Three-dimensional structure of the Trypanosome flagellum suggests that the paraflagellar rod functions as a biomechanical spring.

Directory of Open Access Journals (Sweden)

Louise C Hughes

Full Text Available Flagellum motility is critical for normal human development and for transmission of pathogenic protozoa that cause tremendous human suffering worldwide. Biophysical principles underlying motility of eukaryotic flagella are conserved from protists to vertebrates. However, individual cells exhibit diverse waveforms that depend on cell-specific elaborations on basic flagellum architecture. Trypanosoma brucei is a uniflagellated protozoan parasite that causes African sleeping sickness. The T. brucei flagellum is comprised of a 9+2 axoneme and an extra-axonemal paraflagellar rod (PFR, but the three-dimensional (3D arrangement of the underlying structural units is poorly defined. Here, we use dual-axis electron tomography to determine the 3D architecture of the T. brucei flagellum. We define the T. brucei axonemal repeating unit. We observe direct connections between the PFR and axonemal dyneins, suggesting a mechanism by which mechanochemical signals may be transmitted from the PFR to axonemal dyneins. We find that the PFR itself is comprised of overlapping laths organized into distinct zones that are connected through twisting elements at the zonal interfaces. The overall structure has an underlying 57 nm repeating unit. Biomechanical properties inferred from PFR structure lead us to propose that the PFR functions as a biomechanical spring that may store and transmit energy derived from axonemal beating. These findings provide insight into the structural foundations that underlie the distinctive flagellar waveform that is a hallmark of T. brucei cell motility.

Spatial ecology of the coachwhip, Masticophis flagellum (Squamata: Colubridae), in eastern Texas

Science.gov (United States)

Richard W. Johnson; Robert R. Fleet; Michael B. Keck; D. Craig Rudolph

2007-01-01

We radio-tracked nine Masticophis flagellum (Coachwhips) to determine home range, habitat use, and movements in eastern Texas from April to October 2000. Home ranges of Coachwhips contained more oak savanna macrohabitat than early-successional pine plantation or forested seep, based on the availability of these three macrohabitats in the study area....

THE STRUCTURE, ORIGIN, ISOLATION, AND COMPOSITION OF THE TUBULAR MASTIGONEMES OF THE OCHROMONAS FLAGELLUM

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Bouck, G. Benjamin

1971-01-01

The structure, assembly, and composition of the extracellular hairs (mastigonemes) of Ochromonas are detailed in this report. These mastigonemes form two lateral unbalanced rows, each row on opposite sides of the long anterior flagellum. Each mastigoneme consists of lateral filaments of two distinct sizes attached to a tubular shaft. The shaft is further differentiated into a basal region at one end and a group of from one to three terminal filaments at the free end. Mastigoneme ontogeny as revealed especially in deflagellated and regenerating cells appears to begin by assembly of the basal region and shaft within the perinuclear continuum. However, addition of lateral filaments to the shaft and extrusion of the mastigonemes to the cell surface is mediated by the Golgi complex. The ultimate distribution of mastigonemes on the flagellar surface seems to be the result of extrusion of mastigonemes near the base of the flagellum, and it is suggested that mastigonemes are then pulled up the flagellum as the axoneme elongates. Efforts to characterize mastigonemes biochemically after isolation and purification on cesium chloride (CsCl) followed by electrophoresis on acrylamide gels have demonstrated what appear to be a single major polypeptide and several differentially migrating carbohydrates. The polypeptide is not homologous with microtuble protein. The functionally anomalous role of mastigonemes in reversing flagellar thrust is discussed in relation to their distribution relative to flagellar anatomy and to the plane of flagellar undulations. PMID:5123323

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

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Zúñiga-Pérez, Jesús; Consonni, Vincent; Lymperakis, Liverios; Kong, Xiang; Trampert, Achim; Fernández-Garrido, Sergio; Brandt, Oliver; Renevier, Hubert; Keller, Stacia; Hestroffer, Karine; Wagner, Markus R.; Reparaz, Juan Sebastián; Akyol, Fatih; Rajan, Siddharth; Rennesson, Stéphanie; Palacios, Tomás; Feuillet, Guy

2016-12-01

The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade.

Divergence in Patterns of Leaf Growth Polarity Is Associated with the Expression Divergence of miR396.

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Das Gupta, Mainak; Nath, Utpal

2015-10-01

Lateral appendages often show allometric growth with a specific growth polarity along the proximo-distal axis. Studies on leaf growth in model plants have identified a basipetal growth direction with the highest growth rate at the proximal end and progressively lower rates toward the distal end. Although the molecular mechanisms governing such a growth pattern have been studied recently, variation in leaf growth polarity and, therefore, its evolutionary origin remain unknown. By surveying 75 eudicot species, here we report that leaf growth polarity is divergent. Leaf growth in the proximo-distal axis is polar, with more growth arising from either the proximal or the distal end; dispersed with no apparent polarity; or bidirectional, with more growth contributed by the central region and less growth at either end. We further demonstrate that the expression gradient of the miR396-GROWTH-REGULATING FACTOR module strongly correlates with the polarity of leaf growth. Altering the endogenous pattern of miR396 expression in transgenic Arabidopsis thaliana leaves only partially modified the spatial pattern of cell expansion, suggesting that the diverse growth polarities might have evolved via concerted changes in multiple gene regulatory networks. © 2015 American Society of Plant Biologists. All rights reserved.

Step-flow growth mode instability of N-polar GaN under N-excess

International Nuclear Information System (INIS)

Chèze, C.; Sawicka, M.; Siekacz, M.; Łucznik, B.; Boćkowski, M.; Skierbiszewski, C.; Turski, H.; Cywiński, G.; Smalc-Koziorowska, J.; Weyher, J. L.; Kryśko, M.

2013-01-01

GaN layers were grown on N-polar GaN substrates by plasma-assisted molecular beam epitaxy under different III/V ratios. Ga-rich conditions assure step-flow growth with atomically flat surface covered by doubly-bunched steps, as for Ga-polar GaN. Growth under N-excess however leads to an unstable step-flow morphology. Particularly, for substrates slightly miscut towards , interlacing fingers are covered by atomic steps pinned on both sides by small hexagonal pits. In contrast, a three-dimensional island morphology is observed on the Ga-polar equivalent sample. We attribute this result to lower diffusion barriers on N-polar compared to Ga-polar GaN under N-rich conditions

Comparison of Chlamydia trachomatis serovar L2 growth in polarized genital epithelial cells grown in three-dimensional culture with non-polarized cells.

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Dessus-Babus, Sophie; Moore, Cheryl G; Whittimore, Judy D; Wyrick, Priscilla B

2008-04-01

A common model for studying Chlamydia trachomatis and growing chlamydial stocks uses Lymphogranuloma venereum serovar L2 and non-polarized HeLa cells. However, recent publications indicate that the growth rate and progeny yields can vary considerably for a particular strain depending on the cell line/type used, and seem to be partially related to cell tropism. In the present study, the growth of invasive serovar L2 was compared in endometrial HEC-1B and endocervical HeLa cells polarized on collagen-coated microcarrier beads, as well as in HeLa cells grown in tissue culture flasks. Microscopy analysis revealed no difference in chlamydial attachment/entry patterns or in inclusion development throughout the developmental cycle between cell lines. Very comparable growth curves in both cell lines were also found using real-time PCR analysis, with increases in chlamydial DNA content of 400-500-fold between 2 and 36 h post-inoculation. Similar progeny yields with comparable infectivity were recovered from HEC-1B and HeLa cell bead cultures, and no difference in chlamydial growth was found in polarized vs. non-polarized HeLa cells. In conclusion, unlike other C. trachomatis strains such as urogenital serovar E, invasive serovar L2 grows equally well in physiologically different endometrial and endocervical environments, regardless of the host cell polarization state.

Dependence of N-polar GaN rod morphology on growth parameters during selective area growth by MOVPE

Science.gov (United States)

Li, Shunfeng; Wang, Xue; Mohajerani, Matin Sadat; Fündling, Sönke; Erenburg, Milena; Wei, Jiandong; Wehmann, Hergo-Heinrich; Waag, Andreas; Mandl, Martin; Bergbauer, Werner; Strassburg, Martin

2013-02-01

Selective area growth of GaN rods by metalorganic vapor phase epitaxy has attracted great interest due to its novel applications in optoelectronic and photonics. In this work, we will present the dependence of GaN rod morphology on various growth parameters i.e. growth temperature, H2/N2 carrier gas concentration, V/III ratio, total carrier gas flow and reactor pressure. It is found that higher growth temperature helps to increase the aspect ratio of the rods, but reduces the height homogeneity. Furthermore, H2/N2 carrier gas concentration is found to be a critical factor to obtain vertical rod growth. Pure nitrogen carrier gas leads to irregular growth of GaN structure, while an increase of hydrogen carrier gas results in vertical GaN rod growth. Higher hydrogen carrier gas concentration also reduces the diameter and enhances the aspect of the GaN rods. Besides, increase of V/III ratio causes reduction of the aspect ratio of N-polar GaN rods, which could be explained by the relatively lower growth rate on (000-1) N-polar top surface when supplying more ammonia. In addition, an increase of the total carrier gas flow leads to a decrease in the diameter and the average volume of GaN rods. These phenomena are tentatively explained by the change of partial pressure of the source materials and boundary layer thickness in the reactor. Finally, it is shown that the average volume of the N-polar GaN rods keeps a similar value for a reactor pressure PR of 66 and 125 mbar, while an incomplete filling of the pattern opening is observed with PR of 250 mbar. Room temperature photoluminescence spectrum of the rods is also briefly discussed.

Tip-induced domain growth on the non-polar cuts of lithium niobate single-crystals

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Alikin, D. O.; Ievlev, A. V.; Turygin, A. P.; Lobov, A. I.; Kalinin, S. V.; Shur, V. Ya.

2015-05-01

Currently, ferroelectric materials with designed domain structures are considered as a perspective material for new generation of photonic, data storage, and data processing devices. Application of external electric field is the most convenient way of the domain structure formation. Lots of papers are devoted to the investigation of domain kinetics on polar surface of crystals while the forward growth remains one of the most mysterious stages due to lack of experimental methods allowing to study it. Here, we performed tip-induced polarization reversal on X- and Y-non-polar cuts in single-crystal of congruent lithium niobate which allows us to study the forward growth with high spatial resolution. The revealed difference in the shape and length of domains induced on X- and Y-cuts is beyond previously developed theoretical approaches used for the theoretical consideration of the domains growth at non-polar ferroelectric surfaces. To explain experimental results, we used kinetic approach with anisotropy of screening efficiency along different crystallographic directions.

Thermal Thresholds of Phytoplankton Growth in Polar Waters and Their Consequences for a Warming Polar Ocean

KAUST Repository

Coello-Camba, Alexandra

2017-06-02

Polar areas are experiencing the steepest warming rates on Earth, a trend expected to continue in the future. In these habitats, phytoplankton communities constitute the basis of the food web and their thermal tolerance may dictate how warming affects these delicate environments. Here, we compiled available data on thermal responses of phytoplankton growth in polar waters. We assembled 53 growth-vs.-temperature curves (25 from the Arctic, 28 from the Southern oceans), indicating the limited information available for these ecosystems. Half of the data from Arctic phytoplankton came from natural communities where low ambient concentrations could limit growth rates. Phytoplankton from polar waters grew faster under small temperature increases until reaching an optimum (TOPT), and slowed when temperatures increased beyond this value. This left-skewed curves were characterized by higher activation energies (Ea) for phytoplankton growth above than below the TOPT. Combining these thermal responses we obtained a community TOPT of 6.5°C (±0.2) and 5.2°C (±0.1) for Arctic and Southern Ocean phytoplankton communities, respectively. These threshold temperatures were already exceeded at 70°N during the first half of August 2013, evidenced by sea surface temperatures (SSTs, satellite data, http://www.ncdc.noaa.gov). We forecasted SSTs for the end of the twenty-first century by assuming an overall 3°C increase, equivalent to a low emission scenario. Our forecasts show that SSTs at 70°N are expected to exceed TOPT during summer by 2100, and during the first half of August at 75°N. While recent Arctic spring temperatures average 0.5°C and −0.7°C at 70°N and 75°N, respectively, they could increase to 2.8°C at 70°N and 2.2°C at 75°N as we approach 2100. Such temperature increases could lead to intense phytoplankton blooms, shortened by fast nutrient consumption. As SSTs increase, thermal thresholds for phytoplankton growth would be eventually exceeded during bloom

Thermal Thresholds of Phytoplankton Growth in Polar Waters and Their Consequences for a Warming Polar Ocean

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Alexandra Coello-Camba

2017-06-01

Full Text Available Polar areas are experiencing the steepest warming rates on Earth, a trend expected to continue in the future. In these habitats, phytoplankton communities constitute the basis of the food web and their thermal tolerance may dictate how warming affects these delicate environments. Here, we compiled available data on thermal responses of phytoplankton growth in polar waters. We assembled 53 growth-vs.-temperature curves (25 from the Arctic, 28 from the Southern oceans, indicating the limited information available for these ecosystems. Half of the data from Arctic phytoplankton came from natural communities where low ambient concentrations could limit growth rates. Phytoplankton from polar waters grew faster under small temperature increases until reaching an optimum (TOPT, and slowed when temperatures increased beyond this value. This left-skewed curves were characterized by higher activation energies (Ea for phytoplankton growth above than below the TOPT. Combining these thermal responses we obtained a community TOPT of 6.5°C (±0.2 and 5.2°C (±0.1 for Arctic and Southern Ocean phytoplankton communities, respectively. These threshold temperatures were already exceeded at 70°N during the first half of August 2013, evidenced by sea surface temperatures (SSTs, satellite data, http://www.ncdc.noaa.gov. We forecasted SSTs for the end of the twenty-first century by assuming an overall 3°C increase, equivalent to a low emission scenario. Our forecasts show that SSTs at 70°N are expected to exceed TOPT during summer by 2100, and during the first half of August at 75°N. While recent Arctic spring temperatures average 0.5°C and −0.7°C at 70°N and 75°N, respectively, they could increase to 2.8°C at 70°N and 2.2°C at 75°N as we approach 2100. Such temperature increases could lead to intense phytoplankton blooms, shortened by fast nutrient consumption. As SSTs increase, thermal thresholds for phytoplankton growth would be eventually exceeded

Thermal Thresholds of Phytoplankton Growth in Polar Waters and Their Consequences for a Warming Polar Ocean

KAUST Repository

Coello-Camba, Alexandra; Agusti, Susana

2017-01-01

Polar areas are experiencing the steepest warming rates on Earth, a trend expected to continue in the future. In these habitats, phytoplankton communities constitute the basis of the food web and their thermal tolerance may dictate how warming affects these delicate environments. Here, we compiled available data on thermal responses of phytoplankton growth in polar waters. We assembled 53 growth-vs.-temperature curves (25 from the Arctic, 28 from the Southern oceans), indicating the limited information available for these ecosystems. Half of the data from Arctic phytoplankton came from natural communities where low ambient concentrations could limit growth rates. Phytoplankton from polar waters grew faster under small temperature increases until reaching an optimum (TOPT), and slowed when temperatures increased beyond this value. This left-skewed curves were characterized by higher activation energies (Ea) for phytoplankton growth above than below the TOPT. Combining these thermal responses we obtained a community TOPT of 6.5°C (±0.2) and 5.2°C (±0.1) for Arctic and Southern Ocean phytoplankton communities, respectively. These threshold temperatures were already exceeded at 70°N during the first half of August 2013, evidenced by sea surface temperatures (SSTs, satellite data, http://www.ncdc.noaa.gov). We forecasted SSTs for the end of the twenty-first century by assuming an overall 3°C increase, equivalent to a low emission scenario. Our forecasts show that SSTs at 70°N are expected to exceed TOPT during summer by 2100, and during the first half of August at 75°N. While recent Arctic spring temperatures average 0.5°C and −0.7°C at 70°N and 75°N, respectively, they could increase to 2.8°C at 70°N and 2.2°C at 75°N as we approach 2100. Such temperature increases could lead to intense phytoplankton blooms, shortened by fast nutrient consumption. As SSTs increase, thermal thresholds for phytoplankton growth would be eventually exceeded during bloom

Identification of capsule, biofilm, lateral flagellum, and type IV pili in Vibrio mimicus strains.

Science.gov (United States)

Tercero-Alburo, J J; González-Márquez, H; Bonilla-González, E; Quiñones-Ramírez, E I; Vázquez-Salinas, C

2014-11-01

Vibrio mimicus is a bacterium that causes gastroenteritis; it is closely related to Vibrio cholerae, and can cause acute diarrhea like cholera- or dysentery-type diarrhea. It is distributed worldwide. Factors associated with virulence (such as hemolysins, enterotoxins, proteases, phospholipases, aerobactin, and hemagglutinin) have been identified; however, its pathogenicity mechanism is still unknown. In pathogenic Vibrio species such as V. cholerae, Vibrio. parahaemolyticus and Vibrio vulnificus, capsule, biofilms, lateral flagellum, and type IV pili are structures described as essential for pathogenicity. These structures had not been described in V. mimicus until this work. We used 20 V. mimicus strains isolated from water (6), oyster (9), and fish (5) samples and we were able to identify the capsule, biofilm, lateral flagellum, and type IV pili through phenotypic tests, electron microscopy, PCR, and sequencing. In all tested strains, we observed and identified the presence of capsular exopolysaccharide, biofilm formation in an in vitro model, as well as swarming, multiple flagellation, and pili. In addition, we identified homologous genes to those described in other bacteria of the genus in which these structures have been found. Identification of these structures in V. mimicus is a contribution to the biology of this organism and can help to reveal its pathogenic behavior. Copyright © 2014 Elsevier Ltd. All rights reserved.

Gene co-expression analysis identifies gene clusters associated with isotropic and polarized growth in Aspergillus fumigatus conidia.

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Baltussen, Tim J H; Coolen, Jordy P M; Zoll, Jan; Verweij, Paul E; Melchers, Willem J G

2018-04-26

Aspergillus fumigatus is a saprophytic fungus that extensively produces conidia. These microscopic asexually reproductive structures are small enough to reach the lungs. Germination of conidia followed by hyphal growth inside human lungs is a key step in the establishment of infection in immunocompromised patients. RNA-Seq was used to analyze the transcriptome of dormant and germinating A. fumigatus conidia. Construction of a gene co-expression network revealed four gene clusters (modules) correlated with a growth phase (dormant, isotropic growth, polarized growth). Transcripts levels of genes encoding for secondary metabolites were high in dormant conidia. During isotropic growth, transcript levels of genes involved in cell wall modifications increased. Two modules encoding for growth and cell cycle/DNA processing were associated with polarized growth. In addition, the co-expression network was used to identify highly connected intermodular hub genes. These genes may have a pivotal role in the respective module and could therefore be compelling therapeutic targets. Generally, cell wall remodeling is an important process during isotropic and polarized growth, characterized by an increase of transcripts coding for hyphal growth and cell cycle/DNA processing when polarized growth is initiated. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

A new model for the spectral induced polarization signature of bacterial growth in porous media

Science.gov (United States)

Zhang, C.; Revil, A.; Atekwana, E. A.; Jardani, A.; Smith, S.

2012-12-01

Recent biogeophysics studies demonstrated the sensitivity of complex conductivity to bacterial growth and microbial mediated mineral transformations in porous media. Frequency-domain induced polarization is a minimally invasive manner to measure the complex conductivity of a material over a broad range of frequencies. The real component of complex conductivity is associated with electromigration of the charge carriers, and the imaginary component represents reversible energy storage of charge carriers at polarization length scales. Quantitative relationship between frequency-domain induced polarization responses and bacterial growth and decay in porous media is analyzed in this study using a new developed model. We focus on the direct contribution of bacteria themselves to the complex conductivity in porous media in the absence of biomineralization. At low frequencies, the induced polarization of bacteria (α-polarization) is related to the properties of the electrical double layer surrounding the membrane surface of bacteria. Surface conductivity and α-polarization are due to the Stern layer of the counterions occurring in a brush of polymers coating the surface of the bacteria, and can be related to the cation exchange capacity of the bacteria. From the modeling results, at low frequencies (model with reactive transport modeling in which the evolution of bacterial populations are usually described by Monod kinetics, we show that the changes in imaginary conductivity with time can be used to determine bacterial growth kinetics parameters such as the growth and endogenous decay coefficient.

Comparison of Chlamydia trachomatis serovar L2 growth in polarized genital epithelial cells grown in three-dimensional culture with non-polarized cells

OpenAIRE

Dessus-Babus, Sophie; Moore, Cheryl G.; Whittimore, Judy D.; Wyrick, Priscilla B.

2008-01-01

A common model for studying Chlamydia trachomatis and growing chlamydial stocks uses Lymphogranuloma venereum serovar L2 and non-polarized HeLa cells. However, recent publications indicate that the growth rate and progeny yields can vary considerably for a particular strain depending on the cell line/type used, and seem to be partially related to cell tropism. In the present study, the growth of invasive serovar L2 was compared in endometrial HEC-1B and endocervical HeLa cells polarized on co...

Comparison of efficacies of bovine immune colostral antibody and each immunoglobulin class against verotoxin 2, flagellum and somatic cells of Escherichia coli O157:H7 in mice.

Science.gov (United States)

Seita, Tetsurou; Kuribayashi, Takashi; Honjo, Toshio; Yamamoto, Shizuo

2013-04-01

The efficacy of bovine immune colostral (colostral) antibodies against verotoxin (VT) 2, flagellum and somatic cells of Escherichia coli (E. coli) O157:H7 in mice was determined. Three major immunoglobulin (Ig) classes were isolated from the colostral antibody against VT2 by affinity chromatography and were used for estimation. Mice inoculated with VT2 were administered each Ig class from the colostral antibody, colostral antibody (colostral whey containing antibody) or serum antibody against VT2 at 1 hour after VT2 inoculation. All control mice (20/20) died after administration of sterilized saline instead of the colostral antibody. The survival rate was 93.3% (14/15) after administration of S-IgA or IgM antibody, or colostral antibody. Survival rates for IgG antibody and serum antibody administration were 80% (12/15) and 60% (9/15), respectively. Serum concentrations of VT2, which was absorbed from the small intestine in mice after administration of VT2 and colostral antibody, were measured by fluorescence enzyme immunoassay (FEIA). Serum concentrations of VT2 after administration of colostral antibody were lower than those after administration of sterilized saline. Mice inoculated with VT2-producing E. coli 157:H7 were administered anti-flagellum or anti-somatic colostral antibodies. Survival rates for E. coli O157:H7-infected mice administered the anti-flagellum and anti-somatic colostral antibodies were 52.4% (11/21) and 22.2% (4/18), respectively. Furthermore, survival rates increased to 89.5% (17/19) with combined administration of anti-flagellum and anti-VT2 colostral antibodies. These results suggest that colostral antibodies against VT2, flagellum and somatic cells are effective against E. coli O157:H7 infection. Copyright © 2012. Published by Elsevier B.V.

Growth and characterization of semi-polar (11-22) GaN on patterned (113) Si substrates

International Nuclear Information System (INIS)

Bai, J; Yu, X; Gong, Y; Hou, Y N; Zhang, Y; Wang, T

2015-01-01

Patterned (113) Si substrates have been fabricated for the growth of (11-22) semi-polar GaN, which completely eliminates one of the great issues in the growth of semi-polar GaN on silicon substrates, ‘Ga melting-back’. Furthermore, unlike any other mask patterning approaches which normally lead to parallel grooves along a particular orientation, our approach is to form periodic square window patterns. As a result, crack-free semi-polar (11-22) GaN with a significant improvement in crystal quality has been achieved, in particular, basal stacking faults (BSFs) have been significantly reduced. The mechanism for the defect suppression has been investigated based on detailed transmission electron microscopy measurements. It has been found that the BSFs can be impeded effectively at an early growth stage due to the priority growth along the 〈0001〉 direction. The additional 〈1-100〉 lateral growth above the masks results in a further reduction in dislocation density. The significant reduction in BSFs has been confirmed by low temperature photoluminescence measurements. (paper)

Avoiding polar catastrophe in the growth of polarly orientated nickel perovskite thin films by reactive oxide molecular beam epitaxy

International Nuclear Information System (INIS)

Yang, H. F.; Liu, Z. T.; Fan, C. C.; Xiang, P.; Zhang, K. L.; Li, M. Y.; Liu, J. S.; Yao, Q.; Shen, D. W.

2016-01-01

By means of the state-of-the-art reactive oxide molecular beam epitaxy, we synthesized (001)- and (111)-orientated polar LaNiO 3 thin films. In order to avoid the interfacial reconstructions induced by polar catastrophe, screening metallic Nb-doped SrTiO 3 and iso-polarity LaAlO 3 substrates were chosen to achieve high-quality (001)-orientated films in a layer-by-layer growth mode. For largely polar (111)-orientated films, we showed that iso-polarity LaAlO 3 (111) substrate was more suitable than Nb-doped SrTiO 3 . In situ reflection high-energy electron diffraction, ex situ high-resolution X-ray diffraction, and atomic force microscopy were used to characterize these films. Our results show that special attentions need to be paid to grow high-quality oxide films with polar orientations, which can prompt the explorations of all-oxide electronics and artificial interfacial engineering to pursue intriguing emergent physics like proposed interfacial superconductivity and topological phases in LaNiO 3 based superlattices.

FliO Regulation of FliP in the Formation of the Salmonella enterica Flagellum

OpenAIRE

Barker, Clive S.; Meshcheryakova, Irina V.; Kostyukova, Alla S.; Samatey, Fadel A.

2010-01-01

The type III secretion system of the Salmonella flagellum consists of 6 integral membrane proteins: FlhA, FlhB, FliO, FliP, FliQ, and FliR. However, in some other type III secretion systems, a homologue of FliO is apparently absent, suggesting it has a specialized role. Deleting the fliO gene from the chromosome of a motile strain of Salmonella resulted in a drastic decrease of motility. Incubation of the ΔfliO mutant strain in motility agar, gave rise to pseudorevertants containing extrageni...

Age, growth rate, and otolith growth of polar cod (Boreogadus saida in two fjords of Svalbard, Kongsfjorden and Rijpfjorden

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Dariusz P. Fey

2017-10-01

Full Text Available This work presents biological information for polar cod (Boreogadus saida collected with a Campelen 1800 shrimp bottom trawl in Kongsfjorden (two stations located in the inner part of the fjord adjacent to the glacier and Rijpfjorden (one station at the entrance to the fjord in September and October 2013. The otolith-based ages of polar cod collected in Kongsfjorden (6.1–24 cm total length TL; n = 813 ranged from 0 to 4 years. The growth rate was relatively constant at approximately 4.7 cm year−1 between years 1 and 4, which indicates that growth was fast in the glacier area. The ages of polar cod collected in Rijpfjorden (8.6–15.9 cm TL; n = 64 ranged from 2 to 3 years. The fish from Rijpfjorden were smaller at age than those from Kongsfjorden, and their growth rate between years 2 and 3 (no other age classes were available was approximately 3.3 cm year−1. In both fjords, males and females were of the same size-at-age and the same weight-at-TL. The small sampling area means that the results on growth rate are not representative of the entire fjords. Instead, the results can be discussed as presenting the possible growth rates of some populations. A strong relationship was identified between otolith size (length and weight and fish size (TL and TW, with no differences between males and females or the fjords. A significant, strong relationship was also noted between fish and otolith growth rates.

Modulation of flagellum attachment zone protein FLAM3 and regulation of the cell shape in Trypanosoma brucei life cycle transitions

Czech Academy of Sciences Publication Activity Database

Sunter, J.C.; Benz, C.; Andre, L.; Whipple, S.; McKean, P.G.; Gull, K.; Ginger, M. L.; Lukeš, Julius

2015-01-01

Roč. 128, č. 16 (2015), s. 3117-3130 ISSN 0021-9533 R&D Projects: GA MŠk(CZ) EE2.3.30.0032; GA MŠk LH12104 EU Projects: European Commission(XE) 316304 Institutional support: RVO:60077344 Keywords : Trypanosomes * Morphogenesis * Flagellum attachment zone Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 4.706, year: 2015

The non-flagellar type III secretion system evolved from the bacterial flagellum and diversified into host-cell adapted systems.

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Sophie S Abby

2012-09-01

Full Text Available Type 3 secretion systems (T3SSs are essential components of two complex bacterial machineries: the flagellum, which drives cell motility, and the non-flagellar T3SS (NF-T3SS, which delivers effectors into eukaryotic cells. Yet the origin, specialization, and diversification of these machineries remained unclear. We developed computational tools to identify homologous components of the two systems and to discriminate between them. Our analysis of >1,000 genomes identified 921 T3SSs, including 222 NF-T3SSs. Phylogenomic and comparative analyses of these systems argue that the NF-T3SS arose from an exaptation of the flagellum, i.e. the recruitment of part of the flagellum structure for the evolution of the new protein delivery function. This reconstructed chronology of the exaptation process proceeded in at least two steps. An intermediate ancestral form of NF-T3SS, whose descendants still exist in Myxococcales, lacked elements that are essential for motility and included a subset of NF-T3SS features. We argue that this ancestral version was involved in protein translocation. A second major step in the evolution of NF-T3SSs occurred via recruitment of secretins to the NF-T3SS, an event that occurred at least three times from different systems. In rhizobiales, a partial homologous gene replacement of the secretin resulted in two genes of complementary function. Acquisition of a secretin was followed by the rapid adaptation of the resulting NF-T3SSs to multiple, distinct eukaryotic cell envelopes where they became key in parasitic and mutualistic associations between prokaryotes and eukaryotes. Our work elucidates major steps of the evolutionary scenario leading to extant NF-T3SSs. It demonstrates how molecular evolution can convert one complex molecular machine into a second, equally complex machine by successive deletions, innovations, and recruitment from other molecular systems.

Ferroelectric Polarization Switching Dynamics and Domain Growth of Triglycine Sulfate and Imidazolium Perchlorate

KAUST Repository

Ma, He; Gao, Wenxiu; Wang, Junling; Wu, Tao; Yuan, Guoliang; Liu, Junming; Liu, Zhiguo

2016-01-01

The weak bond energy and large anisotropic domain wall energy induce many special characteristics of the domain nucleation, growth, and polarization switch in triglycine sulfate (TGS) and imidazolium perchlorate (IM), two typical molecular

Rational growth of semi-polar ZnO texture on a glass substrate for optoelectronic applications

Science.gov (United States)

Lu, B.; Ma, M. J.; Ye, Y. H.; Lu, J. G.; He, H. P.; Ye, Z. Z.

2013-02-01

Semi-polar ZnO films with surface texture were grown on glass substrates via pulsed-laser deposition (PLD) through Co-Ga co-doping. Oxygen pressure (PO2) was found to have significant effects on the structural and optical properties of the Zn(Co, Ga)O (ZCGO) films. A self-textured film with (1\\,0\\,\\bar {1}\\,1) preferred orientation (PO) was achieved by varying the growth conditions including a crucial narrow PO2 window and growth time. A possible mechanism underlying the PO evolution and the final texture of the films was proposed, which can be attributed to the collaboration of the doping effect and the PO2-dependent evolutionary selection process, in which certain grains can have increased vertical growth rate with respect to the substrate surface through interplane diffusion. Moreover, the growth of undoped pure ZnO films proceeded by using the (1\\,0\\,\\bar {1}\\,1) ZCGO film as a buffer layer. The ZnO layers retained a semi-polar characteristic with improved crystallinity and better optical quality. The epitaxy-like orientation of ZnO layers grown on (1\\,0\\,\\bar {1}\\,1) ZCGO films has applications in the development of semi-polar ZnO-based light-emitting diodes.

Polarity, cell division, and out-of-equilibrium dynamics control the growth of epithelial structures

Science.gov (United States)

Cerruti, Benedetta; Puliafito, Alberto; Shewan, Annette M.; Yu, Wei; Combes, Alexander N.; Little, Melissa H.; Chianale, Federica; Primo, Luca; Serini, Guido; Mostov, Keith E.; Celani, Antonio

2013-01-01

The growth of a well-formed epithelial structure is governed by mechanical constraints, cellular apico-basal polarity, and spatially controlled cell division. Here we compared the predictions of a mathematical model of epithelial growth with the morphological analysis of 3D epithelial structures. In both in vitro cyst models and in developing epithelial structures in vivo, epithelial growth could take place close to or far from mechanical equilibrium, and was determined by the hierarchy of time-scales of cell division, cell–cell rearrangements, and lumen dynamics. Equilibrium properties could be inferred by the analysis of cell–cell contact topologies, and the nonequilibrium phenotype was altered by inhibiting ROCK activity. The occurrence of an aberrant multilumen phenotype was linked to fast nonequilibrium growth, even when geometric control of cell division was correctly enforced. We predicted and verified experimentally that slowing down cell division partially rescued a multilumen phenotype induced by altered polarity. These results improve our understanding of the development of epithelial organs and, ultimately, of carcinogenesis. PMID:24145168

Polarized Emission from Conjugated Polymer Chains Aligned by Epitaxial Growth during Off-Center Spin-Coating

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Takuya Anzai

2017-01-01

Full Text Available Due to their macromolecular nature, conjugated polymers can be relatively easily aligned by applying a variety of processes resulting in either elongation or ordering of their conjugated backbones. Processes that induce chain alignment include electrospinning, mechanical rubbing, epitaxial growth, and nanoconfinement and unidirectional deposition techniques such as off-center spin-coating. In this study, we compare these deposition techniques by applying them to a green-emitting conjugated polymer material that exhibits liquid crystalline phase behavior. Our study reveals that while methods such as electrospinning and mechanical rubbing can be useful to locally generate polymer chain alignment, the combination of epitaxial growth using 1,3,5-trichlorobenzene as crystallizing agent with off-center spin-coating results in the formation of anisotropic nanofiber-like structures with enhanced crystallinity degree and polarized light-emission properties. The unidirectional epitaxial growth was also applied to a red-emitting polymer that exhibits polarization ratios up to 4.1. Our results emphasize that this simple solution formulation and process can be used for the fabrication of polarized thin films of a variety of conjugated polymers with potential applications in the advanced display technologies or analytical equipment fields.

Endothelial Cell Migration and Vascular Endothelial Growth Factor Expression Are the Result of Loss of Breast Tissue Polarity

Energy Technology Data Exchange (ETDEWEB)

Chen, Amy; Cuevas, Ileana; Kenny, Paraic A; Miyake, Hiroshi; Mace, Kimberley; Ghajar, Cyrus; Boudreau, Aaron; Bissell, Mina; Boudreau, Nancy

2009-05-26

Recruiting a new blood supply is a rate-limiting step in tumor progression. In a three-dimensional model of breast carcinogenesis, disorganized, proliferative transformed breast epithelial cells express significantly higher expression of angiogenic genes compared with their polarized, growth-arrested nonmalignant counterparts. Elevated vascular endothelial growth factor (VEGF) secretion by malignant cells enhanced recruitment of endothelial cells (EC) in heterotypic cocultures. Significantly, phenotypic reversion of malignant cells via reexpression of HoxD10, which is lost in malignant progression, significantly attenuated VEGF expression in a hypoxia-inducible factor 1{alpha}-independent fashion and reduced EC migration. This was due primarily to restoring polarity: forced proliferation of polarized, nonmalignant cells did not induce VEGF expression and EC recruitment, whereas disrupting the architecture of growth-arrested, reverted cells did. These data show that disrupting cytostructure activates the angiogenic switch even in the absence of proliferation and/or hypoxia and restoring organization of malignant clusters reduces VEGF expression and EC activation to levels found in quiescent nonmalignant epithelium. These data confirm the importance of tissue architecture and polarity in malignant progression.

Polarity control and growth mode of InN on yttria-stabilized zirconia (111) surfaces

International Nuclear Information System (INIS)

Kobayashi, Atsushi; Okubo, Kana; Ohta, Jitsuo; Oshima, Masaharu; Fujioka, Hiroshi

2012-01-01

We have found that polarity of epitaxial InN layers has been controlled by choice of a capping material during high-temperature annealing of yttria-stabilized zirconia (YSZ) (111) substrates in air. Angle-resolved X-ray photoelectron spectroscopy has revealed that the amount of segregation of Y atoms to the YSZ surface depended on the capping material of the substrates. In-polar and N-polar InN have been reproducibly grown on Y-segregated and Y-segregation-free YSZ surfaces, respectively. We have also found that the growth of the first monolayer (ML) of N-polar InN proceeds in a step-flow mode which then switches to layer-by-layer mode after the coverage by 1-ML-thick InN. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Two New Cyathane Diterpenoids from Mycelial Cultures of the Medicinal Mushroom Hericium erinaceus and the Rare Species, Hericium flagellum

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Zeljka Rupcic

2018-03-01

Full Text Available Basidiomycetes of the genus Hericium are among the most praised medicinal and edible mushrooms, which are known to produce secondary metabolites with the potential to treat neurodegenerative diseases. This activity has been attributed to the discovery of various terpenoids that can stimulate the production of nerve growth factor (NGF or (as established more recently brain-derived neurotrophic factor (BDNF in cell-based bioassays. The present study reports on the metabolite profiles of a Lion’s Mane mushroom (Hericium erinaceus strain and a strain of the rare species, Hericium flagellum (synonym H. alpestre. While we observed highly similar metabolite profiles between the two strains that were examined, we isolated two previously undescribed metabolites, given the trivial names erinacines Z1 and Z2. Their chemical structures were elucidated by means of nuclear magnetic resonance (NMR spectroscopy and high resolution mass spectrometry. Along with six further, previously identified cyathane diterpenes, the novel erinacines were tested for neurotrophin inducing effects. We found that erinacines act on BDNF, which is a neurotrophic factor that has been reported recently by us to be induced by the corallocins, but as well on NGF expression, which is consistent with the literature.

Two New Cyathane Diterpenoids from Mycelial Cultures of the Medicinal Mushroom Hericium erinaceus and the Rare Species, Hericium flagellum.

Science.gov (United States)

Rupcic, Zeljka; Rascher, Monique; Kanaki, Sae; Köster, Reinhard W; Stadler, Marc; Wittstein, Kathrin

2018-03-06

Basidiomycetes of the genus Hericium are among the most praised medicinal and edible mushrooms, which are known to produce secondary metabolites with the potential to treat neurodegenerative diseases. This activity has been attributed to the discovery of various terpenoids that can stimulate the production of nerve growth factor ( NGF ) or (as established more recently) brain-derived neurotrophic factor ( BDNF ) in cell-based bioassays. The present study reports on the metabolite profiles of a Lion's Mane mushroom ( Hericium erinaceus ) strain and a strain of the rare species, Hericium flagellum (synonym H. alpestre ). While we observed highly similar metabolite profiles between the two strains that were examined, we isolated two previously undescribed metabolites, given the trivial names erinacines Z1 and Z2. Their chemical structures were elucidated by means of nuclear magnetic resonance (NMR) spectroscopy and high resolution mass spectrometry. Along with six further, previously identified cyathane diterpenes, the novel erinacines were tested for neurotrophin inducing effects. We found that erinacines act on BDNF , which is a neurotrophic factor that has been reported recently by us to be induced by the corallocins, but as well on NGF expression, which is consistent with the literature.

Dynamics of actin cables in polarized growth of the filamentous fungus Aspergillus nidulans

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Anna eBergs

2016-05-01

Full Text Available Highly polarized growth of filamentous fungi requires a continuous supply of proteins and lipids to the hyphal tip. This transport is managed by vesicle trafficking via the actin and microtubule cytoskeletons and their associated motor proteins. Particularly, actin cables originating from the hyphal tip are essential for hyphal growth. Although specific marker proteins to visualize actin cables have been developed in filamentous fungi, the exact organization and dynamics of actin cables has remained elusive. Here we visualized actin cables using tropomyosin (TpmA and Lifeact fused to fluorescent proteins in Aspergillus nidulans and studied the dynamics and regulation. GFP tagged TpmA visualized dynamic actin cables formed from the hyphal tip with cycles of elongation and shrinkage. The elongation and shrinkage rates of actin cables were similar and approximately 0.6 μm/s. Comparison of actin markers revealed that high concentrations of Lifeact reduced actin dynamics. Simultaneous visualization of actin cables and microtubules suggests temporally and spatially coordinated polymerization and depolymerization between the two cytoskeletons. Our results provide new insights into the molecular mechanism of ordered polarized growth regulated by actin cables and microtubules.

Ferroelectric Polarization Switching Dynamics and Domain Growth of Triglycine Sulfate and Imidazolium Perchlorate

KAUST Repository

Ma, He

2016-04-10

The weak bond energy and large anisotropic domain wall energy induce many special characteristics of the domain nucleation, growth, and polarization switch in triglycine sulfate (TGS) and imidazolium perchlorate (IM), two typical molecular ferroelectrics. Their domain nucleation and polarization switch are rather slower than those of conventional oxide ferroelectrics, which may be due to the weaker bond energy of hydrogen bond or van der Waals bond than that of ionic bond. These chemical bonds dominate the elastic energy, with the latter being an important component of domain wall energy and playing an important role in domain nucleation and domain growth. The ratio of anisotropic domain wall energy to Gibbs free energy is large in TGS and IM, which allows a favorable domain shape and a special domain evolution under a certain electric field. Therefore, this study not only sheds light on the physical nature but also indicates the application direction for molecular ferroelectrics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Carbon nanotube growth on nanozirconia under strong cathodic polarization in steam and carbon dioxide

DEFF Research Database (Denmark)

Tao, Youkun; Ebbesen, Sune Dalgaard; Zhang, Wei

2014-01-01

nanozirconia acting as a catalyst for the growth of carbon nanotubes (CNTs) during electrochemical conversion of carbon dioxide and water in a nickel-yttria- stabilized zirconia cermet under strong cathodic polarization. An electrocatalytic mechanism is proposed for the growth of the CNTs. ${{{\\rm {\\rm V......Growth of carbon nanotubes (CNTs) catalyzed by zirconia nanoparticles was observed in the Ni-yttria doped zirconia (YSZ) composite cathode of a solid oxide electrolysis cell (SOEC) at approximately 875 °C during co-electrolysis of CO2 and H2O to produce CO and H 2. CNT was observed to grow under...

Material and device studies for the development of ultra-violet light emitting diodes (UV-LEDS) along polar, non-polar and semi-polar directions

Science.gov (United States)

Chandrasekaran, Ramya

Over the past few years, significant effort was dedicated to the development of ultraviolet light emitting diodes (UV-LEDs) for a variety of applications. Such applications include chemical and biological detection, water purification and solid-state lighting. III-Nitride LEDs based on multiple quantum wells (MQWs) grown along the conventional [0001] (polar) direction suffer from the quantum confined Stark effect (QCSE), due to the existence of strong electric fields that arise from spontaneous and piezoelectric polarization. Thus, there is strong motivation to develop MQW-based III-nitride LED structures grown along non-polar and semi-polar directions. The goal of this dissertation is to develop UV-LEDs along the [0001] polar and [11 2¯ 0] non-polar directions by the method of Molecular Beam Epitaxy (MBE). The polar and non-polar LEDs were grown on the C-plane and R-plane sapphire substrates respectively. This work is a combination of materials science studies related to the nucleation, growth and n- and p-type doping of III-nitride films on these two substrates, as well as device studies related to fabrication and characterization of UV-LEDs. It was observed that the crystallographic orientation of the III-nitride films grown on R-plane sapphire depends strongly on the kinetic conditions of growth of the Aluminum Nitride (AIN) buffer. Specifically, growth of the AIN buffer under group III-rich conditions leads to nitride films having the (11 2¯ 0) non polar planes parallel to the sapphire surface, while growth of the buffer under nitrogen rich conditions leads to nitride films with the (11 2¯ 6) semi-polar planes parallel to the sapphire surface. The electron concentration and mobility for the films grown along the polar, non-polar and semi-polar directions were investigated. P-type doping of Gallium Nitride (GaN) films grown on the nonpolar (11 2¯ 0) plane do not suffer from polarity inversion and thus the material was doped p-type with a hole concentration

Mechanosensation Dynamically Coordinates Polar Growth and Cell Wall Assembly to Promote Cell Survival.

Science.gov (United States)

Davì, Valeria; Tanimoto, Hirokazu; Ershov, Dmitry; Haupt, Armin; De Belly, Henry; Le Borgne, Rémi; Couturier, Etienne; Boudaoud, Arezki; Minc, Nicolas

2018-04-23

How growing cells cope with size expansion while ensuring mechanical integrity is not known. In walled cells, such as those of microbes and plants, growth and viability are both supported by a thin and rigid encasing cell wall (CW). We deciphered the dynamic mechanisms controlling wall surface assembly during cell growth, using a sub-resolution microscopy approach to monitor CW thickness in live rod-shaped fission yeast cells. We found that polar cell growth yielded wall thinning and that thickness negatively influenced growth. Thickness at growing tips exhibited a fluctuating behavior with thickening phases followed by thinning phases, indicative of a delayed feedback promoting thickness homeostasis. This feedback was mediated by mechanosensing through the CW integrity pathway, which probes strain in the wall to adjust synthase localization and activity to surface growth. Mutants defective in thickness homeostasis lysed by rupturing the wall, demonstrating its pivotal role for walled cell survival. Copyright © 2018 Elsevier Inc. All rights reserved.

Impact of AlN seeding layer growth rate in MOVPE growth of semi-polar gallium nitride structures on high index silicon

Energy Technology Data Exchange (ETDEWEB)

Ravash, Roghaiyeh; Blaesing, Juergen; Hempel, Thomas; Noltemeyer, Martin; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-University Magdeburg, FNW/IEP/AHE, Postfach 4120, 39016 Magdeburg (Germany)

2011-03-15

We present metal organic vapor phase epitaxy growth of semi-polar GaN structures on high index silicon surfaces. The crystallographic structure of GaN grown on Si(112), (115), and (117) substrates is investigated by X-ray analysis and scanning electron microscopy. X-ray diffraction was performed in Bragg Brentano geometry as well as pole figure measurements. The results demonstrate that the orientation of GaN crystallites on Si is significantly dependent on thickness of the AlN seeding layer and TMAl-flow rate. We observe that the crystallographic structures of GaN by applying thin AlN seeding layers grown with high TMAl-flow rate depend on Si surface direction while they are independent for thicker layers. By applying such seeding layer we obtain single crystalline semi-polar GaN on Si(112), while GaN structures grown with the same growth parameters on Si(117) show four components of GaN(0002). (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Epidermal growth factor induction of front–rear polarity and migration in keratinocytes is mediated by integrin-linked kinase and ELMO2

Science.gov (United States)

Ho, Ernest; Dagnino, Lina

2012-01-01

Epidermal growth factor (EGF) is a potent chemotactic and mitogenic factor for epidermal keratinocytes, and these properties are central for normal epidermal regeneration after injury. The involvement of mitogen-activated protein kinases as mediators of the proliferative effects of EGF is well established. However, the molecular mechanisms that mediate motogenic responses to this growth factor are not clearly understood. An obligatory step for forward cell migration is the development of front–rear polarity and formation of lamellipodia at the leading edge. We show that stimulation of epidermal keratinocytes with EGF, but not with other growth factors, induces development of front–rear polarity and directional migration through a pathway that requires integrin-linked kinase (ILK), Engulfment and Cell Motility-2 (ELMO2), integrin β1, and Rac1. Furthermore, EGF induction of front–rear polarity and chemotaxis require the tyrosine kinase activity of the EGF receptor and are mediated by complexes containing active RhoG, ELMO2, and ILK. Our findings reveal a novel link between EGF receptor stimulation, ILK-containing complexes, and activation of small Rho GTPases necessary for acquisition of front–rear polarity and forward movement. PMID:22160594

Epidermal growth factor induction of front-rear polarity and migration in keratinocytes is mediated by integrin-linked kinase and ELMO2.

Science.gov (United States)

Ho, Ernest; Dagnino, Lina

2012-02-01

Epidermal growth factor (EGF) is a potent chemotactic and mitogenic factor for epidermal keratinocytes, and these properties are central for normal epidermal regeneration after injury. The involvement of mitogen-activated protein kinases as mediators of the proliferative effects of EGF is well established. However, the molecular mechanisms that mediate motogenic responses to this growth factor are not clearly understood. An obligatory step for forward cell migration is the development of front-rear polarity and formation of lamellipodia at the leading edge. We show that stimulation of epidermal keratinocytes with EGF, but not with other growth factors, induces development of front-rear polarity and directional migration through a pathway that requires integrin-linked kinase (ILK), Engulfment and Cell Motility-2 (ELMO2), integrin β1, and Rac1. Furthermore, EGF induction of front-rear polarity and chemotaxis require the tyrosine kinase activity of the EGF receptor and are mediated by complexes containing active RhoG, ELMO2, and ILK. Our findings reveal a novel link between EGF receptor stimulation, ILK-containing complexes, and activation of small Rho GTPases necessary for acquisition of front-rear polarity and forward movement.

Loss of the flagellum happened only once in the fungal lineage: phylogenetic structure of Kingdom Fungi inferred from RNA polymerase II subunit genes

Directory of Open Access Journals (Sweden)

Hodson Matthew C

2006-09-01

Full Text Available Abstract Background At present, there is not a widely accepted consensus view regarding the phylogenetic structure of kingdom Fungi although two major phyla, Ascomycota and Basidiomycota, are clearly delineated. Regarding the lower fungi, Zygomycota and Chytridiomycota, a variety of proposals have been advanced. Microsporidia may or may not be fungi; the Glomales (vesicular-arbuscular mycorrhizal fungi may or may not constitute a fifth fungal phylum, and the loss of the flagellum may have occurred either once or multiple times during fungal evolution. All of these issues are capable of being resolved by a molecular phylogenetic analysis which achieves strong statistical support for major branches. To date, no fungal phylogeny based upon molecular characters has satisfied this criterion. Results Using the translated amino acid sequences of the RPB1 and RPB2 genes, we have inferred a fungal phylogeny that consists largely of well-supported monophyletic phyla. Our major results, each with significant statistical support, are: (1 Microsporidia are sister to kingdom Fungi and are not members of Zygomycota; that is, Microsporidia and fungi originated from a common ancestor. (2 Chytridiomycota, the only fungal phylum having a developmental stage with a flagellum, is paraphyletic and is the basal lineage. (3 Zygomycota is monophyletic based upon sampling of Trichomycetes, Zygomycetes, and Glomales. (4 Zygomycota, Basidiomycota, and Ascomycota form a monophyletic group separate from Chytridiomycota. (5 Basidiomycota and Ascomycota are monophyletic sister groups. Conclusion In general, this paper highlights the evolutionary position and significance of the lower fungi (Zygomycota and Chytridiomycota. Our results suggest that loss of the flagellum happened only once during early stages of fungal evolution; consequently, the majority of fungi, unlike plants and animals, are nonflagellated. The phylogeny we infer from gene sequences is the first one that is

Loss of the flagellum happened only once in the fungal lineage: phylogenetic structure of kingdom Fungi inferred from RNA polymerase II subunit genes.

Science.gov (United States)

Liu, Yajuan J; Hodson, Matthew C; Hall, Benjamin D

2006-09-29

At present, there is not a widely accepted consensus view regarding the phylogenetic structure of kingdom Fungi although two major phyla, Ascomycota and Basidiomycota, are clearly delineated. Regarding the lower fungi, Zygomycota and Chytridiomycota, a variety of proposals have been advanced. Microsporidia may or may not be fungi; the Glomales (vesicular-arbuscular mycorrhizal fungi) may or may not constitute a fifth fungal phylum, and the loss of the flagellum may have occurred either once or multiple times during fungal evolution. All of these issues are capable of being resolved by a molecular phylogenetic analysis which achieves strong statistical support for major branches. To date, no fungal phylogeny based upon molecular characters has satisfied this criterion. Using the translated amino acid sequences of the RPB1 and RPB2 genes, we have inferred a fungal phylogeny that consists largely of well-supported monophyletic phyla. Our major results, each with significant statistical support, are: (1) Microsporidia are sister to kingdom Fungi and are not members of Zygomycota; that is, Microsporidia and fungi originated from a common ancestor. (2) Chytridiomycota, the only fungal phylum having a developmental stage with a flagellum, is paraphyletic and is the basal lineage. (3) Zygomycota is monophyletic based upon sampling of Trichomycetes, Zygomycetes, and Glomales. (4) Zygomycota, Basidiomycota, and Ascomycota form a monophyletic group separate from Chytridiomycota. (5) Basidiomycota and Ascomycota are monophyletic sister groups. In general, this paper highlights the evolutionary position and significance of the lower fungi (Zygomycota and Chytridiomycota). Our results suggest that loss of the flagellum happened only once during early stages of fungal evolution; consequently, the majority of fungi, unlike plants and animals, are nonflagellated. The phylogeny we infer from gene sequences is the first one that is congruent with the widely accepted morphology

Random nucleation and growth of Pt nanoparticles at the polarized interface between two immiscible electrolyte solutions

Czech Academy of Sciences Publication Activity Database

Trojánek, Antonín; Langmaier, Jan; Samec, Zdeněk

2007-01-01

Roč. 599, č. 2 (2007), s. 160-166 ISSN 0022-0728 R&D Projects: GA AV ČR IAA4040407 Institutional research plan: CEZ:AV0Z40400503 Keywords : polarized ITIES * deposition * platinum * random nucleation and growth Subject RIV: CG - Electrochemistry Impact factor: 2.580, year: 2007

Polarity Control of Heteroepitaxial GaN Nanowires on Diamond.

Science.gov (United States)

Hetzl, Martin; Kraut, Max; Hoffmann, Theresa; Stutzmann, Martin

2017-06-14

Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

Dynamic gradients of an intermediate filament-like cytoskeleton are recruited by a polarity landmark during apical growth.

Science.gov (United States)

Fuchino, Katsuya; Bagchi, Sonchita; Cantlay, Stuart; Sandblad, Linda; Wu, Di; Bergman, Jessica; Kamali-Moghaddam, Masood; Flärdh, Klas; Ausmees, Nora

2013-05-21

Intermediate filament (IF)-like cytoskeleton emerges as a versatile tool for cellular organization in all kingdoms of life, underscoring the importance of mechanistically understanding its diverse manifestations. We showed previously that, in Streptomyces (a bacterium with a mycelial lifestyle similar to that of filamentous fungi, including extreme cell and growth polarity), the IF protein FilP confers rigidity to the hyphae by an unknown mechanism. Here, we provide a possible explanation for the IF-like function of FilP by demonstrating its ability to self-assemble into a cis-interconnected regular network in vitro and its localization into structures consistent with a cytoskeletal network in vivo. Furthermore, we reveal that a spatially restricted interaction between FilP and DivIVA, the main component of the Streptomyces polarisome complex, leads to formation of apical gradients of FilP in hyphae undergoing active tip extension. We propose that the coupling between the mechanism driving polar growth and the assembly of an IF cytoskeleton provides each new hypha with an additional stress-bearing structure at its tip, where the nascent cell wall is inevitably more flexible and compliant while it is being assembled and matured. Our data suggest that recruitment of cytoskeleton around a cell polarity landmark is a broadly conserved strategy in tip-growing cells.

