbers of animals hunted and biomass extracted declined as hunting distances increased from villages. Average per capita consumption was 4.65 ± 2.7 kg/person/year. Hunting frequencies were similar in forested and agricultural areas. Wildlife use, hunting patterns, and technologies observed in our study sites were similar to those recorded in previous studies for rural Mayan and mestizo communities in the Yucatan Peninsula and other Neotropical sites. The most heavily hunted species were those providing more products and by-products for residents. Large birds such as the Great Curassow and

Wildlife uses and hunting patterns in rural communities of the Yucatan Peninsula, Mexico

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Santos-Fita Dídac

2012-10-01

Full Text Available Abstract Background Subsistence hunting is a traditional practice providing food and many other goods for households in the Yucatan Peninsula, southeast Mexico. Economic, demographic, and cultural change in this region drive wildlife habitat loss and local extinctions. Improving our understanding about current practices of wildlife use may support better management strategies for conserving game species and their habitat. We aimed to evaluate if wildlife use remained relevant for the subsistence of rural residents of the Yucatan Peninsula, as well as if local hunting practices were related to environmental, geographical, and cultural factors. Methods Fieldwork was done between March 2010 and March 2011. Information was obtained through conversations, interviews, and participant observation. Record forms allowed recording animals hunted, biomass extracted, distance intervals to hunting sites, habitat types and seasonality of wildlife harvests. Data were analyzed using one-way Analysis of Variance, and Generalized Linear Models. Results Forty-six terrestrial vertebrate species were used for obtaining food, medicine, tools, adornments, pets, ritual objects, and for sale and mitigating damage. We recorded 968 animals taken in 664 successful hunting events. The Great Curassow, Ocellated Turkey, paca, white-tailed deer, and collared peccary were the top harvested species, providing 80.7% of biomass (10,190 kg. The numbers of animals hunted and biomass extracted declined as hunting distances increased from villages. Average per capita consumption was 4.65 ± 2.7 kg/person/year. Hunting frequencies were similar in forested and agricultural areas. Discussion Wildlife use, hunting patterns, and technologies observed in our study sites were similar to those recorded in previous studies for rural Mayan and mestizo communities in the Yucatan Peninsula and other Neotropical sites. The most heavily hunted species were those providing more products and by

Education, fish consumption, well water, chicken coops, and cooking fires: Using biogeochemistry and ethnography to study exposure of children from Yucatan, Mexico to metals and arsenic

International Nuclear Information System (INIS)

Arcega-Cabrera, Flor; Fargher, Lane F.

2016-01-01

Around the world, the nocuous health effects of exposure to environmental contaminants, especially metals and Arsenic, are a growing health concern. This is especially the case in Mexico, where corruption and ineffective political administration are contributing to increasing deterioration in the environment. Importantly, shallow soils and the karstic nature of bedrock in Yucatan, Mexico make the subterranean aquifer especially susceptible to contamination because contaminates are carried to it with little resistance. Given these environmental conditions, we developed a multi/interdisciplinary project to evaluate the impact of metal and Arsenic pollution on a sample of 107 children, ages 6 to 9 years, living in the urban areas of Progreso, Merida, and Ticul, in the State of Yucatan using urine and blood samples. In addition, ethnographic research was carried out in the homes of the children that participated in the study to identify potential exposure pathways. This research proved invaluable because the complexity of human social organization, lifestyles, and geographical patterning create an intricate array of exposure pathways that vary across social sectors and geographic space. In the following article, we use nonparametric univariate statistical analysis to reveal potential exposure pathways among sub-populations included in our sample. These analyses show that children from poor/marginal families tend to be exposed to Copper, Lead, and Nickel; whereas, children, from wealthier families, tend to be exposed to Cadmium, Arsenic, and inorganic Copper (Copper Sulfate). - Highlights: • Metals and Arsenic exposure in children (age 6–9) from Yucatan, Mexico • Quantification of As, Cd, Hg, Pb, Cr, Cu, Ni in Blood and Urine by AAS • Ethnographic research on sociocultural patterns and exposure pathways • Non-parametric statistical analysis • Variation in exposure based on geography, socioeconomic level, and lifestyles

Education, fish consumption, well water, chicken coops, and cooking fires: Using biogeochemistry and ethnography to study exposure of children from Yucatan, Mexico to metals and arsenic

Energy Technology Data Exchange (ETDEWEB)

Arcega-Cabrera, Flor [Unidad de Química Sisal, Facultad de Química, Universidad Nacional Autónoma de México (Mexico); Fargher, Lane F., E-mail: fargher@mda.cinvestav.mx [Departamento de Ecología Humana, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional — Unidad Mérida (Mexico)

2016-10-15

Around the world, the nocuous health effects of exposure to environmental contaminants, especially metals and Arsenic, are a growing health concern. This is especially the case in Mexico, where corruption and ineffective political administration are contributing to increasing deterioration in the environment. Importantly, shallow soils and the karstic nature of bedrock in Yucatan, Mexico make the subterranean aquifer especially susceptible to contamination because contaminates are carried to it with little resistance. Given these environmental conditions, we developed a multi/interdisciplinary project to evaluate the impact of metal and Arsenic pollution on a sample of 107 children, ages 6 to 9 years, living in the urban areas of Progreso, Merida, and Ticul, in the State of Yucatan using urine and blood samples. In addition, ethnographic research was carried out in the homes of the children that participated in the study to identify potential exposure pathways. This research proved invaluable because the complexity of human social organization, lifestyles, and geographical patterning create an intricate array of exposure pathways that vary across social sectors and geographic space. In the following article, we use nonparametric univariate statistical analysis to reveal potential exposure pathways among sub-populations included in our sample. These analyses show that children from poor/marginal families tend to be exposed to Copper, Lead, and Nickel; whereas, children, from wealthier families, tend to be exposed to Cadmium, Arsenic, and inorganic Copper (Copper Sulfate). - Highlights: • Metals and Arsenic exposure in children (age 6–9) from Yucatan, Mexico • Quantification of As, Cd, Hg, Pb, Cr, Cu, Ni in Blood and Urine by AAS • Ethnographic research on sociocultural patterns and exposure pathways • Non-parametric statistical analysis • Variation in exposure based on geography, socioeconomic level, and lifestyles.

Influenza seasonality goes south in the Yucatan Peninsula: The case for a different influenza vaccine calendar in this Mexican region.

Science.gov (United States)

Ayora-Talavera, Guadalupe; Flores, Gerardo Montalvo-Zurbia; Gómez-Carballo, Jesus; González-Losa, Refugio; Conde-Ferraez, Laura; Puerto-Solís, Marylin; López-Martínez, Irma; Díaz-Quiñonez, Alberto; Barrera-Badillo, Gisela; Acuna-Soto, Rodolfo; Livinski, Alicia A; Alonso, Wladimir J

2017-08-24

While vaccination may be relatively straightforward for regions with a well-defined winter season, the situation is quite different for tropical regions. Influenza activity in tropical regions might be out of phase with the dynamics predicted for their hemispheric group thereby impacting the effectiveness of the immunization campaign. To investigate how the climatic diversity of Mexico hinders its existing influenza immunization strategy and to suggest that the hemispheric vaccine recommendations be tailored to the regional level in order to optimize vaccine effectiveness. We studied the seasonality of influenza throughoutMexico by modeling virological and mortality data.De-trended time series of each Mexican state were analyzed by Fourier decomposition to describe the amplitude and timing of annual influenza epidemic cycles and to compare with each the timing of the WHO's Northern and Southern Hemispheric vaccination schedule. The timings of the primary (major) peaks of both virological and mortality data for most Mexican states are well aligned with the Northern Hemisphere winter (December-February) and vaccine schedule. However, influenza peaks in September in the three states of the Yucatan Peninsula. Influenza-related mortality also peaks in September in Quintana Roo and Yucatan whereas it peaks in May in Campeche. As the current timing of vaccination in Mexico is between October and November, more than half of the annual influenza cases have already occurred in the Yucatan Peninsula states by the time the Northern Hemispheric vaccine is delivered and administered. The current Northern Hemispheric influenza calendar adopted for Mexico is not optimal for the Yucatan Peninsula states thereby likely reducing the effectiveness of the immunization of the population. We recommend that Mexico tailor its immunization strategy to better reflect its climatologic and epidemiological diversity and adopt the WHO Southern Hemisphere influenza vaccine and schedule for the

Effectiveness of a regional self-study perinatal education programme: a successful adaptation in Yucatan, Mexico.

Science.gov (United States)

Osorno, Lorenzo R; Campos, Miriam C; Cook, Lynn J; Vela, Gabriela R; Dávila, Jorge R

2006-08-01

To evaluate the effectiveness of the Perinatal Continuing Education Programme (PCEP) in a Latin American country. We carried out a study within secondary and tertiary care, and rural Mexican Institute of Social Security (IMSS) hospitals on the Yucatan Peninsula. Participants were doctors, nurses and nursing assistants working with pregnant women and newborns at each hospital. The PCEP was translated into Spanish and then implemented between January 1998 and December 2001. Two nurses at each hospital were trained to co-ordinate the programme and the personnel were invited to participate. Participation involved purchasing the self-teaching books, study outside work hours and participation in skills demonstration and practice sessions. Evaluation included the percentage of personnel who participated in and those who completed the programme, an opinion survey of the programme, level of pre- and post-intervention knowledge, and the quality of neonatal care according to expert-recommended routines. Results were analysed with chi-square and Student's t-tests. A total of 65.3% of the 1421 people in the study population began the programme and 72% of those completed it. Improvement was observed in 14 of 23 (Pevaluated neonatal care practices. Participants rated the written material as very clear and useful in daily practice. The PCEP is an effective strategy for improving the level of knowledge and perinatal care in all regional hospitals on the Yucatan Peninsula, Mexico. This initial application of the PCEP in a Spanish-speaking country was successful.

Wind characteristics on the Yucatan Peninsula based on short term data from meteorological stations

International Nuclear Information System (INIS)

Soler-Bientz, Rolando; Watson, Simon; Infield, David

2010-01-01

Due to the availability of sparsely populated and flat open terrain, the Yucatan Peninsula located in eastern Mexico is a promising region from the perspective of wind energy development. Study of the diurnal and seasonal wind resource is an important stage in the move towards commercial exploitation of wind power in this Latin American region. An analysis of the characteristics of the wind resource of the Yucatan Peninsula is presented in this paper, based on 10 min averaged wind speed data from nine meteorological stations, between 2000 and 2007. Hourly and monthly patterns of the main environmental parameters have been examined. Highly directional behaviour was identified that reflects the influence of winds coming from the Caribbean Sea and the Gulf of Mexico. The characteristics of the wind speed variation observed at the studied sites reflected their proximity to the coast and whether they were influenced by wind coming predominantly from over the land or predominantly from over the sea. The atmospheric stability over the eastern seas of the Yucatan Peninsula was also analysed to assess thermal effects for different wind directions. The findings were consistent with the variation in average wind speeds observed at the coastal sites where winds came predominantly from over the sea. The research presented here is to be used as a basis for a wind atlas for the Yucatan Peninsula.

Impact-generated Hydrothermal Activity at the Chicxulub Crater

Science.gov (United States)

Kring, D. A.; Zurcher, L.; Abramov, O.

2007-05-01

Borehole samples recovered from PEMEX exploration boreholes and an ICDP scientific borehole indicate the Chicxulub impact event generated hydrothermal alteration throughout a large volume of the Maya Block beneath the crater floor and extending across the bulk of the ~180 km diameter crater. The first indications of hydrothermal alteration were observed in the crater discovery samples from the Yucatan-6 borehole and manifest itself in the form of anhydrite and quartz veins. Continuous core from the Yaxcopoil-1 borehole reveal a more complex and temporally extensive alteration sequence: following a brief period at high temperatures, impact- melt-bearing polymict breccias and a thin, underlying unit of impact melt were subjected to metasomatism, producing alkali feldspar, sphene, apatite, and magnetite. As the system continued to cool, smectite-series phyllosilicates appeared. A saline solution was involved. Stable isotopes suggest the fluid was dominated by a basinal brine created mostly from existing groundwater of the Yucatan Peninsula, although contributions from down-welling water also occurred in some parts of the system. Numerical modeling of the hydrothermal system suggests circulation occurred for 1.5 to 2.3 Myr, depending on the permeability of the system. Our understanding of the hydrothermal system, however, is still crude. Additional core recovery projects, particularly into the central melt sheet, are needed to better evaluate the extent and duration of hydrothermal alteration.

Petrography of the Nimun and Baca pottery (Ware Celestun Roja): Canbalam Ceramic Sphere of the Yucatan Peninsula, Mexico

International Nuclear Information System (INIS)

Obando, Luis G.; Jimenez Alvarez, Socorro del Pilar

2016-01-01

The ware Celestun Red (of the Nimun and Baca ceramic typologies) is one of the most diagnosis ceramics of the northwestern coast of Mexico's Yucatan Peninsula and subject of ongoing debate regarding its distribution and origin. Although ceramics from coastal Campeche and Yucatan have been the focus of years of investigation, scholars still do not know if Celestun Red was manufactured locally during the Late Classic (A.D. 600-900) or was made and exchanged by the regional elite. The first petrographic description of Celestun Red are provide, and use to contribute to a formal definition of the Cambalan Ceramic Sphere. These petrographic observations show that the detrital components were rhyolite fragments, vitroclastic tuffs, pumice, shards of glass, quartzes, plagioclase, calcite, hematite, magnetite and other minor contributors. The clay matrix is phyllomorphic, with a parallel, rectilinear fabric of fine grains. granulometricaly, the detrital components have been characterized as fine to medium sands. The pastes pastes present evidence of diagenetic processes, most notably porosity in the primary ceramic matrix. These space are in some cases filled by secondary calcite deposits. Evidence of manufacturing was also observed, such as the fracture and bending of the paste that took place to produce the rims of these ceramic objects. (author) [es

Restoring the environment, revitalizing the culture: cenote conservation in Yucatan, Mexico

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Yolanda Lopez-Maldonado

2017-12-01

Full Text Available Cenotes are sinkholes through which groundwater may be accessed from the Yucatan Peninsula Aquifer. Historically and culturally, cenotes are also important cultural and spiritual natural sites for the Maya, but they have been contaminated and degraded. We ask the following: What are the present-day meanings, understanding, and values of cenotes for the Maya? Is it possible to adopt a cultural approach for conservation of cenotes in Yucatan? Participant observation, interviews with stakeholders, and underwater exploration in cenotes were used to obtain data. Results indicate that cenotes often retain some spiritual meaning for people but not as important cultural, spiritual, or sacred sites. Little consensus was found regarding the significance of cenotes and how best to protect them. Informants noted changes in water quality, and identified the threats to cenotes including tourism, poor solid waste management, contamination, and deficiency of interest in preservation. Lack of accurate knowledge was a problem: informants did not seem to understand that cenotes are interconnected through the groundwater system. The Yucatan case illustrates how loss of cultural values can be linked to environmental quality and resource degradation. Conversely, it can be argued that cultural revitalization in indigenous communities has the potential to bring back community-based conservation.

Storm-generated bedforms and relict dissolution pits and channels on the Yucatan carbonate platform

Science.gov (United States)

Gulick, S. P.; Goff, J. A.; Stewart, H. A.; Perez-Cruz, L. L.; Davis, M. B.; Duncan, D.; Saustrup, S.; Sanford, J. C.; Fucugauchi, J. U.

2013-12-01

The Yucatan 2013 (cruise number 2013/4_ECORD) geophysical and geotechnical hazard site survey took place aboard the R/V Justo Sierra in April 2013. Our study was conducted within the Chicxulub impact crater, encompassing three potential IODP drilling sites. The survey was located ~32 km northwest of Progreso, Mexico; data acquired included ~15.6 km2 of complete multibeam bathymetry coverage, ~435 line km of side scan sonar and CHIRP data, 204 line kilometers of magnetometer data, and 194 line kilometers of surface tow boomer profiles. Based on these data, this portion of the Yucatan Shelf consists of flat-lying, hard limestone rock overlain by isolated ribbons of carbonate sand limestone bedrock. This reflector is flat-lying and undisturbed throughout the survey area. Therefore, none of these dissolution pits appear to be underlain by a cenote or sink hole. The NW sector of the survey area exhibits a more complex morphology than the alternating ribbon/bare rock morphology elsewhere, including linear scarps (up to ~1 m relief), deeper pitting (up to ~1 m relief), and sinuous, dendritic channeling (up to ~2 m relief). The geologic origin of these features will require further investigation. Sand drifts are present in this region, but are thinner and cover less area. These observations show the dominant modern sediment formation and transport processes on this starved platform are from large storms and hurricanes that place large regions of the platform at wave base. Remaining observed features were generated during times of lower sea level.

Beyond the colours: discovering hidden diversity in the Nymphalidae of the Yucatan Peninsula in Mexico through DNA barcoding.

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Blanca R Prado

Full Text Available BACKGROUND: Recent studies have demonstrated the utility of DNA barcoding in the discovery of overlooked species and in the connection of immature and adult stages. In this study, we use DNA barcoding to examine diversity patterns in 121 species of Nymphalidae from the Yucatan Peninsula in Mexico. Our results suggest the presence of cryptic species in 8 of these 121 taxa. As well, the reference database derived from the analysis of adult specimens allowed the identification of nymphalid caterpillars providing new details on host plant use. METHODOLOGY/PRINCIPAL FINDINGS: We gathered DNA barcode sequences from 857 adult Nymphalidae representing 121 different species. This total includes four species (Adelpha iphiclus, Adelpha malea, Hamadryas iphtime and Taygetis laches that were initially overlooked because of their close morphological similarity to other species. The barcode results showed that each of the 121 species possessed a diagnostic array of barcode sequences. In addition, there was evidence of cryptic taxa; seven species included two barcode clusters showing more than 2% sequence divergence while one species included three clusters. All 71 nymphalid caterpillars were identified to a species level by their sequence congruence to adult sequences. These caterpillars represented 16 species, and included Hamadryas julitta, an endemic species from the Yucatan Peninsula whose larval stages and host plant (Dalechampia schottii, also endemic to the Yucatan Peninsula were previously unknown. CONCLUSIONS/SIGNIFICANCE: This investigation has revealed overlooked species in a well-studied museum collection of nymphalid butterflies and suggests that there is a substantial incidence of cryptic species that await full characterization. The utility of barcoding in the rapid identification of caterpillars also promises to accelerate the assembly of information on life histories, a particularly important advance for hyperdiverse tropical insect

Beyond the Colours: Discovering Hidden Diversity in the Nymphalidae of the Yucatan Peninsula in Mexico through DNA Barcoding

Science.gov (United States)

Prado, Blanca R.; Pozo, Carmen; Valdez-Moreno, Martha; Hebert, Paul D. N.

2011-01-01

Background Recent studies have demonstrated the utility of DNA barcoding in the discovery of overlooked species and in the connection of immature and adult stages. In this study, we use DNA barcoding to examine diversity patterns in 121 species of Nymphalidae from the Yucatan Peninsula in Mexico. Our results suggest the presence of cryptic species in 8 of these 121 taxa. As well, the reference database derived from the analysis of adult specimens allowed the identification of nymphalid caterpillars providing new details on host plant use. Methodology/Principal Findings We gathered DNA barcode sequences from 857 adult Nymphalidae representing 121 different species. This total includes four species (Adelpha iphiclus, Adelpha malea, Hamadryas iphtime and Taygetis laches) that were initially overlooked because of their close morphological similarity to other species. The barcode results showed that each of the 121 species possessed a diagnostic array of barcode sequences. In addition, there was evidence of cryptic taxa; seven species included two barcode clusters showing more than 2% sequence divergence while one species included three clusters. All 71 nymphalid caterpillars were identified to a species level by their sequence congruence to adult sequences. These caterpillars represented 16 species, and included Hamadryas julitta, an endemic species from the Yucatan Peninsula whose larval stages and host plant (Dalechampia schottii, also endemic to the Yucatan Peninsula) were previously unknown. Conclusions/Significance This investigation has revealed overlooked species in a well-studied museum collection of nymphalid butterflies and suggests that there is a substantial incidence of cryptic species that await full characterization. The utility of barcoding in the rapid identification of caterpillars also promises to accelerate the assembly of information on life histories, a particularly important advance for hyperdiverse tropical insect assemblages. PMID:22132140

REMOVAL EFFICIENCY OF ORGANIC MATTER OF PIG SLURRY WITH BIODIGESTERS IN YUCATAN STATE, MEXICO

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W. Trejo-Lizama

2014-08-01

Full Text Available In the intensive pig production in the state of Yucatan, 62 biodigesters were installed in the last 10 years. However, the complexities of the anaerobic biodigestion enclose difficulties to reach the expected efficiency. The objective of the present study was to determine the removal efficiency of the organic matter in pig slurry using biodigesters in the state of Yucatan. There were visited 15 pig farms in the state of Yucatan to interview the farmer about the management of the farm and the waste disposal and to take samples of the influent of the collector of the pig slurry and the effluent of the biodigestor and evaluating the samples by laboratory analysis. The removal values found in the present study were 7 percentage points below the reference value of total volatile solids, which represent the organic matter fraction of the solids treated in the biodigestor. More than the 50 % of the farms evaluated were similar or higher than the parameters of reference. The removal efficiency of the organic matter in the pig slurry by biodigesters in the state of Yucatan is close to the reference values. However complementary treatments are necessary to continue the waste slurry treatment.

Host-Feeding Preference of the Mosquito, Culex quinquefasciatus, in Yucatan State, Mexico

Science.gov (United States)

Garcia-Rejon, Julian E.; Blitvich, Bradley J.; Farfan-Ale, Jose A.; Loroño-Pino, Maria A.; Chi Chim, Wilberth A.; Flores-Flores, Luis F.; Rosado-Paredes, Elsy; Baak-Baak, Carlos; Perez-Mutul, Jose; Suarez-Solis, Victor; Fernandez-Salas, Ildefonso; Beaty, Barry J.

2010-01-01

Studies were conducted to determine the host-feeding preference of Culex quinquefasciatus Say (Diptera: Culicidae) in relation to the availability of human and domestic animals in the city of Merida, Yucatan State, Mexico. Mosquitoes were collected in the backyards of houses using resting wooden boxes. Collections were made five times per week from January to December 2005. DNA was extracted from engorged females and tested by PCR using universal avian- and mammalian-specific primers. DNA extracted from avian-derived blood was further analyzed by PCR using primers that differentiate among the birds of three avian orders: Passeriformes, Columbiformes and Galliformes. PCR products obtained from mammalian-derived blood were subjected to restriction enzyme digestion to differentiate between human-, dog-, cat-, pig-, and horse-derived blood meals. Overall, 82% of engorged mosquitoes had fed on birds, and 18% had fed on mammals. The most frequent vertebrate hosts were Galliformes (47.1%), Passeriformes (23.8%), Columbiformes (11.2%) birds, and dogs (8.8%). The overall human blood index was 6.7%. The overall forage ratio for humans was 0.1, indicating that humans were not a preferred host for Cx. quinquefasciatus in Merida. PMID:20578953

Levels of persistent organic pollutants in breast milk of Maya women in Yucatan, Mexico.

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Polanco Rodríguez, Ángel G; Inmaculada Riba López, M; Angel DelValls Casillas, T; León, Jesús Alfredo Araujo; Anjan Kumar Prusty, B; Álvarez Cervera, Fernando J

2017-02-01

In this study, 24 breast milk samples, obtained from rural Maya women, from municipalities of Yucatan, Mexico, were analyzed for organochlorine pesticide (OCP) residues by gas chromatography. Recent studies have shown that Maya communities have a poor perception about the proper usage and handling of OCP. The karstic soil in this area has a high vulnerability to groundwater pollution by the use of OCP in agriculture and livestock activities. The impact of the ecosystem on human health is much more critical due to the prevailing poverty and a very low educational level of these communities. About 30% of the Maya population consumes water directly from contaminated wells and sinkholes, resulting in a chronic exposure to OCP. The samples served to identify and quantify high levels of OCP residues (18.43 mg/kg of heptachlor epoxide and 1.92 mg/kg of endrin in the metropolitan zone; 2.10 mg/kg of dieldrin, 0.117 mg/kg of endosulfan II, 0.103 mg/kg of heptachlor, 0.178 mg/kg of endrin, and 0.127 mg/kg of endrin aldehyde in the main agricultural zone and on the west coast). The detected levels of OCP residues are a major concern and represent a potential risk to women and children in the region. This could be associated with the high rates of cervical uterine and breast cancer mortality in Yucatan. Thus, regulations on the usage of OCP and their enforcement are necessary, and it is important to establish a yearly monitoring program for OCP residues in breast milk and groundwater, as well as to implement health promotion programs for women in particular and the general population in general.

Mechanisms of the 40-70 Day Variability in the Yucatan Channel Volume Transport

Science.gov (United States)

van Westen, René M.; Dijkstra, Henk A.; Klees, Roland; Riva, Riccardo E. M.; Slobbe, D. Cornelis; van der Boog, Carine G.; Katsman, Caroline A.; Candy, Adam S.; Pietrzak, Julie D.; Zijlema, Marcel; James, Rebecca K.; Bouma, Tjeerd J.

2018-02-01

The Yucatan Channel connects the Caribbean Sea with the Gulf of Mexico and is the main outflow region of the Caribbean Sea. Moorings in the Yucatan Channel show high-frequent variability in kinetic energy (50-100 days) and transport (20-40 days), but the physical mechanisms controlling this variability are poorly understood. In this study, we show that the short-term variability in the Yucatan Channel transport has an upstream origin and arises from processes in the North Brazil Current. To establish this connection, we use data from altimetry and model output from several high resolution global models. A significant 40-70 day variability is found in the sea surface height in the North Brazil Current retroflection region with a propagation toward the Lesser Antilles. The frequency of variability is generated by intrinsic processes associated with the shedding of eddies, rather than by atmospheric forcing. This sea surface height variability is able to pass the Lesser Antilles, it propagates westward with the background ocean flow in the Caribbean Sea and finally affects the variability in the Yucatan Channel volume transport.

Microbial deterioration of Mayan stone buildings at Uxmal, Yucatan, Mexico

International Nuclear Information System (INIS)

Ortega-Morales, O.; Guezennec, J.; Hernandez D, G.; Jozsa, P.; Sand, W.; Crassous, P.

1998-01-01

The microbial communities associated to Uxmal Mayan monuments (Yucatan, Mexico) and their role in stone deterioration were preliminary characterized by chemical, biochemical, microbiological, microscopical and surface analysis methods under two climatic seasons (1997). The organic matter and organic carbon and nitrogen were in the range of those reported for other stone buildings, indicating that oligo trophic conditions prevail at Uxmal. Quantitative differences in microbial biomass was higher at indoor section were the organic matter content was the highest and micro-environmental conditions (availability of water and protection to direct sunlight) are more suitable for microbial growth. The microbiological analysis underestimated the microbial biomass, as revealed by biochemical approaches. Nitrate and nitrite-oxidizing, metilotrophic and heterotrophic bacteria and fungi were detected in most surfaces. The heterotrophic bacteria were the most abundant microbial group (microbiological data). However, the chlorophyll profiles and Scanning Electron Microscopy showed that the microalgae are the most abundant colonizers in Uxmal stone buildings. EDAX analysis showed that the most surfaces were covered by an organic layer (cells and exo polymers). Gypsum was found in few samples. The large photo trophic biomass seems to play a role in stone bio deterioration by supporting growth of heterotrophic microorganisms (bacteria and fungi) which are known to produce organic acids leading to calcite dissolution and cations chelation. Further studies are being carried out in order to determine the role of exo polysaccharides which are thought to play a role in chemical degradation of limestone substrates in Uxmal. (Author)

Fish community structure and dynamics in a coastal hypersaline lagoon: Rio Lagartos, Yucatan, Mexico

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Vega-Cendejas, Ma. Eugenia; Hernández de Santillana, Mireya

2004-06-01

Rio Lagartos, a tropical coastal lagoon in northern Yucatan Peninsula of Mexico, is characterized by high salinity during most of the year (55 psu annual average). Even though the area has been designated as a wetland of international importance because of its great biodiversity, fish species composition and distribution are unknown. To determine whether the salinity gradient was influencing fish assemblages or not, fish populations were sampled seasonally by seine and trawl from 1992 to 1993 and bimonthly during 1997. We identified 81 fish species, eight of which accounted for 53.1% considering the Importance Value Index ( Floridichthys polyommus, Sphoeroides testudineus, Eucinostomus argenteus, Eucinostomus gula, Fundulus majalis, Strongylura notata, Cyprinodon artifrons and Elops saurus). Species richness and density declined from the mouth to the inner zone where extreme salinity conditions are prominent (>80) and competitive interactions decreased. However, in Coloradas basin (53 average sanity) and in the inlet of the lagoon, the highest fish density and number of species were observed. Greater habitat heterogeneity and fish immigration were considered as the best explanation. Multivariate analysis found three zones distinguished by fish occurrence, abundance and distribution. Ichthyofaunal spatial differences were attributed to selective recruitment from the Gulf of Mexico due to salinity gradient and to changing climatic periods. Estuarine and euryhaline marine species are abundant, with estuarine dependent ones entering the system according to environmental preferences. This knowledge will contribute to the management of the Special Biosphere Reserve through baseline data to evaluate environmental and anthropogenic changes.

Bartonella Infection in Hematophagous, Insectivorous, and Phytophagous Bat Populations of Central Mexico and the Yucatan Peninsula.

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Stuckey, Matthew J; Chomel, Bruno B; Galvez-Romero, Guillermo; Olave-Leyva, José Ignacio; Obregón-Morales, Cirani; Moreno-Sandoval, Hayde; Aréchiga-Ceballos, Nidia; Salas-Rojas, Mónica; Aguilar-Setién, Alvaro

2017-08-01

Although emerging nonviral pathogens remain relatively understudied in bat populations, there is an increasing focus on identifying bat-associated bartonellae around the world. Many novel Bartonella strains have been described from both bats and their arthropod ectoparasites, including Bartonella mayotimonensis , a zoonotic agent of human endocarditis. This cross-sectional study was designed to describe novel Bartonella strains isolated from bats sampled in Mexico and evaluate factors potentially associated with infection. A total of 238 bats belonging to seven genera were captured in five states of Central Mexico and the Yucatan Peninsula. Animals were screened by bacterial culture from whole blood and/or polymerase chain reaction of DNA extracted from heart tissue or blood. Bartonella spp. were isolated or detected in 54 (22.7%) bats, consisting of 41 (38%) hematophagous, 10 (16.4%) insectivorous, and three (4.3%) phytophagous individuals. This study also identified Balantiopteryx plicata as another possible bat reservoir of Bartonella . Univariate and multivariate logistic regression models suggested that Bartonella infection was positively associated with blood-feeding diet and ectoparasite burden. Phylogenetic analysis identified a number of genetic variants across hematophagous, phytophagous, and insectivorous bats that are unique from described bat-borne Bartonella species. However, these strains were closely related to those bartonellae previously identified in bat species from Latin America.

Occurrence of Sciadicleithrum mexicanum Kritsky, Vidal-Martinez et Rodríguez-Canul, 1994 (Monogenea: Dactylogyridae) in the Cichlid Cichlasoma urophthalmus from a flooded quarry in Yucatan, Mexico

OpenAIRE

Mendoza-Franco,E. F.; Vidal-Martínez,V.; Simá-Álvarez,R.; Rodríguez-Canul,R.; Vivas-Rodríguez,C.; Scholz,T.

1995-01-01

Cichlids, Cichlasoma urophthalmus, collected in a flooded quarry in the Yucatan Peninsula, Mexico, from January through June 1992, had high levels of infection with the ancyrocephaline Sciadicleithrum mexicanum (Monogena: Dactylogyridade) in all montlhly samples. Neither occurrence nor maturation of the worms eshibited any pronounced monthly fluctuation. The infection rate was found to be sizedependent, greater in longer fish. The worms occurred on primary lamellae of gill filaments of all ar...

Contaminants in the coastal karst aquifer system along the Caribbean coast of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Metcalfe, Chris D; Beddows, Patricia A; Bouchot, Gerardo Gold; Metcalfe, Tracy L; Li, Hongxia; Van Lavieren, Hanneke

2011-04-01

Intensive land development as a result of the rapidly growing tourism industry in the "Riviera Maya" region of the Yucatan Peninsula, Mexico may result in contamination of groundwater resources that eventually discharge into Caribbean coastal ecosystems. We deployed two types of passive sampling devices into groundwater flowing through cave systems below two communities to evaluate concentrations of contaminants and to indicate the possible sources. Pharmaceuticals and personal care products accumulated in the samplers could only have originated from domestic sewage. PAHs indicated contamination by runoff from highways and other impermeable surfaces and chlorophenoxy herbicides accumulated in samplers deployed near a golf course indicated that pesticide applications to turf are a source of contamination. Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health, thus damaging the tourism-based economy of the region. Copyright © 2010 Elsevier Ltd. All rights reserved.

Capillaria (Hepatocapillaria) cichlasomae (Nematoda: Capillariidae) from the liver of the cichlid fish Cichlasoma urophthalmus from Yucatan, Mexico.

Science.gov (United States)

Moravec, F; Scholz, T; Mendoza Franco, E

1995-01-01

Capillaria (Hepatocapillaria) cichlasomae sp. n., parasitic in the liver of the cichlid Cichlasoma urophthalmus (Günther) from a small freshwater lake ("aguada") Xpoc in Yucatan, Mexico, is described. The parasite is characterized mainly by its small body size (male 1.8 mm, female 4.5 mm), the structure of the stichosome (markedly short stichocytes in one row) and the male (the presence of a pair of small subventral postanal papillae) and female (anus distinctly subterminal) caudal ends, and by the size and structure of the spicule (spicule 0.068-0.085 mm long, with marked transverse grooves on surface) and eggs (size 0.053-0.058 x 0.023 mm, with protruding polar plugs). This is the second known Capillaria species from the liver of fish and the first one from the liver of a freshwater fish.

Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico

Science.gov (United States)

González-Herrera, Roger; Sánchez-y-Pinto, Ismael; Gamboa-Vargas, José

2002-09-01

The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7-10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity. Résumé. Le modèle conceptuel classique de l'aquifère karstique libre de la péninsule du Yucatan (Mexique) consiste en une lentille d'eau douce flottant sur une eau salée plus dense qui pénètre à plus de 40 km à l'intérieur des terres. La transmissivité de l'aquifère est très élevée, en sorte que le gradient hydraulique est très faible, compris entre 7 et 10 mm/km dans la plus grande partie du nord de la péninsule. Le modèle AQUIFER a été utilisé pour explorer les écoulements souterrains régionaux dans cet

Leishmania spp. Epidemiology of Canine Leishmaniasis in the Yucatan Peninsula

Directory of Open Access Journals (Sweden)

A. López-Céspedes

2012-01-01

Full Text Available Canine Leishmaniasis is widespread in various Mexican states, where different species of Leishmania have been isolated from dogs. In the present study, we describe the detection of L. braziliensis, L. infantum, and L. mexicana in serum of dogs from the states of Yucatan and Quintana Roo in the Yucatan Peninsula (Mexico. A total of 412 sera were analyzed by ELISA using the total extract of the parasite and the iron superoxide dismutase excreted by different trypanosomatids as antigens. We found the prevalence of L. braziliensis to be 7.52%, L. infantum to be 6.07%, and L. mexicana to be 20.63%, in the dog population studied. The results obtained with ELISA using iron superoxide dismutase as the antigen were confirmed by western blot analysis with its greater sensitivity, and the agreement between the two techniques was very high.

Leishmania spp. epidemiology of canine leishmaniasis in the Yucatan Peninsula.

Science.gov (United States)

López-Céspedes, A; Longoni, S S; Sauri-Arceo, C H; Sánchez-Moreno, M; Rodríguez-Vivas, R I; Escobedo-Ortegón, F J; Barrera-Pérez, M A; Bolio-González, M E; Marín, C

2012-01-01

Canine Leishmaniasis is widespread in various Mexican states, where different species of Leishmania have been isolated from dogs. In the present study, we describe the detection of L. braziliensis, L. infantum, and L. mexicana in serum of dogs from the states of Yucatan and Quintana Roo in the Yucatan Peninsula (Mexico). A total of 412 sera were analyzed by ELISA using the total extract of the parasite and the iron superoxide dismutase excreted by different trypanosomatids as antigens. We found the prevalence of L. braziliensis to be 7.52%, L. infantum to be 6.07%, and L. mexicana to be 20.63%, in the dog population studied. The results obtained with ELISA using iron superoxide dismutase as the antigen were confirmed by western blot analysis with its greater sensitivity, and the agreement between the two techniques was very high.

Structure and Variability of the Loop Current along the Yucatan Slope and Shelf Break.

Science.gov (United States)

Sheinbaum, J.; Athie, G.; Candela, J.; Ochoa, J.; Romero, A.

2016-02-01

Yucatan Current and Loop Current variability is investigated using data from an array of moorings that was deployed during 2006-2011 at the western Yucatan Channel and two other strategic cross-sections further north over the Campeche Bank, where the core and western edge of the currents are usually located. Measurements show the cores of the Yucatan Current and Loop Current have a more offshore (onshore) position in summer (winter-spring) suggesting seasonality and a relation to transport variations. Some eastward displacements of the currents are associated with periods of positive horizontal shear (cyclonic vorticity anomalies) propagating northward from the Caribbean coast of Mexico into the Gulf. Ten of the thirteen Loop Current eddies released between 2006 and 2011 were found to be clearly related to these propagating cyclonic anomalies that after crossing the Yucatan Channel produce intense pulses of eddy kinetic energy in the mooring sections downstream. Current structure and variability above and below 1000 m depth have very different characteristics. Diffferences are also found between western and eastern mooring measurements at similar depths. Wind forcing, coastally trapped waves and small scale frontal eddies appear to be the source of this east-west asymmetry.

Multivariate Statistical Analysis: a tool for groundwater quality assessment in the hidrogeologic region of the Ring of Cenotes, Yucatan, Mexico.

Science.gov (United States)

Ye, M.; Pacheco Castro, R. B.; Pacheco Avila, J.; Cabrera Sansores, A.

2014-12-01

The karstic aquifer of Yucatan is a vulnerable and complex system. The first fifteen meters of this aquifer have been polluted, due to this the protection of this resource is important because is the only source of potable water of the entire State. Through the assessment of groundwater quality we can gain some knowledge about the main processes governing water chemistry as well as spatial patterns which are important to establish protection zones. In this work multivariate statistical techniques are used to assess the groundwater quality of the supply wells (30 to 40 meters deep) in the hidrogeologic region of the Ring of Cenotes, located in Yucatan, Mexico. Cluster analysis and principal component analysis are applied in groundwater chemistry data of the study area. Results of principal component analysis show that the main sources of variation in the data are due sea water intrusion and the interaction of the water with the carbonate rocks of the system and some pollution processes. The cluster analysis shows that the data can be divided in four clusters. The spatial distribution of the clusters seems to be random, but is consistent with sea water intrusion and pollution with nitrates. The overall results show that multivariate statistical analysis can be successfully applied in the groundwater quality assessment of this karstic aquifer.

Control of the geomorphic evolution of an active crater: Popocatpetl (Mexico) 1994-2003.

Science.gov (United States)

Andrés, N.; Zamorano, J. J.; Palacios, D.; Macias, J. L.; Sanjosé, J. J.

2009-04-01

. References.- Cruz-Reyna, S. de la; Meli, R.; Macías, J.L.; Castillo, F.; & Cabrera, B., 1998. Cyclical dome extrusions that by late 1997 filled one-third of crater capacity, In Smithsonian-GVP Monthly Reports, Popocatépetl, Smithsonian Institution. Bull. Glob. Volcanism Netw, (GVN) 23 (2), 2 - 4. Donnadieu, F.; Kelfoun, K.; Van Wyk de Vries, B.; Decchi, E.; & Merle, O., 2003. Digital photogrammetry as a tool in analogue modelling: applications to volcano instability, Journal of Volcanology and Geothermal Research, 123 (1-2), 161-180. Macías, J.L. & Siebe, C., 2005. Popocatépetl crater filled to the brim: significance for hazard evaluation, Journal of Volcanology and Geothermal Research (141) 327-330. Martín-Del Pozzo, A.L.; Cifuentes-Nava, G.; Cabral-Cano, E.; Bonifaz, F.; Correa, I.; & Mendiola, I.F., 2003. Timing magma ascent at Popocatepetl Volcano, Mexico, 2000-2001, Journal of Volcanology and Geothermal Research ,125, 107-120. Matiella, M.A.; Watson, I.M.; Delgado, H.; Rose, W.I.; , Cárdenas, L.; & Realmuro, V.J., 2008, Volcanic emissions from Popocatépetl volcano, Mexico, quantified using Moderate Resolution Imaging Spectroradiometer (MODIS) infrared data: A case study of the December 2000-January 2001 emissions, Journal of Volcanology and Geothermal Research, 170, 1-2, 76-85. Procter, J.N.; Platz, T.; & Cronin, S.J., 2006. A remnant summit lava dome and its influence on future eruptive hazards, Geophysical Research Abstracts, Vol. 8, 10211. Schilling, S.P.; Ramsey, D.W.; Messerich, J.A.; & Thompson, R.A., 2006. Map: Rebuilding Mount St. Helens. U.S. Geological Survey Scientific Investigations Map 2928. Tanarro, L. M.; Zamorano, J.J.; & Palacios, D., 2005. Glacier degradation and lahar formation on the Popocatépetl volcano (Mexico) during the last eruptive period (1994-2003), Zeitschrift Geomorphologie (140) 73-92. Zamorano, J.J., Gómez, A. 1996 "Análisis geomorfoloógico a detalle,1:10 000 del cráter del volcán Popocatépetl (1989-1996)" IV Reuni

Ancient shoreline reconstruction at a Maritime Maya Port in Yucatan, Mexico

Science.gov (United States)

Jaijel, Roy; Goodman, Beverly; Glover, Jeffrey; Rissolo, Dominique; Beddows, Patricia; Carter, Alice; Smith, Derek; Ben Avraham, Zvi

2017-04-01

Throughout history, worldwide, a major part of the human experience has been to adapt to changing landscapes, and environments. These adaptations can take many forms, sometimes as innovation, manipulation of the conditions, behavioral or technological changes; and in some cases the decision to abandon the area. The northeastern Yucatan peninsula, home of the Maritime maya port site Vista-Alegre, shows signs of such human changes, though little is known about the corresponding landscape and environment. Vista Alegre is located on the meeting point of the Caribbean Sea and the Gulf of Mexico, at the north-eastern tip of the Yucatan peninsula, in the back of the Holbox lagoon. The site was inhabited from the 9th century B.C until the mid 16th century A.D., with an apparent two century abandonment phase from the mid 7th to 9th century A.D. A multidisciplinary effort ("Costa Escondida project") has been investigating the life of past Mayan inhabitants and the broader connections of the site to the Maritime Maya trade network. One of the questions that has arisen is what were the mutual influences between the inhabitants to their surrounding environment. In order to answer that question the site's shoreline geomorphology and climate history is being reconstructed for the past 2-3000 years. The reconstruction is based on multiproxy analysis of marine sediment cores and surface samples, combined with archaeological data. The study presented focuses on the shoreline shifts at the site, revealing the complexity, and significant affect of sea level rise on the marine environment of Vista Alegre. This study contributes to our understanding of the site's possible functions, the environmental challenges the local inhabits contended with, and the identification of ancient harboring locations. The results show five depositional phases over the past 2-3000 years. The ancient shoreline maps show a general trend of sea level rise, though with varying rates over time that relates well

Crater lake and post-eruption hydrothermal activity, El Chichón Volcano, Mexico

Science.gov (United States)

Casadevall, Thomas J.; De la Cruz-Reyna, Servando; Rose, William I.; Bagley, Susan; Finnegan, David L.; Zoller, William H.

1984-01-01

Explosive eruptions of Volcán El Chichón in Chiapas, Mexico on March 28 and April 3–4, 1982 removed 0.2 km3 of rock to form a 1-km-wide 300-m-deep summit crater. By late April 1982 a lake had begun to form on the crater floor, and by November 1982 it attained a maximum surface area of 1.4 × 105 m2 and a volume of 5 × 106 m3. Accumulation of 4–5 m of rainfall between July and October 1982 largely formed the lake. In January 1983, temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115°C; by October 1983 the maximum temperature of fumarole emissions was 99°C. In January 1983 fumarole gas emissions were greater than 99 vol. % H2O with traces of CO2, SO2, and H2S. The water of the lake was a hot (T = 52–58°C), acidic (pH = 0.5), dilute solution (34,046 mg L−1 dissolved solids; Cl/S = 20.5). Sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits, together with less than 1% of elemental sulfur. The composition and temperature of the lake water is attributed to: (1) solution of fumarole emissions; (2) reaction of lake water with hot rocks beneath the lake level; (3) sediments washed into the lake from the crater walls; (4) hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement; (5) evaporation; and (6) precipitation.

Nano particles as the primary cause for long-term sunlight suppression at high southern latitudes following the Chicxulub impact - evidence from ejecta deposits in Belize and Mexico

DEFF Research Database (Denmark)

Vajda, Vivi; Ocampo, Adriana; Ferrow, Embaie

2015-01-01

deposits occur in Belize and southern Mexico where the so called Albion island spheroid bed is superimposed on the target rock (the Barton Creek Formation). We analysed the spheroid bed via Mössbauer spectroscopy, petrology, XRD, and palynology at several sites ~ 350-500 km distance from the crater centre....... Our results show that the relative concentrations of Fe in nano-phase goethite (α-FeOOH) are very high in the spheroid bed samples from Albion Island (Belize) and from Ramonal South (Mexico), but are low to absent in the spheroid bed at Ramonal North, and in the Cretaceous target rock. Moreover, our......Life on Earth was sharply disrupted 66 Ma ago as an asteroid hit the sea-floor in what is today Yucatan Peninsula, Mexico. Approximately 600 km3 of sedimentary rock were vapourized, ejected into the atmosphere and subsequently deposited globally as an ejecta apron and fallout layer. Proximal ejecta...

Education, fish consumption, well water, chicken coops, and cooking fires: Using biogeochemistry and ethnography to study exposure of children from Yucatan, Mexico to metals and arsenic.

Science.gov (United States)

Arcega-Cabrera, Flor; Fargher, Lane F

2016-10-15

Around the world, the nocuous health effects of exposure to environmental contaminants, especially metals and Arsenic, are a growing health concern. This is especially the case in Mexico, where corruption and ineffective political administration are contributing to increasing deterioration in the environment. Importantly, shallow soils and the karstic nature of bedrock in Yucatan, Mexico make the subterranean aquifer especially susceptible to contamination because contaminates are carried to it with little resistance. Given these environmental conditions, we developed a multi/interdisciplinary project to evaluate the impact of metal and Arsenic pollution on a sample of 107 children, ages 6 to 9years, living in the urban areas of Progreso, Merida, and Ticul, in the State of Yucatan using urine and blood samples. In addition, ethnographic research was carried out in the homes of the children that participated in the study to identify potential exposure pathways. This research proved invaluable because the complexity of human social organization, lifestyles, and geographical patterning create an intricate array of exposure pathways that vary across social sectors and geographic space. In the following article, we use nonparametric univariate statistical analysis to reveal potential exposure pathways among sub-populations included in our sample. These analyses show that children from poor/marginal families tend to be exposed to Copper, Lead, and Nickel; whereas, children, from wealthier families, tend to be exposed to Cadmium, Arsenic, and inorganic Copper (Copper Sulfate). Copyright © 2016 Elsevier B.V. All rights reserved.

Meat production perspective in Yucatan

Directory of Open Access Journals (Sweden)

Victor M. Toledo-Lopez

2011-12-01

Full Text Available The evolution of meat production in Mexico during the last decade is the result of the complex interaction between different areas of livestock production and consumers’ preferences, being the former widely influenced by new tendencies and purchasing capacity. In Yucatan, there are two meat product processing plants. Yucatan’s research projects are basically focused to production, handling and genetics. This research is developed in Research Centers like Universidad Autonoma Yucatan’s Ciencias Biologicas Agropecuarias Campus, INIFAP Mococha, Instituto Tecnologico Conkal and Instituto Tecnologoco Merida. Many projects are inter-institutional and others by Cuerpos Academicos inside the institutions. Grants are provided by state, national or international dependencies. In the Instituto Tecnologico Merida research projects are on different animals’ meat quality and novel meat products.

Bothriocephalus pearsei n. sp. (Cestoda: Pseudophyllidea) from cenote fishes of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Scholz, T; Vargas-Vázquez, J; Moravec, F

1996-10-01

The cestode Bothriocephalus pearsei n. sp. is described from the intestine of the cichlid Cichlasoma urophthalmus (Günther) from cenote (= sinkhole) Zaci near Valladolid, Yucatan, Mexico. The pimelodid catfish Rhamdia guatemalensis Günther, which also harbored conspecific cestodes, seems to represent accidental or postcyclic host of B. pearsei. The new species differs from congeners mainly by the morphology of the scolex, which is clavate, with the maximum width in its middle part, has a distinct but weakly muscular apical disc; 2 short and wide bothria distinctly demarcated in their anterior part, becoming indistinct posteriorly in the middle part of the scolex, and 2 elongate, lateral grooves. In addition to the scolex morphology, the new species can be differentiated from Bothriocephalus species parasitizing North American freshwater fishes as follows: B. claviceps (Goeze, 1782), a specific parasite of eels in the Holarctic, B. cuspidatus Cooper, 1917, occurring mostly in perciform fishes in North America, B. musculosus Baer, 1937 found in the cichlid Cichlasoma biocellata (Regan) (= C. octofasciatum (Regan)), and B. texomensis Self, 1954, described from Hiodon alosoides (Rafinesque), are much larger, with strobilae consisting of relatively short and very wide proglottids versus small-sized strobila (length 26-32 mm) composed of about 70 proglottids, which are only slightly wider than they are long (ratio 1:1-3), rectangular, or even longer than wide in the last proglottids in B. pearsei. Bothriocephalus formosus Mueller and Van Cleave, 1932, described from Percopsis omiscomaycus (Walbaum) in the USA, can be distinguished from B. pearsei, besides the different shape of the scolex, by the distribution of vitelline follicles, which are not separated into 2 lateral fields and are present along the midline of proglottids in the former species. Bothriocephalus acheilognathi, a widely distributed parasite of fishes of many families, in particular of cyprinids

Price, Virtues, Principles: How to Discern What Inspires Best Practices in Water Management? A Case Study about Small Farmers in the Yucatan Peninsula of Mexico

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Rafael R. Ramírez

2016-04-01

Full Text Available Improving water practices among small farmers in a water scarce area like the Yucatan Peninsula in Mexico is a complex task. Despite government attempts to enforce regulations and question the possibility of adjusting prices, the misuse of this scarce resource continues. Most farmers are, at best, motivated to aim for a minimum level of compliance, with very few striving to engage in best practices. This article seeks to make a proposal about the best drivers for inspiring best practices in an effort to improve the use of water management in the area. It proposes that a virtue ethics approach that explicitly focuses on the cultivation of an attitude of respect for water founded on three key principles (participation, hydrosolidarity and proactive engagement is the best solution for Yucatan. This hypothesis is the result of developing a singular methodology based on Partial Least Squares (PLS, according to structural equation modeling (SEM, that could be replicated anywhere to ascertain which measures are best suited in a particular context. Using a small sample size, this research ascertains what is required to achieve best practices with regards to the management of water in that particular area.

A Three-Dimensional Sustainability Evaluation of Jatropha Plantations in Yucatan, Mexico

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Julio C. Sacramento Rivero

2016-12-01

Full Text Available This paper presents a unique sustainability analysis of one of the first attempts to establish a biodiesel industry in Mexico. From 2008, several companies established medium to large-sized Jatropha curcas plantations in Yucatan, hiring local peasants to carry out the agricultural work. After five years, the plantations were abandoned due to poor seed yields and a lack of key knowledge for large-scale cultivation. Based on a multidisciplinary approach, we performed a three-dimensional sustainability evaluation of the potential biodiesel production chain, which included household interviews, a socioeconomic survey, and a life-cycle assessment (LCA. We identified both negative and positive effects in the three dimensions analyzed. Socially and culturally, the local peasant families understood sustainability as their ability to preserve their traditional lifestyle, and associated environmental services with their sense of identity. They therefore considered the jatropha plantations to be positive for sustainability, since they brought income, even though some perceived damage to the natural resources of the surrounding areas. Economically, peasants’ annual household income increased by approximately $1080 USD due to the increased salaries paid by the jatropha companies. The LCA predicted large savings of greenhouse gas emissions (>50% compared to fossil diesel, but also potential negative impacts in some categories (human/ecological toxicity and eutrophication potentials associated with the use of mineral fertilizers, insecticides, and pesticides applied during the cultivation stage. Biodiesel production would be potentially energetically self-sufficient, in addition to producing a 40% energy surplus. Finally, even though the sustainability indicators suggested a positive overall assessment, the reality was that the jatropha projects failed because they were predicated on unrealistically optimistic projections and poor agronomic knowledge of the

( Didelphis virginiana ) from Yucatan, Mexico

African Journals Online (AJOL)

Toxoplasma gondii is an obligate intracellular parasite recognized as a causal agent of toxoplasmosis; zoonotic disease endemic in many countries worldwide, including Mexico. Different species of animals participate in the wild cycle infection, including opossums of the species Didelphis virginiana. Thirteen D. virginiana ...

Bioarchaeological investigation of ancient Maya violence and warfare in inland Northwest Yucatan, Mexico.

Science.gov (United States)

Serafin, Stanley; Lope, Carlos Peraza; Uc González, Eunice

2014-05-01

This study investigates evidence of changes and continuities in ancient Maya violence and warfare in inland northwest Yucatan, Mexico from the Middle Preclassic (600-300 BC) to the Postclassic (AD 1050-1542) through bioarchaeological analysis of cranial and projectile trauma. It is hypothesized that the frequency of violence increases before the Classic Maya collapse and remains high during the Postclassic period. It is also hypothesized that the flat, open terrain was conducive to warfare and resulted in higher trauma frequencies than in other parts of the Maya area. Results show that the frequency of cranial trauma decreases before the Classic collapse and increases in the Postclassic, partially matching the expected chronological trends. The frequency of cranial trauma does not differ significantly from other Maya regions but the pattern does: for all periods, males have more healed injuries than females and they are concentrated on the left side of the anterior of the skull. Some injuries appear to be from small points hafted in wooden clubs. In addition, projectile trauma is evident in a scapula with an embedded arrowhead tip, the first such case reported in a Maya skeleton. Overall, these results suggest greater reliance on open combat and less on raids in this region compared with other parts of the Maya area, possibly due to the flat, open terrain, though the identification of perimortem trauma in both women and men indicates surprise raids on settlements were also practiced. Copyright © 2014 Wiley Periodicals, Inc.

The Disruption of Subsistence Agricultural Systems in Rural Yucatan, Mexico may have Contributed to the Coexistence of Stunting in Children with Adult Overweight and Obesity.

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Gurri, Francisco D

2015-12-01

This paper attempts to link last century's disruption of local agricultural systems to today's presence of childhood under nutrition and adult overweight and obesity in the Yucatan Peninsula. It first compares Height for Age (H/A), Weight for Age (W/A) and Body Mass Index (BMI) of children from three rural populations in Yucatan and Campeche, Mexico whose subsistence strategy had been altered to different degrees since 1970. It then compares BMI in adults, in the same regions, born before and after the alteration of their environment in the 1970's. Children in the least disrupted zone were taller and had lower BMI than children in the other two, but were not heavier than children from the richest disrupted zone. Children in the poorest disrupted zone were shorter and lighter than the rest. BMI in adult men was higher in the two most disrupted zones only in those cohorts that grew up after the traditional agricultural regime was altered. It is concluded that disruptions of staple-based subsistence agriculture promoted a stockier phenotype in children and a tendency to accumulate body fat. Persistence of these conditions in the twenty first century has favored the coexistence of stunting during childhood with adults who easily become overweight.

Overview of the Chicxulub impactite and proximal ejecta

Science.gov (United States)

Claeys, Ph

2003-04-01

Several types of impactites have now been recovered from the various wells drilled in the Chicxulub crater in Yucatan. The old Pemex wells (Yucatan 6 and Chicxulub 1) contain a highly heterogeneous and stratified suevite, which upper unit is unusually rich in carbonates, impact breccia and a possibly an impact melt at the very bottom of C1. They are located towards the crater center (C1), on the flank of the peak ring (Y6). The thickness of impactite in this zone exceeds 250 m. The UNAM wells just outside the crater rim reveal sedimentary breccia and a fall-out suevite richer in silicate melt and basement fragments, than its crater equivalent. There, the thickness of the impactite was probably several hundred meters, considering that its top might have been eroded. It can also be speculated that a cover of fall-back suevite extended over the ejecta blanket in Yucatan, all the way to Belize and perhaps even to the region of Tabasco, in Southern Mexico. The recently drilled Yaxcopoil contains about 100 m of impactites, which is currently under study. Preliminary data seem to show less variability than the material recovered from Y6. As in the UNAM well, the impactite is dominated by basement material, and shows alternating severely altered and better preserved horizons.

Recovery of Biomass Following Shifting Cultivation in Dry Tropical Forests of the Yucatan

OpenAIRE

Read, L; Lawrence, Deborah; Foster, David Russell

2003-01-01

Land-use change in the tropics is creating secondary forest at an unprecedented rate. In the tropical Americas, mature dry tropical forest is rapidly being converted to secondary forest during the fallow period of shifting cultivation. This study addresses changes in forest biomass during forest recovery following shifting cultivation of maize (corn) in the Southern Yucatan Peninsular Region (SYPR), Mexico. We sampled stems .1 cm diameter at breast height at 36 study sites in t...

Preliminary study of long-term wind characteristics of the Mexican Yucatan Peninsula

International Nuclear Information System (INIS)

Soler-Bientz, Rolando; Watson, Simon; Infield, David

2009-01-01

Mexico's Yucatan Peninsula is one of the most promising areas for wind energy development within the Latin American region but no comprehensive assessment of wind resource has been previously published. This research presents a preliminary analysis of the meteorological parameters relevant to the wind resource in order to find patterns in their long-term behaviour and to establish a foundation for subsequent research into the wind power potential of the Yucatan Peninsula. Three meteorological stations with data measured for a period between 10 and 20 years were used in this study. The monthly trends of ambient temperature, atmospheric pressure and wind speed data were identified and are discussed. The directional behaviour of the winds, their frequency distributions and the related Weibull parameters are presented. Wind power densities for the study sites have been estimated and have been shown to be relatively low (wind power class 1), though a larger number of suitable sites needs to be studied before a definitive resource evaluation can be reported.

Two new species of dicyemid mesozoans (Dicyemida: Dicyemidae) from Octopus maya Voss & Solis-Ramirez (Octopodidae) off Yucatan, Mexico.

Science.gov (United States)

Castellanos-Martinez, Sheila; Aguirre-Macedo, M Leopoldina; Furuya, Hidetaka

2016-07-01

Two new dicyemid species are described from the endemic cephalopod Octopus maya Voss & Solis-Ramirez collected off Yucatan, Mexico. The renal sacs of 40 juvenile and adult octopuses from four localities were examined. Dicyema hochbergi n. sp. is a medium-sized species that reaches 2,245 µm in length. The vermiform stages consist of 18-24 peripheral cells, a conical calotte and the extension of the axial cell between the base and middle of the metapolar cells. Infusoriform embryos consist of 39 cells with urn cell containing one germinal cell, two nuclei and solid refringent bodies. Dicyema mexcayae n. sp. is a relatively small species that reaches 1,114 µm in length. The vermiform stages are constituted by 14-16 peripheral cells, an elongate calotte and the axial cell extending forward to the middle of the metapolar cells. The infusoriform embryos consist of 37 cells, two solid refringent bodies and urn cells with two nuclei each. The present study represents the first description of a dicyemid species from O. maya and increases the number of described species from Mexican waters to 11.

Occurrence of Pepper Mild Mottle Virus (PMMoV) in Groundwater from a Karst Aquifer System in the Yucatan Peninsula, Mexico.

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Rosiles-González, Gabriela; Ávila-Torres, Gerardo; Moreno-Valenzuela, Oscar A; Acosta-González, Gilberto; Leal-Bautista, Rosa María; Grimaldo-Hernández, Cinthya D; Brown, Judith K; Chaidez-Quiroz, Cristóbal; Betancourt, Walter Q; Gerba, Charles P; Hernández-Zepeda, Cecilia

2017-12-01

The Yucatan Peninsula of Mexico hosts a karst aquifer system that is the only source of freshwater for the area; however, it is vulnerable to human-mediated contamination. Pepper mild mottle virus (PMMoV) is one of the most abundant RNA viruses associated with human feces, making it a viable indicator for tracking fecal pollution in aquatic environments, including groundwater. In this study, groundwater samples collected from a karst aquifer from fresh and brackish water locations were analyzed for fecal indicator bacteria, somatic and male F+ specific coliphages, and PMMoV during the rainy and dry seasons. Total coliform bacteria were detected at all sites, whereas Escherichia coli were found at relatively low levels water type (p > 0.05). Physicochemical and indicator bacteria were not correlated with PMMoV concentrations. The abundance and prevalence of PMMoV in the karst aquifer may reflect its environmental persistence and its potential as a fecal indicator in this karst aquifer system.

Water Consumption as Source of Arsenic, Chromium, and Mercury in Children Living in Rural Yucatan, Mexico: Blood and Urine Levels.

