Impactful times memories of 60 years of shock wave research at Sandia National Laboratories

CERN Document Server

Asay, James R; Lawrence, R Jeffery; Sweeney, Mary Ann

2017-01-01

This book presents a history of shock compression science, including development of experimental, material modeling, and hydrodynamics code technologies over the past six decades at Sandia National Laboratories. The book is organized into a discussion of major accomplishments by decade with over 900 references, followed by a unique collection of 45 personal recollections detailing the trials, tribulations, and successes of building a world-class organization in the field. It explains some of the challenges researchers faced and the gratification they experienced when a discovery was made. Several visionary researchers made pioneering advances that integrated these three technologies into a cohesive capability to solve complex scientific and engineering problems. What approaches worked, which ones did not, and the applications of the research are described. Notable applications include the turret explosion aboard the USS Iowa and the Shoemaker-Levy comet impact on Jupiter. The personal anecdotes and recollec...

Energy levy and competitiveness

International Nuclear Information System (INIS)

Berdowski, P.A.M.

1991-01-01

The principle of regulating levies is that the consumption of products that have negative effects on the environment will be reduced. The income of the levies can be reimbursed to the civilians and companies via tax reduction. One of the impacts of the implementation of energy levies is the negative effect on the competitive position of the Dutch industry and businesses. In this report attention is paid to the micro-economic consequences of energy levies. The flows of fifteen production processes and the position of these processes in the market have been analyzed systematically. The impacts of energy levies on these product flows are investigated. The sectors that have been analyzed are the services sector (mainly determined by households), the agricultural food sector, the transportation sector, and the basic industry (mostly energy-intensive industries). In order to determine the sensitivity of the height of the energy levy three variants were investigated: 25%, 50% and 100% surcharge on the present energy costs. The variants are combined with three geographic levy ranges: national, European and global. 21 figs., 9 tabs

UK's climate change levy: cost effectiveness, competitiveness and environmental impacts

International Nuclear Information System (INIS)

Varma, Adarsh

2003-01-01

This paper intends to examine the cost effectiveness of UK's climate change levy (CCL), its implications on competitiveness of firms and the environmental impact. The paper briefly describes the levy and analyses it under the cannons of a good taxation policy. The economic implications of the levy are discussed with theoretical and empirical perspectives. Change in net exports, investment patterns and productivity and inclusion of compliance cost forms the basis for analysing the effect on competitiveness. It discusses the options available to firms to safeguard their competitiveness if it is adversely affected by the CCL. A description of the current scenario of the levy since its inception is also presented. The paper argues the need for a comprehensive policy involving the use of standards, emission trading as well as energy taxes to achieve emission and energy-use reductions. A focal point of this paper is to elucidate the pros and cons of the CCL (energy tax) with respect to an emission trading scheme

The Impact of a Large Object with Jupiter in July 2009

Science.gov (United States)

Sanchez-Lavega, Agustin; Wesley, A.; Orton, G.; Chodas, P.; Hueso, R.; Perez-Hoyos, S.; Fletcher, L.; Yanamandra-Fisher, P.; Legarreta, J.; Gomez-Forrellad, J. M.

2010-05-01

The only major impact ever observed directly in the Solar System was that of a large fragmented comet with Jupiter in July (1994) (Comet Shoemaker-Levy 9; SL9). We report here the observation of a second, single, large impact on Jupiter that occurred on 19 July 2009 at a latitude of -55° with an orthogonal entry trajectory and a lower incidence angle compared to those of SL9. The size of the initial aerosol cloud debris was 4,800 km East-West and 2,500 km North-South. Comparison its properties with those produced by the SL9 fragments, coupled with dynamical calculations of possible pre-impact orbits, indicates that the impactor was most probably an icy body with a size of 0.5-1 km. We calculate that the rate of collisions of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in the near-infrared methane absorption bands at 890 nm and in the 2.12 to 2.3 μm K methane-hydrogen absorption band, where the high-altitude aerosols detach by their brightness relative to Jupiter's primary clouds. We present measurements of the debris dispersion by Jovian winds from a long-term imaging campaign with ground-based telescopes. Ackowledgements: Work was supported by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07, by NASA funds to JPL, Caltech, by the NASA Postdoctoral Program at JPL, and by the Glasstone Fellowship program at Oxford.

The big comet crash of 1994. Intensive observational campaign at ESO

Science.gov (United States)

1994-01-01

far been observed from Shoemaker-Levy 9, but this is not unusual for a comet at this large distance from the Sun, about 750 million kilometres. The most recent observations obtained with telescopes at Hawaii in mid-January 1994 have shown changes in the relative brightness of the individual nuclei, and many of them have now developed individual comet ``tails''. Where and when will the collision take place ? Accurate determinations of the positions of the individual nuclei have permitted to calculate quite precise orbits and it can now be said with 99 percent certainty that all of them will indeed collide with Jupiter. The points of impact are in the Jovian southern hemisphere, at -43 +- 0.6 deg latitude. Unfortunately, these impacts will happen just behind Jupiter's limb, i.e., out of sight from the Earth. However, due to the rapid rotation of the planet, the impact sites will come into view only about 10 minutes later at the very limb where they will be seen ``from the side''. It is also fortunate that the American spacecraft Galileo, now approaching Jupiter, will then be ``only'' about 200 million km away and will have a good view of the impact sites. On the basis of the recent observations, the impact times can now be predicted to about +-40 minutes. The first, rather small nucleus (``A'') will hit the upper layers of Jupiter's atmosphere on July 16, 1994 at about 18:45 Universal Time (UT); the apparently biggest nucleus (``Q'') on July 20, also at 18:45 UT, and the last one in the train (``W''), on July 22 at 07:00 UT. WHAT IS LIKELY TO HAPPEN AT JUPITER ? The comet nuclei will hit Jupiter at a high velocity, about 60 km/sec. The correspondingly large motion energy (the ``kinetic energy'') will all be deposited in the Jovian atmosphere. For a 1 km fragment, this is about equal to 10^28 erg, or no less than about 250,000 Megatons. When one of the cometary nuclei enters the upper layers of the Jovian atmosphere, it will be heated by the friction, exactly as a

UK's climate change levy: cost effectiveness, competitiveness and environmental impacts

Energy Technology Data Exchange (ETDEWEB)

Varma, Adarsh [Hull Univ., School of Economic Studies, Hull (United Kingdom)

2003-01-01

This paper intends to examine the cost effectiveness of UK's climate change levy (CCL), its implications on competitiveness of firms and the environmental impact. The paper briefly describes the levy and analyses it under the canons of a good taxation policy. The economic implications of the levy are discussed with theoretical and empirical perspectives. Change in net exports, investment patterns and productivity and inclusion of compliance cost forms the basis for analysing the effect on competitiveness. It discusses the options available to firms to safeguard their competitiveness if it is adversely affected by the CCL. A description of the current scenario of the levy since its inception is also presented. The paper argues the need for a comprehensive policy involving the use of standards, emission trading as well as energy taxes to achieve emission and energy-use reductions. A focal point of this paper is to elucidate the pros and cons of the CCL (energy tax) with respect to an emission trading scheme. (Author)

The Jovian ring was imaged at 2.26+/-0.03 microns at approximately 7:00 UT on 12 July, 1994, from NA

Science.gov (United States)

2002-01-01

The Jovian ring was imaged at 2.26+/-0.03 microns at approximately 7:00 UT on 12 July, 1994, from NASA's Infrared Telescope Facility. The image was coadded from three 30-second exposures with sky subtracted. The resolution was 0.31 arcseconds per pixel. A S/N 5 per pixel was obtained for the coadded images. Photometry on the ring image is pending. This is part of a program to monitor the effects of the dust from Comet Shoemaker-Levy 9 on the Jovian ring system. More images will be taken during and after the impacts of the fragments. The image was obtained by Philip Esterle (University of Maryland), Casey Lisse (NASA/Goddard Space Flight Center), and Mark Shure (University of Hawaii).

Levi-Strauss : UNESCO = anthropology : politics

Directory of Open Access Journals (Sweden)

Ljiljana Gavrilović

2016-02-01

Full Text Available This paper discusses Levi-Strauss engagement in UNESCO activities. On the one hand, Levi-Strauss engagement in Pakistan had an important impact on his later work, as well as on his overall view about the world and culture( s; while on the other, Levi-Strauss’s definitions of the relationship between race/nation and culture had an important influence on the ways in which UNESCO dealt with the ideas about culture and on the ways these ideas were implemented in its global strategies of action in/towards culture. On the one hand, this engagement included a delivery of the European world view (as a superior one to everyone who does not have it; while on the other, it also meant a protection of material remains of different cultures world-wide and protection of non-material heritage and/as entire "Othern-ness", whenever it is located, and (at least in theory however it looks like. In that sense, Levi- Strauss public engagement had an important impact not only on anthropology, as a discipline that he dedicated his life to, but also to the formation of contemporary understanding of politically correct relationship towards the "Other".

The Hummingbird GC-IMS: In Situ Analysis of a Cometary Nucleus

Science.gov (United States)

Kojiro, Daniel R.; Carle, Glenn C.; Cohen, Martin J.; Wernlund, Roger F.; Stimac, Robert M.; Takeuchi, Norishige; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Comets are of enormous scientific interest for many reasons. They are primitive bodies that date back to the earliest stages of solar system formation and, because of their small size and because they have been stored in the outer reaches of the solar system, their pristine nature has been preserved better than for any other class of body. They are extremely rich in highly volatile elements, many in the form of ices, and are richer in organic matter than any other known solar system body. It is strongly suspected that in addition to their content of primordial solar nebular material, they also incorporate unprocessed matter from the interstellar medium. Impacts by comets occur onto all the planets and satellites, often with major consequences (e.g., the dinosaur extinction event at the KIT boundary), or sometimes just providing a spectacular cosmic event (e.g., the collision of comet Shoemaker-Levy 9 with Jupiter). A mission to analyze a cometary nucleus must be capable of detecting and identifying over 30 molecular species among several different chemical groups. The Hummingbird Mission will rendezvous with, orbit, characterize, and make multiple descents to the nucleus of a comet. Hummingbird will employ a Gas Chromatograph - Ion Mobility Spectrometer (GC-IMS) as part-of a suite of sophisticated instruments for a comprehensive in situ elemental, molecular, and isotopic analysis of the comet.

Endogenous enforcement and effectiveness of China's pollution levy system

OpenAIRE

Hua Wang; Wheeler, David

2000-01-01

The authors investigate two aspects of China's pollution levy system, which was first implemented about 20 years ago. First, they analyze what determines differences in enforcement of the pollution levy in various urban areas. They find that collection of the otherwise uniform pollution levy is sensitive to differences in economic development and environmental quality. Air and water pollution levies are higher in areas that are heavily polluted. Second, they analyze the impact of pollution ch...

Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis

Science.gov (United States)

Boslough, M.

2009-12-01

One breakthrough of 20th-century Earth science was the recognition of impacts as an important geologic process. The most obvious result is a crater. There are more than 170 confirmed terrestrial impact structures with a non-uniform spatial distribution suggesting more to be found. Many have been erased by tectonics and erosion. Deep water impacts do not form craters, and craters in ice sheets disappear when the ice melts. There is growing speculation that such hidden impacts have caused frequent major environmental events of the Holocene, but this is inconsistent with the astronomically-constrained population of Earth-crossing asteroids. Impacts can have consequences much more significant than excavation of a crater. The K/T boundary mass extinction is attributed to the environmental effects of a major impact, and some researchers argue that other extinctions, abrupt climate changes, and even civilization collapses have resulted from impacts. Nuclear winter models suggest that 2-km diameter asteroids exceed a "global catastrophe threshold" by injecting sufficient dust into the stratosphere to cause short-term climate changes, but would not necessarily collapse most natural ecosystems or cause mass extinctions. Globally-catastrophic impacts recur on timescales of about one million years. The 1994 collision of Comet Shoemaker-Levy 9 with Jupiter led us recognize the significance of terrestrial airbursts caused by objects exploding violently in Earth’s atmosphere. We have invoked airbursts to explain rare forms of non-volcanic glasses and melts by using high-resolution computational models to improve our understanding of atmospheric explosions, and have suggested that multiple airbursts from fragmented impactors could be responsible for regional effects. Our models have been cited in support of the widely-publicized YDB impact hypothesis. Proponents claim that a broken comet exploded over North America, with some fragments cratering the Laurentide Ice Sheet. They

Study on the Application of 6σ Method in Shoemaking Enterprise Quality Improvement

Directory of Open Access Journals (Sweden)

Wang Ting

2017-01-01

Full Text Available With the development of science as well as technology and the influx of shoemaking companies abroad, our traditional shoemaking enterprises face greater pressure to survive, and product quality problems are in urgent need of improvement. Aiming at the quality problems of M shoemaking enterprise, DMAIC method is used to conduct the product quality improvement, and a mathematical statistics software Minitab is used to analyze the data. Moreover, the optimum combination of the key influencing factors is determined by orthogonal experiment design as well as a set of specific quality improvement plans are put forward. Finally, the production process capability of M enterprise is improved, the product bonding strength is enhanced, customer satisfaction is improved, and the thoughts of product quality improvement and reference are provided for domestic traditional shoemaking enterprises.

ISO's analysis of Comet Hale-Bopp

Science.gov (United States)

1997-03-01

spatial resolution of ISO. We have a long time coverage of the comet, so we hope to determine the light-curve of the nucleus -- which, in turn, will reveal its gross shape and an estimate of its rotation period." A commanding role in comet research As comets are relics from the construction of the Solar System, and played a major role in the formation of the planets, they are a link between the Earth and the wider Universe of stars. The carbon compounds contained in comets probably contributed raw materials for the origin of life on the Earth, and according to one theory the Earth's oceans were made from comet ice. Growing knowledge of the composition and behaviour of comets is therefore crucial for a fuller understanding of our cosmic origins. ESA has a commanding role in space research on comets. Its Giotto spacecraft was the most daring of the international fleet of spacecraft that visited Halley's Comet in March 1986. Giotto obtained exceptional pictures and other data as it passed within 600 kilometres of the nucleus. Dust from the comet badly damaged the spacecraft, but in a navigational tour de force Giotto made an even closer approach to Comet Grigg-Skjellerup in July 1992. Now ESA is planning the Rosetta mission that will rendezvous with Comet Wirtanen and fly in company with it, making observations far more detailed than the fast flybys of Halley's Comet and Comet Grigg-Skjellerup could achieve. As for space astronomy, the International Ultraviolet Explorer, in which ESA was a partner, made unrivalled observations of Halley's Comet by ultraviolet light. ESA is also a partner in the Hubble Space Telescope, which saw the historic impacts of Comet Shoemaker-Levy 9 on Jupiter in July 1994, and has recently observed Comet Hyakutake as well as Hale-Bopp. The SOHO spacecraft, built by ESA for a joint ESA-NASA project to examine the Sun, has a distinctive view of comets. It has observed the hydrogen coronas of comets with its SWAN instrument. SOHO's coronagraph LASCO

Meet EPA Scientist Jody Shoemaker, Ph.D.

Science.gov (United States)

EPA research chemist Jody Shoemaker, Ph.D., works to support Agency efforts to protect drinking water. She helps develop methods for analyzing organic chemicals on the Drinking Water Contaminant Candidate List (CCL).

Detection of CS in Neptune's atmosphere from ALMA observations

Science.gov (United States)

Moreno, R.; Lellouch, E.; Cavalié, T.; Moullet, A.

2017-12-01

Context. The large and vertically non-uniform abundance of CO in Neptune's atmosphere has been interpreted as the result of past cometary impact(s), either single or distributed in size and time, which could also be at the origin of Neptune's HCN. Aims: We aim to provide observational support for this scenario by searching for other comet-induced species, in particular carbon sulfide (CS) which has been observed continuously in Jupiter since the 1994 Shoemaker-Levy 9 impacts. Methods: In April 2016 we used the ALMA interferometer to search for CS(7-6) at 342.883 GHz in Neptune. Results: We report on the detection of CS in Neptune's atmosphere, the first unambiguous observation of a sulfur-bearing species in a giant planet beyond Jupiter. Carbon sulfide appears to be present only at submillibar levels, with a column density of (2.0-3.1) × 1012 cm-2, and a typical mixing ratio of (2-20) × 10-11 that depends on its precise vertical location. The favoured origin of CS is deposition by a putative large comet impact several centuries ago, and the strong depletion of CS with respect to CO - compared to the Jupiter case - is likely due to the CS sticking to aerosols or clustering to form polymers in Neptune's lower stratosphere. Conclusions: The CS detection, along with recent analyses of the CO profile, reinforces the presumption of a large comet impact into Neptune 1000 yr ago, that delivered CO, CS, and HCN at the same time.

Levy Foraging in a Dynamic Environment – Extending the Levy Search

Directory of Open Access Journals (Sweden)

Vincenzo Fioriti

2015-07-01

Full Text Available A common task for robots is the patrolling of an unknown area with inadequate information about target locations. Under these circumstances it has been suggested that animal foraging could provide an optimal or at least sub-optimal search methodology, namely the Levy flight search. Although still in debate, it seems that predators somehow follow this search pattern when foraging, because it avoids being trapped in a local search if the food is beyond the sensory range. A Levy flight is a particular case of the random walk. Its displacements on a 2-D surface are drawn from the Pareto-Levy probability distribution, characterized by power law tails. The Levy flight search has many applications in optical material, ladars, optics, large database search, earthquake data analysis, location of DNA sites, human mobility, stock return analysis, online auctions, astronomy, ecology and biology. Almost all studies and simulations concerning the Levy flight foraging examine static or slowly moving (with respect to the forager uniformly distributed resources. Moreover, in recent works a small swarm of underwater autonomous vehicles has been used to test the standard Levy search in the underwater environment, with good results. In this paper we extend the classical Levy foraging framework taking into consideration a moving target allocated on a 2-D surface according to a radial probability distribution and comparing its performance with the random walk search. The metric used in the numerical simulations is the detection rate. Simulations include the sensor resolution, intended as the maximum detection distance of the forager from the target. Furthermore, contrarily to the usual Levy foraging framework, we use only one target. Results show that Levy flight outperforms the random walk if the sensor detection radius is not too small or too large. We also find the Levy flight in the velocity of the center of mass model of a fish school according the Kuramoto

Levy-free part in energy tax is not wanted

International Nuclear Information System (INIS)

Gilijamse, W.

1995-01-01

The Dutch government proposed to implement an energy levy for small-scale consumers in 1996. The yields will be reimbursed by means of a reduction of the tax burden. By applying a levy-free tax allowance the tax reduction can be limited. However, it appears that this allowance does not work: it reduces the energy saving impact of the energy levy, because it does not stimulate investments in energy saving housing construction and energy saving heat supply. It also interferes with a just compensation of income. It is recommended to cancel the levy-free tax allowance and to realize compensation by raising the tax free allowance in the income tax. 2 figs., 1 tab., 6 refs

Final report of the Steering Group Regulating Energy Levies

International Nuclear Information System (INIS)

Wolfson, D.J.; Frijns, J.M.G.; Opschoor, J.B.; Rissik, S.A.; Stevens, L.G.M.

1992-02-01

The aim is to determine to what extent regulating energy levies can generate energy savings, and to gain insight into the economic impacts of energy levies. Special attention is paid to the consequences for the competitive position and the development of economic and industrial activities, employment, distribution of incomes and purchasing power. An indication is given to what extent policy tools for regulating energy levies meet the criteria for efficiency, effectivity and legitimacy. Three hypothetic measures to map the energy saving effects and economic side-effects are discussed for two tax-levels: 50% and 100%. Variant A is a fixed levy on all the primary energy carriers, implemented on an OECD-level, equally based on the carbon content and the energy content. Variant B is the same as variant A, but only implemented in the Netherlands. Variant C is a fixed levy on the energy consumption of small energy consumers in the Netherlands, which variant spares and protects the energy-intensive industry. In the chapters 5, 6 and 7 the results of preliminary studies on price elasticities and energy consumption in the road traffic sector, households, and housing construction are discussed, as well as energy conservation in the rental sector and the Dutch production economies, and the competitive impacts of energy levies on industry and business in the Netherlands. In chapter 8 and 9 possibilities to reimburse the revenues to the government, the businesses or industries, and the households, are mentioned and considered. Attention is paid to the financial consequences and the impacts on spending power. In chapter (10) the economic effects of the levy variants, as calculated by the Centraal Plan Bureau (CPB, Dutch government institute for economic planning), are described. Variant A will result in substantial negative economic effects: loss of income and a limited growth of employment, caused by transfer of part of the energy-intensive industry to outside the OECD

Comet Dust After Deep Impact

Science.gov (United States)

Wooden, Diane H.; Harker, David E.; Woodward, Charles E.

2006-01-01

When the Deep Impact Mission hit Jupiter Family comet 9P/Tempel 1, an ejecta crater was formed and an pocket of volatile gases and ices from 10-30 m below the surface was exposed (A Hearn et aI. 2005). This resulted in a gas geyser that persisted for a few hours (Sugita et al, 2005). The gas geyser pushed dust grains into the coma (Sugita et a1. 2005), as well as ice grains (Schulz et al. 2006). The smaller of the dust grains were submicron in radii (0-25.3 micron), and were primarily composed of highly refractory minerals including amorphous (non-graphitic) carbon, and silicate minerals including amorphous (disordered) olivine (Fe,Mg)2SiO4 and pyroxene (Fe,Mg)SiO3 and crystalline Mg-rich olivine. The smaller grains moved faster, as expected from the size-dependent velocity law produced by gas-drag on grains. The mineralogy evolved with time: progressively larger grains persisted in the near nuclear region, having been imparted with slower velocities, and the mineralogies of these larger grains appeared simpler and without crystals. The smaller 0.2-0.3 micron grains reached the coma in about 1.5 hours (1 arc sec = 740 km), were more diverse in mineralogy than the larger grains and contained crystals, and appeared to travel through the coma together. No smaller grains appeared at larger coma distances later (with slower velocities), implying that if grain fragmentation occurred, it happened within the gas acceleration zone. These results of the high spatial resolution spectroscopy (GEMINI+Michelle: Harker et 4. 2005, 2006; Subaru+COMICS: Sugita et al. 2005) revealed that the grains released from the interior were different from the nominally active areas of this comet by their: (a) crystalline content, (b) smaller size, (c) more diverse mineralogy. The temporal changes in the spectra, recorded by GEMIM+Michelle every 7 minutes, indicated that the dust mineralogy is inhomogeneous and, unexpectedly, the portion of the size distribution dominated by smaller grains has

Comets, Charisma, and Celebrity: Reflections on Their Deep Impact

Science.gov (United States)

Olson, R. J. M.; Pasachoff, J. M.

In celebration of the Deep Impact Mission, this essay explores the influence of comets on the arts and sciences since the beginning of recorded time. Through images, ranging from the sublime to the humorous, it probes the reasons why comets are among the most charismatic visual spectacles in the universe and why, even as scientific missions unmask their mysteries, they remain iconic symbols and harbingers of change.

Greening of taxes and energy. Effects of increased energy levies and specific exemptions

International Nuclear Information System (INIS)

1997-06-01

The study on the title subject is part of a new long-term outlook for the period 1990-2020, focusing on the environment, mobility, space (physical planning) and energy. The environmental, employment and economic impacts of two levy variants have been analyzed. The first is the so-called Regulating Energy Levy (REB, abbreviated in Dutch), and the second is the Environment-Based Tax Law (WBM, abbreviated in Dutch). Tax rebates to households and businesses are in the form of a lower income tax and lower employer contributions. It is concluded that it is possible to double existing energy levies or to triple them for small-scale consumers without large economic impacts, provided that (1) large-scale consumers are spared; (2) the levies are rebated totally or partly; and (3) levy and rebate will be accepted by the Dutch society

The economic consequences of a fuel levy reform in South Africa

Directory of Open Access Journals (Sweden)

Ramos Mabugu

2011-06-01

Full Text Available This paper assesses the economic effects of a hypothetical fuel levy imposed by South African provinces. The welfare effects of increasing the fuel levy by 10 per cent are negative but very small. Similarly, the marginal excess burdens for efficiency and equity (poverty are quite low, suggesting much smaller impacts of the intervention on both economic activity and equity.  Furthermore, a fiscal policy reform that raises fuel levy by 10 per cent is progressive as it has stronger negative effects on higher income households than the lower income households. A potential source of instability for the macroeconomy and total government revenue is the negative effect on economic activity induced by the fuel levy increase. The remedies suggested are that policymakers should make tax room elsewhere in the intergovernmental fiscal system to accommodate the fuel levy increase.

Hydrodynamic Modeling of the Deep Impact Mission into Comet Tempel 1

Science.gov (United States)

Sorli, Kya; Remington, Tané; Bruck Syal, Megan

2018-01-01

Kinetic impact is one of the primary strategies to deflect hazardous objects off of an Earth-impacting trajectory. The only test of a small-body impact is the 2005 Deep Impact mission into comet Tempel 1, where a 366-kg mass impactor collided at ~10 km/s into the comet, liberating an enormous amount of vapor and ejecta. Code comparisons with observations of the event represent an important source of new information about the initial conditions of small bodies and an extraordinary opportunity to test our simulation capabilities on a rare, full-scale experiment. Using the Adaptive Smoothed Particle Hydrodynamics (ASPH) code, Spheral, we explore how variations in target material properties such as strength, composition, porosity, and layering affect impact results, in order to best match the observed crater size and ejecta evolution. Benchmarking against this unique small-body experiment provides an enhanced understanding of our ability to simulate asteroid or comet response to future deflection missions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-739336-DRAFT.

Stochastic Levy Divergence and Maxwell's Equations

Directory of Open Access Journals (Sweden)

B. O. Volkov

2015-01-01

Full Text Available One of the main reasons for interest in the Levy Laplacian and its analogues such as Levy d'Alembertian is a connection of these operators with gauge fields. The theorem proved by Accardi, Gibillisco and Volovich stated that a connection in a bundle over a Euclidean space or over a Minkowski space is a solution of the Yang-Mills equations if and only if the corresponding parallel transport to the connection is a solution of the Laplace equation for the Levy Laplacian or of the d'Alembert equation for the Levy d'Alembertian respectively (see [5, 6]. There are two approaches to define Levy type operators, both of which date back to the original works of Levy [7]. The first is that the Levy Laplacian (or Levy d'Alembertian is defined as an integral functional generated by a special form of the second derivative. This approach is used in the works [5, 6], as well as in the paper [8] of Leandre and Volovich, where stochastic Levy-Laplacian is discussed. Another approach to the Levy Laplacian is defining it as the Cesaro mean of second order derivatives along the family of vectors, which is an orthonormal basis in the Hilbert space. This definition of the Levy Laplacian is used for the description of solutions of the Yang-Mills equations in the paper [10].The present work shows that the definitions of the Levy Laplacian and the Levy d'Alembertian based on Cesaro averaging of the second order directional derivatives can be transferred to the stochastic case. In the article the values of these operators on a stochastic parallel transport associated with a connection (vector potential are found. In this case, unlike the deterministic case and the stochastic case of Levy Laplacian from [8], these values are not equal to zero if the vector potential corresponding to the stochastic parallel transport is a solution of the Maxwell's equations. As a result, two approaches to definition of the Levy Laplacian in the stochastic case give different operators. This

The Data of Levy and Levy (2002) ÜProspect Theory: Much Ado About Nothing?Ý Actually Support Prospect Theory

OpenAIRE

Peter P. Wakker

2003-01-01

Levy and Levy (Management Science2002) present data that, according to their claims, violate prospect theory. They suggest that prospect theory's hypothesis of an S-shaped value function, concave for gains and convex for losses, is incorrect. However, all the data of Levy and Levy are perfectly consistent with the predictions of prospect theory, as can be verified by simply applying prospect theory formulas. The mistake of Levy and Levy is that they, incorrectly, thought that probability weig...

Solar wind interaction with comet 67P: Impacts of corotating interaction regions

Science.gov (United States)

Edberg, N. J. T.; Eriksson, A. I.; Odelstad, E.; Vigren, E.; Andrews, D. J.; Johansson, F.; Burch, J. L.; Carr, C. M.; Cupido, E.; Glassmeier, K.-H.; Goldstein, R.; Halekas, J. S.; Henri, P.; Koenders, C.; Mandt, K.; Mokashi, P.; Nemeth, Z.; Nilsson, H.; Ramstad, R.; Richter, I.; Wieser, G. Stenberg

2016-02-01

We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7 AU from the Sun and the neutral outgassing rate ˜1025-1026 s-1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30 km. The ionospheric low-energy (˜5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (˜10-100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

CO2-impacts of a small-scale consumers levy

International Nuclear Information System (INIS)

1995-02-01

Because of a number of developments (altered budgets of Dutch ministries and implementation of environmental policy plans of energy distribution companies in the Netherlands) the 1993 analyses of the effects of a small-scale consumer levy on the emission of CO 2 are updated. First, attention is paid to the conservation impetus as a result of an increase of the energy price for small-scale consumers. Next, the effects that can occur as a consequence of the presently suggested form of the levy (in particular, the exemption of renewable energy and waste heat) are discussed. Subsequently, the alterations of other policy tools, that are necessary in case a higher effectiveness of conservation measures is realized, are dealt with. The direct effect of a higher energy price on the saving behavior of the small-scale consumers is calculated by means of the CENECA-model. 4 tabs., 1 appendix, 8 refs

Congestion levies; Congestieheffingen

Energy Technology Data Exchange (ETDEWEB)

Verhoef, E.T. [Vakgroep Ruimtelijke Economie, Vrije Universiteit en Tinbergen Instituut, Amsterdam (Netherlands)

1998-02-20

Traffic jams or congestion can be controlled by means of Pigouvian levies. Congestion costs comprise both time losses as scheduling costs. Because a part of those costs are external costs, the free market output is not Pareto-efficient, and therefore levies are required to recover the efficiency. With some restrictions, road-pricing for the western part of the Netherlands is considered to be a feasible option

Piaget and Levy-Bruhl.

Science.gov (United States)

Jahoda, G

2000-08-01

Levy-Bruhl exerted a powerful influence, seldom considered, on Piaget. The Levy-Bruhlian thesis of a "pre-logical mentality" characterized by "mystical participation" is outlined, together with its initial reception. The first evidence of Piaget's interest in it dates from 1920, and when he began his studies of children's thinking he compared it with that of 'primitives," also adopting Levy-Bruhl's concept of "participation." By 1928 Piaget had elaborated a theory of the social foundations of different types of thought, which he regarded as also explaining the alleged similarity between the thinking of primitives and children. Both are subject to constraint, primitives by elders and children by parents and teachers. Logical as opposed to pre-logical thought was said to depend on cooperation in free social interaction. Piaget continued to maintain essentially the same views long after Levy-Bruhl himself had renounced the notion of pre-logicality.

Survival of Glycolaldehyde and Production of Sugar Compounds via Comet Impact Delivery

Science.gov (United States)

Zellner, N.; McCaffrey, V.; Crake, C.; Butler, J.; Robbins, J.; Fodor, A.

2017-12-01

Impact experiments using glycolaldehyde (GLA), a two-carbon sugar precursor that has been detected in regions of the interstellar medium and on comets, have been conducted at the Experimental Impact Laboratory at NASA's Johnson Space Center. Samples of GLA and GLA mixed with montmorillonite clays were subjected to the pressure conditions that are found during impact delivery of biomolecules by comets, asteroids, or meteors; pressures ranged from 4.5 GPa to 25 GPa. Results show that large amounts of GLA survived the impacts and moderate amounts of threose, erythrose, and glycolic acid were produced in these impacts. Total amounts are dependent on impact pressure. Ethylene glycol, a reduced variant of GLA that has also been detected in the interstellar medium and on comets, was also produced. The results of these experimental impacts provide evidence that large amounts of GLA, EG, and other biomolecules were available on habitable moons or planets, especially during the era of late heavy bombardment ( 4.2 to 3.7 billion years ago) when life may have been developing on Earth. The presence and availability of these biomolecules, under appropriate conditions, may be important for understanding the origin of life as we know it. Glycolaldehyde in particular, may be an important molecule in the production of ribose, the five-carbon sugar in RNA.

Participation of firms in the skills development levy system

Directory of Open Access Journals (Sweden)

GJ Lee

2004-04-01

Full Text Available Skills development levies are increasingly being utilised to increase enterprise provided training in developing economies. South Africa is one such example. The impact of such incentive systems on the bottom-line of firms is a vital consideration in such programs. Particularly important are the economic conditions under which the incentive will stimulate participation by organisations. The transaction costs of participation must be taken into account: while a levy-grant system clearly creates a prima-facie incentive, it may be prohibitively expensive for some firms to enter the grant disbursement systems. Accordingly, through a simple model of the incentives for firms, the participation level of the firm under various types of levy systems is assessed. Non-monetary considerations are also considered. The implications for participation by firms, along with managerial and policy implications, are discussed.

[Bipolaris bicolor (Mitra) Shoemaker: Species associated to folial spot in pupunha palm (Bactris gasipaes Kunth) in Brazil.].

Science.gov (United States)

Rodríguez-Morejón, K; Kimati, H; Fancelli, M I

1998-03-01

One species of hiphomycetos group, belonging to the genus Bipolaris Shoemaker that was identified like Bipolaris bicolor (Mitra) Shoemaker is recorded for the first time on pupunha palm (Bactris gasipaes Kunth) from Brazil. The comparison with other close species reported like pathogenic folial spot in genus Arecaceae is made. Its morphological and cultural characteristics are described.

Who is paying for the energy levy?

International Nuclear Information System (INIS)

Kazemier, B.; Keuning, S.J.; Zijlmans, G.M.

1992-01-01

An analysis of the consequences of an energy levy should not only be aimed at the direct energy consumption (heating, lighting, engine fuels), but also on energy used for the production of goods and services, and the conversion of one energy carrier into the other. Attention is paid to the distribution of direct and indirect public purchasing power effects of three different types of levies. The levies considered here are (1) an energy levy on primary energy sources only in the Netherlands; (2) as (1) but for the whole world; and (3) an energy levy on the energy consumption of households. The effects will be best equallly spread over the households in the case of a worldwide, uniform levy. 3 tabs., 2 refs

Tying Extinction Events to Comet Impacts Large Enough to Cause an Extinction in Themselves.

Science.gov (United States)

Burgener, J. A.

2017-12-01

Comets over 35 km in size impacting Earth will create vast fireballs, and will boil large parts of the oceans, causing extinction events in themselves. They will likely provide enough energy to shatter the crust and eject large masses of molten rock from the mantle, forming traps. Traps are clearly associated with extinction events, but are not expected to cause extinctions. While Chicxulub is recognized to have occurred at the time of the K/Pg boundary layer, it is recognized as being too small in itself to cause an extinction. Are large comet impacts likely? The Kuiper belt has more than 100,000 objects over 100 km in diameter and millions over 10 km. Typically their orbits are less stable than asteroid orbits due to large bodies such as Pluto moving through the belt. The asteroid belt has only 10,000 objects over 10 km diameter. Comet impacts should be more common than asteroid impacts, yet none of the recognized craters are expected to be due to comets. There are many features on Earth that are poorly explained by Plate Tectonics that would be well explained if they were considered to be comet impact craters. A consideration of the Black Sea and the Tarim Basin will show that impact interpretations are a better fit than the present Plate Tectonics' explanations. Both basins are in the midst of mountain building from plate collisions, but are themselves not being disturbed by the plate collisions. Both are ellipses angled at 23.4 degrees to the equator, matching the angle expected for a low angle impact from a comet traveling in the ecliptic. Both are too deep at 15 km depths to be standard oceans (typically 5 km deep). Both are filled with horizontal layers of sediments, undisturbed by the mountain building occurring at the edges. Both have thin crusts and high Moho boundaries. Both have thin lithosphere. Yet both show GPS movement of the land around them moving away from them, as though they were much thicker and stronger than the surrounding land. The Tarim

ECONOMY AND PARA-FISCAL LEVIES IN BOSNIA AND HERZEGOVINA

Directory of Open Access Journals (Sweden)

Hasan Mahmutović

2017-04-01

Full Text Available The system of para-fiscal levies implies different types of benefits or compensation and payment of citizens and companies for the use of goods or services of state administration which are para-fiscal sources of income of the state. The main characteristics of para-fiscal levies are: they do not originate from all tax payers, but only from members of certain social groups that are linked to some common economic or social interests; they are not part of the budget funds and not regulate them fiscal authorities; they have the character of destined public revenues, as they regularly represent a dedicated revenue whit which a specific task of economic or social character would be solved; they represent a secondary tax levy, which means that they exist along with the country’s tax levy, to draw funds from the same economic resources and to have almost the same economic effects, as well as the collection of taxes; they shall be paid on the basis of laws and decisions or decision of the competent authorities (general obligation or by contract (a specific levy, ie. an individual obligation; they shall be paid in the event of use of property of general interest and / or services of state administration; they represent giving of money, which is always direct, ie. giving cash on the basis of the decision and with the issuance of a receipt of payment (receipt from a box office or bank. Para-fiscal levies should be understood as fees that economic operators and citizens pay for the use of certain goods or services. These are not taxes and they do not serve to fill the budget. However, in Bosnia and Herzegovina the biggest part of para-fiscal levies is used as a parallel budget revenue, as revenue for the operation of the costly administrative apparatus. A large number of studies on para-fiscal levies in Bosnia and Herzegovina showed that they have a negative impact on economic growth and development. Basically para-fiscal levies, for business entities at

Green taxes by doubling energy levies

International Nuclear Information System (INIS)

De Vos, R.

1998-01-01

An overview is given of green taxes, levies and investment facilities in the Netherlands. Also, attention is paid to the main issues in the Third Dutch National Environmental Plan (NMP3). Energy levies are imported for the Dutch government to shift taxes on labor further towards taxes on pollution. However, the proposed doubling of the energy levies meets strong opposition from industry and businesses. 2 fig., 3 tabs

Fluctuations in a Levy flight gas

International Nuclear Information System (INIS)

Fogedby, H.C.; Jensen, H.J.

1991-01-01

We consider the density fluctuations of an ideal Brownian gas of particles performing Levy flights characterized by the index f. We find that the fluctuations scale as ΔN(t)∝t H , where the Hurst exponent H locks onto the universal value 1/4 for Levy flights with a finite root mean square range (f>2). For Levy flights with a finite mean range but infinite root mean square range (1< f<2) the Hurst exponent H=1/2f. For infinite range Levy flights (f<1) the Hurst exponent locks onto the value 1/2. The corresponding power spectrum scales with an exponent 1+2H, independent of dimension. (orig.)

The economics of the CDM levy: Revenue potential, tax incidence and distortionary effects

International Nuclear Information System (INIS)

Fankhauser, Samuel; Martin, Nat

2010-01-01

A levy on the Clean Development Mechanism and other carbon trading schemes is a potential source of finance for climate change adaptation. An adaptation levy of 2% is currently imposed on all CDM transactions which could raise around $500 million between now and 2012. This paper analyses the scope for raising further adaptation finance from the CDM, the economic costs (deadweight loss) of such a measure and the incidence of the levy, that is, the economic burden the levy would impose on the buyers and sellers of credits. We find that a levy of 2% could raise up to $2 billion a year in 2020 if there are no restrictions on demand. This could rise to $10 billion for a 10% tax. Restrictions on credit demand (called supplementarity limits, the requirement that most emission abatement should happen domestically) curtail trade volumes and consequently tax revenues. They also alter the economic impact of the CDM levy. Without supplementarity restrictions sellers (developing countries) bear two-thirds of the cost of the tax. If there are supplementarity limits they can pass on the tax burden to buyers (developed countries) more or less in full. Without supplementarity restrictions the distortionary effect of the levy (its deadweight loss) rises sharply with the tax rate. With them the deadweight loss is close to zero.

K/T boundary stratigraphy: Evidence for multiple impacts and a possible comet stream

Science.gov (United States)

Shoemaker, E. M.; Izett, G. A.

1992-01-01

A critical set of observations bearing on the K/T boundary events were obtained from several dozen sites in western North America. Thin strata at and adjacent to the K/T boundary are locally preserved in association with coal beds at these sites. The strata were laid down in local shallow basins that were either intermittently flooded or occupied by very shallow ponds. Detailed examination of the stratigraphy at numerous sites led to the recognition of two distinct strata at the boundary. From the time that the two strata were first recognized, E.M. Shoemaker has maintained that they record two impact events. We report some of the evidence that supports this conclusion.

Comets, impacts, and atmospheres

Science.gov (United States)

Owen, Tobias; Bar-Nun, Akiva

Studies of element abundances and values of D/H in the atmospheres of the giant planets and Titan have emphasized the important role of icy planetesimals in the formation of these bodies. In these atmospheres, C/H and D/H increase as the relative masses of the 'cores' of the planets increase. N/H appears to deviate from this trend in an interesting way. In the inner solar system, the traditional approach of using carbonaceous chondrites as the source of planetary volatiles is in serious trouble because of the depletion of xenon and the unusual pattern of xenon isotopes found in the atmospheres of Earth and Mars, and because of the solar-type abundance ratios of argon, krypton and xenon and the large amounts of neon and argon on Venus. Recent studies of elemental abundances in comets, especially P/Halley, coupled with laboratory studies of the trapping of gas in ice formed at low temperatures by A. Bar-Nun et al. provide a consistent interpretation of all of these results. This interpretation emphasizes the fundamental importance of icy planetesimals (comets) and the randomness of early impacts in the formation of planetary systems. Cometary delivery by itself will not explain the noble gas abundances on the inner planets. There is good evidence for at least one additional source, which presumably consists of the rocky material making up the bulk of the planets. The existence of this rocky reservoir is manifested in the nucleogenic isotopes and in the neon which is found in all these atmospheres and is also present in the Earth's mantle. This neon may well be a relic of the planets' earliest, accretional atmospheres.

Scale-free animal movement patterns: Levy walks outperform fractional Brownian motions and fractional Levy motions in random search scenarios

International Nuclear Information System (INIS)

Reynolds, A M

2009-01-01

The movement patterns of a diverse range of animals have scale-free characteristics. These characteristics provide necessary but not sufficient conditions for the presence of movement patterns that can be approximated by Levy walks. Nevertheless, it has been widely assumed that the occurrence of scale-free animal movements can indeed be attributed to the presence of Levy walks. This is, in part, because it is known that the super-diffusive properties of Levy walks can be advantageous in random search scenarios when searchers have little or no prior knowledge of target locations. However, fractional Brownian motions (fBms) and fractional Levy motions (fLms) are both scale-free and super-diffusive, and so it is possible that these motions rather than Levy walks underlie some or all occurrences of scale-free animal movement patterns. Here this possibility is examined in numerical simulations through a determination of the searching efficiencies of fBm and fLm searches. It is shown that these searches are less efficient than Levy walk searches. This finding does not rule out the possibility that some animals with scale-free movement patterns are executing fBm and fLm searches, but it does make Levy walk searches the more likely possibility.

Primo Levi and Franz Kafka: an Unheimlich Encounter

Directory of Open Access Journals (Sweden)

Stefano Bellin

2016-11-01

Full Text Available In 1983 Giulio Einaudi asked Primo Levi to translate Kafka’s Trial for the new series «Scrittori tradotti da scrittori». The proposal sounded original and provocative, and Levi accepted eagerly. The translation, however, had a negative effect on him. While working on The Trial, Levi relived his Auschwitz season, revived his deepest fears, and fell back into depression: he felt as if he was himself on trial. This was partially due to a clash of literary styles as well as to two contrasting – and yet at times kindred – conceptions of language and communication. The present study addresses the following questions: were Levi and Kafka’s literary styles as opposed as Levi implies? How is Levi’s “obscure part” connected to Kafka? Why did Levi associate The Trial with his Holocaust experience and identify himself with Josef K.? What does Levi’s encounter with Kafka tell us about the shame of being human and our capacity to give an account of ourselves? By investigating Levi’s uncanny encounter with Kafka, my essay will discuss Levi’s theory of language, showing how the Levi-Kafka intersection opens up new ways of interpreting Levi’s concerns about communication, the work of the witness, moral responsibility, and shame, which coalesced into the reflections of The Drowned and the Saved.Nel 1983 Giulio Einaudi chiese a Primo Levi di tradurre Il processo di Kafka per la nuova serie Scrittori tradotti da scrittori. La proposta parse a Levi originale ed intelligente, sicché la accettò immediatamente. La traduzione ebbe tuttavia un effetto negativo su di lui. Mentre lavorava al Processo, Levi rivisse la stagione di Auschwitz, risentì le sue più profonde paure e ricadde in depressione. Si sentiva come se fosse lui stesso processato. Ciò era in parte dovuto a due opposte concezioni di stile letterario e a due divergenti – anche se a volte paradossalmente affini – concezioni del linguaggio e della comunicazione. Il presente

The variability of meteoroid falling

Science.gov (United States)

Velasco Herrera, V. M.; Cordero, G.

2016-10-01

We analysed a historical catalogue of meteoroid falling during the last 400 years. We report here for the first time the synchronization between observed meteors and solar barycentric parameters in 19.6 and 13.2 years periodicities using a new multiple cross wavelet. The group of moderated number of meteors is distributed around the positive phase of the solar barycentric periodicity of 13.2 years. While the group of severe number of meteors are distributed on the positive phase of the solar barycentric periodicity of 19.6 years. These periodicities could be associated with Jupiter periodicities. So understanding the modulation of meteoroid falling is important for determining the falling patterns of these objects and for knowing when it is more likely to expect the entry of one of these objects into the Earth's atmosphere, because bodies falling onto the Earth can cause damage from minor impacts to mass-extinctions events. One of the most extreme events was the formation of the Chicxulub impact crater 65,000,000 years ago that caused one of the five major mass extinctions in the last 500,000,000 years. During the 20th and 21st centuries, a series of events demonstrated the importance of collisions between planets and small bodies (comets and asteroids), which included our own planet. In the case of the Earth, we can cite three examples: Tunguska, Curuça and Chelyabinsk. These events invite us to think that perhaps the occurrence of this phenomenon might be more common than we realize, but the lack of communication or people in the area where they happened prevents us from having a complete record. Modern man has not witnessed the impact of large asteroids or comets on our planet, but it has been observed on other planetary bodies. The most spectacular of these events was the collision of fragments of the comet Shoemaker-Levy 9 with Jupiter in 1994. The total energy of the 21 impacts on Jupiter's atmosphere was estimated as the equivalent of tens of millions of

Collisional Histories of Comets and Trojan Asteroids: Insights from Forsterite and Enstatite Impact Studies

Science.gov (United States)

Lederer. S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Smith, D. C.; Cintala, M. J.; Nakamura-Messenger, K.; Keller, L. P.

2012-01-01

Impacts into forsterite and orthoenstatite at speeds typically encountered by comets demonstrate that shock imparted by collisions is detectable in the infrared signatures of their dust. The spectral signatures can be traced to physical alterations in their crystalline structures, as observed in TEM imaging and modeled using a dipole approximation. These results yield tantalizing insights into the collisional history of our solar system, as well as the history of individual comets and Trojan asteroids.

100 and counting : SOHO's score as the world's top comet finder

Science.gov (United States)

2000-02-01

comet hunters," said Shanklin, who is director of the British Astronomical Association's comet section. "It allows amateurs to discover some of the smallest comets ever seen. Yet they link us to sightings of great comets going back more than 2000 years." Nine of the comets found with LASCO, including SOHO-100, 101 and 102, passed the Sun at a safe distance. SOHO-49, which showed up in LASCO images in May 1998 and was designated as Comet 1998 J1, became visible to the naked eye in the southern hemisphere. But the great majority of SOHO's comets failed to survive very close encounters with the Sun. Snowballs in hell Of the first 100 SOHO comets, 92 vaporized in the solar atmosphere. Isaac Newton suggested 300 years ago that infalling comets might supply the Sun with fuel, but no one has ever tracked a comet that definitely hit the bright surface. Near misses are well known, and 100 years ago Heinrich Kreutz in Kiel, Germany, realized that several comets seen buzzing the Sun seemed to have a common origin, because they came from the same direction among the stars. These comets are now called the Kreutz sungrazers, and the 92 vanishing SOHO comets belong to that class. They were not unexpected. Between 1979 and 1989 the P78-1 and SMM solar satellites spotted 16 comets closing with the Sun. Life is perilous for a sungrazer. The mixture of ice and dust that makes up a comet's nucleus is heated like the proverbial snowball in hell, and can survive its visit to the Sun only if it is quite large. What's more, the very strong tidal effect of the Sun's gravity can tear the loosely glued nucleus apart. The disruption that created the many SOHO sungrazers was similar to the fate of Comet Shoemaker-Levy 9, which went too close to Jupiter and broke up into many pieces that eventually fell into the massive planet in 1994. "SOHO is seeing fragments from the gradual break-up of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC," commented Brian Marsden of the

27 CFR 70.162 - Levy and distraint on salary and wages.

Science.gov (United States)

2010-04-01

... salary and wages. 70.162 Section 70.162 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... § 70.162 Levy and distraint on salary and wages. (a) Notice of intent to levy. Levy may be made for any... salary or wages. A levy on salary or wages is continuous from the time of the levy until the liability...

The Influence of the Number of Different Stocks on the Levy-Levy-Solomon Model

Science.gov (United States)

Kohl, R.

The stock market model of Levy, Levy, Solomon is simulated for more than one stock to analyze the behavior for a large number of investors. Small markets can lead to realistic looking prices for one and more stocks. A large number of investors leads to a semi-regular fashion simulating one stock. For many stocks, three of the stocks are semi-regular and dominant, the rest is chaotic. Aside from that we changed the utility function and checked the results.

Comet Tempel 1 Went Back to Sleep

Science.gov (United States)

2005-07-01

Astronomers Having Used ESO Telescopes Start Analysing Unique Dataset on the Comet Following the Deep Impact Mission Ten days after part of the Deep Impact spacecraft plunged onto Comet Tempel 1 with the aim to create a crater and expose pristine material from beneath the surface, astronomers are back in the ESO Offices in Santiago, after more than a week of observing at the ESO La Silla Paranal Observatory. In this unprecedented observing campaign - among the most ambitious ever conducted by a single observatory - the astronomers have collected a large amount of invaluable data on this comet. The astronomers have now started the lengthy process of data reduction and analysis. Being all together in a single place, and in close contacts with the space mission' scientific team, they will try to assemble a clear picture of the comet and of the impact. The ESO observations were part of a worldwide campaign to observe this unique experiment. During the campaign, ESO was connected by phone, email, and videoconference with colleagues in all major observatories worldwide, and data were freely exchanged between the different groups. This unique collaborative spirit provides astronomers with data taken almost around the clock during several days and this, with the largest variety of instruments, making the Deep Impact observing campaign one of the most successful of its kind, and thereby, ensuring the greatest scientific outcome. From the current analysis, it appears most likely that the impactor did not create a large new zone of activity and may have failed to liberate a large quantity of pristine material from beneath the surface. ESO PR Photo 22/05 ESO PR Photo 22/05 Evolution of Comet Tempel 1 (FORS2/VLT) [Preview - JPEG: 400 x 701 pix - 128k] [Normal - JPEG: 800 x 1401 pix - 357k] ESO PR Photo 22/05 Animated Gif Caption: ESO PR Photo 22/05 shows the evolution of Comet Tempel 1 as observed with the FORS2 instrument on Antu (VLT). The images obtained at the VLT show that

On the existence of Levi Foliations

Directory of Open Access Journals (Sweden)

RENATA N. OSTWALD

2001-03-01

Full Text Available Let L be a real 3 dimensional analytic variety. For each regular point p L there exists a unique complex line l p on the space tangent to L at p. When the field of complex line p l p is completely integrable, we say that L is Levi variety. More generally; let L M be a real subvariety in an holomorphic complex variety M. If there exists a real 2 dimensional integrable distribution on L which is invariant by the holomorphic structure J induced by M, we say that L is a Levi variety. We shall prove: Theorem. Let be a Levi foliation and let be the induced holomorphic foliation. Then, admits a Liouvillian first integral. In other words, if is a 3 dimensional analytic foliation such that the induced complex distribution defines an holomorphic foliation ; that is, if is a Levi foliation; then admits a Liouvillian first integral--a function which can be constructed by the composition of rational functions, exponentiation, integration, and algebraic functions (Singer 1992. For example, if f is an holomorphic function and if theta is real a 1-form on ; then the pull-back of theta by f defines a Levi foliation : f*theta = 0 which is tangent to the holomorphic foliation : df = 0. This problem was proposed by D. Cerveau in a meeting (see Fernandez 1997.Seja L Ì uma variedade real de dimensão 3. Para todo ponto regular p Î L existe uma única reta complexa l p no espaço tangente à L em p. Quando o campo de linhas complexas p l p é completamente integrável, dizemos que L é uma variedade de Levi. Mais geralmente, seja L Ì M uma subvariedade real em uma variedade analítica complexa. Se existe uma distribuição real integrável de dimensão 2 em L que é invariante pela estrutura holomorfa J induzida pela variedade complexa M, dizemos que L é uma variedade de Levi. Vamos provar: Teorema. Seja uma folheação de Levi e seja a folheação holomorfa induzida. Então tem integral primeira Liouvilliana. Em outras palavras, se é uma folheação real de

The Age of Lunar South Circumpolar Craters Haworth, Shoemaker, Faustini, and Shackleton: Implications for Regional Geology, Surface Processes, and Volatile Sequestration

Science.gov (United States)

Tye, A. R.; Fassett, C. I.; Head, J. W.; Mazarico, E.; Basilevsky, A. T.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2015-01-01

The interiors of the lunar south circumpolar craters Haworth, Shoemaker, Faustini, and Shackleton contain permanently shadowed regions (PSRs) and have been interpreted to contain sequestered volatiles including water ice. Altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter provide a new means of examining the permanently shadowed interiors of these craters in unprecedented detail. In this study, we used extremely high-resolution gridded LOLA data of Haworth, Shoemaker, Faustini, and Shackleton to determine the size-frequency distributions and the spatial density of craters superposing their rims, inner slopes, and floors. Based on their population of superposed D greater than or equal to 2 km craters, Haworth, Shoemaker, and Faustini have pre-Nectarian formation ages. Shackleton is interpreted as having a Late Imbrian age on the basis of craters with diameter D greater than or equal to 0.5 km superposed on its rim. The local density of craters with sub-km diameters across our study area is strongly dependent on slope; because of its steep interior slopes, the lifetime of craters on the interior of Shackleton is limited. The slope-dependence of the small crater population implies that the population in this size range is controlled primarily by the rate at which craters are destroyed. This is consistent with the hypothesis that crater removal and resurfacing is a result of slopedependent processes such as diffusive mass wasting and seismic shaking, linked to micrometeorite and meteorite bombardment. Epithermal neutron flux data and UV albedo data show that these circumpolar PSRs, particularly Shoemaker, may have approximately 1-2% water ice by mass in their highly porous surface regolith, and that Shoemaker may have approximately 5% or more water ice by mass in the near subsurface. The ancient formation ages of Shoemaker, Faustini and Haworth, and the Late Imbrian (approximately 3.5 Ga) crater retention ages of their

The quantum Levy walk

International Nuclear Information System (INIS)

Caceres, Manuel O; Nizama, Marco

2010-01-01

We introduce the quantum Levy walk to study transport and decoherence in a quantum random model. We have derived from second-order perturbation theory the quantum master equation for a Levy-like particle that moves along a lattice through scale-free hopping while interacting with a thermal bath of oscillators. The general evolution of the quantum Levy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation and the probability to be in a lattice site, all of them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general, our approach allows us to study analytically quantum fluctuations and decoherence in a long-range hopping model.

Correlated Levy Noise in Linear Dynamical Systems

International Nuclear Information System (INIS)

Srokowski, T.

2011-01-01

Linear dynamical systems, driven by a non-white noise which has the Levy distribution, are analysed. Noise is modelled by a specific stochastic process which is defined by the Langevin equation with a linear force and the Levy distributed symmetric white noise. Correlation properties of the process are discussed. The Fokker-Planck equation driven by that noise is solved. Distributions have the Levy shape and their width, for a given time, is smaller than for processes in the white noise limit. Applicability of the adiabatic approximation in the case of the linear force is discussed. (author)

Tax corrections at the external borders of the European Community at the implementation of an energy levy: An inventory

International Nuclear Information System (INIS)

De Wit, G.

1993-09-01

There are several methods to implement an energy levy in the European Union without having a negative impact on the competitive position of energy-intensive industries and businesses in the EU: (1) a worldwide energy levy; (2) partly exemption of energy-intensive industries or businesses in the EU; and (3) an import levy on energy-intensive products from outside the EU, and refunds for industries and businesses in the EU for paid energy levies on products, exported to countries outside the EU. The third option is investigated in this report for two variants: the input variant (levy only on primary energy sources) and the output variant (levies on all the energy-intensive products). Energy-intensive products discussed in this report are energy carriers, food products, paper and board, chemical and synthetic products, ceramic products, and primary products of the metal industry. Attention is paid to the practical execution, the extent to which such a levy can be enforced, and its relation with the GATT. Finally, the advantages and disadvantages of the two variants with tax corrections at the external borders are discussed in relation with the first two options (1) and (2) to guarantee the competitive position of energy-intensive industries and businesses. 4 tabs., 2 appendices, 30 refs

Using nudges to reduce waste? The case of Toronto's plastic bag levy.

