bluuebunny/crossref_metadata_2025 huggingface dataset:
Factor analysis of objective and subjective characteristics of a night's sleep
Authors: Johns M. W.
Published: July 2009

Synopsis

Factor analysis was performed on objectively measured and subjectively reported characteristics of 46 nights' sleep in four healthy male subjects. The fragmentation of sleep by awakenings during the night, the delay before falling asleep, the total duration of sleep, and the amount of delta-wave sleep formed the bases of four separate factors.
3. Standardized assessment of the needs for care in a cohort of patients with schizophrenic psychoses
Authors: Lesage A. D. , Mignolli G. , Faccincani C. , Tansella M.
Published: July 2009

There is a well-established tradition in standardized evaluation of the symptomatology and the social performance of psychiatric patients (Winget al.1974; WHO, 1983b; Platt, 1983) together with instruments for describing the pattern of contacts with services, like Psychiatric Case Registers (Wing & Hailey, 1972; ten Hornet al.1986). Interest in a systematic assessment procedure for recording which action should be taken by services in the presence of a problem is more recent. Instruments for these evaluations are still experimental.
Erdős–Ko–Rado in Random Hypergraphs
Authors: BALOGH JÓZSEF , BOHMAN TOM , MUBAYI DHRUV
Published: July 2009

Let 3 ≤k<n/2. We prove the analogue of the Erdős–Ko–Rado theorem for the randomk-uniform hypergraphGk(n,p) whenk< (n/2)1/3; that is, we show that with probability tending to 1 asn→ ∞, the maximum size of an intersecting subfamily ofGk(n,p) is the size of a maximum trivial family. The analogue of the Erdős–Ko–Rado theorem does not hold for allpwhenk≫n1/3.

We give quite precise results fork<n1/2−ϵ. For largerkwe show that the random Erdős–Ko–Rado theorem holds as long aspis not too small, and fails to hold for a wide range of smaller values ofp. Along the way, we prove that every non-trivial intersectingk-uniform hypergraph can be covered byk2−k+ 1 pairs, which is sharp as evidenced by projective planes. This improves upon a result of Sanders [7]. Several open questions remain.
Finding an Unknown Acyclic Orientation of a Given Graph
Authors: PIKHURKO OLEG
Published: July 2009

Let c(G) be the smallest number of edges we have to test in order to determine an unknown acyclic orientation of the given graph G in the worst case. For example, if G is the complete graph on n vertices, then c(G) is the smallest number of comparisons needed to sort n numbers.

We prove that c(G) ≤ (1/4 + o(1))n2 for any graph G on n vertices, answering in the affirmative a question of Aigner, Triesch and Tuza [Discrete Mathematics144 (1995) 3–10]. Also, we show that, for every ϵ > 0, it is NP-hard to approximate the parameter c(G) within a multiplicative factor 74/73 − ϵ.
Fine structural observation on the oogenesis and vitellogenesis of the Chinese soft-shelled turtle (Pelodiseus sinensis)
Authors: Nainan Hei , Ping Yang , Yang Yang , Jinxiong Liu , Huijun Bao , Haili Liu , Hui Zhang , Qiusheng Chen
Published: July 2009

Fine structure observations were performed by means of electron microscopy on oogenesis and vitellogenesis and the special functions of follicular cells in the Chinese soft-shelled turtle (Pelodiseus sinensis). Histological examination of the ovary showed a well developed lacunae system containing fine granules, fibres or gelatiniform materials with one or two germinal beds dispersed on the dorsal surface of the ovarian cortex. The process of oogenesis comprised 10 consecutive phases according to the morphology of the yolk platelets, follicular cells and zona pellucida (ZP). Electron microscopy of vitellogenesis revealed some of the mitochondria gradually being transformed into yolk granules. In the advanced stage of vitellogenesis, large amounts of rough endoplasmic reticula, Golgiosomes and other cell organelles that are involved in synthesis and secretion were observed in follicular cells. The ZP was formed by microvilli, thus increasing the absorptive surface of the oocyte and facilitating transport of nutrients from the follicular epithelium to the ooplasm. This study demonstrated that the ovaries of members of the Testudinidae share more features with Archosaurs than with Squamates, indicating that these features were phylogenetically conserved in the Archosauria. The present observations suggest that the accumulation of yolk materials was controlled by the intrinsic and extrinsic pathways as well as by the activity of follicular cells. These results might also support a sibling relationship of the Testudinidae with the Archosauria and not with all extant reptiles.
(Southern) African Anglican Biblical Interpretation: A Postcolonial Project
Authors: West Gerald
Published: July 2009