Science.gov (United States)

Arcega-Cabrera, F; Fargher, L F; Oceguera-Vargas, I; Noreña-Barroso, E; Yánez-Estrada, L; Alvarado, J; González, L; Moo-Puc, R; Pérez-Herrera, N; Quesadas-Rojas, M; Pérez-Medina, S

2017-10-01

Studies investigating the correlation between metal content in water and metal levels in children are scarce worldwide, but especially in developing nations. Therefore, this study investigates the correlation between arsenic, chromium, and mercury concentrations in drinking and cooking water and in blood and urine samples collected from healthy and supposedly non-exposed children from a rural area in Yucatan, Mexico. Mercury in water shows concentrations above the recommended World Health Organization (WHO) value for drinking and cooking water. Also, 25% of the children show mercury in urine above the WHO recommended value. Multivariate analyses show a significant role for drinking and cooking water as a vector of exposure in children. Also, the factor analysis shows chronic exposure in the case of arsenic, as well as an ongoing detoxification process through urine in the case of mercury. Further studies should be done in order to determine other potential metal exposure pathways among children.

ESTABLISHMENT OF TREE ASSOCIATION WITH CAOBA AND RAMON IN AN ABANDONED QUARRY IN YUCATAN, MEXICO

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Patricia Montañez Escalante

2009-02-01

Full Text Available The influence of the association trees on the height and diameter growth  of mahogany (Swietenia macrophylla King and ramón (Brosimum alicastrum Sw. plantations during the establishment period in an quarry near the city of Merida, Yucatan, Mexico, was evaluated. Associated trees to mahogany were  tamarindo (Tamarindus indica L. and achiote (Bixa orellana L.. Associated trees to ramón were huaxin (Leucaena leucocephala (Lam de Wit. and pixoy (Guazuma ulmifolia Lam.. Tree association effects on the growth in height and diameter of mahogany and ramón were analyzed. The production of fruits and forage in the associated tree species was determined. There were no significant differences in mahogany and ramón diameter and height growth (p> 0.05 among treatments. To associate the ramón with other species of fast growth like huaxin and pixoy pruning was repeatedly conducted on this species to obtain the light levels required for ramón. The forage production of haxin and pixoy was 2 t dry matter ha-1 y-1 and there were not significant differences (p>0.05. The time required to get productive age in the species like ramon and mahogany offer opportunities to use the interspaces during growth period.

Seroprevalence of antibodies against the excreted antigen superoxide dismutase by Trypanosoma cruzi in dogs from the Yucatan Peninsula (Mexico).

Science.gov (United States)

López-Cespedes, A; Longoni, S S; Sauri-Arceo, C H; Rodríguez-Vivas, R I; Villegas, N; Escobedo-Ortegón, J; Barrera-Pérez, M A; Sánchez-Moreno, M; Bolio González, M E; Marín, C

2013-06-01

Numerous studies have shown the role of dogs as a reservoir for the American trypanosomiasis, as the bridge connecting sylvatic and peridomestic cycles. The objective of this study was to determine the prevalence of American trypanosomiasis in the dog population (630 sera) from seven localities in the Yucatan Peninsula (city of Mérida and the towns of Molas, Playa del Carmen, Akumal, Xcalacoop, Xcalac and Xahuachol). These data are key for developing control measures for the disease. The sera were analysed to detect antibodies against Trypanosoma cruzi, using Fe-SOD excreted as the antigenic fraction by ELISA and Western blot as confirmation. The total prevalence found in the Yucatan Peninsula was some 14.76%, with 10.74% in the state of Yucatan (city of Mérida, towns of Molas and Xcalacoop) and 21.34% in the state of Quintana Roo (towns of Playa del Carmen, Akumal, Xcalac and Xahuachol). However, a more thorough epidemiological study of the dog population, both wild and urban, in the Yucatan Peninsula will be required to design a control strategy for these diseases, paying particular attention to the population affected and even broadening the study to other Mexican states as well as neighbouring countries. These results again confirm that iron-superoxide dismutase excreted by T. cruzi constitutes a good source of antigen for serodiagnosis in epidemiological studies. © 2012 Blackwell Verlag GmbH.

Characterization of constitutive materials and technology of the mural painting of the acropolis of the archaeological zone of Ek Balam, Yucatan, Mexico; Caracterizacion de materiales constitutivos y tecnologia de la pintura mural de la acropolis de la zona arquelogica de Ek Balam, Yucatan, Mexico

Energy Technology Data Exchange (ETDEWEB)

Alonso O, A.; Vazquez N, J.; Ruiz M, C. [INAH, 11000 Mexico D.F. (Mexico); Mendoza A, D.; Espinosa P, M. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Ruvalcaba, J.L. [IFUNAM, 04510 Mexico D.F. (Mexico); Vandenabeele, P. [Universidad de Ghent, Belgica (Belgium)]. e-mail: alealonsolvera@yahoo.com

2005-07-01

The conservation project of Ek'Balam is one of the few experiences of systematic conservation applied in an archaeological Maya site at the Yucatan Peninsula in Mexico. The project started in the year 2001 when important stone, stucco and painting decorations were discovered during archaeological excavations. Being a recently discovered site, the conservation program includes a research program based on particular conservation issues detected as potential risk of archaeological data losses. One of the research topics is based on deter- mining the ancient painting technology used in mural and stucco decorations through the characterization of building and decorative composite materials. Archaeometric techniques have been used to fulfil the proposed goal. Raman, X-ray Fluorescence, Light and Electron Microscopy were practiced on a set of 35 wall painting samples. Preliminary results obtained on pigments characterization have partially revealed general features of wall painting technique at Ek'Balam during the late Classic period. Some particular pigments, not reported ever for mural paintings, have been identified in Ek'Balam samples. (Author)

Eco-bio-social determinants for house infestation by non-domiciliated Triatoma dimidiata in the Yucatan Peninsula, Mexico.

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Eric Dumonteil

Full Text Available BACKGROUND: Chagas disease is a vector-borne disease of major importance in the Americas. Disease prevention is mostly limited to vector control. Integrated interventions targeting ecological, biological and social determinants of vector-borne diseases are increasingly used for improved control. METHODOLOGY/PRINCIPAL FINDINGS: We investigated key factors associated with transient house infestation by T. dimidiata in rural villages in Yucatan, Mexico, using a mixed modeling approach based on initial null-hypothesis testing followed by multimodel inference and averaging on data from 308 houses from three villages. We found that the presence of dogs, chickens and potential refuges, such as rock piles, in the peridomicile as well as the proximity of houses to vegetation at the periphery of the village and to public light sources are major risk factors for infestation. These factors explain most of the intra-village variations in infestation. CONCLUSIONS/SIGNIFICANCE: These results underline a process of infestation distinct from that of domiciliated triatomines and may be used for risk stratification of houses for both vector surveillance and control. Combined integrated vector interventions, informed by an Ecohealth perspective, should aim at targeting several of these factors to effectively reduce infestation and provide sustainable vector control.

A new genus of speleophriid copepod (Copepoda: Misophrioida) from a cenote in the Yucatan, Mexico with a phylogenetic analysis at the species level.

Science.gov (United States)

Boxshall, Geoff A; Zylinski, Sarah; Jaume, Damià; Iliffe, Thomas M; Suárez-Morales, Eduardo

2014-06-23

A new genus and species of speleophriid copepod, Mexicophria cenoticola gen. et sp. nov., is described based on material collected from a cenote in the Yucatan Peninsula of Mexico. It is characterised by relatively reduced fifth legs that are located adjacent to the ventral midline in both sexes, by the possession of a bulbous swelling on the first antennulary segment in both sexes, and by the reduced setation of the swimming legs. The presence of just one inner margin seta on the second endopodal segment of legs 2 to 4 is a unique feature for the family. A phylogenetic analysis places the new genus on a basal lineage of the family together with its sister taxon, Boxshallia Huys, 1988, from Lanzarote in the Canary Islands, and recovers the existing genera as monophyletic units. The zoogeography is discussed at local, regional, ocean basin  and global scales.

Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

Science.gov (United States)

Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

1993-03-01

Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

Floristic affinities of the lowland savannahs of Belize and southern Mexico.

Science.gov (United States)

Canché-Estrada, Idalia Arely; Ortiz-Díaz, Juan Javier; Tun-Garrido, Juan

2018-01-01

Environmental heterogeneity of Belize and southern Mexico savannahs as well as their geographical location suggest that these plant communities share floristic elements, making them conducive to a phytogeographical analysis. The aim of this study was to analyse the floristic affinities of nine savannahs of Belize and southern Mexico and to explain the similarities and differences amongst them. A binary data matrix containing 915 species was built based on the authors' own collections and on nine floristic lists already published. A second data matrix, consisting of 113 species representing trees, was also used since most literature on neotropical savannahs has focused on this life form. In addition, the ten most species-rich families as well as the characteristic species present in more than five savannahs were analysed. Floristic similarities were calculated using the Jaccard index. Dendrograms obtained in both types of analysis showed clusters with low similarity values, corresponding to geographic locations formed by the savannahs of Belize-Tabasco and the Yucatan Peninsula. The floristic affinities of the savannahs may be explained in terms of heterogeneity in climate and physiography. The Yucatan Peninsula and Belize-Tabasco groups have differences in climate type and the amount of rainfall. In addition, the Yucatan Peninsula savannahs are established at the bottom of karstic valleys, while the Belize and Tabasco savannahs develop on extensive flatlands. The savannahs of Oaxaca have the same climate type and amount of rainfall as those of the Yucatan Peninsula but they are distributed along peaks and the slopes of shale hills. Fabaceae and Poaceae mainly dominated the local floras with 121 and 116 species each; remarkably, Melastomataceae was absent in the Yucatan Peninsula and Oaxaca. Nine species occurred in five to seven savannahs, confirming that they are widespread in both Belize and southern Mexico, and the Neotropics. Geographic location and floristic

Indication of a species in an extinction vortex: The ocellated turkey on the Yucatan peninsula, Mexico

NARCIS (Netherlands)

Kampichler, C.; Calmé, S.; Weissenberger, H.; Arriaga-Weiss, S.

2010-01-01

The ocellated turkey Meleagris ocellata (OT) is a large, unmistakable endemic bird of the Yucatan peninsula. The species has suffered a considerable loss of distributional area as well as local abundance between 1980 and 2000 and is classified as endangered according to Mexican norms. We applied

Frequency of Varroa destructor, Nosema spp and Acarapis woodi in commercial colonies of bees (Apis mellifera in Yucatan, Mexico

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Martínez-Puc Jesús Froylán

2015-10-01

Full Text Available Today it has been observed that diseases affecting bees (Apis mellifera have caused significant economic losses in the European continent and in parts of the United States due to high mortality in honey bee colonies without a cause apparent, which is known as the syndrome of depopulation of hives. It is noteworthy that this mortality is not yet presented in Yucatan. In order to determine the frequency and levels of infestation Acarapis woodi and Varroa destructor, and the frequency and levels of infection Nosema spp. commercial colonies of bees (A. mellifera in Yucatan, was collected from June to December 2006, a total of 165 samples distributed in 13 towns of Yucatan. V. destructor frequency was 63.6%, with an average level of infestation of 2.85 ± 0.79 (mites / 100 bees. The frequency of Nosema spp. was 81.8%, with an average infection level = 1'234000 ± 118000 (spores / bee, the presence of A. woodi in the samples analyzed was detected. The existence of an association between V. destructor and Nosema spp was observed. (X2 = 6.53, df = 1, p = 0.01.

The malleability of infant motor development: cautions based on studies of child-rearing practices in Yucatan.

Science.gov (United States)

Solomons, H C

1978-11-01

Tests with the Bayley Motor Scale were given to 288 infants, equally divided by sex, in Yucatan, Mexico. These were 2 to 54 weeks in age and came from three sociocultural levels. In comparison to USA infants, early acceleration of motor development was followed by a marked downward trend. This phenomenon, if observed in a single child, may indicate progressive neurologic disease. Child-rearing practices would appear to account for the difference in pattern of test performance.

Exploring the KT source crater: Progress and future prospects

Science.gov (United States)

Sharpton, Virgil L.

It has been 15 years since an iridium-enriched clay layer at the Cretaceous-Tertiary (KT) boundary was discovered, providing the first hard evidence linking the most recent mass extinction event to a comet or asteroid strike [Alvarez et al., 1980]. Now it is widely accepted that the site of this collision is on the Yucatan platform, centered near Progreso, Mexico. The 200-300-km-wide crater lies buried beneath 300-1000 m of limestone laid down in the intervening 65 million years, and few clues of its presence remain at the surface, save an arcuate arrangement of water-filled sinkholes centered approximately on the structure (Figure 1). Yet prominent circular anomalies in gravity and magnetic anomaly maps gained the interest of Petroleos Mexicanos (Pemex), and in the early 1950s they began an exploration campaign that included deep drilling to recover samples of the subsurface rocks. The buried feature became known as the Chicxulub structure. Pemex drilling continued throughout the early 1970s and by that time, three wells near the center had recovered silicate rocks with igneous textures, initially mistaken for volcanic rocks. Other wells, located between 130 km and 210 km from ground zero recovered breccia deposits hundreds of meters thick that showed evidence of catastropic or explosive conditions. By 1980, Antonio Camargo, a geophysicist at Pemex, felt the evidence pointed to impact, although a volcanic origin for the Chicxulub structure could not be ruled out.

Changes in stature, weight, and nutritional status with tourism-based economic development in the Yucatan.

Science.gov (United States)

Leatherman, Thomas L; Goodman, Alan H; Stillman, Tobias

2010-07-01

Over the past 40 years, tourism-based economic development has transformed social and economic conditions in the Yucatan Peninsula, Mexico. We address how these changes have influenced anthropometric indicators of growth and nutritional status in Yalcoba, a Mayan farming community involved in the circular migration of labor in the tourist economy. Data are presented on stature and weight for children measured in 1938 in the Yucatan Peninsula and from 1987 to 1998 in the Mayan community of Yalcoba. In addition, stature, weight and BMI are presented for adults in Yalcoba based on clinic records. Childhood stature varied little between 1938 and 1987. Between 1987 and 1998 average male child statures increased by 2.6cm and female child statures increased by 2.7cm. Yet, 65% of children were short for their ages. Between 1987 and 1998, average child weight increased by 1.8kg. Child BMIs were similar to US reference values and 13% were considered to be above average for weight. Forty percent of adult males and 64% of females were overweight or obese. The anthropometric data from Yalcoba suggest a pattern of stunted children growing into overweight adults. This pattern is found elsewhere in the Yucatan and in much of the developing world where populations have experienced a nutrition transition toward western diets and reduced physical activity levels. 2010 Elsevier B.V. All rights reserved.

First Detection of the Kdr Mutation T929I in Head Lice (Phthiraptera: Pediculidae) in Schoolchildren of the Metropolitan Area of Nuevo Leon and Yucatan, Mexico.

Science.gov (United States)

Ponce-Garcia, Gustavo; Villanueva-Segura, Karina; Trujillo-Rodriguez, Gerardo; Rodriguez-Sanchez, Iram P; Lopez-Monroy, Beatriz; Flores, Adriana E

2017-07-01

The head louse Pediculus humanus capitis (De Geer) is a hematophagous ectoparasite that inhabits the human scalp. Infestations by this insect are commonly known as pediculosis, which is more common in younger groups. These infestations are asymptomatic; however, skin irritation from scratching occasionally may cause secondary bacterial infections. In recent years, the prevalence of pediculosis has increased in children; this increase has been attributed to louse resistance to the insecticides used as a control measure for infestation. The aim of the present study was to determine the presence and frequency of the knockdown resistance mutation (kdr) T929I in 468 head lice collected from 32 elementary schools in the metropolitan area of Nuevo Leon (24) and Yucatan (8), Mexico. This is the first report of a knockdown resistance (kdr) mechanism in head lice from Mexico. The T929I mutation was present in all of the sampled schools, with variability observed in its allelic and genotypic frequencies. © The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Fish community structure in freshwater karstic water bodies of the Sian Ka'an Reserve in the Yucatan peninsula, Mexico

Science.gov (United States)

Zambrano, L.; Vazquez-Dominguez, E.; Garcia-Bedoya, D.; Loftus, W.F.; Trexler, J.C.

2006-01-01

We evaluated the relationship between limnetic characteristics and fish community structure (based on species richness, abundance and individual size) in contrasting but interconnected inland aquatic habitats of freshwater karstic wetlands in the Yucatan peninsula, Mexico. In the western hemisphere, freshwater karstic wetlands are found in south-eastern Mexico, northern Belize, western Cuba, Andros Island, Bahamas and the Everglades of southern Florida. Only in the Everglades have fish communities been well described. Karstic wetlands are typically oligotrophic because calcium carbonate binds phosphorus, making it relatively unavailable for plants. Fourteen permanent and seasonally flooded water bodies were sampled in both wet and dry seasons in Sian Ka'an Biosphere Reserve, in the Mexican state of Quintana Roo. Water systems were divided by morphology in four groups: cenotes with vegetation (CWV), cenotes without vegetation (CNV), wetlands (WTL), and temporal cenotes (TPC). Discriminant analysis based on physical characteristics such as turbidity, temperature, depth and oxygen confirmed that these habitats differed in characteristics known to influence fish communities. A sample-based rarefaction test showed that species richness was significantly different between water systems groups, showing that WTL and CWV had higher richness values than CNV and TPC. The most abundant fish families, Poeciliidae, Cichlidae and Characidae, differed significantly in average size among habitats and seasons. Seasonal and inter-annual variation, reflecting temporal variation in rainfall, strongly influenced the environmental differences between shallow and deep habitats, which could be linked to fish size and life cycles. Five new records of species were found for the reserve, and one new record for Quintana Roo state. ?? 2006 by Verlag Dr. Friedrich Pfeil.

A third case of amelia in Morelet's crocodile from the Yucatan Peninsula.

Science.gov (United States)

Charruau, Pierre; Niño-Torres, Carlos A

2014-07-03

Congenital defects in crocodilians have received little interest. In the context of global change and increasing threats to biodiversity, data on birth defects occurring in wildlife could be of importance for estimating the health of species populations and their ecosystems. Herein, we report the first case of amelia (i.e. absence of limbs) in Morelet's crocodiles Crocodylus moreletii from Mexico and the third on the southern Yucatan Peninsula. The crocodile in question was a juvenile (41 cm total length) captured in July 2012 in the Río Hondo, the river that forms the border between Mexico and Belize south of the state of Quintana Roo. The prevalence of this malformation in the C. moreletii population of Río Hondo (0.35%) is similar to that reported in 2 previous cases in Belize. Several causes of birth defects in crocodilians have previously been cited in the literature. Although we do not have relevant information to elucidate this case, we discuss some plausible explanations for this birth defect.

Characterization of constitutive materials and technology of the mural painting of the acropolis of the archaeological zone of Ek Balam, Yucatan, Mexico

International Nuclear Information System (INIS)

Alonso O, A.; Vazquez N, J.; Ruiz M, C.; Mendoza A, D.; Espinosa P, M.; Ruvalcaba, J.L.; Vandenabeele, P.

2005-01-01

The conservation project of Ek'Balam is one of the few experiences of systematic conservation applied in an archaeological Maya site at the Yucatan Peninsula in Mexico. The project started in the year 2001 when important stone, stucco and painting decorations were discovered during archaeological excavations. Being a recently discovered site, the conservation program includes a research program based on particular conservation issues detected as potential risk of archaeological data losses. One of the research topics is based on deter- mining the ancient painting technology used in mural and stucco decorations through the characterization of building and decorative composite materials. Archaeometric techniques have been used to fulfil the proposed goal. Raman, X-ray Fluorescence, Light and Electron Microscopy were practiced on a set of 35 wall painting samples. Preliminary results obtained on pigments characterization have partially revealed general features of wall painting technique at Ek'Balam during the late Classic period. Some particular pigments, not reported ever for mural paintings, have been identified in Ek'Balam samples. (Author)

Settlement patterns and communication routes of the western Maya wetlands: An archaeological and remote-sensing survey, Chunchucmil, Yucatan, Mexico

Science.gov (United States)

Hixson, David R.

This dissertation investigates the role of the seasonal wetlands in the political economy and subsistence strategies of the ancient Maya of Chunchucmil, Yucatan, Mexico. A combination of pedestrian surveys and remote-sensing tasks were performed in order to better understand the settlement patterns and potential communication routes in and through the wetlands between Chunchucmil and the Gulf of Mexico. These western wetlands had been proposed as the principal avenue for interregional trade between coastal merchants and inland consumers, yet were thought to be uninhabited and uncultivable. Following the survey tasks outlined in this dissertation, these wetlands were found to contain an abundance of archaeological settlements and features indicating habitation, utilization, and trade throughout this diverse ecological zone. The remote-sensing platforms utilized in this study include both multispectral (Landsat) and synthetic aperture radar (AirSAR), combined with additional remotely sensed resources. One of the goals of this survey was to test the capabilities of these two sensors for the direct detection of archaeological features from air and space. The results indicate that Landsat can be highly successful at detecting site location and measuring site size under certain environmental conditions. The Airborne Synthetic Aperture Radar proved to be adept at detecting large mounded architecture within the Yucatecan karstic plain, but its further utility is hampered by limitations of resolution, scale, and land cover. One of the salient features of the landscape west of Chunchucmil is a network of stone pathways called andadores. These avenues through the wetlands outline a dendritic network of communication, trade, and extraction routes. The following dissertation places this network and its associated settlements (from suburban centers to diminutive camps) within their regional context, examining the roles they may have played in supporting a large mercantile

Chitons (Mollusca, Polyplacophora from Alacranes Reef, Yucatan, Mexico

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Adriana Reyes-Gómez

2017-04-01

Full Text Available This study represents the first comprehensive chiton study from Alacranes Reef, the largest reef system in the Gulf of Mexico. Nine chiton species were found in seven localities within the area, in the intertidal and subtidal to 12 m depth. SEM examination of C. janeirensis, A. hemphilli, T. schrammi and C. floridanus, showed variations in the sculpture and radular teeth morphology when compared to specimens of the same species from Florida Keys, Bahamas and Puerto Rico. The distribution ranges of T. schrammi, L. liozonis and S. floridana are extended into the south-western area of the Gulf of Mexico. Altogether, combining previous literature and the present survey, reports eleven chiton species which have now been recorded within the Alacranes reef area.

Chitons (Mollusca, Polyplacophora) from Alacranes Reef, Yucatan, Mexico

Science.gov (United States)

Reyes-Gómez, Adriana; Ortigosa, Deneb; Simões, Nuno

2017-01-01

Abstract This study represents the first comprehensive chiton study from Alacranes Reef, the largest reef system in the Gulf of Mexico. Nine chiton species were found in seven localities within the area, in the intertidal and subtidal to 12 m depth. SEM examination of C. janeirensis, A. hemphilli, T. schrammi and C. floridanus, showed variations in the sculpture and radular teeth morphology when compared to specimens of the same species from Florida Keys, Bahamas and Puerto Rico. The distribution ranges of T. schrammi, L. liozonis and S. floridana are extended into the south-western area of the Gulf of Mexico. Altogether, combining previous literature and the present survey, reports eleven chiton species which have now been recorded within the Alacranes reef area. PMID:28769624

Interaction of landscape varibles on the potential geographical distribution of parrots in the Yucatan Peninsula, Mexico

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Plasencia–Vázquez, A. H.

2014-12-01

Full Text Available The loss, degradation, and fragmentation of forested areas are endangering parrot populations. In this study, we determined the influence of fragmentation in relation to vegetation cover, land use, and spatial configuration of fragments on the potential geographical distribution patterns of parrots in the Yucatan Peninsula, Mexico. We used the potential geographical distribution for eight parrot species, considering the recently published maps obtained with the maximum entropy algorithm, and we incorporated the probability distribution for each species. We calculated 71 metrics/variables that evaluate forest fragmentation, spatial configuration of fragments, the ratio occupied by vegetation, and the land use in 100 plots of approximately 29 km², randomly distributed within the presence and absence areas predicted for each species. We also considered the relationship between environmental variables and the distribution probability of species. We used a partial least squares regression to explore patterns between the variables used and the potential distribution models. None of the environmental variables analyzed alone determined the presence/absence or the probability distribution of parrots in the Peninsula. We found that for the eight species, either due to the presence/absence or the probability distribution, the most important explanatory variables were the interaction among three variables, particularly the interactions among the total forest area, the total edge, and the tropical semi–evergreen medium– height forest. Habitat fragmentation influenced the potential geographical distribution of these species in terms of the characteristics of other environmental factors that are expressed together with the geographical division, such as the different vegetation cover ratio and land uses in deforested areas.

Occurrence of Sciadicleithrum mexicanum Kritsky, Vidal-Martinez et Rodríguez-Canul, 1994 (Monogenea: Dactylogyridae in the Cichlid Cichlasoma urophthalmus from a flooded quarry in Yucatan, Mexico

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E. F. Mendoza-Franco

1995-06-01

Full Text Available Cichlids, Cichlasoma urophthalmus, collected in a flooded quarry in the Yucatan Peninsula, Mexico, from January through June 1992, had high levels of infection with the ancyrocephaline Sciadicleithrum mexicanum (Monogena: Dactylogyridade in all montlhly samples. Neither occurrence nor maturation of the worms eshibited any pronounced monthly fluctuation. The infection rate was found to be sizedependent, greater in longer fish. The worms occurred on primary lamellae of gill filaments of all arches, with lower numbers of parasites attached to the fourth gill arch. Otherwise, there was no significant site preference of worms. Only minor histopathological changes were found at the sites of attachment, and these were restricted to the epithelial cells of the primary lamellae of thegill filaments. The lack of seasonal periodicity in this tropical monogenean is compared to seasonal cycles typical of temperate species.

A new species of predaceous midge of the genus Monohelea Kieffer from Mexico (Diptera: Ceratopogonidae).

Science.gov (United States)

Felippe-Bauer, M L; Huerta, H; Bernal, S I

2000-01-01

A description and illustrations of Monohelea maya, new species, based on male and female characteristics are provided. The specimens were collected in the special biosphere Reserves of Ria Lagartos and Ria Celestun, Yucatan State, Mexico.

Origin of honeybees (Apis mellifera L.) from the Yucatan peninsula inferred from mitochondrial DNA analysis.

Science.gov (United States)

Clarke, K E; Oldroyd, B P; Javier, J; Quezada-Euán, G; Rinderer, T E

2001-06-01

Honeybees (Apis mellifera L.) sampled at sites in Europe, Africa and South America were analysed using a mitochondrial DNA restriction fragment length polymorphism (RFLP) marker. These samples were used to provide baseline information for a detailed analysis of the process of Africanization of bees from the neotropical Yucatan peninsula of Mexico. Radical changes in mitochondrial haplotype (mitotype) frequencies were found to have occurred in the 13-year period studied. Prior to the arrival of Africanized bees (1986) the original inhabitants of the Yucatan peninsula appear to have been essentially of southeastern European origin with a smaller proportion having northwestern European ancestry. Three years after the migration of Africanized bees into the area (1989), only very low levels of maternal gene flow from Africanized populations into the resident European populations had occurred. By 1998, however, there was a sizeable increase in the proportion of African mitotypes in domestic populations (61%) with feral populations having 87% of mitotypes classified as African derived. The results suggest that the early stages of Africanization did not involve a rapid replacement of European with African mitotypes and that earlier studies probably overestimated the prevalence of African mitotypes.

A new species of predaceous midge of the genus Monohelea Kieffer from Mexico (Diptera: Ceratopogonidae

Directory of Open Access Journals (Sweden)

Maria Luiza Felippe-Bauer

2000-12-01

Full Text Available A description and illustrations of Monohelea maya, new species, based on male and female characteristics are provided. The specimens were collected in the special biosphere Reserves of Ria Lagartos and Ria Celestun, Yucatan State, Mexico.

The Sac Actun System, Quintana Roo, Mexico; Sistema Sac Actun, Quintana Roo, Mexico

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Kambesis, P. N.; Coke, J. G.

2016-07-01

The Sac Actun system, located in northeast Quintana Roo, Mexico, is among the most extensive underwater cave systems located along the Caribbean coast of the Yucatan Peninsula. The cave is composed of linear phreatic conduits that have two forms. The coastal sections of the Sac Actun system are characterized by low horizontal tunnels that form mazes paralleling the coast and rudimentary conduits broken by fracture-controlled rooms. Inland passages are fault/fracture controlled, have a linear, anastomotic configuration, and align perpendicular to the coast. Access to the cave system is gained through cenotes which are the portals into the Yucatan underwater cave systems. The occurrence of drowned speleothems in many parts of the cave system, and sections of air-filled upper level passages are indicative of major fluctuations in sea level. The Sac Actun system is part of one of the most extensive and significant eogenetic karst aquifers in the world. The development of the Sac Actun system, as well as the many other caves systems along the Yucatan Caribbean Coast is controlled by the coastal hydrologic regime, driven by glacio-eustatics, and influenced by stratigraphic and structural controls. The karstic permeability of the aquifer makes it and the Sac Actun system vulnerable to the anthropogenic impacts of increased population growth, quarries, and infrastructure development associated with the burgeoning tourist industry that dominates land use in the region. (Author)

[Analysis of the impact of mortality due to suicides in Mexico, 2000-2012].

Science.gov (United States)

Dávila Cervantes, Claudio Alberto; Ochoa Torres, María del Pilar; Casique Rodríguez, Irene

2015-12-01

The objective of this study was to analyze the burden of disease due to suicide in Mexico using years of life lost (YLL) between 2000 and 2012 by sex, age group (for those under 85 years of age) and jurisdiction. Vital statistics on mortality and population estimates were used to calculate standardized mortality rates and years of life lost due to suicide. Between 2000 and 2012 a sustained increase in the suicide mortality rate was observed in Mexico. The age group with the highest rate was 85 years of age or older for men, and 15-19 years of age for women. The highest impact in life expectancy due to suicide occurred at 20 to 24 years of age in men and 15 to 19 years of age in women. The states with the highest mortality due to suicide were located in the Yucatan Peninsula (Yucatan, Quintana Roo and Campeche). Mortality due to suicide in Mexico has increased continually. As suicides are preventable, the implementation of health public policies through timely identification, integral prevention strategies and the detailed study of associated risk factors is imperative.

Deep Drilling Into the Chicxulub Impact Crater: Pemex Oil Exploration Boreholes Revisited

Science.gov (United States)

Fucugauchi, J. U.; Perez-Cruz, L.

2007-05-01

The Chicxulub structure was recognized in the 1940´s from gravity anomalies in oil exploration surveys by Pemex. Geophysical anomalies occur over the carbonate platform in NW Yucatan, where density and magnetic susceptibility contrasts with the carbonates suggested a buried igneous complex or basement uplift. The exploration program developed afterwards included several boreholes, starting with the Chicxulub-1 in 1952 and eventually comprising eight deep boreholes completed through the 1970s. The investigations showing Chicxulub as a large impact crater formed at the K/T boundary have relayed on the Pemex decades-long exploration program. Despite frequent reference to Pemex information, original data have not been openly available for detailed evaluation and incorporation with results from recent efforts. Logging data and core samples remain to be analyzed, reevaluated and integrated in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we discuss the paleontological data, stratigraphic columns and geophysical logs for the Chicxulub-1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m) and Ticul-1 (3575m) boreholes. These boreholes remain the deepest ones drilled in Chicxulub and the only ones providing samples of the melt-rich breccias and melt sheet. Other boreholes include the Y1 (3221m), Y2 (3474m), Y4 (2398m) and Y5A (3003m), which give information on pre-impact stratigraphy and crystalline basement. We concentrate on log and microfossil data, stratigraphic columns, lateral correlation, integration with UNAM and ICDP borehole data, and analyses of sections of melt, impact breccias and basal Paleocene carbonates. Current plans for deep drilling in Chicxulub crater focus in the peak ring zone and central sector, with proposed marine and on-land boreholes to the IODP and ICDP programs. Future ICDP borehole will be located close to Chicxulub-1 and Sacapuc-1, which intersected

A dataset on the species composition of amphipods (Crustacea) in a Mexican marine national park: Alacranes Reef, Yucatan.

Science.gov (United States)

Paz-Ríos, Carlos E; Simões, Nuno; Pech, Daniel

2018-01-01

Alacranes Reef was declared as a National Marine Park in 1994. Since then, many efforts have been made to inventory its biodiversity. However, groups such as amphipods have been underestimated or not considered when benthic invertebrates were inventoried. Here we present a dataset that contributes to the knowledge of benthic amphipods (Crustacea, Peracarida) from the inner lagoon habitats from the Alacranes Reef National Park, the largest coral reef ecosystem in the Gulf of Mexico. The dataset contains information on records collected from 2009 to 2011. Data are available through Global Biodiversity Information Facility (GBIF). A total of 110 amphipod species distributed in 93 nominal species and 17 generic species, belonging to 71 genera, 33 families and three suborders are presented here. This information represents the first online dataset of amphipods from the Alacranes Reef National Park. The biological material is currently deposited in the crustacean collection from the regional unit of the National Autonomous University of Mexico located at Sisal, Yucatan, Mexico (UAS-Sisal). The biological material includes 588 data records with a total abundance of 6,551 organisms. The species inventory represents, until now, the richest fauna of benthic amphipods registered from any discrete coral reef ecosystem in Mexico.

Effects of precipitation regime and soil nitrogen on leaf traits in seasonally dry tropical forests of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Roa-Fuentes, Lilia L; Templer, Pamela H; Campo, Julio

2015-10-01

Leaf traits are closely associated with nutrient use by plants and can be utilized as a proxy for nutrient cycling processes. However, open questions remain, in particular regarding the variability of leaf traits within and across seasonally dry tropical forests. To address this, we considered six leaf traits (specific area, thickness, dry matter content, N content, P content and natural abundance (15)N) of four co-occurring tree species (two that are not associated with N2-fixing bacteria and two that are associated with N2-fixing bacteria) and net N mineralization rates and inorganic N concentrations along a precipitation gradient (537-1036 mm per year) in the Yucatan Peninsula, Mexico. Specifically we sought to test the hypothesis that leaf traits of dominant plant species shift along a precipitation gradient, but are affected by soil N cycling. Although variation among different species within each site explains some leaf trait variation, there is also a high level of variability across sites, suggesting that factors other than precipitation regime more strongly influence leaf traits. Principal component analyses indicated that across sites and tree species, covariation in leaf traits is an indicator of soil N availability. Patterns of natural abundance (15)N in foliage and foliage minus soil suggest that variation in precipitation regime drives a shift in plant N acquisition and the openness of the N cycle. Overall, our study shows that both plant species and site are important determinants of leaf traits, and that the leaf trait spectrum is correlated with soil N cycling.

Molecular characterization of atypical antigenic variants of canine rabies virus reveals its reintroduction by wildlife vectors in southeastern Mexico.

Science.gov (United States)

Garcés-Ayala, Fabiola; Aréchiga-Ceballos, Nidia; Ortiz-Alcántara, Joanna M; González-Durán, Elizabeth; Pérez-Agüeros, Sandra I; Méndez-Tenorio, Alfonso; Torres-Longoria, Belem; López-Martínez, Irma; Hernández-Rivas, Lucía; Díaz-Quiñonez, José Alberto; Ramírez-González, José Ernesto

2017-12-01

Rabies is an infectious viral disease that is practically always fatal following the onset of clinical signs. In Mexico, the last case of human rabies transmitted by dogs was reported in 2006 and canine rabies has declined significantly due to vaccination campaigns implemented in the country. Here we report on the molecular characterization of six rabies virus strains found in Yucatan and Chiapas, remarkably, four of them showed an atypical reaction pattern when antigenic characterization with a reduced panel of eight monoclonal antibodies was performed. Phylogenetic analyses on the RNA sequences unveiled that the three atypical strains from Yucatan are associated with skunks. Analysis using the virus entire genome showed that they belong to a different lineage distinct from the variants described for this animal species in Mexico. The Chiapas atypical strain was grouped in a lineage that was considered extinct, while the others are clustered within classic dog variants.

The Sac Actun System, Quintana Roo, Mexico

International Nuclear Information System (INIS)

Kambesis, P. N.; Coke, J. G.

2016-01-01

The Sac Actun system, located in northeast Quintana Roo, Mexico, is among the most extensive underwater cave systems located along the Caribbean coast of the Yucatan Peninsula. The cave is composed of linear phreatic conduits that have two forms. The coastal sections of the Sac Actun system are characterized by low horizontal tunnels that form mazes paralleling the coast and rudimentary conduits broken by fracture-controlled rooms. Inland passages are fault/fracture controlled, have a linear, anastomotic configuration, and align perpendicular to the coast. Access to the cave system is gained through cenotes which are the portals into the Yucatan underwater cave systems. The occurrence of drowned speleothems in many parts of the cave system, and sections of air-filled upper level passages are indicative of major fluctuations in sea level. The Sac Actun system is part of one of the most extensive and significant eogenetic karst aquifers in the world. The development of the Sac Actun system, as well as the many other caves systems along the Yucatan Caribbean Coast is controlled by the coastal hydrologic regime, driven by glacio-eustatics, and influenced by stratigraphic and structural controls. The karstic permeability of the aquifer makes it and the Sac Actun system vulnerable to the anthropogenic impacts of increased population growth, quarries, and infrastructure development associated with the burgeoning tourist industry that dominates land use in the region. (Author)

Gully formation in terrestrial simple craters: Meteor Crater, USA and Lonar Crater, India

Science.gov (United States)

Kumar, P.; Head, J. W.; Kring, D. A.

2007-12-01

Geomorphic features such as gullies, valley networks, and channels on Mars have been used as a proxy to understand the climate and landscape evolution of Mars. Terrestrial analogues provide significant insight as to how the various exogenic and endogenic processes might contribute to the evolution of these martian landscapes. We describe here a terrestrial example from Meteor Crater, which shows a spectacular development of gullies throughout the inner wall in response to rainwater precipitation, snow melting and groundwater discharge. As liquid water has been envisaged as one of the important agents of landscape sculpturing, Meteor Crater remains a useful landmark, where planetary geologists can learn some lessons. We also show here how the lithology and structural framework of this crater controls the gully distribution. Like many martian impact craters, it was emplaced in layered sedimentary rocks with an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels and fans. Some of the gullies originate from the rim crest and others from the middle crater wall, where a lithologic transition occurs. Deeply incised alcoves are well-developed on the soft sandstones of the Coconino Formation exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of groundwater flow and discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing degradation. Like martian craters, channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when groundwater seeped from springs on the crater wall. Caves exposed on the lower crater level may point to percolation of surface runoff

[Distribution of Ecteinascidia turbinata (Ascidiacea: Perophoridae) in mangroves of the Yucatán Peninsula, Mexico].

Science.gov (United States)

Carballo, J L

2000-01-01

The ascidian Ecteinascidia turbinata synthesizes some of the most promising substances against solid-type tumors, but the only available source are the natural populations of this tunicate, which is reared or collected in different parts of the world. A total of 33 locations were sampled in the Gulf of Mexico and the Yucatan Peninsula. The tunicate was not found in Veracruz, Tabasco and Campeche, but it was well established on mangrove roots in the Yucatan Peninsula where we estimated densities more or less equal to one colony and an average production of 115 g of biomass per lineal meter of mangrove coastline in one location (Río Lagartos). Sustainable management appears to be possible.

The Blue-gray Tanager (Thraupis episcopus in the state of Guerrero, Mexico

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Epifanio Blancas-Calva

2017-10-01

Full Text Available We recorded the Blue-gray Tanager (Thraupis episcopus on the southeastern coastal plain of the state of Guerrero, Mexico, in urban areas with cover of scattered trees of native and introduced species. The current range known for this taxon comprises lowlands of eastern Mexico, from south-central Nuevo Leon to the Yucatan peninsula, including eastern Oaxaca and the Pacific slope on the coastal plain of Chiapas. However, there are no published previous records of the species in Guerrero. Possibly T. episcopus is a species that has expanded its range in episodes of active dispersal.

Mesozoic Continental Sediment-dispersal Systems of Mexico Linked to Development of the Gulf of Mexico

Science.gov (United States)

Lawton, T. F.; Molina-Garza, R. S.; Barboza-Gudiño, R.; Rogers, R. D.

2013-05-01

continental-margin arc blocked westward drainage and detritus was captured in rift basins. Latest Middle Jurassic fluvial systems formed as the Yucatan block rotated counterclockwise and the Gulf of Mexico began to open. Sediment dispersal, partly equivalent to salt deposition in the Gulf, was largely southward in southern Oaxaquia, but large-volume braided river systems on the Maya (Yucatan) block, represented by the Todos Santos Formation in Chiapas, evidently flowed northward along graben axes toward the western part of the Gulf of Mexico Basin. River systems of nuclear Mexico, or Oaxaquia, occupied a broad sedimentary basin west and south of a divide formed adjacent to the translating Maya block. Despite their big-river characteristics, these deposits contain mainly Grenville and Permo-Triassic grains derived from Oaxaquia basement and subordinate Early and Middle Jurassic grains derived from volcanic rocks and plutons of the arc. Early Late Jurassic (Oxfordian) marine flooding of the entire Gulf rim and nuclear Mexico, evidently resulting in part from marginal subsidence adjoining newly-formed oceanic crust, terminated fluvial deposition adjacent to the young Gulf of Mexico.

Copro-necrophagous beetle (Coleoptera: Scarabaeidae diversity in an agroecosystem in Yucatan, Mexico

Directory of Open Access Journals (Sweden)

Enrique Reyes Novelo

2007-03-01

Full Text Available Scarabaeinae are sensitive to structural habitat changes caused by disturbance. We compared copronecrophagous beetle (Scarabaeinae community structure in three differently managed zones within an agroecosystem of the northern Yucatan Peninsula, Mexico. We placed dung and carrion traps once a month from June 2004 through May 2005. The beetle community included 17 species from the genera Canthon, Canthidium, Deltochilum, Pseudocanthon, Malagoniella, Onthophagus, Phanaeus, Copris, Uroxys, Sisyphus and Ateuchus. The secondary vegetation had a higher beetle diversity than the other two zones. Species richness was highest in the Brosimum alicastrum plantation. The pasture had the lowest species diversity and richness, but exhibited the highest abundance of Scarabaeinae in the dry season. The two zones with extensive tree cover were the most diverse. Roller beetles were dominant over burrower species and small-sized species outnumbered large species. Our data show two important issues: beetle species in the pasture extended their activity to the beginning of the dry season, while abundances dropped in the other, unirrigated zones; and the possibility that the Scarabaeinae living in neotropical forests are opportunistic saprophages and have specialized habits for resources other than dung. The B. alicastrum plantation is beneficial to the entire ranch production system because it functions as a dispersion and development area for stenotopic species limited to tree cover. Rev. Biol. Trop. 55 (1: 83-99. Epub 2007 March. 31.Este estudio describe y compara la estructura de la comunidad de escarabajos copronecrófagos (Scarabaeinae en tres zonas con diferente manejo al interior de un agroecosistema localizado en el norte de la Península de Yucatán. A lo largo de un año de muestreo sistemático se encontraron 17 especies de los géneros Canthon, Canthidium, Deltochilum, Pseudocanthon, Malagoniella, Onthophagus, Phanaeus, Copris, Uroxys, Sisyphus y Ateuchus

Palaeoenvironmental Evolution of Cenote Aktun Ha (Carwash) on the Yucatan Peninsula, Mexico and its Response to Holocene Sea-Level Rise

Science.gov (United States)

Gabriel, J. J.; Reinhardt, E. G.; Peros, M. C.; Davidson, D. E.; van Hengstum, P. J.; Beddows, P. A.

2008-12-01

A 61-cm core was obtained from 4 metres below the water table in Cenote Aktun Ha, on the Yucatan Peninsula, Mexico. The cenote is 8.6 km from the Caribbean coast and its formation and evolution have been largely affected by sea-level change. The base of the core dates to 6940 - 6740 cal yr BP and overlying sediments were deposited rapidly over the subsequent ~200 years. The pollen record shows that the cenote evolved from a marsh dominated by red mangrove (Rhizophora mangle) and fern (Polypodiaceae) to an open-water system. These vegetation changes were controlled by water level and salinity and are thus useful indicators of past sea level. At the base, the d13C isotopic ratios reveal the influence of terrestrial vegetation (-29‰), but shift to more negative values up-core (-33‰), indicating an influence from particulate matter in the flooded cenote pool. Although microfossil populations were nearly absent through most of the core, the microfossil assemblage in the upper 6 cm of the core is dominated by juvenile Ammonia tepida and the thecamoebian genus Centropyxis. These populations indicate open-water conditions in the cenote and a major environmental shift around 6600 cal yr BP, which is related to sea-level rise in the Caribbean basin. These data fit well with previously established sea-level curves for the Caribbean Sea. Our reconstruction of the environmental history of Cenote Aktun Ha helps elucidate the floral and hydrological history of the region, and highlights the utility of cenote sediments for studying the Holocene sea-level history of the Caribbean Sea.

Fecal sterols, seasonal variability, and probable sources along the ring of cenotes, Yucatan, Mexico

Science.gov (United States)

Arcega-Cabrera, F.; Velázquez-Tavera, N.; Fargher, L.; Derrien, M.; Noreña-Barroso, E.

2014-11-01

Rapid development in Yucatan has had a dramatic impact on the environment, especially the water supply. Groundwater is the only source of water in Yucatan, since surface water is virtually absent due to the karstic nature of the soil. The ring of cenotes (RC) is a geological feature which functions as a source of water and as nodes in the underground river system that canalizes water towards the coast. Numerous productive and domestic activities take place around the RC in the absence of wastewater treatment or sewage systems. Consequently, a number of researchers have hypothesized that pollutants could migrate from the land surface to the underlying aquifer and, eventually, to the coast. Therefore, the present study investigates the relationship among sources of fecal sterols and their levels in cenotes, using the expected levels of fecal sterols obtained by a spatial analysis of the sources and a Pollution Source Index. Accordingly, expected levels are compared with the detected levels of fecal sterols in 5 areas around the RC. Regarding levels, observed during a sampling campaign carried out along the RC during September 2011 (rainy season) and May 2012 (dry season), varied from low to high concentrations of sterols (0.5-2396.42 μg g- 1) and fecal sterols (0.3-1690.18 μg g- 1). These concentrations showed no relationship between neighboring cenotes, where similar fecal sterol concentrations or gradients were expected. When comparing expected fecal sterols levels with the detected ones, only two of the five analyzed areas concur, suggesting that no clear relationship exists among sources and fecal sterols levels at the regional scale. Multivariate analysis showed that fecal sterols were associated with sterols and fine grain particulates during the rainy season, which suggests co-transport. During the dry season, fecal sterols associated with fine grain particulate and organic matter, which indicates a change to a deposition phenomenon. These findings indicate

Public Opinion and Repression in Yucatan: 1808-1816

Directory of Open Access Journals (Sweden)

Laura Machuca Gallegos

2017-04-01

Full Text Available Across the Hispanic world, the first two decades of the 19th Century were characterized by the development of a new political force called public opinion. The objective of this article is to analyze its appearance in Merida, Yucatan: though far from the great centers of power, this city actively participated in the same political, social and cultural processes as the rest of ibero-America in the period starting in 1808. The author centers their attention on the Sanjuanistas, a group active during this time whose goal was to defend the Constitution of Cadiz. Yucatan, far from representing  a local case, instead reveals the ins and outs of new forms of sociability, above all in the field of political practices, and their embrace by society.

Geochemical variability of the Yucatan basement: Constraints from crystalline clasts in Chicxulub impactites

Science.gov (United States)

Kettrup, B.; Deutsch, A.

2003-07-01

The 65 Ma old Chicxulub impact structure with a diameter of about 180 km is again in the focus of the geosciences because of the recently commenced drilling of the scientific well Yaxcopoil- 1. Chicxulub is buried beneath thick post-impact sediments, yet samples of basement lithologies in the drill cores provide a unique insight into age and composition of the crust beneath Yucatan. This study presents major element, Sr, and Nd isotope data for Chicxulub impact melt lithologies and clasts of basement lithologies in impact breccias from the PEMEX drill cores C-1 and Y-6, as well as data for ejecta material from the K/T boundaries at La Lajilla, Mexico, and Furlo, Italy. The impact melt lithologies have an andesitic composition with significantly varying contents of Al, Ca, and alkali elements. Their present day 87Sr/86Sr ratios cluster at about 0.7085, and 143Nd/144Nd ratios range from 0.5123 to 0.5125. Compared to the melt lithologies that stayed inside the crater, data for ejecta material show larger variations. The 87Sr/86Sr ratios range from 0.7081 for chloritized spherules from La Lajilla to 0.7151 for sanidine spherules from Furlo. The 143Nd/144Nd ratio is 0.5126 for La Lajilla and 0.5120 for the Furlo spherules. In an tCHUR(Nd)-tUR(Sr) diagram, the melt lithologies plot in a field delimited by Cretaceous platform sediments, various felsic lithic clasts and a newly found mafic fragment from a suevite. Granite, gneiss, and amphibolite have been identified among the fragments from crystalline basement gneiss. Their 87Sr/86Sr ratios range from 0.7084 to 0.7141, and their 143Nd/144Nd ratios range from 0.5121 to 0.5126. The TNdDM model ages vary from 0.7 to 1.4 Ga, pointing to different source terranes for these rocks. This leads us to believe that the geological evolution and the lithological composition of the Yucatàn basement is probably more complex than generally assumed, and Gondwanan as well as Laurentian crust may be present in the Yucatàn basement.

Emissions from Biomass Burning in the Yucatan

Science.gov (United States)

Yokelson, R.; Crounse, J. D.; DeCarlo, P. F.; Karl, T.; Urbanski, S.; Atlas, E.; Campos, T.; Shinozuka, Y.; Kapustin, V.; Clarke, A. D.;

Initial Time Of Two High Altitude Crater Lakes (Nevado De Toluca, Central Mexico Recorded In Subfossil Cladocera

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Szeroczyńska Krystyna

2015-12-01

Full Text Available The objective of this study was the recognition and reconstruction of the origin of two high altitude lakes and the ecological conditions of their early existence based on subfossil Cladocera and chemical analyses. The study focused on the oldest lacustrine sediments from Lake Sol and Lake Luna, located in the crater of Volcano Nevado de Toluca (Central Mexico. The Nevado de Toluca crater developed approximately 12 ka yr BP. According to the literature, the volcano was last active approximately 3.3 ka yr BP, and the lakes developed after that eruption. The remains of nine Cladocera species were found in the bottom sediments of both lakes. The most dominant taxa were two endemic littoral species: Alona manueli and Iliocryptus nevadensis. The total frequency of Cladocera specimens in both of the sediment cores was very low. No Cladocera remains were recorded in the sediment layer at depths between 123–103 m from Lake Luna. The results of the lithological and geochemical analyses showed that this sediment layer was composed of allochthonous material, probably originating from slid down from the volcanic cone. This was suggested by the content of silica (up to 13%, iron (up to 12%, and titanium (up to 4%. The Cladocera remains recorded in the bottom sediments suggested that both reservoirs developed as freshwater lakes at the beginning of the sedimentation. The calibrated radiocarbon dates obtained for the bottom samples were 4040 to 3990 yr BP for Lake Luna (129 cm and 4485 to 4485 yr BP for Lake Sol (89 cm. The obtained ages were older than the dates of the last eruption, which occurred approximately 3300 yr BP. This result was likely related to the type of radiocarbon dated materials (charcoals.

Connectivity among sinkholes and complex networks: The case of Ring of Cenotes in northwest Yucatan, Mexico

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Gomez-Nicolas, Mariana; Rebolledo-Vieyra, Mario; Huerta-Quintanilla, Rodrigo; Canto-Lugo, Efrain

2014-05-01

A 180-km-diameter semicircular alignment of abundant karst sinkholes (locally known as cenotes) in northwestern Yucatán, México, coincides approximately with a concentric ring of the buried Chicxulub structure, a circular feature manifested in Cretaceous and older rocks, that has been identified as the product of the impact of a meteorite. The secondary permeability generated by the fracturing and faulting of the sedimentary sequence in the Chicxulub impact, has favored the karstification process and hence the development of genuine underground rivers that carry water from the continent to the sea. The study of the structure and morphology of the crater has allowed researchers to understand the key role of the crater in the Yucatán hydrogeology. It is generally accepted that the Ring of Cenotes, produced by the gravitational deformation of the Tertiary sedimentary sequence within the crater, controls the groundwater in northern Yucatán. However, today there is not solid evidence about the connectivity among cenotes, which is important because if established, public policies could be designed to manage sanitary infrastructure, septic control, regulation of agricultural and industrial activities and the protection of water that has not been compromised by anthropogenic pollution. All these directly affect more than half a million people whose main source of drinking water lies in the aquifer. In this contribution we investigated a set of 16 cenotes located in the vicinity of a gravimetric anomaly of Chicxulub crater ring, using complex networks to model the interconnectivity among them. Data from a geoelectrical tomography survey, collected with SuperSting R1/IP equipment, with multi-electrodes (72 electrodes), in a dipole-dipole configuration was used as input of our model. Since the total number of cenotes on the ring structure amounts to about 2000, the application of graph theoretic algorithms and Monte Carlo simulation to efficiently investigate network

Hydrochemistry of waters from five cenotes and evaluation of their suitability for drinking-water supplies, northeastern Yucatan, Mexico

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Alcocer, Javier; Lugo, Alfonso; Marín, Luis E.; Escobar, Elva

Waters from five cenotes that are currently being used for aquatic recreational activities and that lie along the Cancun-Tulum touristic corridor, Mexico, were evaluated hydrochemically to determine whether the cenotes may be considered as potential drinking-water sources. Several parameters exceed the Mexican Drinking Water Standards (MDWS), but since they do not pose a significant health threat, four of the five cenotes may be used as drinking-water sources. The common contaminants in the Yucatan Peninsula, fecal coliforms and nitrate, are in most cases below the MDWS (0-460 MPN/100ml and 0.31-1.18mg/L, respectively). Although these four cenotes meet the MDWS, a careful groundwater management policy needs to be developed to avoid contamination (fecal and nitrates) and salt-water intrusion. Résumé Les eaux de cinq cénotés, qui sont normalement utilisées pour des activités de plein air, dans la région touristique de Cancun-Tulum (Mexique), ont été soumises à analyses chimiques pour savoir si les cénotés peuvent être considérés comme des sources d'eau potable. Plusieurs paramètres dépassent les normes mexicaines en matière d'eau potable; mais comme ceux-ci ne posent pas de problème réel de santé, quatre des cinq cénotés peuvent être captés pour l'eau potable. Les contaminants habituels dans les eaux de la presqu'île du Yucatan, coliformes fécaux et concentrations élevées en nitrate, sont la plupart du temps au-dessous des normes (respectivement 0 à 460 germes/100ml et 0,31 à 1,18mg/l). Bien que ces quatre cénotés satisfassent aux normes, il est nécessaire de mettre en place des règles précises de l'utilisation de l'eau souterraine, afin d'éviter la contamination par les germes fécaux et par les nitrates, ainsi que l'intrusion marine. Resumen Se analizó hidroquímica y bacteriológicamente el agua de algunos cenotes localizados a lo largo del corredor turístico Cancun-Tulum, que actualmente se utilizan para diversas actividades

A serological survey for avian infectious bronchitis virus and Newcastle disease virus antibodies in backyard (free-range) village chickens in Mexico.

Science.gov (United States)

Gutierrez-Ruiz, E J; Ramirez-Cruz, G T; Camara Gamboa, E I; Alexander, D J; Gough, R E

2000-12-01

The commercial flocks in Yucatan, Mexico are free of Newcastle disease virus (NDV) in its velogenic viscerotropic form, but little is known about the disease status of backyard poultry. A seroprevalence survey in 30 villages using haemagglutination inhibition (HI) tests for infectious bronchitis virus (IBV) and NDV antibodies was carried out from December 1997 to June 1998. The seroprevalences were 56.5% (95% CI 50-63%) for IBV and 2.2% (95% CI 0.5-3.8%) for NDV. All the villages had chickens that were positive for antibodies to IBV and nine of the villages had chickens that were positive for antibodies to NDV. This suggests that IBV may be responsible for a large proportion of the respiratory disease observed in backyard chickens in Yucatan. The implications of these findings are discussed, including the highly susceptible status of the backyard chickens in Yucatan to NDV and the possibility of this virus being one cause of the syndrome known as mortandad by the local people.

Shock pressure estimation in basement rocks of the Chicxulub impact crater using cathodoluminescence spectroscopy of quartz

Science.gov (United States)

Tomioka, N.; Tani, R.; Kayama, M.; Chang, Y.; Nishido, H.; Kaushik, D.; Rae, A.; Ferrière, L.; Gulick, S. P. S.; Morgan, J. V.

2017-12-01

The Chicxulub impact structure, located in the northern Yucatan Peninsula, Mexico, was drilled by the joint IODP-ICDP Expedition 364 in April-May 2016. This expedition is the first attempt to obtain materials from the topographic peak ring within the crater previously identified by seismic imaging. A continuous core was successfully recovered from the peak ring at depths between 505.7 and 1334.7 mbsf. Uplifted, fractured, and shocked granitic basement rocks forming the peak ring were found below, in the impact breccia and impact melt rock unit (747.0-1334.7 mbsf; Morgan et al. 2016). In order to constrain impact crater formation, we investigated shock pressure distribution in the peak-ring basement rocks. Thin sections of the granitic rocks were prepared at intervals of 60 m. All the samples contains shocked minerals, with quartz grains frequently showing planar deformation features (PDFs). We determined shock pressures based on the cathodoluminescence (CL) spectroscopy of quartz. The strong advantage of the CL method is its applicability to shock pressure estimation for individual grains for both quartz and diaplectic SiO2 glass with high-spatial resolution ( 1 μm) (Chang et al. 2016). CL spectra of quartz shows a blue emission band caused by shock-induced defect centers, where its intensity increases with shock pressure. A total of 108 quartz grains in ten thin sections were analyzed using a scanning electron microscope with a CL spectrometer attached (an acceleration voltage of 15 kV and a beam current of 2 nA were used). Natural quartz single crystals, which were experimentally shocked at 0-30 GPa, were used for pressure calibration. CL spectra of all the quartz grains in the basement rocks showed broad blue emission band at the wavelength range of 300-500 nm and estimated shock pressures were in the range of 15-20 GPa. The result is consistent with values obtained from PDFs analysis in quartz using the universal stage (Ferrière et al. 2017; Rae et al. 2017

Multivariate analyses of crater parameters and the classification of craters

Science.gov (United States)

Siegal, B. S.; Griffiths, J. C.

1974-01-01

Multivariate analyses were performed on certain linear dimensions of six genetic types of craters. A total of 320 craters, consisting of laboratory fluidization craters, craters formed by chemical and nuclear explosives, terrestrial maars and other volcanic craters, and terrestrial meteorite impact craters, authenticated and probable, were analyzed in the first data set in terms of their mean rim crest diameter, mean interior relief, rim height, and mean exterior rim width. The second data set contained an additional 91 terrestrial craters of which 19 were of experimental percussive impact and 28 of volcanic collapse origin, and which was analyzed in terms of mean rim crest diameter, mean interior relief, and rim height. Principal component analyses were performed on the six genetic types of craters. Ninety per cent of the variation in the variables can be accounted for by two components. Ninety-nine per cent of the variation in the craters formed by chemical and nuclear explosives is explained by the first component alone.

Long-Term Recovery of Life in the Chicxulub Crater

Science.gov (United States)

Lowery, C.; Jones, H.; Bralower, T. J.; Smit, J.; Rodriguez-Tovar, F. J.; Whalen, M. T.; Owens, J. D.; Expedition 364 Science Party, I. I.

2017-12-01

The Chicxulub Crater on the Yucatán Peninsula of Mexico was formed by the impact of an asteroid 66 Ma that caused the extinction of 75% of genera on Earth. Immediately following the impact, the decimated ecosystem began the long process of recovery, both in terms of primary productivity and species diversity. This well-documented process was heterogeneous across the world ocean, but until the present time it has been inaccessible at ground zero of the impact. IODP/ICDP Exp. 364 recovered 9.5 m of pelagic limestone spanning the entire Paleocene, including a continuous section spanning the first 5 myr following the impact. The Chicxulub Crater is the largest known marine impact crater on Earth, and the recovery of the ecosystem presented here is the first such record of long-term primary succession in the sterile zone of a large impact crater. Planktic and benthic foraminifera, calcareous nannoplankton, calcispheres, bioturbation, and geochemical proxies all indicate that export productivity in the Chicxulub Crater recovered rapidly (within 30 kyr) following the impact. Recovery in terms of diversity and species abundance took much longer, and varied between groups. Planktic foraminifera quickly diversified, with all common Paleocene tropical/subtropical species appearing roughly when expected. Trace fossils appear rapidly after the event, with a progressive recovery through the lowermost Paleocene. Calcareous nannoplankton took much longer to recover, and disaster taxa like Braarudosphaera dominated the assemblage well into the late Paleocene. Paleoecology and geochemistry relate these trends to oceanographic conditions within the Chicxulub Crater. Planktic foraminifera from known depth habitats, including Morozovellids, Acarininids, Chiloguembelinids, and Subbotinids, track changes in the water column structure and paleoredox conditions within the crater. Diverse and abundant macro- and microbenthic organisms indicate food availability and good oxygen conditions

Degraded Crater Rim

Science.gov (United States)

2002-01-01

(Released 3 May 2002) The Science The eastern rim of this unnamed crater in Southern Arabia Terra is very degraded (beaten up). This indicates that this crater is very ancient and has been subjected to erosion and subsequent bombardment from other impactors such as asteroids and comets. One of these later (younger) craters is seen in the upper right of this image superimposed upon the older crater rim material. Note that this smaller younger crater rim is sharper and more intact than the older crater rim. This region is also mantled with a blanket of dust. This dust mantle causes the underlying topography to take on a more subdued appearance. The Story When you think of Arabia, you probably think of hot deserts and a lot of profitable oil reserves. On Mars, however, Southern Arabia Terra is a cold place of cratered terrain. This almost frothy-looking image is the badly battered edge of an ancient crater, which has suffered both erosion and bombardment from asteroids, comets, or other impacting bodies over the long course of its existence. A blanket of dust has also settled over the region, which gives the otherwise rugged landscape a soft and more subdued appearance. The small, round crater (upper left) seems almost gemlike in its setting against the larger crater ring. But this companionship is no easy romance. Whatever formed the small crater clearly whammed into the larger crater rim at some point, obliterating part of its edge. You can tell the small crater was formed after the first and more devastating impact, because it is laid over the other larger crater. How much younger is the small one? Well, its rim is also much sharper and more intact, which gives a sense that it is probably far more youthful than the very degraded, ancient crater.

