bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation mechanism for vapor-to-liquid transition from substrates with nanoscale pores opened at one end
Authors: Liu Yawei , Men Yumei , Zhang Xianren
Published: September 2012

In this work, we study the nucleation mechanism of vapor-to-liquid phase transition from rough substrates, which are modeled as flat substrates decorated with square nanopores with one open end. Our calculations in a constrained lattice density functional theory shows that the presence of nanopores results in an intermediate state, either metastable or unstable, which divides the whole nucleation process into two sequential sub-processes, i.e., pore filling and phase transition outside the pores. Therefore, the nucleation mechanism was found to be one-step (with unstable intermediate states) or two-step (with metastable intermediate states), depending on the fluid-solid interaction, chemical potential, and pore size. The constructed phase diagram of nucleation mechanism shows that there exist six different nucleation mechanisms. In addition, our calculations show that the presence of nanopores on a rough substrate may change the morphology of critical nuclei from their counterpart on a smooth substrate.
Polarization doping: Reservoir effects of the substrate in AlGaN graded layers
Authors: Li Shibin , Ware Morgan E. , Wu Jiang , Kunets Vasyl P. , Hawkridge Mike , Minor Paul , Wang Zhiming , Wu Zhiming , Jiang Yadong , Salamo Gregory J.
Published: September 2012

High electron sheet concentrations of ∼1015 cm−2 result from polarization doping with compositionally graded AlGaN films grown on unintentionally doped GaN templates which exhibit background electron concentrations of ∼1016 cm−3. Similar graded films grown on semi-insulating (SI), free standing GaN substrates exhibited carrier concentrations two orders less. Transport studies of the as-grown materials using temperature dependent Hall effect revealed a very weak temperature dependence of the carrier concentration and mobility as compared to traditionally doped films using Si as a dopant. And qualitative modeling of the electron mobility indicates that alloy scattering and charged dislocation scattering are the most significant contributors to limiting the mobility over the entire temperature range.
Quantitative trap and long range transportation of micro-particles by using phase controllable acoustic wave
Authors: Jia Kun , Yang Keji , Mei Deqing
Published: September 2012

Ultrasonic manipulations, which are widely used as a non-destructive and non-contact technology to trap and transport dense micrometer scale objects in fluids, are of interest to life sciences and micro-technology. In this study, a novel method of quantitatively trapping and transporting the micro-particles over a long range on a two dimensional plane by using phase controllable acoustic wave is proposed. Three phase-controlled piston transducers whose sound beam axes are arranged with an angle of 120° in the x-z plane are used to generate ultrasonic standing waves with arbitrary nodal positions. The synthesized sound field is scanned using a needle hydrophone, and the experimental data show good agreement with the calculated results. The acoustic radiation force drives dense particles towards a pressure node. By adjusting the phase of the lower two transducers, the particles can be transported in the horizontal and vertical direction quantitatively. The longest transporting range can be up to 3 mm. By varying the phase changing rate, the micro-particles can be transported at different velocities. The experimental results illustrate that the relationship between the position and phase show good agreement with the calculated results in the horizontal direction but some deviations in the vertical direction. The influences that may account for these deviations are also discussed.
Structural and micromechanical analyses by polarized Raman spectroscopy of wurtzitic GaN films grown on (0001) sapphire substrates
Authors: Zhu Wenliang , Park Sungkyun , Okumura Yuji , Leto Andrea , Pezzotti Giuseppe
Published: September 2012

Polarized Raman spectroscopy is applied to non-destructively unfold the variation of crystallographic orientation in wurtzitic GaN films that occurred during their growth on (0001)-oriented sapphire substrates as a function of growth conditions. Variations of polarized Raman spectra were clearly observed at different locations along the growth direction by systematically performing line scans on cross sections of different film/substrate systems. Such variations showed a strong dependence on the type of buffer layer, deposition temperature, and reactor pressure. The observed trends suggested the occurrence of inhomogeneous lateral growth of GaN films near the buffer layer and a continuous adjustment of the structure of the tilted-grown epilayer during the growth process until reaching the expected stable structure. The large elastic/thermal mismatch, which could not be fully relaxed by the effect of the buffer layer, resulted in a non-uniform distribution of residual strain. Such strain, mainly stored at the interface, gradually relaxed by the occurrence of tilting and twisting of the crystal cells along the film growth direction: a process that spontaneously occurred minimizing the strain energy stored in the film/substrate system. Varying reactor pressure caused a variation of residual strain in the epilayer and thus a different adjustment of the GaN microstructure during the growth process. Relatively homogenous GaN films with a low density of dislocations could be achieved on patterned sapphire substrates, despite the presence of crystallographic tilting of the film.
Void evolution in silicon under inert and dry oxidizing ambient annealing and the role of a Si1−xGex epilayer cap
Authors: Hasanuzzaman Mohammad , Haddara Yaser M. , Knights Andrew P.
Published: September 2012