Science.gov (United States)

Rivers, Nicholas; Shenstone-Harris, Sarah; Young, Nathan

2017-03-01

The overuse of disposable plastic bags is a major environmental problem across the globe. In recent years, numerous jurisdictions have sought to curb disposable bag use by implementing a levy or fee at the point of purchase. These levies are typically small and symbolic (around $0.05 per bag), but serve as a highly-visible and continuous reminder to consumers. As such, they are consistent with nudging policies that seek to encourage broad changes in behaviour through small, non-coercive measures that influence people's thinking about an issue. While existing empirical evidence suggests that nudges are highly effective in reducing disposable bag use, we argue that many of these studies are flawed because they lack adequate temporal and geographic controls. We use longitudinal data from four waves of a major Canadian survey to analyze the effect of a disposable bag levy in the City of Toronto. Controlling for demographics and changes in social norms over time, we find that the levy increased the use of reusable shopping bags by 3.4 percentage points. Moreover, we find that the impact of the policy was highly variable across behavioural and demographic groups. The levy was highly effective in encouraging people who already used reusable bags to use them more frequently, while having no effect on infrequent users. We also find that the effects are limited to households with high socio-economic status (as measured by income, educational attainment, and housing situation). This suggests important limitations for nudging policy more generally, as people with lower socio-economic status appear to have been unaffected by this behavioural prompt. Copyright © 2016 Elsevier Ltd. All rights reserved.

The impact imperative: Laser ablation for deflecting asteroids, meteoroids, and comets from impacting the earth

Energy Technology Data Exchange (ETDEWEB)

Campbell, Jonathan W [Advanced Projects/FD02, National Space Science and Technology Center, NASA/MSFC, Huntsville, Alabama, 35812 (United States); Phipps, Claude [Photonics Associates 200A Ojo de la Vaca Road Santa Fe, NM 87505 (United States); Smalley, Larry [Department of Physics, University of Alabama, Huntsville (United States); Reilly, James [Northeast Science and Technology, East Sandwich, MA (United States); Boccio, Dona [Queensborough Community College of the City, University of New York, New York (United States)

2003-05-14

Impacting at hypervelocity, an asteroid struck the Earth approximately 65 million years ago in the Yucatan Peninsula area. This triggered the extinction of almost 70% of the species of life on Earth including the dinosaurs. Other impacts prior to this one have caused even greater extinctions. Preventing collisions with the Earth by hypervelocity asteroids, meteoroids, and comets is the most important immediate space challenge facing human civilization. This is the Impact Imperative. We now believe that while there are about 2000 earth orbit crossing rocks greater than 1 kilometer in diameter, there may be as many as 200,000 or more objects in the 100 m size range. Can anything be done about this fundamental existence question facing our civilization? The answer is a resounding yes{exclamation_point} By using an intelligent combination of Earth and space based sensors coupled with an infra-structure of high-energy laser stations and other secondary mitigation options, we can deflect inbound asteroids, meteoroids, and comets and prevent them from striking the Earth. This can be accomplished by irradiating the surface of an inbound rock with sufficiently intense pulses so that ablation occurs. This ablation acts as a small rocket incrementally changing the shape of the rock's orbit around the Sun. One-kilometer size rocks can be moved sufficiently in about a month while smaller rocks may be moved in a shorter time span.

The impact imperative: Laser ablation for deflecting asteroids, meteoroids, and comets from impacting the earth

International Nuclear Information System (INIS)

Campbell, Jonathan W.; Phipps, Claude; Smalley, Larry; Reilly, James; Boccio, Dona

2003-01-01

Impacting at hypervelocity, an asteroid struck the Earth approximately 65 million years ago in the Yucatan Peninsula area. This triggered the extinction of almost 70% of the species of life on Earth including the dinosaurs. Other impacts prior to this one have caused even greater extinctions. Preventing collisions with the Earth by hypervelocity asteroids, meteoroids, and comets is the most important immediate space challenge facing human civilization. This is the Impact Imperative. We now believe that while there are about 2000 earth orbit crossing rocks greater than 1 kilometer in diameter, there may be as many as 200,000 or more objects in the 100 m size range. Can anything be done about this fundamental existence question facing our civilization? The answer is a resounding yes! By using an intelligent combination of Earth and space based sensors coupled with an infra-structure of high-energy laser stations and other secondary mitigation options, we can deflect inbound asteroids, meteoroids, and comets and prevent them from striking the Earth. This can be accomplished by irradiating the surface of an inbound rock with sufficiently intense pulses so that ablation occurs. This ablation acts as a small rocket incrementally changing the shape of the rock's orbit around the Sun. One-kilometer size rocks can be moved sufficiently in about a month while smaller rocks may be moved in a shorter time span

48 CFR 252.225-7033 - Waiver of United Kingdom levies.

Science.gov (United States)

2010-10-01

... waiver of levies included in the price of this contract, the U.S. Government reserves the right to reduce the contract price by the amount of the levy waived plus associated indirect costs and profit or fee... attempt to obtain a waiver of any commercial exploitation levies included in the price of this contract...

NUMERICAL MODELING OF THE 2009 IMPACT EVENT ON JUPITER

Energy Technology Data Exchange (ETDEWEB)

Pond, Jarrad W. T.; Palotai, Csaba; Gabriel, Travis; Harrington, Joseph; Rebeli, Noemi [Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Korycansky, Donald G., E-mail: jarradpond@gmail.com [Department of Earth and Planetary Science, University of California, Santa Cruz, CA 95064 (United States)

2012-02-01

We have investigated the 2009 July impact event on Jupiter using the ZEUS-MP 2 three-dimensional hydrodynamics code. We studied the impact itself and the following plume development. Eight impactors were considered: 0.5 km and 1 km porous ({rho} = 1.760 g cm{sup -3}) and non-porous ({rho} = 2.700 g cm{sup -3}) basalt impactors, and 0.5 km and 1 km porous ({rho} = 0.600 g cm{sup -3}) and non-porous ({rho} = 0.917 g cm{sup -3}) ice impactors. The simulations consisted of these bolides colliding with Jupiter at an incident angle of {theta} = 69 Degree-Sign from the vertical and with an impact velocity of v = 61.4 km s{sup -1}. Our simulations show the development of relatively larger, faster plumes created after impacts involving 1 km diameter bodies. Comparing simulations of the 2009 event with simulations of the Shoemaker-Levy 9 (SL9) events reveals a difference in plume development, with the higher incident angle of the 2009 impact leading to a shallower terminal depth and a smaller and slower plume. We also studied the amount of dynamical chaos present in the simulations conducted at the 2009 incident angle. Compared to the chaos of the SL9 simulations, where {theta} Almost-Equal-To 45 Degree-Sign , we find no significant difference in chaos at the higher 2009 incident angle.

EPOXI at comet Hartley 2.

Science.gov (United States)

A'Hearn, Michael F; Belton, Michael J S; Delamere, W Alan; Feaga, Lori M; Hampton, Donald; Kissel, Jochen; Klaasen, Kenneth P; McFadden, Lucy A; Meech, Karen J; Melosh, H Jay; Schultz, Peter H; Sunshine, Jessica M; Thomas, Peter C; Veverka, Joseph; Wellnitz, Dennis D; Yeomans, Donald K; Besse, Sebastien; Bodewits, Dennis; Bowling, Timothy J; Carcich, Brian T; Collins, Steven M; Farnham, Tony L; Groussin, Olivier; Hermalyn, Brendan; Kelley, Michael S; Kelley, Michael S; Li, Jian-Yang; Lindler, Don J; Lisse, Carey M; McLaughlin, Stephanie A; Merlin, Frédéric; Protopapa, Silvia; Richardson, James E; Williams, Jade L

2011-06-17

Understanding how comets work--what drives their activity--is crucial to the use of comets in studying the early solar system. EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) flew past comet 103P/Hartley 2, one with an unusually small but very active nucleus, taking both images and spectra. Unlike large, relatively inactive nuclei, this nucleus is outgassing primarily because of CO(2), which drags chunks of ice out of the nucleus. It also shows substantial differences in the relative abundance of volatiles from various parts of the nucleus.

Satellite orbits in Levi-Civita space

Science.gov (United States)

Humi, Mayer

2018-03-01

In this paper we consider satellite orbits in central force field with quadratic drag using two formalisms. The first using polar coordinates in which the satellite angular momentum plays a dominant role. The second is in Levi-Civita coordinates in which the energy plays a central role. We then merge these two formalisms by introducing polar coordinates in Levi-Civita space and derive a new equation for satellite orbits which unifies these two paradigms. In this equation energy and angular momentum appear on equal footing and thus characterize the orbit by its two invariants. Using this formalism we show that equatorial orbits around oblate spheroids can be expressed analytically in terms of Elliptic functions. In the second part of the paper we derive in Levi-Civita coordinates a linearized equation for the relative motion of two spacecrafts whose trajectories are in the same plane. We carry out also a numerical verification of these equations.

Benzene exposure in the shoemaking industry in China, a literature survey, 1978-2004.

Science.gov (United States)

Wang, Laiming; Zhou, Yimei; Liang, Youxin; Wong, Otto; Armstrong, Thomas; Schnatter, A Robert; Wu, Qiangen; Fang, Jinbin; Ye, Xibiao; Fu, Hua; Irons, Richard D

2006-11-01

This article presents a summary of benzene exposure levels in the shoemaking industry in China reported in the Chinese medical literature between 1978 and 2004. A comprehensive search identified 182 papers reporting such exposure data. These papers could be classified into two categories: benzene poisoning case reports and industrial hygiene surveys. From each paper, the following information was abstracted whenever available: location and year of occurrence, occupation and/or task involved, benzene content in adhesives/solvents, work environment, working conditions, working hours, diagnosis, and air monitoring data of benzene. A total of 333 benzene measurements (88 averages, 116 minimums, 129 maximums) in the shoemaking industry were reported in the 182 papers identified. The data were analyzed in terms of geographical location, time period, type of ownership (state, township, or foreign), type of report (benzene poisoning reports vs. industrial hygiene surveys), and job title (work activity) or process. The reported data covered a wide range; some measurements were in excess of 4500 mg/m(3). Thirty-five percent of the reported benzene concentrations were below 40 mg/m(3), which was the national occupational exposure limit (OEL) for benzene between 1979 and 2001. The remaining 65% measurements, which exceeded the national OEL in effect at the time, and were distributed as follows: 40-100 mg/m(3), 11%; 100-300 mg/m(3), 21%; 300-500 mg/m(3), 13%; and 500+ mg/m(3), 20%. However, only 24% of the reported measurements after 2002 were below 6 mg/m(3), i.e., Permissible Concentration-Time Weighted Average (PC-TWA) and 10 mg/m(3), i.e., Permissible Concentration-Short Term Exposure Limit (PC-STEL), the newly amended benzene OELs in effect after May 2002. The data demonstrated that the majority of the facilities in the shoemaking industry reported in the literature were not in compliance of the OEL for benzene in effect at the time. Overall, the data show a clear downward

Comets and the origin and evolution of life

CERN Document Server

McKay, Christopher P

2006-01-01

Nine years after the publication of Comets and the Origin and Evolution of Life, one of the pioneering books in Astrobiology, this second edition revisits the role comets may have played in the origins and evolution of life. Recent analyses of Antarctic micrometeorites and ancient rocks in Australia and South Africa, the continuing progress in discovering complex organic macromolecules in comets, protostars and interstellar clouds, new insights into organic synthesis in comets, and numerical simulations of comet impacts on the Earth and other members of the solar system yield a spectacular wea

Energy levy and consequences for the incomes

International Nuclear Information System (INIS)

De Kam, C.A.

1992-01-01

Attention is paid to levies proposed for the domestic energy consumption in the Netherlands. Possibilities to compensate households for such levies by means of burden reductions are discussed. Given the starting point of the present Dutch coalition agreement that the macro-economic level of levies should not increase, a compensating reduction of the Value Added Tax (VAT) or the income tax seems to be the most obvious measure. Considering the large diversity in the energy consumption of households it is impossible to compensate precisely every household via such general measures. Moreover, this is actual undesirable, because otherwise the stimulus to save energy will be lost. However, a compensation, that will leave the personal income distribution on the whole unaltered, should be feasible. 1 fig., 4 tabs., 14 refs

CO2 Orbital Trends in Comets

Science.gov (United States)

Kelley, Michael; Feaga, Lori; Bodewits, Dennis; McKay, Adam; Snodgrass, Colin; Wooden, Diane

2014-12-01

Spacecraft missions to comets return a treasure trove of details of their targets, e.g., the Rosetta mission to comet 67P/Churyumov-Gerasimenko, the Deep Impact experiment at comet 9P/Tempel 1, or even the flyby of C/2013 A1 (Siding Spring) at Mars. Yet, missions are rare, the diversity of comets is large, few comets are easily accessible, and comet flybys essentially return snapshots of their target nuclei. Thus, telescopic observations are necessary to place the mission data within the context of each comet's long-term behavior, and to further connect mission results to the comet population as a whole. We propose a large Cycle 11 project to study the long-term activity of past and potential future mission targets, and select bright Oort cloud comets to infer comet nucleus properties, which would otherwise require flyby missions. In the classical comet model, cometary mass loss is driven by the sublimation of water ice. However, recent discoveries suggest that the more volatile CO and CO2 ices are the likely drivers of some comet active regions. Surprisingly, CO2 drove most of the activity of comet Hartley 2 at only 1 AU from the Sun where vigorous water ice sublimation would be expected to dominate. Currently, little is known about the role of CO2 in comet activity because telluric absorptions prohibit monitoring from the ground. In our Cycle 11 project, we will study the CO2 activity of our targets through IRAC photometry. In conjunction with prior observations of CO2 and CO, as well as future data sets (JWST) and ongoing Earth-based projects led by members of our team, we will investigate both long-term activity trends in our target comets, with a particular goal to ascertain the connections between each comet's coma and nucleus.

COMET SHOWERS ARE NOT INDUCED BY INTERSTELLAR CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Morris, D.E.

1985-11-01

Encounters with interstellar clouds (IC) have been proposed by Rampino and Stothers as a cause of quasi-periodic intense comet showers leading to earth impacts, in order to explain the periodicity in marine mass extinctions found by Raup and Sepkoski. The model was described further, criticized and defended. The debate has centered on the question of whether the scale height of the clouds is small enough (in comparison to the amplitude of the oscillation of the solar system about the plane of the Galaxy) to produce a modulation in the rate of encounters. We wish to point out another serious, we believe fatal, defect in this model - the tidal fields of ICs are not strong enough to produce intense comet showers leading to earth impacts by bringing comets of the postulated inner Oort cloud into earth crossing orbits, except possibly during very rare encounters with very dense clouds. We will show that encounters with abundant clouds of low density cannot produce comet showers; cloud density N > 10{sup 3} atoms cm{sup -3} is needed to produce an intense comet shower leading to earth impacts. Furthermore, the tidal field of a dense cloud during a distant encounter is too weak to produce such showers. As a consequence, comet showers induced by ICs will be far less frequent than showers caused by passing stars. This conclusion is independent of assumptions about the radial distribution of comets in the inner Oort cloud.

Basics of Swiss water levy politics - Legal aspects; Grundlagen Wasserzinspolitik. Rechtliche Ueberlegungen - Schlussbericht

Energy Technology Data Exchange (ETDEWEB)

Leimbacher, J.

2008-10-15

This comprehensive final report for the Swiss Federal Office of Energy (SFOE) takes a look at the legal aspects involved in setting up the basics for the definition of the interest to be levied on water commodities. This levy is raised in Switzerland on the use of water and represents the payment made to a commune for the use of its water resources. The original aims of the levy, to encourage the use of water resources, are noted. Limits on the height of the levy and the definition and adjustment of the maximum rate by government are discussed. Various legal aspects are examined and the fact that the levy must be economically reasonable and economically acceptable is discussed. Various pragmatic approaches to being able to adjust or index the levy are discussed. The introduction of an additional levy to cover the storage of water is discussed, as is the definition of the part use of the proceeds to provide funding for the high-voltage electricity grid, for example. The history of the levy and various political initiatives are noted and even the abolition of the levy is discussed.

Comet/Asteroid Impacts and Human Society An Interdisciplinary Approach

CERN Document Server

Bobrowsky, Peter T

2007-01-01

In 1908 an atmospheric explosion in northern Siberia released energy equivalent to 15 Mton of TNT. Can a comparable or larger NEO affect us again? When the next NEO strikes Earth will it be large enough to destroy a city? Will the climate change significantly? Can archaeology and anthropology provide insights into the expected cultural responses with NEO interactions? Does society have a true grasp of the actual risks involved? Is the Great Depression a good model for the economic collapse that could follow a NEO catastrophe? This volume provides a necessary link between various disciplines and comet/asteroid impacts.

26 CFR 301.6331-1 - Levy and distraint.

Science.gov (United States)

2010-04-01

... intangible, belonging to the taxpayer. The district director may also levy upon property with respect to...), the 30-day period provided in section 6331(d), or the limitation on levy provided in section 6331(g)(1... either a Federal or a State court, the assets of the taxpayer are in general under the control of the...

Make the Alberta Carbon Levy Revenue Neutral

Directory of Open Access Journals (Sweden)

Kenneth J. McKenzie

2016-04-01

Full Text Available The new carbon levy of $30 per tonne, announced in November 2015 as part of the report issued by the Alberta government’s Climate Leadership Panel, is a positive move in the direction of pricing carbon emissions. The levy is expected to generate $3 billion in net revenue by 2018, and possibly as much as $5 billion by 2030. While there is some discussion in the report of what should be done with the revenues generated by the carbon levy, it is somewhat vague on the details, leaving a number of options open to the government. The purpose of this briefing paper is to argue that the revenues from the carbon levy should be used to lower existing taxes – the carbon tax should be revenue neutral, generating no new net revenue for the government. The basic argument is that the carbon levy can be viewed through two lenses. The first lens is the imposition of a price on carbon emissions which (at least partly reflects the social costs of emissions. Viewed through this price lens, the carbon levy plays an important role in incenting firms and individuals to change their behaviour and move towards less carbon intensive activities. The second lens is the role of a carbon tax as a part of the broad revenue system. Viewed through this tax lens, a carbon tax is not a very good, or efficient, way of generating revenue. The reason for this is somewhat nuanced, but the basic idea is that the carbon tax is applied to a narrower base than broader-based taxes. Broad based taxes generally impose lower costs on the economy than narrow based taxes. Moreover, carbon taxes interact with other taxes in the economy, exacerbating the economic costs associated with those taxes. And those costs are quite high – research shows that the total cost to the economy of raising an additional $1 in revenue through the corporate income tax in Alberta is $3.79; for the personal income tax the cost is $1.71. These taxes therefore impose higher costs on the economy than they raise

Zimbabwe's national AIDS levy: A case study.

Science.gov (United States)

Bhat, Nisha; Kilmarx, Peter H; Dube, Freeman; Manenji, Albert; Dube, Medelina; Magure, Tapuwa

2016-01-01

We conducted a case study of the Zimbabwe National AIDS Trust Fund ('AIDS Levy') as an approach to domestic government financing of the response to HIV and AIDS. Data came from three sources: a literature review, including a search for grey literature, review of government documents from the Zimbabwe National AIDS Council (NAC), and key informant interviews with representatives of the Zimbabwean government, civil society and international organizations. The literature search yielded 139 sources, and 20 key informants were interviewed. Established by legislation in 1999, the AIDS Levy entails a 3% income tax for individuals and 3% tax on profits of employers and trusts (which excluded the mining industry until 2015). It is managed by the parastatal NAC through a decentralized structure of AIDS Action Committees. Revenues increased from inception to 2006 through 2008, a period of economic instability and hyperinflation. Following dollarization in 2009, annual revenues continued to increase, reaching US$38.6 million in 2014. By policy, at least 50% of funds are used for purchase of antiretroviral medications. Other spending includes administration and capital costs, HIV prevention, and monitoring and evaluation. Several financial controls and auditing systems are in place. Key informants perceived the AIDS Levy as a 'homegrown' solution that provided country ownership and reduced dependence on donor funding, but called for further increased transparency, accountability, and reduced administrative costs, as well as recommended changes to increase revenue. The Zimbabwe AIDS Levy has generated substantial resources, recently over US$35 million per year, and signals an important commitment by Zimbabweans, which may have helped attract other donor resources. Many key informants considered the Zimbabwe AIDS Levy to be a best practice for other countries to follow.

SQCX X-ray Observations Of The Deep Impact Spacecraft Close Encounters With Comets 9P/Tempel 1 And 103P/Hartley 2

Science.gov (United States)

Lisse, Carey M.; Dennerl, K.; Wolk, S. J.; Christian, D. J.; Bodewits, D.; Zurbuchen, T. H.; Combi, M.

2010-03-01

We present results from the extensive Chandra, SWIFT, Spitzer, and groundbased observing campaigns studying Comet 9P/Tempel 1 in support of NASA's Deep Impact (DI) mission as an indication of the results expected for the next DI flyby of comet 103P/Hartley 2 at 0.1 AU geocentric distance in November 2010. 9P/Tempel 1 was observed for 300 ksec between 30th June and 24th July 2005, and continuously for 60 ksec on July 4th during the impact event. X-ray emission qualitatively similar to that observed for the collisionally thin, cold wind comet 2P/Encke system (Lisse et al. 2005) was found, with emission morphology centered on the nucleus and emission lines due to C, N, O, and Ne solar wind minor ions. The comet was relatively faint on July 4th, and the total increase in x-ray flux due to the Deep Impact excavation was small, 20% of the immediate pre-impact value, consistent with estimates that the total coma neutral gas release due to the impact was 5 x 106 kg ( 10 hrs of normal coma outflow). Over time, other temporally variable spectral features due to changing solar wind flux densities and charge states were clearly seen. Good agreement between the Chandra and SWIFT x-ray photometry was found. Two flares, much stronger than the man-made increase due to Deep Impact, were found in the observed x-rays on June 30th and July 8th, 2005, and are coincident with increases in the solar wind flux arriving at the comet. Modeling of the Chandra data using observed Spitzer gas production rates and ACE solar wind ion fluxes with a SWCX mechanism for the emission was found to be consistent with the temporal- and spectral behavior expected for a slow, hot wind typical of low latitude emission from the solar corona interacting with the comet's neutral coma.

Levy's zero-one law in game-theoretic probability

OpenAIRE

Shafer, Glenn; Vovk, Vladimir; Takemura, Akimichi

2009-01-01

We prove a game-theoretic version of Levy's zero-one law, and deduce several corollaries from it, including non-stochastic versions of Kolmogorov's zero-one law, the ergodicity of Bernoulli shifts, and a zero-one law for dependent trials. Our secondary goal is to explore the basic definitions of game-theoretic probability theory, with Levy's zero-one law serving a useful role.

Levy flights and random searches

Energy Technology Data Exchange (ETDEWEB)

Raposo, E P [Laboratorio de Fisica Teorica e Computacional, Departamento de Fisica, Universidade Federal de Pernambuco, Recife-PE, 50670-901 (Brazil); Buldyrev, S V [Department of Physics, Yeshiva University, New York, 10033 (United States); Da Luz, M G E [Departamento de Fisica, Universidade Federal do Parana, Curitiba-PR, 81531-990 (Brazil); Viswanathan, G M [Instituto de Fisica, Universidade Federal de Alagoas, Maceio-AL, 57072-970 (Brazil); Stanley, H E [Center for Polymer Studies and Department of Physics, Boston University, Boston, MA 02215 (United States)

2009-10-30

In this work we discuss some recent contributions to the random search problem. Our analysis includes superdiffusive Levy processes and correlated random walks in several regimes of target site density, mobility and revisitability. We present results in the context of mean-field-like and closed-form average calculations, as well as numerical simulations. We then consider random searches performed in regular lattices and lattices with defects, and we discuss a necessary criterion for distinguishing true superdiffusion from correlated random walk processes. We invoke energy considerations in relation to critical survival states on the edge of extinction, and we analyze the emergence of Levy behavior in deterministic search walks. Finally, we comment on the random search problem in the context of biological foraging.

On the generation of log-Levy distributions and extreme randomness

International Nuclear Information System (INIS)

Eliazar, Iddo; Klafter, Joseph

2011-01-01

The log-normal distribution is prevalent across the sciences, as it emerges from the combination of multiplicative processes and the central limit theorem (CLT). The CLT, beyond yielding the normal distribution, also yields the class of Levy distributions. The log-Levy distributions are the Levy counterparts of the log-normal distribution, they appear in the context of ultraslow diffusion processes, and they are categorized by Mandelbrot as belonging to the class of extreme randomness. In this paper, we present a natural stochastic growth model from which both the log-normal distribution and the log-Levy distributions emerge universally-the former in the case of deterministic underlying setting, and the latter in the case of stochastic underlying setting. In particular, we establish a stochastic growth model which universally generates Mandelbrot's extreme randomness. (paper)

Eesti allilm suudab tõkestada GSM-levi / Rasmus Kagge

Index Scriptorium Estoniae

Kagge, Rasmus, 1977-

2006-01-01

Ilmunud ka: Postimees : na russkom jazõke 10. mai lk. 2. Politsei andmetel on Eesti kuritegelike jõukude käes praegu vähemalt paar GSM-levi segajat ehk jammerit. Politseil on õnnestunud konfiskeerida autovarastelt üks GSM-levi tõkestaja. Lisa. Kasutajapiirang. Vt. samas: Jammereid saab osta internetist

Tax levy financing for local public health: fiscal allocation, effort, and capacity.

Science.gov (United States)

Riley, William J; Gearin, Kimberly J; Parrotta, Carmen D; Briggs, Jill; Gyllstrom, M Elizabeth

2013-12-01

Local health departments (LHDs) rely on a wide variety of funding sources, and the level of financing is associated with both LHD performance in essential public health services and population health outcomes. Although it has been shown that funding sources vary across LHDs, there is no evidence regarding the relationship between fiscal allocation (local tax levy); fiscal effort (tax capacity); and fiscal capacity (community wealth). The purpose of this study is to analyze local tax levy support for LHD funding. Three research questions are addressed: (1) What are tax levy trends in LHD fiscal allocation? (2) What is the role of tax levy in overall LHD financing? and (3) How do local community fiscal capacity and fiscal effort relate to LHD tax levy fiscal allocation? This study focuses on 74 LHDs eligible for local tax levy funding in Minnesota. Funding and expenditure data for 5 years (2006 to 2010) were compiled from four governmental databases, including the Minnesota Department of Health, the State Auditor, the State Demographer, and the Metropolitan Council. Trends in various funding sources and expenditures are described for the time frame of interest. Data were analyzed in 2012. During the 2006-2010 time period, total average LHD per capita expenditures increased 13%, from $50.98 to $57.63. Although the overall tax levy increase in Minnesota was 25%, the local tax levy for public health increased 5.6% during the same period. There is a direct relationship between fiscal effort and LHD expenditures. Local funding reflects LHD community priorities and the relative importance in comparison to funding other local programs with tax dollars. In Minnesota, local tax levy support for local public health services is not keeping pace with local tax support for other local government services. These results raise important questions about the relationship between tax levy resource effort, resource allocation, and fiscal capacity as they relate to public health

Dynamics of comets: their origin and evolution

International Nuclear Information System (INIS)

Carusi, A.; Valsecchi, G.B.

1985-01-01

Comets can be considered as remnants of the original population of planetesimals and the study of their origin and dynamical histories can provide insight into the accretion phenomena; the original mass, energy and angular momentum distribution across the solar system; the collisional fragmentation of minor bodies; the impact rates on planets and the nature of impacting bodies. The interaction of comets with other solar system bodies certainly provides one of the best possibilities for a deeper understanding of the dynamics of the whole system, and a challenging test for all theories of celestial mechanics dealing with the gravitational behaviour of multiple-body systems. Comets could also be considered as the last footprints left by the interaction of the protosun and its original galactic environment. (orig.)

Collisional Histories of Comets and Trojan Asteroids: Diopside, Magnesite, and Fayalite Impact Studies

Science.gov (United States)

Lederer, S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Nakamura-Messenger, K.; Smith, D. C.; Keller, L. P.; Cintala, M. J.; Zolensky, M. E.

2012-01-01

Comets and asteroids have weathered dynamic histories, as evidenced by their rough surfaces. The Nice model describes a violent reshuffling of small bodies during the Late Heavy Bombardment, with collisions acting to grind these planetesimals away. This creates an additional source of impact material that can re-work the surfaces of the larger bodies over the lifetime of the solar system. Here, we investigate the possibility that signatures due to impacts (e.g. from micrometeoroids or meteoroids) could be detected in their spectra, and how that can be explained by the physical manifestation of shock in the crystalline structure of minerals. All impact experiments were conducted in the Johnson Space Center Experimental Impact Laboratory using the vertical gun. Impact speeds ranged from approx.2.0 km/s to approx.2.8 km/s. All experiments were conducted at room temperature. Minerals found in comets and asteroids were chosen as targets, including diopside (MgCaSi2O6, monoclinic pyroxene), magnesite (MgCO3, carbonate), and fayalite (FeSiO4, olivine). Impacted samples were analyzed using a Fourier Transform Infrared Spectrometer (FTIR) and a Transmission Electron Microscope (TEM). Absorbance features in the 8-13 m spectral region demonstrate relative amplitude changes as well as wavelength shifts. Corresponding TEM images exhibit planar shock dislocations in the crystalline structure, attributed to deformation at high strain and low temperatures. Elongating or shortening the axes of the crystalline structure of forsterite (Mg2SiO4, olivine) using a discrete dipole approximation model (Lindsay et al., submitted) yields changes in spectral features similar to those observed in our impacted laboratory minerals.

Observation of freakish-asteroid-discovered-resembles support my idea that many dark comets were arrested and lurked in the solar system after every impaction

Science.gov (United States)

Cao, Dayong

2014-03-01

New observations show that some asteroids are looked like comets. http://www.astrowatch.net/2013/11/freakish-asteroid-discovered-resembles.html, http://www.astrowatch.net/2013/11/astronomers-puzzle-over-newfound.html. It supports my idea that ``many dark comets with very special tilted orbits were arrested and lurked in the solar system'' - ``Sun's companion-dark hole seasonal took its dark comets belt and much dark matter to impact near our earth. And some of them probability hit on our earth. So this model kept and triggered periodic mass extinctions on our earth every 25 to 27 million years. After every impaction, many dark comets with very special tilted orbits were arrested and lurked in the solar system. Because some of them picked up many solar matter, so it looked like the asteroids. When the dark hole-Tyche goes near the solar system again, they will impact near planets.'' The idea maybe explains why do the asteroid looks like the comet? Where are the asteroids come from? What relationship do they have with the impactions and extinctions? http://meetings.aps.org/link/BAPS.2011.CAL.C1.7, http://meetings.aps.org/Meeting/CAL12/Event/181168, http://meetings.aps.org/link/BAPS.2013.MAR.H1.267. During 2009 to 2010, I had presented there are many dark comets like dark Asteroids near the orbit of Jupiter in ASP Meetings. In 2010, NASA's WISE found them. http://meetings.aps.org/link/BAPS.2011.APR.K1.17, http://www.nasa.gov/mission_pages/WISE/news/wise20100122.html Avoid Earth Extinction Associ.

Looking before we leap: an ongoing, quantative investigation of asteroid and comet impact hazard mitigation

Energy Technology Data Exchange (ETDEWEB)

Plesko, Catherine S [Los Alamos National Laboratory; Weaver, Robert P [Los Alamos National Laboratory; Bradley, Paul A [Los Alamos National Laboratory; Huebner, Walter F [Los Alamos National Laboratory

2010-01-01

There are many outstanding questions about the correct response to an asteroid or comet impact threat on Earth. Nuclear munitions are currently thought to be the most efficient method of delivering an impact-preventing impulse to a potentially hazardous object (PHO). However, there are major uncertainties about the response of PHOs to a nuclear burst, and the most appropriate ways to use nuclear munitions for hazard mitigation.

Ricordare per interrogare: Percorsi della memoria in Primo Levi ...

African Journals Online (AJOL)

This commemorative essay traces the function of memory and the relation between memory and imagination in the works of Primo Levi. It looks at the common matrix and the subtle link between Levi works of testimony and his fictional writings, suggesting that his fantasy and science fiction stories be read as metaphors or ...

Comet Mineralogy as Inferred from Infrared Spectra of Comets

Science.gov (United States)

Wooden, Diane H.

2006-01-01

For most comets, infrared (IR) spectroscopy (remote sensing) is the method through which we diagnose the mineralogy and size distribution of dust in their comae. The shape and contrast of the IR spectral features depend on the particle size: optically active minerals (absorbing of visible and near-IR solar photons) and submicron solid grains or highly porous (> 90% vacuum) grains primarily contribute to the shapes of the observed resonances. Comet mineralogies typically are determined by fitting thermal emission models of ensembles of discrete mineral grains to observed IR spectral energy distributions. The absorptivities (Q-abs) and scattering efficiencies (Q-scat) of the discrete mineral grains are computed using Mie scattering, Maxwell-Garnet mixing, Discrete Dipole Approximation, and Multi-Layered Sphere codes. These techniques when applied to crystalline minerals, specifically olivine (Mg_x, Fe_1-x)2 Si04, x>0.9, require the use of ellipsoidal shaped particles with elongated axial ratios or hollow spheres to produce the shapes of the resonances observed both from comet comae and laboratory samples. The wavelength positions of the distinct resonances from submicron-radii crystalline silicates, as well as their thermal equilibrium temperatures, constrain the crystalline olivine to have a relatively high Mg-content (x>0.9, or Fo>90). Only resonances computed for submicron Mg-rich crystalline olivine and crystalline orthopyroxene match the observed IR spectral features. However, this has led to the interpretation that micron-radii and larger crystals are absent from comet comae. Furthermore, the mass fraction of silicate crystals is dependent upon whether just the submicron portion of the size distribution is being compared or the submicron crystals compare to the aggregates of porous amorphous silicates that are computationally tractable as porous spheres. We will discuss the Deep Impact results as examples of these challenges to interpreting mid-IR spectra of

The Levy sections theorem revisited

International Nuclear Information System (INIS)

Figueiredo, Annibal; Gleria, Iram; Matsushita, Raul; Silva, Sergio Da

2007-01-01

This paper revisits the Levy sections theorem. We extend the scope of the theorem to time series and apply it to historical daily returns of selected dollar exchange rates. The elevated kurtosis usually observed in such series is then explained by their volatility patterns. And the duration of exchange rate pegs explains the extra elevated kurtosis in the exchange rates of emerging markets. In the end, our extension of the theorem provides an approach that is simpler than the more common explicit modelling of fat tails and dependence. Our main purpose is to build up a technique based on the sections that allows one to artificially remove the fat tails and dependence present in a data set. By analysing data through the lenses of the Levy sections theorem one can find common patterns in otherwise very different data sets

The Levy sections theorem revisited

Science.gov (United States)

Figueiredo, Annibal; Gleria, Iram; Matsushita, Raul; Da Silva, Sergio

2007-06-01

This paper revisits the Levy sections theorem. We extend the scope of the theorem to time series and apply it to historical daily returns of selected dollar exchange rates. The elevated kurtosis usually observed in such series is then explained by their volatility patterns. And the duration of exchange rate pegs explains the extra elevated kurtosis in the exchange rates of emerging markets. In the end, our extension of the theorem provides an approach that is simpler than the more common explicit modelling of fat tails and dependence. Our main purpose is to build up a technique based on the sections that allows one to artificially remove the fat tails and dependence present in a data set. By analysing data through the lenses of the Levy sections theorem one can find common patterns in otherwise very different data sets.

The data of Lelvy and Levy , "Prospect theory: much ado about nothing??", support prospect theory

NARCIS (Netherlands)

Wakker, P.P.

2003-01-01

Levy and Levy (Management Science, 2002) present data that, according to their claims, violate prospect theory. They suggest that prospect theoryys hypothesis of an S-shaped value function, concave for gains and convex for losses, is incorrect. However, all of the data of Levy and Levy are perfectly

Una complessa chiarezza: gli ipertesti di Primo Levi

Directory of Open Access Journals (Sweden)

Tommaso Pepe

2016-11-01

Full Text Available Scrittore poliedrico e versatile, Primo Levi è stato anche un costruttore di estesi e articolati ipertesti: strutture macrotestuali fondate su legami e interrelazioni tese fra opere cronologicamente e tipologicamente differenziate. Un esempio straordinario, ma non certo isolato, di questa scrittura di secondo grado, organizzata in complessi palinsesti testuali, è quello che già Marco Belpoliti ha definito nei termini di «macrotesto del Lager»: un reticolo intra- e intertestuale che, a partire da Se questo è un uomo, si è sviluppato con un andamento rizomatico attraverso diverse stratificazioni scrittorie e genealogiche, sino a I sommersi e i salvati. Il «rizoma» tuttavia è semplicemente una delle varie macrostrutture individuabili nell’opera di Levi. Attraverso un confronto contrastivo con l’opera di Calvino, il saggio si propone di indagare alcune delle caratteristiche salienti di questa scrittura ipertestuale, mostrando come l’intensa sperimentazione scrittoria perseguita da Levi sia da ricollegarsi a una parallela svolta epistemologica, data dall’insorgere di quella che Edgar Morin ha definito come «sfida della complessità».Primo Levi can be considered a versatile and polyhedral writer, capable of building long and articulated hypertexts, i.e., macrotextual structures based on the links and interrelations among works which differ both from a chronological and typological point of view. An extraordinary, but certainly not isolated, example of this writing, organized according to complex textual palimpsests, is the one that Marco Belpoliti defined as the «macrotext of the Lager»: it is an intra- and intertextual network that, starting from If This is a Man, developed according to a rhizomatic structure through his different works and genealogical stratifications, ending with The Drowned and the Saved. The «rhizome», however, is only one of the different macrostructures which may be singled out in Levi’s work. By

Comets

International Nuclear Information System (INIS)

Hughes, D.W.

1982-01-01

Comets are objects of considerable fascination and this paper reviews the present knowledge of the physical structure of the cometary nucleus, coma and tail, the orbits of comets in the Solar System, the proposed mechanisms of cometary origin, the decay processes suffered by comets, and the ways in which they can be observed from Earth and by spacecraft. (author)

On levies to reduce the nitrogen surplus: the case of Dutch pig farms.

NARCIS (Netherlands)

Fontein, P.; Thijssen, G.; Magnus, J.; Dijk, J.

1994-01-01

Pig farms in the Netherlands pay a zero or low price for using the environment. As a consequence, the environment is overused. The Dutch government wants to reduce the emissions of nitrogen and phosphorus. Possible instruments are regulation and levies. In this study a levy on feed and a levy on the

Mixtures in nonstable Levy processes

International Nuclear Information System (INIS)

Petroni, N Cufaro

2007-01-01

We analyse the Levy processes produced by means of two interconnected classes of nonstable, infinitely divisible distribution: the variance gamma and the Student laws. While the variance gamma family is closed under convolution, the Student one is not: this makes its time evolution more complicated. We prove that-at least for one particular type of Student processes suggested by recent empirical results, and for integral times-the distribution of the process is a mixture of other types of Student distributions, randomized by means of a new probability distribution. The mixture is such that along the time the asymptotic behaviour of the probability density functions always coincide with that of the generating Student law. We put forward the conjecture that this can be a general feature of the Student processes. We finally analyse the Ornstein-Uhlenbeck process driven by our Levy noises and show a few simulations of it

Photochemistry of comets

International Nuclear Information System (INIS)

Huebner, W.F.

1985-01-01

The classification of comets, chemically rich mixtures of volatile materials and refractory grains, is described. The developments of coma and tails, and the composition and structure of coma, plasma tails, dust, and nucleus are examined. The differences between comets and planetary atmospheres are investigated. Three hypotheses on the origin of comets are proposed; one states that comets formed in the region of the giant planets, the second theory has the development of comets occuring in the outer parts of the solar nebula, and the third states that comets formed in a companion fragment of the nebula. The use of radar, photometric, spectral, and laboratory measurements for modeling comets is discussed. The physics and main photolytic and chemical reaction processes of a collision-dominated coma are analyzed; the influence of the solar wind on the coma is studied. A comparison of the model with observed data is presented; good correlation of data is observed. The features of Halley's Comet and other comets with distinctive characteristics are examined. Future comet exploration missions and the need to improve comet models are discussed. 31 references

Visually observing comets

CERN Document Server

Seargent, David A J

2017-01-01

In these days of computers and CCD cameras, visual comet observers can still contribute scientifically useful data with the help of this handy reference for use in the field. Comets are one of the principal areas for productive pro-amateur collaboration in astronomy, but finding comets requires a different approach than the observing of more predictable targets. Principally directed toward amateur astronomers who prefer visual observing or who are interested in discovering a new comet or visually monitoring the behavior of known comets, it includes all the advice needed to thrive as a comet observer. After presenting a brief overview of the nature of comets and how we came to the modern understanding of comets, this book details the various types of observations that can usefully be carried out at the eyepiece of a telescope. Subjects range from how to search for new comets to visually estimating the brightness of comets and the length and orientation of tails, in addition to what to look for in comet heads a...

OpenComet: An automated tool for comet assay image analysis

Directory of Open Access Journals (Sweden)

Benjamin M. Gyori

2014-01-01

Full Text Available Reactive species such as free radicals are constantly generated in vivo and DNA is the most important target of oxidative stress. Oxidative DNA damage is used as a predictive biomarker to monitor the risk of development of many diseases. The comet assay is widely used for measuring oxidative DNA damage at a single cell level. The analysis of comet assay output images, however, poses considerable challenges. Commercial software is costly and restrictive, while free software generally requires laborious manual tagging of cells. This paper presents OpenComet, an open-source software tool providing automated analysis of comet assay images. It uses a novel and robust method for finding comets based on geometric shape attributes and segmenting the comet heads through image intensity profile analysis. Due to automation, OpenComet is more accurate, less prone to human bias, and faster than manual analysis. A live analysis functionality also allows users to analyze images captured directly from a microscope. We have validated OpenComet on both alkaline and neutral comet assay images as well as sample images from existing software packages. Our results show that OpenComet achieves high accuracy with significantly reduced analysis time.

Levi-Strauss and the Opera

Directory of Open Access Journals (Sweden)

Vlado Kotnik

2016-02-01

Full Text Available This paper is dedicated to Claude Levi-Strauss and his structural reading of opera as metaphorical ‘composing’ of an anthropological grand opera, materialized in the four-volume study of Mythologiques, which refers to Wagner’s tetralogy of The Ring. He created a type of comparative view of the function and structure of myth schemes in Amerindian culture and the orchestral scores of Wagner’s operas, and implicitly signalled that European music, with its eminent representation – opera – has had the same value or similar symbolic position in the mind and life of a contemporary European that myth has had in ‘the savage mind’. Through this, he can lead us to the understanding of opera as myth and metaphor. However, the paper extends the discussion on Levi-Strauss to a broader historical picture of the relationship between opera and mythology as two symbolic systems of European culture.

Physical Mechanism of Comet Outbursts: The Movie

Science.gov (United States)

Hartmann, William K.

2014-11-01

During experiments conducted in 1976 at the NASA Ames Research Center’s Vertical Gun Facility (VGF), the author studied low velocity impacts into simulated regolith powders and gravels, in order to examine physics of low-velocity collisions during early solar system planetesimal formation. In one “accidental” experiment, the bucket of powder remained gas-charged during evacuation of the VGF vacuum chamber. The impactor, moving at 5.5 m/s, disturbed the surface, initiating eruptions of dust-charged gas, shooting in jets from multiple vents at speeds up to about 3 m/s, with sporadic venting until 17 seconds after the impact. This experiment was described in [1], which concluded that it simulated comet eruption phenomena. In this hypothesis, a comet nucleus develops a lag deposit of regolith in at least some regions. At a certain distance from the sun, the thermal wave penetrates to an ice-rich depth, causing sublimation. Gas rises into the regolith, collects in pore spaces, and creates a gas-charged powder, as in our experiment. Any surface disturbance, such as a meteoroid, may initiate a temporary eruption, or eventually the gas pressure becomes sufficient to blow off the overburden. Our observed ejection speed would be sufficient to launch dust off of a kilometer-scale comet nucleus.Film (100 frames/s) of the event was obtained, but was partially torn up in a projector. It has recently been reconstituted (Centric Photo Labs, Tucson) and dramatically illustrates various cometary phenomena. Parabolic curtains of erupted material resemble curtains of material photographed from earth in real comet comas, “falling back” under solar wind forces. In retrospect, the mechanism photographed here helps explain:*sporadic eruptions in Comet P/Schwassmann-Wachmann 1 (near-circular orbit at ~6 A.U., where repeated recharge may occur).*sporadic eruptions on “asteroid” 2060 Chiron (which stays beyond 8.5 A.U.). *the thicker dust curtain (and longer eruption?) than

The LCO/Gemini-South campaign for Deep Impact target Comet 9P/Tempel 1: Temporally resolved wide-field narrowband imaging results

Science.gov (United States)

Lederer, S. M.; Osip, D. J.; Thomas-Osip, J. E.; DeBuizer, J. M.; Mondragon, L. A.; Schweiger, D. L.; Viehweg, J.; SB Collaboration

2005-08-01

An extensive observing campaign to monitor Comet 9P/Tempel 1 will be conducted from 20 June to 19 July, 2005 at Las Campanas Observatory, Chile. These observations will precede and follow the impact of the Deep Impact projectile, which is likely to create a crater on the nucleus that will act as a fresh active area on the surface of the comet. Discreet nucleus active areas, believed to be the source of coma gas and dust jets, will likely result in changing morphology in the coma. We present the initial results of the wide-field narrowband visible imaging of the comet. Data will be taken with the 2.5m DuPont telescope from 27 June - 9 July, following the comet from 4 rotations prior to impact, to 4 rotations after impact using the narrowband Hale-Bopp filters, including CN, C2, and two continuum filters. These data will allow an accurate determination of the rotation state of the embedded nucleus immediately preceding the impact event as well as a measure of any changes to the rotation state due to the impact. In addition, modeling of these data will provide the total dust and gas production rates from the unaltered nucleus compared to the enhanced dust and gas emission from the newly created active region and freely sublimating pieces of mantle material ejected into the coma by the impactor. We will monitor temporal changes (on hours and days time-scales) in the morphology of both the gas and refractory components. We will use coma morphology studies to estimate the dust and gas outflow velocities and infer the presence of discreet nucleus source regions (pre- and post-impact). Of particular interest is the study of the gas-to-dust ratio and the ratio of the minor carbon species emitted from the newly created active region relative to the pre-impact coma environment.

Encounters between degenerate stars and extrasolar comet clouds

International Nuclear Information System (INIS)

Pineault, S.; Poisson, E.

1989-01-01

Under the assumption that the presence of comet clouds around otherwise normal stars is a common occurrence in the Galaxy, the observational consequences of random penetration encounters between the general Galactic population of degenerate stars and these comet clouds is considered. The only case considered is where the compact stars is a single star. For this scenario, encounters involving neutron stars (NSs) result in impact rates 1000-10,000 times slower than in the model of Tremaine and Zytkow (1986). The rate for white dwarfs (WDs) is larger than the one for NSs by a factor of about 30 times the ratio of the degenerate star number densities. The mean impact rate is significantly increased if the number of comets in a cloud is nearly independent of the mass of the central star. It is concluded that some of the observed gamma-ray bursts may be caused by accretion of comets onto NSs and that this scenario, but with a WD as the accretor, probably contributes to the optical flash background rate. 38 refs

[An illustrious unknown. Giuseppe Levi among science, anti-fascism and Nobel Prizes].

Science.gov (United States)

Grignolio, Andrea; De Sio, Fabio

2009-01-01

The anatomist Giuseppe Levi (1872-1965) is unanimously considered one of the major figures of Italian biomedical sciences in the 20th century. His fame, however, is mainly derived from having nurtured three Nobel Prize winners, namely Salvador E. Luria, Rita Levi Montalcini and Renato Dulbecco. In reappraising Levi's role in the development of Italian science and culture in general, this article aims at questioning both the narrowness of earlier accounts and a certain kind of genealogical approach to the history of scientific disciplines and academic schools. We will here consider Giuseppe Levi as an instance of two major cultural phenomena: the development of experimental biology in Italy and continental Europe and the anti-fascist socialist culture expressed by a part of the Italian intellectuals. In so doing, we will reassess the historical specificity of the scientific maturation of Levi's three famous students, on the one hand, while on the other we will consider in some depth the cultural and moral environment in which Levi thrived and his role as a moral example for his students. Such revision, we will argue, have a direct bearing on more general historiographical issues, namely, the need for a stronger contextualization of the birth and consolidation of research traditions, implying a rejection of simplistic genealogical reconstructions, and the role of academic schools and institutional settings in the definition of novel, multidisciplinary scientific approaches. Finally, the following will highlight the importance of a more careful outlook on the master-pupil relationship in academic context, addressing issues of both continuity and rupture. The article is subdivided in two main sections, the first devoted to Levi as a scientist, the second to his Anti-fascism.

MEST-Tyche will take its dark comets to impact our solar system in 20 years

Science.gov (United States)

Cao, Dayong

2012-03-01

Tyche has many dark comets like Oort cloud. It went near our solar system every 25-27 million years. It could take its dark comets to impact our earth. Tyche and its dark comet absorb light like a dark light which is a negative black-body radiation. (1) Eddν=-c1dνd^3dνe^c2dνd/Td-1. Among it, Ed: the dark energy, νd: the dark frequence, Td: the dark temperature, c1d,c2d: the constant. So when they go near us, their wave has a against Doppler redshift as 0.000165. And they will inbreak solar system at the rate of 99AU/y, from the distance of 1,500AU and in 20 years. It can cause the broken ozonosphere, the lithosphere to crack, many big activity volcanic and the continental drift. And it can darked the light and colded the climate to the Great Ice Age. Not only it will break our environment by a special ``nuclear explosion'' under low temperature, but also the dark life will change the Genetic code of our life. So it will kill many lives and will produce new life. So it could trigger the Mass Extinction. We can bulid up a new pair of nuclear reactor (include dark nuclear energy) to drive a universal craft and can change the orbit of our earth for evading the impaction. We need a new life-information technology to develop our life and consciousness.

THE TEMPORAL CHANGES IN THE EMISSION SPECTRUM OF COMET 9P/TEMPEL 1 AFTER DEEP IMPACT

International Nuclear Information System (INIS)

Jackson, William M.; Yang Xueliang; Shi Xiaoyu; Cochran, Anita L.

2009-01-01

The time dependence of the changes in the emission spectra of Comet 9P/Tempel 1 after Deep Impact is derived and discussed. This was a unique event because for the first time it gave astronomers the opportunity to follow the time history of the formation and decay of O( 1 S), OH, CN, C 2 , C 3 , NH, and NH 2 . Least-squares fits of a modified Haser model with constraints using known rate constants were fit to the observed data. In the case of OH, a simple two-step Haser model provides a reasonable fit to the observations. Fitting the emissions from O( 1 S), CN, C 2 , C 3 , NH, and NH 2 requires the addition of a delayed component to a regular two- or three-step Haser model. From this information, a picture of the Deep Impact encounter emerges where there is an initial formation of gas and dust, which is responsible for the prompt emission that occurs right after impact. A secondary source of gas starts later after impact when the initial dust has dissipated enough so that solar radiation can reach the surface of freshly exposed material. The implications of this and other results are discussed in terms of the structure and composition of the comet's nucleus.

Implications of theories of asteroid and comet impact for policy options for management of spent nuclear fuel and high-level radioactive wastes

International Nuclear Information System (INIS)

Trask, N.J.

1994-01-01

Concern with the threat posed by terrestrial asteroid and comet impacts has heightened as the catastrophic consequences of such events have become better appreciated. Although the probabilities of such impacts are very small, a reasonable question for debate is whether such phenomena should be taken into account in deciding policy for the management of spent fuel and high-level radioactive waste. The rate at which asteroid or comet impacts would affect areas of surface storage of radioactive waste is about the same as the estimated rate at which volcanic activity would affect the Yucca Mountain area. The Underground Retrievable Storage (URS) concept could satisfactorily reduce the risk from cosmic impact with its associated uncertainties in addition to providing other benefits described by previous authors

Implications of theories of asteroid and comet impact for policy options for management of spent nuclear fuel and high-level radioactive wastes

Science.gov (United States)

Trask, Newell J.

1994-01-01

Concern with the threat posed by terrestrial asteroid and comet impacts has heightened as the catastrophic consequences of such events have become better appreciated. Although the probabilities of such impacts are very small, a reasonable question for debate is whether such phenomena should be taken into account in deciding policy for the management of spent fuel and high-level radioactive waste. The rate at which asteroid or comet impacts would affect areas of surface storage of radioactive waste is about the same as the estimated rate at which volcanic activity would affect the Yucca Mountain area. The Underground Retrievable Storage (URS) concept could satisfactorily reduce the risk from cosmic impact with its associated uncertainties in addition to providing other benefits described by previous authors.

77 FR 51832 - Atomic Safety and Licensing Board; In the Matter of Progress Energy Florida, Inc. (Levy County...

Science.gov (United States)

2012-08-27

...] Atomic Safety and Licensing Board; In the Matter of Progress Energy Florida, Inc. (Levy County Nuclear... testimony are being heard, all of the proceedings will be open to the public. See 10 CFR 2.328. A. Matters.... Impacts resulting from active and passive dewatering; 2. Impacts resulting from the connection of the site...

Species diversity in rock—paper—scissors game coupling with Levy flight

International Nuclear Information System (INIS)

Wang Dong; Zhuang Qian; Fan Ying; Di Zeng-Ru

2013-01-01

The rock—paper—scissors (RPS) game is a nice model to study the biodiversity in an ecosystem. However, in the previous studies only the nearest-neighbor interaction among the species was considered. In this paper, taking the long-range migration into account, the effects of the interplay between nearest-neighbor-interaction and long-range-interaction given by Levy flight with distance distribution l h (−3 ≤ h < −1) in the spatial RPS game are investigated. Taking the probability, exchange rate, and power-law exponent of Levy flight as parameters, the coexistence conditions of three species are given. The critical curves for stable coexistence of three species in the parameter space are presented. It is also found that Levy flight has interesting effects on the final spatiotemporal pattern of the system. The results reveal that the long-range-interaction given by Levy flight exhibits pronounced effects on biodiversity of the ecosystem. (interdisciplinary physics and related areas of science and technology)

Energy Efficiency instead of CO2 levy

International Nuclear Information System (INIS)

Uetz, R.

2005-01-01

This article takes a look at ways of avoiding a future, planned Swiss CO 2 levy by improving the efficiency of energy use. The political situation concerning the reduction of CO 2 emissions in Switzerland is reviewed and the likeliness of the introduction of a CO 2 levy is discussed. Strategies for the reduction of fossil fuel consumption and therefore of CO 2 emissions are looked at, including process optimisation. Recommendations are made on how to approach this work systematically - data collection, assessment of the potential for reduction and the planning of measures to be taken are looked at. The high economic efficiency of immediate action is stressed and typical middle and long-term measures are listed

On the relationship between gas and dust in 15 comets: an application to Comet 103P/Hartley 2 target of the NASA EPOXI mission of opportunity

Science.gov (United States)

Sanzovo, G. C.; Sanzovo, D. Trevisan; de Almeida, A. A.

After the success of Deep Impact mission to hit the nucleus of Comet 9P/Tempel 1 with an impactor, the concerns are turned now to the possible reutilization of this dormant flyby spacecraft in the study of another comet, for only about 10% of the cost of the original mission. Comet 103P/Hartley 2 on UT 2010 October 11 is the most attractive target in terms of available fuel at rendezvous and arrival time at the comet. In addition, the comet has a low inclination so that major orbital plane changes in the spacecraft trajectory are unnecessary. In an effort to provide information concerning the planning of this new NASA EPOXI space mission of opportunity, we use in this work, visual magnitudes measurements available from International Comet Quarterly (ICQ) to obtain, applying the Semi-Empirical Method of Visual Magnitudes - SEMVM (de Almeida, Singh, & Huebner 1997), the water production rates (in molecules/s) related to its perihelion passage of 1997. When associated to the water vaporization theory of Delsemme (1982), these rates allowed the acquisition of the minimum dimension for the effective nuclear radius of the comet. The water production rates were then converted into gas production rates (in g/s) so that, with the help of the strong correlation between gas and dust found for 12 periodic comets and 3 non-period comets (Trevisan Sanzovo 2006), we obtained the dust loss rates (in g/s), its behavior with the heliocentric distance and the dust-to-gas ratios in this physically attractive rendezvous target-comet to Deep Impact spacecraft at a closest approach of 700 km.

[From psychotherapy to psychoanalysis: Max Levy-Suhl (1876-1947)].

Science.gov (United States)

Hermanns, Ludger M; Schröter, Michael; Stroeken, Harry

2014-01-01

From psychotherapy to psychoanalysis: Max Levy-Suhl (1876-1947). Levy-Suhl can be considered one of the great practising psychotherapists in early 20th century Berlin. He was active in various fields, including ophthalmology, forensic adolescent psychiatry and hypnosis. Prominent among his publications were two handbooks of psychotherapeutic methods. His attitude towards psychoanalysis shifted from initial criticism to acceptance. Ca. 1930 he experienced some kind of conversion, resulting in his training at the Berlin Institute and becoming a member of the German Psychoanalytic Society. As a Jew being forced to emigrate in 1933, Levy-Suhl turned to the Netherlands where he had a psychoanalytic children's home in Amersfoort, followed by an analyst's practice in Amsterdam. He survived the German occupation, but apparently as a broken man. After the war he committed suicide.--The paper is complemented by an appendix, containing documents and an extensive bibliography.

Terrestrial cometary tail and lunar corona induced by small comets: Predictions for Galileo

International Nuclear Information System (INIS)

Dessler, A.J.; Sandel, B.R.; Vasyliunas, V.M.