Return to the Strangelove Ocean?: Preliminary results of carbon and oxygenisotope compositions of post-impact sediments, IODP Expedition 364 "Chicxulub Impact Crater"

Science.gov (United States)

Yamaguchi, K. E.; Ikehara, M.; Hayama, H.; Takiguchi, S.; Masuda, S.; Ogura, C.; Fujita, S.; Kurihara, E.; Matsumoto, T.; Oshio, S.; Ishihata, K.; Fuchizawa, Y.; Noda, H.; Sakurai, U.; Yamane, T.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub crater in the northern Yucatan Peninsula, Mexico was formed by the asteroid impact at the Cretaceous-Paleogene boundary (66.0 Ma). In early 2016 the IODP Exp. 364 successfully drilled the materials from the topographic peak ring within the crater that was previously identified by seismological observations. A continuous core was recovered. The 112m-thick uppermost part of the continuous core (505.7-1334.7 mbsf) is post-impact sediments, including the PETM, that are mainly composed of carbonate with intercalation of siliciclastics and variable contents of organic carbon. More than 300 samples from the post-impact section were finely powdered for a variety of geochemical analysis. Here we report their carbon and oxygen isotope compositions of the carbonate fraction (mostly in the lower part of the analyzed section) and carbon and nitrogen isotope compositions of organic matter (mostly in the middle-upper part of the analyzed section). Isotope mass spectrometer Isoprime was used for the former analysis, and EA-irMS (elemental analyzer - isotope ratio mass spectrometer) was used for the latter analysis, both at CMCR, Kochi Univ. Depth profile of oxygen isotope compositions of carbonate fraction is variable and somewhat similar to those of Zachos et al. (2001; Science). Carbon isotope compositions of carbonate and organic carbon in the lower part of the analyzed section exhibit some excursions that could correspond to the hyperthemals in the early Paleogene. Their variable nitrogen isotope compositions reflect temporal changes in the style of biogeochemical cycles involving denitrification and nitrogen fixation. Coupled temporal changes in the carbon isotope compositions of organic and carbonate carbon immediately after the K-Pg boundary might support a Strangelove ocean (Kump, 1991; Geology), however high export production (Ba/Ti, nannoplankton and calcisphere blooms, high planktic foram richness, and diverse and abundant micro- and macrobenthic organisms

Horizontal movements of Atlantic blue marlin (Makaira nigricans) in the Gulf of Mexico

Science.gov (United States)

Kraus, R.T.; Wells, R.J.D.; Rooker, J.R.

2011-01-01

We examined movements of Atlantic blue marlin (Makaira nigricans) from the Gulf of Mexico based upon 42 pop-up archival transmitting (PAT) tags. Long deployments (including one 334-day track) revealed diverse movement patterns within the Gulf of Mexico. North-south seasonal changes in blue marlin distribution showed strong correspondence with established seasonal patterns of sea surface temperature and primary production. During the summer spawning season, blue marlin utilized outer shelf and shelf edge waters in the northern Gulf of Mexico, and longer duration tracks indicated overwintering habitats in the Bay of Campeche. Egress occurred throughout the year and was difficult to determine because some tracks ended in the Straits of Florida (n = 3) while other tracks recorded movement through it or the Yucatan Channel (n = 4). Our results indicate that Atlantic blue marlin have a more restricted geographic range of habitats than previously recognized and that the Gulf of Mexico provides spatially dynamic suitable habitat that is utilized year-round through seasonal movements. ?? 2011 Springer-Verlag.

Superficial methane emissions from a landfill in Merida, Yucatan, Mexico; Emisiones superficiales de metano en un relleno sanitario en Merida, Yucatan, Mexico

Energy Technology Data Exchange (ETDEWEB)

Sauri-Riancho, Maria Rosa [Universidad Autonoma de Yucatan, Yucatan (Mexico)]. E-mail: sriancho@uady.mx; Stentiford, Edward I. [University of Leeds (UK)]. E-mail: e.i.stentiford@leeds.ac.uk; Gamboa-Marrufo, Mauricio; Reza-Bacelis, Gabriela; Cahuich-Poot, Nayla; Mendez-Novelo, Roger [Universidad Autonoma de Yucatan, Yucatan (Mexico)]. E-mails: gmarrufo@uady.mx; gabriela.reza@proactiva.com.mx; nayre63@hotmail.com; mnovelo@uady.mx

2013-07-15

On worldwide scale, one of the most important anthropogenic methane sources is landfill disposal for solid wastes. The main goal of this work was to quantify methane emissions at one landfill built in Merida, Mexico. This site had venting wells by which a passive control for biogas movement was exerted. At the venting wells, methane concentrations were measured monthly during a 6 months period. Methane surface emission rate was estimated with the close chamber technique. Obtained results indicated that there are both spatial and seasonal variations in biogas composition. The average methane value during the monitoring period was 21.9% (12.7 to 32.5 V/V) and the surface flow rate was in the range of 0 to 6,004 g CH{sub 4} m-2 d-1, with an average value of 1,480 g CH{sub 4} m-2 d-1, which is a high value in respect to these reported in publications. [Spanish] Entre las fuentes antropogenicas mas importantes de metano a escala mundial se encuentra la disposicion final de los residuos solidos. El objetivo de este trabajo fue cuantificar las emisiones de metano provenientes de un relleno sanitario en Merida, Mexico, en el que el movimiento del biogas se controlaba pasivamente utilizando pozos de venteo. Las concentraciones de metano se midieron mensualmente en los pozos de venteo del sitio a lo largo de un periodo de 6 meses. La tasa de emision superficial de metano se determino utilizando la tecnica de camara cerrada. Los resultados indicaron que existen variaciones considerables tanto espaciales como estacionales de la composicion del biogas proveniente de los pozos de venteo con un promedio de concentracion de metano en el sitio, durante todo el periodo de monitoreo, de 21.9% (12.7 a 32.5 V/V). Los flujos superficiales de gas medidos en diversos puntos a lo largo de la superficie del relleno sanitario tuvieron un promedio de 1,480 g CH{sub 4} m-2 d-1, lo que se considero un valor muy alto cuando se comparo con la informacion hallada en la literatura. El intervalo

Measuring the Wavelength of a Diode Laser and the Birefringence of Mica: The Experimental Examination of the IPHO 40 Held in Mexico

Science.gov (United States)

Moran-Lopez, J. L.; Ortiz, M. E.; Rodriguez, L. F.; Romero-Rochin, V.

2010-01-01

The experimental examination applied in the 40th International Physics Olympiad held in Merida, Yucatan, Mexico, is presented. The examination consisted of two parts: (1) based on the measurements of a diffraction pattern produced by a diode laser impinging on a sharp edge of a razor blade, the students were asked to estimate the wavelength of the…

Differences in coastal and oceanic SST trends north of Yucatan Peninsula

Science.gov (United States)

Varela, R.; Costoya, X.; Enriquez, C.; Santos, F.; Gómez-Gesteira, M.

2018-06-01

The coastal area north of Yucatan has experienced a cooling SST trend from 1982 to 2015 during the upwelling season (May-September) that contrasts with the warming observed at the adjacent ocean area. Different drivers were analyzed to identify the possible causes of that unusual coastal cooling. Changes in coastal upwelling and in sea-atmosphere heat fluxes are not consistent with the observed coastal cooling. The eastward shift of the Yucatan Current observed over the last decades is hypothesized as the most probable cause of coastal cooling. This shift enhances the vertical transport of cold deeper water to the continental shelf from where it is pumped to the surface by upwelling favorable westerly winds.

Dome craters on Ganymede

International Nuclear Information System (INIS)

Moore, J.M.; Malin, M.C.

1987-01-01

Voyager observations reveal impact craters on Ganymede that are characterized by the presence of broad, high albedo, topographic domes situated within a central pit. Fifty-seven craters with central domes were identified in images covering approx. 50% of the surface. Owing to limitations in resolution, and viewing and illumination angles, the features identified are most likely a subset of dome craters. The sample appears to be sufficiently large to infer statistically meaningful trends. Dome craters appear to fall into two distinct populations on plots of the ratio of dome diameter to crater rim diameter, large-dome craters and small-dome craters. The two classes are morphologically distinct from one another. In general, large dome craters show little relief and their constituent landforms appear subdued with respect to fresh craters. The physical attributes of small-dome craters are more sharply defined, a characteristic they share with young impact craters of comparable size observed elsewhere in the solar system. Both types of dome craters exhibit central pits in which the dome is located. As it is difficult to produce domes by impact and/or erosional processes, an endogenic origin for the domes is reasonably inferred. Several hypotheses for their origin are proposed. These hypotheses are briefly reviewed

Experimental infection of Contracaecum multipapillatum (Nematoda: Anisakinae) from Mexico in the domestic cat.

Science.gov (United States)

Vidal-Martínez, V M; Osorio-Sarabia, D; Overstreet, R M

1994-08-01

Juveniles of Contracaecum multipapillatum infected the Mayan cichlid (Cichlasoma urophthalmus) and adults infected the olivaceous cormorant (Phalacrocorax olivaceus) and the great egret (Casmerodius albus) in the coastal lagoon at Celestun, State of Yucatan, Mexico. All are new host records, and, even though the geographic locality record of Mexico for the species has not been published, unidentified but presumably conspecific specimens have been reported from there. When juveniles of C. multipapillatum were fed to a kitten, but not rats, ducks, or chickens, they developed into adults. Measurements and morphological data are provided on the specimens from the kitten. Development of an avian ascaridoid in the intestine of a mammal increases the potential of this widespread species to infect other mammals, including humans.

The Securing of a Precarious Commerce: Exchanges between Seville and Yucatan (1590- 1600

Directory of Open Access Journals (Sweden)

Manuela Cristina García Bernal

2000-10-01

Full Text Available This work underlines the importance of Yucatan's commercial relations across the Atlantic Ocean, as opposed to the traditional belief  that  these exchanges were small and  infrequent. Due to the margination and poverty of the province, in 1590 the Span­ish Crown granted Yucatan a license  to send two small  ships each year, with the necessary products. This license  allowed the securing of a trade that until  then had  been quite  precarious. This is why the quantitative and qualitative analyses of the move­ments of ships and merchandise between 1590 and 1600 lets us understand why, despite being considered secondary, this re­gion's commerce occupied, as seen from Seville, a considerable position among the  great amount of Atlantic trade. These analy­ses also reveal  why  during the  seventeenth  century Yucatan would come  to be  the  most  favored of the smaller posts along the Spain-Indies trading route.

Final Environmental Assessment for Continued Personnel Recovery Training Operations Within the Gulf of Mexico WTA Moody Air Force Base, Georgia

Science.gov (United States)

2010-06-01

occurring on the Eastern Yucatan Peninsula, Mexico (Marquez 1990 and TEWG 2000); and (5) a Dry Tortugas nesting subpopulation, occurring in the...islands of the Dry Tortugas , near Key West, Florida (NMFS SEFSC 2001). The recently published recovery plan for the Northwest Atlantic population of...southern Virginia); (2) the Peninsular Florida Recovery Unit (Florida/Georgia border through Pinellas County, Florida); (3) the Dry Tortugas Recovery

Feeding ecology of juvenile marine fish in a shallow coastal lagoon of southeastern Mexico

OpenAIRE

Daniel Arceo-Carranza; Xavier Chiappa-Carrara

2015-01-01

Many species of marine fish use coastal lagoons during early stages of their life cycles due to the protection provided by their turbid waters and complex structure of the environment, such as mangroves and mudflats, and the availability of food derived from the high productivity of these sites. In this study, we analyzed the diet of six species of juvenile marine fishes that use a karstic lagoon system in the northwest portion of the Yucatan Peninsula, Mexico. Through stomach contents analys...

The Chicxulub Multiring Impact Crater and the Cretaceous/Paleogene Boundary: Results From Geophysical Surveys and Drilling

Science.gov (United States)

Urrutia-Fucugauchi, J.; Perez-Cruz, Ligia

2010-03-01

The Chicxulub crater has attracted considerable attention as one of the three largest terrestrial impact structures and its association with the Cretaceous/Paleogene boundary (K/Pg). Chicxulub is a 200 km-diameter multi-ring structure formed 65.5 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Paleogene and Neogene carbonates. Chicxulub is one of few large craters with preserved ejecta deposits, which include the world-wide K/Pg boundary clay layer. The impact has been related to the global major environmental and climatic effects and the organism mass extinction that mark the K/Pg boundary, which affected more than 70 % of organisms, including the dinosaurs, marine and flying reptiles, ammonites and a large part of the marine microorganisms. The impact and crater formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of second and lower crust uplift and crater formation in a few hundreds of seconds. Energy released by impact and crustal deformation generates seismic waves traveling the whole Earth, and resulting in intense fracturing and deformation at the target site. Understanding of the physics of impacts on planetary surfaces and modeling of processes of crustal deformation, rheological behavior of materials at high temperatures and pressures remain a major challenge in geosciences. Study of the Chicxulub crater and the global effects and mass extinction requires inter- and multidisciplinary approaches, with researchers from many diverse fields beyond the geosciences. With no surface exposures, geophysical surveys and drilling are required to study the crater. Differential compaction between the impact breccias and the surrounding carbonate rocks has produced a ring-fracture structure that at the surface reflects in a small topographic depression and the karstic cenote ring. The crater structure, located half offshore and half on-land, has been imaged by

Never judge an iguana by its spines: Systematics of the Yucatan spiny tailed iguana, Ctenosaura defensor (Cope, 1866).

Science.gov (United States)

Malone, Catherine L; Reynoso, Víctor Hugo; Buckley, Larry

2017-10-01

Spiny tailed iguanas are highly diverse clade of lizards in Mesoamerica, ranging from northern Mexico through Panama. Utilizing 2 regions of mitochondrial DNA (1948bp) and 4 nuclear loci (2232bp) we explored the relationships between these species and the phylogeographic history of the major clades. We discovered that the lineage endemic to the Yucatan Peninsula renders the genus Ctenosaura paraphyletic. To resolve this non-monophyly, we resurrect the taxon Cachryx Cope, 1866, and provide a new diagnosis for the genus. We also find that small body-size and highly spinose tails in the species previously referred to the subgenus Enyaliosaurus, have evolved independently 3 times. Cachryx were recovered as sister to the lineage of iguanines endemic to the Galapagos Islands, and we discuss biogeographic scenarios to explain this relationship as well as those among the primary clades of Ctenosaura in Mesoamerica. Copyright © 2017 Elsevier Inc. All rights reserved.

FINANCIAL MANAGEMENT IN THE FAMILY AND NON-FAMILY SME´S IN THE TEXTILE INDUSTRY IN MEXICO

OpenAIRE

Martha Isabel Bojorquez Zapata; Antonio Emmanuel Perez Brito; Jorge Humberto Basulto Triay

2014-01-01

In this paper, we analyze differences in financial management practices between family and non-family Small and Medium Enterprises (SMEs) in the textile industry. We hypothesize that family SMEs use different sources of funding for new investments, tend to have less debt, are more profitable and use less financial and accounting information for decision making than non-family SMEs. We survey 24 textile SMEs located in Yucatan, Mexico. The results show that family SMEs rely more heavily on int...

Centrifuge impact cratering experiment 5

Science.gov (United States)

1984-01-01

Transient crates motions, cratering flow fields, crates dynamics, determining impact conditions from total crater welt, centrifuge quarter-space cratering, and impact cratering mechanics research is documented.

Craters on comets

Science.gov (United States)

Vincent, J.; Oklay, N.; Marchi, S.; Höfner, S.; Sierks, H.

2014-07-01

This paper reviews the observations of crater-like features on cometary nuclei. ''Pits'' have been observed on almost all cometary nuclei but their origin is not fully understood [1,2,3,4]. It is currently assumed that they are created mainly by the cometary activity with a pocket of volatiles erupting under a dust crust, leaving a hole behind. There are, however, other features which cannot be explained in this way and are interpreted alternatively as remnants of impact craters. This work focusses on the second type of pit features: impact craters. We present an in-depth review of what has been observed previously and conclude that two main types of crater morphologies can be observed: ''pit-halo'' and ''sharp pit''. We extend this review by a series of analysis of impact craters on cometary nuclei through different approaches [5]: (1) Probability of impact: We discuss the chances that a Jupiter Family Comet like 9P/Tempel 1 or the target of Rosetta 67P/Churyumov-Gerasimenko can experience an impact, taking into account the most recent work on the size distribution of small objects in the asteroid Main Belt [6]. (2) Crater morphology from scaling laws: We present the status of scaling laws for impact craters on cometary nuclei [7] and discuss their strengths and limitations when modeling what happens when a rocky projectile hits a very porous material. (3) Numerical experiments: We extend the work on scaling laws by a series of hydrocode impact simulations, using the iSALE shock physics code [8,9,10] for varying surface porosity and impactor velocity (see Figure). (4) Surface processes and evolution: We discuss finally the fate of the projectile and the effects of the impact-induced surface compaction on the activity of the nucleus. To summarize, we find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. In the case of a collision between a rocky body and a highly porous

Experimental impact crater morphology

Science.gov (United States)

Dufresne, A.; Poelchau, M. H.; Hoerth, T.; Schaefer, F.; Thoma, K.; Deutsch, A.; Kenkmann, T.

2012-04-01

The research group MEMIN (Multidisciplinary Experimental and Impact Modelling Research Network) is conducting impact experiments into porous sandstones, examining, among other parameters, the influence of target pore-space saturation with water, and projectile velocity, density and mass, on the cratering process. The high-velocity (2.5-7.8 km/s) impact experiments were carried out at the two-stage light-gas gun facilities of the Fraunhofer Institute EMI (Germany) using steel, iron meteorite (Campo del Cielo IAB), and aluminium projectiles with Seeberg Sandstone as targets. The primary objectives of this study within MEMIN are to provide detailed morphometric data of the experimental craters, and to identify trends and characteristics specific to a given impact parameter. Generally, all craters, regardless of impact conditions, have an inner depression within a highly fragile, white-coloured centre, an outer spallation (i.e. tensile failure) zone, and areas of arrested spallation (i.e. spall fragments that were not completely dislodged from the target) at the crater rim. Within this general morphological framework, distinct trends and differences in crater dimensions and morphological characteristics are identified. With increasing impact velocity, the volume of craters in dry targets increases by a factor of ~4 when doubling velocity. At identical impact conditions (steel projectiles, ~5km/s), craters in dry and wet sandstone targets differ significantly in that "wet" craters are up to 76% larger in volume, have depth-diameter ratios generally below 0.19 (whereas dry craters are almost consistently above this value) at significantly larger diameters, and their spallation zone morphologies show very different characteristics. In dry craters, the spall zone surfaces dip evenly at 10-20° towards the crater centre. In wet craters, on the other hand, they consist of slightly convex slopes of 10-35° adjacent to the inner depression, and of sub-horizontal tensile

Impacts of geochemical and environmental factors on seasonal variation of heavy metals in a coastal lagoon Yucatan, Mexico.

Science.gov (United States)

Arcega-Cabrera, F; Garza-Pérez, R; Noreña-Barroso, E; Oceguera-Vargas, I

2015-01-01

This study investigated the influence of geochemical and environmental factors on seasonal variation in metals in Yucatan's Chelem lagoon. Anthropogenic activities discharge non-treated wastewater directly into it with detrimental environmental consequences. Accordingly, this study established the spatial and temporal patterns of fine grain sediments and concentrations of heavy metals. Multivariate analyses showed fine grain facies deposition, transition sites dominated by fine grain transport, and fine grain erosion sites. Spatial and temporal variations of heavy metals concentration were significant for Cd, Cu, Cr, and Pb. As, Cd, and Sn were as much as 12 times higher than SQuiRTs standards (Buchman 2008). The results indicate that aquifer water is bringing metals from relatively far inland and releasing them into the lagoon. Thus, it appears that the contamination of this lagoon is highly complex and must take into account systemic connections with inland anthropogenic activates and pollution, as well as local factors.

Metazoan parasite infracommunities of Florida pompano (Trachinotus carolinus) from the coast of the Yucatan Peninsula, Mexico.

Science.gov (United States)

Sánchez-Ramírez, Claudia; Vidal-Martínez, Victor M

2002-12-01

Metazoan parasite infracommunities of the Florida pompano (Trachinotus carolinus) were studied in terms of species composition, species richness, diversity, numerical dominance, and similarity. Seventy-five fishes were collected from 4 localities along the Yucatan Peninsula coast and 24 parasite species recovered. Most were digeneans (8 species) and nematodes (7). Other species were monogeneans (3). aspidogastreans (2), cestodes (1), acanthocephalans (1), and crustaceans (2). Only 4 species were common in at least I locality. Mean values for species richness, abundance, diversity, numerical dominance, and similarity in total (all species in the individual fish), gastrointestinal, and ectoparasite infracommunities were within ranges observed for most helminth infracommunities of marine fishes from temperate and tropical latitudes. These infracommunities had low species richness, abundance, diversity, and predictability (except ectoparasite infracommunities) and high dominance. Within the predictable element (common species), the specialist monogenean Pseudobicotylophora atlantica was the main reason for the increase in predictability because it was the only common species at all 4 localities. Host feeding habits, the distribution of intermediate hosts and infective stages, the local species pool, and a phylogenetic component seem to be determining the characteristics of these metazoan parasite infracommunities.

Evidence for rapid topographic evolution and crater degradation on Mercury from simple crater morphometry

Science.gov (United States)

Fassett, Caleb I.; Crowley, Malinda C.; Leight, Clarissa; Dyar, M. Darby; Minton, David A.; Hirabayashi, Masatoshi; Thomson, Bradley J.; Watters, Wesley A.

2017-06-01

Examining the topography of impact craters and their evolution with time is useful for assessing how fast planetary surfaces evolve. Here, new measurements of depth/diameter (d/D) ratios for 204 craters of 2.5 to 5 km in diameter superposed on Mercury's smooth plains are reported. The median d/D is 0.13, much lower than expected for newly formed simple craters ( 0.21). In comparison, lunar craters that postdate the maria are much less modified, and the median crater in the same size range has a d/D ratio that is nearly indistinguishable from the fresh value. This difference in crater degradation is remarkable given that Mercury's smooth plains and the lunar maria likely have ages that are comparable, if not identical. Applying a topographic diffusion model, these results imply that crater degradation is faster by a factor of approximately two on Mercury than on the Moon, suggesting more rapid landform evolution on Mercury at all scales.Plain Language SummaryMercury and the Moon are both airless bodies that have experienced numerous impact events over billions of years. These impacts form craters in a geologic instant. The question examined in this manuscript is how fast these craters erode after their formation. To simplify the problem, we examined craters of a particular size (2.5 to 5 km in diameter) on a particular geologic terrain type (volcanic smooth plains) on both the Moon and Mercury. We then measured the topography of hundreds of craters on both bodies that met these criteria. Our results suggest that craters on Mercury become shallower much more quickly than craters on the Moon. We estimate that Mercury's topography erodes at a rate at least a factor of two faster than the Moon's.

Martian Low-Aspect-Ratio Layered Ejecta (LARLE) craters: Distribution, characteristics, and relationship to pedestal craters

Science.gov (United States)

Barlow, Nadine G.; Boyce, Joseph M.; Cornwall, Carin

2014-09-01

Low-Aspect-Ratio Layered Ejecta (LARLE) craters are a unique landform found on Mars. LARLE craters are characterized by a crater and normal layered ejecta pattern surrounded by an extensive but thin outer deposit which terminates in a sinuous, almost flame-like morphology. We have conducted a survey to identify all LARLE craters ⩾1-km-diameter within the ±75° latitude zone and to determine their morphologic and morphometric characteristics. The survey reveals 140 LARLE craters, with the majority (91%) located poleward of 40°S and 35°N and all occurring within thick mantles of fine-grained deposits which are likely ice-rich. LARLE craters range in diameter from the cut-off limit of 1 km up to 12.2 km, with 83% being smaller than 5 km. The radius of the outer LARLE deposit displays a linear trend with the crater radius and is greatest at higher polar latitudes. The LARLE deposit ranges in length between 2.56 and 14.81 crater radii in average extent, with maximum length extending up to 21.4 crater radii. The LARLE layer is very sinuous, with lobateness values ranging between 1.45 and 4.35. LARLE craters display a number of characteristics in common with pedestal craters and we propose that pedestal craters are eroded versions of LARLE craters. The distribution and characteristics of the LARLE craters lead us to propose that impact excavation into ice-rich fine-grained deposits produces a dusty base surge cloud (like those produced by explosion craters) that deposits dust and ice particles to create the LARLE layers. Salts emplaced by upward migration of water through the LARLE deposit produce a surficial duricrust layer which protects the deposit from immediate removal by eolian processes.

Fishery of the Goliath grouper, Epinephelus itajara (Teleostei: Epinephelidae based on local ecological knowledge and fishery records in Yucatan, Mexico

Directory of Open Access Journals (Sweden)

Alfonso Aguilar-Perera

2009-09-01

Full Text Available The Goliath grouper, Epinephelus itajara, a large-bodied (~ 2.5 m TL, > 400 kg and critically endangered fish (Epinephelidae, is highly vulnerable to overfishing. Although protected from fishing in many countries, its exploitation in Mexico is unregulated; a situation that puts its populations at risk. Fishery records of E. itajara are scarce, which prevents determination of its fishery status. This work aimed to elucidate the E. itajara fishery in the northern Yucatan Peninsula by 1 analyzing available catch records and 2 interviewing veteran fishermen (local ecological knowledge from two traditional landing sites: Dzilam de Bravo and Puerto Progreso. Historic fishery records from two fishing cooperatives were analyzed in order to elucidate the current situation and offer viable alternatives for conservation and management. Catches have decreased severely. Local knowledge obtained from fishermen represented a very important source of information for reconstructing the fisheries history of this species. Conservation measures that incorporate regional and international regulations on critically endangered fish species are suggested. Rev. Biol. Trop. 57 (3: 557-566. Epub 2009 September 30.La cherna, Epinephelus itajara, un mero (Epinephelidae corpulento (~ 2.5 m TL, > 400 kg y amenazado, es altamente vulnerable a la sobrepesca. Si bien es protegido en varios países, en México su explotación no está regulada; situación que pone a su población en riesgo. Sus registros pesqueros son escasos, lo que impide determinar su condición pesquera. Este trabajo intentó ilustrar la pesquería en el norte de la Península de Yucatán usando procedimientos que involucraron analizar registros y entrevistar a pescadores veteranos (conocimiento ecológico tradicional de dos sitios de desembarque: Dzilam de Bravo y Puerto Progreso. Se analizaron registros pesqueros históricos de dos cooperativas pesqueras para determinar la situación actual y ofrecer

Meteor Crater (Barringer Meteorite Crater), Arizona: Summary of Impact Conditions

Science.gov (United States)

Roddy, D. J.; Shoemaker, E. M.

1995-09-01

Meteor Crater in northern Arizona represents the most abundant type of impact feature in our Solar System, i.e., the simple bowl-shaped crater. Excellent exposures and preservation of this large crater and its ejecta blanket have made it a critical data set in both terrestrial and planetary cratering research. Recognition of the value of the crater was initiated in the early 1900's by Daniel Moreau Barringer, whose 27 years of exploration championed its impact origin [1]. In 1960, Shoemaker presented information that conclusively demonstrated that Meteor Crater was formed by hypervelocity impact [2]. This led the U.S. Geological Survey to use the crater extensively in the 1960-70's as a prime training site for the Apollo astronauts. Today, Meteor Crater continues to serve as an important research site for the international science community, as well as an educational site for over 300,000 visitors per year. Since the late 1950's, studies of this crater have presented an increasingly clearer view of this impact and its effects and have provided an improved view of impact cratering in general. To expand on this data set, we are preparing an upgraded summary on the Meteor Crater event following the format in [3], including information and interpretations on: 1) Inferred origin and age of the impacting body, 2) Inferred ablation and deceleration history in Earth's atmosphere, 3) Estimated speed, trajectory, angle of impact, and bow shock conditions, 4) Estimated coherence, density, size, and mass of impacting body, 5) Composition of impacting body (Canyon Diablo meteorite), 6) Estimated kinetic energy coupled to target rocks and atmosphere, 7) Terrain conditions at time of impact and age of impact, 8) Estimated impact dynamics, such as pressures in air, meteorite, and rocks, 9) Inferred and estimated material partitioning into vapor, melt, and fragments, 10) Crater and near-field ejecta parameters, 11) Rock unit distributions in ejecta blanket, 12) Estimated far

Evaluation of the health status of a coastal ecosystem in southeast Mexico: Assessment of water quality, phytoplankton and submerged aquatic vegetation.

Science.gov (United States)

Herrera-Silveira, Jorge A; Morales-Ojeda, Sara M

2009-01-01

The coastal environment of the Yucatan Peninsula (SE, Mexico) includes a wide variety of ecosystems ranging from mangroves to coral reefs, resulting in a heterogeneous landscape. Specifically, the marine system is characterized by environmental differences which respond to regional and local forcing functions such as marine currents and groundwater discharges (GD). Such functional characteristics were used here to define four subregions across the Yucatan coast and diagnose the health status of this coastal marine ecosystem. To achieve this goal, we conducted an analysis and integration of water quality variables, an eutrophic assessment, evaluated changes in submerged aquatic vegetation (SAV), and analyzed the community structure and distribution of harmful phytoplankton. The first step was to determine the reference values for each subregion based on data previously collected from 2002 to 2006 along the coast of Yucatan, 200m offshore. The trophic index (TRIX) and Canadian index for aquatic life (CCMEWQI) were used to diagnose each subregion and then the ASSETS approach was conducted for Dzilam and Progreso, sampling localities on each end of the health status continuum (those with the best and worst conditions). Overall, results indicated that the marine coastal ecosystem of Yucatan is in good condition; however, differences were observed between subregions that can be attributed to local forcing functions and human impacts. Specifically, the central region (zone HZII, Progreso-Telchac) showed symptoms of initial eutrophication due to nutrient inputs from human activities. The eastern region (zone HZ III, Dzilam-Las Bocas) showed a meso-eutrophic condition linked to natural groundwater discharges, while the other two subregions western (zone HZI Celestun-Palmar) and caribbean (zone HZ IV Ria Lagartos-El Cuyo) exhibited symptoms of oligo-mesotrophic condition. These findings may be considered baseline information for coastal ecosystem monitoring programs in

Drainage systems of Lonar Crater, India: Contributions to Lonar Lake hydrology and crater degradation

Science.gov (United States)

Komatsu, Goro; Senthil Kumar, P.; Goto, Kazuhisa; Sekine, Yasuhito; Giri, Chaitanya; Matsui, Takafumi

2014-05-01

Lonar, a 1.8-km-diameter impact crater in India, is a rare example of terrestrial impact craters formed in basaltic bedrock. The estimated age of the crater ranges widely from less than 12 ka to over 600 ka, but the crater preserves a relatively pristine morphology. We conducted a study of various drainage systems of Lonar Crater. The crater floor hosts a shallow 5-m-deep lake, which fluctuates seasonally. Our investigation reveals that the lake level is influenced by surface runoff that is active during the monsoon and groundwater input effective during both the rainy and the dry seasons. The groundwater discharge is observed as springs on the inner rim walls corresponding to weathered vesicular basalt and/or proximal ejecta, which are underlain by thick massive basalt layers. This observation indicates that groundwater movement is lithologically controlled: it passes preferentially through permeable vesicular basalt or proximal ejecta but is hindered in less permeable massive basalt. It is hypothesized that groundwater is also structurally controlled by dipping of basalt layers, interconnectivity of the permeable lithologic units through fractures, and preferential pathways such as fractures within the permeable lithologic units. Investigation on hydrological processes at Lonar Crater and its lake could provide useful insights into purported paleo-crater lakes presumably formed in the basaltic crust of Mars. The Lonar Crater interior shows signs of degradation in the forms of gullies and debris flows, and the Dhar valley incising in the rim leading to form a fan delta. The ejecta surface is characterized by the presence of channels, originating from the rim area and extending radially away from the crater center. The channels probably resulted from surface runoff, and its erosion contributes to the removal of the ejecta. Lonar Crater is a valuable analog site for studying degradation processes with potential application to impact craters occurring on

Centrifuge Impact Cratering Experiments

Science.gov (United States)

Schmidt, R. M.; Housen, K. R.; Bjorkman, M. D.

1985-01-01

The kinematics of crater growth, impact induced target flow fields and the generation of impact melt were determined. The feasibility of using scaling relationships for impact melt and crater dimensions to determine impactor size and velocity was studied. It is concluded that a coupling parameter determines both the quantity of melt and the crater dimensions for impact velocities greater than 10km/s. As a result impactor radius, a, or velocity, U cannot be determined individually, but only as a product in the form of a coupling parameter, delta U micron. The melt volume and crater volume scaling relations were applied to Brent crater. The transport of melt and the validity of the melt volume scaling relations are examined.

Benthic amphipods (Amphipoda: Gammaridea and Corophiidea) from the Mexican southeast sector of the Gulf of Mexico: checklist, new records and zoogeographic comments.

Science.gov (United States)

Paz-Ríos, Carlos E; Ardisson, Pedro-Luis

2013-01-01

The southeast region of the Gulf of Mexico is considered to be biologically important, because it is a connection and transition zone between the Caribbean and the Gulf of Mexico, harboring great marine biodiversity. Nevertheless, benthic amphipods have been poorly studied in the Mexican southeast sector of the Gulf of Mexico with few studies listing species. The aim of this study is to provide an update checklist of species for the Mexican southeast sector (based on literature review and records from the present study) as well as a brief zoogeographical analysis for the Gulf of Mexico amphipod fauna, putting them in context with the fauna on the tropical western Atlantic. Fifty-five species were listed for the Mexican southeast sector; 36 of them showed a geographical extension to the Yucatan continental shelf representing 23 new records for the Mexican southeast sector, nine for the southeast region and four for the Gulf of Mexico. Based on the zoogeographical analysis, there is support of the application of Carolinian and Caribbean zoogeographic provinces to amphipods in the Gulf of Mexico.

Mercury's Densely Cratered Surface

Science.gov (United States)

1974-01-01

Mariner 10 took this picture (FDS 27465) of the densely cratered surface of Mercury when the spacecraft was 18,200 kilometers (8085 miles) from the planet on March 29. The dark line across top of picture is a 'dropout' of a few TV lines of data. At lower left, a portion of a 61 kilometer (38 mile) crater shows a flow front extending across the crater floor and filling more than half of the crater. The smaller, fresh crater at center is about 25 kilometers (15 miles) in diameter. Craters as small as one kilometer (about one-half mile) across are visible in the picture.The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.Image Credit: NASA/JPL/Northwestern University

Buried Craters of Utopia

Science.gov (United States)

2003-01-01

MGS MOC Release No. MOC2-365, 19 May 2003Beneath the northern plains of Mars are numerous buried meteor impact craters. One of the most heavily-cratered areas, although buried, occurs in Utopia Planitia, as shown in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. The history of Mars is complex; impact craters provide a tool by which to understand some of that history. In this case, a very ancient, cratered surface was thinly-buried by younger material that is not cratered at all. This area is near 48.1oN, 228.2oW; less than 180 km (112 mi) west of the Viking 2 lander site. Sunlight illuminates the scene from the lower left.

Frecuencia de anticuerpos contra el virus C de la hepatitis en pacientes con cirrosis hepática en Yucatán, México Frequency of antibodies against the hepatitis C virus in patients with hepatic cirrhosis in Yucatan, Mexico

Directory of Open Access Journals (Sweden)

Renán A Góngora-Biachi

2003-10-01

Full Text Available OBJETIVO: En este estudio reportamos la prevalencia de anticuerpos contra el virus C de la hepatitis (Ac-VCH en un grupo de pacientes con cirrosis hepática (CH. MATERIAL Y MÉTODOS: Se hizo un estudio prospectivo, transversal y descriptivo, de marzo de 1998 a mayo de 1999. Se estudiaron a 153 pacientes (117 (76% hombres y 36 (24% mujeres con diagnóstico de CH, que eran atendidos en el Hospital General Agustín O' Horan y en el Centro de Investigaciones Regionales Doctor Hideyo Noguchi, en la ciudad de Mérida, Yucatán, México. Se aplicó un cuestionario con datos clínico-epidemiológicos y se determinó la presencia de Ac-VCH (ELISA de 2ª generación y RIBA-2 para confirmar el diagnóstico a cada paciente. Se determinó también el antígeno de superficie de la hepatitis B (AgsHB y anticuerpos contra el antígeno central de la hepatitis B (Anti-HBc mediante el método de ELISA. La presencia de Ac-VCH fue relacionada con las variables epidemiológicas de los sujetos. La prevalencia de anti-HCV y la frecuencia de características se compararon entre los pacientes positivos y negativos con las pruebas de c² y exacta de Fisher. RESULTADOS: El 32% de los pacientes con CH (35/117 (30% hombres y 14/36 (39% mujeres fueron positivos para los Ac-VCH. El alcoholismo estuvo presente en todos los hombres serorreactivos y en ninguna de las mujeres positivas (pOBJECTIVE: To report the prevalence of antibodies against the hepatitis C virus (anti-HCV in a group of patients with hepatic cirrhosis (HC. MATERIAL AND METHODS: A prospective transversal and descriptive study was carried out from March 1998 to May 1999. Study subjects were 153 patients; 117 (76% male and 36 (24% female, diagnosed with HC. They were attended at the General Hospital Agustín O' Horan and at Regional Research Center Doctor Hideyo Noguchi, in Merida, Yucatan, Mexico. A clinical-epidemiologic questionnaire completed by interview was used for data collection. Anti-HCV were detected

Prevalencia y factores de riesgo en Yucatán, México, para litiasis urinaria Urolithiasis prevalence and risk factors in Yucatan, Mexico

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Martha Medina-Escobedo

2002-11-01

Full Text Available Objetivo. Determinar la prevalencia de urolitiasis en el estado de Yucatán, México, y una posible asociación de ésta con antecedentes familiares de la enfermedad y la dureza del agua. Material y métodos. Durante 1996 se efectuó una encuesta transversal en población abierta mayor de un año de edad, del estado de Yucatán. Los sujetos se clasificaron como litiasis definitiva (LD, litiasis probable (LP y sin litiasis (SL. Se determinó dureza total, dureza de calcio y dureza de magnesio a las muestras de agua empleadas para el consumo humano. Se emplearon ji cuadrada y t de student para comparación de medias de muestras independientes en el análisis. Resultados. De un total de 5 832 encuestas, 323 sujetos (5.5% se catalogaron como LD, y 282 (4.8% como LP. La prevalencia de litiasis se incrementó con la edad, partiendo de 1% en población de 18 años o menor, hasta 11.3% en los mayores de 50. El 44% del grupo LD y 34% del LP tuvieron antecedente familiar de urolitiasis, comparado con 28% del grupo SL (pObjective. To measure the prevalence of urolithiasis in Yucatan, and to establish a possible association of the disease with family history and water hardness. Material and Methods. During 1996, a survey was conducted on the population over one year of age in the State of Yucatan. Subjects were classified as having definite lithiasis (DL, probable lithiasis (PL, or no lithiasis (NL. Total hardness, calcium hardness, and magnesium hardness, were determined in drinking water samples. Results. From a total of 5 832 questionnaires, 323 subjects (5.5% were found to have DL, and 282 (4.8% PL. The prevalence of lithiasis increased sharply with age, ranging from 1% in the population 18 years or younger, to 11.3% in those over 50 years. A family history of urolithiasis was positive in 44% of subjects with DL and in 34 % of those with PL, compared to 28% of those with NL (OR=2.8, 95% CI=2.2-3.4, p<0.0001, and OR=1.8, 95% CI=1.4-2.4, p<0

Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico

Science.gov (United States)

Smit, J.; Montanari, A.; Swinburne, N. H.; Alvarez, W.; Hildebrand, A. R.; Margolis, S. V.; Claeys, P.; Lowrie, W.; Asaro, F.

1992-01-01

The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatan, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatan.

Size-Frequency Distribution of Small Lunar Craters: Widening with Degradation and Crater Lifetime

Science.gov (United States)

Ivanov, B. A.

2018-01-01

The review and new measurements are presented for depth/diameter ratio and slope angle evolution during small ( D model. The uncertainty of crater retention age due to crater degradational widening is estimated. The collected and analyzed data are discussed to be used in the future updating of mechanical models for lunar crater aging.

Use of enzyme linked immunosorbent assay (ELISA) for the diagnosis of brucellosis in cattle in Yucatan, Mexico

International Nuclear Information System (INIS)

Dajer, A.; Gutierrez, E.; Zapata, D.

1998-01-01

Sera (247) from non-vaccinated brucellosis negative herds, 328 negative sera from Brucella abortus strain 19 vaccinated herds (brucellosis free), and 95 sera positive to the Rose Bengal test (RBT) and Complement Fixation test (CFT) from Brucella abortus-infected herds, were used to determine the relative sensitivity and specificity of a FAO/IAEA I-ELISA kit and the Rivanol Agglutination Test (RAT), using the CFT as a 'gold standard'. A threshold value for the I-ELISA was determined to be 37 PP using the mean plus 3 standard deviations of the negative sera from vaccinated animals. The I-ELISA showed a high relative sensitivity (100%) and a good relative specificity (92.5%), using the threshold determined for local conditions. The RAT gave a lower sensitivity value than the CFT (97.8%) and good specificity (99.3%). The I-ELISA could be used as a screening test under Yucatan conditions or as a confirmatory test in places where vaccination is not carried out. The RAT lacks sensitivity and is therefore not recommended for use in final stages of eradication programs but could be used in control programmes or early stages of eradication campaigns as a confirmatory test. (author)

Chemical characteristics of the crater lakes of Popocatetetl, El Chichon, and Nevado de Toluca volcanoes, Mexico

Science.gov (United States)

Armienta, M. A.; De la Cruz-Reyna, S.; Macías, J. L.

2000-04-01

Three crater lakes from Mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics. Strong differences were observed in the chemistry among the three lakes: Nevado de Toluca, considered as dormant, El Chichón at a post-eruptive stage, and Popocatépetl at a pre-eruptive stage. Not surprisingly, no influence of volcanic activity was found at the Nevado de Toluca volcano, while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends. Low pHs (Nevado de Toluca Sun lake. Changes with time were observed at Popocatépetl and El Chichón. Concentrations of volcanic-gas derived species like Cl-, SO42- and F- decreased irregularly at El Chichón from 1983 until 1997. Major cations concentrations also diminished at El Chichón. A 100% increase in the SO42- content was measured at Popocatépetl between 1985 and 1994. An increase in the Mg/Cl ratio between 1992 (Mg/Cl=0.085) and 1994 (Mg/Cl=0.177) was observed at Popocatépetl, before the disappearance of the crater lake in 1994. It is concluded that chemical analysis of crater lakes may provide a useful additional tool for active-volcano monitoring.

The Orphans of Cholera Morbus in Yucatan, 1833

OpenAIRE

Elsa Malvido; Paola Peniche Moreno

2013-01-01

This essay discusses the phenomenon of orphanhood which affected a large number of children after the cholera epidemic that struck Yucatan in July 1833. Moreover, it inquires into the fate of children whose parents died of cholera, the role played by kinship networks to provide them with shelter, and the influence of the Church and the State on the situation. Based on first hand sources, the author suggests that the orphanhood produced by cholera served as a pretext for economically and socia...

ISVEE 14 Yucatan 2015 14th Symposium of the International Society for Veterinary Epidemiology and Economics.

Science.gov (United States)

de Anda, Jorge Hernández

2017-02-01

The 14th Symposium of the International Society for Veterinary Epidemiology and Economics (ISVEE 14) was held in Merida, Yucatan, Mexico during 3-7 November. 2015. The purpose of ISVEE 14 Yucatan 2015 was to provide a global forum for graduate students, postdoctoral fellows, junior and senior investigators, as well as health policymakers to exchange information that can advance the fields of veterinary epidemiology and economics, and other disciplines in the health and social sciences. The main theme of ISVEE 14 was Planning Our Future. Human population growth is predicted to increase nearly 50% to 11 billion by 2050, and climate change and changing land use can have an impact on local and global food systems, interactions among humans, wildlife and domestic animals, as well as local, regional, and global public health alerts. How can we help our systems of education, research, and public policy adapt? Are new veterinary graduates and epidemiology practitioners prepared to become active protagonists in the solution of health issues that affect humans and animal populations in a changing environment? What innovative research is needed to understand and enhance the food systems of the future? What are the expected roles or contributions of veterinarians or epidemiology practitioners on future climate change, food systems, and health? Is our profession or discipline leading One Health initiatives? Are there current or new models that make national veterinary services more efficacious and efficient for disease control and eradication? To help us answer these questions, the organizing committee of ISVEE 14 invited five distinguished keynote speakers to share their vision and innovative ideas on education, technological developments, research, and public policy of our future with a concentration in the following five areas: (i) One Health (Jonna Mazet), (ii) climate change (Bernard Bett), (iii) animal health economics (Jonathan Rushton), (iv) national veterinary services

A model for the dynamics of crater-centered intrusion: Application to lunar floor-fractured craters

Science.gov (United States)

Thorey, Clément; Michaut, Chloé

2014-01-01

Lunar floor-fractured craters are a class of craters modified by post-impact mechanisms. They are defined by distinctive shallow floors that are convex or plate-like, sometimes with a wide floor moat bordering the wall region. Radial, concentric, and polygonal floor fractures suggest an endogenous process of modification. Two mechanisms have been proposed to account for such deformations: viscous relaxation and spreading of a magma intrusion at depth below the crater. To test the second assumption and bring more constraints on the intrusion process, we develop a model for the dynamics of magma spreading below an elastic overlying layer with a crater-like topography. As predicted in earlier more qualitative studies, the increase in lithostatic pressure at the crater wall zone prevents the intrusion from spreading laterally, leading to the thickening of the intrusion. Additionally, our model shows that the final crater floor appearance after the uplift, which can be convex or flat, with or without a circular moat bordering the wall zone, depends on the elastic thickness of the layer overlying the intrusion and on the crater size. Our model provides a simple formula to derive the elastic thickness of the overlying layer hence a minimum estimate for the intrusion depth. Finally, our model suggests that crust redistribution by cratering must have controlled magma ascent below most of these craters.

Cubic Satellites, Vanguard Technology Integration, an Educational Opportunity of Modernization in Mexico

Science.gov (United States)

Moreno-Franco, Olmo A.; Muñoz-Ubando, L. A.; Moreno-Moreno, Prudenciano; Vargas-Méndez, Eduardo E.

This paper provides a theoretical approach on the CubeSat standard making a cost-benefit analysis in the use of pico-satellites at the education and technology integration model for educational modernization. With the CubeSat format is planned to develop an orbit LEO pico-satellite as part of a multidisciplinary project led by the Robotics Institute of Yucatan (TRIY), assisted with previous experience in Mexico and Colombia, to build a satellite capable of stabilizing through a robotic device, which will be a training model for human resources in Mexico. The CubeSat initiative represents a technological development of more than 10 years who is still alive and growing, attracting new participants from different educational institutions and global business, which has proven to be a project that would be made and successful results with a significant low budget compared to other space missions, and finally is an opportunity to bring students and teachers to the aerospace industry, through a convergence of technology, and academic discipline.

Crater in Utopia

Science.gov (United States)

2004-01-01

23 March 2004 Craters of the martian northern plains tend to be somewhat shallow because material has filled them in. Their ejecta blankets, too, are often covered by younger materials. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example--a crater in Utopia Planitia near 43.7oN, 227.3oW. Erosion has roughened some of the surfaces of the material that filled the crater and covered its ejecta deposit. The picture covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

Energy Technology Data Exchange (ETDEWEB)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-06-01

A computational approach used for subsurface explosion cratering was extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for the first computer simulation because it is one of the most thoroughly studied craters. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s, meteorite mass of 1.67 x 10/sup 8/ kg, with a corresponding kinetic energy of 1.88 x 10/sup 16/ J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation, a Tillotson equation-of-state description for iron and limestone was used with no shear strength. Results obtained for this preliminary calculation of the formation of Meteor Crater are in good agreement with field measurements. A color movie based on this calculation was produced using computer-generated graphics. 19 figures, 5 tables, 63 references.

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

International Nuclear Information System (INIS)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-06-01

A computational approach used for subsurface explosion cratering was extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for the first computer simulation because it is one of the most thoroughly studied craters. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s, meteorite mass of 1.67 x 10 8 kg, with a corresponding kinetic energy of 1.88 x 10 16 J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation, a Tillotson equation-of-state description for iron and limestone was used with no shear strength. Results obtained for this preliminary calculation of the formation of Meteor Crater are in good agreement with field measurements. A color movie based on this calculation was produced using computer-generated graphics. 19 figures, 5 tables, 63 references

It takes two to tango: self incompatibility in the bromeliad Tillandsia streptophylla (Bromeliaceae) in Mexico.

Science.gov (United States)

Ramírez Morillo, Ivón M; Chi May, Francisco; Carnevali, Germán; May Pat, Filogonio

2009-09-01

Floral phenology and breeding system of Tillandsia streptophylla (Bromeliaceae) were studied in a low inundated forest in Yucatan, Mexico. During the flowering season, from March to August, terminal scapose 1-branched, paniculate inflorescences are produced with one flower per branch opening per day, over a period of 11-29 days. Flowers are tubular, light violet, with the stigma placed below the anthers, both protruding above the corolla. Flowers are protandrous, with anthers releasing pollen from 0500 hours and stigma becoming receptive around 0900 hours. Controlled experimental crosses suggest that Tillandsia streptophylla is self incompatible and therefore, pollinator-dependent.

Snow-avalanche impact craters in southern Norway: Their morphology and dynamics compared with small terrestrial meteorite craters

Science.gov (United States)

Matthews, John A.; Owen, Geraint; McEwen, Lindsey J.; Shakesby, Richard A.; Hill, Jennifer L.; Vater, Amber E.; Ratcliffe, Anna C.

2017-11-01

This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact craters (mean diameter 85 m, range 10-185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths (α = 28-59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path (β) typically exceeds 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on crater size. Proximal erosional scars ('blast zones') up to 40 m high indicate up-range ejection of material from the crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a crater of similar size

Crater Degradation on Mercury: A Global Perspective

Science.gov (United States)

Kinczyk, M. J.; Byrne, P. K.; Prockter, L. M.; Susorney, H. C. M.; Chapman, C. R.; Barnouin, O. S.

2017-12-01

On geologic timescales, initially fresh craters are subjected to many weathering mechanisms. Whereas water and wind are, or were, effective erosive mechanisms such as on Earth and Mars, micrometeorite bombardment and modification due to subsequent impacts are the dominant processes that degrade craters and crater rays on airless bodies like the Moon and Mercury. Classifying craters based on their state of degradation can help determine the relative ages of landforms proximal to, and crosscut by, these craters. However, this method is most effective when used together with statistical analysis of crater distributions. Pre-MESSENGER degradation classification schemes lacked sufficient detail to be consistently applied to craters of various sizes and morphological types—despite evidence suggesting that the ejecta deposits of large basins persist much longer than those of smaller craters, for instance—yet broad assumptions have been made regarding the correlation of crater class to the planet's time-stratigraphic sequence. Moreover, previous efforts to categorize craters by degradation state have either been restricted to regional study sites or applied only to a subset of crater age or size. As a result, numerous interpretations of crater degradation state persist for Mercury, challenging a complete understanding of this process on the innermost planet. We report on the first global survey of crater degradation on Mercury. By modifying an established 5-class scheme, we have systematically applied a rigorous set of criteria to all craters ≥40 km in diameter on the planet. These criteria include the state and morphology of crater deposits separately (e.g., rim, floor, wall, ejecta) and degradation classes were assigned as the collection of these individual attributes. This approach yields a consistent classification of craters of different sizes. Our results provide the first comprehensive assessment of how craters of various states of degradation are distributed

HYDROGEOLOGY AND CONCEPTUAL MODEL OF THE KARSTIC COASTAL AQUIFER IN NORTHERN YUCATAN STATE, MEXICO

Directory of Open Access Journals (Sweden)

Miguel J Villasuso-Pino

2011-04-01

Full Text Available The coastal zone of northern Yucatan Peninsula (YP is mainly constituted by Tertiary limestones, covered by Pleistocen limestones, where there exist swamps and estuary systems, locally called “rías”, with mouths connecting them to the sea and hence being a way for an important amount of groundwater to discharge, like in Ría Lagartos and Celestún. These limestones have karstic layers located at depths from 8 to 16 meters below terrain surface.  It is in these layers where groundwater mainly flows toward coast, passing below the sand dune and discharging in the sea in the form of submarine springs which in many cases manifest themselves on the marine surface depending on the hydraulic or piezometric fresh water head. The width of the superficial limestone within this coastal fringe, called “caliche”, varies from 5 to 10 kilometers in the study zone (Chuburna-Progreso-Chicxulub.  Its permeability is extremely low, so it constitutes a confining layer that impedes superficial waters to percolate toward groundwater.  The hydraulic head of the groundwater below this confining layer is over the mean sea level and also over the swamp water level, coastal lagoons and estuaries. There are two important hydrological phenomena that occur in this coastal fringe: 1 There is no recharge to the aquifer (groundwater due to limestone rock outcrops is impermeable or semipermeable; and 2 groundwater pressure is not lost, nor saline interfase is rised if the superficial layer is broken.  The groundwater pollution vulnerability within this coastal fringe is less than that for the superficial saline waters of swamps and estuaries, because of caliche’s low intrinsic permeability that impedes percolation.

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

International Nuclear Information System (INIS)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-04-01

A computational approach used for subsurface explosion cratering has been extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for our first computer simulation because it was the most thoroughly studied. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Shoemaker estimates that the impact occurred about 20,000 to 30,000 years ago [Roddy (1977)]. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s. meteorite mass of 1.57E + 08 kg, with a corresponding kinetic energy of 1.88E + 16 J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation a Tillotson equation-of-state description for iron and limestone was used with no shear strength. A color movie based on this calculation was produced using computer-generated graphics. Results obtained for this preliminary calculation of the formation of Meteor Crater, Arizona, are in good agreement with Meteor Crater Measurements

The first educational interferometer in Mexico (FEYMANS): A novel project

Science.gov (United States)

Villicana Pedraza, Ilhuiyolitzin; Guesten, Rolf; Saucedo Morales, Julio Cesar; Carreto, Francisco; Valdes Estrada, Erik; Wendolyn Blanco Cardenas, Monica; Rodríguez Garza, Carolina B.; Pech Castillo, Gerardo A.; Ángel Vaquerizo, Juan

2016-07-01

An interferometer is composed of several radio telescopes (dishes) separated by a defined distance and used in synchrony. This kind of array produces a superior angular resolution, better than the resolution achieved by a single dish of the same combined area. In this work we propose the First Educational Youth Mexican Array North South, FEYMANS. It consists of an educational interferometer with initially four dishes. This array harvests Mexico's geography by locating each dish at the periphery of the country; creating new scientific links of provincial populations with the capital. The FEYMANS project focus in high school students and their projects on physics, chemistry and astronomy as a final project. Also, it can be used for bachelor theses. The initial and central dish-node is planed to be in Mexico City. After its construction, the efforts will focus to build subsequent nodes, on the Northwest region, Northeast, or Southeast. Region Northwest will give service to Baja California, Sonora and Chihuahua states. Region Northeast will cover Coahuila, Nuevo Leon and Tamaulipas. Finally, region Southeast will give access to Yucatan, Quintana Roo, Campeche, Tabasco and Chiapas. This project has been conceived by young professional astronomers and Mexican experts that will operate each node. Also, we have the technical support of the "Max Planck Institute fuer Radioastronomy in Bonn Germany" and the educational model of the "PARTNeR" project in Spain. This interferometer will be financed by Mexico's Federal Congress and by Mexico City's Legislative Assembly (ALDF).

Planktonic cyanobacteria of the tropical karstic lake Lagartos from the Yucatan Peninsula, Mexico.

Science.gov (United States)

Valadez, Francisco; Rosiles-González, Gabriela; Almazán-Becerril, Antonio; Merino-Ibarra, Martin

2013-06-01

The tropical karstic lakes on the Mexican Caribbean Sea coast are numerous. However, there is an enormous gap of knowledge about their limnological conditions and micro-algae communities. In the present study, surface water samples were collected monthly from November 2007 to September 2008 to provide taxonomical composition and biovolume of planktonic cyanobacteria of the lake Lagartos from State of Quintana Roo, Mexico. Water temperature, pH, conductivity, salinity, soluble reactive phosphorus (SRP), dissolved inorganic nitrogen (DIN), and soluble reactive silica (SRSi) levels were also analyzed. A total of 22 species were identified. Chroococcales and Oscillatoriales dominated the phytoplankton assemblages during the study period. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum and Planktolyngbya contorta were recorded for the first time in Mexico. A surplus of DIN (mean value of 42.7 microM) and low concentrations of SRP (mean value of 1.0 microM) promoted the enhanced growth and bloom formation of cyanobacteria. The mean biovolume was 3.22 x 10(8) microm3/mL, and two biovolume peaks were observed; the first was dominated by Microcystis panniformis in November 2007 (7.40 x 10(8) microm3/mL), and the second was dominated by Oscillatoriaprinceps in April 2008 (6.55 x 10(8) microm3/mL). Water quality data, nitrates enrichment, and trophic state based on biovolume, indicated that Lagartos is a hyposaline, secondarily phosphorus-limited, and eutrophic lake, where the cyanobacteria flora was composed mainly by non-heterocystous groups.

Determination of 137Cs and 60Co pollution in the area of the Laguna Verde Nuclear Power Plant, Mexico

International Nuclear Information System (INIS)

Salas Mar, Bernardo

2015-01-01

The project 'Radiological Analysis of Environmental Samples in the Gulf of Mexico and the coast of Quintana Roo', had the aim of identifying and quantifying anthropogenic radionuclides in environmental samples consisting of silt, sand and sea water. This paper presents the results of the radiological analysis of these samples, which was made in the multichannel system for gamma spectrometry with hyper-pure germanium detector in the Laboratory of Radiological Analysis of Environmental Samples, located at the Physics Department, Faculty of Sciences, of the Autonomous National University of Mexico (UNAM). The sampled points are along the coast of the contiguous states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatan and Quintana Roo. This paper presents the qualitative and quantitative concentrations of the main identified anthropogenic radionuclides 60 Co and 137 Cs. (authors)

A Tale of 3 Craters

Science.gov (United States)

2004-01-01

11 November 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image captures some of the complexity of the martian upper crust. Mars does not simply have an impact-cratered surface, it's upper crust is a cratered volume. Over time, older craters on Mars have been eroded, filled, buried, and in some cases exhumed and re-exposed at the martian surface. The crust of Mars is layered to depths of 10 or more kilometers, and mixed in with the layered bedrock are a variety of ancient craters with diameters ranging from a few tens of meters (a few tens of yards) to several hundred kilometers (more than one or two hundred miles). The picture shown here captures some of the essence of the layered, cratered volume of the upper crust of Mars in a very simple form. The image shows three distinct circular features. The smallest, in the lower right quarter of the image, is a meteor crater surrounded by a mound of material. This small crater formed within a layer of bedrock that once covered the entire scene, but today is found only in this small remnant adjacent to the crater. The intermediate-sized crater, west (left) of the small one, formed either in the next layer down--that is, below the layer in which the small crater formed--or it formed in some layers that are now removed, but was big enough to penetrate deeply into the rock that is near the surface today. The largest circular feature in the image, in the upper right quarter of the image, is still largely buried. It formed in layers of rock that are below the present surface. Erosion has brought traces of its rim back to the surface of Mars. This picture is located near 50.0oS, 77.8oW, and covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates this October 2004 image from the upper left.

Stability of nuclear crater slopes in rock

International Nuclear Information System (INIS)

Fleming, Robert W.; Frandsen, Alton D.; LaFrenz, Robert L.

