bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear saturated states of the magnetic-curvature-driven Rayleigh–Taylor instability in three dimensions
Authors: Das Amita , Sen Abhijit , Kaw Predhiman , Benkadda S. , Beyer Peter
Published: February 2005

Three-dimensional electromagnetic fluid simulations of the magnetic-curvature-driven Rayleigh–Taylor instability are presented. Issues related to the existence of nonlinear saturated states and the nature of the temporal evolution to such states from random initial conditions are addressed. It is found that nonlinear saturated states arising from generation of zonal shear flows continue to exist in certain parametric domains but their spectrum and spatial characteristics have important differences from earlier two-dimensional results reported in Phys. Plasmas 4, 1018 (1997) and Phys. Plasmas 8, 5104 (2001). In particular, the three-dimensional nonlinear states possess a significant power level in short scales and the spatial structures of the potential and density fluctuations appear not to develop any functional correlations. Electromagnetic effects are found to inhibit the formation of zonal flows and thereby to considerably restrict the parametric domain of nonlinear stabilization. The role of finite k‖ and the contribution of the unstable drift wave branch are also discussed and delineated through a number of simulation studies carried out in special simplified limits.
Imaging temperature-dependent field emission from carbon nanotube films: Single versus multiwalled
Authors: Gupta S. , Wang Y. Y. , Garguilo J. M. , Nemanich R. J.
Published: February 2005

Field emission properties of vertically aligned single- and multiwalled carbon nanotube films at temperatures up to 1000°C are investigated by electron emission microscopy, enabling real-time imaging of electron emission to provide information on emission site density, the temporal variation of the emission intensity, and insight into the role of adsorbates. The nanotube films showed an emission site density of 104∼105∕cm2, which is compared to the areal density (from 1012–1013∕cm2to108–109∕cm2). At ambient temperature, the emission indicated temporal fluctuation (∼6%–8%) in emission current with minimal changes in the emission pattern. At elevated temperatures, the emission site exhibited an increase in emission site intensity. From the experimental observations, it is proposed that the chemisorbed molecules tend to desorb presumably at high applied electric fields (field-induced) in combination with thermal effects (thermal-induced) and provide a contrasting comparison between semiconducting (single-walled) and metallic (multiwalled) nanotubes.
Quantum statistical and wave packet studies of insertion reactions of S(D1) with H2, HD, and D2
Authors: Ying Lin Shi , Guo Hua
Published: February 2005

A thorough theoretical investigation of the reactions between S(D1) and various hydrogen isotopomers (H2, D2, and HD) has been carried out using a recent ab initio potential energy surface. State-resolved integral and differential cross sections, thermal rate constants, and their dependence on energy or temperature were obtained from quantum mechanical capture probabilities within a statistical model. For comparison, the J=0 reaction probabilities were also computed using an exact wave packet method. The statistical results are in excellent agreement with available exact differential and integral cross sections. The comparison with experimental results shows that the agreement is reasonably good in general, but some significant differences exist, particularly for the SD/SH branching ratio in the S(D1)+HD reaction.
Potential dominance of oscillating crescent waves in finite width tanks
Authors: Fuhrman David R. , Madsen Per A.
Published: February 2005

Recently, it has been proposed that the emergence of previously observed oscillating crescent water wave patterns, created by class II (three-dimensional) instabilities which are in principle not dominant, could in fact be explained as an artifact of a finite width tank, combined with a suppression of the class I (Benjamin–Feir) instability. Within this context, we investigate quantitatively the dominance of class II deep water wave instabilities for particular transversal wavenumbers, and it is shown that the regions where non-phase-locked (oscillating) crescent wave patterns are locally dominant is surprisingly large, particularly for low to moderate wave steepness. This is an important realization for both experimentalists and numerical modelers currently studying these phenomena.
Current singularities in planar magnetic X points of finite compressibility
Authors: Craig I. J. D. , Litvinenko Yuri E.
Published: February 2005