1990-01-01

A search for small comets near 1 AU is an objective of the Galileo mission. If small comets are as numerous and behave as has been proposed, two near-Earth signatures of small comets should be observable by the UVS experiment on the Earth flybys of Galileo; (1) a comet-like tail of Earth created by small comets that come close to Earth, break up and vaporize, but just miss the atmosphere and proceed back into interplanetary space, and (2) a corona surrounding the Moon induced by lunar impact of small comets

Education Funding Crisis in the Suburbs: The Impact of the 2007-09 Recession Recovery Policies and the New York State Tax Levy Cap on School District Financial Planning Practices

Science.gov (United States)

Galligan, John J.; Annunziato, Anthony

2017-01-01

This article examines the impact of the fiscal recovery policies stemming from the 2007-09 economic recession and the implementation of the 2011 New York State Property Tax Levy Cap on the budgets of school districts located within a Long Island, New York suburban township. The research basis of this paper is based on two studies conducted by the…

Progress of Cometary Science in the Past 100 Years

Science.gov (United States)

Sekanina, Zdenek

1999-01-01

's celebrated comet; (ii) the impact of an extensively fragmented comet Shoemaker-Levy 9 into Jupiter - a once-in-a-millenium episode; (iii) a closeup, appearance of a small but very active Earth-approaching comet Hyakutake; and (iv) an unforgettable celestial show of comet Hale-Bopp, one of the brightest and the most massive comets ever observed. We have been - and for many years to come will be - harvesting scientifically lucrative findings based on the flood of data accumulated during observational campaigns organized for these and other recent objects. Our understanding of cometary phenomena will continue to grow as observing techniques are further being improved and as more sophisticated theories are being developed. Recent accomplishments achieved in the rapidly expanding field of comets are certain to stimulate the members of this astronomical community in their quest for new discoveries in the 21st century!

Modeling Formaldehyde Emission in Comets

Science.gov (United States)

Disanti, M. A.; Reuter, D. C.; Bonev, B. P.; Mumma, M. J.; Villanueva, G. L.

Modeling fluorescent emission from monomeric formaldehyde (H2CO) forms an integral part of our overall comprehensive program of measuring the volatile composition of comets through high-resolution (RP ~ 25,000) infrared spectroscopy using CSHELL at the IRTF and NIRSPEC at Keck II. The H2CO spectra contain lines from both the nu1 (symmetric CH2 stretch) and nu5 (asymmetric CH2 stretch) bands near 3.6 microns. We have acquired high-quality spectra of twelve Oort cloud comets, and at least six of these show clear emission from H2CO. We also detected H2CO with NIRSPEC in one Jupiter Family comet, 9P/Tempel 1, during Deep Impact observations. Our H2CO model, originally developed to interpret low-resolution spectra of comets Halley and Wilson (Reuter et al. 1989 Ap J 341:1045), predicts individual line intensities (g-factors) as a function of rotational temperature for approximately 1300 lines having energies up to approximately 400 cm^-1 above the ground state. Recently, it was validated through comparison with CSHELL spectra of C/2002 T7 (LINEAR), where newly developed analyses were applied to obtain robust determinations of both the rotational temperature and abundance of H2CO (DiSanti et al. 2006 Ap J 650:470). We are currently in the process of extending the model to higher rotational energy (i.e., higher rotational quantum number) in an attempt to improve the fit to high-J lines in our spectra of C/T7 and other comets. Results will be presented, and implications discussed.Modeling fluorescent emission from monomeric formaldehyde (H2CO) forms an integral part of our overall comprehensive program of measuring the volatile composition of comets through high-resolution (RP ~ 25,000) infrared spectroscopy using CSHELL at the IRTF and NIRSPEC at Keck II. The H2CO spectra contain lines from both the nu1 (symmetric CH2 stretch) and nu5 (asymmetric CH2 stretch) bands near 3.6 microns. We have acquired high-quality spectra of twelve Oort cloud comets, and at least six of

Persistence and extinction for stochastic logistic model with Levy noise and impulsive perturbation

OpenAIRE

Chun Lu; Qiang Ma; Xiaohua Ding

2015-01-01

This article investigates a stochastic logistic model with Levy noise and impulsive perturbation. In the model, the impulsive perturbation and Levy noise are taken into account simultaneously. This model is new and more feasible and more accordance with the actual. The definition of solution to a stochastic differential equation with Levy noise and impulsive perturbation is established. Based on this definition, we show that our model has a unique global positive solut...

Comets, Asteroids, and the Origin of the Biosphere

Science.gov (United States)

Hoover, Richard B.

2006-01-01

During the past few decades, the role of comets in the delivery of water, organics, and prebiotic chemicals to the Biosphere of Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment has become more widely accepted. However comets are still largely regarded as frigid, pristine bodies of protosolar nebula material that are entirely devoid of liquid water and consequently unsuitable for life in any form. Complex organic compounds have been observed comets and on the water rich asteroid 1998 KY26, which has color and radar reflectivity similar to the carbonaceous meteorites. Near infrared observations have indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar with resurfacing that may indicate cryovolcanic outgassing and the Cassini spacecraft has detected water-ice geysers on Saturn s moon Enceladus. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have now firmly established that comets contain a suite of complex organic chemicals; water is the predominant volatile; and that extremely high temperatures (approx.350-400 K) can be reached on the surface of the very black (albedo-0.03) nuclei when the comets are with 1.5 AU from the Sun. Impact craters and pinnacles observed on comet Wild 2 suggest a thick crust and episodic outbursts and jets observed on the nuclei of several comets are interpreted as indications that localized regimes of liquid water and water vapor can periodically exist beneath the crust of some comets. The Deep Impact observations indicate that the temperature on the nucleus of of comet Tempel 1 at 1.5 AU varied from 330K on the sunlit side to a minimum of 280+/-8 K. It is interesting that even the coldest region of the comet surface was slightly above the ice/liquid water phase transition temperature. These results suggest that pools and films of liquid water can exist in a wide

Entrevista con Giovanni Levi

Directory of Open Access Journals (Sweden)

Monica Oliveira

2017-06-01

Full Text Available En esta entrevista, Giovanni Levi - como un conocedor del tema de Familia - realiza una importante evaluación sobre el actual estado de las investigaciones realizadas en el Brasil y em el exterior. Con estilo franco, agudo y lucido critica las visiones tradicionales y sus ilusiones ypropone nuevos conceptos y métodos. La historia de la familia debería ceder espacio para el estudio de las redes relacionales o de los mundos relacionales. De la misma forma, la historia cuantitativa debería abrir espacio para el estudio de las cualidades. Ya con relación a la historia de las elites, tan estudiada y reproducida en una diversidad de trabajos, que deberíase mirar en otra perspectiva. Es decir, no mirar a las reglas sociales predeterminadas, sino a los desvíos y a las variaciones. Levi defiende que los historiadores deben trascender a los documentos que se encuentran fácilmente y que pueden fortalecer perspectivas deformadas y esequilibradas de la sociedad. Para él, los historiadores deben esforzarse por estudiar a aquellos grupos que dejaron pocos rastros documentales. En ese esfuerzo existiría una nueva mirada sobre la historia de la familia.

LEVIS ion source and beam characterization on PBFA-II

International Nuclear Information System (INIS)

Renk, T.J.; Tisone, G.C.; Adams, R.G.; Bailey, J.E.; Filuk, A.B.; Johnson, D.J.; Pointon, T.D.

1993-01-01

We report on the continuing development of the LEVIS (Laser Evaporation Ion Source) lithium active ion source for the 15-cm radial focussing ion diode on PBFA-11. We found previously that DC-heating of the anode surface to 150 degrees C maximum for 5 hours resulted in a pure lithium beam. This paper discusses the characterization of LEVIS source uniformity by Faraday cup arrays and multiple lines of sight for visible light spectroscopy. These diagnostics give some evidence of nonuniformity in both A-K gap electric fields and ion current density. Despite this, however, the measured focal spot size appears smaller than with a passive LiF source operated in the same magnetic field topology. Experiments using a curved anode for vertical beam focussing show reduced ion beam turn-on delay by 5 ns by altering the magnetic field topology as well as anode curvature. Another 3--5 ns reduction was achieved by switching from a passive LiF to the active LEVIS source

Reservoirs for Comets: Compositional Differences Based on Infrared Observations

Science.gov (United States)

Disanti, Michael A.; Mumma, Michael J.

Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution. This requires building a taxonomy of comets from both present-day dynamical reservoirs: the Kuiper Belt (hereafter KB), sampled through observation of ecliptic comets (primarily Jupiter Family comets, or JFCs), and the Oort cloud (OC), represented observationally by the long-period comets and by Halley Family comets (HFCs). Because of their short orbital periods, JFCs are subjected to more frequent exposure to solar radiation compared with OC comets. The recent apparitions of the JFCs 9P/Tempel 1 and 73P/Schwassmann-Wachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class, which is under-represented in studies of cometary parent volatiles. This chapter reviews the latest techniques developed for analysis of high-resolution spectral observations from ˜2-5 μm, and compares measured abundances of native ices among comets. While no clear compositional delineation can be drawn along dynamical lines, interesting comparisons can be made. The sub-surface composition of comet 9P, as revealed by the Deep Impact ejecta, was similar to the majority of OC comets studied. Meanwhile, 73P was depleted in all native ices except HCN, similar to the disintegrated OC comet C/1999 S4 (LINEAR). These results suggest that 73P may have formed in the inner giant planets' region while 9P formed farther out or, alternatively, that both JFCs formed farther from the Sun but with 73P forming later in time.

Overview of levies on energy carriers in Europe

International Nuclear Information System (INIS)

Iten, R.; Gehrig, S.; Koenig, Ch.

2000-01-01

This short report for the Swiss Federal Office of Energy (SFOE) examines the situation with respect to levies and steering taxes on various forms of energy in European countries. Comparisons are made with the situation in Switzerland regarding energy prices for various consumer groups, taxation of energy carriers and exceptions for energy-intensive industries. Details are given on prices of energy and the levies imposed, in particular with respect to carbon taxes. Data are given for 11 European countries and detailed information on regulations concerning exceptions is presented for selected countries. Finally, fuel price differences between neighbouring countries are examined and the role of 'motor-fuel-tourism' is discussed

Mystery of comets

International Nuclear Information System (INIS)

Whipple, F.L.

1985-01-01

An account is given of the growth of human understanding of comets with emphasis initially placed on theories developed before the twentieth century and subsequently on information regarding the nature of comets, their origin and possible relation to life on earth. Special consideration is given to a description of how the author arrived at his own model of the origin and nature of comets, the dirty snowball theory. The significance of comets (i.e. the hazards they may represent) is assessed and space missions to Halley's comet together with the first landing on a comet (tentatively planned for 1995) are described. It is noted that this growth of cometary understanding is presented as an integral part of the growth of science and technology. 14 references

Prevention before profits: a levy on food and alcohol advertising.

Science.gov (United States)

Harper, Todd A; Mooney, Gavin

2010-04-05

The recent interest in health promotion and disease prevention has drawn attention to the role of the alcohol and junk-food industries. Companies supplying, producing, advertising or selling alcohol or junk food (ie, foods with a high content of fat, sugar or salt) do so to generate profits. Even companies marketing "low-carbohydrate" beers, "mild" cigarettes, or "high-fibre" sugary cereals are not primarily concerned about population health, more so increased sales and profits. In a competitive market, it is assumed that consumers make fully informed choices about costs and benefits before purchasing. However, consumers are not being fully informed of the implications of their junk-food and alcohol choices, as advertising of these products carries little information on the health consequences of consumption. We propose that there should be a levy on advertising expenditure for junk food and alcoholic beverages to provide an incentive for industry to promote healthier products. Proceeds of the levy could be used to provide consumers with more complete and balanced information on the healthy and harmful impacts of food and alcohol choices. Our proposal addresses two of the greatest challenges facing Australia's preventable disease epidemic - the imbalance between the promotion of healthier and unhealthy products, and securing funds to empower consumer choice.

Physics of comets

CERN Document Server

Krishna Swamy, K S

1997-01-01

The study of Comet Halley in 1986 was a tremendous success for cometary science. In March of that year, six spacecrafts passed through Comet Halley as close as 600 km from the nucleus and made the in situ measurements of various kinds. These space missions to Comet Halley and that of the ICE spacecraft to Comet Giacobini-Zinner combined with studies, both ground-based and above the atmosphere, have increased our knowledge of cometary science in a dramatic way.This new edition of Physics of Comets incorporates these new and exciting findings. The emphasis of the book is on the physical processe

Levy-Student processes for a stochastic model of beam halos

Energy Technology Data Exchange (ETDEWEB)

Petroni, N. Cufaro [Department of Mathematics, University of Bari, and INFN Sezione di Bari, via E. Orabona 4, 70125 Bari (Italy)]. E-mail: cufaro@ba.infn.it; De Martino, S. [Department of Physics, University of Salerno, and INFN Sezione di Napoli (gruppo di Salerno), Via S. Allende, I-84081 Baronissi (SA) (Italy); De Siena, S. [Department of Physics, University of Salerno, and INFN Sezione di Napoli (gruppo di Salerno), Via S. Allende, I-84081 Baronissi (SA) (Italy); Illuminati, F. [Department of Physics, University of Salerno, and INFN Sezione di Napoli (gruppo di Salerno), Via S. Allende, I-84081 Baronissi (SA) (Italy)

2006-06-01

We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of the stochastic mechanics which produces time reversal invariant diffusion processes. In this paper we analyze the consequences of introducing the generalized Student laws, namely non-Gaussian, Levy infinitely divisible (but not stable) distributions. We will analyze this idea from two different standpoints: (a) first by supposing that the stationary distribution of our (Wiener powered) stochastic model is a Student distribution; (b) by supposing that our model is based on a (non-Gaussian) Levy process whose increments are Student distributed. In the case (a) the longer tails of the power decay of the Student laws, and in the case (b) the discontinuities of the Levy-Student process can well account for the rare escape of particles from the beam core, and hence for the formation of a halo in intense beams.

Levy-Student processes for a stochastic model of beam halos

International Nuclear Information System (INIS)

Petroni, N. Cufaro; De Martino, S.; De Siena, S.; Illuminati, F.

2006-01-01

We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of the stochastic mechanics which produces time reversal invariant diffusion processes. In this paper we analyze the consequences of introducing the generalized Student laws, namely non-Gaussian, Levy infinitely divisible (but not stable) distributions. We will analyze this idea from two different standpoints: (a) first by supposing that the stationary distribution of our (Wiener powered) stochastic model is a Student distribution; (b) by supposing that our model is based on a (non-Gaussian) Levy process whose increments are Student distributed. In the case (a) the longer tails of the power decay of the Student laws, and in the case (b) the discontinuities of the Levy-Student process can well account for the rare escape of particles from the beam core, and hence for the formation of a halo in intense beams

Autonomous Navigation Performance During The Hartley 2 Comet Flyby

Science.gov (United States)

Abrahamson, Matthew J; Kennedy, Brian A.; Bhaskaran, Shyam

2012-01-01

On November 4, 2010, the EPOXI spacecraft performed a 700-km flyby of the comet Hartley 2 as follow-on to the successful 2005 Deep Impact prime mission. EPOXI, an extended mission for the Deep Impact Flyby spacecraft, returned a wealth of visual and infrared data from Hartley 2, marking the fifth time that high-resolution images of a cometary nucleus have been captured by a spacecraft. The highest resolution science return, captured at closest approach to the comet nucleus, was enabled by use of an onboard autonomous navigation system called AutoNav. AutoNav estimates the comet-relative spacecraft trajectory using optical measurements from the Medium Resolution Imager (MRI) and provides this relative position information to the Attitude Determination and Control System (ADCS) for maintaining instrument pointing on the comet. For the EPOXI mission, AutoNav was tasked to enable continuous tracking of a smaller, more active Hartley 2, as compared to Tempel 1, through the full encounter while traveling at a higher velocity. To meet the mission goal of capturing the comet in all MRI science images, position knowledge accuracies of +/- 3.5 km (3-?) cross track and +/- 0.3 seconds (3-?) time of flight were required. A flight-code-in-the-loop Monte Carlo simulation assessed AutoNav's statistical performance under the Hartley 2 flyby dynamics and determined optimal configuration. The AutoNav performance at Hartley 2 was successful, capturing the comet in all of the MRI images. The maximum residual between observed and predicted comet locations was 20 MRI pixels, primarily influenced by the center of brightness offset from the center of mass in the observations and attitude knowledge errors. This paper discusses the Monte Carlo-based analysis that led to the final AutoNav configuration and a comparison of the predicted performance with the flyby performance.

Bunker Levy Schemes for Greenhouse Gas (GHG) Emission Reduction in International Shipping

DEFF Research Database (Denmark)

Kosmas, Vasileios; Acciaro, Michele

2017-01-01

, the extent of which depend on the structure of the levy and market conditions. Since there is concern that the costs resulting from the policy will be passed from shipping companies to their customers along the supply chain, the paper dwells on how the costs arising from the enforcement of the levy...

Comets and their origin the tools to decipher a comet

CERN Document Server

Meierhenrich, Uwe

2014-01-01

Divided into two parts, the first four chapters of Comets and their Origin refer to comets and their formation in general, describing cometary missions, comet remote observations, astrochemistry, artificial comets, and the chirality phenomenon.The second part covers the cometary Rosetta mission, its launch, journey, scientific objectives, and instrumentations, as well as the landing scenario on a cometary nucleus. Along the way, the author presents general questions concerning the origin of terrestrial water and the molecular beginnings of lifeon Earth, as well as how the instruments used on

Rotationally invariant family of Levy-like random matrix ensembles

International Nuclear Information System (INIS)

Choi, Jinmyung; Muttalib, K A

2009-01-01

We introduce a family of rotationally invariant random matrix ensembles characterized by a parameter λ. While λ = 1 corresponds to well-known critical ensembles, we show that λ ≠ 1 describes 'Levy-like' ensembles, characterized by power-law eigenvalue densities. For λ > 1 the density is bounded, as in Gaussian ensembles, but λ < 1 describes ensembles characterized by densities with long tails. In particular, the model allows us to evaluate, in terms of a novel family of orthogonal polynomials, the eigenvalue correlations for Levy-like ensembles. These correlations differ qualitatively from those in either the Gaussian or the critical ensembles. (fast track communication)

Comets, Asteroids, Meteorites, and the Origin of the Biosphere

Science.gov (United States)

Hoover, Richard B.

2006-01-01

During the past few decades, the delivery of water, organics, and prebiotic chemicals to the Biosphere of Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment by comets and asteroids has become more widely accepted. Comets are still largely regarded as frigid, pristine bodies of protosolar nebula material that are devoid of liquid water and therefore unsuitable for life. Complex organic compounds have been observed in comets and on the water-rich asteroid 1998 KY26 and near IR observations have indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar that has resurfacing suggesting cryovolcanic outgassing. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have shown that comets contain complex organic chemicals; that water is the predominant volatile; and that extremely high temperatures (approx. 350-400 K) can be reached on the surfae of the very black (albedo approx. 0.03) nuclei of comets when they approach the Sun. Impact craters and pinnacles observed on comet Wild 2 suggest a thick crust. Episodic outbursts and jets from the nuclei of several comets indicate that localized regimes of liquid water and water vapor can periodically exist beneath the comet crust. The Deep Impact mission found the temperature of the nucleus of comet Tempel 1 at 1.5 AU varied from a minimum of 280 plus or minus 8 K the 330K (57 C) on the sunlit side. In this paper it is argued that that pools and films of liquid water exist (within a wide range of temperatures) in cavities and voids just beneath the hot, black crust. The possibility of liquid water existing over a wide range of temperatures significantly enhances the possibility that comets might contain niches suitable for the growth of microbial communities and ecosystems. These regimes would be ideal for the growth of psychrophilic, mesophilic, and thermophilic

Basics of Swiss water levy politics - Economic considerations; Grundlagen Wasserzinspolitik. Oekonomische Ueberlegungen - Schlussbericht

Energy Technology Data Exchange (ETDEWEB)

Ott, W.; Staub, C. [econcept AG, Zuerich (Switzerland); Leimbacher, J. [Joerg Leimbacher, Bern (Switzerland)

2008-10-15

This comprehensive final report for the Swiss Federal Office of Energy (SFOE) takes a look at the economic considerations involved in defining the basics for the handling of levies on water commodities. This levy is raised in Switzerland on the use of water and represents the payment made to a commune for the use of its water resources. The report first takes a look at the current situation, the reasons behind the Swiss water levy concept and the reasons why they have to be newly regulated. Changes in market factors are discussed, e.g. the liberalisation of the power market and past and future price developments. Also, the situation on the spot and futures markets for electricity is discussed. The actual production costs for hydropower are discussed and compared with other means of electricity generation. Proposals for readjusting the regulations concerning water levies are discussed.

Spiral arms, comets and terrestrial catastrophism

International Nuclear Information System (INIS)

Clube, S.V.M.; Napier, W.M.

1982-01-01

A review is presented of an hypothesis of terrestrial catastrophism in which comets grow in molecular clouds and are captured by the Sun as it passes through the spiral arms of the Galaxy. Assuming that comets are a major supplier of the Earth-crossing (Appollo) asteroid population, the latter fluctuates correspondingly and leads to episodes of terrestrial bombardment. Changes in the rotational momentum of core and mantle, generated by impacts, lead to episodes of magnetic field reversal and tectonic activity, while surface phenomena lead to ice-ages and mass extinctions. An episodic geophysical history with an interstellar connection is thus implied. If comets in spiral arms are necessary intermediaries in the process of star formation, the theory also has implications relating to early solar system history and galactic chemistry. These aspects are briefly discussed with special reference to the nature of spiral arms. (author)

Comet Giacobini-Zinner - a normal comet?

International Nuclear Information System (INIS)

Cochran, A.L.; Barker, E.S.

1987-01-01

Observations of Comet Giacobini-Zinner were obtained during its 1985 apparition using an IDS spectrograph at McDonald Observatory. Column densities and production rates were computed. The production rates were compared to observations of other normal comets. Giacobini-Zinner is shown to be depleted in C2 and C3 relative to CN. These production rates are down by a factor of 5. 12 references

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

Origin and development of comets

International Nuclear Information System (INIS)

Kresak, L.

1989-01-01

The comets are the most primitive and probably also the oldest members of the solar system. Comet cores are brittle bodies of an irregular shape and of a size of 1 to 10 km whose main component is ice. Around 130 comets move along short-period paths whose aphelia are concentrated in the area of Jupiter. They are in the last stage of development. About 20 comets have periods of 20 to 200 years and feature higher motion stability. Roughly 180 comets have elliptical orbits of a period exceeding 200 years, 200 comets have parabolic and 120 comets have hyperbolic orbits. The most distant comets form the Oort cloud around the solar system consisting of about one billion comets. Comets originated roughly 4.6 thousand million years ago together with planets, probably inside the Oort cloud. (M.D.). 11 figs

Campaign Expenditures in School Levy Referenda and Their Relationship to Voter Approval: Evidence from Ohio, 2007-2010

Science.gov (United States)

Ingle, William Kyle; Johnson, Paul Andrew; Givens, Matt Ryan; Rampelt, Jerry

2013-01-01

Using logistic regression, this study sought to understand the relationship between district characteristics, district finances, levy characteristics, and campaign expenditures with new operating levy outcomes. We found that employee benefits as a percentage of the district's budget were negatively associated with levy outcomes, while salaries…

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Science.gov (United States)

2010-04-01

... 26 Internal Revenue 18 2010-04-01 2010-04-01 false Minimum exemption from levy for wages, salary... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or... him as wages, salary, or other income. Under section 6331(d)(3), a levy upon wages or salary is...

Batik Kreatif Amri Yahya dalam Perspektif Strukturalisme Levi-Strauss

Directory of Open Access Journals (Sweden)

Irfa'ina Rohana Salma

2016-04-01

Full Text Available ABSTRAKPada saat ini sebagaian besar pengembangan motif batik mengacu pada ragam hias tradisional, sehingga hasilnya cenderung monoton. Perlu penyegaran visual dan diversifikasi gagasan untuk menghasilkan motif batik modern yang baru, unik, kreatif, dan inovatif. Tujuan kajian ini adalah menginspirasi para seniman, perajin, desainer untuk menciptakan motif kreatif sebagai diversifikasi produk yang semakin memperkaya khasanah batik Indonesia, dengan mengkaji batik kreatif karya Amri Yahya. Batik kreatif Amri Yahya telah mendapat pengakuan internasional sebagai batik modern. Metode yang digunakan yaitu deskriptif analitis untuk mendeskripsikan dan menganalisis objek seni yaitu batik karya Amri Yahya dengan perspektif Strukturalisme Levi-Strauss. Dari kajian ini dapat disimpulkan bahwa batik kreatif karya Amri Yahya dihasilkan dari keberanian dan kebebasan berekspresi serta konsistensi dalam berkarya seni.Kata kunci: batik, kreatif, Amri Yahya, strukturalisme Levi-StraussABSTRACTAt this time almost all of the batik motive bulk development refers to the traditional decoration, so the results tend to be monotonous. It needs a visual refreshment and diversity idea to produce a modern motive that is new, unique, creative, and innovative. The purpose of this study was to inspire the artists, craft men, designers to create the creative motifs as the diversified products to enrichIndonesian batik, reviewing creative batik of Amri Yahya. These Amri Yahya creative batik hasreceived international recognition as a modern batik. The method used is descriptive analysis todescribe artwork object that is Amri Yahya batik with Levi -Strauss's Structuralism perspective. From this study it can be concluded that the creative work of Amri Yahya batik produced from the encouragement and independecy of expression, as well as consistency in the artwork.Keywords: batik, creative, Amri Yahya, levi - strauss structuralis

Adaptive nonparametric estimation for L\\'evy processes observed at low frequency

OpenAIRE

Kappus, Johanna

2013-01-01

This article deals with adaptive nonparametric estimation for L\\'evy processes observed at low frequency. For general linear functionals of the L\\'evy measure, we construct kernel estimators, provide upper risk bounds and derive rates of convergence under regularity assumptions. Our focus lies on the adaptive choice of the bandwidth, using model selection techniques. We face here a non-standard problem of model selection with unknown variance. A new approach towards this problem is proposed, ...

Unveiling the formation and evolution of comets

Science.gov (United States)

Lasue, J.; Levasseur-Regourd, A. C.; Botet, R.; Coradini, A.; Desanctis, M. C.; Kofman, W.

2007-08-01

Comet nuclei are considered as the most pristine bodies of the solar system and consequently their study sheds an important light on the processes occurring during the initial stages of the solar system formation. The analysis of the porosity and bulk density of such primordial bodies is especially important to understand their capacity to retain volatile components (organics and ices) present in the early solar nebula. Typical tensile strengths deduced for comet nuclei range from below 102N.m-2 from the Deep Impact mission [1] up to 104N.m-2 from the study of comet C/1999 S4 LINEAR breakup [2] and meteoroids [3]. A bulk density of about 350 kg/m3 has been obtained for 9P/Tempel 1 from the Deep Impact mission [4]. Moreover the properties of dust released from the comets strongly confirm such values. Instruments flying-by comet 1P/Halley had discovered the presence of organics, and pointed out the dust low albedo and extremely low density while analyses of Interplanetary Dust Particles collected in the stratosphere and remote spectroscopic observations have indicated that cometary dust consists of an un-equilibrated heterogeneous mixture of organic refractory materials and of amorphous and crystalline silicate minerals [5], as recently confirmed by Stardust [6]. Observations of the solar scattered light, together with elaborate simulations, give an estimation of the mass ratio between silicates and absorbing organics, the size distribution and the structure of the dust particles, suggesting that a fair amount consists in fluffy aggregates built up from submicronic grains [7,8], as recently confirmed by the analysis of dust craters and aerogel tracks on Stardust collector showing for some large particles (up to 100 μm) an extraordinary fluffy structure [9]. Simulations have been developed in our teams to describe the aspects of comet aggregation and evolution that have not been thoroughly explained yet. Particle aggregation simulations taking into account cohesive

Spectrophotometry of 25 comets - Post-Halley updates for 17 comets plus new observations for eight additional comets

Science.gov (United States)

Newburn, Ray L., Jr.; Spinrad, Hyron

1989-01-01

The best possible production figures within the current post-Halley framework and available observations are given for H2O, O(1D), CN, C3, C2 and dust in 25 comets. Of these, the three objects with the smallest mixing ratios of all minor species have moderate to little or no dust and appear 'old'. Comets with large amounts of CN are very dusty, and there is a clear correlation of CN with dust, although comets with little or no dust still have some CN. Thus, CN appears to have at least two sources, dust and one or more parent gases. Also, the C2/CN production ratio changes continuously with heliocentric distance in every comet considered, suggesting that C2 production may be a function of coma density as well as parental abundance. Dust production ranges from essentially zero in Comet Sugano-Saigusa-Fujikawa up to 67,000 kg/s for Halley on March 14, 1986.

Spectrophotometry of 25 comets - Post-Halley updates for 17 comets plus new observations for eight additional comets

International Nuclear Information System (INIS)

Newburn, R.L. Jr.; Spinrad, H.

1989-01-01

The best possible production figures within the current post-Halley framework and available observations are given for H2O, O(1D), CN, C3, C2 and dust in 25 comets. Of these, the three objects with the smallest mixing ratios of all minor species have moderate to little or no dust and appear 'old'. Comets with large amounts of CN are very dusty, and there is a clear correlation of CN with dust, although comets with little or no dust still have some CN. Thus, CN appears to have at least two sources, dust and one or more parent gases. Also, the C2/CN production ratio changes continuously with heliocentric distance in every comet considered, suggesting that C2 production may be a function of coma density as well as parental abundance. Dust production ranges from essentially zero in Comet Sugano-Saigusa-Fujikawa up to 67,000 kg/s for Halley on March 14, 1986. 61 references

Numerical simulations of comets - predictions for Comet Giacobini-Zinner

International Nuclear Information System (INIS)

Fedder, J.A.; Lyon, J.G.; Giuliani, J.L. Jr.

1986-01-01

Simulations of Comet Giacobini-Zinner's interaction with solar wind are described and results are presented. The simulations are carried out via the numerical solution of the ideal MHD equations as an initial value problem in a uniform solar wind. The calculations are performed on a Cartesian mesh centered at the comet. Results reveal that the first significant modifications of the solar wind along the ISEE/ICE trajectory will occur 100,000 km from the solar wind comet axis. 6 references

Mission to the comets

International Nuclear Information System (INIS)

Hughes, D.

1980-01-01

The plans of space agencies in the United States and Europe for an exploratory comet mission including a one year rendezvous with comet Temple-2 and a fast fly-by of comet Halley are discussed. The mission provides an opportunity to make comparative measurements on the two different types of comets and also satisfies the three major scientific objectives of cometary missions namely: (1) To determine the chemical nature and the physical structure of cometary nuclei, and the changes that occur with time and orbital position. (2) To study the chemical and physical nature of the atmospheres and ionospheres of comets, the processes that occur in them, and their development with time and orbital position. (3) To determine the nature of the tails of comets and the processes by which they are formed, and to characterise the interaction of comets with solar wind. (UK)

76 FR 77561 - Atomic Safety and Licensing Board; In the Matter of Progress Energy Florida, Inc.; (Levy County...

Science.gov (United States)

2011-12-13

...] Atomic Safety and Licensing Board; In the Matter of Progress Energy Florida, Inc.; (Levy County Nuclear....\\1\\ On February 23, 2009, this Board was established to handle the matter and to preside over any... resulting from active and passive dewatering; 2. Impacts resulting from the connection of the site to the...

Persistence and extinction for stochastic logistic model with Levy noise and impulsive perturbation

Directory of Open Access Journals (Sweden)

Chun Lu

2015-09-01

Full Text Available This article investigates a stochastic logistic model with Levy noise and impulsive perturbation. In the model, the impulsive perturbation and Levy noise are taken into account simultaneously. This model is new and more feasible and more accordance with the actual. The definition of solution to a stochastic differential equation with Levy noise and impulsive perturbation is established. Based on this definition, we show that our model has a unique global positive solution and obtains its explicit expression. Sufficient conditions for extinction are established as well as nonpersistence in the mean, weak persistence and stochastic permanence. The threshold between weak persistence and extinction is obtained.

Ammonia abundances in comets

Science.gov (United States)

Wyckoff, S.; Tegler, S.; Engel, L.

The emission band strengths of the NH2 bands of Comets Halley, Hartley-Good, Thiele, and Borrelly were measured to determine the NH2 column densities for the comets. Production rates obtained using the Haser and vectorial models are in agreement within the observational errors, suggesting that a simple two-step decay model may be used to approximate the NH2 distribution in a comet's coma. Ammonia-to-water abundance ratios from 0.01 to 0.4 percent were found for the four comets. The ratio in Comet Halley is found to be Q(NH3)/Q(H2O) = 0.002 + or - 0.001. No significant difference in the ammonia abundance was found before or after perihelion in Comet Halley.

Cooperative random Levy flight searches and the flight patterns of honeybees

International Nuclear Information System (INIS)

Reynolds, A.M.

2006-01-01

The most efficient Levy flight (scale-free) searching strategy for N independent searchers to adopt when target sites are randomly and sparsely distributed is identified. For N=1, it is well known that the optimal searching strategy is attained when μ=2, where the exponent μ characterizes the Levy distribution, P(l)=l -μ , of flight-lengths. For N>1, the optimal searching strategy is attained as μ->1. It is suggested that the orientation flights of honeybees can be understood within the context of such an optimal cooperative random Levy flight searching strategy. Upon returning to their hive after surveying a landscape honeybees can exchange information about the locations of target sites through the waggle dance. In accordance with observations it is predicted that the waggle dance can be disrupted without noticeable influence on a hive's ability to maintain weight when forage is plentiful

33 CFR 135.103 - Levy and payment of barrel fee on OCS oil.

Science.gov (United States)

2010-07-01

... SECURITY (CONTINUED) MARINE POLLUTION FINANCIAL RESPONSIBILITY AND COMPENSATION OFFSHORE OIL POLLUTION COMPENSATION FUND Levy of Fees § 135.103 Levy and payment of barrel fee on OCS oil. (a) A fee of $.03 per... paragraph (a) of this section applies whenever the unobligated Fund balance is less than $200,000,000. (d...

New Mission Old Spacecraft: EPOXI's Approach to the Comet Hartley-2

Science.gov (United States)

Rieber, Richard R.; LaBorde, Gregory R.

2012-01-01

NASA's Deep Impact mission ended successfully in 2005 after an impact and close flyby of the comet 9P/Tempel-1. The Flyby spacecraft was placed in hibernation and was left to orbit the sun. In 2007, engineers at the Jet Propulsion Laboratory brought the spacecraft out of hibernation and successfully performed two additional missions. These missions were EPOCh, Extra-solar Planetary Observation and Characterization, a photometric investigation of transiting exo-planets, and DIXI, Deep Impact eXtended Investigation, which maneuvered the Flyby spacecraft towards a close encounter with the comet 103P/Hartley- 2 on 4 November 2010. The names of these two scientific investigations combine to form the overarching mission's name, EPOXI. The encounter with 103P/Hartley-2 was vastly different from the prime mission's encounter with 9P/Tempel-1. The geometry of encounter was nearly 180 ? different and 103P/Hartley-2 was approximately one-quarter the size of 9P/Tempel-1. Mission operations for the comet flyby were broken into three phases: a) Approach, b) Encounter, and c) Departure. This paper will focus on the approach phase of the comet encounter. It will discuss the strategies used to decrease both cost and risk while maximizing science return and some of the challenges experienced during operations.

Comets in Australian Aboriginal Astronomy

Science.gov (United States)

Hamacher, Duane W.; Norris, Ray P.

2011-03-01

We present 25 accounts of comets from 40 Australian Aboriginal communities, citing both supernatural perceptions of comets and historical accounts of historically bright comets. Historical and ethnographic descriptions include the Great Comets of 1843, 1861, 1901, 1910, and 1927. We describe the perceptions of comets in Aboriginal societies and show that they are typically associated with fear, death, omens, malevolent spirits, and evil magic, consistent with many cultures around the world. We also provide a list of words for comets in 16 different Aboriginal languages.

D'Alembert's paradox, 1900-1914: Levi-Civita and his Italian and French followers

Science.gov (United States)

Tazzioli, Rossana

2017-07-01

Before the First World War, Tullio Levi-Civita (1873-1941) was already a well-known mathematician in Italy and abroad, in particular in France. Professor at the University of Padua since 1898, he had published important contributions to tensor calculus, theory of relativity, differential geometry, hydrodynamics, and the three-body problem. In 1918, when he moved to the University of Rome, he created an international school of mathematics. In this paper, we focus on d'Alembert's paradox to which Levi-Civita and some of his Italian and French followers contributed remarkable solutions. This case-study is used to illustrate Levi-Civita's approach to hydrodynamics and its influence in Italy and France, especially in the period 1910-1914.

Comet showers and the steady-state infall of comets from the Oort cloud

International Nuclear Information System (INIS)

Hills, J.G.

1981-01-01

The appearance of an inner edge to the Oort comet cloud at a semimajor axis of a = (1--2) x 10 4 AU is an observational artifact. Stellar perturbations are frequent enough and strong enough to assure that a constant fraction of the comets with semimajor axes greater than this are in orbits which bring them within the planetary region. Only infrequent, close stellar encounters are able to repopulate the planet-crossing orbits of comets with smaller semimajor axes. Owing to their relatively short orbital periods which return them frequently to the planetary system, the comets in these more tightly bound orbits will be deflected by Jupiter into drastically different orbits or be destroyed by solar heating before another close stellar passage repopulates their numbers. Comets with semimajor axes less than 2 x 10 4 AU appear in the inner solar system only in intense bursts or showers which last for a few orbital periods after the close passage of a star to the Sun. This is followed by a much longer span of time during which only comets with a>2 x 10 4 AU enter the planetary system. The theoretically determined location of the boundary between the semimajor axes of those comets which enter the planetary system only in bursts or showers and those which arrive in a steady stream is very abrupt and falls at the observed inner edge of the Oort cloud. We propose that the comets formed in the outer parts of the collapsing protosun, which had a radius of less than 5 x 10 3 AU. If this produced a first-generation comet cloud with a radius of 10 3 AU or greater, the coupled dynamical perturbations of passing stars and Jupiter will, of necessity, lead to the formation of a comet cloud similar that of the observed Oort comet cloud

Truncated Levy flights and agenda-based mobility are useful for the assessment of personal human exposure

International Nuclear Information System (INIS)

Schlink, Uwe; Ragas, Ad M.J.

2011-01-01

Receptor-oriented approaches can assess the individual-specific exposure to air pollution. In such an individual-based model we analyse the impact of human mobility to the personal exposure that is perceived by individuals simulated in an exemplified urban area. The mobility models comprise random walk (reference point mobility, RPM), truncated Levy flights (TLF), and agenda-based walk (RPMA). We describe and review the general concepts and provide an inter-comparison of these concepts. Stationary and ergodic behaviour are explained and applied as well as performance criteria for a comparative evaluation of the investigated algorithms. We find that none of the studied algorithm results in purely random trajectories. TLF and RPMA prove to be suitable for human mobility modelling, because they provide conditions for very individual-specific trajectories and exposure. Suggesting these models we demonstrate the plausibility of their results for exposure to air-borne benzene and the combined exposure to benzene and nonane. - Highlights: → Human exposure to air pollutants is influenced by a person's movement in the urban area. → We provide a simulation study of approaches to modelling personal exposure. → Agenda-based models and truncated Levy flights are recommended for exposure assessment. → The procedure is demonstrated for benzene exposure in an urban region. - Truncated Levy flights and agenda-based mobility are useful for the assessment of personal human exposure.

Ammonia abundances in four comets

International Nuclear Information System (INIS)

Wickoff, S.; Tegler, S.C.; Engel, L.

1991-01-01

NH2 emission band strengths were measured in four comets and the NH2 column densities were determined in order to measure the ammonia content of the comets. The mean ammonia/water abundance ratio derived for the four comets is found to be 0.13 + or - 0.06 percent, with no significant variation among the comets. The uniformity of this abundance attests to a remarkable degree of chemical homogeneity over large scales in the comet-forming region of the primordial solar nebula, and contrasts with the CO abundance variations found previously in comets. The N2 and NH3 abundances indicate a condensation temperature in the range 20-160 K, consistent with virtually all comet formation hypotheses. 64 refs

Levi-Strauss's "Bricolage" and Theorizing Teachers' Work.

Science.gov (United States)

Hatton, Elizabeth

1989-01-01

A teacher's work is compared to Claude Levi-Strauss's concept of "bricolage." A "bricoleur" is a professional do-it-yourself person, falling somewhere between an odd-job person and a craftsperson. The concept helps to explain pedagogical inadequacy by linking inherent limiting features of teachers' work and some causal…

Kernel-Correlated Levy Field Driven Forward Rate and Application to Derivative Pricing

Energy Technology Data Exchange (ETDEWEB)

Bo Lijun [Xidian University, Department of Mathematics (China); Wang Yongjin [Nankai University, School of Business (China); Yang Xuewei, E-mail: xwyangnk@yahoo.com.cn [Nanjing University, School of Management and Engineering (China)

2013-08-01

We propose a term structure of forward rates driven by a kernel-correlated Levy random field under the HJM framework. The kernel-correlated Levy random field is composed of a kernel-correlated Gaussian random field and a centered Poisson random measure. We shall give a criterion to preclude arbitrage under the risk-neutral pricing measure. As applications, an interest rate derivative with general payoff functional is priced under this pricing measure.

Infrared imaging and photometry of Comet Giacobini-Zinner

International Nuclear Information System (INIS)

Campins, H.

1986-01-01

Infrared images and photometry were obtained to determine the spatial distribution and physical characteristics (temperature, albedo, size distribution, total mass, etc.) of the grains in the coma of Comet GZ. A 10.8 m image of Comet GZ obtained on August 4 represents the first ground-based thermal-infrared image of a Comet. Among the most significant results are: (1) an estimate of the number of grains that the ICE spacecraft must have encountered, which led the plasma wave team to conclude that they could only detect impacts on the antennae and not on the whole body of the ICE spacecraft; (2) the discovery of a population of large grains (radius > 100 micrometer), not observed in most other comets, which formed a curved tail near the nucleus (within 80 arcsec or 34,000 km); and (3) the detection of structure in the spatial distribution in the coma of the particle albedo, which was tentatively attributed to the presence of very fluffy grains which are likely to have multiple internal scattering of incident sunlight. The albedo map of Comet GZ was obtained by combining the 10.8 micrometer image shown with a simultaneous image taken at 0.68 micrometer, a bandpass which isolates the scattered continuum

Realm of the comets

International Nuclear Information System (INIS)

Weissman, P.R.

1987-01-01

Studies of Jovian perturbations of the orbits of long-period comets led to the concept of the Oort cloud of 180 billion comets at 50,000-150,000 AU from the sun. Several comets are induced to move toward the sun every million years by the passage of a star at a distance of a few light years. The location of the cloud has since been revised to 20,000-100,000 AU, and comets are now accepted as remnant material fron the proto-solar system epoch. The galactic disk and random, close-passing stars may also cause rare, large perturbations in the orbits of the cloud comets, sending large numbers of comets through the inner solar system. The resulting cometary storm is a candidate cause for the wholesale extinction of dinosaurs in the Cretaceous-Terniary transition due to large number of planetesimals, or one large comet, striking the earth, in a short period of time. The IRAS instruments have detected similar clouds of material around other stars

The comet assay: ready for 30 more years.

Science.gov (United States)

Møller, Peter

2018-02-24

During the last 30 years, the comet assay has become widely used for the measurement of DNA damage and repair in cells and tissues. A landmark achievement was reached in 2016 when the Organization for Economic Co-operation and Development adopted a comet assay guideline for in vivo testing of DNA strand breaks in animals. However, the comet assay has much more to offer than being an assay for testing DNA strand breaks in animal organs. The use of repair enzymes increases the range of DNA lesions that can be detected with the assay. It can also be modified to measure DNA repair activity. Still, despite the long-term use of the assay, there is a need for studies that assess the impact of variation in specific steps of the procedure. This is particularly important for the on-going efforts to decrease the variation between experiments and laboratories. The articles in this Special Issue of Mutagenesis cover important technical issues of the comet assay procedure, nanogenotoxicity and ionising radiation sensitivity on plant cells. The included biomonitoring studies have assessed seasonal variation and certain predictors for the basal level of DNA damage in white blood cells. Lastly, the comet assay has been used in studies on genotoxicity of environmental and occupational exposures in human biomonitoring studies and animal models. Overall, the articles in this Special Issue demonstrate the versatility of the comet assay and they hold promise that the assay is ready for the next 30 years.

Levy-Student distributions for halos in accelerator beams

International Nuclear Information System (INIS)

Cufaro Petroni, Nicola; De Martino, Salvatore; De Siena, Silvio; Illuminati, Fabrizio

2005-01-01

We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of stochastic mechanics (SM) which produces time reversal invariant diffusion processes. This leads to a linearized theory summarized in a Schroedinger-like (SL) equation. The space charge effects have been introduced in recent papers by coupling this S-L equation with the Maxwell equations. We analyze the space-charge effects to understand how the dynamics produces the actual beam distributions, and in particular we show how the stationary, self-consistent solutions are related to the (external and space-charge) potentials both when we suppose that the external field is harmonic (constant focusing), and when we a priori prescribe the shape of the stationary solution. We then proceed to discuss a few other ideas by introducing generalized Student distributions, namely, non-Gaussian, Levy infinitely divisible (but not stable) distributions. We will discuss this idea from two different standpoints: (a) first by supposing that the stationary distribution of our (Wiener powered) SM model is a Student distribution; (b) by supposing that our model is based on a (non-Gaussian) Levy process whose increments are Student distributed. We show that in the case (a) the longer tails of the power decay of the Student laws and in the case (b) the discontinuities of the Levy-Student process can well account for the rare escape of particles from the beam core, and hence for the formation of a halo in intense beams

Detectability of Sungrazing Comet Soft X-ray Irradiance

Directory of Open Access Journals (Sweden)

Su Yeon Oh

2007-12-01

Full Text Available Originating from the Oort cloud, some comets disappear to impact against the Sun or to split up by strong gravitational force. Then they don't go back to the Oort cloud. They are called sungrazing comets. The comets are detected by sublimation of ices and ejection of gas and dust through solar heat close to the Sun. There exists the charge transfer from heavy ions in the solar wind to neutral atoms in the cometary atmosphere by interaction with the solar wind. Cometary atoms would be excited to high electronic levels and their de-excitation would result in X-ray emission, or it would be scattering of solar X-ray emission by very small cometary grains. We calculated the X-ray emission applying the model suggested by Mendis & Flammer (1984 and Cravens (1997. In our estimation, the sungrazing comet whose nucleus size is about 1 km in radius might be detectable within a distance of 3 solar radius from the sun on soft X-ray solar camera.

Comet thermal modeling

International Nuclear Information System (INIS)

Weissman, P.R.; Kieffer, H.H.

1987-01-01

The past year was one of tremendous activity because of the appearance of Halley's Comet. Observations of the comet were collected from a number of sources and compared with the detailed predictions of the comet thermal modeling program. Spacecraft observations of key physical parameters for cometary nucleus were incorporated into the thermal model and new cases run. These results have led to a much better understanding of physical processes on the nucleus and have pointed the way for further improvements to the modeling program. A model for the large-scale structure of cometary nuclei was proposed in which comets were envisioned as loosely bound agglomerations of smaller icy planetesimals, essentially a rubble pile of primordial dirty snowballs. In addition, a study of the physical history of comets was begun, concentrating on processes during formation and in the Oort cloud which would alter the volatile and nonvolatile materials in cometary nuclei from their pristine state before formation

Can collective searches profit from Levy walk strategies?

Energy Technology Data Exchange (ETDEWEB)

Santos, M C; Da Luz, M G E [Departamento de Fisica, Universidade Federal do Parana, Curitiba-PR, 81531-990 (Brazil); Raposo, E P [Laboratorio de Fisica Teorica e Computacional, Departamento de Fisica, Universidade Federal de Pernambuco, Recife-PE, 50670-901 (Brazil); Viswanathan, G M [Instituto de Fisica, Universidade Federal de Alagoas, Maceio-AL, 57072-970 (Brazil)], E-mail: luz@fisica.ufpr.br

2009-10-30

We address the problem of collective searching in which a group of walkers, guided by a leader, looks for randomly located target sites. In such a process, the necessity to maintain the group aggregated imposes a constraint in the foraging dynamics. We discuss four different models for the system collective behavior, with the leader and followers performing Gaussian as well as truncated Levy walks. In environments with low density of targets we show that Levy foraging is advantageous for the whole group, when compared with Gaussian strategy. Furthermore, certain extra rules must be incorporated in the individuals' dynamics, so that a compromise between the trend to keep the group together and the global efficiency of search is met. The exact character of these rules depends on specific details of the foraging process, such as regeneration of target sites and energy costs.

Major energy users at heart of debate over climate change levy

International Nuclear Information System (INIS)

Anon.

1999-01-01

The UK government's decision to introduce a climate change levy on energy-intensive industry and use the revenues from the levy to cut employers national insurance contributions are discussed. The dispute over energy prices, energy savings potential, industry sectors that have approached the government regarding voluntary agreement concerning energy saving measures and tax relief, the Marshall report examining options for reducing business use of energy, possible exemptions for electricity produced from renewable sources, and the encouragement of businesses to conduct pilot emissions trading schemes are considered. (UK)

Can voter-approved tax levies provide fiscal advantages and stability for local public health agencies?

Science.gov (United States)

Schmalzried, Hans D; Fallon, L Fleming

2013-01-01

Major funding cuts have occurred throughout the United States public health system during the past several years. Funding for local public health agency (LPHA) services and programs is obtained through a patchwork of sources that vary both within and among states. Even though local city and county sources provide a significant proportion of funding for LPHAs, information available in the literature about these revenues is sparse and is not clearly described. This study focused on a single specific revenue stream included in the local sources (local city and county) category: funds voted on directly by the public. The primary purpose of this study was to examine whether this type of funding source provided fiscal advantages for LPHAs. Specifically, we wanted to see how sensitive levy votes were to changing general economic conditions. A questionnaire to collect LPHA levy data was developed, approved, and mailed to county boards of elections in Ohio (n = 88). Elections officials were asked to provide voting results for all LPHA levy ballot attempts since 1994 regardless of outcome. In the study period (1994 through 2011), 250 LPHA property tax levies were placed on election ballots in Ohio. LPHAs were successful in 155 (62.0%) and unsuccessful in 95 (38.0%) attempts. Over the 18-year period, the most noteworthy outcome was a 94.6% pass rate for renewal levies. Our study demonstrated that voter-approved tax levies provide some fiscal advantages for LPHAs: higher per capita revenues than those who have to rely on other sources of income and predictable revenue streams. This translates into more funds being available for public health programs and services. Property tax levies allow citizens to make direct investments in their local health departments.

The McDonald Observatory Faint Comet Survey - Gas production in 17 comets

Science.gov (United States)

Cochran, Anita L.; Barker, Edwin S.; Ramseyer, Tod F.; Storrs, Alex D.

1992-01-01

The complete Intensified Dissector Scanner data set on 17 comets is presented, and production rates are derived and analyzed. It is shown that there is a strong degree of homogenization in the production rate ratios of many comets. It also appears that the ratio of the production rates of the various species has no heliocentric distance dependence, except for the case of NH2. When speaking of the gas in the coma of a comet, it appears that comets must have been formed under remarkably uniform conditions, and that they must have evolved and formed their comae in a similar manner. The data presented here constitute strong evidence that the minor species must be bound up in a lattice and that the interior of a comet must be reasonably uniform.

Disintegration of comet nuclei

International Nuclear Information System (INIS)

Ksanfomality, Leonid V

2012-01-01

The breaking up of comets into separate pieces, each with its own tail, was seen many times by astronomers of the past. The phenomenon was in sharp contrast to the idea of the eternal and unchangeable celestial firmament and was commonly believed to be an omen of impending disaster, especially for comets with tails stretching across half the sky. It is only now that we have efficient enough space exploration tools to see comet nuclei and even - in the particular case of small comet Hartley-2 in 2010 - to watch their disintegration stage. There are also other suspected candidates for disintegration in the vast family of comet nuclei and other Solar System bodies. (physics of our days)

Disintegration of comet nuclei

Science.gov (United States)

Ksanfomality, Leonid V.

2012-02-01

The breaking up of comets into separate pieces, each with its own tail, was seen many times by astronomers of the past. The phenomenon was in sharp contrast to the idea of the eternal and unchangeable celestial firmament and was commonly believed to be an omen of impending disaster, especially for comets with tails stretching across half the sky. It is only now that we have efficient enough space exploration tools to see comet nuclei and even - in the particular case of small comet Hartley-2 in 2010 - to watch their disintegration stage. There are also other suspected candidates for disintegration in the vast family of comet nuclei and other Solar System bodies.

Optical observation of comets

International Nuclear Information System (INIS)

Tanabe, Hiroyoshi

1974-01-01

The observation of comets is proposed to study the state of interplanetary space. The behavior of the tails of comets shows the state of solar wind. On July 4, 1964, large bending was seen in the tail of the Tomita-Gerber-Handa comet. Then, on July 7, 1964, geomagnetic disturbance was observed. Disturbance in the tail of Kohoutek comet was seen on Jan. 19, 1974, and Ksub(p)--5 on the ground on Jan. 25. The effort for the quantitative measurement of the parameters of solar wind has been continued in various countries. Recently, the large scale observation of the Kohoutek comet was carried out in the world. Preliminary report is presented in this paper. Waving in the type 1 tail of the comet was seen, and this phenomenon may show some instability due to the interaction between the tail and the solar wind. Periodic variation of the direction of the tail has been reported. The present result also confirmed this report. In case of small comets, flare-up occurs and original luminous intensity is regained after several days. Measurement of the spectrum at the time of flare-up may show information concerning temporary variation of the state of interplanetary space. For the tracking of time variation of comets, cooperation of a number of stations at different positions is required. (Kato, T.)

Disappearance and disintegration of comets

Science.gov (United States)

Sekanina, Z.

1984-01-01

The present investigation has the objective to provide a summary of the existing evidence on the disappearance of comets and to draw conclusions regarding the physical processes involved in the disappearance. Information concerning the classification of evidence and the causes of apparent disappearance of comets is presented in a table. Attention is given to the dissipating comets, the headless sungrazing comet 1887 I, and the physical behavior of the dissipating comets and the related phenomena. It is found that all comets confined to the planetary region of the solar system decay on astronomically short time scales. However, only some of them appear to perish catastrophically. Some of the observed phenomena could be successfully interpreted. But little insight has been obtained into the character of the processes which the dissipating comets experience.

26 CFR 301.6331-3 - Restrictions on levy while offers to compromise are pending.

Science.gov (United States)

2010-04-01

... are pending. 301.6331-3 Section 301.6331-3 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF... for Collection of Taxes § 301.6331-3 Restrictions on levy while offers to compromise are pending. Cross-reference. For provisions relating to the making of levies while an offer to compromise is pending...

Hyperactivity and Dust Composition of Comet 103P/Hartley 2 During the EPOXI Encounter

Science.gov (United States)

Harker, David E.; Woodward, Charles E.; Kelley, Michael S. P.; Wooden, Diane H.

2018-05-01

Short-period comet 103P/Hartley 2 (103P) was the flyby target of the Deep Impact eXtended Investigation on 2010 November 4 UT. This comet has a small hyperactive nucleus, i.e., it has a high water production rate for its surface area. The underlying cause of the hyperactivity is unknown; the relative abundances of volatiles in the coma of 103P are not unusual. However, the dust properties of this comet have not been fully explored. We present four epochs of mid-infrared spectra and images of comet 103P observed from Gemini-South +T-ReCS on 2010 November 5, 7, 21 and December 13 UT, near and after the spacecraft encounter. Comet 103P exhibited a weak 10 μm emission feature ≃1.14 ± 0.01 above the underlying local 10 μm continuum. Thermal dust grain modeling of the spectra shows the grain composition (mineralogy) was dominated by amorphous carbon and amorphous pyroxene with evidence for Mg-rich crystalline olivine. The grain size has a peak grain radius range of a peak ∼ 0.5–0.9 μm. On average, the crystalline silicate mass fraction is ≃0.24, fairly typical of other short-period comets. In contrast, the silicate-to-carbon ratio of ≃0.48–0.64 is lower compared to other short-period comets, which indicates that the flux measured in the 10 μm region of 103P was dominated by amorphous carbon grains. We conclude that the hyperactivity in comet 103P is not revealing dust properties similar to the small grains seen with the Deep Impact experiment on comet 9P/Tempel 1 or from comet C/1995 O1 (Hale–Bopp).

High-Resolution Spectroscopy of Stratospheric Ethane Following the Jupiter Impact of 2009

Science.gov (United States)

Fast, Kelly; Kostiuk, Theodor; Livengood, Timothy A.; Hewagama, Tilak; Amen, John

2010-01-01

We report on high-resolution infrared spectroscopy of ethane (C2H6) performed at the latitude of an impact site on Jupiter discovered on 19 July 2009 by A. Wesley from a location in Murrumbateman, Australia. The observations used the NASA Goddard Space Flight Center's Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. HIPWAC is a mid-infrared (9-12 microns) heterodyne spectrometer operating at the highest limit of spectral resolving power (lambda\\Delta\\lambda > l06), providing information on atmospheric constituent abundance and temperature through fully resolved tine shapes. Ethane is a stable trace product of methane photochemistry that is nearly uniformly mixed in Jupiter's stratosphere, providing an effective probe of that altitude region. Ethane emission line profiles near 11,74 microns in the Ug band were measured in Jupiter's stratosphere at 25 MHz (11.00083/cm) resolution. A sequence of spectra of ethane acquired over a range of longitude at the impact latitude (56S planetocentric) probes constituent abundance and temperature profile, both on and off the impact region. Near the site of the impact, ethane emission increased above levels measured well outside the impact region. Radiative transfer analysis indicates increased ethane mole fraction (30% greater). Variation in the measured continuum level and line intensities within 75deg of the impact longitude indicate the presence of an opacity source (haze) at altitudes near and above the tropopause and as high as the 10-mbar level near the impact site. The indication of possible haze opacity up to the 10-mbar level in the atmosphere is consistent with measurements made by HIPWAC's predecessor as part of the IRTF Shoemaker Levy-9 campaign in 1994.