This article argues that context is an important fourth factor, alongside the more familiar three, in understanding Anglicanism in (Southern) Africa. As imperialism was an important part of the early context of the Bible’s presence within Southern African Anglicanism, the bulk of the present article charts the contours of imperial Southern African Anglicanism. Having mapped this territory, the article then probes what a postcolonial analysis of Southern African Anglican biblical interpretation might look like, outlining two related components: a descriptive component and an interventionist component. The descriptive task asks how Southern African Anglicans have read the Scriptures, and the interventionist task asks how Southern African Anglicans should read the Scriptures. The former requires a careful Foucault-like ‘archaeological’ analysis and the latter a recognition of the contextually-related resources of African biblical scholarship.
Directly dating geologic events: U‐Pb dating of carbonates
Authors: Rasbury E. Troy , Cole Jennifer M.
Published: July 2009

Carbonates are ubiquitous, forming in a variety of settings including caves, soils, the oceans, during burial from hydrothermal fluids, and along faults. U‐Pb dating of carbonates is applicable to almost the entire geologic time scale, with results from Pleistocene speleothems showing great promise for dating records <1 Ma old. Here we review studies of U‐Pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of U and Pb in various fluids. We detail the steps required to select suitable samples, summarize current laboratory techniques, and provide directions for improvement of analytical protocols. The U‐Pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped.
Statistical properties of flux closure induced by solar wind dynamic pressure fronts
Authors: Hubert B. , Blockx C. , Milan S. E. , Cowley S. W. H.
Published: July 2009

We present a statistical study of flux closure intervals induced by solar wind dynamic pressure fronts. We consider that a dynamic pressure front reaches the Earth when a dayside subauroral proton flash is observed in the SI2 channel of the IMAGE‐FUV experiment. This pragmatic criterion selects both weak and strong pressure fronts. It is found that the preconditioning of the magnetosphere prior to the pressure pulse arrival mainly governs the magnetospheric response to a weak solar wind dynamic pressure front. This preconditioning includes the amount of open magnetic flux available in the magnetosphere prior to the pressure front arrival and the size of the magnetospheric cavity. However, in the case of a strong pressure pulse, the magnetospheric response is more sensitive to the solar wind properties characterizing the dynamic pressure front. The pressure jump is not the only one important, but also the variation of the solar wind velocity and IMF magnitude. In overall terms, we find that a strong dynamic pressure front is typically characterized by a dynamic pressure increase larger than ∼2.8 nPa that takes place on timescales of the order of a few minutes.
Diurnal variation of precipitation over southeastern China: Spatial distribution and its seasonality
Authors: Chen Guixing , Sha Weiming , Iwasaki Toshiki
Published: July 2009

Using the satellite data, spatial patterns of precipitation diurnal cycles and their seasonality were examined with emphasis on southeastern China (SEC). Results show that spatial distributions of diurnal cycles over SEC have a robust large‐scale seasonality in which the regional differences are evidently embedded. Rainfall diurnal variability is weak in spring but it becomes more pronounced from presummer. Both the mean rain rates and amplitudes of diurnal cycles experience remarkable amplification during presummer. The widespread and strong morning rainfall dominates the SEC area, especially inland valleys and plains, and offshore areas. The morning peak rainfall over western SEC is largely contributed by the increasing rain frequency and diurnally varying intense rain rates. Even over eastern SEC, morning rainfall still has a comparable magnitude to afternoon rainfall. In contrast, spatial distributions of diurnal cycles in midsummer are dependent primarily on topography. The morning (afternoon) rainfall is mainly located over valleys, basins, and oceans (plateaus and mountains). The afternoon peak rainfall becomes a notable feature over southern China. The signature of widespread morning rainfall decays during midsummer and remains apparent only in central eastern China, which is likely related to the north shift of summer rainband.
On the effects of scintillation of low‐latitude bubbles on transionospheric paths of propagation
Authors: Zernov Nikolay N. , Gherm Vadim E. , Strangeways Hal J.
Published: July 2009

A previously developed scintillation propagation model for L band signals on transionospheric paths has been further extended to describe the effects caused by the localized structure of plasma bubbles in the low‐latitude ionosphere. This takes into account quasi‐deterministic and random structures typical of bubbles. The model can produce signal statistical moments (power spectra, correlation functions, scintillation index, etc.) and generate random time series including the case of through bubble propagation. The simulated random time series of the field demonstrate the characteristic nonstationary behavior caused by the presence and motion of the bubble structures through the path of propagation, showing that strong enhancements of the scintillation index (S4) can occur depending on the parameters of the bubble and the path. Modeling results are compared with scintillation records due to bubbles passing through GPS signal paths to a receiver at Douala, Cameroon. This shows good agreement providing validation for the bubble and propagation model.
Optimizing system capacity expansion schedules for groundwater supply
Authors: Chang Liang‐Cheng , Chen Yu‐Wen , Yeh Ming‐Sheng
Published: July 2009