Voids were formed in silicon (Si) and silicon germanium/silicon (Si1−xGex/Si) samples containing 5% or 9% Ge (at. %) by 30 keV, 5 × 1016 cm−2 helium (He+) implantation followed by annealing in nitrogen (N2) or dry oxygen (O2) atmospheres in the temperature range 960–1110 °C. Si1−xGex thicknesses were 60 nm and 20 nm for 5% and 9% Ge, respectively. He+ implantation energy was set such that in Si1−xGex/Si samples voids were formed inside the Si substrate. An increase in annealing temperature resulted in an increase in the average void diameter and decrease in the average void density. Due to the presence of implantation damage and the relatively high temperature anneals, Ge diffusion occurs, which results in a stress gradient in the sample that interacts with the void layer. The presence of Ge also results in weaker Si-Ge bonds (compared to Si-Si bonds). This leads to an increase in the rate of cavity migration providing a likely explanation for the increase in the average void diameter and decrease in the average void density in Si1−xGex/Si samples when compared to the similarly prepared Si samples. No impact on the void evolution process was observed as a result of changing the anneal atmosphere from N2 to dry O2.
Electronic and transport gaps of graphene opened by grain boundaries
Authors: Zhang Junfeng , Gao Junfeng , Liu Lizhao , Zhao Jijun
Published: September 2012

The electronic and transport properties of graphene grain boundaries (GBs) are studied using density functional theory and nonequilibrium Green's function method. Most GBs preserve the semi-metal properties of perfect graphene; however, some GBs can open a moderate band gap up to 0.5 eV, which provides a potential way for band engineering of graphene-based materials. Nonequilibrium calculations of transmission coefficients showed that the conduction channels for transport electrons at Fermi level can be totally blocked or reduced due to existence of GBs. Moreover, the detailed defect arrangements have some influence on the transport behavior of graphene GBs.
Inhomogeneous stationary and oscillatory regimes in coupled chaotic oscillators
Authors: Liu Weiqing , Volkov Evgeny , Xiao Jinghua , Zou Wei , Zhan Meng , Yang Junzhong
Published: September 2012

The dynamics of linearly coupled identical Lorenz and Pikovsky-Rabinovich oscillators are explored numerically and theoretically. We concentrate on the study of inhomogeneous stable steady states (“oscillation death (OD)” phenomenon) and accompanying periodic and chaotic regimes that emerge at an appropriate choice of the coupling matrix. The parameters, for which OD occurs, are determined by stability analysis of the chosen steady state. Three model-specific types of transitions to and from OD are observed: (1) a sharp transition to OD from a nonsymmetric chaotic attractor containing random intervals of synchronous chaos; (2) transition to OD from the symmetry-breaking chaotic regime created by negative coupling; (3) supercritical bifurcation of OD into inhomogeneous limit cycles and further evolution of the system to inhomogeneous chaotic regimes that coexist with complete synchronous chaos. These results may fill a gap in the understanding of the mechanism of OD in coupled chaotic systems.
TiO2 brookite nanostructured thin layer on magneto-optical surface plasmon resonance transductor for gas sensing applications
Authors: Manera M. G. , Colombelli A. , Rella R. , Caricato A. , Cozzoli P. D. , Martino M. , Vasanelli L.
Published: September 2012

The sensing performance comparisons presented in this work were carried out by exploiting a suitable magneto-plasmonic sensor in both the traditional surface plasmon resonance configuration and the innovative magneto-optic surface plasmon resonance one. The particular multilayer transducer was functionalized with TiO2 Brookite nanorods layers deposited by matrix assisted pulsed laser evaporation, and its sensing capabilities were monitored in a controlled atmosphere towards different concentrations of volatile organic compounds mixed in dry air.
Transient photoconductivity responses in amorphous In-Ga-Zn-O films
Authors: Yasuno Satoshi , Kita Takashi , Morita Shinya , Kugimiya Toshihiro , Hayashi Kazushi , Sumie Shingo
Published: September 2012