Physical processes in comets

International Nuclear Information System (INIS)

Newburn, R.L. Jr.

1988-01-01

When this program began in 1975 only limited photometry had been carried out on comets at any wavelength. Program goals were to observe many comets, including faint periodic comets, at a range of heliocentric distances in order to begin to understand the range of behavior among comets and in a given comet during its approach and departure from the sun. Then a study of the continuum of scattered light from dust was added. More recently the value of joint team observations in visible and infrared light has been recognized and utilized as often as possible. All 1978 to 1982 data was reanalyzed and 1983 to 1986 data analyzed in the framwork of the post-Halley paradigm, covering 25 comets in all. Four observing runs (June, July, Sept., and Jan.) with Hanner produced excellent results on Wilson, Bradfield, P/Klemola, and P/Borrelly and lesser data on other objects, including the last reported IR photometry of P/Halley. The Wilson and Halley data have been reduced

Mass transport around comets and its impact on the seasonal differences in water production rates

Energy Technology Data Exchange (ETDEWEB)

Rubin, M.; Altwegg, K.; Thomas, N. [Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern (Switzerland); Fougere, N.; Combi, M. R.; Tenishev, V. M. [Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States); Le Roy, L. [Center for Space and Habitability, University of Bern, Sidlerstrasse 5, 3012 Bern (Switzerland)

2014-06-20

Comets are surrounded by a thin expanding atmosphere, and although the nucleus' gravity is small, some molecules and grains, possibly with the inclusion of ices, can get transported around the nucleus through scattering (atoms/molecules) and gravitational pull (grains). Based on the obliquity of the comet, it is also possible that volatile material and icy grains get trapped in regions, which are in shadow until the comet passes its equinox. When the Sun rises above the horizon and the surface starts to heat up, this condensed material starts to desorb and icy grains will sublimate off the surface, possibly increasing the comet's neutral gas production rate on the outbound path. In this paper we investigate the mass transport around the nucleus, and based on a simplified model, we derive the possible contribution to the asymmetry in the seasonal gas production rate that could arise from trapped material released from cold areas once they come into sunlight. We conclude that the total amount of volatiles retained by this effect can only contribute up to a few percent of the asymmetry observed in some comets.

Cometography a catalog of comets

CERN Document Server

Kronk, Gary W; Seargent, David A J

2017-01-01

Cometography is a multi-volume catalog of every comet observed from ancient times up to the 1990s, when the internet took off as a medium of scientific record. It uses the most reliable orbits known to determine the distances from the Earth and Sun at the time of discovery and last observation, as well as the largest and smallest angular distance to the Sun, most northerly and southerly declination, closest distance to the Earth, and other details, to enable the reader to understand each comet's physical appearance. Volume 6, the final volume in the catalog, covers the observations and pertinent calculations for every comet seen between 1983 and 1993. The comets are listed in chronological order, with complete references to publications relating to each comet and physical descriptions of each comet's development throughout its apparition. Cometography is the definitive reference on comets through the ages, for astronomers and historians of science.

Detecting active comets with SDSS

Energy Technology Data Exchange (ETDEWEB)

Solontoi, Michael; Ivezic, Zeljko; /Washington U., Seattle, Astron. Dept.; West, Andrew A.; /MIT, MKI; Claire, Mark; /Washington U., Seattle, Astron. Dept.; Juric, Mario; /Princeton U. Observ.; Becker, Andrew; Jones, Lynne; /Washington U., Seattle, Astron. Dept.; Hall, Patrick B.; /York U., Canada; Kent, Steve; /Fermilab; Lupton, Robert H.; /Princeton U. Observ.; Quinn, Tom; /Washington U., Seattle, Astron. Dept. /Princeton U. Observ.

2010-12-01

Using a sample of serendipitously discovered active comets in the Sloan Digital Sky Survey (SDSS), we develop well-controlled selection criteria for greatly increasing the efficiency of comet identification in the SDSS catalogs. After follow-up visual inspection of images to reject remaining false positives, the total sample of SDSS comets presented here contains 19 objects, roughly one comet per 10 million other SDSS objects. The good understanding of selection effects allows a study of the population statistics, and we estimate the apparent magnitude distribution to r {approx} 18, the ecliptic latitude distribution, and the comet distribution in SDSS color space. The most surprising results are the extremely narrow range of colors for comets in our sample (e.g. root-mean-square scatter of only {approx}0.06 mag for the g-r color), and the similarity of comet colors to those of jovian Trojans. We discuss the relevance of our results for upcoming deep multi-epoch optical surveys such as the Dark Energy Survey, Pan-STARRS, and the Large Synoptic Survey Telescope (LSST), and estimate that LSST may produce a sample of about 10,000 comets over its 10-year lifetime.

Fundraising flights: a levy on international air travel for adaptation

Energy Technology Data Exchange (ETDEWEB)

Birch, Tom; Chambwera, Muyeye

2011-03-15

Adapting to climate change will not be cheap: it will cost an estimated tens of billions of dollars each year. But where will the money come from? The UN climate negotiations have set up dedicated funds for the task but domestic politics have resulted in insufficient, variable and unreliable contributions from governments. An innovative adaptation levy on international air travel could help fill the gap. A small charge to individual travellers would raise up to US$10 billion a year. The levy, which follows the 'polluter pays' principle, could be implemented very quickly and at minimal cost and would go a long way to raising sums that could make a significant difference.

Postencounter view of comets

International Nuclear Information System (INIS)

Mendis, D.A.

1988-01-01

Ground-based and space observations of Comet Halley during its 1986 perihelion passage are reviewed, with an emphasis on their implications for theoretical models. Consideration is given to the shape, surface morphology, and composition of the comet nucleus; the shape, dynamics, and composition of the dust tail; neutral and ionic gas species in the head and plasma tail; and the comet/solar-wind interaction. Extensive diagrams, graphs, and sample images are provided, and the potential value of the new kinds of data to be obtained with the NASA Comet-Rendezvous/Asteroid-Flyby spacecraft is discussed. 139 references

CometQ: An automated tool for the detection and quantification of DNA damage using comet assay image analysis.

Science.gov (United States)

Ganapathy, Sreelatha; Muraleedharan, Aparna; Sathidevi, Puthumangalathu Savithri; Chand, Parkash; Rajkumar, Ravi Philip

2016-09-01

DNA damage analysis plays an important role in determining the approaches for treatment and prevention of various diseases like cancer, schizophrenia and other heritable diseases. Comet assay is a sensitive and versatile method for DNA damage analysis. The main objective of this work is to implement a fully automated tool for the detection and quantification of DNA damage by analysing comet assay images. The comet assay image analysis consists of four stages: (1) classifier (2) comet segmentation (3) comet partitioning and (4) comet quantification. Main features of the proposed software are the design and development of four comet segmentation methods, and the automatic routing of the input comet assay image to the most suitable one among these methods depending on the type of the image (silver stained or fluorescent stained) as well as the level of DNA damage (heavily damaged or lightly/moderately damaged). A classifier stage, based on support vector machine (SVM) is designed and implemented at the front end, to categorise the input image into one of the above four groups to ensure proper routing. Comet segmentation is followed by comet partitioning which is implemented using a novel technique coined as modified fuzzy clustering. Comet parameters are calculated in the comet quantification stage and are saved in an excel file. Our dataset consists of 600 silver stained images obtained from 40 Schizophrenia patients with different levels of severity, admitted to a tertiary hospital in South India and 56 fluorescent stained images obtained from different internet sources. The performance of "CometQ", the proposed standalone application for automated analysis of comet assay images, is evaluated by a clinical expert and is also compared with that of a most recent and related software-OpenComet. CometQ gave 90.26% positive predictive value (PPV) and 93.34% sensitivity which are much higher than those of OpenComet, especially in the case of silver stained images. The

Composition of faint comets

International Nuclear Information System (INIS)

Brown, L.W.

1986-01-01

The study uses an emission line, differential imaging camera built by the Science Operations Branch. This instrument allows photometric data to be obtained over a large area of a comet in a large number of resolution elements. The detector is a 100x100 Reticon array which with interchangeable optics can give resolutions from 2'' to 30'' over a field of 1' to 15'. The camera through its controlling computer can simultaneously take images in on-line and continuum filters and through computer subtraction and calibration present a photometric image of the comet produced by only the emission of the molecule under study. Initial work has shown two significant problems. First the auxiliary equipment of the telescope has not allowed the unambiguous location of faint comets so that systematic observations could be made, and secondly initial data has not shown much molecular emission from the faint comets which were located. Work last year on a software and hardware display system and this year on additional guide motors on the 36-inch telescope has allowed the differential camera to act as its own finder and guide scope. Comet IRAS was observed in C2 and CO+, as well as an occultation by the comet of SAO029103. The perodic comet Giacobini-Zinner was also observed in C2

Physics of comets

CERN Document Server

Krishna Swamy, K S

2010-01-01

This revised edition places a unique emphasis on all the new results from ground-based, satellites and space missions - detection of molecule H2 and prompt emission lines of OH for the first time; discovery of X-rays in comets; observed diversity in chemical composition among comets; the puzzle of the constancy of spin temperature; the well-established mineralogy of cometary dust; extensive theoretical modeling carried out for understanding the observed effects; and, the similarity in the mineralogy of dust in circumstellar shell of stars, comets, meteorites, asteroids and IDPs, thus indicatin

Comets in UV

Science.gov (United States)

Shustov, B.; Sachkov, M.; Gómez de Castro, A. I.; Vallejo, J. C.; Kanev, E.; Dorofeeva, V.

2018-04-01

Comets are important "eyewitnesses" of Solar System formation and evolution. Important tests to determine the chemical composition and to study the physical processes in cometary nuclei and coma need data in the UV range of the electromagnetic spectrum. Comprehensive and complete studies require additional ground-based observations and in situ experiments. We briefly review observations of comets in the ultraviolet (UV) and discuss the prospects of UV observations of comets and exocomets with space-borne instruments. A special reference is made to the World Space Observatory-Ultraviolet (WSO-UV) project.

Comet radar explorer

Science.gov (United States)

Farnham, Tony; Asphaug, Erik; Barucci, Antonella; Belton, Mike; Bockelee-Morvan, Dominique; Brownlee, Donald; Capria, Maria Teresa; Carter, Lynn; Chesley, Steve; Farnham, Tony; Gaskell, Robert; Gim, Young; Heggy, Essam; Herique, Alain; Klaasen, Ken; Kofman, Wlodek; Kreslavsky, Misha; Lisse, Casey; Orosei, Roberto; Plaut, Jeff; Scheeres, Dan

The Comet Radar Explorer (CORE) is designed to perform a comprehensive and detailed exploration of the interior, surface, and inner coma structures of a scientifically impor-tant Jupiter family comet. These structures will be used to investigate the origins of cometary nuclei, their physical and geological evolution, and the mechanisms driving their spectacular activity. CORE is a high heritage spacecraft, injected by solar electric propulsion into orbit around a comet. It is capable of coherent deep radar imaging at decameter wavelengths, high resolution stereo color imaging, and near-IR imaging spectroscopy. Its primary objective is to obtain a high-resolution map of the interior structure of a comet nucleus at a resolution of ¿100 elements across the diameter. This structure shall be related to the surface geology and morphology, and to the structural details of the coma proximal to the nucleus. This is an ideal complement to the science from recent comet missions, providing insight into how comets work. Knowing the structure of the interior of a comet-what's inside-and how cometary activity works, is required before we can understand the requirements for a cryogenic sample return mission. But more than that, CORE is fundamental to understanding the origin of comets and their evolution in time. The mission is made feasible at low cost by the use of now-standard MARSIS-SHARAD reflec-tion radar imaging hardware and data processing, together with proven flight heritage of solar electric propulsion. Radar flight heritage has been demonstrated by the MARSIS radar on Mars Express (Picardi et al., Science 2005; Plaut et al., Science 2007), the SHARAD radar onboard the Mars Reconnaissance Orbiter (Seu et al., JGR 2007), and the LRS radar onboard Kaguya (Ono et al, EPS 2007). These instruments have discovered detailed subsurface structure to depths of several kilometers in a variety of terrains on Mars and the Moon. A reflection radar deployed in orbit about a comet

Periodic Comet Machholz and its idiosyncrasies

International Nuclear Information System (INIS)

Sekanina, Z.

1990-01-01

The dynamics and physical characteristics of Comet P/Machholz are analyzed. The discovery of the comet (Machholz, 1986) is discussed, including the observational conditions and the theory that the comet is inactive over extensive periods of time. Consideration is given to observations of the two tails of Comet P/Machholz (Emerson, 1986), the brightness variations and light curve of the comet, and nuclear photometry of the comet (Green, 1987). It is suggested that the increase in activity beginning one day after perihelion was triggered by a discrete source within 15 deg of the rotation pole that became sunlit after perihelion. Also, the possibility that Comet P/Machholz is associated with a meteor stream is examined. 45 refs

Dynamics of landslides on comets of irregular shape

Science.gov (United States)

Czechowski, Leszek

2017-04-01

Landslides were observed on a few comet's nuclei, e.g. [1], [2]. The mechanism of their origin is not obvious because of very low gravity. According to [2] fluidization and multiphase transport of cometary material could be an explanation. We investigate here motion of the mass on a comet of irregular shape. The mechanism responsible for the low friction is not considered here. In fact, mass motion often occurs without contact with the surface. The motion could be triggered by meteoroids impacts or by the tidal forces. Comets nuclei are believed to be built of soft materials like snow and dust. The landing of Philae on the comet 67P/Czuriumow-Gierasimienko indicates a different situation. According to [1]: "thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength". Here we assume that elastic properties of comet's nuclei could be similar to elastic properties of dry snow, namely Young modulus is assumed to be 1 - 100 MPa, see [3] and [4]. We consider nucleus of the shape of 67P/Churyumov-Gerasimenko with density 470 kg/m3. The impact or tidal forces result in changing of rotation of the comet. In general, the vector of angular velocity will be a subject to nutation that results in changing of centrifugal force, and consequently could be a factor triggering landslides. Note that nucleus' shape does not resemble the shape of surface of constant value of gravitational potential (i.e. 'geoid'). Our numerical models indicate the parts of the nucleus where landslides start and other parts where landslides stop. Of course, the regolith from the first type of regions would be removed to the regions of the second class. The motion of the mass is often complicated because of complicated distribution of the gravity and complicated shape of the nucleus. Acknowledgement: The research is partly supported by Polish National Science Centre

How to Run a Successful School Levy Campaign.

Science.gov (United States)

Meyers, Judith K.

This document describes the public relations strategies employed by the Lakewood (Ohio) City School district to obtain voter support for a school levy. Various aspects of this successful campaign are described, including the formation of administrative committees to oversee campaign activities, steering and citizens' committees, the use of…

The Implementation of Effluent Taxes for Cambodian Industry: An Assessment of Pollutant Levies

OpenAIRE

Sideth Muong

2006-01-01

This study looks at how the Cambodian government might introduce a pollution levy system to address the country's industrial pollution problem. Using information drawn from a variety of sources, including a recent industrial survey, it estimates the levels of pollution charges that would reduce pollution by 25%-85%. It also calculates the overall revenue that such levies would produce and estimates the costs that industry would have to bear in terms of abatement costs and pollution charges. B...

Energy levies and endogenous technology in an empirical simulation model for the Netherlands

International Nuclear Information System (INIS)

Den Butter, F.A.G.; Dellink, R.B.; Hofkes, M.W.

1995-01-01

The belief in beneficial green tax swaps has been particularly prevalent in Europe, where high levels of unemployment and strong preferences for a large public sector (and hence high tax levels) accentuate the desire for revenue-neutral, growth-enhancing reductions in labor income taxes. In this context an empirical simulation model is developed for the Netherlands, especially designed to reckon with the effects of changes in prices on the level and direction of technological progress. It appears that the so-called employment double dividend, i.e. increasing employment and decreasing energy use at the same time, can occur. A general levy yields stronger effects than a levy on household use only. However, the stronger effects of a general levy on employment and energy use are accompanied by shrinking production and, in the longer run, by decreasing disposable income of workers or non-workers. 1 fig., 4 tabs., 1 appendix, 20 refs

Molecular ions in comet tails

International Nuclear Information System (INIS)

Wyckoff, S.; Wehinger, P.A.

1976-01-01

Band intensities of the molecular ions CH + , CO + , N 2 + , and H 2 O + have been determined on an absolute scale from tail spectra of comet Kohoutek (1973f) and comet Bradfield (1974b). Photoionization and photodissociation rates have been computed for CH, CO, and N 2 . Also emission rate excitation g-factors for (1) photoionization plus excitation and (2) resonance fluorescence have been computed for the observed ions. It is shown that resonance fluorescence is the dominant excitation mechanism for observed comet tail ions at rapprox. =1 AU. Band system luminosities and molecular ion abundances within a projected nuclear distance rho 4 km have been determined for CH + , CO + , N 2 + , and H 2 O + in comet Kohoutek, and for H 2 O + in comet Bradfield. Estimates are also given for column densities of all observed ions at rhoapprox. =10 4 km on the tailward side of the coma. The observed H 2 O + column densities were found to be roughly the same in comet Kohoutek and comet Bradfield et equal heliocentric distances, while CO + was found to be approximately 100 times more abundant than H 2 O + , N 2 + , and CH + at rhoapprox. =10 4 km in comet Kohoutek. Finally, the relative abundances of the observed ions and of the presumed parent neutral species are briefly discussed

Comets and their composition

International Nuclear Information System (INIS)

Spinrad, H.

1987-01-01

Recent theoretical and observational studies of comets are reviewed, with an emphasis on in situ data from spacecraft encounters with P/Giacobini-Zinner (September 1985) and P/Halley (March 1986). Topics addressed include clues on the origin and permanence of the Oort cometary cloud, observations of cometary nuclei far from the sun, the Halley nucleus, compositional and physical data from comae studies, and the parent molecules in comet ices. Also discussed are quantitative analyses of coma production; special features in the tail of P/Giacobini-Zinner; and proposals for (1) observations to detect distant giant comets, (2) high-resolution spectroscopic studies of comae, and (3) additional spacecraft missions such as the NASA Comet Rendezvous and Asteroid Flyby. 121 references

Reasonable threshold value used to segment the individual comet from the comet assay image

International Nuclear Information System (INIS)

Yan Xuekun; Chen Ying; Du Jie; Zhang Xueqing; Luo Yisheng

2009-01-01

Reasonable segmentation of the individual comet contour from the Comet Assay (CA) images is the precondition for all of parameters analysis during the automatic analyzing for the CA. The Otsu method and several arithmetic operators for image segmentation, such as Sobel, Prewitt, Roberts and Canny were used to segment the comet contour, and characters of the CA images were analyzed firstly. And then the segmentation methods which had been adopted in the software for CA automatic analysis, such as the CASP, the TriTek CometScore TM , were put for-ward and compared. At last, a two-step procedure for threshold calculation based on image-content analysis is adopted to segment the individual comet from the CA images, and several principles for the segmentation are put forward too.(authors)

The starlight night the sky in the writings of Shakespeare, Tennyson, and Hopkins

CERN Document Server

Levy, David H

2016-01-01

In this updated second edition renowned amateur comet-searcher David H. Levy expands on his work about the intricate relationship between the night sky and the works of English Literature. This revised and expanded text includes new sections on Alfred Lord Tennyson and Gerald Manley Hopkins (both amateur astronomers), extending the time period analyzed in the first edition from early modern literature to encompass the Victorian age. Although the sky enters into much of literature through the ages, British authors offer an especially fertile connection to the heavens, and Levy links the works of seminal authors from Shakespeare on to specific celestial events and scientific advances.  From the impact of comets and supernovae to eclipses, Levy’s ultimate goal in this book is to inspire his readers to do the same thing as their ancestors did so long ago—look up and appreciate the stars. His insights in this revised book spread farther and wider than ever before in this learned and enchanting tour of the ski...

DIRBE Comet Trails

Science.gov (United States)

Arendt, Richard G.

2015-01-01

Re-examination of the COBE DIRBE data reveals the thermal emission of several comet dust trails.The dust trails of 1P/Halley, 169P/NEAT, and 3200 Phaethon have not been previously reported.The known trails of 2P/Encke, and 73P/Schwassmann-Wachmann 3 are also seen. The dust trails have 12 and 25 microns surface brightnesses of trails are very difficult to see in any single daily image of the sky, but are evident as rapidly moving linear features in movies of the DIRBE data. Some trails are clearest when crossing through the orbital plane of the parent comet, but others are best seen at high ecliptic latitudes as the Earth passes over or under the dust trail. All these comets have known associations with meteor showers. This re-examination also reveals one additional comet and 13 additional asteroids that had not previously been recognized in the DIRBE data.

Singing comet changes its song

Science.gov (United States)

Volwerk, M.; Goetz, C.; Delva, M.; Richter, I.; Tsurutani, B. T.; Eriksson, A.; Odelstad, E.; Meier, P.; Nilsson, H.; Glassmeier, K.-H.

2017-09-01

The singing comet was discovered at the beginning of the Rosetta mission around comet 67P/Churyumov-Gerasimenko. Large amplitude compressional waves with frequencies between 10 and 100 mHz were observed. When the comet became more active this signal was no longer measured. During the so-called tail excursion, late in the mission after perihelion, with again a less active comet, the singing was observed again and interestingly, going from 26 March to 27 March 2016 the character of the singing changed.

Physical Mechanism of Comet (and Asteroid) Outbursts: The Movie

Science.gov (United States)

Hartmann, W. K.

2015-07-01

A film made during impact experiments at NASA Ames illustrates a mechanism in which regolith can become gas charged and then erupt to create outbursts as observed on comets (and "asteroids" such as 2060 Chiron).

Nature and origin of comets

International Nuclear Information System (INIS)

Fernandez, J.A.; Jockers, K.

1983-01-01

The review examines basic history and morphology, motion, dynamic evolution, physical properties of neutral gaseous matter, vaporization of gases and outflow from the nucleus, chemistry of the coma gases, the comet nucleus, dust particles, solar wind-comet interactions and tail formation and the origin of comets. (U.K.)

Delivery of organics to Mars through asteroid and comet impacts

NARCIS (Netherlands)

Frantseva, K.; Mueller, M.; van der Tak, F. F. S.; ten Kate, I. L.; Greenstreet, S.

2017-01-01

Preliminary results show that the asteroid-borne organic flux on Mars is comparable to the IPD rate; asteroids certainly cannot be neglected. Comets, on the other hand, contribute only 0.01% of the IDP-borne rate and can be neglected in the process of organic delivery to Mars.

A New Orbit for Comet C/1865 B1 (Great Southern Comet of 1865)

Science.gov (United States)

Branham, Richard L., Jr.

2018-04-01

Comet C/1865 B1 (Great southern comet of 1865), observed only in the southern hemisphere, is one of a large number of comets with parabolic orbits. Given that there are 202 observations in right ascension and 165 in declination it proves possible to calculate a better orbit than that Körber published in 1887, the orbit used in various catalogs and data bases. C/1865 B1's orbit is hyperbolic and statistically distinguishable from a parabola. This object, therefore, cannot be considered an NEO. The comet has a small perihelion distance of 0.026 AU.

Halley comet, implication on the origin

International Nuclear Information System (INIS)

Festou, M.C.

1990-01-01

One will first give a rapid description of the different parts that compose a comet coma. Then one will describe the spectrum of comets from the UV to the IR regions with special emphasis on how information relative to the physico-chemistry of comet atmospheres can be retrieved. Our basic knowledge about the composition of comets before 1985 will be summarized and the input of the 1985-86 observing campaign of comet Halley will be shown (in situ, ground-based and space borne observations). One will see then that the chemical composition of comets appears as of today completely compatible with a formation from pre-solar matter that condensed inside the solar system [fr

Magnetic reversal spurts: Rain gauges for comet showers

International Nuclear Information System (INIS)

Lutz, T.M.

1988-01-01

Abrupt increases in the rate of magnetic reversals (magnetic reversal spurts) were first studied by many others. They hypothesized that spurts result from increased turbulence in the earth's core dynamo during episodes of intense bolide bombardment of the earth. Mechanisms for creating episodes of intense bombardment of the earth involve gravitational perturbation of the Oort cloud of comets, either by a hidden planet, a solar companion, or massive matter in the galactic plane. Herein, the time variation in reversal rate is analyzed using methods of statistical density estimation. A smooth, continuous estimate of reversal rate is obtained using an adaptive kernel method, in which the kernel width is adjusted as a function of reversal rate. The estimates near the ends of the data series (at 165 my ago and the present) are obtained by extending the data by reflection. The results show that the reversal spurts are not associated demonstrably with extinctions or well-dated impacts. If the spurts do record episodes of intense bombardment of the earth, then the mass extinctions do not, in general, occur at times of impacts. Furthermore, the large impact craters seen are not obviously related to the spurts, suggesting that the craters may have been caused by bolides of a different nature and with a different temporal pattern. However, the most simple explanation seems to be that the spurts do not record comet showers, either because the recording mechanism suggested by Muller and Morris is not effective or because comet showers are not triggered in the ways considered by Hut et al

Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Haley 2

Science.gov (United States)

Luna, Michael E.; Collins, Stephen M.

2011-01-01

On November 4, 2010 the already "in-flight" Deep Impact spacecraft flew within 700km of comet 103P/Hartley 2 as part of its extended mission EPOXI, the 5th time to date any spacecraft visited a comet. In 2005, the spacecraft had previously imaged a probe impact comet Tempel 1. The EPOXI flyby marked the first time in history that two comets were explored with the same instruments on a re-used spacecraft-with hardware and software originally designed and optimized for a different mission. This made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby. As part of the spacecraft team preparations, the ADCS team had to perform thorough sequence reviews, key spacecraft activities and onboard calibrations. These activities included: review of background sequences for the initial conditions vector, sun sensor coefficients, and reaction wheel assembly (RWA) de-saturations; design and execution of 10 trajectory correction maneuvers; science calibration of the two telescope instruments; a flight demonstration of the fastest turns conducted by the spacecraft between Earth and comet point; and assessment of RWA health (given RWA problems on other spacecraft).

A Comet Engulfs Mars: MAVEN Observations of Comet Siding Spring's Influence on the Martian Magnetosphere

Science.gov (United States)

Espley, Jared R.; Dibraccio, Gina A.; Connerney, John E. P.; Brain, David; Gruesbeck, Jacob; Soobiah, Yasir; Halekas, Jasper S.; Combi, Michael; Luhmann, Janet; Ma, Yingjuan

2015-01-01

The nucleus of comet C/2013 A1 (Siding Spring) passed within 141,000?km of Mars on 19 October 2014. Thus, the cometary coma and the plasma it produces washed over Mars for several hours producing significant effects in the Martian magnetosphere and upper atmosphere. We present observations from Mars Atmosphere and Volatile EvolutioN's (MAVEN's) particles and field's instruments that show the Martian magnetosphere was severely distorted during the comet's passage. We note four specific major effects: (1) a variable induced magnetospheric boundary, (2) a strong rotation of the magnetic field as the comet approached, (3) severely distorted and disordered ionospheric magnetic fields during the comet's closest approach, and (4) unusually strong magnetosheath turbulence lasting hours after the comet left. We argue that the comet produced effects comparable to that of a large solar storm (in terms of incident energy) and that our results are therefore important for future studies of atmospheric escape, MAVEN's primary science objective.

ESA Unveils Its New Comet Chaser.

Science.gov (United States)

1999-07-01

into the surface immediately on impact. By this time, the warmth of the Sun will probably have begun to vapourise parts of the nucleus, initiating some form of surface outgassing. For a period of about a month, data from the lander's eight experiments will be relayed to Earth via the orbiter. They will send back unique information on the nature and composition of the nucleus. Samples for chemical analysis will be taken of the organic crust and ices to a depth of at least 20 cm. Other instruments will measure characteristics such as near-surface strength, density, texture, porosity and thermal properties. Meanwhile, as Comet Wirtanen approaches the Sun, the Rosetta orbiter will fly alongside it, mapping its surface and studying changes in its activity. As its icy nucleus evaporates, 12 experiments on the orbiter will map its surface and study the dust and gas particles it ejects. For the first time, scientists will be able to monitor at close quarters the dramatic changes which take place as a comet plunges sunwards at a speed of 46,000 kph. The stream of data will include a mass of new information about the comet's changes in behaviour as it approaches the Sun, including: * variations in the temperature of the nucleus, * changing intensity and location of gas and dust jets on the nucleus, * the amount of gas and dust emitted from the nucleus, * the size, composition and impact velocity of dust particles, * the nature of the comet's interaction with the charged particles of the solar wind. By mission's end in July 2013, Rosetta will have spent almost two years chasing the comet for millions of kilometres through space. It will also have returned a treasure trove of data, which will enable us to learn more about how the planets formed and where we came from. Why Rosetta? Space exploration is all about discovering the unknown. Just as, 200 years ago, the discovery of the Rosetta Stone eventually enabled Champollion to unravel the mysteries of ancient Egyptian

Shape, Density, and Geology of the Nucleus of Comet 103P/Hartley 2

Science.gov (United States)

Thomas, P.C.; A'hearn, Michael F.; Veverka, Joseph; Belton, Michael J. S.; Kissel, Jochen; Belton, Michael J. S.; Klaasen, Kenneth P.; McFadden, Lucy A.; Melosh, H. Jay; Schultz, Peter H.;

The paradigm of description in ethnographic translation: the translator Levi-Strauss in Tristes Tropiques

Directory of Open Access Journals (Sweden)

Alice Maria de Araújo Ferreira

2014-11-01

Full Text Available Published in 1955, Tristes Tropiques by Claude Levi-Strauss is an account of the journey that the author and ethnographer made on the American continent, especially in Brazil, in 1930. With a free poetic style not restricted by the austerity of scientific work, Levi-Strauss introduced a reflection that established a crucial rupture in ethnographic studies and in the humanities in general, or rather, the rupture of the gaze. His aim is not precisely the culture of the indigenous people in Brazil, but Levi-Strauss himself as the subject of the gaze. How may one grasp an object that changes as one gazes at it? How does the gaze affect the object while gazing, observing, analyzing, describing, and translating it? Current essay discusses what the translator does to the speech of the other when translating it. Different translation strategies from Portuguese into French proposed by Levi-Strauss in Tristes Tropiques are discussed. Conceiving ethnographic translation from the description paradigm and as an encounter of cultures (but not as replacement, the author analyzes the process performed within the gap between the gaze experience and the production of speech of such gaze to understand the value produced at the end of the axis corresponding to the ethnographic translation-description.

A Study on L-Asparaginase of Nocardia levis MK-VL_113

Directory of Open Access Journals (Sweden)

Alapati Kavitha

2012-01-01

Full Text Available An enzyme-based drug, L-asparaginase, was produced by Nocardia levis MK-VL_113 isolated from laterite soils of Guntur region. Cultural parameters affecting the production of L-asparaginase by the strain were optimized. Maximal yields of L-asparaginase were recorded from 3-day-old culture grown in modified asparagine-glycerol salts broth with initial pH 7.0 at temperature 30∘C. Glycerol (2% and yeast extract (1.5% served as good carbon and nitrogen sources for L-asparaginase production, respectively. Cell-disrupting agents like EDTA slightly enhanced the productivity of L-asparaginase. Ours is the first paper on the production of L-asparaginase by N. levis.

Reply to Boslough et al.: Decades of comet research counter their claims

Czech Academy of Sciences Publication Activity Database

Napier, W. M.; Bunch, T. E.; Kennett, J. P.; Wittke, J. H.; Tankersley, K. B.; Kletetschka, Günther; Howard, G. A.; West, A.

2013-01-01

Roč. 110, č. 45 (2013), E4171-E4171 ISSN 0027-8424 Institutional support: RVO:67985831 Keywords : comet * Oort cloud * impact hazard Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 9.809, year: 2013

DRBE comet trails

International Nuclear Information System (INIS)

Arendt, Richard G.

2014-01-01

Re-examination of the Cosmic Background Explorer Diffuse Infrared Background Experiment (DIRBE) data reveals the thermal emission of several comet dust trails. The dust trails of 1P/Halley, 169P/NEAT, and 3200 Phaethon have not been previously reported. The known trails of 2P/Encke and 73P/Schwassmann–Wachmann 3 are also seen. The dust trails have 12 and 25 μm surface brightnesses of <0.1 and <0.15 MJy sr −1 , respectively, which is <1% of the zodiacal light intensity. The trails are very difficult to see in any single daily image of the sky, but are evident as rapidly moving linear features in movies of the DIRBE data. Some trails are clearest when crossing through the orbital plane of the parent comet, but others are best seen at high ecliptic latitudes as the Earth passes over or under the dust trail. All these comets have known associations with meteor showers. This re-examination also reveals 1 additional comet and 13 additional asteroids that had not previously been recognized in the DIRBE data.

DRBE comet trails

Energy Technology Data Exchange (ETDEWEB)

Arendt, Richard G., E-mail: Richard.G.Arendt@nasa.gov [CREST/UMBC, Code 665, NASA/GSFC, Greenbelt, MD 20771 (United States)

2014-12-01

Re-examination of the Cosmic Background Explorer Diffuse Infrared Background Experiment (DIRBE) data reveals the thermal emission of several comet dust trails. The dust trails of 1P/Halley, 169P/NEAT, and 3200 Phaethon have not been previously reported. The known trails of 2P/Encke and 73P/Schwassmann–Wachmann 3 are also seen. The dust trails have 12 and 25 μm surface brightnesses of <0.1 and <0.15 MJy sr{sup −1}, respectively, which is <1% of the zodiacal light intensity. The trails are very difficult to see in any single daily image of the sky, but are evident as rapidly moving linear features in movies of the DIRBE data. Some trails are clearest when crossing through the orbital plane of the parent comet, but others are best seen at high ecliptic latitudes as the Earth passes over or under the dust trail. All these comets have known associations with meteor showers. This re-examination also reveals 1 additional comet and 13 additional asteroids that had not previously been recognized in the DIRBE data.

Recovering the Elemental Composition of Comet Wild 2 Dust in Five Stardust Impact Tracks and Terminal Particles in Aerogel

International Nuclear Information System (INIS)

Ishii, H A; Brennan, S; Bradley, J P; Luening, K; Ignatyev, K; Pianetta, P

2007-01-01

The elemental (non-volatile) composition of five Stardust impact tracks and terminal particles left from capture of Comet 81P/Wild 2 dust were mapped in a synchrotron x-ray scanning microprobe with full fluorescence spectra at each pixel. Because aerogel includes background levels of several elements of interest, we employ a novel 'dual threshold' approach to discriminate against background contaminants: an upper threshold, above which a spectrum contains cometary material plus aerogel and a lower threshold below which it contains only aerogel. The difference between normalized cometary-plus-background and background-only spectra is attributable to cometary material. The few spectra in between are discarded since misallocation is detrimental: cometary material incorrectly placed in the background spectrum is later subtracted from the cometary spectrum, doubling the loss of reportable cometary material. This approach improves precision of composition quantification. We present the refined whole impact track and terminal particle elemental abundances for the five impact tracks. One track shows mass increases in Cr and Mn (1.4x), Cu, As and K (2x), Zn (4x) and total mass (13%) by dual thresholds compared to a single threshold. Major elements Fe and Ni are not significantly affected. The additional Cr arises from cometary material containing little Fe. We exclude Au intermixed with cometary material because it is found to be a localized surface contaminant carried by comet dust into an impact track. The dual threshold technique can be used in other situations where elements of interest in a small sample embedded in a matrix are also present in the matrix itself

Studying Short-Period Comets and Long-Period Comets Detected by WISE/NEOWISE

Science.gov (United States)

Kramer, Emily A.; Fernández, Yanga R.; Bauer, James M.; Stevenson, Rachel; Mainzer, Amy K.; Grav, Tommy; Masiero, Joseph; Walker, Russell G.; Lisse, Carey M.

2014-11-01

The Wide-field Infrared Survey Explorer (WISE) mission surveyed the sky in four infrared wavelength bands (3.4, 4.6, 12 and 22-micron) between January 2010 and February 2011 [1, 2]. During the mission, WISE serendipitously observed 160 comets, including 21 newly discovered objects. About 89 of the comets observed by WISE displayed a significant dust tail in the 12 and 22-micron (thermal emission) bands, showing a wide range of activity levels and dust morphology. Since the observed objects are a mix of both long-period comets (LPCs) and short-period comets (SPCs), differences in their activity can be used to better understand the thermal evolution that each of these populations has undergone. For the comets that displayed a significant dust tail, we have estimated the sizes and ages of the particles using dynamical models based on the Finson-Probstein method [3, 4]. For a selection of 40 comets, we have then compared these models to the data using a novel tail-fitting method that allows the best-fit model to be chosen analytically rather than subjectively. For comets that were observed multiple times by WISE, the dust tail particle properties were estimated separately, and then compared. We find that the dust tails of both LPCs and SPCs are primarily comprised of ~mm to cm sized particles, which were the result of emission that occurred several months to several years prior to the observations. The LPCs nearly all have strong dust emission close to the comet's perihelion distance, and the SPCs mostly have strong dust emission close to perihelion, but some have strong dust emission well before perihelion. Acknowledgments: This publication makes use of data products from (1) WISE, which is a joint project of UCLA and JPL/Caltech, funded by NASA; and (2) NEOWISE, which is a project of JPL/Caltech, funded by the Planetary Science Division of NASA. EK was supported by a NASA Earth and Space Sciences Fellowship. RS gratefully acknowledges support from the NASA

Inside look at Halley's comet

International Nuclear Information System (INIS)

Beatty, J.K.

1986-01-01

The 1985-1986 emergence of Halley's comet, the first since the advent of the space age, was explored by a variety of spacecraft. The Vega 1, launched by the USSR together with the Eastern-block alliance, passed 5523 miles from the comet's nucleus at 7:20:06 Universal time. It indicated that the comet was about 300 miles closer to the sun than had been predicted. The Japanese spacecraft, Suisei, was created to map the distribution of neutral hydrogen atoms outside Halley's visible coma. Its pictures indicated that the comet's output of water varied between 25 and 60 tons per second. Five days after the Vega 2's passage through the comet, the Giotto (sponsored by the European Space Agency) probe appeared. Giotto's close approach took place 3.1 minutes after midnight UT on March 14th; the craft had passed 376 miles from its target. Giotto's data indicated that the nucleus was bigger than expected, and that the comet was composed primarily of water, CO2 and N2. The Vegas and Giotto found that as the solar wind approaches Halley, it slows gradually and the solar magnetic lines embedded in the wind begin to pile up. Pick-up ions, from the comet's halo of neutral hydrogen, were found in this solar wind. Sensors on the Vega spacecraft found a variety of plasma waves propagating inside the bow wave. In order to synthesize all the results, a conference on the exploration of Halley's comet will be held this October

Comet Halley and interstellar chemistry

International Nuclear Information System (INIS)

Snyder, L.E.

1989-01-01

How complex is the chemistry of the interstellar medium? How far does it evolve and how has it interacted with the chemistry of the solar system? Are the galactic chemical processes destroyed, preserved, or even enhanced in comets? Are biogenic molecules formed in space and have the formation mechanisms interacted in any way with prebiotic organic chemical processes on the early earth? Radio molecular studies of comets are important for probing deep into the coma and nuclear region and thus may help answer these questions. Comets are believed to be pristine samples of the debris left from the formation of the solar system and may have been the carrier between interstellar and terrestrial prebiotic chemistries. Recent observations of Comet Halley and subsequent comets have given the author an excellent opportunity to study the relationship between interstellar molecular chemistry and cometary chemistry

Origin of Short-Perihelion Comets

Science.gov (United States)

Guliyev, A. S.

2011-01-01

New regularities for short-perihelion comets are found. Distant nodes of cometary orbits of Kreutz family are concentrated in a plane with ascending node 76 and inclination 267 at the distance from 2 up to 3 a.u. and in a very narrow interval of longitudes. There is a correlation dependence between q and cos I concerning the found plane (coefficient of correlation 0.41). Similar results are received regarding to cometary families of Meyer, Kracht and Marsden. Distant nodes of these comets are concentrated close three planes (their parameters are discussed in the article) and at distances 1.4; 0.5; 6 a.u. accordingly. It is concluded that these comet groups were formed as a result of collision of parent bodies with meteoric streams. One more group, consisting of 7 comets is identified. 5 comet pairs are selected among sungrazers.

X-rays from comets - a surprising discovery

CERN Document Server

CERN. Geneva

2000-01-01

Comets are kilometre-size aggregates of ice and dust, which remained from the formation of the solar system. It was not obvious to expect X-ray emission from such objects. Nevertheless, when comet Hyakutake (C/1996 B2) was observed with the ROSAT X-ray satellite during its close approach to Earth in March 1996, bright X-ray emission from this comet was discovered. This finding triggered a search in archival ROSAT data for comets, which might have accidentally crossed the field of view during observations of unrelated targets. To increase the surprise even more, X-ray emission was detected from four additional comets, which were optically 300 to 30 000 times fainter than Hyakutake. For one of them, comet Arai (C/1991 A2), X-ray emission was even found in data which were taken six weeks before the comet was optically discovered. These findings showed that comets represent a new class of celestial X-ray sources. The subsequent detection of X-ray emission from several other comets in dedicated observations confir...

Can the comet assay be used reliably to detect nanoparticle-induced genotoxicity?

Science.gov (United States)

Karlsson, Hanna L; Di Bucchianico, Sebastiano; Collins, Andrew R; Dusinska, Maria

2015-03-01

The comet assay is a sensitive method to detect DNA strand breaks as well as oxidatively damaged DNA at the level of single cells. Today the assay is commonly used in nano-genotoxicology. In this review we critically discuss possible interactions between nanoparticles (NPs) and the comet assay. Concerns for such interactions have arisen from the occasional observation of NPs in the "comet head", which implies that NPs may be present while the assay is being performed. This could give rise to false positive or false negative results, depending on the type of comet assay endpoint and NP. For most NPs, an interaction that substantially impacts the comet assay results is unlikely. For photocatalytically active NPs such as TiO2 , on the other hand, exposure to light containing UV can lead to increased DNA damage. Samples should therefore not be exposed to such light. By comparing studies in which both the comet assay and the micronucleus assay have been used, a good consistency between the assays was found in general (69%); consistency was even higher when excluding studies on TiO2 NPs (81%). The strong consistency between the comet and micronucleus assays for a range of different NPs-even though the two tests measure different endpoints-implies that both can be trusted in assessing the genotoxicity of NPs, and that both could be useful in a standard battery of test methods. © 2014 Wiley Periodicals, Inc.

The Halley comet

International Nuclear Information System (INIS)

Encrenaz, T.; Festou, M.

1985-01-01

The conspicuous part of a comet, made of tenuous gas and dusts, represents only a tiny part of its mass. The main information is hidden in the central part: a solid nucleus, ice and rock blocks with a radius less than 10 km, completely invisible from the Earth. The knowledge of the nucleus structure and its composition could give the key of the planet creation mechanisms. That is a reason why it has been decided to send an automatic device to penetrate the Halley comet atmosphere and that two Soviet probes, Vega 1 and 2, one European probe Giotto, and two Japanese, Planet-A and MS-TS, will explore in-situ in March 1986, for the first time, a comet at atmosphere [fr

I. T. - R. O. C. K. S. Comet Nuclei Sample Return Mission

Science.gov (United States)

Dalcher, N.

2009-04-01

Ices, organics and minerals recording the chemical evolution of the outer regions of the early solar nebula are the main constituents of comets. Because comets maintain the nearly pristine nature of the cloud where they formed, the analyses of their composition, structure, thermodynamics and isotope ratios will increase our understanding of the processes that occurred in the early phases of the solar system as well as the Interstellar Medium (ISM) Cloud that predated the formation of the solar nebula [1]. While the deep impact mission aimed at determining the internal structure of comet Temple1's nuclei [e.g. 3], the stardust mission sample return has dramatically increased our understanding of comets. Its first implications indicated that some of the comet material originated in the inner solar system and was later transported outward beyond the freezing line [4]. A wide range of organic compounds identified within different grains of the aerogel collectors has demonstrated the heterogeneity in their assemblages [5]. This suggests either many histories associated with these material or possibly analytical constraints imposed by capture heating of Wild2 material in silica aerogel. The current mission ROSETTA, will further expand our knowledge about comets considerably through rigorous in situ analyses of a Jupiter Family Comet (JFC). As the next generation of comet research post ROSETTA, we present the comet nuclei sample return mission IT - ROCKS (International Team - Return Of Comet's Key Samples) to return several minimally altered samples from various locations of comet 88P/Howell, a typical JFC. The mission scenario includes remote sensing of the comet's nucleus with onboard instruments similar to the ROSETTA instruments [6, 7, 8] (VIS, IR, Thermal IR, X-Ray, Radar) and gas/dust composition measurements including a plasma science package. Additionally two microprobes [9] will further investigate the physical properties of the comet's surface. Retrieving of the

Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Hartley 2

Science.gov (United States)

Luna, Michael E.; Collins, Steven M.

2011-01-01

On November 4, 2010 the former "Deep Impact" spacecraft, renamed "EPOXI" for its extended mission, flew within 700km of comet 103P/Hartley 2. In July 2005, the spacecraft had previously imaged a probe impact of comet Tempel 1. The EPOXI flyby was the fifth close encounter of a spacecraft with a comet nucleus and marked the first time in history that two comet nuclei were imaged at close range with the same suite of onboard science instruments. This challenging objective made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby.As part of the spacecraft flyby preparations, the ADCS operations team had to perform meticulous sequence reviews, implement complex spacecraft engineering and science activities and perform numerous onboard calibrations. ADCS contributions included design and execution of 10 trajectory correction maneuvers, the science calibration of the two telescopic instruments, an in-flight demonstration of high-rate turns between Earth and comet point, and an ongoing assessment of reaction wheel health. The ADCS team was also responsible for command sequences that included updates to the onboard ephemeris and sun sensor coefficients and implementation of reaction wheel assembly (RWA) de-saturations.

In regard to Levi-Strauss’s "motive of oblivion". Structure of disturbed communication and styles of thoughts in transitory Serbia

Directory of Open Access Journals (Sweden)

Dragana Antonijević

2016-02-01

Full Text Available This paper starts with Levi-Strauss’s semantic concept that consists of oblivion, misunderstanding, indiscretion and nostalgia. Through his analysis of North American and Greek myths, Levi-Strauss concluded that "semantic filed of oblivion" has an important meaning especially in the construction of particular rules and rituals; or, in other words, it has an important part in the introduction of culture to the nature of cognitive and social processes. After the introduction of concept Structure of disturbed communication and some corrections to the Levi-Strauss’s concept, I start with the proposition that the period of transition represents unstable and ‘slippery’ time in which society negotiates different meanings. That is the time when different styles of thoughts, represented by different and powerful groups that have an impact on current social, political and ideological processes, compete with each other fighting for supremacy. Their field of communication can be seen as a field of "disturbed communication", which in the final instance has a normative function: to reinforce and regulate certain attitudes, ideas and knowledge. This is achieved through the narratives which symbolise a community of newly established order in the moment of its supposed sociohistorical stabilisation. Finally, combining two different theoretical models – Levi-Strauss’s one described above with Greimas’s ideas about structures of modes of veridiction, this paper predicts chances of particular paradigmatic forms of thought in transitory Serbia to became dominant modes of thought, despite of their current low visibility in the public sphere. In mythical terms, it seems though that their domineering efforts are predetermined to success or fail, since they position themselves according to the laws immanent to these structures themselves, which on their part a priori position these structures as powerful orpowerless, influential or non

Rosetta - a comet ride to solve planetary mysteries

Science.gov (United States)

2003-01-01

Comets are very interesting objects for scientists, since their composition reflects how the Solar System was when it was very young and still 'unfinished', more than 4600 million years ago. Comets have not changed much since then. By orbiting Comet Wirtanen and landing on it, Rosetta will collect essential information to understand the origin and evolution of our Solar System. It will also help discover whether comets contributed to the beginnings of life on Earth. In fact comets are carriers of complex organic molecules, that - delivered to Earth through impacts - perhaps played a role in the origin of living forms. Furthermore, “volatile” light elements carried by comets may have also played an important role in forming the Earth’s oceans and atmopshere. “Rosetta is one of the most challenging missions ever undertaken so far”, says Prof. David Southwood, ESA Director of Science, “No one before attempted a similar mission, unique for its scientific implications as well as for its complex and spectacular interplanetary space manoeuvres”. Before reaching its target in 2011, Rosetta will circle the Sun almost four times on wide loops in the inner Solar System. During its long trek, the spacecraft will have to endure some extreme thermal conditions. Once it is close to Comet Wirtanen, scientists will take it through a delicate braking manoeuvre; then the spacecraft will closely orbit the comet, and gently drop a lander on it. It will be like landing on a small, fast-moving cosmic bullet that still has - at present - an almost unknown 'geography'. An amazing 8-year interplanetary trek Rosetta is a 3-tonne box-type spacecraft about 3 metres high, with two 14-metre long solar panels. It consists of an orbiter and a lander. The lander is approximately 1 metre across and 80 centimetres high. It will be attached to the side of the Rosetta orbiter during the journey to Comet Wirtanen. Rosetta carries 21 experiments in total, 10 of them on the lander. They will

Comet prospects for 2004

Science.gov (United States)

Shanklin, J. D.

2003-12-01

2004 sees the return of 18 periodic comets. None are particularly bright and the best are likely to be 78P/Gehrels and 88P/Howell. Three new long period comets are likely to put on a good show: 2001 Q4 (NEAT) reaches perihelion in May, when it could make at least 3rd magnitude. Northern hemisphere observers will first pick it up just after perihelion as it rapidly moves north. 2002 T7 (LINEAR) could also reach 3rd magnitude at closest approach in May, however northern hemisphere observers will have lost it as a binocular object in mid-March. Observers at far southern latitudes may be able to see these two naked eye comets at the same time. 2003 K4 (LINEAR) could reach 6th magnitude as it brightens on its way to perihelion. Several other long period comets discovered in previous years are also still visible.

LEVIS lithium ion source experiments on PBFA-II

International Nuclear Information System (INIS)

Renk, T.J.; Tisone, G.C.; Adams, R.G.; Lopez, M.; Clark, B.F.; Schroeder, J.; Bailey, J.E.; Filuk, A.B.; Carlson, A.L.

1992-01-01

PBFA-II is a pulsed power generator designed to apply up to a 25 MV, 20 ns pulse to a focusing 15 cm-radius Applied-B ion diode for inertial confinement fusion applications. Several different approaches have been pursued to produce a high-purity (> 90%), high-current density (5--10 kA/cm 2 ) singly ionized lithium ion source for acceleration in this diode. In addition to having high source purity, such a source should be active, i.e. the ions should be produced before the power pulse arrives, to provide better electrical coupling from the accelerator to the diode. In the LEVIS (Laser EVaporation Ion Source) process, energy from two lasers impinges on a thin (500 nm) lithium or lithium-bearing film on an insulating substrate. The authors will discuss a new series of LEVIS experiments, with a number of improvements: (1) the laser distribution cone was redesigned, resulting in a more uniform illumination of the 4 cm-tall Li-producing surface; (2) the anode surface is being slow-heated to 120--150 C to help drive off contaminants; and (3) they have expanded the number of source and beam diagnostics

Meteoroid Streams from Sunskirter Comet Breakup

Science.gov (United States)

Jenniskens, P. M.

2012-12-01

In its first year of operations, the CAMS project (Cameras for Allsky Meteor Surveillance) has measured 47,000 meteoroid orbits at Earth, including some that pass the Sun as close as 0.008 AU. The population density increases significantly above perihelion distance q = 0.037 AU. Meteoroid streams are known with q about 0.1 AU. The Sun has a profound effect on comets that pass at 0.04-0.16 AU distance, called the sunskirter comets. SOHO and STEREO see families of small comets called the Marsden and Kracht groups. Sunlight is efficiently scattered by small 10-m sized fragments, making those fragments visible even when far from Earth. These comet groups are associated with meteor showers on Earth, in particular the Daytime Arietids and Delta Aquariids. All are related to 96P/Machholz, a highly inclined short-period (5.2 year) Jupiter family comet that comes to within 0.12 AU from the Sun, the smallest perihelion distance known among numbered comets. The proximity of the Sun speeds up the disintegration process, providing us a unique window on this important decay mechanism of Jupiter family comets and creating meteoroid streams. These are not the only sunskirting comets, however. In this presentation, we will present CAMS observations of the complete low-q meteoroid population at Earth and review their association with known parent bodies.

X-ray emission from comets

International Nuclear Information System (INIS)

Dennerl, Konrad

1999-01-01

When comet Hyakutake (C/1996 B2) encountered Earth in March 1996 at a minimum distance of only 15 million kilometers (40 times the distance of the moon), x-ray and extreme ultraviolet emission was discovered for the first time from a comet. The observations were performed with the astronomy satellites ROSAT and EUVE. A systematic search for x-rays from comets in archival data, obtained during the ROSAT all-sky survey in 1990/91, resulted in the discovery of x-ray emission from four additional comets. They were detected at seven occasions in total, when they were optically 300 to 30 000 times fainter than Hyakutake. These findings indicated that comets represent a new class of celestial x-ray sources. Subsequent detections of x-ray emission from additional comets with the satellites ROSAT, EUVE, and BeppoSAX confirmed this conclusion. The x-ray observations have obviously revealed the presence of a process in comets which had escaped attention until recently. This process is most likely charge exchange between highly charged heavy ions in the solar wind and cometary neutrals. The solar wind, a stream of particles continuously emitted from the sun with ≅ 400 km s -1 , consists predominantly of protons, electrons, and alpha particles, but contains also a small fraction (≅0.1%) of highly charged heavier ions, such as C 6+ ,O 6+ ,Ne 8+ ,Si 9+ ,Fe 11+ . When these ions capture electrons from the cometary gas, they attain highly excited states and radiate a large fraction of their excitation energy in the extreme ultraviolet and x-ray part of the spectrum. Charge exchange reproduces the intensity, the morphology and the spectrum of the observed x-ray emission from comets very well

Comet Dust: The Story of Planet Formation as Told by the Tiniest of Particles

Science.gov (United States)

Wooden, D. H.

2005-01-01

Our planetary system formed out of a gas-rich disk-shaped nebula with the early Sun at its center. Many small icy bodies were consumed by the formation of the giant planets. However, many km-size icy bodies were tossed out of the giant-planet region to the cold, distant reaches of our solar system. Comets remained in their places of cold storage until perturbed into orbits that carry them into the inner solar system where they pass relatively close to the Sun. Comets are warmed by the Sun and shed material from their outer layers. The ices and gases shed by comets reveal simple and complex organic molecules were present at the time and in the region of the formation of the giant planets. Where the Earth was forming was too hot and had too intense sunlight for many of these ices and molecules to survive. The dust shed by comets tells us that some stardust survived unaltered but much of the dust was heated and crystallized before becoming part of the comet. Therefore, comet dust grains tell of large radial migrations from the cold outer reaches near Neptune into the hot regions near the forming Sun, and then back out to the cold regions where icy comets were accreting and forming. On 2005 July 4, the NASA Deep Impact Mission hit a comet and ejected primitive materials fiom its interior. These materials were not released into the comet s coma during normal activity. Despite the many passages of this comet close to the Sun, these primitive volatile gases and dust grains survived in its interior. Comet dust grains show that cold and hot materials were mixed into the same tiny particle very early in the formation of the solar system, and these aggregate dust grains never saw high temperatures again. The survival of primitive materials in comet nuclei suggests comets could have delivered organic molecules and primitive dust grains to early Earth.

The future of levies in a digital environment: final report

NARCIS (Netherlands)

Hugenholtz, P.B.; Guibault, L.; van Geffen, S.

2003-01-01

Copyright levy systems have been premised on the assumption that private copying of protected works cannot be controlled and exploited individually. With the advent of digital rights management (DRM), this assumption must be re-examined. In the digital environment, technical protection measures and

Simulation of Prebiotic Processing by Comet and Meteoroid Impact: Implications for Life on Early Earth and Other Planets

Science.gov (United States)

Dateo, Christopher E.

2003-01-01

We develop a reacting flow model to simulate the shock induced chemistry of comets and meteoroids entering planetary atmospheres. Various atmospheric compositions comprising of simpler molecules (i.e., CH4, CO2, H2O, etc.) are investigated to determine the production efficiency of more complex prebiotic molecules as a function of composition, pressure, and entry velocity. The possible role of comets and meteoroids in creating the inventory of prebiotic material necessary for life on Early Earth is considered. Comets and meteoroids can also introduce new materials from the Interstellar Medium (ISM) to planetary atmospheres. The ablation of water from comets, introducing the element oxygen into Titan's atmosphere will also be considered and its implications for the formation of organic and prebiotic material.

"Word of Discovery": A Planetary Example from Volume I of the Astronomical Journal

Science.gov (United States)

Hockey, T.