Groundwater plays a vital role in regional water resources management. In conventional design, a full‐scale network system is installed initially to use groundwater resources. However, the system capacity may exceed water demand in the early stages because water demand generally increases with time. Therefore, this work proposes a novel optimal capacity expansion model capable of determining an optimal schedule to expand system capacity according to increasing water demand. The proposed algorithm hybridizes a genetic algorithm (GA) and constrained differential dynamic programming (CDDP). The chromosomes of the GA represent a possible design alternative, a groundwater network with capacity that expands with time. The CDDP algorithm is then used to compute the optimal pumping policy associated with the chromosome. Simulation results indicate that the capacity expansion model saves more total present value cost than conventional designs for the same annual interest rate and water demand. Results of this study demonstrate promise for the proposed model in facilitating a cost‐effective groundwater network design with capacity expansion for regional groundwater supply.
On the influence of coarse fragments on soil water retention
Authors: Baetens J. M. , Verbist K. , Cornelis W. M. , Gabriels D. , Soto G.
Published: July 2009

The classical determination of the soil water retention curve (SWRC) by measuring soil water content θ at different matric potentials ψ using undisturbed soil samples is time consuming and expensive. Furthermore, undisturbed soil sampling can be an intricate task when coarse soil fragments (>2 mm) are present. The objective of this study was to test whether tension infiltrometry could be used to estimate the SWRC of stony soils and to investigate to what extent the coarse fragments affected the SWRC. Tension infiltrometer measurements were conducted at 44 sites with stony soils in arid Chile. Soil water retention curves obtained through inverse modeling were compared with laboratory‐determined water retention (θ, ψ) data pairs. Differences were found to be small, confirming the applicability of the inverse modeling method. Rock fragments had a significant indirect influence on water retention for matric potentials higher than −0.30 kPa, which could be attributed to their direct influence on pore size distribution.
Bacterial succession in a glacier foreland of the High Arctic
Authors: Schütte Ursel M E , Abdo Zaid , Bent Stephen J , Williams Christopher J , Schneider G Maria , Solheim Bjørn , Forney Larry J
Published: July 2009

Succession is defined as changes in biological communities over time. It has been extensively studied in plant communities, but little is known about bacterial succession, in particular in environments such as High Arctic glacier forelands. Bacteria carry out key processes in the development of soil, biogeochemical cycling and facilitating plant colonization. In this study we sampled two roughly parallel chronosequences in the foreland of Midre Lovén glacier on Svalbard, Norway and tested whether any of several factors were associated with changes in the structure of bacterial communities, including time after glacier retreat, horizontal variation caused by the distance between chronosequences and vertical variation at two soil depths. The structures of soil bacterial communities at different locations were compared using terminal restriction fragment length polymorphisms of 16S rRNA genes, and the data were analyzed by sequential analysis of log-linear statistical models. Although no significant differences in community structure were detected between the two chronosequences, statistically significant differences between sampling locations in the surface and mineral soils could be demonstrated even though glacier forelands are patchy and dynamic environments. These findings suggest that bacterial succession occurs in High Arctic glacier forelands but may differ in different soil depths.
Systematic artifacts in metagenomes from complex microbial communities
Authors: Gomez-Alvarez Vicente , Teal Tracy K , Schmidt Thomas M
Published: July 2009

Metagenomics is providing an unprecedented view of the taxonomic diversity, metabolic potential and ecological role of microbial communities in biomes as diverse as the mammalian gastrointestinal tract, the marine water column and soils. However, we have found a systematic error in metagenomes generated by 454-based pyrosequencing that leads to an overestimation of gene and taxon abundance; between 11% and 35% of sequences in a typical metagenome are artificial replicates. Here we document the error in several published and original datasets and offer a web-based solution (http://microbiomes.msu.edu/replicates) for identifying and removing these artifacts.
Novel organization of aromatic degradation pathway genes in a microbial community as revealed by metagenomic analysis
Authors: Suenaga Hikaru , Koyama Yoshinori , Miyakoshi Masatoshi , Miyazaki Ryo , Yano Hirokazu , Sota Masahiro , Ohtsubo Yoshiyuki , Tsuda Masataka , Miyazaki Kentaro
Published: July 2009

Several types of environmental bacteria that can aerobically degrade various aromatic compounds have been identified. The catabolic genes in these bacteria have generally been found to form operons, which promote efficient and complete degradation. However, little is known about the degradation pathways in bacteria that are difficult to culture in the laboratory. By functionally screening a metagenomic library created from activated sludge, we had earlier identified 91 fosmid clones carrying genes for extradiol dioxygenase (EDO), a key enzyme in the degradation of aromatic compounds. In this study, we analyzed 38 of these fosmids for the presence and organization of novel genes for aromatics degradation. Only two of the metagenomic clones contained complete degradation pathways similar to those found in known aromatic compound-utilizing bacteria. The rest of the clones contained only subsets of the pathway genes, with novel gene arrangements. A circular 36.7-kb DNA form was assembled from the sequences of clones carrying genes belonging to a novel EDO subfamily. This plasmid-like DNA form, designated pSKYE1, possessed genes for DNA replication and stable maintenance as well as a small set of genes for phenol degradation; the encoded enzymes, phenol hydroxylase and EDO, are capable of the detoxification of aromatic compounds. This gene set was found in 20 of the 38 analyzed clones, suggesting that this ‘detoxification apparatus’ may be widespread in the environment.
Carrier proteins for fusion expression of antimicrobial peptides in Escherichia coli
Authors: Li Yifeng
Published: July 2009