We studied the photoconductivity responses in amorphous In-Ga-Zn-O (a-IGZO) films using a time-resolved microwave photoconductivity decay (μ-PCD) technique. The a-IGZO film characteristics are correlated with three components in the photoconductivity response: the peak value and two decay constants. The peak value originated from the density of the photo-generated free carriers through carrier generation and recombination processes during laser pulse irradiation. Power law characteristics indicated that the peak values are attributed to recombination process related to the exponential distribution of the conduction band tail states. After the laser pulse was turned off, the reflectivity signal decreased rapidly, indicating fast recombination of the photo-generated carriers. This fast decay component is suggested to be related to the recombination processes through the deep level states. Following the fast decay, a slow decay with a decay constant on the order of microseconds appeared. This slow decay was attributed to the reemission of trapped carriers with an activation energy of ∼0.2 eV. In addition, both the fast and slow decays for the wet annealed a-IGZO film were longer than those of the as-deposited a-IGZO film. The decay constants are considered to reflect the density of the subgap states that act as trapping or recombination centers. The μ-PCD method provides a useful estimation of the film quality, such as the density of the defect states, and the physical properties of electronic devices using a-IGZO films.
Collisionless kinetic-fluid simulation of zonal flows in non-circular tokamaks
Authors: Yamagishi Osamu , Sugama Hideo
Published: September 2012

Fluid simulation of linear zonal flow damping is done with a closure model based on the collisionless gyrokinetics [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. Simulation results of residual zonal flow for low radial wavenumbers are compared with theoretical formulas for circular and non-circular tokamaks. The effects of the elongation and the triangularity are shown to be properly treated in the closure model. Effects of initial parallel flows on zonal flow evolution are also clarified. An appropriate choice of the initial parallel flow gives a much higher residual level than the conventional result with no initial parallel flow. Besides, the zonal flow simulations are done with the E × B nonlinearity as initial sources, which is evaluated from linear gyrokinetic microinstabilities such as ion temperature gradient modes, trapped electron modes, and electron temperature gradient modes, in order to estimate efficiency of zonal flow generation by the source instabilities.
Vorticity scaling and intermittency in drift-interchange plasma turbulence
Authors: Dura P. D. , Hnat B. , Robinson J. , Dendy R. O.
Published: September 2012

The effects of spatially varying magnetic field strength on the scaling properties of plasma turbulence, modelled by an extended form of Hasegawa-Wakatani model, are investigated. We study changes in the intermittency of the velocity, density, and vorticity fields, as functions of the magnetic field inhomogeneity C=−∂ ln B/∂x. While the velocity fluctuations are always self-similar and their scaling is unaffected by the value of C, the intermittency levels in density and vorticity change with parameter C, reflecting morphological changes in the coherent structures due to the interchange mechanism. Given the centrality of vorticity in conditioning plasma transport, this result is of interest in scaling the results of transport measurements and simulations in tokamak edge plasmas, where drift-interchange turbulence in the presence of a magnetic field gradient is likely to occur.
Visible photoluminescence in polycrystalline terbium doped aluminum nitride (Tb:AlN) ceramics with high thermal conductivity
Authors: Wieg A. T. , Kodera Y. , Wang Z. , Imai T. , Dames C. , Garay J. E.
Published: September 2012

Thermal management continues to be one of the major challenges in the development of high powered light sources such as solid state lasers. In particular, the relatively low thermal conductivity of standard photoluminescent (PL) materials limits the overall power output and/or duty cycle. We present a method based on current activated pressure assisted densification for the fabrication of high thermal conductivity PL materials: rare earth doped polycrystalline bulk aluminum nitride. Specifically, the ceramics are translucent and are doped with Tb3+, allowing for emission in the visible. Remarkably, the ceramics have a room temperature thermal conductivity of 94 W/(m K) which is almost seven times higher than that of the state of the art host material, Nd-doped yttrium aluminum garnet. These light emitting properties coupled with very high thermal conductivity should enable the development of a wide variety of more powerful light sources.
Surface-tension driven self-assembly of microchips on hydrophobic receptor sites with water using forced wetting
Authors: Chang Bo , Shah Ali , Routa Iiris , Lipsanen Harri , Zhou Quan
Published: September 2012

This letter reports water droplet self-alignment methods for self-assembly of microchips on hydrophobic receptor sites in ambient air environment. It is an open question if lyophobic receptor site of the self-alignment medium can be used for self-assembly. We investigate this question using both numerical simulation and experimental studies on hydrophobic receptor sites (advancing contact angle of 118°) with superhydrophobic substrate (contact angle of 180°). We demonstrate that self-alignment is possible using two forced wetting methods: (a) introducing an excessive amount of water and (b) applying external pressure. The results suggest that surface-tension driven self-alignment can be applied in a wider combination of materials and mediums.
Revisiting the cylindrical positive column in an axial magnetic field
Authors: Franklin R. N.
Published: September 2012

This paper seeks to bring together past and present work in this area and to remove some recent inconsistencies. It concludes that while some aspects were not completely correct in the early work, the general picture of azimuthal motion of electrons and ions is an important feature and accounts for the diamagnetism of a bounded active plasma and other features of an axially magnetised plasma. It also introduces a means of testing the equations derived by interchanging electrons and positive ions; under such a “transformation,” the equations to be solved should be identical. This is a fundamental principle and is implicit in treatments given in many of the standard texts, but not made explicit.
Chaotic dynamics and oxygen transport in thin films of aerotactic bacteria
Authors: Ezhilan Barath , Pahlavan Amir Alizadeh , Saintillan David
Published: September 2012