Effect of III/V ratio on the polarity of AlN and GaN layers grown in the metal rich growth regime on Si(111) by plasma assisted molecular beam epitaxy

International Nuclear Information System (INIS)

Agrawal, Manvi; Dharmarasu, Nethaji; Radhakrishnan, K.; Pramana, Stevin Snellius

2015-01-01

Wet chemical etching, reflection high energy electron diffraction, scanning electron microscope and convergent beam electron diffraction have been employed to study the polarities of AlN and the subsequently grown GaN as a function of metal flux in the metal rich growth regime. Both AlN and GaN exhibited metal polarity in the intermediate growth conditions. However, in the droplet growth regime, the polarity of AlN and GaN were N polar and Ga polar, respectively. It was observed that Ga polar GaN could be obtained on both Al and N polar AlN. AlGaN/GaN high electron mobility transistor (HEMT) heterostructure exhibiting hall mobility of 900 cm 2 V -1 s -1 and sheet carrier density of 1.2 × 10 13 cm -2 was demonstrated using N polar AlN which confirmed Ga polarity of GaN. Al metal flux was likely to play an important role in controlling the polarity of AlN and determining the polarity of the subsequent GaN grown on Si(111) by plasma assisted molecular beam epitaxy (PA-MBE). (author)

EDITORIAL: Non-polar and semipolar nitride semiconductors Non-polar and semipolar nitride semiconductors

Science.gov (United States)

Han, Jung; Kneissl, Michael

2012-02-01

topics including growth and heteroepitaxy, bulk GaN substrates, theory and modelling, optical properties, laser diodes and LEDs as well as transport properties and electronics. Farrell et al review materials and growth issues for high-performance non- and semipolar light-emitting devices, and Scholz provides an overview of heteroepitaxial growth of semipolar GaN. Okada et al review growth mechanisms of non- and semipolar GaN layers on patterned sapphire substrates, and Vennéguès discusses defect reduction methods for heteroepitaxially grown non- and semipolar III-nitride films. Leung et al explain how kinetic Wulff plots can be used to design and control non-polar and semipolar GaN heteroepitaxy, and a contribution by Sawaki et al explores the impurity incorporation in (1-101) GaN grown on Si substrates. In the area of bulk crystal growth Kucharski et al review non- and semipolar GaN substrates by ammonothermal growth, and Chichibu et al discuss the challenges for epitaxial growth of InGaN on free-standing m-plane GaN substrates. Calculation of semipolar orientations for wurtzitic semiconductor heterostructures and their application to nitrides and oxides are reviewed by Bigenwald et al, and Ito et al present an ab initio approach to reconstruction, adsorption, and incorporation on GaN surfaces. Finally, the theoretical description of non-polar and semipolar nitride semiconductor quantum-well structures is presented by Ahn et al. In a discussion of the optical properties, Kisin et al discuss the effect of the quantum well population on the optical characteristics of polar, semipolar and non-polar III-nitride light emitters, and Jönen et al investigate the indium incorporation and optical properties of non- and semipolar GaInN QW structures. Wernicke et al explore the emission wavelength of polar, non-polar, and semipolar InGaN quantum wells and the incorporation of indium. In a contribution by Melo et al, the gain in polar and non-polar/semipolar gallium

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires

KAUST Repository

Wang, Ping

2015-12-22

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001 ̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.18 and 1.0 eV, respectively) are about two-fold larger in magnitude than those on the (0001 ̅) plane (0.07 and 0.52 eV), as calculated by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices.

3-Amino 1,8-naphthalimide, a structural analog of the anti-cholera drug virstatin inhibits chemically-biased swimming and swarming motility in vibrios

Science.gov (United States)

Wang, Hongxia; Silva, Anisia J.; Benitez, Jorge A.

2017-01-01

A screen for inhibitors of Vibrio cholerae motility identified the compound 3-amino 1,8-naphthalimide (3-A18NI), a structural analog of the cholera drug virstatin. Similar to virstatin, 3-A18NI diminished cholera toxin production. In contrast, 3-A18NI impeded swimming and/or swarming motility of V. cholerae and V. parahemolyticus suggesting that it could target the chemotaxis pathway shared by the polar and lateral flagellar system of vibrios. 3-A18NI did not inhibit the expression of V. cholerae major flagellin FlaA or the assembly of its polar flagellum. Finally, 3-A18NI enhanced V. cholerae colonization mimicking the phenotype of chemotaxis mutants that exhibit counterclockwise-biased flagellum rotation. PMID:28392408

Rhizoids and protonemata of characean algae: model cells for research on polarized growth and plant gravity sensing.

Science.gov (United States)

Braun, M; Limbach, C

2006-12-01

Gravitropically tip-growing rhizoids and protonemata of characean algae are well-established unicellular plant model systems for research on gravitropism. In recent years, considerable progress has been made in the understanding of the cellular and molecular mechanisms underlying gravity sensing and gravity-oriented growth. While in higher-plant statocytes the role of cytoskeletal elements, especially the actin cytoskeleton, in the mechanisms of gravity sensing is still enigmatic, there is clear evidence that in the characean cells actin is intimately involved in polarized growth, gravity sensing, and the gravitropic response mechanisms. The multiple functions of actin are orchestrated by a variety of actin-binding proteins which control actin polymerisation, regulate the dynamic remodelling of the actin filament architecture, and mediate the transport of vesicles and organelles. Actin and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Experiments performed in microgravity provided evidence that actomyosin is a key player for gravity sensing: it coordinates the position of statoliths and, upon a change in the cell's orientation, directs sedimenting statoliths to specific areas of the plasma membrane, where contact with membrane-bound gravisensor molecules elicits short gravitropic pathways. In rhizoids, gravitropic signalling leads to a local reduction of cytoplasmic free calcium and results in differential growth of the opposite subapical cell flanks. The negative gravitropic response of protonemata involves actin-dependent relocation of the calcium gradient and displacement of the centre of maximal growth towards the upper flank. On the basis of the results obtained from the gravitropic model cells, a similar fine-tuning function of the actomyosin system is discussed for the early steps of gravity sensing in higher-plant statocytes.

Application of the Indirect Immunoperoxidase Stain Technique to the Flagella of Azospirillum brasilense

Science.gov (United States)

Hall, Patrick G.; Krieg, Noel R.

1984-01-01

An indirect immunoperoxidase stain was used to demonstrate by electron microscopy that an antigenic difference exists between the polar flagellum and the lateral flagella of Azospirillum brasilense ATCC 29145. Images PMID:16346482

Genetic control of organ shape and tissue polarity.

Directory of Open Access Journals (Sweden)

Amelia A Green

2010-11-01

Full Text Available The mechanisms by which genes control organ shape are poorly understood. In principle, genes may control shape by modifying local rates and/or orientations of deformation. Distinguishing between these possibilities has been difficult because of interactions between patterns, orientations, and mechanical constraints during growth. Here we show how a combination of growth analysis, molecular genetics, and modelling can be used to dissect the factors contributing to shape. Using the Snapdragon (Antirrhinum flower as an example, we show how shape development reflects local rates and orientations of tissue growth that vary spatially and temporally to form a dynamic growth field. This growth field is under the control of several dorsoventral genes that influence flower shape. The action of these genes can be modelled by assuming they modulate specified growth rates parallel or perpendicular to local orientations, established by a few key organisers of tissue polarity. Models in which dorsoventral genes only influence specified growth rates do not fully account for the observed growth fields and shapes. However, the data can be readily explained by a model in which dorsoventral genes also modify organisers of tissue polarity. In particular, genetic control of tissue polarity organisers at ventral petal junctions and distal boundaries allows both the shape and growth field of the flower to be accounted for in wild type and mutants. The results suggest that genetic control of tissue polarity organisers has played a key role in the development and evolution of shape.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane.

Science.gov (United States)

Hermo, Louis; Pelletier, R-Marc; Cyr, Daniel G; Smith, Charles E

2010-04-01

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review. Copyright 2009 Wiley-Liss, Inc.

Effect of Pulse Polarity on Thresholds and on Non-monotonic Loudness Growth in Cochlear Implant Users.

Science.gov (United States)

Macherey, Olivier; Carlyon, Robert P; Chatron, Jacques; Roman, Stéphane

2017-06-01

Most cochlear implants (CIs) activate their electrodes non-simultaneously in order to eliminate electrical field interactions. However, the membrane of auditory nerve fibers needs time to return to its resting state, causing the probability of firing to a pulse to be affected by previous pulses. Here, we provide new evidence on the effect of pulse polarity and current level on these interactions. In experiment 1, detection thresholds and most comfortable levels (MCLs) were measured in CI users for 100-Hz pulse trains consisting of two consecutive biphasic pulses of the same or of opposite polarity. All combinations of polarities were studied: anodic-cathodic-anodic-cathodic (ACAC), CACA, ACCA, and CAAC. Thresholds were lower when the adjacent phases of the two pulses had the same polarity (ACCA and CAAC) than when they were different (ACAC and CACA). Some subjects showed a lower threshold for ACCA than for CAAC while others showed the opposite trend demonstrating that polarity sensitivity at threshold is genuine and subject- or electrode-dependent. In contrast, anodic (CAAC) pulses always showed a lower MCL than cathodic (ACCA) pulses, confirming previous reports. In experiments 2 and 3, the subjects compared the loudness of several pulse trains differing in current level separately for ACCA and CAAC. For 40 % of the electrodes tested, loudness grew non-monotonically as a function of current level for ACCA but never for CAAC. This finding may relate to a conduction block of the action potentials along the fibers induced by a strong hyperpolarization of their central processes. Further analysis showed that the electrodes showing a lower threshold for ACCA than for CAAC were more likely to yield a non-monotonic loudness growth. It is proposed that polarity sensitivity at threshold reflects the local neural health and that anodic asymmetric pulses should preferably be used to convey sound information while avoiding abnormal loudness percepts.

3-Amino 1,8-naphthalimide, a structural analog of the anti-cholera drug virstatin inhibits chemically-biased swimming and swarming motility in vibrios.

Science.gov (United States)

Wang, Hongxia; Silva, Anisia J; Benitez, Jorge A

2017-06-01

A screen for inhibitors of Vibrio cholerae motility identified the compound 3-amino 1,8-naphthalimide (3-A18NI), a structural analog of the cholera drug virstatin. Similar to virstatin, 3-A18NI diminished cholera toxin production. In contrast, 3-A18NI impeded swimming and/or swarming motility of V. cholerae and V. parahemolyticus suggesting that it could target the chemotaxis pathway shared by the polar and lateral flagellar system of vibrios. 3-A18NI did not inhibit the expression of V. cholerae major flagellin FlaA or the assembly of its polar flagellum. Finally, 3-A18NI enhanced V. cholerae colonization mimicking the phenotype of chemotaxis mutants that exhibit counterclockwise-biased flagellum rotation. Copyright © 2017 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

Dopamine induces growth inhibition and vascular normalization through reprogramming M2-polarized macrophages in rat C6 glioma

International Nuclear Information System (INIS)

Qin, Tian; Wang, Chenlong; Chen, Xuewei; Duan, Chenfan; Zhang, Xiaoyan; Zhang, Jing; Chai, Hongyan; Tang, Tian; Chen, Honglei; Yue, Jiang; Li, Ying; Yang, Jing

2015-01-01

Dopamine (DA), a monoamine catecholamine neurotransmitter with antiangiogenic activity, stabilizes tumor vessels in colon, prostate and ovarian cancers, thus increases chemotherapeutic efficacy. Here, in the rat C6 glioma models, we investigated the vascular normalization effects of DA and its mechanisms of action. DA (25, 50 mg/kg) inhibited tumor growth, while a precursor of DA (levodopa) prolonged the survival time of rats bearing orthotopic C6 glioma. DA improved tumor perfusion, with significant effects from day 3, and a higher level at days 5 to 7. In addition, DA decreased microvessel density and hypoxia-inducible factor-1α expression in tumor tissues, while increasing the coverage of pericyte. Conversely, an antagonist of dopamine receptor 2 (DR2) (eticlopride) but not DR1 (butaclamol) abrogated DA-induced tumor regression and vascular normalization. Furthermore, DA improved the delivery and efficacy of temozolomide therapy. Importantly, DA increased representative M1 markers (iNOS, CXCL9, etc.), while decreasing M2 markers (CD206, arginase-1, etc.). Depletion of macrophages by clodronate or zoledronic acid attenuated the effects of DA. Notably, DA treatment induced M2-to-M1 polarization in RAW264.7 cells and mouse peritoneal macrophages, and enhanced the migration of pericyte-like cells (10T1/2), which was reversed by eticlopride or DR2-siRNA. Such changes were accompanied by the downregulation of VEGF/VEGFR2 signaling. In summary, DA induces growth inhibition and vascular normalization through reprogramming M2-polarized macrophages. Thus, targeting the tumor microvasculature by DA represents a promising strategy for human glioma therapy. - Highlights: • Dopamine induces tumor growth inhibition and vascular normalization in rat C6 glioma. • Dopamine switches macrophage phenotype from M2 to M1. • Dopamine-induced vascular normalization is mediated by macrophage polarization. • Dopamine is a promising agent targeting the microvasculature in tumor

Dopamine induces growth inhibition and vascular normalization through reprogramming M2-polarized macrophages in rat C6 glioma

Energy Technology Data Exchange (ETDEWEB)

Qin, Tian; Wang, Chenlong; Chen, Xuewei; Duan, Chenfan; Zhang, Xiaoyan [Department of Pharmacology, School of Basic Medical Sciences, Wuhan University, Wuhan 430071 (China); Zhang, Jing [Animal Experimental Center of Wuhan University, Wuhan 430071 (China); Chai, Hongyan [Center for Gene Diagnosis, Zhongnan Hospital, Wuhan University, Wuhan 430071 (China); Tang, Tian [Department of Oncology, Renmin Hospital of Wuhan University, Wuhan 430060 (China); Chen, Honglei [Department of Pathology and Pathophysiology, School of Medicine, Wuhan University, Wuhan 430071 (China); Yue, Jiang [Department of Pharmacology, School of Basic Medical Sciences, Wuhan University, Wuhan 430071 (China); Li, Ying, E-mail: lyying0@163.com [Department of Pharmacology, School of Basic Medical Sciences, Wuhan University, Wuhan 430071 (China); Yang, Jing, E-mail: yangjingliu2013@163.com [Department of Pharmacology, School of Basic Medical Sciences, Wuhan University, Wuhan 430071 (China)

2015-07-15

Dopamine (DA), a monoamine catecholamine neurotransmitter with antiangiogenic activity, stabilizes tumor vessels in colon, prostate and ovarian cancers, thus increases chemotherapeutic efficacy. Here, in the rat C6 glioma models, we investigated the vascular normalization effects of DA and its mechanisms of action. DA (25, 50 mg/kg) inhibited tumor growth, while a precursor of DA (levodopa) prolonged the survival time of rats bearing orthotopic C6 glioma. DA improved tumor perfusion, with significant effects from day 3, and a higher level at days 5 to 7. In addition, DA decreased microvessel density and hypoxia-inducible factor-1α expression in tumor tissues, while increasing the coverage of pericyte. Conversely, an antagonist of dopamine receptor 2 (DR2) (eticlopride) but not DR1 (butaclamol) abrogated DA-induced tumor regression and vascular normalization. Furthermore, DA improved the delivery and efficacy of temozolomide therapy. Importantly, DA increased representative M1 markers (iNOS, CXCL9, etc.), while decreasing M2 markers (CD206, arginase-1, etc.). Depletion of macrophages by clodronate or zoledronic acid attenuated the effects of DA. Notably, DA treatment induced M2-to-M1 polarization in RAW264.7 cells and mouse peritoneal macrophages, and enhanced the migration of pericyte-like cells (10T1/2), which was reversed by eticlopride or DR2-siRNA. Such changes were accompanied by the downregulation of VEGF/VEGFR2 signaling. In summary, DA induces growth inhibition and vascular normalization through reprogramming M2-polarized macrophages. Thus, targeting the tumor microvasculature by DA represents a promising strategy for human glioma therapy. - Highlights: • Dopamine induces tumor growth inhibition and vascular normalization in rat C6 glioma. • Dopamine switches macrophage phenotype from M2 to M1. • Dopamine-induced vascular normalization is mediated by macrophage polarization. • Dopamine is a promising agent targeting the microvasculature in tumor

Swimming Motility Mediates the Formation of Neutrophil Extracellular Traps Induced by Flagellated Pseudomonas aeruginosa.

Directory of Open Access Journals (Sweden)

Madison Floyd

2016-11-01

Full Text Available Pseudomonas aeruginosa is an opportunistic pathogen causing severe infections often characterized by robust neutrophilic infiltration. Neutrophils provide the first line of defense against P. aeruginosa. Aside from their defense conferred by phagocytic activity, neutrophils also release neutrophil extracellular traps (NETs to immobilize bacteria. Although NET formation is an important antimicrobial process, the details of its mechanism are largely unknown. The identity of the main components of P. aeruginosa responsible for triggering NET formation is unclear. In this study, our focus was to identify the main bacterial factors mediating NET formation and to gain insight into the underlying mechanism. We found that P. aeruginosa in its exponential growth phase promoted strong NET formation in human neutrophils while its NET-inducing ability dramatically decreased at later stages of bacterial growth. We identified the flagellum as the primary component of P. aeruginosa responsible for inducing NET extrusion as flagellum-deficient bacteria remained seriously impaired in triggering NET formation. Purified P. aeruginosa flagellin, the monomeric component of the flagellum, does not stimulate NET formation in human neutrophils. P. aeruginosa-induced NET formation is independent of the flagellum-sensing receptors TLR5 and NLRC4 in both human and mouse neutrophils. Interestingly, we found that flagellar motility, not flagellum binding to neutrophils per se, mediates NET release induced by flagellated bacteria. Immotile, flagellar motor-deficient bacterial strains producing paralyzed flagella did not induce NET formation. Forced contact between immotile P. aeruginosa and neutrophils restored their NET-inducing ability. Both the motAB and motCD genetic loci encoding flagellar motor genes contribute to maximal NET release; however the motCD genes play a more important role. Phagocytosis of P. aeruginosa and superoxide production by neutrophils were also

Polar transport in plants mediated by membrane transporters: focus on mechanisms of polar auxin transport.

Science.gov (United States)

Naramoto, Satoshi

2017-12-01

Directional cell-to-cell transport of functional molecules, called polar transport, enables plants to sense and respond to developmental and environmental signals. Transporters that localize to plasma membranes (PMs) in a polar manner are key components of these systems. PIN-FORMED (PIN) auxin efflux carriers, which are the most studied polar-localized PM proteins, are implicated in the polar transport of auxin that in turn regulates plant development and tropic growth. In this review, the regulatory mechanisms underlying polar localization of PINs, control of auxin efflux activity, and PIN abundance at PMs are considered. Up to date information on polar-localized nutrient transporters that regulate directional nutrient movement from soil into the root vasculature is also discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Semi-polar GaN heteroepitaxy an high index Si-surfaces

Energy Technology Data Exchange (ETDEWEB)

Ravash, Roghaiyeh; Blaesing, Juergen; Hempel, Thomas; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-University Magdeburg, FNW/IEP/AHE, Magdeburg (Germany)

2011-07-01

Due to the lack of GaN homosubstrates, the growth of GaN-based devices is usually performed on heterosubstrates as sapphire or SiC. These substrates are either insulating or expensive, and both unavailable in large diameters. Meanwhile, silicon can meet the requirements for a low price and thermally well conducting substrate and also enabling the integration of optoelectronic devices with Si-based electronics. Up to now, the good matching of hexagonal GaN with the three-fold symmetry of Si(111) greatly promotes the c-axis orientated growth of GaN on this surface plane. A large spontaneous and piezoelectric polarization oriented along the c-axis exists in such hexagonal structure leading to low efficiencies for thick quantum wells. The attention to the growth of non-polar or semi-polar GaN based epitaxial structures has been increased recently because of reducing the effect of the polarization fields in these growth directions. Therefore we studied semi-polar GaN epilayers grown by metalorganic vapor phase epitaxy on silicon substrates with different orientations from Si(211) to Si(711). We observed that AlN seeding layer growth time play a significant role in obtaining the different GaN texture.

Activation of Wnt Planar Cell Polarity (PCP) signaling promotes growth plate column formation in vitro.

Science.gov (United States)

Randall, Rachel M; Shao, Yvonne Y; Wang, Lai; Ballock, R Tracy

2012-12-01

Disrupting the Wnt Planar Cell Polarity (PCP) signaling pathway in vivo results in loss of columnar growth plate architecture, but it is unknown whether activation of this pathway in vitro is sufficient to promote column formation. We hypothesized that activation of the Wnt PCP pathway in growth plate chondrocyte cell pellets would promote columnar organization in these cells that are normally oriented randomly in culture. Rat growth plate chondrocytes were transfected with plasmids encoding the Fzd7 cell-surface Wnt receptor, a Fzd7 deletion mutant lacking the Wnt-binding domain, or Wnt receptor-associated proteins Ror2 or Vangl2, and then cultured as three-dimensional cell pellets in the presence of recombinant Wnt5a or Wnt5b for 21 days. Cellular morphology was evaluated using histomorphometric measurements. Activation of Wnt PCP signaling components promoted the initiation of columnar morphogenesis in the chondrocyte pellet culture model, as measured by histomorphometric analysis of the column index (ANOVA p = 0.01). Activation of noncanonical Wnt signaling through overexpression of both the cell-surface Wnt receptor Fzd7 and receptor-associated protein Ror2 with addition of recombinant Wnt5a promotes the initiation of columnar architecture of growth plate chondrocytes in vitro, representing an important step toward growth plate regeneration. Copyright © 2012 Orthopaedic Research Society.

Spin-polarized photoemission

International Nuclear Information System (INIS)

Johnson, Peter D.

1997-01-01

Spin-polarized photoemission has developed into a versatile tool for the study of surface and thin film magnetism. In this review, we examine the methodology of the technique and its application to a number of different problems, including both valence band and core level studies. After a detailed review of spin-polarization measurement techniques and the related experimental requirements we consider in detail studies of the bulk properties both above and below the Curie temperature. This section also includes a discussion of observations relating to unique metastable phases obtained via epitaxial growth. The application of the technique to the study of surfaces, both clean and adsorbate covered, is reviewed. The report then examines, in detail, studies of the spin-polarized electronic structure of thin films and the related interfacial magnetism. Finally, observations of spin-polarized quantum well states in non-magnetic thin films are discussed with particular reference to their mediation of the oscillatory exchange coupling in related magnetic multilayers. (author)

Linearly polarized emission from an embedded quantum dot using nanowire morphology control.

Science.gov (United States)

Foster, Andrew P; Bradley, John P; Gardner, Kirsty; Krysa, Andrey B; Royall, Ben; Skolnick, Maurice S; Wilson, Luke R

2015-03-11

GaAs nanowires with elongated cross sections are formed using a catalyst-free growth technique. This is achieved by patterning elongated nanoscale openings within a silicon dioxide growth mask on a (111)B GaAs substrate. It is observed that MOVPE-grown vertical nanowires with cross section elongated in the [21̅1̅] and [1̅12] directions remain faithful to the geometry of the openings. An InGaAs quantum dot with weak radial confinement is realized within each nanowire by briefly introducing indium into the reactor during nanowire growth. Photoluminescence emission from an embedded nanowire quantum dot is strongly linearly polarized (typically >90%) with the polarization direction coincident with the axis of elongation. Linearly polarized PL emission is a result of embedding the quantum dot in an anisotropic nanowire structure that supports a single strongly confined, linearly polarized optical mode. This research provides a route to the bottom-up growth of linearly polarized single photon sources of interest for quantum information applications.

High-quality ZnO growth, doping, and polarization effect

Science.gov (United States)

Kun, Tang; Shulin, Gu; Jiandong, Ye; Shunming, Zhu; Rong, Zhang; Youdou, Zheng

2016-03-01

The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding (1) the development of high-quality epitaxy techniques, (2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and (3) the design, realization, and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an iso-valent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO. Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk. Project supported by the National Natural Science Foundation of China (Nos. 61025020, 61274058, 61322403, 61504057, 61574075), the Natural Science Foundation of Jiangsu Province (Nos. BK2011437, BK20130013, BK20150585), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Fundamental Research Funds for the Central Universities.

Competition of circularly polarized laser modes in the modulation instability of hot magnetoplasma

International Nuclear Information System (INIS)

Sepehri Javan, N.

2013-01-01

The present study is aimed to investigate the problem of modulation instability of an intense laser beam in the hot magnetized plasma. The propagation of intense circularly polarized laser beam along the external magnetic field is considered using a relativistic fluid model. The nonlinear equation describing the interaction of laser pulse with magnetized hot plasma is derived in the quasi-neutral approximation, which is valid for hot plasma. Nonlinear dispersion equation for hot plasma is obtained. For left- and right-hand polarizations, the growth rate of instability is achieved and the effect of temperature, external magnetic field, and kind of polarization on the growth rate is considered. It is observed that for the right-hand polarization, increase of magnetic field leads to the increasing of growth rate. Also for the left-hand polarization, increase of magnetic field inversely causes decrease of the growth rate.

Role of polarized G protein signaling in tracking pheromone gradients

Science.gov (United States)

McClure, Allison W.; Minakova, Maria; Dyer, Jayme M.; Zyla, Trevin R.; Elston, Timothy C.; Lew, Daniel J.

2015-01-01

Summary Yeast cells track gradients of pheromones to locate mating partners. Intuition suggests that uniform distribution of pheromone receptors over the cell surface would yield optimal gradient sensing. However, yeast cells display polarized receptors. The benefit of such polarization was unknown. During gradient tracking, cell growth is directed by a patch of polarity regulators that wanders around the cortex. Patch movement is sensitive to pheromone dose, with wandering reduced on the up-gradient side of the cell, resulting in net growth in that direction. Mathematical modeling suggests that active receptors and associated G proteins lag behind the polarity patch and act as an effective drag on patch movement. In vivo, the polarity patch is trailed by a G protein-rich domain, and this polarized distribution of G proteins is required to constrain patch wandering. Our findings explain why G protein polarization is beneficial, and illuminate a novel mechanism for gradient tracking. PMID:26609960

Crystal structure and crystal growth of the polar ferrimagnet CaBaFe4O7

Science.gov (United States)

Perry, R. S.; Kurebayashi, H.; Gibbs, A.; Gutmann, M. J.

2018-05-01

Magnetic materials are a cornerstone for developing spintronic devices for the transport of information via magnetic excitations. To date, relatively few materials have been investigated for the purpose of spin transport, mostly due to the paucity of suitable candidates as these materials are often chemically complex and difficult to synthesize. We present the crystal growth and a structure solution on the high-temperature crystal structure of the layered, polar ferrimagnet CaBaFe4O7 , which is a possible new contender for spintronics research. The space group is identified as P 3 by refinement of single crystal and powder neutron diffraction data. At 400 K, the trigonal lattice parameters are a =11.0114 (11 )Å and c =10.330 (3 )Å . The structure is similar to the low-temperature phase with alternating layers of triangular and Kagome-arranged Fe-O tetrahedra. We also present details of the crystal growth by traveling solvent method.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long

2018-05-03

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng

2018-01-01

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Job Market Polarization and Employment Protection in Europe

DEFF Research Database (Denmark)

Pertold-Gebicka, Barbara

Although much attention has been paid to the polarization of national labor markets, with employment and wage growth occurring in both low- and high- but not middle-skill occupations, there is little consistent evidence on cross-country dierences in this process. I analyze job polarization in 12...

Multilayer graphene growth on polar dielectric substrates using chemical vapour deposition

Science.gov (United States)

Karamat, S.; Çelik, K.; Shah Zaman, S.; Oral, A.

2018-06-01

High quality of graphene is necessary for its applications at industrial scale production. The most convenient way is its direct growth on dielectrics which avoid the transfer route of graphene from metal to dielectric substrate usually followed by graphene community. The choice of a suitable dielectric for the gate material which can replace silicon dioxide (SiO2) is in high demand. Various properties like permittivity, thermodynamic stability, film morphology, interface quality, bandgap and band alignment of other dielectrics with graphene needs more exploration. A potential dielectric material is required which could be used to grow graphene with all these qualities. Direct growth of graphene on magnesium oxide (MgO) substrates is an interesting idea and will be a new addition in the library of 2D materials. The present work is about the direct growth of graphene on MgO substrates by an ambient pressure chemical vapour deposition (CVD) method. We address the surface instability issue of the polar oxides which is the most challenging factor in MgO. Atomic force microscopy (AFM) measurements showed the topographical features of the graphene coated on MgO. X-ray photoelectron spectroscopy (XPS) study is carried out to extract information regarding the presence of necessary elements, their bonding with substrates and to confirm the sp-2 hybridization of carbon, which is a characteristic feature of graphene film. The chemical shift is due to the surface reconstruction of MgO in the prepared samples. For graphene-MgO interface, valence band offset (VBO) and conduction band offset (CBO) extracted from valence band spectra reported. Further, we predicted the energy band diagram for single layer and thin film of graphene. By using the room-temperature energy band gap values of MgO and graphene, the CBO is calculated to be 6.85 eV for single layer and 5.66 eV for few layer (1-3) of graphene layers.

3D Architecture of the Trypanosoma brucei Flagella Connector, a Mobile Transmembrane Junction.

Directory of Open Access Journals (Sweden)

Johanna L Höög

2016-01-01

Full Text Available Cellular junctions are crucial for the formation of multicellular organisms, where they anchor cells to each other and/or supportive tissue and enable cell-to-cell communication. Some unicellular organisms, such as the parasitic protist Trypanosoma brucei, also have complex cellular junctions. The flagella connector (FC is a three-layered transmembrane junction that moves with the growing tip of a new flagellum and attaches it to the side of the old flagellum. The FC moves via an unknown molecular mechanism, independent of new flagellum growth. Here we describe the detailed 3D architecture of the FC suggesting explanations for how it functions and its mechanism of motility.We have used a combination of electron tomography and cryo-electron tomography to reveal the 3D architecture of the FC. Cryo-electron tomography revealed layers of repetitive filamentous electron densities between the two flagella in the interstitial zone. Though the FC does not change in length and width during the growth of the new flagellum, the interstitial zone thickness decreases as the FC matures. This investigation also shows interactions between the FC layers and the axonemes of the new and old flagellum, sufficiently strong to displace the axoneme in the old flagellum. We describe a novel filament, the flagella connector fibre, found between the FC and the axoneme in the old flagellum.The FC is similar to other cellular junctions in that filamentous proteins bridge the extracellular space and are anchored to underlying cytoskeletal structures; however, it is built between different portions of the same cell and is unique because of its intrinsic motility. The detailed description of its structure will be an important tool to use in attributing structure / function relationships as its molecular components are discovered in the future. The FC is involved in the inheritance of cell shape, which is important for the life cycle of this human parasite.

An Element of Determinism in a Stochastic Flagellar Motor Switch.

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Xie, Li; Altindal, Tuba; Wu, Xiao-Lun

2015-01-01

Marine bacterium Vibrio alginolyticus uses a single polar flagellum to navigate in an aqueous environment. Similar to Escherichia coli cells, the polar flagellar motor has two states; when the motor is counter-clockwise, the cell swims forward and when the motor is clockwise, the cell swims backward. V. alginolyticus also incorporates a direction randomization step at the start of the forward swimming interval by flicking its flagellum. To gain an understanding on how the polar flagellar motor switch is regulated, distributions of the forward Δf and backward Δb intervals are investigated herein. We found that the steady-state probability density functions, P(Δf) and P(Δb), of freely swimming bacteria are strongly peaked at a finite time, suggesting that the motor switch is not Poissonian. The short-time inhibition is sufficiently strong and long lasting, i.e., several hundred milliseconds for both intervals, which is readily observed and characterized. Treating motor reversal dynamics as a first-passage problem, which results from conformation fluctuations of the motor switch, we calculated P(Δf) and P(Δb) and found good agreement with the measurements.

From epitaxial growth of ferrite thin films to spin-polarized tunnelling

International Nuclear Information System (INIS)

Moussy, Jean-Baptiste

2013-01-01

This paper presents a review of the research which is focused on ferrite thin films for spintronics. First, I will describe the potential of ferrite layers for the generation of spin-polarized currents. In the second step, the structural and chemical properties of epitaxial thin films and ferrite-based tunnel junctions will be presented. Particular attention will be given to ferrite systems grown by oxygen-assisted molecular beam epitaxy. The analysis of the structure and chemistry close to the interfaces, a key-point for understanding the spin-polarized tunnelling measurements, will be detailed. In the third part, the magnetic and magneto-transport properties of magnetite (Fe 3 O 4 ) thin films as a function of structural defects such as the antiphase boundaries will be explained. The spin-polarization measurements (spin-resolved photoemission, tunnel magnetoresistance) on this oxide predicted to be half-metallic will be discussed. Fourth, the potential of magnetic tunnel barriers, such as CoFe 2 O 4 , NiFe 2 O 4 or MnFe 2 O 4 , whose insulating behaviour and the high Curie temperatures make it exciting candidates for spin filtering at room temperature will be described. Spin-polarized tunnelling experiments, involving either Meservey–Tedrow or tunnel magnetoresistance measurements, will reveal significant spin-polarizations of the tunnelling current at low temperatures but also at room temperatures. Finally, I will mention a few perspectives with ferrite-based heterostructures. (topical review)

The apical actin fringe contributes to localized cell wall deposition and polarized growth in the lily pollen tube.

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Rounds, Caleb M; Hepler, Peter K; Winship, Lawrence J

2014-09-01

In lily (Lilium formosanum) pollen tubes, pectin, a major component of the cell wall, is delivered through regulated exocytosis. The targeted transport and secretion of the pectin-containing vesicles may be controlled by the cortical actin fringe at the pollen tube apex. Here, we address the role of the actin fringe using three different inhibitors of growth: brefeldin A, latrunculin B, and potassium cyanide. Brefeldin A blocks membrane trafficking and inhibits exocytosis in pollen tubes; it also leads to the degradation of the actin fringe and the formation of an aggregate of filamentous actin at the base of the clear zone. Latrunculin B, which depolymerizes filamentous actin, markedly slows growth but allows focused pectin deposition to continue. Of note, the locus of deposition shifts frequently and correlates with changes in the direction of growth. Finally, potassium cyanide, an electron transport chain inhibitor, briefly stops growth while causing the actin fringe to completely disappear. Pectin deposition continues but lacks focus, instead being delivered in a wide arc across the pollen tube tip. These data support a model in which the actin fringe contributes to the focused secretion of pectin to the apical cell wall and, thus, to the polarized growth of the pollen tube. © 2014 American Society of Plant Biologists. All Rights Reserved.

Involvement of SPI-2-encoded SpiC in flagellum synthesis in Salmonella enterica serovar Typhimurium

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Sugita Asami

2009-08-01

Full Text Available Abstract Background SpiC encoded within Salmonella pathogenicity island 2 on the Salmonella enterica serovar Typhimurium chromosome is required for survival within macrophages and systemic infection in mice. Additionally, SpiC contributes to Salmonella-induced activation of the signal transduction pathways in macrophages by affecting the expression of FliC, a component of flagella filaments. Here, we show the contribution of SpiC in flagellum synthesis. Results Quantitative RT-PCR shows that the expression levels of the class 3 fliD and motA genes that encode for the flagella cap and motor torque proteins, respectively, were lower for a spiC mutant strain than for the wild-type Salmonella. Further, this mutant had lower expression levels of the class 2 genes including the fliA gene encoding the flagellar-specific alternative sigma factor. We also found differences in flagella assembly between the wild-type strain and the spiC mutant. Many flagella filaments were observed on the bacterial surface of the wild-type strain, whereas the spiC mutant had only few flagella. The absence of spiC led to reduced expression of the FlhD protein, which functions as the master regulator in flagella gene expression, although no significant difference at the transcription level of the flhDC operon was observed between the wild-type strain and the spiC mutant. Conclusion The data show that SpiC is involved in flagella assembly by affecting the post-transcription expression of flhDC.

Mg Incorporation Efficiency in Pulsed MOCVD of N-Polar GaN:Mg

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Marini, Jonathan; Mahaboob, Isra; Hogan, Kasey; Novak, Steve; Bell, L. D.; Shahedipour-Sandvik, F.

2017-10-01

We report on the effect of growth polarity and pulsed or δ -doped growth mode on impurity incorporation in metalorganic chemical vapor deposition-grown GaN. In Ga-polar orientation, up to 12× enhancement in Mg concentration for given Mg flow rate is observed, resulting in enhanced p-type conductivity for these samples. In contrast, this enhancement effect is greatly diminished for N-polar samples, falling off with increasing Mg flow and showing maximum enhancement of 2.7× at 30 nmol/min Mg flow. At higher Mg flow rates, Mg incorporation at normal levels did not correspond to p-type conductivity, which may be due to Mg incorporation at nonacceptor sites. Concentrations of C, O, and Si were also investigated, revealing dependence on Mg flow in N-polar pulsed samples. Carbon incorporation was found to decrease with increasing Mg flow, and oxygen incorporation was found to remain high across varied Mg flow. These effects combine to result in N-polar samples that are not p-type when using the pulsed growth mode.

High current polarized electron source

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Suleiman, R.; Adderley, P.; Grames, J.; Hansknecht, J.; Poelker, M.; Stutzman, M.

2018-05-01

Jefferson Lab operates two DC high voltage GaAs photoguns with compact inverted insulators. One photogun provides the polarized electron beam at the Continuous Electron Beam Accelerator Facility (CEBAF) up to 200 µA. The other gun is used for high average current photocathode lifetime studies at a dedicated test facility up to 4 mA of polarized beam and 10 mA of un-polarized beam. GaAs-based photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed facilities that must operate in excess of tens of mA of polarized average current. This contribution describes techniques to maintain good vacuum while delivering high beam currents, and techniques that minimize damage due to ion bombardment, the dominant mechanism that reduces photocathode yield. Advantages of higher DC voltage include reduced space-charge emittance growth and the potential for better photocathode lifetime. Highlights of R&D to improve the performance of polarized electron sources and prolong the lifetime of strained-superlattice GaAs are presented.

GENUS DESULFOMICROBIUM

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Short, straight rod- or ellipsoidal-shaped cells (0.5-0.9 x 1.3-2.9 |m) with rounded ends, either singly or in pairs (Sharak Genthner et al., 1994). Gram-negative stain reaction and cell-wall structure. Cells are motile, usually by a single polar flagellum. Obligate anaerobe. End...

CELSR2, encoding a planar cell polarity protein, is a putative gene in Joubert syndrome with cortical heterotopia, microophthalmia, and growth hormone deficiency.

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Vilboux, Thierry; Malicdan, May Christine V; Roney, Joseph C; Cullinane, Andrew R; Stephen, Joshi; Yildirimli, Deniz; Bryant, Joy; Fischer, Roxanne; Vemulapalli, Meghana; Mullikin, James C; Steinbach, Peter J; Gahl, William A; Gunay-Aygun, Meral

2017-03-01

Joubert syndrome is a ciliopathy characterized by a specific constellation of central nervous system malformations that result in the pathognomonic "molar tooth sign" on imaging. More than 27 genes are associated with Joubert syndrome, but some patients do not have mutations in any of these genes. Celsr1, Celsr2, and Celsr3 are the mammalian orthologues of the drosophila planar cell polarity protein, flamingo; they play important roles in neural development, including axon guidance, neuronal migration, and cilium polarity. Here, we report bi-allelic mutations in CELSR2 in a Joubert patient with cortical heterotopia, microophthalmia, and growth hormone deficiency. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

A comparative study on MOVPE InN grown on Ga- and N-polarity bulk GaN

International Nuclear Information System (INIS)

Wang, W.J.; Miwa, H.; Hashimoto, A.; Yamamoto, A.

2006-01-01

The influence of substrate polarity on the growth of InN film by MOVPE was investigated using bulk GaN as a substrate. Single-crystalline In- and N-polarity InN films were obtained on Ga- and N-polarity GaN substrate, respectively. Significant difference of the morphologies between the In- and N-polarity InN films was found. For the In-polarity InN film, the morphology was similar to that grown on sapphire substrate. The film surface was consisted of grains with small facets. In contrast, for the N-polarity InN film, the surface was consisted of large hexagonal shape crystal grains with flat surface. The grain size was about 2 μm in diameter on the average, and two-dimensional growth was enhanced obviously for each crystal grain. The influence of the growth temperature on the morphology, polarity, and optical property was also investigated. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Growth of GaN nanostructures with polar and semipolar orientations for the fabrication of UV LEDs

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Brault, Julien; Damilano, Benjamin; Courville, Aimeric; Leroux, Mathieu; Kahouli, Abdelkarim; Korytov, Maxim; Vennéguès, Philippe; Randazzo, Gaetano; Chenot, Sébastien; Vinter, Borge; De Mierry, Philippe; Massies, Jean; Rosales, Daniel; Bretagnon, Thierry; Gil, Bernard

2014-03-01

(Al,Ga)N light emitting diodes (LEDs), emitting over a large spectral range from 360 nm (GaN) down to 210 nm (AlN), have been successfully fabricated over the last decade. Clear advantages compared to the traditional mercury lamp technology (e.g. compactness, low-power operation, lifetime) have been demonstrated. However, LED efficiencies still need to be improved. The main problems are related to the structural quality and the p-type doping efficiency of (Al,Ga)N. Among the current approaches, GaN nanostructures, which confine carriers along both the growth direction and the growth plane, are seen as a solution for improving the radiative recombination efficiency by strongly reducing the impact of surrounding defects. Our approach, based on a 2D - 3D growth mode transition in molecular beam epitaxy, can lead to the spontaneous formation of GaN nanostructures on (Al,Ga)N over a broad range of Al compositions. Furthermore, the versatility of the process makes it possible to fabricate nanostructures on both (0001) oriented "polar" and (11 2 2) oriented "semipolar" materials. We show that the change in the crystal orientation has a strong impact on the morphological and optical properties of the nanostructures. The influence of growth conditions are also investigated by combining microscopy (SEM, TEM) and photoluminescence techniques. Finally, their potential as UV emitters will be discussed and the performances of GaN / (Al,Ga)N nanostructure-based LED demonstrators are presented.

A spindle pole antigen gene MoSPA2 is important for polar cell growth of vegetative hyphae and conidia, but is dispensable for pathogenicity in Magnaporthe oryzae.

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Li, Chao; Yang, Jun; Zhou, Wei; Chen, Xiao-Lin; Huang, Jin-Guang; Cheng, Zhi-Hua; Zhao, Wen-Sheng; Zhang, Yan; Peng, You-Liang

2014-11-01

Spa2 is an important component of the multiprotein complex polarisome, which is involved in the establishment, maintenance, termination of polarized cell growth and is important for defining tip growth of filamentous fungi. In this study, we isolated an insertional mutant of the rice blast fungus Magnaporthe oryzae that formed smaller colony and conidia compared with the wild type. In the mutant, a spindle pole antigen gene MoSPA2 was disrupted by the integration of an exogenous plasmid. Targeted gene deletion and complementation assays demonstrated the gene disruption was responsible for the defects of the insertional mutant. Interestingly, the MoSpa2-GFP fusion protein was found to accumulate as a spot at hyphal tips, septa of hyphae and conidial tip cells where germ tubes are usually produced, but not in appressoria, infection hyphae or at the septa of conidia. Furthermore, the deletion mutants of MoSPA2 exhibited slower hyphal tip growth, more hyphal branches, and smaller size of conidial tip cells. However, MoSPA2 is not required for plant infection. These results indicate that MoSPA2 is required for vegetative hyphal growth and maintaining conidium morphology and that spotted accumulation of MoSpa2 is important for its functions during cell polar growth.

Targeting NCK-Mediated Endothelial Cell Front-Rear Polarity Inhibits Neovascularization.

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Dubrac, Alexandre; Genet, Gael; Ola, Roxana; Zhang, Feng; Pibouin-Fragner, Laurence; Han, Jinah; Zhang, Jiasheng; Thomas, Jean-Léon; Chedotal, Alain; Schwartz, Martin A; Eichmann, Anne

2016-01-26

Sprouting angiogenesis is a key process driving blood vessel growth in ischemic tissues and an important drug target in a number of diseases, including wet macular degeneration and wound healing. Endothelial cells forming the sprout must develop front-rear polarity to allow sprout extension. The adaptor proteins Nck1 and 2 are known regulators of cytoskeletal dynamics and polarity, but their function in angiogenesis is poorly understood. Here, we show that the Nck adaptors are required for endothelial cell front-rear polarity and migration downstream of the angiogenic growth factors VEGF-A and Slit2. Mice carrying inducible, endothelial-specific Nck1/2 deletions fail to develop front-rear polarized vessel sprouts and exhibit severe angiogenesis defects in the postnatal retina and during embryonic development. Inactivation of NCK1 and 2 inhibits polarity by preventing Cdc42 and Pak2 activation by VEGF-A and Slit2. Mechanistically, NCK binding to ROBO1 is required for both Slit2- and VEGF-induced front-rear polarity. Selective inhibition of polarized endothelial cell migration by targeting Nck1/2 prevents hypersprouting induced by Notch or Bmp signaling inhibition, and pathological ocular neovascularization and wound healing, as well. These data reveal a novel signal integration mechanism involving NCK1/2, ROBO1/2, and VEGFR2 that controls endothelial cell front-rear polarity during sprouting angiogenesis. © 2015 American Heart Association, Inc.

A Kinome RNAi Screen in Drosophila Identifies Novel Genes Interacting with Lgl, aPKC, and Crb Cell Polarity Genes in Epithelial Tissues.

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Parsons, Linda M; Grzeschik, Nicola A; Amaratunga, Kasun; Burke, Peter; Quinn, Leonie M; Richardson, Helena E

2017-08-07

In both Drosophila melanogaster and mammalian systems, epithelial structure and underlying cell polarity are essential for proper tissue morphogenesis and organ growth. Cell polarity interfaces with multiple cellular processes that are regulated by the phosphorylation status of large protein networks. To gain insight into the molecular mechanisms that coordinate cell polarity with tissue growth, we screened a boutique collection of RNAi stocks targeting the kinome for their capacity to modify Drosophila "cell polarity" eye and wing phenotypes. Initially, we identified kinase or phosphatase genes whose depletion modified adult eye phenotypes associated with the manipulation of cell polarity complexes (via overexpression of Crb or aPKC). We next conducted a secondary screen to test whether these cell polarity modifiers altered tissue overgrowth associated with depletion of Lgl in the wing. These screens identified Hippo, Jun kinase (JNK), and Notch signaling pathways, previously linked to cell polarity regulation of tissue growth. Furthermore, novel pathways not previously connected to cell polarity regulation of tissue growth were identified, including Wingless (Wg/Wnt), Ras, and lipid/Phospho-inositol-3-kinase (PI3K) signaling pathways. Additionally, we demonstrated that the "nutrient sensing" kinases Salt Inducible Kinase 2 and 3 ( SIK2 and 3 ) are potent modifiers of cell polarity phenotypes and regulators of tissue growth. Overall, our screen has revealed novel cell polarity-interacting kinases and phosphatases that affect tissue growth, providing a platform for investigating molecular mechanisms coordinating cell polarity and tissue growth during development. Copyright © 2017 Parsons et al.

L-Band H Polarized Microwave Emission During the Corn Growth Cycle

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Joseph, A. T.; va der Velde, R.; O'Neill, P. E.; Kim, E.; Lang, R. H.; Gish, T.

2012-01-01

Hourly L-band (1.4 GHz) horizontally (H) polarized brightness temperatures (T(sub B))'s measured during five episodes (more than two days of continuous measurements) of the 2002 corn growth cycle are analyzed. These T(sub B)'s measurements were acquired as a part of a combined active/passive microwave field campaign, and were obtained at five incidence and three azimuth angles relative to the row direction. In support of this microwave data collection, intensive ground sampling took place once a week. Moreover, the interpretation of the hourly T(sub B)'s could also rely on the data obtained using the various automated instruments installed in the same field. In this paper, the soil moisture and temperature measured at fixed time intervals have been employed as input for the tau-omega model to reproduce the hourly T(sub B). Through the calibration of the vegetation and surface roughness parameterizations, the impact of the vegetation morphological changes on the microwave emission and the dependence of the soil surface roughness parameter, h(sub r), on soil moisture are investigated. This analysis demonstrates that the b parameter, appearing in the representation of the canopy opacity, has an angular dependence that varies throughout the growing period and also that the parameter hr increases as the soil dries in a portion of the dry-down cycle. The angular dependence of the b parameter imposes the largest uncertainty on T(sub B) simulations near senescence as the response of b to the incidence is also affected by the crop row orientation. On the other hand, the incorporation of a soil moisture dependent h(sub r) parameterization was responsible for the largest error reduction of T(sub B) simulations in the early growth cycle.

Surface contact stimulates the just-in-time deployment of bacterial adhesins.

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Li, Guanglai; Brown, Pamela J B; Tang, Jay X; Xu, Jing; Quardokus, Ellen M; Fuqua, Clay; Brun, Yves V

2012-01-01

The attachment of bacteria to surfaces provides advantages such as increasing nutrient access and resistance to environmental stress. Attachment begins with a reversible phase, often mediated by surface structures such as flagella and pili, followed by a transition to irreversible attachment, typically mediated by polysaccharides. Here we show that the interplay between pili and flagellum rotation stimulates the rapid transition between reversible and polysaccharide-mediated irreversible attachment. We found that reversible attachment of Caulobacter crescentus cells is mediated by motile cells bearing pili and that their contact with a surface results in the rapid pili-dependent arrest of flagellum rotation and concurrent stimulation of polar holdfast adhesive polysaccharide. Similar stimulation of polar adhesin production by surface contact occurs in Asticcacaulis biprosthecum and Agrobacterium tumefaciens. Therefore, single bacterial cells respond to their initial contact with surfaces by triggering just-in-time adhesin production. This mechanism restricts stable attachment to intimate surface interactions, thereby maximizing surface attachment, discouraging non-productive self-adherence, and preventing curing of the adhesive. © 2011 Blackwell Publishing Ltd.

Targeting NCK-Mediated Endothelial Cell Front-Rear Polarity Inhibits Neo-Vascularization

Science.gov (United States)

Dubrac, Alexandre; Genet, Gael; Ola, Roxana; Zhang, Feng; Pibouin-Fragner, Laurence; Han, Jinah; Zhang, Jiasheng; Thomas, Jean-Léon; Chedotal, Alain; Schwartz, Martin A.; Eichmann, Anne

2015-01-01

Background Sprouting angiogenesis is a key process driving blood vessel growth in ischemic tissues and an important drug target in a number of diseases, including wet macular degeneration and wound healing. Endothelial cells forming the sprout must develop front-rear polarity to allow sprout extension. The adaptor proteins Nck1 and 2 are known regulators of cytoskeletal dynamics and polarity, but their function in angiogenesis is poorly understood. Here we show that the Nck adaptors are required for endothelial cell front-rear polarity and migration downstream of the angiogenic growth factors VEGF-A and Slit2. Methods and Results Mice carrying inducible, endothelial-specific Nck1/2 deletions fail to develop front-rear polarized vessel sprouts and exhibit severe angiogenesis defects in the postnatal retina and during embryonic development. Inactivation of NCK1 and 2 inhibits polarity by preventing Cdc42 and Pak2 activation by VEGF-A and Slit2. Mechanistically, NCK binding to ROBO1 is required for both Slit2 and VEGF induced front-rear polarity. Selective inhibition of polarized endothelial cell migration by targeting Nck1/2 prevents hypersprouting induced by Notch or Bmp signaling inhibition, as well as pathological ocular neovascularization and wound healing. Conclusions These data reveal a novel signal integration mechanism involving NCK1/2, ROBO1/2 and VEGFR2 that controls endothelial cell front-rear polarity during sprouting angiogenesis. PMID:26659946

Thermococcus kodakarensis modulates its polar membrane lipids and elemental composition according to growth stage and phosphate availability

Directory of Open Access Journals (Sweden)

Travis B. Meador

2014-01-01

Full Text Available We observed significant changes in the elemental and intact polar lipid (IPL composition of the archaeon Thermococcus kodakarensis (KOD1 in response to growth stage and phosphorus supply. Reducing the amount of organic supplements and phosphate in growth media resulted in significant decreases in cell size and cellular quotas of carbon (C, nitrogen (N, and phosphorus (P, which coincided with significant increases in cellular IPL quota and IPLs comprising multiple P atoms and hexose moieties. Relatively more cellular P was stored as IPLs in P-limited cells (2-8% compared to control cells (< 0.8%. We also identified a specific IPL biomarker containing a phosphatidyl-N-acetylhexoseamine headgroup that was relatively enriched during rapid cell division. These observations serve as empirical evidence of IPL adaptations in Archaea that will help to interpret the distribution of these biomarkers in natural systems. The reported cell quotas of C, N, and P represent the first such data for a specific archaeon and suggest that thermophiles are C-rich compared to the cell carbon-to-volume relationship reported for planktonic bacteria.

High Arctic summer warming tracked by increased Cassiope tetragona growth in the world's northernmost polar desert.

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Weijers, Stef; Buchwal, Agata; Blok, Daan; Löffler, Jörg; Elberling, Bo

2017-11-01

Rapid climate warming has resulted in shrub expansion, mainly of erect deciduous shrubs in the Low Arctic, but the more extreme, sparsely vegetated, cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. Dwarf shrub dendrochronology may reveal climatological causes of past changes in growth, but is hindered at many High Arctic sites by short and fragmented instrumental climate records. Moreover, only few High Arctic shrub chronologies cover the recent decade of substantial warming. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the northernmost polar desert at 83°N in North Greenland. We analysed climate-growth relationships over the period with available instrumental data (1950-2012) between a 102-year-long C. tetragona shoot length chronology and instrumental climate records from the three nearest meteorological stations, gridded climate data, and North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices. July extreme maximum temperatures (JulT emx ), as measured at Alert, Canada, June NAO, and previous October AO, together explained 41% of the observed variance in annual C. tetragona growth and likely represent in situ summer temperatures. JulT emx explained 27% and was reconstructed back to 1927. The reconstruction showed relatively high growing season temperatures in the early to mid-twentieth century, as well as warming in recent decades. The rapid growth increase in C. tetragona shrubs in response to recent High Arctic summer warming shows that recent and future warming might promote an expansion of this evergreen dwarf shrub, mainly through densification of existing shrub patches, at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost, contrasting earlier notions of limited shrub growth sensitivity to

Langmuir instability in partially spin polarized bounded degenerate plasma

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Iqbal, Z.; Jamil, M.; Murtaza, G.

2018-04-01

Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.

Polarity and microstructure in InN thin layers grown by MOVPE

International Nuclear Information System (INIS)

Kuwano, N.; Nakahara, Y.; Amano, H.