1970-01-01

The United States Army Engineer Nuclear Cratering Group was established in 1962 to participate with the Atomic Energy Commission in a joint research and development program to develop nuclear engineering and construction technology. A major part of this research effort has been devoted to studies of the engineering properties of craters. The program to date has included field investigations of crater properties in various media over a broad range of chemical and nuclear explosive yields, studies of man-made and natural slopes, and studies directed toward the development of analytical and empirical methods of crater stability analysis. From this background, a general understanding has been developed of the effects of a cratering explosion on the surrounding medium and of physical nature of the various crater zones which are produced. The stability of nuclear crater slopes has been a subject of prime interest in the feasibility study being conducted for an Atlantic-Pacific sea-level canal. Based on experimental evidence assembled to date, nuclear crater slopes in dry dock and dry alluvium have an initially stable configuration. There have been five nuclear craters produced to date with yields of 0.4 kt or more on which observations are based and the initial configurations of these craters have remained stable for over seven years. The medium, yield, crater dimensions, and date of event for these craters are summarized. It is interesting to note that the Sedan Crater has been subjected to strong seismic motions from nearby detonations without adverse effects

Stability of nuclear crater slopes in rock

Energy Technology Data Exchange (ETDEWEB)

Fleming, Robert W; Frandsen, Alton D; LaFrenz, Robert L [U.S. Army Engineer Nuclear Cratering Group, Lawrence Radiation Laboratory, Livermore, CA (United States)

1970-05-15

The United States Army Engineer Nuclear Cratering Group was established in 1962 to participate with the Atomic Energy Commission in a joint research and development program to develop nuclear engineering and construction technology. A major part of this research effort has been devoted to studies of the engineering properties of craters. The program to date has included field investigations of crater properties in various media over a broad range of chemical and nuclear explosive yields, studies of man-made and natural slopes, and studies directed toward the development of analytical and empirical methods of crater stability analysis. From this background, a general understanding has been developed of the effects of a cratering explosion on the surrounding medium and of physical nature of the various crater zones which are produced. The stability of nuclear crater slopes has been a subject of prime interest in the feasibility study being conducted for an Atlantic-Pacific sea-level canal. Based on experimental evidence assembled to date, nuclear crater slopes in dry dock and dry alluvium have an initially stable configuration. There have been five nuclear craters produced to date with yields of 0.4 kt or more on which observations are based and the initial configurations of these craters have remained stable for over seven years. The medium, yield, crater dimensions, and date of event for these craters are summarized. It is interesting to note that the Sedan Crater has been subjected to strong seismic motions from nearby detonations without adverse effects.

[Trend analysis of acquired syphilis in Mexico from 2003 to 2013].

Science.gov (United States)

Herrera-Ortiz, Antonia; Uribe-Salas, Felipe J; Olamendi-Portugal, Ma Leonidez; García-Cisneros, Santa; Conde-Glez, Carlos Jesús; Sánchez-Alemán, Miguel A

2015-01-01

To identify the population group in which syphilis increase was concentrated. The information was collected from the Mexico health statistical yearbooks. The information disaggregated by sex, age group and state during the period 2003 to 2013 was used to form different databases. Linear regression analysis with confidence interval at 95% was used to evaluate changes over time in different population groups. An increase of 0.67 cases per 100,000 population (95%CI 0.30-1.04) in men was detected from 2010. The increase was concentrated in each group of 20-24 and 25-44. The highest incidence of acquired syphilis was reported in the last two years: 2012 and 2013. The last year reported a 1.85 times higher incidence than reported in 2003. Aguascalientes, Distrito Federal, Durango, Mexico, Oaxaca, Puebla, Quintana Roo, Yucatan and Zacatecas reported that syphilis increased during the study period. Acquired syphilis may be reemerging in our country among young men; this increase is not uniform across the country, it is necessary to focus intervention measures for this sexually transmitted infection.

Crater Mound Formation by Wind Erosion on Mars

Science.gov (United States)

Steele, L. J.; Kite, E. S.; Michaels, T. I.

2018-01-01

Most of Mars' ancient sedimentary rocks by volume are in wind-eroded sedimentary mounds within impact craters and canyons, but the connections between mound form and wind erosion are unclear. We perform mesoscale simulations of different crater and mound morphologies to understand the formation of sedimentary mounds. As crater depth increases, slope winds produce increased erosion near the base of the crater wall, forming mounds. Peak erosion rates occur when the crater depth is ˜2 km. Mound evolution depends on the size of the host crater. In smaller craters mounds preferentially erode at the top, becoming more squat, while in larger craters mounds become steeper sided. This agrees with observations where smaller craters tend to have proportionally shorter mounds and larger craters have mounds encircled by moats. If a large-scale sedimentary layer blankets a crater, then as the layer recedes across the crater it will erode more toward the edges of the crater, resulting in a crescent-shaped moat. When a 160 km diameter mound-hosting crater is subject to a prevailing wind, the surface wind stress is stronger on the leeward side than on the windward side. This results in the center of the mound appearing to "march upwind" over time and forming a "bat-wing" shape, as is observed for Mount Sharp in Gale crater.

Geological mapping of lunar highland crater Lalande: Topographic configuration, morphology and cratering process

Science.gov (United States)

Li, Bo; Ling, Zongcheng; Zhang, Jiang; Chen, Jian; Liu, ChangQing; Bi, Xiangyu

2018-02-01

Highland crater Lalande (4.45°S, 8.63°W; D = 23.4 km) is located on the PKT area of the lunar near side, southeast of the Mare Insularum. It is a complex crater in Copernican era and has three distinguishing features: high silicic anomaly, the highest Th abundance and special landforms on its floor. There are some low-relief bulges on the left of Lalande's floor with regular circle or ellipse shapes. They are ∼250-680 m wide and ∼30-91 m high with maximum flank slopes >20°. There are two possible scenarios for the formation of these low-relief bulges which are impact melt products or young silicic volcanic eruptions. We estimated the absolute model ages of the ejecta deposits, several melt ponds and the hummocky floor and determined the ratio of diameter and depth of the crater Lalande. In addition, we found some similar bugle features within other Copernican-aged craters and there were no volcanic source vents on Lalande's floor. Thus, we hypothesized that these low-relief bulges were most consistent with an origin of impact melts during the crater formation instead of small and young volcanic activities occurring on the floor. Based on Kaguya Terrain Camera (TC) ortho-mosaic and Digital Terrain Model (DTM) data produced by TC imagery in stereo, geological units and some linear features on the floor and wall of Lalande have been mapped. Eight geological units are organized by crater floor units: hummocky floor, central peak and low-relief bulges; and crater wall units: terraced walls, channeled and veneered walls, interior walls, mass wasting areas, blocky areas, and melt ponds. These geological units and linear features provided us a chance to understand some details of the cratering process and elevation differences on the floor. We proposed that subsidence due to melt cooling, late-stage wall collapse and rocks uplifted from beneath the surface could be the possible causes of the observed elevation differences on Lalande's floor.

Planktonic Cyanobacteria of the tropical karstic lake Lagartos from the Yucatan Peninsula, Mexico

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Francisco Valadez

2013-06-01

Full Text Available The tropical karstic lakes on the Mexican Caribbean Sea coast are numerous. However, there is an enormous gap of knowledge about their limnological conditions and micro-algae communities. In the present study, surface water samples were collected monthly from November 2007 to September 2008 to provide taxonomical composition and biovolume of planktonic cyanobacteria of the lake Lagartos from State of Quintana Roo, Mexico. Water temperature, pH, conductivity, salinity, soluble reactive phosphorus (SRP, dissolved inorganic nitrogen (DIN, and soluble reactive silica (SRSi levels were also analyzed. A total of 22 species were identified. Chroococcales and Oscillatoriales dominated the phytoplankton assemblages during the study period. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum and Planktolyngbya contorta were recorded for the first time in Mexico. A surplus of DIN (mean value of 42.7µM and low concentrations of SRP (mean value of 1.0µM promoted the enhanced growth and bloom formation of cyanobacteria. The mean biovolume was 3.22X10(8µm³/mL, and two biovolume peaks were observed; the first was dominated by Microcystis panniformis in November 2007 (7.40X10(8µm³/mL, and the second was dominated by Oscillatoria princeps in April 2008 (6.55X10(8µm³/mL. Water quality data, nitrates enrichment, and trophic state based on biovolume, indicated that Lagartos is a hyposaline, secondarily phosphorus-limited, and eutrophic lake, where the cyanobacteria flora was composed mainly by non-heterocystous groups.

What Really Happened to Earth's Older Craters?

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Bottke, William; Mazrouei, Sara; Ghent, Rebecca; Parker, Alex

2017-10-01

Most assume the Earth’s crater record is heavily biased, with erosion/tectonics destroying older craters. This matches expectations, but is it actually true? To test this idea, we compared Earth’s crater record, where nearly all D ≥ 20 km craters are pick out from older craters with eroded fragments. Moreover, an inverse relationship between rock abundance (RA) and crater age exists. Using measured RA values, we computed ages for 111 rocky craters with D ≥ 10 km that formed between 80°N and 80°S over the last 1 Gyr.We found several surprising results. First, the production rate of D ≥ 10 km lunar craters increased by a factor of 2.2 [-0.9, +4.4; 95% confidence limits] over the past 250 Myr compared to the previous 750 Myr. Thus, the NEO population is higher now than it has been for the last billion years. Second, the size and age distributions of lunar and terrestrial craters for D ≥ 20 km over the last 650 Myr have similar shapes. This implies that crater erasure must be limited on stable terrestrial terrains; in an average sense, for a given region, the Earth either keeps all or loses all of its D ≥ 20 craters at the same rate, independent of size. It also implies the observed deficit of large terrestrial craters between 250-650 Myr is not preservation bias but rather reflects a distinctly lower impact flux. We predict 355 ± 86 D ≥ 20 km craters formed on Earth over the last 650 Myr. Only 38 ± 6 are known, so the ratio, 10.7 ± 3.1%, is a measure of the Earth’s surface that is reasonably stable to large crater formation over 650 Myr. If erosion had dominated, the age distribution of terrestrial craters would be strongly skewed toward younger ages, which is not observed. We predict Chicxulub-type impacts were rare over the last Gyr, with the event 66 Ma a probable byproduct of the current high terrestrial impact flux.

How old is Autolycus crater?

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Hiesinger, Harald; Pasckert, Jan Henrik; van der Bogert, Carolyn H.; Robinson, Mark S.

2016-04-01

Accurately determining the lunar cratering chronology is prerequisite for deriving absolute model ages (AMAs) across the lunar surface and throughout the Solar System [e.g., 1]. However, the lunar chronology is only constrained by a few data points over the last 1 Ga and there are no calibration data available between 1 and 3 Ga and beyond 3.9 Ga [2]. Rays from Autolycus and Aristillus cross the Apollo 15 landing site and presumably transported material to this location [3]. [4] proposed that at the Apollo 15 landing site about 32% of any exotic material would come from Autolycus crater and 25% would come from Aristillus crater. [5,6] proposed that the 39Ar-40Ar age of 2.1 Ga derived from three petrologically distinct, shocked Apollo 15 KREEP basalt samples, date Autolycus crater. Grier et al. [7] reported that the optical maturity (OMAT) characteristics of these craters are indistinguishable from the background values despite the fact that both craters exhibit rays that were used to infer relatively young, i.e., Copernican ages [8,9]. Thus, both OMAT characteristics and radiometric ages of 2.1 Ga and 1.29 Ga for Autolycus and Aristillus, respectively, suggest that these two craters are not Copernican in age. [10] interpreted newer U-Pb ages of 1.4 and 1.9 Ga from sample 15405 as the formation ages of Aristillus and Autolycus. If Autolycus is indeed the source of the dated exotic material collected at the Apollo 15 landing site, than performing crater size frequency distribution (CSFD) measurements for Autolycus offers the possibility to add a new calibration point to the lunar chronology, particularly in an age range that was previously unconstrained. We used calibrated and map-projected LRO NAC images to perform CSFD measurements within ArcGIS, using CraterTools [11]. CSFDs were then plotted with CraterStats [12], using the production and chronology functions of [13]. We determined ages of 3.72 and 3.85 Ga for the interior (Ai1) and ejecta area Ae3, which we

Experimental simulation of impact cratering on icy satellites

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Greeley, R.; Fink, J. H.; Gault, D. E.; Guest, J. E.

1982-01-01

Cratering processes on icy satellites were simulated in a series of 102 laboratory impact experiments involving a wide range of target materials. For impacts into homogeneous clay slurries with impact energies ranging from five million to ten billion ergs, target yield strengths ranged from 100 to 38 Pa, and apparent viscosities ranged from 8 to 200 Pa s. Bowl-shaped craters, flat-floored craters, central peak craters with high or little relief, and craters with no relief were observed. Crater diameters increased steadily as energies were raised. A similar sequence was seen for experiment in which impact energy was held constant but target viscosity and strength progressively decreases. The experiments suggest that the physical properties of the target media relative to the gravitationally induced stresses determined the final crater morphology. Crater palimpsests could form by prompt collapse of large central peak craters formed in low target strength materials. Ages estimated from crater size-frequency distributions that include these large craters may give values that are too high.

Radiological analysis of environmental samples in some points of the coast of the Gulf of Mexico and Coast of Quintana Roo, Mexico

International Nuclear Information System (INIS)

Salas Mar, Bernardo; Martinez Negrete, Marco Antonio; Ruiz Chavarria, Gerardo; Abarca Munguia, Jose

2008-01-01

Full text: We describe in this paper the results obtained by the project 'Radiological analysis of environmental samples in some points of the coast of the Gulf of Mexico and coast of Quintana Roo, Mexico'. The purpose of the study is to identify and quantify the natural and anthropogenic radionuclides present from sediments, sand and seawater from several sites located along the coast of the Gulf of Mexico and the Caribean Sea. The samples are analysed in a Canberra Multichannel analyzer system for gamma spectrometry, equipped with a detector of hyper pure germanium and a Genie 2000 software, in the 'Laboratory of Radiological Analysis of Environmental Samples', belonging to the Physics Department, Faculty of Sciences, National Autonomous University of Mexico (UNAM). The geographic sites were samples were taken include the states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatan and Quintana Roo. The results of this studies will be published at the end of the project and we hope they will be useful for the national health and industrial sectors. Until now we have identified and measured the presence of natural radionuclides such as Potassium-40 (K-40), Bismuth 212 (Bi-212), Lead-212 (Pb-212), Bismuth-214 (Bi-214), Lead-214 (Pb-214), Radium-226 (Ra-226), Actinium 228 (Ac-228), Uranium-235 (U-235), as well as some anthropogenic radionuclides found near the Laguna Verde Nuclear Power Plant. The project is scheduled to last for three years, finishing in 2009. At its ending we shall be able to present conclusions and identify some tendencies, in connection with the background and possible radioactive contamination of the studied zones. This project takes place under the auspice of the 'Program of Support to Projects of Research and Technological Innovation' of the National Autonomous University of Mexico. (author)

Lunar Bouguer gravity anomalies - Imbrian age craters

Science.gov (United States)

Dvorak, J.; Phillips, R. J.

1978-01-01

The Bouguer gravity of mass anomalies associated with four Imbrian age craters, analyzed in the present paper, are found to differ considerably from the values of the mass anomalies associated with some young lunar craters. Of the Imbrian age craters, only Piccolomini exhibits a negative gravity anomaly (i.e., a low density region) which is characteristic of the young craters studied. The Bouguer gravity anomalies are zero for each of the remaining Imbrian age craters. Since, Piccolomini is younger, or at least less modified, than the other Imbrian age craters, it is suggested that the processes responsible for the post-impact modification of the Imbrian age craters may also be responsible for removing the negative mass anomalies initially associated with these features.

SMALL CRATERS AND THEIR DIAGNOSTIC POTENTIAL

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R. Bugiolacchi

2017-07-01

Full Text Available I analysed and compared the size-frequency distributions of craters in the Apollo 17 landing region, comprising of six mare terrains with varying morphologies and cratering characteristics, along with three other regions allegedly affected by the same secondary event (Tycho secondary surge. I propose that for the smaller crater sizes (in this work 9–30 m, a] an exponential curve of power −0.18D can approximate Nkm−2 crater densities in a regime of equilibrium, while b] a power function D−3 closely describes the factorised representation of craters by size (1 m. The saturation level within the Central Area suggests that c] either the modelled rates of crater erosion on the Moon should be revised, or that the Tycho event occurred much earlier in time than the current estimate. We propose that d] the size-frequency distribution of small secondary craters may bear the signature (in terms of size-frequency distribution of debris/surge of the source impact and that this observation should be tested further.

The Orphans of Cholera Morbus in Yucatan, 1833

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Elsa Malvido

2013-07-01

Full Text Available This essay discusses the phenomenon of orphanhood which affected a large number of children after the cholera epidemic that struck Yucatan in July 1833. Moreover, it inquires into the fate of children whose parents died of cholera, the role played by kinship networks to provide them with shelter, and the influence of the Church and the State on the situation. Based on first hand sources, the author suggests that the orphanhood produced by cholera served as a pretext for economically and socially privileged groups to get hold of free labor force both for domestic service and hacienda work.

LU60645GT and MA132843GT Catalogues of Lunar and Martian Impact Craters Developed Using a Crater Shape-based Interpolation Crater Detection Algorithm for Topography Data

Science.gov (United States)

Salamuniccar, Goran; Loncaric, Sven; Mazarico, Erwan Matias

2012-01-01

For Mars, 57,633 craters from the manually assembled catalogues and 72,668 additional craters identified using several crater detection algorithms (CDAs) have been merged into the MA130301GT catalogue. By contrast, for the Moon the most complete previous catalogue contains only 14,923 craters. Two recent missions provided higher-quality digital elevation maps (DEMs): SELENE (in 1/16° resolution) and Lunar Reconnaissance Orbiter (we used up to 1/512°). This was the main motivation for work on the new Crater Shape-based interpolation module, which improves previous CDA as follows: (1) it decreases the number of false-detections for the required number of true detections; (2) it improves detection capabilities for very small craters; and (3) it provides more accurate automated measurements of craters' properties. The results are: (1) LU60645GT, which is currently the most complete (up to D>=8 km) catalogue of Lunar craters; and (2) MA132843GT catalogue of Martian craters complete up to D>=2 km, which is the extension of the previous MA130301GT catalogue. As previously achieved for Mars, LU60645GT provides all properties that were provided by the previous Lunar catalogues, plus: (1) correlation between morphological descriptors from used catalogues; (2) correlation between manually assigned attributes and automated measurements; (3) average errors and their standard deviations for manually and automatically assigned attributes such as position coordinates, diameter, depth/diameter ratio, etc; and (4) a review of positional accuracy of used datasets. Additionally, surface dating could potentially be improved with the exhaustiveness of this new catalogue. The accompanying results are: (1) the possibility of comparing a large number of Lunar and Martian craters, of e.g. depth/diameter ratio and 2D profiles; (2) utilisation of a method for re-projection of datasets and catalogues, which is very useful for craters that are very close to poles; and (3) the extension of the

Evidence for a Meteoritic Component in Impact Melt Rock from the Chicxulub Structure

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Koeberl, Christian; Sharpton, Virgil L.; Schuraytz, Benjamin C.; Shirey, Steven B.; Blum, Joel D.; Marin, Luis E.

1994-01-01

The Chicxulub structure in Yucatan, Mexico, has recently been recognized as a greater then 200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated iridium concentrations, an osmium concentration of 25 ppb, and a low Os-187/Os-188 ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the Os-187/Os-188 ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an Os-187/0s-188 ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.

Analysis of the Gran Desierto, Pinacte Region, Sonora, Mexico, via shuttle imaging radar

Science.gov (United States)

Greeley, R.; Christensen, P. R.; Mchone, J. F.; Asmerom, Y.; Zimbelman, J. R.

1984-01-01

The radar discriminability of geolian features and their geological setting as imaged by the SIR-A experiment is examined. The Gran Desierto and Pincate volcanio field of Sonora, Mexico was used to analyze the radar characteristics of the interplay of aeolian features and volcano terrain. The area in the Gran Desierto covers 4000 sq. km. and contains sand dunes of several forms. The Pincate volcanio field covers more than 2.000 sq. km. and consists primarily of basaltic lavas. Margins of the field, especially on the western and northern sides, include several maar and maar-like craters; thus obtaining information on their radar characteristics for comparison with impact craters.

Blocky craters: implications about the lunar megaregolith

International Nuclear Information System (INIS)

Thompson, T.W.; Roberts, W.J.; Hartmann, W.K.; Shorthill, R.W.; Zisk, S.H.

1979-01-01

Radar, infrared, and photogeologic properties of lunar craters have been studied to determine whether there is a systematic difference in blocky craters between the maria and terrae and whether this difference may be due to a deep megaregolith of pulverized material forming the terra surface, as opposed to a layer of semi-coherent basalt flows forming the mare surface. Some 1310 craters from about 4 to 100 km diameter have been catalogued as radar and/or infrared anomalies. In addition, a study of Apollo Orbital Photography confirmed that the radar and infrared anomalies are correlated with blocky rubble around the crater. Analysis of the radar and infrared data indicated systematic terra-mare differences. Fresh terra craters smaller than 12 km were less likely to be infrared and radar anomalies than comparable mare craters: but terra and mare craters larger than 12 km had similar infrared and radar signatures. Also, there are many terra craters which are radar bright but not infrared anomalies. The authors interpretation of these data is that while the maria are rock layers (basaltic flow units) where craters eject boulder fields, the terrae are covered by relatively pulverized megaregolith at least 2 km deep, where craters eject less rocky rubble. Blocky rubble, either in the form of actual rocks or partly consolidated blocks, contributes to the radar and infrared signatures of the crater. However, aging by impacts rapidly destroys these effects, possibly through burial by secondary debris or by disintegration of the blocks themselves, especially in terra regions. (Auth.)

Machine cataloging of impact craters on Mars

Science.gov (United States)

Stepinski, Tomasz F.; Mendenhall, Michael P.; Bue, Brian D.

2009-09-01

This study presents an automated system for cataloging impact craters using the MOLA 128 pixels/degree digital elevation model of Mars. Craters are detected by a two-step algorithm that first identifies round and symmetric topographic depressions as crater candidates and then selects craters using a machine-learning technique. The system is robust with respect to surface types; craters are identified with similar accuracy from all different types of martian surfaces without adjusting input parameters. By using a large training set in its final selection step, the system produces virtually no false detections. Finally, the system provides a seamless integration of crater detection with its characterization. Of particular interest is the ability of our algorithm to calculate crater depths. The system is described and its application is demonstrated on eight large sites representing all major types of martian surfaces. An evaluation of its performance and prospects for its utilization for global surveys are given by means of detailed comparison of obtained results to the manually-derived Catalog of Large Martian Impact Craters. We use the results from the test sites to construct local depth-diameter relationships based on a large number of craters. In general, obtained relationships are in agreement with what was inferred on the basis of manual measurements. However, we have found that, in Terra Cimmeria, the depth/diameter ratio has an abrupt decrease at ˜38°S regardless of crater size. If shallowing of craters is attributed to presence of sub-surface ice, a sudden change in its spatial distribution is suggested by our findings.

Composition and fluxes of submarine groundwater along the Caribbean coast of the Yucatan Peninsula

Science.gov (United States)

Null, Kimberly A.; Knee, Karen L.; Crook, Elizabeth D.; de Sieyes, Nicholas R.; Rebolledo-Vieyra, Mario; Hernández-Terrones, Laura; Paytan, Adina

2014-04-01

Submarine groundwater discharge (SGD) to the coastal environment along the eastern Yucatan Peninsula, Quintana Roo, Mexico was investigated using a combination of tracer mass balances and analytical solutions. Two distinct submarine groundwater sources including water from the unconfined surficial aquifer discharging at the beach face and water from a deeper aquifer discharging nearshore through submarine springs (ojos) were identified. The groundwater of nearshore ojos was saline and significantly enriched in short-lived radium isotopes (223Ra, 224Ra) relative to the unconfined aquifer beach face groundwater. We estimated SGD from ojos using 223Ra and used a salinity mass balance to estimate the freshwater discharge at the beach face. Analytical calculations were also used to estimate wave set-up and tidally driven saline seepage into the surf zone and were compared to the salinity-based freshwater discharge estimates. Results suggest that average SGD from ojos along the Yucatan Peninsula Caribbean coast is on the order of 308 m3 d-1 m-1 and varies between sampling regions. Higher discharge was observed in the southern regions (568 m3 d-1 m-1) compared to the north (48 m3 d-1 m-1). Discharge at the beach face was in the range of 3.3-8.5 m3 d-1 m-1 for freshwater and 2.7 m3 d-1 m-1 for saline water based on the salinity mass balance and wave- and tidally-driven discharge, respectively. Although discharge from the ojos was larger in volume than discharge from the unconfined aquifer at the beach face, dissolved inorganic nitrogen (DIN) was significantly higher in beach groundwater; thus, discharge of this unconfined beach aquifer groundwater contributed significantly to total DIN loading to the coast. DIN fluxes were up to 9.9 mol d-1 m-1 from ojos and 2.1 mol d-1 m-1 from beach discharge and varied regionally along the 500 km coastline sampled. These results demonstrate the importance of considering the beach zone as a significant nutrient source to coastal waters

[Obesity, body morphology, and blood pressure in urban and rural population groups of Yucatan].

Science.gov (United States)

Arroyo, Pedro; Fernández, Victoria; Loría, Alvar; Pardío, Jeannette; Laviada, Hugo; Vargas-Ancona, Lizardo; Ward, Ryk

2007-01-01

To characterize body morphology and blood pressure of adults of the Mexican state of Yucatan. Rural-urban differences in weight, height, waist, and hip circumferences, and blood pressure were analyzed in 313 urban and 271 rural subjects. No rural-urban differences in prevalence of obesity and overweight were found. Hypertension was marginally higher in urban subjects. Rural abnormal waist circumference was higher in young men and young women. Comparison with two national surveys and a survey in the aboriginal population (rural mixtecos) showed similar prevalence of obesity as ENSA-2000 and higher than mixtecos and ENEC-1993. Abnormal waist circumference was intermediate between ENSANUT-2006 and mixtecos and hypertension was intermediate between ENEC and mixtecos. The Maya and mestizo population of Yucatan showed a high prevalence of obesity and abnormal waist circumference not accompanied by a comparable higher hypertension frequency. This finding requires further confirmation.

Nuclear cratering on a digital computer

International Nuclear Information System (INIS)

Terhune, R.W.; Stubbs, T.F.; Cherry, J.T.

1970-01-01

Computer programs based on the artificial viscosity method are applied to developing an understanding of the physics of cratering, with emphasis on cratering by nuclear explosives. Two established codes, SOC (spherical symmetry) and TENSOR (cylindrical symmetry), are used to illustrate the effects of variations in the material properties of various media on the cratering processes, namely shock, spall, and gas acceleration. Water content is found to be the most important material property, followed by strength, porosity, and compressibility. Crater profile calculations are presented for Pre-Gondola Charley (20-ton nitromethane detonation in shale) and Sedan (100-kt nuclear detonation in alluvium). Calculations also are presented for three 1-Mt yields in saturated Divide basalt and 1-Mt yield in dry Buckboard basalt, to show crater geometry as a function of the burial depth for large explosive yields. The calculations show, for megaton-level yields, that gas acceleration is the dominate mechanism in determining crater size and depends in turn on the water content in the medium. (author)

Nuclear cratering on a digital computer

Energy Technology Data Exchange (ETDEWEB)

Terhune, R W; Stubbs, T F; Cherry, J T [Lawrence Radiation Laboratory, University of California, Livermore, CA (United States)

1970-05-01

Computer programs based on the artificial viscosity method are applied to developing an understanding of the physics of cratering, with emphasis on cratering by nuclear explosives. Two established codes, SOC (spherical symmetry) and TENSOR (cylindrical symmetry), are used to illustrate the effects of variations in the material properties of various media on the cratering processes, namely shock, spall, and gas acceleration. Water content is found to be the most important material property, followed by strength, porosity, and compressibility. Crater profile calculations are presented for Pre-Gondola Charley (20-ton nitromethane detonation in shale) and Sedan (100-kt nuclear detonation in alluvium). Calculations also are presented for three 1-Mt yields in saturated Divide basalt and 1-Mt yield in dry Buckboard basalt, to show crater geometry as a function of the burial depth for large explosive yields. The calculations show, for megaton-level yields, that gas acceleration is the dominate mechanism in determining crater size and depends in turn on the water content in the medium. (author)

Comparison of small mammal prevalence of Leishmania (Leishmania) mexicana in five foci of cutaneous leishmaniasis in the State of Campeche, Mexico.

Science.gov (United States)

Van Wynsberghe, N R; Canto-Lara, S B; Sosa-Bibiano, E I; Rivero-Cárdenas, N A; Andrade-Narváez, F J

2009-01-01

In the Yucatan Peninsula of Mexico, 95% of the human cases of Cutaneous Leishmaniasis are caused by Leishmania (Leishmania) mexicana with an incidence rate of 5.08 per 100,000 inhabitants. Transmission is limited to the winter months (November to March). One study on wild rodents has incriminated Ototylomys phyllotis and Peromyscus yucatanicus as primary reservoirs of L. (L.) mexicana in the focus of La Libertad, Campeche. In the present study, the prevalence of both infection and disease caused by L. (L.) mexicana in small terrestrial mammals were documented during five transmission seasons (1994-2004) in five foci of Leishmaniasis in the state of Campeche. Foci separated by only 100 km, with similar relative abundances of small mammals, were found to differ significantly in their prevalence of both symptoms and infection. Transmission rates and reservoir species seemed to change in space as well as in time which limited the implementation of effective control measures of the disease even in a small endemic area such as the south of the Yucatan Peninsula.

Enhancing Diversity In The Geosciences; Intensive Field Experience In USA And Mexico For Middle And High School Teachers Serving Large Hispanic Populations.

Science.gov (United States)

Leal-Bautista, R. M.; Kitts, K. B.; Velazquez Oliman, G.; Perry, E. C.

2008-12-01

To encourage Hispanic participation and enrolment in the geosciences and ultimately enhance diversity within the discipline, we recruited ten middle and high school science teachers serving large Hispanic populations (60-97%) for a paid three-week field experience supported by an NSF Opportunities for Enhancing Diversity in the Geosciences grant. In 2006, the field experiences focused on volcanic events and the water problems of the Central part of Mexico. In 2008, the field experiences focused on karstic and hydrogeological conditions of the Yucatan Peninsula. In addition to the geological aspects of the fieldwork experience, the trip to Mexico exposed the teachers to a social environment outside of their community where they interacted with a diverse group of scientists from the Universidad National Autonoma de Mexico (UNAM), Centro de Investigacion Cientifica de Yucatan (CICY) and Centro Nacional de Desastres (CENAPRED). A key part of this project was the encounter between American and Mexican teachers that included a day of presentations, panel discussion and some class-room activities. Direct interaction between the cooperating teachers and the American and Mexican geoscientists provided actual scientific research experiences to educate and to help dispel misconceptions the teachers themselves may have had about who geoscientists really are and what they do. Teachers of the 2006 group produced educational materials from their field experiences and presented these materials at professional conferences. We measured the efficacy of these activities quantitatively via pre- and post-tests assessing confidence levels, preconceptions and biases, NIU staff observations of participants in their home institutions, and evaluations of participants' field books and pedagogical materials. We present these data here and identify specific activities that are both effective and efficient in changing teacher behaviours and attitudes enabling them to better connect with their

Polygons on Crater Floor

Science.gov (United States)

2003-01-01

MGS MOC Release No. MOC2-357, 11 May 2003This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows a pattern of polygons on the floor of a northern plains impact crater. These landforms are common on crater floors at high latitudes on Mars. Similar polygons occur in the arctic and antarctic regions of Earth, where they indicate the presence and freeze-thaw cycling of ground ice. Whether the polygons on Mars also indicate water ice in the ground is uncertain. The image is located in a crater at 64.8oN, 292.7oW. Sunlight illuminates the scene from the lower left.

Voices of Mayan Women in Plaza Comunitaria: Poética y Educación Desde Yucatán

Science.gov (United States)

Ceballos Zapata, Abraham

2017-01-01

This study took place in a village in Yucatan, Mexico in the context of two adult education programs in Yucatan [Plaza Comunitaria and Preparatoria Abierta]. I interacted in "convivencia" with bilingual (Mayan-Spanish) Yucatec Mayan women who took on the challenge of completing their formal schooling through those adult education…

Floor-Fractured Craters through Machine Learning Methods

Science.gov (United States)

Thorey, C.

2015-12-01

Floor-fractured craters are impact craters that have undergone post impact deformations. They are characterized by shallow floors with a plate-like or convex appearance, wide floor moats, and radial, concentric, and polygonal floor-fractures. While the origin of these deformations has long been debated, it is now generally accepted that they are the result of the emplacement of shallow magmatic intrusions below their floor. These craters thus constitute an efficient tool to probe the importance of intrusive magmatism from the lunar surface. The most recent catalog of lunar-floor fractured craters references about 200 of them, mainly located around the lunar maria Herein, we will discuss the possibility of using machine learning algorithms to try to detect new floor-fractured craters on the Moon among the 60000 craters referenced in the most recent catalogs. In particular, we will use the gravity field provided by the Gravity Recovery and Interior Laboratory (GRAIL) mission, and the topographic dataset obtained from the Lunar Orbiter Laser Altimeter (LOLA) instrument to design a set of representative features for each crater. We will then discuss the possibility to design a binary supervised classifier, based on these features, to discriminate between the presence or absence of crater-centered intrusion below a specific crater. First predictions from different classifier in terms of their accuracy and uncertainty will be presented.

Geology of Lofn Crater, Callisto

Science.gov (United States)

Greeley, Ronald; Heiner, Sarah; Klemaszewski, James E.

2001-01-01

Lofn crater is a 180-km-diameter impact structure in the southern cratered plains of Callisto and is among the youngest features seen on the surface. The Lofn area was imaged by the Galileo spacecraft at regional-scale resolutions (875 m/pixel), which enable the general geology to be investigated. The morphology of Lofn crater suggests that (1) it is a class of impact structure intermediate between complex craters and palimpsests or (2) it formed by the impact of a projectile which fragmented before reaching the surface, resulting in a shallow crater (even for Callisto). The asymmetric pattern of the rim and ejecta deposits suggests that the impactor entered at a low angle from the northwest. The albedo and other characteristics of the ejecta deposits from Lofn also provide insight into the properties of the icy lithosphere and subsurface configuration at the time of impact. The "target" for the Lofn impact is inferred to have included layered materials associated with the Adlinda multiring structure northwest of Loh and ejecta deposits from the Heimdall crater area to the southeast. The Lofn impact might have penetrated through these materials into a viscous substrate of ductile ice or possibly liquid water. This interpretation is consistent with models of the current interior of Callisto based on geophysical information obtained from the Galileo spacecraft.

Characteristics of ejecta and alluvial deposits at Meteor Crater, Arizona and Odessa Craters, Texas: Results from ground penetrating radar

Science.gov (United States)

Grant, J. A.; Schultz, P. H.

1991-01-01

Previous ground penetrating radar (GRP) studies around 50,000 year old Meteor Crater revealed the potential for rapid, inexpensive, and non-destructive sub-surface investigations for deep reflectors (generally greater than 10 m). New GRP results are summarized focusing the shallow sub-surfaces (1-2 m) around Meteor Crater and the main crater at Odessa. The following subject areas are covered: (1) the thickness, distribution, and nature of the contact between surrounding alluvial deposits and distal ejecta; and (2) stratigraphic relationships between both the ejecta and alluvium derived from both pre and post crater drainages. These results support previous conclusions indicating limited vertical lowering (less than 1 m) of the distal ejecta at Meteor Crater and allow initial assessment of the gradational state if the Odessa craters.

Creation of High Resolution Terrain Models of Barringer Meteorite Crater (Meteor Crater) Using Photogrammetry and Terrestrial Laser Scanning Methods

Science.gov (United States)

Brown, Richard B.; Navard, Andrew R.; Holland, Donald E.; McKellip, Rodney D.; Brannon, David P.

2010-01-01

Barringer Meteorite Crater or Meteor Crater, AZ, has been a site of high interest for lunar and Mars analog crater and terrain studies since the early days of the Apollo-Saturn program. It continues to be a site of exceptional interest to lunar, Mars, and other planetary crater and impact analog studies because of its relatively young age (est. 50 thousand years) and well-preserved structure. High resolution (2 meter to 1 decimeter) digital terrain models of Meteor Crater in whole or in part were created at NASA Stennis Space Center to support several lunar surface analog modeling activities using photogrammetric and ground based laser scanning techniques. The dataset created by this activity provides new and highly accurate 3D models of the inside slope of the crater as well as the downslope rock distribution of the western ejecta field. The data are presented to the science community for possible use in furthering studies of Meteor Crater and impact craters in general as well as its current near term lunar exploration use in providing a beneficial test model for lunar surface analog modeling and surface operation studies.

Low-velocity impact cratering experiments in granular slopes

Science.gov (United States)

Hayashi, Kosuke; Sumita, Ikuro

2017-07-01

Low-velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle θ on the crater shape and its scales. We use two types of granular matter, sand and glass beads, former of which has a larger friction coefficient μs = tanθr , where θr is the angle of repose. Experiments show that as θ increases, the crater becomes shallower and elongated in the direction of the slope. Furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side, thus forming an asymmetric profile. High-speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor. Such asymmetric ejecta dispersal can be explained by combining the Z-model and a ballistic model. Using the topographic maps of the craters, we classify crater shape regimes I-III, which transition with increasing θ : a full-rim crater (I), a broken-rim crater (II), and a depression (III). The critical θ for the regime transitions are larger for sand compared to glass beads, but collapse to close values when we use a normalized slope θ^ = tanθ / tanθr . Similarly we derive θ^-dependences of the scaled crater depth, length, width and their ratios which collapse the results for different targets and impact energies. We compare the crater profiles formed in our experiments with deep craters on asteroid Vesta and find that some of the scaled profiles nearly overlap and many have similar depth / length ratios. This suggests that these Vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient.

Moon - 'Ghost' craters formed during Mare filling.

Science.gov (United States)

Cruikshank, D. P.; Hartmann, W. K.; Wood, C. A.

1973-01-01

This paper discusses formation of 'pathological' cases of crater morphology due to interaction of craters with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small impact craters (D less than 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental craters deformed by isostatic filling.

Determination of 137Cs and 60Co pollution in the area of the Laguna Verde Nuclear Power Plant, Mexico.

Science.gov (United States)

Salas Mar, Bernardo

2015-11-01

The project 'Radiological Analysis of Environmental Samples in the Gulf of Mexico and the coast of Quintana Roo', had the aim of identifying and quantifying anthropogenic radionuclides in environmental samples consisting of silt, sand and sea water. This paper presents the results of the radiological analysis of these samples, which was made in the multichannel system for gamma spectrometry with hyperpure germanium detector in the Laboratory of Radiological Analysis of Environmental Samples, located at the Physics Department, Faculty of Sciences, of the Autonomous National University of Mexico (UNAM). The sampled points are along the coast of the contiguous states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatan and Quintana Roo. This paper presents the qualitative and quantitative concentrations of the main identified anthropogenic radionuclides (60)Co and (137)Cs. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Investigations of Ceres's Craters with Straightened Rim

Science.gov (United States)

Frigeri, A.; De Sanctis, M. C.; Ammannito, E.; Raponi, A.; Formisano, M.; Ciarniello, M.; Magni, G.; Combe, J. P.; Marchi, S.; Raymond, C. A.; Schwartz, S. J.

2017-12-01

Dwarf planet Ceres hosts some geological features that are unique in the solar system because its composition, rich in aqueously-altered silicates, is usually found on full-size planets, whereas its mean radius is smaller than most natural satellites in the solar system. For example, the local high-albedo, carbonate-rich areas or faculaeare specific to Ceres; also, the absence of big impact crater structures is key to understand the overall mechanical behaviour of the Cerean crust. After the first findings of water ice occurring in the shadowed areas of craters on Ceres by the NASA/Dawn mission (1, 2), we analyzed the morphology of craters looking for features similar to the ones where the water ice composition has been detected analyzing the data from the VIR spectrometer (3). These craters fall outside of the family of polygonal craters which are mainly related to regional or global scale tectonics (4). We analyzed the morphology on the base of the global mosaic, the digital terrain model derived by using the stereo photogrammetry method and the single data frames of the Framing Camera. Our investigation started from crater Juling, which is characterized by a portion of the rim which forms a straight segment instead of a portion of a circle. This linear crater wall is also steep enough that it forms a cliff that is in the shadowed area in all images acquired by Dawn. Very smooth and bright deposits lay at the foot of this crater-wall cliff. Then, we identified several other craters, relatively fresh, with radius of 2 to 10 kilometers, showing one or two sectors of the crater-rim being truncated by a mass-wasting process, probably a rockfall. Our first analysis show that in the selected craters, the truncated sectors are always in the north-eastern sector of the rim for the craters in the southern hemisphere. Conversely, the craters on the northern hemisphere exhibit a truncated rim in their south-eastern sector. Although a more detailed analysis is mandatory

Asteroid families from cratering: Detection and models

Science.gov (United States)

Milani, A.; Cellino, A.; Knežević, Z.; Novaković, B.; Spoto, F.; Paolicchi, P.

2014-07-01

A new asteroid families classification, more efficient in the inclusion of smaller family members, shows how relevant the cratering impacts are on large asteroids. These do not disrupt the target, but just form families with the ejecta from large craters. Of the 12 largest asteroids, 8 have cratering families: number (2), (4), (5), (10), (87), (15), (3), and (31). At least another 7 cratering families can be identified. Of the cratering families identified so far, 7 have >1000 members. This imposes a remarkable change from the focus on fragmentation families of previous classifications. Such a large dataset of asteroids believed to be crater ejecta opens a new challenge: to model the crater and family forming event(s) generating them. The first problem is to identify which cratering families, found by the similarity of proper elements, can be formed at once, with a single collision. We have identified as a likely outcome of multiple collisions the families of (4), (10), (15), and (20). Of the ejecta generated by cratering, only a fraction reaches the escape velocity from the surviving parent body. The distribution of velocities at infinity, giving to the resulting family an initial position and shape in the proper elements space, is highly asymmetric with respect to the parent body. This shape is deformed by the Yarkovsky effect and by the interaction with resonances. All the largest asteroids have been subjected to large cratering events, thus the lack of a family needs to be interpreted. The most interesting case is (1) Ceres, which is not the parent body of the nearby family of (93). Two possible interpretations of the low family forming efficiency are based on either the composition of Ceres with a significant fraction of ice, protected by a thin crust, or with the larger escape velocity of ~500 m/s.

The Global Contribution of Secondary Craters on the Icy Satellites

Science.gov (United States)

Hoogenboom, T.; Johnson, K. E.; Schenk, P.

2014-12-01

At present, surface ages of bodies in the Outer Solar System are determined only from crater size-frequency distributions (a method dependent on an understanding of the projectile populations responsible for impact craters in these planetary systems). To derive accurate ages using impact craters, the impactor population must be understood. Impact craters in the Outer Solar System can be primary, secondary or sesquinary. The contribution of secondary craters to the overall population has recently become a "topic of interest." Our objective is to better understand the contribution of dispersed secondary craters to the small crater populations, and ultimately that of small comets to the projectile flux on icy satellites in general. We measure the diameters of obvious secondary craters (determined by e.g. irregular crater shape, small size, clustering) formed by all primary craters on Ganymede for which we have sufficiently high resolution data to map secondary craters. Primary craters mapped range from approximately 40 km to 210 km. Image resolution ranges from 45 to 440 m/pixel. Bright terrain on Ganymede is our primary focus. These resurfaced terrains have relatively low crater densities and serve as a basis for characterizing secondary populations as a function of primary size on an icy body for the first time. Although focusing on Ganymede, we also investigate secondary crater size, frequency, distribution, and formation, as well as secondary crater chain formation on icy satellites throughout the Saturnian and Jovian systems principally Rhea. We compare our results to similar studies of secondary cratering on the Moon and Mercury. Using Galileo and Voyager data, we have identified approximately 3,400 secondary craters on Ganymede. In some cases, we measured crater density as a function of distance from a primary crater. Because of the limitations of the Galileo data, it is necessary to extrapolate from small data sets to the global population of secondary craters

Impact cratering experiments in Bingham materials and the morphology of craters on Mars and Ganymede

Science.gov (United States)

Fink, J. H.; Greeley, R.; Gault, D. E.

1982-01-01

Results from a series of laboratory impacts into clay slurry targets are compared with photographs of impact craters on Mars and Ganymede. The interior and ejecta lobe morphology of rampart-type craters, as well as the progression of crater forms seen with increasing diameter on both Mars and Ganymede, are equalitatively explained by a model for impact into Bingham materials. For increasing impact energies and constant target rheology, laboratory craters exhibit a morphologic progression from bowl-shaped forms that are typical of dry planetary surfaces to craters with ejecta flow lobes and decreasing interior relief, characteristic of more volatile-rich planets. A similar sequence is seen for uniform impact energy in slurries of decreasing yield strength. The planetary progressions are explained by assuming that volatile-rich or icy planetary surfaces behave locally in the same way as Bingham materials and produce ejecta slurries with yield strenghs and viscosities comparable to terrestrial debris flows. Hypothetical impact into Mars and Ganymede are compared, and it is concluded that less ejecta would be produced on Ganymede owing to its lower gravitational acceleration, surface temperature, and density of surface materials.

Presence of Toxoplasma gondii in Drinking Water from an Endemic Region in Southern Mexico.

Science.gov (United States)

Hernandez-Cortazar, Ivonne B; Acosta-Viana, Karla Y; Guzman-Marin, Eugenia; Ortega-Pacheco, Antonio; Segura-Correa, Jose C; Jimenez-Coello, Matilde

2017-05-01

Toxoplasmosis can be acquired through the ingestion of contaminated drinking water with oocysts of Toxoplasma gondii, highly resistant to the routinely disinfection processes; based on chlorination commonly used in the water supply industry. The aim of this study was to determine the presence of T. gondii DNA in samples of public drinking water from an endemic region of southern Mexico. In total 74 samples of water (5 L each) were collected from the three well fields (I, II, and III) and 71 independent wells, distributing public drinking water to the city of Merida Yucatan, after passing through the chlorination process. Water samples were filtered and concentrated by a sucrose solution, then DNA was extracted and evaluated through a nested-PCR (nPCR) specific for T. gondii. Positive samples were detected in 5.4% (4/74) of the water samples. This is the first report of the presence of T. gondii DNA in public drinking water from a large city in southern Mexico, where their consumption without any postpurification treatment could pose a risk for acquiring the infection in the urban population.

Technical problems and future cratering experiments

Energy Technology Data Exchange (ETDEWEB)

Knox, J B [Lawrence Radiation Laboratory, Livermore, CA (United States)

1969-07-01

This paper reviews some of the key technical problems that remain to be solved in nuclear cratering technology. These include: (1) developing a broader understanding of the effects that material properties and water content of the earth materials around the shot have on cratering behavior, (2) extending the experimental investigation of retarc formation to include intermediate yields and various materials, and (3) improving our ability to predict the escape of radioactive material to the atmosphere to form the cloud source responsible for fallout. The formation processes of ejecta craters, retarcs, and subsidence craters are described in the light of our present understanding, and the major gaps in our understanding are indicated. Methods of calculating crater and retarc formation are discussed, with particular reference to the input information needed. Methods for calculating fallout are presented, and their shortcomings are discussed. A preliminary analysis of the safety factors associated with the presently proposed nuclear excavation concepts is presented. (author)

Technical problems and future cratering experiments

International Nuclear Information System (INIS)

Knox, J.B.

1969-01-01

This paper reviews some of the key technical problems that remain to be solved in nuclear cratering technology. These include: (1) developing a broader understanding of the effects that material properties and water content of the earth materials around the shot have on cratering behavior, (2) extending the experimental investigation of retarc formation to include intermediate yields and various materials, and (3) improving our ability to predict the escape of radioactive material to the atmosphere to form the cloud source responsible for fallout. The formation processes of ejecta craters, retarcs, and subsidence craters are described in the light of our present understanding, and the major gaps in our understanding are indicated. Methods of calculating crater and retarc formation are discussed, with particular reference to the input information needed. Methods for calculating fallout are presented, and their shortcomings are discussed. A preliminary analysis of the safety factors associated with the presently proposed nuclear excavation concepts is presented. (author)

Cratering statistics on asteroids: Methods and perspectives

Science.gov (United States)

Chapman, C.

2014-07-01

Crater size-frequency distributions (SFDs) on the surfaces of solid-surfaced bodies in the solar system have provided valuable insights about planetary surface processes and about impactor populations since the first spacecraft images were obtained in the 1960s. They can be used to determine relative age differences between surficial units, to obtain absolute model ages if the impactor flux and scaling laws are understood, to assess various endogenic planetary or asteroidal processes that degrade craters or resurface units, as well as assess changes in impactor populations across the solar system and/or with time. The first asteroid SFDs were measured from Galileo images of Gaspra and Ida (cf., Chapman 2002). Despite the superficial simplicity of these studies, they are fraught with many difficulties, including confusion by secondary and/or endogenic cratering and poorly understood aspects of varying target properties (including regoliths, ejecta blankets, and nearly-zero-g rubble piles), widely varying attributes of impactors, and a host of methodological problems including recognizability of degraded craters, which is affected by illumination angle and by the ''personal equations'' of analysts. Indeed, controlled studies (Robbins et al. 2014) demonstrate crater-density differences of a factor of two or more between experienced crater counters. These inherent difficulties have been especially apparent in divergent results for Vesta from different members of the Dawn Science Team (cf. Russell et al. 2013). Indeed, they have been exacerbated by misuse of a widely available tool (Craterstats: hrscview.fu- berlin.de/craterstats.html), which incorrectly computes error bars for proper interpretation of cumulative SFDs, resulting in derived model ages specified to three significant figures and interpretations of statistically insignificant kinks. They are further exacerbated, and for other small-body crater SFDs analyzed by the Berlin group, by stubbornly adopting

Usability of small impact craters on small surface areas in crater count dating: Analysing examples from the Harmakhis Vallis outflow channel, Mars

Science.gov (United States)

Kukkonen, S.; Kostama, V.-P.

2018-05-01

The availability of very high-resolution images has made it possible to extend crater size-frequency distribution studies to small, deca/hectometer-scale craters. This has enabled the dating of small and young surface units, as well as recent, short-time and small-scale geologic processes that have occurred on the units. Usually, however, the higher the spatial resolution of space images is, the smaller area is covered by the images. Thus the use of single, very high-resolution images in crater count age determination may be debatable if the images do not cover the studied region entirely. Here we compare the crater count results for the floor of the Harmakhis Vallis outflow channel obtained from the images of the ConTeXt camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). The CTX images enable crater counts for entire units on the Harmakhis Vallis main valley, whereas the coverage of the higher-resolution HiRISE images is limited and thus the images can only be used to date small parts of the units. Our case study shows that the crater count data based on small impact craters and small surface areas mainly correspond with the crater count data based on larger craters and more extensive counting areas on the same unit. If differences between the results were founded, they could usually be explained by the regional geology. Usually, these differences appeared when at least one cratering model age is missing from either of the crater datasets. On the other hand, we found only a few cases in which the cratering model ages were completely different. We conclude that the crater counts using small impact craters on small counting areas provide useful information about the geological processes which have modified the surface. However, it is important to remember that all the crater counts results obtained from a specific counting area always primarily represent the results from the counting area-not the whole

The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage

Science.gov (United States)

Kenkmann, T.; Artemieva, N. A.; Wünnemann, K.; Poelchau, M. H.; Elbeshausen, D.; Núñez Del Prado, H.

2009-08-01

The recent Carancas meteorite impact event caused a worldwide sensation. An H4-5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye-witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter-sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100-1000 MJ (0.024- 0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12- 14 kms-1) and shallow entry angles (<20°) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40-60°), and an impact velocity of 350-600 ms-1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of

Nevada Test Site craters used for astronaut training

Science.gov (United States)

Moore, H. J.

1977-01-01

Craters produced by chemical and nuclear explosives at the Nevada Test Site were used to train astronauts before their lunar missions. The craters have characteristics suitable for reconnaissance-type field investigations. The Schooner test produced a crater about 300 m across and excavated more than 72 m of stratigraphic section deposited in a fairly regular fashion so that systematic observations yield systematic results. Other features common on the moon, such as secondary craters and glass-coated rocks, are present at Schooner crater. Smaller explosive tests on Buckboard Mesa excavated rocks from three horizontal alteration zones within basalt flows so that the original sequence of the zones could be determined. One crater illustrated the characteristics of craters formed across vertical boundaries between rock units. Although the exercises at the Nevada Test Site were only a small part of the training of the astronauts, voice transcripts of Apollo missions 14, 16, and 17 show that the exercises contributed to astronaut performance on the moon.

PREVALENCE AND RISK FACTORS ASSOCIATED WITH THE PRRS VIRUS IN SEMEN OF BOARS IN PIG FARMS OF YUCATAN

Directory of Open Access Journals (Sweden)

Aremi Jordan-Craviotto

2009-07-01

Full Text Available The objectives of the present study were to estimate the prevalence of and to determine the risk factors associated with the porcine reproductive and respiratory syndrome virus (PRRSV, American strain in semen of boars in pig herds of Yucatan, Mexico. Ninety two boars from 26 herds were ejaculated once. Semen samples were processed by the RT-nPCR test using the ORF7 primer to detect the PRRS virus. The true prevalence estimated was 10.1% (95% CI = 4.1-16.1%. Significance of risk factors was determined by Fisher-exact test. The odds of detecting genetic material of the PRRSV was greater (OR = 9.2 in semen of boars used under natural mating than those used in artificial insemination. In herds where boar’s acclimatization was not practiced the odds of a positive boar was 4.3. Another risk factor (P < 0.05 was the origin of the animals. In conclusion, the prevalence of the PRRSV in boar semen was smaller to the notified in the literature and determinate in blood serum. Management practices, such as the use of the artificial insemination and acclimatization of the boar, could be useful in reducing the prevalence of the PRRS virus in the pig farms.

Multifocal epithelial hyperplasia in a community in the Mayan area of Mexico.

Science.gov (United States)

González-Losa, Maria R; Suarez-Allén, Rosa E; Canul-Canche, Jaqueline; Conde-Ferráez, Laura; Eljure-Lopez, Nixma

2011-03-01

Multifocal epithelial hyperplasia is a pathology of the oral mucosa which has been reported in diverse ethnic groups. Human papillomavirus (HPV) types 13 and 32 DNA has been detected in these lesions. The aims of this paper are to describe the epidemiological and clinical characteristics of an outbreak in a rural community in the Mayan area of Mexico and to identify a possible route of transmission through saliva. A cross-sectional study was conducted in Chemax (Yucatan, Mexico). Clinical and epidemiological data were obtained through direct interviews. Samples of oral cells and saliva were taken. HPV 13 and 32 were identified by polymerase chain reaction using specific primers. A total of 57 patients were studied, of whom 79.1% were aged jugal mucosa, and more frequently, the tongue. HPV 13 was found in all the patients and HPV 32 in none. A total of 42 saliva samples were positive for HPV 13. Human papillomavirus type 13 is involved in multifocal epithelial hyperplasia among the Mexican Mayan population. The presence of HPV 13 in cells from saliva, combined with poor hygiene behaviors, may explain the familial distribution of the pathology. © 2011 The International Society of Dermatology.

Fresh Impact Crater and Rays in Tharsis

Science.gov (United States)

2002-01-01

The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Extended Mission has included dozens of opportunities to point the spacecraft directly at features of interest so that pictures of things not seen during the earlier Mapping Mission can be obtained. The example shown here is a small meteorite impact crater in northern Tharsis near 17.2oN, 113.8oW. Viking Orbiter images from the late 1970's showed at this location what appeared to be a dark patch with dark rays emanating from a brighter center. The MOC team surmised that the dark rays may be indicating the location of afresh crater formed by impact sometime in the past few centuries (since dark ray are quickly covered by dust falling out of the martian atmosphere). All through MOC's Mapping Mission in 1999 and 2000, attempts were made to image the crater as predictions indicated that the spacecraft would pass over the site, but the crater was never seen. Finally, in June 2001, Extended Mission operations allowed the MOC team to point the spacecraft (and hence the camera, which is fixed to the spacecraft)directly at the center of the dark rays, where we expected to find the crater.The picture on the left (above, A) is a mosaic of three MOC high resolution images and one much lower-resolution Viking image. From left to right, the images used in the mosaic are: Viking 1 516A55, MOC E05-01904, MOCM21-00272, and MOC M08-03697. Image E05-01904 is the one taken in June 2001 by pointing the spacecraft. It captured the impact crater responsible for the rays. A close-up of the crater, which is only 130 meters (427 ft)across, is shown on the right (above, B). This crater is only one-tenth the size of the famous Meteor Crater in northern Arizona.The June 2001 MOC image reveals many surprises about this feature. For one, the crater is not located at the center of the bright area from which the dark rays radiate. The rays point to the center of this bright area, not the crater. Further, the dark material ejected from the

Effect of an axially-symmetric cyclonic vortex on the sea surface temperature in the Gulf of Mexico

Energy Technology Data Exchange (ETDEWEB)

Villanueva, E.E.; Mendoza, V.M.; Adem, J. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)]. E-mail: eevu@atmosfera.unam.mx

2006-04-15

A model for the mixed layer of the Gulf of Mexico has been used to determine the effect that an idealized cyclonic vortex has in the sea surface temperature. The model consists of the equations of conservation of thermal energy and this of balance between mechanical energy and thermal energy, last based on the Kraus-Turner theory; both equations are vertically integrated in the mixed layer. As atmospheric forcing, we prescribe the surface wind associated with an axially-symmetric cyclonic vortex characterized by two parameters: the maximum tangential velocity and the radius at which that velocity is reached. The values of these two parameters, which depend on the position of the vortex, correspond to two cases: hurricane Hilda, which crossed the central part of the Gulf of Mexico between September 29 and October 3, 1964 and hurricane Gilbert whose trajectory between 11 and 17 September, 1988 crossed the Caribbean Sea, the Yucatan Peninsula and the southwest Gulf of Mexico. The results show that a cyclonic vortex with such characteristics, produce during its passage by the sea vertical turbulent water transport through the thermocline (entrainment) that is able to cool down the mixed layer in several degrees and increases the thermocline depth in several meters, in agreement with the observations. [Spanish] Se aplica un modelo de capa de mezcla para el Golfo de Mexico con el objeto de determinar el efecto de un vortice ciclonico idealizado sobre la temperatura de la superficie del mar. El modelo consiste basicamente de dos ecuaciones, la de conservacion de energia termica y la de balance entre energia mecanica y energia termica, esta ultima derivada de la teoria de Kraus-Turner; ambas ecuaciones son verticalmente integradas y acopladas en la capa de mezcla. Como forzamiento atmosferico sobre la superficie del mar se prescribe el viento asociado a un vortice ciclonico axialmente simetrico caracterizado por dos parametros: la velocidad tangencial maxima y el radio al

Determining long-term regional erosion rates using impact craters

Science.gov (United States)

Hergarten, Stefan; Kenkmann, Thomas

2015-04-01

More than 300,000 impact craters have been found on Mars, while the surface of Moon's highlands is even saturated with craters. In contrast, only 184 impact craters have been confirmed on Earth so far with only 125 of them exposed at the surface. The spatial distribution of these impact craters is highly inhomogeneous. Beside the large variation in the age of the crust, consumption of craters by erosion and burial by sediments are the main actors being responsible for the quite small and inhomogeneous crater record. In this study we present a novel approach to infer long-term average erosion rates at regional scales from the terrestrial crater inventory. The basic idea behind this approach is a dynamic equilibrium between the production of new craters and their consumption by erosion. It is assumed that each crater remains detectable until the total erosion after the impact exceeds a characteristic depth depending on the crater's diameter. Combining this model with the terrestrial crater production rate, i.e., the number of craters per unit area and time as a function of their diameter, allows for a prediction of the expected number of craters in a given region as a function of the erosion rate. Using the real crater inventory, this relationship can be inverted to determine the regional long-term erosion rate and its statistical uncertainty. A limitation by the finite age of the crust can also be taken into account. Applying the method to the Colorado Plateau and the Deccan Traps, both being regions with a distinct geological history, yields erosion rates in excellent agreement with those obtained by other, more laborious methods. However, these rates are formally exposed to large statistical uncertainties due to the small number of impact craters. As higher crater densities are related to lower erosion rates, smaller statistical errors can be expected when large regions in old parts of the crust are considered. Very low long-term erosion rates of less than 4

Investigation of Secondary Craters in the Saturnian System

Science.gov (United States)

Hoogenboom, T.; Schenk, P.; White, O. L.

2012-03-01

To derive accurate ages using impact craters, the impact source must be determined. We investigate secondary crater size, frequency, distribution, formation, and crater chain formation on icy satellites throughout the Jupiter and Saturn systems.

Cratering Equations for Zinc Orthotitanate Coated Aluminum

Science.gov (United States)

Hyde, James; Christiansen, Eric; Liou, Jer-Chyi; Ryan, Shannon

2009-01-01

The final STS-125 servicing mission (SM4) to the Hubble Space Telescope (HST) in May of 2009 saw the return of the 2nd Wide Field Planetary Camera (WFPC2) aboard the shuttle Discovery. This hardware had been in service on HST since it was installed during the SM1 mission in December of 1993 yielding one of the longest low Earth orbit exposure times (15.4 years) of any returned space hardware. The WFPC2 is equipped with a 0.8 x 2.2 m radiator for thermal control of the camera electronics (Figure 1). The space facing surface of the 4.1 mm thick aluminum radiator is coated with Z93 zinc orthotitanate thermal control paint with a nominal thickness of 0.1 0.2 mm. Post flight inspections of the radiator panel revealed hundreds of micrometeoroid/orbital debris (MMOD) impact craters ranging in size from less than 300 to nearly 1000 microns in diameter. The Z93 paint exhibited large spall areas around the larger impact sites (Figure 2) and the craters observed in the 6061-T651 aluminum had a different shape than those observed in uncoated aluminum. Typical hypervelocity impact craters in aluminum have raised lips around the impact site. The craters in the HST radiator panel had suppressed crater lips, and in some cases multiple craters were present instead of a single individual crater. Humes and Kinard observed similar behavior after the WFPC1 post flight inspection and assumed the Z93 coating was acting like a bumper in a Whipple shield. Similar paint behavior (spall) was also observed by Bland2 during post flight inspection of the International Space Station (ISS) S-Band Antenna Structural Assembly (SASA) in 2008. The SASA, with similar Z93 coated aluminum, was inspected after nearly 4 years of exposure on the ISS. The multi-crater phenomena could be a function of the density, composition, or impact obliquity angle of the impacting particle. For instance, a micrometeoroid particle consisting of loosely bound grains of material could be responsible for creating the

Pancam Peek into 'Victoria Crater' (Stereo)

Science.gov (United States)

2006-01-01

[figure removed for brevity, see original site] Left-eye view of a stereo pair for PIA08776 [figure removed for brevity, see original site] Right-eye view of a stereo pair for PIA08776 A drive of about 60 meters (about 200 feet) on the 943rd Martian day, or sol, of Opportunity's exploration of Mars' Meridiani Planum region (Sept. 18, 2006) brought the NASA rover to within about 50 meters (about 160 feet) of the rim of 'Victoria Crater.' This crater has been the mission's long-term destination for the past 21 Earth months. Opportunity reached a location from which the cameras on top of the rover's mast could begin to see into the interior of Victoria. This stereo anaglyph was made from frames taken on sol 943 by the panoramic camera (Pancam) to offer a three-dimensional view when seen through red-blue glasses. It shows the upper portion of interior crater walls facing toward Opportunity from up to about 850 meters (half a mile) away. The amount of vertical relief visible at the top of the interior walls from this angle is about 15 meters (about 50 feet). The exposures were taken through a Pancam filter selecting wavelengths centered on 750 nanometers. Victoria Crater is about five times wider than 'Endurance Crater,' which Opportunity spent six months examining in 2004, and about 40 times wider than 'Eagle Crater,' where Opportunity first landed. The great lure of Victoria is the expectation that a thick stack of geological layers will be exposed in the crater walls, potentially several times the thickness that was previously studied at Endurance and therefore, potentially preserving several times the historical record.