A kinetic model and three-dimensional numerical simulations are applied to study the dynamics in suspensions of run-and-tumble aerotactic bacteria confined in free-standing liquid films surrounded by air. In thin films, oxygen and bacterial concentration profiles approach steady states. In thicker films, a transition to chaotic dynamics is shown to occur and is characterized by unsteady correlated motions, the formation of bacterial plumes, and enhanced oxygen transport and consumption. This transition, also observed in previous experiments, arises as a result of the coupling between the aerotactic response of the bacteria and the flow fields they generate via hydrodynamic interactions.
Understanding male sterility in Miconia species (Melastomataceae): a morphological approach
Authors: Cortez Priscila Andressa , Carmello-Guerreiro Sandra Maria , Teixeira Simone Pádua
Published: September 2012

Pollen abortion occurs in virtually all species and often does not prejudice reproductive success. However, large numbers of abnormal pollen grains are characteristic of some groups. Among them is Miconia, in which partial and complete male sterility is often related to apomixis. In this study, we compared the morphology of pollen grains over several developmental stages in Miconia species with different rates of male sterility. Our aim was to improve the knowledge of mechanisms that lead to male sterility in this ecologically important tropical group. Routine techniques for microscopy were used to examine anthers in several developmental stages collected from the apomictic species Miconia albicans and M. stenostachya. Both species are completely male sterile since even the pollen grains with apparently normal cytoplasm were not able to develop a pollen tube. Meiosis is a rare event in M. albicans anthers and happens in an irregular way in M. stenostachya, leading to the pollen abortion. M. albicans has more severe abnormalities than M. stenostachya since even the microspores and pollen grain walls were affected. Moreover, in M. stenostachya, most mitosis occurring during microgametogenesis was also abnormal, leading to the formation of bicellular pollen grains with two similar cells, in addition to the formation of pollen grains of different sizes. Notably, abnormalities in both species did not reach the production of Übisch bodies, suggesting little or no tapetum involvement in male sterility in these two species.
MODIS time series as a tool for monitoring fires and their effects on savanna bird diversity
Authors: Levin Noam , Legge Sarah , Price Bronwyn , Bowen Michiala , Litvack Emily , Maron Martine , McAlpine Clive
Published: September 2012

In this study, we aimed to explore the effect of fires on bird diversity in Australia’s tropical savannas. Bird surveys were conducted at 69 sites between 2005 and 2007 to estimate bird species richness and abundance within the Mornington Sanctuary, the Kimberley, north-west Australia. We used MODIS (Moderate Resolution Imaging Spectroradiometer) and Landsat satellite imagery to map fire scars and to quantify vegetation cover parameters, and QuickBird imagery to map the percentage tree cover. Bird species richness and abundance were higher in areas exhibiting minimum seasonal and interannual changes, e.g. in riparian areas, near water and where tree cover was high. We found a significant negative effect of fire on bird diversity following the extensive late dry-season fires of 2006. These findings support the view that intense and large fires are threatening biodiversity and reinforce the importance of reducing the occurrence of late dry-season fires, which are the most severe and extensive. MODIS satellite imagery was found to provide a cost-effective approach to monitoring savanna landscapes, assessing the state of vegetation and monitoring fire dynamics.
A comparison of bushfire fuel hazard assessors and assessment methods in dry sclerophyll forest near Sydney, Australia
Authors: Watson Penny J. , Penman Sandra H. , Bradstock Ross A.
Published: September 2012

Over the last decade, fire managers in Australia have embraced the concept of ‘fuel hazard’, and guides for its assessment have been produced. The reliability of these new metrics, however, remains to be determined. This study compared fuel hazard ratings generated by five assessment teams using two Australian hazard assessment methods, in two dry sclerophyll forest sites on Sydney’s urban fringe. Attributes that underpin hazard scores, such as cover and height of various fuel layers, were also assessed. We found significant differences between teams on most variables, including hazard scores. These differences were more apparent when fuel hazard assessments focussed on individual fuel layers than when teams’ assessments were summarised into an overall fuel hazard score. Ratings of surface (litter) fuel hazard were higher when one assessment method was used than when assessors employed the other; however, ratings of elevated (shrub) and bark fuel hazard were relatively consistent across assessment methods. Fuel load estimates based on the two hazard assessment methods differed considerably, with differences between teams also significant. Inconsistency in scoring fuel hazard may lead to discrepancies in a range of management applications, which in turn may affect firefighting safety and effectiveness.
Forecasting intentional wildfires using temporal and spatiotemporal autocorrelations
Authors: Prestemon Jeffrey P. , Chas-Amil María L. , Touza Julia M. , Goodrick Scott L.
Published: September 2012