Antimicrobial peptides are an essential component of innate immunity and play an important role in host defence against microbial pathogens. They have received increasing attention recently as potential novel pharmaceutical agents. To meet the requirement for necessary basic science studies and clinical trials, large quantities of these peptides are needed. In general, isolation from natural sources and chemical synthesis are not cost‐effective. The relatively low cost and easy scale‐up of the recombinant approach renders it the most attractive means for large‐scale production of antimicrobial peptides. Among the many systems available for protein expression, Escherichia coli remains the most widely used host. Antimicrobial peptides produced in E. coli are often expressed as fusion proteins, which effectively masks these peptides' potential lethal effect towards the bacterial host and protects the peptides from proteolytic degradation. Although some carriers confer peptide solubility, others promote the formation of inclusion bodies. The present minireview considers the most commonly used carrier proteins for fusion expression of antimicrobial peptides in E. coli. The favourable properties of SUMO (small ubiquitin‐related modifier) as a novel fusion partner are also discussed.
Transient atomic behavior and surface kinetics of GaN
Authors: Moseley Michael , Billingsley Daniel , Henderson Walter , Trybus Elaissa , Doolittle W. Alan
Published: July 2009

An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.
The largest eigenvalues of sample covariance matrices for a spiked population: Diagonal case
Authors: Féral Delphine , Péché Sandrine
Published: July 2009

We consider large complex random sample covariance matrices obtained from “spiked populations,” that is, when the true covariance matrix is diagonal with all but finitely many eigenvalues equal to 1. We investigate the limiting behavior of the largest eigenvalues when the population and the sample sizes both become large. Under some conditions on moments of the sample distribution, we prove that the asymptotic fluctuations of the largest eigenvalues are the same as for a complex Gaussian sample with the same true covariance. The real setting is also considered.
The H2O2+ potential energy surfaces dissociating into H+/OH+: Theoretical analysis of the isotopic effect
Authors: Gervais B. , Giglio E. , Adoui L. , Cassimi A. , Duflot D. , Galassi M. E.
Published: July 2009

We present a detailed study of the potential energy surfaces of the water dication correlating asymptotically with O(P3) and O(D1). Using ab initio multireference configuration interaction method, we computed a large ensemble of data, which was used to generate a fit of each potential energy surface for bending angles θ≥80° degrees and OH distances ROH≥1.0 a.u. The fit is used to investigate the dissociation dynamics along each potential energy surface for several initial geometries corresponding to Franck–Condon transition from neutral or singly ionized water molecule. For each case, we determine the dissociation channels and we compute the kinetic energy release and angular momentum distribution of the final arrangements. Among the eight potential energy surfaces investigated here, only the lowest triplet and the three lowest singlet can lead to the formation of bound residual fragment. The dissociation of HOD2+ presents a strong preference for OH rather than OD bond breakage. It is characterized by the isotopic ratio, defined as the number of OD+ over the number of OH+ residual fragments. This ratio depends strongly on the shape of each potential energy surface and on the initial conditions.
Modification of electronic states of √3×√3-Ag structure by strained Ge/Si(111) substrate
Authors: Mochizuki Izumi , Negishi Ryota , Shigeta Yukichi
Published: July 2009

To make clear the relationship between strain and electronic stricture, the strain-induced √3×√3-Ag structure formed on the Ge/Si(111) surface was investigated by using scanning tunneling microscopy and angle resolved ultraviolet photoelectron spectroscopy. The compressive strain is induced by epitaxial growth of Ge on the Si(111) substrate. The interatomic spacing in the surface plane is altered with the coverage of the Ge, and the strain of the surface is also varied. The stress reaches to a maximum value when the Ge layer covers up the surface completely. The band dispersion of the two dimensional metallic state on the √3×√3-Ag surface becomes steeper with the compressive strain, which means a reduction in the effective mass. It is confirmed that the electronic states of the √3×√3-Ag surface could be modified by using the lattice strain.
Impurity-modified Fano effect in a double quantum dot Aharonov–Bohm interferometer
Authors: Gong Weijiang , Jiang Cui
Published: July 2009

The impurity-related electron transport properties of a double quantum dot Aharonov–Bohm interferometer are theoretically studied, by considering impurities to side couple to the quantum dots in the two arms of the interferometer. We show that the existence of impurity states influences the Fano interference in a nontrivial way. When impurities laterally couple to the quantum dot in the resonant channel multiple Fano line shapes come about in the linear conductance spectrum. However the side coupling of impurities to the quantum dot in the nonresonant channel destroys the Fano interference to a great extent. Interestingly, when the quantum dot in either channel couples to impurities, the conductance spectrum is divided into several groups, the number of which is dependent on the number of impurity states. Besides, in each group with the adjustment of magnetic flux the reversal of the Fano line shape is similar to that in the absence of impurity.
A first principles study of the properties of Al:ZnO and its adhesion to Ag in an optical coating
Authors: Lin Zheshuai , Bristowe Paul D.
Published: July 2009