2006-01-01

Microstructures in InN grown on sapphire (0001) and yttria-stabilized zirconia (YSZ) (111) by metal-organic vapor phase epitaxy (MOVPE) were analyzed by means of transmission electron microscopy (TEM) in order to clarify the growth process. Special attention was paid to the selectivity of the crystal polarity of InN. The InN thin films grown on sapphire after nitridation has a flat surface while those grown on YSZ has hillocks on the surface. The crystal polarity was determined by comparing the experimentally observed intensity distribution in convergent beam electron diffraction (CBED) disks with those simulated by the Broch-wave method. It was found that the InN grown on the sapphire has a nitrogen-polarity and the one on YSZ has a mixture of In- and N-polarities. The effect of surface-nitridation of sapphire on the growth process is also discussed (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Control of polarization and dipole moment in low-dimensional semiconductor nanostructures

International Nuclear Information System (INIS)

Li, L. H.; Ridha, P.; Mexis, M.; Smowton, P. M.; Blood, P.; Bozkurt, M.; Koenraad, P. M.; Patriarche, G.; Fiore, A.

2009-01-01

We demonstrate the control of polarization and dipole moment in semiconductor nanostructures, through nanoscale engineering of shape and composition. Rodlike nanostructures, elongated along the growth direction, are obtained by molecular beam epitaxial growth. By varying the aspect ratio and compositional contrast between the rod and the surrounding matrix, we rotate the polarization of the dominant interband transition from transverse-electric to transverse-magnetic, and modify the dipole moment producing a radical change in the voltage dependence of absorption spectra. This opens the way to the optimization of quantum dot amplifiers and electro-optical modulators.

Defect-Induced Hedgehog Polarization States in Multiferroics

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Li, Linze; Cheng, Xiaoxing; Jokisaari, Jacob R.; Gao, Peng; Britson, Jason; Adamo, Carolina; Heikes, Colin; Schlom, Darrell G.; Chen, Long-Qing; Pan, Xiaoqing

2018-03-01

Continuous developments in nanotechnology require new approaches to materials synthesis that can produce novel functional structures. Here, we show that nanoscale defects, such as nonstoichiometric nanoregions (NSNRs), can act as nano-building blocks for creating complex electrical polarization structures in the prototypical multiferroic BiFeO3 . An array of charged NSNRs are produced in BiFeO3 thin films by tuning the substrate temperature during film growth. Atomic-scale scanning transmission electron microscopy imaging reveals exotic polarization rotation patterns around these NSNRs. These polarization patterns resemble hedgehog or vortex topologies and can cause local changes in lattice symmetries leading to mixed-phase structures resembling the morphotropic phase boundary with high piezoelectricity. Phase-field simulations indicate that the observed polarization configurations are mainly induced by charged states at the NSNRs. Engineering defects thus may provide a new route for developing ferroelectric- or multiferroic-based nanodevices.

Stochastic multistep polarization switching in ferroelectrics

Science.gov (United States)

Genenko, Y. A.; Khachaturyan, R.; Schultheiß, J.; Ossipov, A.; Daniels, J. E.; Koruza, J.

2018-04-01

Consecutive stochastic 90° polarization switching events, clearly resolved in recent experiments, are described by a nucleation and growth multistep model. It extends the classical Kolmogorov-Avrami-Ishibashi approach and includes possible consecutive 90°- and parallel 180° switching events. The model predicts the results of simultaneous time-resolved macroscopic measurements of polarization and strain, performed on a tetragonal Pb (Zr ,Ti ) O3 ceramic in a wide range of electric fields over a time domain of seven orders of magnitude. It allows the determination of the fractions of individual switching processes, their characteristic switching times, activation fields, and respective Avrami indices.

The Apical Actin Fringe Contributes to Localized Cell Wall Deposition and Polarized Growth in the Lily Pollen Tube1[W][OPEN

Science.gov (United States)

Rounds, Caleb M.; Hepler, Peter K.; Winship, Lawrence J.

2014-01-01

In lily (Lilium formosanum) pollen tubes, pectin, a major component of the cell wall, is delivered through regulated exocytosis. The targeted transport and secretion of the pectin-containing vesicles may be controlled by the cortical actin fringe at the pollen tube apex. Here, we address the role of the actin fringe using three different inhibitors of growth: brefeldin A, latrunculin B, and potassium cyanide. Brefeldin A blocks membrane trafficking and inhibits exocytosis in pollen tubes; it also leads to the degradation of the actin fringe and the formation of an aggregate of filamentous actin at the base of the clear zone. Latrunculin B, which depolymerizes filamentous actin, markedly slows growth but allows focused pectin deposition to continue. Of note, the locus of deposition shifts frequently and correlates with changes in the direction of growth. Finally, potassium cyanide, an electron transport chain inhibitor, briefly stops growth while causing the actin fringe to completely disappear. Pectin deposition continues but lacks focus, instead being delivered in a wide arc across the pollen tube tip. These data support a model in which the actin fringe contributes to the focused secretion of pectin to the apical cell wall and, thus, to the polarized growth of the pollen tube. PMID:25037212

Polarization measurement for internal polarized gaseous targets

International Nuclear Information System (INIS)

Ye Zhenyu; Ye Yunxiu; Lv Haijiang; Mao Yajun

2004-01-01

The authors present an introduction to internal polarized gaseous targets, polarization method, polarization measurement method and procedure. To get the total nuclear polarization of hydrogen atoms (including the polarization of the recombined hydrogen molecules) in the target cell, authors have measured the parameters relating to atomic polarization and polarized hydrogen atoms and molecules. The total polarization of the target during our measurement is P T =0.853 ± 0.036. (authors)

The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem

Energy Technology Data Exchange (ETDEWEB)

Humphreys, C.J., E-mail: colin.humphreys@msm.cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Griffiths, J.T., E-mail: jg641@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Tang, F., E-mail: ft274@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Oehler, F., E-mail: fabrice.oehler@lpn.cnrs.fr [CNRS/C2N, Paris Sud University, Route de Nozay, 91460 Marcoussis (France); Findlay, S.D., E-mail: scott.findlay@monash.edu [School of Physics and Astronomy, Monash University, Victoria 3800 (Australia); Zheng, C., E-mail: changlin.zheng@monash.edu [Monash Centre for Electron Microscopy, Monash University, Victoria 3800 (Australia); Etheridge, J., E-mail: joanne.etheridge@mcem.monash.edu [Department of Materials Science and Engineering, Monash University, Victoria 3800 (Australia); Martin, T.L., E-mail: tomas.martin@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Bagot, P.A.J., E-mail: paul.bagot@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Moody, M.P., E-mail: michael.moody@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Sutherland, D., E-mail: danny.sutherland@manchester.ac.uk [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Dawson, P., E-mail: philip.dawson@manchester.ac.uk [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Schulz, S., E-mail: stefan.schulz@tyndall.ie [Tyndall National Institute, Lee Maltings Complex, Dyke Parade, Cork (Ireland); and others

2017-05-15

Highlights: • We have studied the atomic structure of polar and non-polar InGaN quantum wells. • The non-polar (11-20) InGaN quantum wells contain indium-rich clusters, unlike the polar (0001) quantum wells. • The electrons and holes in the quantum wells are localised by different mechanisms. - Abstract: We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20 meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60 meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.

ATP-binding motifs play key roles in Krp1p, kinesin-related protein 1, function for bi-polar growth control in fission yeast

International Nuclear Information System (INIS)

Rhee, Dong Keun; Cho, Bon A; Kim, Hyong Bai

2005-01-01

Kinesin is a microtubule-based motor protein with various functions related to the cell growth and division. It has been reported that Krp1p, kinesin-related protein 1, which belongs to the kinesin heavy chain superfamily, localizes on microtubules and may play an important role in cytokinesis. However, the function of Krp1p has not been fully elucidated. In this study, we overexpressed an intact form and three different mutant forms of Krp1p in fission yeast constructed by site-directed mutagenesis in two ATP-binding motifs or by truncation of the leucine zipper-like motif (LZiP). We observed hyper-extended microtubules and the aberrant nuclear shape in Krp1p-overexpressed fission yeast. As a functional consequence, a point mutation of ATP-binding domain 1 (G89E) in Krp1p reversed the effect of Krp1p overexpression in fission yeast, whereas the specific mutation in ATP-binding domain 2 (G238E) resulted in the altered cell polarity. Additionally, truncation of the leucine zipper-like domain (LZiP) at the C-terminal of Krp1p showed a normal nuclear division. Taken together, we suggest that krp1p is involved in regulation of cell-polarized growth through ATP-binding motifs in fission yeast

Monitoring microbial growth and activity using spectral induced polarization and low-field nuclear magnetic resonance

Science.gov (United States)

Zhang, Chi; Keating, Kristina; Revil, Andre

2015-04-01

Microbes and microbial activities in the Earth's subsurface play a significant role in shaping subsurface environments and are involved in environmental applications such as remediation of contaminants in groundwater and oil fields biodegradation. Stimulated microbial growth in such applications could cause wide variety of changes of physical/chemical properties in the subsurface. It is critical to monitor and determine the fate and transportation of microorganisms in the subsurface during such applications. Recent geophysical studies demonstrate the potential of two innovative techniques, spectral induced polarization (SIP) and low-field nuclear magnetic resonance (NMR), for monitoring microbial growth and activities in porous media. The SIP measures complex dielectric properties of porous media at low frequencies of exciting electric field, and NMR studies the porous structure of geologic media and characterizes fluids subsurface. In this laboratory study, we examined both SIP and NMR responses from bacterial growth suspension as well as suspension mixed with silica sands. We focus on the direct contribution of microbes to the SIP and NMR signals in the absence of biofilm formation or biomineralization. We used Zymomonas mobilis and Shewanella oneidensis (MR-1) for SIP and NMR measurements, respectively. The SIP measurements were collected over the frequency range of 0.1 - 1 kHz on Z. mobilis growth suspension and suspension saturated sands at different cell densities. SIP data show two distinct peaks in imaginary conductivity spectra, and both imaginary and real conductivities increased as microbial density increased. NMR data were collected using both CPMG pulse sequence and D-T2 mapping to determine the T2-distribution and diffusion properties on S. oneidensis suspension, pellets (live and dead), and suspension mixed with silica sands. NMR data show a decrease in the T2-distribution in S. oneidensis suspension saturated sands as microbial density increase. A

The Growth, Polarization, and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20

Energy Technology Data Exchange (ETDEWEB)

Taylor, G

2005-04-20

The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater (SGR) 1806-20 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR1806-20, consisting of previously reported 8.5 GHz data covering days 7 to 20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. For a symmetric outflow, we find a deceleration in the expansion, from {approx}4.5 mas/day to <2.5 mas/day. The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium, and transitions from a coasting phase to the Sedov-Taylor regime. The radio afterglow is elongated and maintains a 2:1 axis ratio with an average position angle of -40{sup o} (north through east), oriented perpendicular to the average intrinsic linear polarization angle. We also report on the discovery of motion in the flux centroid of the afterglow, at an average velocity of 0.26 {+-} 0.03 c (assuming a distance of 15 kpc) at a position angle of -45{sup o}. This motion, in combination with the growth and polarization measurements, suggests an initially asymmetric outflow, mainly from one side of the magnetar.

Electron distribution in polar heterojunctions within a realistic model

Energy Technology Data Exchange (ETDEWEB)

Tien, Nguyen Thanh, E-mail: thanhtienctu@gmail.com [College of Natural Science, Can Tho University, 3-2 Road, Can Tho City (Viet Nam); Thao, Dinh Nhu [Center for Theoretical and Computational Physics, College of Education, Hue University, 34 Le Loi Street, Hue City (Viet Nam); Thao, Pham Thi Bich [College of Natural Science, Can Tho University, 3-2 Road, Can Tho City (Viet Nam); Quang, Doan Nhat [Institute of Physics, Vietnamese Academy of Science and Technology, 10 Dao Tan Street, Hanoi (Viet Nam)

2015-12-15

We present a theoretical study of the electron distribution, i.e., two-dimensional electron gas (2DEG) in polar heterojunctions (HJs) within a realistic model. The 2DEG is confined along the growth direction by a triangular quantum well with a finite potential barrier and a bent band figured by all confinement sources. Therein, interface polarization charges take a double role: they induce a confining potential and, furthermore, they can make some change in other confinements, e.g., in the Hartree potential from ionized impurities and 2DEG. Confinement by positive interface polarization charges is necessary for the ground state of 2DEG existing at a high sheet density. The 2DEG bulk density is found to be increased in the barrier, so that the scattering occurring in this layer (from interface polarization charges and alloy disorder) becomes paramount in a polar modulation-doped HJ.

FliO Regulation of FliP in the Formation of the Salmonella enterica Flagellum

Science.gov (United States)

Barker, Clive S.; Meshcheryakova, Irina V.; Kostyukova, Alla S.; Samatey, Fadel A.

2010-01-01

The type III secretion system of the Salmonella flagellum consists of 6 integral membrane proteins: FlhA, FlhB, FliO, FliP, FliQ, and FliR. However, in some other type III secretion systems, a homologue of FliO is apparently absent, suggesting it has a specialized role. Deleting the fliO gene from the chromosome of a motile strain of Salmonella resulted in a drastic decrease of motility. Incubation of the ΔfliO mutant strain in motility agar, gave rise to pseudorevertants containing extragenic bypass mutations in FliP at positions R143H or F190L. Using membrane topology prediction programs, and alkaline phosphatase or GFPuv chimeric protein fusions into the FliO protein, we demonstrated that FliO is bitopic with its N-terminus in the periplasm and C-terminus in the cytoplasm. Truncation analysis of FliO demonstrated that overexpression of FliO43–125 or FliO1–95 was able to rescue motility of the ΔfliO mutant. Further, residue leucine 91 in the cytoplasmic domain was identified to be important for function. Based on secondary structure prediction, the cytoplasmic domain, FliO43–125, should contain beta-structure and alpha-helices. FliO43–125-Ala was purified and studied using circular dichroism spectroscopy; however, this domain was disordered, and its structure was a mixture of beta-sheet and random coil. Coexpression of full-length FliO with FliP increased expression levels of FliP, but coexpression with the cytoplasmic domain of FliO did not enhance FliP expression levels. Overexpression of the cytoplasmic domain of FliO further rescued motility of strains deleted for the fliO gene expressing bypass mutations in FliP. These results suggest FliO maintains FliP stability through transmembrane domain interaction. The results also demonstrate that the cytoplasmic domain of FliO has functionality, and it presumably becomes structured while interacting with its binding partners. PMID:20941389

FliO regulation of FliP in the formation of the Salmonella enterica flagellum.

Directory of Open Access Journals (Sweden)

Clive S Barker

2010-09-01

Full Text Available The type III secretion system of the Salmonella flagellum consists of 6 integral membrane proteins: FlhA, FlhB, FliO, FliP, FliQ, and FliR. However, in some other type III secretion systems, a homologue of FliO is apparently absent, suggesting it has a specialized role. Deleting the fliO gene from the chromosome of a motile strain of Salmonella resulted in a drastic decrease of motility. Incubation of the ΔfliO mutant strain in motility agar, gave rise to pseudorevertants containing extragenic bypass mutations in FliP at positions R143H or F190L. Using membrane topology prediction programs, and alkaline phosphatase or GFPuv chimeric protein fusions into the FliO protein, we demonstrated that FliO is bitopic with its N-terminus in the periplasm and C-terminus in the cytoplasm. Truncation analysis of FliO demonstrated that overexpression of FliO₄₃-₁₂₅ or FliO₁-₉₅ was able to rescue motility of the ΔfliO mutant. Further, residue leucine 91 in the cytoplasmic domain was identified to be important for function. Based on secondary structure prediction, the cytoplasmic domain, FliO₄₃-₁₂₅, should contain beta-structure and alpha-helices. FliO₄₃-₁₂₅-Ala was purified and studied using circular dichroism spectroscopy; however, this domain was disordered, and its structure was a mixture of beta-sheet and random coil. Coexpression of full-length FliO with FliP increased expression levels of FliP, but coexpression with the cytoplasmic domain of FliO did not enhance FliP expression levels. Overexpression of the cytoplasmic domain of FliO further rescued motility of strains deleted for the fliO gene expressing bypass mutations in FliP. These results suggest FliO maintains FliP stability through transmembrane domain interaction. The results also demonstrate that the cytoplasmic domain of FliO has functionality, and it presumably becomes structured while interacting with its binding partners.

Polarization mechanism in a ns laser-induced plasma spectroscopy of Al alloy

Science.gov (United States)

Aghababaei Nejad, Mahboobeh; Soltanolkotabi, Mahmood; Eslami Majd, Abdollah

2018-01-01

Polarization emission from aluminum alloy by ns laser-induced breakdown spectroscopy (LIBS) is carefully investigated in air using a non-gated CCD camera at integration time of 100 ms. First, the analysis reveals that the small polarization degree is the same for both continuum and discrete line emission spectra which also increases slowly with wavelength growth; second, laser fluence in the range of 347.81-550.10 J/cm2 has no significant changes in plasma polarization; and third, larger polarization in comparison with polarization introduced by preferential reflection of emission from the target surface (Fresnel reflectivity) is observed. The residual fluctuations of the anisotropic recombining plasma and the dynamic polarization of an ion's core are suggested as the possible main sources for observed polarized radiation in ns-LIBS.

Study of proton polarization in charge exchange process on optically oriented sodium atoms

International Nuclear Information System (INIS)

Zelenskij, A.N.; Kokhanovskij, S.A.

1984-01-01

Using high-power adjustable dye lasers for electron spin orientation in a charge-exchange target enables to significantly increase the proton polarization efficiency. A device is described that permits to avoid growth of the polarized proton beam emittance in a charge-exchange process in a strong magnetic field. The devise main feature is the use of an intensive source of neutral hydrogen atoms and the presence of a helium additional charge-exchange target which actualy is a proton ''source''. The helium charge-exchange cell is placed in the same magnetic field of a solenoid where a cell with oriented sodium is placed, a polarized electron being captured by a proton in the latter cell. In this case the beam at the solenoid inlet and outlet is in a neutral state; emittance growth related to the effect of end magnetic fields is not observed. The device after all prouduces polarized protons, their polarization degree is measured and the effect of various factors on polarization degree is studied. The description of the laser source and laser system is given. Measurement results have shown the beam intensity of neutral 7 keV atoms which passed through a polarizer to be 2 mA. The proton current doesn't depend. On the beeld fin the region of chrge exchange for the 8 kGs magnetic field. The degree of sodium polarization was 80% and polarized proton current approximately 70 μA at a temperature of the polarized sodium cell corresponding to the density of sodium vapar approximately 3x10 13 at/cm 2

Luxury-based Growth

OpenAIRE

Shiro Kuwahara

2006-01-01

Assuming that there exists a preference for luxury goods and a knowledge spillover from luxury goods production to goods production, this paper constructs an endogenous economic growth model. The model predicts two steady states: one is a steady positive growth state with regard to luxury goods production, and the other is a zero growth state in the absence of luxury goods production. Thus, this study examines the polarization of economies based on luxury goods consumption

Selective area growth of GaN rod structures by MOVPE: Dependence on growth conditions

Energy Technology Data Exchange (ETDEWEB)

Li, Shunfeng; Fuendling, Soenke; Wang, Xue; Erenburg, Milena; Al-Suleiman, Mohamed Aid Mansur; Wei, Jiandong; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Bergbauer, Werner [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Osram Opto Semiconductors GmbH, Leibnizstr. 4, 93055 Regensburg (Germany); Strassburg, Martin [Osram Opto Semiconductors GmbH, Leibnizstr. 4, 93055 Regensburg (Germany)

2011-07-15

Selective area growth of GaN nanorods by metalorganic vapor phase epitaxy is highly demanding for novel applications in nano-optoelectronic and nanophotonics. Recently, we report the successful selective area growth of GaN nanorods in a continuous-flow mode. In this work, as examples, we show the morphology dependence of GaN rods with {mu}m or sub-{mu}m in diameters on growth conditions. Firstly, we found that the nitridation time is critical for the growth, with an optimum from 90 to 180 seconds. This leads to more homogeneous N-polar GaN rods growth. A higher temperature during GaN rod growth tends to increase the aspect ratio of the GaN rods. This is due to the enhanced surface diffusion of growth species. The V/III ratio is also an important parameter for the GaN rod growth. Its increase causes reduction of the aspect ratio of GaN rods, which could be explained by the relatively lower growth rate on (000-1) N-polar top surface than it on {l_brace}1-100{r_brace} m-planes by supplying more NH{sub 3} (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Optical properties of InN nanocolumns: Electron accumulation at InN non-polar surfaces and dependence on the growth conditions

Energy Technology Data Exchange (ETDEWEB)

Segura-Ruiz, J.; Cantarero, A. [Materials Science Institute, University of Valencia (Spain); Garro, N. [Materials Science Institute, University of Valencia (Spain); Fundacio General de la Universitat de Valencia, Valencia (Spain); Iikawa, F. [Instituto de Fisica ' ' Gleb Wataghin' ' , UNICAMP, Campinas-SP (Brazil); Denker, C.; Malindretos, J.; Rizzi, A. [IV. Physikalisches Institut, Georg-August Universitaet Goettingen (Germany)

2009-06-15

InN nanocolumns grown by plasma-assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red-shifted with respect to the PLE onset and both energies were higher than the low temperature band-gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present at the non-polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the density of free electrons can be somehow controlled by the growth parameters. It was observed that In-BEP and substrate temperature leading to shorter In diffusion lengths diminished the effects of the electron accumulation layer on the optical properties. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Optical properties of InN nanocolumns: Electron accumulation at InN non-polar surfaces and dependence on the growth conditions

International Nuclear Information System (INIS)

Segura-Ruiz, J.; Cantarero, A.; Garro, N.; Iikawa, F.; Denker, C.; Malindretos, J.; Rizzi, A.

2009-01-01

InN nanocolumns grown by plasma-assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red-shifted with respect to the PLE onset and both energies were higher than the low temperature band-gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present at the non-polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the density of free electrons can be somehow controlled by the growth parameters. It was observed that In-BEP and substrate temperature leading to shorter In diffusion lengths diminished the effects of the electron accumulation layer on the optical properties. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Interfacial B-site atomic configuration in polar (111) and non-polar (001) SrIrO3/SrTiO3 heterostructures

Science.gov (United States)

Anderson, T. J.; Zhou, H.; Xie, L.; Podkaminer, J. P.; Patzner, J. J.; Ryu, S.; Pan, X. Q.; Eom, C. B.

2017-09-01

The precise control of interfacial atomic arrangement in ABO3 perovskite heterostructures is paramount, particularly in cases where the subsequent electronic properties of the material exhibit geometrical preferences along polar crystallographic directions that feature inevitably complex surface reconstructions. Here, we present the B-site interfacial structure in polar (111) and non-polar (001) SrIrO3/SrTiO3 interfaces. The heterostructures were examined using scanning transmission electron microscopy and synchrotron-based coherent Bragg rod analysis. Our results reveal the preference of B-site intermixing across the (111) interface due to the polarity-compensated SrTiO3 substrate surface prior to growth. By comparison, the intermixing at the non-polar (001) interface is negligible. This finding suggests that the intermixing may be necessary to mitigate epitaxy along heavily reconstructed and non-stoichiometric (111) perovskite surfaces. Furthermore, this preferential B-site configuration could allow the geometric design of the interfacial perovskite structure and chemistry to selectively engineer the correlated electronic states of the B-site d-orbital.

Interfacial B-site atomic configuration in polar (111 and non-polar (001 SrIrO3/SrTiO3 heterostructures

Directory of Open Access Journals (Sweden)

T. J. Anderson

2017-09-01

Full Text Available The precise control of interfacial atomic arrangement in ABO3 perovskite heterostructures is paramount, particularly in cases where the subsequent electronic properties of the material exhibit geometrical preferences along polar crystallographic directions that feature inevitably complex surface reconstructions. Here, we present the B-site interfacial structure in polar (111 and non-polar (001 SrIrO3/SrTiO3 interfaces. The heterostructures were examined using scanning transmission electron microscopy and synchrotron-based coherent Bragg rod analysis. Our results reveal the preference of B-site intermixing across the (111 interface due to the polarity-compensated SrTiO3 substrate surface prior to growth. By comparison, the intermixing at the non-polar (001 interface is negligible. This finding suggests that the intermixing may be necessary to mitigate epitaxy along heavily reconstructed and non-stoichiometric (111 perovskite surfaces. Furthermore, this preferential B-site configuration could allow the geometric design of the interfacial perovskite structure and chemistry to selectively engineer the correlated electronic states of the B-site d-orbital.

Knockin' on pollen's door: live cell imaging of early polarization events in germinating Arabidopsis pollen

Science.gov (United States)

Vogler, Frank; Konrad, Sebastian S. A.; Sprunck, Stefanie

2015-01-01

Pollen tubes are an excellent system for studying the cellular dynamics and complex signaling pathways that coordinate polarized tip growth. Although several signaling mechanisms acting in the tip-growing pollen tube have been described, our knowledge on the subcellular and molecular events during pollen germination and growth site selection at the pollen plasma membrane is rather scarce. To simultaneously track germinating pollen from up to 12 genetically different plants we developed an inexpensive and easy mounting technique, suitable for every standard microscope setup. We performed high magnification live-cell imaging during Arabidopsis pollen activation, germination, and the establishment of pollen tube tip growth by using fluorescent marker lines labeling either the pollen cytoplasm, vesicles, the actin cytoskeleton or the sperm cell nuclei and membranes. Our studies revealed distinctive vesicle and F-actin polarization during pollen activation and characteristic growth kinetics during pollen germination and pollen tube formation. Initially, the germinating Arabidopsis pollen tube grows slowly and forms a uniform roundish bulge, followed by a transition phase with vesicles heavily accumulating at the growth site before switching to rapid tip growth. Furthermore, we found the two sperm cells to be transported into the pollen tube after the phase of rapid tip growth has been initiated. The method presented here is suitable to quantitatively study subcellular events during Arabidopsis pollen germination and growth, and for the detailed analysis of pollen mutants with respect to pollen polarization, bulging, or growth site selection at the pollen plasma membrane. PMID:25954283

Growth and characterization of polar and nonpolar ZnO film grown on sapphire substrates by using atomic layer deposition

International Nuclear Information System (INIS)

Kim, Ki-Wook; Son, Hyo-Soo; Choi, Nak-Jung; Kim, Jihoon; Lee, Sung-Nam

2013-01-01

We investigated the electrical and the optical properties of polar and nonpolar ZnO films grown on sapphire substrates with different crystallographic planes. High resolution X-ray results revealed that polar c-plane (0001), nonpolar m-plane (10-10) and a-plane (11-20) ZnO thin films were grown on c-plane, m- and r-sapphire substrates by atomic layer deposition, respectively. Compared with the c-plane ZnO film, nonpolar m-plane and a-plane ZnO films showed smaller surface roughness and anisotropic surface structures. Regardless of ZnO crystal planes, room temperature photoluminescence spectra represented two emissions which consisted of the near bandedge (∼ 380 nm) and the deep level emission (∼ 500 nm). The a-plane ZnO films represented better optical and electrical properties than c-plane ZnO, while m-plane ZnO films exhibited poorer optical and electrical properties than c-plane ZnO. - Highlights: • Growth and characterization of a-, c- and m-plane ZnO film by atomic layer deposition. • The a-plane ZnO represented better optical and electrical properties than c-plane ZnO. • The m-plane ZnO exhibited poorer optical and electrical properties than c-plane ZnO

Remotely Interrogated Passive Polarizing Dosimeter (RIPPeD).

Energy Technology Data Exchange (ETDEWEB)

Kemme, Shanalyn A.; Buller, Daniel L.; Dirk, Shawn M.; Boye, Robert R.; Samora, Sally; Washburn, Cody M.; Wheeler, David Roger

2008-09-01

Conductive polymers have become an extremely useful class of materials for many optical applications. We have developed an electrochemical growth method for depositing highly conductive ({approx}100 S/cm) polypyrrole. Additionally, we have adapted advanced fabrication methods for use with the polypyrrole resulting in gratings with submicron features. This conductive polymer micro-wire grid provides an optical polarizer with unique properties. When the polymer is exposed to ionizing radiation, its conductivity is affected and the polarization properties of the device, specifically the extinction ratio, change in a corresponding manner. This change in polarization properties can be determined by optically interrogating the device, possibly from a remote location. The result is a passive radiation-sensitive sensor with very low optical visibility. The ability to interrogate the device from a safe standoff distance provides a device useful in potentially dangerous environments. Also, the passive nature of the device make it applicable in applications where external power is not available. We will review the polymer deposition, fabrication methods and device design and modeling. The characterization of the polymer's sensitivity to ionizing radiation and optical testing of infrared polarizers before and after irradiation will also be presented. These experimental results will highlight the usefulness of the conductive infrared polarizer to many security and monitoring applications.

Remotely Interrogated Passive Polarizing Dosimeter (RIPPeD)

International Nuclear Information System (INIS)

Kemme, Shanalyn A.; Buller, Daniel L.; Dirk, Shawn M.; Boye, Robert R.; Samora, Sally; Washburn, Cody M.; Wheeler, David Roger

2008-01-01

Conductive polymers have become an extremely useful class of materials for many optical applications. We have developed an electrochemical growth method for depositing highly conductive (∼100 S/cm) polypyrrole. Additionally, we have adapted advanced fabrication methods for use with the polypyrrole resulting in gratings with submicron features. This conductive polymer micro-wire grid provides an optical polarizer with unique properties. When the polymer is exposed to ionizing radiation, its conductivity is affected and the polarization properties of the device, specifically the extinction ratio, change in a corresponding manner. This change in polarization properties can be determined by optically interrogating the device, possibly from a remote location. The result is a passive radiation-sensitive sensor with very low optical visibility. The ability to interrogate the device from a safe standoff distance provides a device useful in potentially dangerous environments. Also, the passive nature of the device make it applicable in applications where external power is not available. We will review the polymer deposition, fabrication methods and device design and modeling. The characterization of the polymer's sensitivity to ionizing radiation and optical testing of infrared polarizers before and after irradiation will also be presented. These experimental results will highlight the usefulness of the conductive infrared polarizer to many security and monitoring applications

Myosin helical pitch angle as a quantitative imaging biomarker for characterization of cardiac programming in fetal growth restriction measured by polarization second harmonic microscopy

Science.gov (United States)

Amat-Roldan, I.; Psilodimitrakopoulos, S.,; Eixarch, E.,; Torre, I.; Wotjas, B.; Crispi, F.; Figueras, F.; Artigas, D.,; Loza-Alvarez, P.; Gratacos, E.,

2009-07-01

Fetal growth restriction (FGR) has recently shown a strong association with cardiac programming which predisposes to cardiovascular mortality in adulthood. Polarization Second Harmonic Microscopy can quantify molecular architecture changes with high sensitivity in cardiac myofibrils. In this work, we use myosin helical pitch angle as an example to quantify such alterations related to this high risk population. Importantly, this shows a potential use of the technique as an early diagnostic tool and an alternative method to understand pathophysiological processes.

Inward Greenfield FDI and Patterns of Job Polarization

Directory of Open Access Journals (Sweden)

Sara Amoroso

2018-04-01

Full Text Available The unprecedented growth in foreign direct investment in the last few decades has caused drastic changes in the labor markets of the host countries. The major part of FDI takes place in low-tech industries, where the wages and skills are low, or in high-tech, where they offer a wage premium for the highly skilled workers. This mechanism may increase the polarization of employment into high-wage and low-wage jobs, at the expense of middle-skill jobs. This paper looks at the effects of two types of FDI inflows, namely foreign investment in high-skill and low-skill activities, on job polarization. We match data on greenfield FDI aggregated by country and sector with data on employment by occupational skill to investigate the extent to which different types of greenfield FDI are responsible for skill polarization. Our results show that low-skill foreign investment shifts employment from high- to medium- and low-skill jobs, while skill-intensive FDI generally leads to skill upgrading. Only FDI in information and communication technology (ICT is associated with job polarization, but only when accounting for the plurality of job polarization patterns across European sectors.

Pseudomonas mesophilica and an unnamed taxon, clinical isolates of pink-pigmented oxidative bacteria.

OpenAIRE

Gilardi, G L; Faur, Y C

1984-01-01

Twenty-one strains of pink-pigmented bacteria, isolated from human clinical specimens and an environmental source, were compared with Pseudomonas mesophilica ATCC 29983 and Protaminobacter ruber ATCC 8457. These isolates were gram-negative, oxidative rods which were motile by means of a single polar flagellum; gave positive catalase, indophenol oxidase, urease, and amylase reactions; and grew slowly at 30 degrees C. Fourteen isolates conformed to the designated type strains Pseudomonas mesoph...

Polarization of lanthanum nucleus by dynamic polarization method

International Nuclear Information System (INIS)

Adachi, Toshikazu; Ishimoto, Shigeru; Masuda, Yasuhiro; Morimoto, Kimio

1989-01-01

Preliminary studies have been carried out concerning the application of a dynamic polarization method to polarizing lanthanum fluoride single crystal to be employed as target in experiments with time reversal invariance. The present report briefly outlines the dynamic polarization method and describes some preliminary studies carried out so far. Dynamic polarization is of particular importance because no techniques are currently available that can produce highly polarized static nucleus. Spin interaction between electrons and protons (nuclei) plays a major role in the dynamic polarization method. In a thermal equilibrium state, electrons are polarized almost completely while most protons are not polarized. Positively polarized proton spin is produced by applying microwave to this system. The most hopeful candidate target material is single crystal of LaF 3 containing neodymium because the crystal is chemically stable and easy to handle. The spin direction is of great importance in experiments with time reversal invariance. The spin of neutrons in the target can be cancelled by adjusting the external magnetic field applied to a frozen polarized target. In a frozen spin state, the polarity decreases slowly with a relaxation time that depends on the external magnetic field and temperature. (N.K.)

Polarized neutrons

International Nuclear Information System (INIS)

Williams, W.G.

1988-01-01

The book on 'polarized neutrons' is intended to inform researchers in condensed matter physics and chemistry of the diversity of scientific problems that can be investigated using polarized neutron beams. The contents include chapters on:- neutron polarizers and instrumentation, polarized neutron scattering, neutron polarization analysis experiments and precessing neutron polarization. (U.K.)

Knockin’ on pollen’s door: live cell imaging of early polarization events in germinating Arabidopsis pollen

Directory of Open Access Journals (Sweden)

Frank eVogler

2015-04-01

Full Text Available Pollen tubes are an excellent system for studying the cellular dynamics and complex signaling pathways that coordinate polarized tip growth. Although several signaling mechanisms acting in the tip-growing pollen tube have been described, our knowledge on the subcellular and molecular events during pollen germination and growth site selection at the pollen plasma membrane is rather scarce. To simultaneously track germinating pollen from up to 12 genetically different plants we developed an inexpensive and easy mounting technique, suitable for every standard microscope setup. We performed high magnification live-cell imaging during Arabidopsis pollen activation, germination, and the establishment of pollen tube tip growth by using fluorescent marker lines labeling either the pollen cytoplasm, vesicles, the actin cytoskeleton or the sperm cell nuclei and membranes. Our studies revealed distinctive vesicle and F-actin polarization during pollen activation and characteristic growth kinetics during pollen germination and pollen tube formation. Initially, the germinating Arabidopsis pollen tube grows slowly and forms a uniform roundish bulge, followed by a transition phase with vesicles heavily accumulating at the growth site before switching to rapid tip growth. Furthermore, we found the two sperm cells to be transported into the pollen tube after the phase of rapid tip growth has been initiated. The method presented here is suitable to quantitatively study subcellular events during Arabidopsis pollen germination and growth, and for the detailed analysis of pollen mutants with respect to pollen polarization, bulging, or growth site selection at the pollen plasma membrane.

Polarization of stacking fault related luminescence in GaN nanorods

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G. Pozina

2017-01-01

Full Text Available Linear polarization properties of light emission are presented for GaN nanorods (NRs grown along [0001] direction on Si(111 substrates by direct-current magnetron sputter epitaxy. The near band gap photoluminescence (PL measured at low temperature for a single NR demonstrated an excitonic line at ∼3.48 eV and the stacking faults (SFs related transition at ∼3.43 eV. The SF related emission is linear polarized in direction perpendicular to the NR growth axis in contrast to a non-polarized excitonic PL. The results are explained in the frame of the model describing basal plane SFs as polymorphic heterostructure of type II, where anisotropy of chemical bonds at the interfaces between zinc blende and wurtzite GaN subjected to in-built electric field is responsible for linear polarization parallel to the interface planes.

Polarization of eigenmodes in laser diode waveguides on semipolar and nonpolar GaN

Energy Technology Data Exchange (ETDEWEB)

Rass, Jens; Vogt, Patrick [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Wernicke, Tim; Einfeldt, Sven; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany); Scheibenzuber, Wolfgang G.; Schwarz, Ulrich T. [Department of Physics, Regensburg University (Germany); Kupec, Jan [Integrated Systems Laboratory, ETH Zurich (Switzerland); Witzigmann, Bernd [Computational Electronics and Photonics Group, University of Kassel (Germany); Kneissl, Michael [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany)

2010-02-15

Recent calculations of the eigenmodes in waveguides grown on semipolar GaN suggest that the optical polarization of the emitted light as well as the optical gain depends on the orientation of the resonator. Our measurements on separate confinement heterostructures on semipolar (11 anti 22) and (10 anti 12) GaN show that for laser resonators along the semipolar [11 anti 2 anti 3 ] and [0 anti 111] directions (i.e. the projection of the c-axis onto the plane of growth) the threshold for amplified spontaneous emission is lower than for the nonpolar direction and that the stimulated emission is linearly polarized as TE mode. For the waveguide structures along the nonpolar [1 anti 100] or [11 anti 20] direction on the other hand, birefringence and anisotropy of the optical gain in the plane of growth leads not only to a higher threshold but also to a rotation of the optical polarization which is not any more TE- or TM-polarized but influenced by the ordinary and extraordinary refractive index of the material. We observe stimulated emission into a mode which is linearly polarized in extraordinarydirection nearly parallel to the c-axis. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Topical Review: Development of overgrown semi-polar GaN for high efficiency green/yellow emission

Science.gov (United States)

Wang, T.

2016-09-01

The most successful example of large lattice-mismatched epitaxial growth of semiconductors is the growth of III-nitrides on sapphire, leading to the award of the Nobel Prize in 2014 and great success in developing InGaN-based blue emitters. However, the majority of achievements in the field of III-nitride optoelectronics are mainly limited to polar GaN grown on c-plane (0001) sapphire. This polar orientation poses a number of fundamental issues, such as reduced quantum efficiency, efficiency droop, green and yellow gap in wavelength coverage, etc. To date, it is still a great challenge to develop longer wavelength devices such as green and yellow emitters. One clear way forward would be to grow III-nitride device structures along a semi-/non-polar direction, in particular, a semi-polar orientation, which potentially leads to both enhanced indium incorporation into GaN and reduced quantum confined Stark effects. This review presents recent progress on developing semi-polar GaN overgrowth technologies on sapphire or Si substrates, the two kinds of major substrates which are cost-effective and thus industry-compatible, and also demonstrates the latest achievements on electrically injected InGaN emitters with long emission wavelengths up to and including amber on overgrown semi-polar GaN. Finally, this review presents a summary and outlook on further developments for semi-polar GaN based optoelectronics.

Induced polarization and self-potential geophysical signature of bacterial activity in porous media (Invited)

Science.gov (United States)

Revil, A.

2013-12-01

The first part of the presentation will be dedicated to the spectral induced polarization signature of bacteria in porous media. We developed a quantitative model to investigate frequency-domain induced polarization response of suspensions of bacteria and bacteria growth in porous media. Induced polarization of bacteria (alpha-polarization) is related to the properties of the electrical double layer of the bacteria. Surface conductivity and alpha-polarization are due to the Stern layer of counterions occurring in a brush of polymers coating the surface of the bacteria. These phenomena can be related to the cation exchange capacity of the bacteria. The mobility of the counterions in this Stern layer is found to be very small (4.7×10-10 m2s-1 V-1 at 25°C). This implies a very low relaxation frequency for the alpha-polarization of the bacteria cells (typically around 0.1 to 5 Hertz) in agreement with experimental observations. This new model can be coupled to reactive transport modeling codes in which the evolution of bacterial populations are usually described by Monod kinetics. We show that the growth rate and endogenous decay coefficients of bacteria in a porous sand can be inferred non-intrusively from time lapse frequency-domain induced polarization data. The second part of the presentation will concern the biogeobattery mechanism showing new data, the concept of transient biogeobattery and the influence of the concentration of the electron acceptors in the process.

Workshop on polarized neutron filters and polarized pulsed neutron experiments

International Nuclear Information System (INIS)

Itoh, Shinichi

2004-07-01

The workshop was held in KEK by thirty-three participants on April 26, 2004. The polarized neutron filter method was only discussed. It consists of three parts; the first part was discussed on the polarized neutron methods, the second part on the polarized neutron experiments and the third on the pulse neutron spectrometer and polarized neutron experiments. The six papers were presented such as the polarized 3 He neutron spin filter, neutron polarization by proton polarized filter, soft master and neutron scattering, polarized neutron in solid physics, polarization experiments by chopper spectroscope and neutron polarization system in superHRPD. (S.Y.)

The polarization response in InAs quantum dots: theoretical correlation between composition and electronic properties

International Nuclear Information System (INIS)

Usman, Muhammad; O’Reilly, Eoin P; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; Passaseo, Adriana; Klimeck, Gerhard

2012-01-01

III–V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In–Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response. (paper)

Enhanced polarization and dielectric properties of Pb(Zr1-xTix)O3 thin films

Science.gov (United States)

Ortega, N.; Kumar, Ashok; Katiyar, R. S.

2008-10-01

We report the fabrication of PbZr0.57Ti0.43O3 (PZT) thin films with preferential growth along (111) and random crystalline orientation on the platinized silicon substrates using pulsed laser deposition technique. X-ray diffraction patterns and surface morphology indicate increase in grain size and nucleation, which support better perovskite matrix with increase in annealing temperature. We observed large dielectric constant (˜4000) and enhanced remanent polarization 70 μC/cm2 at room temperature attributed to grain growth and intermetallic Pt-Pb transient phase. Frequency dependent polarization showed minor reduction in polarization above 10 kHz frequencies. Normalized fatigue characteristic of PZT thin films showed minimal 25% degradation in remanent polarization after 109 cycles, which may be useful for memory devices. ac conductivity spectra illustrated that anomaly near the phase transition temperature with activation energy (Ea˜0.60-0.75 eV) supports the intrinsic nature of ferroelectric phase transition.

Hierarchical super-structure identified by polarized light microscopy, electron microscopy and nanoindentation: Implications for the limits of biological control over the growth mode of abalone sea shells

Directory of Open Access Journals (Sweden)

Schneider Andreas S

2012-09-01

Full Text Available Abstract Background Mollusc shells are commonly investigated using high-resolution imaging techniques based on cryo-fixation. Less detailed information is available regarding the light-optical properties. Sea shells of Haliotis pulcherina were embedded for polishing in defined orientations in order to investigate the interface between prismatic calcite and nacreous aragonite by standard materialographic methods. A polished thin section of the interface was prepared with a defined thickness of 60 μm for quantitative birefringence analysis using polarized light and LC-PolScope microscopy. Scanning electron microscopy images were obtained for comparison. In order to study structural-mechanical relationships, nanoindentation experiments were performed. Results Incident light microscopy revealed a super-structure in semi-transparent regions of the polished cross-section under a defined angle. This super-structure is not visible in transmitted birefringence analysis due to the blurred polarization of small nacre platelets and numerous organic interfaces. The relative orientation and homogeneity of calcite prisms was directly identified, some of them with their optical axes exactly normal to the imaging plane. Co-oriented "prism colonies" were identified by polarized light analyses. The nacreous super-structure was also visualized by secondary electron imaging under defined angles. The domains of the super-structure were interpreted to consist of crystallographically aligned platelet stacks. Nanoindentation experiments showed that mechanical properties changed with the same periodicity as the domain size. Conclusions In this study, we have demonstrated that insights into the growth mechanisms of nacre can be obtained by conventional light-optical methods. For example, we observed super-structures formed by co-oriented nacre platelets as previously identified using X-ray Photo-electron Emission Microscopy (X-PEEM [Gilbert et al., Journal of the

Neutron polarization in polarized 3He targets

International Nuclear Information System (INIS)

Friar, J.L.; Gibson, B.F.; Payne, G.L.; Bernstein, A.M.; Chupp, T.E.

1990-01-01

Simple formulas for the neutron and proton polarizations in polarized 3 He targets are derived assuming (1) quasielastic final states; (2) no final-state interactions; (3) no meson-exchange currents; (4) large momentum transfers; (5) factorizability of 3 He SU(4) response-function components. Numerical results from a wide variety of bound-state solutions of the Faddeev equations are presented. It is found that this simple model predicts the polarization of neutrons in a fully polarized 3 He target to be 87%, while protons should have a slight residual polarization of -2.7%. Numerical studies show that this model works very well for quasielastic electron scattering

Molecular Memory of Morphologies by Septins during Neuron Generation Allows Early Polarity Inheritance.

Science.gov (United States)

Boubakar, Leila; Falk, Julien; Ducuing, Hugo; Thoinet, Karine; Reynaud, Florie; Derrington, Edmund; Castellani, Valérie

2017-08-16

Transmission of polarity established early during cell lineage history is emerging as a key process guiding cell differentiation. Highly polarized neurons provide a fascinating model to study inheritance of polarity over cell generations and across morphological transitions. Neural crest cells (NCCs) migrate to the dorsal root ganglia to generate neurons directly or after cell divisions in situ. Using live imaging of vertebrate embryo slices, we found that bipolar NCC progenitors lose their polarity, retracting their processes to round for division, but generate neurons with bipolar morphology by emitting processes from the same locations as the progenitor. Monitoring the dynamics of Septins, which play key roles in yeast polarity, indicates that Septin 7 tags process sites for re-initiation of process growth following mitosis. Interfering with Septins blocks this mechanism. Thus, Septins store polarity features during mitotic rounding so that daughters can reconstitute the initial progenitor polarity. Copyright © 2017 Elsevier Inc. All rights reserved.

When measured spin polarization is not spin polarization

International Nuclear Information System (INIS)

Dowben, P A; Wu Ning; Binek, Christian

2011-01-01

Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO 2 and Cr 2 O 3 illustrate some of the complications which hinders comparisons of spin polarization values. (viewpoint)

Evolution of Calcareous Deposits and Passive Film on 304 Stainless Steel with Cathodic Polarization in Sea Water

Directory of Open Access Journals (Sweden)

Tianxiang Sun

2018-05-01

Full Text Available The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS, and surface analysis techniques of scanning electron microscopy (SEM, energy dispersive X-ray (EDX microanalysis and X-ray diffraction (XRD were used to characterize the surface conditions. It was found that the protective current density was smaller for keeping polarization at −0.80 V (vs. saturated calomel electrode (SCE, same as below than that at −0.65 V. The calcareous deposits could not be formed on 304 SS with polarization at −0.50 V while it was well protected. The formation rate, the morphology, and the constituent of the calcareous deposits depended on the applied potential. The resistance of passive film on 304 SS decreased at the first stage and then increased when polarized at −0.80 V and −0.65 V, which was related to the reduction and the repair of passive film. For the stainless steel polarized at −0.50 V, the film resistance increased with polarization time, indicating that the growth of oxide film was promoted.

Research on generating various polarization-modes in polarized illumination system

Science.gov (United States)

Huang, Jinping; Lin, Wumei; Fan, Zhenjie

2013-08-01

With the increase of the numerical aperture (NA), the polarization of light affects the imaging quality of projection lens more significantly. On the contrary, according to the mask pattern, the resolution of projection lens can be improved by using the polarized illumination. That is to say, using the corresponding polarized beam (or polarization-mode) along with the off-axis illumination will improve the resolution and the imaging quality of the of projection lens. Therefore, the research on the generation of various polarization modes and its conversion methods become more and more important. In order to realize various polarization modes in polarized illumination system, after read a lot of references, we provide a way that fitting for the illumination system with the wavelength of 193nm.Six polarization-modes and a depolarized mode are probably considered. Wave-plate stack is used to generate linearly polarization-mode, which have a higher degree polarization. In order to generate X-Y and Y-X polarization mode, the equipment consisting of four sectors of λ/2 wave plate was used. We combined 16 sectors of λ/2 wave plate which have different orientations of the "slow" axis to generate radial and azimuthal polarization. Finally, a multi-polarization control device was designed. Using the kind of multi-polarization control device which applying this method could help to choose the polarization modes conveniently and flexibility for the illumination system.

Polarization properties of linearly polarized parabolic scaling Bessel beams

Energy Technology Data Exchange (ETDEWEB)

Guo, Mengwen; Zhao, Daomu, E-mail: zhaodaomu@yahoo.com

2016-10-07

The intensity profiles for the dominant polarization, cross polarization, and longitudinal components of modified parabolic scaling Bessel beams with linear polarization are investigated theoretically. The transverse intensity distributions of the three electric components are intimately connected to the topological charge. In particular, the intensity patterns of the cross polarization and longitudinal components near the apodization plane reflect the sign of the topological charge. - Highlights: • We investigated the polarization properties of modified parabolic scaling Bessel beams with linear polarization. • We studied the evolution of transverse intensity profiles for the three components of these beams. • The intensity patterns of the cross polarization and longitudinal components can reflect the sign of the topological charge.

Effect of polarization force on the Jeans instability of self-gravitating dusty plasma

International Nuclear Information System (INIS)

Prajapati, R.P.

2011-01-01

The effect of polarization force acting on massive charged dust grains is investigated analytically on the Jeans instability of self-gravitating dusty plasma. The gravitational force acting on the massive negatively charged interstellar dust grains are considered in presence of both electrical and polarization forces. The basic equations of the problem are formulated and a general dispersion relation is obtained using plane wave approximation in low frequency wave mode. The effect of polarization force in the dispersion relation of the problem, condition of the Jeans instability and expression of the critical Jeans wave number is examined. The unstable growing modes due to self-gravitational force are studied in the situation when polarization force on the dust grain exceeds over the electrical force in magnitude. It is observed that the polarization force increases the growth rate of the system. -- Highlights: → Jeans instability of gravitating dusty plasma with polarization force is investigated. → The fundamental Jeans instability criterion is modified due to polarization effect. → The critical Jeans length decreases due to increase in polarization force. → Polarization force destabilizes the unstable Jeans mode. → The collapsing of interstellar dusty cloud is discussed.

Social motility in african trypanosomes.

Directory of Open Access Journals (Sweden)

Michael Oberholzer

2010-01-01

Full Text Available African trypanosomes are devastating human and animal pathogens that cause significant human mortality and limit economic development in sub-Saharan Africa. Studies of trypanosome biology generally consider these protozoan parasites as individual cells in suspension cultures or in animal models of infection. Here we report that the procyclic form of the African trypanosome Trypanosoma brucei engages in social behavior when cultivated on semisolid agarose surfaces. This behavior is characterized by trypanosomes assembling into multicellular communities that engage in polarized migrations across the agarose surface and cooperate to divert their movements in response to external signals. These cooperative movements are flagellum-mediated, since they do not occur in trypanin knockdown parasites that lack normal flagellum motility. We term this behavior social motility based on features shared with social motility and other types of surface-induced social behavior in bacteria. Social motility represents a novel and unexpected aspect of trypanosome biology and offers new paradigms for considering host-parasite interactions.

Polarized nuclear target based on parahydrogen induced polarization

OpenAIRE

Budker, D.; Ledbetter, M. P.; Appelt, S.; Bouchard, L. S.; Wojtsekhowski, B.

2012-01-01

We discuss a novel concept of a polarized nuclear target for accelerator fixed-target scattering experiments, which is based on parahydrogen induced polarization (PHIP). One may be able to reach a 33% free-proton polarization in the ethane molecule. The potential advantages of such a target include operation at zero magnetic field, fast ($\\sim$100 Hz) polarization reversal, and operation with large intensity of an electron beam.

Investigating dust trapping in transition disks with millimeter-wave polarization

Science.gov (United States)

Pohl, A.; Kataoka, A.; Pinilla, P.; Dullemond, C. P.; Henning, Th.; Birnstiel, T.

2016-08-01

Context. Spatially resolved polarized (sub-)mm emission has been observed for example in the protoplanetary disk around HL Tau. Magnetically aligned grains are commonly interpreted as the source of polarization. However, self-scattering by large dust grains with a high enough albedo is another polarization mechanism, which is becoming a compelling method independent of the spectral index to constrain the dust grain size in protoplanetary disks. Aims: We study the dust polarization at mm wavelengths in the dust trapping scenario proposed for transition disks, when a giant planet opens a gap in the disk. We investigate the characteristic polarization patterns and their dependence on disk inclination, dust size evolution, planet position, and observing wavelength. Methods: We combine two-dimensional hydrodynamical simulations of planet-disk interactions with self-consistent dust growth models. These size-dependent dust density distributions are used for follow-up three-dimensional radiative transfer calculations to predict the polarization degree at ALMA bands due to scattered thermal emission. Results: Dust self-scattering has been proven to be a viable mechanism for producing polarized mm-wave radiation. We find that the polarization pattern of a disk with a planetary gap after 1 Myr of dust evolution shows a distinctive three-ring structure. Two narrow inner rings are located at the planet gap edges. A third wider ring of polarization is situated in the outer disk beyond 100 au. For increasing observing wavelengths, all three rings change their position slightly, where the innermost and outermost rings move inward. This distance is detectable when comparing the results at ALMA bands 3, 6, and 7. Within the highest polarized intensity regions the polarization vectors are oriented in the azimuthal direction. For an inclined disk there is an interplay between polarization originating from a flux gradient and inclination-induced quadrupole polarization. For

Mocvd Growth of Group-III Nitrides on Silicon Carbide: From Thin Films to Atomically Thin Layers

Science.gov (United States)

Al Balushi, Zakaria Y.

Group-III nitride semiconductors (AlN, GaN, InN and their alloys) are considered one of the most important class of materials for electronic and optoelectronic devices. This is not limited to the blue light-emitting diode (LED) used for efficient solid-state lighting, but other applications as well, such as solar cells, radar and a variety of high frequency power electronics, which are all prime examples of the technological importance of nitride based wide bandgap semiconductors in our daily lives. The goal of this dissertation work was to explore and establish new growth schemes to improve the structural and optical properties of thick to atomically thin films of group-III nitrides grown by metalorganic chemical vapor deposition (MOCVD) on SiC substrates for future novel devices. The first research focus of this dissertation was on the growth of indium gallium nitride (InGaN). This wide bandgap semiconductor has attracted much research attention as an active layer in LEDs and recently as an absorber material for solar cells. InGaN has superior material properties for solar cells due to its wavelength absorption tunability that nearly covers the entire solar spectrum. This can be achieved by controlling the indium content in thick grown material. Thick InGaN films are also of interest as strain reducing based layers for deep-green and red light emitters. The growth of thick films of InGaN is, however, hindered by several combined problems. This includes poor incorporation of indium in alloys, high density of structural and morphological defects, as well as challenges associated with the segregation of indium in thick films. Overcoming some of these material challenges is essential in order integrate thick InGaN films into future optoelectronics. Therefore, this dissertation research investigated the growth mechanism of InGaN layers grown in the N-polar direction by MOCVD as a route to improve the structural and optical properties of thick InGaN films. The growth

Fusion of a polarized projectile with a polarized target

International Nuclear Information System (INIS)

Christley, J.A.; Johnson, R.C.; Thompson, I.J.