We report daily time series models containing both temporal and spatiotemporal lags, which are applied to forecasting intentional wildfires in Galicia, Spain. Models are estimated independently for each of the 19 forest districts in Galicia using a 1999–2003 training dataset and evaluated out-of-sample with a 2004–06 dataset. Poisson autoregressive models of order P – PAR(P) models – significantly out-perform competing alternative models over both in-sample and out-of-sample datasets, reducing out-of-sample root-mean-squared errors by an average of 15%. PAR(P) and static Poisson models included covariates deriving from crime theory, including the temporal and spatiotemporal autoregressive time series components. Estimates indicate highly significant autoregressive components, lasting up to 3 days, and spatiotemporal autoregression, lasting up to 2 days. Models also applied to predict the effect of increased arrest rates for illegal intentional firesetting indicate that the direct long-run effect of an additional firesetting arrest, summed across forest districts in Galicia, is –139.6 intentional wildfires, equivalent to a long-run elasticity of –0.94.
Compartmentalization of superoxide dismutase 1 (SOD1G93A) aggregates determines their toxicity
Authors: Weisberg Sarah J. , Lyakhovetsky Roman , Werdiger Ayelet-chen , Gitler Aaron D. , Soen Yoav , Kaganovich Daniel
Published: September 2012

Neurodegenerative diseases constitute a class of illnesses marked by pathological protein aggregation in the brains of affected individuals. Although these disorders are invariably characterized by the degeneration of highly specific subpopulations of neurons, protein aggregation occurs in all cells, which indicates that toxicity arises only in particular cell biological contexts. Aggregation-associated disorders are unified by a common cell biological feature: the deposition of the culprit proteins in inclusion bodies. The precise function of these inclusions remains unclear. The starting point for uncovering the origins of disease pathology must therefore be a thorough understanding of the general cell biological function of inclusions and their potential role in modulating the consequences of aggregation. Here, we show that in human cells certain aggregate inclusions are active compartments. We find that toxic aggregates localize to one of these compartments, the juxtanuclear quality control compartment (JUNQ), and interfere with its quality control function. The accumulation of SOD1G93A aggregates sequesters Hsp70, preventing the delivery of misfolded proteins to the proteasome. Preventing the accumulation of SOD1G93A in the JUNQ by enhancing its sequestration in an insoluble inclusion reduces the harmful effects of aggregation on cell viability.
Silurian horseshoe crab illuminates the evolution of arthropod limbs
Authors: Briggs Derek E. G. , Siveter Derek J. , Siveter David J. , Sutton Mark D. , Garwood Russell J. , Legg David
Published: September 2012

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living
Limulus
, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of
Limulus
. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.
On the weight of phrase-final prosodic words in a sign language
Authors: Crasborn Onno A. , van der Kooij Els , Ros Johan
Published: September 2012

This article seeks to explore a prosodic explanation for the frequent occurrence of pointing signs phrase-finally. Corpus data from Sign Language of the Netherlands (NGT) show that indeed pointing signs occur highly frequently at the end of sentences, and an elicitation study shows that pointing signs, other light lexical elements, and phonetic phenomena like final holds occur in alternation in NGT. The addition of a final mora to the end of a phrase is argued not to be sufficient to account for these alternations. A complementary analysis in terms of prosodic and metrical phonology is sketched, whereby the final foot or prosodic word is required to be minimally trimoraic.
The perceptibility of long-distance coarticulation in speech and sign
Authors: Grosvald Michael , Corina David P.
Published: September 2012

This paper describes a cross-modality investigation of the perception of long-distance coarticulation. We present the results of a sign study investigating anticipatory location-to-location (LL) effects in American Sign Language (ASL), and compare these findings with results of analogous research on anticipatory vowel-to-vowel (VV) effects in English. While listeners in speech studies showed great sensitivity to coarticulatory effects, relatively little evidence of sensitivity to coarticulation was found among sign study participants, even for the closest-distance effects. This was the case for both signing and sign-naive subjects. In addition, deaf subjects’ results were not significantly influenced by their ages of acquisition of ASL.
These results parallel those of earlier research finding that LL coarticulatory effects in ASL appear to be weaker than the coarticulatory effects that are present in speech, at least in the contexts examined here. The outcome of this perception study may thus be due to the apparent weakness of coarticulatory information in the sign signal relative to the speech signal: to the extent that such information is available, users will tend to make use of it, as appears to be the case in speech perception. Where such information is not generally available, users will be less accustomed to making use of it even in cases in which it is present
Beyond the siege state – tracing hybridity during a recent visit to Eritrea
Authors: Müller Tanja R.
Published: September 2012

This article offers an alternative reading of the current situation in Eritrea that goes beyond the narrative of dictatorship and oppression. Based on recent fieldwork in Eritrea and among Eritrean refugees in Tel Aviv, it offers a hybrid interpretation of developments within Eritrea. The article argues that a transition process instigated by the current leadership is still possible. At the same time rising inequalities and other dynamics may ultimately jeopardise any such transition. More generally important sections of the population have become suspicious of grand political projects, but rather focus on the microcosms of potentially intangible transformations from within.