A first principles density functional study of the atomistic properties of Al:ZnO and its adhesion to Ag is presented. Optical coatings often contain interfaces between ZnO (0001) and Ag (111) layers whose bonding can be improved by incorporating small amounts of Al into the ZnO but the underlying strengthening mechanism remains unclear. It is assumed that Al relaxes the internal compressive stress in the film but the situation is complicated by the presence of hydrogen and/or water which can adsorb on the ZnO surface during fabrication of the coating. Hydrogen and/or water are known to weaken the Ag/ZnO interface particularly when it is O terminated. In this paper it is shown that aluminum substitutes on Zn sites in ZnO and this does indeed reduce the internal stress in the layer under compression. However, it is also shown that Al segregates to the ZnO surface when it is O terminated (but not Zn terminated) and this reduces the propensity for hydrogen adsorption. Thus by eliminating some of the hydrogen from the ZnO surface which is more likely to be O terminated than Zn terminated under ambient conditions, the strength of the Ag/ZnO interface can be increased. The effect of aluminum incorporation into the ZnO layer is therefore twofold: it relaxes the residual stresses in the coating and also improves the chemical bonding at the metal/oxide interface by removing the weakening effects of gaseous adsorption. The changes in interfacial bonding are explained in terms of an electron redistribution and compensation model.
Effective-mode representation of non-Markovian dynamics: A hierarchical approximation of the spectral density. I. Application to single surface dynamics
Authors: Hughes Keith H. , Christ Clara D. , Burghardt Irene
Published: July 2009

An approach to non-Markovian system-environment dynamics is described which is based on the construction of a hierarchy of coupled effective environmental modes that is terminated by coupling the final member of the hierarchy to a Markovian bath. For an arbitrary environment, which is linearly coupled to the subsystem, the discretized spectral density is replaced by a series of approximate spectral densities involving an increasing number of effective modes. This series of approximants, which are constructed analytically in this paper, guarantees the accurate representation of the overall system-plus-bath dynamics up to increasing times. The hierarchical structure is manifested in the approximate spectral densities in the form of the imaginary part of a continued fraction similar to Mori theory. The results are described for cases where the hierarchy is truncated at the first-, second-, and third-order level. It is demonstrated that the results generated from a reduced density matrix equation of motion and large dimensional system-plus-bath wavepacket calculations are in excellent agreement. For the reduced density matrix calculations, the system and hierarchy of effective modes are treated explicitly and the effects of the bath on the final member of the hierarchy are described by the Caldeira–Leggett equation and its generalization to zero temperature.
Nonlinear stage of instability development in a stratified shear flow with an inflection-free velocity profile
Authors: Churilov S. M.
Published: July 2009

A plane-parallel shear flow with an inflection-free velocity profile Vx=U(y), having an embedded thin layer of stable density stratification, is known to be unstable in ideal incompressible fluid, for an arbitrary bulk Richardson number J>0 [S. M. Churilov, J. Fluid Mech. 539, 25 (2005); S. M. Churilov, J. Fluid Mech.617, 301 (2008)], and it is the three- rather than two-dimensional (z-independent) disturbances that are most unstable within a wide range of parameters. We examine the weakly nonlinear evolution of a pair of unstable oblique waves in such a flow, in the unsteady critical layer regime. For this purpose, we derive the evolution equation which has the form of a nonlinear integral equation and is valid for both thin and thick critical layers, including the case where the critical layer width exceeds the stratification layer thickness. The solutions of this equation are inspected both analytically and numerically, and it is shown that during the nonlinear stage, the disturbance evolves, as a rule, explosively.
Real time characterization of hydrogenation mechanism of palladium thin films by in situ spectroscopic ellipsometry
Authors: Yamada Y. , Tajima K. , Bao S. , Okada M. , Roos A. , Yoshimura K.
Published: July 2009

The hydrogenation mechanism of Pd thin films was analyzed in real time by measuring the variation in ellipsometric Ψ and Δ using in situ spectroscopic ellipsometry. In the initial stage, the hydrogenation proceeded from the film surface and a mixture layer of metal and hydride, not a uniform hydride layer, was formed at the surface. With time evolution, the thickness of the mixture layer increased and that of the Pd metal layer decreased rapidly. After the whole Pd metal layer changed to the mixture layer, the concentration of hydride in the mixture layer increased. Finally, the concentration reached one and hydrogenation of Pd was finished.
Effects of strength of dispersion and dust density on the formation of solitons and shocks in unmagnetized dusty plasma
Authors: Asgari H. , Muniandy S. V. , Wong C. S.
Published: July 2009