1998-09-01

In 1850, William Lassell (1799-1880) discovered a series of bright white spots, in the south temperate latitudes of Jupiter, unlike any that that been seen before. Lassell's note on these STZ features is a useful example of how astronomical discoveries of the day were communicated among astronomers. Word of Lassell's Spots spread quickly by nineteenth-century standards. This was due, in part, to the recent appearance of journals devoted exclusively to astronomy. The transition from letters as a means of conveying scientific information to journals is reflected in the propagation of Lassell's announcement: a report of Lassell's description of the white spots to the Royal Astronomical Society appeared in the Monthly Notices of the Royal Astronomical Society along with a woodblock print of one of his drawings. This report reappeared shortly thereafter in German translation. It was part of a letter to the editor of the Astronomische Nachrichten, Heinrich Schumacher (1780-1850), from an English correspondent of his, the Reverend Richard Sheepshanks (1974-1855). (Sheepshanks was himself editor of the Monthly Notices of the Royal Astronomical Society.) It then made its way across the Atlantic as a letter from Schumacher to Benjamin Gould (1824-1896), who published it in the first volume of his upstart Astronomical Journal. There it appears in English, again, as Schumacher quoting Sheepshanks quoting Lassell! The observations by Lassell and William Dawes (1799-1868) of this phenomenon also were the first major planetary discovery made using a silvered-glass reflecting telescope. Lassell's Spots have remained in the "astronomical news" of the last 150 years: Most recently, they appeared worldwide in images showing the Comet Shoemaker-Levy 9 impact sites.

OpenComet: An automated tool for comet assay image analysis

OpenAIRE

Gyori, Benjamin M.; Venkatachalam, Gireedhar; Thiagarajan, P.S.; Hsu, David; Clement, Marie-Veronique

2014-01-01

Reactive species such as free radicals are constantly generated in vivo and DNA is the most important target of oxidative stress. Oxidative DNA damage is used as a predictive biomarker to monitor the risk of development of many diseases. The comet assay is widely used for measuring oxidative DNA damage at a single cell level. The analysis of comet assay output images, however, poses considerable challenges. Commercial software is costly and restrictive, while free software generally requires ...

Comets and How to Observe Them

CERN Document Server

Schmude, Richard

2010-01-01

Comets have inspired wonder, excitement and even fear ever since they were first observed. They contain material from early in the life of the Solar System, held in deep-freeze. This makes them key in our understanding of the formation and evolution of many Solar System bodies. Recent ground- and space-based observations have changed much in our understanding of comets. Comets and How to Observe Them gives a summary of our current knowledge and describes how amateur astronomers can contribute to the body of scientific knowledge of comets. This book contains many practical examples of how to construct comet light-curves, measure how fast a comet’s coma expands, and determine the rotation period of the nucleus. All these examples are illustrated with drawings and photographs.

La costruzione de Il sistema periodico di Primo Levi

Directory of Open Access Journals (Sweden)

Martina Bertoldi

2016-11-01

Full Text Available Tra le opere prodotte nel laboratorio del chimico-scrittore Levi quella che meglio rappresenta l'insensatezza della separazione tra letteratura e scienza e la volontà leviana di ricomporre tale frattura è senz'altro Il sistema periodico. Qui infatti, come sostanze chimiche tra loro reagenti, le due discipline partecipano al processo creativo, consentendo allo scrittore la realizzazione di un'opera la cui forma è data dalla successione di una serie di elementi ed il cui contenuto è costituito da un amalgama significativo di spunti autobiografici, storie chimiche ed inserti metaletterari, in un continuo gioco di rinvii tra le due culture. “Costruire”, verbo che accomuna chimica e scrittura, è quanto fa Levi nell'ideare l'architettura del Sistema periodico, che vede rispecchiate nella disposizione dei suoi componenti tematiche costitutive dell'opera stessa, di conseguenza conferendo ai testi un significato che trascende il loro contenuto specifico per risultare dall'analisi dell'ordinamento della raccolta. Un approccio filologico al testo mostra come la particolare conformazione della raccolta sia il risultato di successivi interventi sull'assetto dei testi. In particolare il quadro variantistico ottenuto dal confronto di un gruppo di racconti anticipati su quotidiani o riviste e dei dattiloscritti originali conservati nell'Archivio storico della casa editrice Einaudi con la loro redazione definitiva, testimonia la cura di Levi nel non lasciare alcun racconto irrelato nell'intento di costruire una struttura ordinata e di per se stessa significante, che veicolando elementi tematici offra un ulteriore simbolo di quanto avviene nei testi, sfumando la distinzione tra forma e contenuto. Among Levi’s works, the The Periodic Table is the one which best represents the senselessness of the division between science and literature and the author’s will to achieve a necessary recomposition between the two. Just like chemical substances that react

Model of Comet P/Giacobini-Zinner

International Nuclear Information System (INIS)

Boice, D.C.; Huebner, W.F.; Keady, J.J.; Schmidt, H.U.; Wegmann, R.

1986-01-01

A computer model of Comet P/Giacobini-Zinner is presented which contains photo-processes, gas-phase chemical kinetics, energy balance. Multifluid hydrodynamics with a transition to free molecular flow, and solar wind interaction. Recently, the physics for electrons in the model has been improved by including electron impact ionization and dissociation and separately accounting for electron energetics. Electron heating and cooling mechanisms include photoprocesses, recombination processes, inelastic and elastic collisions with heavy molecules, and expansion cooling. The model incorporates an internally consistent interaction of the solar wind with the coma gas using the axisymmetric ideal fluid dynamic equations. The nuclear size and composition have been chosen to make the calculations relevant to the 11 September 1985 International Cometary Explorer (ICE) encounter with Comet P/Giacobini-Zinner. Model profiles of the temperature, velocity, and number density of the electrons are in good agreement with measurements along ICE's trajectory. These results indicate that the probe passed through a region of the coma at the onset of the plasma tail

Aerial Photography and Imagery, Ortho-Corrected - 2008 Digital Orthophotos - Levy County

Data.gov (United States)

NSGIC Education | GIS Inventory — This data set is one component of a digital orthophoto coverage (DOI) over Levy County, FL. This dataset is comprised of 3-band 24-bit (red, green, and blue bands)...

Functional spaces and operators connected with some L\\'evy noises

OpenAIRE

Lytvynov, E.

2006-01-01

We review some recent developments in white noise analysis and quantum probability. We pay a special attention to spaces of test and generalized functionals of some L\\'evy white noises, as well as as to the structure of quantum white noise on these spaces.

Cloning and adoption: a reply to Levy and Lotz.

Science.gov (United States)

Strong, Carson

2008-02-01

In previous articles I discussed the ethics of human reproductive cloning, focusing on a possible future scenario in which reproductive cloning can be accomplished without an elevated risk of anomalies to the children who are created. I argued that in such a scenario it would be ethically permissible for infertile couples to use cloning as a way to have genetically related children and that such use should not be prohibited. In 'Reproductive Cloning and a (Kind of) Genetic Fallacy', Neil Levy and Mianna Lotz raise objections to my conclusions. They disagree with the view, for which I argued, that some couples can have defensible reasons for desiring genetically related children. They also offer several new arguments against reproductive cloning, including an argument that it would diminish the number of adoptions, thereby adversely affecting the welfare of children who need to be adopted. In this paper I point out that Levy and Lotz's criticisms misconstrue my arguments and that there are serious problems with their arguments for prohibiting infertile couples from using cloning, including their argument from adoption.

Levy Stable Processes. From Stationary to Self-Similar Dynamics and Back. An Application to Finance

International Nuclear Information System (INIS)

Burnecki, K.; Weron, A.

2004-01-01

We employ an ergodic theory argument to demonstrate the foundations of ubiquity of Levy stable self-similar processes in physics and present a class of models for anomalous and nonextensive diffusion. A relationship between stationary and self-similar models is clarified. The presented stochastic integral description of all Levy stable processes could provide new insights into the mechanism underlying a range of self-similar natural phenomena. Finally, this effect is illustrated by self-similar approach to financial modelling. (author)

The use of comet assay in plant toxicology: recent advances

Directory of Open Access Journals (Sweden)

Conceição LV Santos

2015-06-01

Full Text Available The systematic study of genotoxicity in plants induced by contaminants and other stress agents has been hindered to date by the lack of reliable and robust biomarkers. The comet assay is a versatile and sensitive method for the evaluation of DNA damages and DNA repair capacity at single-cell level. Due to its simplicity and sensitivity, and the small number of cells required to obtain robust results, the use of plant comet assay has drastically increased in the last decade. For years its use was restricted to a few model species, e.g. Allium cepa, Nicotiana tabacum, Vicia faba, or Arabidopsis thaliana but this number largely increased in the last years. Plant comet assay has been used to study the genotoxic impact of radiation, chemicals including pesticides, phytocompounds, heavy metals, nanoparticles or contaminated complex matrices. Here we will review the most recent data on the use of this technique as a standard approach for studying the genotoxic effects of different stress conditions on plants. Also, we will discuss the integration of information provided by the comet assay with other DNA-damage indicators, and with cellular responses including oxidative stress, cell division or cell death. Finally, we will focus on putative relations between transcripts related with DNA damage pathways, DNA replication and repair, oxidative stress and cell cycle progression that have been identified in plant cells with comet assays demonstrating DNA damage.

The use of comet assay in plant toxicology: recent advances

Science.gov (United States)

Santos, Conceição L. V.; Pourrut, Bertrand; Ferreira de Oliveira, José M. P.

2015-01-01

The systematic study of genotoxicity in plants induced by contaminants and other stress agents has been hindered to date by the lack of reliable and robust biomarkers. The comet assay is a versatile and sensitive method for the evaluation of DNA damages and DNA repair capacity at single-cell level. Due to its simplicity and sensitivity, and the small number of cells required to obtain robust results, the use of plant comet assay has drastically increased in the last decade. For years its use was restricted to a few model species, e.g., Allium cepa, Nicotiana tabacum, Vicia faba, or Arabidopsis thaliana but this number largely increased in the last years. Plant comet assay has been used to study the genotoxic impact of radiation, chemicals including pesticides, phytocompounds, heavy metals, nanoparticles or contaminated complex matrices. Here we will review the most recent data on the use of this technique as a standard approach for studying the genotoxic effects of different stress conditions on plants. Also, we will discuss the integration of information provided by the comet assay with other DNA-damage indicators, and with cellular responses including oxidative stress, cell division or cell death. Finally, we will focus on putative relations between transcripts related with DNA damage pathways, DNA replication and repair, oxidative stress and cell cycle progression that have been identified in plant cells with comet assays demonstrating DNA damage. PMID:26175750

Comet/Asteroid Protection System (CAPS): A Space-Based System Concept for Revolutionizing Earth Protection and Utilization of Near-Earth Objects

Science.gov (United States)

Mazanek, Daniel D.; Roithmayr, Carlos M.; Antol, Jeffrey; Kay-Bunnell, Linda; Werner, Martin R.; Park, Sang-Young; Kumar, Renjith R.

2002-01-01

There exists an infrequent, but significant hazard to life and property due to impacting asteroids and comets. There is currently no specific search for long-period comets, smaller near-Earth asteroids, or smaller short-period comets. These objects represent a threat with potentially little or no warning time using conventional ground-based telescopes. These planetary bodies also represent a significant resource for commercial exploitation, long-term sustained space exploration, and scientific research. The Comet/Asteroid Protection System (CAPS) would expand the current detection effort to include long-period comets, as well as small asteroids and short-period comets capable of regional destruction. A space-based detection system, despite being more costly and complex than Earth-based initiatives, is the most promising way of expanding the range of detectable objects, and surveying the entire celestial sky on a regular basis. CAPS is a future spacebased system concept that provides permanent, continuous asteroid and comet monitoring, and rapid, controlled modification of the orbital trajectories of selected bodies. CAPS would provide an orbit modification system capable of diverting kilometer class objects, and modifying the orbits of smaller asteroids for impact defense and resource utilization. This paper provides a summary of CAPS and discusses several key areas and technologies that are being investigated.

Astrobiology of Comets

Science.gov (United States)

Hoover, Richard B.; Wickramasinghe, Nalin C.; Wallis, Max K.; Sheldon, Robert B.

2004-01-01

We review the current state of knowledge concerning microbial extremophiles and comets and the potential significance of comets to Astrobiology. We model the thermal history of a cometary body, regarded as an assemblage of boulders, dust, ices and organics, as it approaches a perihelion distance of - IAU. The transfer of incident energy from sunlight into the interior leads to the melting of near surface ices, some under stable porous crust, providing possible habitats for a wide range of microorganisms. We provide data concerning new evidence for indigenous microfossils in CI meteorites, which may be the remains of extinct cometary cores. We discuss the dominant microbial communities of polar sea-ice, Antarctic ice sheet, and cryoconite environments as possible analogs for microbial ecosystems that may grow in sub-crustal pools or in ice/water films in comets.

Spazi d’autore. Riscrittura e passaggi di testo ne La strada di Levi

Directory of Open Access Journals (Sweden)

Matteo Martelli

2016-07-01

Full Text Available L’articolo propone un percorso d’analisi sulle strategie di riscrittura e di ripresa di alcuni testi di Primo Levi nel film documentario La strada di Levi e nell’opera parallela La prova. Focalizzandosi sul secondo romanzo di Levi, La tregua, questi lavori evadono dalle consuete pratiche di adattamento, sviluppando forme di riscrittura nelle quali la manipolazione critica delle testualità pregresse è posta in tensione con nuovi testi messi in scena, immagini, video, riorientando la percezione dell’ipotesto entro ulteriori linguaggi. È attraverso tale spazio di circolazione di linguaggi artistici e di pratiche intermediali, che gli autori Davide Ferrario e Marco Belpoliti sembrano poter condurre una riflessione sulle forme culturali dello sguardo e delle odierne pratiche di lettura della realtà (nella sua temporalità e memoria come nella sua spazialità e della sua traduzione attraverso codici semiotici molteplici. In tale spostamento costante del proprio oggetto di riscrittura, La strada di Levi e La prova si mostrano così quali nodi o reti di un processo di lettura dialettico del presente e del passato, in un tentativo di tracciare alcune mappe del mondo contemporaneo.   The essay suggests an analysis of the documentary film La strada di Levi and the correlated work La prova. Focusing on Primo Levi’s book La tregua, these works show a different attitude about adaptation through a constant reorientation of the source text and its juxtaposition with new texts and images, and through a projection of these elements within additional languages. In this way, the authors, Davide Ferrario and Marco Belpoliti, offer an experience of an intermedial artistic practice that involves a reflection on the cultural forms through which the texts interpret the reality (and its temporality or memory and its translation through multiple semiotic codes. The effect of this kind of work is the perception of the documentary film as a network that

TRIGGERING SUBLIMATION-DRIVEN ACTIVITY OF MAIN BELT COMETS

Energy Technology Data Exchange (ETDEWEB)

Haghighipour, N. [Institute for Astronomy, University of Hawaii-Manoa, Honolulu, HI 96825 (United States); Maindl, T. I.; Dvorak, R. [Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Schäfer, C. [Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen (Germany); Speith, R., E-mail: nader@ifa.hawaii.edu [Physikalisches Institut, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen (Germany)

2016-10-10

It has been suggested that the comet-like activity of main belt comets (MBCs) is due to the sublimation of sub-surface water–ice that has been exposed as a result of their surfaces being impacted by meter-sized bodies. We have examined the viability of this scenario by simulating impacts between meter-sized and kilometer-sized objects using a smooth particle hydrodynamics approach. Simulations have been carried out for different values of the impact velocity and impact angle, as well as different target material and water-mass fractions. Results indicate that for the range of impact velocities corresponding to those in the asteroid belt, the depth of an impact crater is slightly larger than 10 m, suggesting that if the activation of MBCs is due to the sublimation of sub-surface water–ice, this ice has to exist no deeper than a few meters from the surface. Results also show that ice exposure occurs in the bottom and on the interior surface of impact craters, as well as on the surface of the target where some of the ejected icy inclusions are re-accreted. While our results demonstrate that the impact scenario is indeed a viable mechanism to expose ice and trigger the activity of MBCs, they also indicate that the activity of the current MBCs is likely due to ice sublimation from multiple impact sites and/or the water contents of these objects (and other asteroids in the outer asteroid belt) is larger than the 5% that is traditionally considered in models of terrestrial planet formation, providing more ice for sublimation. We present the details of our simulations and discuss their results and implications.

Attraction of Sphenophorus levis Vaurie adults (Coleoptera: Curculionidae) to vegetal tissues at different conservation levels; Atracao de adultos de Sphenophorus levis Vaurie (Coleoptera: Curculionidae) a fragmentos vegetais em diferentes estados de conservacao

Energy Technology Data Exchange (ETDEWEB)

Giron-Perez, Katherine; Nakano, Octavio; Silva, Amanda C; Oda-Souza, Melissa [Escola Superior de Agricultura Luiz de Queiroz (ESALQ/USP), Piracicaba, SP (Brazil). Dept. de Entomologia e Acarologia], e-mail: entomologa@ymail.com, e-mail: onakano@esalq.usp.br

2009-07-01

The occurrence of the sugarcane weevil Sphenophorus levis Vaurie is important in sugarcane in some regions in Brazil. Damage is caused by the larvae as they bore into the nodes and can reach 30 ton/ha/year. Many control alternatives have been attempted, but none were satisfactory, except for the use of toxic baits. Therefore, it is necessary to optimize their efficiency or to propose new techniques. The objective of the current study was to evaluate the attractiveness of adults of S. levis to sugarcane nodes and pineapple peelings in an 'Y' tube olfactometer. The sugarcane internodes were treated with 10% molasses, and tested after different periods of fermentation (24, 48 e 72h), at different times of the day (diurnal and nocturnal) and with both sexes. These tests were carried out in order to correlate the response of S. levis to ethyl acetate and ethanol release as a result of the fermentation process. The release of both compounds was monitored by gas chromatography-mass spectrometry (GC-MS). Our data indicated that sugarcane internodes mixed with 10% molasses fermented for 24h and 48h were the most attractive to S. levis (up to 90%). Pineapple peelings attracted 62.5% of the tested insects. The olfactory response was higher during the day, and no differences were found between the sexes. The production of ethanol in all plant substrates was higher than ethyl acetate, but we could not establish a clear correlation with the insect response to baits. (author)

Distribution of the Largest Eigenvalues of the Levi-Smirnov Ensemble

International Nuclear Information System (INIS)

Wieczorek, W.

2004-01-01

We calculate the distribution of the k-th largest eigenvalue in the random matrix Levi - Smirnov Ensemble (LSE), using the spectral dualism between LSE and chiral Gaussian Unitary Ensemble (GUE). Then we reconstruct universal spectral oscillations and we investigate an asymptotic behavior of the spectral distribution. (author)

COMET concept; COMET-Konzept

Energy Technology Data Exchange (ETDEWEB)

Alsmeyer, H.; Tromm, W.

1995-08-01

Studies of the COMET core catcher concept developed for a future PWR have been continued. The concept is based on the spreading of a core melt on a sacrificial layer and its erosion, until a subsequent addition of water from below causes a fragmentation of the melt. A porous solidification of the melt would then admit a complete flooding within a short period. (orig.)

Comet and meteorite traditions of Aboriginal Australians

Science.gov (United States)

Hamacher, Duane W.

2014-06-01

This research contributes to the disciplines of cultural astronomy (the academic study of how past and present cultures understand and utilise celestial objects and phenomena) and geomythology (the study of geological events and the formation of geological features described in oral traditions). Of the hundreds of distinct Aboriginal cultures of Australia, many have oral traditions rich in descriptions and explanations of comets, meteors, meteorites, airbursts, impact events, and impact craters. These views generally attribute these phenomena to spirits, death, and bad omens. There are also many traditions that describe the formation of meteorite craters as well as impact events that are not known to Western science.

Asteroids, Comets, Meteors 2014

Science.gov (United States)

Muinonen, K.; Penttilä, A.; Granvik, M.; Virkki, A.; Fedorets, G.; Wilkman, O.; Kohout, T.

2014-08-01

Asteroids, Comets, Meteors focuses on the research of small Solar System bodies. Small bodies are the key to understanding the formation and evolution of the Solar System, carrying signals from pre-solar times. Understanding the evolution of the Solar System helps unveil the evolution of extrasolar planetary systems. Societally, small bodies will be important future resources of minerals. The near-Earth population of small bodies continues to pose an impact hazard, whether it be small pieces of falling meteorites or larger asteroids or cometary nuclei capable of causing global environmental effects. The conference series entitled ''Asteroids, Comets, Meteors'' constitutes the leading international series in the field of small Solar System bodies. The first three conferences took place in Uppsala, Sweden in 1983, 1985, and 1989. The conference is now returning to Nordic countries after a quarter of a century. After the Uppsala conferences, the conference has taken place in Flagstaff, Arizona, U.S.A. in 1991, Belgirate, Italy in 1993, Paris, France in 1996, Ithaca, New York, U.S.A. in 1999, in Berlin, Germany in 2002, in Rio de Janeiro, Brazil in 2005, in Baltimore, Maryland, U.S.A. in 2008, and in Niigata, Japan in 2012. ACM in Helsinki, Finland in 2014 will be the 12th conference in the series.

Comets in Indian Scriptures

Science.gov (United States)

Das Gupta, P.

2016-01-01

The Indo-Aryans of ancient India observed stars and constellations for ascertaining auspicious times in order to conduct sacrificial rites ordained by the Vedas. Naturally, they would have sighted comets and referred to them in the Vedic texts. In Rigveda (circa 1700-1500 BC) and Atharvaveda (circa 1150 BC), there are references to dhumaketus and ketus, which stand for comets in Sanskrit. Rigveda speaks of a fig tree whose aerial roots spread out in the sky (Parpola 2010). Had this imagery been inspired by the resemblance of a comet's tail with long and linear roots of a banyan tree (ficus benghalensis)? Varahamihira (AD 550) and Ballal Sena (circa AD 1100-1200) described a large number of comets recorded by ancient seers, such as Parashara, Vriddha Garga, Narada, and Garga, to name a few. In this article, we propose that an episode in Mahabharata in which a radiant king, Nahusha, who rules the heavens and later turns into a serpent after he kicked the seer Agastya (also the star Canopus), is a mythological retelling of a cometary event.

Jupiter Laser Facility - COMET Laser

Data.gov (United States)

Federal Laboratory Consortium — COMET has 4 beam configurations with uncompressed pulse lengths from 500 ps to 6 ns, compressed pulses to 0.5 ps, and beam energies up to 20 J. COMET can fire every...

Comet-Narval acquisition notice

International Nuclear Information System (INIS)

Le Bris, J.; Sellem, R.; Artiges, J.C.; Clavelin, J.F.; Du, S.; Grave, X.; Hubert, O.; Sauvage, J.; Roussiere, B.

2006-01-01

The COMET cards (encoding and time marking) serve to determine the energies and the time correlations of radiations detected during a multiparameter experiment while avoiding any extra specific module like coincidence circuits or delays) to set this time correlation. For each detected radiation, the arrival time information as well as the amplitude of the detected signal, are encoded. The results of these amplitude and time coding are associated to create an event. In this way, each detector is an independent source which provides a building block of the general information obtained by all the detectors. The COMET cards are associated with a NARVAL data acquisition system. This document is the instruction booklet of the COMET-NARVAL acquisition system

Comet: Multifunction VOEvent broker

Science.gov (United States)

Swinbank, John

2014-04-01

Comet is a Python implementation of the VOEvent Transport Protocol (VTP). VOEvent is the IVOA system for describing transient celestial events. Details of transients detected by many projects, including Fermi, Swift, and the Catalina Sky Survey, are currently made available as VOEvents, which is also the standard alert format by future facilities such as LSST and SKA. The core of Comet is a multifunction VOEvent broker, capable of receiving events either by subscribing to one or more remote brokers or by direct connection from authors; it can then both process those events locally and forward them to its own subscribers. In addition, Comet provides a tool for publishing VOEvents to the global VOEvent backbone.

Comets in the space age

International Nuclear Information System (INIS)

Whipple, F.L.

1989-01-01

The historical development of the study of the nature of comets and their origin is discussed, emphasizing the use of aerospace technology in cometary science. The use of satellites to study the Comet Kohoutek 1973 XII, advances between Kohoutek and P/Halley, and studies of P/Halley during its 1986 return are examined. Consideration is given to data from ground, air, and space sensors, and from the Giotto and Vega spacecraft missions. Also, the physical structure of the nucleus of Comet Halley is described. 136 refs

Report of Some Comets: The Discovery of Uranus and Comets by William, Caroline, and John Herschel

Science.gov (United States)

Pasachoff, Jay M.; Olson, R. J. M.

2011-01-01

We report on the discovery and drawings of comets by William, Caroline, and John Herschel. The first discovery, by William Herschel, in 1781 from Bath, published in the Philosophical Transactions of the Royal Society with the title "Report of a Comet," turned out to be Uranus, the first planet ever discovered, Mercury through Saturn having been known since antiquity. William's sister Caroline was given duties of sweeping the skies and turned out to be a discoverer of 8 comets in her own right, in addition to keeping William's notes. Caroline's comets were discovered from Slough between 1786 and 1797. In the process, we also discuss original documents from the archives of the Royal Society and of the Royal Astronomical Society. We conclude by showing comet drawings that we have recently attributed to John Herschel, including Halley's Comet from 1836, recently located in the Ransom Center of the University of Texas at Austin. Acknowledgments: Planetary astronomy at Williams College is supported in part by grant NNX08AO50G from NASA Planetary Astronomy. We thank Peter Hingley of the Royal Astronomical Society and Richard Oram of the Harry Ransom Center of The University of Texas at Austin for their assistance.

A betterment levy in Poland and a „fee payable to development” in the Slovak Republic – differences and similarities

Directory of Open Access Journals (Sweden)

Karol Król

2017-06-01

Full Text Available An attempt to compare two public levies calculated by units of territorial government in order to collect resources for infrastructure investments – a betterment levy in Poland and “a fee payable to development” (in Slovak: poplatek za rozvoj in the Slovak Republic was made in the paper. It was assumed that the pursued research objective will be realized by means of the desk research analysis as well as the descriptive and logical one. Legal acts that govern issues of calculating a betterment levy in Poland and also selected legal acts which are obligatory in the Slovak Republic were subject to the detailed analysis. In conclusion, it was revealed that in spite of the fact that both fees are single levies collected for infrastructure investments, their calculating way as well as legal construction are radically different.

Nucleus of Comet IRAS-Araki-Alcock (1983 VII)

International Nuclear Information System (INIS)

Sekanina, Z.

1988-01-01

Optical, radar, infrared, UV, and microwave-continuum observations of Comet IRAS-Araki-Alcok were obtained in May 1983, the week of the comet's close approach to earth. The comet has a nucleus dimension and a rotation period which are similar to those of Comet Halley, but a different morphological signature (a persisting sunward fan-shaped coma). Time variations are noted in the projected nucleus cross section. Results suggest significant limb-darkening effects in the relevant domains of radio waves, and that the comet's interior must be extremely cold. It is found that the thermal-infrared fluxes from the inner coma of the comet are dominated by the nucleus. 63 references

Abundant Solar Nebula Solids in Comets

Science.gov (United States)

Messenger, S.; Keller, L. P.; Nakamura-Messenger, K.; Nguyen, A. N.; Clemett, S.

2016-01-01

Comets have been proposed to consist of unprocessed interstellar materials together with a variable amount of thermally annealed interstellar grains. Recent studies of cometary solids in the laboratory have shown that comets instead consist of a wide range of materials from across the protoplanetary disk, in addition to a minor complement of interstellar materials. These advances were made possible by the return of direct samples of comet 81P/Wild 2 coma dust by the NASA Stardust mission and recent advances in microscale analytical techniques. Isotopic studies of 'cometary' chondritic porous interplanetary dust particles (CP-IDPs) and comet 81P/Wild 2 Stardust samples show that preserved interstellar materials are more abundant in comets than in any class of meteorite. Identified interstellar materials include sub-micron-sized presolar silicates, oxides, and SiC dust grains and some fraction of the organic material that binds the samples together. Presolar grain abundances reach 1 weight percentage in the most stardust-rich CP-IDPs, 50 times greater than in meteorites. Yet, order of magnitude variations in presolar grain abundances among CP-IDPs suggest cometary solids experienced significant variations in the degree of processing in the solar nebula. Comets contain a surprisingly high abundance of nebular solids formed or altered at high temperatures. Comet 81P/Wild 2 samples include 10-40 micron-sized, refractory Ca- Al-rich inclusion (CAI)-, chondrule-, and ameboid olivine aggregate (AOA)-like materials. The O isotopic compositions of these refractory materials are remarkably similar to their meteoritic counterparts, ranging from 5 percent enrichments in (sup 16) O to near-terrestrial values. Comet 81P/Wild 2 and CP-IDPs also contain abundant Mg-Fe crystalline and amorphous silicates whose O isotopic compositions are also consistent with Solar System origins. Unlike meteorites, that are dominated by locally-produced materials, comets appear to be composed of

Emissions trading and the climate change levy

International Nuclear Information System (INIS)

Connett, Richard

2000-01-01

This paper discusses the flexible mechanisms established in the Kyoto Protocol of the UN Framework on Climate Change focussing on the mechanism whereby countries achieving their target for reducing the emissions of greenhouse gases can trade their excess to countries having difficulty achieving their target. UK measures to meet their commitment, the UK government's proposed climate change levy on the use of energy, negotiated agreements, emissions trading, and the nature, supply and trading of permits are examined. Compatibility with international agreements and the Integrated Pollution Prevention and Control (IPPC) Directive, monitoring, and penalties are considered

COMET- co-ordination and implementation of a pan-European instrument for radioecology - COMET- co-ordination and implementation of a pan-European project for radioecology

Energy Technology Data Exchange (ETDEWEB)

Vandenhove, Hildegarde [SCK.CEN, Belgian Nuclear Research Centre, Boeretang 200, 2400 Mol (Belgium); Muikku, Maarit [STUK, Radiation and Nuclear Safety Authority, P.O. Box 14, FI-00881 Helsinki (Finland); Liland, Astrid [NRPA, Norwegian Radiation Protection Authority, Grini Naeringspark 13, Oesteraas, 1332 (Norway); Adam-Guillermin, Christelle [IRSN-Institut de Radioprotection et de Surete Nucleaire, 31, Avenue de la Division Leclerc, 92260 Fontenay-Aux-Roses (France); Howard, Brenda [NERC Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Av., Bailrigg, Lancaster, LA1 4AP (United Kingdom)

2014-07-01

The EC-FP7 project COMET (June 2013 - May 2017) intends to strengthen the pan-European research initiative on the impact of radiation on man and the environment by facilitating the integration of 'radioecological' research. The COMET consortium currently has thirteen partners; eight from EU member states, two from Norway, two from Ukraine and one from Japan. COMET operates in close association with the FP7-STAR Network of Excellence[1]and the Radioecology Alliance[2], COMET will develop initiatives to encourage organisations from the European (and larger) radioecological research community to join the Radioecology Alliance to help address the priorities identified in the Strategic Research Agenda (SRA) for radioecological research. Capacity, competence and skills in radioecology will thus be strengthened at a pan-European level. Mechanisms for knowledge exchange, dissemination and training will be established to enhance and maintain European capacity, competence and skills in radioecology, partially through an open access web site, topical workshops and training activities. COMET will develop innovative mechanisms for joint programming and implementation of radioecological research. Mechanisms for planning and carrying out joint research activities in radioecology will be developed based on the scientific requirements identified in the SRA and via interaction with a wide range of stakeholders. COMET will strengthen the bridge with other radiation protection and ecological communities. A roadmap and associated implementation plan is being developed in collaboration with the Radioecology Alliance and the allied platforms on low dose risk research (MELODI[3]), and emergency management research (NERIS[4]) and the radioecology community at large who is invited to become associated to the development of roadmap and implementation plan. COMET will initiate innovative research on key needs identified by the radioecology community, the (post) emergency management

Comet formation

Science.gov (United States)

Blum, J.

2014-07-01

There has been vast progress in our understanding of planetesimal formation over the past decades, owing to a number of laboratory experiments as well as to refined models of dust and ice agglomeration in protoplanetary disks. Coagulation rapidly forms cm-sized ''pebbles'' by direct sticking in collisions at low velocities (Güttler et al. 2010; Zsom et al. 2010). For the further growth, two model approaches are currently being discussed: (1) Local concentration of pebbles in nebular instabilities until gravitational instability occurs (Johansen et al. 2007). (2) A competition between fragmentation and mass transfer in collisions among the dusty bodies, in which a few ''lucky winners'' make it to planetesimal sizes (Windmark et al. 2012a,b; Garaud et al. 2013). Predictions of the physical properties of the resulting bodies in both models allow a distinction of the two formation scenarios of planetesimals. In particular, the tensile strength (i.e, the inner cohesion) of the planetesimals differ widely between the two models (Skorov & Blum 2012; Blum et al. 2014). While model (1) predicts tensile strengths on the order of ˜ 1 Pa, model (2) results in rather compactified dusty bodies with tensile strengths in the kPa regime. If comets are km-sized survivors of the planetesimal-formation era, they should in principle hold the secret of their formation process. Water ice is the prime volatile responsible for the activity of comets. Thermophysical models of the heat and mass transport close to the comet-nucleus surface predict water-ice sublimation temperatures that relate to maximum sublimation pressures well below the kPa regime predicted for formation scenario (2). Model (1), however, is in agreement with the observed dust and gas activity of comets. Thus, a formation scenario for cometesimals involving gravitational instability is favored (Blum et al. 2014).

Comet Halley Returns. A Teacher's Guide, 1985-1986.

Science.gov (United States)

Chapman, Robert D.; Bondurant, R. Lynn, Jr.

This booklet was designed as an aid for elementary and secondary school teachers. It is divided into two distinct parts. Part I is a brief tutorial which introduces some of the most important concepts about comets. Areas addressed include: the historical importance of Comet Halley; how comets are found and names; cometary orbits; what Comet Halley…

27 CFR 70.164 - Surrender of property subject to levy in the case of life insurance and endowment contracts.

Science.gov (United States)

2010-04-01

... the case of life insurance and endowment contracts. (a) In general. This section provides special rules relating to the surrender of property subject to levy in the case of life insurance and endowment... subject to levy in the case of life insurance and endowment contracts. 70.164 Section 70.164 Alcohol...

Extreme events as foundation of Levy walks with varying velocity

International Nuclear Information System (INIS)

Kutner, Ryszard

2002-01-01

In this work we study the role of extreme events [E.W. Montroll, B.J. West, in: J.L. Lebowitz, E.W. Montrell (Eds.), Fluctuation Phenomena, SSM, vol. VII, North-Holland, Amsterdam, 1979, p. 63; J.-P. Bouchaud, M. Potters, Theory of Financial Risks from Statistical Physics to Risk Management, Cambridge University Press, Cambridge, 2001; D. Sornette, Critical Phenomena in Natural Sciences. Chaos, Fractals, Selforganization and Disorder: Concepts and Tools, Springer, Berlin, 2000] in determining the scaling properties of Levy walks with varying velocity. This model is an extension of the well-known Levy walks one [J. Klafter, G. Zumofen, M.F. Shlesinger, in M.F. Shlesinger, G.M. Zaslavsky, U. Frisch (Eds.), Levy Flights and Related Topics ion Physics, Lecture Notes in Physics, vol. 450, Springer, Berlin, 1995, p. 196; G. Zumofen, J. Klafter, M.F. Shlesinger, in: R. Kutner, A. Pekalski, K. Sznajd-Weron (Eds.), Anomalous Diffusion. From Basics to Applications, Lecture Note in Physics, vol. 519, Springer, Berlin, 1999, p. 15] introduced in the context of chaotic dynamics where a fixed value of the walker velocity is assumed for simplicity. Such an extension seems to be necessary when the open and/or complex system is studied. The model of Levy walks with varying velocity is spanned on two coupled velocity-temporal hierarchies: the first one consisting of velocities and the second of corresponding time intervals which the walker spends between the successive turning points. Both these hierarchical structures are characterized by their own self-similar dimensions. The extreme event, which can appear within a given time interval, is defined as a single random step of the walker having largest length. By finding power-laws which describe the time-dependence of this displacement and its statistics we obtained two independent diffusion exponents, which are related to the above-mentioned dimensions and which characterize the extreme event kinetics. In this work we show the

Detection of radiation-induced apoptosis using the comet assay

International Nuclear Information System (INIS)

Wada, Seiichi; Kobayashi, Yasuhiko; Funayama, Tomoo; Yamamoto, Kazuo; Khoa, Tran Van; Natsuhori, Masahiro; Ito, Nobuhiko

2003-01-01

The electrophoresis pattern of apoptotic cells detected by the comet assay has a characteristic small head and spread tail. This image has been referred to as an apoptotic comet, but it has not been previously proven to be apoptotic cells by any direct method. In order to identify this image obtained by the comet assay as corresponding to an apoptotic cell, the frequency of appearance of apoptosis was examined using CHO-K1 and L5178Y cells which were exposed to gamma irradiation. As a method for detecting apoptosis, the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay was used. When the frequency of appearance of apoptotic cells following gamma irradiation was observed over a period of time, there was a significant increase in appearance of apoptosis when using the TUNEL assay. However, there was only a slight increase when using the comet assay. In order to verify the low frequency of appearance of apoptosis when using the comet assay, we attempted to use the TUNEL assay to satin the apoptotic comets detected in the comet assay. The apoptotic comets were TUNEL positive and the normal comets were TUNEL negative. This indicates that the apoptotic comets were formed from DNA fragments with 3'-hydroxy ends that are generated as cells undergo apoptosis. Therefore, it was understood that the characteristic pattern of apoptotic comets detected by the comet assay corresponds to cells undergoing apoptosis. (author)

Comets - cosmic 'snowballs'

International Nuclear Information System (INIS)

Luest, R.

1979-01-01

Non-periodic comets come from regions at the limit of our solar system and have conserved their original structure and composition since they have originated from a pre-solar nebuly together with the sun and the planets about 4.5 x 10 9 years ago. They are icy bodies of kilometer size whose structure and chemical composition is of great interest also with respect to the origin of the solar system. It is hoped to send a space craft to comet Halley in 1986 to get more detailed informations. (orig.) [de

Nitrogen abundance in Comet Halley

International Nuclear Information System (INIS)

Wyckoff, S.; Tegler, S.C.; Engel, L.

1991-01-01

Data on the nitrogen-containing compounds that observed spectroscopically in the coma of Comet Halley are summarized, and the elemental abundance of nitrogen in the Comet Halley nucleus is derived. It is found that 90 percent of elemental nitrogen is in the dust fraction of the coma, while in the gas fraction, most of the nitrogen is contained in NH3 and CN. The elemental nitrogen abundance in the ice component of the nucleus was found to be deficient by a factor of about 75, relative to the solar photosphere, indicating that the chemical partitioning of N2 into NH3 and other nitrogen compounds during the evolution of the solar nebula cannot account completely for the low abundance ratio N2/NH3 = 0.1, observed in the comet. It is suggested that the low N2/NH3 ratio in Comet Halley may be explained simply by physical fractionation and/or thermal diffusion. 88 refs

the priests and the descendants of levi in the book of malachi

African Journals Online (AJOL)

Fanie Snyman for his hospitality and for all his generous efforts to make my stay ... This interpretation of the descendants of Levi has long since found many ...... 1998. Malachi. A New Translation with Introduction and Commentary. New.

Comet nuclei and Trojan asteroids - A new link and a possible mechanism for comet splittings

International Nuclear Information System (INIS)

Hartmann, W.K.; Tholen, D.J.

1990-01-01

Relatively elongated shapes, implied by recent evidence of a greater incidence of high amplitude lightcurves for comet nuclei and Trojan asteroids than for similarly scaled main belt asteroids, are suggested to have evolved among comet nuclei and Trojans due to volatile loss. It is further suggested that such an evolutionary course may account for observed comet splitting; rotational splitting may specifically occur as a result of evolution in the direction of an elongated shape through sublimation. Supporting these hypotheses, the few m/sec separation velocities projected for rotationally splitting elongated nuclei are precisely in the observed range. 40 refs

Solar wind interaction with type-1 comet tails

International Nuclear Information System (INIS)

Ershkovich, A.I.

1977-01-01

A comet tail is considered as a plasma cylinder separated by a tangential discontinuity surface from the solar wind. Under typical conditions a comet tail boundary is shown to undergo the Kelvin-Helmholtz instability. With infinite amplitude the stabilizing effect of the magnetic field increases, and waves become stable. The proposed model supplies the detailed quantitative description of helical waves observed in type-1 comet tails. This theory enables the evaluation of the comet tail magnetic field by means of the observations of helical waves. The magnetic field in the comet tail turns out to be of the order of the interplanetary field. This conclusion seems to be in accordance with Alfven's idea that the magnetic field in type-1 comet tails is a captured interplanetary field. (Auth.)

Where are the mini Kreutz-family comets?

International Nuclear Information System (INIS)

Ye, Quan-Zhi; Wiegert, Paul A.; Hui, Man-To; Kracht, Rainer

2014-01-01

The Kreutz family of sungrazing comets contains over 2000 known members, many of which are believed to be under ∼100 m sizes (mini comets) and have only been studied at small heliocentric distances (r H ) with space-based SOHO/STEREO spacecraft. To understand the brightening process of mini Kreutz comets, we conducted a survey using CFHT/MegaCam at moderate r H guided by SOHO/STEREO observations. We identify two comets that should be in our search area but are not detected, indicating that the comets have either followed a steeper brightening rate within the previously reported rapid brightening stage (the brightening burst), or the brightening burst starts earlier than expected. We present a composite analysis of the pre-perihelion light curves of five Kreutz comets that cover to ∼1 AU. We observe significant diversity in the light curves that can be used to grossly classify them into two types: C/Ikeya-Seki and C/SWAN follow the canonical r H −4 while the others follow r H −7 . In particular, C/SWAN seems to have undergone an outburst (Δm > 5 mag) or a rapid brightening (n ≳ 11) between r H = 1.06 AU and 0.52 AU, and shows hints of structural/compositional differences compared to other bright Kreutz comets. We also find evidence that the Kreutz comets as a population lose their mass less efficiently than the dynamically new comet, C/ISON, and are relatively devoid of species that drive C/ISON's activity at large r H . Concurrent observations of C/STEREO in different wavelengths also suggest that a blueward species such as CN may be the main driver for brightening bursts, instead of sodium as previously thought

COLOR SYSTEMATICS OF COMETS AND RELATED BODIES

Energy Technology Data Exchange (ETDEWEB)

Jewitt, David, E-mail: jewitt@ucla.edu [Department of Earth, Planetary and Space Sciences, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095-1567 (United States)

2015-12-15

Most comets are volatile-rich bodies that have recently entered the inner solar system following long-term storage in the Kuiper belt and the Oort cloud reservoirs. These reservoirs feed several distinct, short-lived “small body” populations. Here, we present new measurements of the optical colors of cometary and comet-related bodies including long-period (Oort cloud) comets, Damocloids (probable inactive nuclei of long-period comets) and Centaurs (recent escapees from the Kuiper belt and precursors to the Jupiter family comets). We combine the new measurements with published data on short-period comets, Jovian Trojans and Kuiper belt objects to examine the color systematics of the comet-related populations. We find that the mean optical colors of the dust in short-period and long-period comets are identical within the uncertainties of measurement, as are the colors of the dust and of the underlying nuclei. These populations show no evidence for scattering by optically small particles or for compositional gradients, even at the largest distances from the Sun, and no evidence for ultrared matter. Consistent with earlier work, ultrared surfaces are common in the Kuiper belt and on the Centaurs, but not in other small body populations, suggesting that this material is hidden or destroyed upon entry to the inner solar system. The onset of activity in the Centaurs and the disappearance of the ultrared matter in this population begin at about the same perihelion distance (∼10 AU), suggesting that the two are related. Blanketing of primordial surface materials by the fallback of sub-orbital ejecta, for which we calculate a very short timescale, is the likely mechanism. The same process should operate on any mass-losing body, explaining the absence of ultrared surface material in the entire comet population.

Theories of comets to the age of Laplace

Science.gov (United States)

Heidarzadeh, Tofigh

Although the development of ideas about cometary motion has been investigated in several projects, a comprehensive and detailed survey of physical theories of comets has not been conducted. The available works either illustrate relatively short periods in the history of physical cometology or portray a landscape view without adequate details. The present study is an attempt to depict the details of the major physical theories of comets from Aristotle to the age of Laplace. The basic question from which this project originated was simple: how did natural philosophers and astronomers define the nature and place of a new category of celestial objects--the comets--after Brahe's estimation of cometary distances? However, a study starting merely from Brahe without covering classical and medieval thought about comets would be incomplete. Thus, based on the fundamental physical characteristics attributed to comets, the history of cometology may be divided into three periods: from Aristotle to Brahe, in which comets were assumed to be meteorological phenomena; from Brahe to Newton, when comets were admitted as celestial bodies but with unknown trajectories; and from Newton to Laplace, in which they were treated as members of the solar system having more or less the same properties of the planets. By estimating the mass of comets in the 1800s, Laplace diverted cometology into a different direction wherein they were considered among the smallest bodies in the solar system and deprived of the most important properties that had been used to explain their physical constitution during the previous two millennia. Ideas about the astrological aspects of comets are not considered in this study. Also, topics concerning the motion of comets are explained to the extent that is helpful in illustrating their physical properties. The main objective is to demonstrate the foundations of physical theories of comets, and the interaction between observational and mathematical astronomy, and

Cosmogenic nuclide production within the atmosphere and long period comets

Science.gov (United States)

Overholt, Andrew C.

The Earth is constantly bombarded by cosmic rays. These high energy particles collide with target nuclei, producing a shower of secondary particles. These secondaries contribute significantly to the radiation background at sea level and in the atmosphere, as well as producing rare cosmogenic nuclides. This contribution is variable over long time scales as astrophysical events change the cosmic ray flux incident on the Earth. Our work re-examines a previously proposed climate effect of increased cosmic ray flux due to galactic location. Although our work does not support this effect, cosmic ray secondaries remain a threat to terrestrial biota. We calculate the cosmogenic neutron flux within the atmosphere as a function of primary spectrum. This work is pivotal in determining the radiation dose due to any arbitrary astrophysical event where the primary spectrum is known. Additionally, this work can be used to determine the cosmogenic nuclide production from such an event. These neutrons are the fundamental source of cosmogenic nuclides within our atmosphere and extraterrestrial matter. We explore the idea that excursions in 14C and 10Be abundances in the atmosphere may arise from direct deposition by long-period comet impacts, and those in 26Al from any bolide. We find that the amount of nuclide mass on large long-period comets entering the Earth's atmosphere may be sufficient for creating anomalies in the records of 14C and 10Be from past impacts. In particular, the estimated mass of the proposed Younger Dryas comet is consistent with its having deposited sufficient isotopes to account for recorded nuclide increases at that time. The 26Al/10Be ratio is much larger in extraterrestrial objects than in the atmosphere, and so, we note that measuring this ratio in ice cores is a suitable further test for the Younger Dryas impact hypothesis. This portion of our work may be used to find possible impact events in the geologic record as well as determination of a large

Attraction of Sphenophorus levis Vaurie adults (Coleoptera: Curculionidae) to vegetal tissues at different conservation levels

International Nuclear Information System (INIS)

Giron-Perez, Katherine; Nakano, Octavio; Silva, Amanda C; Oda-Souza, Melissa

2009-01-01

The occurrence of the sugarcane weevil Sphenophorus levis Vaurie is important in sugarcane in some regions in Brazil. Damage is caused by the larvae as they bore into the nodes and can reach 30 ton/ha/year. Many control alternatives have been attempted, but none were satisfactory, except for the use of toxic baits. Therefore, it is necessary to optimize their efficiency or to propose new techniques. The objective of the current study was to evaluate the attractiveness of adults of S. levis to sugarcane nodes and pineapple peelings in an 'Y' tube olfactometer. The sugarcane internodes were treated with 10% molasses, and tested after different periods of fermentation (24, 48 e 72h), at different times of the day (diurnal and nocturnal) and with both sexes. These tests were carried out in order to correlate the response of S. levis to ethyl acetate and ethanol release as a result of the fermentation process. The release of both compounds was monitored by gas chromatography-mass spectrometry (GC-MS). Our data indicated that sugarcane internodes mixed with 10% molasses fermented for 24h and 48h were the most attractive to S. levis (up to 90%). Pineapple peelings attracted 62.5% of the tested insects. The olfactory response was higher during the day, and no differences were found between the sexes. The production of ethanol in all plant substrates was higher than ethyl acetate, but we could not establish a clear correlation with the insect response to baits. (author)

THE PLASMA ENVIRONMENT IN COMETS OVER A WIDE RANGE OF HELIOCENTRIC DISTANCES: APPLICATION TO COMET C/2006 P1 (MCNAUGHT)

Energy Technology Data Exchange (ETDEWEB)

Shou, Y.; Combi, M.; Gombosi, T.; Toth, G. [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI (United States); Jia, Y.-D. [IGPP, and EPSS, University of California, Los Angeles, CA 90095 (United States); Rubin, M. [Physikalisches Institut, University of Bern, Sidlerstrasse. 5, CH-3012 Bern (Switzerland)

2015-08-20

On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at 0.17 AU. Abundant remote observations offer plenty of information on the neutral composition and neutral velocities within 1 million kilometers of the comet nucleus. In early February, the Ulysses spacecraft made an in situ measurement of the ion composition, plasma velocity, and magnetic field when passing through the distant ion tail and the ambient solar wind. The measurement by Ulysses was made when the comet was at around 0.8 AU. With the constraints provided by remote and in situ observations, we simulated the plasma environment of Comet C/2006 P1 (McNaught) using a multi-species comet MHD model over a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction of the comet at various locations is characterized and typical subsolar standoff distances of the bow shock and contact surface are presented and compared to analytic solutions. We find the variation in the bow shock standoff distances at different heliocentric distances is smaller than the contact surface. In addition, we modified the multi-species model for the case when the comet was at 0.7 AU and achieved comparable water group ion abundances, proton densities, plasma velocities, and plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We discuss the dominating chemical reactions throughout the comet-solar wind interaction region and demonstrate the link between the ion composition near the comet and in the distant tail as measured by Ulysses.

THE PLASMA ENVIRONMENT IN COMETS OVER A WIDE RANGE OF HELIOCENTRIC DISTANCES: APPLICATION TO COMET C/2006 P1 (MCNAUGHT)

International Nuclear Information System (INIS)

Shou, Y.; Combi, M.; Gombosi, T.; Toth, G.; Jia, Y.-D.; Rubin, M.

2015-01-01

On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at 0.17 AU. Abundant remote observations offer plenty of information on the neutral composition and neutral velocities within 1 million kilometers of the comet nucleus. In early February, the Ulysses spacecraft made an in situ measurement of the ion composition, plasma velocity, and magnetic field when passing through the distant ion tail and the ambient solar wind. The measurement by Ulysses was made when the comet was at around 0.8 AU. With the constraints provided by remote and in situ observations, we simulated the plasma environment of Comet C/2006 P1 (McNaught) using a multi-species comet MHD model over a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction of the comet at various locations is characterized and typical subsolar standoff distances of the bow shock and contact surface are presented and compared to analytic solutions. We find the variation in the bow shock standoff distances at different heliocentric distances is smaller than the contact surface. In addition, we modified the multi-species model for the case when the comet was at 0.7 AU and achieved comparable water group ion abundances, proton densities, plasma velocities, and plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We discuss the dominating chemical reactions throughout the comet-solar wind interaction region and demonstrate the link between the ion composition near the comet and in the distant tail as measured by Ulysses

To Catch A Comet...Learning From Halley's.

Science.gov (United States)

National Aeronautics and Space Administration, Washington, DC.

Comet chronicles and stories extend back over thousands of years. A common theme has been that comets are a major cause of catastrophe and tragedy here on earth. In addition, both Aristotle and Ptolemy believed that comets were phenomena within the earth's atmosphere, and it wasn't until the 16th century, when Danish astronomer Tycho Brache…

Autonomous Onboard Science Data Analysis for Comet Missions

Science.gov (United States)

Thompson, David R.; Tran, Daniel Q.; McLaren, David; Chien, Steve A.; Bergman, Larry; Castano, Rebecca; Doyle, Richard; Estlin, Tara; Lenda, Matthew

2012-01-01

Coming years will bring several comet rendezvous missions. The Rosetta spacecraft arrives at Comet 67P/Churyumov-Gerasimenko in 2014. Subsequent rendezvous might include a mission such as the proposed Comet Hopper with multiple surface landings, as well as Comet Nucleus Sample Return (CNSR) and Coma Rendezvous and Sample Return (CRSR). These encounters will begin to shed light on a population that, despite several previous flybys, remains mysterious and poorly understood. Scientists still have little direct knowledge of interactions between the nucleus and coma, their variation across different comets or their evolution over time. Activity may change on short timescales so it is challenging to characterize with scripted data acquisition. Here we investigate automatic onboard image analysis that could act faster than round-trip light time to capture unexpected outbursts and plume activity. We describe one edge-based method for detect comet nuclei and plumes, and test the approach on an existing catalog of comet images. Finally, we quantify benefits to specific measurement objectives by simulating a basic plume monitoring campaign.

What's Causing the Activity on Comet 67P?

Science.gov (United States)

Kohler, Susanna

2015-09-01

Comet 67P/ChuryumovGerasimenko made famous by the explorations of the Rosetta mission has been displaying puzzling activity as it hurtles toward the Sun. However, recent modeling of the comet by a group of scientists from the Cte dAzur University may now explain whats causing 67Ps activity.Shadowed ActivityA model of comet 67P, with the colors indicating the rate of change of the temperature on the comets surface. The most rapid temperature changes are seen at the comets neck, in the same locations as the early activity seen in the Rosetta images. [Al-Lagoa et al. 2015] Between June and September of 2014, Rosetta observed comet 67P displaying early activity in the form of jets of dust emitted from near the neck of the comet (its narrowest point). Such activity is usually driven by the sublimation of volatiles from the comets surface as a result of sun exposure. But the neck of the comet is frequently shadowed as the comet rotates, and it receives significantly less sunlight than the rest of the comet. So why would the early activity originate from the comets neck?The authors of a recent study, led by Victor Al-Lagoa, hypothesize that its precisely because the neck is receiving alternating sunlight/shadows that its displaying activity. They suggest that thermal cracking of the surface of the comet is happening faster in this region, due to the rapid changes in temperature that result from the shadows cast by the surrounding terrain. The cracking exposes subsurface ices in the neck faster than in other regions, and the ensuing sublimation of that ice is what creates the activity were seeing.Temperature Models: To test their hypothesis, the authors study the surface temperatures on comet 67P by means of a thermophysical model a model used to calculate the temperatures on an airless body, both on and below the surface. The model takes into account factors like thermal inertia (how quickly the bodys temperature responds to changes in the incident energy), shadowing, and

Dark matter as a trigger for periodic comet impacts.

Science.gov (United States)

Randall, Lisa; Reece, Matthew

2014-04-25

Although statistical evidence is not overwhelming, possible support for an approximately 35×106  yr periodicity in the crater record on Earth could indicate a nonrandom underlying enhancement of meteorite impacts at regular intervals. A proposed explanation in terms of tidal effects on Oort cloud comet perturbations as the Solar System passes through the galactic midplane is hampered by lack of an underlying cause for sufficiently enhanced gravitational effects over a sufficiently short time interval and by the time frame between such possible enhancements. We show that a smooth dark disk in the galactic midplane would address both these issues and create a periodic enhancement of the sort that has potentially been observed. Such a disk is motivated by a novel dark matter component with dissipative cooling that we considered in earlier work. We show how to evaluate the statistical evidence for periodicity by input of appropriate measured priors from the galactic model, justifying or ruling out periodic cratering with more confidence than by evaluating the data without an underlying model. We find that, marginalizing over astrophysical uncertainties, the likelihood ratio for such a model relative to one with a constant cratering rate is 3.0, which moderately favors the dark disk model. Our analysis furthermore yields a posterior distribution that, based on current crater data, singles out a dark matter disk surface density of approximately 10M⊙/pc2. The geological record thereby motivates a particular model of dark matter that will be probed in the near future.

Estimating Resource Costs of Levy Campaigns in Five Ohio School Districts

Science.gov (United States)

Ingle, W. Kyle; Petroff, Ruth Ann; Johnson, Paul A.

2011-01-01

Using Levin and McEwan's (2001) "ingredients method," this study identified the major activities and associated costs of school levy campaigns in five districts. The ingredients were divided into one of five cost categories--human resources, facilities, fees, marketing, and supplies. As to overall costs of the campaigns, estimates ranged…

The COMET Sleep Research Platform.

Science.gov (United States)

Nichols, Deborah A; DeSalvo, Steven; Miller, Richard A; Jónsson, Darrell; Griffin, Kara S; Hyde, Pamela R; Walsh, James K; Kushida, Clete A

2014-01-01

The Comparative Outcomes Management with Electronic Data Technology (COMET) platform is extensible and designed for facilitating multicenter electronic clinical research. Our research goals were the following: (1) to conduct a comparative effectiveness trial (CET) for two obstructive sleep apnea treatments-positive airway pressure versus oral appliance therapy; and (2) to establish a new electronic network infrastructure that would support this study and other clinical research studies. The COMET platform was created to satisfy the needs of CET with a focus on creating a platform that provides comprehensive toolsets, multisite collaboration, and end-to-end data management. The platform also provides medical researchers the ability to visualize and interpret data using business intelligence (BI) tools. COMET is a research platform that is scalable and extensible, and which, in a future version, can accommodate big data sets and enable efficient and effective research across multiple studies and medical specialties. The COMET platform components were designed for an eventual move to a cloud computing infrastructure that enhances sustainability, overall cost effectiveness, and return on investment.