1995-01-01

The fusion cross sections for a polarized target with both unpolarized and polarized projectiles are studied. Expressions for the observables are given for the case when both nuclei are polarized. Calculations for fusion of an aligned 165 Ho target with 16 O and polarized 7 Li beams are presented

The development of the Asian Forum for Polar Sciences (AFoPS)

Science.gov (United States)

Kim, Yeadong; Jeong, Jihoon

2015-12-01

The Asian Forum for Polar Sciences (AFoPS), an international forum of Asian polar research institutes, was established for the advancement of polar sciences among its members in 2004. The Forum has served as an important medium of Asian collective endeavors for polar affairs in human and information exchange, research collaboration, and logistics cooperation for the last decade. The historical development of the AFoPS in retrospect can be divided into four phases: inception and establishment (2003-2004), growth and expansion (2005-2007), review and restructuring (2008-2011), and achievements and further measures (2012-2014). The progress of the AFoPS has not been linear and this trend will continue into the next decades. The Forum, however, clearly made achievements in this period of time, realizing multilateral research and logistics cooperation that would have been previously unimaginable; by doing so, it has laid the foundation for the future. Responsible for a great portion of the world's polar activities, the AFoPS will rise to meet the expectations of the world by producing notable research output, initiating international cooperative programs, and supporting non-polar Asian countries with education and research collaboration. These are the tasks of the AFoPS for the next decade and they require strategy that promotes and facilitates collaboration in a practical way and draws attention of non-polar Asian countries to the polar sciences.

Transfection efficiency and uptake process of polyplexes in human lung endothelial cells: a comparative study in non-polarized and polarized cells.

Science.gov (United States)

Mennesson, Eric; Erbacher, Patrick; Piller, Véronique; Kieda, Claudine; Midoux, Patrick; Pichon, Chantal

2005-06-01

Following systemic administration, polyplexes must cross the endothelium barrier to deliver genes to the target cells underneath. To design an efficient gene delivery system into lung epithelium, we evaluated capture and transfection efficiencies of DNA complexed with either Jet-PEI (PEI-polyplexes) or histidylated polylysine (His-polyplexes) in human lung microvascular endothelial cells (HLMEC) and tracheal epithelial cells. After optimizing growth conditions to obtain a tight HLMEC monolayer, we characterized uptake of polyplexes by flow cytometry and evaluated their transfection efficiency. Polyplexes were formulated as small particles. YOYO-labelled plasmid fluorescence intensity and luciferase activity were used as readouts for uptake and gene expression, respectively. PEI-polyplexes were more efficiently taken up than His-polyplexes by both non-polarized (2-fold) and polarized HLMEC (10-fold). They were mainly internalized by a clathrin-dependent pathway whatever the cell state. In non-polarized cells, His-polyplexes entered also mainly via a clathrin-dependent pathway but with an involvement of cholesterol. The cell polarization decreased this way and a clathrin-independent pathway became predominant. PEI-polyplexes transfected more efficiently HLMEC than His-polyplexes (10(7) vs. 10(5) relative light units (RLU)/mg of proteins) with a more pronounced difference in polarized cells. In contrast, no negative effect of the cell polarization was observed with tracheal epithelial cells in which both polyplexes had comparable efficiency. We show that the efficiency of polyplex uptake by HLMEC and their internalization mechanism are polymer-dependent. By contrast with His-polyplexes, the HLMEC polarization has little influence on the uptake process and on the transfection efficiency of PEI-polyplexes. Copyright (c) 2005 John Wiley & Sons, Ltd.

Spatial and temporal variation in size of polar bear (Ursus maritimus) sexual organs and its use in pollution and climate change studies.

Science.gov (United States)

Sonne, Christian; Dietz, Rune; Born, Erik W; Riget, Frank F; Leifsson, Pall S; Bechshøft, Thea Ø; Kirkegaard, Maja

2007-11-15

Sexual organs and their development are susceptible to atmospheric transported environmental xenoendocrine pollutants and climate change (food availability). We therefore investigated sexual organs from 55 male and 44 female East Greenland polar bears (Ursus maritimus) to obtain information about growth/size and sexual maturity. Then, the genitalia size was compared with those previously reported from Canadian and Svalbard polar bears. Growth models showed that East Greenland male polar bears reached sexual maturity around 7 years of age and females around 4 years of age. When comparing East Greenland and Svalbard polar bears, the size of baculum and uterus were significantly lower in the East Greenland polar bears (ANOVA: all p polar bears, a similar baculum pattern was found for East Greenland vs. Canadian polar bears. It is speculated whether this could be a result of the general high variation in polar bear body size, temporal distribution patterns of anthropogenic long-range transported persistent organic pollutants or climate change (decreasing food availability). The present investigation represents conservation and background data for future spatial and temporal assessments of hunting, pollution and climate change scenarios.

The endosomal recycling of FgSnc1 by FgSnx41-FgSnx4 heterodimer is essential for polarized growth and pathogenicity in Fusarium graminearum.

Science.gov (United States)

Zheng, Wenhui; Lin, Yahong; Fang, Wenqin; Zhao, Xu; Lou, Yi; Wang, Guanghui; Zheng, Huawei; Liang, Qifu; Abubakar, Yakubu Saddeeq; Olsson, Stefan; Zhou, Jie; Wang, Zonghua

2018-04-20

Endosomal sorting machineries regulate the transport of their cargoes among intracellular compartments. However, the molecular nature of such intracellular trafficking processes in pathogenic fungal development and pathogenicity remains unclear. Here, we dissect the roles and molecular mechanisms of two sorting nexin proteins and their cargoes in endosomal recycling in Fusarium graminearum using high-resolution microscopy and high-throughput co-immunoprecipitation strategies. We show that the sorting nexins, FgSnx41 and FgSnx4, interact with each other and assemble into a functionally interdependent heterodimer through their respective BAR domains. Further analyses demonstrate that the dimer localizes to the early endosomal membrane and coordinates endosomal sorting. The small GTPase FgRab5 regulates the correct localization of FgSnx41-FgSnx4 and is consequently required for its trafficking function. The protein FgSnc1 is a cargo of FgSnx41-FgSnx4 and regulates the fusion of secreted vesicles with the fungal growing apex and plasma membrane. In the absence of FgSnx41 or FgSnx4, FgSnc1 is mis-sorted and degraded in the vacuole, and null deletion of either component causes defects in the fungal polarized growth and virulence. Overall, for the first time, our results reveal the mechanism of FgSnc1 endosomal recycling by FgSnx41-FgSnx4 heterodimer which is essential for polarized growth and pathogenicity in F. graminearum. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Tip-induced domain structures and polarization switching in ferroelectric amino acid glycine

Energy Technology Data Exchange (ETDEWEB)

Seyedhosseini, E., E-mail: Seyedhosseini@ua.pt; Ivanov, M. [CICECO-Aveiro Institute of Materials and Department of Physics, University of Aveiro, 3810-193 Aveiro (Portugal); Bdikin, I. [TEMA and Department of Mechanical Engineering, University of Aveiro, 3810-193 Aveiro (Portugal); Vasileva, D. [Institute of Natural Sciences, Ural Federal University, 620000 Ekaterinburg (Russian Federation); Kudryavtsev, A. [Moscow State Institute of Radioengineering, Electronics and Automation, 119454 Moscow (Russian Federation); Rodriguez, B. J. [Conway Institute of Biomolecular and Biomedical Research and School of Physics, University College Dublin, Dublin (Ireland); Kholkin, A. L. [CICECO-Aveiro Institute of Materials and Department of Physics, University of Aveiro, 3810-193 Aveiro (Portugal); Institute of Natural Sciences, Ural Federal University, 620000 Ekaterinburg (Russian Federation)

2015-08-21

Bioorganic ferroelectrics and piezoelectrics are becoming increasingly important in view of their intrinsic compatibility with biological environment and biofunctionality combined with strong piezoelectric effect and a switchable polarization at room temperature. Here, we study tip-induced domain structures and polarization switching in the smallest amino acid β-glycine, representing a broad class of non-centrosymmetric amino acids. We show that β-glycine is indeed a room-temperature ferroelectric and polarization can be switched by applying a bias to non-polar cuts via a conducting tip of atomic force microscope (AFM). Dynamics of these in-plane domains is studied as a function of an applied voltage and pulse duration. The domain shape is dictated by polarization screening at the domain boundaries and mediated by growth defects. Thermodynamic theory is applied to explain the domain propagation induced by the AFM tip. Our findings suggest that the properties of β-glycine are controlled by the charged domain walls which in turn can be manipulated by an external bias.

Update of the Polar SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2)

Science.gov (United States)

Wohltmann, Ingo; Lehmann, Ralph; Rex, Markus

2017-07-01

The Polar SWIFT model is a fast scheme for calculating the chemistry of stratospheric ozone depletion in polar winter. It is intended for use in global climate models (GCMs) and Earth system models (ESMs) to enable the simulation of mutual interactions between the ozone layer and climate. To date, climate models often use prescribed ozone fields, since a full stratospheric chemistry scheme is computationally very expensive. Polar SWIFT is based on a set of coupled differential equations, which simulate the polar vortex-averaged mixing ratios of the key species involved in polar ozone depletion on a given vertical level. These species are O3, chemically active chlorine (ClOx), HCl, ClONO2 and HNO3. The only external input parameters that drive the model are the fraction of the polar vortex in sunlight and the fraction of the polar vortex below the temperatures necessary for the formation of polar stratospheric clouds. Here, we present an update of the Polar SWIFT model introducing several improvements over the original model formulation. In particular, the model is now trained on vortex-averaged reaction rates of the ATLAS Chemistry and Transport Model, which enables a detailed look at individual processes and an independent validation of the different parameterizations contained in the differential equations. The training of the original Polar SWIFT model was based on fitting complete model runs to satellite observations and did not allow for this. A revised formulation of the system of differential equations is developed, which closely fits vortex-averaged reaction rates from ATLAS that represent the main chemical processes influencing ozone. In addition, a parameterization for the HNO3 change by denitrification is included. The rates of change of the concentrations of the chemical species of the Polar SWIFT model are purely chemical rates of change in the new version, whereas in the original Polar SWIFT model, they included a transport effect caused by the

Sonic Hedgehog switches on Wnt/planar cell polarity signaling in commissural axon growth cones by reducing levels of Shisa2

Science.gov (United States)

Onishi, Keisuke

2017-01-01

Commissural axons switch on responsiveness to Wnt attraction during midline crossing and turn anteriorly only after exiting the floor plate. We report here that Sonic Hedgehog (Shh)-Smoothened signaling downregulates Shisa2, which inhibits the glycosylation and cell surface presentation of Frizzled3 in rodent commissural axon growth cones. Constitutive Shisa2 expression causes randomized turning of post-crossing commissural axons along the anterior–posterior (A–P) axis. Loss of Shisa2 led to precocious anterior turning of commissural axons before or during midline crossing. Post-crossing commissural axon turning is completely randomized along the A–P axis when Wntless, which is essential for Wnt secretion, is conditionally knocked out in the floor plate. This regulatory link between Shh and planar cell polarity (PCP) signaling may also occur in other developmental processes. PMID:28885142

Host-Polarized Cell Growth in Animal Symbionts.

Science.gov (United States)

Pende, Nika; Wang, Jinglan; Weber, Philipp M; Verheul, Jolanda; Kuru, Erkin; Rittmann, Simon K-M R; Leisch, Nikolaus; VanNieuwenhze, Michael S; Brun, Yves V; den Blaauwen, Tanneke; Bulgheresi, Silvia

2018-04-02

To determine the fundamentals of cell growth, we must extend cell biological studies to non-model organisms. Here, we investigated the growth modes of the only two rods known to widen instead of elongating, Candidatus Thiosymbion oneisti and Thiosymbion hypermnestrae. These bacteria are attached by one pole to the surface of their respective nematode hosts. By incubating live Ca. T. oneisti and T. hypermnestrae with a peptidoglycan metabolic probe, we observed that the insertion of new cell wall starts at the poles and proceeds inward, concomitantly with FtsZ-based membrane constriction. Remarkably, in Ca. T. hypermnestrae, the proximal, animal-attached pole grows before the distal, free pole, indicating that the peptidoglycan synthesis machinery is host oriented. Immunostaining of the symbionts with an antibody against the actin homolog MreB revealed that it was arranged medially-that is, parallel to the cell long axis-throughout the symbiont life cycle. Given that depolymerization of MreB abolished newly synthesized peptidoglycan insertion and impaired divisome assembly, we conclude that MreB function is required for symbiont widening and division. In conclusion, our data invoke a reassessment of the localization and function of the bacterial actin homolog. Copyright © 2018 The Author(s). Published by Elsevier Ltd.. All rights reserved.

How the embryo makes a limb: determination, polarity and identity.

Science.gov (United States)

Tickle, Cheryll

2015-10-01

The vertebrate limb with its complex anatomy develops from a small bud of undifferentiated mesoderm cells encased in ectoderm. The bud has its own intrinsic polarity and can develop autonomously into a limb without reference to the rest of the embryo. In this review, recent advances are integrated with classical embryology, carried out mainly in chick embryos, to present an overview of how the embryo makes a limb bud. We will focus on how mesoderm cells in precise locations in the embryo become determined to form a limb and express the key transcription factors Tbx4 (leg/hindlimb) or Tbx5 (wing/forelimb). These Tbx transcription factors have equivalent functions in the control of bud formation by initiating a signalling cascade involving Wnts and fibroblast growth factors (FGFs) and by regulating recruitment of mesenchymal cells from the coelomic epithelium into the bud. The mesoderm that will form limb buds and the polarity of the buds is determined with respect to both antero-posterior and dorso-ventral axes of the body. The position in which a bud develops along the antero-posterior axis of the body will also determine its identity - wing/forelimb or leg/hindlimb. Hox gene activity, under the influence of retinoic acid signalling, is directly linked with the initiation of Tbx5 gene expression in the region along the antero-posterior axis of the body that will form wings/forelimbs and determines antero-posterior polarity of the buds. In contrast, Tbx4 expression in the regions that will form legs/hindlimbs is regulated by the homeoprotein Pitx1 and there is no evidence that Hox genes determine antero-posterior polarity of the buds. Bone morphogenetic protein (BMP) signalling determines the region along the dorso-ventral axis of the body in which both wings/forelimbs and legs/hindlimbs develop and dorso-ventral polarity of the buds. The polarity of the buds leads to the establishment of signalling regions - the dorsal and ventral ectoderm, producing Wnts and BMPs

Neutron polarization

International Nuclear Information System (INIS)

Firk, F.W.K.

1976-01-01

Some recent experiments involving polarized neutrons are discussed; they demonstrate how polarization studies provide information on fundamental aspects of nuclear structure that cannot be obtained from more traditional neutron studies. Until recently, neutron polarization studies tended to be limited either to very low energies or to restricted regions at higher energies, determined by the kinematics of favorable (p, vector n) and (d, vector n) reactions. With the advent of high intensity pulsed electron and proton accelerators and of beams of vector polarized deuterons, this is no longer the case. One has entered an era in which neutron polarization experiments are now being carried out, in a routine way, throughout the entire range from thermal energies to tens-of-MeV. The significance of neutron polarization studies is illustrated in discussions of a wide variety of experiments that include the measurement of T-invariance in the β-decay of polarized neutrons, a search for the effects of meson exchange currents in the photo-disintegration of the deuteron, the determination of quantum numbers of states in the fission of aligned 235 U and 237 Np induced by polarized neutrons, and the double- and triple-scattering of fast neutrons by light nuclei

Proteomic Analysis of Intact Flagella of Procyclic Trypanosoma brucei Cells Identifies Novel Flagellar Proteins with Unique Sub-localization and Dynamics*

Science.gov (United States)

Subota, Ines; Julkowska, Daria; Vincensini, Laetitia; Reeg, Nele; Buisson, Johanna; Blisnick, Thierry; Huet, Diego; Perrot, Sylvie; Santi-Rocca, Julien; Duchateau, Magalie; Hourdel, Véronique; Rousselle, Jean-Claude; Cayet, Nadège; Namane, Abdelkader; Chamot-Rooke, Julia; Bastin, Philippe

2014-01-01

Cilia and flagella are complex organelles made of hundreds of proteins of highly variable structures and functions. Here we report the purification of intact flagella from the procyclic stage of Trypanosoma brucei using mechanical shearing. Structural preservation was confirmed by transmission electron microscopy that showed that flagella still contained typical elements such as the membrane, the axoneme, the paraflagellar rod, and the intraflagellar transport particles. It also revealed that flagella severed below the basal body, and were not contaminated by other cytoskeletal structures such as the flagellar pocket collar or the adhesion zone filament. Mass spectrometry analysis identified a total of 751 proteins with high confidence, including 88% of known flagellar components. Comparison with the cell debris fraction revealed that more than half of the flagellum markers were enriched in flagella and this enrichment criterion was taken into account to identify 212 proteins not previously reported to be associated to flagella. Nine of these were experimentally validated including a 14-3-3 protein not yet reported to be associated to flagella and eight novel proteins termed FLAM (FLAgellar Member). Remarkably, they localized to five different subdomains of the flagellum. For example, FLAM6 is restricted to the proximal half of the axoneme, no matter its length. In contrast, FLAM8 is progressively accumulating at the distal tip of growing flagella and half of it still needs to be added after cell division. A combination of RNA interference and Fluorescence Recovery After Photobleaching approaches demonstrated very different dynamics from one protein to the other, but also according to the stage of construction and the age of the flagellum. Structural proteins are added to the distal tip of the elongating flagellum and exhibit slow turnover whereas membrane proteins such as the arginine kinase show rapid turnover without a detectible polarity. PMID:24741115

Proteomic analysis of intact flagella of procyclic Trypanosoma brucei cells identifies novel flagellar proteins with unique sub-localization and dynamics.

Science.gov (United States)

Subota, Ines; Julkowska, Daria; Vincensini, Laetitia; Reeg, Nele; Buisson, Johanna; Blisnick, Thierry; Huet, Diego; Perrot, Sylvie; Santi-Rocca, Julien; Duchateau, Magalie; Hourdel, Véronique; Rousselle, Jean-Claude; Cayet, Nadège; Namane, Abdelkader; Chamot-Rooke, Julia; Bastin, Philippe

2014-07-01

Cilia and flagella are complex organelles made of hundreds of proteins of highly variable structures and functions. Here we report the purification of intact flagella from the procyclic stage of Trypanosoma brucei using mechanical shearing. Structural preservation was confirmed by transmission electron microscopy that showed that flagella still contained typical elements such as the membrane, the axoneme, the paraflagellar rod, and the intraflagellar transport particles. It also revealed that flagella severed below the basal body, and were not contaminated by other cytoskeletal structures such as the flagellar pocket collar or the adhesion zone filament. Mass spectrometry analysis identified a total of 751 proteins with high confidence, including 88% of known flagellar components. Comparison with the cell debris fraction revealed that more than half of the flagellum markers were enriched in flagella and this enrichment criterion was taken into account to identify 212 proteins not previously reported to be associated to flagella. Nine of these were experimentally validated including a 14-3-3 protein not yet reported to be associated to flagella and eight novel proteins termed FLAM (FLAgellar Member). Remarkably, they localized to five different subdomains of the flagellum. For example, FLAM6 is restricted to the proximal half of the axoneme, no matter its length. In contrast, FLAM8 is progressively accumulating at the distal tip of growing flagella and half of it still needs to be added after cell division. A combination of RNA interference and Fluorescence Recovery After Photobleaching approaches demonstrated very different dynamics from one protein to the other, but also according to the stage of construction and the age of the flagellum. Structural proteins are added to the distal tip of the elongating flagellum and exhibit slow turnover whereas membrane proteins such as the arginine kinase show rapid turnover without a detectible polarity. © 2014 by The

Three-photon polarization ququarts: polarization, entanglement and Schmidt decompositions

International Nuclear Information System (INIS)

Fedorov, M V; Miklin, N I

2015-01-01

We consider polarization states of three photons, propagating collinearly and having equal given frequencies but with arbitrary distributed horizontal or vertical polarizations of photons. A general form of such states is a superposition of four basic three-photon polarization modes, to be referred to as the three-photon polarization ququarts (TPPQ). All such states can be considered as consisting of one- and two-photon parts, which can be entangled with each other. The degrees of entanglement and polarization, as well as the Schmidt decomposition and Stokes vectors of TPPQ are found and discussed. (paper)

Polarization splitter and polarization rotator designs based on transformation optics.

Science.gov (United States)

Kwon, Do-Hoon; Werner, Douglas H

2008-11-10

The transformation optics technique is employed in this paper to design two optical devices - a two-dimensional polarization splitter and a three-dimensional polarization rotator for propagating beams. The polarization splitter translates the TM- and the TE-polarized components of an incident beam in opposite directions (i.e., shifted up or shifted down). The polarization rotator rotates the polarization state of an incoming beam by an arbitrary angle. Both optical devices are reflectionless at the entry and exit interfaces. Design details and full-wave simulation results are provided.

Polarization dynamics and polarization time of random three-dimensional electromagnetic fields

International Nuclear Information System (INIS)

Voipio, Timo; Setaelae, Tero; Shevchenko, Andriy; Friberg, Ari T.

2010-01-01

We investigate the polarization dynamics of random, stationary three-dimensional (3D) electromagnetic fields. For analyzing the time evolution of the instantaneous polarization state, two intensity-normalized polarization autocorrelation functions are introduced, one based on a geometric approach with the Poincare vectors and the other on energy considerations with the Jones vectors. Both approaches lead to the same conclusions on the rate and strength of the polarization dynamics and enable the definition of a polarization time over which the state of polarization remains essentially unchanged. For fields obeying Gaussian statistics, the two correlation functions are shown to be expressible in terms of quantities characterizing partial 3D polarization and electromagnetic coherence. The 3D degree of polarization is found to have the same meaning in the 3D polarization dynamics as the usual two-dimensional (2D) degree of polarization does with planar fields. The formalism is demonstrated with several examples, and it is expected to be useful in applications dealing with polarization fluctuations of 3D light.

Polarized electron sources

Energy Technology Data Exchange (ETDEWEB)

Prepost, R. [Univ. of Wisconsin, Madison, WI (United States)

1994-12-01

The fundamentals of polarized electron sources are described with particular application to the Stanford Linear Accelerator Center. The SLAC polarized electron source is based on the principle of polarized photoemission from Gallium Arsenide. Recent developments using epitaxially grown, strained Gallium Arsenide cathodes have made it possible to obtain electron polarization significantly in excess of the conventional 50% polarization limit. The basic principles for Gallium and Arsenide polarized photoemitters are reviewed, and the extension of the basic technique to strained cathode structures is described. Results from laboratory measurements of strained photocathodes as well as operational results from the SLAC polarized source are presented.

Polarized electron sources

International Nuclear Information System (INIS)

Prepost, R.

1994-01-01

The fundamentals of polarized electron sources are described with particular application to the Stanford Linear Accelerator Center. The SLAC polarized electron source is based on the principle of polarized photoemission from Gallium Arsenide. Recent developments using epitaxially grown, strained Gallium Arsenide cathodes have made it possible to obtain electron polarization significantly in excess of the conventional 50% polarization limit. The basic principles for Gallium and Arsenide polarized photoemitters are reviewed, and the extension of the basic technique to strained cathode structures is described. Results from laboratory measurements of strained photocathodes as well as operational results from the SLAC polarized source are presented

Digital growth of thick N-polar InGaN films on relaxed InGaN pseudosubstrates

Science.gov (United States)

Lund, Cory; Hestroffer, Karine; Hatui, Nirupam; Nakamura, Shuji; DenBaars, Steven P.; Mishra, Umesh K.; Keller, Stacia

2017-11-01

Smooth relaxed N-polar InGaN films were grown by metal-organic CVD (MOCVD) on N-polar InGaN pseudosubstrates (PSs) using a novel digital approach consisting of a constant In precursor flow with the pulsed injection of H2 carrier gas. InGaN layers grown on PSs exhibited an In composition of about 50% higher than those of the layers grown on N-polar GaN templates, assuming the in-plane lattice constant of the relaxed PSs, corresponding to In0.11Ga0.89N. Additionally, the luminescence recorded from InGaN layers grown on PSs at 490 nm was twice as intense as that obtained from the layers deposited on coloaded GaN-on-sapphire templates, which emitted at 430 nm.

Update of the Polar SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2

Directory of Open Access Journals (Sweden)

I. Wohltmann

2017-07-01

Full Text Available The Polar SWIFT model is a fast scheme for calculating the chemistry of stratospheric ozone depletion in polar winter. It is intended for use in global climate models (GCMs and Earth system models (ESMs to enable the simulation of mutual interactions between the ozone layer and climate. To date, climate models often use prescribed ozone fields, since a full stratospheric chemistry scheme is computationally very expensive. Polar SWIFT is based on a set of coupled differential equations, which simulate the polar vortex-averaged mixing ratios of the key species involved in polar ozone depletion on a given vertical level. These species are O3, chemically active chlorine (ClOx, HCl, ClONO2 and HNO3. The only external input parameters that drive the model are the fraction of the polar vortex in sunlight and the fraction of the polar vortex below the temperatures necessary for the formation of polar stratospheric clouds. Here, we present an update of the Polar SWIFT model introducing several improvements over the original model formulation. In particular, the model is now trained on vortex-averaged reaction rates of the ATLAS Chemistry and Transport Model, which enables a detailed look at individual processes and an independent validation of the different parameterizations contained in the differential equations. The training of the original Polar SWIFT model was based on fitting complete model runs to satellite observations and did not allow for this. A revised formulation of the system of differential equations is developed, which closely fits vortex-averaged reaction rates from ATLAS that represent the main chemical processes influencing ozone. In addition, a parameterization for the HNO3 change by denitrification is included. The rates of change of the concentrations of the chemical species of the Polar SWIFT model are purely chemical rates of change in the new version, whereas in the original Polar SWIFT model, they included a transport effect

Significantly improved surface morphology of N-polar GaN film grown on SiC substrate by the optimization of V/III ratio

Science.gov (United States)

Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

2018-04-01

In this paper, N-polar GaN films with different V/III ratios were grown on vicinal C-face SiC substrates by metalorganic chemical vapor deposition. During the growth of N-polar GaN film, the V/III ratio was controlled by adjusting the molar flow rate of ammonia while keeping the trimethylgallium flow rate unchanged. The influence of the V/III ratio on the surface morphology of N-polar GaN film has been studied. We find that the surface root mean square roughness of N-polar GaN film over an area of 20 × 20 μm2 can be reduced from 8.13 to 2.78 nm by optimization of the V/III ratio. Then, using the same growth conditions, N-polar InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) were grown on the rough and the smooth N-polar GaN templates, respectively. Compared with the LED grown on the rough N-polar GaN template, dramatically improved interface sharpness and luminescence uniformity of the InGaN/GaN MQWs are achieved for the LED grown on the smooth N-polar GaN template.

Promoting Diversity Through Polar Interdisciplinary Coordinated Education (Polar ICE)

Science.gov (United States)

McDonnell, J. D.; Hotaling, L. A.; Garza, C.; Van Dyk, P. B.; Hunter-thomson, K. I.; Middendorf, J.; Daniel, A.; Matsumoto, G. I.; Schofield, O.

2017-12-01

Polar Interdisciplinary Coordinated Education (ICE) is an education and outreach program designed to provide public access to the Antarctic and Arctic regions through polar data and interactions with the scientists. The program provides multi-faceted science communication training for early career scientists that consist of a face-to face workshop and opportunities to apply these skills. The key components of the scientist training workshop include cultural competency training, deconstructing/decoding science for non-expert audiences, the art of telling science stories, and networking with members of the education and outreach community and reflecting on communication skills. Scientists partner with educators to provide professional development for K-12 educators and support for student research symposia. Polar ICE has initiated a Polar Literacy initiative that provides both a grounding in big ideas in polar science and science communication training designed to underscore the importance of the Polar Regions to the public while promoting interdisciplinary collaborations between scientists and educators. Our ultimate objective is to promote STEM identity through professional development of scientists and educators while developing career awareness of STEM pathways in Polar science.

Polarization-independent broadband meta-holograms via polarization-dependent nanoholes.

Science.gov (United States)

Zhang, Xiaohu; Li, Xiong; Jin, Jinjin; Pu, Mingbo; Ma, Xiaoliang; Luo, Jun; Guo, Yinghui; Wang, Changtao; Luo, Xiangang

2018-05-17

Composed of ultrathin metal or dielectric nanostructures, metasurfaces can manipulate the phase, amplitude and polarization of electromagnetic waves at a subwavelength scale, which is promising for flat optical devices. In general, metasurfaces composed of space-variant anisotropic units are sensitive to the incident polarization due to the inherent polarization dependent geometric phase. Here, we implement polarization-independent broadband metasurface holograms constructed by polarization-dependent anisotropic elliptical nanoholes by elaborate design of complex amplitude holograms. The fabricated meta-hologram exhibits a polarization insensitive feature with an acceptable image quality. We verify the feasibility of the design algorithm for three-dimensional (3D) meta-holograms with simulation and the feasibility for two-dimensional (2D) meta-holograms is experimentally demonstrated at a broadband wavelength range from 405 nm to 632.8 nm. The effective polarization-independent broadband complex wavefront control with anisotropic elliptical nanoholes proposed in this paper greatly promotes the practical applications of the metasurface in technologies associated with wavefront manipulation, such as flat lens, colorful holographic displays and optical storage.

Cathodoluminescence study of Mg activation in non-polar and semi-polar faces of undoped/Mg-doped GaN core-shell nanorods

Science.gov (United States)

Hortelano, V.; Martínez, O.; Cuscó, R.; Artús, L.; Jiménez, J.

2016-03-01

Spectrally and spatially resolved cathodoluminescence (CL) measurements were carried out at 80 K on undoped/Mg-doped GaN core-shell nanorods grown by selective area growth metalorganic vapor phase epitaxy in order to investigate locally the optical activity of the Mg dopants. A study of the luminescence emission distribution over the different regions of the nanorods is presented. We have investigated the CL fingerprints of the Mg incorporation into the non-polar lateral prismatic facets and the semi-polar facets of the pyramidal tips. The amount of Mg incorporation/activation was varied by using several Mg/Ga flow ratios and post-growth annealing treatment. For lower Mg/Ga flow ratios, the annealed nanorods clearly display a donor-acceptor pair band emission peaking at 3.26-3.27 eV and up to 4 LO phonon replicas, which can be considered as a reliable indicator of effective p-type Mg doping in the nanorod shell. For higher Mg/Ga flow ratios, a substantial enhancement of the yellow luminescence emission as well as several emission subbands are observed, which suggests an increase of disorder and the presence of defects as a consequence of the excess Mg doping.

Ga- and N-polar GaN Growths on SiC Substrate

Science.gov (United States)

2018-03-15

transverse-electric-polarized emission of an AlGaN deep -ultraviolet quantum well,” Optics Express, Vol. 25, No. 22, pp. 26365-26377, 30 October 2017. 3...23, No. 25, pp. 32274-32288, 14 December 2015. 11. Yang Kuo, Wen -Yen Chang, Chun-Han Lin, C. C. Yang, and Yean-Woei Kiang, “Evaluating the blue...unlimited. 50 dielectric interlayers,” Plasmonics, Vol. 10, No. 5, pp. 1029-1040, October 2015. 14. Yang Kuo, Chia-Ying Su, Chieh Hsieh, Wen -Yen Chang

Polarization digital holographic microscopy using low-cost liquid crystal polarization rotators

Science.gov (United States)

Dovhaliuk, Rostyslav Yu

2018-02-01

Polarization imaging methods are actively used to study anisotropic objects. A number of methods and systems, such as imaging polarimeters, were proposed to measure the state of polarization of light that passed through the object. Digital holographic and interferometric approaches can be used to quantitatively measure both amplitude and phase of a wavefront. Using polarization modulation optics, the measurement capabilities of such interference-based systems can be extended to measure polarization-dependent parameters, such as phase retardation. Different kinds of polarization rotators can be used to alternate the polarization of a reference beam. Liquid crystals are used in a rapidly increasing number of different optoelectronic devices. Twisted nematic liquid crystals are widely used as amplitude modulators in electronic displays and light valves or shutter glass. Such devices are of particular interest for polarization imaging, as they can be used as polarization rotators, and due to large-scale manufacturing have relatively low cost. A simple Mach-Zehnder polarized holographic setup that uses modified shutter glass as a polarization rotator is demonstrated. The suggested approach is experimentally validated by measuring retardation of quarter-wave film.

Polarization holography

DEFF Research Database (Denmark)

Nikolova, L.; Ramanujam, P.S.

Current research into holography is concerned with applications in optically storing, retrieving, and processing information. Polarization holography has many unique properties compared to conventional holography. It gives results in high efficiency, achromaticity, and special polarization...... properties. This books reviews the research carried out in this field over the last 15 years. The authors provide basic concepts in polarization and the propagation of light through anisotropic materials, before presenting a sound theoretical basis for polarization holography. The fabrication...... and characterization of azobenzene based materials, which remain the most efficient for the purpose, is described in detail. This is followed by a description of other materials that are used in polarization holography. An in-depth description of various applications, including display holography and optical storage...

Polarized neutron spectrometer

International Nuclear Information System (INIS)

Abov, Yu.G.; Novitskij, V.V.; Alfimenkov, V.P.; Galinskij, E.M.; Mareev, Yu.D.; Pikel'ner, L.B.; Chernikov, A.N.; Lason', L.; Tsulaya, V.M.; Tsulaya, M.I.

2000-01-01

The polarized neutron spectrometer, intended for studying the interaction of polarized neutrons with nuclei and condensed media in the area of energies from thermal up to several electron-volt, is developed at the IBR-2 reactor (JINR, Dubna). Diffraction on the Co(92%)-Fe(8%) magnetized monocrystals is used for the neutron polarization and polarization analysis. The neutron polarization within the whole energy range equals ∼ 95% [ru

PolarTrack: Optical Outside-In Device Tracking that Exploits Display Polarization

DEFF Research Database (Denmark)

Rädle, Roman; Jetter, Hans-Christian; Fischer, Jonathan

2018-01-01

PolarTrack is a novel camera-based approach to detecting and tracking mobile devices inside the capture volume. In PolarTrack, a polarization filter continuously rotates in front of an off-the-shelf color camera, which causes the displays of observed devices to periodically blink in the camera feed....... The periodic blinking results from the physical characteristics of current displays, which shine polarized light either through an LC overlay to produce images or through a polarizer to reduce light reflections on OLED displays. PolarTrack runs a simple detection algorithm on the camera feed to segment...... displays and track their locations and orientations, which makes PolarTrack particularly suitable as a tracking system for cross-device interaction with mobile devices. Our evaluation of PolarTrack's tracking quality and comparison with state-of-the-art camera-based multi-device tracking showed a better...

Crystal growth, polarized spectroscopy and Judd-Ofelt analysis of Tb:YAlO3.

Science.gov (United States)

Liu, Bin; Shi, Jiaojiao; Wang, Qingguo; Tang, Huili; Liu, Junfang; Zhao, Hengyu; Li, Dongzhen; Liu, Jian; Xu, Xiaodong; Wang, Zhanshan; Xu, Jun

2018-07-05

Tb 3+ -doped YAlO 3 (YAP) single crystal was grown by Czochralski (Cz) method. Based on the polarized absorption spectra, the spectroscopic parameters were calculated to be Ω 2 =3.49×10 -20 cm 2 , Ω 4 =5.87×10 -20 cm 2 and Ω 6 =2.55×10 -20 cm 2 , and then the spontaneous transition rate, fluorescent branching ratio and radiative lifetime of 5 D 4 multiplet were obtained. The yellow emission cross sections of 5 D 4 → 7 F 4 transition were calculated to be 1.72×10 -22 cm 2 , 2.73×10 -22 cm 2 and 2.65×10 -22 cm 2 for a, b and c polarization, respectively. The fluorescence lifetime of the 5 D 4 multiplet was fitted to be 1.72ms. All the data indicate that Tb:YAP crystal is a promising candidate for yellow laser operation. Copyright © 2018. Published by Elsevier B.V.

Lunar true polar wander inferred from polar hydrogen.

Science.gov (United States)

Siegler, M A; Miller, R S; Keane, J T; Laneuville, M; Paige, D A; Matsuyama, I; Lawrence, D J; Crotts, A; Poston, M J

2016-03-24

The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers, and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures. This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury's poles. Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history, which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon

Polarized proton beams

International Nuclear Information System (INIS)

Roser, T.

1995-01-01

The acceleration of polarized proton beams in circular accelerators is complicated by the presence of numerous depolarizing spin resonances. Careful and tedious minimization of polarization loss at each of these resonances allowed acceleration of polarized proton beams up to 22 GeV. It has been the hope that Siberian Snakes, which are local spin rotators inserted into ring accelerators, would eliminate these resonances and allow acceleration of polarized beams with the same ease and efficiency that is now routine for unpolarized beams. First tests at IUCF with a full Siberian Snake showed that the spin dynamics with a Snake can be understood in detail. The author now has results of the first tests of a partial Siberian Snake at the AGS, accelerating polarized protons to an energy of about 25 GeV. These successful tests of storage and acceleration of polarized proton beams open up new possibilities such as stored polarized beams for internal target experiments and high energy polarized proton colliders

Flagellation of Pseudomonas aeruginosa in newly divided cells

Science.gov (United States)

Zhao, Kun; Lee, Calvin; Anda, Jaime; Wong, Gerard

2015-03-01

For monotrichous bacteria, Pseudomonas aeruginosa, after cell division, one daughter cell inherits the old flagellum from its mother cell, and the other grows a new flagellum during or after cell division. It had been shown that the new flagellum grows at the distal pole of the dividing cell when the two daughter cells haven't completely separated. However, for those daughter cells who grow new flagella after division, it still remains unknown at which pole the new flagellum will grow. Here, by combining our newly developed bacteria family tree tracking techniques with genetic manipulation method, we showed that for the daughter cell who did not inherit the old flagellum, a new flagellum has about 90% chances to grow at the newly formed pole. We proposed a model for flagellation of P. aeruginosa.

Anodic polarization of carbon graphite electrodes in chloride fluoride melts zirconium containing

International Nuclear Information System (INIS)

Lyapustin, A.A.; Kanashin, Yu.P.; Nichkov, I.F.; Smyshlyaev, V.Yu.

1985-01-01

Polarization of carbon graphite anodes in zircorium containing chloride fluoride melts of the KCl-K 2 ZrF 6 -KF composition at molar ratios [F]:[Zr] being equal to 6, 12, 18, 24, 30 has been studied. K 2 ZrF 6 concentration constitutes 25; 18.9; 15.2; 12.7; 11.8% (by mass), correspondingly. Vitreous carbon (VC-2500), high purity graphite and graphite EhG-0 have been used as anodic materials. Anodic polarization curves have been obtained under electrotype steady-state conditions at 973, 1023, 1073 K. Influence of concentration of fluorine ions in melt on polarization of carbon graphite anodes is shown. Content growth of fluorine ions in melt leads to shift of steady-state anode potentials to their negative values regardless a graphite mark. The most con siderable potential shift on 0.5 V takes plase at molar ratio [F]:[Zr] increasing from 6 to 12. Temperature increase, as measurements showed, doesn't influence greatly on polarization curve shape

The Sensitivity of Income Polarization - Time, length of accounting periods, equivalence scales, and income definitions

DEFF Research Database (Denmark)

Azhar, Hussain

This study looks at polarization and its components’ sensitivity to assumptions about equivalence scales, income definition, ethical income distribution parameters, and the income accounting period. A representative sample of Danish individual incomes from 1984 to 2002 is utilised. Results show...... that polarization has increased over time, regardless of the applied measure, when the last part of the period is compared to the first part of the period. Primary causes being increased inequality (alienation) and faster income growth among high incomes relative to those in the middle of the distribution....... Increasing the accounting period confirms the reduction in inequality found for shorter periods, but polarization is virtually unchanged, because income group identification increases. Applying different equivalence scales does not change polarization ranking for different years, but identification ranks...

The effect of shear flow and the density gradient on the Weibel instability growth rate in the dense plasma

Science.gov (United States)

Amininasab, S.; Sadighi-Bonabi, R.; Khodadadi Azadboni, F.

2018-02-01

Shear stress effect has been often neglected in calculation of the Weibel instability growth rate in laser-plasma interactions. In the present work, the role of the shear stress in the Weibel instability growth rate in the dense plasma with density gradient is explored. By increasing the density gradient, the shear stress threshold is increasing and the range of the propagation angles of growing modes is limited. Therefore, by increasing steps of the density gradient plasma near the relativistic electron beam-emitting region, the Weibel instability occurs at a higher stress flow. Calculations show that the minimum value of the stress rate threshold for linear polarization is greater than that of circular polarization. The Wiebel instability growth rate for linear polarization is 18.3 times circular polarization. One sees that for increasing stress and density gradient effects, there are smaller maximal growth rates for the range of the propagation angles of growing modes /π 2 propagation angles of growing modes /π 2 < θ m i n < π and /3 π 2 < θ m i n < 2 π in circular polarized plasma.

Charge transport in non-polar and semi-polar III-V nitride heterostructures

International Nuclear Information System (INIS)

Konar, Aniruddha; Verma, Amit; Fang, Tian; Zhao, Pei; Jana, Raj; Jena, Debdeep

2012-01-01

Compared to the intense research focus on the optical properties, the transport properties in non-polar and semi-polar III-nitride semiconductors remain relatively unexplored to date. The purpose of this paper is to discuss charge-transport properties in non-polar and semi-polar orientations of GaN in a comparative fashion to what is known for transport in polar orientations. A comprehensive approach is adopted, starting from an investigation of the differences in the electronic bandstructure along different polar orientations of GaN. The polarization fields along various orientations are then discussed, followed by the low-field electron and hole mobilities. A number of scattering mechanisms that are specific to non-polar and semi-polar GaN heterostructures are identified, and their effects are evaluated. Many of these scattering mechanisms originate due to the coupling of polarization with disorder and defects in various incarnations depending on the crystal orientation. The effect of polarization orientation on carrier injection into quantum-well light-emitting diodes is discussed. This paper ends with a discussion of orientation-dependent high-field charge-transport properties including velocity saturation, instabilities and tunneling transport. Possible open problems and opportunities are also discussed. (paper)

The effect of polarized light on the organization of collagen secreted by fibroblasts.

Science.gov (United States)

Akilbekova, Dana; Boddupalli, Anuraag; Bratlie, Kaitlin M

2018-04-01

Recent studies have demonstrated the beneficial effect of low-power lasers and polarized light on wound healing, inflammation, and the treatment of rheumatologic and neurologic disorders. The overall effect of laser irradiation treatment is still controversial due to the lack of studies on the biochemical mechanisms and the optimal parameters for the incident light that should be chosen for particular applications. Here, we study how NIH/3T3 fibroblasts respond to irradiation with linearly polarized light at different polarization angles. In particular, we examined vascular endothelial growth factor (VEGF) secretion, differentiation to myofibroblasts, and collagen organization in response to 800 nm polarized light at 0°, 45°, 90°, and 135° with a power density of 40 mW/cm 2 for 6 min every day for 6 days. Additional experiments were conducted in which the polarization angle of the incident was changed every day to induce an isotropic distribution of collagen. The data presented here shows that polarized light can upregulate VEGF production, myofibroblast differentiation, and induce different collagen organization in response to different polarization angles of the incident beam. These results are encouraging and demonstrate possible methods for controlling cell response through the polarization angle of the laser light, which has potential for the treatment of wounds.

Polarization-sensitive color in butterfly scales: polarization conversion from ridges with reflecting elements.

Science.gov (United States)

Zhang, Ke; Tang, Yiwen; Meng, Jinsong; Wang, Ge; Zhou, Han; Fan, Tongxiang; Zhang, Di

2014-11-03

Polarization-sensitive color originates from polarization-dependent reflection or transmission, exhibiting abundant light information, including intensity, spectral distribution, and polarization. A wide range of butterflies are physiologically sensitive to polarized light, but the origins of polarized signal have not been fully understood. Here we systematically investigate the colorful scales of six species of butterfly to reveal the physical origins of polarization-sensitive color. Microscopic optical images under crossed polarizers exhibit their polarization-sensitive characteristic, and micro-structural characterizations clarify their structural commonality. In the case of the structural scales that have deep ridges, the polarization-sensitive color related with scale azimuth is remarkable. Periodic ridges lead to the anisotropic effective refractive indices in the parallel and perpendicular grating orientations, which achieves form-birefringence, resulting in the phase difference of two different component polarized lights. Simulated results show that ridge structures with reflecting elements reflect and rotate the incident p-polarized light into s-polarized light. The dimensional parameters and shapes of grating greatly affect the polarization conversion process, and the triangular deep grating extends the outstanding polarization conversion effect from the sub-wavelength period to the period comparable to visible light wavelength. The parameters of ridge structures in butterfly scales have been optimized to fulfill the polarization-dependent reflection for secret communication. The structural and physical origin of polarization conversion provides a more comprehensive perspective on the creation of polarization-sensitive color in butterfly wing scales. These findings show great potential in anti-counterfeiting technology and advanced optical material design.

The Kinesin Adaptor Calsyntenin-1 Organizes Microtubule Polarity and Regulates Dynamics during Sensory Axon Arbor Development

Directory of Open Access Journals (Sweden)

Mary C. Halloran

2017-04-01

Full Text Available Axon growth and branching, and development of neuronal polarity are critically dependent on proper organization and dynamics of the microtubule (MT cytoskeleton. MTs must organize with correct polarity for delivery of diverse cargos to appropriate subcellular locations, yet the molecular mechanisms regulating MT polarity remain poorly understood. Moreover, how an actively branching axon reorganizes MTs to direct their plus ends distally at branch points is unknown. We used high-speed, in vivo imaging of polymerizing MT plus ends to characterize MT dynamics in developing sensory axon arbors in zebrafish embryos. We find that axonal MTs are highly dynamic throughout development, and that the peripheral and central axons of sensory neurons show differences in MT behaviors. Furthermore, we show that Calsyntenin-1 (Clstn-1, a kinesin adaptor required for sensory axon branching, also regulates MT polarity in developing axon arbors. In wild type neurons the vast majority of MTs are directed in the correct plus-end-distal orientation from early stages of development. Loss of Clstn-1 causes an increase in MTs polymerizing in the retrograde direction. These misoriented MTs most often are found near growth cones and branch points, suggesting Clstn-1 is particularly important for organizing MT polarity at these locations. Together, our results suggest that Clstn-1, in addition to regulating kinesin-mediated cargo transport, also organizes the underlying MT highway during axon arbor development.

System for measuring the proton polarization in a polarized target

International Nuclear Information System (INIS)

Karnaukhov, I.M.; Lukhanin, A.A.; Telegin, Yu.N.; Trotsenko, V.I.; Chechetenko, V.F.

1984-01-01

The system for measuring the proton polarization in a polarized target representing the high-sensitivity nuclear magnetic resonance (NMR) is described Q-meter with series connection and a circuit for measuring system resonance characteristic is used for NMR-absorption signal recording. Measuring coil is produced of a strip conductor in order to obtain uniform system sensitivity to polarization state in all target volume and improve signal-to-noise ratio. Polarization measuring system operates ion-line with the M-6000 computer. The total measuring error for the value of free proton polarization in target taking into account the error caused by local depolarization of working substance under irradiation by high-intense photon beam is <= 6%. Long-term application of the described system for measuring the proton polarization in the LUEh-20000 accelerator target used in the pion photoproduction experiments has demonstrated its high reliability

Sources of polarized neutrons

International Nuclear Information System (INIS)

Walter, L.

1983-01-01

Various sources of polarized neutrons are reviewed. Monoenergetic source produced with unpolarized or polarized beams, white sources of polarized neutrons, production by transmissions through polarized hydrogen targets and polarized thermal neutronsare discussed, with appropriate applications included. (U.K.)

PolarHub: A Global Hub for Polar Data Discovery

Science.gov (United States)

Li, W.

2014-12-01

This paper reports the outcome of a NSF project in developing a large-scale web crawler PolarHub to discover automatically the distributed polar dataset in the format of OGC web services (OWS) in the cyberspace. PolarHub is a machine robot; its goal is to visit as many webpages as possible to find those containing information about polar OWS, extract this information and store it into the backend data repository. This is a very challenging task given huge data volume of webpages on the Web. Three unique features was introduced in PolarHub to make it distinctive from earlier crawler solutions: (1) a multi-task, multi-user, multi-thread support to the crawling tasks; (2) an extensive use of thread pool and Data Access Object (DAO) design patterns to separate persistent data storage and business logic to achieve high extendibility of the crawler tool; (3) a pattern-matching based customizable crawling algorithm to support discovery of multi-type geospatial web services; and (4) a universal and portable client-server communication mechanism combining a server-push and client pull strategies for enhanced asynchronous processing. A series of experiments were conducted to identify the impact of crawling parameters to the overall system performance. The geographical distribution pattern of all PolarHub identified services is also demonstrated. We expect this work to make a major contribution to the field of geospatial information retrieval and geospatial interoperability, to bridge the gap between data provider and data consumer, and to accelerate polar science by enhancing the accessibility and reusability of adequate polar data.

Shifting balances in U.S. metropolitan and nonmetropolitan area growth.

Science.gov (United States)

Garnick, D H

1984-12-01

"This paper assesses some of the recent attempts to explain the perceived growth reversal between metropolitan and nonmetropolitan areas in the United States during the 1970s. The paper argues that the reversal in population trends was not a one-time, radical shift in settlement trends, but rather the result of more continuous underlying industrial trends. Indeed, since 1979, population growth has again become faster in metropolitan than nonmetropolitan areas." The paper includes three sections. Regional and area population and industrial earnings growth patterns are first summarized for the 1960s, 1970s, and 1980s. Theories of polarization and polar reversal are then evaluated and found to be inadequate. Finally, a reconstruction of the neoclassical model is proposed. excerpt

Polarization extinction ratio of the polarization crosstalk caused by point pressure force in the polarization-maintaining fiber

Science.gov (United States)

Mukhtubayev, Azamat B.; Aksarin, Stanislav M.; Strigalev, Vladimir E.

2017-11-01

A study of the orthogonal polarization modes crosstalk changes in the point of different mechanical actions (pressure force) in the polarization-maintaining fiber with straining elliptical cladding is presented. It was found that by increasing of the pressure force the polarization extinction ratio increases nonlinearly. Also revealed the dependence of the extinction coefficient and the angle between vector of the mechanical action and polarization axes of the test fiber, which leads to change the extinction coefficient variable from -57 dB to -25 dB under the pressure force of 0.7 N. Also it was found that the cross angle of the fiber axes doesn't influence on the extinction ratio value of the mechanical induced polarization crosstalk.

Polarized secondary radioactive beams

International Nuclear Information System (INIS)

Zaika, N.I.

1992-01-01

Three methods of polarized radioactive nuclei beam production: a) a method nuclear interaction of the non-polarized or polarized charged projectiles with target nuclei; b) a method of polarization of stopped reaction radioactive products in a special polarized ion source with than following acceleration; c) a polarization of radioactive nuclei circulating in a storage ring are considered. Possible life times of the radioactive ions for these methods are determined. General schemes of the polarization method realizations and depolarization problems are discussed

Retention of intermediate polarization states in ferroelectric materials enabling memories for multi-bit data storage

Energy Technology Data Exchange (ETDEWEB)

Zhao, Dong; Asadi, Kamal; Blom, Paul W. M.; Leeuw, Dago M. de, E-mail: deleeuw@mpip-mainz.mpg.de [Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Katsouras, Ilias [Holst Centre, High Tech Campus 31, 5656AE Eindhoven (Netherlands); Groen, Wilhelm A. [Holst Centre, High Tech Campus 31, 5656AE Eindhoven (Netherlands); Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1 2629 HS, Delft (Netherlands)

2016-06-06

A homogeneous ferroelectric single crystal exhibits only two remanent polarization states that are stable over time, whereas intermediate, or unsaturated, polarization states are thermodynamically instable. Commonly used ferroelectric materials however, are inhomogeneous polycrystalline thin films or ceramics. To investigate the stability of intermediate polarization states, formed upon incomplete, or partial, switching, we have systematically studied their retention in capacitors comprising two classic ferroelectric materials, viz. random copolymer of vinylidene fluoride with trifluoroethylene, P(VDF-TrFE), and Pb(Zr,Ti)O{sub 3}. Each experiment started from a discharged and electrically depolarized ferroelectric capacitor. Voltage pulses were applied to set the given polarization states. The retention was measured as a function of time at various temperatures. The intermediate polarization states are stable over time, up to the Curie temperature. We argue that the remarkable stability originates from the coexistence of effectively independent domains, with different values of polarization and coercive field. A domain growth model is derived quantitatively describing deterministic switching between the intermediate polarization states. We show that by using well-defined voltage pulses, the polarization can be set to any arbitrary value, allowing arithmetic programming. The feasibility of arithmetic programming along with the inherent stability of intermediate polarization states makes ferroelectric materials ideal candidates for multibit data storage.

Retention of intermediate polarization states in ferroelectric materials enabling memories for multi-bit data storage

Science.gov (United States)

Zhao, Dong; Katsouras, Ilias; Asadi, Kamal; Groen, Wilhelm A.; Blom, Paul W. M.; de Leeuw, Dago M.

2016-06-01

A homogeneous ferroelectric single crystal exhibits only two remanent polarization states that are stable over time, whereas intermediate, or unsaturated, polarization states are thermodynamically instable. Commonly used ferroelectric materials however, are inhomogeneous polycrystalline thin films or ceramics. To investigate the stability of intermediate polarization states, formed upon incomplete, or partial, switching, we have systematically studied their retention in capacitors comprising two classic ferroelectric materials, viz. random copolymer of vinylidene fluoride with trifluoroethylene, P(VDF-TrFE), and Pb(Zr,Ti)O3. Each experiment started from a discharged and electrically depolarized ferroelectric capacitor. Voltage pulses were applied to set the given polarization states. The retention was measured as a function of time at various temperatures. The intermediate polarization states are stable over time, up to the Curie temperature. We argue that the remarkable stability originates from the coexistence of effectively independent domains, with different values of polarization and coercive field. A domain growth model is derived quantitatively describing deterministic switching between the intermediate polarization states. We show that by using well-defined voltage pulses, the polarization can be set to any arbitrary value, allowing arithmetic programming. The feasibility of arithmetic programming along with the inherent stability of intermediate polarization states makes ferroelectric materials ideal candidates for multibit data storage.

Scattering of polarized electrons from polarized targets: Coincidence reactions and prescriptions for polarized half-off-shell single-nucleon cross sections

International Nuclear Information System (INIS)

Caballero, J.A.; Massachusetts Inst. of Tech., Cambridge, MA; Donnelly, T.W.; Massachusetts Inst. of Tech., Cambridge, MA; Poulis, G.I.; Massachusetts Inst. of Tech., Cambridge, MA

1993-01-01

Coincidence reactions of the type vector A( vector e, e'N)B involving the scattering of polarized electrons from polarized targets are discussed within the context of the plane-wave impulse approximation. Prescriptions are developed for polarized half-off single-nucleon cross sections; the different prescriptions are compared for typical quasi-free kinematics. Illustrative results are presented for coincidence polarized electron scattering from typical polarized nuclei. (orig.)