The formation of current singularities in nonresistive, line-tied magnetic X points is addressed. It is pointed out that, although gas pressure suppresses the current singularity development when strictly antiparallel, one-dimensional magnetic fields implode, the pressure is likely to be less effective in the more realistic case of two-dimensional magnetic fields. Detailed nonlinear relaxation computations at various levels of compressibility confirm that singularity is present even in the incompressible limit, but its strength, as determined by the amplitude and morphology of the current density, is considerably reduced. The singularity strength is quantified by computing the scalings of the peak current density with resolution. The scalings show that localized current structures can be expected only for negligible gas pressures. The numerical results imply that the inclusion of gas pressure effectively stalls fast magnetic reconnection in line-tied X-point geometries.
A Penning-assisted subkilovolt coaxial plasma source
Authors: Wang Zhehui , Beinke Paul D. , Barnes Cris W. , Martin Michael W. , Mignardot Edward , Wurden Glen A. , Hsu Scott C. , Intrator Thomas P. , Munson Carter P.
Published: February 2005

A Penning-assisted 20MW coaxial plasma source (plasma gun), which can achieve breakdown at sub-kV voltages, is described. The minimum breakdown voltage is about 400V, significantly lower than previously reported values of 1–5kV. The Penning region for electrons is created using a permanent magnet assembly, which is mounted to the inside of the cathode of the coaxial plasma source. A theoretical model for the breakdown is given. A 900V 0.5F capacitor bank supplies energy for gas breakdown and plasma sustainment from 4to6ms duration. Typical peak gun current is about 100kA and gun voltage between anode and cathode after breakdown is about 200V. A circuit model is used to understand the current-voltage characteristics of the coaxial gun plasma. Energy deposited into the plasma accounts for about 60% of the total capacitor bank energy. This plasma source is uniquely suitable for studying multi-MW multi-ms plasmas with sub-MJ capacitor bank energy.
Studies of band alignment and two-dimensional electron gas in InGaPN∕GaAs heterostructures
Authors: Hwang J. S. , Lin K. I. , Lin H. C. , Hsu S. H. , Chen K. C. , Lu Y. T. , Hong Y. G. , Tu C. W.
Published: February 2005

Room-temperature photoreflectance (PR) and photoluminescence (PL) spectra are measured for a series of In0.54Ga0.46P1−yNy∕GaAs heterostructures grown on GaAs (100) substrate. Redshifts of the PR and PL peaks indicate that the band gap of In0.54Ga0.46P1−yNy is dramatically reduced as nitrogen is incorporated. The emergence of additional peaks in PR spectra as nitrogen is incorporated indicates that the band alignment switches from type I to type II, due to the lowering of the conduction band, thus forming a two-dimensional electron gas (2DEG) in the interface region between In0.54Ga0.46P1−yNy and GaAs. The band gap energy and transition energies between the confined levels in the 2DEG are determined for samples with various nitrogen concentrations y. The number of confined levels in the 2DEG is found to increase with y; the composition-dependent bowing parameter is determined.
Efficient blue organic light-emitting diodes based on an oligoquinoline
Authors: Kulkarni Abhishek P. , Gifford Angela P. , Tonzola Christopher J. , Jenekhe Samson A.
Published: February 2005

An oligoquinoline 6,6′-bis(2,4-diphenylquinoline), with excellent thermal stability and a high glass transition temperature (Tg=133°C), was used as a blue-emitting and electron-transport material to achieve efficient blue electroluminescence. The diodes based on poly(N-vinylcarbazole) hole-transport layer and LiF∕Al cathode had a stable blue emission with a peak at 453nm, chromaticity coordinates at (0.15, 0.12), and a maximum brightness of 925cd∕m2 in air. The external quantum efficiency of 4.1% and luminous efficiency of 3.33cd∕A at 100cd∕m2 are comparable to the best blue organic light-emitting diodes (OLEDs) in the literature. These results demonstrate that oligoquinolines are promising as both blue emitters and electron-transport materials for developing high-efficiency OLEDs with a simpler architecture.
Mechanism of stress relaxation in Ge nanocrystals embedded in SiO2
Authors: Sharp I. D. , Yi D. O. , Xu Q. , Liao C. Y. , Beeman J. W. , Liliental-Weber Z. , Yu K. M. , Zakharov D. N. , Ager J. W. , Chrzan D. C. , Haller E. E.
Published: February 2005