The Electricity Feed Law levy - how reliably can it be predicted?; Wie verlaesslich laesst sich die EEG-Umlage prognostizieren?

Energy Technology Data Exchange (ETDEWEB)

Bause, Rainer; Schulz, Woldemar [Amprion GmbH, Dortmund (Germany); Buehler, Holger [EnBW TNG, Stuttgart (Germany); Hodurek, Claus [50Hertz Transmission GmbH, Berlin (Germany); Kiessling, Axel [TenneT TSO GmbH, Bayreuth (Germany)

2011-10-15

By paying their monthly electricity bill German consumers are promoting the transition to tomorrow's resource-efficient electricity supply system, in which the largest part of electricity used is to come from renewable energy resources. Every year Germany's transmission system operators publish what is referred to as the ''EEG-Umlage'' (report on the Electricity Feed Law levy, or EEG levy), which shows how much every German household will be paying for the promotion of renewable energies in the coming year. The determination of the EEG levy involves uncertainties and imponderabilities which have to be taken into account in its calculation. The crucial task is to find a suitable systematic scheme for predicting the renewable energy yield.

Comet Halley and its historic passages during the past millennium

International Nuclear Information System (INIS)

Legrand, J.P.

1986-01-01

The March 12, 1759 return of Comet Halley verified Halley's hypothesis on the existence of periodic comets and supported Newton's principle of universal attraction. Comet Halley's appearances before the 16th century are traced and it is noted that the length of the comet's tail has varied greatly. The comet's rendezvous with ESA's satellite Giotto is discussed briefly

The Comet Halley Handbook: An Observer's Guide. Second Edition.

Science.gov (United States)

Yeomans, Donald K.

This handbook contains information on: (1) the orbit of comet Halley; (2) the expected physical behavior of comet Halley in 1985-1986, considering brightness estimates, coma diameters, and tail lengths; (3) observing conditions for comet Halley in 1985-1986; and (4) observing conditions for the dust tail of comet Halley in 1985-1986. Additional…

67P, Singing Comet

Science.gov (United States)

Smirnova, Ekaterina

2017-04-01

I would like to propose to present a short science-art-music collaboration film called "67P, Singing Comet" (5:27 min). If time of the session will allow, prior to the film I would like to make a slide show introduction to this project, highlighting the inspiration - the mission Rosetta by the European Space Agency (ESA) - and the artistic collaboration that took place in creating this piece. Inspired by the ESA Rosetta mission to the comet 67P, Ekaterina Smirnova (artist and project director, New York), Lee Mottram (clarinetist, Wales), Takuto Fukuda (composer, Japan) and Brian Hekker (video editor, New York) collaborated to create a unique atmospheric piece. Water and the origins of life throughout the Universe (specifically the Earth) is an element of the mission and the focus of Ekaterina's artistic vision. Ekaterina literally and figuratively paints a sensory assemblage using a combination of synthetic and natural elements to shape this artistic creation. To paint her watercolor works she is using a replica of the water found on the comet and implementing her own heartbeat into the music to create a recognizable inward sound of life. The Electro-Acoustic composition by Takuto Fukuda features an electronically manipulated performance by clarinetist Lee Mottram. The piece ceremoniously begins with reverberant bursts of low-register atonal bells transporting the listener to their ethereal inner origins of body and mind. The imagination takes the experience to an unknown destination as it gains speed gliding through the visual and audible textures of space and time. The comet's water similarly reacts with an ebb and flow thawing ice to potentially give life a chance as it is thrust along an orbit around the Sun. Near then far from the heat the comet forms frozen particles from vapors as it reaches it's furthest stretches creating an aerodynamic tail of icicles that slowly dissipate in a cycle that repeats itself until the comet's ultimate collision with an

Study of Comets Composition and Structure

Science.gov (United States)

Khalaf, S. Z.; Selman, A. A.; Ali, H. S.

2008-12-01

The present paper focuses on the nature of the different interactions between cometary nucleus and tail with solar wind. The dynamics of the comet will impose many features that provide unique behavior of the comet when entering the solar system. These features are reviewed in this paper and few investigations are made. The calculations made in this work represent the analysis and interpretation of the different features of the comet, such as perihelion and eccentricity dependence on the gas production rate, and the dependence of the latter on the composition of the comet nucleus. The dependences of the heliocentric, bow shock, contact surface, and stand-off distances with gas production rate for many types of comets that cover linear and non-linear types are studied in this work. Important results are obtained which indicated the different physical interactions between cometary ions and solar wind. Furthermore, the important relation between mean molecular weight and gas production rate are analyzed and studied in this work and a conclusion is made that, as the gas production rate increases, the mean molecular weight will decrease exponentially. A detailed discussion for this unique relation is given.

Comet assay on mice testicular cells

Directory of Open Access Journals (Sweden)

Anoop Kumar Sharma

2015-05-01

Full Text Available Heritable mutations may result in a variety of adverse outcomes including genetic disease in the offspring. In recent years the focus on germ cell mutagenicity has increased and the “Globally Harmonized System of Classification and Labelling of Chemicals (GHS” has published classification criteria for germ cell mutagens (Speit et al., 2009. The in vivo Comet assay is considered a useful tool for investigating germ cell genotoxicity. In the present study DNA strand breaks in testicular cells of mice were investigated. Different classes of chemicals were tested in order to evaluate the sensitivity of the comet assay in testicular cells. The chemicals included environmentally relevant substances such as Bisphenol A, PFOS and Tetrabrombisphenol A. Statistical power calculations will be presented to aid in the design of future Comet assay studies on testicular cells. Power curves were provided with different fold changes in % tail DNA, different number of cells scored and different number of gels (Hansen et al., 2014. An example is shown in Figure 1. A high throughput version of the Comet assay was used. Samples were scored with a fully automatic comet assay scoring system that provided faster scoring of randomly selected cells.

A GREAT search for Deuterium in Comets

Science.gov (United States)

Mumma, Michael

2013-10-01

Comets are understood to be the most pristine bodies in the Solar System. Their compositions reflect the chemical state of materials at the very earliest evolutionary stages of the protosolar nebula and, as such, they provide detailed insight into the physical and chemical processes operating in planet-forming disks. Isotopic fractionation ratios of the molecular ices in the nucleus are regarded as signatures of formation processes. These ratios provide unique information on the natal heritage of those ices, and can also test the proposal that Earth's water and other volatiles were delivered by cometary bombardment. Measurement of deuterium fractionation ratios is thus a major goal in contemporary cometary science and the D/H ratio of water - the dominant volatile in comets - holds great promise for testing the formation history of cometary matter. The D/H ratio in cometary water has been measured in only eight comets. Seven were from the Oort Cloud reservoir and the D/H ratio was about twice that of the Earth's oceans. However, the recent Herschel measurement of HDO/H2O in 103P/Hartley-2 (the first from the Kuiper Belt) was consistent with exogenous delivery of Earth's water by comets. Outstanding questions remain: are cometary HDO/H2O ratios consistent with current theories of nebular chemical evolution or with an interstellar origin? Does the HDO/H2O ratio vary substantially among comet populations? Hartley-2 is the only Kuiper Belt comet with measured HDO/H2O, are there comets with similar ratios in the Oort cloud? These questions can only be addressed by measuring HDO/H2O ratios in many more suitable bright comets. We therefore propose to measure the D/H ratio in water in a suitable target-of-opportunity comet by performing observations of HDO and OH with the GREAT spectrometer on SOFIA. A multi-wavelength, ground-based observing campaign will also be conducted in support of the airborne observations.

A quantitative comet infection assay for influenza virus

Science.gov (United States)

Lindsay, Stephen M.; Timm, Andrea; Yin, John

2011-01-01

Summary The virus comet assay is a cell-based virulence assay used to evaluate an antiviral drug or antibody against a target virus. The comet assay differs from the plaque assay in allowing spontaneous flows in 6-well plates to spread virus. When implemented quantitatively the comet assay has been shown to have an order-of-magnitude greater sensitivity to antivirals than the plaque assay. In this study, a quantitative comet assay for influenza virus is demonstrated, and is shown to have a 13-fold increase in sensitivity to ribavirin. AX4 cells (MDCK cells with increased surface concentration of α2–6 sialic acid, the influenza virus receptor) have reduced the comet size variability relative to MDCK cells, making them a better host cell for use in this assay. Because of enhanced antiviral sensitivity in flow-based assays, less drug is required, which could lead to lower reagent costs, reduced cytotoxicity, and fewer false-negative drug screen results. The comet assay also serves as a readout of flow conditions in the well. Observations from comets formed at varying humidity levels indicate a role for evaporation in the mechanism of spontaneous fluid flow in wells. PMID:22155578

CLATHRATE HYDRATES FORMATION IN SHORT-PERIOD COMETS

International Nuclear Information System (INIS)

Marboeuf, Ulysse; Mousis, Olivier; Petit, Jean-Marc; Schmitt, Bernard

2010-01-01

The initial composition of current models of cometary nuclei is only based on two forms of ice: crystalline ice for long-period comets and amorphous ice for short-period comets. A third form of ice, i.e., clathrate hydrate, could exist within the short-period cometary nuclei, but the area of formation of this crystalline structure in these objects has never been studied. Here, we show that the thermodynamic conditions in the interior of short-period comets allow the existence of clathrate hydrates in Halley-type comets. We show that their existence is viable in the Jupiter family comets only when the equilibrium pressure of CO clathrate hydrate is at least 1 order of magnitude lower than the usually assumed theoretical value. We calculate that the amount of volatiles that could be trapped in the clathrate hydrate layer may be orders of magnitude greater than the daily amount of gas released at the surface of the nucleus at perihelion. The formation and the destruction of the clathrate hydrate cages could then explain the diversity of composition of volatiles observed in comets, as well as some pre-perihelion outbursts. We finally show that the potential clathrate hydrate layer in comet 67P/Churyumov-Gerasimenko would, unfortunately, be deep inside the nucleus, out of reach of the Rosetta lander. However, such a clathrate hydrate layer would show up by the gas composition of the coma.

Linguagem e tradição em Carlo Levi: marcas do arcaico no sul italiano

Directory of Open Access Journals (Sweden)

Amarilis Gallo Coelho

2011-10-01

Full Text Available Carlo Levi, escritor italiano que objetiva documentar as peculiaridades e a diversidade social de seu país, utiliza, além do léxico colorido constante em sua obra, outros artifícios de expressão, tais como o emprego de formas-símbolo, como pedra, e amostras de linguagem, que caracterizam não só o plurilinguismo italiano, mas também a manutenção do arcaico e da história, através dos hábitos lingüísticos e sociais. Pelo uso estilístico e a constatação real de formas greco-latinas, assim como seus reflexos nos dialetos locais, Levi retrata com autenticidade o apego à tradição e a imobilidade espaço-temporal do homem meridional italiano.Carlo Levi raggiunge, nel contatto amoroso con le immagini ed i suoni meridionali, il passato arcaico presente, “dipinto” con spontaneità e autenticità, attraverso la gente, le cose e le voci di quello che lui chiama affettuosamente “mia terra” e miei “contadini”.

The "silent world" of Comet 15P/Finlay

CERN Document Server

Beech, M; Jones, J

1999-01-01

Comet 15P/Finlay is unusual in that, contrary to ab initio expectations, it demonstrates no apparent linkage to any known meteor shower. Using data contained within the Electronic Atlas of Dynamical Evolutions of Short-Period Comets, the authors evaluate theoretical shower radiants for Comet 15P/Finlay, but find no evidence to link it to any meteoric anomalies in recorded antiquity. This result, however, must be tempered by the fact that any Comet 15P/Finlay- derived meteoroids will have a low, 16 km s/sup -1/, encounter velocity with Earth's atmosphere. Typically, therefore, one would expect mostly faint meteors to be produced during an encounter with a Comet 15P/Finlay-derived meteoroid stream. they have conducted a D- criterion survey of meteoroid orbits derived from three southern hemisphere meteor radar surveys conducted during the 1960s, and again they find no evidence for any Comet 15P/Finlay-related activity. Numerical calculations following the orbital evolution of hypothetical meteoroids ejected fro...

Stardust: Catching a Comet and Bringing it Home

Science.gov (United States)

Brownlee, Donald E.

2007-01-01

The NASA STARDUST mission collected thousands of particles from Comet Wild 2 that are now being studied by two hundred scientists around the world. The spacecraft captured the samples during a close flyby of the comet in 2004 and returned them to Earth with a dramatic entry into the atmosphere early in 2006. The precious cargo of comet dust is being studied to determine new information about the origin of the Sun and planets. The comet formed at the edge of the solar system, beyond the orbit of Neptune, and is a sample of the material from which the solar system was formed. One of the most dramatic early findings from the mission was that a comet that formed in the coldest place in the solar system contained minerals that formed in the hottest place in the solar system. The comet samples are telling stories of fire and ice and they providing fascinating and unexpected information about our origins.

ACTIVITY OF 50 LONG-PERIOD COMETS BEYOND 5.2 au

Energy Technology Data Exchange (ETDEWEB)

Sárneczky, K.; Szabó, Gy. M.; Csák, B.; Kelemen, J.; Pál, A.; Szakáts, R.; Szegedi-Elek, E.; Vida, K.; Vinkó, J.; Kiss, L. L. [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17 (Hungary); Marschalkó, G. [Eötvös Loránd Tudományegyetem, H-1117 Pázmány Péter sétány 1/A, Budapest (Hungary); Szalai, T. [Department of Optics and Quantum Electronics, University of Szeged, H-6720 Szeged, Dóm tér 9 (Hungary); Székely, P. [Department of Experimental Physics, University of Szeged, Szeged H-6720, Dóm tér 9 (Hungary)

2016-12-01

Remote investigations of ancient matter in the solar system have traditionally been carried out through observations of long-period (LP) comets, which are less affected by solar irradiation than their short-period counterparts orbiting much closer to the Sun. Here we summarize the results of our decade-long survey of the distant activity of LP comets. We found that the most important separation in the data set is based on the dynamical nature of the objects. Dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by Afρ values >3–4, higher than those for our most active returning comets. New comets develop more symmetric comae, suggesting a generally isotropic outflow. In contrast to this, the comae of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, which suggest sudden variations in matter production. The morphological appearance of the observed comets is rather diverse. A surprisingly large fraction of the comets have long, tenuous tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets.

ACTIVITY OF 50 LONG-PERIOD COMETS BEYOND 5.2 au

International Nuclear Information System (INIS)

Sárneczky, K.; Szabó, Gy. M.; Csák, B.; Kelemen, J.; Pál, A.; Szakáts, R.; Szegedi-Elek, E.; Vida, K.; Vinkó, J.; Kiss, L. L.; Marschalkó, G.; Szalai, T.; Székely, P.

2016-01-01

Remote investigations of ancient matter in the solar system have traditionally been carried out through observations of long-period (LP) comets, which are less affected by solar irradiation than their short-period counterparts orbiting much closer to the Sun. Here we summarize the results of our decade-long survey of the distant activity of LP comets. We found that the most important separation in the data set is based on the dynamical nature of the objects. Dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by Afρ values >3–4, higher than those for our most active returning comets. New comets develop more symmetric comae, suggesting a generally isotropic outflow. In contrast to this, the comae of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, which suggest sudden variations in matter production. The morphological appearance of the observed comets is rather diverse. A surprisingly large fraction of the comets have long, tenuous tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets.

Physical characteristics of Comet Nucleus C/2001 OG108 (LONEOS)

Czech Academy of Sciences Publication Activity Database

Abell, P.A.; Fernandéz, Y.R.; Pravec, Petr; French, L.M.; Farnham, T.L.; Gaffey, M.J.; Hardersen, P.S.

2005-01-01

Roč. 179, č. 1 (2005), s. 174-194 ISSN 0019-1035 R&D Projects: GA AV ČR IAA3003204; GA ČR GA205/99/0255 Institutional research plan: CEZ:AV0Z10030501 Keywords : comet s * composition * infrared observations Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.244, year: 2005

Giacobini-Zinner comet: polarimetric and physical observations

International Nuclear Information System (INIS)

Martel, M.T.; Maines, P.; Grudzinska, S.; Stawikowski, A.

1984-10-01

The results of observations of the Giacobini-Zinner comet on 25 and 31 October 1959 are presented. The magnitude of the comet was measured photoelectrically in two spectral regions. The radius is on the order of one kilometer. The photoelectric measurements of comets 1959b and 1957c were used to measure the abundances of the CN and C2 radicals and of solid particles in the heads

Constraints on Comet 332P/Ikeya-Murakami

Science.gov (United States)

Hui, Man-To; Ye, Quan-Zhi; Wiegert, Paul

2017-01-01

Encke-type comet 332P/Ikeya-Murakami is experiencing cascading fragmentation events during its 2016 apparition. It is likely the first splitting Encke-type comet ever observed. A nongravitational solution to the astrometry reveals a statistical detection of the radial and transverse nongravitational parameters, {A}1=(1.54+/- 0.39)× {10}-8 au day‑2 and {A}2=(7.19+/- 1.92)× {10}-9 au day‑2, respectively, which implies a nucleus erosion rate of (9.1+/- 1.7)‰ per orbital revolution. The mass-loss rate likely has to be supported by a much larger fraction of an active surface area than known cases of short-period comets; it may be relevant to the ongoing fragmentation. We failed to detect any serendipitous pre-discovery observations of the comet in archival data from major sky surveys, whereby we infer that 332P used to be largely inactive, and is perhaps among the few short-period comets that have been reactivated from weakly active or dormant states. We therefore constrain an upper limit to the nucleus size as 2.0 ± 0.2 km in radius. A search for small bodies in similar orbits to that of 332P reveals comet P/2010 B2 (WISE) to be the best candidate. From an empirical generalized Jupiter-family (Encke-type included) comet population model, we estimate the likelihood of a chance alignment of the 332P–P/2010 B2 pair to be 1 in 33, a small number indicative of a genetic linkage between the two comets on a statistical basis. The pair possibly originated from a common progenitor, which underwent a disintegration event well before the twentieth century.

On the origin of comets

Science.gov (United States)

Mendis, A.; Alfven, H.

1976-01-01

Physico-chemical processes leading to the dynamic formation and physical evolution of comets are reviewed in relationship to the various theories that propose solar origins, protoplanetary origins, planetary origins and interstellar origins. Evidence points to the origins of comets by the growth and agglomeration of small particles from gas and dust at very low temperatures at undetermined regions in space.

Planetary perturbations and the origins of short-period comets

International Nuclear Information System (INIS)

Quinn, T.; Tremaine, S.; Duncan, M.

1990-01-01

To investigate the dynamical plausibility of possible sources for the short-period comets, a representative sample of comet orbits in the field of the sun and the giant planets was integrated, with the aim to determine whether the distribution of orbits from a proposed source that reach observable perihelia (q less than 2.5 AU) matches the observed distribution of short-period orbits. It is found that the majority of the short-period comets, those with orbital period P less than 20 yr (the Jupiter family), cannot arise from isotropic orbits with perihelia near Jupiter's orbit, because the resulting observable comet orbits have the wrong distribution in period, inclination, and argument of perihelion. The simulations also show that Jupiter-family comets cannot arise from isotropic orbits with perihelia in the Uranus-Neptune region. On the other hand, a source of low-inclination Neptune-crossing orbits yields a distribution of observable Jupiter-family comets that is consistent with the data in all respects. These results imply that the Jupiter-family comets arise from a disk source in the outer solar system rather than from the Oort comet cloud. 30 refs

Subordinated Levy Processes and Applications to Crude Oil Options

OpenAIRE

Noureddine Krichene

2005-01-01

One approach to oil markets is to treat oil as an asset, besides its role as a commodity. Speculative and nonspeculative activity by investors in the derivatives markets could be responsible for a sizable increase in oil prices. This paper recognizes both the consumption and investment aspects of crude oil and proposes Levy processes for modeling uncertainty and options pricing. Calibration to crude oil futures' options shows high volatility of oil futures prices, fat-tailed, and right-skewed...

Random, double- and single-strand DNA breaks can be differentiated in the method of Comet assay by the shape of the comet image.

Science.gov (United States)

Georgieva, Milena; Zagorchev, Plamen; Miloshev, George

2015-10-01

Comet assay is an invaluable tool in DNA research. It is widely used to detect DNA damage as an indicator of exposure to genotoxic stress. A canonical set of parameters and specialized software programs exist for Comet assay data quantification and analysis. None of them so far has proven its potential to employ a computer-based algorithm for assessment of the shape of the comet as an indicator of the exact mechanism by which the studied genotoxins cut in the molecule of DNA. Here, we present 14 unique measurements of the comet image based on the comet morphology. Their mathematical derivation and statistical analysis allowed precise description of the shape of the comet image which in turn discriminated the cause of genotoxic stress. This algorithm led to the development of the "CometShape" software which allowed easy discrimination among different genotoxins depending on the type of DNA damage they induce. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A dynamical study on extrasolar comets

Science.gov (United States)

Loibnegger, B.; Dvorak, R.

2017-09-01

Since the detection of absorption features in spectra of beta Pictoris varying on short time scales it is known that comets exist in other stellar systems. We investigate the dynamics of comets in two differently build systems (HD 10180 and HIP 14810). The outcomes of the scattering process, as there are collisions with the planets, captures and ejections from the systems are analysed statistically. Collisions and close encounters with the planets are investigated in more detail in order to conclude about transport of water and organic material. We will also investigate the possibility of detection of comets in other planetary systems.

Temporal Evolution of Water and Dust in Comet 9P/Tempel 1 after the Deep Impact Event, as Observed from Spitzer

Science.gov (United States)

Gicquel, Adeline; Bockelée-Morvan, D.; Kelley, M. S.; Woodward, C. E.; Wooden, D. H.

2010-10-01

The Deep Impact (DI) spacecraft encountered comet 9P/Tempel 1 on July 4th, 2005. The spacecraft released an impactor that collided with the comet nucleus and excavated (possibly unprocessed) cometary material in a prominent ejecta plume. Spectral maps covering 20'' x 67'' (1.85''/pixel) were acquired with the IRS instrument on the Spitzer Space Telescope at different times around the DI event: twice before impact (TI-41.3hrs and TI-22.9hrs) and twelve times after impact (between TI+0.67hrs and TI+1027hrs). These IRS observations are stored in the Spitzer data archive and presented by Lisse et al. (2006, Science 313, 635). We present the interpretation of 5.2-7.6 micrometer spectra obtained in the second order of the short-wavelength module (SL2). To reduce the contribution of artifacts in the spectra, 5x5 pixel extraction apertures (9.25''x9.25'') were used. The underlying continuum in the spectra provides information on the grain size distribution and color temperature of the dust ejecta. In order to determine the grain size distribution, we assumed that ejecta consist of a composition of both amorphous carbon and silicates. The grains are assumed to be spherical with sizes in range from 0.1 to 100 micrometers. We used the Mie theory to calculate the optical properties of each material and the temperature of the grain. We constrained the grain size distribution and velocities from the spectra and the temporal evolution of the dust flux. The dust mass and dust/gas ratio in the ejecta cloud are also derived and compared with other values published in the literature.

Vaporization of comet nuclei: Light curves and life times

Energy Technology Data Exchange (ETDEWEB)

Cowan, J J [Harvard Univ., Cambridge, MA (USA). Center for Astrophysics; A' Hearn, M F [Maryland Univ., College Park (USA)

1979-10-01

The authors have examined the effects of vaporization from the nucleus of a comet and show that a latitude dependence of vaporization can, in some cases, explain asymmetries in commetary light curves. They also find that a non-uniform distribution of solar radiation over a comet can considerably shorten the vaporization lifetime compared to the results normally obtained by assuming that the nuclear surface is isothermal. Independent of any latitude effects, comets with CO/sub 2/-dominated nuclei and with periherlion distances less than 0.5 AU have vaporization lifetimes less than or comparable to their dynamical ejection times. This may explain the observed deficit of comets with small perihelion distances. Similarly comets with CO/sub 2/-dominated nuclei and perihelia near Jupiter's orbit have vaporization lifetimes that are shorter than the time for capture into short-period orbits. They suggest, therefore, that at least some new comets are composed in large part of CO/sub 2/, while only H/sub 2/O-dominated comets, with lower vaporization rates, can survive to be captured into short-period orbits.

Catastrophic Disruption of Comet ISON

Science.gov (United States)

Keane, Jacqueline V.; Milam, Stefanie N.; Coulson, Iain M.; Kleyna, Jan T.; Sekanina, Zdenek; Kracht, Rainer; Riesen, Timm-Emmanuel; Meech, Karen J.; Charnley, Steven B.

2016-01-01

We report submillimeter 450 and 850 microns dust continuum observations for comet C/2012 S1 (ISON) obtained at heliocentric distances 0.31-0.08 au prior to perihelion on 2013 November 28 (rh?=?0.0125 au). These observations reveal a rapidly varying dust environment in which the dust emission was initially point-like. As ISON approached perihelion, the continuum emission became an elongated dust column spread out over as much as 60? (greater than 10(exp 5) km in the anti-solar direction. Deconvolution of the November 28.04 850 microns image reveals numerous distinct clumps consistent with the catastrophic disruption of comet ISON, producing approximately 5.2?×?10(exp 10) kg of submillimeter-sized dust. Orbital computations suggest that the SCUBA-2 emission peak coincides with the comet's residual nucleus.

Hyakutake, Hale-Bopp and the chemistry of comets

International Nuclear Information System (INIS)

Bachiller, R.; Planesas, P.

1997-01-01

Comets can be regarded as messengers from the primitive solar system which can provide precious pieces of information on the composition of the protosolar nebula. Physical and chemical phenomena within comets (shock waves, photodissociation caused by solar radiation, some endothermic chemical reactions, etc) are of the highest interest and cannot be reproduced at terrestrial laboratories in many cases. The passage of Hyakutake in 1996 and that of Hale-Bopp in 1997 are allowing remarkable progress in the understanding of the physico-chemistry of comets. Observations of such comets can be crucial in the study of the origin of life on Earth. (Author)

Triggering the Activation of Main-belt Comets: The Effect of Porosity

Science.gov (United States)

Haghighipour, N.; Maindl, T. I.; Schäfer, C. M.; Wandel, O. J.

2018-03-01

It has been suggested that the comet-like activity of Main-belt comets (MBCs) is due to the sublimation of sub-surface water-ice that is exposed when these objects are impacted by meter-sized bodies. We recently examined this scenario and showed that such impacts can, in fact, excavate ice and present a plausible mechanism for triggering the activation of MBCs. However, because the purpose of that study was to prove the concept and identify the most viable ice-longevity model, the porosity of the object and the loss of ice due to the heat of impact were ignored. In this paper, we extend our impact simulations to porous materials and account for the loss of ice due to an impact. We show that for a porous MBC, impact craters are deeper, reaching to ∼15 m, implying that if the activation of MBCs is due to the sublimation of sub-surface ice, this ice has to be within the top 15 m of the object. Results also indicate that the loss of ice due to the heat of impact is negligible, and the re-accretion of ejected ice is small. The latter suggests that the activities of current MBCs are most probably from multiple impact sites. Our study also indicates that for sublimation from multiple sites to account for the observed activity of the currently known MBCs, the water content of MBCs (and their parent asteroids) needs to be larger than the values traditionally considered in models of terrestrial planet formation.

Optical Detection of Anomalous Nitrogen in Comets

Science.gov (United States)

2003-12-01

VLT Opens New Window towards Our Origins Summary A team of European astronomers [1] has used the UVES spectrograph on the 8.2-m VLT KUEYEN telescope to perform a uniquely detailed study of Comet LINEAR (C/2000 WM1) . This is the first time that this powerful instrument has been employed to obtain high-resolution spectra of a comet. At the time of the observations in mid-March 2002, Comet LINEAR was about 180 million km from the Sun, moving outwards after its perihelion passage in January. As comets are believed to carry "pristine" material - left-overs from the formation of the solar system, about 4,600 million years ago - studies of these objects are important to obtain clues about the origins of the solar system and the Earth in particular. The high quality of the data obtained of this moving 9th-magnitude object has permitted a determination of the cometary abundance of various elements and their isotopes [2]. Of particular interest is the unambiguous detection and measurement of the nitrogen-15 isotope. The only other comet in which this isotope has been observed is famous Comet Hale-Bopp - this was during the passage in 1997, when it was much brighter than Comet LINEAR. Most interestingly, Comet LINEAR and Comet Hale-Bopp display the same isotopic abundance ratio, about 1 nitrogen-15 atom for each 140 nitrogen-14 atoms ( 14 N/ 15 N = 140 ± 30) . That is about half of the terrestrial value (272). It is also very different from the result obtained by means of radio measurements of Comet Hale-Bopp ( 14 N/ 15 N = 330 ± 75). Optical and radio measurements concern different molecules (CN and HCN, respectively), and this isotopic anomaly must be explained by some differentiation mechanism. The astronomers conclude that part of the cometary nitrogen is trapped in macromolecules attached to dust particles . The successful entry of UVES into cometary research now opens eagerly awaited opportunities for similiar observations in other, comparatively faint comets. These

The spacecraft encounters of Comet Halley

Science.gov (United States)

Asoka Mendis, D.; Tsurutani, Bruce T.

1986-01-01

The characteristics of the Comet Halley spacecraft 'fleet' (VEGA 1 and VEGA 2, Giotto, Suisei, and Sakigake) are presented. The major aims of these missions were (1) to discover and characterize the nucleus, (2) to characterize the atmosphere and ionosphere, (3) to characterize the dust, and (4) to characterize the nature of the large-scale comet-solar wind interaction. While the VEGA and Giotto missions were designed to study all four areas, Suisei addressed the second and fourth. Sakigake was designed to study the solar wind conditions upstream of the comet. It is noted that NASA's Deep Space Network played an important role in spacecraft tracking.

BALTIMORE’S M.S. LEVY AND SONS: Straw Hat Makers to the World, 1870-1960

Directory of Open Access Journals (Sweden)

Jessica I. Elfenbein

2008-01-01

Full Text Available From 1860 to 1960, Baltimore was an important center of the men’s ready-to- wear clothing industries. German-speaking Jews created many businesses that manufactured and sold underwear, men’s suits, and specialty items like hats and umbrellas. The straw hat making firm started by M.S. Levy is an interesting example of a Baltimore-based, family-owned niche business that existedfor 90 years, through three generations ofa singlefamily. The M.S. Levy and Sons story has two main chapters. The first covers the period from its founding by Michael Simon Levy in the 1870s through his son Julius’ death in 1926. This is the story of ascension. A premonition about the coming popularity of straw hats, together with a small but important technological breakthrough, positioned a family and a small industry for significant expansion. The second period began in 1930 with the introduction of wool felt hats and the death of William, M.S. Levy’s oldest son, and includes the Great Depression, unionization, merger, third generation leadership, and finally, in 1959, the family’s withdrawal from the industry. This later period, as told by grandsons of the founder, is the story of struggle followed by decline.

Dynamic Acquisition and Retrieval Tool (DART) for Comet Sample Return : Session: 2.06.Robotic Mobility and Sample Acquisition Systems

Science.gov (United States)

Badescu, Mircea; Bonitz, Robert; Kulczycki, Erick; Aisen, Norman; Dandino, Charles M.; Cantrell, Brett S.; Gallagher, William; Shevin, Jesse; Ganino, Anthony; Haddad, Nicolas;

Ensemble Properties of Comets in the Sloan Digital Sky Survey

Energy Technology Data Exchange (ETDEWEB)

Solontoi, Michael; /Adler Planetarium, Chicago; Ivezic, Zeljko; /Washington U., Seattle, Astron. Dept.; Juric, Mario; /Harvard Coll. Observ.; Becker, Andrew C.; /Washington U., Seattle, Astron. Dept.; Jones, Lynne; /Washington U., Seattle, Astron. Dept.; West, Andrew A.; /Boston U.; Kent, Steve; /Fermilab; Lupton, Robert H.; /Princeton U. Observ.; Claire, Mark; /Washington U., Seattle, Astron. Dept.; Knapp, Gillian R.; /Princeton U. Observ.; Quinn, Tom; /Washington U., Seattle, Astron. Dept. /Princeton U. Observ.

2012-02-01

We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u, g, r, i, z) photometry is used to determine the comets colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afp formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(comets. The resolved comets show an extremely narrow distribution of colors (0.57 {+-} 0.05 in g - r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.

Primo Levi and Ivan Denisovič: The Literary Act between Representation and Expressive Capacity

Directory of Open Access Journals (Sweden)

Pietro Tosco

2011-11-01

Full Text Available Se questo è un uomo di Primo Levi e Una giornata di Ivan Denisovič di Aleksandr Solženicyn sono due “atti letterari” che hanno contribuito in modo significativo alla conoscenza storica del XX secolo: il primo nell’Occidente dei campi di concentramento nazisti, il secondo nell’Oriente del Gulag. Perché sono così famosi? C’è qualcosa che li accomuna? Questo saggio si propone di analizzare la forza della letteratura come luogo di conoscenza e autocoscienza. Se le opere di Levi e Solženicyn hanno un grande valore come testimonianze, in esse la forza della testimonianza è data dal “gesto letterario” che le ha create, un gesto che produce una conoscenza sintetica in cui gli universali esistono solo nel particolare.

Comet 67P Through the Lens of Art

Science.gov (United States)

Smirnova, Ekaterina

2017-04-01

My proposal is to share my artistic exploration of a comet through the bodily senses, while finding inspiration in scientific data. I will present my artwork as a slideshow, showcasing: large scale paintings, ceramic sculptures, music and interactive augmented reality. The Rosetta mission of the European Space Agency (ESA) to comet 67P/ Churyumov-Gerasimenko is remarkable. The scientific investigation of the comet's composition, atmosphere, dust, vapor, surface and internal structure are crucial to help researchers understand the origin of the solar system and our own planet. Sight: Paintings Rosetta mission discovered that the water on the comet is different from the water on Earth; as measured with the ROSINA-DFMS instrument on Rosetta, water on 67P contains approximately 3 times more hydrogen­deuterium oxide - HDO, than found in Earth's oceans. In the art studio I re-create water that is close in composition to the water on the comet, by concentrating the level of HDO. With this water I paint large scale watermedia paintings, based on the photographs by Rosetta (OSIRIS, Nav. Cam.). Touch: Sculptures While exploring the comet's three-dimensional form, I focus more deeply on the composition of the comet. Stoneware clay and my choice of a glaze both include iron oxide, a common constituent of meteorites and comets. Hearing: Music An audio piece "A Singing Comet", by Manuel Senfft, based on the Rosetta Plasma Consortium data, inspired me to make a musical piece. In collaboration with clarinetist Lee Mottram (Wales) and composer Takuto Fukuda (Japan) we created an electro­acoustic composition in which we tell the story of comets visiting our Solar System, repeating their cycle, curving around the sun and releasing water, carrying away dust to form their tails. Smell In collaboration with The Open University, UK, postcards with a smell of the comet were created, introducing the chemical components of the comet. The smell was recreated by combining several molecules

The Deep Impact Coma of Comet 9P/Tempel 1 as a Time-of-Flight Experiment Motivates DDSCAT Models for Porous Aggregate Grains with Silicate Crystal Inclusions

Science.gov (United States)

Wooden, Diane H.; Lindsay, S. S.; Harker, D. E.; Kelley, M. S.; Woodward, C. E.; Richard, D. T.; Kolokolova, L.; Moreno, F.

2010-10-01

Spitzer IRS spectra of short-period Ecliptic Comets (ECs) have silicate features, and many have distinct crystalline silicate peaks. These Spitzer spectra, when fitted with thermal models after subtraction of the relatively strong contribution of the nuclear flux to the IR spectrum (e.g., Harker et al. 2007), demonstrate ECs have weaker silicate features than long-period Nearly-Isotropic Comets (NICs). There are exceptions, however, as some NICs also have weak features like most ECs. Grains with lower porosities (lower fraction of vacuum) can explain weaker silicate features (Kelley and Wooden 2009; Kolokolova et al. 2007). Alternatively, omitting the smallest (submicron) solid grains can reduce the contrast of the silicate feature (Lisse et al. 2006). However, so far, only models for solid submicron crystals fit the crystalline peaks in spectra of comets with weak silicate features. This presents a dilemma: how can the coma be devoid of small grains except for the crystals? The Spitzer spectra of the Deep Impact event with EC 9P/Tempel 1 provides a data set to model larger porous grains with crystal inclusions because the post-impact coma was a time-of-flight experiment: an impulsive release of grains were size-sorted in time by their respective gas velocities so that the smaller grains departed the inner coma quicker than larger grains. A velocity law derived from fitting small beam Gemini spectra (Harker et al. 2007) indicates that at 20 hour post-impact the (pre-impact subtracted) Spitzer IRS spectrum contained grains larger than 10-20 micron radii, moving at 20 m/s, that produced a weak silicate feature with an 11.2 micron crystalline olivine peak. Furthermore, this feature looks like the silicate feature from the nominal coma. We present some results of a computational effort to model discrete crystals and mixed-mineral porous aggregate grains with silicate crystal inclusions using DDSCAT on the NAS Pleiades supercomputer.

Tight Error Bounds for Fourier Methods for Option Pricing for Exponential Levy Processes

KAUST Repository

Crocce, Fabian; Hä ppö lä , Juho; Keissling, Jonas; Tempone, Raul

2016-01-01

for the discontinuities in the asset price. The Levy -Khintchine formula provides an explicit representation of the characteristic function of a L´evy process (cf, [6]): One can derive an exact expression for the Fourier transform of the solution of the relevant PIDE

Migration of Interplanetary Dust and Comets

Science.gov (United States)

Ipatov, S. I.; Mather, J. C.

Our studies of migration of interplanetary dust and comets were based on the results of integration of the orbital evolution of 15,000 dust particles and 30,000 Jupiter-family comets (JFCs) [1-3]. For asteroidal and cometary particles, the values of the ratio β between the radiation pressure force and the gravitational force varied from 1000 and 1 microns. The probability of a collision of a dust particle started from an asteroid or JFC with the Earth during a lifetime of the particle was maximum at diameter d ˜100 microns. For particles started from asteroids and comet 10P, this maximum probability was ˜0.01. Different studies of migration of dust particles and small bodies testify that the fraction of cometary dust particles of the overall dust population inside Saturn's orbit is considerable and can be dominant: (1) Cometary dust particles produced both inside and outside Jupiter's orbit are needed to explain the observed constant number density of dust particles at 3-18 AU. The number density of migrating trans-Neptunian particles near Jupiter's orbit is smaller by a factor of several than that beyond Saturn's orbit. Only a small fraction of asteroidal particles can get outside Jupiter's orbit. (2) Some (less than 0.1%) JFCs can reach typical near-Earth object orbits and remain there for millions of years. Dynamical lifetimes of most of the former JFCs that have typical near-Earth object orbits are about 106 -109 yr, so during most of these times they were extinct comets. Such former comets could disintegrate and produce a lot of mini-comets and dust. (3) Comparison of the velocities of zodiacal dust particles (velocities of MgI line) based on the distributions of particles over their orbital elements obtained in our runs [3-4] with the velocities obtained at the WHAM observations shows that only asteroidal dust particles cannot explain these observations, and particles produced by comets, including high-eccentricity comets, are needed for such explanation

On the existence of a comet belt beyond Neptune

International Nuclear Information System (INIS)

Fernandez, J.A.

1980-01-01

The possible existence of a comet belt in connection with the origin of the short-period comets is analysed. It is noted that the current theory - that these comets originate as near-parabolic comets captured by Jupiter and the other giant planets - implies an excessive wastage of comets lost in hyperbolic orbits, which is avoided in the present model. The following picture is predicted. Solid conglomerates up to approximately 10 18 g were formed by gravitational instabilities in the belt region (about 35 to 50 AU). A further fragmentation-accretion process led to a power-law mass distribution similar to that observed in the asteroids. Since then, close encounters between members of the belt have provoked the diffusion of some of them with the effect that they have become subject to the strong perturbations of Neptune. Of these a small number pass from one planet to the next inside and end as short-period comets. By means of a Monte Carlo method, the influence of close encounters between belt comets is then studied in relation to the diffusion of their orbits. It is concluded that if such a belt contains members with masses equal to or greater than that of Ceres, the orbital diffusion could proceed fast enough to maintain the number of observed short-period comets in a steady state. (author)

CATASTROPHIC DISRUPTION OF COMET ISON

Energy Technology Data Exchange (ETDEWEB)

Keane, Jacqueline V.; Kleyna, Jan T.; Riesen, Timm-Emmanuel; Meech, Karen J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Milam, Stefanie N.; Charnley, Steven B. [Astrochemistry Laboratory, NASA GSFC, MS 690, Greenbelt, MD 20771 (United States); Coulson, Iain M. [Joint Astronomy Center, 660 North Aohoku Place, Hilo, HI 96720 (United States); Sekanina, Zdenek [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Kracht, Rainer, E-mail: keane@ifa.hawaii.edu [Ostlandring 53, D-25335 Elmshorn, Schleswig-Holstein (Germany)

2016-11-10

We report submillimeter 450 and 850 μ m dust continuum observations for comet C/2012 S1 (ISON) obtained at heliocentric distances 0.31–0.08 au prior to perihelion on 2013 November 28 ( r {sub h} = 0.0125 au). These observations reveal a rapidly varying dust environment in which the dust emission was initially point-like. As ISON approached perihelion, the continuum emission became an elongated dust column spread out over as much as 60″ (>10{sup 5} km) in the anti-solar direction. Deconvolution of the November 28.04 850 μ m image reveals numerous distinct clumps consistent with the catastrophic disruption of comet ISON, producing ∼5.2 × 10{sup 10} kg of submillimeter-sized dust. Orbital computations suggest that the SCUBA-2 emission peak coincides with the comet's residual nucleus.

Evolution of comets into asteroids

International Nuclear Information System (INIS)

Weissman, P.R.; A'hearn, M.F.; Rickman, H.; Mcfadden, L.A.

1989-01-01

This paper presents observational evidence, together with recent theoretical developments, supporting the hypothesis that at least some asteroids might be extinct or dormant cometary nuclei. The observations include the discovery of a number of apparent asteroids in chaotic Jupiter-crossing orbits; the IRAS discovery of 1983 TB, an asteroid in the same orbit as the Geminid meteor shower; the apparent low activity levels determined for several short-period comet nuclei including Comet Halley; and observations of possible cometary activity in some earth-crossing asteroids. Theoretical developments include explorations of dynamical mechanisms capable of delivering main-belt asteroids into earth-crossing orbits, and an understanding of possible processes which may affect comets during their long residence in the Oort cloud and lead to the formation of nonvolatile crusts before and after they enter the planetary system. 143 refs

Comet showers and Nemesis, the death star

International Nuclear Information System (INIS)

Hills, J.G.

1984-01-01

The recently proposed hypothesis that the periodic extinctions of terrestrial species are the result of comet showers catalyzed by a hypothetical distant solar companion, Nemesis, a tale of global death by comet bombardment of the earth, is discussed

Comments on comet shapes and aggregation processes

International Nuclear Information System (INIS)

Hartmann, W.K.

1989-01-01

An important question for a comet mission is whether comet nuclei preserve information clarifying aggregation processes of planetary matter. New observational evidence shows that Trojan asteroids, as a group, display a higher fraction of highly-elongated objects than the belt. More recently evidence has accumulated that comet nuclei, as a group, also display highly-elongated shapes at macro-scale. This evidence comes from the several comets whose nuclear lightcurves or shapes have been well studied. Trojans and comet nuclei share other properties. Both groups have extremely low albedos and reddish-to neutral-black colors typical of asteroids of spectral class D, P, and C. Both groups may have had relatively low collision frequencies. An important problem to resolve with spacecraft imaging is whether these elongated shapes are primordial, or due to evolution of the objects. Two hypotheses that might be tested by a combination of global-scale and close-up imaging from various directions are: (1) The irregular shapes are primordial and related to the fact that these bodies have had lower collision frequencies than belt asteroids; or (2) The irregular shapes may be due to volatile loss

New Application of the Comet Assay

Science.gov (United States)

Cortés-Gutiérrez, Elva I.; Dávila-Rodríguez, Martha I.; Fernández, José Luís; López-Fernández, Carmen; Gosálbez, Altea; Gosálvez, Jaime

2011-01-01

The comet assay is a well-established, simple, versatile, visual, rapid, and sensitive tool used extensively to assess DNA damage and DNA repair quantitatively and qualitatively in single cells. The comet assay is most frequently used to analyze white blood cells or lymphocytes in human biomonitoring studies, although other cell types have been examined, including buccal, nasal, epithelial, and placental cells and even spermatozoa. This study was conducted to design a protocol that can be used to generate comets in subnuclear units, such as chromosomes. The new technique is based on the chromosome isolation protocols currently used for whole chromosome mounting in electron microscopy, coupled to the alkaline variant of the comet assay, to detect DNA damage. The results show that migrant DNA fragments can be visualized in whole nuclei and isolated chromosomes and that they exhibit patterns of DNA migration that depend on the level of DNA damage produced. This protocol has great potential for the highly reproducible study of DNA damage and repair in specific chromosomal domains. PMID:21540337

Comet LINEAR C/1999 S4 - an absolutely well-behaved comet before breakup

Science.gov (United States)

Peschke, S. B.; Lisse, C. M.; Fernandez, Y. R.; Ressler, M.; Stickel, M.; Kaminski, C.; Golish, B.

2000-10-01

We present results from infrared imaging of comet LINEAR C/1999 S4 on June 17 - 19, 2000 (pre-breakup), using the near-IR camera NSFCAM and the mid-IR camera MIRLIN at the 3m NASA/IRTF. Images and multi-wavelength spectroscopy were obtained in the zJHK'L'MNQ bands, and were used to create a 1.0 - 25 μ m SED of the comet's dust and nucleus. The coma's contribution at each wavelength was modeled using spatial fitting (Fernandez 1999, PhD thesis; Lisse et al. 1999, Icarus 140, 189). The resulting comatic and nuclear SEDs were then modeled using modified Mie theory (Lisse et al. 1998, ApJ 496, 971) and the standard nuclear thermal models (Lebofsky and Spencer 1989, Asteroids II, 128), respectively. We report the resulting dust PSD, mass loss rate, and albedo, as well as the nuclear radius, and we compare these results to those obtained by others from optical data both before and after the comet's breakup in late July 2000.

The shortage of long-period comets in elliptical orbits

International Nuclear Information System (INIS)

Everhart, E.

1979-01-01

Based on the number of 'new' comets seen on near-parabolic orbits, one can predict the number of comets that should be found on definitely elliptical orbits on their subsequent returns. The author shows that about three out of four of these returning comets are not observed. (Auth.)

Assessment and reduction of comet assay variation in relation to DNA damage: studies from the European Comet Assay Validation Group

DEFF Research Database (Denmark)

Møller, Peter; Möller, Lennart; Godschalk, Roger W L

2010-01-01

The alkaline single cell gel electrophoresis (comet) assay has become a widely used method for the detection of DNA damage and repair in cells and tissues. Still, it has been difficult to compare results from different investigators because of differences in assay conditions and because the data...... are reported in different units. The European Comet Assay Validation Group (ECVAG) was established for the purpose of validation of the comet assay with respect to measures of DNA damage formation and its repair. The results from this inter-laboratory validation trail showed a large variation in measured level...... reliability for the measurement of DNA damage by the comet assay but there is still a need for further validation to reduce both assay and inter-laboratory variation....

Comet West: a view from the HELIOS zodiacal light photometers

International Nuclear Information System (INIS)

Benensohn, R.M.; Jackson, B.V.

1987-01-01

Comet West passed through perihelion on February 25, 1976. The comet crossed the HELIOS A and B spacecraft zodiacal light photometer fields of view as the spacecraft orbited the Sun, allowing them to record the brightness, polarization, and color of the comet and its surrounding interplanetary medium. Data from the U, B, and V photometers across the tail shows a distinct bluing followed by a slight reddening corresponding to the ion and dust tails, respectively, entering the field of view. The non-Earth perspective of the HELIOS photometers allows a comparison of the tail with Earth observations at the same time. Precise location of the nucleus and tail allow the photometer data to be searched for evidence of the comet bow shock and orbital dust. A brightness bump present in the data before the comet reaches some photometer positions, can be shown to approximately form a parabolic shape Sunward and ahead of the orbital motion of the Comet West nucleus. If this is the comet bow shock or bow compression, then it corresponds to a density enhancement of the ambient medium by 1.5 to 2 times in the vicinity of the comet. The distance of the brightness increase from the nucleus by comparison with Comet Halley implies a neutral gas production rate of approximately 3 times that of Halley

Photometry and imaging of Comet 103P/Hartley in the 2010-2011 apparition

Czech Academy of Sciences Publication Activity Database

Milani, G.; Bryssinck, E.; Nicolini, M.; Mikuž, H.; Sostero, G.; Bacci, P.; Borghini, W.; Castellano, D.; Facchini, M.C.; Favero, G.; Galli, G.; Guidou, E.; Hausler, B.; Hornoch, Kamil; Howes, N.; Ligustri, R.; Perrella, C.; Prosperi, E.; Skvarc, J.; Srba, J.; Trabatti, R.; Vinante, C.; Szabo, G.

2013-01-01

Roč. 222, č. 2 (2013), s. 786-798 ISSN 0019-1035 R&D Projects: GA ČR GA205/09/1107 Institutional support: RVO:67985815 Keywords : comet s * dust * photometry Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.840, year: 2013

The Rosetta Mission to Comet 67P/ Churyumov-Gerasimenko

Science.gov (United States)

Buratti, Bonnie J.

2017-06-01

As remnant bodies left over from the formation of the Solar System, comets offer clues to the physical conditions and architecture of the protosolar nebula. The Rosetta spacecraft, which included an orbiter and a lander that were built and managed by the European Space Agency with NASA contributing four instruments and scientific expertise, was the first mission to orbit and study a comet through a perihelion passage. The targeted Jupiter-family comet 67P/ Churyumov-Gerasimenko, is seemingly two distinct planetesimals stuck together. The comet has not melted or been processed substantially, except for its outer layers, which consist of reaccreted dust and a crust of heated, devolatized, and annealed refractory materials and organics. The exceptionally low density (0.53 gm/cc) of 67P/ implies it is a rubble pile. The comet also appears to contain a hierarchy of building blocks: smaller spherically shaped meter-sized bodies can be seen in its interior, and even smaller cm-sized pebbles were imaged by the camera as the spacecraft made a soft crash landing on the comet’s surface on 30 September 2016. The unexpected discovery of molecular oxygen, nitrogen, and hydrogen imply that 67P/ was formed under cold conditions not exceeding 30K. The discovery of many organic compounds, including the amino acid glycine, lends support to the idea that comets, which originate in the Kuiper Belt and the Oort Cloud, brought the building blocks of life to Earth. More laboratory data on organic compounds would help to identify additional organic compounds on the comet. The differences between cometary and terrestrial D/H ratios suggest that comets are not the primary source of terrestrial water, although data on more comets is needed to confirm this result.Besides being primordial objects offering a window into the formation of solar systems, comets are astrophysical laboratories, ejecting dust and charged particles into the plasma comprising the solar wind. Several unusual phenomena

The comet rendezvous asteroid flyby mission

International Nuclear Information System (INIS)

Morrison, D.; Neugebauer, M.; Weissman, P.R.

1989-01-01

The Comet Rendezvous Asteroid Flyby (CRAF) mission is designed to answer the many questions raised by the Halley missions by exploring a cometary nucleus in detail, following it around its orbit and studying its changing activity as it moves closer to and then away from the Sun. In addition, on its way to rendezvous with the comet, CRAF will fly by a large, primitive class main belt asteroid and will return valuable data for comparison with the comet results. The selected asteroid is 449 Hamburga with a diameter of 88 km and a surface composition of carbonaceous chondrite meteorites. The expected flyby date is January, 1998. The CRAF spacecraft will continue to make measurements in orbit around the cometary nucleus as they both move closer to the Sun, until the dust and gas hazard becomes unsafe. At that point the spacecraft will move in and out between 50 and 2,500 kilometers to study the inner coma and the cometary ionosphere, and to collect dust and gas samples for onboard analysis. Following perihelion, the spacecraft will make a 50,000 km excursion down the comet's tail, further investigating the solar wind interaction with the cometary atmosphere. The spacecraft will return to the vicinity of the nucleus about four months after perihelion to observe the changes that have taken place. If the spacecraft remains healthy and adequate fuel is still onboard, an extended mission to follow the comet nucleus out to aphelion is anticipated

Hummingbird Comet Nucleus Analysis Mission

Science.gov (United States)

Kojiro, Daniel; Carle, Glenn C.; Lasher, Larry E.

2000-01-01

Hummingbird is a highly focused scientific mission, proposed to NASA s Discovery Program, designed to address the highest priority questions in cometary science-that of the chemical composition of the cometary nucleus. After rendezvous with the comet, Hummingbird would first methodically image and map the comet, then collect and analyze dust, ice and gases from the cometary atmosphere to enrich characterization of the comet and support landing site selection. Then, like its namesake, Hummingbird would carefully descend to a pre-selected surface site obtaining a high-resolution image, gather a surface material sample, acquire surface temperature and then immediately return to orbit for detailed chemical and elemental analyses followed by a high resolution post-sampling image of the site. Hummingbird s analytical laboratory contains instrumentation for a comprehensive molecular and elemental analysis of the cometary nucleus as well as an innovative surface sample acquisition device.

HT-COMET: a novel automated approach for high throughput assessment of human sperm chromatin quality

Science.gov (United States)

Albert, Océane; Reintsch, Wolfgang E.; Chan, Peter; Robaire, Bernard

2016-01-01

-manual analysis software. Using this method, a cross-sectional study on 123 men showed no significant correlation between sperm concentration and sperm DNA damage, confirming the existence of hidden chromatin damage in men with apparently normal semen characteristics, and a significant correlation between percentage DNA in the tail and percentage of progressively motile spermatozoa. Finally, the use of DNA damage profiles helped to distinguish subjects between and within sperm concentration categories, and allowed a determination of the proportion of highly damaged cells. LIMITATIONS, REASONS FOR CAUTION The main limitations of the HT-COMET are the high, yet indispensable, investment in an automated liquid handling system and heating block to ensure accuracy, and the availability of an automated plate reading microscope and analysis software. WIDER IMPLICATIONS OF THE FINDINGS This standardized HT-COMET assay offers many advantages, including higher accuracy and evenness due to automation of sensitive steps, a 14.4-fold increase in sample analysis capacity, and an imaging and scoring time of 1 min/well. Overall, HT-COMET offers a decrease in total experimental time of more than 90%. Hence, this assay constitutes a more efficient option to assess sperm chromatin quality, paves the way to using this assay to screen large cohorts, and holds prognostic value for infertile patients. STUDY FUNDING/COMPETING INTEREST(S) Funded by the CIHR Institute of Human Development, Child and Youth Health (IHDCYH; RHF 100625). O.A. is a fellow supported by the Fonds de la Recherche du Québec - Santé (FRQS) and the CIHR Training Program in Reproduction, Early Development, and the Impact on Health (REDIH). B.R. is a James McGill Professor. The authors declare no conflicts of interest. PMID:26975326

Rocket Detection of Argon in Comet Hale-Bopp

Science.gov (United States)

Stern, S. A.; Festou, M. C.; Parker, J. Wm.; Slater, D. C.; Gladstone, G. R.; A'Hearn, M. F.

1998-12-01

The EUVS planetary sounding rocket spectrograph was flown on 30.2 March 1997 (UT) from White Sands, New Mexico to observe comet Hale-Bopp in the bandpass from 830--1120 A. At the time of launch the comet was near perihelion, 0.915 AU from the Sun, 1.340 AU from Earth, and traveling at a heliocentric radial velocity of +0.70 km/s. EUVS obtained its primary spectra of the comet at resolution near 12 A, collecting 9340 counts over approximately 330 seconds of integration time. To our knowledge, the resulting dataset is both the most sensitive and the highest spectral resolution probe of a comet in the UV below 1200 A as yet achieved, and contains signatures of both the 1048.2 A and 1066.7 A Ar I resonance lines. These features represent the first-ever detections of any noble gas in a comet. The spectrum also includes significant detections which we tentatively attribute to due to 834 A 0 II, 972 A Lyman gamma, 989 A O I, the 1026 A H I Lyman beta/O I. We will discuss the Ar features, retrieve the Ar column in the coma, and discuss the implications of the total Ar/O abundance ratio in Hale-Bopp for the comet's origin.

A Multi-Verse Optimizer with Levy Flights for Numerical Optimization and Its Application in Test Scheduling for Network-on-Chip.

Directory of Open Access Journals (Sweden)

Cong Hu

Full Text Available We propose a new meta-heuristic algorithm named Levy flights multi-verse optimizer (LFMVO, which incorporates Levy flights into multi-verse optimizer (MVO algorithm to solve numerical and engineering optimization problems. The Original MVO easily falls into stagnation when wormholes stochastically re-span a number of universes (solutions around the best universe achieved over the course of iterations. Since Levy flights are superior in exploring unknown, large-scale search space, they are integrated into the previous best universe to force MVO out of stagnation. We test this method on three sets of 23 well-known benchmark test functions and an NP complete problem of test scheduling for Network-on-Chip (NoC. Experimental results prove that the proposed LFMVO is more competitive than its peers in both the quality of the resulting solutions and convergence speed.

SOHO/SWAN OBSERVATIONS OF SHORT-PERIOD SPACECRAFT TARGET COMETS

International Nuclear Information System (INIS)

Combi, M. R.; Lee, Y.; Patel, T. S.; Maekinen, J. T. T.; Bertaux, J.-L.; Quemerais, E.