A schematic model of crater modification by gravity

Science.gov (United States)

Melosh, H. J.

1982-01-01

The morphology of craters found on planets and moons of the solar system is examined and a development model which can account for the observed crater characteristics is discussed. The prompt collapse of craters to form flat floors, terraced walls, and central peak structures is considered to be the result of an approximate Bingham plastic rheology of the material surrounding the crater. This rheology is induced dynamically by the strong incoherent acoustic 'noise' accompanying excavation of the crater. Central pits, peak rings, and other multiple symmetric-profile rings originate by oscillation of this fluid. Large craters with transient depths comparable to the lithosphere thickness are subject to collapse by fragmentation of the lithosphere as well as fluidization. The considered concepts are developed mathematically. A model emerges which appears capable of explaining most of the qualitative features of large impact structures.

Fine Resolution Termohaline Structure Of The Yuctatan Coastal Sea

Science.gov (United States)

Marino-Tapia, I.; Enriquez-Ortiz, C.; Capurro, L.; Euan-Avila, J.

2007-05-01

In the Yucatan peninsula there are a variety processes that drastically affect the thermohaline structure of the coastal seas. Some of these include hyperhaline lagoons that export salt to the ocean, upwelling events that propagate to the coast, persistent submarine groundwater discharges, and very high evaporation rates caused by the intense solar radiation. On July 2006 a fine resolution oceanographic campaign was performed on the Yucatan coast to study the detailed structure of thermohaline processes and currents from the shore to the 10 m isobath. A total of sixty nine transects that cover the entire northern stretch of the Yucatan coast were made. The transects extend seven kilometers in the offshore direction and have an alongshore spacing of 5 km. The temperature and salinity characteristics of the water column were monitored with a SEABIRD SBE 19 CTD performing profiles every 500 m along each transect. Ocean currents were measures along the same transect using a 1.5 MHz Acoustic Doppler Profiler (Sontek). The results clearly show the effects of coastal lagoons on the adjoining sea, with net salt export associated with hyperhaline lagoons (e.g. Ria Lagartos) or more estuarine influence of lagoons such as Celestun, where groundwater discharges play the role of rivers on the estuary. An assessment of this influence on the coastal ocean will be presented. It is well known the meteor impact at the end of the Cretacic era at Chicxulub, Yucatan, generated a crater with multiple rings which is evident from horizontal gravity gradients of the Yucatan mainland, and that associated with the outer ring there is a high concentration of cenotes (sinkholes) (Pope et al. 1991; Hildebrand, et al. 1995). It has also been shown that groundwater flows along this cenote ring towards the ocean, and the zones where the ring intersects the coast (Celestun and Dzilam Bravo) have impressive geologic features known as `submarine water springs' where freshwater springs as a fountain

Morphometry and Morphology of Fresh Craters on Titan

Science.gov (United States)

Kirk, R. L.; Wood, C. A.; Neish, C.; Lucas, A.; Hayes, A. G.; Cassini Radar Team

2011-12-01

Cassini RADAR imagery obtained on Titan flyby T77 revealed a 40-km diameter fresh impact crater at 11.6° N 44.6° W. This is only the 8th crater identified with high confidence (Wood et al., 2010, Icarus 206, 334), and the 3rd (after Sinlap D=79 km and Ksa D=30 km) for which the depth can be estimated by comparing the foreshortening of the near and far walls. This "autostereo" technique yields an estimated depth of 680 m. The T77 image forms a stereo pair with the T17 discovery image of Ksa from which we estimate the depth of Ksa at 750-800 m, in close agreement with SARTopo data. The depth of Sinlap is 760 m based on SARTopo. Depth-diameter ratios for these craters thus range from 0.01 to 0.025 and the depths are comparable to but 200-400 m shallower than fresh craters of the same size on Ganymede (Bray et al., 2008, Met. Planet Sci. 43, 1979). The depth differences could be explained by initial crater morphometry, by relaxation in a different thermal environment, or (perhaps most plausibly given the bland floors of even the freshest Titan craters) to sedimentary infill. In contrast, the 18x36 km elliptical depression at Sotra Facula is much deeper than Ganymede craters of similar size (d=1500 m from stereo), supporting the conclusion that it is not an impact crater. All three craters exhibit a relatively radar-bright annulus around the outer edge of the floor, possibly as the result of mass wasting of blocky materials from the crater walls. The central part of each crater is darker. The central darker floor of the new crater is symmetrical and featureless, whereas Ksa has a bright central ring 7 km in diameter. Stereo spot heights indicate the ring is 350±100 m above the outer floor. This height is in close agreement with the scaling for Ganymede crater central peaks from Bray et al. (2008). The darker floor area of Sinlap is substantially asymmetrical with a small bright central spot whose elevation is unknown. The new crater has continuous, radar

Crater topography on Titan: Implications for landscape evolution

Science.gov (United States)

Neish, C.; Kirk, R.; Lorenz, R.; Bray, V.; Schenk, P.; Stiles, B.; Turtle, E.; Cassini Radar Team

2012-04-01

Unique among the icy satellites, Titan’s surface shows evidence for extensive modification by fluvial and aeolian erosion, which act to change the topography of its surface over time. Quantifying the extent of this landscape evolution is difficult, since the original, ‘non-eroded’ surface topography is generally unknown. However, fresh craters on icy satellites have a well-known shape and morphology, which has been determined from extensive studies on the airless worlds of the outer solar system (Schenk et al., 2004). By comparing the topography of craters on Titan to similarly sized, pristine analogues on airless bodies, we can obtain one of the few direct measures of the amount of erosion that has occurred on Titan. Cassini RADAR has imaged >30% of the surface of Titan, and more than 60 potential craters have been identified in this data set (Wood et al., 2010; Neish and Lorenz, 2012). Topographic information for these craters can be obtained from a technique known as ‘SARTopo’, which estimates surface heights by comparing the calibration of overlapping synthetic aperture radar (SAR) beams (Stiles et al., 2009). We present topography data for several craters on Titan, and compare the data to similarly sized craters on Ganymede, for which topography has been extracted from stereo-derived digital elevation models (Bray et al., 2012). We find that the depths of craters on Titan are generally within the range of depths observed on Ganymede, but several hundreds of meters shallower than the average (Fig. 1). A statistical comparison between the two data sets suggests that it is extremely unlikely that Titan’s craters were selected from the depth distribution of fresh craters on Ganymede, and that is it much more probable that the relative depths of Titan are uniformly distributed between ‘fresh’ and ‘completely infilled’. This is consistent with an infilling process that varies linearly with time, such as aeolian infilling. Figure 1: Depth of

Detection of lunar floor-fractured craters using machine learning methods

Science.gov (United States)

Thorey, C.

2015-10-01

About 200 Floor Fractured Craters (FFCs) have been identified by Schultz (1976) on the Moon, mainly around the lunar maria. These craters are a class of impact craters that are distinguished by having radi-ally and concentric floor-fractured networks and ab-normally shallow floors. In some cases, the uplift of the crater floor can be as large as 50% of the initial crater depth. These impact craters are interpreted to have undergone endogenous deformations after their formation.

Simple Impact Crater Shapes From Shadows - The Sequel

Science.gov (United States)

Chappelow, J. E.

2008-12-01

At the last LPSC meeting I presented the outline of a method for determining simple impact crater shapes from shadows. In theory the shadow cast within a simple crater provides enough information to derive its cross-sectional shape from shadow measurements, at least to the maximum depth to which the shadow extends. Under certain simple assumptions, this can be done analytically. If the crater is conic-section - shaped, then it can be shown that the down-sun bound of any shadow cast within it is elliptical, with one axis along the direction of illumination and the other (perpendicular to it) of semi-length D/2 (where D is diameter). The properties of this shadow-ellipse can be related to the parameters of the crater shape conic-section, thus measurements of the shadow-ellipse yield not only crater depth and diameter but also the approximate crater shape, in terms of conic sections. The method also does not depend upon the shadow crossing near the crater center, which avoids a pitfall of older shadow measurement methods. The technique is also amenable to computer implementation, which has already been largely completed. Once computerized, crater measurements can be made rapidly and repeatably. The program reads in an image, its resolution, and the solar elevation and azimuth. The user then defines the crater rim by 'clicking' on three points, and the shadow ellipse by clicking on two more. The program calculates and outputs the diameter, the depth, and parameters describing the crater's approximating conic-section. It is highly applicable to situations where only single-image photography is available, for example MESSENGER flybys of Mercury. At the meeting I will present the finished math for this method and give some examples of its use.

A New Species of Ligophorus (Monogenea: Dactylogyridae) from the gills of the Flathead Mullet Mugil cephalus (Teleostei: Mugilidae) from Mexico.

Science.gov (United States)

Rodríguez-González, Abril; Míguez-Lozano, Raúl; Llopis-Belenguer, Cristina; Balbuena, Juan Antonio

2015-12-01

A new monogenean species, Ligophorus yucatanensis n. sp. from the gills of the flathead mullet Mugil cephalus from the Yucatan Peninsula, Mexico, is described. The new species can be differentiated from all other species of Ligophorus by the morphology of the accessory piece of the copulatory organ. Its main lobe is cylindrical, tunnelled expanded distally, slightly bowed with a characteristic membranous opening at level of medial bifurcation of the accessory piece, forming a thick-walled bulbshaped expansion that ends in a round labium. The secondary lobe is spatulate, straight, and shorter than the main lobe. In addition, the new species can be distinguished from other species by the morphology of the haptoral ventral bar, and the distal end of the vaginal duct. Furthermore the ventral anchors are shorter than those of all other species of Ligophorus reported in the Gulf of Mexico and Caribbean Sea. In addition, the zoogeographical records of Ligophorus spp. on the M. cephalus species complex are briefly reviewed and updated.

The Africanization of honeybees (Apis mellifera L.) of the Yucatan: a study of a massive hybridization event across time.

Science.gov (United States)

Clarke, Kylea E; Rinderer, Thomas E; Franck, Pierre; Quezada-Euán, Javier G; Oldroyd, Benjamin P

2002-07-01

Until recently, African and European subspecies of the honeybee (Apis mellifera L.) had been geographically separated for around 10,000 years. However, human-assisted introductions have caused the mixing of large populations of African and European subspecies in South and Central America, permitting an unprecedented opportunity to study a large-scale hybridization event using molecular analyses. We obtained reference populations from Europe, Africa, and South America and used these to provide baseline information for a microsatellite and mitochondrial analysis of the process of Africanization of the bees of the Yucatan Peninsula, Mexico. The genetic structure of the Yucatecan population has changed dramatically over time. The pre-Africanized Yucatecan population (1985) comprised bees that were most similar to samples from southeastern Europe and northern and western Europe. Three years after the arrival of Africanized bees (1989), substantial paternal gene flow had occurred from feral Africanized drones into the resident European population, but maternal gene flow from the invading Africanized population into the local population was negligible. However by 1998, there was a radical shift with both African nuclear alleles (65%) and African-derived mitochondria (61%) dominating the genomes of domestic colonies. We suggest that although European mitochondria may eventually be driven to extinction in the feral population, stable introgression of European nuclear alleles has occurred.

Shallow and deep fresh impact craters in Hesperia Planum, Mars

Science.gov (United States)

Mouginis-Mark, Peter J.; Hayashi, Joan N.

1993-01-01

The depths of 109 impact craters about 2-16 km in diameter, located on the ridged plains materials of Hesperia Planum, Mars, have been measured from their shadow lengths using digital Viking Orbiter images (orbit numbers 417S-419S) and the PICS computer software. On the basis of their pristine morphology (very fresh lobate ejecta blankets, well preserved rim crests, and lack of superposed impact craters), 57 of these craters have been selected for detailed analysis of their spatial distribution and geometry. We find that south of 30 deg S, craters less than 6.0 km in diameter are markedly shallower than similar-sized craters equatorward of this latitude. No comparable relationship is observed for morphologically fresh craters greater than 6.0 km diameter. We also find that two populations exist for older craters less than 6.0 km diameter. When craters that lack ejecta blankets are grouped on the basis of depth/diameter ratio, the deeper craters also typically lie equatorward of 30 S. We interpret the spatial variation in crater depth/diameter ratios as most likely due to a poleward increase in volatiles within the top 400 m of the surface at the times these craters were formed.

Coesite from Wabar crater, near Al Hadida, Arabia

Science.gov (United States)

Chao, E.C.T.; Fahey, J.J.; Littler, J.

1961-01-01

The third natural occurrence of coesite, the high pressure polymorph of silica, is found at the Wabar meteorite crater, Arabia. The Wabar crater is about 300 feet in diameter and about 40 feet deep. It is the smallest of three craters where coesite has been found.

Optimizing laser crater enhanced Raman scattering spectroscopy

Science.gov (United States)

Lednev, V. N.; Sdvizhenskii, P. A.; Grishin, M. Ya.; Fedorov, A. N.; Khokhlova, O. V.; Oshurko, V. B.; Pershin, S. M.

2018-05-01

The laser crater enhanced Raman scattering (LCERS) spectroscopy technique has been systematically studied for chosen sampling strategy and influence of powder material properties on spectra intensity enhancement. The same nanosecond pulsed solid state Nd:YAG laser (532 nm, 10 ns, 0.1-1.5 mJ/pulse) was used for laser crater production and Raman scattering experiments for L-aspartic acid powder. Increased sampling area inside crater cavity is the key factor for Raman signal improvement for the LCERS technique, thus Raman signal enhancement was studied as a function of numerous experimental parameters including lens-to-sample distance, wavelength (532 and 1064 nm) and laser pulse energy utilized for crater production. Combining laser pulses of 1064 and 532 nm wavelengths for crater ablation was shown to be an effective way for additional LCERS signal improvement. Powder material properties (particle size distribution, powder compactness) were demonstrated to affect LCERS measurements with better results achieved for smaller particles and lower compactness.

Preliminary Geochemical and Rock Magnetic Study of a Stalagmite From Quintana Roo, Northeastern Yucatan Peninsula

Science.gov (United States)

Urrutia-Fucugauchi, J.; Perez-Cruz, L.; Zhao, X.; Rebolledo-Vieyra, M.; Rodriguez, A.

2012-04-01

We present the preliminary results of geochemical, stable isotopes and rock magnetic studies of a stalagmite from a cave in eastern Quintana Roo, northern Yucatan peninsula. In the past years, there has been increased interest in understanding the paleoclimatic and paleoenvironmental evolution of the Yucatan peninsula and northern Central America, investigating the relationships between climate variations and the development of the Maya civilization. In particular, the variations in regional precipitation and occurrence of several drought periods, which might have been related to the collapse of the Classic Maya period. Stable isotope data on speleothems from different sites in Yucatan and Central America have provided evidence on changes in precipitation, which have affected the Maya region. The stalagmite is ~47 cm long and about 4-5 cm wide at its base. It was collected from the Hilariós Well cave in Tulum, Quintana Roo. Magnetic susceptibility and geochemical analyses have been completed as part of the initial characterization of the stalagmite, with measurements taken every centimeter. Geochemical analyses have been carried out for x-ray fluorescence, with a Niton XRF analyzer. Magnetic susceptibility was determined with a Bartington MS2 instrument using the high resolution surface probe. Additional rock magnetic analyses include magnetic hysteresis loops and isothermal remanent magnetization (IRM) acquisition, and saturation IRM demagnetization, which have been measured with a MicroMag instrument. Hysteresis loops are diamagnetic, with small varying low-coercivity ferromagnetic components. The elemental compositions of major oxides and trace elements vary with depth. Calcium is the major element and displays a pattern of small amplitude fluctuations with a trend to lower values at the bottom, which are also shown in other elements such as barium. Silica and elements such as titanium and strontium are positively correlated and show an apparent cyclic pattern

Hailar crater - A possible impact structure in Inner Mongolia, China

Science.gov (United States)

Xiao, Zhiyong; Chen, Zhaoxu; Pu, Jiang; Xiao, Xiao; Wang, Yichen; Huang, Jun

2018-04-01

Hailar crater, a probable impact structure, is a circular depression about 300 m diameter in Inner Mongolia, northeast China. With broad elevated rims, the present rim-to-floor depth is 8-20 m. Regional geological background and geomorphological comparison suggest that this feature is likely not formed by surface processes such as salt diapir, karst, aeolian, glacial, or volcanic activity. Its unique occurrence in this region and well-preserved morphology are most consistent with it being a Cenozoic impact crater. Two field expeditions in 2016 and 2017 investigated the origin of this structure, recognizing that (1) no additional craters were identified around Hailar crater in the centimeter-scale digital topography models that were constructed using a drone imaging system and stereo photogrammetry; (2) no bedrock exposures are visible within or adjacent to the crater because of thick regolith coverage, and only small pieces of angular unconsolidated rocks are present on the crater wall and the gently-sloped crater rim, suggesting recent energetic formation of the crater; (3) most samples collected from the crater have identical lithology and petrographic characteristics with the background terrain, but some crater samples contain more abundant clasts and silicate hydrothermal veins, indicating that rocks from depths have been exposed by the crater; (4) no shock metamorphic features were found in the samples after thin section examinations; and (5) a systematic sample survey and iron detector scan within and outside of the crater found no iron-rich meteorites larger than 2 cm in size in a depth of 30 cm. Although no conclusive evidence for an impact origin is found yet, Hailar crater was most likely formed by an impact based on its unique occurrence and comparative geomorphologic study. We suggest that drilling in the crater center is required to verify the impact origin, where hypothesized melt-bearing impactites may be encountered.

3D structure of the Gusev Crater region

NARCIS (Netherlands)

van Kan - Parker, M.; Zegers, T.E.; kneissl, T.; Ivanov, B.; Neukum, G.; Foing, B.

2010-01-01

Gusev Crater lies within the Aeolis Quadrangle of Mars at the boundary between the northern lowlands and southern highlands. The ancient valley Ma'adim Vallis dissects the highlands south of Gusev Crater and is thought to have fed the crater with sediments.High Resolution Stereo Camera data and

Crater ejecta scaling laws: fundamental forms based on dimensional analysis

International Nuclear Information System (INIS)

Housen, K.R.; Schmidt, R.M.; Holsapple, K.A.

1983-01-01

A model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events. General relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events. Specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation: the so-called gravity and strength regimes. In the gravity regime, ejectra velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity. This relation implies geometric similarity of ejecta blankets. That is, the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii. In the strength regime, ejecta velocities are independent of crater size. Consequently, ejecta blankets are not geometrically similar in this regime. For points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws. The exponents in these power laws are functions of an exponent, α, that appears in crater radius scaling relations. Thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta. Predicted ejection velocities and ejecta-blanket profiles, based on measured values of α, are compared to existing measurements of velocities and debris profiles

Crater Topography on Titan: Implications for Landscape Evolution

Science.gov (United States)

Neish, Catherine D.; Kirk, R.L.; Lorenz, R. D.; Bray, V. J.; Schenk, P.; Stiles, B. W.; Turtle, E.; Mitchell, K.; Hayes, A.

2013-01-01

We present a comprehensive review of available crater topography measurements for Saturn's moon Titan. In general, the depths of Titan's craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede's average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 +/- 0.0003 (for the largest crater studied, Menrva, D approximately 425 km) and 0.017 +/- 0.004 (for the smallest crater studied, Ksa, D approximately 39 km). When we evaluate the Anderson-Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan's craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close 'airless' analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan's surface, the only body in the outer Solar System with extensive surface-atmosphere exchange.

High Resolution Digital Elevation Models of Pristine Explosion Craters

Science.gov (United States)

Farr, T. G.; Krabill, W.; Garvin, J. B.

2004-01-01

In order to effectively capture a realistic terrain applicable to studies of cratering processes and landing hazards on Mars, we have obtained high resolution digital elevation models of several pristine explosion craters at the Nevada Test Site. We used the Airborne Terrain Mapper (ATM), operated by NASA's Wallops Flight Facility to obtain DEMs with 1 m spacing and 10 cm vertical errors of 4 main craters and many other craters and collapse pits. The main craters that were mapped are Sedan, Scooter, Schooner, and Danny Boy. The 370 m diameter Sedan crater, located on Yucca Flat, is the largest and freshest explosion crater on Earth that was formed under conditions similar to hypervelocity impact cratering. As such, it is effectively pristine, having been formed in 1962 as a result of a controlled detonation of a 100 kiloton thermonuclear device, buried at the appropriate equivalent depth of burst required to make a simple crater. Sedan was formed in alluvium of mixed lithology and subsequently studied using a variety of field-based methods. Nearby secondary craters were also formed at the time and were also mapped by ATM. Adjacent to Sedan and also in alluvium is Scooter, about 90 m in diameter and formed by a high-explosive event. Schooner (240 m) and Danny Boy (80 m) craters were also important targets for ATM as they were excavated in hard basalt and therefore have much rougher ejecta. This will allow study of ejecta patterns in hard rock as well as engineering tests of crater and rock avoidance and rover trafficability. In addition to the high resolution DEMs, crater geometric characteristics, RMS roughness maps, and other higher-order derived data products will be generated using these data. These will provide constraints for models of landing hazards on Mars and for rover trafficability. Other planned studies will include ejecta size-frequency distribution at the resolution of the DEM and at finer resolution through air photography and field measurements

Geologic map of Tooting crater, Amazonis Planitia region of Mars

Science.gov (United States)

Mouginis-Mark, Peter J.

2015-01-01

Tooting crater has a diameter of 27.2 km, and formed on virtually flat lava flows within Amazonis Planitia ~1,300 km west of the summit of Olympus Mons volcano, where there appear to have been no other major topographic features prior to the impact. The crater formed in an area ~185 x 135 km that is at an elevation between −3,870 m and −3,874 m relative to the Mars Orbiter Laser Altimeter (MOLA) Mars datum. This fortuitous situation (for example, a bland, horizontal target) allows the geometry of the crater and the thickness of the ejecta blanket to be accurately determined by subtracting the appropriate elevation of the surrounding landscape (−3,872 m) from the individual MOLA measurements across the crater. Thus, for the first time, it is possible to determine the radial decrease of ejecta thickness as a function of distance away from the rim crest. On the basis of the four discrete ejecta layers surrounding the crater cavity, Tooting crater is classified as a Multiple-Layered Ejecta (MLE) crater. By virtue of the asymmetric distribution of secondary craters and the greater thickness of ejecta to the northeast, Morris and others (2010) proposed that Tooting crater formed by an oblique impact from the southwest. The maximum range of blocks that produced identifiable secondary craters is ~500 km (~36.0 crater radii) from the northeast rim crest. In contrast, secondary craters are only identifiable ~215 km (15.8 radii) to the southeast and 225 km (16.5 radii) to the west.

Genetic diversity and structure in semiwild and domesticated chiles (Capsicum annuum; Solanaceae) from Mexico.

Science.gov (United States)

Aguilar-Meléndez, Araceli; Morrell, Peter L; Roose, Mikeal L; Kim, Seung-Chul

2009-06-01

The chile of Mesoamerica, Capsicum annuum, is one of five domesticated chiles in the Americas. Among the chiles, it varies the most in size, form, and color of its fruits. Together with maize, C. annuum is one of the principal elements of the neotropical diets of Mesoamerican civilizations. Despite the great economic and cultural importance of C. annuum both worldwide and in Mexico, however, very little is known about its geographic origin and number of domestications. Here we sampled a total of 80 accessions from Mexico (58 semiwild and 22 domesticated) and examined nucleotide sequence diversity at three single- or low-copy nuclear loci, Dhn, G3pdh, and Waxy. Across the three loci, we found an average reduction of ca. 10% in the diversity of domesticates relative to semiwild chiles and geographic structure within Mexican populations. The Yucatan Peninsula contained a large number of haplotypes, many of which were unique, suggesting an important region of chile domestication and center of diversity. The present sampling of loci did not conclusively resolve the number and location of domestications, but several lines of evidence suggest multiple independent domestications from widely distributed progenitor populations.

Optimizing laser crater enhanced Raman spectroscopy.

Science.gov (United States)

Lednev, V N; Sdvizhenskii, P A; Grishin, M Ya; Filichkina, V A; Shchegolikhin, A N; Pershin, S M

2018-03-20

Raman signal enhancement by laser crater production was systematically studied for 785 nm continuous wave laser pumping. Laser craters were produced in L-aspartic acid powder by a nanosecond pulsed solid state neodymium-doped yttrium aluminum garnet laser (532 nm, 8 ns, 1 mJ/pulse), while Raman spectra were then acquired by using a commercial spectrometer with 785 nm laser beam pumping. The Raman signal enhancement effect was studied in terms of the number of ablating pulses used, the lens-to-sample distance, and the crater-center-laser-spot offset. The influence of the experiment parameters on Raman signal enhancement was studied for different powder materials. Maximum Raman signal enhancement reached 11 fold for loose powders but decreased twice for pressed tablets. Raman signal enhancement was demonstrated for several diverse powder materials like gypsum or ammonium nitrate with better results achieved for the samples tending to give narrow and deep craters upon the laser ablation stage. Alternative ways of cavity production (steel needle tapping and hole drilling) were compared with the laser cratering technique in terms of Raman signal enhancement. Drilling was found to give the poorest enhancement of the Raman signal, while both laser ablation and steel needle tapping provided comparable results. Here, we have demonstrated for the first time, to the best of our knowledge, that a Raman signal can be enhanced 10 fold with the aid of simple cavity production by steel needle tapping in rough highly reflective materials. Though laser crater enhancement Raman spectroscopy requires an additional pulsed laser, this technique is more appropriate for automatization compared to the needle tapping approach.

Tidal currents in the Yucatan Channel

Energy Technology Data Exchange (ETDEWEB)

Carrillo Gonzalez, Fatima [Centro Universitario de la Costa, Universidad de Guadalajara, Guadalajara, Jalisco (Mexico); Ochoa, Jose; Candela, Julio; Badan, Antonio; Sheinbaum; Gonzalez Navarro, Juan Ignacio [Departamento de Oceanografia Fisica, Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Ensenada, Baja California (Mexico)

2007-07-15

Currents data from a ten-month period at 197 measuring points covering all Yucatan Channel were processed by harmonic analysis to estimate tidal parameters for the O{sub 1}, K{sub 1}, M{sub 2} and S{sub 2} components. The highly detailed coverage confirms the known dominance for the O{sub 1} and K{sub 1} diurnal components, but also showed, for the first time, their intensification in the deep eastern margin of the channel where maximum amplitudes in main axis are 17 and 19 cm.s{sup -}1. The data also confirms weak semi-diurnal components, of which the most intense, M{sub 2} and S{sub 2}, have amplitudes only up to 2 cm.s{sup -}1. The tidal ellipses were elongated (i.e. with eccentricities close to one) in the NNW direction. The O{sub 1}, K{sub 1}, M{sub 2} and S{sub 2} contributions in transport variability through the channel have amplitudes of 11.7, 12.5, 1.2 and 1.0 Sv, all well determined above noise. [Spanish] Se presentan, a detalle sin precedente, las caracteristicas de las corrientes de marea O{sub 1}, K{sub 1}, M{sub 2} y S{sub 2} en el canal de Yucatan. Mapas de los parametros que definen las elipses, como son las amplitudes en los ejes principales, la orientacion, la fase y la razon-senal-ruido se obtienen, por el clasico analisis armonico en mediciones de 10 meses en duracion, en 197 puntos que cubren ampliamente un plano vertical del canal. En acuerdo con reportes anteriores, las senales diurnas O{sub 1} y K{sub 1} dominan, demostrandose aqui que sus amplitudes alcanzan, en la parte profunda y Este, 17 y 19 cm.s{sup -}1. El analisis tambien revela senales semidiurnas M{sub 2} y S{sub 2} muy debiles con amplitudes maximas de 2 y 1cm.s{sup -}1. Las elipses son muy alargadas (i.e. con excentricidad cercana a uno) y orientadas al nornoroeste. Los valores de la razon senal a ruido indican que los parametros de las dos constituyentes diurnas se encuentran bien determinados, mientras que las semidiurnas quedan muy contaminadas por el ruido. El rasgo mas

100 New Impact Crater Sites Found on Mars

Science.gov (United States)

Kennedy, M. R.; Malin, M. C.

2009-12-01

Recent observations constrain the formation of 100 new impact sites on Mars over the past decade; 19 of these were found using the Mars Global Surveyor Mars Orbiter Camera (MOC), and the other 81 have been identified since 2006 using the Mars Reconnaissance Orbiter Context Camera (CTX). Every 6 meter/pixel CTX image is examined upon receipt and, where they overlap images of 0.3-240 m/pixel scale acquired by the same or other Mars-orbiting spacecraft, we look for features that may have changed. New impact sites are initially identified by the presence of a new dark spot or cluster of dark spots in a CTX image. Such spots may be new impact craters, or result from the effect of impact blasts on the dusty surface. In some (generally rare) cases, the crater is sufficiently large to be resolved in the CTX image. In most cases, however, the crater(s) cannot be seen. These are tentatively designated as “candidate” new impact sites, and the CTX team then creates an opportunity for the MRO spacecraft to point its cameras off-nadir and requests that the High Resolution Imaging Science Experiment (HiRISE) team obtain an image of ~0.3 m/pixel to confirm whether a crater or crater cluster is present. It is clear even from cursory examination that the CTX observations are areographically biased to dusty, higher albedo areas on Mars. All but 3 of the 100 new impact sites occur on surfaces with Lambert albedo values in excess of 23.5%. Our initial study of MOC images greatly benefited from the initial global observations made in one month in 1999, creating a baseline date from which we could start counting new craters. The global coverage by MRO Mars Color Imager is more than a factor of 4 poorer in resolution than the MOC Wide Angle camera and does not offer the opportunity for global analysis. Instead, we must rely on partial global coverage and global coverage that has taken years to accumulate; thus we can only treat impact rates statistically. We subdivide the total data

Geological Mapping of Impact Melt Deposits at Lunar Complex Craters: New Insights into Morphological Diversity, Distribution and the Cratering Process

Science.gov (United States)

Dhingra, D.; Head, J. W., III; Pieters, C. M.

2014-12-01

We have completed high resolution geological mapping of impact melt deposits at the young lunar complex craters (wall and rim impact melt units and their relation to floor units have also been mapped. Among the distinctive features of these impact melt deposits are: 1) Impact Melt Wave Fronts: These are extensive (sometimes several kilometers in length) and we have documented their occurrence and distribution in different parts of the crater floor at Jackson and Tycho. These features emphasize melt mobility and style of emplacement during the modification stage of the craters. 2) Variations in Floor Elevations: Spatially extensive and coherent sections of crater floors have different elevations at all the three craters. The observed elevation differences could be caused by subsidence due to cooling of melt and/or structural failure, together with a contribution from regional slope. 3) Melt-Covered Megablocks: We also observe large blocks/rock-fragments (megablocks) covered in impact melt, which could be sections of collapsed wall or in some cases, subdued sections of central peaks. 4) Melt-Covered Central Peaks: Impact melt has also been mapped on the central peaks but varies in spatial extent among the craters. The presence of melt on peaks must be taken into account when interpreting peak mineralogy as exposures of deeper crust. 5) Boulder Distribution: Interesting trends are observed in the distribution of boulder units of various sizes; some impact melt units have spatially extensive boulders, while boulder distribution is very scarce in other units on the floor. We interpret these distributions to be influenced by a) the differential collapse of the crater walls during the modification stage, and b) the amount of relative melt volume retained in different parts of the crater floor. These observations provide important documentation of the morphological diversity and better understanding of the emplacement and final distribution of impact melt deposits.

Genetic Resources in the “Calabaza Pipiana” Squash (Cucurbita argyrosperma) in Mexico: Genetic Diversity, Genetic Differentiation and Distribution Models

Science.gov (United States)

Sánchez-de la Vega, Guillermo; Castellanos-Morales, Gabriela; Gámez, Niza; Hernández-Rosales, Helena S.; Vázquez-Lobo, Alejandra; Aguirre-Planter, Erika; Jaramillo-Correa, Juan P.; Montes-Hernández, Salvador; Lira-Saade, Rafael; Eguiarte, Luis E.

2018-01-01

Analyses of genetic variation allow understanding the origin, diversification and genetic resources of cultivated plants. Domesticated taxa and their wild relatives are ideal systems for studying genetic processes of plant domestication and their joint is important to evaluate the distribution of their genetic resources. Such is the case of the domesticated subspecies C. argyrosperma ssp. argyrosperma, known in Mexico as calabaza pipiana, and its wild relative C. argyrosperma ssp. sororia. The main aim of this study was to use molecular data (microsatellites) to assess the levels of genetic variation and genetic differentiation within and among populations of domesticated argyrosperma across its distribution in Mexico in comparison to its wild relative, sororia, and to identify environmental suitability in previously proposed centers of domestication. We analyzed nine unlinked nuclear microsatellite loci to assess levels of diversity and distribution of genetic variation within and among populations in 440 individuals from 19 populations of cultivated landraces of argyrosperma and from six wild populations of sororia, in order to conduct a first systematic analysis of their genetic resources. We also used species distribution models (SDMs) for sororia to identify changes in this wild subspecies’ distribution from the Holocene (∼6,000 years ago) to the present, and to assess the presence of suitable environmental conditions in previously proposed domestication sites. Genetic variation was similar among subspecies (HE = 0.428 in sororia, and HE = 0.410 in argyrosperma). Nine argyrosperma populations showed significant levels of inbreeding. Both subspecies are well differentiated, and genetic differentiation (FST) among populations within each subspecies ranged from 0.152 to 0.652. Within argyrosperma we found three genetic groups (Northern Mexico, Yucatan Peninsula, including Michoacan and Veracruz, and Pacific coast plus Durango). We detected low levels of gene

Genetic Resources in the “Calabaza Pipiana” Squash (Cucurbita argyrosperma in Mexico: Genetic Diversity, Genetic Differentiation and Distribution Models

Directory of Open Access Journals (Sweden)

Guillermo Sánchez-de la Vega

2018-03-01

Full Text Available Analyses of genetic variation allow understanding the origin, diversification and genetic resources of cultivated plants. Domesticated taxa and their wild relatives are ideal systems for studying genetic processes of plant domestication and their joint is important to evaluate the distribution of their genetic resources. Such is the case of the domesticated subspecies C. argyrosperma ssp. argyrosperma, known in Mexico as calabaza pipiana, and its wild relative C. argyrosperma ssp. sororia. The main aim of this study was to use molecular data (microsatellites to assess the levels of genetic variation and genetic differentiation within and among populations of domesticated argyrosperma across its distribution in Mexico in comparison to its wild relative, sororia, and to identify environmental suitability in previously proposed centers of domestication. We analyzed nine unlinked nuclear microsatellite loci to assess levels of diversity and distribution of genetic variation within and among populations in 440 individuals from 19 populations of cultivated landraces of argyrosperma and from six wild populations of sororia, in order to conduct a first systematic analysis of their genetic resources. We also used species distribution models (SDMs for sororia to identify changes in this wild subspecies’ distribution from the Holocene (∼6,000 years ago to the present, and to assess the presence of suitable environmental conditions in previously proposed domestication sites. Genetic variation was similar among subspecies (HE = 0.428 in sororia, and HE = 0.410 in argyrosperma. Nine argyrosperma populations showed significant levels of inbreeding. Both subspecies are well differentiated, and genetic differentiation (FST among populations within each subspecies ranged from 0.152 to 0.652. Within argyrosperma we found three genetic groups (Northern Mexico, Yucatan Peninsula, including Michoacan and Veracruz, and Pacific coast plus Durango. We detected low

Dynamics of crater formations in immersed granular materials

Science.gov (United States)

Varas, G.; Vidal, V.; Géminard, J.

2009-12-01

Craters are part of the widespread phenomena observed in nature. Among the main applications to natural phenomena, aside from meteorite impact craters, are the formation and growth of volcanic edifices, by successive ejecta emplacement and/or erosion. The time evolution and dynamics play a crucial role here, as the competition between volcanic-jet mass-flux (degassing and ejecta) and crater-size evolution may control directly the eruptive regime. Crater morphology in dry granular material has been extensively studied, both experimentally and theoretically. Most of these studies investigate the final, steady crater shape resulting from the collision of solid bodies with the material surface and scaling laws are derived. In immersed granular material, craters generated by an underwater vortex ring, or underwater impact craters generated by landslide, have been reported. In a previous experimental study, Gostiaux et al. [Gran. Matt., 2002] have investigated the dynamics of air flowing through an immersed granular layer. They reported that, depending on the flow rate, the system exhibits two qualitatively different regimes: At small flow rate, the bubbling regime during which bubbles escape the granular layer independently one from another; At large flow rate, the open-channel regime which corresponds to the formation of a channel crossing the whole thickness of the granular bed through which air escapes almost continuously. At intermediate flow rate, a spontaneous alternation between these two regimes is observed. Here, we report the dynamics of crater formations at the free surface of an immersed granular bed, locally crossed by an ascending gas flow. We reproduce the experimental conditions of Gostiaux et al. (2002) in two dimensions: In a vertical Hele-Shaw cell, the crater consists of two sand piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas

Shatter Complex Formation in the Twin Craters Lava Flow, Zuni-Bandera Field, New Mexico

Science.gov (United States)

von Meerscheidt, H. C.; Bleacher, J. E.; Brand, B. D.; deWet, A.; Samuels, R.; Hamilton, C.; Garry, W. B.; Bandfield, J. L.

2013-12-01

Lava channels, tubes and sheets are transport structures that deliver flowing lava to a flow front. The type of structure can vary within a flow field and evolve throughout an eruption. The 18.0 × 1.0 ka Twin Craters lava flow in the Zuni-Bandera lava field provides a unique opportunity to study morphological changes of a lava flow partly attributable to interaction with a topographic obstacle. Facies mapping and airborne image analysis were performed on an area of the Twin Craters flow that includes a network of channels, lava tubes, shatter features, and disrupted pahoehoe flows surrounding a 45 m tall limestone bluff. The bluff is 1000 m long (oriented perpendicular to flow.) The general flow characteristics upstream from the bluff include smooth, lobate pahoehoe flows and a >2.5 km long lava tube (see Samuels et al., this meeting.) Emplacement characteristics change abruptly where the flow encountered the bluff, to include many localized areas of disrupted pahoehoe and several pahoehoe-floored depressions. Each depression is fully or partly surrounded by a raised rim of blocky material up to 4 m higher than the surrounding terrain. The rim is composed of 0.05 - 4 m diameter blocks, some of which form a breccia that is welded by lava, and some of which exhibit original flow textures. The rim-depression features are interpreted as shatter rings based on morphological similarity to those described by Orr (2011.Bul Volcanol.73.335-346) in Hawai';i. Orr suggests that shatter rings develop when fluctuations in the lava supply rate over-pressurize the tube, causing the tube roof to repeatedly uplift and subside. A rim of shattered blocks and breccias remains surrounding the sunken tube roof after the final lava withdraws from the system. One of these depressions in the Twin Craters flow is 240 m wide and includes six mounds of shattered material equal in height to the surrounding undisturbed terrain. Several mounds have depressed centers floored with rubbly pahoehoe

Surface age of venus: use of the terrestrial cratering record

International Nuclear Information System (INIS)

Schaber, G.G.; Shoemaker, E.M.; Kozak, R.C.

1987-01-01

The average crater age of Venus' northern hemisphere may be less than 250 m.y. assuming equivalence between the recent terrestrial cratering rate and that on Venus for craters ≥ 20 km in diameter. For craters larger than this threshold size, below which crater production is significantly affected by the Venusian atmosphere, there are fairly strong observational grounds for concluding that such an equivalence in cratering rates on Venus and Earth may exist. However, given the uncertainties in the role of both active and inactive comet nuclei in the cratering history of Earth, we conclude that the age of the observed surface in the northern hemisphere of Venus could be as great as the 450-m.y. mean age of the Earth's crust. The observed surface of Venus might be even older, but no evidence from the crater observations supports an age as great as 1 b.y. If the age of the observed Venusian surface were 1 b.y., it probably should bear the impact scars of a half dozen or more large comet nuclei that penetrated the atmosphere and formed craters well over 100 km in diameter. Venera 15/16 mapped only about 25% of Venus; the remaining 75% may tell us a completely different story

Impact spacecraft imagery and comparative morphology of craters

International Nuclear Information System (INIS)

Moutsoulas, M.; Piteri, S.

1979-01-01

The use of hard-landing 'simple' missions for wide-scale planetary exploration is considered. As an example of their imagery potentialities, Ranger VII data are used for the study of the morphological characteristics of 16 Mare Cognitum craters. The morphological patterns of lunar craters, expressed in terms of the Depth/Diameter ratios appear to be in most cases independent of the crater location or size. (Auth.)

Geomorphology of crater and basin deposits - Emplacement of the Fra Mauro formation

Science.gov (United States)

Morrison, R. H.; Oberbeck, V. R.

1975-01-01

Characteristics of continuous deposits near lunar craters larger than about 1 km wide are considered, and it is concluded that (1) concentric dunes, radial ridges, and braided lineations result from deposition of the collision products of ejecta from adjacent pairs of similarly oriented secondary-crater chains and are, therefore, concentrations of secondary-crater ejecta; (2) intracrater ridges are produced within preexisting craters surrounding a fresh primary crater by ricocheting and focusing of secondary-crater ejecta from the preexisting craters' walls; and (3) secondary cratering has produced many of the structures of the continuous deposits of relatively small lunar craters and is the dominant process for emplacement of most of the radial facies of the continuous deposits of large lunar craters and basins. The percentages of Imbrium ejecta in deposits and the nature of Imbrium sculpturing are investigated.

A concept of row crater enhancement

International Nuclear Information System (INIS)

Redpath, B.B.

1970-01-01

Linear craters formed by the simultaneous detonation of a row of buried explosives will probably have a wider application than single charges in the explosive excavation of engineering structures. Most cratering experience to date has been with single charges, and an analytical procedure for the design of a row of charges to excavate a crater with a specified configuration has been lacking. There are no digital computer codes having direct application to a row of charges as there are for single charges. This paper derives a simple relationship which can be used to design row charges with some assurance of achieving the desired result and with considerable flexibility in the choice of explosive yield of the individual charges

The Annual Meeting of the American Society of Tropical Medicine and Hygiene (38th) Held in Honolulu, Hawaii on 10-14 December 1989

Science.gov (United States)

1991-01-01

FOR IgG ANTIBODIES TO LEISHMANIA MEXICANA MEXICANA. M.R. Garcia*, F. Andrade, R. Esquivel, E. Simmonds, S. Canto, and A.L. Cruz. University of Yucatan ...Baltimore, MD; Universidad Peruana Cayetano Heredia; and Instituto de Investigacin Nutricional .?? 4:15 437 CHICKENPOX IN THE U.S. ARMY: A DEVELOPING... Yucatan (Mexico) Tropical Diseases Research Unit. Reference Center for Leishmaniasis Control. A total of 223 sera from human beings were processed by

Cutting Craters

Science.gov (United States)

2003-01-01

[figure removed for brevity, see original site] Released 12 November 2003The rims of two old and degraded impact craters are intersected by a graben in this THEMIS image taken near Mangala Fossa. Yardangs and low-albedo wind streaks are observed at the top of the image as well as interesting small grooves on the crater floor. The origin of these enigmatic grooves may be the result of mud or lava and volatile interactions. Variable surface textures observed in the bottom crater floor are the result of different aged lava flows.Image information: VIS instrument. Latitude -15.2, Longitude 219.2 East (140.8 West). 19 meter/pixel resolution.Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Regional reduction in paleogroundwater discharge and rainfall in the Late Holocene Yucatan Peninsula reconstructed from trace metals in benthic foraminifera

Science.gov (United States)

Broach, K. H.; Chapman, B. L.; Paytan, A.; Street, J.

2017-12-01

As climate change progresses, droughts are predicted to become more common in regions dominated by seasonal precipitation, a problem compounded where precipitation provides significant freshwater resources. The Yucatan Peninsula relies on rain-recharged groundwater for potable water, and regional development due to tourism will further strain supply. Historical and geochemical evidence suggest extensive droughts harmed Mayan Civilization and may again impact the Yucatan in the near future, but proxies around the Yucatan and Caribbean region are complicated by variability and even opposing interpretations. An integrated rainfall signal is needed to smooth variability and separate local aberrations from long-term regional trends that can be used for risk assessment. Here we present a 5,000 year record of rainfall sourced from a broad swath of the peninsula and recorded as trace metal ratios in the foram Ammonia parkinsoniana. Rainwater percolation across the western peninsula forms a groundwater lens that discharges as brackish springs in our field site Celestun Lagoon resulting in trace metal gradients (Li, B, Sr, Ba, Nd) along the lagoon that oscillate with discharge. Sr/Ca and Ba/Ca ratios in the forams suggest a long-term decrease in spring water discharge for the western Yucatan during the last 2,500 years with notable drops coinciding with known droughts (e.g. 800-950 CE) and more variability on a regional scale to 5,000 years. B/Ca ratios appear to depend on proximity to springs and may respond to low-pH discharge water while Nd/Ca ratios suggest sporadic incursions of seawater into the lagoon, possibly related to severely reduced spring water discharge or large hurricane events. We interpret these results to mean that periods of decreased rainfall broadly affect the western peninsula which may pose problems for large population centers like Merida. Future work will focus on periodicity of such rainfall changes and impact on the ecological environment of

Crater populations in the early history of Mercury

International Nuclear Information System (INIS)

Guest, J.E.; Gault, D.E.

1976-01-01

Crater populations on two major geologic units of Mercury have been classified into three morphologic types which characterize their state of degradation. The results indicate that one or more processes either prior to or contemporary with the formation of the 1300 km diameter Caloris Planitia reduced the population of fresh craters smaller than 70--80 km diameter and totally erased the population of fresh craters smaller than 20--30 km

Cratering on Small Bodies: Lessons from Eros

Science.gov (United States)

Chapman, C. R.

2003-01-01

Cratering and regolith processes on small bodies happen continuously as interplanetary debris rains down on asteroids, comets, and planetary satellites. Butthey are very poorly observed and not well understood. On the one hand, we have laboratory experimentation at small scales and we have examination of large impact craters (e.g. Meteor Crater on Earth and imaging of abundant craters on terrestrial planets and outer planet moons). Understanding cratering on bodies of intermediate scales, tens of meters to hundreds of km in size, involves either extrapolation from our understanding of cratering phenomena at very different scales or reliance on very preliminary, incomplete examination of the observational data we now have for a few small bodies. I review the latter information here. It has been generally understood that the role of gravity is greatly diminished for smaller bodies, so a lot of cratering phenomena studied for larger bodies is less applicable. But it would be a mistake to imagine that laboratory experiments on gravitationless rocks (usually at 1 g) are directly applicable, except perhaps to those monolithic Near Earth Asteroids (NEAs) some tens of meters in size that spin very rapidly and can be assumed to be "large bare rocks" with "negative gravity". Whereas it had once been assumed that asteroids smaller than some tens of km diameter would retain little regolith, it is increasingly apparent that regolith and megoregolith processes extend down to bodies only hundreds of meters in size, perhaps smaller. Yet these processes are very different from those that pertain to the Moon, which is our chief prototype of regolith processes. The NEAR Shoemaker spacecraft's studies of Eros provide the best evidence to date about small-body cratering processes, as well as a warning that our theoretical understanding requires anchoring by direct observations. Eros: "Ponds", Paucity of Small Craters, and Other Mysteries. Although Eros is currently largely detached

New records of ectoparasitic Acari (Arachnida) and Streblidae (Diptera) from bats in Jalisco, Mexico.

Science.gov (United States)

Martínez, Maria M Ramírez; Lopez, M Pilar Ibarra; Iñiguez-Dávalos, Luis Ignacio; Yuill, Thomas; Orlova, Maria V; Reeves, Will K

2016-12-01

Ectoparasites of bats in the Neotropics are diverse and play numerous ecological roles as vectors of microbial pathogens and endoparasites and as food sources for other cave fauna living both on their hosts and in bat roosts. The ectoparasites of bats in Jalisco State of western Mexico have not been as well described as those of other states with recent checklists that have focused primarily on the Yucatan Peninsula. We captured bats from 2011-2015 on the south coast and Sierra de Amula, Jalisco using mist nets, and we removed ectoparasites by hand. We identified 24 species of streblid bat flies and six ectoparasitic mites from bats caught in mist nets. There were an additional eight possibly undescribed species of Streblidae. Our collections extend the known range of species into Jalisco. © 2016 The Society for Vector Ecology.

The impact of biogenic carbon emissions on aerosol absorption inMexico City

Energy Technology Data Exchange (ETDEWEB)

Marley, N; Gaffney, J; Tackett, M J; Sturchio, N; Hearty, L; Martinez, N; Hardy, K D; Machany-Rivera, A; Guilderson, T P; MacMillan, A; Steelman, K

2009-02-24

In order to determine the wavelength dependence of atmospheric aerosol absorption in the Mexico City area, the absorption angstrom exponents (AAEs) were calculated from aerosol absorption measurements at seven wavelengths obtained with a seven-channel aethalometer during two field campaigns, the Mexico City Metropolitan Area study in April 2003 (MCMA 2003) and the Megacity Initiative: Local and Global Research Observations in March 2006 (MILAGRO). The AAEs varied from 0.76 to 1.56 in 2003 and from 0.54 to 1.52 in 2006. The AAE values determined in the afternoon were consistently higher than the corresponding morning values, suggesting the photochemical formation of absorbing secondary organic aerosols (SOA) in the afternoon. The AAE values were compared to stable and radiocarbon isotopic measurements of aerosol samples collected at the same time to determine the sources of the aerosol carbon. The fraction of modern carbon (fM) in the aerosol samples, as determined from {sup 14}C analysis, showed that 70% of the carbonaceous aerosols in Mexico City were from modern sources, indicating a significant impact from biomass burning during both field campaigns. The {sup 13}C/{sup 12}C ratios of the aerosol samples illustrate the significant impact of Yucatan forest fires (C-3 plants) in 2003 and local grass fires (C-4 plants) at site T1 in 2006. A direct comparison of the fM values, stable carbon isotope ratios, and calculated aerosol AAEs suggested that the wavelength dependence of the aerosol absorption was controlled by the biogenically derived aerosol components.

Impact cratering on porous targets in the strength regime

Science.gov (United States)

Nakamura, Akiko M.

2017-12-01

Cratering on small bodies is crucial for the collision cascade and also contributes to the ejection of dust particles into interplanetary space. A crater cavity forms against the mechanical strength of the surface, gravitational acceleration, or both. The formation of moderately sized craters that are sufficiently larger than the thickness of the regolith on small bodies, in which mechanical strength plays the dominant role rather than gravitational acceleration, is in the strength regime. The formation of microcraters on blocks on the surface is also within the strength regime. On the other hand, the formation of a crater of a size comparable to the thickness of the regolith is affected by both gravitational acceleration and cohesion between regolith particles. In this short review, we compile data from the literature pertaining to impact cratering experiments on porous targets, and summarize the ratio of spall diameter to pit diameter, the depth, diameter, and volume of the crater cavity, and the ratio of depth to diameter. Among targets with various porosities studied in the laboratory to date, based on conventional scaling laws (Holsapple and Schmidt, J. Geophys. Res., 87, 1849-1870, 1982) the cratering efficiency obtained for porous sedimentary rocks (Suzuki et al., J. Geophys. Res. 117, E08012, 2012) is intermediate. A comparison with microcraters formed on a glass target with impact velocities up to 14 km s-1 indicates a different dependence of cratering efficiency and depth-to-diameter ratio on impact velocity.

Cratering record in the inner solar system: Implications for earth

International Nuclear Information System (INIS)

Barlow, N.G.

1988-01-01

Internal and external processes have reworked the Earth's surface throughout its history. In particular, the effect of meteorite impacts on the early history of the earth is lost due to fluvial, aeolian, volcanic and plate tectonic action. The cratering record on other inner solar system bodies often provides the only clue to the relative cratering rates and intensities that the earth has experienced throughout its history. Of the five major bodies within the inner solar system, Mercury, Mars, and the Moon retain scars of an early episode of high impact rates. The heavily cratered regions on Mercury, Mars, and the Moon show crater size-frequency distribution curves similar in shape and crater density, whereas the lightly cratered plains on the Moon and Mars show distribution curves which, although similar to each other, are statistically different in shape and density from the more heavily cratered units. The similarities among crater size-frequency distribution curves for the Moon, Mercury, and Mars suggest that the entire inner solar system was subjected to the two populations of impacting objects but Earth and Venus have lost their record of heavy bombardment impactors. Thus, based on the cratering record on the Moon, Mercury, and Mars, it can be inferred that the Earth experienced a period of high crater rates and basin formation prior to about 3.8 BY ago. Recent studies have linked mass extinctions to large terrestrial impacts, so life forms were unable to establish themselves until impact rates decreased substantially and terrestrial conditions became more benign. The possible periodicity of mass extinctions has led to the theory of fluctuating impact rates due to comet showers in the post heavy bombardment period. The active erosional environment on the Earth complicates attempts to verify these showers by erasing geological evidence of older impact craters

New meaning from old collections- figurines from the Museo de Jonuta, Chapas Mexico

International Nuclear Information System (INIS)

Sears, Erin L.

2001-01-01

Old collections of archaeological ceramics, often with diverse histories can be a rich source of new information when they are linked with new excavation materials through instrumental neutron activation analysis or other comparable analytical technique. INAA has been applied to study of Maya ceramics from southern Mexico for more than forty years, specially in the modern states of Tabasco, Chapas, Campeche and Yucatan and the Guatemala region of El Peten, More than 1.100 analyzes of fine paste orange and gray pottery provides an extensive compositional background against which to view the chemical variation of a recently analyzed collection of Maya figurines from the Museo de Jonuta, Tabasco Mexico. These figurines constitute an important assemblage of archaeological pottery as they reveal stylistic patterns of continuity in artistic traditions and aspects of stylistics change at and immediately before the time of the so called a Maya Collapse. Since the town of Jonuta is located in hypothesized home of non Maya invaders who are thought to be factors in the Maya collapse. INAA data on the figurines sources of production and related patterns of representational style, provide new data to address the social changes that took place in the lowland Maya regions at the end of the 8 th Century

Topography of the Martian Impact Crater Tooting

Science.gov (United States)

Mouginis-Mark, P. J.; Garbeil, H.; Boyce, J. M.

2009-01-01

Tooting crater is approx.29 km in diameter, is located at 23.4degN, 207.5degE, and is classified as a multi-layered ejecta crater [1]. Our mapping last year identified several challenges that can now be addressed with HiRISE and CTX images, but specifically the third dimension of units. To address the distribution of ponded sediments, lobate flows, and volatile-bearing units within the crater cavity, we have focused this year on creating digital elevation models (DEMs) for the crater and ejecta blanket from stereo CTX and HiRISE images. These DEMs have a spatial resolution of approx.50 m for CTX data, and 2 m for HiRISE data. Each DEM is referenced to all of the available individual MOLA data points within an image, which number approx.5,000 and 800 respectively for the two data types

A global catalogue of Ceres impact craters ≥ 1 km and preliminary analysis

Science.gov (United States)

Gou, Sheng; Yue, Zongyu; Di, Kaichang; Liu, Zhaoqin

2018-03-01

The orbital data products of Ceres, including global LAMO image mosaic and global HAMO DTM with a resolution of 35 m/pixel and 135 m/pixel respectively, are utilized in this research to create a global catalogue of impact craters with diameter ≥ 1 km, and their morphometric parameters are calculated. Statistics shows: (1) There are 29,219 craters in the catalogue, and the craters have a various morphologies, e.g., polygonal crater, floor fractured crater, complex crater with central peak, etc.; (2) The identifiable smallest crater size is extended to 1 km and the crater numbers have been updated when compared with the crater catalogue (D ≥ 20 km) released by the Dawn Science Team; (3) The d/D ratios for fresh simple craters, obviously degraded simple crater and polygonal simple crater are 0.11 ± 0.04, 0.05 ± 0.04 and 0.14 ± 0.02 respectively. (4) The d/D ratios for non-polygonal complex crater and polygonal complex crater are 0.08 ± 0.04 and 0.09 ± 0.03. The global crater catalogue created in this work can be further applied to many other scientific researches, such as comparing d/D with other bodies, inferring subsurface properties, determining surface age, and estimating average erosion rate.

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komla

seven soils: Yucatan (from Mexico), San Isidro or low; shape as flat or raised; and colour as. (Costa Rica), Itabela ..... (Mexico) soil, isolates did not form clusters either according to host or geographical origin. Isolates obtained ... Biodiversity of rhizobia which nodulate fast-growing tree legumes in tropical soils. PhD thesis,.

Research Program In Tropical Infectious Diseases

Science.gov (United States)

1991-12-15

Central America at the base of the Yucatan Peninsula, surrounded on the west and north by Guatemala and Mexico and on the east by the Caribbean Sea...inferred that in Belize, 2 tropical infectious diseases are common. Yellow fever has been known to occur in the Yucatan ,1 dengue and malaria are...Centro Americano) representatives in Belize City. Two ERC technologists and two CML technicians attended an INCAP (Instituto de Nutricion de Centro

Resistance of Mayan Women against Obstetric Violence

OpenAIRE

Gonzalez-Flores, Marina

2015-01-01

Mayan women are often victims of obstetric violence in the Yucatan Peninsula. Obstetric violence is defined as violence women experience by health officials or midwives during birth. This article will examine five different communities within the states of Yucatan, Campeche, and Quintana Roo in Mexico and compare and contrast activism efforts against obstetric violence among Mayan women. Mayan women are organizing to create unions for midwives, workshops on reproductive rights and health care...

Hydrogeology of the south-eastern Yucatan Peninsula: New insights from water level measurements, geochemistry, geophysics and remote sensing

DEFF Research Database (Denmark)

Gondwe, Bibi Ruth Neuman; Lerer, Sara Maria; Stisen, S.

2010-01-01

The Yucatan Peninsula is one of the world’s largest karstic aquifer systems. It is the sole freshwater source for human users and ecosystems. The region hosts internationally important groundwater-dependent ecosystems (GDEs) in the 5280km2 Sian Ka’an Biosphere Reserve. The GDEs are threatened by ...

Leakage of active crater lake brine through the north flank at Rincon de la Vieja volcano, northwest Costa Rica, and implications for crater collapse

Science.gov (United States)

Kempter, K.A.; Rowe, G.L.