[Au de-là de l’état de siège – retracer le contexte pragmatique tel constaté lors d'une récente visite en Érythrée.] Cet article propose une lecture alternative de la situation actuelle en Érythrée qui va au-delà du récit de la dictature et de l'oppression. Basé sur des travaux récents en Érythrée et parmi les réfugiés érythréens à Tel Aviv, il offre une interprétation mitigée des développements au sein de l’Érythrée. L'article fait valoir que le processus de transition initié par la direction actuelle est encore possible. Dans le même temps, les inégalités croissantes et d'autres dynamiques peuvent même menacer une telle transition. Plus généralement, d'importants groupements d'individus au sein de la population deviennent méfiants à l’égard des grands projets politiques, et se concentrent plutôt sur les microcosmes de transformations potentiellement incorprels de l'intérieur.

Mots-clés: Érythrée; état de siège; hybridité
Optimal Coverage Level Choice with Individual and Area Insurance Plans
Authors: Bulut Harun , Collins Keith J. , Zacharias Thomas P.
Published: September 2012

We theoretically examine a farmer's optimal use of area and individual crop insurance when area and individual losses are positively but imperfectly correlated. If premium rates for both plans are actuarially fair,the farmer will demand full individual insurance and no area insurance. If area insurance is free and individual insurance is offered at an actuarially fair rate, area insurance replaces a portion of individual insurance demand. If individual insurance is offered as a wrap around the area plan at an actuarially fair rate and area insurance is free, the farmer will demand excess individual insurance and some area insurance.
Limited conformational flexibility in the paratope may be responsible for degenerate specificity of HIV epitope recognition
Authors: Bhowmick Arijit , Salunke Dinakar M.
Published: September 2012

Exquisite specificity is the hallmark of antigen–antibody recognition. However, breakdown in the specific recognition potential culminating in the binding to multiple antigens by a single antibody has been observed, even after the maturation of the humoral response. While such a broad specificity may be expected to assist the host to counter the antigenic variations associated with an immune-evading pathogen, escape from immune surveillance by subtle epitopic mutations in pathogens like HIV and influenza virus has been clearly established. In the light of this dichotomy, the issues of degeneracy/specificity in the humoral response against such epitopes were analysed using three HIV-neutralizing epitopes and their variants as a model system. Cross-reactivity was observed in the polyclonal response against two of the epitopes. Multi-reactive mAb KEL10 was isolated against one of the epitopes, ELDKWA from this response. It is evident that even after the affinity maturation, antibodies showing binding to multiple variants of an immunizing peptide epitope existed. Binding kinetics and in silico structural analyses indicated that conserved interactions across epitopes and limited conformational flexibility in the paratope may account for the observed multi-reactivity. Though the affinity maturation process is expected to incorporate an extent of specificity to the paratope, there appear to be still some B-cell clones producing antibodies with subtle flexibility in their binding site, as demonstrated in case of KEL10. Generation of such antibodies against effective immunogens could be a possible approach for countering the antibody neutralization escape by various immune-evading pathogens.
Preparation and Structure Characterization of Carboxymethyl Corn Starch Under Ultrasonic Irradiation
Authors: Shi Haixin , Hu Xiaoxi
Published: September 2012

To discover new synthesis technology and increase the degree of substitution (DS) of carboxymethyl starch (CMS), ultrasound‐modified CMS (U‐CMS) was successfully prepared under ultrasonic irradiation in the alkali condition with corn starch (CS) as the raw material, ethyl alcohol as the solvent, and monochloroacetic acid as the carboxymethylated reagent. The effects of ultrasound conditions (ultrasonic action sequence, ultrasonic radiation time, and ultrasonic power) and etherification time after ultrasonic irradiation on DS of U‐CMS were studied separately through single‐factor experiments. Meanwhile, the granule morphology, crystal type, and molecular structure of U‐CMS were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT‐IR). The results showed that DS of U‐CMS prepared under certain conditions (ultrasonic radiation time before alkalization, 40 min; ultrasonic radiation temperature, 35°C; ultrasonic power, 170 W; and etherification time, 180 min) improved 38.7% compared with that without ultrasonic radiation. The SEM, XRD, and FT‐IR results illustrated that crystal‐type change of the starch granule after ultrasonic irradiation was not obvious. However, the number of sunken points and holes on the granule surface increased, so that the specific surface expanded, which improved the carboxymethylation.
VALSALVA RETINOPATHY DEVELOPING DURING JAPANESE CHEERLEADING TRAINING (“OUENDAN”)
Authors: Hanazono Gen , Shinoda Kei , Obazawa Minoru , Imamura Yutaka , Matsumoto Soiti C. , Satofuka Shingo , Mizota Atsushi , Ando Yasutaka
Published: September 2012