2011-01-01

SWAN, the Solar Wind ANisotropies all-sky hydrogen Lyα camera on the Solar and Heliospheric Observatory spacecraft that makes all-sky images of interplanetary neutral hydrogen, has an ongoing campaign to make special observations of comets, both short- and long-period ones, in addition to the serendipitous observations of comets as part of the all-sky monitoring program. We report here on a study of several short-period comets that were detected by SWAN: 21P/Giacobini-Zinner (1998 and 2005 apparitions), 19P/Borrelly (2001 apparition), 81P/Wild 2 (1997 apparition), and 103P/Hartley 2 (1997 apparition). SWAN observes comets over long continuous stretches of their visible apparitions and therefore provides excellent temporal coverage of the water production. For some of the observations we are also able to analyze an entire sequence of images over many days to several weeks/months using our time-resolved model and extract daily average water production rates over continuous periods of several days to months. The short-term (outburst) and long-term behavior can be correlated with other observations. The overall long-term variation is examined in light of seasonal effects seen in the pre- to post-perihelion differences. For 21P/Giacobini-Zinner and 81P/Wild 2 the activity variations over each apparition were more continuously monitored but nonetheless consistent with previous observations. For 19P/Borrelly we found a very steep variation of water production rates, again consistent with some previous observations, and a variation over six months around perihelion that was reasonably consistent with the spin-axis model of Schleicher et al. and the illumination of the main active areas. During the 1997-1998 apparition of 103P/Hartley 2, the target comet of the EPOXI mission (the Deep Impact extended mission), we found a variation with heliocentric distance (∼r -3.6 ) that was almost as steep as 19P/Borrelly and, given the small measured radius near aphelion, this places

Outbursting comet P/2010 V1 (Ikeya-Murakami): A miniature comet Holmes

Energy Technology Data Exchange (ETDEWEB)

Ishiguro, Masateru [Department of Physics and Astronomy, Seoul National University, Gwanak, Seoul 151-742 (Korea, Republic of); Jewitt, David [Department of Earth, Planetary and Space Sciences, University of California at Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095-1567 (United States); Hanayama, Hidekazu; Miyaji, Takeshi; Fukushima, Hideo; Watanabe, Jun-ichi [Ishigakijima Astronomical Observatory, National Astronomical Observatory of Japan, Ishigaki, Okinawa 907-0024 (Japan); Usui, Fumihiko [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Sekiguchi, Tomohiko [Department of Teacher Training, Hokkaido University of Education, 9 Hokumon, Asahikawa 070-8621 (Japan); Yanagisawa, Kenshi; Kuroda, Daisuke [Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asaguchi, Okayama 719-0232 (Japan); Yoshida, Michitoshi [Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Ohta, Kouji [Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan); Kawai, Nobuyuki [Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)

2014-05-20

The short-period comet P/2010 V1 (Ikeya-Murakami, hereafter {sup V}1{sup )} was discovered visually by two amateur astronomers. The appearance of the comet was peculiar, consisting of an envelope, a spherical coma near the nucleus and a tail extending in the anti-solar direction. We investigated the brightness and the morphological development of the comet by taking optical images with ground-based telescopes. Our observations show that V1 experienced a large-scale explosion between UT 2010 October 31 and November 3. The color of the comet was consistent with the Sun (g' – R {sub C} = 0.61 ± 0.20, R {sub C} – I {sub C} = 0.20 ± 0.20, and B – R {sub C} = 0.93 ± 0.25), suggesting that dust particles were responsible for the brightening. We used a dynamical model to understand the peculiar morphology, and found that the envelope consisted of small grains (0.3-1 μm) expanding at a maximum speed of 500 ± 40 m s{sup –1}, while the tail and coma were composed of a wider range of dust particle sizes (0.4-570 μm) and expansion speeds 7-390 m s{sup –1}. The total mass of ejecta is ∼5 × 10{sup 8} kg and kinetic energy ∼5 × 10{sup 12} J. These values are much smaller than in the historic outburst of 17P/Holmes in 2007, but the energy per unit mass (1 × 10{sup 4} J kg{sup –1}) is comparable. The energy per unit mass is about 10% of the energy released during the crystallization of amorphous water ice suggesting that crystallization of buried amorphous ice can supply the mass and energy of the outburst ejecta.

The Comet Assay: Tails of the (Unexpected. Use of the comet assay in pharmaceutical development.

Directory of Open Access Journals (Sweden)

Bas-jan Van Der Leede

2015-08-01

Full Text Available In genotoxicity testing of pharmaceuticals the rodent alkaline comet assay is being increasingly used as a second in vivo assay in addition to the in vivo micronucleus assay to mitigate in vitro positive results as recommended by regulatory guidance. In this presentation we want to give insight into the circumstances in vivo comet assay is deployed in a Genetic Toxicology Department of a pharmaceutical company. As the in vivo comet assay is a salvage assay, it means that some events have occurred in an in vitro assay and that the compound (or metabolite responsible for this signal is potentially deselected for further development. More than often the decision to perform an in vivo comet assay is at a very early stage in development and the first time that the compound will be tested in vivo at high/toxic dose levels. As almost no toxicokinetic data and tissue distribution data are available a careful design with maximizes the chances for successful mitigation is necessary. Decisions on acute or repeated dosing need to be made and arrangements for combining the in vivo comet assay with the in vivo micronucleus assay are to be considered. Often synthesis methods need to be scaled up fast to provide the required amount of compound and information on suitable formulations needs to be in place. As exposure data is crucial for interpretation of results, analytical methods need to be brought in place rapidly. An experienced multi skilled and communicative team needs to be available to deploy successfully this kind of assays at an early stage of development. We will present a few scenarios on study conduct and demonstrate how this assay can make a difference for the further development of a new drug.

Time-dependent injection of Oort Cloud comets into earth-crossing orbits

International Nuclear Information System (INIS)

Fernandez, J.A.; Ip, W.H.; Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau, West Germany)

1987-01-01

The present consideration of close stellar encounter-induced modulations of the influx rate of Oort Cloud comets notes that comet showers sufficiently intense for emergence in cratering statistics are produced at 80-Myr intervals, on the assumption of an Oort Cloud heavy comet core. Numerical simulations of the time evolution of comet showers or bursts indicate that a long tail of residual shower comets follows the major event with an intensity of about 0.01 of the peak rate after 20-30 Myr, thereby suggesting that residual comet showers are primarily clustered in certain areas of the sky, rendering them observable at virtually any time. 33 references

Dynamical evolution and disintegration of comets

Science.gov (United States)

Kresak, L.

Current concepts of the origin and evolution of comets are reviewed. The place of their formation from which they have been delivered into the Oort reservoir is still an open problem, but the region of the outermost planets appears most probable. The interplay of stellar and planetary perturbations can be traced by model computations which reveal both the general trends and the variety of individual evolutionary paths. The present structure of the system of comets is controlled by the dynamical evolution of its individual members, limited by their physical aging by disintegration. Where the lifetimes are short, as in the Jupiter family of short-period comets, an equilibrium between elimination and replenishment is established. The role of different destructive processes and the resulting survival times are discussed.

Observations of faint comets at McDonald Observatory: 1978-1980

Science.gov (United States)

Barker, E. S.; Cochran, A. L.; Rybski, P. M.

1981-01-01

Modern observational techniques, developed for spectroscopy and photometry of faint galaxies and quasars, successfully applied to faint comets on the 2.7 m telescope. The periodic comets Van Biesbrock, Ashbrook-Jackson, Schwassmann-Wachmann 1, Tempel 2, Encke, Forbes, Brooks 2, Stephan-Oterma and the new comets Bradfield (19791), Bowell (1980b), Chernis-Petrauskas (1980k) were observed. The comets ranged in magnitude from 10th to 20th magnitude. For comets fainter than 19th magnitude, reflectance spectra at 100A resolution and area photometry were obtained. On comets of 17th or 18th magnitude, spectrometric scans (6A resolution) of the nucleus or inner coma region. On those comets which are brighter than 16th magnitude spatial spectrophotometric (6A resolution) studies of the inner and extended comae were done. An extensive spatial study of the comae of P/Encke and P/Stephen-Oterma, correlated with heliocentric distance is taking place. The observing process used is described and examples of the results obtained to date are discussed.

Primo Levi and the Periodic Table: Teaching Chemistry Using A Literary Text (Excerpt)

Science.gov (United States)

Osorio, Viktoria Klara Lakatos; Tiedemann, Peter Wilhelm; Porto, Paulo Alves

2007-01-01

The excerpts from The Periodic Table book written by Primo Levi is discussed related to chemical concepts. The use of a literary text as a starting point of discussions of chemical concepts has allowed the integration of various topics covered in separate courses of the undergraduate program in chemistry.

The Composition of Comet C/2012 K1 (PanSTARRS) and the Distribution of Primary Volatile Abundances Among Comets

Energy Technology Data Exchange (ETDEWEB)

Roth, Nathan X.; Gibb, Erika L. [Department of Physics and Astronomy, University of Missouri-St. Louis, 503 Benton Hall, One University Blvd., St. Louis, MO 63121 (United States); Bonev, Boncho P.; DiSanti, Michael A.; Mumma, Michael J.; Villanueva, Geronimo L.; Paganini, Lucas, E-mail: nxrq67@mail.umsl.edu [Goddard Center for Astrobiology, NASA Goddard Space Flight Center, Mail Stop 690, Greenbelt, MD 20771 (United States)

2017-04-01

On 2014 May 22 and 24 we characterized the volatile composition of the dynamically new Oort cloud comet C/2012 K1 (PanSTARRS) using the long-slit, high resolution ( λ /Δ λ  ≈ 25,000) near-infrared echelle spectrograph (NIRSPEC) at the 10 m Keck II telescope on Maunakea, Hawaii. We detected fluorescent emission from six primary volatiles (H{sub 2}O, HCN, CH{sub 4}, C{sub 2}H{sub 6}, CH{sub 3}OH, and CO). Upper limits were derived for C{sub 2}H{sub 2}, NH{sub 3}, and H{sub 2}CO. We report rotational temperatures, production rates, and mixing ratios (relative to water). Compared with median abundance ratios for primary volatiles in other sampled Oort cloud comets, trace gas abundance ratios in C/2012 K1 (PanSTARRS) for CO and HCN are consistent, but CH{sub 3}OH and C{sub 2}H{sub 6} are enriched while H{sub 2}CO, CH{sub 4}, and possibly C{sub 2}H{sub 2} are depleted. When placed in context with comets observed in the near-infrared to date, the data suggest a continuous distribution of abundances of some organic volatiles (HCN, C{sub 2}H{sub 6}, CH{sub 3}OH, CH{sub 4}) among the comet population. The level of “enrichment” or “depletion” in a given comet does not necessarily correlate across all molecules sampled, suggesting that chemical diversity among comets may be more complex than the simple organics-enriched, organics-normal, and organics-depleted framework.

Disintegration phenomena in Comet West

Science.gov (United States)

Sekanina, Z.

1976-01-01

Two peculiarities of Comet West, the multiple splitting of the nucleus as seen in telescope observations and the complex structure of the dust tail, are discussed. A method of analysis based on the premise that the observed rate of separation of a fragment from the principal nucleus is determined by the difference in effective solar attraction acting on the bodies is applied to investigate the motion of the four fragments that separated from the nucleus of Comet West. The predicted motion of the fragments is in good agreement with available observations. It is suggested that the 'synchronic' bands of the dust tail consist of tiny fragments from relatively large particles that burst after release from the comet. The unusual orientation of these bands and their high surface brightness relative to the diffuse tail are explained by a sudden increase in the particle acceleration and in the total scattering surface as the result of the disintegration of the larger particles.

Origin of comets - implications for planetary formation

International Nuclear Information System (INIS)

Weissman, P.R.; Arizona Univ., Tucson)

1985-01-01

Primordial and episodic theories for the origin of comets are discussed. The implications of the former type for the origin of the solar system are considered. Candidate sites for the formation of comets are compared. The possible existence of a massive inner Oort cloud is discussed

LEVIS active anode lithium ion source development on PBFA-II

International Nuclear Information System (INIS)

Renk, T.J.; Tisone, G.C.; Adams, R.G.; Clark, B.F.; Reyes, C.; Bailey, J.E.; Filuk, A.B.; Desjarlais, M.P.; Johnson, D.J.; Carlson, A.L.; Lake, P.

1993-01-01

Experiments are ongoing on the PBFA-II Accelerator (10 MV typical, 50 ns) to optimize an active lithium ion source in a 15-cm focusing Applied-B ion diode using the LEVIS (Laser Evaporation Ion Source) process. Two laser pulses impinge on a thin (500 nm) Li or Li-bearing alloy on an insulating substrate. A Nd:YAG laser beam (1 μm, 8 ns, 0.1--0.2 J/cm 2 ) creates a thin (∼1 mm) Li vapor, which is then ionized by a 30--60 mJ/cm 2 dye laser tuned to the first resonant transition of Li (670.8 nm). In order to achieve a high-purity Li beam on PBFA-II with LEVIS, it has proven necessary to clean the anode surface in some way. The principal technique has been DC-heating of the anode to temperatures of 150--200 C for typically 5 hours, and for as long as 13 hours, prior to machine firing. Use of a LiAg alloy and YAG energy densities of 200 mJ/cm 2 have yielded beams of Li purity greater than 90%. They authors also plan to test a diode configuration that deposits Li in-situ on the anode surface just prior to the machine shot, as an alternative to DC-heating

Asteroid Family Associations of Main-Belt Comets

Science.gov (United States)

Hsieh, Henry H.; Novakovic, Bojan; Kim, Yoonyoung; Brasser, Ramon

2016-10-01

We present a population-level analysis of the asteroid family associations of known main-belt comets or main-belt comet candidates (which, to date, have largely just been analyzed on individual bases as they have been discovered). In addition to family associations that have already been reported in the literature, we have identified dynamical relationships between 324P/La Sagra and the Alauda family, P/2015 X6 (PANSTARRS) and the Aeolia family, and P/2016 G1 (PANSTARRS) and the Adeona family. We will discuss the overall implications of these family associations, particularly as they pertain to the hypothesis that members of primitive asteroid family members may be more susceptible to producing observable sublimation-driven dust emission activity, and thus becoming main-belt comets. We will also discuss the significance of other dynamical and physical properties of a family or sub-family as they relate to the likelihood of that family containing one or more currently active main-belt comets.

Learned modesty and the first lady's comet: a commentary on Caroline Herschel (1787) 'An account of a new comet'.

Science.gov (United States)

Winterburn, Emily

2015-04-13

Long before women were allowed to become Fellows of the Royal Society, or obtain university degrees, one woman managed to get her voice heard, her discovery verified and her achievement celebrated. That woman was Caroline Herschel, who, as this paper will discuss, managed to find ways to fit comet discoveries into her domestic life, and present them in ways that were socially acceptable. Caroline lived in a time when strict rules dictated how women (and men) should behave and present themselves and their work. Caroline understood these rules, and used them carefully as she announced each discovery, starting with this comet which she found in 1786. Caroline discovered her comets at a time when astronomers were mainly concerned with position, identifying where things were and how they were moving. Since her discoveries, research has moved on, as astronomers, using techniques from other fields, and most recently sending experiments into space, have learned more about what comets are and what they can tell us about our solar system. Caroline's paper marks one small, early step in this much bigger journey to understand comets. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

Influence of experimental conditions on data variability in the liver comet assay.

Science.gov (United States)

Guérard, M; Marchand, C; Plappert-Helbig, U

2014-03-01

The in vivo comet assay has increasingly been used for regulatory genotoxicity testing in recent years. While it has been demonstrated that the experimental execution of the assay, for example, electrophoresis or scoring, can have a strong impact on the results; little is known on how initial steps, that is, from tissue sampling during necropsy up to slide preparation, can influence the comet assay results. Therefore, we investigated which of the multitude of steps in processing the liver for the comet assay are most critical. All together eight parameters were assessed by using liver samples of untreated animals. In addition, two of those parameters (temperature and storage time of liver before embedding into agarose) were further investigated in animals given a single oral dose of ethyl methanesulfonate at dose levels of 50, 100, and 200 mg/kg, 3 hr prior to necropsy. The results showed that sample cooling emerged as the predominant influence factor, whereas variations in other elements of the procedure (e.g., size of the liver piece sampled, time needed to process the liver tissue post-mortem, agarose temperature, or time of lysis) seem to be of little relevance. Storing of liver samples of up to 6 hr under cooled conditions did not cause an increase in tail intensity. In contrast, storing the tissue at room temperature, resulted in a considerable time-dependent increase in comet parameters. Copyright © 2013 Wiley Periodicals, Inc.

The C-12/C-13 abundance ratio in Comet Halley

International Nuclear Information System (INIS)

Wyckoff, S.; Lindholm, E.; Wehinger, P.A.; Peterson, B.A.; Zucconi, J.M.

1989-01-01

The individual (C-13)N rotational lines in Comet Halley are resolved using high-resolution spectra of the CN B2Sigma(+)-X2Sigma(+) (0,0) band. The observe C-12/C-13 abundance ratio excludes a site of origin for the comet near Uranus and Neptune and suggests a condensation environment quite distinct from other solar system bodies. Two theories are presented for the origin of Comet Halley. One theory suggest that the comet originated 4.5 Gyr ago in an inner Oort cloud at a heliocentric distance greater than 100 AU where chemical fractionation led to the C-13 enrichment in the CN parent molecule prior to condensation of the comet nucleus. According to the other, more plausible theory, the comet nucleus condensed relatively recently from the interstellar medium which has become enriches in C-13 and was subsequently gravitationally captured by the solar system. 107 refs

On the nature of the Halley comet

International Nuclear Information System (INIS)

Dobrovol'skij, O.V.; Ioffe, Z.M.

1987-01-01

The results of study of the Halley comet by means of the ''Vega'', ''Suisej'', ''Sakigaki'' and ''Jotton'' space probes are presented in the popular form. The form and composition of the comet nucleus, its atmosphere and processes ocurring when moving in the near-the-solar space are described

The exploration of Halley's comet - An example of international cooperation

Science.gov (United States)

Rahe, Jurgen H.; Newburn, Ray L., Jr.

1987-01-01

The history of international cooperation in studies of comets started with observations in 1577 and 1680, when Tycho Brahe and Newton, respectively, collected position measurements made in different countries to determine the paths of the comets observed. In the fall of 1979, a worldwide Comet Halley watch was proposed. As a result of international cooperation, Comet Halley was explored during its recent appearance from the ground, earth orbit, Venus orbit, interplanetary space, and from within the comet itself. The various activities in space were coordinated by the ESA, the USSR Intercosmos, the Japanese ISAS, and NASA, through the Inter-Agency Consultative Group. The activities of the ground-based observers were coordinated by the International Halley Watch.

Efficient Option Pricing under Levy Processes, with CVA and FVA

Directory of Open Access Journals (Sweden)

Jimmy eLaw

2015-07-01

Full Text Available We generalize the Piterbarg (2010 model to include 1 bilateral default risk as in Burgard and Kjaer (2012, and 2 jumps in the dynamics of the underlying asset using general classes of L'evy processes of exponential type. We develop an efficient explicit-implicit scheme for European options and barrier options taking CVA-FVA into account. We highlight the importance of this work in the context of trading, pricing and management a derivative portfolio given the trajectory of regulations.

Dynamical evolution and disintegration of comets

International Nuclear Information System (INIS)

Kresak, L.

1982-01-01

Current concepts of the origin and evolution of comets are reviewed. The place of their formation from which they have been delivered into the Oort reservoir is still an open problem, but the region of the outermost planets appears most probable. The interplay of stellar and planetary perturbations can be traced by model computations which reveal both the general trends and the variety of individual evolutionary paths. The present structure of the system of comets is controlled by the dynamical evolution of its individual members limited by their physical aging by disintegration. Where the lifetimes are short, as in the Jupiter family of short-period comets, an equilibrium between elimination and replenishment is established. The role of different destructive processes and the resulting survival times are discussed. (Auth.)

Bangs and meteors from the quiet comet 15P/Finlay

Czech Academy of Sciences Publication Activity Database

Ye, Q.Z.; Brown, P. G.; Bell, Ch.; Gao, X.; Mašek, Martin; Hui, M.T.

2015-01-01

Roč. 814, č. 1 (2015), s. 1-10, č. článku 79. ISSN 0004-637X R&D Projects: GA MŠk(CZ) LG13007 EU Projects: European Commission(XE) 283783 - GLORIA Institutional support: RVO:68378271 Keywords : comet s * 15P/Finlay * meteorites * meteors * meteoroids Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.909, year: 2015

Alternatives to the EEG levy. Possible effects of a reform of the energy transition financing on the industry

International Nuclear Information System (INIS)

Scheyhing, Joerg

2017-01-01

Although it has been adjusted six times since the year 2000, it has not yet been possible to manage the unrestricted growth of the EEG levy. In the 2017 election year, it becomes therefore ever more obvious that an alternative way to finance the energy transition is high on the political agenda. This would lead to significant changes for energy-intensive companies, regardless of whether they have benefited from a release from the levy or not. At the same time, the alternatives currently discussed have quite different effects on the industrial companies concerned and thereby the industry location Germany. [de

AKARI NEAR-INFRARED SPECTROSCOPIC SURVEY FOR CO2 IN 18 COMETS

International Nuclear Information System (INIS)

Ootsubo, Takafumi; Kawakita, Hideyo; Hamada, Saki; Kobayashi, Hitomi; Yamaguchi, Mitsuru; Usui, Fumihiko; Nakagawa, Takao; Ueno, Munetaka; Ishiguro, Masateru; Sekiguchi, Tomohiko; Watanabe, Jun-ichi; Sakon, Itsuki; Shimonishi, Takashi; Onaka, Takashi

2012-01-01

We conducted a spectroscopic survey of cometary volatiles with the Infrared Camera on board the Japanese infrared satellite AKARI in the wavelength range from 2.5 to 5 μm. In our survey, 18 comets, including both the Oort cloud comets and the Jupiter-family comets, were observed in the period from 2008 June to 2010 January, most of which were observed at least twice. The prominent emission bands in the observed spectra are the fundamental vibrational bands of water (H 2 O) at 2.7 μm and carbon dioxide (CO 2 ) at 4.3 μm. The fundamental vibrational band of carbon monoxide (CO) around 4.7 μm and the broad emission feature, probably related to carbon-hydrogen-bearing molecules, can also be recognized around the 3.3-3.5-μm region in some of the comets. With respect to H 2 O, gas production rate ratios of CO 2 have been derived in 17 comets, except for the comet 29P/Schwassmann-Wachmann 1. Our data set provides the largest homogeneous database of CO 2 /H 2 O production rate ratios in comets obtained so far. The CO 2 /H 2 O production rate ratios are considered to reflect the composition of cometary ice when a comet is observed at a heliocentric distance within ∼2.5 AU, since H 2 O ice fully sublimates there. The CO 2 /H 2 O ratio in cometary ice spans from several to ∼30% among the comets observed at 2 in the comets seems to be smaller than unity based on our observations, although we only obtain upper limits for CO in most of the comets.

The effect of different methods and image analyzers on the results of the in vivo comet assay.

Science.gov (United States)

Kyoya, Takahiro; Iwamoto, Rika; Shimanura, Yuko; Terada, Megumi; Masuda, Shuichi

2018-01-01

The in vivo comet assay is a widely used genotoxicity test that can detect DNA damage in a range of organs. It is included in the Organisation for Economic Co-operation and Development Guidelines for the Testing of Chemicals. However, various protocols are still used for this assay, and several different image analyzers are used routinely to evaluate the results. Here, we verified a protocol that largely contributes to the equivalence of results, and we assessed the effect on the results when slides made from the same sample were analyzed using two different image analyzers (Comet Assay IV vs Comet Analyzer). Standardizing the agarose concentrations and DNA unwinding and electrophoresis times had a large impact on the equivalence of the results between the different methods used for the in vivo comet assay. In addition, there was some variation in the sensitivity of the two different image analyzers tested; however this variation was considered to be minor and became negligible when the test conditions were standardized between the two different methods. By standardizing the concentrations of low melting agarose and DNA unwinding and electrophoresis times between both methods used in the current study, the sensitivity to detect the genotoxicity of a positive control substance in the in vivo comet assay became generally comparable, independently of the image analyzer used. However, there may still be the possibility that other conditions, except for the three described here, could affect the reproducibility of the in vivo comet assay.

MOLECULAR OXYGEN IN OORT CLOUD COMET 1P/HALLEY

Energy Technology Data Exchange (ETDEWEB)

Rubin, M.; Altwegg, K. [Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Dishoeck, E. F. van [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Schwehm, G. [ESA (retired) Science Operations Department, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands)

2015-12-10

Recently, the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O{sub 2}, in the coma of Jupiter family comet 67P/Churyumov–Gerasimenko of O{sub 2}/H{sub 2}O = 3.80 ± 0.85%. It could be shown that O{sub 2} is indeed a parent species and that the derived abundances point to a primordial origin. Crucial questions are whether the O{sub 2} abundance is peculiar to comet 67P/Churyumov–Gerasimenko or Jupiter family comets in general, and also whether Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained by the Neutral Mass Spectrometer instrument during the flyby by the European Space Agency's Giotto probe of comet 1P/Halley. Our investigation indicates that a production rate of O{sub 2} of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O{sub 2} might be a rather common and abundant parent species.

Trajectories for spacecraft encounters with Comet Honda-Mrkos-Pajdusakova in 1996

Science.gov (United States)

Dunham, David W.; Jen, Shao-Chiang; Farquhar, Robert W.

1989-01-01

Early in 1996, the relatively bright short-period Comet Honda-Mrkos-Pajdusakova (HMP) will pass only 0.17 astronomical unit from the earth, providing both an unusually favorable apparition for ground-based observers and an opportunity for a spacecraft to reach Comet HMP on relatively low-energy trajectories. The Japanense Institute of Space and Astronautical Sciences Sakigake spacecraft is expected to fly by Comet HMP on February 3, 1996, after utilizing four earth swingbys to modify its orbit. If the camera on the ESA Giotto spacecraft is inoperable, Giotto may also be sent to Comet HMP. In addition, 1-year earth-return trajectories to Comet HMP are described, along with some that can be extended to encounter Comet Giacobini-Zinner in 1998.

On the observed excess of retrograde orbits among long-period comets

International Nuclear Information System (INIS)

Fernandez, J.A.

1981-01-01

The distribution of orbital inclinations of the observed long-period comets is analysed. An excess of retrograde orbits is found which increases with the perihelion distance, except for the range 1.1 10 3 A U) has the same behaviour as the total sample. It is thus suggested that the excess of retrograde orbits among long-period comets is related to an already existent excess among the incoming new comets (i.e. comets driven into the planetary region by stellar perturbations). Using theoretical considerations and a numerical model it is proposed that an important fraction of the so-called new comets are actually repeating passages through the planetary region. Nearly a half of the new comets with q > 2 A U may be repeating passages. An important consequence of the presence of comets repeating passages among the new ones is the production of an excess of retrograde orbits in the whole sample. (author)

Simulation-based computation of the workload correlation function in a Levy-driven queue

NARCIS (Netherlands)

P. Glynn; M.R.H. Mandjes (Michel)

2009-01-01

htmlabstractIn this paper we consider a single-server queue with Levy input, and in particular its workload process (Q_t), focusing on its correlation structure. With the correlation function defined as r(t) := Cov(Q_0, Q_t)/Var Q_0 (assuming the workload process is in stationarity at time 0), we

Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko

International Nuclear Information System (INIS)

Mousis, O.; Drouard, A.; Vernazza, P.; Le Deun, T.; Lunine, J. I.; Monnereau, M.; Rème, H.; Maggiolo, R.; Cessateur, G.; De Keyser, J.; Gasc, S.; Altwegg, K.; Balsiger, H.; Rubin, M.; Tzou, C.-Y.; Berthelier, J.-J.; Fuselier, S. A.; Korth, A.; Mall, U.; Marty, B.

2017-01-01

Because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminum and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon, or carbon monoxide during their accretion phase in the protosolar nebula (PSN). Here, we investigate how heat generated by the radioactive decay of "2"6Al and "6"0Fe influences the formation of comet 67P/Churyumov–Gerasimenko, as a function of its accretion time and the size of its parent body. We use an existing thermal evolution model that includes various phase transitions, heat transfer in the ice-dust matrix, and gas diffusion throughout the porous material, based on thermodynamic parameters derived from Rosetta observations. Two possibilities are considered: either, to account for its bilobate shape, 67P/Churyumov–Gerasimenko was assembled from two primordial ∼2 km sized planetesimals, or it resulted from the disruption of a larger parent body with a size corresponding to that of comet Hale–Bopp (∼70 km). To fully preserve its volatile content, we find that either 67P/Churyumov–Gerasimenko’s formation was delayed between ∼2.2 and 7.7 Myr after that of Ca–Al-rich Inclusions in the PSN or the comet’s accretion phase took place over the entire time interval, depending on the primordial size of its parent body and the composition of the icy material considered. Our calculations suggest that the formation of 67P/Churyumov–Gerasimenko is consistent with both its accretion from primordial building blocks formed in the nebula or from debris issued from the disruption of a Hale–Bopp-like body.

Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko

Energy Technology Data Exchange (ETDEWEB)

Mousis, O.; Drouard, A.; Vernazza, P.; Le Deun, T. [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Lunine, J. I. [Department of Astronomy and Carl Sagan Institute, Space Sciences Building Cornell University, Ithaca, NY 14853 (United States); Monnereau, M.; Rème, H. [Université de Toulouse, UPS-OMP-CNRS, IRAP, Toulouse (France); Maggiolo, R.; Cessateur, G.; De Keyser, J.; Gasc, S. [Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Ringlaan 3, B-1180 Brussels (Belgium); Altwegg, K.; Balsiger, H.; Rubin, M.; Tzou, C.-Y. [Physikalisches Institut, University of Bern, Sidlerstr. 5, CH-3012 Bern (Switzerland); Berthelier, J.-J. [LATMOS/IPSL-CNRS-UPMC-UVSQ, 4 Avenue de Neptune F-94100, Saint-Maur (France); Fuselier, S. A. [Department of Space Science, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228 (United States); Korth, A.; Mall, U. [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Marty, B., E-mail: olivier.mousis@lam.fr [Centre de Recherches Pétrographiques et Géochimiques, CRPG-CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, F-54501 Vandoeuvre lès Nancy (France); and others

2017-04-10

Because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminum and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon, or carbon monoxide during their accretion phase in the protosolar nebula (PSN). Here, we investigate how heat generated by the radioactive decay of {sup 26}Al and {sup 60}Fe influences the formation of comet 67P/Churyumov–Gerasimenko, as a function of its accretion time and the size of its parent body. We use an existing thermal evolution model that includes various phase transitions, heat transfer in the ice-dust matrix, and gas diffusion throughout the porous material, based on thermodynamic parameters derived from Rosetta observations. Two possibilities are considered: either, to account for its bilobate shape, 67P/Churyumov–Gerasimenko was assembled from two primordial ∼2 km sized planetesimals, or it resulted from the disruption of a larger parent body with a size corresponding to that of comet Hale–Bopp (∼70 km). To fully preserve its volatile content, we find that either 67P/Churyumov–Gerasimenko’s formation was delayed between ∼2.2 and 7.7 Myr after that of Ca–Al-rich Inclusions in the PSN or the comet’s accretion phase took place over the entire time interval, depending on the primordial size of its parent body and the composition of the icy material considered. Our calculations suggest that the formation of 67P/Churyumov–Gerasimenko is consistent with both its accretion from primordial building blocks formed in the nebula or from debris issued from the disruption of a Hale–Bopp-like body.

Levy-like behaviour in deterministic models of intelligent agents exploring heterogeneous environments

International Nuclear Information System (INIS)

Boyer, D; Miramontes, O; Larralde, H

2009-01-01

Many studies on animal and human movement patterns report the existence of scaling laws and power-law distributions. Whereas a number of random walk models have been proposed to explain observations, in many situations individuals actually rely on mental maps to explore strongly heterogeneous environments. In this work, we study a model of a deterministic walker, visiting sites randomly distributed on the plane and with varying weight or attractiveness. At each step, the walker minimizes a function that depends on the distance to the next unvisited target (cost) and on the weight of that target (gain). If the target weight distribution is a power law, p(k) ∼ k -β , in some range of the exponent β, the foraging medium induces movements that are similar to Levy flights and are characterized by non-trivial exponents. We explore variations of the choice rule in order to test the robustness of the model and argue that the addition of noise has a limited impact on the dynamics in strongly disordered media.

Halley comet position in structure of the comet origin general scheme

International Nuclear Information System (INIS)

Davydov, V.D.

1988-01-01

Attempt to explain data on the Halley comet nucleus figure by photographes received from space probes in 1986 was undertaken. Peanut-like nucleus might be formed from two bodies former system under specific conditions. This hypothesis preliminary development is made; solution way for the problem about quantitative characteristics of collision and destruction is found. Quantitative assessments confirm retention possibility of two space icebergs original form after their ''docking'' within relative velocity range up to a few meters per second. Then complex with visible saddle point between two jointed fragments is formed. The hypothesis suggested is well inscribed in the origin general scheme of comets with nucleus different types, and from general scheme one may draw up the most important details to this hypothesis (for example, power mechanism of binary system formation and reasons of its destabilization)

Mid-IR Spectra of Refractory Minerals Relevant to Comets

Science.gov (United States)

Jauhari, Shekeab

2008-09-01

On 4 July 2005 the Spitzer Space Telescope obtained mid-IR ( 5-40 µm) spectra of the ejecta from the hypervelocity impact of the Deep Impact projectile with comet 9P/Tempel 1. Spectral modeling demonstrates that there are abundant minerals present in the ejecta including Ca/Fe/Mg-rich silicates, carbonates, phyllosilicates, water ice, amorphous carbon, and sulfides [1]. However, precise mineralogical identifications are hampered by the lack of comprehensive 5 - 40 µm spectral measurements of the emissivity for a broad compositional range of these materials. Here, we present our initial results for 2 - 50 µm transmission spectra and absorption constants for materials relevant to comets, including pyrrhotite, pyrite, and several phyllosilicate (clay) minerals. Measuring the transmission of materials over the full spectral range sensitive by Spitzer requires grinding the minerals into submicron powders and then mixing them with KBr (for the 1-25 um region) and polyethylene (16-50 um region) to form pellets. Transmission measurements of sub-micron sulfides are particularly difficult to obtain because the minerals oxidize rapidly upon grinding and subsequent handling unless special care is taken. A detailed description of our sample preparation and measurement technique will be provided to assist other researchers in their attempts to acquire similar spectra. References: [1] Lisse, C.M. et al., Science 313, 635 - 640 (2006)

Transport properties of a piecewise linear transformation and deterministic Levy flights

International Nuclear Information System (INIS)

Miyaguchi, Tomoshige

2006-01-01

The transport properties of a 1-dimensional piecewise linear dynamical system are investigated through the spectrum of its Frobenius-Perron operator. For a class of initial densities, eigenvalues and eigenfunctions of the Frobenius-Perron operator are obtained explicitly. It is also found that in the long length wave limit, this system exhibits normal diffusion and super diffusion called Levy flight. The diffusion constant and stable index are derived from the eigenvalues. (author)

Self-similar anomalous diffusion and Levy-stable laws

International Nuclear Information System (INIS)

Uchaikin, Vladimir V

2003-01-01

Stochastic principles for constructing the process of anomalous diffusion are considered, and corresponding models of random processes are reviewed. The self-similarity and the independent-increments principles are used to extend the notion of diffusion process to the class of Levy-stable processes. Replacing the independent-increments principle with the renewal principle allows us to take the next step in generalizing the notion of diffusion, which results in fractional-order partial space-time differential equations of diffusion. Fundamental solutions to these equations are represented in terms of stable laws, and their relationship to the fractality and memory of the medium is discussed. A new class of distributions, called fractional stable distributions, is introduced. (reviews of topical problems)

Comet Kohoutek, 1973-1974, A Teachers' Guide with Student Activities.

Science.gov (United States)

Chapman, Robert D.

This teacher's guide provides background information, curriculum source materials, and suggested class activities for class discussion and study. Information related to the discovery of the comet is presented as well as photographic and schematic pictures showing the sky through which the comet travels. Historical data regarding comets of the past…

An analysis of the BVRI colors of 22 active comets

Science.gov (United States)

Betzler, A. S.; Almeida, R. S.; Cerqueira, W. J.; Araujo, L. A.; Prazeres, C. J. M.; Jesus, J. N.; Bispo, P. A. S.; Andrade, V. B.; Freitas, Y. A. S.; Betzler, L. B. S.

2017-08-01

Our aim was to analyze the variation of Johnson-Kron-Cousins BVRI color indexes of a sample with 22 active comets of various dynamic groups with the time, geometrical, observational and dynamical parameters. We performed photometric observations of 16 comets between 2010 and 2014, using robotic telescopes in three continents. In addition to the sample, we used data of six comets available in the literature. A statistical comparison between the distributions of color indexes was performed using the Kruskal-Wallis H-test. The color indexes of active comets can vary a few tenths up to a magnitude on time scales that range from hours to weeks. Using the B-V colors of the observed comets, we generated a relationship that correlates the cometary visual and CCD magnitudes. We did not identify any relationship between B-V and V-R colors with heliocentric distance and phase angle. The color B-V is correlated with the photometric aperture that can be described by a logarithmic function. We did not identify any differences in the distribution of B-V color among the comets analyzed at a confidence level equal to or greater than 95%. The mean color of active comets are B-R = 1.20 ± 0.24 , B-V = 0.76 ± 0.16 and V-R = 0.42 ± 0.16 . Active comets with V-R colors outside the three standard deviation interval can be considered objects with unusual physical characteristics.

The Rotation Temperature of Methanol in Comet 103P/Hartley 2

Science.gov (United States)

Chuang, Yo-Ling; Kuan, Yi-Jehng; Milam, Stefanie; Charnley, Steven B.; Coulson, Iain M.

2012-01-01

Considered to be relics from Solar System formation, comets may provide the vital information connecting Solar Nebula and its parent molecular cloud. Study of chemical and physical properties of comets is thus important for our better understanding of the formation of Solar System. In addition, observing organic molecules in comets may provide clues fundamental to our knowledge on the formation of prebiotically important organic molecules in interstellar space, hence, may shed light on the origin of life on the early Earth. Comet 103PIHartley 2 was fIrst discovered in 1986 and had gone through apparitions in 1991, 1997, and 2004 with an orbital period of about 6 years, before its latest return in 2010. 2010 was also a special year for Comet 103PIHartley 2 because of the NASA EPOXI comet-flyby mission.

Silicate emission feature in the spectrum of comet Mueller 1993a

Science.gov (United States)

Hanner, Martha S.; Hackwell, John A.; Russell, Ray W.; Lynch, David K.

1994-01-01

An 8- to 13-micron spectrum of comet Mueller 1993a, a dynamically new comet, was acquired when the comet was at R = 2 AU. Strong, structured silicate emission is present, closely resembling that seen in Comet P/Halley at smaller R. For the first time in a new comet, the 11.2-micron peak of crystalline olivine was detected, demonstrating that crystalline olivine particles were widespread in the solar nebula. Crystalline olivine particles could have formed in the inner protosolar nebula at temperatures greater than 1200 K; extensive radial mixing would have been required to transport these grains to the region of comet formation. Either there was more radial mixing in the solar nebula than some current theories predict or the olivine grains have a presolar origin.

Geertz versus Levi-Strauss: latent structural dispositions in Geertz "theory of culture"?

Directory of Open Access Journals (Sweden)

Gordana Gorunović

2016-02-01

Full Text Available These are two authors, in Foucauldian terms that certainly belong to the most influential individuals in socio-cultural anthropology, as well as in the social sciences and interdisciplinary research more broadly. Claude Levi- Strauss became some kind of an "intellectual hero" during the domination of structuralism in the mid-twentieth century and during the 1960s, while Clifford Geertz was an ‘icon and ambassador’ of anthropology in the second half of the twentieth century. They are both one of the founders of the discourse theory. They not only established a distinct theoretical approaches and methods – structural (Levi-Strauss and interpretative anthropology (Clifford Geertz, but through their intellectual authority they also inspired paradigms and intellectual movements making structuralism and "interpretation of culture" more than some passing episodes in the history of social though (in terms of "trendy ideas". My aim is to make some parallels between these two authors, who despite all the differences that are evident in their epistemological discourses, theoretical approaches and methods (as well as in their ethnographic and anthropological writings itself still have some similarities in their theorisation and interpretation of culture, which I would like to stress in this paper.

On the relationship between visual magnitudes and gas and dust production rates in target comets to space missions

Science.gov (United States)

de Almeida, A. A.; Sanzovo, G. C.; Singh, P. D.; Misra, A.; Miguel Torres, R.; Boice, D. C.; Huebner, W. F.

In this paper, we report the results of a cometary research, developed during the last 10 years by us, involving a criterious analysis of gas and dust production rates in comets directly associated to recent space missions. For the determination of the water release rates we use the framework of the semi-empirical model of observed visual magnitudes [Newburn Jr., R.L. A semi-empirical photometric theory of cometary gas and dust production. Application to P/Halley's production rates, ESA-SP 174, 3, 1981; de Almeida, A.A., Singh, P.D., Huebner, W.F. Water release rates, active areas, and minimum nuclear radius derived from visual magnitudes of comets - an application to Comet 46P/Wirtanen, Planet. Space Sci. 45, 681-692, 1997; Sanzovo, G.C., de Almeida, A.A., Misra, A. et al. Mass-loss rates, dust particle sizes, nuclear active areas and minimum nuclear radii of target comets for missions STARDUST and CONTOUR, MNRAS 326, 852-868, 2001.], which once obtained, were directly converted into gas production rates. In turn, the dust release rates were obtained using the photometric model for dust particles [Newburn Jr., R.L., Spinrad, H. Spectrophotometry of seventeen comets. II - the continuum, AJ 90, 2591-2608, 1985; de Freitas Pacheco, J.A., Landaberry, S.J.C., Singh, P.D. Spectrophotometric observations of the Comet Halley during the 1985-86 apparition, MNRAS 235, 457-464, 1988; Sanzovo, G.C., Singh, P.D., Huebner, W.F. Dust colors, dust release rates, and dust-to-gas ratios in the comae of six comets, A&AS 120, 301-311, 1996.]. We applied these models to seven target comets, chosen for space missions of "fly-by"/impact and rendezvous/landing.

The persistent coma of Comet P/Schwassmann-Wachmann 1

International Nuclear Information System (INIS)

Jewitt, D.

1990-01-01

Time-series photometry of Comet P/Schwassmann-Wachmann 1 in both 1987 and 1988 shows that this comet is continually active despite its large heliocentric distance. The observed activity, upon which the famous outbursts of this comet are superposed, may be driven by the sublimation of crystalline water ice at the nucleus surface. A simple model which accounts for both the continuous activity and the sporadic outbursts is suggested. 34 refs

The mass disruption of Jupiter Family comets

Science.gov (United States)

Belton, Michael J. S.

2015-01-01

I show that the size-distribution of small scattered-disk trans-neptunian objects when derived from the observed size-distribution of Jupiter Family comets (JFCs) and other observational constraints implies that a large percentage (94-97%) of newly arrived active comets within a range of 0.2-15.4 km effective radius must physically disrupt, i.e., macroscopically disintegrate, within their median dynamical lifetime. Additional observational constraints include the numbers of dormant and active nuclei in the near-Earth object (NEO) population and the slope of their size distributions. I show that the cumulative power-law slope (-2.86 to -3.15) of the scattered-disk TNO hot population between 0.2 and 15.4 km effective radius is only weakly dependent on the size-dependence of the otherwise unknown disruption mechanism. Evidently, as JFC nuclei from the scattered disk evolve into the inner Solar System only a fraction achieve dormancy while the vast majority of small nuclei (e.g., primarily those with effective radius <2 km) break-up. The percentage disruption rate appears to be comparable with that of the dynamically distinct Oort cloud and Halley type comets (Levison, H.F., Morbidelli, A., Dones, L., Jedicke, R., Wiegert, P.A., Bottke Jr., W.F. [2002]. Science 296, 2212-2215) suggesting that all types of comet nuclei may have similar structural characteristics even though they may have different source regions and thermal histories. The typical disruption rate for a 1 km radius active nucleus is ∼5 × 10-5 disruptions/year and the dormancy rate is typically 3 times less. We also estimate that average fragmentation rates range from 0.01 to 0.04 events/year/comet, somewhat above the lower limit of 0.01 events/year/comet observed by Chen and Jewitt (Chen, J., Jewitt, D.C. [1994]. Icarus 108, 265-271).

Comet P/Machholtz and the Quadrantid meteor stream

International Nuclear Information System (INIS)

Mcintosh, B.A.

1990-01-01

Attention is drawn to the suggestive similarities between the calculated perturbation behavior of Comet P/Machholtz 1986 VIII, on the one hand, and on the other those of the Quadrantid, Delta Aquarid, and Arietid meteor streams. There appears to be adequate evidence for the formation by the Comets P/Machholtz and 1491-I, together with the three meteor streams, of a related complex controlled by Jupiter's gravitational perturbations; there is no comparably compelling information, however, bearing on the questions of parent-offspring or sibling relationships among these comets and meteor streams. 13 refs

The development and validation of EpiComet-Chip, a modified high-throughput comet assay for the assessment of DNA methylation status.

Science.gov (United States)

Townsend, Todd A; Parrish, Marcus C; Engelward, Bevin P; Manjanatha, Mugimane G

2017-08-01

DNA damage and alterations in global DNA methylation status are associated with multiple human diseases and are frequently correlated with clinically relevant information. Therefore, assessing DNA damage and epigenetic modifications, including DNA methylation, is critical for predicting human exposure risk of pharmacological and biological agents. We previously developed a higher-throughput platform for the single cell gel electrophoresis (comet) assay, CometChip, to assess DNA damage and genotoxic potential. Here, we utilized the methylation-dependent endonuclease, McrBC, to develop a modified alkaline comet assay, "EpiComet," which allows single platform evaluation of genotoxicity and global DNA methylation [5-methylcytosine (5-mC)] status of single-cell populations under user-defined conditions. Further, we leveraged the CometChip platform to create an EpiComet-Chip system capable of performing quantification across simultaneous exposure protocols to enable unprecedented speed and simplicity. This system detected global methylation alterations in response to exposures which included chemotherapeutic and environmental agents. Using EpiComet-Chip on 63 matched samples, we correctly identified single-sample hypermethylation (≥1.5-fold) at 87% (20/23), hypomethylation (≥1.25-fold) at 100% (9/9), with a 4% (2/54) false-negative rate (FNR), and 10% (4/40) false-positive rate (FPR). Using a more stringent threshold to define hypermethylation (≥1.75-fold) allowed us to correctly identify 94% of hypermethylation (17/18), but increased our FPR to 16% (7/45). The successful application of this novel technology will aid hazard identification and risk characterization of FDA-regulated products, while providing utility for investigating epigenetic modes of action of agents in target organs, as the assay is amenable to cultured cells or nucleated cells from any tissue. Environ. Mol. Mutagen. 58:508-521, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Plasma Waves Associated with Mass-Loaded Comets

Science.gov (United States)

Tsurutani, Bruce; Glassmeier, Karl-Heinz

2015-01-01

Plasma waves and instabilities are integrally involved with the plasma "pickup" process and the mass loading of the solar wind (thus the formation of ion tails and the magnetic tails). Anisotropic plasmas generated by solar wind-comet interactions (the bow shock, magnetic field pileup) cause the generation of plasma waves which in turn "smooth out" these discontinuities. The plasma waves evolve and form plasma turbulence. Comets are perhaps the best "laboratories" to study waves and turbulence because over time (and distance) one can identify the waves and their evolution. We will argue that comets in some ways are better laboratories than magnetospheres, interplanetary space and fusion devices to study nonlinear waves and their evolution.

New Image of Comet Halley in the Cold

Science.gov (United States)

2003-09-01

VLT Observes Famous Traveller at Record Distance Summary Seventeen years after the last passage of Comet Halley , the ESO Very Large Telescope at Paranal (Chile) has captured a unique image of this famous object as it cruises through the outer solar system. It is completely inactive in this cold environment. No other comet has ever been observed this far - 4200 million km from the Sun - or that faint - nearly 1000 million times fainter than what can be perceived with the unaided eye. This observation is a byproduct of a dedicated search [1] for small Trans-Neptunian Objects, a population of icy bodies of which more than 600 have been found during the past decade. PR Photo 27a/03 : VLT image (cleaned) of Comet Halley PR Photo 27b/03 : Sky field in which Comet Halley was observed PR Photo 27c/03 : Combined VLT image with star trails and Comet Halley The Halley image ESO PR Photo 27a/03 ESO PR Photo 27a/03 [Preview - JPEG: 546 x 400 pix - 207k] [Normal - JPEG: 1092 x 800 pix - 614k] [FullRes - JPEG: 1502 x 1100 pix - 1.1M] Caption : PR Photo 27a/03 shows the faint, star-like image of Comet Halley (centre), observed with the ESO Very Large Telescope (VLT) at the Paranal Observatory on March 6-8, 2003. 81 individual exposures from three of the four 8.2-m VLT telescopes with a total exposure time of about 9 hours were combined to show the magnitude 28.2 object. At this time, Comet Halley was about 4200 million km from the Sun (28.06 AU) and 4080 million km (27.26 AU) from the Earth. All images of stars and galaxies in the field were removed during the extensive image processing needed to produce this unique image. Due to the remaining, unavoidable "background noise", it is best to view the comet image from some distance. The field measures 60 x 40 arcsec 2 ; North is up and East is left. Remember Comet Halley - the famous "haired star" that has been observed with great regularity - about once every 76 years - during more than two millennia? Which was visited by an

Results from the UMD physical properties of comets survey

Science.gov (United States)

Lisse, Carey M.; A'Hearn, Michael F.; Fernandez, Yanga R.

2005-01-01

We report on an ongoing statistical study of the emitted dust and exposed nuclei of a survey of the brightest near-Earth comets over the last 13 years. Combined thermal infrared and optical observations are analyzed using dynamical spectral and morphological coma models [123] to update and improve dust emission rates [4] and nucleus size estimates [5]. Using these results we show that 1) there is more than enough dust emitted from short period comets into bound solar system orbits to create and support the current interplanetary dust cloud (IPD); 2) that a population of dormant or extinct comets in the solar system is quite plausible; and 3) that the lifetime versus sublimation for the short period comets is much longer than their dynamical lifetime. [1] C.M. Lisse et al. (1998) Ap J 496 971. [2] C.M. Lisse et al. (1999) Icarus 140 189. [3] Y.R. Fernandez et al. (2000) Icarus 147 145 [4] L. Kresak and M. Kresakova (1987) in Symposium on Diversity and Similarity of Comets ESA SP-278 739 [5] D.C.Jewitt (1991) in Comets in the Post-Halley Era (R.L. Newburn M. Neugebauer and J. Rahe Eds.) Kluwer Academic Dordecht 19.

Competitive Memory Training (COMET) for OCD: a self-treatment approach to obsessions.

Science.gov (United States)

Schneider, Brooke C; Wittekind, Charlotte E; Talhof, Alina; Korrelboom, Kees; Moritz, Steffen

2015-01-01

Competitive Memory Training (COMET) is a cognitive intervention that aims to change the maladaptive cognitive-emotional networks underlying obsessive-compulsive disorder (OCD). COMET has not been previously tried as a self-help intervention. The present study tested the preliminary feasibility, acceptability, and effectiveness of COMET for OCD implemented as a self-help intervention. Sixty-five participants with OCD recruited through online OCD self-help fora completed an online baseline assessment including measures of OCD symptoms, self-esteem, and depression. Participants were randomly assigned to either COMET or a wait-list control group. All participants were approached 4 weeks later to complete an online post-assessment. There was no evidence for a greater decline of OCD symptoms or depression under COMET. When analyses were limited to only those participants who reported reading the entire manual at least once, self-esteem was higher at post-assessment in the COMET group. Although 78.1% of patients in the COMET group rated it as appropriate for self-administration, only 56.5% performed COMET exercises regularly and 26.4% read the entire manual at least once. The feasibility and effectiveness of COMET as a self-help internet intervention for OCD was not supported in this study. Further work is needed to better understand if modifications to our implementation of COMET may yield improved outcomes.

Recommendations for safety testing with the in vivo comet assay.

Science.gov (United States)

Vasquez, Marie Z

2012-08-30

While the in vivo comet assay increases its role in regulatory safety testing, deliberations about the interpretation of comet data continue. Concerns can arise regarding comet assay publications with limited data from non-blind testing of positive control compounds and using protocols (e.g. dose concentrations, sample times, and tissues) known to give an expected effect. There may be a tendency towards bias when the validation or interpretation of comet assay data is based on results generated by widely accepted but non-validated assays. The greatest advantages of the comet assay are its sensitivity and its ability to detect genotoxicity in tissues and at sample times that could not previously be evaluated. Guidelines for its use and interpretation in safety testing should take these factors into account. Guidelines should be derived from objective review of data generated by blind testing of unknown compounds dosed at non-toxic concentrations and evaluated in a true safety-testing environment, where the experimental design and conclusions must be defensible. However, positive in vivo comet findings with such compounds are rarely submitted to regulatory agencies and this data is typically unavailable for publication due to its proprietary nature. To enhance the development of guidelines for safety testing with the comet assay, and with the permission of several sponsors, this paper presents and discusses relevant data from multiple GLP comet studies conducted blind, with unknown pharmaceuticals and consumer products. Based on these data and the lessons we have learned through the course of conducting these studies, I suggest significant adjustments to the current conventions, and I provide recommendations for interpreting in vivo comet assay results in situations where risk must be evaluated in the absence of carcinogenicity or clinical data. Copyright © 2012 Elsevier B.V. All rights reserved.

Improved orbits of two periodic comets: Tsuchinshan 1 and Tsuchinshan 2

International Nuclear Information System (INIS)

Szutowicz, S.

1986-01-01

The observations made during four apparitions of two comets were collected and the orbits of the comets were improved; 86 observations of Comet Tsuchinshan 1 and 50 observations of Comet Tsuchinshan 2 made in the period 1965-1985 were used. The orbit of Comet Tsuchinshan 1 was improved taking into account nongravitational effects in its motion as well as a displacement of the photometric center from the center of mass. The following values of nongravitational parameters and of observational parameter D were obtained: A 1 = 0.75953 x 10 -8 , A 2 0.00375 x 10 -8 , D = 0.34698 x 10 -3 . To link all observations of Comet Tsuchinshan 2 by one system of elements it was sufficient to add observational effects as a displacement of the photometric center from the center of mass. The following value of parameter D was obtained: D = 1.00200 x 10 -3 . The equations of motion of both comets were integrated backwards and forwards till 1992. Ephemerides for their next returns were computed. 6 refs., 5 tabs. (author)

Comets Nature, Dynamics, Origin, and their Cosmogonical Relevance

CERN Document Server

Fernández, Julio Angel

2005-01-01

The book covers the most recent ideas about the nature and dynamics of comets, including a thorough discussion on Oort cloud dynamics which has not received due attention in other books on the subject. It also discusses the most relevant aspects of the physics and chemistry of comet nuclei, highlighting their importance as relics of the protoplanetary disk and, perhaps, as carriers of water and organics that permitted the development of life on Earth. The book contains several tables with useful data, and an ample bibliography covering the most recent work as well as some historical key contributions to the subject. It may be suitable as a textbook for graduate students with some basic knowledge of celestial mechanics and astrophysics, as well as a consult book for comet researchers, or researchers from other related fields willing to start working on comets, or get an updated view of the subject.

AKARI NEAR-INFRARED SPECTROSCOPIC SURVEY FOR CO{sub 2} IN 18 COMETS

Energy Technology Data Exchange (ETDEWEB)

Ootsubo, Takafumi [Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Kawakita, Hideyo; Hamada, Saki; Kobayashi, Hitomi; Yamaguchi, Mitsuru [Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-Ku, Kyoto 603-8555 (Japan); Usui, Fumihiko; Nakagawa, Takao; Ueno, Munetaka [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Ishiguro, Masateru [Department of Physics and Astronomy, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Sekiguchi, Tomohiko [Department of Teacher Training, Hokkaido University of Education, Asahikawa Campus, Hokumon 9, Asahikawa, Hokkaido 070-8621 (Japan); Watanabe, Jun-ichi [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Sakon, Itsuki; Shimonishi, Takashi; Onaka, Takashi, E-mail: ootsubo@astr.tohoku.ac.jp [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2012-06-10

We conducted a spectroscopic survey of cometary volatiles with the Infrared Camera on board the Japanese infrared satellite AKARI in the wavelength range from 2.5 to 5 {mu}m. In our survey, 18 comets, including both the Oort cloud comets and the Jupiter-family comets, were observed in the period from 2008 June to 2010 January, most of which were observed at least twice. The prominent emission bands in the observed spectra are the fundamental vibrational bands of water (H{sub 2}O) at 2.7 {mu}m and carbon dioxide (CO{sub 2}) at 4.3 {mu}m. The fundamental vibrational band of carbon monoxide (CO) around 4.7 {mu}m and the broad emission feature, probably related to carbon-hydrogen-bearing molecules, can also be recognized around the 3.3-3.5-{mu}m region in some of the comets. With respect to H{sub 2}O, gas production rate ratios of CO{sub 2} have been derived in 17 comets, except for the comet 29P/Schwassmann-Wachmann 1. Our data set provides the largest homogeneous database of CO{sub 2}/H{sub 2}O production rate ratios in comets obtained so far. The CO{sub 2}/H{sub 2}O production rate ratios are considered to reflect the composition of cometary ice when a comet is observed at a heliocentric distance within {approx}2.5 AU, since H{sub 2}O ice fully sublimates there. The CO{sub 2}/H{sub 2}O ratio in cometary ice spans from several to {approx}30% among the comets observed at <2.5 AU (13 out of the 17 comets). Alternatively, the ratio of CO/CO{sub 2} in the comets seems to be smaller than unity based on our observations, although we only obtain upper limits for CO in most of the comets.