M2 polarization enhances silica nanoparticle uptake by macrophages

Directory of Open Access Journals (Sweden)

Jessica eHoppstädter

2015-03-01

Full Text Available While silica nanoparticles have enabled numerous industrial and medical applications, their toxicological safety requires further evaluation. Macrophages are the major cell population responsible for nanoparticle clearance in vivo. The prevailing macrophage phenotype largely depends on the local immune status of the host. Whereas M1-polarized macrophages are considered as pro-inflammatory macrophages involved in host defense, M2 macrophages exhibit anti-inflammatory and wound-healing properties, but also promote tumor growth.We employed different models of M1 and M2 polarization: GM-CSF/LPS/IFN-gamma was used to generate primary human M1 cells and M-CSF/IL-10 to differentiate M2 monocyte-derived macrophages. PMA-differentiated THP-1 cells were polarized towards an M1 type by LPS/IFN-gamma and towards M2 by IL-10. Uptake of fluorescent silica nanoparticles (Ø 26 and 41 nm and microparticles (Ø 1.75 µm was quantified. At the concentration used (50 µg/ml, silica nanoparticles did not influence cell viability as assessed by MTT assay. Nanoparticle uptake was enhanced in M2-polarized primary human monocyte-derived macrophages compared with M1 cells, as shown by flow cytometric and microscopic approaches. In contrast, the uptake of microparticles did not differ between M1 and M2 phenotypes. M2 polarization was also associated with increased nanoparticle uptake in the macrophage-like THP-1 cell line. In accordance, in vivo polarized M2-like primary human tumor-associated macrophages (TAM obtained from lung tumors took up more nanoparticles than M1-like alveolar macrophages isolated from the surrounding lung tissue.In summary, our data indicate that the M2 polarization of macrophages promotes nanoparticle internalization. Therefore, the phenotypical differences between macrophage subsets should be taken into consideration in future investigations on nanosafety, but might also open up therapeutic perspectives allowing to specifically target M2

High-Frequency Dynamic Nuclear Polarization in the Nuclear Rotating Frame

DEFF Research Database (Denmark)

Farrar, C. T.; Hall, D. A.; Gerfen, G. J.

2000-01-01

A proton dynamic nuclear polarization (DNP) NMR signal enhancement (ϵ) close to thermal equilibrium, ϵ = 0.89, has been obtained at high field (B0 = 5 T, νepr = 139.5 GHz) using 15 mM trityl radical in a 40:60 water/glycerol frozen solution at 11 K. The electron-nuclear polarization transfer...... is performed in the nuclear rotating frame with microwave irradiation during a nuclear spin-lock pulse. The growth of the signal enhancement is governed by the rotating frame nuclear spin–lattice relaxation time (T1ρ), which is four orders of magnitude shorter than the nuclear spin–lattice relaxation time (T1n......). Due to the rapid polarization transfer in the nuclear rotating frame the experiment can be recycled at a rate of 1/T1ρ and is not limited by the much slower lab frame nuclear spin–lattice relaxation rate (1/T1n). The increased repetition rate allowed in the nuclear rotating frame provides an effective...

Ortho-Babinet polarization-interrogating filter: an interferometric approach to polarization measurement.

Science.gov (United States)

Van Delden, Jay S

2003-07-15

A novel, interferometric, polarization-interrogating filter assembly and method for the simultaneous measurement of all four Stokes parameters across a partially polarized irradiance image in a no-moving-parts, instantaneous, highly sensitive manner is described. In the reported embodiment of the filter, two spatially varying linear retarders and a linear polarizer comprise an ortho-Babinet, polarization-interrogating (OBPI) filter. The OBPI filter uniquely encodes the incident ensemble of electromagnetic wave fronts comprising a partially polarized irradiance image in a controlled, deterministic, spatially varying manner to map the complete state of polarization across the image to local variations in a superposed interference pattern. Experimental interferograms are reported along with a numerical simulation of the method.

Coronal Polarization of Pseudostreamers and the Solar Polar Field Reversal

Science.gov (United States)

Rachmeler, L. A.; Guennou, C.; Seaton, D. B.; Gibson, S. E.; Auchere, F.

2016-01-01

The reversal of the solar polar magnetic field is notoriously hard to pin down due to the extreme viewing angle of the pole. In Cycle 24, the southern polar field reversal can be pinpointed with high accuracy due to a large-scale pseudostreamer that formed over the pole and persisted for approximately a year. We tracked the size and shape of this structure with multiple observations and analysis techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP polarization data, and 3D tomographic reconstructions. We find that the heliospheric field reversed polarity in February 2014, whereas in the photosphere, the last vestiges of the previous polar field polarity remained until March 2015. We present here the evolution of the structure and describe its identification in the Fe XII 1074nm coronal emission line, sensitive to the Hanle effect in the corona.

Experiments with Fermilab polarized proton and polarized antiproton beams

International Nuclear Information System (INIS)

Yokosawa, A.

1990-01-01

We summarize activities concerning the Fermilab polarized beams. They include a brief description of the polarized-beam facility, measurements of beam polarization by polarimeters, asymmetry measurements in the π degree production at high p perpendicular and in the Λ (Σ degree), π ± , π degree production at large x F , and Δσ L (pp, bar pp) measurements. 18 refs

Wenzhouxiangella sediminis sp. nov. isolated from coastal sediment

Science.gov (United States)

A novel Gram-stain-negative, non-spore-forming, no flagellum, facultatively anaerobic, oxidase-negative, catalase- positive, rod-shaped strain, designated XDB06**T, was isolated from coastal sediment of Xiaoshi Island, Weihai, China. Optimal growth occurred at 37 °C, pH 7.5 and with 4.0% (w/v) NaCl....

Identifying polar bear resource selection patterns to inform offshore development in a dynamic and changing Arctic

Science.gov (United States)

Wilson, Ryan R.; Horne, Jon S.; Rode, Karyn D.; Regehr, Eric V.; Durner, George M.

2014-01-01

Although sea ice loss is the primary threat to polar bears (Ursus maritimus), little can be done to mitigate its effects without global efforts to reduce greenhouse gas emissions. Other factors, however, could exacerbate the impacts of sea ice loss on polar bears, such as exposure to increased industrial activity. The Arctic Ocean has enormous oil and gas potential, and its development is expected to increase in the coming decades. Estimates of polar bear resource selection will inform managers how bears use areas slated for oil development and to help guide conservation planning. We estimated temporally-varying resource selection patterns for non-denning adult female polar bears in the Chukchi Sea population (2008–2012) at two scales (i.e., home range and weekly steps) to identify factors predictive of polar bear use throughout the year, before any offshore development. From the best models at each scale, we estimated scale-integrated resource selection functions to predict polar bear space use across the population's range and determined when bears were most likely to use the region where offshore oil and gas development in the United States is slated to occur. Polar bears exhibited significant intra-annual variation in selection patterns at both scales but the strength and annual patterns of selection differed between scales for most variables. Bears were most likely to use the offshore oil and gas planning area during ice retreat and growth with the highest predicted use occurring in the southern portion of the planning area. The average proportion of predicted high-value habitat in the planning area was >15% of the total high-value habitat for the population during sea ice retreat and growth and reached a high of 50% during November 2010. Our results provide a baseline on which to judge future changes to non-denning adult female polar bear resource selection in the Chukchi Sea and help guide offshore development in the region. Lastly, our study provides a

Synergistic promotion of polar phase crystallization of PVDF by ionic liquid with PEG segment

Science.gov (United States)

Xu, Pei; Fu, Weijia; Cui, Zhaopei; Ding, Yunsheng

2018-06-01

To investigate the effect of imidazolium ionic liquid with poly(ethylene glycol) segment (IL) on the polar phase crystallization behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL composites were prepared using solution-cast method. The crystallization peak temperature of PVDF composites and the growth speed of samples decrease with increasing of IL. The >CF2 groups in amorphous region are retained and >CF2 groups in crystalline region are liberated by the PEG long soft segments of IL. The intensity of peaks represented as α phase reduces, moreover polar phase content increases with increasing of IL. The interaction between the >CF2 and the imidazolium cation can induce the polar phase, and the interaction between the >CF2 and PEG soft segment can strengthen polar crystalline induction. PVDF/12IL composite can form big γ spherulite circled by β phase.

Linearly polarized photoluminescence of InGaN quantum disks embedded in GaN nanorods.

Science.gov (United States)

Park, Youngsin; Chan, Christopher C S; Nuttall, Luke; Puchtler, Tim J; Taylor, Robert A; Kim, Nammee; Jo, Yongcheol; Im, Hyunsik

2018-05-25

We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn't show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures. In order to characterize a single nanostructure, the quantum disks were dispersed on a SiO 2 substrate patterned with a metal reference grid. By rotating the excitation polarization angle from parallel to perpendicular relative to the nanorods, the variation of overall PL for the 3.21 eV peak was recorded and it clearly showed the degree of linear polarization (DLP) of 51.5%.

Recent advance in polar seismology: Global impact of the International Polar Year

Science.gov (United States)

Kanao, Masaki; Zhao, Dapeng; Wiens, Douglas A.; Stutzmann, Éléonore

2015-03-01

The most exciting initiative for the recent polar studies was the International Polar Year (IPY) in 2007-2008. The IPY has witnessed a growing community of seismologists who have made considerable efforts to acquire high-quality data in polar regions. It also provided an excellent opportunity to make significant advances in seismic instrumentation of the polar regions to achieve scientific targets involving global issues. Taking these aspects into account, we organize and publish a special issue in Polar Science on the recent advance in polar seismology and cryoseismology as fruitful achievements of the IPY.

A Kinome RNAi Screen in Drosophila Identifies Novel Genes Interacting with Lgl, aPKC, and Crb Cell Polarity Genes in Epithelial Tissues

NARCIS (Netherlands)

Parsons, Linda M.; Grzeschik, Nicola A; Amaratunga, Kasun; Burke, Peter; Quinn, Leonie M; Richardson, Helena E

2017-01-01

In both Drosophila melanogaster and mammalian systems, epithelial structure and underlying cell polarity are essential for proper tissue morphogenesis and organ growth. Cell polarity interfaces with multiple cellular processes that are regulated by the phosphorylation status of large protein

Study of excess carrier dynamics in polar, semi-polar, and non-polar (In,Ga)N epilayers and QWs

Energy Technology Data Exchange (ETDEWEB)

Aleksiejunas, R. [Institute of Applied Research, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Laser Research Center, Vilnius University, Sauletekio Ave. 10, 10222 Vilnius (Lithuania); Lubys, L.; Jarasiunas, K. [Institute of Applied Research, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Vengris, M. [Laser Research Center, Vilnius University, Sauletekio Ave. 10, 10222 Vilnius (Lithuania); Wernicke, T.; Hoffmann, V.; Netzel, C.; Knauer, A.; Weyers, M. [Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12498 Berlin (Germany); Kneissl, M. [Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12498 Berlin (Germany); Institute of Solid State Physics, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)

2011-07-15

We studied carrier recombination and diffusion in GaN/sapphire templates, (In,Ga)N layers, and (In,Ga)N quantum well structures oriented along the polar [0001], semi-polar [11-22], and non-polar [11-20] orientations by means of light induced transient grating, differential transmission, and photoluminescence optical techniques. We show that the lifetime of excess carriers drops by orders of magnitude when changing the orientation from polar to non-polar, both in GaN templates and (In,Ga)N layers. We attribute the shorter lifetime to carrier trapping by extended structural defects that are more abundant in non-polar grown samples. In addition, we observe pronounced carrier localization effects in the semi- and non-polar layers. We show that thick (In,Ga)N layers inherit the properties of the GaN templates. However, the thin quantum well structures show a lower carrier trapping activity. So, a better electrical quality can be assumed as compared to the thick (In,Ga)N layers. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Polarized targets and beams

International Nuclear Information System (INIS)

Meyer, W.

1985-01-01

First the experimental situation of the single-pion photoproduction and the photodisintegration of the deuteron is briefly discussed. Then a description of the Bonn polarization facilities is given. The point of main effort is put on the polarized target which plays a vital role in the program. A facility for photon induced double polarization experiments at ELSA will be presented in section 4. Properties of a tensor polarized deuteron target are discussed in section 5. The development in the field of polarized targets, especially on new target materials, enables a new generation of polarized target experiments with (polarized) electrons. Some comments on the use of a polarized target in combination with electron beams will be discussed in section 6. Electron deuteron scattering from a tensor polarized deuteron target is considered and compared with other experimental possibilities. (orig./HSI)

Dust around young stars. Observations of the polarization of UX Ori in deep minima

International Nuclear Information System (INIS)

Voshchinnikov, N.V.; Grinin, V.P.; Kiselev, N.N.; Minikulov, N.K.

1988-01-01

Photometric and polarimetric monitoring observations of UX Ori begun in 1986 in the Crimea and Bolivia have resulted in the observation of two deep minima of the brightness during which a growth of the linear polarization (to ≅7%) was observed, together with a tendency for the circular polarization to increase (up to ≅1%). Analysis of the observational data shows that the main source of the polarized radiation in the deep minima is the emission of the star scattered by grains of circumstellar dust. On the basis of Mie's theory for a polydisperse graphite-silicate mixtures of particles the optical properties of ellipsoidal dust envelopes have been calculated and a model of the Algol-like minimum constructed

Polarization reversal during the solar noise storm activity of August 1971

International Nuclear Information System (INIS)

Kurihara, Masahiro

1975-01-01

Reversals of the sense of circular polarization of solar radio emission were observed for active type I storms in August 1971. Observations with a 160-MHz interferometer revealed that the reversals were caused by sudden growth and decay of a secondary storm source whose sense of polarization was opposite to that of the long-lasting main source. The time variations of both the associated S-component sources and sunspots are compared with that of the storm sources. The role of the magnetic field, which presumably connects the storm sources, the S-component sources, and the sunspots, is discussed in relation to the origin of the storm activity. (author)

Reduction of coating induced polarization aberrations by controlling the polarization state variation

International Nuclear Information System (INIS)

Li, Yanghui; Shen, Weidong; Zheng, Zhenrong; Zhang, Yueguang; Liu, Xu; Hao, Xiang

2011-01-01

The mechanism of coating induced polarization state variation is analysed by the Jones matrix. Pauli spin matrices are used to establish the relationship between coating induced polarization state variation and polarization aberrations. To reduce coating induced polarization aberrations, we propose that δ = 0 and T s = T p at arbitrary incident angle should be appended as two additional optimization goals of optical coating design when the requirements of transmittance are met. Two typical anti-reflection (AR) coatings are designed and the polarization state variation induced by them is simulated. The MTF (modulation transfer function) calculated by polarization ray tracing is applied to evaluate the polarization aberrations of the practical lithography objective system with the two AR coatings. All the obtained results show that the coating induced polarization aberrations can be reduced by optimizing the angle dependent properties of the optical coating without additional optical elements

Inverted Polarity Thunderstorms Linked with Elevated Cloud Base Height

Science.gov (United States)

Cummins, K. L.; Williams, E.

2016-12-01

The great majority of thunderstorms worldwide exhibit gross positive dipole structure, produce intracloud lightning that reduces this positive dipole (positive intracloud flashes), and produce negative cloud-to-ground lightning from the lower negative end of this dipole. During the STEPS experiment in 2000 much new evidence for thunderstorms (or cells within multi-cellular storms) with inverted polarity came to light, both from balloon soundings of electric field and from LMA analysis. Many of the storms with inverted polarity cells developed in eastern Colorado. Fleenor et al. (2009) followed up after STEPS to document a dominance of positive polarity CG lightning in many of these cases. In the present study, surface thermodynamic observations (temperature and dew point temperature) have been used to estimate the cloud base heights and temperatures at the time of the Fleenor et al. lightning observations. It was found that when more than 90% of the observed CG lightning polarity within a storm is negative, the cloud base heights were low (2000 m AGL or lower, and warmer, with T>10 C), and when more than 90% of the observed CG lightning within a storm was positive, the cloud base heights were high (3000 m AGL or higher, and colder, with Tmixed polarity were generally associated with intermediate cloud base heights. These findings on inverted polarity thunderstorms are remarkably consistent with results in other parts of the world where strong instability prevails in the presence of high cloud base height: the plateau regions of China (Liu et al., 1989; Qie et al., 2005), and in pre-monsoon India (Pawar et al., 2016), particularly when mixed polarity cases are excluded. Calculations of adiabatic cloud water content for lifting from near 0 oC cast some doubt on earlier speculation (Williams et al., 2005) that the graupel particles in these inverted polarity storms attain a wet growth condition, and so exhibit positive charging following laboratory experiments. This

Effect of 3D Polarization profiles on polarization measurements and colliding beam experiments

Energy Technology Data Exchange (ETDEWEB)

Fischer, W.; Bazilevsky, A.

2011-08-18

The development of polarization profiles are the primary reason for the loss of average polarization. Polarization profiles have been parametrized with a Gaussian distribution. We derive the effect of 3-dimensional polarization profiles on the measured polarization in polarimeters, as well as the observed polarization and the figure of merit in single and double spin experiments. Examples from RHIC are provided. The Relativistic Heavy Ion Collider (RHIC) is the only collider of spin polarized protons. During beam acceleration and storage profiles of the polarization P develop, which affect the polarization measured in a polarimeter, and the polarization and figure of merit (FOM) in colliding beam experiments. We calculate these for profiles in all dimensions, and give examples for RHIC. Like in RHIC we call the two colliding beams Blue and Yellow. We use the overbar to designate intensity-weighted averages in polarimeters (e.g. {bar P}), and angle brackets to designate luminosity-weighted averages in colliding beam experiments (e.g.

).

Effect of 3D Polarization profiles on polarization measurements and colliding beam experiments

International Nuclear Information System (INIS)

Fischer, W.; Bazilevsky, A.

2011-01-01

The development of polarization profiles are the primary reason for the loss of average polarization. Polarization profiles have been parametrized with a Gaussian distribution. We derive the effect of 3-dimensional polarization profiles on the measured polarization in polarimeters, as well as the observed polarization and the figure of merit in single and double spin experiments. Examples from RHIC are provided. The Relativistic Heavy Ion Collider (RHIC) is the only collider of spin polarized protons. During beam acceleration and storage profiles of the polarization P develop, which affect the polarization measured in a polarimeter, and the polarization and figure of merit (FOM) in colliding beam experiments. We calculate these for profiles in all dimensions, and give examples for RHIC. Like in RHIC we call the two colliding beams Blue and Yellow. We use the overbar to designate intensity-weighted averages in polarimeters (e.g. (bar P)), and angle brackets to designate luminosity-weighted averages in colliding beam experiments (e.g. ).

Nuclear polarization and neutrons

International Nuclear Information System (INIS)

Glaettli, H.

1985-01-01

Different possibilities for the use of polarized nuclei in thermal neutron scattering on condensed matter are reviewed. Highly polarized nuclei are the starting point for studying dipolar magnetic order. Systematic measurement of spin-dependent scattering lengths is possible on samples with polarized nuclei. Highly polarized hydrogen should help to unravel complicated structures in chemistry and biology. The use of polarized proton targets as an energy-independent neutron polarizer in the thermal and epithermal region should be considered afresh. (author)

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors.

Science.gov (United States)

Hardy, Matthew T; Storm, David F; Katzer, D Scott; Downey, Brian P; Nepal, Neeraj; Meyer, David J

2016-11-24

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm 2 /V∙sec for devices with a sheet charge density of 1.7 x 10 13 cm -2 .

NUCLEON POLARIZATION IN 3-BODY MODELS OF POLARIZED LI-6

NARCIS (Netherlands)

SCHELLINGERHOUT, NW; KOK, LP; COON, SA; ADAM, RM

1993-01-01

Just as He-3 --> can be approximately characterized as a polarized neutron target, polarized Li-6D has been advocated as a good isoscalar nuclear target for the extraction of the polarized gluon content of the nucleon. The original argument rests upon a presumed ''alpha + deuteron'' picture of Li-6,

Growth mechanism of InGaN nanodots on three-dimensional GaN structures

Energy Technology Data Exchange (ETDEWEB)

Park, Donghwy; Min, Daehong; Nam, Okhyun [Department of Nano-Optical Engineering, Convergence Center for Advanced Nano-Semiconductor (CANS), Korea Polytechnic University (KPU), Siheung-si, Gyeonggi-do (Korea, Republic of)

2017-07-15

In this study, we investigated the growth mechanism of indium gallium nitride (InGaN) nanodots (NDs) and an InGaN layer, which were simultaneously formed on a three-dimensional (3D) gallium nitride (GaN) structure, having (0001) polar, (11-22) semi-polar, and (11-20) nonpolar facets. We observed the difference in the morphological and compositional properties of the InGaN structures. From the high resolution transmission electron microscopy (HR-TEM) images, it can be seen that the InGaN NDs were formed only on the polar and nonpolar facets, whereas an InGaN layer was formed on the semi-polar facet. The indium composition variation in all the InGaN structures was observed using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray spectroscopy (EDS). The different growth mechanism can be explained by two reasons: (i) The difference in the diffusivities of indium and gallium adatoms at each facet of 3D GaN structure; and (ii) the difference in the kinetic Wulff plots of polar, semi-polar, and nonpolar GaN planes. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Superconducting polarizing magnet for a movable polarized target

International Nuclear Information System (INIS)

Anishchenko, N.G.; Bartenev, V.D.; Blinov, N.A.

1998-01-01

The superconducting polarizing magnet was constructed for the JINR (Dubna) movable polarized target (MPT) with working volume 200 mm long and 30 mm in diameter. The magnet provides a polarizing magnetic field up to 6 T in the centre with the uniformity of 4.5 x 10 -4 in the working volume of the target. The magnet contains a main solenoidal winding 558 mm long and 206/144 mm in diameters, and compensating and correcting winding placed at its ends. The windings are made of a NbTi wire, impregnated with the epoxy resin and placed in the horizontal cryostat. The diameter of the 'warm' aperture of the magnet cryostat is 96 mm. The design and technology of the magnet winding are described. Results of the magnetic field map measurements, using a NMR-magnetometer are given. A similar magnet constructed at DAPNIA, CEA/Saclay (France), represented a model for the present development. The MPT array is installed in the beam line of polarized neutrons produced by break-up of polarized deuterons extracted from the synchrophasotron of the Laboratory of High Energies (LHE), JINR (Dubna)

CMB polarization at large angular scales: Data analysis of the POLAR experiment

International Nuclear Information System (INIS)

O'Dell, Christopher W.; Keating, Brian G.; Oliveira-Costa, Angelica de; Tegmark, Max; Timbie, Peter T.

2003-01-01

The coming flood of cosmic microwave background (CMB) polarization experiments, spurred by the recent detection of CMB polarization by the DASI and WMAP instruments, will be confronted by many new analysis tasks specific to polarization. For the analysis of CMB polarization data sets, the devil is truly in the details. With this in mind, we present details of the data analysis for the POLAR experiment, which recently led to the tightest upper limits on the polarization of the cosmic microwave background radiation at large angular scales. We discuss the data selection process, map-making algorithms, offset removal, and likelihood analysis which were used to find upper limits on the polarization. Stated using the modern convention for reporting CMB Stokes parameters, these limits are 5.0 μK on both E- and B-type polarization at 95% confidence. Finally, we discuss simulations used to test our analysis techniques and to probe the fundamental limitations of the experiment

Few-body experiments with polarized beams and polarized targets

International Nuclear Information System (INIS)

Simmons, J.E.

1983-01-01

A survey is presented concerning recent polarization experiments in the elastic p-d, p- 3 He, and p- 4 He systems. Mention is made of selected neutron experiments. The nominal energy range is 10 to 1000 MeV. Recent results and interpretations of the p-d system near 10 MeV are discussed. New experiments on the energy dependence of back angle p-d tensor polarization are discussed with respect to resolution of discrepancies and difficulty of theoretical interpretation. Progress is noted concerning multiple scattering interpretation of forward p-d deuteron polarization. Some new results are presented concerning the p- 3 He system and higher energy p- 4 He polarization experiments. 52 references

Imaging of polarity during zygotic and somatic embryogenesis of carrot (Daucus carota L.)

NARCIS (Netherlands)

Timmers, A.C.J.

1993-01-01

In this thesis a study of the regulation of coordinated growth and the development of polarity during embryogenesis of carrot, Daucus carota L., is described. To this end, several microscopical techniques were used, such as light microscopy, fluorescence microscopy,

Cultural diversity and economic growth

DEFF Research Database (Denmark)

Ager, Philipp; Brückner, Markus

2013-01-01

We exploit the large inflow of immigrants to the US during the 1870–1920 period to examine the effects that within-county changes in the cultural composition of the US population had on output growth. We construct measures of fractionalization and polarization to distinguish between the different...

Long-period polar rain variations, solar wind and hemispherically symmetric polar rain

International Nuclear Information System (INIS)

Makita, K.; Meng, C.

1987-01-01

On the basic of electron data obtained by the Defense Meteorological Satellite Program (DMSP) F2 satellite the long-period variations of the polar rain flux are examined for four consecutive solar rotations. It is clearly demonstrated that the asymmetric enhancement of the polar rain flux is strongly controlled by the sector structure of the interplanetary magnetic field (IMF). However, the orbit-to-orbit and day-to-day variations of the polar rain flux are detected even during a very stable sector period, and the polar rain flux does not have any clear relationship to the magnitude of the IMF B/sub x/ or B/sub y/. Thus the polarity of B/sub x/ controls only the accessibility of a polar region. It is also noticed that the intensity of polar rain fluxes does not show any relationship to the density of the solar wind, suggesting that the origin of the polar rain electrons is different from the commonly observed part of the solar wind electron distribution function. In addition to the asymmetric polar rain distribution, increasing polar rain fluxes of similar high intensity are sometimes detected over both polar caps. An examination of more than 1 year's data from the DMSP F2 and F4 satellites shows that simultaneous intense uniform precipitations (>10 7 electrons/cm 2 s sr) over both polar caps are not coincidental; it also shows that the spectra are similar. The occurrence of hemispherically symmetric events is not common. They generally are observed after an IMF sector transition period, during unstable periods in the sector structure, and while the solar wind density is high. copyright American Geophysical Union 1987

Dipole-Oriented Molecular Solids Can Undergo a Phase Change and Still Maintain Electrical Polarization

Energy Technology Data Exchange (ETDEWEB)

Glavic, Artur G [ORNL; Cassidy, Andrew M [ORNL; Jorgensen, Mads Ry Ry [University of Aarhus, Denmark; Lauter, Valeria [ORNL; Rosu-Finsen, Alexander [Heriot-Watt University, Edinburgh, UK; Lasne, Jérôme [Heriot-Watt University, Edinburgh, UK; Jorgensen, Jakob [Aarhus University, Denmark; Iversen, Bo [ORNL; McCoustra, Martin [Heriot-Watt University, Edinburgh, UK; Field, David [University of Aarhus, Denmark

2016-10-02

It has recently been demonstrated that nanoscale molecular films can spontaneously assemble to self-generate intrinsic electric fields that can exceed 10⁸ V/m. These electric fields originate from polarization charges in the material that arise because the films self-assemble to orient molecular dipole moments. This has been called the spontelectric effect. Such growth of spontaneously polarized layers of molecular solids has implications for our understanding of how intermolecular interactions dictate the structure of molecular materials used in a range of applications, for example, molecular semiconductors, sensors, and catalysts. In this paper, we present the first in situ structural characterization of a representative spontelectric solid, nitrous oxide. Infrared spectroscopy, temperature-programmed desorption, and neutron reflectivity measurements demonstrate that polarized films of nitrous oxide undergo a structural phase transformation upon heating above 48 K. A mean-field model can be used to describe quantitatively the magnitude of the spontaneously generated field as a function of film-growth temperature, and this model also recreates the phase change. Finally, this reinforces the spontelectric model as a means of describing long-range dipole–dipole interactions and points to a new type of ordering in molecular thin films.

Polarity-inverted lateral overgrowth and selective wet-etching and regrowth (PILOSWER) of GaN.

Science.gov (United States)

Jang, Dongsoo; Jue, Miyeon; Kim, Donghoi; Kim, Hwa Seob; Lee, Hyunkyu; Kim, Chinkyo

2018-03-07

On an SiO 2 -patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H 3 PO 4 , this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO 2 -patterned sapphire.

Degree of polarization and source counts of faint radio sources from Stacking Polarized intensity

International Nuclear Information System (INIS)

Stil, J. M.; George, S. J.; Keller, B. W.; Taylor, A. R.

2014-01-01

We present stacking polarized intensity as a means to study the polarization of sources that are too faint to be detected individually in surveys of polarized radio sources. Stacking offers not only high sensitivity to the median signal of a class of radio sources, but also avoids a detection threshold in polarized intensity, and therefore an arbitrary exclusion of sources with a low percentage of polarization. Correction for polarization bias is done through a Monte Carlo analysis and tested on a simulated survey. We show that the nonlinear relation between the real polarized signal and the detected signal requires knowledge of the shape of the distribution of fractional polarization, which we constrain using the ratio of the upper quartile to the lower quartile of the distribution of stacked polarized intensities. Stacking polarized intensity for NRAO VLA Sky Survey (NVSS) sources down to the detection limit in Stokes I, we find a gradual increase in median fractional polarization that is consistent with a trend that was noticed before for bright NVSS sources, but is much more gradual than found by previous deep surveys of radio polarization. Consequently, the polarized radio source counts derived from our stacking experiment predict fewer polarized radio sources for future surveys with the Square Kilometre Array and its pathfinders.

Polarization developments

International Nuclear Information System (INIS)

Prescott, C.Y.

1993-07-01

Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist

Geographical Income Polarization

DEFF Research Database (Denmark)

Azhar, Hussain; Jonassen, Anders Bruun

inter municipal income inequality. Counter factual simulations show that rising property prices to a large part explain the rise in polarization. One side-effect of polarization is tendencies towards a parallel polarization of residence location patterns, where low skilled individuals tend to live...

Perceiving polarization with the naked eye: characterization of human polarization sensitivity

Science.gov (United States)

Temple, Shelby E.; McGregor, Juliette E.; Miles, Camilla; Graham, Laura; Miller, Josie; Buck, Jordan; Scott-Samuel, Nicholas E.; Roberts, Nicholas W.

2015-01-01

Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger's brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger's brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger's brushes. The rotational dynamics of Haidinger's brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration. PMID:26136441

Measurement of the polarized neutron---polarized 3He total cross section

International Nuclear Information System (INIS)

Keith, C.D.; Gould, C.R.; Haase, D.G.; Seely, M.L.; Huffman, P.R.; Roberson, N.R.; Tornow, W.; Wilburn, W.S.

1995-01-01

The first measurements of polarized neutron--polarized 3 He scattering in the few MeV energy region are reported. The total cross section difference Δσ T for transversely polarized target and beam has been measured for neutron energies between 1.9 and 7.5 MeV. Comparison is made to predictions of Δσ T using various descriptions of the 4 He continuum. A brute-force polarized target of solid 3 He has been developed for these measurements. The target is 4.3x10 22 atoms/cm 2 thick and is polarized to 38% at 7 Telsa and 12 mK. copyright 1995 American Institute of Physics

Scattering with polarized neutrons

International Nuclear Information System (INIS)

Schweizer, J.

2007-01-01

In the history of neutron scattering, it was shown very soon that the use of polarized neutron beams brings much more information than usual scattering with unpolarized neutrons. We shall develop here the different scattering methods that imply polarized neutrons: 1) polarized beams without polarization analysis, the flipping ratio method; 2) polarized beams with a uniaxial polarization analysis; 3) polarized beams with a spherical polarization analysis. For all these scattering methods, we shall give examples of the physical problems which can been solved by these methods, particularly in the field of magnetism: investigation of complex magnetic structures, investigation of spin or magnetization densities in metals, insulators and molecular compounds, separation of magnetic and nuclear scattering, investigation of magnetic properties of liquids and amorphous materials and even, for non magnetic material, separation between coherent and incoherent scattering. (author)

Allee effect in polar bears: a potential consequence of polychlorinated biphenyl contamination.

Science.gov (United States)

Pavlova, Viola; Nabe-Nielsen, Jacob; Dietz, Rune; Sonne, Christian; Grimm, Volker

2016-11-30

Polar bears (Ursus maritimus) from East Greenland and Svalbard exhibited very high concentrations of polychlorinated biphenyls (PCBs) in the 1980s and 1990s. In Svalbard, slow population growth during that period was suspected to be linked to PCB contamination. In this case study, we explored how PCBs could have impacted polar bear population growth and/or male reproductive success in Svalbard during the mid-1990s by reducing the fertility of contaminated males. A dose-response relationship linking the effects of PCBs to male polar bear fertility was extrapolated from studies of the effects of PCBs on sperm quality in rodents. Based on this relationship, an individual-based model of bear interactions during the breeding season predicted fertilization success under alternative assumptions regarding male-male competition for females. Contamination reduced pregnancy rates by decreasing the availability of fertile males, thus triggering a mate-finding Allee effect, particularly when male-male competition for females was limited or when infertile males were able to compete with fertile males for females. Comparisons of our model predictions on age-dependent reproductive success of males with published empirical observations revealed that the low representation of 10-14-year-old males among breeding males documented in Svalbard in mid-1990s could have resulted from PCB contamination. We conclude that contamination-related male infertility may lead to a reduction in population growth via an Allee effect. The magnitude of the effect is largely dependent on the population-specific mating system. In eco-toxicological risk assessments, appropriate consideration should therefore be given to negative effects of contaminants on male fertility and male mating behaviour. © 2016 The Author(s).

Dynamically polarized hydrogen target as a broadband, wavelength-independent thermal neutron spin polarizer

International Nuclear Information System (INIS)

Zhao Jinkui; Garamus, Vasil M.; Mueller, Wilhelm; Willumeit, Regine

2005-01-01

A hydrogen-rich sample with dynamically polarized hydrogen nuclei was tested as a wavelength-independent neutron transmission spin polarizer. The experiment used a modified setup of the dynamic nuclear polarization target station at the GKSS research center. The standard solvent sample at the GKSS DNP station was used. It is 2.8mm thick and consists of 43.4wt% water, 54.6wt% glycerol, and 2wt% of EHBA-Cr(v) complex. The wavelength of the incident neutrons for the transmission experiment was λ=8.1A with Δλ/λ=10%. The polarization of neutron beam after the target sample was analyzed with a supermirror analyzer. A neutron polarization of -52% was achieved at the hydrogen polarization of -69%. Further experiments will test the feasibility of other hydrogen-rich materials, such as methane, as the polarizer. A theoretical calculation shows that a polarized methane target would allow over 95% neutron polarizations with more than 30% transmission

Recent experience in accelerating polarized beam at the AGS

International Nuclear Information System (INIS)

Ratner, L.G.

1988-01-01

The most recent operation of the AGS for polarized protons occurred in December, 1987 and January, 1988. The primary purpose during this period was to tune up the accelerator as soon as possible and to provide a usable polarized beam for high energy physics. We succeeded in providing 1--2 /times/ 10 10 polarized protons per pulse at 18.5 GeV/c with an average polarization of 43 +- 3% and a peak of 52%. The conditions for this run differed in some respects from the previous run done in 1986. Due to problems with the main ring power supply, we were forced to use a back-up MG set which was only capable of 60% of the normal field rate of rise. This, of course enhanced the effect of the depolarizing resonances. A second difference was the fact that a complete horizontal and vertical realignment of the ring magnets was done during the 1987 summer shutdown. In addition, the fast pulsed quadrupole positions were readjusted with respect to the equilibrium orbit. It had been suspected that misalignment of these quads was responsible for large transverse emittance growth in both planes. We will look at the effects of these differences, but the bottom line is that the ''standard correction techniques'' worked as expected. 2 refs., 6 figs

Possibility of determining gluon polarization via polarized top pairs in gamma-proton scattering

International Nuclear Information System (INIS)

Atag, S.; Billur, A.A.

2009-01-01

We study the possibility for directly measuring the polarized gluon distribution in the process γp→t-bar t. It is shown that polarization asymmetry of the final top quarks is proportional to the gluon polarization. With available energy and luminosity, the collision of a polarized proton beam and a Compton backscattered photon beam can create polarized top quarks which carry the spin information of the process. Energy dependence and angular distributions of the polarization asymmetry of the top pairs has been discussed including statistical uncertainty.

Peculiarities of annihilation of polarized positronium in polarized media

International Nuclear Information System (INIS)

Silenko, A.Ya.

2005-01-01

Features of positronium annihilation (PA) in polarized media are investigated. Strong exchange interaction with nonpaired electrons of paramagnetic atoms essentially accelerates the PA in comparison with annihilation of free positrons. The value of the spin projection on the direction of polarized nonpaired electrons has essential effect on the orthopositronium lifetime and on the width of the gamma spectrum annihilation line. It is shown that these features of PA permit to use it for studying the paramagnetic polarization [ru

Angular distribution coefficients for γ-ray polarization produced in polarized capture reactions

International Nuclear Information System (INIS)

Wulf, E.A.; Guillemette, J.; Weller, H.R.; Seyler, R.G.

1999-01-01

The previous publications have dealt with the angular momentum formalism of both linear and circularly polarized photons in (γ, x) reactions on both polarized and unpolarized targets, and the inverse (capture) reactions initiated by polarized beams. In the present work, utilizing the general formalism of Welton, the authors deal with the linear polarization of the γ-rays which are produced in capture reactions on unpolarized targets, including the possibility of having incident polarized spin 1/2 projectiles. These capture reactions are denoted by a(rvec x, rvec L)c, where rvec x is the incident polarized spin 1/2 projectile and rvec L represents the outgoing polarized γ-ray. They present here the formalism in a convenient form, display a sample table of coefficients, and illustrate its use by means of several examples. A FORTRAN code will be made available for generating similar coefficients for other reactions

Polarization effects. Volume 2

Energy Technology Data Exchange (ETDEWEB)

Courant, E.

1981-01-01

The use of polarized proton beams in ISABELLE is important for several general reasons: (1) With a single longitudinally polarized proton beam, effects involving parity violation can be identified and hence processes involving weak interactions can be separated from those involving strong and electromagnetic interactions. (2) Spin effects are important in the strong interactions and can be useful for testing QCD. The technique for obtaining polarized proton beams in ISABELLE appears promising, particularly in view of the present development of a polarized proton beam for the AGS. Projections for the luminosity in ISABELLE for collisions of polarized protons - one or both beams polarized with longitudinal or transverse polarization - range from 1/100 to 1 times the luminosity for unpolarized protons.

Polarized lepton-nucleon scattering

Energy Technology Data Exchange (ETDEWEB)

Hughes, E. [Stanford Univ., CA (United States)

1994-12-01

The author provides a summary of the proposed and published statistical (systematic) uncertainties from the world experiments on nucleon spin structure function integrals. By the time these programs are complete, there will be a vast resource of data on nucleon spin structure functions. Each program has quite different experimental approaches regarding the beams, targets, and spectrometers thus ensuring systematically independent tests of the spin structure function measurements. Since the field of spin structure function measurements began, there has been a result appearing approximately every five years. With advances in polarized target technology and high polarization in virtually all of the lepton beams, results are now coming out each year; this is a true signature of the growth in the field. Hopefully, the experiments will provide a consistent picture of nucleon spin structure at their completion. In summary, there are still many open questions regarding the internal spin structure of the nucleon. Tests of QCD via the investigation of the Bjorken sum rule is a prime motivator for the field, and will continue with the next round of precision experiments. The question of the origin of spin is still a fundamental problem. Researchers hope is that high-energy probes using spin will shed light on this intriguing mystery, in addition to characterizing the spin structure of the nucleon.

Polarized lepton-nucleon scattering

International Nuclear Information System (INIS)

Hughes, E.

1994-01-01

The author provides a summary of the proposed and published statistical (systematic) uncertainties from the world experiments on nucleon spin structure function integrals. By the time these programs are complete, there will be a vast resource of data on nucleon spin structure functions. Each program has quite different experimental approaches regarding the beams, targets, and spectrometers thus ensuring systematically independent tests of the spin structure function measurements. Since the field of spin structure function measurements began, there has been a result appearing approximately every five years. With advances in polarized target technology and high polarization in virtually all of the lepton beams, results are now coming out each year; this is a true signature of the growth in the field. Hopefully, the experiments will provide a consistent picture of nucleon spin structure at their completion. In summary, there are still many open questions regarding the internal spin structure of the nucleon. Tests of QCD via the investigation of the Bjorken sum rule is a prime motivator for the field, and will continue with the next round of precision experiments. The question of the origin of spin is still a fundamental problem. Researchers hope is that high-energy probes using spin will shed light on this intriguing mystery, in addition to characterizing the spin structure of the nucleon

The bone microstructure of polar "hypsilophodontid" dinosaurs from Victoria, Australia.

Science.gov (United States)

Woodward, Holly N; Rich, Thomas H; Vickers-Rich, Patricia

2018-01-18

High-latitude (i.e., "polar") Mesozoic fauna endured months of twilight and relatively low mean annual temperatures. Yet non-avian dinosaurs flourished in this taxing environment. Fossils of basal ornithopod dinosaurs ("hypsilophodontids") are common in the Early Cretaceous high-latitude sediments of Victoria, Australia, and four taxa have been described; although their ontogenetic histories are largely unexplored. In the present study, eighteen tibiae and femora were utilized in the first multi-specimen ontogenetic histological analysis of Australian polar hypsilophodontids. The sample consists of eleven individuals from the Flat Rocks locality (Late Valanginian or Barremian), and five from the Dinosaur Cove locality (Albian). In both groups, growth was most rapid during the first three years, and skeletal maturity occurred between five and seven years. There is a weak asymptotic trend in a plot of growth mark count versus femur length, with considerable individual variation. Histology suggests two genera are present within the Dinosaur Cove sample, but bone microstructure alone could not distinguish genera within the Flat Rocks sample, or across the two geologically separate (~ 26 Ma) localities. Additional histologic sampling, combined with morphological analyses, may facilitate further differentiation between ontogenetic, individual, and species variation.

Semi-polar GaN materials technology for high IQE green LEDs.

Energy Technology Data Exchange (ETDEWEB)

Koleske, Daniel; Lee, Stephen Roger; Crawford, Mary H; Coltrin, Michael Elliott; Fini, Paul

2013-06-01

The goal of this NETL funded program was to improve the IQE in green (and longer wavelength) nitride- based LEDs structures by using semi-polar GaN planar orientations for InGaN multiple quantum well (MQW) growth. These semi-polar orientations have the advantage of significantly reducing the piezoelectric fields that distort the QW band structure and decrease electron-hole overlap. In addition, semipolar surfaces potentially provide a more open surface bonding environment for indium incorporation, thus enabling higher indium concentrations in the InGaN MQW. The goal of the proposed work was to select the optimal semi-polar orientation and explore wafer miscuts around this orientation that produced the highest quantum efficiency LEDs. At the end of this program we had hoped to have MQWs active regions at 540 nm with an IQE of 50% and an EQE of 40%, which would be approximately twice the estimated current state-of-the-art.

Instrumentation with polarized neutrons

International Nuclear Information System (INIS)

Boeni, P.; Muenzer, W.; Ostermann, A.

2009-01-01

Neutron scattering with polarization analysis is an indispensable tool for the investigation of novel materials exhibiting electronic, magnetic, and orbital degrees of freedom. In addition, polarized neutrons are necessary for neutron spin precession techniques that path the way to obtain extremely high resolution in space and time. Last but not least, polarized neutrons are being used for fundamental studies as well as very recently for neutron imaging. Many years ago, neutron beam lines were simply adapted for polarized beam applications by adding polarizing elements leading usually to unacceptable losses in neutron intensity. Recently, an increasing number of beam lines are designed such that an optimum use of polarized neutrons is facilitated. In addition, marked progress has been obtained in the technology of 3 He polarizers and the reflectivity of large-m supermirrors. Therefore, if properly designed, only factors of approximately 2-3 in neutron intensity are lost. It is shown that S-benders provide neutron beams with an almost wavelength independent polarization. Using twin cavities, polarized beams with a homogeneous phase space and P>0.99 can be produced without significantly sacrificing intensity. It is argued that elliptic guides, which are coated with large m polarizing supermirrors, provide the highest flux.

Feasibility studies of a polarized positron source based on the Bremsstrahlung of polarized electrons

International Nuclear Information System (INIS)

Dumas, J.

2011-09-01

The nuclear and high-energy physics communities have shown a growing interest in the availability of high current, highly-polarized positron beams. A sufficiently energetic polarized photon or lepton incident on a target may generate, via Bremsstrahlung and pair creation within a solid target foil, electron-positron pairs that should carry some fraction of the initial polarization. Recent advances in high current (> 1 mA) spin polarized electron sources at Jefferson Lab offer the perspective of creating polarized positrons from a low energy electron beam. This thesis discusses polarization transfer from electrons to positrons in the perspective of the design optimization of a polarized positron source. The PEPPo experiment, aiming at a measurement of the positron polarization from a low energy (< 10 MeV) highly spin polarized electron beam is discussed. A successful demonstration of this technique would provide an alternative scheme for the production of low energy polarized positrons and useful information for the optimization of the design of polarized positron sources in the sub-GeV energy range. (author)

Dispersing surface-modified imogolite nanotubes in polar and non-polar solvents

Science.gov (United States)

Li, Ming; Brant, Jonathan A.

2018-02-01

Furthering the development of nanocomposite structures, namely membranes for water treatment applications, requires that methods be developed to ensure nanoparticle dispersion in polar and non-polar solvents, as both are widely used in associated synthesis techniques. Here, we report on a two-step method to graft polyvinylpyrrolidone (PVP), and a one-step method for octadecylphosphonic acid (OPA), onto the outer surfaces of imogolite nanotubes. The goal of these approaches was to improve and maintain nanotube dispersion in polymer compatible polar and non-polar solvents. The PVP coating modified the imogolite surface charge from positive to weakly negative at pH ≤ 9; the OPA made it weakly positive at acidic pH values to negative at pH ≥ 7. The PVP surface coating stabilized the nanotubes through steric hindrance in polar protic, dipolar aprotic, and chloroform. In difference to the PVP, the OPA surface coating allowed the nanotubes to be dispersed in n-hexane and chloroform, but not in the polar solvents. The lack of miscibility in the polar solvents, as well as the better dispersion in n-hexane, was attributed to the stronger hydrophobicity of the OPA polymer relative to the PVP. [Figure not available: see fulltext.

MBE-growth, characterization and properties of InN and InGaN

International Nuclear Information System (INIS)

Nanishi, Y.; Saito, Y.; Yamaguchi, T.; Hori, M.; Matsuda, F.; Araki, T.; Suzuki, A.; Miyajima, T.

2003-01-01

Recent developments on RF-MBE growth of InN and InGaN and their structural and property characterizations are reviewed. For successful growth of high quality InN, (1) nitridation of the sapphire substrates, (2) two-step growth, (3) precise control of V/III ratio and (4) selection of optimum growth temperature are found to be essential. Characterization using XRD, TEM, EXAFS and Raman scattering have clearly demonstrated that InN films have ideal hexagonal wurtzite structure. It is also found that the film has N-polarity. Studies on optimum growth condition dependence on substrate polarity using C and Si face SiC substrates and Ga and N face free-standing GaN substrates are also demonstrated. The result explains why high-quality InN grown by RF-MBE has N-polarity. PL and CL studies on these well-characterized high-quality InN have shown luminescence peaks at approximately 0.75 eV at 77 K. These values, however, change slightly depending on measurement temperatures and probably on the residual carrier concentrations. InGaN with full compositional range are also successfully grown on sapphire substrates and band gap energies of these alloys are also studied using PL and CL. Based on these results, true band gap energies of InN are discussed. This paper also includes latest study on single crystalline InN growth on Si (111) substrates. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

MBE-growth, characterization and properties of InN and InGaN

Energy Technology Data Exchange (ETDEWEB)

Nanishi, Y.; Saito, Y.; Yamaguchi, T.; Hori, M.; Matsuda, F.; Araki, T. [Dept. of Photonics, Ritsumeikan Univ., 1-1-1 Noji-higashi, Kusatsu (Japan); Suzuki, A. [Res. Org. of Sci. and Eng., Ritsumeikan Univ., 1-1-1 Noji-higashi, Kusatsu (Japan); Miyajima, T. [Sony Corp. Core Technology and Network Company, 4-14-1 Asahi, Atsugi, Kanagawa 243-0014 (Japan)

2003-11-01

Recent developments on RF-MBE growth of InN and InGaN and their structural and property characterizations are reviewed. For successful growth of high quality InN, (1) nitridation of the sapphire substrates, (2) two-step growth, (3) precise control of V/III ratio and (4) selection of optimum growth temperature are found to be essential. Characterization using XRD, TEM, EXAFS and Raman scattering have clearly demonstrated that InN films have ideal hexagonal wurtzite structure. It is also found that the film has N-polarity. Studies on optimum growth condition dependence on substrate polarity using C and Si face SiC substrates and Ga and N face free-standing GaN substrates are also demonstrated. The result explains why high-quality InN grown by RF-MBE has N-polarity. PL and CL studies on these well-characterized high-quality InN have shown luminescence peaks at approximately 0.75 eV at 77 K. These values, however, change slightly depending on measurement temperatures and probably on the residual carrier concentrations. InGaN with full compositional range are also successfully grown on sapphire substrates and band gap energies of these alloys are also studied using PL and CL. Based on these results, true band gap energies of InN are discussed. This paper also includes latest study on single crystalline InN growth on Si (111) substrates. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Modeling optical and UV polarization of AGNs. IV. Polarization timing

Science.gov (United States)

Rojas Lobos, P. A.; Goosmann, R. W.; Marin, F.; Savić, D.

2018-03-01

Context. Optical observations cannot resolve the structure of active galactic nuclei (AGN), and a unified model for AGN was inferred mostly from indirect methods, such as spectroscopy and variability studies. Optical reverberation mapping allowed us to constrain the spatial dimension of the broad emission line region and thereby to measure the mass of supermassive black holes. Recently, reverberation was also applied to the polarized signal emerging from different AGN components. In principle, this should allow us to measure the spatial dimensions of the sub-parsec reprocessing media. Aim. We conduct numerical modeling of polarization reverberation and provide theoretical predictions for the polarization time lag induced by different AGN components. The model parameters are adjusted to the observational appearance of the Seyfert 1 galaxy NGC 4151. Methods: We modeled scattering-induced polarization and tested different geometries for the circumnuclear dust component. Our tests included the effects of clumpiness and different dust prescriptions. To further extend the model, we also explored the effects of additional ionized winds stretched along the polar direction, and of an equatorial scattering ring that is responsible for the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code. Results: Our modeling confirms the previously found polarization characteristics as a function of the observer`s viewing angle. When the dust adopts a flared-disk geometry, the lags reveal a clear difference between type 1 and type 2 AGN. This distinction is less clear for a torus geometry where the time lag is more sensitive to the geometry and optical depth of the inner surface layers of the funnel. The presence of a scattering equatorial ring and ionized outflows increased the recorded polarization time lags, and the polar outflows smooths out dependence on viewing angle, especially for the higher optical depth of the

Study on polarized optical flow algorithm for imaging bionic polarization navigation micro sensor

Science.gov (United States)

Guan, Le; Liu, Sheng; Li, Shi-qi; Lin, Wei; Zhai, Li-yuan; Chu, Jin-kui

2018-05-01

At present, both the point source and the imaging polarization navigation devices only can output the angle information, which means that the velocity information of the carrier cannot be extracted from the polarization field pattern directly. Optical flow is an image-based method for calculating the velocity of pixel point movement in an image. However, for ordinary optical flow, the difference in pixel value as well as the calculation accuracy can be reduced in weak light. Polarization imaging technology has the ability to improve both the detection accuracy and the recognition probability of the target because it can acquire the extra polarization multi-dimensional information of target radiation or reflection. In this paper, combining the polarization imaging technique with the traditional optical flow algorithm, a polarization optical flow algorithm is proposed, and it is verified that the polarized optical flow algorithm has good adaptation in weak light and can improve the application range of polarization navigation sensors. This research lays the foundation for day and night all-weather polarization navigation applications in future.

N-polar GaN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor formed on sapphire substrate with minimal step bunching

Science.gov (United States)

Prasertsuk, Kiattiwut; Tanikawa, Tomoyuki; Kimura, Takeshi; Kuboya, Shigeyuki; Suemitsu, Tetsuya; Matsuoka, Takashi

2018-01-01

The metal-insulator-semiconductor (MIS) gate N-polar GaN/AlGaN/GaN high-electron-mobility transistor (HEMT) on a (0001) sapphire substrate, which can be expected to operate with lower on-resistance and more easily work on the pinch-off operation than an N-polar AlGaN/GaN HEMT, was fabricated. For suppressing the step bunching and hillocks peculiar in the N-polar growth, a sapphire substrate with an off-cut angle as small as 0.8° was introduced and an N-polar GaN/AlGaN/GaN HEMT without the step bunching was firstly obtained by optimizing the growth conditions. The previously reported anisotropy of transconductance related to the step was eliminated. The pinch-off operation was also realized. These results indicate that this device is promising.

Design and simulation of a novel circularly polarized antenna with polarization reconfigurable characteristics

Directory of Open Access Journals (Sweden)

Zhang Hai

2016-01-01

Full Text Available A novel circularly polarized antenna with polarization reconfigurable characteristics was designed using co-simulation of Ansoft HFSS and Designer software. It consists of a dual-polarized antenna and phase switching network which act as the feed network for the dual-polarized antenna. The phase switching network was designed based on a Wilkinson power divider, where the output port was connected with SPDT to form a switching network. By controlling the SPDT state-off / on, the phase difference of the two ports could be alternated, which generated the orthogonal modes between the two ports of dual-polarized antenna. So that Left-hand circular polarization (LHCP and Right-hand circular polarization (RHCP could be achieved. The simulation shown that reflection coefficient was less than -12 dB and the axial ratio was below 3 dB between 1.8 GHz and 2.4 GHz with polarization reconfigurable characteristics.

Endocytic recycling via the TGN underlies the polarized hyphal mode of life.