The effects of strength of dispersion on the formation of solitons and shock waves in unmagnetized dusty plasma are studied using reductive perturbative technique. Different relational forms of the strength parameter ε can be chosen to stretch the space and time variables, thereby leading to different types of nonlinearities. The Korteweg–de Vries (KdV) equation for the unmodulated dust acoustic wave is derived and the solitary wave solution is obtained. It is shown that there exists a critical dust density ndc at which the formation of the dust acoustic solitary waves is not possible. Furthermore, the solution of the KdV represents a rarefactive (compressive) solitary wave if ndndc) where nd is the dust density. Using another type of coordinate transformation that reduces the strength of dispersion, the Burgers' equation with shock wave solution is obtained. Shocks with negative (positive) potentials are observed when ndndc), respectively.
Surface chemical modification induces nanometer scale electron confinement in field effect device
Authors: Shalev Gil , Halpern Eliezer , Doron Amihood , Cohen Ariel , Rosenwaks Yossi , Levy Ilan
Published: July 2009

Design, preparation, and study of physicochemical properties of molecular assemblies are extremely challenging multidisciplinary research fields. Understanding the elementary principles that correlate these properties with molecular level of electronic behavior will enable us to control basic properties of molecule-based compounds as well as of classical semiconductors. In particular, chemical modification of field effect sensor devices where the metal gate is replaced with organic molecular layer, projects a crucial impact upon the electrical properties of the sensor. In these cases it is important to control the effects in order to ensure that the organic gate is optimized for sensing. Here we used fully depleted silicon-on-insulator (SOI) ion sensitive field effect transistor in order to analyze the projection of surface chemical modification on electronic performance. We suggest that surface activation and the application of 3-aminopropyltrimethoxysilane on top of the gate dielectric introduces negative charge at the Si/SiO2 interface or/and on top of the gate dielectric and consequently an accumulation layer that confines the electrons to the bottom of the SOI channel. The transistor gain postmodification is characteristic of volume inversion, and therefore suggests that, following modification, the channel electrons are confined to SOI thickness of <10 nm. Finally, measurements of pH sensitivity indicate that the pH sensitivity post-UV/O3 treatment is maximized suggesting that the negative charge is introduced during the activation process, where the density of the negatively charged amphoteric sites maximized.
The influence of copper top electrodes on the resistive switching effect in TiO2 thin films studied by conductive atomic force microscopy
Authors: Yang Lin , Kuegeler Carsten , Szot Krzysztof , Ruediger Andreas , Waser Rainer
Published: July 2009

Titanium dioxide thin films (30 nm) are deposited on platinized substrates by atomic layer deposition and locally studied by conductive atomic force microscopy showing repetitive bipolar resistive switching. Experiments using macroscopic copper top electrodes, which are electroformed, bipolar switched, and removed again from the TiO2–Pt stack, prove the formation of local conductive filaments with bipolar switching properties. The localized filaments can be switched repetitively with a resistance ratio of 30. Our findings underline that Cu diffusion and the formation of filaments are the major mechanism for the resistive switching in Cu/TiO2/Pt cells.
Time-resolved zero field vortex oscillations in point contacts
Authors: Devolder T. , Kim Joo-Von , Crozat P. , Chappert C. , Manfrini M. , van Kampen M. , Van Roy W. , Lagae L. , Hrkac G. , Schrefl T.
Published: July 2009

We study vortex spin torque oscillators based on magnetic point contacts that operate in zero applied magnetic field. Static and dynamic vortex modes are shown to exist and have distinct electrical signatures. For the oscillatory mode, a spectrally pure slightly asymmetric voltage waveform is observed. It is subject to phase noise as sole fluctuations. The waveforms observed indicate that the vortex orbits outside the point contact region, with a pinned layer magnetization that is static but spatially nonuniform as a result of the current. This nonuniformity results in a reduction in the dc to rf power transduction yield.
A robust control algorithm based high voltage direct current system connected to a weak ac grid
Authors: Kumar Vinod , Bansal R. C. , Joshi R. R.
Published: July 2009

During various faults in a high voltage direct current (HVDC) system, the voltage gets reduced, which in turn results into commutation failure, which can deteriorate the availability of HVDC links and thus affect the performance of the power system. In this paper, efforts are made to ride through these faults and so to lower the effect of commutation failure on the power system, and the remedy is implemented by using a robust control algorithm which utilizes a new space vector modulation-based strategy. The validity and effectiveness of the control algorithm are verified by PSCAD/EMTDC-based simulation which shows that with the proposed control, the system can operate steadily, has the capability to restore steady state condition when short-circuit fault occurs, and is feasible technically and obvious in advantages.
The effect of liquid viscosity on bubble pinch-off
Authors: Bolaños-Jiménez R. , Sevilla A. , Martínez-Bazán C. , van der Meer D. , Gordillo J. M.
Published: July 2009