2000-01-01

The Active Crater at Rincon de la Vieja volcano, Costa Rica, reaches an elevation of 1750 m and contains a warm, hyper-acidic crater lake that probably formed soon after the eruption of the Rio Blanco tephra deposit approximately 3500 years before present. The Active Crater is buttressed by volcanic ridges and older craters on all sides except the north, which dips steeply toward the Caribbean coastal plains. Acidic, above-ambient-temperature streams are found along the Active Crater's north flank at elevations between 800 and 1000 m. A geochemical survey of thermal and non-thermal waters at Rincon de la Vieja was done in 1989 to determine whether hyper-acidic fluids are leaking from the Active Crater through the north flank, affecting the composition of north-flank streams. Results of the water-chemistry survey reveal that three distinct thermal waters are found on the flanks of Rincon de la Vieja volcano: acid chloride-sulfate (ACS), acid sulfate (AS), and neutral chloride (NC) waters. The most extreme ACS water was collected from the crater lake that fills the Active Crater. Chemical analyses of the lake water reveal a hyper-acidic (pH ~ 0) chloride-sulfate brine with elevated concentrations of calcium, magnesium, aluminum, iron, manganese, copper, zinc, fluorine, and boron. The composition of the brine reflects the combined effects of magmatic degassing from a shallow magma body beneath the Active Crater, dissolution of andesitic volcanic rock, and evaporative concentration of dissolved constituents at above-ambient temperatures. Similar cation and anion enrichments are found in the above-ambient-temperature streams draining the north flank of the Active Crater. The pH of north-flank thermal waters range from 3.6 to 4.1 and chloride:sulfate ratios (1.2-1.4) that are a factor of two greater than that of the lake brine (0.60). The waters have an ACS composition that is quite different from the AS and NC thermal waters that occur along the southern flank of Rincon

Wrinkle Ridges and Young Fresh Crater

Science.gov (United States)

2002-01-01

(Released 10 May 2002) The Science Wrinkle ridges are a very common landform on Mars, Mercury, Venus, and the Moon. These ridges are linear to arcuate asymmetric topographic highs commonly found on smooth plains. The origin of wrinkle ridges is not certain and two leading hypotheses have been put forth by scientists over the past 40 years. The volcanic model calls for the extrusion of high viscosity lavas along linear conduits. This thick lava accumulated over these conduits and formed the ridges. The other model is tectonic and advocates that the ridges are formed by compressional faulting and folding. Today's THEMIS image is of the ridged plains of Lunae Planum located between Kasei Valles and Valles Marineris in the northern hemisphere of the planet. Wrinkle ridges are found mostly along the eastern side of the image. The broadest wrinkle ridges in this image are up to 2 km wide. A 3 km diameter young fresh crater is located near the bottom of the image. The crater's ejecta blanket is also clearly seen surrounding the sharp well-defined crater rim. These features are indicative of a very young crater that has not been subjected to erosional processes. The Story The great thing about the solar system is that planets are both alike and different. They're all foreign enough to be mysterious and intriguing, and yet familiar enough to be seen as planetary 'cousins.' By comparing them, we can learn a lot about how planets form and then evolve geologically over time. Crinkled over smooth plains, the long, wavy raised landforms seen here are called 'wrinkle ridges,' and they've been found on Mars, Mercury, Venus, and the Moon - that is, on rocky bodies that are a part of our inner solar system. We know from this observation that planets (and large-enough moons) follow similar processes. What we don't know for sure is HOW these processes work. Scientists have been trying to understand how wrinkle ridges form for 40 years, and they still haven't reached a conclusion. That

Aboriginal oral traditions of Australian impact craters

Science.gov (United States)

Hamacher, Duane W.; Goldsmith, John

2013-11-01

In this paper we explore Aboriginal oral traditions that relate to Australian meteorite craters. Using the literature, first-hand ethnographic records and field trip data, we identify oral traditions and artworks associated with four impact sites: Gosses Bluff, Henbury, Liverpool and Wolfe Creek. Oral traditions describe impact origins for Gosses Bluff, Henbury and Wolfe Creek Craters, and non-impact origins for Liverpool Crater, with Henbury and Wolfe Creek stories having both impact and non-impact origins. Three impact sites that are believed to have been formed during human habitation of Australia -- Dalgaranga, Veevers, and Boxhole -- do not have associated oral traditions that are reported in the literature.

Stratigraphic architecture of bedrock reference section, Victoria Crater, Meridiani Planum, Mars

Science.gov (United States)

Edgar, Lauren A.; Grotzinger, John P.; Hayes, Alex G.; Rubin, David M.; Squyres, Steve W.; Bell, James F.; Herkenhoff, Ken E.

2012-01-01

The Mars Exploration Rover Opportunity has investigated bedrock outcrops exposed in several craters at Meridiani Planum, Mars, in an effort to better understand the role of surface processes in its geologic history. Opportunity has recently completed its observations of Victoria crater, which is 750 m in diameter and exposes cliffs up to ~15 m high. The plains surrounding Victoria crater are ~10 m higher in elevation than those surrounding the previously explored Endurance crater, indicating that the Victoria crater exposes a stratigraphically higher section than does the Endurance crater; however, Victoria strata overlap in elevation with the rocks exposed at the Erebus crater. Victoria crater has a well-developed geomorphic pattern of promontories and embayments that define the crater wall and that reveal thick bedsets (3–7m) of large-scale cross-bedding, interpreted as fossil eolian dunes. Opportunity was able to drive into the crater at Duck Bay, located on the western margin of Victoria crater. Data from the Microscopic Imager and Panoramic Camera reveal details about the structures, textures, and depositional and diagenetic events that influenced the Victoria bedrock. A lithostratigraphic subdivision of bedrock units was enabled by the presence of a light-toned band that lines much of the upper rim of the crater. In ascending order, three stratigraphic units are named Lyell, Smith, and Steno; Smith is the light-toned band. In the Reference Section exposed along the ingress path at Duck Bay, Smith is interpreted to represent a zone of diagenetic recrystallization; however, its upper contact also coincides with a primary erosional surface. Elsewhere in the crater the diagenetic band crosscuts the physical stratigraphy. Correlation with strata present at nearby promontory Cape Verde indicates that there is an erosional surface at the base of the cliff face that corresponds to the erosional contact below Steno. The erosional contact at the base of Cape Verde

The Morphology of Craters on Mercury: Results from MESSENGER Flybys

Science.gov (United States)

Barnouin, Oliver S.; Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Herrick, Robert R.; Chappelow, John E.; Murchie, Scott L.; Prockter, Louise M.

2012-01-01

Topographic data measured from the Mercury Laser Altimeter (MLA) and the Mercury Dual Imaging System (MDIS) aboard the MESSENGER spacecraft were used for investigations of the relationship between depth and diameter for impact craters on Mercury. Results using data from the MESSENGER flybys of the innermost planet indicate that most of the craters measured with MLA are shallower than those previously measured by using Mariner 10 images. MDIS images of these same MLA-measured craters show that they have been modified. The use of shadow measurement techniques, which were found to be accurate relative to the MLA results, indicate that both small bowl-shaped and large complex craters that are fresh possess depth-to-diameter ratios that are in good agreement with those measured from Mariner 10 images. The preliminary data also show that the depths of modified craters are shallower relative to fresh ones, and might provide quantitative estimates of crater in-filling by subsequent volcanic or impact processes. The diameter that defines the transition from simple to complex craters on Mercury based on MESSENGER data is consistent with that reported from Mariner 10 data.

Morphological indicators of a mascon beneath Ceres' largest crater, Kerwan

Science.gov (United States)

Bland, Michael T.; Ermakov, Anton; Raymond, Carol A.; Williams, David A.; Bowling, Tim J.; Preusker, F.; Park, Ryan S.; Marchi, Simone; Castillo-Rogez, Julie C.; Fu, R.R.; Russell, Christopher T.

2018-01-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long‐term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact‐induced uplift of the high‐density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest‐degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin‐associated gravity anomalies, although their origin may differ substantially.

Morphological Indicators of a Mascon Beneath Ceres's Largest Crater, Kerwan

Science.gov (United States)

Bland, M. T.; Ermakov, A. I.; Raymond, C. A.; Williams, D. A.; Bowling, T. J.; Preusker, F.; Park, R. S.; Marchi, S.; Castillo-Rogez, J. C.; Fu, R. R.; Russell, C. T.

2018-02-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long-term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact-induced uplift of the high-density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest-degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin-associated gravity anomalies, although their origin may differ substantially.

Summary of results of cratering experiments

International Nuclear Information System (INIS)

Toman, J.

1969-01-01

The use of nuclear excavation as a construction technique for producing harbors, canals, highway cuts, and other large excavations requires a high assurance that the yield and depth of burst selected for the explosive will produce the desired configuration within an acceptable degree of tolerance. Nuclear excavation technology advanced significantly during 1968 as a result of the successful execution of Projects Cabriolet, Buggy, and Schooner. Until these experiments were conducted, the only nuclear data available for designing large excavations were derived from Sedan (100 kt in alluvium), Danny Boy (0.42 kt in basalt), and Sulky (0.090 kt in basalt). Applicable experience has now been extended to include two additional rock types: tuff and porphyritic trachyte, non-homogeneous formations with severe geologic layering, and a nuclear row in hard rock. The continued development of cratering calculations using in situ geophysical measurements and high-pressure test data have provided a means for predicting the cratering characteristics of untested materials. Chemical explosive cratering experiments conducted in the pre-Gondola series during the past several years have been directed toward determining the behavior of weak, wet clay shales. This material is important to nuclear excavation because of potential long-term stability problems which may affect the cratered slopes. (author)

Summary of results of cratering experiments

Energy Technology Data Exchange (ETDEWEB)

Toman, J [Lawrence Radiation Laboratory, Livermore, CA (United States)

1969-07-01

The use of nuclear excavation as a construction technique for producing harbors, canals, highway cuts, and other large excavations requires a high assurance that the yield and depth of burst selected for the explosive will produce the desired configuration within an acceptable degree of tolerance. Nuclear excavation technology advanced significantly during 1968 as a result of the successful execution of Projects Cabriolet, Buggy, and Schooner. Until these experiments were conducted, the only nuclear data available for designing large excavations were derived from Sedan (100 kt in alluvium), Danny Boy (0.42 kt in basalt), and Sulky (0.090 kt in basalt). Applicable experience has now been extended to include two additional rock types: tuff and porphyritic trachyte, non-homogeneous formations with severe geologic layering, and a nuclear row in hard rock. The continued development of cratering calculations using in situ geophysical measurements and high-pressure test data have provided a means for predicting the cratering characteristics of untested materials. Chemical explosive cratering experiments conducted in the pre-Gondola series during the past several years have been directed toward determining the behavior of weak, wet clay shales. This material is important to nuclear excavation because of potential long-term stability problems which may affect the cratered slopes. (author)

Goat paddock cryptoexplosion crater, Western Australia

Science.gov (United States)

Harms, J.E.; Milton, D.J.; Ferguson, J.; Gilbert, D.J.; Harris, W.K.; Goleby, B.

1980-01-01

Goat Paddock, a crater slightly over 5 km in diameter (18??20??? S, 126??40???E), lies at the north edge of the King Leopold Range/Mueller Range junction in the Kimberley district, Western Australia (Fig. 1). It was noted as a geological anomaly in 1964 during regional mapping by the Bureau of Mineral Resources, Geology and Geophysics and the Geological Survey of Western Australia. The possibility of its being a meteorite impact crater has been discussed1, although this suggestion was subsequently ignored2. Two holes were drilled by a mining corporation in 1972 to test whether kimberlite underlay the structure. Here we report the findings of five days of reconnaissance in August 1979 which established that Goat Paddock is a cryptoexplosion crater containing shocked rocks and an unusually well exposed set of structural features. ?? 1980 Nature Publishing Group.

EL FOGÓN ABIERTO DE TRES PIEDRAS EN LA PENÍNSULA DE YUCATÁN: TRADICIÓN Y TRANSFERENCIA TECNOLÓGICA

Directory of Open Access Journals (Sweden)

Citlalli Cantú Gutiérrez

2012-06-01

In Mexico and particularly on the Yucatan peninsula, the use of the three-stone open fire cook stove and fire wood fuel is a phenomenon of great importance due to the number of people using it, its historical-cultural background and its meaning within the complex of traditional technologies. Its current existence represents a process of autonomy of the indigenous, peasant and poor populations with respect to the hegemonic networks of conventional sources of energy. Based on observations of 4000 households in 39 locations in Yucatan and Quintana Roo, Mexico, this article describes the characteristics of the open fire cook stove as well as the preferred types of firewood. It analyzes the transfer of technology and describes the process of delivery of open fire cook stoves by the federal government in Yucatan, interpreting it as a carbon subsidy policy for both local capitalist industry and developed countries, and as a way of neutralizing traditional autonomy and the efforts of organized civil society to promote participatory and community development.

Rock spatial densities on the rims of the Tycho secondary craters in Mare Nectaris

Science.gov (United States)

Basilevsky, A. T.; Michael, G. G.; Kozlova, N. A.

2018-04-01

The aim of this work is to check whether the technique of estimation of age of small lunar craters based on spatial density of rock boulders on their rims described in Basilevsky et al. (2013, 2015b) and Li et al. (2017) for the craters rock counts on the rims of four craters having diameters 1000, 1100, 1240 and 1400 m located in Mare Nectaris. These craters are secondaries of the primary crater Tycho, whose age was found to be 109 ± 4 Ma (Stoffler and Ryder, 2001) so this may be taken as the age of the four craters, too. Using the dependence of the rock spatial densities at the crater rims on the crater age for the case of mare craters (Li et al., 2017) our measured rock densities correspond to ages from ∼100 to 130 Ma. These estimates are reasonably close to the given age of the primary crater Tycho. This, in turn, suggests that this technique of crater age estimation is applicable to craters up to ∼1.5 km in diameter. For the four considered craters we also measured their depth/diameter ratios and the maximum angles of the crater inner slopes. For the considered craters it was found that with increasing crater diameter, the depth/diameter ratios and maximum angles of internal slopes increase, but the values of these parameters for specific craters may deviate significantly from the general trends. The deviations probably result from some dissimilarities in the primary crater geometries, that may be due to crater to crater differences in characteristics of impactors (e.g., in their bulk densities) and/or differences in the mechanical properties of the target. It may be possible to find secondaries of crater Tycho in the South pole area and, if so, they may be studied to check the specifics and rates of the rock boulder degradation in the lunar polar environment.

Preliminary study of the offshore wind and temperature profiles at the North of the Yucatan Peninsula

International Nuclear Information System (INIS)

Soler-Bientz, Rolando; Watson, Simon; Infield, David; Ricalde-Cab, Lifter

2011-01-01

Highlights: → This is the first study that reports the properties of the vertical wind resources for the offshore conditions of the North coast of the Yucatan Peninsula. → A significant and detailed analysis of the thermal patterns has revealed a complex structure of the atmospheric boundary layer close to the shore. → The structure of the diurnal wind patterns was assessed to produce an important reference for the wind resource availability in the study region. → It was identified that the sea breeze blows in directions almost parallel to the shoreline of the North of the Yucatan Peninsula during the majority of the 24 h cycle. → The analysis of the offshore data revealed a persistent non-uniform surface boundary layer developed as result of the advection of a warn air over a cold sea. - Abstract: The stability conditions in the atmospheric boundary layer, the intensity of the wind speeds and consequently the energy potential available in offshore conditions are highly influenced by the distance from the coastline and the differences between the air and sea temperatures. This paper presents a preliminary research undertook to study the offshore wind and temperature vertical profiles at the North-West of the Yucatan Peninsula coast. Ten minute averages were recorded over approximately 2 years from sensors installed at two different heights on a communication tower located at 6.65 km from the coastline. The results have shown that the offshore wind is thermally driven by differential heating of land and sea producing breeze patterns which veer to blow parallel to the coast under the action of the Coriolis force. To investigate further, a dataset of hourly sea surface temperatures derived from GEOS Satellite thermal maps was combined with the onsite measured data to study its effect on the vertical temperature profile. The results suggested largely unstable conditions and the potentially development of a shallow Stable Internal Boundary Layer which occurs

Some Studies of Terrestrial Impact Cratering Rate

Directory of Open Access Journals (Sweden)

Jetsu L.

2011-06-01

Full Text Available In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 Myr periodicity in the epochs of mass extinctions of species. Periodic comet showers from the Oort cloud seemed to cause catastrophic events linked to mass extinctions of species. Our first study revealed that the only significant detected periodicity is the “human signal” caused by the rounding of these data into integer numbers. The second study confirmed that the original 28.4 Myr periodicity detection was not significant. The third study revealed that the quality and the quantity of the currently available data would allow detection of real periodicity only if all impacts have been periodic, which cannot be the case. The detection of a periodic signal, if present, requires that more craters should be discovered and the accuracy of age estimates improved. If we sometimes will be able to find the difference between the craters caused by asteroid and comet impacts, the aperiodic component could be removed. The lunar impact craters may eventually provide the required supplementary data.

Floor-fractured craters on Ceres and implications for interior processes

Science.gov (United States)

Buczkowski, Debra; Schenk, Paul M.; Scully, Jennifer E. C.; Park, Ryan; Preusker, Frank; Raymond, Carol; Russell, Christopher T.

2016-10-01

Several of the impact craters on Ceres have patterns of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs) [Schultz, 1976].Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures, and have been classified into crater classes, Types 1 through 6, based on their morphometric properties [Schultz, 1976; Jozwiak et al, 2012, 2015]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater or floor shallowing due to viscous relaxation. However, the observation that the depth versus diameter (d/D) relationship of the FFCs is distinctly shallower than the same association for other lunar craters supports the hypotheses that the floor fractures form due to shallow magmatic intrusion under the crater [Jozwiak et al, 2012, 2015].FFCs have also been identified on Mars [Bamberg et al., 2014]. Martian FFCs exhibit morphological characteristics similar to the lunar FFCs, and analyses suggest that the Martian FCCs also formed due to volcanic activity, although heavily influenced by interactions with groundwater and/or ice.We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. Large (>50 km) Ceres FFCs are most consistent with Type 1 lunar FFCs, having deep floors, central peaks, wall terraces, and radial and/or concentric fractures. Smaller craters on Ceres are more consistent with Type 4 lunar FFCs, having less-pronounced floor fractures and a v-shaped moats separating the wall scarp from the crater interior.An analysis of the d/D ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. This suggests that the fractures on the floor of Ceres FFCs may be due the intrusion of a low-density material below the craters that is uplifting their floors. While on the Moon and Mars the intrusive material is hypothesized

Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Science.gov (United States)

Matsumoto, Toru; Hasegawa, S.; Nakao, S.; Sakai, M.; Yurimoto, H.

2018-03-01

We investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 μm to 240 μm in size. Craters with average diameters ranging from 10 nm to 2.8 μm were identified on 13 Itokawa particles larger than 80 μm. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 μm2 to 4.5 μm2; a fraction of the craters was locally concentrated with a density of 0.1 μm2. The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 102 to 104 yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter- to meter-sized depressions on Itokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary

Microbial diversity and biomarker analysis of modern freshwater microbialites from Laguna Bacalar, Mexico.

Science.gov (United States)

Johnson, D B; Beddows, P A; Flynn, T M; Osburn, M R

2018-05-01

Laguna Bacalar is a sulfate-rich freshwater lake on the Yucatan Peninsula that hosts large microbialites. High sulfate concentrations distinguish Laguna Bacalar from other freshwater microbialite sites such as Pavilion Lake and Alchichica, Mexico, as well as from other aqueous features on the Yucatan Peninsula. While cyanobacterial populations have been described here previously, this study offers a more complete characterization of the microbial populations and corresponding biogeochemical cycling using a three-pronged geobiological approach of microscopy, high-throughput DNA sequencing, and lipid biomarker analyses. We identify and compare diverse microbial communities of Alphaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria that vary with location along a bank-to-bank transect across the lake, within microbialites, and within a neighboring mangrove root agglomeration. In particular, sulfate-reducing bacteria are extremely common and diverse, constituting 7%-19% of phylogenetic diversity within the microbialites, and are hypothesized to significantly influence carbonate precipitation. In contrast, Cyanobacteria account for less than 1% of phylogenetic diversity. The distribution of lipid biomarkers reflects these changes in microbial ecology, providing meaningful biosignatures for the microbes in this system. Polysaturated short-chain fatty acids characteristic of cyanobacteria account for Bacalar microbialites. By contrast, even short-chain and monounsaturated short-chain fatty acids attributable to both Cyanobacteria and many other organisms including types of Alphaproteobacteria and Gammaproteobacteria constitute 43%-69% and 17%-25%, respectively, of total abundance in microbialites. While cyanobacteria are the largest and most visible microbes within these microbialites and dominate the mangrove root agglomeration, it is clear that their smaller, metabolically diverse associates are responsible for significant biogeochemical cycling in this

Are pre-crater mounds gas-inflated?

Science.gov (United States)

Leibman, Marina; Kizyakov, Alexandr; Khomutov, Artem; Dvornikov, Yury; Babkina, Elena; Arefiev, Stanislav; Khairullin, Rustam

2017-04-01

Gas-emission craters (GEC) on Yamal peninsula, which occupied minds of researches for the last couple of years since first discovered in 2014, appeared to form on the place of specifically shaped mounds. There was a number of hypotheses involving pingo as an origin of these mounds. This arouse an interest in mapping pingo thus marking the areas of GEC formation risk. Our field research allows us to suggest that remote-sensing-based mapping of pingo may result in mix up of mounds of various origin. Thus, we started with classification of the mounds based on remote-sensing, field observations and survey from helicopter. Then we compared indicators of mounds of various classes to the properties of pre-crater mounds to conclude on their origin. Summarizing field experience, there are three main mound types on Yamal. (1) Outliers (remnant hills), separated from the main geomorphic landform by erosion. Often these mounds comprise polygonal blocks, kind of "baydzherakh". Their indicators are asymmetry (short gentle slope towards the main landform, and steep slope often descending into a small pond of thermokarst-nivation origin), often quadrangle or conic shape, and large size. (2) Pingo, appear within the khasyrei (drain lake basin); often are characterized by open cracks resulting from expansion of polygonal network formed when re-freezing of lake talik prior to pingo formation; old pingo may bear traces of collapse on the top, with depression which differs from the GEC by absence of parapet. (3) Frost-heave mounds (excluding pingo) may form on deep active layer, reducing due to moss-peat formation and forming ice lenses from an active layer water, usually they appear in the drainage hollows, valley bottoms, drain-lake basins periphery. These features are smaller than the first two types of mounds. Their tops as a rule are well vegetated. We were unable to find a single or a set of indicators unequivocally defining any specific mound type, thus indicators of pre-crater

Monturaqui meteorite impact crater, Chile: A field test of the utility of satellite-based mapping of ejecta at small craters

Science.gov (United States)

Rathbun, K.; Ukstins, I.; Drop, S.

2017-12-01

Monturaqui Crater is a small ( 350 m diameter), simple meteorite impact crater located in the Atacama Desert of northern Chile that was emplaced in Ordovician granite overlain by discontinuous Pliocene ignimbrite. Ejecta deposits are granite and ignimbrite, with lesser amounts of dark impact melt and rare tektites and iron shale. The impact restructured existing drainage systems in the area that have subsequently eroded through the ejecta. Satellite-based mapping and modeling, including a synthesis of photographic satellite imagery and ASTER thermal infrared imagery in ArcGIS, were used to construct a basic geological interpretation of the site with special emphasis on understanding ejecta distribution patterns. This was combined with field-based mapping to construct a high-resolution geologic map of the crater and its ejecta blanket and field check the satellite-based geologic interpretation. The satellite- and modeling-based interpretation suggests a well-preserved crater with an intact, heterogeneous ejecta blanket that has been subjected to moderate erosion. In contrast, field mapping shows that the crater has a heavily-eroded rim and ejecta blanket, and the ejecta is more heterogeneous than previously thought. In addition, the erosion rate at Monturaqui is much higher than erosion rates reported elsewhere in the Atacama Desert. The bulk compositions of the target rocks at Monturaqui are similar and the ejecta deposits are highly heterogeneous, so distinguishing between them with remote sensing is less effective than with direct field observations. In particular, the resolution of available imagery for the site is too low to resolve critical details that are readily apparent in the field on the scale of 10s of cm, and which significantly alter the geologic interpretation. The limiting factors for effective remote interpretation at Monturaqui are its target composition and crater size relative to the resolution of the remote sensing methods employed. This

Acoustic fluidization and the scale dependence of impact crater morphology

Science.gov (United States)

Melosh, H. J.; Gaffney, E. S.

1983-01-01

A phenomenological Bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters. This paper demonstrates that the Bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater. Experimental support for the theoretical flow law is presented. Although the Bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field, the Bingham viscosity is derived from a simple argument which shows that it increases as the 3/2 power of crater diameter, consistent with observation. Crater collapse may occur in material with internal dissipation Q as low as 100, comparable to laboratory observations of dissipation in granular materials. Crater collapse thus does not require that the acoustic field be regenerated during flow.

Heavy Cratering near Callisto's South Pole

Science.gov (United States)

1997-01-01

Images from NASA's Galileo spacecraft provide new insights into this region near Callisto's south pole. This two frame mosaic shows a heavily cratered surface with smooth plains in the areas between craters. North is to the top of the image. The smoothness of the plains appears to increase toward the south pole, approximately 480 kilometers (293 miles) south of the bottom of the image. This smoothness of Callisto's surface was not evident in images taken during the 1979 flyby of NASA's Voyager spacecraft because the resolution was insufficient to show the effect. This smooth surface, and the process(es) that cause it, are among the most intriguing aspects of Callisto. Although not fully understood, the process(es) responsible for this smoothing could include erosion by tiny meteorites and energetic ions. Some craters, such as Keelut, the 47 kilometer (29 mile) crater in the lower right corner, have sharp, well defined rims. Keelut contains an inner ring surrounding a central depression about 17 kilometers (11 miles) in diameter. Keelut, and the more irregularly shaped, degraded Reginleif, the 32 kilometer (19.5 mile) crater in the top center of the image, are very shallow and have flat floors. Crater forms can be seen down to less than 2 kilometers (1.2 miles) in diameter in the image. Each picture element (pixel) in this image is approximately 0.68 kilometers (0.41 miles) across.This image which was taken by the Galileo spacecraft's solid state imaging (CCD) system during its eighth orbit around Jupiter, on May 6th, 1997. The center of the image is located at 71.3 degrees south latitude, 97.6 degrees west longitude, and was taken when the spacecraft was approximately 35,470 kilometers (21,637 miles) from Callisto.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http

BOVINE RESPIRATORY SYNCYTIAL VIRUS EPIDEMIOLOGY AND RISK FACTORS ON CATTLE HERDS OF CAMPECHE STATE, MEXICO

Directory of Open Access Journals (Sweden)

Lisandro Alberto Encalada Mena

2016-12-01

Full Text Available High seroprevalence in Yucatan and proximity to the state of Campeche make it necessary to determine the seroprevalence and risk factors of bovine respiratory syncytial virus (VRSB in the state of Campeche, Mexico. Thus the objective of the present work was to determine the seroprevalence and risk factors bovine respiratory syncytial virus (BRSV of the state of Campeche, Mexico. The sampled of 36 cattle herds (842 sera were analyzed by indirect ELISA kit, in the 11 municipalities of Campeche. A survey to obtain risk factors (sex, age of animals, number of animals grazing density, management system, presence of sheep on the farm and access to the roadside was applied and calculated X2 for each variable considered. Of the total number of samples analyzed (842, 273 were positive (32.47%. The prevalence ranges found ranged from 0% to 84%, so in 9 of the herds there were no positive samples, indicating a 75% (27/36 of dispersion of this virus. X2 analysis indicated that all variables were significant and are risk factors regarding with respect to the variable seroprevalence of BRSV. The results indicate a wide circulation of BRSV and we suggest implement recommendations that will enable a lower spread of this virus in the cattle population.

Crater relaxation on Titan aided by low thermal conductivity sand infill

Science.gov (United States)

Schurmeier, Lauren R.; Dombard, Andrew J.

2018-05-01

Titan's few impact craters are currently many hundreds of meters shallower than the depths expected. Assuming these craters initially had depths equal to that of similar-size fresh craters on Ganymede and Callisto (moons of similar size, composition, and target lithology), then some process has shallowed them over time. Since nearly all of Titan's recognized craters are located within the arid equatorial sand seas of organic-rich dunes, where rain is infrequent, and atmospheric sedimentation is expected to be low, it has been suggested that aeolian infill plays a major role in shallowing the craters. Topographic relaxation at Titan's current heat flow was previously assumed to be an unimportant process on Titan due to its low surface temperature (94 K). However, our estimate of the thermal conductivity of Titan's organic-rich sand is remarkably low (0.025 W m-1 K-1), and when in thick deposits, will result in a thermal blanketing effect that can aid relaxation. Here, we simulate the relaxation of Titan's craters Afekan, Soi, and Sinlap including thermal effects of various amounts of sand inside and around Titan's craters. We find that the combination of aeolian infill and subsequent relaxation can produce the current crater depths in a geologically reasonable period of time using Titan's current heat flow. Instead of needing to fill completely the missing volume with 100% sand, only ∼62%, ∼71%, and ∼97%, of the volume need be sand at the current basal heat flux for Afekan, Soi, and Sinlap, respectively. We conclude that both processes are likely at work shallowing these craters, and this finding contributes to why Titan overall lacks impact craters in the arid equatorial regions.

Experimental investigation of crater growth dynamics

Science.gov (United States)

Schmidt, R. M.; Housen, K. R.; Bjorkman, M. D.; Holsapple, K. A.

1985-01-01

This work is a continuation of an ongoing program whose objective is to perform experiments and to develop scaling relationships for large-body impacts onto planetary surfaces. The centrifuge technique is used to provide experimental data for actual target materials of interest. With both power and gas guns mounted on the rotor arm, it is possible to match various dimensionless similarity parameters, which have been shown to govern the behavior of large-scale impacts. The development of the centrifuge technique has been poineered by the present investigators and is documented by numerous publications, the most recent of which are listed below. Understanding the dependence of crater size upon gravity has been shown to be key to the complete determination of the dynamic and kinematic behavior of crater formation as well as ejecta phenomena. Three unique time regimes in the formation of an impact crater have been identified.

Meteor Crater, AZ

Science.gov (United States)

2002-01-01

The Barringer Meteorite Crater (also known as 'Meteor Crater') is a gigantic hole in the middle of the arid sandstone of the Arizona desert. A rim of smashed and jumbled boulders, some of them the size of small houses, rises 50 m above the level of the surrounding plain. The crater itself is nearly a 1500 m wide, and 180 m deep. When Europeans first discovered the crater, the plain around it was covered with chunks of meteoritic iron - over 30 tons of it, scattered over an area 12 to 15 km in diameter. Scientists now believe that the crater was created approximately 50,000 years ago. The meteorite which made it was composed almost entirely of nickel-iron, suggesting that it may have originated in the interior of a small planet. It was 50 m across, weighed roughly 300,000 tons, and was traveling at a speed of 65,000 km per hour. This ASTER 3-D perspective view was created by draping an ASTER bands 3-2-1image over a digital elevation model from the US Geological Survey National Elevation Dataset.This image was acquired on May 17, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet.ASTER is one of five Earth-observing instruments launched December 18,1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. Science team leader; Bjorn Eng of JPL is the project manager. ASTER is the only high resolution imaging sensor on Terra. The Terra mission is part of NASA's Earth Science Enterprise, along

Measuring impact crater depth throughout the solar system

Science.gov (United States)

Robbins, Stuart J.; Watters, Wesley A.; Chappelow, John E.; Bray, Veronica J.; Daubar, Ingrid J.; Craddock, Robert A.; Beyer, Ross A.; Landis, Margaret E.; Ostrach, Lillian; Tornabene, Livio L.; Riggs, Jamie D.; Weaver, Brian P.

2018-01-01

One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data‐gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared.

Noachian and more recent phyllosilicates in impact craters on Mars.

Science.gov (United States)

Fairén, Alberto G; Chevrier, Vincent; Abramov, Oleg; Marzo, Giuseppe A; Gavin, Patricia; Davila, Alfonso F; Tornabene, Livio L; Bishop, Janice L; Roush, Ted L; Gross, Christoph; Kneissl, Thomas; Uceda, Esther R; Dohm, James M; Schulze-Makuch, Dirk; Rodríguez, J Alexis P; Amils, Ricardo; McKay, Christopher P

2010-07-06

Hundreds of impact craters on Mars contain diverse phyllosilicates, interpreted as excavation products of preexisting subsurface deposits following impact and crater formation. This has been used to argue that the conditions conducive to phyllosilicate synthesis, which require the presence of abundant and long-lasting liquid water, were only met early in the history of the planet, during the Noachian period (> 3.6 Gy ago), and that aqueous environments were widespread then. Here we test this hypothesis by examining the excavation process of hydrated minerals by impact events on Mars and analyzing the stability of phyllosilicates against the impact-induced thermal shock. To do so, we first compare the infrared spectra of thermally altered phyllosilicates with those of hydrated minerals known to occur in craters on Mars and then analyze the postshock temperatures reached during impact crater excavation. Our results show that phyllosilicates can resist the postshock temperatures almost everywhere in the crater, except under particular conditions in a central area in and near the point of impact. We conclude that most phyllosilicates detected inside impact craters on Mars are consistent with excavated preexisting sediments, supporting the hypothesis of a primeval and long-lasting global aqueous environment. When our analyses are applied to specific impact craters on Mars, we are able to identify both pre- and postimpact phyllosilicates, therefore extending the time of local phyllosilicate synthesis to post-Noachian times.

Physics of soft impact and cratering

CERN Document Server

Katsuragi, Hiroaki

2016-01-01

This book focuses on the impact dynamics and cratering of soft matter to describe its importance, difficulty, and wide applicability to planetary-related problems. A comprehensive introduction to the dimensional analysis and constitutive laws that are necessary to discuss impact mechanics and cratering is first provided. Then, particular coverage is given to the impact of granular matter, which is one of the most crucial constituents for geophysics. While granular matter shows both solid-like and fluid-like behaviors, neither solid nor fluid dynamics is sufficient to fully understand the physics of granular matter. In order to reveal its fundamental properties, extensive impact tests have been carried out recently. The author reveals the findings of these recent studies as well as what remains unsolved in terms of impact dynamics. Impact crater morphology with various soft matter impacts also is discussed intensively. Various experimental and observational results up to the recent Itokawa asteroid’s terrain...

Crater monitoring through social media observations

Science.gov (United States)

Gialampoukidis, I.; Vrochidis, S.; Kompatsiaris, I.

2017-09-01

We have collected more than one lunar image per two days from social media observations. Each one of the collected images has been clustered into two main groups of lunar images and an additional cluster is provided (noise) with pictures that have not been assigned to any cluster. The proposed lunar image clustering process provides two classes of lunar pictures, at different zoom levels; the first showing a clear view of craters grouped into one cluster and the second demonstrating a complete view of the Moon at various phases that are correlated with the crawling date. The clustering stage is unsupervised, so new topics can be detected on-the-fly. We have provided additional sources of planetary images using crowdsourcing information, which is associated with metadata such as time, text, location, links to other users and other related posts. This content has crater information that can be fused with other planetary data to enhance crater monitoring.

Planetary boundary layer and circulation dynamics at Gale Crater, Mars

Science.gov (United States)

Fonseca, Ricardo M.; Zorzano-Mier, María-Paz; Martín-Torres, Javier

2018-03-01

The Mars implementation of the Planet Weather Research and Forecasting (PlanetWRF) model, MarsWRF, is used here to simulate the atmospheric conditions at Gale Crater for different seasons during a period coincident with the Curiosity rover operations. The model is first evaluated with the existing single-point observations from the Rover Environmental Monitoring Station (REMS), and is then used to provide a larger scale interpretation of these unique measurements as well as to give complementary information where there are gaps in the measurements. The variability of the planetary boundary layer depth may be a driver of the changes in the local dust and trace gas content within the crater. Our results show that the average time when the PBL height is deeper than the crater rim increases and decreases with the same rate and pattern as Curiosity's observations of the line-of-sight of dust within the crater and that the season when maximal (minimal) mixing is produced is Ls 225°-315° (Ls 90°-110°). Thus the diurnal and seasonal variability of the PBL depth seems to be the driver of the changes in the local dust content within the crater. A comparison with the available methane measurements suggests that changes in the PBL depth may also be one of the factors that accounts for the observed variability, with the model results pointing towards a local source to the north of the MSL site. The interaction between regional and local flows at Gale Crater is also investigated assuming that the meridional wind, the dynamically important component of the horizontal wind at Gale, anomalies with respect to the daily mean can be approximated by a sinusoidal function as they typically oscillate between positive (south to north) and negative (north to south) values that correspond to upslope/downslope or downslope/upslope regimes along the crater rim and Mount Sharp slopes and the dichotomy boundary. The smallest magnitudes are found in the northern crater floor in a region that

Laboratory and Field Investigations of Small Crater Repair Technologies

National Research Council Canada - National Science Library

Priddy, Lucy P; Tingle, Jeb S; McCaffrey, Timothy J; Rollings, Ray S

2007-01-01

.... This airfield damage repair (ADR) investigation consisted of laboratory testing of selected crater fill and capping materials, as well as full-scale field testing of small crater repairs to evaluate field mixing methods, installation...

Postshot distribution and movement of radionuclides in nuclear crater ejecta

Energy Technology Data Exchange (ETDEWEB)

Koranda, John J; Martin, John R; Wikkerink, Robert; Stuart, Marshall [Bio-Medical Division, Lawrence Radiation Laboratory, University of California, Livermore, CA (United States)

1970-05-01

The distribution and postshot movement of radionuclides in nuclear crater ejecta are discussed in this report. Continuing studies of tritium movement in ejecta at SEDAN crater demonstrate that variations in tritium concentration are correlated with seasonal rainfall and soil water movements. Losses of 27 mCi H{sup 3}/ft{sup 2} are evident on SEDAN crater lip at the end of a three year period of measurements in -which an unusually large flux of rain was received. The distribution of gamma emitting radionuclides and tritium is described in the recently created SCHOONER crater ejecta field. The specific activity of radionuclides in the SCHOONER ejecta continuum is shown for ejecta collected from the crater lip to 17 miles from GZ. The movement of W{sup 181} and tritium into the sub-ejecta preshot soil is described at a site 3000 feet from GZ. (author)

Mass Movement on Vesta at Steep Scarps and Crater Rims

Science.gov (United States)

Krohn, K.; Jaumann, R.; Otto, K.; Hoogenboom, T.; Wagner, R.; Buczkowski, D. L.; Garry, B.; Williams, D. A.; Yingst, R. A.; Scully, J.;

Mass movement on Vesta at steep scarps and crater rims

Science.gov (United States)

Krohn, K.; Jaumann, R.; Otto, K.; Hoogenboom, T.; Wagner, R.; Buczkowski, D. L.; Garry, B.; Williams, D. A.; Yingst, R. A.; Scully, J.; De Sanctis, M. C.; Kneissl, T.; Schmedemann, N.; Kersten, E.; Stephan, K.; Matz, K.-D.; Pieters, C. M.; Preusker, F.; Roatsch, T.; Schenk, P.; Russell, C. T.; Raymond, C. A.

2014-12-01

The Quadrangles Av-11 and Av-12 on Vesta are located at the northern rim of the giant Rheasilvia south polar impact basin. The primary geologic units in Av-11 and Av-12 include material from the Rheasilvia impact basin formation, smooth material and different types of impact crater structures (such as bimodal craters, dark and bright crater ray material and dark ejecta material). Av-11 and Av-12 exhibit almost the full range of mass wasting features observed on Vesta, such as slump blocks, spur-and-gully morphologies and landslides within craters. Processes of collapse, slope instability and seismically triggered events force material to slump down crater walls or scarps and produce landslides or rotational slump blocks. The spur-and-gully morphology that is known to form on Mars is also observed on Vesta; however, on Vesta this morphology formed under dry conditions.

Environmental Exposure of Children to Toxic Trace Elements (Hg, Cr, As) in an Urban Area of Yucatan, Mexico: Water, Blood, and Urine Levels.

Science.gov (United States)

Arcega-Cabrera, F; Fargher, L; Quesadas-Rojas, M; Moo-Puc, R; Oceguera-Vargas, I; Noreña-Barroso, E; Yáñez-Estrada, L; Alvarado, J; González, L; Pérez-Herrera, N; Pérez-Medina, S

2018-05-01

Merida is the largest urban center in the Mexican State of Yucatan. Here domestic sewage is deposited in poorly built septic tanks and is not adequately treated. Because of contamination from such waste, water from the top 20 m of the aquifer is unsuitable for human consumption. Given this situation and because children are highly vulnerable to environmental pollution, including exposure to toxic trace elements, this study focused on evaluating the exposure of children to arsenic (As), chromium (Cr), and mercury (Hg) in water. It also evaluated the relationship between the levels of these elements in water and their concentrations in urine and blood. Among the 33 children monitored in the study, arsenic surpassed WHO limits for blood in 37% of the cases, which could result from the ingestion of poultry contaminated with organoarsenic compounds. In the case of WHO limits for Mercury, 65% of the water samples analyzed, 28% of urine samples, and 12% of blood samples exceeded them. Mercury exposure was correlated with biological sex, some lifestyle factors, and the zone in Merida in which children live. These data suggest that the levels of some toxic metals in children may be affected by water source, socioeconomic factors, and individual behavior.

Crater Highlands, Tanzania

Science.gov (United States)

2006-01-01

The Shuttle Radar Topography Mission (SRTM), flown aboard Space Shuttle Endeavour in February 2000, acquired elevation measurements for nearly all of Earth's landmass between 60oN and 56oS latitudes. For many areas of the world SRTM data provide the first detailed three-dimensional observation of landforms at regional scales. SRTM data were used to generate this view of the Crater Highlands along the East African Rift in Tanzania. Landforms are depicted with colored height and shaded relief, using a vertical exaggeration of 2X and a southwestwardly look direction. Lake Eyasi is depicted in blue at the top of the image, and a smaller lake occurs in Ngorongoro Crater. Near the image center, elevations peak at 3648 meters (11,968 feet) at Mount Loolmalasin, which is south of Ela Naibori Crater. Kitumbeine (left) and Gelai (right) are the two broad mountains rising from the rift lowlands. Mount Longido is seen in the lower left, and the Meto Hills are in the right foreground. Tectonics, volcanism, landslides, erosion and deposition -- and their interactions -- are all very evident in this view. The East African Rift is a zone of spreading between the African (on the west) and Somali (on the east) crustal plates. Two branches of the rift intersect here in Tanzania, resulting in distinctive and prominent landforms. One branch trends nearly parallel the view and includes Lake Eyasi and the very wide Ngorongoro Crater. The other branch is well defined by the lowlands that trend left-right across the image (below center, in green). Volcanoes are often associated with spreading zones where magma, rising to fill the gaps, reaches the surface and builds cones. Craters form if a volcano explodes or collapses. Later spreading can fracture the volcanoes, which is especially evident on Kitumbeine and Gelai Mountains (left and right, respectively, lower center). The Crater Highlands rise far above the adjacent savannas, capture moisture from passing air masses, and host rain

180 Teneurs en tanins de 15 ligneux fourragers du Burkina Faso ...

African Journals Online (AJOL)

ASUS

ISSN 1813-548X, http://www.afriquescience.info ... browse forages. But the levels of anti-nutritional ... Keywords : Burkina Faso, browses, secondary metabolites, tannins, content, anti-nutritional factors. 1. ..... Merida, Yucatan, Mexico, 2004. pp.

MaritimeMaya2011: The Costa Escondida Project: Exploring the Hidden World of the Maritime Maya on the Yucatan Peninsula between 20110509 and 20110531

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The northeast tip of the Yucatan Peninsula is a largely unexplored coastline where ancient Maya traders traveled in massive dugout canoes filled with goods from...

Observational constraints on the identification of shallow lunar magmatism : insights from floor-fractured craters

OpenAIRE

Jozwiak, Lauren; Head, James; Neumann, G. A.; Wilson, Lionel

2017-01-01

Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity so...

A Numerical Investigation into Low-Speed Impact Cratering Events

Science.gov (United States)

Schwartz, Stephen; Richardson, D. C.; Michel, P.

2012-10-01

Impact craters are the geological features most commonly observed on the surface of solid Solar System bodies. Crater shapes and features are crucial sources of information regarding past and present surface environments, and can provide indirect information about the internal structures of these bodies. In this study, we consider the effects of low-speed impacts into granular material. Studies of low-speed impact events are suitable for understanding the cratering process leading, for instance, to secondary craters. In addition, upcoming asteroid sample return missions will employ surface sampling strategies that use impacts into the surface by a projectile. An understanding of the process can lead to better sampling strategies. We use our implementation of the Soft-Sphere Discrete Element Method (SSDEM) (Schwartz et al. 2012, Granular Matter 14, 363-380) into the parallel N-body code PKDGRAV (cf. Richardson et al. 2011, Icarus 212, 427-437) to model the impact cratering process into granular material. We consider the effects of boundary conditions on the ejecta velocity profile and discuss how results relate to the Maxwell Z-Model during the crater growth phase. Cratering simulations are compared to those of Wada et al. 2006 (Icarus 180, 528-545) and to impact experiments performed in conjunction with Hayabusa 2. This work is supported in part by grants from the National Science Foundation under grant number AST1009579 and from the Office of Space Science of NASA under grant number NNX08AM39G. Part of this study resulted from discussions with the International Team (#202) sponsored by ISSI in Bern (Switzerland). Some simulations were performed on the YORP cluster administered by the Center for Theory and Computation of the Department of Astronomy at the University of Maryland in College Park and on the SIGGAM computer cluster hosted by the Côte d'Azur Observatory in Nice (France).

Search Results | Page 122 | IDRC - International Development ...

International Development Research Centre (IDRC) Digital Library (Canada)

System dynamics and GIS in the simulation of environmental change to coastal ... Extreme meteorological events and risk management in the Andes of Peru ... Traditional maize storage methods of Mayan farmers in Yucatan, Mexico ...

Crater Lake Controls on Volcano Stability: Insights From White Island, New Zealand

Science.gov (United States)

Hamling, Ian J.

2017-11-01

Many volcanoes around the world host summit crater lakes but their influence on the overall stability of the edifice remains poorly understood. Here I use satellite radar data acquired by TerraSAR-X from early 2015 to July 2017 over White Island, New Zealand, to investigate the interaction of the crater lake and deformation of the surrounding edifice. An eruption in April 2016 was preceded by a period of uplift within the crater floor and drop in the lake level. Modeling of the uplift indicates a shallow source located at ˜100 m depth in the vicinity of the crater lake, likely coinciding with the shallow hydrothermal system. In addition to the drop in the lake level, stress changes induced by the inflation suggest that the pressurization of the shallow hydrothermal system helped promote failure along the edge of the crater lake which collapsed during the eruption. After the eruption, and almost complete removal of the crater lake, large areas of the crater wall and lake edge began moving downslope at rates approaching 400 mm/yr. The coincidence between the rapid increase in the displacement rates and removal of the crater lake suggests that the lake provides a physical control on the stability of the surrounding edifice.

Role of impact cratering for Mars sample return

International Nuclear Information System (INIS)

Schultz, P.H.

1988-01-01

The preserved cratering record of Mars indicates that impacts play an important role in deciphering Martian geologic history, whether as a mechanism to modify the lithosphere and atmosphere or as a tool to sample the planet. The various roles of impact cratering in adding a broader understanding of Mars through returned samples are examined. Five broad roles include impact craters as: (1) a process in response to a different planetary localizer environment; (2) a probe for excavating crustal/mantle materials; (3) a possible localizer of magmatic and hydrothermal processes; (4) a chronicle of changes in the volcanic, sedimentary, atmospheric, and cosmic flux history; and (5) a chronometer for extending the geologic time scale to unsampled regions. The evidence for Earth-like processes and very nonlunar styles of volcanism and tectonism may shift the emphasis of a sampling strategy away from equally fundamental issues including crustal composition, unit ages, and climate history. Impact cratering not only played an important active role in the early Martian geologic history, it also provides an important tool for addressing such issues

Site characterization requirements for nuclear-cratering design

International Nuclear Information System (INIS)

Terhune, R.W.; Carlson, R.C.

1977-01-01

A material properties measurement program for the design of large engineering nuclear-excavation projects by computer calculation is presented. Material properties of the site and their relative effect on crater size are analyzed and ordered in relation to their importance in determining the overall cratering efficiency. The measurement program includes both in situ logging and laboratory measurement of core samples, together with the reason for each measurement and its use in the calculations

Contamination des eaux de puits traditionnels par les nitrates sur le ...

African Journals Online (AJOL)

SARAH

30 juin 2014 ... Objectif : La contamination des eaux souterraines par les nitrates est un ... Methodology and Results: the origin of nitrate water from traditional wells of Lobo's watershed was ...... 12 water supply wells, Yucatan, Mexico.

Crater Morphometry and Crater Degradation on Mercury: Mercury Laser Altimeter (MLA) Measurements and Comparison to Stereo-DTM Derived Results

Science.gov (United States)

Leight, C.; Fassett, C. I.; Crowley, M. C.; Dyar, M. D.

2017-01-01

Two types of measurements of Mercury's surface topography were obtained by the MESSENGER (MErcury Surface Space ENvironment, GEochemisty and Ranging) spacecraft: laser ranging data from Mercury Laser Altimeter (MLA) [1], and stereo imagery from the Mercury Dual Imaging System (MDIS) camera [e.g., 2, 3]. MLA data provide precise and accurate elevation meaurements, but with sparse spatial sampling except at the highest northern latitudes. Digital terrain models (DTMs) from MDIS have superior resolution but with less vertical accuracy, limited approximately to the pixel resolution of the original images (in the case of [3], 15-75 m). Last year [4], we reported topographic measurements of craters in the D=2.5 to 5 km diameter range from stereo images and suggested that craters on Mercury degrade more quickly than on the Moon (by a factor of up to approximately 10×). However, we listed several alternative explanations for this finding, including the hypothesis that the lower depth/diameter ratios we observe might be a result of the resolution and accuracy of the stereo DTMs. Thus, additional measurements were undertaken using MLA data to examine the morphometry of craters in this diameter range and assess whether the faster crater degradation rates proposed to occur on Mercury is robust.

Floor-fractured craters on the Moon: an evidence of past intrusive magmatic activity

Science.gov (United States)

Thorey, C.; Michaut, C.

2012-12-01

Floor-fractured lunar craters (FFC's) are a class of craters modified by post impact mechanisms. They are defined by distinctive shallow, often plate-like or convex floors, wide floor moats and radial, concentric and polygonal floor-fractures, suggesting an endogenous process of modification. Two main mechanisms have been proposed to account for such observations : 1) viscous relaxation and 2) spreading of magmatic intrusions at depth below the crater. Here, we propose to test the case of magmatic intrusions. We develop a model for the dynamics of magma spreading below an elastic crust with a crater-like topography and above a rigid horizontal surface. Results show first that the lithostatic pressure increase at the crater rim prevents the intrusion from spreading horizontally giving rise to intrusion thickening and to an uplift of the crater floor. Second, the deformation of the overlying crust exerts a strong control on the intrusion shape, and hence, on the nature of the crater floor uplift. As the deformation can only occur over a minimum flexural wavelength noted Λ, the intrusion shape shows a bell-shaped geometry for crater radius smaller than 3Λ, or a flat top with smooth edges for crater radius larger than 3Λ. For given crustal elastic properties, the crust flexural wavelength increases with the intrusion depth. Therefore, for a large intrusion depth or small crater size, we observe a convex uplift of the crater floor. On the contrary, for a small intrusion depth or large crater size, the crater floor undergoes a piston-like uplift and a circular moat forms just before the rim. The depth of the moat is controlled by the thickening of the crust at the crater rim. On the contrary to viscous relaxation models, our model is thus able to reproduce most of the features of FFC's, including small-scale features. Spreading of a magmatic intrusion at depth can thus be considered as the main endogenous mechanism at the origin of the deformations observed at FFC

East Part of Sapas Mons with Flooded Crater

Science.gov (United States)

1991-01-01

This Magellan image centered near 9.6 degrees north latitude, 189.5 degrees east longitude of an area 140 kilometers (87 miles) by 110 kilometers (68 miles) covers part of the eastern flank of the volcano Sapas Mons on the western edge of Atla Regio. The bright lobate features along the southern and the western part of the image, oriented in northeast to southwest directions, are lava flows that are rough at the 12.6 centimeter wavelength of the radar. These flows range in width from 5 kilometers to 25 kilometers (3 to 16 miles) with lengths of 50 kilometers to 100 kilometers (31 to 62 miles), extending off the area shown here. Additional radar-dark (smooth) flows are also present. The radar-bright linear structures in the northwest part of the image are interpreted to be faults and fractures possibly associated with the emplacement of magma in the subsurface. Located near the center of the image is a 20 kilometer (12 mile) diameter impact crater. This crater is superimposed on a northeast/southwest trending fracture while the southern part of the crater's ejecta blanket is covered by a 6 kilometer (4 mile) wide radar-bright lava flow. These relations indicate that the crater post dates an episode of fracturing and is older than the lava flows covering its southern edge. This is one of only a few places on Venus in which an impact crater is seen to be covered by volcanic deposits.

Floor-Fractured Craters on Ceres and Implications for Internal Composition and Processes

Science.gov (United States)

Buczkowski, D.; Schenk, P.; Scully, J. E. C.; Park, R. S.; Preusker, F.; Raymond, C. A.; Russell, C. T.

2016-12-01

Several of the impact craters on Ceres have patterns of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs) [1]. Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures, and have been classified into crater classes, Types 1 through 6, based on their morphometric properties [1,2]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater or floor shallowing due to viscous relaxation. However, the observation that the depth versus diameter (d/D) relationship of the FFCs is distinctly shallower than the same association for other lunar craters supports the hypotheses that the floor fractures form due to shallow magmatic intrusion under the crater [2]. We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. Large (>50 km) Ceres FFCs are most consistent with Type 1 lunar FFCs, having deep floors, central peaks, wall terraces, and radial and/or concentric fractures. Smaller craters on Ceres are more consistent with Type 4 lunar FFCs, having less-pronounced floor fractures and v-shaped moats separating the wall scarp from the crater interior. An analysis of the d/D ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. This suggests that the fractures on the floor of Ceres FFCs may be due the intrusion of a low-density material below the craters that is uplifting their floors. While on the Moon the intrusive material is hypothesized to be silicate magma, this is unlikely for Ceres. However, a cryovolcanic extrusive edifice has been identified on Ceres [3], suggesting that cryomagmatic intrusions could be responsible for the formation of the Ceres FFCs. References: [1] Schultz P. (1976) Moon, 15, 241-273 [2] Jozwiak L.M. et al (2015) JGR 117, doi: 10.1029/2012JE004134 [3] Ruesch O. et al (2016

Reproductive biology of Hechtia schottii, a dioecious Bromeliaceae, in Mexico

Directory of Open Access Journals (Sweden)

Ivón M Ramírez Morillo

2008-03-01

Full Text Available Hechtia schottii is a terrestrial, rosetofilous, dioecious, polycarpic succulent herb, that grows mainly in shrubby associations, and less frequently, in secondary low caducifolious forests, both on calcareous soils or limestone outcrops in Yucatan and Campeche States, Mexico. We studied phenology, floral and pollination biology, and breeding system at Calcehtok, Yucatan, during two flowering seasons. Plants bloom mainly during the dry season (November-April and disperse seeds during the rainy season (May-October. Both floral morphs have diurnal anthesis; pollen is removed ca. 1 h after anthesis starts and both floral morphs are visited by several insect species, especially bees, but results suggest that the introduced honey bee, Apis mellifera, is the pollinator. Controlled crossings show that the species is functionally dioecious and requires to be serviced by pollinators based on fruit setting only in unassisted cross pollination crosses. Rev. Biol. Trop. 56 (1: 279-289. Epub 2008 March 31.Hechtia schottii es una hierba terrestre, suculenta, rosetófila, dioica y policárpica, que crece en asociaciones arbustivas y selva baja caducifolia secundaria, ambos en suelos calcáreos o limosos. Estudiamos la fenología, la biología floral, reproductiva y de la polinización en una población en Calcehtok, Yucatán, México, durante dos estaciones de floración. Las plantas florecen principalmente en la época de secas (noviembre-abril y la dispersión de semillas es durante la estación de lluvias (mayo-octubre. Ambas formas (morphs florales tienen antesis diurna; el polen es removido ca. 1 h después del comienzo de la antesis y ambas formas florales son visitadas por varias especies de insectos, especialmente abejas, pero los resultados sugieren que la abeja introducida, Apis mellifera, es el polinizador. Cruces controlados muestran que la especie es funcionalmente dioica y que requiere de un polinizador, ya que solo produce frutos por polinizaci

Prediction of gamma exposure rates in large nuclear craters

Energy Technology Data Exchange (ETDEWEB)

Tami, Thomas M; Day, Walter C [U.S. Army Engineer Nuclear Cratering Group, Lawrence Radiation Laboratory, Livermore, CA (United States)

1970-05-15

In many civil engineering applications of nuclear explosives there is the need to reenter the crater and lip area as soon as possible after the detonation to carry out conventional construction activities. These construction activities, however, must be delayed until the gamma dose rate, or exposure rate, in and around the crater decays to acceptable levels. To estimate the time of reentry for post-detonation construction activities, the exposure rate in the crater and lip areas must be predicted as a function of time after detonation. An accurate prediction permits a project planner to effectively schedule post-detonation activities.

Enhancing Magnetic Interpretation Towards Meteorite Impact Crater at Bukit Bunuh, Perak, Malaysia

Science.gov (United States)

Nur Amalina, M. K. A.; Nordiana, M. M.; Saad, Rosli; Saidin, Mokhtar

2017-04-01

Bukit Bunuh is the most popular area of suspected meteorite impact crater. In the history of meteorite impact hitting the earth, Bukit Bunuh has complex crater of a rebound zone of positive magnetic anomaly value. This study area was located at Lenggong, Perak of peninsular Malaysia. The crater rim extended 5 km outwards with a clear subdued zone and immediately surround by a positive magnetic residual crater rim zone. A recent study was done to enhance the magnetic interpretation towards meteorite impact crater on this study area. The result obtained is being correlated with boreholes data to determine the range of local magnetic value. For the magnetic survey, the equipment used is Geometric G-856 Proton Precision magnetometers with the aids of other tools such as compass and GPS. In advance, the using of proton precision magnetometer causes it able in measures the magnetic fields separately within interval of second. Also, 18 boreholes are accumulated at study area to enhance the interpretation. The additional boreholes data had successfully described the structure of the impact crater at Bukit Bunuh in detailed where it is an eroded impact crater. Correlations with borehole records enlighten the results acquired from magnetic methods to be more reliable. A better insight of magnetic interpretation of Bukit Bunuh impact crater was done with the aid of geotechnical methods.

Detection and characterization of buried lunar craters with GRAIL data

Science.gov (United States)

Sood, Rohan; Chappaz, Loic; Melosh, Henry J.; Howell, Kathleen C.; Milbury, Colleen; Blair, David M.; Zuber, Maria T.

2017-06-01

We used gravity mapping observations from NASA's Gravity Recovery and Interior Laboratory (GRAIL) to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria. In this paper we focus on two prominent anomalies detected in the GRAIL data using the gravity gradiometry technique. Our detection strategy is applied to both free-air and Bouguer gravity field observations to identify gravitational signatures that are similar to those observed over buried craters. The presence of buried craters is further supported by individual analysis of regional free-air gravity anomalies, Bouguer gravity anomaly maps, and forward modeling. Our best candidate, for which we propose the informal name of Earhart Crater, is approximately 200 km in diameter and forms part of the northwestern rim of Lacus Somniorum, The other candidate, for which we propose the informal name of Ashoka Anomaly, is approximately 160 km in diameter and lies completely buried beneath Mare Tranquillitatis. Other large, still unrecognized, craters undoubtedly underlie other portions of the Moon's vast mare lavas.

Georadar Archaeological Prospection at the Historical Center of the Merida City, Yucatan, Mexico.

Science.gov (United States)

Barba, L.; Ortiz, A.; Blancas, J.; Ligorred, J.

2007-05-01

This paper shows the results of the georadar archaeological prospection carried out by the Laboratorio de Prospección Arqueologica from the Instituto de Investigaciones Antropologicas (IIA) of the Universidad Nacional Autonoma de Mexico (UNAM) verifing the archaeological and historical information recovered by the Departamento de Patrimonio Arqueologico y Natural del Municipio (DPANM) del Ayuntamiento de Merida en el Centro Histerico de la Ciudad de Merida under a joint project. The Historical Center of Merida has been classified as a "zone of high patrimonial value" after the topographic data and the historical documents recovered showed a long-term occupation, non interrupted since pre-Columbian times, when T Ho was the great capital of the northern region of the Maya area. For the rehabilitation program of the Historical Center of Merida has been a great priority to verify the existence of archaeological remains, pre-Columbian or colonial, under the present streets, gardens and plazas that could be damaged during the public infrastructure works. In order to prevent any damage to the patrimony a large georadar study was carried out pulling 200 and 400 MHz antennas of the GSSI SIR System 2 for 16500 m of the city streets, focusing in the areas where infrastructure works were imminent. After the analysis of the radar data it was possible to build up a map with the location of the most noticeable archaeological remains under the pavement of the streets that confirmed many of the topographic and documental proposed places. As a final result, by the first time a city government has available information to take present urban decisions, while preventing the damage to the archaeological patrimony of the same city.

Using Landsat 5 TM Data to Identify and Map Areas of Mangrove in Tulum, Quintana Roo, Mexico

Science.gov (United States)

Meachum, Samuel Standish

Mangroves are recognized worldwide as a major ecosystem that provides significant ecosystem services. They are threatened due to rising pressures from human overpopulation and economic development. The Caribbean Coast of Mexico's Yucatan Peninsula contains mangrove habitat that have been negatively impacted by the development of the region's tourist industry. However, little research has been done to map and quantify the extent of mangrove in the region. This study used remote sensing techniques to identify mangrove in the Municipality of Tulum located in Quintana Roo, and to produce an accurate vector based thematic map that inventories these areas. Anatomical differences were analyzed and related to high-resolution field spectral data for each mangrove species. A vector map of mangrove habitat, including areas of inland mangrove, was produced with an overall accuracy of 88%. The 19,262 ha. of mangrove identified by this study represents a 140% increase in area over previous studies.

Methane and sulfate dynamics in sediments from mangrove-dominated tropical coastal lagoons, Yucatan, Mexico

Science.gov (United States)

Chuang, P. C.; Young, Megan B.; Dale, Andrew W.; Miller, Laurence G.; Herrera-Silveira, Jorge A.; Paytan, Adina

2016-01-01

Porewater profiles in sediment cores from mangrove-dominated coastal lagoons (Celestún and Chelem) on the Yucatán Peninsula, Mexico, reveal the widespread coexistence of dissolved methane and sulfate. This observation is interesting since dissolved methane in porewaters is typically oxidized anaerobically by sulfate. To explain the observations we used a numerical transport-reaction model that was constrained by the field observations. The model suggests that methane in the upper sediments is produced in the sulfate reduction zone at rates ranging between 0.012 and 31 mmol m−2 d−1, concurrent with sulfate reduction rates between 1.1 and 24 mmol SO42− m−2 d−1. These processes are supported by high organic matter content in the sediment and the use of non-competitive substrates by methanogenic microorganisms. Indeed sediment slurry incubation experiments show that non-competitive substrates such as trimethylamine (TMA) and methanol can be utilized for microbial methanogenesis at the study sites. The model also indicates that a significant fraction of methane is transported to the sulfate reduction zone from deeper zones within the sedimentary column by rising bubbles and gas dissolution. The shallow depths of methane production and the fast rising methane gas bubbles reduce the likelihood for oxidation, thereby allowing a large fraction of the methane formed in the sediments to escape to the overlying water column.