Science.gov (United States)

Hernández-González, Miguel; Bravo-Plaza, Ignacio; Pinar, Mario; de Los Ríos, Vivian; Arst, Herbert N; Peñalva, Miguel A

2018-04-01

Intracellular traffic in Aspergillus nidulans hyphae must cope with the challenges that the high rates of apical extension (1μm/min) and the long intracellular distances (>100 μm) impose. Understanding the ways in which the hyphal tip cell coordinates traffic to meet these challenges is of basic importance, but is also of considerable applied interest, as fungal invasiveness of animals and plants depends critically upon maintaining these high rates of growth. Rapid apical extension requires localization of cell-wall-modifying enzymes to hyphal tips. By combining genetic blocks in different trafficking steps with multidimensional epifluorescence microscopy and quantitative image analyses we demonstrate that polarization of the essential chitin-synthase ChsB occurs by indirect endocytic recycling, involving delivery/exocytosis to apices followed by internalization by the sub-apical endocytic collar of actin patches and subsequent trafficking to TGN cisternae, where it accumulates for ~1 min before being re-delivered to the apex by a RAB11/TRAPPII-dependent pathway. Accordingly, ChsB is stranded at the TGN by Sec7 inactivation but re-polarizes to the apical dome if the block is bypassed by a mutation in geaAgea1 that restores growth in the absence of Sec7. That polarization is independent of RAB5, that ChsB predominates at apex-proximal cisternae, and that upon dynein impairment ChsB is stalled at the tips in an aggregated endosome indicate that endocytosed ChsB traffics to the TGN via sorting endosomes functionally located upstream of the RAB5 domain and that this step requires dynein-mediated basipetal transport. It also requires RAB6 and its effector GARP (Vps51/Vps52/Vps53/Vps54), whose composition we determined by MS/MS following affinity chromatography purification. Ablation of any GARP component diverts ChsB to vacuoles and impairs growth and morphology markedly, emphasizing the important physiological role played by this pathway that, we propose, is central

VIIRS-J1 Polarization Narrative

Science.gov (United States)

Waluschka, Eugene; McCorkel, Joel; McIntire, Jeff; Moyer, David; McAndrew, Brendan; Brown, Steven W.; Lykke, Keith; Butler, James; Meister, Gerhard; Thome, Kurtis J.

2015-01-01

The VIS/NIR bands polarization sensitivity of Joint Polar Satellite Sensor 1 (JPSS1) Visible/Infrared Imaging Radiometer Suite (VIIRS) instrument was measured using a broadband source. While polarization sensitivity for bands M5-M7, I1, and I2 was less than 2.5%, the maximum polarization sensitivity for bands M1, M2, M3, and M4 was measured to be 6.4%, 4.4%, 3.1%, and 4.3%, respectively with a polarization characterization uncertainty of less than 0.3%. A detailed polarization model indicated that the large polarization sensitivity observed in the M1 to M4 bands was mainly due to the large polarization sensitivity introduced at the leading and trailing edges of the newly manufactured VISNIR bandpass focal plane filters installed in front of the VISNIR detectors. This was confirmed by polarization measurements of bands M1 and M4 bands using monochromatic light. Discussed are the activities leading up to and including the instruments two polarization tests, some discussion of the polarization model and the model results, the role of the focal plane filters, the polarization testing of the Aft-Optics-Assembly, the testing of the polarizers at Goddard and NIST and the use of NIST's T-SIRCUS for polarization testing and associated analyses and results.

Polarization of Be stars

International Nuclear Information System (INIS)

Johns, M.W.

1975-01-01

Linear polarization of starlight may be produced by electron scattering in the extended atmospheres of early type stars. Techniques are investigated for the measurement and interpretation of this polarization. Polarimetric observations were made of twelve visual double star systems in which at least one member was a B type star as a means of separating the intrinsic stellar polarization from the polarization produced in the interstellar medium. Four of the double stars contained a Be star. Evidence for intrinsic polarization was found in five systems including two of the Be systems, one double star with a short period eclipsing binary, and two systems containing only normal early type stars for which emission lines have not been previously reported. The interpretation of these observations in terms of individual stellar polarizations and their wavelength dependence is discussed. The theoretical basis for the intrinsic polarization of early type stars is explored with a model for the disk-like extended atmospheres of Be stars. Details of a polarimeter for the measurement of the linear polarization of astronomical point sources are also presented with narrow band (Δ lambda = 100A) measurements of the polarization of γ Cas from lambda 4000 to lambda 5800

Ionic polarization

International Nuclear Information System (INIS)

Mahan, G.D.

1992-01-01

Ferroelectricity occurs in many different kinds of materials. Many of the technologically important solids, which are ferroelectric, can be classified as ionic. Any microscopic theory of ferroelectricity must contain a description of local polarization forces. We have collaborated in the development of a theory of ionic polarization which is quite successful. Its basic assumption is that the polarization is derived from the properties of the individual ions. We have applied this theory successfully to diverse subjects as linear and nonlinear optical response, phonon dispersion, and piezoelectricity. We have developed numerical methods using the local Density approximation to calculate the multipole polarizabilities of ions when subject to various fields. We have also developed methods of calculating the nonlinear hyperpolarizability, and showed that it can be used to explain light scattering experiments. This paper elaborates on this polarization theory

Growth and biochemical composition of Chlorella vulgaris in different growth media

Directory of Open Access Journals (Sweden)

MATHIAS A. CHIA

2013-10-01

Full Text Available The need for clean and low-cost algae production demands for investigations on algal physiological response under different growth conditions. In this research, we investigated the growth, biomass production and biochemical composition of Chlorella vulgaris using semi-continuous cultures employing three growth media (LC Oligo, Chu 10 and WC media. The highest cell density was obtained in LC Oligo, while the lowest in Chu medium. Chlorophyll a, carbohydrate and protein concentrations and yield were highest in Chu and LC Oligo media. Lipid class analysis showed that hydrocarbons (HC, sterol esthers (SE, free fatty acids (FFA, aliphatic alcohols (ALC, acetone mobile polar lipids (AMPL and phospholipids (PL concentrations and yields were highest in the Chu medium. Triglyceride (TAG and sterol (ST concentrations were highest in the LC Oligo medium. The results suggested that for cost effective cultivation, LC Oligo medium is the best choice among those studied, as it saved the cost of buying vitamins and EDTA associated with the other growth media, while at the same time resulted in the best growth performance and biomass production.

Directed Assembly of Janus Cylinders by Controlling the Solvent Polarity.

Science.gov (United States)

Kim, Jongmin; Choi, Chang-Hyung; Yeom, Su-Jin; Eom, Naye; Kang, Kyoung-Ku; Lee, Chang-Soo

2017-08-01

This study demonstrates the possibility of controlling the directed self-assembly of microsized Janus cylinders by changing the solvent polarity of the assembly media. Experimental results are analyzed and theoretical calculations of the free energy of adhesion (ΔG ad ) are performed to elucidate the underlying basic principles and investigate the effects of the solvent on the self-assembled structures. This approach will pave a predictive route for controlling the structures of assembly depending on the solvent polarity. In particular, we find that a binary solvent system with precisely controlled polarity induces directional assembly of the microsized Janus cylinders. Thus, the formation of two-dimensional (2D) and three-dimensional (3D) assembled clusters can be reliably tuned by controlling the numbers of constituent Janus cylinders in a binary solvent system. Finally, this approach is expanded to stepwise assembly, which forms unique microstructures via secondary growth of primary seed clusters formed by the Janus cylinders. We envision that this investigation is highly promising for the construction of desired superstructures using a wide variety of polymeric Janus microparticles with chemical and physical multicompartments.

Generation and control of spin-polarized photocurrents in GaMnAs heterostructures

Energy Technology Data Exchange (ETDEWEB)

Bezerra, Anibal T., E-mail: anibal@df.ufscar.br; Farinas, Paulo F.; Studart, Nelson [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil); Castelano, Leonardo K. [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); Degani, Marcos H.; Maialle, Marcelo Z. [Faculdade de Ciências Aplicadas, Universidade Estadual de Campinas, 13484-350 Limeira, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil)

2014-01-13

Photocurrents are calculated for a specially designed GaMnAs semiconductor heterostructure. The results reveal regions in the infrared range of the energy spectrum, in which the proposed structure is remarkably spin-selective. For such photon energies, the generated photocurrents are strongly spin-polarized. Application of a relatively small static bias in the growth direction of the structure is predicted to efficiently reverse the spin-polarization for some photon energies. This behavior suggests the possibility of conveniently simple switching mechanisms. The physics underlying the results is studied and understood in terms of the spin-dependent properties emerging from the particular potential profile of the structure.

Structural properties, crystal quality and growth modes of MOCVD-grown AlN with TMAl pretreatment of sapphire substrate

KAUST Repository

Sun, Haiding; Wu, Feng; Altahtamouni, Talal Mohammed Ahmad; Alfaraj, Nasir; Li, Kun; Detchprohm, Theeradetch; Dupuis, Russell; Li, Xiaohang

2017-01-01

The growth of high quality AlN epitaxial films relies on precise control of the initial growth stages. In this work, we examined the influence of the trimethylaluminum (TMAl) pretreatment of sapphire substrates on the structural properties, crystal quality and growth modes of heteroepitaxial AlN films on (0001) sapphire substrates. Without the pretreatment, the AlN films nucleated on the smooth surface but exhibited mixed crystallographic Al- (N-) polarity, resulting in rough AlN film surfaces. With increasing the pretreatment time from 1 to 5 s, the N-polarity started to be impeded. However, small islands were formed on sapphire surface due to the decompostion of TMAl. As a result, small voids became noticeable at the nucleation layer (NL) because the growth started as quasi three-dimensional (3D) but transformed to 2D mode as the film grew thicker and got coalesced, leading to smoother and Al-polar films. On the other hand, longer pretreatment time of 40 s formed large 3D islands on sapphire, and thus initiated a 3D-growth mode of the AlN film, generating Al-polar AlN nanocolumns with different facets, which resulted into rougher film surfaces. The epitaxial growth modes and their correlation with the AlN film crystal quality under different TMAl pretreatments are also discussed.

Structural properties, crystal quality and growth modes of MOCVD-grown AlN with TMAl pretreatment of sapphire substrate

KAUST Repository

Sun, Haiding

2017-08-08

The growth of high quality AlN epitaxial films relies on precise control of the initial growth stages. In this work, we examined the influence of the trimethylaluminum (TMAl) pretreatment of sapphire substrates on the structural properties, crystal quality and growth modes of heteroepitaxial AlN films on (0001) sapphire substrates. Without the pretreatment, the AlN films nucleated on the smooth surface but exhibited mixed crystallographic Al- (N-) polarity, resulting in rough AlN film surfaces. With increasing the pretreatment time from 1 to 5 s, the N-polarity started to be impeded. However, small islands were formed on sapphire surface due to the decompostion of TMAl. As a result, small voids became noticeable at the nucleation layer (NL) because the growth started as quasi three-dimensional (3D) but transformed to 2D mode as the film grew thicker and got coalesced, leading to smoother and Al-polar films. On the other hand, longer pretreatment time of 40 s formed large 3D islands on sapphire, and thus initiated a 3D-growth mode of the AlN film, generating Al-polar AlN nanocolumns with different facets, which resulted into rougher film surfaces. The epitaxial growth modes and their correlation with the AlN film crystal quality under different TMAl pretreatments are also discussed.

Characterization of InAs quantum wires on (001) InP: toward the realization of VCSEL structures with a stabilized polarization

OpenAIRE

Lamy , Jean-Michel; Levallois , Christophe; Nakkar , Abdulhadi; Caroff , Philippe; Paranthoen , Cyril; Dehaese , Olivier; Le Corre , Alain; Ramdane , Abderrahim; Loualiche , Slimane

2006-01-01

International audience; We propose a new type of long-wavelength vertical cavity surface emitting laser (VCSEL) which consists of quantum wires (QWires) layers of InAs/InGaAsP grown on InP(001) and dielectrics Bragg mirrors, in order to control the in plane polarization of output power. QWires and quantum wells growth are performed by molecular beam epitaxy. QWires present a strong photoluminescence dependence to the polarization in contrast to the quantum wells, a polarization rate of 33% is...

Diffusion as a Ruler: Modeling Kinesin Diffusion as a Length Sensor for Intraflagellar Transport.

Science.gov (United States)

Hendel, Nathan L; Thomson, Matthew; Marshall, Wallace F

2018-02-06

An important question in cell biology is whether cells are able to measure size, either whole cell size or organelle size. Perhaps cells have an internal chemical representation of size that can be used to precisely regulate growth, or perhaps size is just an accident that emerges due to constraint of nutrients. The eukaryotic flagellum is an ideal model for studying size sensing and control because its linear geometry makes it essentially one-dimensional, greatly simplifying mathematical modeling. The assembly of flagella is regulated by intraflagellar transport (IFT), in which kinesin motors carry cargo adaptors for flagellar proteins along the flagellum and then deposit them at the tip, lengthening the flagellum. The rate at which IFT motors are recruited to begin transport into the flagellum is anticorrelated with the flagellar length, implying some kind of communication between the base and the tip and possibly indicating that cells contain some mechanism for measuring flagellar length. Although it is possible to imagine many complex scenarios in which additional signaling molecules sense length and carry feedback signals to the cell body to control IFT, might the already-known components of the IFT system be sufficient to allow length dependence of IFT? Here we investigate a model in which the anterograde kinesin motors unbind after cargo delivery, diffuse back to the base, and are subsequently reused to power entry of new IFT trains into the flagellum. By mathematically modeling and simulating such a system, we are able to show that the diffusion time of the motors can in principle be sufficient to serve as a proxy for length measurement. We found that the diffusion model can not only achieve a stable steady-state length without the addition of any other signaling molecules or pathways, but also is able to produce the anticorrelation between length and IFT recruitment rate that has been observed in quantitative imaging studies. Copyright © 2017 Biophysical

Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Reich, Christoph, E-mail: Christoph.Reich@tu-berlin.de; Guttmann, Martin; Wernicke, Tim; Mehnke, Frank; Kuhn, Christian [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, Berlin 10623 (Germany); Feneberg, Martin; Goldhahn, Rüdiger [Institut für Experimentelle Physik, Otto-von-Guericke-Universität, Universitätsplatz 2, Magdeburg 39106 (Germany); Rass, Jens; Kneissl, Michael [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, Berlin 10623 (Germany); Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany); Lapeyrade, Mickael; Einfeldt, Sven; Knauer, Arne; Kueller, Viola; Weyers, Markus [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany)

2015-10-05

The optical polarization of emission from ultraviolet (UV) light emitting diodes (LEDs) based on (0001)-oriented Al{sub x}Ga{sub 1−x}N multiple quantum wells (MQWs) has been studied by simulations and electroluminescence measurements. With increasing aluminum mole fraction in the quantum well x, the in-plane intensity of transverse-electric (TE) polarized light decreases relative to that of the transverse-magnetic polarized light, attributed to a reordering of the valence bands in Al{sub x}Ga{sub 1−x}N. Using k ⋅ p theoretical model calculations, the AlGaN MQW active region design has been optimized, yielding increased TE polarization and thus higher extraction efficiency for bottom-emitting LEDs in the deep UV spectral range. Using (i) narrow quantum wells, (ii) barriers with high aluminum mole fractions, and (iii) compressive growth on patterned aluminum nitride sapphire templates, strongly TE-polarized emission was observed at wavelengths as short as 239 nm.

POLARIZED BEAMS: 1 - Longitudinal electron spin polarization at HERA

Energy Technology Data Exchange (ETDEWEB)

Anon.

1994-09-15

Wednesday 4 May marked a turning point in the art of the manipulation of spins in electron storage rings: longitudinal electron spin polarization (with the spins oriented along the electrons' direction of motion) was established in the electron ring of HERA, the electronproton collider at DESY in Hamburg. A polarization level of about 55% was obtained and polarizations of over 60% were reproducibly obtained in the following days. The beam energy was 27.52 GeV, corresponding to half integer spin tune of 62.5.

Adapting to Population Growth: The Evolutionary Alternative to Malthus

OpenAIRE

Axel Kristinsson; Árni Daníel Júlíusson

2016-01-01

A long-standing debate on the dynamics of population growth in human history has become polarized between a Malthusian stance and a Boserupian one. The former tends to view population growth as limited by carrying capacity, dependent on environment and technology, whereas the latter sees population growth itself as a major inducement to social, economic and technological developments. In this paper the authors experiment with approaching this debate by using recent developments in evolutionar...

Polarization of the vaccination debate on Facebook.

Science.gov (United States)

Schmidt, Ana Lucía; Zollo, Fabiana; Scala, Antonio; Betsch, Cornelia; Quattrociocchi, Walter

2018-06-14

Vaccine hesitancy has been recognized as a major global health threat. Having access to any type of information in social media has been suggested as a potential influence on the growth of anti-vaccination groups. Recent studies w.r.t. other topics than vaccination show that access to a wide amount of content through the Internet without intermediaries resolved into major segregation of the users in polarized groups. Users select information adhering to theirs system of beliefs and tend to ignore dissenting information. The goal was to assess whether users' attitudes are polarized on the topic of vaccination on Facebook and how this polarization develops over time. We perform a thorough quantitative analysis by studying the interaction of 2.6 M users with 298,018 Facebook posts over a time span of seven years and 5 months. We applied community detection algorithms to automatically detect the emergence of communities accounting for the users' activity on the pages. Also, we quantified the cohesiveness of these communities over time. Our findings show that the consumption of content about vaccines is dominated by the echo chamber effect and that polarization increased over the years. Well-segregated communities emerge from the users' consumption habits i.e., the majority of users consume information in favor or against vaccines, not both. The existence of echo chambers may explain why social-media campaigns that provide accurate information have limited reach and be effective only in sub-groups, even fomenting further opinion polarization. The introduction of dissenting information into a sub-group is disregarded and can produce a backfire effect, thus reinforcing the pre-existing opinions within the sub-group. Public health professionals should try to understand the contents of these echo chambers, for example by getting passively involved in such groups. Only then it will be possible to find effective ways of countering anti-vaccination thinking. Copyright �

The temporal and spatial dynamics of income and population growth in Ohio, 1950-1990.

Science.gov (United States)

Fan, C C

1994-01-01

"This paper focuses on spatial variation of growth within a state. Using Ohio as a case study, two hypotheses are extracted from the literature. First, the theories of polarization and polarization reversal suggest that in the old industrial core the leading sector role of manufacturing has diminished in old manufacturing poles, and that income growth trends differ substantially between these old poles and new centres of development. Second, the theories of suburbanization and migration reversals suggest that population growth is contingent upon level of urbanization, and that the relationship has changed drastically between the pre-1970s, 1970s, and post-1970s periods." (SUMMARY IN FRE AND GER) excerpt

Polarized Electrons at Jefferson Laboratory

Energy Technology Data Exchange (ETDEWEB)

Sinclair, C.K.

1997-12-31

The CEBAF accelerator at Jefferson laboratory can deliver CW electron beams to three experimental halls simultaneously. A large fraction of the approved scientific program at the lab requires polarized electron beams. Many of these experiments, both polarized and unpolarized, require high average beam current as well. Since all electrons delivered to the experimental halls originate from the same cathode, delivery of polarized beam to a single hall requires using the polarized source to deliver beam to all experiments in simultaneous operation. The polarized source effort at Jefferson Lab is directed at obtaining very long polarized source operational lifetimes at high average current and beam polarization; at developing the capability to deliver all electrons leaving the polarized source to the experimental halls; and at delivering polarized beam to multiple experimental halls simultaneously.initial operational experience with the polarized source will be presented.

Gellertiella hungarica gen. nov., sp. nov., a novel bacterium of the family Rhizobiaceae isolated from a spa in Budapest.

Science.gov (United States)

Tóth, Erika; Szuróczki, Sára; Kéki, Zsuzsa; Bóka, Károly; Szili-Kovács, Tibor; Schumann, Peter

2017-11-01

A novel alphaproteobacterium, strain RAM11 T , belonging to the family Rhizobiaceae was isolated from the pool water of a thermal bath in Budapest, Hungary. Based on the 16S rRNA gene sequence strain RAM11 T shows the highest sequence similarity values to Ensifer adhaerens Casida A (97.44 %), to Ensifer (syn. Sinorhizobium) americanus CFNEI 156 T (96.87 %) and to Rhizobium azooxidifex Po 20/26 T (96.76 %). The new bacterium is strictly aerobic, its optimum growth occurs at 20-37 °C, between pH 7 and 9 and without NaCl. It is motile due to a single polar flagellum, capable of budding and forms rosettes in liquid culture. The major isoprenoid quinone of strain RAM11 T is Q-10, the major cellular fatty acids are C18 : 1ω7c and 11-MeC18 : 1ω7c. The polar lipid profile contains phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine, an unidentified aminolipid and an unidentified phospholipid. The G+C content of DNA of the type strain is 62.9 mol%. Strain RAM11 T (=DSM 29853 T =NCAIM B.02618 T ) is proposed as type strain of a new genus and species with the proposed name Gellertiella hungarica gen. nov., sp. nov.

Adapting the HSV polarization-color mapping for regions with low irradiance and high polarization.

Science.gov (United States)

Scott Tyo, J; Ratliff, Bradley M; Alenin, Andrey S

2016-10-15

Many mappings from polarization into color have been developed so that polarization information can be displayed. One of the most common of these maps the angle of linear polarization into color hue and degree of linear polarization into color saturation, while preserving the irradiance information from the polarization data. While this strategy enjoys wide popularity, there is a large class of polarization images for which it is not ideal. It is common to have images where the strongest polarization signatures (in terms of degree of polarization) occur in regions of relatively low irradiance: either in shadow in reflective bands or in cold regions in emissive bands. Since the irradiance is low, the chromatic properties of the resulting images are generally not apparent. Here we present an alternate mapping that uses the statistics of the angle of polarization as a measure of confidence in the polarization signature, then amplifies the irradiance in regions of high confidence, and leaves it unchanged in regions of low confidence. Results are shown from an LWIR and a visible spectrum imager.

SuperDARN HF Scattering and Propagation in the Presence of Polar Patches Imaged Using RISR

Science.gov (United States)

Gillies, R. G.; Perry, G. W.; Varney, R. H.; Gillies, D. M.; Donovan, E.

2017-12-01

The global array of High Frequency (HF) Super Dual Auroral Radar Network (SuperDARN) radars continuously monitors ionospheric convection in the middle-to-high latitude region. The radars measure coherent backscatter from decameter scale field-aligned irregularities. One of the main generation mechanisms for these field-aligned irregularities is the gradient drift instability (GDI). The edges of ionospheric density structures, such as polar cap patches, provide ideal locations for GDI growth. The geometry required for GDI growth results in irregularities forming on the trailing edge of polar patches. However, irregularities generated by the non-linear evolution of the GDI can become prevalent throughout the patch within minutes. Modelling the irregularity growth and measurements of backscatter within patches have both confirmed this. One aspect that has often been overlooked in studies of coherent backscatter within patches is the effect of HF propagation on echo location. This study examines HF echo locations in the vicinity of patches that were imaged using the Resolute Bay Incoherent Scatter Radars (RISR). The effect of both vertical and lateral refraction of the HF wave on echo location is examined.

Polarized Moessbauer transitions

International Nuclear Information System (INIS)

Barb, D.

1975-01-01

Theoretical aspects of the emission, absorption and scattering of polarized gamma rays are reviewed for a general case of combined magnetic and electric hyperfine interactions; various possibilities of obtaining polarized gamma sources are described and examples are given of the applications of Moessbauer spectroscopy with polarized gamma rays in solving problems of solid state physics. (A.K.)

Polarization division multiple access with polarization modulation for LOS wireless communications

Directory of Open Access Journals (Sweden)

Cao Bin

2011-01-01

Full Text Available Abstract In this paper, we discuss a potential multiple access and modulation scheme based on polarized states (PS of electromagnetic (EM waves for line-of-sight (LOS communications. The proposed scheme is theoretic different from the existing polar modulation for EDGE and WCDMA systems. We propose the detailed bit representation (modulation and multiple access scheme using PS. Because of the inflexibility of polarization information in the time and frequency domains, as well as independence of frequency and space, the polarization information can be used independently for wireless communications, i.e., another independent resource domain that can be utilized. Due to the independence between the PS and the specific features of signals (such as waveform, bandwidth and data rate, the discussed polarization division multiple access (PDMA and polarization modulation (PM are expected to improve the spectrum utilization effectively. It is proved that the polarization filtering technique can be adopted in the PDMA-PM wireless communications to separate the multiuser signals and demodulate the bit information representing by PS for desired user. Some theoretical analysis is done to demonstrate the feasibility of the proposed scheme, and the simulation results are made to evaluate the performance of the suggested system.

Polarization at SLC

International Nuclear Information System (INIS)

Swartz, M.L.

1988-07-01

The SLAC Linear Collider has been designed to readily accommodate polarized electron beams. Considerable effort has been made to implement a polarized source, a spin rotation system, and a system to monitor the beam polarization. Nearly all major components have been fabricated. At the current time, several source and polarimeter components have been installed. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. It is expected that a beam polarization of 45% will be achieved with no loss in luminosity. 13 refs., 15 figs

Climate change threatens polar bear populations: a stochastic demographic analysis.

Science.gov (United States)

Hunter, Christine M; Caswell, Hal; Runge, Michael C; Regehr, Eric V; Amstrup, Steve C; Stirling, Ian

2010-10-01

The polar bear (Ursus maritimus) depends on sea ice for feeding, breeding, and movement. Significant reductions in Arctic sea ice are forecast to continue because of climate warming. We evaluated the impacts of climate change on polar bears in the southern Beaufort Sea by means of a demographic analysis, combining deterministic, stochastic, environment-dependent matrix population models with forecasts of future sea ice conditions from IPCC general circulation models (GCMs). The matrix population models classified individuals by age and breeding status; mothers and dependent cubs were treated as units. Parameter estimates were obtained from a capture-recapture study conducted from 2001 to 2006. Candidate statistical models allowed vital rates to vary with time and as functions of a sea ice covariate. Model averaging was used to produce the vital rate estimates, and a parametric bootstrap procedure was used to quantify model selection and parameter estimation uncertainty. Deterministic models projected population growth in years with more extensive ice coverage (2001-2003) and population decline in years with less ice coverage (2004-2005). LTRE (life table response experiment) analysis showed that the reduction in lambda in years with low sea ice was due primarily to reduced adult female survival, and secondarily to reduced breeding. A stochastic model with two environmental states, good and poor sea ice conditions, projected a declining stochastic growth rate, log lambdas, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log lambdas approximately - 0.01, which agrees with available (albeit crude) observations of population size. The stochastic model was linked to a set of 10 GCMs compiled by the IPCC; the models were chosen for their ability to reproduce historical observations of sea ice and were forced with "business as usual" (A1B) greenhouse gas emissions. The resulting stochastic population

Polarized electrons at Jefferson laboratory

International Nuclear Information System (INIS)

Sinclair, C.K.

1998-01-01

The CEBAF accelerator at Jefferson laboratory can deliver CW electron beams to three experimental halls simultaneously. A large fraction of the approved scientific program at the lab requires polarized electron beams. Many of these experiments, both polarized and unpolarized, require high average beam current as well. Since all electrons delivered to the experimental halls originate from the same cathode, delivery of polarized beam to a single hall requires using the polarized source to deliver beam to all experiments in simultaneous operation. The polarized source effort at Jefferson Lab is directed at obtaining very long polarized source operational lifetimes at high average current and beam polarization; at developing the capability to deliver all electrons leaving the polarized source to the experimental halls; and at delivering polarized beam to multiple experimental halls simultaneously. Initial operational experience with the polarized source will be presented. copyright 1998 American Institute of Physics

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

International Nuclear Information System (INIS)

Feng, Shih-Wei; Liao, Po-Hsun; Leung, Benjamin; Han, Jung; Yang, Fann-Wei; Wang, Hsiang-Chen

2015-01-01

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantages of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

International Nuclear Information System (INIS)

Zhang, Zi-Hui; Liu, Wei; Ju, Zhengang; Tiam Tan, Swee; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Wang, Liancheng; Wei Sun, Xiao; Volkan Demir, Hilmi

2014-01-01

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zi-Hui; Liu, Wei; Ju, Zhengang; Tiam Tan, Swee; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Wang, Liancheng; Wei Sun, Xiao, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Volkan Demir, Hilmi, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara (Turkey)

2014-06-16

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Feng, Shih-Wei, E-mail: swfeng@nuk.edu.tw; Liao, Po-Hsun [Department of Applied Physics, National University of Kaohsiung, No. 700, Kaohsiung University Rd., Nan Tzu Dist., 811 Kaohsiung, Taiwan (China); Leung, Benjamin; Han, Jung [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Yang, Fann-Wei [Department of Electronic Engineering, Southern Taiwan University of Science and Technology, Tainan, Taiwan (China); Wang, Hsiang-Chen [Graduate Institute of Opto-Mechatronics and Advanced Institute of Manufacturing with High-Tech Innovations (AIM-HI), National Chung Cheng University, Chia-Yi, Taiwan (China)

2015-07-28

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantages of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED.

When the swimming gets tough, the tough form a biofilm.

Science.gov (United States)

Belas, Robert

2013-10-01

Bacteria live either as independent planktonic cells or as members of surface-attached communities called biofilms. Motility and biofilm development are mutually exclusive events, and control of the phase of this 'swim-or-stick' switch involves the ability of the bacterium to sense and respond appropriately to a surface. Cairns et al. (2013) report that the Bacillus subtilis flagellum functions in surface-sensing. Using mutants of B. subtilis that prevent flagellum rotation, they measured the expression and activity of DegU, the response regulator of the two-component DegS-DegU circuit. DegU activity and degU transcription increased when flagellum rotation was prevented, and were dependent on the DegS kinase. Inhibiting flagellar rotation by overexpressing the EpsE flagellar 'clutch' or addition of anti-flagellin antiserum also increased degU transcription and activity. These results suggest B. subtilis senses restriction of flagellum rotation as the cell nears a surface. Inhibition of the flagellum activates the DegS-DegU circuit to turn on biofilm formation, i.e. the flagellum is acting as a mechanosensor of surfaces. B. subtilis joins an ever-expanding group of bacteria, including species of Vibrio, Proteus and Caulobacter that use the flagellum as a surface sensor. © 2013 John Wiley & Sons Ltd.

Suomi National Polar-Orbiting Partnership Visible Infrared Imaging Radiometer Suite Polarization Sensitivity Analysis

Science.gov (United States)

Sun, Junqiang; Xiong, Xiaoxiong; Waluschka, Eugene; Wang, Menghua

2016-01-01

The Visible Infrared Imaging Radiometer Suite (VIIRS) is one of five instruments onboard the Suomi National Polar-Orbiting Partnership (SNPP) satellite that launched from Vandenberg Air Force Base, California, on October 28, 2011. It is a whiskbroom radiometer that provides +/-56.28deg scans of the Earth view. It has 22 bands, among which 14 are reflective solar bands (RSBs). The RSBs cover a wavelength range from 410 to 2250 nm. The RSBs of a remote sensor are usually sensitive to the polarization of incident light. For VIIRS, it is specified that the polarization factor should be smaller than 3% for 410 and 862 nm bands and 2.5% for other RSBs for the scan angle within +/-45deg. Several polarization sensitivity tests were performed prelaunch for SNPP VIIRS. The first few tests either had large uncertainty or were less reliable, while the last one was believed to provide the more accurate information about the polarization property of the instrument. In this paper, the measured data in the last polarization sensitivity test are analyzed, and the polarization factors and phase angles are derived from the measurements for all the RSBs. The derived polarization factors and phase angles are band, detector, and scan angle dependent. For near-infrared bands, they also depend on the half-angle mirror side. Nevertheless, the derived polarization factors are all within the specification, although the strong detector dependence of the polarization parameters was not expected. Compared to the Moderate Resolution Imaging Spectroradiometer on both Aqua and Terra satellites, the polarization effect on VIIRS RSB is much smaller.

Filamentous Growth in Eremothecium Fungi

DEFF Research Database (Denmark)

Oskarsson, Therese

, this thesis deals with some of the aspects of hyphal growth, which is an important virulence factor for pathogenic fungi infecting both humans and plants. Hyphal establishment through continuous polar growth is a complex process, requiring the careful coordination of a large subset of proteins involved......-regulatory activity of AgGts1, the protein could have additional actin organizing properties. In the second and third part, this thesis addresses the use of A. gossypii and its relative E. cymbalariae as model organisms for filamentous growth. A series of assays analyzed the capability of Eremothecium genus fungi...... of molecular tools for E. cymbalariae to enable a faster and more efficient approach for genetic comparisons between Eremothecium genus fungi....

A Si nanocube array polarizer

Science.gov (United States)

Chen, Linghua; Jiang, Yingjie; Xing, Li; Yao, Jun

2017-10-01

We have proposed a full dielectric (silicon) nanocube array polarizer based on a silicon dioxide substrate. Each polarization unit column includes a plurality of equal spaced polarization units. By optimizing the length, the width, the height of the polarization units and the center distance of adjacent polarization unit (x direction and y direction), an extinction ratio (ER) of higher than 25dB was obtained theoretically when the incident light wavelength is 1550nm. while for applications of most polarization optical elements, ER above 10dB is enough. With this condition, the polarizer we designed can work in a wide wavelength range from 1509.31nm to 1611.51nm. Compared with the previous polarizer, we have introduced a polarizer which is a full dielectric device, which solves the problems of low efficiency caused by Ohmic loss and weak coupling. Furthermore, compared with the existing optical polarizers, our polarizer has the advantages of thin thickness, small size, light weight, and low processing difficulty, which is in line with the future development trend of optical elements.

Epitaxial growth of a methoxy-functionalized quaterphenylene on alkali halide surfaces

Energy Technology Data Exchange (ETDEWEB)

Balzer, F., E-mail: fbalzer@mci.sdu.dk [University of Southern Denmark, Mads Clausen Institute, Alsion 2, DK-6400 Sønderborg (Denmark); Sun, R. [University of Southern Denmark, Mads Clausen Institute, Alsion 2, DK-6400 Sønderborg (Denmark); Parisi, J. [University of Oldenburg, Energy and Semiconductor Research Laboratory, Institute of Physics, Carl-von-Ossietzky-Str. 9-11, D-26111 Oldenburg (Germany); Rubahn, H.-G. [University of Southern Denmark, Mads Clausen Institute, Alsion 2, DK-6400 Sønderborg (Denmark); Lützen, A. [University of Bonn, Kekulé Institute of Organic Chemistry and Biochemistry, Gerhard-Domagk-Str. 1, D-53121 Bonn (Germany); Schiek, M. [University of Oldenburg, Energy and Semiconductor Research Laboratory, Institute of Physics, Carl-von-Ossietzky-Str. 9-11, D-26111 Oldenburg (Germany)

2015-12-31

The epitaxial growth of the methoxy functionalized para-quaterphenylene (MOP4) on the (001) faces of the alkali halides NaCl and KCl and on glass is investigated by a combination of low energy electron diffraction (LEED), polarized light microscopy (PLM), atomic force microscopy (AFM), and X-ray diffraction (XRD). Both domains from upright molecules as well as fiber-like crystallites from lying molecules form. Neither a wetting layer from lying molecules nor widespread epitaxial fiber growth on the substrates is detected. Our results focus on the upright standing molecules, which condense into a thin film phase with an enlarged layer spacing compared to the bulk phase. - Highlights: • Growth of a methoxy-functionalized para-phenylene on dielectric surfaces is investigated. • Low-energy electron diffraction and X-ray diffraction techniques are employed for structural characterization. • Epitaxial growth of upright molecules only is documented. • Polarized optical microscopy together with atomic force microscopy complements the findings.

Epitaxial growth of a methoxy-functionalized quaterphenylene on alkali halide surfaces

International Nuclear Information System (INIS)

Balzer, F.; Sun, R.; Parisi, J.; Rubahn, H.-G.; Lützen, A.; Schiek, M.

2015-01-01

The epitaxial growth of the methoxy functionalized para-quaterphenylene (MOP4) on the (001) faces of the alkali halides NaCl and KCl and on glass is investigated by a combination of low energy electron diffraction (LEED), polarized light microscopy (PLM), atomic force microscopy (AFM), and X-ray diffraction (XRD). Both domains from upright molecules as well as fiber-like crystallites from lying molecules form. Neither a wetting layer from lying molecules nor widespread epitaxial fiber growth on the substrates is detected. Our results focus on the upright standing molecules, which condense into a thin film phase with an enlarged layer spacing compared to the bulk phase. - Highlights: • Growth of a methoxy-functionalized para-phenylene on dielectric surfaces is investigated. • Low-energy electron diffraction and X-ray diffraction techniques are employed for structural characterization. • Epitaxial growth of upright molecules only is documented. • Polarized optical microscopy together with atomic force microscopy complements the findings.

Beyond the Mean: Sensitivities of the Variance of Population Growth.

Science.gov (United States)

Trotter, Meredith V; Krishna-Kumar, Siddharth; Tuljapurkar, Shripad

2013-03-01

Populations in variable environments are described by both a mean growth rate and a variance of stochastic population growth. Increasing variance will increase the width of confidence bounds around estimates of population size, growth, probability of and time to quasi-extinction. However, traditional sensitivity analyses of stochastic matrix models only consider the sensitivity of the mean growth rate. We derive an exact method for calculating the sensitivity of the variance in population growth to changes in demographic parameters. Sensitivities of the variance also allow a new sensitivity calculation for the cumulative probability of quasi-extinction. We apply this new analysis tool to an empirical dataset on at-risk polar bears to demonstrate its utility in conservation biology We find that in many cases a change in life history parameters will increase both the mean and variance of population growth of polar bears. This counterintuitive behaviour of the variance complicates predictions about overall population impacts of management interventions. Sensitivity calculations for cumulative extinction risk factor in changes to both mean and variance, providing a highly useful quantitative tool for conservation management. The mean stochastic growth rate and its sensitivities do not fully describe the dynamics of population growth. The use of variance sensitivities gives a more complete understanding of population dynamics and facilitates the calculation of new sensitivities for extinction processes.

Polarization: A Must for Fusion

Directory of Open Access Journals (Sweden)

Guidal M.

2012-10-01

Full Text Available Recent realistic simulations confirm that the polarization of the fuel would improve significantly the DT fusion efficiency. We have proposed an experiment to test the persistence of the polarization in a fusion process, using a terawatt laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse producing a 3He and a neutron in the final state. The angular distribution of the neutrons and the change in the corresponding total cross section are related to the polarization persistence. The experimental polarization of DT fuel is a technological challenge. Possible paths for Magnetic Confinement Fusion (MCF and for Inertial Confinement Fusion (ICF are reviewed. For MCF, polarized gas can be used. For ICF, cryogenic targets are required. We consider both, the polarization of gas and the polarization of solid DT, emphasizing the Dynamic Nuclear polarization (DNP of HD and DT molecules.

PolarTREC—A Model Program for Taking Polar Literacy into the Future

Science.gov (United States)

Warburton, J.; Timm, K.; Larson, A. M.

2009-12-01

Polar TREC—Teachers and Researchers Exploring and Collaborating, is a three-year (2007-2009) NSF-funded International Polar Year (IPY) teacher professional development program that advances Science, Technology, Engineering, and Mathematics (STEM) education by improving teacher content knowledge and instructional practices through Teacher Research Experiences (TRE) in the Arctic and Antarctic. Leveraging profound changes and fascinating science taking place in the polar regions, PolarTREC broadly disseminates activities and products to students, educators, researchers, and the public, connecting them with the Arctic and Antarctica and sustaining the widespread interest in the polar regions and building on the enthusiasm that was generated through IPY. Central to the PolarTREC Teacher Research Experience Model, over 40 teachers have spent two to eight weeks participating in hands-on research in the polar regions and sharing their experiences with diverse audiences via live events, online multimedia journals, and interactive bulletin boards. The Connecting Arctic/Antarctic Researchers and Educators (CARE) Network unifies learning community members participants, alumni, and others, developing a sustainable association of education professionals networking to share and apply polar STEM content and pedagogical skills. Educator and student feedback from preliminary results of the program evaluation has shown that PolarTREC’s comprehensive program activities have many positive impacts on educators and their ability to teach science concepts and improve their teaching methods. Additionally, K-12 students polled in interest surveys showed significant changes in key areas including amount of time spent in school exploring research activities, importance of understanding science for future work, importance of understanding the polar regions as a person in today’s world, as well as increased self-reported knowledge and interest in numerous science content areas. Building

Generating highly polarized nuclear spins in solution using dynamic nuclear polarization

DEFF Research Database (Denmark)

Wolber, J.; Ellner, F.; Fridlund, B.

2004-01-01

A method to generate strongly polarized nuclear spins in solution has been developed, using Dynamic Nuclear Polarization (DNP) at a temperature of 1.2K, and at a field of 3.354T, corresponding to an electron spin resonance frequency of 94GHz. Trityl radicals are used to directly polarize 13C...... and other low-γ nuclei. Subsequent to the DNP process, the solid sample is dissolved rapidly with a warm solvent to create a solution of molecules with highly polarized nuclear spins. Two main applications are proposed: high-resolution liquid state NMR with enhanced sensitivity, and the use...

Effect of magnetic field and radiative condensation on the Jeans instability of dusty plasma with polarization force

International Nuclear Information System (INIS)

Prajapati, R.P.

2013-01-01

The Jeans instability of self-gravitating dusty plasma with polarization force is investigated considering the effects of magnetic field, dust temperature and radiative condensation. The condition of Jeans instability and expression of critical Jeans wave number are obtained which depend upon polarization force and dust temperature but these are unaffected by the presence of magnetic field. The radiative heat-loss functions also modify the Jeans condition of instability and expression of critical Jeans wave number. It is observed that the polarization force and ratio of radiative heat-loss functions have destabilizing while magnetic field and dust temperature have stabilizing influence on the growth rate of Jeans instability.

Polarized Light Microscopy

Science.gov (United States)

Frandsen, Athela F.

2016-01-01

Polarized light microscopy (PLM) is a technique which employs the use of polarizing filters to obtain substantial optical property information about the material which is being observed. This information can be combined with other microscopy techniques to confirm or elucidate the identity of an unknown material, determine whether a particular contaminant is present (as with asbestos analysis), or to provide important information that can be used to refine a manufacturing or chemical process. PLM was the major microscopy technique in use for identification of materials for nearly a century since its introduction in 1834 by William Fox Talbot, as other techniques such as SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared spectroscopy), XPD (X-ray Powder Diffraction), and TEM (Transmission Electron Microscopy) had not yet been developed. Today, it is still the only technique approved by the Environmental Protection Agency (EPA) for asbestos analysis, and is often the technique first applied for identification of unknown materials. PLM uses different configurations in order to determine different material properties. With each configuration additional clues can be gathered, leading to a conclusion of material identity. With no polarizing filter, the microscope can be used just as a stereo optical microscope, and view qualities such as morphology, size, and number of phases. With a single polarizing filter (single polars), additional properties can be established, such as pleochroism, individual refractive indices, and dispersion staining. With two polarizing filters (crossed polars), even more can be deduced: isotropy vs. anisotropy, extinction angle, birefringence/degree of birefringence, sign of elongation, and anomalous polarization colors, among others. With the use of PLM many of these properties can be determined in a matter of seconds, even for those who are not highly trained. McCrone, a leader in the field of polarized light microscopy, often

Non-polar InGaN quantum dot emission with crystal-axis oriented linear polarization

Energy Technology Data Exchange (ETDEWEB)

Reid, Benjamin P. L., E-mail: benjamin.reid@physics.ox.ac.uk; Chan, Christopher C. S.; Taylor, Robert A. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Kocher, Claudius [Department of Physics, University of Konstanz, Konstanz 78457 (Germany); Zhu, Tongtong; Oehler, Fabrice; Oliver, Rachel A. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

2015-04-27

Polarization sensitive photoluminescence is performed on single non-polar InGaN quantum dots. The studied InGaN quantum dots are found to have linearly polarized emission with a common polarization direction defined by the [0001] crystal axis. Around half of ∼40 studied dots have a polarization degree of 1. For those lines with a polarization degree less than 1, we can resolve fine structure splittings between −800 μeV and +800 μeV, with no clear correlation between fine structure splitting and emission energy.

The Physics of Polarization

Science.gov (United States)

Landi Degl'Innocenti, Egidio

2015-10-01

The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

Fiber-Based Polarization Diversity Detection for Polarization-Sensitive Optical Coherence Tomography

Directory of Open Access Journals (Sweden)

Hamid Pahlevaninezhad

2014-09-01

Full Text Available We present a new fiber-based polarization diversity detection (PDD scheme for polarization sensitive optical coherence tomography (PSOCT. This implementation uses a new custom miniaturized polarization-maintaining fiber coupler with single mode (SM fiber inputs and polarization maintaining (PM fiber outputs. The SM fiber inputs obviate matching the optical lengths of the two orthogonal OCT polarization channels prior to interference while the PM fiber outputs ensure defined orthogonal axes after interference. Advantages of this detection scheme over those with bulk optics PDD include lower cost, easier miniaturization, and more relaxed alignment and handling issues. We incorporate this PDD scheme into a galvanometer-scanned OCT system to demonstrate system calibration and PSOCT imaging of an achromatic quarter-wave plate, fingernail in vivo, and chicken breast, salmon, cow leg, and basa fish muscle samples ex vivo.

Bringing Society to a Changing Polar Ocean: Polar Interdisciplinary Coordinated Education (ICE)

Science.gov (United States)

Schofield, O.

2015-12-01

Environmental changes in the Arctic and Antarctic appear to be accelerating and scientists are trying to understand both the patterns and the impacts of change. These changes will have profound impact on humanity and create a need for public education about these critical habitats. We have focused on a two-pronged strategy to increase public awareness as well as enable educators to discuss comfortably the implications of climate change. Our first focus is on entraining public support through the development of science documentaries about the science and people who conduct it. Antarctic Edge is a feature length award-winning documentary about climate change that has been released in May 2015 and has garnered interest in movie theatres and on social media stores (NetFlix, ITunes). This broad outreach is coupled with our group's interest assisting educators formally. The majority of current polar education is focused on direct educator engagement through personal research experiences that have impact on the participating educators' classrooms. Polar Interdisciplinary Coordinated Education (ICE) proposes to improve educator and student engagement in polar sciences through exposure to scientists and polar data. Through professional development and the creation of data tools, Polar ICE will reduce the logistical costs of bringing polar science to students in grades 6-16. We will provide opportunities to: 1) build capacity of polar scientists in communicating and engaging with diverse audiences; 2) create scalable, in-person and virtual opportunities for educators and students to engage with polar scientists and their research through data visualizations, data activities, educator workshops, webinars, and student research symposia; and 3) evaluate the outcomes of Polar ICE and contribute to our understanding of science education practices. We will use a blended learning approach to promote partnerships and cross-disciplinary sharing. This combined multi-pronged approach

Stochastic models for tumoral growth

Science.gov (United States)

Escudero, Carlos

2006-02-01

Strong experimental evidence has indicated that tumor growth belongs to the molecular beam epitaxy universality class. This type of growth is characterized by the constraint of cell proliferation to the tumor border and the surface diffusion of cells at the growing edge. Tumor growth is thus conceived as a competition for space between the tumor and the host, and cell diffusion at the tumor border is an optimal strategy adopted for minimizing the pressure and helping tumor development. Two stochastic partial differential equations are reported in this paper in order to correctly model the physical properties of tumoral growth in (1+1) and (2+1) dimensions. The advantage of these models is that they reproduce the correct geometry of the tumor and are defined in terms of polar variables. An analysis of these models allows us to quantitatively estimate the response of the tumor to an unfavorable perturbation during growth.

Identification of the arabidopsis RAM/MOR signalling network: adding new regulatory players in plant stem cell maintenance and cell polarization

Science.gov (United States)

Zermiani, Monica; Begheldo, Maura; Nonis, Alessandro; Palme, Klaus; Mizzi, Luca; Morandini, Piero; Nonis, Alberto; Ruperti, Benedetto

2015-01-01

Background and Aims The RAM/MOR signalling network of eukaryotes is a conserved regulatory module involved in co-ordination of stem cell maintenance, cell differentiation and polarity establishment. To date, no such signalling network has been identified in plants. Methods Genes encoding the bona fide core components of the RAM/MOR pathway were identified in Arabidopsis thaliana (arabidopsis) by sequence similarity searches conducted with the known components from other species. The transcriptional network(s) of the arabidopsis RAM/MOR signalling pathway were identified by running in-depth in silico analyses for genes co-regulated with the core components. In situ hybridization was used to confirm tissue-specific expression of selected RAM/MOR genes. Key Results Co-expression data suggested that the arabidopsis RAM/MOR pathway may include genes involved in floral transition, by co-operating with chromatin remodelling and mRNA processing/post-transcriptional gene silencing factors, and genes involved in the regulation of pollen tube polar growth. The RAM/MOR pathway may act upstream of the ROP1 machinery, affecting pollen tube polar growth, based on the co-expression of its components with ROP-GEFs. In silico tissue-specific co-expression data and in situ hybridization experiments suggest that different components of the arabidopsis RAM/MOR are expressed in the shoot apical meristem and inflorescence meristem and may be involved in the fine-tuning of stem cell maintenance and cell differentiation. Conclusions The arabidopsis RAM/MOR pathway may be part of the signalling cascade that converges in pollen tube polarized growth and in fine-tuning stem cell maintenance, differentiation and organ polarity. PMID:26078466

Techniques in polarization physics

International Nuclear Information System (INIS)

Clausnitzer, G.

1974-01-01

A review of the current status of the technical tools necessary to perform different kinds of polarization experiments is presented, and the absolute and relative accuracy with which data can be obtained is discussed. A description of polarized targets and sources of polarized fast neutrons is included. Applications of polarization techniques to other fields is mentioned briefly. (14 figures, 3 tables, 110 references) (U.S.)

Polarization: A must for fusion

Directory of Open Access Journals (Sweden)

Didelez J.-P.

2013-11-01

Full Text Available The complete polarization of DT fuel would increase the fusion reactivity by 50% in magnetic as well as in inertial confinements. The persistence of polarization in a fusion process could be tested, using a terawatt laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse producing a 3He and a neutron in the final state. The angular distribution of the emitted neutrons and the change in the corresponding total Cross Section (CS can sign the polarization persistence. The polarization of solid H2, D2 or T2 Hydrogen isotopes is very difficult. However, it has been possible to polarize HD, a hetero-molecular form of Hydrogen, by static polarization, at very low temperature and very high field. The radioactivity of DT molecules forbids there high polarization by the static method, therefore one has to develop the Dynamic Nuclear Polarization (DNP by RF transitions. The DNP of HD has been investigated in the past. The magnetic properties of HD and DT molecules are very similar, it is therefore expected that any polarization result obtained with HD could be extrapolated to DT.

An elliptically-polarizing undulator with phase adjustable energy and polarization

International Nuclear Information System (INIS)

Lidia, S.

1993-08-01

The authors present a planar helical undulator designed to produce elliptically polarized light. Helical magnetic fields may be produced by a variety of undulators with four parallel cassettes of magnets. In their design, all cassettes are mounted in two planes on slides so that they may be moved parallel to the electron beam. This allows the undulator to produce x-rays of left- or right-handed elliptical or circular polarization as well as horizontal or vertical linear polarization. In model calculations, they have found that by sliding the top pair of rows with respect to the bottom pair, or the left pair with respect to the right pair, they retain the polarization setting but change the magnetic field strength, and hence the x-ray energy. This allows them to select both energy and polarization by independent phase adjustments alone, without changing the gap between the rows. Such a design may be simpler to construct than an adjustable gap machine. The authors present calculations that model its operation and its effects on an electron beam

Linearly polarized photons at ELSA

Energy Technology Data Exchange (ETDEWEB)

Eberhardt, Holger [Physikalisches Institut, Universitaet Bonn (Germany)

2009-07-01

To investigate the nucleon resonance regime in meson photoproduction, double polarization experiments are currently performed at the electron accelerator ELSA in Bonn. The experiments make use of a polarized target and circularly or linearly polarized photon beams. Linearly polarized photons are produced by coherent bremsstrahlung from an accurately aligned diamond crystal. The orientation of the crystal with respect to the electron beam is measured using the Stonehenge-Technique. Both, the energy of maximum polarization and the plane of polarization, can be deliberately chosen for the experiment. The linearly polarized beam provides the basis for the measurement of azimuthal beam asymmetries, such as {sigma} (unpolarized target) and G (polarized target). These observables are extracted in various single and multiple meson photoproduction channels.

Polarized atomic beams for targets

International Nuclear Information System (INIS)

Grueebler, W.

1984-01-01

The basic principle of the production of polarized atomic hydrogen and deuterium beams are reviewed. The status of the present available polarization, density and intensity are presented. The improvement of atomic beam density by cooling the hydrogen atoms to low velocity is discussed. The possible use of polarized atomic beams as targets in storage rings is shown. It is proposed that polarized atomic beams can be used to produce polarized gas targets with high polarization and greatly improved density

Polarized Proton Collisions at RHIC

CERN Document Server

Bai, Mei; Alekseev, Igor G; Alessi, James; Beebe-Wang, Joanne; Blaskiewicz, Michael; Bravar, Alessandro; Brennan, Joseph M; Bruno, Donald; Bunce, Gerry; Butler, John J; Cameron, Peter; Connolly, Roger; De Long, Joseph; Drees, Angelika; Fischer, Wolfram; Ganetis, George; Gardner, Chris J; Glenn, Joseph; Hayes, Thomas; Hseuh Hsiao Chaun; Huang, Haixin; Ingrassia, Peter; Iriso, Ubaldo; Laster, Jonathan S; Lee, Roger C; Luccio, Alfredo U; Luo, Yun; MacKay, William W; Makdisi, Yousef; Marr, Gregory J; Marusic, Al; McIntyre, Gary; Michnoff, Robert; Montag, Christoph; Morris, John; Nicoletti, Tony; Oddo, Peter; Oerter, Brian; Osamu, Jinnouchi; Pilat, Fulvia Caterina; Ptitsyn, Vadim; Roser, Thomas; Satogata, Todd; Smith, Kevin T; Svirida, Dima; Tepikian, Steven; Tomas, Rogelio; Trbojevic, Dejan; Tsoupas, Nicholaos; Tuozzolo, Joseph; Vetter, Kurt; Wilinski, Michelle; Zaltsman, Alex; Zelenski, Anatoli; Zeno, Keith; Zhang, S Y

2005-01-01

The Relativistic Heavy Ion Collider~(RHIC) provides not only collisions of ions but also collisions of polarized protons. In a circular accelerator, the polarization of polarized proton beam can be partially or fully lost when a spin depolarizing resonance is encountered. To preserve the beam polarization during acceleration, two full Siberian snakes were employed in RHIC to avoid depolarizing resonances. In 2003, polarized proton beams were accelerated to 100~GeV and collided in RHIC. Beams were brought into collisions with longitudinal polarization at the experiments STAR and PHENIX by using spin rotators. RHIC polarized proton run experience demonstrates that optimizing polarization transmission efficiency and improving luminosity performance are significant challenges. Currently, the luminosity lifetime in RHIC is limited by the beam-beam effect. The current state of RHIC polarized proton program, including its dedicated physics run in 2005 and efforts to optimize luminosity production in beam-beam limite...

Polarization recovery through scattering media.