The collapse stage of an air bubble immersed in a stagnant viscous liquid is experimentally and theoretically investigated, focusing on the effect of liquid viscosity on the final instants previous to pinch-off. Our experiments are consistent with recent investigations, and at the same time highlight several important limitations of previous works. In particular, it is shown that the use of a power law to describe the collapse dynamics of the bubble is not appropriate in an intermediate range of liquid viscosities, for which a transition from an inviscid to a fully viscous pinch-off takes place. Under these conditions, the instantaneous exponent α(τ) varies during a single pinch-off event from the typical values of inviscid collapse, α≃0.58, to the value corresponding to a fully viscous dynamics, α≃1. Consequently, the effective exponent of the power law is not correctly defined in these cases. However, as in the work of Bolaños-Jiménez et al. [Phys. Fluids 20, 112104 (2008)], we show that the pinch-off process can be accurately described by the use of a pair of Rayleigh-like differential equations for the time evolution of the minimum radius, R0, and half the axial curvature evaluated at the minimum radius, r1. In particular, the theoretical model is able to describe the smooth transition which takes place from inviscid to viscous-dominated pinch-off in liquids of intermediate viscosity, 10≤μ≤100 cP, and accounts for the fact that the axial curvature remains constant when the local Reynolds number becomes small enough, in close agreement with our experimental measurements.
Confocal terahertz imaging
Authors: Zinov’ev N. N. , Andrianov A. V.
Published: July 2009

We report on a configuration of confocal spatial filtering applied to terahertz imaging. Theoretical analysis of the confocal terahertz imaging layout agrees fairly well with the experimental observations of the enhancement of optical resolving power, both lateral and axial, leading to three-dimensional optical slicing, in comparison with the image properties obtained with a generic terahertz imaging.
Temperature effects on the nonstationary Karpman–Washimi ponderomotive magnetization in quantum plasmas
Authors: Na Sang-Chul , Jung Young-Dae
Published: July 2009

The temperature effects on the nonstationary Karpman–Washimi ponderomotive magnetization are investigated in quantum Fermi plasmas. The cyclotron frequency due to the ponderomotive force of the electromagnetic wave has been obtained as a function of the Fermi Debye length and quantum wavelength. It is found that the Karpman–Washimi ponderomotive magnetization decreases with increasing Fermi temperature. The maximum position of the Fermi Debye length is found to be increased with an increase in the frequency in the small Fermi Debye length domain. It is also shown that the Fermi ponderomotive magnetization decreases with increasing frequency in the large Fermi Debye length domain. In addition, it is shown that the frequency dependence on the ponderomotive magnetization diminishes with increasing Fermi temperature.
Fasting hyperglycemia is not associated with increased expression of PEPCK or G6Pc in patients with Type 2 Diabetes
Authors: Samuel Varman T. , Beddow Sara A. , Iwasaki Takanori , Zhang Xian-Man , Chu Xin , Still Christopher D. , Gerhard Glenn S. , Shulman Gerald I.
Published: July 2009

Fasting hyperglycemia in patients with type 2 diabetes mellitus (T2DM) is attributed to increased hepatic gluconeogenesis, which has been ascribed to increased transcriptional expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase, catalytic (G6Pc). To test this hypothesis, we examined hepatic expression of these 2 key gluconeogenic enzymes in 2 rodent models of fasting hyperglycemia and in patients with T2DM. In rats, high-fat feeding (HFF) induces insulin resistance but a robust β-cell response prevents hyperglycemia. Fasting hyperglycemia was induced in the first rat model by using nicotinamide and streptozotocin to prevent β-cell compensation, in combination with HFF (STZ/HFF). In a second model, control and HFF rats were infused with somatostatin, followed by portal vein infusion of insulin and glucagon. Finally, the expression of these enzymes was measured in liver biopsy samples obtained from insulin sensitive, insulin resistant, and untreated T2DM patients undergoing bariatric surgery. Rats treated with STZ/HFF developed modest fasting hyperglycemia (119 ± 4 vs. 153 ± 6 mg/dL,
P
< 0.001) and increased rates of endogenous glucose production (EGP) (4.6 ± 0.6 vs. 6.9 ± 0.6 mg/kg/min,
P
= 0.02). Surprisingly, the expression of PEPCK or G6Pc was not increased. Matching plasma insulin and glucagon with portal infusions led to higher plasma glucoses in the HFF rats (147 ± 4 vs. 161 ± 4 mg/dL,
P
= 0.05) with higher rates of EGP and gluconeogenesis. However, PEPCK and G6Pc expression remained unchanged. Finally, in patients with T2DM, hepatic expression of PEPCK or G6Pc was not increased. Thus, in contrast to current dogma, these data demonstrate that increased transcriptional expression of PEPCK1 and G6Pc does not account for increased gluconeogenesis and fasting hyperglycemia in patients with T2DM.
Intracellular activation of vasopressin V2 receptor mutants in nephrogenic diabetes insipidus by nonpeptide agonists
Authors: Robben Joris H. , Kortenoeven Marleen L. A. , Sze Mozes , Yae Chris , Milligan Graeme , Oorschot Viola M. , Klumperman Judith , Knoers Nine V. A. M. , Deen Peter M. T.
Published: July 2009