CINE: Comet INfrared Excitation

Science.gov (United States)

de Val-Borro, Miguel; Cordiner, Martin A.; Milam, Stefanie N.; Charnley, Steven B.

2017-08-01

CINE calculates infrared pumping efficiencies that can be applied to the most common molecules found in cometary comae such as water, hydrogen cyanide or methanol. One of the main mechanisms for molecular excitation in comets is the fluorescence by the solar radiation followed by radiative decay to the ground vibrational state. This command-line tool calculates the effective pumping rates for rotational levels in the ground vibrational state scaled by the heliocentric distance of the comet. Fluorescence coefficients are useful for modeling rotational emission lines observed in cometary spectra at sub-millimeter wavelengths. Combined with computational methods to solve the radiative transfer equations based, e.g., on the Monte Carlo algorithm, this model can retrieve production rates and rotational temperatures from the observed emission spectrum.

Mission to a comet that could save earth

CERN Multimedia

Utton, T

2003-01-01

Scientists are going to attempt to land a probe on the comet Wirtanen. The GBP640million unmanned craft will travel four billion miles before catching up with the comet Wirtanen and launching a robotic lander called Rosetta, on to its surface (1/2 page).

Catastrophic disruptions as the origin of bilobate comets

Science.gov (United States)

Schwartz, Stephen R.; Michel, Patrick; Jutzi, Martin; Marchi, Simone; Zhang, Yun; Richardson, Derek C.

2018-05-01

Several comets observed at close range have bilobate shapes1, including comet 67P/Churyumov-Gerasimenko (67P/C-G), which was imaged by the European Space Agency's Rosetta mission2,3. Bilobate comets are thought to be primordial because they are rich in supervolatiles (for example, N2 and CO) and have a low bulk density, which implies that their formation requires a very low-speed accretion of two bodies. However, slow accretion does not only occur during the primordial phase of the Solar System; it can also occur at later epochs as part of the reaccumulation process resulting from the collisional disruption of a larger body4, so this cannot directly constrain the age of bilobate comets. Here, we show by numerical simulation that 67P/C-G and other elongated or bilobate comets can be formed in the wake of catastrophic collisional disruptions of larger bodies while maintaining their volatiles and low density throughout the process. Since this process can occur at any epoch of our Solar System's history, from early on through to the present day5, there is no need for these objects to be formed primordially. These findings indicate that observed prominent geological features, such as pits and stratified surface layers4,5, may not be primordial.

Comet mission hopes to uncover Earth's origins

CERN Multimedia

Henderson, M

2004-01-01

"A European spacecraft that will hunt down a comet in search of clues to the origin of life on Earth will blast off tomorrow from the Kourou spaceport in French Guiana. The Rosetta probe will take 12 years to catch up with Churyumov-Gerasimenko before becoming the first spacecraft to make a soft, controlled landing on a comet's nucleus" (1 page).

Comet Hyakutake to Approach the Earth in Late March 1996

Science.gov (United States)

1996-03-01

Astronomers Prepare for a Rare Event In the early morning of January 31, 1996, Japanese amateur astronomer Yuji Hyakutake made his second comet discovery within five weeks. He found the new comet near the border between the southern constellations of Hydra (The Water-Snake) and Libra (The Scales), amazingly just three degrees from the position where he detected another comet on December 26, 1995. After two weeks of hectic activity among amateur and professional astronomers all over the world, much interesting information has now been gathered about the new comet which has been designated C/1996 B2 (Hyakutake) . In particular, it has been found to move in a near-parabolic orbit that will bring it unusually close to the Earth next month. It is then expected to become bright enough to be seen with the unaided eye and to remain so during several weeks thereafter. Preparations are now made to observe the celestial visitor with a large number of telescopes, on the ground and in space. This event offers a rare opportunity to study the immediate surroundings of a cometary nucleus in detail and the specialists intend to make the most of it. Discovery and orbit Yuji Hyakutake, of profession photoengraver and a well-known amateur astronomer, announced his new discovery without delay, and within 24 hours, it had been sighted by several other observers in Japan and Australia. Experienced comet-watchers described its appearance as `diffuse with central condensation and of magnitude 11-12', i.e. a little more than 100 times fainter than what can be seen with the unaided eye. This brightness is not unusual for a comet discovered by an amateur, although it would probably have been missed, had it been just a little fainter. In the present case, the decisive factors for Hyakutake's success were undoubtedly his very powerful equipment (25 x 150 binoculars) and the advantageous combination of the comet's southern position in the sky and his location in Kagoshima, the southernmost

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

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

Science.gov (United States)

Jones, Geraint H.; Knight, Matthew M.; Battams, Karl; Boice, Daniel C.; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass, Colin; Steckloff, Jordan K.; Weissman, Paul; Fitzsimmons, Alan; Lisse, Carey; Opitom, Cyrielle; Birkett, Kimberley S.; Bzowski, Maciej; Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick

2018-02-01

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and

COMET concept

International Nuclear Information System (INIS)

Alsmeyer, H.; Tromm, W.

1995-01-01

Studies of the COMET core catcher concept developed for a future PWR have been continued. The concept is based on the spreading of a core melt on a sacrificial layer and its erosion, until a subsequent addition of water from below causes a fragmentation of the melt. A porous solidification of the melt would then admit a complete flooding within a short period. (orig.)

Fairer flying: an international air travel levy for adaptation

Energy Technology Data Exchange (ETDEWEB)

Chambwera, Muyeye; Muller, Benito

2008-11-15

For the world's poorest countries and communities, adaptation to climate change is urgently needed, but costly: estimates run into tens of billions of dollars a year. Given the shortfall in current international adaptation funding, how can resources for the developing world be raised? An adaptation levy on international air travel could help fill the gap. A small per-trip payment by passengers could contribute US$8 billion to US$10 billion a year towards adaptation. Similar schemes in France and elsewhere show that this kind of ethical solidarity and 'polluter pays' approach would be simple to implement in practical and institutional terms.

Kelvin-Helmholtz instability in type-1 comet tails and associated phenomena

International Nuclear Information System (INIS)

Ershkovich, A.I.

1980-01-01

Selected problems of the solar wind - comet tail coupling that are currently accessible to quantitative analysis are reviewed. The model of a comet tail as a plasma cylinder separated by a tangential discontinuity surface from the solar wind is discussed in detail. This model is compatible with the well-known Alfven mechanism of formation of the comet tail. The stability problem of the comet tail boundary (considered as a discontinuity surface) is solved. Under typical conditions a comet tail boundary can undergo the Kelvin-Helmholtz instability. With finite amplitude the stabilizing effect of the magnetic field increases, and waves become stabilized. This model supplies a detailed quantitative description of helical waves observed in type-1 comet tails. A more general model of the tail boundary as a transition layer with a continuous change of the plasma parameters within it is also considered. This theory, in principle, enables us to solve one of the fundamental problems of cometary physics: the magnetic field of the comet tail can be derived from the observations of helical waves. This field turns out to be of the order of the interplanetary field. Various other considerations, discussed in this review also support this conclusion. (orig.)

Application of the DNA comet assay for detection of irradiated meat

International Nuclear Information System (INIS)

Kruszewski, M.; Iwanenko, T.; Wojewodzka, M.; Malec-Czechowska, K.; Dancewicz, A. M.; Szot, Z.

1998-01-01

Radiation induces damage to the DNA. This damage (fragmentation) can be assessed in the irradiated food using Single Cell Gel Electrophoresis (SCGE), known as DNA comet assay. Fragmentation of DNA may also be caused by improper storage of meat and repeated freezing and thawing. This makes identification of irradiated meat by this assay not reliable enough. In order to know the scale of the processes imitating radiation effects in DNA of the comets, their shape and lengths were examined in both irradiated and unirradiated fresh meat (D = 1.5 or 3.0 kGy) stored at 4 o C or frozen (-21 o ) up to 5 months. Comets formed upon SCGE were stained with DAPI or silver and examined in fluorescent or light microscope. They were divided arbitrarily into 4 classes. Comets of IV class were found quite often in fresh meat stored at 4 o C. In meat samples that were irradiated and stored frozen, comets of class I, II and III were observed. The negative comet test is univocal. Positive comet test, however, needs confirmation. The meat should be subjected to further analysis with other validated methods. (author)

On the formation of meteor showers of comet Halley

International Nuclear Information System (INIS)

Babadzhanov, P.B.; Obrubov, J.V.; Pushkarev, A.N.; Hajduk, A.

1987-01-01

The orbits of test particles ejected from the nucleus of Halley comet at its perihelion passage in 1910 with different velocities are studied for the next three passages of the comet up to 2134 taking into consideration perturbations from all planets. Some characteristics of the stream formation are presented. The calculations show that the return of the comet to its perihelion cannot produce an immediate influence on the activity of its meteor showers. (author). 2 figs., 1 tab., 13 refs

Prediction of the return of Comet P/Grigg-Skjellerup in 1987

International Nuclear Information System (INIS)

Sitarski, G.

1986-01-01

Using 82 observations made in the period 1966-1982 during the last four apparitions of the comet, the corrections of orbital elements were determined together with nongravitational parameters A 1 , A 2 and with a parameter D of a displacement of the photometric center from the center of mass of the comet. It was found that a value of the secular acceleration diminished in comparison with such a value before the close approach of the comet Jupiter in 1964; the nongravitational parameters of Style 2 in Marsden's notation now are: A 1 = +0.0371, A 2 = +0.008. To make the best prediction of the comet's return in 1987, the orbit was improved using 67 observations from the last two apparitions of the comet in 1977 and 1982, and taking the constant values of A 1 , A 2 as determined earlier; basing on the latter orbit the ephemeris of the comet for 1987 was computed. 3 refs., 2 tabs. (author)

COMET Multimedia modules and objects in the digital library system

Science.gov (United States)

Spangler, T. C.; Lamos, J. P.

2003-12-01

Over the past ten years of developing Web- and CD-ROM-based training materials, the Cooperative Program for Operational Meteorology, Education and Training (COMET) has created a unique archive of almost 10,000 multimedia objects and some 50 web based interactive multimedia modules on various aspects of weather and weather forecasting. These objects and modules, containing illustrations, photographs, animations,video sequences, audio files, are potentially a valuable resource for university faculty and students, forecasters, emergency managers, public school educators, and other individuals and groups needing such materials for educational use. The COMET Modules are available on the COMET educational web site http://www.meted.ucar.edu, and the COMET Multimedia Database (MMDB) makes a collection of the multimedia objects available in a searchable online database for viewing and download over the Internet. Some 3200 objects are already available at the MMDB Website: http://archive.comet.ucar.edu/moria/

Spitzer Observations of Comet 9P/Tempel 1 During Deep Impact : Water and Dust Production and Spatial Distribution

Science.gov (United States)

Gicquel, Adeline; Bockelée-Morvan, D.; Kelley, M. S.; Woodward, C. E.

2009-09-01

The Deep Impact (DI) spacecraft encountered comet 9P/Tempel 1 on July 4th, 2005 (rh = 1.506 AU). Spectral maps covering 20'' x 67'' (1.85''/pixel) were acquired with the IRS instrument on the Spitzer Space Telescope (ΔSpitzer = 0.72 AU) at different times around the Deep Impact event: twice before impact (TI-41.3hrs and TI-22.9hrs) and twelve times after impact (between TI+0.67hrs and TI+1027hrs). These IRS observations (Lisse et al 2006, Sciences 313, 635) were taken from the Spitzer data archive. We present the interpretation of 5.2-7.6 µm spectra obtained in the second order of the short-wavelength module (SL2). To reduce the contribution of artifacts in the spectra, 5x5 pixel extraction apertures (9.25''x9.25'') were used. On the first stage we studied the water ν2 vibrational band emission at 6.4µm, which is present in most spectra. The water production rate before impact is deduced ( 4.25e27 molecules/sec). In order to study both the amount and origin of the water molecules released after impact, we used extractions centered on the nucleus and along the length of the slit. We analyzed the spatial distribution of water and its time evolution with a time-dependent model which describes the evolution of the water cloud after impact. The underlying continuum in the spectra provides information on the evolution and color temperature of the dust ejecta. The dust mass and dust/gas ratio in the ejecta cloud are derived and compared with other values published in the literature.

Inverting Comet Acoustic Surface Sounding Experiment (CASSE) touchdown signals to measure the elastic modulus of comet material

Science.gov (United States)

Arnold, W.; Faber, C.; Knapmeyer, M.; Witte, L.; Schröder, S.; Tune, J.; Möhlmann, D.; Roll, R.; Chares, B.; Fischer, H.; Seidensticker, K.

2014-07-01

The landing of Philae on comet 67P/Churyumov-Gerasimenko is scheduled for November 11, 2014. Each of the three landing feet of Philae house a triaxial acceleration sensor of CASSE, which will thus be the first sensors to be in mechanical contact with the cometary surface. CASSE will be in listening mode to record the deceleration of the lander, when it impacts with the comet at a velocity of approx. 0.5 m/s. The analysis of this data yields information on the reduced elastic modulus and the yield stress of the comet's surface material. We describe a series of controlled landings of a lander model. The tests were conducted in the Landing & Mobility Test Facility (LAMA) of the DLR Institute of Space Systems in Bremen, Germany, where an industrial robot can be programmed to move landers or rovers along predefined paths, allowing to adapt landing procedures with predefined velocities. The qualification model of the Philae landing gear was used in the tests. It consists of three legs manufactured of carbon fiber and metal joints. A dead mass of the size and mass of the lander housing is attached via a damper above the landing gear to represent the lander structure as a whole. Attached to each leg is a foot with two soles and a mechanically driven fixation screw (''ice screw'') to secure the lander on the comet. The right soles, if viewed from the outside towards the lander body, house a Brüel & Kjaer DeltaTron 4506 triaxial piezoelectric accelerometer as used on the spacecraft. Orientation of the three axes was such that one of the axes, here the X-axis of the accelerometer, points downwards, while the Y- and Z-axes are horizontal. Data were recorded at a sampling rate of 8.2 kHz within a time gate of 2 s. In parallel, a video sequence was taken, in order to monitor the touchdown on the sand and the movement of the ice screws. Touchdown measurements were conducted on three types of ground with landing velocities between 0.1 to 1.1 m/s. Landings with low velocities were

Characterizing Outbursts and Nucleus Properties of Comet 29P/Schwassmann-Wachmann 1

Science.gov (United States)

Fernandez, Yanga

2015-10-01

Today's comets are remnant bodies leftover from the era of planet formation in our own Solar System. Therefore characterizing cometary structure and composition can give clues to the thermal, physical, and chemical environment of the protoplanetary disk. However before this long-term 'holy grail' of planetary astronomy can be achieved, we must understand cometary evolution so that we can know how comets have changed since their formation. The phenomenon of cometary activity, where a porous matrix of icy and rocky material turns into the gases and the dust grains we see in a comet's coma, remains a poorly-understood puzzle of short-term cometary evolution. We are in the midst of an ongoing project to understand cometary activity in a particular comet, 29P/Schwassmann-Wachmann 1, by taking advantage of existing imaging datasets that show the comet in outburst. Outbursts are useful for constraining the nucleus's spin state and the location of active areas. We propose here to analyze archival WFPC2 images of comet 29P obtained in March 1996 (Cycle 5, Project 5829), spanning 21 hours, that show the comet in outburst. These data are the highest-resolution imaging of this comet ever obtained while it was in outburst. We will analyze the morphology of the comet's dust coma to constrain properties of the nucleus and of the dust grains themselves. Additionally, we will analyze images taken in May 2000 (Cycle 8, Project 8274) that show the comet at its steady-state level of activity but may also allow us to place further constraints on the nucleus's active regions.

Comet or Asteroid?

Science.gov (United States)

1997-11-01

When is a minor object in the solar system a comet? And when is it an asteroid? Until recently, there was little doubt. Any object that was found to display a tail or appeared diffuse was a comet of ice and dust grains, and any that didn't, was an asteroid of solid rock. Moreover, comets normally move in rather elongated orbits, while most asteroids follow near-circular orbits close to the main plane of the solar system in which the major planets move. However, astronomers have recently discovered some `intermediate' objects which seem to possess properties that are typical for both categories. For instance, a strange object (P/1996 N2 - Elst-Pizarro) was found last year at ESO ( ESO Press Photo 36/96 ) which showed a cometary tail, while moving in a typical asteroidal orbit. At about the same time, American scientists found another (1996 PW) that moved in a very elongated comet-type orbit but was completely devoid of a tail. Now, a group of European scientists, by means of observations carried out at the ESO La Silla observatory, have found yet another object that at first appeared to be one more comet/asteroid example. However, continued and more detailed observations aimed at revealing its true nature have shown that it is most probably a comet . Consequently, it has received the provisional cometary designation P/1997 T3 . The Uppsala-DLR Trojan Survey Some time ago, Claes-Ingvar Lagerkvist (Astronomical Observatory, Uppsala, Sweden), in collaboration with Gerhard Hahn, Stefano Mottola, Magnus Lundström and Uri Carsenty (DLR, Institute of Planetary Exploration, Berlin, Germany), started to study the distribution of asteroids near Jupiter. They were particularly interested in those that move in orbits similar to that of Jupiter and which are located `ahead' of Jupiter in the so-called `Jovian L4 Lagrangian point'. Together with those `behind' Jupiter, these asteroids have been given the names of Greek and Trojan Heroes who participated in the famous Trojan war

Detection of garlic gamma-irradiated by assay comet

International Nuclear Information System (INIS)

Moreno Alvarez, Damaris L.; Miranda, Enrique F. Prieto; Carro, Sandra; Iglesias Enrique, Isora; Matos, Wilberto

2009-01-01

The garlic samples were irradiated in a facility with 60 Co sources, at absorbed dose values of 0-0,15 kGy. The detection method utilized for the identification of the irradiated garlic was biological comet assay. The samples were classified post-irradiation several times. The irradiated samples showed high strand breaks of DNA exhibiting comets of several forms, while the not irradiated and lower dose samples showed a behavior like round shape and light comets. Significant differences were found for higher absorbed dose values at 0.06 kGy, this absorbed dose value is corresponding with the applied dose value at this food in order to avoid the germination. (author)

Comets As Objects of High Energy Astrophysics

Science.gov (United States)

Ibadov, S.

2000-10-01

Strong soft X-ray emission from comet Hyakutake C/1996 B2 was discovered with ROSAT in March 27, 1996 (Lisse et al. 1996, Science 274, 205-209) and the results of a theoretical approach (Ibadov 1990, Icarus 86, 283-288) served as a motive for that observations (Dennerl, Lisse and Truemper 1998, Private Communications). It is now well established that comets emit EUV and X-rays regularly (Dennerl, Englhauser and Truemper 1997, Science 277, 1625-1630; Dennerl 1998, Proc. 16th Int. Conf. Atomic Physics, Windsor, Ontario, Canada). To explain this phenomenon different theoretical models were proposed (Krasnopolsky 1997, Icarus 128, 365-385; Ibadov 1998, Proc. First XMM Workshop, Noordwijk, The Netherlands, and references therein). In the paper the problem of identifying X-ray generation mechanisms in comets will be considered.

Isotopic ratios in outbursting comet C/2015 ER61

Science.gov (United States)

Yang, Bin; Hutsemékers, Damien; Shinnaka, Yoshiharu; Opitom, Cyrielle; Manfroid, Jean; Jehin, Emmanuël; Meech, Karen J.; Hainaut, Olivier R.; Keane, Jacqueline V.; Gillon, Michaël

2018-02-01

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0, 0) band and found that 12C/13C = 100 ± 15, 14N/15N = 130 ± 15. In addition, we determined the 14N/15N ratio from four pairs of NH2 isotopolog lines and measured 14N/15N = 140 ± 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.

Comet Halley - Chapter I in cometary exploration

International Nuclear Information System (INIS)

Newburn, R.L. Jr.

1986-01-01

The information gained on the Comet Halley by the international probe studies is presented. The new information includes data on the true size and shape of the cometary nucleus and the mass of its dust grains, the chemical composition of the nucleus, and the characteristics of the bow wave of the comet. The requirements of future missions for solving the many questions that are still open are discussed

THE NEOWISE-DISCOVERED COMET POPULATION AND THE CO + CO{sub 2} PRODUCTION RATES

Energy Technology Data Exchange (ETDEWEB)

Bauer, James M.; Stevenson, Rachel; Kramer, Emily; Mainzer, A. K.; Masiero, Joseph R.; Weissman, Paul R.; Nugent, Carrie R.; Sonnett, Sarah [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 183-401, Pasadena, CA 91109 (United States); Grav, Tommy [Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395 (United States); Fernández, Yan R. [Department of Physics, University of Central Florida, 4000 Central Florida Blvd., P.S. Building, Orlando, FL 32816-2385 (United States); Cutri, Roc M.; Dailey, John W.; Masci, Frank J.; Blair, Nathan; Lucas, Andrew [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Meech, Karen J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Manoa, HI 96822 (United States); Walker, Russel [Monterey Institute for Research in Astronomy, 200 Eighth Street, Marina, CA 93933 (United States); Lisse, C. M. [Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road Laurel, MD 20723-6099 (United States); McMillan, Robert S. [Lunar and Planetary Laboratory, University of Arizona, 1629 East University Blvd., Kuiper Space Science Bldg. 92, Tucson, AZ 85721-0092 (United States); Wright, Edward L., E-mail: bauer@scn.jpl.nasa.gov [Department of Physics and Astronomy, University of California, P.O. Box 91547, Los Angeles, CA 90095-1547 (United States); Collaboration: WISE and NEOWISE Teams

2015-12-01

The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO{sub 2} production. We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO{sub 2} production, as well as possible differences in the sizes of long and short period comet nuclei.

The Meteoroid Fluence at Mars Due to Comet Siding Spring

Science.gov (United States)

Moorhead, Althea V.

2014-01-01

Long-period comet C/2013 A1 (Siding Spring) is headed for a close encounter with Mars on 2014 Oct 19. A collision between the comet and the planet has been ruled out, but the comets coma may envelop Mars and its man-made satellites. We present an analytic model of the dust component of cometary comae that describes the spatial distribution of cometary dust and meteoroids and their size distribution. If the coma reaches Mars, we estimate a total incident particle fluence on the planet and its satellites of 0.01 particles per square meter. We compare our model with numerical simulations, data from past comet missions, and recent Siding Spring observations.

Comet assay optimization for assessment of DNA damage due to radiation exposure

International Nuclear Information System (INIS)

Dwi Ramadhani; Devita Tetriana; Viria Agesti Suvifan

2016-01-01

Comet assay can be used to measure the deoxyribonucleic acid (DNA) damage level caused by ionizing radiation exposure in peripheral blood lymphocytes. The principle of the comet assay is based on the amount of denatured DNA fragments that migrated out of the cell nucleus during electrophoresis. There are several aspects that must be concerned when doing the comet assay. For example the agarose concentration, duration of alkaline incubation, electrophoresis conditions (time, temperature, and voltage gradient), and the measurement parameters that used in analyze the comet. Percentage of DNA in the comet tail (% tail DNA) is strongly recommended as a parameter when analyze the comet because it can be converted to lesions per 106 base pairs (bp) using calibration curve that show relationship between the dose of ionizing radiation and % tail DNA. To obtain an accurate result, the calibration curve must be made and comet should be analyzing using image processing analysis software since it can be increase the precision and reduce the subjectivity of the measurement process. (author)

Comet 2001 Q2

Czech Academy of Sciences Publication Activity Database

Pravec, Petr; Kušnirák, Peter; Bouma, R. J.; Raymundo, P. M.

č. 7687 (2001), s. 1 ISSN 0081-0304 R&D Projects: GA ČR GA205/99/0255 Institutional research plan: CEZ:AV0Z1003909 Keywords : comet s * astrometry Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

Weird comets and asteroids the strange little worlds of the sun's family

CERN Document Server

Seargent, David A J

2017-01-01

This book concentrates on some of the odd aspects of comets and asteroids. Strange behavior of comets, such as outbursts and schisms, and how asteroids can temporally act as comets are discussed, together with the possible threat of Centaurs-class objects like the Taurid complex. Recent years have seen the distinction between comets and asteroids become less prominent. Comets in "asteroid" orbits and vice versa have become almost commonplace and a clearer view of the role of small bodies in the formation of the Solar System and their effect on Earth has become apparent. Seargent covers this development in detail by including new data and information from space probes. .

New levy on nitrogen oxide emissions: First 'refundable' pollution charge

International Nuclear Information System (INIS)

Andersson, Sus; Hanneberg, P.

1991-01-01

A new law imposing a charge on nitrogen oxide emissions from combustion installations will soon be coming into force in Sweden. The money generated by the charge will not stay in the exchequer, however, but will be repaid to the plants concerned in proportion to the amount of useful energy they produce. This will be the first environment levy in Sweden to be based on measurements of actual emissions. Emissions of sulphur and carbon dioxide are already taxed. These taxes, unlike other environmental charges, not only have an incentive function, but are also a source of income for the state

Properties of comet Halley derived from thermal models and astrometric data

International Nuclear Information System (INIS)

Hechler, F.W.; Morley, T.A.; Mahr, P.

1986-01-01

The motion of a comet nucleus is influenced by outgassing forces. The orbit determination from astrometric data of comet Halley using empiric force and observation bias models and the incorporation of thermal models developed at ESOC into the orbit determination allows to draw some conclusions on the comet Halley dynamics and physics. 21 references

Decrease of energy and emission prices undesired. Unfair attack on CO2-levies

International Nuclear Information System (INIS)

Blom, M.; De Keizer, I.; Benner, J.

2005-01-01

Recently, in the Netherlands, fuel taxes and prices for CO2 emission are criticised. High energy prices are used to suggest other forms of pricing regulations. However, the higher energy prices and CO2-levies are very useful in realizing a sustainable energy supply. More transparency in the market for emissions trading is required to prevent unfair on-charge expenses of CO2-charges [nl

Detection of garlic gamma-irradiated by assay comet

Energy Technology Data Exchange (ETDEWEB)

Moreno Alvarez, Damaris L.; Miranda, Enrique F. Prieto; Carro, Sandra; Iglesias Enrique, Isora; Matos, Wilberto [Centro de Aplicaciones Tecnologicas y Desarrollo Nuclear (CEADEN), Ciudad de La Habana (Cuba)], e-mail: damaris@ceaden.edu.cu

2009-07-01

The garlic samples were irradiated in a facility with {sup 60}Co sources, at absorbed dose values of 0-0,15 kGy. The detection method utilized for the identification of the irradiated garlic was biological comet assay. The samples were classified post-irradiation several times. The irradiated samples showed high strand breaks of DNA exhibiting comets of several forms, while the not irradiated and lower dose samples showed a behavior like round shape and light comets. Significant differences were found for higher absorbed dose values at 0.06 kGy, this absorbed dose value is corresponding with the applied dose value at this food in order to avoid the germination. (author)

Rationalization of Comet Halley's periods

Science.gov (United States)

Belton, Michael J. S.

1990-01-01

The sense of long axis orientation of Comet Halley during the Vega 1 encounter must be reversed from that deduced by Sagdeev et al. (1986) in order to harmonize the comet nucleus' Vega/Giotto-observed orientations with periodicities extracted from time-series brightness data. It is also demonstrated that Vega/Giotto observations can be satisfied by either a 2.2- or 3.7-day long-axis free precession period. A novel Fourier algorithm is used to reanalyze five independent data sets; strong evidence is adduced for periods harmonically related to a 7.4-day period. The preferred candidate models for Halley's nuclear rotation are characterized by a long-axis precession period of 3.7 days.

Comet Assay in Cancer Chemoprevention.

Science.gov (United States)

Santoro, Raffaela; Ferraiuolo, Maria; Morgano, Gian Paolo; Muti, Paola; Strano, Sabrina

2016-01-01

The comet assay can be useful in monitoring DNA damage in single cells caused by exposure to genotoxic agents, such as those causing air, water, and soil pollution (e.g., pesticides, dioxins, electromagnetic fields) and chemo- and radiotherapy in cancer patients, or in the assessment of genoprotective effects of chemopreventive molecules. Therefore, it has particular importance in the fields of pharmacology and toxicology, and in both environmental and human biomonitoring. It allows the detection of single strand breaks as well as double-strand breaks and can be used in both normal and cancer cells. Here we describe the alkali method for comet assay, which allows to detect both single- and double-strand DNA breaks.

Radar observations of Comet Halley

International Nuclear Information System (INIS)

Campbell, D.B.; Harmon, J.K.; Shapiro, I.I.

1989-01-01

Five nights of Arecibo radar observations of Comet Halley are reported which reveal a feature in the overall average spectrum which, though weak, seems consistent with being an echo from the comet. The large radar cross section and large bandwidth of the feature suggest that the echo is predominantly from large grains which have been ejected from the nucleus. Extrapolation of the dust particle size distribution to large grain sizes gives a sufficient number of grains to account for the echo. The lack of a detectable echo from the nucleus, combined with estimates of its size and rotation rate from spacecraft encounters and other data, indicate that the nucleus has a surface of relatively high porosity. 33 references

Epithelial cells as alternative human biomatrices for comet assay.

Science.gov (United States)

Rojas, Emilio; Lorenzo, Yolanda; Haug, Kristiane; Nicolaissen, Bjørn; Valverde, Mahara

2014-01-01

The comet assay is a valuable experimental tool aimed at mapping DNA damage in human cells in vivo for environmental and occupational monitoring, as well as for therapeutic purposes, such as storage prior to transplant, during tissue engineering, and in experimental ex vivo assays. Furthermore, due to its great versatility, the comet assay allows to explore the use of alternative cell types to assess DNA damage, such as epithelial cells. Epithelial cells, as specialized components of many organs, have the potential to serve as biomatrices that can be used to evaluate genotoxicity and may also serve as early effect biomarkers. Furthermore, 80% of solid cancers are of epithelial origin, which points to the importance of studying DNA damage in these tissues. Indeed, studies including comet assay in epithelial cells have either clear clinical applications (lens and corneal epithelial cells) or examine genotoxicity within human biomonitoring and in vitro studies. We here review improvements in determining DNA damage using the comet assay by employing lens, corneal, tear duct, buccal, and nasal epithelial cells. For some of these tissues invasive sampling procedures are needed. Desquamated epithelial cells must be obtained and dissociated prior to examination using the comet assay, and such procedures may induce varying amounts of DNA damage. Buccal epithelial cells require lysis enriched with proteinase K to obtain free nucleosomes. Over a 30 year period, the comet assay in epithelial cells has been little employed, however its use indicates that it could be an extraordinary tool not only for risk assessment, but also for diagnosis, prognosis of treatments and diseases.

Comets: Role and importance to exobiology

Science.gov (United States)

Delsemme, Armand H.

1992-01-01

The transfer of organic compounds from interstellar space to the outskirts of a protoplanetary disk, their accretion into cometary objects, and the transport of the latter into the inner solar system by orbital diffusion throw a new light on the central problem of exobiology. It suggests the existence of a cosmic mechanism, working everywhere, that can supply prebiotic compounds to ubiquitous rocky planets, in search of the proper environment to start life in many places in the Universe. Under the heading of chemistry of the cometary nucleus, the following topics are covered: radial homogeneity of the nucleus; the dust-to-ice ratio; nature of the dust grains; origin of the dust in comets; nature of the volatile fraction; the CO distribution in comet Halley; dust contribution to the volatile fraction; elemental balance sheet of comet Halley; quantitative molecular analysis of the volatile fraction; and isotopic ratios. Under the heading of exogenous origin of carbon on terrestrial planets the following topics are covered: evidence for a high-temperature phase; from planetesimals to planets; a veneer of volatile and organic material; and cometary contribution.

Asteroids, meteorites, and comets

CERN Document Server

Elkins-Tanton, Linda T

2010-01-01

Asteroids, Comets, and Meteorites provides students, researchers, and general readers with the most up-to-date information on this fascinating field. From the days of the dinosaurs to our modern environment, this book explores all aspects of these cosmic invaders.

Death of a comet

CERN Multimedia

Hawkes, N

2000-01-01

The comet Linear dissolved as it made its closest approach to the sun on July 25th. The first stages of its breakup had been witnessed by the Hubble telescope when it threw off a piece of its crust (3 paragraphs).

Nonlinear low frequency (LF) waves - Comets and foreshock phenomena

Science.gov (United States)

Tsurutani, Bruce T.

1991-01-01

A review is conducted of LF wave nonlinear properties at comets and in the earth's foreshock, engaging such compelling questions as why there are no cometary cyclotron waves, the physical mechanism responsible for 'dispersive whiskers', and the character of a general description of linear waves. Attention is given to the nonlinear properties of LF waves, whose development is illustrated by examples of waves and their features at different distances from the comet, as well as by computer simulation results. Also discussed is a curious wave mode detected from Comet Giacobini-Zinner, both at and upstream of the bow shock/wave.

Younger Dryas Boundary (YDB) impact : physical and statistical impossibility.

Energy Technology Data Exchange (ETDEWEB)

Boslough, Mark Bruce Elrick

2010-08-01

The YDB impact hypothesis of Firestone et al. (2007) is so extremely improbable it can be considered statistically impossible in addition to being physically impossible. Comets make up only about 1% of the population of Earth-crossing objects. Broken comets are a vanishingly small fraction, and only exist as Earth-sized clusters for a very short period of time. Only a small fraction of impacts occur at angles as shallow as proposed by the YDB impact authors. Events that are exceptionally unlikely to take place in the age of the Universe are 'statistically impossible'. The size distribution of Earth-crossing asteroids is well-constrained by astronomical observations, DoD satellite bolide frequencies, and the cratering record. This distribution can be transformed to a probability density function (PDF) for the largest expected impact of the past 20,000 years. The largest impact of any kind expected over the period of interest is 250 m. Anything larger than 2 km is exceptionally unlikely (probability less than 1%). The impact hypothesis does not rely on any sound physical model. A 4-km diameter comet, even if it fragmented upon entry, would not disperse or explode in the atmosphere. It would generate a crater about 50 km in diameter with a transient cavity as deep as 10 km. There is no evidence for such a large, young crater associated with the YDB. There is no model to suggest that a comet impact of this size is capable of generating continental-wide fires or blast damage, and there is no physical mechanism that could cause a 4-km comet to explode at the optimum height of 500 km. The highest possible altitude for a cometary optimum height is about 15 km, for a 120-m diameter comet. To maximize blast and thermal damage, a 4-km comet would have to break into tens of thousands fragments of this size and spread out over the entire continent, but that would require lateral forces that greatly exceed the drag force, and would not conserve energy. Airbursts are

DNA comet assay for rice seeds treated with low energy electrons ('soft-electrons')

International Nuclear Information System (INIS)

Todoriki, Setsuko; Hayashi, Toru

1999-01-01

As rice seeds are sometimes contaminated with phytopathogenic organisms such as blast disease fungi and nematodes, a novel non-chemical disinfection method for rice seeds is highly required. In order to develop a disinfection method, the effect of low energy electron ('soft-electrons') on seed DNA was examined by using the neutral comet assay. Rice seeds (whole grain) were treated with electrons of different acceleration voltages (180 kV to 1 MV) at a dose of 5 kGy. Nucleus suspensions were prepared from whole brown rice and subjected to electrophoresis. DNA from un-irradiated (control) seeds relaxed and produced comets with a short tail, most of the comets distributed within the range of comet length between 30 μm to 70 μm. In the case of seeds treated with electrons at acceleration voltages up to 190 kV, cells without seed coats were not damaged and the frequency histograms of comet length showed almost the same pattern as that for control. At acceleration voltages higher than 200 kV, the cells were distributed into two categories; DNA comets with a short tail (with little DNA damages, less than 70 μm in the comet length) and DNA comets with long tails (with sever strand breaks, more than 130 μm in the comet length). The ratios of damaged cells increased with increasing acceleration voltage. The growths of rice seedlings were not affected by the treatment with electrons at up to 200 kV. On the contrary, the cells of gamma-irradiated seed showed small variations in the comet length, and which were depending on radiation dose. The individual cells of gamma-irradiated seeds at 1 kGy showed shorter comet than the damaged cells with soft electron, seed treated with gamma rays (1-5 kGy) did not shoot nor root. (author)

Modeling the Deep Impact Near-nucleus Observations of H2O and CO2 in Comet 9P/Tempel 1 Using Asymmetric Spherical Coupled Escape Probability

Science.gov (United States)

Gersch, Alan M.; A’Hearn, Michael F.; Feaga, Lori M.

2018-04-01

We have applied our asymmetric spherical adaptation of Coupled Escape Probability to the modeling of optically thick cometary comae. Expanding on our previously published work, here we present models including asymmetric comae. Near-nucleus observations from the Deep Impact mission have been modeled, including observed coma morphology features. We present results for two primary volatile species of interest, H2O and CO2, for comet 9P/Tempel 1. Production rates calculated using our best-fit models are notably greater than those derived from the Deep Impact data based on the assumption of optically thin conditions, both for H2O and CO2 but more so for CO2, and fall between the Deep Impact values and the global pre-impact production rates measured at other observatories and published by Schleicher et al. (2006), Mumma et al. (2005), and Mäkinen et al. (2007).

Comets as Messengers from the Early Solar System - Emerging Insights on Delivery of Water, Nitriles, and Organics to Earth

Science.gov (United States)

Mumma, Michael J.; Charnley, Steven B.

2012-01-01

The question of exogenous delivery of water and organics to Earth and other young planets is of critical importance for understanding the origin of Earth's volatiles, and for assessing the possible existence of exo-planets similar to Earth. Viewed from a cosmic perspective, Earth is a dry planet, yet its oceans are enriched in deuterium by a large factor relative to nebular hydrogen and analogous isotopic enrichments in atmospheric nitrogen and noble gases are also seen. Why is this so? What are the implications for Mars? For icy Worlds in our Planetary System? For the existence of Earth-like exoplanets? An exogenous (vs. outgassed) origin for Earth's atmosphere is implied, and intense debate on the relative contributions of comets and asteroids continues - renewed by fresh models for dynamical transport in the protoplanetary disk, by revelations on the nature and diversity of volatile and rocky material within comets, and by the discovery of ocean-like water in a comet from the Kuiper Belt (cf., Mumma & Charnley 2011). Assessing the creation of conditions favorable to the emergence and sustenance of life depends critically on knowledge of the nature of the impacting bodies. Active comets have long been grouped according to their orbital properties, and this has proven useful for identifying the reservoir from which a given comet emerged (OC, KB) (Levison 1996). However, it is now clear that icy bodies were scattered into each reservoir from a range of nebular distances, and the comet populations in today's reservoirs thus share origins that are (in part) common. Comets from the Oort Cloud and Kuiper Disk reservoirs should have diverse composition, resulting from strong gradients in temperature and chemistry in the proto-planetary disk, coupled with dynamical models of early radial transport and mixing with later dispersion of the final cometary nuclei into the long-term storage reservoirs. The inclusion of material from the natal interstellar cloud is probable

Measurement of plasma and energetic charged particles in the proximity of Halley's comet

International Nuclear Information System (INIS)

Erdoes, Geza; Gombosi, Tamas; Kecskemety, Karoly; Somogyi, Antal; Tatrallyay, Mariella; Varga, Andras

1987-01-01

The instrumentation aboard the space probe VEGA for the exploration of Halley's comet contained the particle analyzers PLAZMAG and TUENDE-M. PLAZMAG was used for the measurement of the interaction between the low-energy solar plasma and the heavy ions from the comet. From the energy spectra measured near the nucleus of the comet the density distribution of ion groups can also be determined. TUENDE-M recorded the distribution of energetic heavy ions from the comet. The properties of various plasma regions within the 10 million km range from the comet's nucleus are discussed in detail. (R.P.)

Evaluation of irradiation in foods using DNA comet assay

International Nuclear Information System (INIS)

Khawar, Affaf; Bhatti, Ijaz Ahmad; Khan, Q.M.; Ali, T.; Khan, A.I.; Asi, M.R.

2011-01-01

Comet assay is a rapid, inexpensive and sensitive biological technique to detect DNA damage in food stuffs by irradiation. In this study the Comet assay is applied on foods of plant and animal origins. Samples were irradiated by using 60 Co gamma-radiation source. The applied doses were 2, 6 and 10 kGy for food of plant origin and 0.5, 1 and 2 kGy for meat items. The un-irradiated and irradiated samples were clearly differentiated on the basis of DNA fragmentation. During the electrophoresis study, it was found that in un-irradiated cells DNA remained intact and appeared as Comets without tail whereas in irradiated cells Comets with tails were visible due to stretching of fragmented DNA. Moreover, it was also revealed that the DNA tail length was dose dependent. Dry food stuffs (seeds) showed good results as compared to moist foods (meat, fruits and vegetables) due to the absence of background damage. (author)

COMETARY VOLATILES AND THE ORIGIN OF COMETS

International Nuclear Information System (INIS)

A'Hearn, Michael F.; Feaga, Lori M.; Sunshine, Jessica M.; Besse, Sebastien; Bodewits, Dennis; Farnham, Tony L.; Kelley, Michael S.; Keller, H. Uwe; Kawakita, Hideyo; Hampton, Donald L.; Kissel, Jochen; Klaasen, Kenneth P.; Yeomans, Donald K.; McFadden, Lucy A.; Meech, Karen J.; Schultz, Peter H.; Thomas, Peter C.; Veverka, Joseph; Groussin, Olivier; Lisse, Carey M.

2012-01-01

We describe recent results on the CO/CO 2 /H 2 O composition of comets together with a survey of older literature (primarily for CO/H 2 O) and compare these with models of the protoplanetary disk. Even with the currently small sample, there is a wide dispersion in abundance ratios and little if any systematic difference between Jupiter-family comets (JFCs) and long-period and Halley-type comets (LPCs and HTCs). We argue that the cometary observations require reactions on grain surfaces to convert CO to CO 2 and also require formation of all types of comets in largely, but not entirely, overlapping regions, probably between the CO and CO 2 snow lines. Any difference in the regions of formation is in the opposite direction from the classical picture with the JFCs having formed closer to the Sun than the LPCs. In the classical picture, the LPCs formed in the region of the giant planets and the JFCs formed in the Kuiper Belt. However, these data suggest, consistent with suggestions on dynamical grounds, that the JFCs and LPCs formed in largely overlapping regions where the giant planets are today and with JFCs on average forming slightly closer to the Sun than did the LPCs. Presumably at least the JFCs passed through the scattered disk on their way to their present dynamical family.

COMETARY VOLATILES AND THE ORIGIN OF COMETS

Energy Technology Data Exchange (ETDEWEB)

A' Hearn, Michael F.; Feaga, Lori M.; Sunshine, Jessica M.; Besse, Sebastien; Bodewits, Dennis; Farnham, Tony L.; Kelley, Michael S. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Keller, H. Uwe [Institute for Geophysics and Extraterrestrial Physics, Technische Universitaet Braunschweig, D-38106 Braunschweig (Germany); Kawakita, Hideyo [Department of Physics, Kyoto Sangyo University, Kamigamo JP Kita-ku, Kyoto 603-8555 (Japan); Hampton, Donald L. [Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775 (United States); Kissel, Jochen [Max-Planck-Institut for Solar System Research, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany); Klaasen, Kenneth P.; Yeomans, Donald K. [Jet Propulsion Laboratory/Caltech, Pasadena, CA 91109 (United States); McFadden, Lucy A. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Meech, Karen J. [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Schultz, Peter H. [Department of Geological Sciences, Brown University, Providence, RI 02912 (United States); Thomas, Peter C.; Veverka, Joseph [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Groussin, Olivier [Laboratoire d' Astrophysique de Marseille, Universite d' Aix-Marseille and CNRS, UMR7326, 38 rue F. Joliot-Curie, F-13388 Marseille Cedex 13 (France); Lisse, Carey M., E-mail: ma@astro.umd.edu [Space Department, JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States); and others

2012-10-10

We describe recent results on the CO/CO{sub 2}/H{sub 2}O composition of comets together with a survey of older literature (primarily for CO/H{sub 2}O) and compare these with models of the protoplanetary disk. Even with the currently small sample, there is a wide dispersion in abundance ratios and little if any systematic difference between Jupiter-family comets (JFCs) and long-period and Halley-type comets (LPCs and HTCs). We argue that the cometary observations require reactions on grain surfaces to convert CO to CO{sub 2} and also require formation of all types of comets in largely, but not entirely, overlapping regions, probably between the CO and CO{sub 2} snow lines. Any difference in the regions of formation is in the opposite direction from the classical picture with the JFCs having formed closer to the Sun than the LPCs. In the classical picture, the LPCs formed in the region of the giant planets and the JFCs formed in the Kuiper Belt. However, these data suggest, consistent with suggestions on dynamical grounds, that the JFCs and LPCs formed in largely overlapping regions where the giant planets are today and with JFCs on average forming slightly closer to the Sun than did the LPCs. Presumably at least the JFCs passed through the scattered disk on their way to their present dynamical family.

Asteroid-comet continuum objects in the solar system.

Science.gov (United States)

Hsieh, Henry H

2017-07-13

In this review presented at the Royal Society meeting, 'Cometary science after Rosetta', I present an overview of studies of small solar system objects that exhibit properties of both asteroids and comets (with a focus on so-called active asteroids). Sometimes referred to as 'transition objects', these bodies are perhaps more appropriately described as 'continuum objects', to reflect the notion that rather than necessarily representing actual transitional evolutionary states between asteroids and comets, they simply belong to the general population of small solar system bodies that happen to exhibit a continuous range of observational, physical and dynamical properties. Continuum objects are intriguing because they possess many of the properties that make classical comets interesting to study (e.g. relatively primitive compositions, ejection of surface and subsurface material into space where it can be more easily studied, and orbital properties that allow us to sample material from distant parts of the solar system that would otherwise be inaccessible), while allowing us to study regions of the solar system that are not sampled by classical comets.This article is part of the themed issue 'Cometary science after Rosetta'. © 2017 The Author(s).

Comet assay as a cold chain control tool

International Nuclear Information System (INIS)

Duarte, Renato Cesar

2009-01-01

Bearing in mind an ever more demanding market regarding the quality of food, it has been necessary to develop processes that meet the demands of consumers. Within the existing processes the cold chain and irradiation stand out. The cold chain comprises all the stages of conserving food from production, cooling, freezing, storing and transportation to the final consumer. Irradiation, as a means of conserving food, prolongs the shelf life, inhibits budding and reduces pathogenic contamination among other benefits. Is very important the identification of food degradation in function of failure on the processes which they were subjected. The comet assay is a screening test widely studied, considerate fast and with low cost. By the fact of the test identify breaks on the DNA, may be possible use the comet test on the control of cold chain failures that degrade de food. The labels and stamp, do not consider the previous food situation and indicate failures from the moment where they be placed in contact with the product. With the comet assay is possible to check the degradation that has occurred in liver chicken samples until the moment of comet's test realization. (author)

Comet Dust: The Diversity of Primitive Particles and Implications

Science.gov (United States)

John Bradley; Zolensky, Michael E.

2016-01-01

Comet dust is primitive and shows significant diversity. Our knowledge of the properties of primitive particles has expanded significantly through microscale investigations of cosmic dust samples (IDPs and AMMs) and of comet dust samples (Stardust and Rosetta's COSIMA), as well as through remote sensing (spectroscopy and imaging) via Spitzer and via spacecraft encounters with 103P/Hartley 2 and 67P/Churyumov-Gerasimenko. Microscale investigations show that comet dust and cosmic dust are particles of unequilibrated materials, including aggregates of materials unequilibrated at submicron scales. We call unequilibrated materials "primitive" and we deduce they were incorporated into ice-­-rich (H2O-, CO2-, and CO-ice) parent bodies that remained cold, i.e., into comets, because of the lack of aqueous or thermal alteration since particle aggregation; yet some Stardust olivines suggest mild thermal metamorphism. Primitive particles exhibit a diverse range of: structure and typology; size and size distribution of constituents; concentration and form of carbonaceous and organic matter; D-, N-, and O- isotopic enhancements over solar; Mg-, Fe-contentsof thesilicate minerals; the compositions and concentrations of sulfides, and of less abundant mineral species such as chondrules, CAIs and carbonates. The unifomity within a group of samples points to: aerodynamic sorting of particles and/or particle constituents; the inclusion of a limited range of oxygen fugacities; the inclusion or exclusion of chondrules; a selection of organics. The properites of primitive particles imply there were disk processes that resulted in different comets having particular selections of primitive materials. The diversity of primitive particles has implications for the diversity of materials in the protoplanetary disk present at the time and in the region where the comets formed.

Disruption of microtubule network rescues aberrant actin comets in dynamin2-depleted cells.

Directory of Open Access Journals (Sweden)

Yuji Henmi

Full Text Available A large GTPase dynamin, which is required for endocytic vesicle formation, regulates the actin cytoskeleton through its interaction with cortactin. Dynamin2 mutants impair the formation of actin comets, which are induced by Listeria monocytogenes or phosphatidylinositol-4-phosphate 5-kinase. However, the role of dynamin2 in the regulation of the actin comet is still unclear. Here we show that aberrant actin comets in dynamin2-depleted cells were rescued by disrupting of microtubule networks. Depletion of dynamin2, but not cortactin, significantly reduced the length and the speed of actin comets induced by Listeria. This implies that dynamin2 may regulate the actin comet in a cortactin-independent manner. As dynamin regulates microtubules, we investigated whether perturbation of microtubules would rescue actin comet formation in dynamin2-depleted cells. Treatment with taxol or colchicine created a microtubule-free space in the cytoplasm, and made no difference between control and dynamin2 siRNA cells. This suggests that the alteration of microtubules by dynamin2 depletion reduced the length and the speed of the actin comet.

Levy-taxis: a novel search strategy for finding odor plumes in turbulent flow-dominated environments

International Nuclear Information System (INIS)

Pasternak, Zohar; Grasso, Frank W; Bartumeus, Frederic

2009-01-01

Locating chemical plumes in aquatic or terrestrial environments is important for many economic, conservation, security and health related human activities. The localization process is composed mainly of two phases: finding the chemical plume and then tracking it to its source. Plume tracking has been the subject of considerable study whereas plume finding has received little attention. We address here the latter issue, where the searching agent must find the plume in a region often many times larger than the plume and devoid of the relevant chemical cues. The probability of detecting the plume not only depends on the movements of the searching agent but also on the fluid mechanical regime, shaping plume intermittency in space and time; this is a basic, general problem when exploring for ephemeral resources (e.g. moving and/or concealing targets). Here we present a bio-inspired search strategy named Levy-taxis that, under certain conditions, located odor plumes significantly faster and with a better success rate than other search strategies such as Levy walks (LW), correlated random walks (CRW) and systematic zig-zag. These results are based on computer simulations which contain, for the first time ever, digitalized real-world water flow and chemical plume instead of their theoretical model approximations. Combining elements of LW and CRW, Levy-taxis is particularly efficient for searching in flow-dominated environments: it adaptively controls the stochastic search pattern using environmental information (i.e. flow) that is available throughout the course of the search and shows correlation with the source providing the cues. This strategy finds natural application in real-world search missions, both by humans and autonomous robots, since it accommodates the stochastic nature of chemical mixing in turbulent flows. In addition, it may prove useful in the field of behavioral ecology, explaining and predicting the movement patterns of various animals searching for food

Levy-taxis: a novel search strategy for finding odor plumes in turbulent flow-dominated environments

Energy Technology Data Exchange (ETDEWEB)

Pasternak, Zohar; Grasso, Frank W [BioMimetic and Cognitive Robotics Laboratory, Department of Psychology, Brooklyn College, The City University of New York, 2900 Bedford Avenue, Brooklyn 11210, NY (United States); Bartumeus, Frederic [Department of Ecology and Evolutionary Biology and Princeton Environmental Institute, 106 Guyot Hall, Princeton University, Princeton 08544, NJ (United States)], E-mail: zpast@yahoo.com

2009-10-30

Locating chemical plumes in aquatic or terrestrial environments is important for many economic, conservation, security and health related human activities. The localization process is composed mainly of two phases: finding the chemical plume and then tracking it to its source. Plume tracking has been the subject of considerable study whereas plume finding has received little attention. We address here the latter issue, where the searching agent must find the plume in a region often many times larger than the plume and devoid of the relevant chemical cues. The probability of detecting the plume not only depends on the movements of the searching agent but also on the fluid mechanical regime, shaping plume intermittency in space and time; this is a basic, general problem when exploring for ephemeral resources (e.g. moving and/or concealing targets). Here we present a bio-inspired search strategy named Levy-taxis that, under certain conditions, located odor plumes significantly faster and with a better success rate than other search strategies such as Levy walks (LW), correlated random walks (CRW) and systematic zig-zag. These results are based on computer simulations which contain, for the first time ever, digitalized real-world water flow and chemical plume instead of their theoretical model approximations. Combining elements of LW and CRW, Levy-taxis is particularly efficient for searching in flow-dominated environments: it adaptively controls the stochastic search pattern using environmental information (i.e. flow) that is available throughout the course of the search and shows correlation with the source providing the cues. This strategy finds natural application in real-world search missions, both by humans and autonomous robots, since it accommodates the stochastic nature of chemical mixing in turbulent flows. In addition, it may prove useful in the field of behavioral ecology, explaining and predicting the movement patterns of various animals searching for food

Comet 81P/Wild 2 under a microscope

Energy Technology Data Exchange (ETDEWEB)

Brownlee, D; Tsou, P; Aleon, J; Alexander, C; Araki, T; Bajt, S; Baratta, G A; Bastien, R; Bland, P; Bleuet, P; Borg, J; Bradley, J P; Brearley, A; Brenker, F; Brennan, S; Bridges, J C; Browning, N; Brucato, J R; Bullock, E; Burchell, M J; Busemann, H; Butterworth, A; Chaussidon, M; Cheuvront, A; Chi, M; Cintala, M J; Clark, B C; Clemett, S J; Cody, G; Colangeli, L; Cooper, G; Cordier, P; Daghlian, C; Dai, Z R; D' Hendecourt, L; Djouadi, Z; Dominguez, G; Duxbury, T; Dworkin, J P; Ebel, D; Economou, T E; Fairey, S J; Fallon, S; Ferrini, G; Ferroir, T; Fleckenstein, H; Floss, C; Flynn, G; Franchi, I A; Fries, M; Gainsforth, Z; Gallien, J; Genge, M; Gilles, M K; Gillet, P; Gilmour, J; Glavin, D P; Gounelle, M; Grady, M M; Graham, G A; Grant, P G; Green, S F; Grossemy, F; Grossman, L; Grossman, J; Guan, Y; Hagiya, K; Harvey, R; Heck, P; Herzog, G F; Hoppe, P; Horz, F; Huth, J; Hutcheon, I D; Ishii, H; Ito, M; Jacob, D; Jacobsen, C; Jacobsen, S; Joswiak, D; Kearsley, A T; Keller, L; Khodja, H; Kilcoyne, A D; Kissel, J; Krot, A; Langenhorst, F; Lanzirotti, A; Le, L; Leshin, L; Leitner, J; Lemelle, L; Leroux, H; Liu, M; Luening, K; Lyon, I; MacPherson, G; Marcus, M A; Marhas, K; Matrajt, G; Meibom, A; Mennella, V; Messenger, K; Mikouchi, T; Mostefaoui, S; Nakamura, T; Nakano, T; Newville, M; Nittler, L R; Ohnishi, I; Ohsumi, K; Okudaira, K; Papanastassiou, D A; Palma, R; Palumbo, M E; Pepin, R O; Perkins, D; Perronnet, M; Pianetta, P; Rao, W; Rietmeijer, F; Robert, F; Rost, D; Rotundi, A; Ryan, R; Sandford, S A; Schwandt, C S; See, T H; Schlutter, D; Sheffield-Parker, J; Simionovici, A; Simon, S; Sitnitsky, I; Snead, C J; Spencer, M K; Stadermann, F J; Steele, A; Stephan, T; Stroud, R; Susini, J; Sutton, S R; Taheri, M; Taylor, S; Teslich, N; Tomeoka, K; Tomioka, N; Toppani, A; Trigo-Rodriguez, J M; Troadec, D; Tsuchiyama, A; Tuzolino, A J; Tyliszczak, T; Uesugi, K; Velbel, M; Vellenga, J; Vicenzi, E; Vincze, L; Warren, J; Weber, I; Weisberg, M; Westphal, A J; Wirick, S; Wooden, D; Wopenka, B; Wozniakiewicz, P; Wright, I; Yabuta, K; Yano, H; Young, E D; Zare, R N; Zega, T

2006-10-12

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales. Stardust was the first mission to return solid samples from a specific astronomical body other than the Moon. The mission, part of the NASA Discovery program, retrieved samples from a comet that is believed to have formed at the outer fringe of the solar nebula, just beyond the most distant planet. The samples, isolated from the planetary region of the solar system for billions of years, provide new insight into the formation of the solar system. The samples provide unprecedented opportunities both to corroborate astronomical (remote sensing) and sample analysis information (ground truth) on a known primitive solar system body and to compare preserved building blocks from the edge of the planetary system with sample-derived and astronomical data for asteroids, small bodies that formed more than an order of magnitude closer to the Sun. The asteroids, parents of most meteorites, formed by accretion of solids in warmer, denser, more collisionally evolved inner regions of the solar nebula where violent nebular events were capable of flash-melting millimeter-sized rocks, whereas comets formed in the coldest, least dense region. The samples collected by Stardust are the first primitive materials from a known body, and as such they provide contextual insight for all primitive meteoritic samples. About 200 investigators