Science.gov (United States)

de Aguiar, Hilton B; Gigan, Sylvain; Brasselet, Sophie

2017-09-01

The control and use of light polarization in optical sciences and engineering are widespread. Despite remarkable developments in polarization-resolved imaging for life sciences, their transposition to strongly scattering media is currently not possible, because of the inherent depolarization effects arising from multiple scattering. We show an unprecedented phenomenon that opens new possibilities for polarization-resolved microscopy in strongly scattering media: polarization recovery via broadband wavefront shaping. We demonstrate focusing and recovery of the original injected polarization state without using any polarizing optics at the detection. To enable molecular-level structural imaging, an arbitrary rotation of the input polarization does not degrade the quality of the focus. We further exploit the robustness of polarization recovery for structural imaging of biological tissues through scattering media. We retrieve molecular-level organization information of collagen fibers by polarization-resolved second harmonic generation, a topic of wide interest for diagnosis in biomedical optics. Ultimately, the observation of this new phenomenon paves the way for extending current polarization-based methods to strongly scattering environments.

On feasibility of the experiments with a polarized deuteron beam and a polarized target at Charles University in relation with polarized fusion

International Nuclear Information System (INIS)

Plis, Yu.A.

2001-01-01

There is an interest in the problem of polarized fusion with the neutron-free d 3 He reaction. Up to now, the experimental data on the cross sections of two dd reactions, which produce neutrons at once or through secondary dt reaction, are absent for polarized deuterons. There is a relatively cheap way to carry out the experiments with polarized deuterons at the Charles University in Prague. A polarized deuteron beam with energy from 100 keV up to approximately 1 MeV may be produced on the Van de Graaff accelerator by the channeling of a deuteron beam through magnetized Ni single crystal foil, according M. Kaminsky [Phys. Rev. Lett. 23, 819 (1969)]. This method permits to produce a polarized deuteron beam of an energy ≤1 MeV with a current of ∼1 nA, vector polarization P 3 up to 2/3 and tensor polarization P 33 =0. It will be necessary to modify the existing polarized target at Charles University for work with a low energy deuteron beam [N. S. Borisov et al., Nucl. Instr. and Meth. A 345, 421 (1994)

Polarized particles in storage rings

International Nuclear Information System (INIS)

Derbenev, Ya.S.; Kondratenko, A.M.; Serednyakov, S.I.; Skrinskij, A.N.; Tumajkin, G.M.; Shatunov, Yu.M.

1977-01-01

Experiments with polarized beams on the VEPP-2M and SPEAK storage rings are described. Possible methods of producing polarized particle beams in storage rings as well as method of polarization monitoring are counted. Considered are the processes of radiation polarization of electrons and positrons. It is shown, that to preserve radiation polarization the introduction of regions with a strong sign-variable magnetic field is recommended. Methods of polarization measurement are counted. It is suggested for high energies to use dependence of synchrotron radiation power on transverse polarization of electrons and positrons. Examples of using polarizability of colliding beams in storage rings are presented

Polarized neutron capture in polarized 59Co and 165Ho nuclei

International Nuclear Information System (INIS)

Bosman, J.J.

1976-01-01

Gamma spectroscopy on the reactions 59 Co(n,γ) 60 Co and 165 Ho(n,γ) 166 Ho with polarized neutrons and polarized targets enabled the assignment of spins to 36 levels in 60 Co and 15 levels in 166 Ho. Several of them had not been reported earlier. The techniques used to polarize neutron beams and targets and the gamma-spectroscopy are extensively discussed

Review of polarized ammonium target

International Nuclear Information System (INIS)

Matsuda, Tatsuo

1987-01-01

Recently, ammonia (NH 3 ) and deutron ammonia (ND 3 ), instead of conventional alcohol substances, have been used more frequently as a polarized target substance for experiments of polarization at high energy regions. This article reviews major features of the polarized (deutron) ammonia targets. The dynamic nuclear polarization (DNT) method is widely used in high energy polarization experiments. While only a low polarization degree of hydrogen nucleus of 1.7 percent can be obtained by the Brute force method, DNP can produce polarization as high as ∼ 90 percent (2.5 T, ∼ 200 mK). In 1979, ammonia was irradiated with radiations to form NH 2 free radicals, resulting in the achievement of a high polarization degree of greater than 90 percent (hydrogen). Since then, ammonia and deutron ammonia have increasingly been replacing alcohols including butanol. Irradiation of a target substance with radiations destroys the structure of the substance, leading to a decrease in polarization degree. However, ammonia produces unpaired electrons as a result of irradiation, allowing it to be highly resistant to radiation. This report also present some study results, including observations on effects of radiation on the polarization degree of a target, effects of annealing, and polarization of 14 N. A process for producing an ammonia target is also described. (Nogami, K.)

Achievement of transportable polarized D, in solid HD, with a one day passively maintained polarization

International Nuclear Information System (INIS)

Honig, A.; Alexander, N.; Fan, Q.; Wei, X.; Yu, Y.Y.

1993-01-01

At a previous workshop, we discussed evaporating solid HD with spin-polarized deuterons to produce a high density polarized deuteron gaseous internal target. Since then, we have achieved in solid HD 38% polarized D, whose spin-lattice relaxation time at 1.5 K in a field of 0.1 T is of the order of a day. Optimization of the procedure with the present apparatus should result in 60% D polarization, and longer polarization holding times. The polarized sample of approximately 0.2 cm 3 volume used here is extractable from the dilution refrigerator with a cold-transfer apparatus which maintains the sample at or below 5 K, insuring retention of the high polarization. It is subsequently insertable into a variety of systems, and employable as a polarized solid, liquid, or gas. We are exploring the possibility of extending the polarization maintenance time to about a month (with a matched 1 month preparation time), of polarizing metastably H as well as D, and of producing much larger samples, of the order of 100 cm 3

Acceleration of polarized particles

International Nuclear Information System (INIS)

Buon, J.

1992-05-01

The spin kinetics of polarized beams in circular accelerators is reviewed in the case of spin-1/2 particles (electrons and protons) with emphasis on the depolarization phenomena. The acceleration of polarized proton beams in synchrotrons is described together with the cures applied to reduce depolarization, including the use of 'Siberian Snakes'. The in-situ polarization of electrons in storage rings due to synchrotron radiation is studied as well as depolarization in presence of ring imperfections. The applications of electron polarization to accurately calibrate the rings in energy and to use polarized beams in colliding-beam experiments are reviewed. (author) 76 refs., 19 figs., 1 tab

Role of calmodulin and calcineurin in regulating flagellar motility and wave polarity in Leishmania.

Science.gov (United States)

Mukhopadhyay, Aakash Gautam; Dey, Chinmoy Sankar

2017-11-01

We have previously reported the involvement of cyclic AMP in regulating flagellar waveforms in Leishmania. Here, we investigated the roles of calcium, calmodulin, and calcineurin in flagellar motility regulation in L. donovani. Using high-speed videomicroscopy, we show that calcium-independent calmodulin and calcineurin activity is necessary for motility in Leishmania. Inhibition of calmodulin and calcineurin induced ciliary beats interrupting flagellar beating in both live (in vivo) and ATP-reactivated (in vitro) parasites. Our results indicate that signaling mediated by calmodulin and calcineurin operates antagonistically to cAMP signaling in regulating the waveforms of Leishmania flagellum. These two pathways are possibly involved in maintaining the balance between the two waveforms, essential for responding to environmental cues, survival, and infectivity.

Determination of the polarization states of an arbitrary polarized terahertz beam: vectorial vortex analysis.

Science.gov (United States)

Wakayama, Toshitaka; Higashiguchi, Takeshi; Oikawa, Hiroki; Sakaue, Kazuyuki; Washio, Masakazu; Yonemura, Motoki; Yoshizawa, Toru; Tyo, J Scott; Otani, Yukitoshi

2015-03-24

Vectorial vortex analysis is used to determine the polarization states of an arbitrarily polarized terahertz (0.1-1.6 THz) beam using THz achromatic axially symmetric wave (TAS) plates, which have a phase retardance of Δ = 163° and are made of polytetrafluorethylene. Polarized THz beams are converted into THz vectorial vortex beams with no spatial or wavelength dispersion, and the unknown polarization states of the incident THz beams are reconstructed. The polarization determination is also demonstrated at frequencies of 0.16 and 0.36 THz. The results obtained by solving the inverse source problem agree with the values used in the experiments. This vectorial vortex analysis enables a determination of the polarization states of the incident THz beam from the THz image. The polarization states of the beams are estimated after they pass through the TAS plates. The results validate this new approach to polarization detection for intense THz sources. It could find application in such cutting edge areas of physics as nonlinear THz photonics and plasmon excitation, because TAS plates not only instantaneously elucidate the polarization of an enclosed THz beam but can also passively control THz vectorial vortex beams.

Extensive molecular differences between anterior- and posterior-half-sclerotomes underlie somite polarity and spinal nerve segmentation

Directory of Open Access Journals (Sweden)

Keynes Roger J

2009-05-01

Full Text Available Abstract Background The polarization of somite-derived sclerotomes into anterior and posterior halves underlies vertebral morphogenesis and spinal nerve segmentation. To characterize the full extent of molecular differences that underlie this polarity, we have undertaken a systematic comparison of gene expression between the two sclerotome halves in the mouse embryo. Results Several hundred genes are differentially-expressed between the two sclerotome halves, showing that a marked degree of molecular heterogeneity underpins the development of somite polarity. Conclusion We have identified a set of genes that warrant further investigation as regulators of somite polarity and vertebral morphogenesis, as well as repellents of spinal axon growth. Moreover the results indicate that, unlike the posterior half-sclerotome, the central region of the anterior-half-sclerotome does not contribute bone and cartilage to the vertebral column, being associated instead with the development of the segmented spinal nerves.

Polarized light and optical measurement

CERN Document Server

Clarke, D N; Ter Haar, D

2013-01-01

Polarized Light and Optical Measurement is a five-chapter book that begins with a self-consistent conceptual picture of the phenomenon of polarization. Chapter 2 describes a number of interactions of light and matter used in devising optical elements in polarization studies. Specific optical elements are given in Chapter 3. The last two chapters explore the measurement of the state of polarization and the various roles played in optical instrumentation by polarization and polarization-sensitive elements. This book will provide useful information in this field of interest for research workers,

Characterization of as-grown and adsorbate-covered N-polar InN surfaces using in situ photoelectron spectroscopy

International Nuclear Information System (INIS)

Eisenhardt, Anja; Himmerlich, Marcel; Krischok, Stefan

2012-01-01

The surface electronic properties and adsorption behaviour of as-grown and oxidized N-polar InN films are characterized by photoelectron spectroscopy (XPS, UPS). The epitaxial growth of the InN layers was performed by plasma-assisted molecular beam epitaxy on GaN/6H-SiC(000-1). After growth and in situ characterization the InN surfaces were exposed to molecular oxygen to evaluate the adsorption behaviour of O 2 on N-polar InN and to study its impact on the surface electronic properties of the III-nitride material. The results are compared with studies on In-polar InN on GaN/sapphire templates. The as-grown N-polar InN surface exhibits a pronounced surface state at a binding energy of ∝1.6 eV. The valence band minimum lies about 0.8-1.0 eV below the surface Fermi level. Additionally, the XPS core level binding energies for InN(000-1) are reduced compared to InN(0001) films, indicating different surface band bending for clean N-polar and In-polar InN, respectively. The interaction of molecular oxygen with the InN(000-1) surface leads to a downward band bending by 0.1 eV compared to the initial state. Additional adsorption of species from the residual gas of the UHV chamber increases the surface downward band bending. Furthermore two pronounced oxygen related states with an energy distance of ∝5 eV could be detected in the valence band region. The adsorbed oxygen results in an additional component in the N1s core level spectra, which is interpreted as formation of NO x bonds. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Towards helium-3 neutron polarizers

International Nuclear Information System (INIS)

Tasset, F.

1995-01-01

With a large absorption cross-section entirely due to antiparallel spin capture, polarized helium-3 is presently the most promising broad-band polarizer for thermal and epithermal neutrons. Immediate interest was raised amongst the neutron community when a dense gaseous 3 He polarizer was used for the first time in 1988, on a pulsed neutron beam at Los Alamos. With 20 W of laser power on a 30 cm long, 8.6 atm target, 40% 3 He polarization was achieved in a recent polarized electron scattering experiment at SLAC. In this technique the 3 He nuclei are polarized directly at an appropriate high pressure through spin-exchange collisions with a thick, optically pumped rubidium vapor. A different and competitive approach is being presently developed at Mainz University in collaboration with ENS Paris and now the ILL. A discharge is established in pure 3 He at low pressure producing excited metastable atoms which can be optically pumped with infra-red light. Highly effective exchange collision with the atoms remaining in the ground state quickly produces 75% polarization at 1.5 mbar. A truly non-magnetic system then compresses the polarized gas up to several bars as required. The most recent machine comprises a two-stage glass-titanium compressor. In less than 1 h it can inflate a 100 cm 3 target cell with three bars of polarized gas. The very long relaxation times (several days) now being obtained at high pressure with a special metallic coating on the glass walls, the polarized cell can be detached and inserted in the neutron beam as polarizer. We expect 50% 3 He-polarization to be reached soon, allowing such filters to compete favorably with existing Heusler-crystal polarizers at thermal and short neutron wavelengths. It must be stressed that such a system based on a 3 He polarization factory able to feed several passive, transportable, polarizers is well matched to neutron scattering needs. (orig.)

Design of reproducible polarized and non-polarized edge filters using genetic algorithm

International Nuclear Information System (INIS)

Ejigu, Efrem Kebede; Lacquet, B M

2010-01-01

Recent advancement in optical fibre communications technology is partly due to the advancement of optical thin film technology. The advancement of optical thin film technology includes the development of new and existing optical filter design methods. The genetic algorithm is one of the new design methods that show promising results in designing a number of complicated design specifications. It is the finding of this study that the genetic algorithm design method, through its optimization capability, can give more reliable and reproducible designs of any specifications. The design method in this study optimizes the thickness of each layer to get to the best possible solution. Its capability and unavoidable limitations in designing polarized and non-polarized edge filters from absorptive and dispersive materials is well demonstrated. It is also demonstrated that polarized and non-polarized designs from the genetic algorithm are reproducible with great success. This research has accomplished the great task of formulating a computer program using the genetic algorithm in a Matlab environment for the design of a reproducible polarized and non-polarized filters of any sort from any kind of materials

A link between mitotic entry and membrane growth suggests a novel model for cell size control.

Science.gov (United States)

Anastasia, Steph D; Nguyen, Duy Linh; Thai, Vu; Meloy, Melissa; MacDonough, Tracy; Kellogg, Douglas R

2012-04-02

Addition of new membrane to the cell surface by membrane trafficking is necessary for cell growth. In this paper, we report that blocking membrane traffic causes a mitotic checkpoint arrest via Wee1-dependent inhibitory phosphorylation of Cdk1. Checkpoint signals are relayed by the Rho1 GTPase, protein kinase C (Pkc1), and a specific form of protein phosphatase 2A (PP2A(Cdc55)). Signaling via this pathway is dependent on membrane traffic and appears to increase gradually during polar bud growth. We hypothesize that delivery of vesicles to the site of bud growth generates a signal that is proportional to the extent of polarized membrane growth and that the strength of the signal is read by downstream components to determine when sufficient growth has occurred for initiation of mitosis. Growth-dependent signaling could explain how membrane growth is integrated with cell cycle progression. It could also control both cell size and morphogenesis, thereby reconciling divergent models for mitotic checkpoint function.

Polarized target as analyzer of polarization of particle beam with spin Ssub(B)=1/2

International Nuclear Information System (INIS)

Golovin, V.M.; Golubeva, M.B.; Gornushkin, Yu.A.

1982-01-01

A possibility of using a polarized target as a target analyzer of beam particle polarization (Ssub(T)=1/2 Psub(T) vector) so that all the components of beam polarization Ssub(B)=1/2 anti Psub(B) should be determined in one experiment, is revealed. A proton polarization target is considered as a polarization target-analyzer. Asub(SK) and Asub(kk) asymmetry tensors are considered for elastic pp and pn scatterings by amplitudes of NN scattering which attain the values of 0.3-0.9 at 95-400 MeV. Asub(kk)(pp) and Asub(sk)(pp) are experimentally measured in the 445-576 MeV range. It is found that their highest absolute values are equal to 0.4-0.5 and 0.2-0.3 respectively. Elastic proton scattering on polarized electrons may be another variant of using polarized target for measuring proton beam polarization. Asub(sk) and Asub(kk) components of asymmetry tensor of elastic pe scattering are graphically presented. A possibility of using a polarized charge with spin I=1/2 as a target-analyzer of particle beam polarization is marked

Jeans instability in collisional strongly coupled dusty plasma with radiative condensation and polarization force

International Nuclear Information System (INIS)

Prajapati, R. P.; Bhakta, S.; Chhajlani, R. K.

2016-01-01

The influence of dust-neutral collisions, polarization force, and electron radiative condensation is analysed on the Jeans (gravitational) instability of partially ionized strongly coupled dusty plasma (SCDP) using linear perturbation (normal mode) analysis. The Boltzmann distributed ions, dynamics of inertialess electrons, charged dust and neutral particles are considered. Using the plane wave solutions, a general dispersion relation is derived which is modified due to the presence of dust-neutral collisions, strong coupling effect, polarization force, electron radiative condensation, and Jeans dust/neutral frequencies. In the long wavelength perturbations, the Jeans instability criterion depends upon strong coupling effect, polarization interaction parameter, and thermal loss, but it is independent of dust-neutral collision frequency. The stability of the considered configuration is analysed using the Routh–Hurwitz criterion. The growth rates of Jeans instability are illustrated, and stabilizing influence of viscoelasticity and dust-neutral collision frequency while destabilizing effect of electron radiative condensation, polarization force, and Jeans dust-neutral frequency ratio is observed. This work is applied to understand the gravitational collapse of SCDP with dust-neutral collisions.

Applying a particle filtering technique for canola crop growth stage estimation in Canada

Science.gov (United States)

Sinha, Abhijit; Tan, Weikai; Li, Yifeng; McNairn, Heather; Jiao, Xianfeng; Hosseini, Mehdi

2017-10-01

Accurate crop growth stage estimation is important in precision agriculture as it facilitates improved crop management, pest and disease mitigation and resource planning. Earth observation imagery, specifically Synthetic Aperture Radar (SAR) data, can provide field level growth estimates while covering regional scales. In this paper, RADARSAT-2 quad polarization and TerraSAR-X dual polarization SAR data and ground truth growth stage data are used to model the influence of canola growth stages on SAR imagery extracted parameters. The details of the growth stage modeling work are provided, including a) the development of a new crop growth stage indicator that is continuous and suitable as the state variable in the dynamic estimation procedure; b) a selection procedure for SAR polarimetric parameters that is sensitive to both linear and nonlinear dependency between variables; and c) procedures for compensation of SAR polarimetric parameters for different beam modes. The data was collected over three crop growth seasons in Manitoba, Canada, and the growth model provides the foundation of a novel dynamic filtering framework for real-time estimation of canola growth stages using the multi-sensor and multi-mode SAR data. A description of the dynamic filtering framework that uses particle filter as the estimator is also provided in this paper.

Calculation of polarization effects

International Nuclear Information System (INIS)

Chao, A.W.

1983-09-01

Basically there are two areas of accelerator applications that involve beam polarization. One is the acceleration of a polarized beam (most likely a proton beam) in a synchrotron. Another concerns polarized beams in an electron storage ring. In both areas, numerical techniques have been very useful

Copepods in ice-covered seas—Distribution, adaptations to seasonally limited food, metabolism, growth patterns and life cycle strategies in polar seas

Science.gov (United States)

Conover, R. J.; Huntley, M.

1991-07-01

While a seasonal ice cover limits light penetration into both polar seas for up to ten months a year, its presence is not entirely negative. The mixed layer under sea ice will generally be shallower than in open water at the same latitude and season. Ice forms a substrate on which primary production can be concentrated, a condition which contrasts with the generally dilute nutritional conditions which prevail in the remaining ocean. The combination of a shallow, generally stable mixed layer with a close proximity to abundant food make the under-ice zone a suitable nursery for both pelagic and benthic species, an upside-down benthos for opportunistic substrate browsers, and a rich feeding environment for species often considered to be neritic in temperate environments. Where the ice cover is not continuous there may be a retreating ice edge that facilitates the seasonal production of phytoplankton primarily through increased stability from the melt water. Ice edge blooms similarly encourage secondary production by pelagic animals. Pseudocalanus acuspes, which may be the most abundant and productive copepod in north polar latitudes, initiates growth at the start of the "spring bloom" of epontic algae, reaching sexual maturity at breakup or slightly before. In the Southern Hemisphere, the small neritic copepod Paralabidocera antarctica and adult krill have been observed to utilize ice algae. Calanus hyperboreus breeds in the dark season at depth and its buoyant eggs, slowly developing on the ascent, reach the under-ice layer in April as nauplii ready to benefit from the primary production there. On the other hand, C. glacialis may initiate ontogenetic migrations and reproduction in response to increased erosion of ice algae due to solar warming and melting at the ice-water interface. While the same species in a phytoplankton bloom near the ice edge reproduces actively, those under still-consolidated ice nearby can have immature gonads. Diel migration and diel feeding

Preliminary Analysis of Chinese GF-3 SAR Quad-Polarization Measurements to Extract Winds in Each Polarization

Directory of Open Access Journals (Sweden)

Lin Ren

2017-11-01

Full Text Available This study analyzed the noise equivalent sigma zero (NESZ and ocean wind sensitivity for Chinese C-band Gaofen-3 (GF-3 quad-polarization synthetic aperture radar (SAR measurements to facilitate further operational wind extraction from GF-3 data. Data from the GF-3 quad-polarization SAR and collocated winds from both NOAA/NCEP Global Forecast System (GFS atmospheric model and National Data Buoy Center (NDBC buoys were used in the analysis. For NESZ, the co-polarization was slightly higher compared to the cross-polarization. Regarding co-polarization and cross-polarization, NESZ was close to RadarSAT-2 and Sentinel-1 A. Wind sensitivity was analyzed by evaluating the dependence on winds in terms of normalized radar cross-sections (NRCS and polarization combinations. The closest geophysical model function (GMF and the polarization ratio (PR model to GF-3 data were determined by comparing data and the model results. The dependence of co-polarized NRCS on wind speed and azimuth angle was consistent with the proposed GMF models. The combination of CMOD5 and CMOD5.N was considered to be the closest GMF in co-polarization. The cross-polarized NRCS exhibited a strong linear relationship with moderate wind speeds higher than 4 m·s−1, but a weak correlation with the azimuth angle. The proposed model was considered as the closest GMF in cross-polarization. For polarization combinations, PR and polarization difference (PD were considered. PR increased only with the incidence angle, whereas PD increased with wind speed and varied with azimuth angle. There were three very close PR models and each can be considered as the closest. Preliminary results indicate that GF-3 quad-polarization data are valid and have the ability to extract winds in each polarization.

Depletion of stratospheric ozone over the Antarctic and Arctic: Responses of plants of polar terrestrial ecosystems to enhanced UV-B, an overview

International Nuclear Information System (INIS)

Rozema, Jelte; Boelen, Peter; Blokker, Peter

2005-01-01

Depletion of stratospheric ozone over the Antarctic has been re-occurring yearly since 1974, leading to enhanced UV-B radiation. Arctic ozone depletion has been observed since 1990. Ozone recovery has been predicted by 2050, but no signs of recovery occur. Here we review responses of polar plants to experimentally varied UV-B through supplementation or exclusion. In supplementation studies comparing ambient and above ambient UV-B, no effect on growth occurred. UV-B-induced DNA damage, as measured in polar bryophytes, is repaired overnight by photoreactivation. With UV exclusion, growth at near ambient may be less than at below ambient UV-B levels, which relates to the UV response curve of polar plants. UV-B screening foils also alter PAR, humidity, and temperature and interactions of UV with environmental factors may occur. Plant phenolics induced by solar UV-B, as in pollen, spores and lignin, may serve as a climate proxy for past UV. Since the Antarctic and Arctic terrestrial ecosystems differ essentially (e.g. higher species diversity and more trophic interactions in the Arctic), generalization of polar plant responses to UV-B needs caution. - Polar plant responses to UV-B may be different in the Arctic than Antarctic regions

[Intermediate energy studies of polarization transfer, polarized deuteron scattering, and (p,π+-) reactions: Rapporteur's report

International Nuclear Information System (INIS)

Moss, J.M.

1985-01-01

An overview of intermediate energy (80 to 1000 MeV) study contributions to the International Polarization Symposium in Osaka, Japan, August 1985 is presented in this report. Contributions fall into three categories: polarization transfer, polarized deuteron scattering and polarized (p,π +- ) reactions

Enhancement of molecular NMR signal induced by polarization transfer from laser-polarized 129Xe

International Nuclear Information System (INIS)

Sun Xianping

2001-01-01

There is a large non-equilibrium nuclear polarization and a longer relaxation time in the laser-polarized 129 Xe produced by means of optical pumping and spin exchange. The characteristics of the laser-polarized 129 Xe permit the transfer of the polarization to enhance the atomic nuclear spin in liquid, solid and surface of solid molecules. Therefore, the sensitivity in nuclear magnetic resonance measurements for the molecules is enhanced and applications in the investigations of materials and surface sciences are expanded. The progress in the investigations of materials and surface sciences are expanded. The progress in the investigations of the polarization transfer between laser-polarized 129 Xe and the atomic nuclei in the molecules, the relative physics and the measurement of some parameters are introduced

Graphics of polar figure; Graficado de figura polar

Energy Technology Data Exchange (ETDEWEB)

Macias B, L.R

1991-11-15

The objective of this work, is that starting from a data file coming from a spectra that has been softened, and of the one that have been generated its coordinates to project it in stereographic form, to create the corresponding polar figure making use of the Cyber computer of the ININ by means of the GRAPHOS package. This work only requires a Beta, Fi and Intensity (I) enter data file. It starts of the existence of a softened spectra of which have been generated already with these data, making use of some language that in this case was FORTRAN for the Cyber computer, a program is generated supported in the Graphos package that allows starting of a reading of the Beta, Fi, I file, to generate the points in a stereographic projection and that it culminates with the graph of the corresponding polar figure. The program will request the pertinent information that is wanted to capture in the polar figure just as: date, name of the enter file, indexes of the polar figure, number of levels, radio of the stereographic projection (cms.), crystalline system to which belongs the sample, name the neuter graph file by create and to add the own general data. (Author)

Airborne Laser Polarization Sensor

Science.gov (United States)

Kalshoven, James, Jr.; Dabney, Philip

1991-01-01

Instrument measures polarization characteristics of Earth at three wavelengths. Airborne Laser Polarization Sensor (ALPS) measures optical polarization characteristics of land surface. Designed to be flown at altitudes of approximately 300 m to minimize any polarizing or depolarizing effects of intervening atmosphere and to look along nadir to minimize any effects depending on look angle. Data from measurements used in conjunction with data from ground surveys and aircraft-mounted video recorders to refine mathematical models used in interpretation of higher-altitude polarimetric measurements of reflected sunlight.

Polarization-preserving holey fibers

DEFF Research Database (Denmark)

Broeng, Jes; Mogilevtsev, Dmitri; Libori, Stig E. Barkou

2001-01-01

In this work we suggest and discuss a microstructure of air capillaries with elliptical cross-section in a tread of glass that gives opportunity for Creation of polarization-preserving fiber with very small beat length between the fundamental modes of different polarization......In this work we suggest and discuss a microstructure of air capillaries with elliptical cross-section in a tread of glass that gives opportunity for Creation of polarization-preserving fiber with very small beat length between the fundamental modes of different polarization...

Development of polarized {sup 3}He filter for polarized neutron experiment

Energy Technology Data Exchange (ETDEWEB)

Sakai, K.; Sato, H.; Yoshimi, A.; Asahi, K. [Tokyo Inst. of Tech. (Japan). Faculty of Science; Masuda, Y.; Muto, S.; Ishimoto, S.; Morimoto, K.

1996-08-01

A high-pressure polarized {sup 3}He gas cell, pumped with two diode lasers, has been developed at KEK for use as a polarizer and a spin analyzer for low energy neutrons. The polarization attained of {sup 3}He was determined through the measurement of the transmission of the unpolarized neutrons through the {sup 3}He cell. So far we obtained P{sub He}=18% at 10 atm and P{sub He}=12% at 20 atm. (author)

Toxicity of natural mixtures of organic pollutants in temperate and polar marine phytoplankton

KAUST Repository

Echeveste, Pedro

2016-07-26

Semivolatile and persistent organic pollutants (POPs) undergo atmospheric transport before being deposited to the oceans, where they partition to phytoplankton organic matter. The goal of this study was to determine the toxicity of naturally occurring complex mixtures of organic pollutants to temperate and polar phytoplankton communities from the Mediterranean Sea, the North East (NE) Atlantic, and Southern Oceans. The cell abundance of the different phytoplankton groups, chlorophyll a concentrations, viability of the cells, and growth and decay constants were monitored in response to addition of a range of concentrations of mixtures of organic pollutants obtained from seawater extracts. Almost all of the phytoplankton groups were significantly affected by the complex mixtures of non-polar and polar organic pollutants, with toxicity being greater for these mixtures than for single POPs or simple POP mixtures. Cocktails\\' toxicity arose at concentrations as low as tenfold the field oceanic levels, probably due to a higher chemical activity of the mixture than of simple POPs mixtures. Overall, smaller cells were the most affected, although Mediterranean picophytoplankton was significantly more tolerant to non-polar POPs than picophytoplankton from the Atlantic Ocean or the Bellingshausen Sea microphytoplankton. © 2016 Elsevier B.V.

Direct Numerical Simulations of Concentration and Temperature Polarization in Direct Contact Membrane Distillation

Science.gov (United States)

Lou, Jincheng; Tilton, Nils

2017-11-01

Membrane distillation (MD) is a method of desalination with boundary layers that are challenging to simulate. MD is a thermal process in which warm feed and cool distilled water flow on opposite sides of a hydrophobic membrane. The temperature difference causes water to evaporate from the feed, travel through the membrane, and condense in the distillate. Two challenges to MD are temperature and concentration polarization. Temperature polarization represents a reduction in the transmembrane temperature difference due to heat transfer through the membrane. Concentration polarization describes the accumulation of solutes near the membrane. These phenomena reduce filtration and lead to membrane fouling. They are difficult to simulate due to the coupling between the velocity, temperature, and concentration fields on the membrane. Unsteady regimes are particularly challenging because noise at the outlets can pollute the near-membrane flow fields. We present the development of a finite-volume method for the simulation of fluid flow, heat, and mass transport in MD systems. Using the method, we perform a parametric study of the polarization boundary layers, and show that the concentration boundary layer shows self-similar behavior that satisfies power laws for the downstream growth. Funded by the U.S. Bureau of Reclamation.

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

International Nuclear Information System (INIS)

Choi, Yunju; Kim, Yangsoo; Ahn, Kwang-Soon; Kim, Hyunsoo

2014-01-01

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10 −3 , 4.3 × 10 −4 , and 1.1 × 10 −3 Ω cm 2 for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N 2 ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

Energy Technology Data Exchange (ETDEWEB)

Choi, Yunju [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Kim, Yangsoo [Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Ahn, Kwang-Soon, E-mail: kstheory@ynu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 712-749 (Korea, Republic of); Kim, Hyunsoo, E-mail: hskim7@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

2014-10-30

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10{sup −3}, 4.3 × 10{sup −4}, and 1.1 × 10{sup −3} Ω cm{sup 2} for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N{sub 2} ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples.

Polarized proton colliders

International Nuclear Information System (INIS)

Roser, T.

1995-01-01

High energy polarized beam collisions will open up the unique physics opportunities of studying spin effects in hard processes. This will allow the study of the spin structure of the proton and also the verification of the many well documented expectations of spin effects in perturbative QCD and parity violation in W and Z production. Proposals for polarized proton acceleration for several high energy colliders have been developed. A partial Siberian Snake in the AGS has recently been successfully tested and full Siberian Snakes, spin rotators, and polarimeters for RHIC are being developed to make the acceleration of polarized beams to 250 GeV possible. This allows for the unique possibility of colliding two 250 GeV polarized proton beams at luminosities of up to 2 x 10 32 cm -2 s -1

Renal epithelial cell growth can occur in absence of Na+-H+ exchanger activity

International Nuclear Information System (INIS)

Mohrmann, M.; Cantiello, H.F.; Ausiello, D.A.

1987-01-01

An electroneutral Na+-H+ exchange system has been described in a variety of tissues and cell types, including those of renal origin, and has been proposed to play a role in the activation of growth. We have recently characterized the presence of this ubiquitous transporter in the apical domain of confluent epithelial LLC-PK1 cells. Because most apical membrane proteins appear late in cell growth, accompanying epithelial cell polarization, we determined whether the Na+-H+ exchanger is required for the growth of LLC-PK1 cells. The studies reported here show that there is no obligatory requirement for increased H+ efflux or Na+ entry via the Na+-H+ exchanger for the initiation of cell growth in this epithelial cell line. We used 22 Na+ influx, acid extrusion, and intracellular pH determinations to show that onset of cell growth, as measured by DNA content, precedes the activity of the Na+-H+ exchanger in exponentially growing cells, whereas confluent monolayers express Na+-H+ exchanger activity. When confluent cells are replated at low density, Na+-H+ exchanger activity disappears within 8 h in contrast to high-density replated cells. The fact that Na+-H+ exchanger activity is only present in confluent monolayers suggests that the development of tight junctions and polar differentiation play a role in the expression of the Na+-H+ exchanger and that this exchanger is more important to the polar epithelial cell for transepithelial transport than for the maintenance of intracellular pH

Pseudomonas mesophilica and an unnamed taxon, clinical isolates of pink-pigmented oxidative bacteria.

Science.gov (United States)

Gilardi, G L; Faur, Y C

1984-10-01

Twenty-one strains of pink-pigmented bacteria, isolated from human clinical specimens and an environmental source, were compared with Pseudomonas mesophilica ATCC 29983 and Protaminobacter ruber ATCC 8457. These isolates were gram-negative, oxidative rods which were motile by means of a single polar flagellum; gave positive catalase, indophenol oxidase, urease, and amylase reactions; and grew slowly at 30 degrees C. Fourteen isolates conformed to the designated type strains Pseudomonas mesophilica ATCC 29983 and Protaminobacter ruber ATCC 8457. The remaining seven strains represented an undescribed taxon. These pink bacteria appear to be invaders of debilitated patients with an underlying chronic disease.

Prey capture by freely swimming flagellates

Science.gov (United States)

Andersen, Anders; Dolger, Julia; Nielsen, Lasse Tor; Kiorboe, Thomas

2017-11-01

Flagellates are unicellular microswimmers that propel themselves using one or several beating flagella. Here, we explore the dependence of swimming kinematics and prey clearance rate on flagellar arrangement and determine optimal flagellar arrangements and essential trade-offs. To describe near-cell flows around freely swimming flagellates we consider a model in which the cell is represented by a no-slip sphere and each flagellum by a point force. For uniflagellates pulled by a single flagellum the model suggests that a long flagellum favors fast swimming, whereas high clearance rate is favored by a very short flagellum. For biflagellates with both a longitudinal and a transversal flagellum we explore the helical swimming kinematics and the prey capture sites. We compare our predictions with observations of swimming kinematics, prey capture, and flows around common marine flagellates. The Centre for Ocean Life is a VKR Centre of Excellence supported by the Villum Foundation.

Polarization and resistivity measurements of post-crystallization changes in amorphous Fe-B-Si alloys

International Nuclear Information System (INIS)

Chattoraj, I.; Bhattamishra, A.K.; Mitra, A.

1993-01-01

The effects of grain growth and compositional changes on the electrochemical behavior and the resistivity of amorphous iron-boron-silicon (Fe 77.5 B 15 Si 7.5 ) alloys after crystallization were studied. Deterioration of the protective passive film was observed, along with increased annealing. Potentiodynamic polarization provided excellent information about microstructural and chemical changes. It was concluded that electrochemical measurements could be used in conjunction with resistivity measurements in direct studies of grain growth and chemical changes occurring in different phases of the devitrified alloy

Coupling of magnetopause-boundary layer to the polar ionosphere

International Nuclear Information System (INIS)

Wei, C.Q.; Lee, L.C.

1993-01-01

The authors develop a model which seeks to explain ultraviolet auroral images from the Viking satellite which show periodic bright regions which resemble open-quotes beadsclose quotes or open-quotes pearlsclose quotes aligned along the postnoon auroral oval. ULF geomagnetic pulsations observed in the cusp region are also addressed by this model. The model addresses plasma dynamics in the low-latitude boundary layer and interactions with the polar ionosphere by means of field-aligned current. The Kelvin-Helmholtz instability can develop in the presence of driven plasma flow, which can lead to the formation and growth of plasma vortices in the boundary layer. The finite conductivity of the earth ionosphere causes these vortices to decay. However regions of enhanced field-aligned power density in the postnoon auroral oval can be associated with field-aligned current filaments and boundary layer vortices. These structures may explain the observed bright spots. The authors also discuss the frequency spectrum and the polarization state of the pulsations

Polarization and Persuasion: Integrating the Elaboration Likelihood Model with Explanations of Group Polarization.

Science.gov (United States)

Mongeau, Paul A.

Interest has recently focused on group polarization as a function of attitude processes. Several recent reviewers have challenged polarization researchers to integrate the explanations of polarization to existing theories of attitude change. This review suggests that there exists a clear similarity between the social comparison and persuasive…

Tumor cell-derived microparticles polarize M2 tumor-associated macrophages for tumor progression.

Science.gov (United States)

Ma, Ruihua; Ji, Tiantian; Chen, Degao; Dong, Wenqian; Zhang, Huafeng; Yin, Xiaonan; Ma, Jingwei; Liang, Xiaoyu; Zhang, Yi; Shen, Guanxin; Qin, Xiaofeng; Huang, Bo

2016-04-01

Despite identification of macrophages in tumors (tumor-associated macrophages, TAM) as potential targets for cancer therapy, the origin and function of TAM in the context of malignancy remain poorly characterized. Here, we show that microparticles (MPs), as a by-product, released by tumor cells act as a general mechanism to mediate M2 polarization of TAM. Taking up tumor MPs by macrophages is a very efficient process, which in turn results in the polarization of macrophages into M2 type, not only leading to promoting tumor growth and metastasis but also facilitating cancer stem cell development. Moreover, we demonstrate that the underlying mechanism involves the activation of the cGAS/STING/TBK1/STAT6 pathway by tumor MPs. Finally, in addition to murine tumor MPs, we show that human counterparts also possess consistent effect on human M2 polarization. These findings provide new insights into a critical role of tumor MPs in remodeling of tumor microenvironment and better understanding of the communications between tumors and macrophages.

Polar bears at risk

Energy Technology Data Exchange (ETDEWEB)

Norris, S.; Rosentrater, L.; Eid, P.M. [WWF International Arctic Programme, Oslo (Norway)

2002-05-01

Polar bears, the world's largest terrestrial carnivore, spend much of their lives on the arctic sea ice. This is where they hunt and move between feeding, denning, and resting areas. The world population, estimated at 22,000 bears, is made up of 20 relatively distinct populations varying in size from a few hundred to a few thousand animals. About 60 per cent of all polar bears are found in Canada. In general, the status of this species is stable, although there are pronounced differences between populations. Reductions in the extent and thickness of sea ice has lead the IUCN Polar Bear Specialist Group to describe climate change as one of the major threats facing polar bears today. Though the long-term effects of climate change will vary in different areas of the Arctic, impacts on the condition and reproductive success of polar bears and their prey are likely to be negative. Longer ice-free periods resulting from earlier break-up of sea ice in the spring and later formation in the fall is already impacting polar bears in the southern portions of their range. In Canada's Hudson Bay, for example, bears hunt on the ice through the winter and into early summer, after which the ice melts completely, forcing bears ashore to fast on stored fat until freeze-up in the fall. The time bears have on the ice to hunt and build up their body condition is cut short when the ice melts early. Studies from Hudson Bay show that for every week earlier that ice break-up occurs, bears will come ashore 10 kg lighter and in poorer condition. It is likely that populations of polar bears dividing their time between land and sea will be severely reduced and local extinctions may occur as greenhouse gas emissions continue to rise and sea ice melts. Expected changes in regional weather patterns will also impact polar bears. Rain in the late winter can cause maternity dens to collapse before females and cubs have departed, thus exposing occupants to the elements and to predators. Such

Active Polar Two-Fluid Macroscopic Dynamics

Science.gov (United States)

Pleiner, Harald; Svensek, Daniel; Brand, Helmut R.

2014-03-01

We study the dynamics of systems with a polar dynamic preferred direction. Examples include the pattern-forming growth of bacteria (in a solvent, shoals of fish (moving in water currents), flocks of birds and migrating insects (flying in windy air). Because the preferred direction only exists dynamically, but not statically, the macroscopic variable of choice is the macroscopic velocity associated with the motion of the active units. We derive the macroscopic equations for such a system and discuss novel static, reversible and irreversible cross-couplings connected to this second velocity. We find a normal mode structure quite different compared to the static descriptions, as well as linear couplings between (active) flow and e.g. densities and concentrations due to the genuine two-fluid transport derivatives. On the other hand, we get, quite similar to the static case, a direct linear relation between the stress tensor and the structure tensor. This prominent ``active'' term is responsible for many active effects, meaning that our approach can describe those effects as well. In addition, we also deal with explicitly chiral systems, which are important for many active systems. In particular, we find an active flow-induced heat current specific for the dynamic chiral polar order.

Asymptotic behaviour in polarized and half-polarized U(1) symmetric vacuum spacetimes

International Nuclear Information System (INIS)

Isenberg, James; Moncrief, Vincent

2002-01-01

We use the Fuchsian algorithm to study the behaviour near the singularity of certain families of U(1) symmetric solutions of the vacuum Einstein equations (with the U(1) isometry group acting spatially). We consider an analytic family of polarized solutions with the maximum number of arbitrary functions consistent with the polarization condition (one of the 'gravitational degrees of freedom' is turned off) and show that all members of this family are asymptotically velocity term dominated (AVTD) as one approaches the singularity. We show that the same AVTD behaviour holds for a family of 'half-polarized' solutions, which is defined by adding one extra arbitrary function to those characterizing the polarized solutions. (The full set of nonpolarized solutions involves two extra arbitrary functions.) Using SL(2, R) Geroch transformations, we produce a further class of U(1) symmetric solutions with AVTD behaviour. We begin to address the issue of whether AVTD behaviour is independent of the choice of time foliation by showing that indeed AVTD behaviour is seen for a wide class of choices of harmonic time in the polarized and half-polarized (U(1) symmetric vacuum) solutions discussed here

Microglia M2A Polarization as Potential Link between Food Allergy and Autism Spectrum Disorders

Directory of Open Access Journals (Sweden)

Hans O. Kalkman

2017-12-01

Full Text Available Atopic diseases are frequently co-morbid with autism spectrum disorders (ASD. Allergic responses are associated with an activation of mast cells, innate lymphoid cells, and Th2 cells. These cells produce type-2 cytokines (IL4 and IL13, which stimulate microglia and macrophages to adopt a phenotype referred to as ‘alternative activation’ or ‘M2A’. M2A-polarized macrophages and microglia play a physiological role in tissue repair by secreting growth factors such as brain-derived neurotrophic factor (BDNF and insulin-like growth factor-1. In ASD there is evidence for increased type-2 cytokines, microglia activation, M2A polarization, and increased levels of growth factors. In neurons, these growth factors drive a signal transduction pathway that leads to activation of the enzyme mammalian Target of Rapamycin (mTOR, and thereby to the inhibition of autophagy. Activation of mTOR is an effect that is also common to several of the genetic forms of autism. In the central nervous system, redundant synapses are removed via an autophagic process. Activation of mTOR would diminish the pruning of redundant synapses, which in the context of ASD is likely to be undesired. Based on this line of reasoning, atopic diseases like food allergy, eczema or asthma would represent risk factors for autism spectrum disorders.

The polarization of fast neutrons

International Nuclear Information System (INIS)

Talov, V.V.

2000-01-01

The present work is the review of polarization of fast neutrons and methods of polarization analysis. This also includes information about polarization of fast neutrons from first papers, which described polarization in the D(d,n) 3 He, 7 Li(p,n) 7 Be, and T(p,n) 3 He reactions. (authors)

RNG1 is a Late Marker of the Apical Polar Ring in Toxoplasma gondii

Science.gov (United States)

Tran, Johnson Q.; de Leon, Jessica C.; Li, Catherine; Huynh, My-Hang; Beatty, Wandy; Morrissette, Naomi S.

2010-01-01

The asexually proliferating stages of apicomplexan parasites cause acute symptoms of diseases such as malaria, cryptosporidiosis and toxoplasmosis. These stages are characterized by the presence of two independent microtubule organizing centers (MTOCs). Centrioles are found at the poles of the intranuclear spindle. The apical polar ring (APR), a MTOC unique to apicomplexans, organizes subpellicular microtubules which impose cell shape and apical polarity on these protozoa. Here we describe the characteristics of a novel protein that localizes to the APR of Toxoplasma gondii which we have named ring-1 (RNG1). There are related RNG1 proteins in Neospora caninum and Sarcocystis neurona but no obvious homologs in Plasmodium spp., Cryptosporidium spp. or Babesia spp. RNG1 is a small, low-complexity, detergent-insoluble protein that assembles at the APR very late in the process of daughter parasite replication. We were unable to knock-out the RNG1 gene, suggesting that its gene product is essential. Tagged RNG1 lines have also allowed us to visualize the APR during growth of Toxoplasma in the microtubule-disrupting drug oryzalin. Oryzalin inhibits nuclear division and cytokinesis although Toxoplasma growth continues, and similar to earlier observations of unchecked centriole duplication in oryzalin-treated parasites, the APR continues to duplicate during aberrant parasite growth. PMID:20658557

Elite Polarization and Public Opinion

DEFF Research Database (Denmark)

Robison, Joshua; Mullinix, Kevin

2016-01-01

Elite polarization has reshaped American politics and is an increasingly salient aspect of news coverage within the United States. As a consequence, a burgeoning body of research attempts to unravel the effects of elite polarization on the mass public. However, we know very little about how...... polarization is communicated to the public by news media. We report the results of one of the first content analyses to delve into the nature of news coverage of elite polarization. We show that such coverage is predominantly critical of polarization. Moreover, we show that unlike coverage of politics focused...... on individual politicians, coverage of elite polarization principally frames partisan divisions as rooted in the values of the parties rather than strategic concerns. We build on these novel findings with two survey experiments exploring the influence of these features of polarization news coverage on public...

FDTD simulation of trapping nanowires with linearly polarized and radially polarized optical tweezers.

Science.gov (United States)

Li, Jing; Wu, Xiaoping

2011-10-10

In this paper a model of the trapping force on nanowires is built by three dimensional finite-difference time-domain (FDTD) and Maxwell stress tensor methods, and the tightly focused laser beam is expressed by spherical vector wave functions (VSWFs). The trapping capacities on nanoscale-diameter nanowires are discussed in terms of a strongly focused linearly polarized beam and radially polarized beam. Simulation results demonstrate that the radially polarized beam has higher trapping efficiency on nanowires with higher refractive indices than linearly polarized beam.

Polarization Property Measurement of the Long Undulator Radiation Using Cr/C Multilayer Polarization Elements

International Nuclear Information System (INIS)

Niibe, Masahito; Mukai, Mikihito; Shoji, Yoshihiko; Kimura, Hiroaki

2004-01-01

A rotating analyzer ellipsometry (RAE) system was developed with Cr/C multilayers that function as polarization elements for photon energy range of 110 - 280 eV. Polarization properties of a planar undulator change axisymmetrically in off-axial manner, and the second harmonic is more remarkable for the change. By using the RAE system, the polarization property of the second harmonic radiation from the NewSUBARU long undulator at the energy of 180 eV was examined. The degree of linear polarization of the on-axis radiation was over 0.996. The spatial distribution of the polarization azimuth was measured and was in fair agreement with the theoretical calculation. A peculiar behavior of the polarization property near the radiation peak of the second harmonic was observed by changing the height of the undulator gap

PolarTREC: Successful Methods and Tools for Attaining Broad Educational Impacts with Interdisciplinary Polar Science

Science.gov (United States)

Timm, K. M.; Warburton, J.; Owens, R.; Warnick, W. K.

2008-12-01

PolarTREC--Teachers and Researchers Exploring and Collaborating, a program of the Arctic Research Consortium of the U.S. (ARCUS), is a National Science Foundation (NSF)-funded International Polar Year (IPY) project in which K-12 educators participate in hands-on field experiences in the polar regions, working closely with IPY scientists as a pathway to improving science education. Developing long-term teacher- researcher collaborations through PolarTREC ensures up-to-date climate change science content will permeate the K-12 education system long after the IPY. By infusing education with the cutting edge science from the polar regions, PolarTREC has already shown an increase in student and public knowledge of and interest in the polar regions and global climate change. Preliminary evaluations have shown that PolarTREC's program activities have many positive impacts on educators and their ability to teach science concepts and improve their teaching methods. Additionally, K-12 students polled in interest surveys showed significant changes regarding the importance of understanding the polar regions as a person in today's world. Researchers have been overwhelmingly satisfied with PolarTREC and cited several specific strengths, including the program's crucial link between the teachers' field research experiences and their classroom and the extensive training provided to teachers prior to their expedition. This presentation will focus on other successful components of the PolarTREC program and how researchers and organizations might use these tools to reach out to the public for long-term impacts. Best practices include strategies for working with educators and the development of an internet-based platform for teachers and researchers to interact with the public, combining several communication tools such as online journals and forums, real-time Internet seminars, lesson plans, activities, audio, and other educational resources that address a broad range of scientific

Mechanisms of impact of greenhouse gases on the Earth's ozone layer in the Polar Regions

Science.gov (United States)

Zadorozhny, Alexander; Dyominov, Igor

A numerical 2-D zonally averaged interactive dynamical radiative-photochemical model of the atmosphere including aerosol physics is used to examine the impact of the greenhouse gases CO2, CH4, and N2O on the future long-term changes of the Earth's ozone layer, in particular on its expected recovery after reduction of anthropogenic discharges of chlorine and bromine compounds into the atmosphere. The model allows calculating self-consistently diabatic circu-lation, temperature, gaseous composition of the troposphere and stratosphere at latitudes from the North to South Poles, as well as distribution of sulphate aerosol particles and polar strato-spheric clouds (PSCs) of types I and II. The scenarios of expected changes of the anthropogenic pollutants for the period from 1980 through 2050 are taken from Climate Change 2001. The processes, which determine the influence of anthropogenic growth of atmospheric abun-dance of the greenhouse gases on the long-term changes of the Earth's ozone layer in the Polar Regions, have been studied in details. Expected cooling of the stratosphere caused by increases of greenhouse gases, most importantly CO2, essentially influences the ozone layer by two ways: through temperature dependencies of the gas phase reaction rates and through enhancement of polar ozone depletion via increased PSC formation. The model calculations show that a weak-ness in efficiencies of all gas phase catalytic cycles of the ozone destruction due to cooling of the stratosphere is a dominant mechanism of the impact of the greenhouse gases on the ozone layer in Antarctic as well as at the lower latitudes. This mechanism leads to a significant acceleration of the ozone layer recovery here because of the greenhouse gases growth. On the contrary, the mechanism of the impact of the greenhouse gases on the ozone through PSC modification be-gins to be more effective in Arctic in comparison with the gas phase mechanism in springs after about 2020, which leads to retard

The influence of climate variability on polar bear (Ursus maritimus) and ringed seal (Pusa hispida) population dynamics

DEFF Research Database (Denmark)

Rosing-Asvid, A.

2006-01-01

Unusually high polar bear (Ursus maritimus Phipps, 1774) predation on ringed seal (Pusa hispida (Schreber, 1775)) pups and increased survival of polar bear cubs during mild springs is documented in published articles. Strong predation on newborn ringed seal pups in early spring, however, is likely...... to lower the overall energy intake of polar bears if ringed seal pups are their main food, because the energetic value of ringed seal pups increases 7-8 times during the 6 week lactation period. So although hunting success in early spring increases cub survival during the period after den emergence......,when they are most vulnerable, it is likely to increase the number of starving bears later in the season. This negative-feedback effect of strong spring predation will not occur in areas where other seal species are abundant during summer, and polar bears in such areas are likely to exhibit population growth during...

The evolution of tensor polarization

International Nuclear Information System (INIS)

Huang, H.; Lee, S.Y.; Ratner, L.

1993-01-01

By using the equation of motion for the vector polarization, the spin transfer matrix for spin tensor polarization, the spin transfer matrix for spin tensor polarization is derived. The evolution equation for the tensor polarization is studied in the presence of an isolate spin resonance and in the presence of a spin rotor, or snake

System for measuring of proton polarization in polarized target

International Nuclear Information System (INIS)

Derkach, A.Ya.; Lukhanin, A.A.; Karnaukhov, I.M.; Kuz'menko, V.S.; Telegin, Yu.N.; Trotsenko, V.I.; Chechetenko, V.F.

1981-01-01

Measurement system of proton polarization in the target, which uses the method of nuclear magnetic resonance is described. To record the signal of NMR-absorption a parallel Q-meter of voltage with analogous subtraction of resonance characteristics of measurement circuit is used. To obtain gradual sensitivity of the system to polarization state in the whole volume of the target the measurement coils is made of tape conductor. The analysis and mathematical modelling of Q-meter are carried out. Corrections for nonlinearity and dispersion are calculated. Key diagrams of the main electron blocks of Q-meter are presented. The system described operates on line with the M6000 computer. Total error of measurement of polarization value of free protons in the target does not exceed 6% [ru

Polarization experiments

International Nuclear Information System (INIS)

Halzen, F.

1977-02-01

In a theoretical review of polarization experiments two important points are emphasized: (a) their versatility and their relevance to a large variety of aspects of hadron physics (tests of basic symmetries; a probe of strong interaction dynamics; a tool for hadron spectroscopy); (b) the wealth of experimental data on polarization parameters in pp and np scattering in the Regge language and in the diffraction language. (author)

Study of Jupiter polarization properties

International Nuclear Information System (INIS)

Bolkvadze, O.R.

1980-01-01

Investigations into polarization properties of the Jupiter reflected light were carried on at the Abastumani astrophysical observatory in 1967, 1968 and 1969 in the four spectral ranges: 4000, 4800, 5400 and 6600 A deg. Data on light polarization in different parts of the Jupiter visible disk are given. Curves of dependence of the planet light polarization degree on a phase angle are plotted. It is shown that in the central part of the visible planet disk the polarization degree is low. Atmosphere is in a stable state in this part of Jupiter. Mean radius of particles of a cloud layer is equal to 0.26μ, and optical thickness of overcloud atmosphere tau=0.05. Height of transition boundary of the cloud layer into overcloud gas atmosphere changes from year to year at the edges of the equatorial zone. Optical thickness of overcloud atmosphere changes also with changing height of a transient layer. The polar Jupiter regions possess a high degree of polarization which depends on a latitude. Polarization increases monotonously with the latitude and over polar regions accepts a maximum value [ru

Climate change threatens polar bear populations: A stochastic demographic analysis

Science.gov (United States)

Hunter, C.M.; Caswell, H.; Runge, M.C.; Regehr, E.V.; Amstrup, Steven C.; Stirling, I.