Geomorphometric analysis of selected Martian craters using polar coordinate transformation

Science.gov (United States)

Magyar, Zoltán; Koma, Zsófia; Székely, Balázs

2016-04-01

Centrally symmetric landform elements are very common features on the surface of the planet Mars. The most conspicuous ones of them are the impact craters of various size. However, a closer look on these features reveals that they show often asymmetric patterns as well. These are partially related to the geometry of the trajectory of the impacting body, but sometimes it is a result of surface processes (e.g., freeze/thaw cycles, mass movements). Geomorphometric studies have already been carried out to reveal these pecularities. Our approach, the application of polar coordinate transformation (PCT) very sensitively enhances the non-radial and non-circular shapes. We used digital terrain models (DTMs) derived from the ESA Mars Express HRSC imagery. The original DTM or its derivatives (e.g. slope angle or aspect) are PCT transformed. We analyzed the craters inter alia with scattergrams in polar coordinates. The resulting point cloud can be used directly for the analysis, but in some cases an interpolation should be applied to enhance certain non-circular features (especially in case of smaller craters). Visual inspection of the crater slopes, coloured by the aspect, reveals smaller features. Some of them are processing artefacts, but many of them are related to local undulations in the topography or indications of mass movements. In many cases the undulations of the crater rim are due to erosional processes. The drawbacks of the technology are related to the uneven resolution of the projected image: features in the crater centre should be left out from the analysis because PCT has a low resolution around the projection center. Furthermore, the success of the PCT depends on the correct definition of the projection centre: erroneously centered images are not suitable for analysis. The PCT transformed images are also suitable for radial averaging and calculation of standard deviations, resulting in typical, comparable craters shapes. These studies may lead to a deeper

Relaxed impact craters on Ganymede: Regional variation and high heat flows

Science.gov (United States)

Singer, Kelsi N.; Bland, Michael T.; Schenk, Paul M.; McKinnon, William B.

2018-05-01

Viscously relaxed craters provide a window into the thermal history of Ganymede, a satellite with copious geologic signs of past high heat flows. Here we present measurements of relaxed craters in four regions for which suitable imaging exists: near Anshar Sulcus, Tiamat Sulcus, northern Marius Regio, and Ganymede's south pole. We describe a technique to measure apparent depth, or depth of the crater with respect to the surrounding terrain elevation. Measured relaxation states are compared with results from finite element modeling to constrain heat flow scenarios [see companion paper: Bland et al. (2017)]. The presence of numerous, substantially relaxed craters indicates high heat flows-in excess of 30-40 mW m-2 over 2 Gyr, with many small (heat flows. Crater relaxation states are bimodal for some equatorial regions but not in the region studied near the south pole, which suggests regional variations in Ganymede's thermal history.

Climate Change Scenarios in the Yucatan Peninsula to the year 2020

Science.gov (United States)

Orellana, R.; Espadas, C.; Conde, C.; Gay, C.

2010-03-01

A topic that has not been sufficiently analyzed is that the global warming is already affecting, and that it will have worst consequences in those regions with transitional climates, which have more sensibility to changes. This is the case of the Yucatan Peninsula which is semi-arid in their northern portion, and toward the south is subhumid, with a tendency to be more rainy toward the south. To have an estimation of what could happen in the future, the Intergovernmental Panel of Climatic Change (IPCC) has promoted the use of General Circulation Models (GCM), as well as the construction of possible emission scenarios that integrate different global and regional socioeconomic and demographic conditions, which project then a possible increase of emissions of greenhouse gases. These conditions are recognized as the decisive forces that will determine the variations of temperature and of precipitation. These projections are useful for the analysis of climatic change, and in particular for the assessments of the possible impacts and of the initiatives of adaptation and of mitigation that should be implemented in every country or region. In Mexico, most of those evaluations of climate change have been carried out generally at country level. For that reason, it is necessary to direct the research at regional level. In this work, we evaluated the potential climatic changes on the Yucatan Peninsula, considering the different changes of temperature and precipitation as a consequence for different emission scenarios and for the horizon 2020. To project the environmental responses of the region, we used as a base scenario the available temperature and precipitation information of the period 1961-1990, registered in 85 meteorological stations of the peninsula. With these data, we generated climate change scenarios using the outputs of four General Circulation Models: HADLEY, ECHAM, GFDL and CGCM, and the emission scenarios A1FI, A2, B1 and B2. The outputs of these models were

Mars Climate History: Insights From Impact Crater Wall Slope Statistics

Science.gov (United States)

Kreslavsky, Mikhail A.; Head, James W.

2018-02-01

We use the global distribution of the steepest slopes on crater walls derived from Mars Orbiter Laser Altimeter profile data to assess the magnitudes of degradational processes with latitude, altitude, and time. We independently confirm that Amazonian polar/high-latitude crater slope modification is substantial, but that craters in the low latitudes have essentially escaped significant slope modification since the Early Hesperian. We find that the total amount of crater wall degradation in the Late Noachian is very small in comparison to the circumpolar regions in the Late Amazonian, an observation that we interpret to mean that the Late Noachian climate was not characterized by persistent and continuous warm and wet conditions. A confirmed elevational zonality in degradation in the Early Hesperian is interpreted to mean that the atmosphere was denser than today.

Oblique view of crater Theophilus at northwest edge of Sea of Nectar

Science.gov (United States)

1969-01-01

An Apollo 11 oblique view of the large crater Theophilus located at the northwest edge of the Sea of Nectar on the lunar nearside. Theophilus is about 60 statute miles in diameter. the smooth area is Mare Nectaris. The smaller crater Madler, about 14 statute miles in diameter, is located to the east of Theophilus. Visible in the background are the large crater Fracastorius and the smaller crater Beaumont. The coordinates of the center of this photograph are 29 degrees east longitude and 11 degrees south latitude.

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

Science.gov (United States)

Grotzinger, J. P.; Gupta, S.; Malin, M. C.; Rubin, D. M.; Schieber, J.; Siebach, K.; Sumner, D. Y.; Stack, K. M.; Vasavada, A. R.; Arvidson, R. E.; Calef, F.; Edgar, L.; Fischer, W. F.; Grant, J. A.; Griffes, J.; Kah, L. C.; Lamb, M. P.; Lewis, K. W.; Mangold, N.; Minitti, M. E.; Palucis, M.; Rice, M.; Williams, R. M. E.; Yingst, R. A.; Blake, D.; Blaney, D.; Conrad, P.; Crisp, J.; Dietrich, W. E.; Dromart, G.; Edgett, K. S.; Ewing, R. C.; Gellert, R.; Hurowitz, J. A.; Kocurek, G.; Mahaffy, P.; McBride, M. J.; McLennan, S. M.; Mischna, M.; Ming, D.; Milliken, R.; Newsom, H.; Oehler, D.; Parker, T. J.; Vaniman, D.; Wiens, R. C.; Wilson, S. A.

2015-10-01

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

A case for archaeological reconnaissance of the Cabo Catoche-Porvenir region of the northeastern Yucatan Peninsula

Science.gov (United States)

Duller, Charles E.

1990-01-01

Satellite remote sensing technology is a tool with which archaeologists can, with relative ease, survey a region that is otherwise inaccessible. The northeast corner of the Yucatan Peninsula is such an area: it is isolated and sparsely inhabited, with dense forest and extensive swamps. From Cabo Catoche inland to Cancun, this remote corner of the ancient Maya world is virtually unexplored. Recent satellite images disclose evidence of past human activity in this unexplored region and offer a compelling argument for an archaeological reconnaissance.

[Study of enhancement effect of laser-induced crater on plasma radiation].

Science.gov (United States)

Chen, Jin-Zhong; Zhang, Xiao-Ping; Guo, Qing-Lin; Su, Hong-Xin; Li, Guang

2009-02-01

Single pulses exported from high-energy neodymium glass laser were used to act on the same position of soil sample surface repeatedly, and the plasma emission spectra generated from sequential laser pulse action were collected by spectral recording system. The experimental results show that the laser-induced soil plasma radiation was enhanced continuously under the confinement effect of the crater walls, and the line intensities and signal-to-background ratios both had different improvements along with increasing the number of acting pulses. The photographs of the plasma image and crater appearance were taken to study the plasma shape, laser-induced crater appearance, and the mass of the ablated sample. The internal mechanism behind that laser-induced crater enhanced plasma radiation was researched. Under the sequential laser pulse action, the forming plasma as a result enlarges gradually first, leading to distortion at the trail of plasma plume, and then, its volume diminishes slowly. And also, the color of the plasma changes from buff to white gradually, which implies that the temperature increases constantly. The laser-induced crater had a regular shape, that is, the diameter increased from its bottom to top gradually, thus forming a taper. The mass of the laser-ablated substance descends along with increasing the amount of action pulse. Atomization degree of vaporized substance was improved in virtue of the crater confinement effect, Fresnel absorption produced from the crater walls reflection, and the inverse bremsstrahlung, and the plasma radiation intensity was enhanced as a result.

The Quaternary Environmental Change in the Northeast of Quintana Roo, Mexico:The Paleopedological Proxies

Science.gov (United States)

Cabadas Báez, H. V.; Sedov, S.; Solleiro Rebolledo, E.

2010-03-01

The Yucatán Peninsula, located in the southeast part of Mexico, is characterized to be an extended and low altitude platform constituted by calcareous rocks. These rocks are mainly limestones formed since Cretaceous under a marine shelf environment. In the northeast coast, the youngest sediments are found, as products of Quaternary sea level changes. We studied various profiles in quarries, following north-south transect in the Yucatan coast, near Cancún. In such profiles a sequence consisting of different kind of calcareous sediments and a soil in the surface were analyzed. The base of the sequence is constituted by a petrocalcic horizon (calcrete) that was formed during the last interglacial, 125,000 yrs. ago. Under the calcrete, a transgressive sequence appears with calcareous sediments of lagoon and reef facies. The uppermost part consists of dune-like sediments with crossed stratification overlied by another petrocalcic horizon, maybe formed during the Pleistocene-Holocene transition. Soils of the Yucatan Peninsula are very thin, rich in organic matter, neutral and well structured, and their image do not correspond to that found in tropical soils (deep, strongly weathered, leached). They are directly associated with the dune sediment dissolution because are infilling the "space" generated by rock dissolution. Calcrete is always in the uppermost part, but is broken and crossed by soil. This sequence reveals some aspects of the environmental dynamic during Late Pleistocene-Holocene. First, a dryer environment is assumed due to the presence of the calcrete in the base. During the glacial period, a transgressive environment prevailed and marine calcareous sedimentation started. During Last Glacial Maximum a regression occurred, the climate was drier and the formation of dune sediments and another calcrete occurred. In the Holocene climate changed shifting toward more humid conditions that produced the modern soil cover, under tropical conditions.

Characterization of the Morphometry of Impact Craters Hosting Polar Deposits in Mercury's North Polar Region

Science.gov (United States)

Talpe Matthieu; Zuber, Maria T.; Yang, Di; Neumann, Gregory A.; Solomon, Sean C.; Mazarico, Erwan; Vilas, Faith

2012-01-01

Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet s poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury s north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45 N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (< 170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.

Cratering Studies in Thin Plastic Films

Science.gov (United States)

Shu, A. J.; Bugiel, S.; Gruen, E.; Hillier, J.; Horanyi, M.; Munsat, T. L.; Srama, R.

2013-12-01

Thin plastic films, such as Polyvinylidene Fluoride (PVDF), have been used as protective coatings or dust detectors on a number of missions including the Dust Counter and Mass Analyzer (DUCMA) instrument on Vega 1 and 2, the High Rate Detector (HRD) on the Cassini Mission, and the Student Dust Counter (SDC) on New Horizons. These types of detectors can be used on the lunar surface or in lunar orbit to detect dust grain size distributions and velocities. Due to their low power requirements and light weight, large surface area detectors can be built for observing low dust fluxes. The SDC dust detector is made up of a permanently polarized layer of PVDF coated on both sides with a thin layer (≈ 1000 Å) of aluminum nickel. The operation principle is that a micrometeorite impact removes a portion of the metal surface layer exposing the permanently polarized PVDF underneath. This causes a local potential near the crater changing the surface charge of the metal layer. The dimensions and shape of the crater determine the strength of the potential and thus the signal generated by the PVDF. The theoretical basis for signal interpretation uses a crater diameter scaling law which was not intended for use with PVDF. In this work, a crater size scaling law has been experimentally determined, and further simulation work is being done to enhance our understanding of the mechanisms of crater formation. LS-Dyna, a smoothed particle hydrodynamics (SPH) code from the Livermore Software Technology Corp. was chosen to simulate micrometeorite impacts. SPH is known to be well suited to the large deformities found in hypervelocity impacts. It is capable of incorporating key physics phenomena, including fracture, heat transfer, melting, etc. Furthermore, unlike Eulerian methods, SPH is gridless allowing large deformities without the inclusion of unphysical erosion algorithms. Material properties are accounted for using the Grüneisen Equation of State. The results of the SPH model can

Relaxed impact craters on Ganymede: Regional variation and high heat flows

Science.gov (United States)

Singer, Kelsi N.; Bland, Michael T.; Schenk, Paul M.; McKinnon, William B.

2018-01-01

Viscously relaxed craters provide a window into the thermal history of Ganymede, a satellite with copious geologic signs of past high heat flows. Here we present measurements of relaxed craters in four regions for which suitable imaging exists: near Anshar Sulcus, Tiamat Sulcus, northern Marius Regio, and Ganymede's south pole. We describe a technique to measure apparent depth, or depth of the crater with respect to the surrounding terrain elevation. Measured relaxation states are compared with results from finite element modeling to constrain heat flow scenarios [see companion paper: Bland et al. (2017)]. The presence of numerous, substantially relaxed craters indicates high heat flows—in excess of 30–40 mW m−2 over 2 Gyr, with many small (heat flows. Crater relaxation states are bimodal for some equatorial regions but not in the region studied near the south pole, which suggests regional variations in Ganymede's thermal history.

Geophysical Data Define Boundaries and Sub-Regions of the Northern Gulf of Mexico Basin: Structural Histories and Causes are Hypothesized.

Science.gov (United States)

Kinsland, G. L.

2017-12-01

Within the last several years new types of geophysical data of the southern margin of the North American Craton and the Northern Gulf of Mexico Basin (NGoMB) have become available, e.g., results from the USArray experiment, high resolution satellite gravity data of the GoM itself and new heat flow data. These data when combined with previously existing geophysical data (gravity, magnetic and seismic) and shallow structural data offer new insights into the boundaries and sub-regions of the NGoMB. I offer hypotheses for the development of the structures of the buried crust and upper mantle which cause these features. Of particular interest might be my suggestion that the NGoMB might have extended in a southeasterly direction prior to the counter-clockwise rotation of the Yucatan Peninsula which ultimately resulted in the GoM.

Ejecta from single-charge cratering explosions

Energy Technology Data Exchange (ETDEWEB)

Carlson, R H

1970-05-15

The objective was to obtain experimental data tracing the location of ejecta to its origin within the crater region. The experiment included ten high-explosive spherical charges weighing from 8 to 1000 pounds and detonated in a playa dry lake soil on the Tonopah Test Range. Each event included from 24 to 40 locations of distinctly different tracer material embedded in a plane in the expected crater region. Tracers consisted of glass, ceramic and bugle beads, chopped metal, and plastic wire. Results of this experiment yielded data on tracer dispersion as a function of charge weight, charge burial depth and tracer emplacement position. Tracer pattern parameters such as center-of-tracer mass, range to center-of-tracer mass, and angle to center-of-tracer mass were determined. There is a clear tendency for range (to center-of-tracer mass) and the size of the dispersion pattern to decrease as tracer emplacement depth increases. Increasing tracer emplacement depth and range tends to decrease the area over which tracers are dispersed on the ground surface. Tracers at the same scaled position relative to the charge were deposited closer to the crater (on a scaled basis) as charge weight was increased. (author)

Emerging deforestation trends in tropical dry forests ecoregions of Mexico and Central America

Science.gov (United States)

Portillo, C. A.; Cao, G.; Smith, V.

2015-12-01

Neotropical dry forests (TDF) have experienced an unprecedented deforestation that is leading to the loss of tropical biodiversity at a rapid pace, but information on deforestation dynamics in TDF is scarce. In this study, we present a sub-continental and national level assessment of TDF loss patterns in Mexico and Central America at high spatial and temporal resolution using remote sensing and GIS technologies. We used the Global Forest Change (GFC) dataset published by Hansen et al. (2013) which shows results from time-series analysis of Landsat images in characterizing global forest extent and change from 2000 through 2013. We analyzed forest loss within and around mapped TDF cover mapped by Portillo-Quintero et al. 2010. In order to minimize errors in source data, we overlaid a 25 x 25 km grid on top of the regional dataset and conducted a cell by cell and country by country inspection at multiple scales using high resolution ancillary data. We identified trends in the clustering of space-time TDF deforestation data using ArcGIS, categorizing trends in: new, consecutive, intensifying, persistent, diminishing, sporadic, oscillating and historical hotspots (high frequency of deforestation events) and cold spots (low frequency of deforestation). In general, the region is experiencing less frequent deforestation events with a higher number of intensifying and new cold spots across TDF landscapes. However, an important number of intensifying and persistent hotspots exist so no general trend in forest loss was detected for the period 2001-2013, except for El Salvador which shows a significant decreasing trend in forest loss. Mexico, Nicaragua, Honduras and Guatemala are the major sources of intensifying, persistent and new deforestation hot spots. These were identified in the southern pacific coast and the Yucatan Peninsula in Mexico, northwestern Guatemala, both western and eastern Honduras and around Lake Nicaragua in Nicaragua.

[Prevalence of high blood pressure and their association with body mass index in children between 5 and 11 years of Nahbalam, Yucatan].

Science.gov (United States)

Saury-Paredes, Leonel Alejandro

To determine the prevalence of high blood pressure in children aged between 5-11 years in the community of Nahbalam, Yucatan, and its association with the body mass index. A transversal study with children of the primary school "Lazaro Cardenas del Rio" was performed, measuring blood pressure, height, and weight of 259 girls and boys; systolic and/or diastolic blood pressure equal or greater than percentile 95 for gender, age, and height at three measures was considered as hypertension; prehypertension was considered as blood pressure equal or greater than percentile 90 but lower than percentile 95. A prevalence of 11.9% prehypertension and 6.1% hypertension was found. There is an association between hypertension and overweight and obesity (p ≤ 0.001). The prevalence of high blood pressure in children of the community of Nahbalam, Yucatan, is 18%. The children with overweight and obesity have an almost tenfold greater risk of hypertension than the eutrophic children (OR: 9.896; 95% CI: 2.738-35.764).

Potential for observing and discriminating impact craters and comparable volcanic landforms on Magellan radar images

International Nuclear Information System (INIS)

Ford, J.P.

1989-01-01

Observations of small terrestrial craters by Seasat synthetic aperture radar (SAR) at high resolution (approx. 25 m) and of comparatively large Venusian craters by Venera 15/16 images at low resolution (1000 to 2000 m) and shorter wavelength show similarities in the radar responses to crater morphology. At low incidence angles, the responses are dominated by large scale slope effects on the order of meters; consequently it is difficult to locate the precise position of crater rims on the images. Abrupt contrasts in radar response to changing slope (hence incidence angle) across a crater produce sharp tonal boundaries normal to the illumination. Crater morphology that is radially symmetrical appears on images to have bilateral symmetry parallel to the illumination vector. Craters are compressed in the distal sector and drawn out in the proximal sector. At higher incidence angles obtained with the viewing geometry of SIR-A, crater morphology appears less compressed on the images. At any radar incidence angle, the distortion of a crater outline is minimal across the medial sector, in a direction normal to the illumination. Radar bright halos surround some craters imaged by SIR-A and Venera 15 and 16. The brightness probably denotes the radar response to small scale surface roughness of the surrounding ejecta blankets. Similarities in the radar responses of small terrestrial impact craters and volcanic craters of comparable dimensions emphasize the difficulties in discriminating an impact origin from a volcanic origin in the images. Similar difficulties will probably apply in discriminating the origin of small Venusian craters, if they exist. Because of orbital considerations, the nominal incidence angel of Magellan radar at the center of the imaging swath will vary from about 45 deg at 10 deg N latitude to about 16 deg at the north pole and at 70 deg S latitude. Impact craters and comparable volcanic landforms will show bilateral symmetry

Henequén'ın Dönüşü, Bir Yeşil Lif İle Yucatan'da Karmaşık Bir Tarih

OpenAIRE

ANAYA, Yosi

2014-01-01

Meksika Mayaları ve Orta Amerika'nın önde gelen liflerinden birisi, sisal olarak bilinen Henequéndir. Sömürgecilik döneminin üretim merkezlerinden birisi olan Yucatan'ınadını alan Henequén, yüzyıllarca Yucatan Yarımadasının “Yeşil Altın”ı olarak bilindi. Yucatek ekonomisi, 20. yüzyıl boyunca ihtiyaç duyulan her türlü ip, halı,çuval ve kaba kumaşları sağlayan henequén tarlaları etrafında gelişti, yerleşti ve serpildi. 20. yüzyılda henequén lifi, daha ucuz fiyatlarla Madagaskar ve Ken...

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars.

Science.gov (United States)

Grotzinger, J P; Gupta, S; Malin, M C; Rubin, D M; Schieber, J; Siebach, K; Sumner, D Y; Stack, K M; Vasavada, A R; Arvidson, R E; Calef, F; Edgar, L; Fischer, W F; Grant, J A; Griffes, J; Kah, L C; Lamb, M P; Lewis, K W; Mangold, N; Minitti, M E; Palucis, M; Rice, M; Williams, R M E; Yingst, R A; Blake, D; Blaney, D; Conrad, P; Crisp, J; Dietrich, W E; Dromart, G; Edgett, K S; Ewing, R C; Gellert, R; Hurowitz, J A; Kocurek, G; Mahaffy, P; McBride, M J; McLennan, S M; Mischna, M; Ming, D; Milliken, R; Newsom, H; Oehler, D; Parker, T J; Vaniman, D; Wiens, R C; Wilson, S A

2015-10-09

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp). Copyright © 2015, American Association for the Advancement of Science.

Hypervelocity impact cratering calculations

Science.gov (United States)

Maxwell, D. E.; Moises, H.

1971-01-01

A summary is presented of prediction calculations on the mechanisms involved in hypervelocity impact cratering and response of earth media. Considered are: (1) a one-gram lithium-magnesium alloys impacting basalt normally at 6.4 km/sec, and (2) a large terrestrial impact corresponding to that of Sierra Madera.

Hydrodynamics of the groundwater-fed Sian Ka'an Wetlands, Mexico, From InSAR and SAR Data

DEFF Research Database (Denmark)

Gondwe, Bibi Ruth Neuman; Hong, S.; Wdowinski, S.

2008-01-01

The 5300 km2 pristine Sian Ka'an wetland in Mexico is fed entirely by groundwater from the karst aquifer of the Yucatan Peninsula. The area is undeveloped and hence difficult to access. The inflow through underground rivers and karst structures is hard to observe resulting in difficulties......-changes of the backscattered radar signal, which can be related to the water level changes in vegetated wetlands. SAR data reveals information of surface properties such as the degree of flooding through the amplitude of the backscattered signal. We used RADARSAT-1 InSAR and SAR data to form 36 interferograms and 13 flooding...... maps with 24 to 48 day intervals covering the time span of October 2006 to March 2008. The dataset has a high spatial resolution of ca. 20 to 60 m. Sian Ka'an consists of a mosaic of freshwater sloughs, canals, floodplains and brackish tidally-influenced areas. Throughout most of the year, water level...

The Mechanics of Peak-Ring Impact Crater Formation from the IODP-ICDP Expedition 364

Science.gov (United States)

Melosh, H.; Collins, G. S.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub impact crater is one of very few peak-ring impact craters on Earth. While small (less than 3 km on Earth) impact craters are typically bowl-shaped, larger craters exhibit central peaks, which in still larger (more than about 100 km on Earth) craters expand into mountainous rings with diameters close to half that of the crater rim. The origin of these peak rings has been contentious: Such craters are far too large to create in laboratory experiments and remote sensing of extraterrestrial examples has not clarified the mechanics of their formation. Two principal models of peak ring formation are currently in vogue, the "nested crater" model, in which the peak ring originates at shallow depths in the target, and the "dynamic collapse" model in which the peak ring is uplifted at the base of a collapsing, over-steepened central peak and its rocks originate at mid-crustal depths. IODP-ICDP Expedition 364 sought to elucidate, among other important goals, the mechanics of peak ring formation in the young (66 Myr), fresh, but completely buried Chicxulub impact crater. The cores from this borehole now show unambiguously that the rocks in the Chicxulub peak ring originated at mid-crustal depths, apparently ruling out the nested crater model. These rocks were shocked to pressures on the order of 10-35 GPa and were so shattered that their densities and seismic velocities now resemble those of sedimentary rocks. The morphology of the final crater, its structure as revealed in previous seismic imaging, and the results from the cores are completely consistent with modern numerical models of impact crater excavation and collapse that incorporate a model for post-impact weakening. Subsequent to the opening of a ca. 100 km diameter and 30 km deep transient crater, this enormous hole in the crust collapsed over a period of about 10 minutes. Collapse was enabled by movement of the underlying rocks, which briefly behaved in the manner of a high-viscosity fluid, a brittle

Phosphatised limestones and associated sediments from the western continental shelf of India

Digital Repository Service at National Institute of Oceanography (India)

Rao, V.P.; Natarajan, R.; Parthiban, G.; Mascarenhas, A.

Quaternary carbonate sediments: Rao, Ch.M., Paropkari~ A.L., Mascarenhas, A. and Murty, carbonate sediments and reefs, Yucatan shelf, Mexico. Am. P.S.N., 1987. Distribution of phosphorus and phosphatisa- Assoc. Pet. Geol. Mem., 11: 1-128. tion along...

Ceres' intriguing Occator crater and its faculae: formation and evolution

Science.gov (United States)

Buczkowski, D.; Scully, J. E. C.; Bowling, T.; Bu, C.; Castillo, J. C.; Jaumann, R.; Longobardo, A.; Nathues, A.; Neesemann, A.; Palomba, E.; Platz, T.; Quick, L. C.; Raponi, A.; Raymond, C. A.; Ruesch, O.; Russell, C. T.; Schenk, P.; Stein, N.

2017-12-01

Since March 2015, the Dawn spacecraft has orbited and explored Ceres, which is a dwarf planet and the largest object in the asteroid belt (radius 470 km). One of the most intriguing features on Ceres' surface is Occator crater, a 92-km-diameter impact crater that contains distinctive bright spots, called faculae, within its floor (Nathues et al., 2015; Russell et al., 2016; Schenk et al., 2017). Occator crater has been dated to 20-30 million years old (Nathues et al., 2017; Neesemann et al., 2017). The single scattering albedo of Occator's faculae is 0.67-0.80, which is greater than Ceres' average single scattering albedo of 0.09-0.11 (Li et al., 2016). The central facula is named Cerealia Facula, and is located in a 9 km wide and 700 m deep pit. There are also multiple additional faculae in the eastern crater floor, which are named the Vinalia Faculae. The faculae are mostly composed of sodium carbonate, are distinct from Ceres' average surface composition and are proposed to be the solid residues of crystallized brines (De Sanctis et al., 2016). The presence of such bright, apparently fresh, material on the surface of a dwarf planet that is billions of years old is intriguing, and indicates that active processes involving brines occurred within the geologically recent past. The Dawn Science Team has investigated whether the processes that formed the crater and the faculae are entirely endogenic, entirely exogenic or a combination of both. For example, the extensive lobate materials within the crater floor have been proposed to be impact melt, mass wasting deposits or cryolava flows (e.g. Buczkowski et al., 2017; Jaumann et al., 2017; Nathues et al., 2017; Schenk et al., 2017). Each possibility has the potential to provide fascinating insights into Ceres' evolution, including the potential for liquids within Ceres' interior today. The team's in-depth investigation of Occator crater will be presented in an upcoming special issue of the journal Icarus. This special

Effect of climate change on wind waves generated by anticyclonic cold front intrusions in the Gulf of Mexico

Science.gov (United States)

Appendini, Christian M.; Hernández-Lasheras, Jaime; Meza-Padilla, Rafael; Kurczyn, Jorge A.

2018-01-01

Anticyclonic cold surges entering the Gulf of Mexico (Nortes) generate ocean waves that disrupt maritime activities. Norte derived waves are less energetic than the devastating waves from tropical cyclones, but more frequent ( 22 events/year) and with larger spatial influence. Despite their importance, few studies characterize Nortes derived waves and assess the effects of climate change on their occurrence. This study presents a method to identify and characterize Nortes with relation to their derived waves in the Gulf of Mexico. We based the identification of Nortes on synoptic measurements of pressure differences between Yucatan and Texas and wind speed at different buoy locations in the Gulf of Mexico. Subsequently, we identified the events in the CFSR reanalysis (present climate) and the CNRM-M5 model for the present climate and the RCP 8.5 scenario. We then forced a wave model to characterize the wave power generated by each event, followed by a principal component analysis and classification by k-means clustering analysis. Five different Nortes types were identified, each one representing a characteristic intensity and area of influence of the Norte driven waves. Finally, we estimated the occurrence of each Norte type for the present and future climates, where the CNRM-M5 results indicate that the high-intensity events will be less frequent in a warming climate, while mild events will become more frequent. The consequences of such changes may provide relief for maritime and coastal operations because of reduced downtimes. This result is particularly relevant for the operational design of coastal and marine facilities.

Turbulent flow over craters on Mars: Vorticity dynamics reveal aeolian excavation mechanism

Science.gov (United States)

Anderson, William; Day, Mackenzie

2017-10-01

Impact craters are scattered across Mars. These craters exhibit geometric self-similarity over a spectrum of diameters, ranging from tens to thousands of kilometers. The late Noachian-early Hesperian boundary marks a dramatic shift in the role of mid-latitude craters, from depocenter sedimentary basins to aeolian source areas. At present day, many craters contain prominent layered sedimentary mounds with maximum elevations comparable to the rim height. The mounds are remnants of Noachian deposition and are surrounded by a radial moat. Large-eddy simulation has been used to model turbulent flows over synthetic craterlike geometries. Geometric attributes of the craters and the aloft flow have been carefully matched to resemble ambient conditions in the atmospheric boundary layer of Mars. Vorticity dynamics analysis within the crater basin reveals the presence of counterrotating helical vortices, verifying the efficacy of deflationary models put forth recently by Bennett and Bell [K. Bennett and J. Bell, Icarus 264, 331 (2016)], 10.1016/j.icarus.2015.09.041 and Day et al. [M. Day et al., Geophys. Res. Lett. 43, 2473 (2016)], 10.1002/2016GL068011. We show how these helical counterrotating vortices spiral around the outer rim, gradually deflating the moat and carving the mound; excavation occurs faster on the upwind side, explaining the radial eccentricity of the mounds relative to the surrounding crater basin.

Turbulent flow over craters on Mars: Vorticity dynamics reveal aeolian excavation mechanism.

Science.gov (United States)

Anderson, William; Day, Mackenzie

2017-10-01

Impact craters are scattered across Mars. These craters exhibit geometric self-similarity over a spectrum of diameters, ranging from tens to thousands of kilometers. The late Noachian-early Hesperian boundary marks a dramatic shift in the role of mid-latitude craters, from depocenter sedimentary basins to aeolian source areas. At present day, many craters contain prominent layered sedimentary mounds with maximum elevations comparable to the rim height. The mounds are remnants of Noachian deposition and are surrounded by a radial moat. Large-eddy simulation has been used to model turbulent flows over synthetic craterlike geometries. Geometric attributes of the craters and the aloft flow have been carefully matched to resemble ambient conditions in the atmospheric boundary layer of Mars. Vorticity dynamics analysis within the crater basin reveals the presence of counterrotating helical vortices, verifying the efficacy of deflationary models put forth recently by Bennett and Bell [K. Bennett and J. Bell, Icarus 264, 331 (2016)]ICRSA50019-103510.1016/j.icarus.2015.09.041 and Day et al. [M. Day et al., Geophys. Res. Lett. 43, 2473 (2016)]GPRLAJ0094-827610.1002/2016GL068011. We show how these helical counterrotating vortices spiral around the outer rim, gradually deflating the moat and carving the mound; excavation occurs faster on the upwind side, explaining the radial eccentricity of the mounds relative to the surrounding crater basin.

Wind-Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

Science.gov (United States)

Irwin, Rossman P.; Wray, James J.; Mest, Scott C.; Maxwell, Ted A.

2018-02-01

Ancient impact craters with wind-eroded layering on their floors provide a record of resurfacing materials and processes on early Mars. In a 54 km Noachian crater in Terra Sabaea (20.2°S, 42.6°E), eolian deflation of a friable, dark-toned layer up to tens of meters thick has exposed more resistant, underlying light-toned material. These layers differ significantly from strata of similar tone described in other regions of Mars. The light-toned material has no apparent internal stratification, and visible/near-infrared spectral analysis suggests that it is rich in feldspar. Its origin is ambiguous, as we cannot confidently reject igneous, pyroclastic, or clastic alternatives. The overlying dark-toned layer is probably a basaltic siltstone or sandstone that was emplaced mostly by wind, although its weak cementation and inverted fluvial paleochannels indicate some modification by water. Negative-relief channels are not found on the crater floor, and fluvial erosion is otherwise weakly expressed in the study area. Small impacts onto this crater's floor have exposed deeper friable materials that appear to contain goethite. Bedrock outcrops on the crater walls are phyllosilicate bearing. The intercrater plains contain remnants of a post-Noachian thin, widespread, likely eolian mantle with an indurated surface. Plains near Hellas-concentric escarpments to the north are more consistent with volcanic resurfacing. A 48 km crater nearby contains similar dark-over-light outcrops but no paleochannels. Our findings indicate that dark-over-light stratigraphy has diverse origins across Mars and that some dark-toned plains with mafic mineralogy are not of igneous origin.

Scientific Drilling of Impact Craters - Well Logging and Core Analyses Using Magnetic Methods (Invited)

Science.gov (United States)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Velasco-Villarreal, M.

2013-12-01

Drilling projects of impact structures provide data on the structure and stratigraphy of target, impact and post-impact lithologies, providing insight on the impact dynamics and cratering. Studies have successfully included magnetic well logging and analyses in core and cuttings, directed to characterize the subsurface stratigraphy and structure at depth. There are 170-180 impact craters documented in the terrestrial record, which is a small proportion compared to expectations derived from what is observed on the Moon, Mars and other bodies of the solar system. Knowledge of the internal 3-D deep structure of craters, critical for understanding impacts and crater formation, can best be studied by geophysics and drilling. On Earth, few craters have yet been investigated by drilling. Craters have been drilled as part of industry surveys and/or academic projects, including notably Chicxulub, Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake, Ries and El gygytgyn craters. Inclusion of continuous core recovery expanded the range of paleomagnetic and rock magnetic applications, with direct core laboratory measurements, which are part of the tools available in the ocean and continental drilling programs. Drilling studies are here briefly reviewed, with emphasis on the Chicxulub crater formed by an asteroid impact 66 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub crater has no surface expression, covered by a kilometer of Cenozoic sediments, thus making drilling an essential tool. As part of our studies we have drilled eleven wells with continuous core recovery. Magnetic susceptibility logging, magnetostratigraphic, rock magnetic and fabric studies have been carried out and results used for lateral correlation, dating, formation evaluation, azimuthal core orientation and physical property contrasts. Contributions of magnetic studies on impact

Reconstruction of precipitation variability in the Strait of Yucatan associated with latitudinal shifts in the position of the Intertropical Convergence Zone since the Last Glacial Maximum

Science.gov (United States)

Staines-Urías, Francisca; Seidenkrantz, Marit-Solveig; Fischel, Andrea; Kuijpers, Antoon

2017-04-01

The elemental composition of sediments from gravity core HOLOVAR11-03 provides a ca. 40 ka record of past climate variability in the Strait of Yucatan, between the Caribbean Sea and the Gulf of Mexico, a region where precipitation variability is determined by the seasonal position of the Intertropical Convergence Zone (ITCZ). Within this region, sea level pressure decreases and rainfall increases as the ITCZ moves north of the equator in response to increased solar insolation in the Northern Hemisphere during boreal summer. In contrast, as the ITCZ retracts southward towards the equator during boreal winter, rainfall diminishes and the regional sea level pressure gradient strengthens. On interannual, multidecadal and millennial timescales, fluctuations in the average latitudinal position of the ITCZ in response to insolation forcing modulate the intensity and duration of the seasonal regimens, determining average regional precipitation and, ultimately, the elemental composition of the marine sedimentary record. Regionally, higher titanium and iron content in marine sediments reflect greater terrigenous input from inland runoff, indicating greater precipitation, hence a more northerly position of the ITCZ. Correspondingly, Ti and Fe concentration data were used to reconstruct regional rainfall variability since the Last Glacial Maxima (LGM ˜24 cal ka BP). HOLOVAR11-03 age model (based on 4 AMS 14C dates obtained from multi-specific samples of planktic foraminifera) shows stable sedimentation rates in the area throughout the cored period. Nonetheless, higher terrestrial mineral input is observed since the LGM and all through the last glacial termination (24 to 12 cal ka BP), indicating a period of increased precipitation. In contrast, lower Ti and Fe values are typical for the period between 12 and 8 cal ka BP, indicating reduced precipitation. A positive trend characterizes the following interval, showing a return to wetter conditions lasting until 5 cal ka BP

Observations of an aeolian landscape: From surface to orbit in Gale Crater

Science.gov (United States)

Day, Mackenzie; Kocurek, Gary

2016-12-01

Landscapes derived solely from aeolian processes are rare on Earth because of the dominance of subaqueous processes. In contrast, aeolian-derived landscapes should typify Mars because of the absence of liquid water, the long exposure times of surfaces, and the presence of wind as the default geomorphic agent. Using the full range of available orbital and Mars Science Laboratory rover Curiosity images, wind-formed features in Gale Crater were cataloged and analyzed in order to characterize the aeolian landscape and to derive the evolution of the crater wind regime over time. Inferred wind directions show a dominance of regional northerly winds over geologic time-scales, but a dominance of topography-driven katabatic winds in modern times. Landscapes in Gale Crater show a preponderance of aeolian features at all spatial scales. Interpreted processes forming these features include first-cycle aeolian abrasion of bedrock, pervasive deflation, organization of available sand into bedforms, abundant cratering, and gravity-driven wasting, all of which occur over a background of slow physical weathering. The observed landscapes are proposed to represent a spectrum of progressive surface denudation from fractured bedrock, to retreating bedrock-capped mesas, to remnant hills capped by bedrock rubble, to desert pavement plains. This model of landscape evolution provides the mechanism by which northerly winds acting over ∼3 Ga excavated tens of thousands of cubic kilometers of material from the once sediment-filled crater, thus carving the intra-crater moat and exhuming Mount Sharp (Aeolis Mons). The current crater surface is relatively sand-starved, indicating that potential sediment deflation from the crater is greater than sediment production, and that most exhumation of Mount Sharp occurred in the ancient geologic past.

Single-charge craters excavated during subsurface high-explosive experiments at Big Black Test Site, Mississippi

International Nuclear Information System (INIS)

Woodruff, W.R.; Bryan, J.B.

1978-01-01

Single-charge and row-charge subsurface cratering experiments were performed to learn how close-spacing enhances single-crater dimensions. Our first experimental phase established cratering curves for 60-lb charges of the chemical explosive. For the second phase, to be described in a subsequent report, the Row-cratering experiments were designed and executed. This data report contains excavated dimensions and auxiliary data for the single-charge cratering experiments. The dimensions for the row-charge experiments will be in the other report. Significant changes in the soil's water content appeared to cause a variability in the excavated dimensions. This variability clouded the interpretation and application of the cratering curves obtained

In plain sight: the Chesapeake Bay crater ejecta blanket

Science.gov (United States)

Griscom, D. L.

2012-02-01

The discovery nearly two decades ago of a 90 km-diameter impact crater below the lower Chesapeake Bay has gone unnoted by the general public because to date all published literature on the subject has described it as "buried". To the contrary, evidence is presented here that the so-called "upland deposits" that blanket ∼5000 km2 of the U.S. Middle-Atlantic Coastal Plain (M-ACP) display morphologic, lithologic, and stratigraphic features consistent with their being ejecta from the 35.4 Ma Chesapeake Bay Impact Structure (CBIS) and absolutely inconsistent with the prevailing belief that they are of fluvial origin. Specifically supporting impact origin are the facts that (i) a 95 %-pure iron ore endemic to the upland deposits of southern Maryland, eastern Virginia, and the District of Columbia has previously been proven to be impactoclastic in origin, (ii) this iron ore welds together a small percentage of well-rounded quartzite pebbles and cobbles of the upland deposits into brittle sheets interpretable as "spall plates" created in the interference-zone of the CBIS impact, (iii) the predominantly non-welded upland gravels have long ago been shown to be size sorted with an extreme crater-centric gradient far too large to have been the work of rivers, but well explained as atmospheric size-sorted interference-zone ejecta, (iv) new evidence is provided here that ~60 % of the non-welded quartzite pebbles and cobbles of the (lower lying) gravel member of the upland deposits display planar fractures attributable to interference-zone tensile waves, (v) the (overlying) loam member of the upland deposits is attributable to base-surge-type deposition, (vi) several exotic clasts found in a debris flow topographically below the upland deposits can only be explained as jetting-phase crater ejecta, and (vii) an allogenic granite boulder found among the upland deposits is deduced to have been launched into space and sculpted by hypervelocity air friction during reentry. An

Mineralogical Diversity and Geology of Humboldt Crater Derived Using Moon Mineralogy Mapper Data

Science.gov (United States)

Martinot, M.; Besse, S.; Flahaut, J.; Quantin-Nataf, C.; Lozac'h, L.; van Westrenen, W.

2018-02-01

Moon Mineralogy Mapper (M3) spectroscopic data and high-resolution imagery data sets were used to study the mineralogy and geology of the 207 km diameter Humboldt crater. Analyses of M3 data, using a custom-made method for M3 spectra continuum removal and spectral parameters calculation, reveal multiple pure crystalline plagioclase detections within the Humboldt crater central peak complex, hinting at its crustal origin. However, olivine, spinel, and glass are observed in the crater walls and rims, suggesting these minerals derive from shallower levels than the plagioclase of the central peak complex. High-calcium pyroxenes are detected in association with volcanic deposits emplaced on the crater's floor. Geologic mapping was performed, and the age of Humboldt crater's units was estimated from crater counts. Results suggest that volcanic activity within this floor-fractured crater spanned over a billion years. The felsic mineralogy of the central peak complex region, which presumably excavated deeper material, and the shallow mafic minerals (olivine and spinel) detected in Humboldt crater walls and rim are not in accordance with the general view of the structure of the lunar crust. Our observations can be explained by the presence of a mafic pluton emplaced in the anorthositic crust prior to the Humboldt-forming impact event. Alternatively, the excavation of Australe basin ejecta could explain the observed mineralogical detections. This highlights the importance of detailed combined mineralogical and geological remote sensing studies to assess the heterogeneity of the lunar crust.

Mineralogical Diversity and Geology of Humboldt Crater Derived Using Moon Mineralogy Mapper Data.

Science.gov (United States)

Martinot, M; Besse, S; Flahaut, J; Quantin-Nataf, C; Lozac'h, L; van Westrenen, W

2018-02-01

Moon Mineralogy Mapper (M 3 ) spectroscopic data and high-resolution imagery data sets were used to study the mineralogy and geology of the 207 km diameter Humboldt crater. Analyses of M 3 data, using a custom-made method for M 3 spectra continuum removal and spectral parameters calculation, reveal multiple pure crystalline plagioclase detections within the Humboldt crater central peak complex, hinting at its crustal origin. However, olivine, spinel, and glass are observed in the crater walls and rims, suggesting these minerals derive from shallower levels than the plagioclase of the central peak complex. High-calcium pyroxenes are detected in association with volcanic deposits emplaced on the crater's floor. Geologic mapping was performed, and the age of Humboldt crater's units was estimated from crater counts. Results suggest that volcanic activity within this floor-fractured crater spanned over a billion years. The felsic mineralogy of the central peak complex region, which presumably excavated deeper material, and the shallow mafic minerals (olivine and spinel) detected in Humboldt crater walls and rim are not in accordance with the general view of the structure of the lunar crust. Our observations can be explained by the presence of a mafic pluton emplaced in the anorthositic crust prior to the Humboldt-forming impact event. Alternatively, the excavation of Australe basin ejecta could explain the observed mineralogical detections. This highlights the importance of detailed combined mineralogical and geological remote sensing studies to assess the heterogeneity of the lunar crust.

Testing models for the formation of the equatorial ridge on Iapetus via crater counting

Science.gov (United States)

Damptz, Amanda L.; Dombard, Andrew J.; Kirchoff, Michelle R.

2018-03-01

Iapetus's equatorial ridge, visible in global views of the moon, is unique in the Solar System. The formation of this feature is likely attributed to a key event in the evolution of Iapetus, and various models have been proposed as the source of the ridge. By surveying imagery from the Cassini and Voyager missions, this study aims to compile a database of the impact crater population on and around Iapetus's equatorial ridge, assess the relative age of the ridge from differences in cratering between on ridge and off ridge, and test the various models of ridge formation. This work presents a database that contains 7748 craters ranging from 0.83 km to 591 km in diameter. The database includes the study area in which the crater is located, the latitude and longitude of the crater, the major and minor axis lengths, and the azimuthal angle of orientation of the major axis. Analysis of crater orientation over the entire study area reveals that there is no preference for long-axis orientation, particularly in the area with the highest resolution. Comparison of the crater size-frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation. One possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population. Finally, the compiled results are used to examine each ridge formation hypothesis. Based on these results, a model of ridge formation via a tidally disrupted sub-satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population.

Geologic Structures in Crater Walls on Vesta

Science.gov (United States)

Mittlefehldt, David W.; Beck, A. W.; Ammannito, E.; Carsenty, U.; DeSanctis, M. C.; LeCorre, L.; McCoy, T. J.; Reddy, V.; Schroeder, S. E.

2012-01-01

The Framing Camera (FC) on the Dawn spacecraft has imaged most of the illuminated surface of Vesta with a resolution of apporpx. 20 m/pixel through different wavelength filters that allow for identification of lithologic units. The Visible and Infrared Mapping Spectrometer (VIR) has imaged the surface at lower spatial resolution but high spectral resolution from 0.25 to 5 micron that allows for detailed mineralogical interpretation. The FC has imaged geologic structures in the walls of fresh craters and on scarps on the margin of the Rheasilvia basin that consist of cliff-forming, competent units, either as blocks or semi-continuous layers, hundreds of m to km below the rims. Different units have different albedos, FC color ratios and VIR spectral characteristics, and different units can be juxtaposed in individual craters. We will describe different examples of these competent units and present preliminary interpretations of the structures. A common occurrence is of blocks several hundred m in size of high albedo (bright) and low albedo (dark) materials protruding from crater walls. In many examples, dark material deposits lie below coherent bright material blocks. In FC Clementine color ratios, bright material is green indicating deeper 1 m pyroxene absorption band. VIR spectra show these to have deeper and wider 1 and 2 micron pyroxene absorption bands than the average vestan surface. The associated dark material has subdued pyroxene absorption features compared to the average vestan surface. Some dark material deposits are consistent with mixtures of HED materials with carbonaceous chondrites. This would indicate that some dark material deposits in crater walls are megabreccia blocks. The same would hold for bright material blocks found above them. Thus, these are not intact crustal units. Marcia crater is atypical in that the dark material forms a semi-continuous, thin layer immediately below bright material. Bright material occurs as one or more layers. In

Assessment of human activities impact on groundwater quality discharging into a reef lagoon

Science.gov (United States)

Rebolledo-Vieyra, M.; Hernandez, L.; Paytan, A.; Merino-Ibarra, M.; Lecossec, A.; Soto, M.

2010-03-01

The Eastern coast of the Yucatan Peninsula has the fastest growth rate in Mexico and groundwater is the only source of drinking water in the region. The consequences of the lack of proper infrastructure to collect and treat wastewater and the impact of human activities on the quality of groundwater are addressed. The groundwater in the coastal aquifer of Quintana Roo (SE Mexico) discharges directly into the ocean (Submarine Groundwater Discharges). In addition, the coral reef of the Eastern Yucatan Peninsula is part of the Mesoamerican Coral Reef System, one of the largest in the world. The interaction of the reef-lagoon hydraulics with the coastal aquifer of Puerto Morelos (NE Yucatan Peninsula), and a major input of NH4, SO4, SiO2, as a consequence of the use of septic tanks and the lack of modern wastewater treatment plants are presented. A conceptual model of the coastal aquifer was developed, in order to explain how the human activities are impacting directly on the groundwater quality that, potentially, will have a direct impact on the coral reef. The protection and conservation of coral reefs must be directly related with a policy of sound management of coastal aquifers and wastewater treatment.

A maternal Western diet during gestation and lactation modifies offspring’s microbiota activity, blood lipid levels, cognitive responses, and hippocampal neurogenesis in Yucatan pigs

NARCIS (Netherlands)

Val-Laillet, David; Besson, M.; Guérin, S.; Coquery, N.; Randuineau, G.; Kanzari, A.; Quesnel, H.; Bonhomme, N.; Bolhuis, J.E.; Kemp, B.; Blat, S.; Huërou-Luron, Le I.; Clouard, C.M.

2017-01-01

A suboptimal early nutritional environment (i.e., excess of energy, sugar, and fat intake) can increase susceptibility to diseases and neurocognitive disorders. The purpose of this study was to investigate in nonobese Yucatan minipigs (Sus scrofa) the impact of maternal diet [standard (SD) vs.

Underwater research methods for study of nuclear bomb craters, Enewetak, Marshall Islands

Science.gov (United States)

Shinn, E.A.; Halley, R.B.; Kindinger, J.L.; Hudson, J.H.; Slate, R.A.

1990-01-01

Three craters, created by the explosion of nuclear fusion devices, were mapped, sampled, core drilled and excavated with airlifts at Enewetak Atoll in the Marshall Islands by using scuba and a research submersible. The craters studied were Mike, Oak, and Koa. Tests took place near sea level at the transition between lithified reef flat and unlithified lagoonal sediments, where water depth ranged from 1 to 4 m. Craters produced by the blasts ranged from 30 to 60 m in depth. The purpose of our study was to determine crater diameter and depth immediately after detonation. Observations of submerged roadways and testing structures and upturned crater rims similar to those characteristic of meteor impacts indicate that the initial, or transient, craters were smaller than their present size. At some later time, while the area was too radioactive for direct examination, the sides of the craters slumped owing to dewatering of under lying pulverized rock. Core drilling of crater margins with a diver-operated hydraulic coring device provided additional data. On the seaward margin of the atoll, opposite Mike, a large portion of the atoll rim approximately the size of a city block had slumped into the deep ocean, leaving a clean vertical rock section more than 400m high. An abundance of aggressive grey reef sharks displaying classic territorial behavior prevented use of scuba at the Mike slump site. The two-person submersible R.V. Delta provided protection and allowed observations down to 300 m. During the 6-week period of study, we made more than 300 scuba and 275 submersible dives. Mapping was with side scan sonar and continuous video sweeps supplemented by tape-recorded verbal descriptions made from within the submersible. A mini-ranger navigation system linked to the submersible allowed plotting of bottom features, depth and sediment type with spatial accuracy to within 2 m.

Blood Feeding Status, Gonotrophic Cycle and Survivorship of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) Caught in Churches from Merida, Yucatan, Mexico.

Science.gov (United States)

Baak-Baak, C M; Ulloa-Garcia, A; Cigarroa-Toledo, N; Tzuc Dzul, J C; Machain-Williams, C; Torres-Chable, O M; Navarro, J C; Garcia-Rejon, J E

2017-12-01

Blood-feeding status, gonotrophic cycle, and survival rates of Aedes (Stegmyia) aegypti (L.) was investigated in catholic churches from Merida, Yucatan. Female Ae. aegypti were caught using backpack aspirator during 25 consecutive days in rainy (2015) and dry season (2016). Blood-feeding status was determined by external examination of the abdomen and classified as unfed, fed, and gravid. Daily changes in the parous-nulliparous ratio were recorded, and the gonotrophic cycle length was estimated by a time series analysis. Also, was observed the vitellogenesis to monitoring egg maturity. In total, 408 females Ae. aegypti were caught, and there was a significant difference in the number of females collected per season (Z = -6.729, P ≤ 0.05). A great number was caught in the rainy season (n = 329). In the dry season, 79 females were caught, which the fed females were twice greatest than the unfed. The length of gonotrophic cycle was estimated on the base of a high correlation coefficient value appearing every 4 days in rainy at 26.7 ± 1.22°C, and 3 days in dry season at 29.8 ± 1.47°C. The daily survival rate of the Ae. aegypti population was higher in both seasons, 0.94 and 0.93 for the rainy and dry season, respectively. The minimum time estimated for developing mature eggs after blood feeding was similar in both seasons (3.5 days in rainy versus 3.25 days in dry). The measurement of the vectorial capacity of Ae. aegypti in catholic churches could help to understand the dynamics of transmission of arboviruses in sites with high human aggregation.

Celebrating the diversity of biogeographical research

DEFF Research Database (Denmark)

Nogues-Bravo, D.; Rahbek, C.

2010-01-01

Biogeography Society took place in Merida on the Yucatan Peninsula, Mexico. Ecography provided financial support, acting as the sponsor of the Symposium of Extinction Biogeography and contributing to student travel awards. In addition, Ecography was the officially designated journal for publishing some...

Crater size-frequency distributions and a revised Martian relative chronology

International Nuclear Information System (INIS)

Barlow, N.G.

1988-01-01

A relative plotting technique is applied to Viking 1:2M photomosaics of 25,826 Martian craters of diameter greater than 8 km and age younger than that of the Martian surface. The size-frequency distribution curves are calculated and analyzed in detail, and the results are presented in extensive tables and maps. It is found that about 60 percent of the crater-containing lithologic units, including many small volcanoes and the ridged planes, were formed during the heavy-bombardment period (HBP), while 40 percent arose after the HBP. Wide region-to-region variation in the crater density is noted, and localized age estimates are provided. 42 references

Proceedings of the Geophysical Laboratory/Lawrence Radiation Laboratory Cratering Symposium

Energy Technology Data Exchange (ETDEWEB)

Nordyke, Milo D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

1961-10-01

The geological papers in this morning's session will deal descriptively with surficial features and end products of impact craters caused by meteorite falls. Such items as breccia, structural deformation, normal and inverse stratigraphy, glass (fused rock), and coesite will frequently be mentioned. Meteor and explosion crater data are presented.

Parameters critical to the morphology of fluidization craters

Science.gov (United States)

Siegal, B. S.; Gold, D. P.

1973-01-01

In order to study further the role of fluidization on the moon, a laboratory investigation was undertaken on two particulate material size fractions to determine the effect of variables, such as, duration of gas streaming, gas pressure, and 'regolith' thickness on the morphology of fluidization craters. A 3.175-mm cylindrical vent was used to simulate a gas streaming conduit. Details of the fluidization chamber are discussed together with questions of experimental control, aspects of nomenclature, crater measurements, and the effect of variables.

Remote Sensing Observations and Numerical Simulation for Martian Layered Ejecta Craters

Science.gov (United States)

Li, L.; Yue, Z.; Zhang, C.; Li, D.

2018-04-01

To understand past Martian climates, it is important to know the distribution and nature of water ice on Mars. Impact craters are widely used ubiquitous indicators for the presence of subsurface water or ice on Mars. Remote sensing observations and numerical simulation are powerful tools for investigating morphological and topographic features on planetary surfaces, and we can use the morphology of layered ejecta craters and hydrocode modeling to constrain possible layering and impact environments. The approach of this work consists of three stages. Firstly, the morphological characteristics of the Martian layered ejecta craters are performed based on Martian images and DEM data. Secondly, numerical modeling layered ejecta are performed through the hydrocode iSALE (impact-SALE). We present hydrocode modeling of impacts onto targets with a single icy layer within an otherwise uniform basalt crust to quantify the effects of subsurface H2O on observable layered ejecta morphologies. The model setup is based on a layered target made up of a regolithic layer (described by the basalt ANEOS), on top an ice layer (described by ANEOS equation of H2O ice), in turn on top of an underlying basaltic crust. The bolide is a 0.8 km diameter basaltic asteroid hitting the Martian surface vertically at a velocity of 12.8 km/s. Finally, the numerical results are compared with the MOLA DEM profile in order to analyze the formation mechanism of Martian layered ejecta craters. Our simulations suggest that the presence of an icy layer significantly modifies the cratering mechanics, and many of the unusual features of SLE craters may be explained by the presence of icy layers. Impact cratering on icy satellites is significantly affected by the presence of subsurface H2O.

Lead from hunting activities and its potential environmental threat to wildlife in a protected wetland in Yucatan, Mexico.

Science.gov (United States)

Arcega-Cabrera, Flor; Noreña-Barroso, Elsa; Oceguera-Vargas, Ismael

2014-02-01

This study provides insights into the status of lead in the protected wetland of El Palmar, located on the northwestern littoral of the Yucatan Peninsula. This reserve is ecologically and economically important because it provides feeding and breeding habitats for many species, as well as being an ecotourism destination (especially for bird watching). Although it is a protected area, duck species are heavily hunted within the reserve during the winter. As a result, animals feeding or living in sediments could be exposed to anthropogenic lead. Total lead and its geochemical fractionated forms were measured in sediment cores from six selected sites in "El Palmar" wetland, during pre- and post-hunting seasons, to approximate the potential environmental threat (especially for benthonic living/feeding organisms). Anthropogenic lead concentrations detected in soil cores ranged from below the minimum infaunal community effect level (30.24 μg g(-1)) during the pre-hunting season, to bordering the probable infaunal community effect level (112.18 μg g(-1)) during the post-hunting season, according to SquiiRTs NOAA guidelines. Yet, these results were lower than expected based on the intensity of hunting. Consequently, this article explores the possibility that the lower than expected lead concentration in sediments results from (1) degradation of shot and transformation to soluble or particulate forms; or (2) ingestion of lead shot by benthic and other lacustrine species living in the protected area. Geochemical fractionation of lead demonstrated that in the top 6 cm of the soil column at heavily active hunting sites (EP5 and EP6), lead was associated with the lithogenic fraction (average 45 percent) and with the organic fraction (average 20 percent). Bioavailable lead (sum of lead adsorbed to the carbonates, Fe/Mn oxyhydroxides and organic fractions) in sediments was lower than 50 percent for the heavily active hunting areas and higher for the rest of the sites

An optical laser device for mapping 3D geometry of underwater karst structures: first tests in the Ox BelHa system, Yucatan, Mexico; Un dispositivo laser optico para la cartografia 3D de la geometria de estructuras karsticas submarinas: primeros resultados en el sistema de Ox BelHa, Yucatan, Mexico

Energy Technology Data Exchange (ETDEWEB)

Schiller, A.; Renard, P.

2016-07-01

In the course of extended hydrological studies in the coastal Karst plain of Yucatan, near the town of Tulum amongst others, a novel laser scanning device was developed and applied for the acquisition of the 3d-geometry of ground water conduits. The method is derived from similar industrial systems and for the first time adapted to the specific measurement conditions in underwater cave systems. The device projects a laser line over the whole perimeter at a certain position. This line represents the intersection of a plane with the cave walls. The line is imaged with a wide angle camera system. Through proper design and calibration of the device it is possible to derive the true scale geometry of the perimeter via special image processing techniques. By acquiring regularly spaced images it is possible to reconstruct the true scale and 3 d-shape of a tunnel through the incorporation of location and attitude data. In a first test in the Ox Bel Ha under-water cave system, about 800 metres of tunnels have been scanned down to water depths of 20 metres. The raw data is further interpolated using the ODSIM-algorithm in order to delineate the 3D geometry of the cave system. The method provides easy, operable acquisition of the 3-D geometry of caves in clear water with superior resolution and speed and significantly facilitates the measurement in underwater tunnels as well as in dry tunnels. The data gathered represents crucial input to the study of the state, dynamics and genesis of the complex karst water regime. (Author)

Surf Zone Sediment Size Variation, Morphodynamics, and Hydrodynamics During Sea/Land Breeze and El-Norte Storm in Sisal, Yucatan, Mexico

Science.gov (United States)

Alrushaid, T.; Figlus, J.; Torres-Freyermuth, A.; Puleo, J. A.; Dellapenna, T. M.