Binding of the peptide hormone vasopressin to its type-2 receptor (V2R) in kidney triggers a cAMP-mediated translocation of Aquaporin-2 water channels to the apical membrane, resulting in water reabsorption and thereby preventing dehydration. Mutations in the V2R gene lead to Nephrogenic Diabetes Insipidus (NDI), a disorder in which this process is disturbed, because the encoded, often intrinsically functional mutant V2 receptors are misfolded and retained in the endoplasmic reticulum (ER). Since plasma membrane expression is thought to be essential for V2R activation, cell permeable V2R antagonists have been used to induce maturation and rescue cell surface expression of V2R mutants, after which they need to be displaced by vasopressin for activation. Here, however, we show that 3 novel nonpeptide V2R agonists, but not vasopressin, activate NDI-causing V2R mutants at their intracellular location, without changing their maturation and at a sufficient level to induce the translocation of aquaporin-2 to the apical membrane. Moreover, in contrast to plasma membrane V2R, degradation of intracellular V2R mutants is not increased by their activation. Our data reveal that G protein-coupled receptors (GPCRs) normally active at the plasma membrane can be activated intracellularly and that intracellular activation does not induce their degradation; the data also indicate that nonpeptide agonists constitute highly promising therapeutics for diseases caused by misfolded GPCRs in general, and NDI in particular.
Polysialic acid governs T-cell development by regulating progenitor access to the thymus
Authors: Drake Penelope M. , Stock Christina M. , Nathan Jay K. , Gip Phung , Golden Kevin P. K. , Weinhold Birgit , Gerardy-Schahn Rita , Bertozzi Carolyn R.
Published: July 2009

Although the polysialyltransferase ST8Sia IV is expressed in both primary and secondary human lymphoid organs, its product, polysialic acid (polySia), has been largely overlooked by immunologists. In contrast, polySia expression and function in the nervous system has been well characterized. In this context, polySia modulates cellular adhesion, migration, cytokine response, and contact-dependent differentiation. Provocatively, these same processes are vital components of immune development and function. We previously established that mouse multipotent hematopoietic progenitors use ST8Sia IV to express polySia on their cell surfaces. Here, we demonstrate that, relative to wild-type controls, ST8Sia IV−/−mice have a 30% reduction in total thymocytes and a concomitant deficiency in the earliest thymocyte precursors. T-cell progenitors originate in the bone marrow and are mobilized to the blood at regular intervals by unknown signals. We performed in vivo reconstitution experiments in which ST8Sia IV−/−progenitors competed with wild-type cells to repopulate depleted or deficient immune subsets. Progenitors lacking polySi exhibited a specific defect in T-cell development because of an inability to access the thymus. This phenotype probably reflects a decreased capacity of the ST8Sia IV−/−progenitors to escape from the bone marrow niche. Collectively, these results provide evidence that polySia is involved in hematopoietic development.
Accelerating loss of seagrasses across the globe threatens coastal ecosystems
Authors: Waycott Michelle , Duarte Carlos M. , Carruthers Tim J. B. , Orth Robert J. , Dennison William C. , Olyarnik Suzanne , Calladine Ainsley , Fourqurean James W. , Heck Kenneth L. , Hughes A. Randall , Kendrick Gary A. , Kenworthy W. Judson , Short Frederick T. , Williams Susan L.
Published: July 2009

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km
2
yr
−1
since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr
−1
before 1940 to 7% yr
−1
since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.
Stepwise acquisition of pyrimethamine resistance in the malaria parasite
Authors: Lozovsky Elena R. , Chookajorn Thanat , Brown Kyle M. , Imwong Mallika , Shaw Philip J. , Kamchonwongpaisan Sumalee , Neafsey Daniel E. , Weinreich Daniel M. , Hartl Daniel L.
Published: July 2009

The spread of high-level pyrimethamine resistance in Africa threatens to curtail the therapeutic lifetime of antifolate antimalarials. We studied the possible evolutionary pathways in the evolution of pyrimethamine resistance using an approach in which all possible mutational intermediates were created by site-directed mutagenesis and assayed for their level of drug resistance. The coding sequence for dihydrofolate reductase (DHFR) from the malaria parasite
Plasmodium falciparum
was mutagenized, and tests were carried out in
Escherichia coli
under conditions in which the endogenous bacterial enzyme was selectively inhibited. We studied 4 key amino acid replacements implicated in pyrimethamine resistance: N51I, C59R, S108N, and I164L. Using empirical estimates of the mutational spectrum in
P. falciparum
and probabilities of fixation based on the relative levels of resistance, we found that the predicted favored pathways of drug resistance are consistent with those reported in previous kinetic studies, as well as DHFR polymorphisms observed in natural populations. We found that 3 pathways account for nearly 90% of the simulated realizations of the evolution of pyrimethamine resistance. The most frequent pathway (S108N and then C59R, N51I, and I164L) accounts for more than half of the simulated realizations. Our results also suggest an explanation for why I164L is detected in Southeast Asia and South America, but not at significant frequencies in Africa.