2010-01-01

The polar bear (Ursus maritimus) depends on sea ice for feeding, breeding, and movement. Significant reductions in Arctic sea ice are forecast to continue because of climate warming. We evaluated the impacts of climate change on polar bears in the southern Beaufort Sea by means of a demographic analysis, combining deterministic, stochastic, environment-dependent matrix population models with forecasts of future sea ice conditions from IPCC general circulation models (GCMs). The matrix population models classified individuals by age and breeding status; mothers and dependent cubs were treated as units. Parameter estimates were obtained from a capture-recapture study conducted from 2001 to 2006. Candidate statistical models allowed vital rates to vary with time and as functions of a sea ice covariate. Model averaging was used to produce the vital rate estimates, and a parametric bootstrap procedure was used to quantify model selection and parameter estimation uncertainty. Deterministic models projected population growth in years with more extensive ice coverage (2001-2003) and population decline in years with less ice coverage (2004-2005). LTRE (life table response experiment) analysis showed that the reduction in ?? in years with low sea ice was due primarily to reduced adult female survival, and secondarily to reduced breeding. A stochastic model with two environmental states, good and poor sea ice conditions, projected a declining stochastic growth rate, log ??s, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log ??s ' - 0.01, which agrees with available (albeit crude) observations of population size. The stochastic model was linked to a set of 10 GCMs compiled by the IPCC; the models were chosen for their ability to reproduce historical observations of sea ice and were forced with "business as usual" (A1B) greenhouse gas emissions. The resulting stochastic population projections showed drastic

High energy polarized electron beams

International Nuclear Information System (INIS)

Rossmanith, R.

1987-01-01

In nearly all high energy electron storage rings the effect of beam polarization by synchrotron radiation has been measured. The buildup time for polarization in storage rings is of the order of 10 6 to 10 7 revolutions; the spins must remain aligned over this time in order to avoid depolarization. Even extremely small spin deviations per revolution can add up and cause depolarization. The injection and the acceleration of polarized electrons in linacs is much easier. Although some improvements are still necessary, reliable polarized electron sources with sufficiently high intensity and polarization are available. With the linac-type machines SLC at Stanford and CEBAF in Virginia, experiments with polarized electrons will be possible

Interferometric polarization control

International Nuclear Information System (INIS)

Chuss, David T.; Wollack, Edward J.; Moseley, S. Harvey; Novak, Giles

2006-01-01

We develop the Jones and Mueller matrices for structures that allow control of the path length difference between two linear orthogonal polarizations and consider the effect of placing multiple devices in series. Specifically, we find that full polarization modulation (measurement of Stokes Q, U, and V) can be achieved by placing two such modulators in series if the relative angles of the beam-splitting grids with respect to the analyzer orientation are appropriately chosen. Such a device has several potential advantages over a spinning wave plate modulator for measuring astronomical polarization in the far infrared through millimeter: (i) The use of small, linear motions eliminates the need for cryogenic rotational bearings; (ii) the phase flexibility allows measurement of circular as well as linear polarization; and (iii) this architecture allows for both multiwavelength and broadband modulation. We also present initial laboratory results

Photonic Crystal Polarizing and Non-Polarizing Beam Splitters

International Nuclear Information System (INIS)

Chun-Ying, Guan; Jin-Hui, Shi; Li-Boo, Yuan

2008-01-01

A polarizing beam splitter (PBS) and a non-polarizing beam splitter (NPBS) based on a photonic crystal (PC) directional coupler are demonstrated. The photonic crystal directional coupler consists of a hexagonal lattice of dielectric pillars in air and has a complete photonic band gap. The photonic band structure and the band gap map are calculated using the plane wave expansion (PWE) method. The splitting properties of the splitter are investigated numerically using the finite difference time domain (FDTD) method

Ab initio-based bulk and surface thermodynamics of InGaN alloys. Investigating the effects of strain and surface polarity

Energy Technology Data Exchange (ETDEWEB)

Duff, Andrew I.; Lymperakis, Liverios; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung, Duesseldorf (Germany)

2015-05-15

The growth of high In content InGaN with sufficiently high crystal quality is challenging due to the differences in the GaN and InN thermodynamics. The surprisingly different thermodynamics is due to a complex competition between strain and chemistry and mediated by the different indium and gallium atomic radii as well as their different bonding enthalpies with nitrogen. In the present work, we investigate bulk and surface thermodynamics of molecular beam epitaxial (MBE) growth of In{sub x}Ga{sub 1-x}N for the technologically relevant (0001) and (000 anti 1) growth planes by means of density functional theory calculations. Our calculations confirm that coherent growth fully suppresses phase separation through spinodal decomposition. However, the biaxial strain is found to have a marginal effect on the critical temperatures for In{sub x}Ga{sub 1-x}N decomposition. Furthermore, the thermal stability of excess indium is found to be remarkably higher on N-polar surfaces than on the Ga-polar surfaces. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Recent results on polarizations and the present status of the Fermilab polarized beams

International Nuclear Information System (INIS)

Yokosawa, Akihiko.

1986-01-01

Experimental results are reviewed on polarization phenomena in nucleon-nucleon scattering at intermediate energies. The present status of S = 0 dibaryon resonances is presented. The status of the Fermilab polarized beam program is presented, including the construction of polarized beam, two polarimeters being installed in the experimental hall, and the experimental program

Reciprocal and dynamic polarization of planar cell polarity core components and myosin

Science.gov (United States)

Newman-Smith, Erin; Kourakis, Matthew J; Reeves, Wendy; Veeman, Michael; Smith, William C

2015-01-01

The Ciona notochord displays planar cell polarity (PCP), with anterior localization of Prickle (Pk) and Strabismus (Stbm). We report that a myosin is polarized anteriorly in these cells and strongly colocalizes with Stbm. Disruption of the actin/myosin machinery with cytochalasin or blebbistatin disrupts polarization of Pk and Stbm, but not of myosin complexes, suggesting a PCP-independent aspect of myosin localization. Wash out of cytochalasin restored Pk polarization, but not if done in the presence of blebbistatin, suggesting an active role for myosin in core PCP protein localization. On the other hand, in the pk mutant line, aimless, myosin polarization is disrupted in approximately one third of the cells, indicating a reciprocal action of core PCP signaling on myosin localization. Our results indicate a complex relationship between the actomyosin cytoskeleton and core PCP components in which myosin is not simply a downstream target of PCP signaling, but also required for PCP protein localization. DOI: http://dx.doi.org/10.7554/eLife.05361.001 PMID:25866928

[Biofilm Formation by the Nonflagellated flhB1 Mutant of Azospirillum brasilense Sp245].

Science.gov (United States)

Shelud'ko, A V; Filip'echeva, Yu A; Shumiliva, E M; Khlebtsov, B N; Burov, A M; Petrova, L P; Katsy, E I

2015-01-01

Azospirillum brasilense Sp245 with mixed flagellation are able to form biofilms on various surfaces. A nonflagellated mutant of this strain with inactivated chromosomal copy of the flhB gene (flhB1) was shown to exhibit specific traits at the later stages of biofilm formation on a hydrophilic (glass) surface. Mature biofilms of the flhB1::Omegon-Km mutant Sp245.1063 were considerably thinner than those of the parent strain Sp245. The biofilms of the mutant were more susceptible to the forces of hydrodynamic shear. A. brasilense Sp245 cells in biofilms were not found to possess lateral flagella. Cells with polar flagella were, however, revealed by atomic force microscopy of mature native biofilms of strain Sp245. Preservation of a polar flagellum (probably nonmotile) on the cells of A. brasilense Sp245 may enhance the biofilm stability.

Polarization transfer from polarized nuclear spin to μ- spin in muonic atom

International Nuclear Information System (INIS)

Kuno, Yoshitaka; Nagamine, Kanetada; Yamazaki, Toshimitsu.

1987-02-01

A theoretical study of polarization transfer from an initially-polarized nuclear spin to a μ - spin in a muonic atom is given. The switching of the hyperfine interaction at excited muonic states as well as at the ground 1s state is taken into account. The upper state of hyperfine doublet at the muonic 1s state is considered to proceed down to the lower state. It is found that as the hyperfine interaction becomes effective at higher excited muonic orbitals, a less extent of polarization is transferred from the nuclear spin to the μ - spin. The theoretical values obtained are compared with the recent experiment of μ - repolarization in a polarized 209 Bi target. (author)

Polarized proton beams since the ZGS

International Nuclear Information System (INIS)

Krisch, A.D.

1994-01-01

The author discusses research involving polarized proton beams since the ZGS's demise. He begins by reminding the attendee that in 1973 the ZGS accelerated the world's first high energy polarized proton beam; all in attendance at this meeting can be proud of this accomplishment. A few ZGS polarized proton beam experiments were done in the early 1970's; then from about 1976 until 1 October 1979, the majority of the ZGS running time was polarized running. A great deal of fundamental physics was done with the polarized beam when the ZGS ran as a dedicated polarized proton beam from about Fall 1977 until it shut down on 1 October 1979. The newly created polarization enthusiats then dispersed; some spread polarized seeds al over the world by polarizing beams elsewhere; some wound up running the High Energy and SSC programs at DOE

Polarization Optics in Telecommunications

CERN Document Server

Damask, Jay N

2005-01-01

The strong investments into optical telecommunications in the late 1990s resulted in a wealth of new research, techniques, component designs, and understanding of polarization effects in fiber. Polarization Optics in Telecommunications brings together recent advances in the field to create a standard, practical reference for component designers and optical fiber communication engineers. Beginning with a sound foundation in electromagnetism, the author offers a dissertation of the spin-vector formalism of polarization and the interaction of light with media. Applications discussed include optical isolators, optical circulators, fiber collimators, and a variety of applied waveplate and prism combinations. Also included in an extended discussion of polarization-mode dispersion (PMD) and polarization-dependent loss (PDL), their representation, behavior, statistical properties, and measurement. This book draws extensively from the technical and patent literature and is an up-to-date reference for researchers and c...

Electroproduction of polarized Λ's

International Nuclear Information System (INIS)

Kunne, R.A.

1992-01-01

Lambdas are a powerful tool to explore spin effects of QCD. The λ polarization is self analyzing, as it is measurable from the angular distribution of the decay products. Two applications of polarized electroproduced λ's are suggested: the measurement of λ polarization at large transverse momentum as a possible test of QCD and the measurement of transversely polarized parton distributions

Polarized proton collider at RHIC

International Nuclear Information System (INIS)

Alekseev, I.; Allgower, C.; Bai, M.; Batygin, Y.; Bozano, L.; Brown, K.; Bunce, G.; Cameron, P.; Courant, E.; Erin, S.; Escallier, J.; Fischer, W.; Gupta, R.; Hatanaka, K.; Huang, H.; Imai, K.; Ishihara, M.; Jain, A.; Lehrach, A.; Kanavets, V.; Katayama, T.; Kawaguchi, T.; Kelly, E.; Kurita, K.; Lee, S.Y.; Luccio, A.; MacKay, W.W.; Mahler, G.; Makdisi, Y.; Mariam, F.; McGahern, W.; Morgan, G.; Muratore, J.; Okamura, M.; Peggs, S.; Pilat, F.; Ptitsin, V.; Ratner, L.; Roser, T.; Saito, N.; Satoh, H.; Shatunov, Y.; Spinka, H.; Syphers, M.; Tepikian, S.; Tominaka, T.; Tsoupas, N.; Underwood, D.; Vasiliev, A.; Wanderer, P.; Willen, E.; Wu, H.; Yokosawa, A.; Zelenski, A.N.

2003-01-01

In addition to heavy ion collisions (RHIC Design Manual, Brookhaven National Laboratory), RHIC will also collide intense beams of polarized protons (I. Alekseev, et al., Design Manual Polarized Proton Collider at RHIC, Brookhaven National Laboratory, 1998, reaching transverse energies where the protons scatter as beams of polarized quarks and gluons. The study of high energy polarized protons beams has been a long term part of the program at BNL with the development of polarized beams in the Booster and AGS rings for fixed target experiments. We have extended this capability to the RHIC machine. In this paper we describe the design and methods for achieving collisions of both longitudinal and transverse polarized protons in RHIC at energies up to √s=500 GeV

Estimating Allee dynamics before they can be observed: polar bears as a case study.

Science.gov (United States)

Molnár, Péter K; Lewis, Mark A; Derocher, Andrew E

2014-01-01

Allee effects are an important component in the population dynamics of numerous species. Accounting for these Allee effects in population viability analyses generally requires estimates of low-density population growth rates, but such data are unavailable for most species and particularly difficult to obtain for large mammals. Here, we present a mechanistic modeling framework that allows estimating the expected low-density growth rates under a mate-finding Allee effect before the Allee effect occurs or can be observed. The approach relies on representing the mechanisms causing the Allee effect in a process-based model, which can be parameterized and validated from data on the mechanisms rather than data on population growth. We illustrate the approach using polar bears (Ursus maritimus), and estimate their expected low-density growth by linking a mating dynamics model to a matrix projection model. The Allee threshold, defined as the population density below which growth becomes negative, is shown to depend on age-structure, sex ratio, and the life history parameters determining reproduction and survival. The Allee threshold is thus both density- and frequency-dependent. Sensitivity analyses of the Allee threshold show that different combinations of the parameters determining reproduction and survival can lead to differing Allee thresholds, even if these differing combinations imply the same stable-stage population growth rate. The approach further shows how mate-limitation can induce long transient dynamics, even in populations that eventually grow to carrying capacity. Applying the models to the overharvested low-density polar bear population of Viscount Melville Sound, Canada, shows that a mate-finding Allee effect is a plausible mechanism for slow recovery of this population. Our approach is generalizable to any mating system and life cycle, and could aid proactive management and conservation strategies, for example, by providing a priori estimates of minimum

Optical properties of polarization-dependent geometrical phase elements with partially polarized light

International Nuclear Information System (INIS)

Gorodetski, Y.; Biener, G.; Niv, A.; Kleiner, V.; Hasman, E.

2005-01-01

Full Text:The behavior of geometrical phase elements illuminated with partially polarized monochromatic beams is being theoretically as well as experimentally investigated. The element discussed in this paper is composed of wave plates with retardation and space-variant orientation angle. We found that a beam emerging from such an element comprises two polarization orders of right and left-handed circularly polarized states with conjugate geometrical phase modification. This phase equals twice the orientation angle of the space-variant wave plate comprising the element. Apart from the two polarization orders, the emerging beam coherence polarization matrix comprises a matrix termed as the vectorial interference matrix. This matrix contains the information concerning the correlation between the two orthogonal circularly polarized portions of the incident beam. In this paper we measure this correlation by a simple interference experiment. Furthermore, we found that the equivalent mutual intensity of the emerging beam is being modulated according to the geometrical phase induced by the element. Other interesting phenomena along propagation will be discussed theoretically and experimentally demonstrated. We demonstrate experimentally our analysis by using a spherical geometrical phase element, which is realized by use of space-variant sub wavelength grating and illuminated with a CO 2 laser radiation of 10.6μm wavelength

POLARIZED BEAMS: 2 - Partial Siberian Snake rescues polarized protons at Brookhaven

International Nuclear Information System (INIS)

Huang, Haixin

1994-01-01

To boost the level of beam polarization (spin orientation), a partial 'Siberian Snake' was recently used to overcome imperfection depolarizing resonances in the Brookhaven Alternating Gradient Synchrotron (AGS). This 9-degree spin rotator recently permitted acceleration with no noticeable polarization loss. The intrinsic AGS depolarizing resonances (which degrade the polarization content) had been eliminated by betatron tune jumps, but the imperfection resonances were compensated by means of harmonic orbit corrections. However, at high energies these orbit corrections are difficult and tedious and a Siberian Snake became an attractive alternative

Nuclear physics with polarized particles

CERN Document Server

Paetz gen Schieck, Hans

2012-01-01

The measurement of spin-polarization observables in reactions of nuclei and particles is of great utility and advantage when the effects of single-spin sub-states are to be investigated. Indeed, the unpolarized differential cross-section encompasses the averaging over the spin states of the particles, and thus loses details of the interaction process. This introductory text combines, in a single volume, course-based lecture notes on spin physics and on polarized-ion sources with the aim of providing a concise yet self-contained starting point for newcomers to the field, as well as for lecturers in search of suitable material for their courses and seminars. A significant part of the book is devoted to introducing the formal theory-a description of polarization and of nuclear reactions with polarized particles. The remainder of the text describes the physical basis of methods and devices necessary to perform experiments with polarized particles and to measure polarization and polarization effects in nuclear rea...

The polarization of fast neutrons

International Nuclear Information System (INIS)

Talov, V.V.

2001-01-01

It is insufficient to know coordinates and momentum to describe a state of a neutron. It is necessary to define a spin orientation. As far as it is known from quantum mechanics, a half spin has a projection in the positive direction or in the negative direction. The probability of both projections in an unpolarized beam is equal. If a direction exists, in which the projection is more probably then beam is called polarized in this direction. It is essential to know polarization of neutrons for characteristics of a neutron source, which is emitting it. The question of polarization of fast neutrons came up in 50's. The present work is the review of polarization of fast neutrons and methods of polarization analysis. This also includes information about polarization of fast neutrons from first papers, which described polarization in the D(d,n) 3 He, 7 Li (p,n) 7 Be, T(p,n) 3 He reactions. (authors)

Scaling rates of true polar wander in convecting planets and moons

Science.gov (United States)

Rose, Ian; Buffett, Bruce

2017-12-01

Mass redistribution in the convecting mantle of a planet causes perturbations in its moment of inertia tensor. Conservation of angular momentum dictates that these perturbations change the direction of the rotation vector of the planet, a process known as true polar wander (TPW). Although the existence of TPW on Earth is firmly established, its rate and magnitude over geologic time scales remain controversial. Here we present scaling analyses and numerical simulations of TPW due to mantle convection over a range of parameter space relevant to planetary interiors. For simple rotating convection, we identify a set of dimensionless parameters that fully characterize true polar wander. We use these parameters to define timescales for the growth of moment of inertia perturbations due to convection and for their relaxation due to true polar wander. These timescales, as well as the relative sizes of convective anomalies, control the rate and magnitude of TPW. This analysis also clarifies the nature of so called "inertial interchange" TPW events, and relates them to a broader class of events that enable large and often rapid TPW. We expect these events to have been more frequent in Earth's past.

Stanford polarized atomic beam target

International Nuclear Information System (INIS)

Mavis, D.G.; Dunham, J.S.; Hugg, J.W.; Glavish, H.F.

1976-01-01

A polarized atomic beam source was used to produce an atomic hydrogen beam which was in turn used as a polarized proton target. A target density of 2 x 10'' atoms/cm 3 and a target polarization of 0.37 without the use of rf transitions were measured. These measurements indicate that a number of experiments are currently feasible with a variety of polarized target beams

Solar Spectral Lines with Special Polarization Properties for the Calibration of Instrument Polarization

Energy Technology Data Exchange (ETDEWEB)

Li, W.; Casini, R.; Alemán, T. del Pino; Judge, P. G. [High Altitude Observatory, National Center for Atmospheric Research 1, P.O. Box 3000, Boulder, CO 80307-3000 (United States)

2017-10-20

We investigate atomic transitions that have previously been identified as having zero polarization from the Zeeman effect. Our goal is to identify spectral lines that can be used for the calibration of instrumental polarization of large astronomical and solar telescopes, such as the Daniel K. Inouye Solar Telescope, which is currently under construction on Haleakala. We use a numerical model that takes into account the generation of scattering polarization and its modification by the presence of a magnetic field of arbitrary strength. We adopt values for the Landé factors from spectroscopic measurements or semi-empirical results, thus relaxing the common assumption of LS-coupling previously used in the literature. The mechanisms dominating the polarization of particular transitions are identified, and we summarize groups of various spectral lines useful for the calibration of spectropolarimetric instruments, classified according to their polarization properties.

Pinpointing chiral structures with front-back polarized neutron reflectometry.

Science.gov (United States)

O'Donovan, K V; Borchers, J A; Majkrzak, C F; Hellwig, O; Fullerton, E E

2002-02-11

A new development in spin-polarized neutron reflectometry enables us to more fully characterize the nucleation and growth of buried domain walls in layered magnetic materials. We applied this technique to a thin-film exchange-spring magnet. After first measuring the reflectivity with the neutrons striking the front, we measure with the neutrons striking the back. Simultaneous fits are sensitive to the presence of spiral spin structures. The technique reveals previously unresolved features of field-dependent domain walls in exchange-spring systems and has sufficient generality to apply to a variety of magnetic systems.

TNF-α decreases VEGF secretion in highly polarized RPE cells but increases it in non-polarized RPE cells related to crosstalk between JNK and NF-κB pathways.

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Hiroto Terasaki

Full Text Available Asymmetrical secretion of vascular endothelial growth factor (VEGF by retinal pigment epithelial (RPE cells in situ is critical for maintaining the homeostasis of the retina and choroid. VEGF is also involved in the development and progression of age-related macular degeneration (AMD. We studied the effect of tumor necrosis factor-α (TNF-α on the secretion of VEGF in polarized and non-polarized RPE cells (P-RPE cells and N-RPE cells, respectively in culture and in situ in rats. A subretinal injection of TNF-α caused a decrease in VEGF expression and choroidal atrophy. Porcine RPE cells were seeded on Transwell™ filters, and their maturation and polarization were confirmed by the asymmetrical VEGF secretion and trans electrical resistance. Exposure to TNF-α decreased the VEGF secretion in P-RPE cells but increased it in N-RPE cells in culture. TNF-α inactivated JNK in P-RPE cells but activated it in N-RPE cells, and TNF-α activated NF-κB in P-RPE cells but not in N-RPE cells. Inhibition of NF-κB activated JNK in both types of RPE cells indicating crosstalk between JNK and NF-κB. TNF-α induced the inhibitory effects of NF-κB on JNK in P-RPE cells because NF-κB is continuously inactivated. In N-RPE cells, however, it was not evident because NF-κB was already activated. The basic activation pattern of JNK and NF-κB and their crosstalk led to opposing responses of RPE cells to TNF-α. These results suggest that VEGF secretion under inflammatory conditions depends on cellular polarization, and the TNF-α-induced VEGF down-regulation may result in choroidal atrophy in polarized physiological RPE cells. TNF-α-induced VEGF up-regulation may cause neovascularization by non-polarized or non-physiological RPE cells.

Fusion with highly spin polarized HD and D2

International Nuclear Information System (INIS)

Honig, A.; Letzring, S.; Skupsky, S.

1993-01-01

Our experimental efforts over the past 5 years have been aimed at cazrying out ICF shots with spin-polarized 0 fuel. We successfully prepared polarized 0 in HD, and solved the problems of loading target shells with our carefully prepared isotopic -rnixt.l.l?-es, polarizing them so that the 0 polarization remains metastably frozen-in for about half a day, and carrying out the various cold transfer requirements at Syracuse, where the target is prepared, and at Rochester, where the cold target is inserted fusion chamber. Upon shooting the accurately positioned unpolarized high density cold target, no neutron yield was observed. Inspection inside the OMEGA tank after the shot indicated the absence of neutron yield was dus to mal-timing or insufficient retraction rate of OMEGA'S fast shroud mechanism, resulting in interception of at least 20 of the 24 laser beams by the faulty shroud. In spits of this, all alements of the complex experiment we originally undertook have been successfully demonstrated, and the cold retrieval concepts and methods we developed are being utilized on the ICF upgrades at Rochester and at Livermore. In addition to the solution of the interface problems, we obtained novel results on polymer shell characteristics at low temperatures, and continuation of these experiments is c = ently supported by KLUP. Extensive additional mappings were ca=ied out of nuclear spin relaxation rates of H and D in solid HD in the temperature-magnetic field rangs of 0.01 to 4.2K and 0 - 13 Tesla. New phenomena were discovered, such as association of impurity clustering with very low temperature motion, and inequality of the growth-rate and decay-rate of the magnetization

Parallel Polarization State Generation.

Science.gov (United States)

She, Alan; Capasso, Federico

2016-05-17

The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security.

Effect of cathodic polarization on coating doxycycline on titanium surfaces

Energy Technology Data Exchange (ETDEWEB)

Geißler, Sebastian; Tiainen, Hanna; Haugen, Håvard J., E-mail: h.j.haugen@odont.uio.no

2016-06-01

Cathodic polarization has been reported to enhance the ability of titanium based implant materials to interact with biomolecules by forming titanium hydride at the outermost surface layer. Although this hydride layer has recently been suggested to allow the immobilization of the broad spectrum antibiotic doxycycline on titanium surfaces, the involvement of hydride in binding the biomolecule onto titanium remains poorly understood. To gain better understanding of the influence this immobilization process has on titanium surfaces, mirror-polished commercially pure titanium surfaces were cathodically polarized in the presence of doxycycline and the modified surfaces were thoroughly characterized using atomic force microscopy, electron microscopy, secondary ion mass spectrometry, and angle-resolved X-ray spectroscopy. We demonstrated that no hydride was created during the polarization process. Doxycycline was found to be attached to an oxide layer that was modified during the electrochemical process. A bacterial assay using bioluminescent Staphylococcus epidermidis Xen43 showed the ability of the coating to reduce bacterial colonization and planktonic bacterial growth. - Highlights: • Titanium hydride was found not to be involved in immobilization of doxycycline. • Doxycycline coating was strongly bound to a modified surface oxide layer. • Effect of coatings tested using a dynamic bacteria assay based on bioluminescence. • Topmost layer of adsorbed doxycycline was shown to have strong antibacterial effect.

Harvesting wildlife affected by climate change: a modelling and management approach for polar bears.

Science.gov (United States)

Regehr, Eric V; Wilson, Ryan R; Rode, Karyn D; Runge, Michael C; Stern, Harry L

2017-10-01

The conservation of many wildlife species requires understanding the demographic effects of climate change, including interactions between climate change and harvest, which can provide cultural, nutritional or economic value to humans.We present a demographic model that is based on the polar bear Ursus maritimus life cycle and includes density-dependent relationships linking vital rates to environmental carrying capacity ( K ). Using this model, we develop a state-dependent management framework to calculate a harvest level that (i) maintains a population above its maximum net productivity level (MNPL; the population size that produces the greatest net increment in abundance) relative to a changing K , and (ii) has a limited negative effect on population persistence.Our density-dependent relationships suggest that MNPL for polar bears occurs at approximately 0·69 (95% CI = 0·63-0·74) of K . Population growth rate at MNPL was approximately 0·82 (95% CI = 0·79-0·84) of the maximum intrinsic growth rate, suggesting relatively strong compensation for human-caused mortality.Our findings indicate that it is possible to minimize the demographic risks of harvest under climate change, including the risk that harvest will accelerate population declines driven by loss of the polar bear's sea-ice habitat. This requires that (i) the harvest rate - which could be 0 in some situations - accounts for a population's intrinsic growth rate, (ii) the harvest rate accounts for the quality of population data (e.g. lower harvest when uncertainty is large), and (iii) the harvest level is obtained by multiplying the harvest rate by an updated estimate of population size. Environmental variability, the sex and age of removed animals and risk tolerance can also affect the harvest rate. Synthesis and applications . We present a coupled modelling and management approach for wildlife that accounts for climate change and can be used to balance trade-offs among multiple conservation

Polarized deuteron elastic scattering from a polarized proton target

International Nuclear Information System (INIS)

Schmelzer, R.; Kuiper, H.; Schoeberl, M.; Berber, S.; Hilmert, H.; Koeppel, R.; Pferdmenges, R.; Zankel, H.

1983-01-01

Measurements are reported of the spin correlation parameter Cy,y for the elastic scattering of 10.0 MeV vector polarized deuterons from a polarized proton target at five CM angles (76 0 ,85 0 ,98 0 ,115 0 ,132 0 ). The experimental results are compared with different predictions. A Faddeev type calculation on the basis of local potentials also including approximate Coulomb distortion is favoured by our experimental results. (orig.)

Polarity control of GaN epitaxial films grown on LiGaO2(001) substrates and its mechanism.

Science.gov (United States)

Zheng, Yulin; Wang, Wenliang; Li, Xiaochan; Li, Yuan; Huang, Liegen; Li, Guoqiang

2017-08-16

The polarity of GaN epitaxial films grown on LiGaO 2 (001) substrates by pulsed laser deposition has been well controlled. It is experimentally proved that the GaN epitaxial films grown on nitrided LiGaO 2 (001) substrates reveal Ga-polarity, while the GaN epitaxial films grown on non-nitrided LiGaO 2 (001) substrates show N-polarity. The growth mechanisms for these two cases are systematically studied by first-principles calculations based on density functional theory. Theoretical calculation presents that the adsorption of a Ga atom preferentially occurs at the center of three N atoms stacked on the nitrided LiGaO 2 (001) substrates, which leads to the formation of Ga-polarity GaN. Whereas the adsorption of a Ga atom preferentially deposits at the top of a N atom stacked on the non-nitrided LiGaO 2 (001) substrates, which results in the formation of N-polarity GaN. This work of controlling the polarity of GaN epitaxial films is of paramount importance for the fabrication of group-III nitride devices for various applications.

Polarized vacuum ultraviolet and X-radiation

International Nuclear Information System (INIS)

Samson, J.A.R.

1978-01-01

The most intense source of polarized vacuum UV and X-radiation is synchrotron radiation, which exhibits a degree of partially polarized light between about 80-100%. However, the radiation transmitted by vacuum UV monochromators can also be highly polarized. The Seya-Namioka type of monochromator can produce partially polarized radiation between 50-80%. For certain experiments it is necessary to know the degree of polarisation of the radiation being used. Also, when synchrotron radiation and a monochromator are combined the polarization characteristic of both should be known in order to make full use of these polarization properties. The polarizing effect on monochromators (i.e. diffraction gratings) have been measured at the Seya angle and at grazing angles for various spectral orders. The author presents the first experimental evidence that the reciprocity law holds for polarization by reflection where the angle of incidence and diffraction are unequal. These results are reviewed along with the techniques for measuring the degree of polarization. (Auth.)

A review of polarized ion sources

International Nuclear Information System (INIS)

Schmor, P.W.

1995-06-01

The two main types of polarized ion sources in use on accelerators today are the Atomic Beam Polarized Ion Source (ABIS) source and the Optically Pumped Polarized Ion Source (OPPIS). Both types can provide beams of nuclearly polarized light ions which are either positively or negatively charged. Heavy ion polarized ion sources for accelerators are being developed. (author). 35 refs., 1 tab

Polarization phenomena in heavy-ion reactions

International Nuclear Information System (INIS)

Sugimoto, K.; Ishihara, M.; Takahashi, N.

1984-01-01

This chapter presents a few key experiments which provide direct evidence of the polarization phenomena in heavy-ion reactions. The theory of polarization observables and measurements is given with the necessary formulae. The polarization phenomena is described and studies of product nuclear polarization in heavy-ion reactions are discussed. Studies of heavy-ion reactions induced by polarized beams are examined

Dynamic nuclear polarization tests in some polymers for polarized targets

International Nuclear Information System (INIS)

Brandt, B. van den; Hautle, P.; Konter, J.A.; Mango, S.; Bunyatova, E.I.

1998-01-01

The results of dynamic polarization tests in polyethylene (PE) and ethylene propylene copolymer (EPC), doped with the stable free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), are presented. Sizable proton polarizations have been achieved in a magnetic field of 2.5 T at a temperature below 0.3 K and 5T at 1 K

Broad-aperture polarized proton target with arbitrary orientation of polarization vector

International Nuclear Information System (INIS)

Belyaev, A.A.; Get'man, V.A.; Derkach, A.Ya.; Karnaukhov, I.M.; Lukhanin, A.A.; Razumnyj, A.A.; Sorokin, P.V.; Sporov, E.A.; Telegin, Yu.N.; Trotsenko, V.I.

1985-01-01

Polarized proton target with the Helmholtz broad-aperture superconducting magnetic system is described. Axial aperture α=95 deg, inter-coil access angle β=23 deg. The structure of the target allows various versions of the installation what make sure an arbitrary orientation of polarization vector. The 0.1 W cold output 3 He evaporation cryostat was used to obtain the work temperature 0.5 K allowing quick transformation to a 3 He- 4 He dilution refrigerator. Results of the study are given on the dynamical proton polarization in 1,2-propylenglycol with various stable Cr 5 complexes

Do embryonic polar bodies commit suicide?

Science.gov (United States)

Fabian, Dušan; Čikoš, Štefan; Rehák, Pavol; Koppel, Juraj

2014-02-01

The extrusion and elimination of unnecessary gametic/embryonic material is one of the key events that determines the success of further development in all living organisms. Oocytes produce the first polar body to fulfill the maturation process just before ovulation, and release the second polar body immediately after fertilization. The aim of this study was to compile a physiological overview of elimination of polar bodies during early preimplantation development in mice. Our results show that three-quarters of the first polar bodies were lost even at the zygotic stage; the 4-cell stage embryos contained only one (second) polar body, and the elimination of second polar bodies proceeded continuously during later development. Both first and second polar bodies showed several typical features of apoptosis: phosphatidylserine redistribution (observed for the first time in the first polar body), specific DNA degradation, condensed nuclear morphology, and inability to exclude cationic dye from the nucleus during the terminal stage of the apoptotic process. Caspase-3 activity was recorded only in the second polar body. From the morphological point of view, mouse polar bodies acted very similarly to damaged embryonic cells which have lost contact with their neighboring blastomeres. In conclusion, polar bodies possess all the molecular equipment necessary for triggering and executing an active suicide process. Furthermore, similarly as in dying embryonic cells, stressing external conditions (culture in vitro) might accelerate and increase the incidence of apoptotic elimination of the polar bodies in embryos.

Spin exchange in polarized deuterium

International Nuclear Information System (INIS)

Przewoski, B. von; Meyer, H.O.; Balewski, J.; Doskow, J.; Ibald, R.; Pollock, R.E.; Rinckel, T.; Wellinghausen, A.; Whitaker, T.J.; Daehnick, W.W.; Haeberli, W.; Schwartz, B.; Wise, T.; Lorentz, B.; Rathmann, F.; Pancella, P.V.; Saha, Swapan K.; Thoerngren-Engblom, P.

2003-01-01

We have measured the vector and tensor polarization of an atomic deuterium target as a function of the target density. The polarized deuterium was produced in an atomic beam source and injected into a storage cell. For this experiment, the atomic beam source was operated without rf transitions, in order to avoid complications from the unknown efficiency of these transitions. In this mode, the atomic beam is vector and tensor polarized and both polarizations can be measured simultaneously. We used a 1.2-cm-diam and 27-cm-long storage cell, which yielded an average target density between 3 and 9x10 11 at/cm 3 . We find that the tensor polarization decreases with increasing target density while the vector polarization remains constant. The data are in quantitative agreement with the calculated effect of spin exchange between deuterium atoms at low field

Characterization of a subunit of the outer dynein arm docking complex necessary for correct flagellar assembly in Leishmania donovani.

Directory of Open Access Journals (Sweden)

Simone Harder

Full Text Available BACKGROUND: In order to proceed through their life cycle, Leishmania parasites switch between sandflies and mammals. The flagellated promastigote cells transmitted by the insect vector are phagocytized by macrophages within the mammalian host and convert into the amastigote stage, which possesses a rudimentary flagellum only. During an earlier proteomic study of the stage differentiation of the parasite we identified a component of the outer dynein arm docking complex, a structure of the flagellar axoneme. The 70 kDa subunit of the outer dynein arm docking complex consists of three subunits altogether and is essential for the assembly of the outer dynein arm onto the doublet microtubule of the flagella. According to the nomenclature of the well-studied Chlamydomonas reinhardtii complex we named the Leishmania protein LdDC2. METHODOLOGY/PRINCIPAL FINDINGS: This study features a characterization of the protein over the life cycle of the parasite. It is synthesized exclusively in the promastigote stage and localizes to the flagellum. Gene replacement mutants of lddc2 show reduced growth rates and diminished flagellar length. Additionally, the normally spindle-shaped promastigote parasites reveal a more spherical cell shape giving them an amastigote-like appearance. The mutants lose their motility and wiggle in place. Ultrastructural analyses reveal that the outer dynein arm is missing. Furthermore, expression of the amastigote-specific A2 gene family was detected in the deletion mutants in the absence of a stage conversion stimulus. In vitro infectivity is slightly increased in the mutant cell line compared to wild-type Leishmania donovani parasites. CONCLUSIONS/SIGNIFICANCE: Our results indicate that the correct assembly of the flagellum has a great influence on the investigated characteristics of Leishmania parasites. The lack of a single flagellar protein causes an aberrant morphology, impaired growth and altered infectiousness of the parasite.

White emission by self-regulated growth of InGaN/GaN quantum wells on in situ self-organized faceted n-GaN islands

International Nuclear Information System (INIS)

Fang Zhilai

2011-01-01

The in situ self-organization of three-dimensional n-GaN islands of distinct sidewall faceting was realized by initial low V/III ratio growth under high reactor pressure followed by variations of the V/III ratio and reactor pressure. The naturally formed faceted islands with top and sidewall facets of various specific polar angles may serve as an ideal template for self-regulated growth of the InGaN/GaN multiple quantum wells (MQWs), i.e. the growth behavior is specific polar angle dependent. Further, the growth behavior and luminescence properties of the InGaN/GaN MQWs on various facets of different specific polar angles are directly compared and discussed. Tetrachromatic white emissions (blue, cyan, green, and red) from single-chip phosphor-free InGaN/GaN MQWs are realized by color tuning through island shaping, shape variations, and self-regulated growth of the InGaN/GaN MQWs.

Study by polarized muon

International Nuclear Information System (INIS)

Yamazaki, Toshimitsu

1977-01-01

Experiments by using polarized muon beam are reported. The experiments were performed at Berkeley, U.S.A., and at Vancouver, Canada. The muon spin rotation is a useful method for the study of the spin polarization of conductive electrons in paramagnetic Pd metal. The muon Larmor frequency and the relaxation time can be obtained by measuring the time distribution of decay electrons of muon-electron process. The anomalous depolarization of negative muon spin rotation in the transitional metal was seen. The circular polarization of the negative muon X-ray was measured to make clear this phenomena. The experimental results show that the anomalous depolarization is caused at the 1-S-1/2 state. For the purpose to obtain the strong polarization of negative muon, a method of artificial polarization is proposed, and the test experiments are in progress. The study of the hyperfine structure of mu-mesic atoms is proposed. The muon capture rate was studied systematically. (Kato, T.)

Experimental and theoretical studies on electropolymerization of polar amino acids on platinum electrode

Energy Technology Data Exchange (ETDEWEB)

Alhedabi, Taleb [Nanomedicine Lab EA4662, Bat. E, Université de Bourgogne Franche-Comté, UFR Sciences & Techniques, 16 route de Gray, 25030 Besançon Cedex (France); Department of Chemistry, College of Science, University of Thi-qar, Thi-qar (Iraq); Cattey, Hélène [Institut ICMUB - CNRS 6302, Université de Bourgogne Franche-Comté, UFR Sciences et Techniques Mirande, 9 Avenue Alain Savary, 21000 Dijon (France); Roussel, Christophe [Ecole Polytechnique Fédérale de Lausanne, Section of Chemistry and Chemical Engineering, Station 6, CH-1015 Lausanne (Switzerland); Blondeau-Patissier, Virginie [Institut FEMTO-ST, UMR CNRS 6174, Department Time-Frequency, 26, Chemin de l' épitaphe, 25030 Besançon Cedex (France); Gharbi, Tijani [Nanomedicine Lab EA4662, Bat. E, Université de Bourgogne Franche-Comté, UFR Sciences & Techniques, 16 route de Gray, 25030 Besançon Cedex (France); Herlem, Guillaume, E-mail: guillaume.herlem@univ-fcomte.fr [Nanomedicine Lab EA4662, Bat. E, Université de Bourgogne Franche-Comté, UFR Sciences & Techniques, 16 route de Gray, 25030 Besançon Cedex (France)

2017-01-01

The anodic oxidation of polar amino acids (L-serine, L-threonine, L-asparagine, and L-glutamine) in aqueous electrolyte on smooth platinum electrode was carried out by cyclic voltammetry coupled to electrochemical quartz crystal microbalance (EQCM). pH (zwitterion, acidic and alkaline) effects on their electrochemical behavior were examined. The maximum current values are measured for zwitterion species. In addition, the current increases with increasing of concentration and scan rate, and decreases with increasing pH. The resulting passivation was studied by spectroscopic analysis such as attenuated total reflection FT infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and mass spectroscopy (MALDI-TOF). From thin film coatings observed on the electrode surface, peptide bonds are found, and are in favor of electropolymerization of these polar amino acids into poly-L-amino acids in an irreversible way. Scanning electronic microscopy was also used to study the morphology of these electrodeposited L-amino acids. The electrodeposited poly-L-amino acids on Pt electrode were tested as bioinspired transducer for pH sensing purposes. - Highlights: • Anodic oxidation of polar amino acids with uncharged R group on platinum electrode. • Polypeptide bonds revealed by ATR-IR and XPS spectroscopies. • The film growth depends on the chemistry of the polar amino acid.

ACCELERATION OF POLARIZED PROTONS AT RHIC

International Nuclear Information System (INIS)

HUANG, H.

2002-01-01

Relativistic Heavy Ion Collider (RHIC) ended its second year of operation in January 2002 with five weeks of polarized proton collisions. Polarized protons were successfully injected in both RHIC rings and maintained polarization during acceleration up to 100 GeV per ring using two Siberian snakes in each ring. This is the first time that polarized protons have been accelerated to 100 GeV. The machine performance and accomplishments during the polarized proton run will be reviewed. The plans for the next polarized proton run will be outlined

Polarized deuteron elastic scattering from a polarized proton target

Energy Technology Data Exchange (ETDEWEB)

Schmelzer, R.; Kuiper, H.; Schoeberl, M.; Berber, S.; Hilmert, H.; Koeppel, R.; Pferdmenges, R. (Erlangen-Nuernberg Univ., Erlangen (Germany, F.R.). Physikalisches Inst.); Zankel, H. (Graz Univ. (Austria). Inst. fuer Theoretische Physik)

1983-01-13

Measurements are reported of the spin correlation parameter Cy,y for the elastic scattering of 10.0 MeV vector polarized deuterons from a polarized proton target at five CM angles (76/sup 0/,85/sup 0/,98/sup 0/,115/sup 0/,132/sup 0/). The experimental results are compared with different predictions. A Faddeev type calculation on the basis of local potentials also including approximate Coulomb distortion is favoured by our experimental results.

A tale of two polar bear populations: Ice habitat, harvest, and body condition

Science.gov (United States)

Rode, Karyn D.; Peacock, Elizabeth; Taylor, Mitchell K.; Stirling, Ian; Born, Erik W.; Laidre, Kristin L.; Wiig, Øystein

2012-01-01

One of the primary mechanisms by which sea ice loss is expected to affect polar bears is via reduced body condition and growth resulting from reduced access to prey. To date, negative effects of sea ice loss have been documented for two of 19 recognized populations. Effects of sea ice loss on other polar bear populations that differ in harvest rate, population density, and/or feeding ecology have been assumed, but empirical support, especially quantitative data on population size, demography, and/or body condition spanning two or more decades, have been lacking. We examined trends in body condition metrics of captured bears and relationships with summertime ice concentration between 1977 and 2010 for the Baffin Bay (BB) and Davis Strait (DS) polar bear populations. Polar bears in these regions occupy areas with annual sea ice that has decreased markedly starting in the 1990s. Despite differences in harvest rate, population density, sea ice concentration, and prey base, polar bears in both populations exhibited positive relationships between body condition and summertime sea ice cover during the recent period of sea ice decline. Furthermore, females and cubs exhibited relationships with sea ice that were not apparent during the earlier period (1977–1990s) when sea ice loss did not occur. We suggest that declining body condition in BB may be a result of recent declines in sea ice habitat. In DS, high population density and/or sea ice loss, may be responsible for the declines in body condition.

C. elegans STRADalpha and SAD cooperatively regulate neuronal polarity and synaptic organization.

Science.gov (United States)

Kim, Joanne S M; Hung, Wesley; Narbonne, Patrick; Roy, Richard; Zhen, Mei

2010-01-01

Neurons are polarized cells with morphologically and functionally distinct axons and dendrites. The SAD kinases are crucial for establishing the axon-dendrite identity across species. Previous studies suggest that a tumour suppressor kinase, LKB1, in the presence of a pseudokinase, STRADalpha, initiates axonal differentiation and growth through activating the SAD kinases in vertebrate neurons. STRADalpha was implicated in the localization, stabilization and activation of LKB1 in various cell culture studies. Its in vivo functions, however, have not been examined. In our present study, we analyzed the neuronal phenotypes of the first loss-of-function mutants for STRADalpha and examined their genetic interactions with LKB1 and SAD in C. elegans. Unexpectedly, only the C. elegans STRADalpha, STRD-1, functions exclusively through the SAD kinase, SAD-1, to regulate neuronal polarity and synaptic organization. Moreover, STRD-1 tightly associates with SAD-1 to coordinate its synaptic localizations. By contrast, the C. elegans LKB1, PAR-4, also functions in an additional genetic pathway independently of SAD-1 and STRD-1 to regulate neuronal polarity. We propose that STRD-1 establishes neuronal polarity and organizes synaptic proteins in a complex with the SAD-1 kinase. Our findings suggest that instead of a single, linear genetic pathway, STRADalpha and LKB1 regulate neuronal development through multiple effectors that are shared in some cellular contexts but distinct in others.

Gβ promotes pheromone receptor polarization and yeast chemotropism by inhibiting receptor phosphorylation.

Science.gov (United States)

Ismael, Amber; Tian, Wei; Waszczak, Nicholas; Wang, Xin; Cao, Youfang; Suchkov, Dmitry; Bar, Eli; Metodiev, Metodi V; Liang, Jie; Arkowitz, Robert A; Stone, David E

2016-04-12

Gradient-directed cell migration (chemotaxis) and growth (chemotropism) are processes that are essential to the development and life cycles of all species. Cells use surface receptors to sense the shallow chemical gradients that elicit chemotaxis and chemotropism. Slight asymmetries in receptor activation are amplified by downstream signaling systems, which ultimately induce dynamic reorganization of the cytoskeleton. During the mating response of budding yeast, a model chemotropic system, the pheromone receptors on the plasma membrane polarize to the side of the cell closest to the stimulus. Although receptor polarization occurs before and independently of actin cable-dependent delivery of vesicles to the plasma membrane (directed secretion), it requires receptor internalization. Phosphorylation of pheromone receptors by yeast casein kinase 1 or 2 (Yck1/2) stimulates their internalization. We showed that the pheromone-responsive Gβγ dimer promotes the polarization of the pheromone receptor by interacting with Yck1/2 and locally inhibiting receptor phosphorylation. We also found that receptor phosphorylation is essential for chemotropism, independently of its role in inducing receptor internalization. A mathematical model supports the idea that the interaction between Gβγ and Yck1/2 results in differential phosphorylation and internalization of the pheromone receptor and accounts for its polarization before the initiation of directed secretion. Copyright © 2016, American Association for the Advancement of Science.

Colonic macrophage polarization in homeostasis, inflammation, and cancer

Science.gov (United States)

Appleyard, Caroline B.

2016-01-01

Our review focuses on the colonic macrophage, a monocyte-derived, tissue-resident macrophage, and the role it plays in health and disease, specifically in inflammatory conditions such as inflammatory bowel disease and cancer of the colon and rectum. We give special emphasis to macrophage polarization, or phenotype, in these different states. We focus on macrophages because they are one of the most numerous leukocytes in the colon, and because they normally contribute to homeostasis through an anti-inflammatory phenotype. However, in conditions such as inflammatory bowel disease, proinflammatory macrophages are increased in the colon and have been linked to disease severity and progression. In colorectal cancer, tumor cells may employ anti-inflammatory macrophages to promote tumor growth and dissemination, whereas proinflammatory macrophages may antagonize tumor growth. Given the key roles that this cell type plays in homeostasis, inflammation, and cancer, the colonic macrophage is an intriguing therapeutic target. As such, potential macrophage-targeting strategies are discussed. PMID:27229123

Green 'agrowth' as a third option: Removing the GDP-growth constraint on human progress

OpenAIRE

Van den Bergh, Jeroen C.J.M.

2015-01-01

WWWforEurope Policy Paper No. 19, 25 pages The debate on growth versus the environment is usually summarized as optimists believing in limitless growth versus pessimists seeing environmental and resource limits to growth. This opposition defines the main strategies: namely, striving for green growth versus some anti-growth approach. In this paper I argue that we should not feel obliged to choose between these polarized opinions, as there is in fact a third option. I call this the “agrowth...

The Polarization of Achernar

Science.gov (United States)

McDavid, D.

2005-11-01

Recent near-infrared measurements of the angular diameter of Achernar (the bright Be star alpha Eridani) with the ESO VLT interferometer have been interpreted as the detection of an extremely oblate photosphere, with a ratio of equatorial to polar radius of at least 1.56 ± 0.05 and a minor axis orientation of 39° ± 1° (from North to East). The optical linear polarization of this star during an emission phase in 1995 September was 0.12 ± 0.02% at position angle 37° ± 8° (in equatorial coordinates), which is the direction of the projection of the rotation axis on the plane of the sky according to the theory of polarization by electron scattering in an equatorially flattened circumstellar disk. These two independent determinations of the orientation of the rotation axis are therefore in agreement. The observational history of correlations between Hα emission and polarization as found in the literature is that of a typical Be star, with the exception of an interesting question raised by the contrast between Schröder's measurement of a small polarization perpendicular to the projected rotation axis in 1969--70 and Tinbergen's measurement of zero polarization in 1974.5, both at times when emission was reportedly absent.

Polarization-Insensitive Surface Plasmon Polarization Electro-Absorption Modulator Based on Epsilon-Near-Zero Indium Tin Oxide

Science.gov (United States)

Jin, Lin; Wen, Long; Liang, Li; Chen, Qin; Sun, Yunfei

2018-02-01

CMOS-compatible plasmonic modulators operating at the telecom wavelength are significant for a variety of on-chip applications. Relying on the manipulation of the transverse magnetic (TM) mode excited on the metal-dielectric interface, most of the previous demonstrations are designed to response only for specific polarization state. In this case, it will lead to a high polarization dependent loss, when the polarization-sensitive modulator integrates to a fiber with random polarization state. Herein, we propose a plasmonic modulator utilizing a metal-oxide indium tin oxide (ITO) wrapped around the silicon waveguide and investigate its optical modulation ability for both the vertical and horizontal polarized guiding light by tuning electro-absorption of ITO with the field-induced carrier injection. The electrically biased modulator with electron accumulated at the ITO/oxide interface allows for epsilon-near-zero (ENZ) mode to be excited at the top or lateral portion of the interface depending on the polarization state of the guiding light. Because of the high localized feature of ENZ mode, efficient electro-absorption can be achieved under the "OFF" state of the device, thus leading to large extinction ratio (ER) for both polarizations in our proposed modulator. Further, the polarization-insensitive modulation is realized by properly tailoring the thickness of oxide in two different stacking directions and therefore matching the ER values for device operating at vertical and horizontal polarized modes. For the optimized geometry configuration, the difference between the ER values of two polarization modes, i.e., the ΔER, as small as 0.01 dB/μm is demonstrated and, simultaneously with coupling efficiency above 74%, is obtained for both polarizations at a wavelength of 1.55 μm. The proposed plasmonic-combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.

Beta4 integrin-dependent formation of polarized three-dimensionalarchitecture confers resistance to apoptosis in normal and malignantmammary epithelium

Energy Technology Data Exchange (ETDEWEB)

Weaver, Valerie M.; Lelievre, Sophie; Lakins, Johnathon N.; Chrenek, Micah A.; Jones, Jonathan C.R.; Giancotti, Filippo; Werb, Zena; Bissell, Mina J.

2002-08-27

Tumor cells can evade chemotherapy by acquiring resistanceto apoptosis. We investigated the molecular mechanism whereby malignantand nonmalignant mammary epithelial cells become insensitive toapoptosis. We show that regardless of growth status formation ofpolarized, three-dimensional structures driven by basement membraneconfers protection to apoptosis in both nonmalignant and malignantmammary epithelial cells. By contrast, irrespective of their malignantstatus, nonpolarized structures are sensitive to induction of apoptosis.Resistance to apoptosis requires ligation of beta4 integrins, whichregulates tissue polarity, hemidesmosome formation and NFkB activation.Expression of beta4 integrin that lacks the hemidesmosome targetingdomain interferes with tissue polarity and NFkB activation and permitsapoptosis. These results indicate that integrin-induced polarity maydrive tumor cell resistance to apoptosis-inducing agents via effects onNFkB.

Polarization-switching dynamics and microstructures of ferroelectric (Bi0.5Na0.5)TiO3 single crystals

Science.gov (United States)

Yanai, Ken; Onozuka, Hiroaki; Kitanaka, Yuuki; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Kurushima, Kousuke; Mori, Shigeo

2013-04-01

Single crystals of ferroelectric (Bi0.5Na0.5)TiO3 were successfully grown by using the top-seeded solution growth method at a high oxygen pressure of 0.9 MPa and their polarization switching dynamics along the c direction and their domain structures were investigated. Piezoelectric force microscope (PFM) observations show that BNT crystals poled along the c direction. had 71-degree domains in which the spontaneous polarization ( P s ) vector was opposite to the direction of the poling electric field. Synchrotron-radiation single-crystal X-ray diffraction analyses and PFM observations revealed that the polarization switching in the BNT crystals along the c direction was achieved by a 71-degree rotation of the P s vector.

Optically pumped electron spin polarized targets for use in the production of polarized ion beams

International Nuclear Information System (INIS)

Anderson, L.W.

1979-01-01

The production of relatively dense electron spin polarized alkali metal vapor targets by optical pumping with intense cw dye lasers is discussed. The target density and electron spin polarization depend on the dye laser intensity and bandwidth, the magnetic field at the target, and the electron spin depolarization time. For example in a magnetic field of 1.5 x 10 3 G, and using 1 W dye laser with a bandwidth of 10 10 Hz one can construct an electron spin polarized Na vapor target with a target thickness of 1.6 x 10 13 atoms/cm 2 and an average electron spin polarization of about 90% even though the Na atoms are completely depolarized at every wall collision. Possible uses of the electron spin polarized targets for the production of intense beams of polarized H - or 3 He - ions are discussed. (orig.)

Design of a tensor polarized deuterium target polarized by spin-exchange with optically pumped NA

International Nuclear Information System (INIS)

Green, M.C.

1984-01-01

A proposed design for a tensor polarized deuterium target (approx. 10 15 atoms/cm 2 ) for nuclear physics studies in an electron storage ring accelerator is presented. The deuterium atoms undergo electron spin exchange with a highly polarized sodium vapor; this polarization is transferred to the deuterium nuclei via the hyperfine interaction. The deuterium nuclei obtain their tensor polarization through repeated electron spin exchange/hyperfine interactions. The sodium vapor polarization is maintained by standard optical pumping techniques. Model calculations are presented in detail leading to a discussion of the expected performance and the technical obstacles to be surmounted in the development of such a target