Purpose:

Valsalva hemorrhagic retinopathy is characterized by retinal hemorrhages that develop after a Valsalva maneuver that consists of a forcible exhalation against a closed glottis, thereby creating a sudden increase in the intrathoracic or intraabdominal pressure. We present a patient who developed retinal and vitreous hemorrhages with multiple retinal nonperfused areas after extreme physical training with shouting on a mountainous area. This exercise was part of his training as a member of a Japanese traditional cheerleading team.

Method:

Case presentation.

Results:

A 19-year-old man developed an acute decrease in the vision to 0.3 in his left eye after running on hilly roads at approximately 800 m while shouting fight songs for several hours. Ophthalmoscopy showed a fresh vitreous hemorrhage that covered the entire macula and was connected to the optic disk in the left eye. The vitreous hemorrhage spontaneously resolved and an intraretinal hemorrhage and nonperfused area emerged. His visual acuity returned to 1.2.

Conclusion:

Prolonged, strenuous physical exertion with shouting during training exercises can lead to Valsalva hemorrhagic retinopathy. Several other factors, such as hot weather, altitude, and dehydration, may have played an additive role in increasing the venous pressure and hypoxia in the retinal vessels, which then caused the retinopathy.
Compass magnetoreception in birds arising from photo-induced radical pairs in rotationally disordered cryptochromes
Authors: Lau Jason C. S. , Rodgers Christopher T. , Hore P. J.
Published: September 2012

According to the radical pair model, the magnetic compass sense of migratory birds relies on photochemical transformations in the eye to detect the direction of the geomagnetic field. Magnetically sensitive radical pairs are thought to be generated in cryptochrome proteins contained in magnetoreceptor cells in the retina. A prerequisite of the current model is for some degree of rotational ordering of both the cryptochromes within the cells and of the cells within the retina so that the directional responses of individual molecules do not average to zero. Here, it is argued that anisotropic distributions of radical pairs can be generated by the photoselection effects that arise from the directionality of the light entering the eye. Light-induced rotational order among the transient radical pairs rather than intrinsic ordering of their molecular precursors is seen as the fundamental condition for a magnetoreceptor cell to exhibit an anisotropic response. A theoretical analysis shows that a viable compass magnetoreceptor could result from randomly oriented cryptochromes contained in randomly oriented cells distributed around the retina.
Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation
Authors: Bomphrey Richard J. , Henningsson Per , Michaelis Dirk , Hollis David
Published: September 2012

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread.
Biomimetic surfaces with controlled direction-dependent adhesion
Authors: Afferrante Luciano , Carbone Giuseppe
Published: September 2012

We propose a novel design of a biomimetic micro-structured surface, which exhibits controlled strongly direction-dependent adhesion properties. The micro-system consists of parallel elastic wall-like structures covered by a thin layer. Numerical calculations have been carried out to study the adhesive properties of the proposed system and to provide design criteria with the aim of obtaining optimized geometries. A numerically equivalent version of the double cantilever beam fracture experiment is, then, simulated by means of finite element analysis to investigate the anisotropic adhesion of the structure. We find that, because of inherent crack trapping properties of these types of structures, the wall-like geometry allows us to strongly enhance adhesion when the detachment direction is perpendicular to the walls. On the other hand, when the detachment occurs parallel to the walls, the system shows low adhesion. This controlled direction-dependent adhesive property of the proposed structure solves one of the key problems of biomimetic adhesive surfaces, which usually show very strong adhesion, even larger than biological systems, but are not suitable for object manipulation and locomotion, as detachment always occurs at high loads and cannot be controlled.
What do molecules do when we are not looking? State sequence analysis for stochastic chemical systems
Authors: Levin Pavel , Lefebvre Jérémie , Perkins Theodore J.
Published: September 2012

Many biomolecular systems depend on orderly sequences of chemical transformations or reactions. Yet, the dynamics of single molecules or small-copy-number molecular systems are significantly stochastic. Here, we propose state sequence analysis—a new approach for predicting or visualizing the behaviour of stochastic molecular systems by computing maximum probability state sequences, based on initial conditions or boundary conditions. We demonstrate this approach by analysing the acquisition of drug-resistance mutations in the human immunodeficiency virus genome, which depends on rare events occurring on the time scale of years, and the stochastic opening and closing behaviour of a single sodium ion channel, which occurs on the time scale of milliseconds. In both cases, we find that our approach yields novel insights into the stochastic dynamical behaviour of these systems, including insights that are not correctly reproduced in standard time-discretization approaches to trajectory analysis.
Gene duplication as a mechanism of genomic adaptation to a changing environment
Authors: Kondrashov Fyodor A.
Published: September 2012