2016-02-01

Coastlines around the world are under ever-increasing pressure due to population trends, commerce, and geophysical processes like tropical storms and erosion. This multi-institutional field campaign was conducted to improve our understanding of complex nearshore processes under varying forcing conditions on a microtidal, sandy beach located in Sisal, Yucatan from 3/27 to 4/12/2014. Hydrodynamics, morphodynamics, and textural variability were investigated during: (1) a cold front event (referred to as El-Norte); (2) land breeze (LB); and (3) sea breeze (SB). The instrumentation layout included three surf/swash zone cross-shore transects where water elevation, suspended sediment concentration, bed load, and current velocities were measured, as well as several offshore ADCP for hydrodynamic measurements. TKE, τb, ɛ and were estimated using the data obtained from surf zone ADV. In addition, Hs and Tsin the surf zone were computed using measurements from ADV pressure sensors, while a separate pressure transducer was used to obtain water free-surface elevation within the swash zone. During SB cycles the study area experienced wind velocities reaching up to 12ms-1, and 15ms-1 during El-Norte. Elevated wind stress during El-Norte resulted in Hs of 1.5m and 0.6m in water depths of 10m and 0.4m, respectively. Surface sediment grab samples during SB/LB cycles showed that the swash zone had a moderately well sorted distribution with a mean grain size of 0.5mm, while poor sorting and a mean grain size of 0.7mm were found during El-Norte. Additionally, measured bathymetry data showed evidence for offshore sandbar migration during strong offshore currents (0.4ms-1) during El-Norte, while onshore sandbar migration was evident during SB/LB periods (0.3ms-1 and 0.1ms-1, respectively). This study highlights how different weather forcing conditions affect hydrodynamics, morphodynamics, and textural variability on a sandy beach. Aside from furthering our knowledge on these complex

A novel thermo-hydraulic coupling model to investigate the crater formation in electrical discharge machining

Science.gov (United States)

Tang, Jiajing; Yang, Xiaodong

2017-09-01

A novel thermo-hydraulic coupling model was proposed in this study to investigate the crater formation in electrical discharge machining (EDM). The temperature distribution of workpiece materials was included, and the crater formation process was explained from the perspective of hydrodynamic characteristics of the molten region. To better track the morphology of the crater and the movement of debris, the level-set method was introduced in this study. Simulation results showed that the crater appears shortly after the ignition of the discharge, and the molten material is removed by vaporizing in the initial stage, then by splashing at the following time. The driving force for the detachment of debris in the splashing removal stage comes from the extremely large pressure difference in the upper part of the molten region, and the morphology of the crater is also influenced by the shearing flow of molten material. It was found that the removal ratio of molten material is only about 7.63% under the studied conditions, leaving most to form the re-solidification layer on the surface of the crater. The size of the crater reaches the maximum at the end of discharge duration then experiences a slight reduction because of the reflux of molten material after the discharge. The results of single pulse discharge experiments showed that the morphologies and sizes between the simulation crater and actual crater are good at agreement, verifying the feasibility of the proposed thermo-hydraulic coupling model in explaining the mechanisms of crater formation in EDM.

The isostatic state of Mead crater

Science.gov (United States)

Banerdt, W. B.; Konopliv, A. S.; Rappaport, N. J.; Sjogren, W. L.; Grimm, R. E.; Ford, P. G.

1994-01-01

We have analyzed high-resolution Magellan Doppler tracking data over Mead crater, using both line-of-sight and spherical harmonic methods, and have found a negative gravity anomaly of about 4-5 mgal (at spacecraft altitude, 182 km). This is consistent with no isostatic compensation of the present topography; the uncertainty in the analysis allows perhaps as much as 30% compensation at shallow dpeths (approximately 25 km). This is similar to observations of large craters on Earth, which are not generally compensated, but contrasts with at least some lunar basins which are inferred to have large Moho uplifts and corresponding positive Bouguer anomalies. An uncompensated load of this size requires a lithosphere with an effective elastic lithosphere thickness greater than 30 km. In order for the crust-mantle boundary not to have participated in the deformation associated with the collapse of the transient cavity during the creation of the crater, the yield strength near the top of the mantle must have been significantly higher on Earth and Venus than on the Moon at the time of basin formation. This might be due to increased strength against frictional sliding at the higher confining pressures within the larger planets. Alternatively, the thinner crusts of Earth and Venus compared to that of the Moon may result in higher creep strength of the upper mantle at shallower depths.

Crater formation by single ions, cluster ions and ion "showers"

CERN Document Server

Djurabekova, Flyura; Timko, Helga; Nordlund, Kai; Calatroni, Sergio; Taborelli, Mauro; Wuensch, Walter

2011-01-01

The various craters formed by giant objects, macroscopic collisions and nanoscale impacts exhibit an intriguing resemblance in shapes. At the same time, the arc plasma built up in the presence of sufficiently high electric fields at close look causes very similar damage on the surfaces. Although the plasma–wall interaction is far from a single heavy ion impact over dense metal surfaces or the one of a cluster ion, the craters seen on metal surfaces after a plasma discharge make it possible to link this event to the known mechanisms of the crater formations. During the plasma discharge in a high electric field the surface is subject to high fluxes (~1025 cm-2s-1) of ions with roughly equal energies typically of the order of a few keV. To simulate such a process it is possible to use a cloud of ions of the same energy. In the present work we follow the effect of such a flux of ions impinging the surface in the ‘‘shower’’ manner, to find the transition between the different mechanisms of crater formati...

Observational Constraints on the Identification of Shallow Lunar Magmatism: Insights from Floor-Fractured Craters

Science.gov (United States)

Jozwiak, L. M.; Head, J. W., III; Neumann, G. A.; Wilson, L.

2016-01-01

Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity solution from GRAIL and also a degree 100-600 band-filtered Bouguer gravity solution. The low-magnitude of anomalies arising from shallow magmatic intrusions makes identification using unfiltered Bouguer gravity solutions inconclusive. The observed anomalies in the degree 100-600 Bouguer gravity solution are spatially heterogeneous, although there is spatial correlation between volcanic surface morphologies and positive Bouguer anomalies. We interpret these observations to mean that the spatial heterogeneity observed in the Bouguer signal is the result of variable degrees of magmatic degassing within the intrusions.

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

OpenAIRE

Grotzinger, JP; Gupta, S; Malin, MC; Rubin, DM; Schieber, J; Siebach, K; Sumner, DY; Stack, KM; Vasavada, AR; Arvidson, RE; Calef, F; Edgar, L; Fischer, WF; Grant, JA; Griffes, J

2015-01-01

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittentl...

91 Évaluation de l'activité inhibitrice des extraits d'une algue brune ...

African Journals Online (AJOL)

AKA BOKO

OLIVERA-ROCHA, E. LISBOA -LEITE, Antioxydant activity of sulfated polysaccarides from brown and red seaweeds, Journal of applied Phycology, 19 (2007) 153-160. [14] - D. ZUBIA, D. ROBLEDO, Y. FREILE-PELEGRIN, Antioxidant activities in tropical marine macroalgae from the Yucatan peninsula Mexico, Journal of ...

An Environmental Expedition Course in Search of the Maya.

Science.gov (United States)

Loret, John

1978-01-01

Sponsoring an interdisciplinary program (over 30 lecture hours of geology, ecology, anthropology, ethnology, and agriculture of the Yucatan and Meso-America), Queens College and the University of Connecticut provide expeditions to Mexico and study of local geomorphology, stratigraphy, climate, topography, soils, archeological sites, flora, and…

Scaling of cratering experiments: an analytical and heuristic approach to the phenomenology

International Nuclear Information System (INIS)

Killian, B.G.; Germain, L.S.

1977-01-01

The phenomenology of cratering can be thought of as consisting of two phases. The first phase, where the effects of gravity are negligible, consists of the energy source dynamically imparting its energy to the surroundings, rock and air. As illustrated in this paper, the first phase can be scaled if: radiation effects are negligible, experiments are conducted in the same rock material, time and distance use the same scaling factor, and distances scale as the cube root of the energy. The second phase of cratering consists of the rock, with its already developed velocity field, being thrown out. It is governed by the ballistics equation, and gravity is of primary importance. This second phase of cratering is examined heuristically by examples of the ballistics equation which illustrate the basic phenomena in crater formation. When gravity becomes significant, in addition to the conditions for scaling imposed in the first phase, distances must scale inversely as the ratio of gravities. A qualitative relationship for crater radius is derived and compared with calculations and experimental data over a wide range of energy sources and gravities

Origin of the outer layer of martian low-aspect ratio layered ejecta craters

Science.gov (United States)

Boyce, Joseph M.; Wilson, Lionel; Barlow, Nadine G.

2015-01-01

Low-aspect ratio layered ejecta (LARLE) craters are one of the most enigmatic types of martian layered ejecta craters. We propose that the extensive outer layer of these craters is produced through the same base surge mechanism as that which produced the base surge deposits generated by near-surface, buried nuclear and high-explosive detonations. However, the LARLE layers have higher aspect ratios compared with base surge deposits from explosion craters, a result of differences in thicknesses of these layers. This characteristics is probably caused by the addition of large amounts of small particles of dust and ice derived from climate-related mantles of snow, ice and dust in the areas where LARLE craters form. These deposits are likely to be quickly stabilized (order of a few days to a few years) from eolian erosion by formation of duricrust produced by diffusion of water vapor out of the deposits.

Relationship between organochlorine pesticides and stress indicators in hawksbill sea turtle (Eretmochelys imbricata) nesting at Punta Xen (Campeche), Southern Gulf of Mexico.

Science.gov (United States)

Tremblay, Nelly; Ortíz Arana, Alejandro; González Jáuregui, Mauricio; Rendón-von Osten, Jaime

2017-03-01

Data on the impact of environmental pollution on the homeostasis of sea turtles remains scarce, particularly in the Southern Gulf of Mexico. As many municipalities along the coastline of the Yucatan Peninsula do not rely on a waste treatment plant, these organisms could be particularly vulnerable. We searched for relationships between the presence of organochlorine pesticides (OCP) and the level of several oxidative and pollutant stress indicators of the hawksbill sea turtle (Eretmochelys imbricata) during the 2010 nesting season at Punta Xen (Campeche, Mexico). Of the 30 sampled sea turtles, endosulfans, aldrin related (aldrin, endrin, dieldrin, endrin ketone, endrin aldehyde) and dichlorodiphenyldichloroethylene (DDT) families were detected in 17, 21 and 26, respectively. Significant correlation existed between the size of sea turtles with the concentration of methoxychlor, cholinesterase activity in plasma and heptachlors family, and catalase activity and hexachlorohexane family. Cholinesterase activity in washed erythrocytes and lipid peroxidation were positively correlated with glutathione reductase activity. Antioxidant enzyme actions seem adequate as no lipids damages were correlated with any OCPs. Future studies are necessary to evaluate the effect of OCPs on males of the area due to the significant detection of methoxychlor, which target endocrine functioning and increases its concentration with sea turtles size.

A crater and its ejecta: An interpretation of Deep Impact

Science.gov (United States)

Holsapple, Keith A.; Housen, Kevin R.

2007-03-01

We apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the Deep Impact event. An important question is whether the cratering event was gravity or strength-dominated; the answer gives important clues about the properties of the surface material of Tempel 1. Gravity scaling was assumed in pre-event calculations and has been asserted in initial studies of the mission results. Because the gravity field of Tempel 1 is extremely weak, a gravity-dominated event necessarily implies a surface with essentially zero strength. The conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution. We address that feature here, and conclude that even strength-dominated craters would result in a plume that appeared to remain attached to the surface. We then calculate the plume characteristics from scaling laws for a variety of material types, and for gravity and strength-dominated cases. We find that no model of cratering alone can match the reported observation of plume mass and brightness history. Instead, comet-like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few-hour time frame. With such mechanisms, and to within the large uncertainties, either gravity or strength craters can provide the levels of estimated observed mass. Thus, the observations are unlikely to answer the questions about the mechanical nature of the Tempel 1 surface.

[Population estimates and conservation of felids (Carnivora: Felidae) in Northern Quintana Roo, Mexico].

Science.gov (United States)

Ávila-Nájera, Dulce María; Chávez, Cuauhtémoc; Lazcano-Barrero, Marco A; Pérez-Elizalde, Sergio; Alcántara-Carbajal, José Luis

2015-09-01

Wildlife density estimates provide an idea of the current state of populations, and in some cases, reflect the conservation status of ecosystems, essential aspects for effective management actions. In Mexico, several regions have been identified as high priority areas for the conservation of species that have some level of risk, like the Yucatan Peninsula (YP), where the country has the largest population of jaguars. However, little is known about the current status of threatened and endangered felids, which coexist in the Northeastern portion of the Peninsula. Our objective was to estimate the wild cats' density population over time at El Eden Ecological Reserve (EEER) and its surrounding areas. Camera trap surveys over four years (2008, 2010, 2011 and 2012) were conducted, and data were obtained with the use of capture-recapture models for closed populations (CAPTURE + MMDM or 1/2 MMDM), and the spatially explicit capture-recapture model (SPACECAP). The species studied were jaguar (Panthera onca), puma (Puma concolor), ocelot (Leopardus pardalis), jaguarundi (Puma yaguaroundi) and margay (Leopardus wiedii). Capture frequency was obtained for all five species and the density for three (individuals/100km2). The density estimated with The Mean Maximum Distance Moved (MMDM), CAPTURE, ranged from 1.2 to 2.6 for jaguars, from 1.7 to 4.3 for pumas and from 1.4 to 13.8 for ocelots. The density estimates in SPACECAP ranged from 0.7 to 3.6 for jaguars, from 1.8 to 5.2 for pumas and 2.1 to 5.1 for ocelots. Spatially explicit capture recapture (SECR) methods in SPACECAP were less likely to overestimate densities, making it a useful tool in the planning and decision making process for the conservation of these species. The Northeastern portion of the Yucatan Peninsula maintains high populations of cats, the EEER and its surrounding areas are valuable sites for the conservation of this group of predators. Rev. Biol.

VNIR Multispectral Observations of Rocks at Spirit of St. Louis Crater and Marathon Valley on Th Rim of Endeavour Crater Made by the Opportunity Rover Pancam

Science.gov (United States)

Farrand, W. H.; Johnson, J. R.; Bell, J. F., III; Mittlefehldt, D.W.

2016-01-01

The Mars Exploration Rover Opportunity has been exploring the western rim of the 22 km diameter Endeavour crater since August, 2011. Recently, Opportunity has reached a break in the Endeavour rim that the rover team has named Mara-thon Valley. This is the site where orbital observations from the MRO CRISM imaging spectrometer indicated the presence of iron smectites. On the outer western portion of Marathon Valley, Opportunity explored the crater-form feature dubbed Spirit of St. Louis (SoSL) crater. This presentation describes the 430 to 1009 nm (VNIR) reflectance, measured by the rover's Pancam, of rock units present both at Spirit of St. Louis and within Marathon Valley.

Geology of McLaughlin Crater, Mars: A Unique Lacustrine Setting with Implications for Astrobiology

Science.gov (United States)

Michalski, J. R.; Niles, P. B.; Rogers, A. D.; Johnson, S. S.; Ashley, J. W.; Golombek, M. P.

2016-01-01

McLaughlin crater is a 92-kmdiameter Martian impact crater that contained an ancient carbonate- and clay mineral-bearing lake in the Late Noachian. Detailed analysis of the geology within this crater reveals a complex history with important implications for astrobiology [1]. The basin contains evidence for, among other deposits, hydrothermally altered rocks, delta deposits, deep water (>400 m) sediments, and potentially turbidites. The geology of this basin stands in stark contrast to that of some ancient basins that contain evidence for transient aqueous processes and airfall sediments (e.g. Gale Crater [2-3]).

Characteristics of small young lunar impact craters focusing on current production and degradation on the Moon

Science.gov (United States)

Kereszturi, Akos; Steinmann, Vilmos

2017-11-01

Analysing the size-frequency distribution of very small lunar craters (sized below 100 m including ones below 10 m) using LROC images, spatial density and related age estimations were calculated for mare and terra terrains. Altogether 1.55 km2 area was surveyed composed of 0.1-0.2 km2 units, counting 2784 craters. The maximal areal density was present at the 4-8 m diameter range at every analysed terrain suggesting the bombardment is areally relatively homogeneous. Analysing the similarities and differences between various areas, the mare terrains look about two times older than the terra terrains using ages ranged between 13 and 20 Ma for mare, 4-6 Ma for terra terrains. Substantial fluctuation (min: 936 craters/km2, max: 2495 craters/km2) was observed without obvious source of nearby secondaries or fresh ejecta blanket produced fresh crater. Randomness analysis and visual inspection also suggested no secondary craters or ejecta blanket from fresh impact could contribute substantially in the observed heterogeneity of the areal distribution of small craters - thus distant secondaries or even other, poorly known resurfacing processes should be considered in the future. The difference between the terra/mare ages might come only partly from the easier identification of small craters on smooth mare terrains, as the differences were observed for larger (30-60 m diameter) craters too. Difference in the target hardness could more contribute in this effect. It was possible to separate two groups of small craters based on their appearance: a rimmed thus less eroded, and a rimless thus more eroded one. As the separate usage of different morphology groups of craters for age estimation at the same area is not justifiable, this was used only for comparison. The SFD curves of these two groups showed characteristic differences: the steepness of the fresh craters' SFD curves are similar to each other and were larger than the isochrones. The eroded craters' SFD curves also resemble

Chemical and biological tracers to determine groundwater flow in karstic aquifer, Yucatan Peninsula

Science.gov (United States)

Lenczewski, M.; Leal-Bautista, R. M.; McLain, J. E.

2013-05-01

Little is known about the extent of pollution in groundwater in the Yucatan Peninsula; however current population growth, both from international tourism and Mexican nationals increases the potential for wastewater release of a vast array of contaminants including personal care products, pharmaceuticals (Rx), and pathogenic microorganisms. Pathogens and Rx in groundwater can persist and can be particularly acute in this region where high permeability of the karst bedrock and the lack of top soil permit the rapid transport of contaminants into groundwater aquifers. The objective of this research is to develop and utilize novel biological and chemical source tracking methods to distinguish between different sources of anthropogenic pollution in degraded groundwater. Although several methods have been used successfully to track fecal contamination sources in small scale studies, little is known about their spatial limitations, as source tracking studies rarely include sample collection over a wide geographical area and with different sources of water. In addition, although source tracking methods to distinguish human from animal fecal contamination are widely available, this work has developed source tracking distinguish between separate human populations is highly unique. To achieve this objective, we collected water samples from a series of drinking wells, cenotes (sinkholes), wastewater treatment plants, and injection wells across the Yucatan Peninsula and examine potential source tracers within the collected water samples. The result suggests that groundwater sources impacted by tourist vs. local populations contain different chemical stressors. This work has developed a more detailed understanding of the presence and persistence of personal care products, pharmaceuticals, and fecal indicators in a karstic system; such understanding will be a vital component for the protection Mexican groundwater and human health. Quantification of different pollution sources

Geomorphology and Geology of the Southwestern Margaritifer Sinus and Argyre Regions of Mars. Part 4: Flow Ejecta Crater Distribution

Science.gov (United States)

Parker, T. J.; Pieri, D. C.

1985-01-01

Flow ejecta craters - craters surrounded by lobate ejecta blankets - are found throughout the study area. The ratio of the crater's diameter to that of the flow ejecta in this region is approximately 40 to 45%. Flow ejecta craters are dominantly sharply defined craters, with slightly degraded craters being somewhat less common. This is probably indicative of the ejecta's relatively low resistence to weathering and susceptibility to burial. Flow ejecta craters here seem to occur within a narrow range of crater sizes - the smallest being about 4km in diameter and the largest being about 27km in diameter. Ejecta blankets of craters at 4km are easily seen and those of smaller craters are simply not seen even in images with better than average resolution for the region. This may be due to the depth of excavation of small impacting bodies being insufficient to reach volatile-rich material. Flow ejecta craters above 24km are rare, and those craters above 27km do not display flow ejecta blankets. This may be a result of an excavation depth so great that the volatile content of the ejecta is insufficient to form a fluid ejecta blanket. The geomorphic/geologic unit appears also to play an important role in the formation of flow ejecta craters. Given the typical size range for the occurrence of flow ejecta craters for most units, it can be seen that the percentage of flow ejecta craters to the total number of craters within this size range varies significantly from one unit to the next. The wide variance in flow ejecta crater density over this relatively small geographical area argues strongly for a lithologic control of their distribution.

Automated Detection of Craters in Martian Satellite Imagery Using Convolutional Neural Networks

Science.gov (United States)

Norman, C. J.; Paxman, J.; Benedix, G. K.; Tan, T.; Bland, P. A.; Towner, M.

2018-04-01

Crater counting is used in determining surface age of planets. We propose improvements to martian Crater Detection Algorithms by implementing an end-to-end detection approach with the possibility of scaling the algorithm planet-wide.

Flat plate film cooling at the coolant supply into triangular and cylindrical craters

Directory of Open Access Journals (Sweden)

Khalatov Artem A.

2017-01-01

Full Text Available The results are given of the film cooling numerical simulation of three different schemes including single-array of the traditional round inclined holes, as well as inclined holes arranged in the cylindrical or triangular dimples (craters. The results of simulation showed that at the medium and high values of the blowing ratio (m > 1.0 the scheme with coolant supply into triangular craters improves the adiabatic film cooling efficiency by 1.5…2.7 times compared to the traditional array of inclined holes, or by 1.3…1.8 times compared to the scheme with coolant supply into cylindrical craters. The greater film cooling efficiency with the coolant supply into triangular craters is explained by decrease in the intensity of secondary vortex structures (“kidney” vortex. This is due to the partial destruction and transformation of the coolant jets structure interacting with front wall of the crater. Simultaneously, the film cooling uniformity is increased in the span-wise direction.

Brightening and Volatile Distribution Within Shackleton Crater Observed by the LRO Laser Altimeter.

Science.gov (United States)

Smith, D. E.; Zuber, M. T.; Head, J. W.; Neumann, G. A.; Mazarico, E.; Torrence, M. H.; Aharonson, O.; Tye, A. R.; Fassett, C. I.; Rosengurg, M. A.;

Layers of 'Cabo Frio' in 'Victoria Crater'

Science.gov (United States)

2006-01-01

This view of 'Victoria crater' is looking southeast from 'Duck Bay' towards the dramatic promontory called 'Cabo Frio.' The small crater in the right foreground, informally known as 'Sputnik,' is about 20 meters (about 65 feet) away from the rover, the tip of the spectacular, layered, Cabo Frio promontory itself is about 200 meters (about 650 feet) away from the rover, and the exposed rock layers are about 15 meters (about 50 feet) tall. This is an approximately true color rendering of images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during the rover's 952nd sol, or Martian day, (Sept. 28, 2006) using the camera's 750-nanometer, 530-nanometer and 430-nanometer filters.

Patterns and correlates of plant diversity differ between common and rare species in a neotropical dry forest

NARCIS (Netherlands)

Tetetla-Rangel, Erika; Dupuy, Juan Manuel; Hernández-Stefanoni, José Luis; Hoekstra, Paul H.

2017-01-01

Determining which factors affect species richness is important for conservation theory and practice. However, richness of common and rare species may be affected by different factors. We use an extensive inventory of woody plants from a tropical dry forest landscape in Yucatan, Mexico to assess the

Microstructural study of pre hispanic and colonial pigments of diverse sites of Mexico

International Nuclear Information System (INIS)

Arenas A, J.; Espinosa P, M.; Fernandez, M.E.; Mondragon G, G.; Perez H, R.; Mendoza A, D.; Rodriguez L, V.; Martinez, G.

2004-01-01

The aim of this work is to show some studies about the pre hispanic paintings, blue paint, green and red colors found in several archaeological sites located in the southeast and center of Mexico, also were analyzed clays samples from Sacalum mine localized in Yucatan state. The samples were analyzed by X Ray Diffraction (XRD), Scanning Electron Microscopy (Sem) and Transmission Electron Microscopy both equipped with a microprobe for chemical elemental analysis by Energy Dispersive Spectroscopy (EDS). The results obtained by Sem showed that all the pre hispanic paintings are made of fiber-like structures of micrometers order. In other zones of the samples were identified irregular morphologies in which the fibers are supported. The EDS analysis identified the elements C, O, Na, Mg, Al, Si, Ca and Fe. The XRD and High Resolution Transmission Electron Microscopy (HREM) results showed fiber crystalline structures at nanoscopic level corresponding to paligorskite clay. Other particles were identified as calcite phase. In the red pigments were identified paligorskite fibers in some of them and another sample was identified cinnabar phase. In these last sample no was identify the paligorskite. (Author) 14 refs., 13 figs

The Geology of the Marcia Quadrangle of Asteroid Vesta: Assessing the Effects of Large, Young Craters

Science.gov (United States)

Williams, David A.; Denevi, Brett W.; Mittlefehldt, David W.; Mest, Scott C.; Schenk, Paul M.; Yingst, R. Aileen; Buczowski, Debra L.; Scully, Jennifer E. C.; Garry, W. Brent; McCord, Thomas B.;

Moon/Mars Landing Commemorative Release: Gusev Crater and Ma'adim Vallis

Science.gov (United States)

1998-01-01

On July 20, 1969, the first human beings landed on the Moon. On July 20, 1976, the first robotic lander touched down on Mars. This July 20th-- 29 years after Apollo 11 and 22 years since the Viking 1 Mars landing-- we take a look forward toward one possible future exploration site on the red planet.One of the advantages of the Mars Global Surveyor Mars Orbiter Camera (MOC) over its predecessors on the Viking and Mariner spacecraft is resolution. The ability to see-- resolve--fine details on the martian surface is key to planning future landing sites for robotic and, perhaps, human explorers that may one day visit the planet.At present, NASA is studying potential landing sites for the Mars Surveyor landers, rovers, and sample return vehicles that are scheduled to be launched in 2001, 2003, and 2005. Among the types of sites being considered for these early 21st Century landings are those with 'exobiologic potential'--that is, locations on Mars that are in some way related to the past presence of water.For more than a decade, two of the prime candidates suggested by various Mars research scientists are Gusev Crater and Ma'adim Vallis. Located in the martian southern cratered highlands at 14.7o S, 184.5o W, Gusev Crater is a large, ancient, meteor impact basin that--after it formed--was breached by Ma'adim Vallis.Viking Orbiter observations provided some evidence to suggest that a fluid--most likely, water--once flowed through Ma'adim Vallis and into Gusev Crater. Some scientists have suggested that there were many episodes of flow into Gusev Crater (as well as flow out of Gusev through its topographically-lower northwestern rim). Some have also indicated that there were times when Ma'adim Vallis, also, was full of water such that it formed a long, narrow lake.The possibility that water flowed into Gusev Crater and formed a lake has led to the suggestion that the materials seen on the floor of this crater--smooth-surfaced deposits, buried craters, and huge mesas near

Polygons and Craters

Science.gov (United States)

2005-01-01

3 September 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows polygons enhanced by subliming seasonal frost in the martian south polar region. Polygons similar to these occur in frozen ground at high latitudes on Earth, suggesting that perhaps their presence on Mars is also a sign that there is or once was ice in the shallow subsurface. The circular features are degraded meteor impact craters. Location near: 72.2oS, 310.3oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

Mexico.

Science.gov (United States)

Semaan, Leslie

The text explores Mexico's history, geography, art, religion, and lifestyles in the context of its complex economy. The text focuses on Mexico's economy and reasons for its current situation. Part I of this teaching unit includes: Teacher Overview, Why Study Mexico, Mexico Fact Sheet, Map of Mexico, the Land and Climate, History, Government,…

Stratigraphy of the crater Copernicus

Science.gov (United States)

Paquette, R.

1984-01-01

The stratigraphy of copernicus based on its olivine absorption bands is presented. Earth based spectral data are used to develop models that also employ cratering mechanics to devise theories for Copernican geomorphology. General geologic information, spectral information, upper and lower stratigraphic units and a chart for model comparison are included in the stratigraphic analysis.

Changes in abundance and nature of microimpact craters on the surfaces of Australasian microtektites with distance from the proposed source crater location

Digital Repository Service at National Institute of Oceanography (India)

ShyamPrasad, M.; Roy, S.K.; Gupta, A.

of the craters are of erosive type (Fig. 2), i.e., those which contain a central pit which is surrounded by radial and concentric cracks, indicative of high velocity impacts (Hörz et al., 1971). This could be misleading, as observed in our earlier studies... of very small particles at high relative velocities. This location also has 9    the highest spatial density of impacts, i.e., it contains 230 micro-craters/cm 2 of the ocean floor (Table 2). AAS 22/8 (4052 km): Location : 07 0 05.289’S & 78 0...

Atypical pit craters on Mars: new insights from THEMIS, CTX and HiRISE observations

Science.gov (United States)

Cushing, Glen; Okubo, Chris H.; Titus, Timothy N.

2015-01-01

More than 100 pit craters in the Tharsis region of Mars exhibit morphologies, diameters and thermal behaviors that diverge from the much larger bowl-shaped pit craters that occur in most regions across Mars. These Atypical Pit Craters (APCs) generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50-350 m, and high depth-to-diameter (d/D) ratios that are usually greater than 0.3 (which is an upper-range value for impacts and bowl-shaped pit craters), and can exceed values of 1.8. Observations by the Mars Odyssey THermal Emission Imaging System (THEMIS) show that APC floor temperatures are warmer at night, and fluctuate with much lower diurnal amplitudes than nearby surfaces or adjacent bowl-shaped pit craters. Kīlauea volcano, Hawai'i, hosts pit craters that formed through subsurface collapse into active volcanic dikes, resulting in pits that can appear morphologically analogous to either APCs or bowl-shaped pit craters. Partially-drained dikes are sometimes exposed within the lower walls and floors of these terrestrial APC analogs and can form extensive cave systems with unique microclimates. Similar caves in martian pit craters are of great interest for astrobiology. This study uses new observations by the Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) to refine previous work where seven APCs were described from lower-resolution THEMIS visible-wavelength (VIS) observations. Here, we identify locations of 115 APCs, map their distribution across the Tharsis region, characterize their internal morphologies with high-resolution observations, and discuss possible formation mechanisms.

Geology of drill hole USW VH-2, and structure of Crater Flat, southwestern Nevada

International Nuclear Information System (INIS)

Carr, W.J.; Parrish, L.D.

1985-01-01

A 1219 meter (4000 ft) drill hole in Crater Flat shows the absence of buried Pliocene or Quaternary volcanic rocks, and penetrates a section of Timber Mountain, Paintbrush, and the upper part of the Crater Flat Tuffs, similar to that exposed adjacent to Crater Flat. A prominent negative aeromagnetic anomaly between the drill hole and Bare Mountain is attributed to a westward thickening section of a reversely magnetized Miocene basalt. The relatively shallow depth of this basalt in the west-central part of Crater Flat indicates that no large amount of tectonic movement has occurred in approximately the last 10 m.y. Massive brecciated wedges of Paleozoic rocks are penetrated in two stratigraphic intervals in the drill hole; the older one, between the Tiva Canyon Member of the Paintbrush Tuff and the Rainier Mesa Member of the Timber Mountain Tuff, correlates with the time of maximum faulting east of Crater Flat in the Yucca Mountain area. The younger slide masses are correlated with a large slide block of probable late Miocene age exposed along the southwestern rim of Crater Flat. The structural pattern and style buried beneath central and western Crater Flat is deduced to be similar to that exposed at Yucca Mountain, but less developed. The major fault system controlling the steep east face of Bare Mountain, though probably still active, is believed to have developed mainly as a result of caldera collapse between 13 and 14 m.y. ago. Relations between faulting and four episodes of basalt eruption in the Crater Flat area strongly suggest contemporaneity of the two processes. 17 refs., 2 figs., 3 tabs

Preliminary results of soil radon gas survey of the Lake Bosomtwi impact crater

International Nuclear Information System (INIS)

Preko, S.; Danuor, S.K.; Menyeh, A.

2004-01-01

Soil radon gas survey was carried out in the Lake Bosomtwi impact crater area on eight profiles, which ran rapidly toward the end of the crater. One thousand soil samples, each weighing about 100g were acquired at a depth of 20 cm and at regular intervals of 10 m. The radon gas decay rate of the soil samples was then determined in the laboratory using the RDA-200 Radon detector and RDU-200 Degassing unit. It was found that generally areas south and east of the crater, which are severally sheared, faulted and fractured recorded high radon gas decay rates of the order of 800 counts/min whilst relatively undisturbed zones west of the crater recorded lower rates of the order of 20 counts/min. the cause of fracturing, shearing and faulting have been attributed to the effect of the meteorite impact in the Bosomtwi area, and therefore the results indicate that the soil radon gas survey could serve as a useful tool in mapping the impact-related structural characteristics of the crater. (author)

Periodic Impact Cratering and Extinction Events Over the Last 260 Million Years

Science.gov (United States)

Rampino, Michael R.; Caldeira, Ken

2015-01-01

The claims of periodicity in impact cratering and biological extinction events are controversial. Anewly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 +/- 0.6 Myr cycle. Using the same method, we found a significant 27.0 +/- 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.

Evaluating the human impact on groundwater quality discharging into a coastal reef lagoon

Science.gov (United States)

Rebolledo-Vieyra, M.; Hernandez-Terrones, L.; Soto, M.; Lecossec, A.; Monroy-Rios, E.

2008-12-01

The Eastern coast of the Yucatan Peninsula has the fastest growth rate in Mexico and groundwater is the only source of drinking water in the region. The consequences of the lack of proper infrastructure to collect and treat wastewater and the impact of human activities on the quality of groundwater are addressed. The groundwater in the coastal aquifer of Quintana Roo (SE Mexico) discharges directly into the ocean. In addition, the coral reef of the Eastern Yucatan Peninsula is part of the Mesoamerican Coral Reef System, one of the largest in the world. The interaction of the reef-lagoon hydraulics with the coastal aquifer of Puerto Morelos (NE Yucatan Peninsula), and a major input of NH4, SO4, SiO2, as a consequence of the use of septic tanks and the lack of modern wastewater treatment plants are presented. No seasonal parameters differences were observed, suggesting that groundwater composition reaching the reef lagoon is not changing seasonally. A conceptual model of the coastal aquifer was developed, in order to explain how the human activities are impacting directly on the groundwater quality that, potentially, will have a direct impact on the coral reef. The protection and conservation of coral reefs must be directly related with a policy of sound management of coastal aquifers and wastewater treatment.

In vitro culture and characterization of putative porcine embryonic germ cells derived from domestic breeds and yucatan mini pig embryos at days 20-24 of gestation

DEFF Research Database (Denmark)

Petkov, Stoyan Gueorguiev; Marks, Hendrik; Klein, Tino

2011-01-01

Embryonic germ cells (EGC) are cultured pluripotent cells derived from primordial germ cells (PGC). This study explored the possibility of establishing porcine EGC from domestic breeds and Yucatan mini pigs using embryos at Days 17-24 of gestation. In vitro culture of PGC from both pooled...

Moon Zoo: Making the public part of a crater survey algorithm

Science.gov (United States)

Gay, P. L.; Brown, S.; Huang, D.; Daus, C.; Lehan, C.; Robbins, S.

2011-10-01

The Moon Zoo citizen science website launched in May 2010 and invited the public to annotate images from the Lunar Reconnaissance Orbiter's Narrow Angle Camera (NAC). Tasks included marking the edges of craters with an ellipse tool, indicating where linear features (e.g. scarps) and special types of craters (e.g. dark haloed) are located with a box, and rating the number of boulders in an image. The goal of this project is to create crater and feature catalogues for large areas of the moon. In addition to doing science, Moon Zoo also seeks to educate its audience through educational content, to engage them through social media, and to understand them through research into their motivations and behaviors.

Zhamanshin and Aouelloul - Craters produced by impact of tektite-like glasses?

Science.gov (United States)

O'Keefe, John A.

1987-01-01

It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.

Preliminary Results from Initial Investigations of Ceres' Cratering Record from Dawn Imaging Data

Science.gov (United States)

Schmedemann, Nico; Michael, Gregory; Ivanov, Boris A.; Kneissl, Thomas; Neesemann, Adrian; Hiesinger, Harald; Jaumann, Ralf; Raymond, Carol A.; Russell, Christopher T.

2015-04-01

The highly successful Dawn mission [1] finished data collection at Vesta in 2012 and is now on its way to the dwarf planet Ceres. According to the current Ceres approach timeline of the Dawn mission, the ground resolution of the Dawn FC camera [2] will be about 10 times better than Hubble data [3] at the time of the presentation of this work. This may allow for identification of craters about 15 km in diameter. Initial mapping of sample areas may provide enough information of the cratering record in order to compare it with the theoretical Ceres crater production function we present at the 46th LPSC conference (March 16-20, 2015, The Woodlands, Texas) [4]. Our preliminary crater production function for Ceres is derived from the assumption of an icy crust just below a thin surface layer of dust [5], and a projectile population that is very similar to the one that impacted the Moon [6]. In order to scale the lunar cratering record to Ceres we use the Ivanov scaling laws [7], which allow for crater scaling based on parameters that can be derived from observations. The lunar-like approach gave reasonable good results for the crater production function on the asteroids Vesta, Ida, Lutetia and Gaspra [8]. Since the lunar surface is of basaltic composition, the correct scaling between the different materials is challenging. One crucial parameter is the transition diameter from simple to complex craters. Based on the simple to complex transition diameter on Iapetus, an icy satellite of Saturn, we expect this transition at about 12 km crater size at Ceres. This value may be slightly different due to the different temperatures at Ceres and Iapetus. If the simple to complex transition is observed at much larger diameters, the reason could be a substantial fraction of rock in the shallow subsurface of Ceres. In an ice-rich surface material high relaxation rates may also be expected that could change the shape of the crater production function. A thorough geological mapping

Geochemical monitoring of volcanic lakes. A generalized box model for active crater lakes

Directory of Open Access Journals (Sweden)

Franco Tassi

2011-06-01

Full Text Available

In the past, variations in the chemical contents (SO42−, Cl−, cations of crater lake water have not systematically demonstrated any relationships with eruptive activity. Intensive parameters (i.e., concentrations, temperature, pH, salinity should be converted into extensive parameters (i.e., fluxes, changes with time of mass and solutes, taking into account all the internal and external chemical–physical factors that affect the crater lake system. This study presents a generalized box model approach that can be useful for geochemical monitoring of active crater lakes, as highly dynamic natural systems. The mass budget of a lake is based on observations of physical variations over a certain period of time: lake volume (level, surface area, lake water temperature, meteorological precipitation, air humidity, wind velocity, input of spring water, and overflow of the lake. This first approach leads to quantification of the input and output fluxes that contribute to the actual crater lake volume. Estimating the input flux of the "volcanic" fluid (Qf- kg/s –– an unmeasurable subsurface parameter –– and tracing its variations with time is the major focus during crater lake monitoring. Through expanding the mass budget into an isotope and chemical budget of the lake, the box model helps to qualitatively characterize the fluids involved. The (calculated Cl− content and dD ratio of the rising "volcanic" fluid defines its origin. With reference to continuous monitoring of crater lakes, the present study provides tips that allow better calculation of Qf in the future. At present, this study offers the most comprehensive and up-to-date literature review on active crater lakes.

Pyroclastic Deposits in the Floor-fractured Crater Alphonsus

Science.gov (United States)

Allen, Carlton C.; Donaldson-Hanna, Kerri L.; Pieters, Carle M.; Moriarty, Daniel P.; Greenhagen, Benjamin T.; Bennett, Kristen A.; Kramer, Georgiana Y.; Paige, David A.

2013-01-01

Alphonsus, the 118 km diameter floor-fractured crater, is located immediately east of Mare Nubium. Eleven pyroclastic deposits have been identified on the crater's floor. Early telescopic spectra suggest that the floor of Alphonsus is noritic, and that the pyroclastic deposits contain mixtures of floor material and a juvenile component including basaltic glass. Head and Wilson contend that Nubium lavas intruded the breccia zone beneath Alphonsus, forming dikes and fractures on the crater floor. In this model, the magma ascended to the level of the mare but cooled underground, and a portion broke thru to the surface in vulcanian (explosive) eruptions. Alternatively, the erupted material could be from a source unrelated to the mare, in the style of regional pyroclastic deposits. High-resolution images and spectroscopy from the Moon Mineralogy Mapper (M3), Diviner Lunar Radiometer, and Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (NAC) provide data to test these formation models. Spectra from M3 confirm that the crater floor is primarily composed of noritic material, and that the Nubium lavas are basaltic. Spectra from the three largest pyroclastic deposits in Alphonsus are consistent with a minor low- Ca pyroxene component in a glass-rich matrix. The centers of the 2 micron absorption bands have wavelengths too short to be of the same origin as the Nubium basalts. Diviner Christiansen feature (CF) values were used to estimate FeO abundances for the crater floor, Nubium soil, and pyroclastic deposits. The estimated abundance for the crater floor (7.5 +/- 1.4 wt.%) is within the range of FeO values for Apollo norite samples. However, the estimated FeO abundance for Nubium soil (13.4 +/- 1.4 wt.%) is lower than those measured in most mare samples. The difference may reflect contamination of the mare soil by highland ejecta. The Diviner-derived FeO abundance for the western pyroclastic deposit is 13.8 +/- 3.3 wt.%. This is lower than the values for mare soil

Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge

Energy Technology Data Exchange (ETDEWEB)

Yang, Changyi [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia); Wu, Yiyong; Lv, Gang [National Key Laboratory of Materials Behavior and Evaluation Technology in Space Environments, Harbin Institute of Technology, Harbin (China); Rubanov, Sergey [Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC 3010 (Australia); Jamieson, David N., E-mail: d.jamieson@unimelb.edu.au [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia)

2015-04-01

Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5–30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11–68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the

Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge

International Nuclear Information System (INIS)

Yang, Changyi; Wu, Yiyong; Lv, Gang; Rubanov, Sergey; Jamieson, David N.

2015-01-01

Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5–30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11–68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the

Geologic field trip guide to Mount Mazama and Crater Lake Caldera, Oregon

Science.gov (United States)

Bacon, Charles R.; Wright, Heather M.

2017-08-08

Crater Lake partly fills one of the most spectacular calderas of the world—an 8 by 10 kilometer (km) basin more than 1 km deep formed by collapse of the Mount Mazama volcano during a rapid series of explosive eruptions ~7,700 years ago. Having a maximum depth of 594 meters (m), Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 square kilometers (km2) of pristine forested and alpine terrain, including the lake itself, and virtually all of Mount Mazama. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama’s climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest United States, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. In addition, many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama provide information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive processes revealed by

Use of multiplex polymerase chain reaction-based assay to conduct epidemiological studies on bovine hemoparasites in Mexico.

Science.gov (United States)

Figueroa, J V; Alvarez, J A; Ramos, J A; Vega, C A; Buening, G M

1993-01-01

A study was conducted to test the applicability of a Polymerase Chain Reaction (PCR)-based approach for the simultaneous detection of the bovine hemoparasites Babesia bigemina, B. bovis and Anaplasma marginale. Bovine blood samples from cattle ranches of a previously determined enzootic zone in the Yucatan Peninsula of Mexico, were collected from peripheral blood and processed for PCR analysis. Blood samples were subjected to DNA amplification by placing an aliquot in a reaction tube containing oligonucleotide primers specific for DNA of each hemoparasite species. The PCR products were detected by Dot-Blot nucleic acid hybridization utilizing nonradioactive, species-specific, digoxigenin PCR-labeled DNA probes. Four hundred twenty one field samples analyzed by the multiplex PCR-DNA probe assay showed 66.7%, 60.1% and 59.6% prevalence rates for B. bigemina, B. bovis and A. marginale, respectively. The multiplex PCR analysis showed that animals with single, double or triple infection could be detected with the parasite specific DNA probes. The procedure is proposed as a valuable tool for the epidemiological analysis in regions where the hemoparasite species are concurrently infecting cattle.

The central uplift of Ritchey crater, Mars

Science.gov (United States)

Ding, Ning; Bray, Veronica J.; McEwen, Alfred S.; Mattson, Sarah S.; Okubo, Chris H.; Chojnacki, Matthew; Tornabene, Livio L.

2015-01-01

Ritchey crater is a ∼79 km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

The central uplift of Ritchey crater, Mars

Science.gov (United States)

Ding, Ning; Bray, Veronica J.; McEwen, Alfred S.; Mattson, Sarah S.; Okubo, Chris H.; Chojnacki, Matthew; Tornabene, Livio L.

2015-05-01

Ritchey crater is a ∼79 km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

Crossing Pedagogical Borders in the Yucatan Peninsula

Science.gov (United States)

Willhauck, Susan

2009-01-01

A challenging intercultural teaching experience provided an opportunity for engaging embodied pedagogies that facilitated border crossings of language, age, gender, and experience. Influenced by the work of Augusto Boal, the author describes how improvisation, role-play, music, and drawing led seminary students in Mexico into sacred time and space…

Publications | Page 609 | IDRC - International Development ...

International Development Research Centre (IDRC) Digital Library (Canada)

Results 6081 - 6090 of 6341 ... For small-scale farmers who maintain genetically diverse crop populations, aspects of the storage of their seeds and harvest may be just as important for successful farming as those related to productivity. The community of Yaxcaba, Yucatan, Mexico was studied to understand how the conditions ...

Global and local re-impact and velocity regime of ballistic ejecta of boulder craters on Ceres

Science.gov (United States)

Schulzeck, F.; Schröder, S. E.; Schmedemann, N.; Stephan, K.; Jaumann, R.; Raymond, C. A.; Russell, C. T.

2018-04-01

Imaging by the Dawn-spacecraft reveals that fresh craters on Ceres below 40 km often exhibit numerous boulders. We investigate how the fast rotating, low-gravity regime on Ceres influences their deposition. We analyze size-frequency distributions of ejecta blocks of twelve boulder craters. Global and local landing sites of boulder crater ejecta and boulder velocities are determined by the analytical calculation of elliptic particle trajectories on a rotating body. The cumulative distributions of boulder diameters follow steep-sloped power-laws. We do not find a correlation between boulder size and the distance of a boulder to its primary crater. Due to Ceres' low gravitational acceleration and fast rotation, ejecta of analyzed boulder craters (8-31 km) can be deposited across the entire surface of the dwarf planet. The particle trajectories are strongly influenced by the Coriolis effect as well as the impact geometry. Fast ejecta of high-latitude craters accumulate close to the pole of the opposite hemisphere. Fast ejecta of low-latitude craters wraps around the equator. Rotational effects are also relevant for the low-velocity regime. Boulders are ejected at velocities up to 71 m/s.

Geologic Map of Mount Mazama and Crater Lake Caldera, Oregon

Science.gov (United States)

Bacon, Charles R.

2008-01-01

Crater Lake partly fills one of the most spectacular calderas of the world, an 8-by-10-km basin more than 1 km deep formed by collapse of the volcano known as Mount Mazama (fig. 1) during a rapid series of explosive eruptions about 7,700 years ago. Having a maximum depth of 594 m, Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 km2 of pristine forested and alpine terrain, including the lake itself, virtually all of Mount Mazama, and most of the area of the geologic map. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama's climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, greatly enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. Lastly, the many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama are a source of information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive

Magma genesis at Gale Crater: Evidence for Pervasive Mantle Metasomatism

Science.gov (United States)

Filiberto, J.

2017-12-01

Basaltic rocks have been analyzed at Gale Crater with a larger range in bulk chemistry than at any other landing site [1]. Therefore, the rocks may have experienced significantly different formation conditions than those experienced by magmas at Gusev Crater or Meridiani Planum. Specifically, the rocks at Gale Crater have higher potassium than other Martian rocks, with a potential analog of the Nakhlite parental magma, and are consistent with forming from a metasomatized mantle source [2-4]. Mantle metasomatism would not only affect the bulk chemistry but mantle melting conditions, as metasomatism fluxes fluids into the source region. Here I will combine differences in bulk chemistry between Martian basalts to calculate formation conditions in the interior and investigate if the rocks at Gale Crater experienced magma genesis conditions consistent with metasomatism - lower temperatures and pressures of formation. To calculate average formation conditions, I rely on experimental results, where available, and silica-activity and Mg-exchange thermometry calculations for all other compositions following [5, 6]. The results show that there is a direct correlation between the calculated mantle potential temperature and the K/Ti ratio of Gale Crater rocks. This is consistent with fluid fluxed metasomatism introducing fluids to the system, which depressed the melting temperature and fluxed K but not Ti to the system. Therefore, all basalts at Gale Crater are consistent with forming from a metasomatized mantle source, which affected not only the chemistry of the basalts but also the formation conditions. References: [1] Cousin A. et al. (2017) Icarus. 288: 265-283. [2] Treiman A.H. et al. (2016) Journal of Geophysical Research: Planets. 121: 75-106. [3] Treiman A.H. and Medard E. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285851. [4] Schmidt M.E. et al. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10

Horizontal movements, migration patterns, and population structure of whale sharks in the Gulf of Mexico and northwestern Caribbean sea.

Science.gov (United States)

Hueter, Robert E; Tyminski, John P; de la Parra, Rafael

2013-01-01

Whale sharks, Rhincodon typus, aggregate by the hundreds in a summer feeding area off the northeastern Yucatan Peninsula, Mexico, where the Gulf of Mexico meets the Caribbean Sea. The aggregation remains in the nutrient-rich waters off Isla Holbox, Isla Contoy and Isla Mujeres, Quintana Roo for several months in the summer and then dissipates between August and October. Little has been known about where these sharks come from or migrate to after they disperse. From 2003-2012, we used conventional visual tags, photo-identification, and satellite tags to characterize the basic population structure and large-scale horizontal movements of whale sharks that come to this feeding area off Mexico. The aggregation comprised sharks ranging 2.5-10.0 m in total length and included juveniles, subadults, and adults of both sexes, with a male-biased sex ratio (72%). Individual sharks remained in the area for an estimated mean duration of 24-33 days with maximum residency up to about 6 months as determined by photo-identification. After leaving the feeding area the sharks showed horizontal movements in multiple directions throughout the Gulf of Mexico basin, the northwestern Caribbean Sea, and the Straits of Florida. Returns of individual sharks to the Quintana Roo feeding area in subsequent years were common, with some animals returning for six consecutive years. One female shark with an estimated total length of 7.5 m moved at least 7,213 km in 150 days, traveling through the northern Caribbean Sea and across the equator to the South Atlantic Ocean where her satellite tag popped up near the Mid-Atlantic Ridge. We hypothesize this journey to the open waters of the Mid-Atlantic was for reproductive purposes but alternative explanations are considered. The broad movements of whale sharks across multiple political boundaries corroborates genetics data supporting gene flow between geographically distinct areas and underscores the need for management and conservation strategies for

Are the London Declaration's 2020 goals sufficient to control Chagas disease?: Modeling scenarios for the Yucatan Peninsula.

Science.gov (United States)

Lee, Bruce Y; Bartsch, Sarah M; Skrip, Laura; Hertenstein, Daniel L; Avelis, Cameron M; Ndeffo-Mbah, Martial; Tilchin, Carla; Dumonteil, Eric O; Galvani, Alison

2018-03-01

The 2020 Sustainable Development goals call for 100% certified interruption or control of the three main forms of Chagas disease transmission in Latin America. However, how much will achieving these goals to varying degrees control Chagas disease; what is the potential impact of missing these goals and if they are achieved, what may be left? We developed a compartmental simulation model that represents the triatomine, human host, and non-human host populations and vector-borne, congenital, and transfusional T. cruzi transmission between them in the domestic and peridomestic settings to evaluate the impact of limiting transmission in a 2,000 person virtual village in Yucatan, Mexico. Interruption of domestic vectorial transmission had the largest impact on T. cruzi transmission and prevalence in all populations. Most of the gains were achieved within the first few years. Controlling vectorial transmission resulted in a 46.1-83.0% relative reduction in the number of new acute Chagas cases for a 50-100% interruption in domestic vector-host contact. Only controlling congenital transmission led to a 2.4-8.1% (30-100% interruption) relative reduction in the total number of new acute cases and reducing only transfusional transmission led to a 0.1-0.3% (30-100% reduction). Stopping all three forms of transmission resulted in 0.5 total transmission events over five years (compared to 5.0 with no interruption); interrupting all forms by 30% resulted in 3.4 events over five years per 2,000 persons. While reducing domestic vectorial, congenital, and transfusional transmission can successfully reduce transmission to humans (up to 82% in one year), achieving the 2020 goals would still result in 0.5 new acute cases per 2,000 over five years. Even if the goals are missed, major gains can be achieved within the first few years. Interrupting transmission should be combined with other efforts such as a vaccine or improved access to care, especially for the population of already

Sulfate-rich eolian and wet interdune deposits, erebus crater, meridiani Planum, Mars

Science.gov (United States)

Metz, J.M.; Grotzinger, J.P.; Rubin, D.M.; Lewis, K.W.; Squyres, S. W.; Bell, J.F.

2009-01-01

This study investigates three bedrock exposures at Erebus crater, an ?? 300 m diameter crater approximately 4 km south of Endurance crater on Mars. These outcrops, called Olympia, Payson, and Yavapai, provide additional evidence in support of the dune-interdune model proposed for the formation of the deposits at the Opportunity landing site in Meridiani Planum. There is evidence for greater involvement of liquid water in the Olympia outcrop exposures than was observed in Eagle or Endurance craters. The Olympia outcrop likely formed in a wet interdune and sand sheet environment. The facies observed within the Payson outcrop, which is likely stratigraphically above the Olympia outcrop, indicate that it was deposited in a damp-wet interdune, sand sheet, and eolian dune environment. The Yavapai outcrop, which likely stratigraphically overlies the Payson outcrop, indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment. These three outcrop exposures may indicate an overall drying-upward trend spanning the stratigraphic section from its base at the Olympia outcrop to its top at the Yavapai outcrop. This contrasts with the wetting-upward trend seen in Endurance and Eagle craters. Thus, the series of outcrops seen at Meridiani by Opportunity may constitute a full climatic cycle, evolving from dry to wet to dry conditions. ?? 2009, SEPM (Society for Sedimentary Geology).

Eastern rim of the Chesapeake Bay impact crater: Morphology, stratigraphy, and structure

Science.gov (United States)

Poag, C.W.

2005-01-01

This study reexamines seven reprocessed (increased vertical exaggeration) seismic reflection profiles that cross the eastern rim of the Chesapeake Bay impact crater. The eastern rim is expressed as an arcuate ridge that borders the crater in a fashion typical of the "raised" rim documented in many well preserved complex impact craters. The inner boundary of the eastern rim (rim wall) is formed by a series of raterfacing, steep scarps, 15-60 m high. In combination, these rim-wall scarps represent the footwalls of a system of crater-encircling normal faults, which are downthrown toward the crater. Outboard of the rim wall are several additional normal-fault blocks, whose bounding faults trend approximately parallel to the rim wall. The tops of the outboard fault blocks form two distinct, parallel, flat or gently sloping, terraces. The innermost terrace (Terrace 1) can be identified on each profile, but Terrace 2 is only sporadically present. The terraced fault blocks are composed mainly of nonmarine, poorly to moderately consolidated, siliciclastic sediments, belonging to the Lower Cretaceous Potomac Formation. Though the ridge-forming geometry of the eastern rim gives the appearance of a raised compressional feature, no compelling evidence of compressive forces is evident in the profiles studied. The structural mode, instead, is that of extension, with the clear dominance of normal faulting as the extensional mechanism. 

Delineating Bukit Bunuh impact crater boundary by geophysical and geotechnical investigation

Energy Technology Data Exchange (ETDEWEB)

Azwin, I. N., E-mail: nurazwinismail@yahoo.com; Rosli, S.; Nordiana, M. M.; Ragu, R. R.; Mark, J. [Geophysics Section, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Mokhtar, S. [Centre for Global Archaeological Research Malaysia, 11800 USM, Penang (Malaysia)

2015-03-30

Evidences of crater morphology and shock metamorphism in Bukit Bunuh, Lenggong, Malaysia were found during the archaeological research conducted by the Centre for Global Archaeological Research Malaysia, Universiti Sains Malaysia. In order to register Bukit Bunuh as one of the world meteorite impact site, detailed studies are needed to verify the boundary of the crater accordingly. Geophysical study was conducted utilising the seismic refraction and 2-D electrical resistivity method. Seismic refraction survey was done using ABEM MK8 24 channel seismograph with 14Hz geophones and 40kg weight drop while 2-D electrical resistivity survey was performed using ABEM SAS4000 Terrameter and ES10-64C electrode selector with pole-dipole array. Bedrock depths were digitized from the sections obtained. The produced bedrock topography map shows that there is low bedrock level circulated by high elevated bedrock and interpreted as crater and rim respectively with diameter approximately 8km. There are also few spots of high elevated bedrock appear at the centre of the crater which interpreted as rebounds zone. Generally, the research area is divided into two layers where the first layer with velocity 400-1100 m/s and resistivity value of 10-800 Om predominantly consists of alluvium mix with gravel and boulders. Second layer represents granitic bedrock with depth of 5-50m having velocity >2100 m/s and resistivity value of >1500 Om. This research is strengthen by good correlation between geophysical data and geotechnical borehole records executed inside and outside of the crater, on the rim, as well as at the rebound area.

Combined analysis of 2-D electrical resistivity, seismic refraction and geotechnical investigations for Bukit Bunuh complex crater

International Nuclear Information System (INIS)

Azwin, I N; Saad, Rosli; Nordiana, M M; Bery, Andy Anderson; Hidayah, I N E; Saidin, Mokhtar

2015-01-01

Interest in studying impact crater on earth has increased tremendously due to its importance in geologic events, earth inhabitant history as well as economic value. The existences of few shock metamorphism and crater morphology evidences are discovered in Bukit Bunuh, Malaysia thus detailed studies are performed using geophysical and geotechnical methods to verify the type of the crater and characteristics accordingly. This paper presents the combined analysis of 2-D electrical resistivity, seismic refraction, geotechnical SPT N value, moisture content and RQD within the study area. Three stages of data acquisition are made starting with regional study followed by detailed study on West side and East side. Bulk resistivity and p-wave seismic velocity were digitized from 2-D resistivity and seismic sections at specific distance and depth for corresponding boreholes and samples taken. Generally, Bukit Bunuh shows the complex crater characteristics. Standard table of bulk resistivity and p-wave seismic velocity against SPT N value, moisture content and RQD are produce according to geological classifications of impact crater; inside crater, rim/slumped terrace and outside crater

Combined analysis of 2-D electrical resistivity, seismic refraction and geotechnical investigations for Bukit Bunuh complex crater

Science.gov (United States)

Azwin, I. N.; Saad, Rosli; Saidin, Mokhtar; Nordiana, M. M.; Anderson Bery, Andy; Hidayah, I. N. E.

2015-01-01

Interest in studying impact crater on earth has increased tremendously due to its importance in geologic events, earth inhabitant history as well as economic value. The existences of few shock metamorphism and crater morphology evidences are discovered in Bukit Bunuh, Malaysia thus detailed studies are performed using geophysical and geotechnical methods to verify the type of the crater and characteristics accordingly. This paper presents the combined analysis of 2-D electrical resistivity, seismic refraction, geotechnical SPT N value, moisture content and RQD within the study area. Three stages of data acquisition are made starting with regional study followed by detailed study on West side and East side. Bulk resistivity and p-wave seismic velocity were digitized from 2-D resistivity and seismic sections at specific distance and depth for corresponding boreholes and samples taken. Generally, Bukit Bunuh shows the complex crater characteristics. Standard table of bulk resistivity and p-wave seismic velocity against SPT N value, moisture content and RQD are produce according to geological classifications of impact crater; inside crater, rim/slumped terrace and outside crater.

Geometric interpretation of the ratio of overall diameter to rim crest diameter for lunar and terrestrial craters.

Science.gov (United States)

Siegal, B. S.; Wickman, F. E.

1973-01-01

An empirical linear relationship has been established by Pike (1967) between the overall diameter and the rim crest diameter for rimmed, flat-floored as well as bowl-shaped, lunar and terrestrial craters formed by impact and explosion. A similar relationship for experimentally formed fluidization craters has been established by Siegal (1971). This relationship is examined in terms of the geometry of the crater and the slope angles of loose materials. The parameter varies from 1.40 to 1.65 and is found to be dependent on mean interior flat floor radius, exterior and interior rim slope angles, angle of aperture of the crater cone, and the volume fraction of crater void accounted for in the rim. The range of the observed parameter can be understood in terms of simple crater geometry by realistic values of the five parameters.

Impact cratering on granular beds: From the impact of raindrops to the strike of hailstones

Science.gov (United States)

Gordillo, Leonardo; Wang, Junping; Japardi, Fred; Teddy, Warren; Gao, Ming; Cheng, Xiang

Impact craters generated by the impact of a spherical object onto a granular bed strongly depend on the material properties of impactors. As an example, impact cratering by liquid drops and by solid spheres exhibits qualitatively different power-law scalings for the size of resulting impact craters. While the basic energy conservation and dimensional analysis provide simple guiding rules, the detailed dynamics governing the relation between these power-law scalings is still far from clear. To analyze the transition between liquid-drop and solid-sphere impact cratering, we investigate impact cratering by liquid drops for a wide range of viscosities over 7 decades. Using high-speed photography and laser profilometry, we delineate the liquid-to-solid transition and show the emergence of the two asymptotic behaviors and their respective power laws. We find that granular avalanches triggered by impacts are crucial in understanding the energy partition between impacted surfaces and impactors, which directly determines the observed scaling relations. A simple model is constructed for the initial stage of the impact that explains the energy partition during crater formation. We ackowledge the support of NSF CAREER DMR-1452180. LG acknowledges fundings from CONICYT/BECAS CHILE 74160007.

Layers of 'Cabo Frio' in 'Victoria Crater' (Stereo)

Science.gov (United States)

2006-01-01

This view of 'Victoria crater' is looking southeast from 'Duck Bay' towards the dramatic promontory called 'Cabo Frio.' The small crater in the right foreground, informally known as 'Sputnik,' is about 20 meters (about 65 feet) away from the rover, the tip of the spectacular, layered, Cabo Frio promontory itself is about 200 meters (about 650 feet) away from the rover, and the exposed rock layers are about 15 meters (about 50 feet) tall. This is a red-blue stereo anaglyph generated from images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during the rover's 952nd sol, or Martian day, (Sept. 28, 2006) using the camera's 430-nanometer filters.