A subject of extensive study in evolutionary theory has been the issue of how neutral, redundant copies can be maintained in the genome for long periods of time. Concurrently, examples of adaptive gene duplications to various environmental conditions in different species have been described. At this point, it is too early to tell whether or not a substantial fraction of gene copies have initially achieved fixation by positive selection for increased dosage. Nevertheless, enough examples have accumulated in the literature that such a possibility should be considered. Here, I review the recent examples of adaptive gene duplications and make an attempt to draw generalizations on what types of genes may be particularly prone to be selected for under certain environmental conditions. The identification of copy-number variation in ecological field studies of species adapting to stressful or novel environmental conditions may improve our understanding of gene duplications as a mechanism of adaptation and its relevance to the long-term persistence of gene duplications.
Response of an arctic predator guild to collapsing lemming cycles
Authors: Schmidt Niels M. , Ims Rolf A. , Høye Toke T. , Gilg Olivier , Hansen Lars H. , Hansen Jannik , Lund Magnus , Fuglei Eva , Forchhammer Mads C. , Sittler Benoit
Published: September 2012

Alpine and arctic lemming populations appear to be highly sensitive to climate change, and when faced with warmer and shorter winters, their well-known high-amplitude population cycles may collapse. Being keystone species in tundra ecosystems, changed lemming dynamics may convey significant knock-on effects on trophically linked species. Here, we analyse long-term (1988–2010), community-wide monitoring data from two sites in high-arctic Greenland and document how a collapse in collared lemming cyclicity affects the population dynamics of the predator guild. Dramatic changes were observed in two highly specialized lemming predators: snowy owl and stoat. Following the lemming cycle collapse, snowy owl fledgling production declined by 98 per cent, and there was indication of a severe population decline of stoats at one site. The less specialized long-tailed skua and the generalist arctic fox were more loosely coupled to the lemming dynamics. Still, the lemming collapse had noticeable effects on their reproductive performance. Predator responses differed somewhat between sites in all species and could arise from site-specific differences in lemming dynamics, intra-guild interactions or subsidies from other resources. Nevertheless, population extinctions and community restructuring of this arctic endemic predator guild are likely if the lemming dynamics are maintained at the current non-cyclic, low-density state.
Mutualism and evolutionary multiplayer games: revisiting the Red King
Authors: Gokhale Chaitanya S. , Traulsen Arne
Published: September 2012

Coevolution of two species is typically thought to favour the evolution of faster evolutionary rates helping a species keep ahead in the Red Queen race, where ‘it takes all the running you can do to stay where you are’. In contrast, if species are in a mutualistic relationship, it was proposed that the Red King effect may act, where it can be beneficial to evolve slower than the mutualistic species. The Red King hypothesis proposes that the species which evolves slower can gain a larger share of the benefits. However, the interactions between the two species may involve multiple individuals. To analyse such a situation, we resort to evolutionary multiplayer games. Even in situations where evolving slower is beneficial in a two-player setting, faster evolution may be favoured in a multiplayer setting. The underlying features of multiplayer games can be crucial for the distribution of benefits. They also suggest a link between the evolution of the rate of evolution and group size.
Positive selection at the ASPM gene coincides with brain size enlargements in cetaceans
Authors: Xu Shixia , Chen Yuan , Cheng Yuefeng , Yang Dan , Zhou Xuming , Xu Junxiao , Zhou Kaiya , Yang Guang
Published: September 2012

The enlargement of cetacean brain size represents an enigmatic event in mammalian evolution, yet its genetic basis remains poorly explored. One candidate gene associated with brain size evolution is the abnormal spindle-like microcephaly associated (ASPM), as mutations in this gene cause severe reductions in the cortical size of humans. Here, we investigated the ASPM gene in representative cetacean lineages and previously published sequences from other mammals to test whether the expansion of the cetacean brain matched adaptive ASPM evolution patterns. Our analyses yielded significant evidence of positive selection on the ASPM gene during cetacean evolution, especially for the Odontoceti and Delphinoidea lineages. These molecular patterns were associated with two major events of relative brain size enlargement in odontocetes and delphinoids. It is of particular interest to find that positive selection was restricted to cetaceans and primates, two distant lineages both characterized by a massive expansion of brain size. This result is suggestive of convergent molecular evolution, although no site-specific convergence at the amino acid level was found.