Ion-beam-synthesized Ge74 nanocrystals embedded in an amorphous silica matrix exhibit large compressive stresses in the as-grown state. The compressive stress is determined quantitatively by evaluating the Raman line shift referenced to the line position of free-standing nanocrystals. Postgrowth thermal treatments lead to stress reduction. The stress relief process is shown to be governed by the diffusive flux of matrix atoms away from the local nanocrystal growth region. A theoretical model that quantitatively describes this process is presented.
Fabrication and optical properties of two-dimensional photonic crystals of CdSe pillars
Authors: Chuang L. M. , Fu H. K. , Chen Y. F.
Published: February 2005

The combination of electron beam lithography and electrochemical deposition has been employed to fabricate well-controlled submicrometer-scale CdSe pillars. The formation of the wurtzite crystal structure of CdSe pillars has been confirmed by x-ray diffraction and Raman spectra. Quite interestingly, we found that the intensity of micro-photoluminescence can be greatly enhanced at the specially designed two-dimensional photonic crystals (PCs) based on Maxwell’s equations. This peculiar phenomenon can be explained quite well in terms of the effects of PCs. PCs can provide a photonic bandgap for the emission in the lateral dimensions so that the emission of CdSe pillars cannot propagate in the lateral plane and can only propagate upward with respect to PCs. Besides, PCs can also provide a pathway for the phase match between guided modes and radiation modes to avoid total internal reflection. Thus, the detected PL intensity normal to the lateral plane can be greatly enhanced.
Large optical power limiting from self-assembly organic complexes
Authors: Yang Zhi , Wu Zhikun , Ma Jinshi , Xia Andong , Li Quanshui , Liu Chunling , Gong Qihuang
Published: February 2005

Optical properties of several synthesized complexes formed by self-assembly of pyrrol-2-yl-methyleneamines with zinc (II) ions are reported. Using a nanosecond optical parametric oscillator as the laser source, strong broadband optical power limiting performances based on two-photon absorption (TPA) have been observed in the visible region, where these materials exhibit large two-photon absorption (TPA) cross sections from 10−18to10−16cm4∕GW in chloroform solution.
Vertically aligned carbon nanofibers and related structures: Controlled synthesis and directed assembly
Authors: Melechko A. V. , Merkulov V. I. , McKnight T. E. , Guillorn M. A. , Klein K. L. , Lowndes D. H. , Simpson M. L.
Published: February 2005

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process.
Volume-variable sample holder for small-angle x-ray scattering measurements of supercritical solutions and its application to the CHF3–CO2 mixture
Authors: Morita Takeshi , Masakawa Tomoko , Arai Asako Ayusawa , Nakagawa Masato , Nishikawa Keiko
Published: February 2005

A sample holder for small-angle x-ray scattering (SAXS) experiments was designed for a volume-variable operation by using a metal bellows. The key point of our design is such that no backup pressure is required. This made the sample cell and peripherals compact so that it can be placed in a limited space typical of synchrotron radiation facilities. Furthermore, the pressure/volume of the sample can be set at any desired value easily. This holder enabled us to carry out precise measurements of SAXS intensities of supercritical solutions with simple operations at many different densities. For performance test, correlation lengths, which provide information on spatial fluctuation of fluid, were evaluated for a supercritical CHF3–CO2 mixture at the 0.005 mole fraction of CHF3 over a wide-density region.
Interdot carrier transfer in asymmetric bilayer InAs∕GaAs quantum dot structures
Authors: Mazur Yu. I. , Wang Zh. M. , Tarasov G. G. , Xiao Min , Salamo G. J. , Tomm J. W. , Talalaev V. , Kissel H.
Published: February 2005

Transient photoluminescence from a series of asymmetric InAs quantum-dot bilayers with a GaAs barrier layer thickness varying from 30 to 60 monolayers between the quantum-dot planes is investigated. The interdot carrier transfer process is analyzed. In the framework of a three-level system, interdot carrier transfer times between 200 and 2500ps are derived and compared with similar data from the literature. Within the semiclassical Wentzel–Kramers–Brillouin approximation, the observed “transfer time-barrier thickness-relation” supports nonresonant tunneling as the microscopic carrier transfer mechanism.
Microsqueeze force sensor useful as contact-free profilometer and viscometer
Authors: Oberti Stefano , Stemmer Andreas , Juncker David , Duerig Urs , Schmid Heinz
Published: February 2005

We present a sensor for measuring viscous friction forces in liquids proximal to a substrate. The sensor is implemented as a mechanical oscillator that is damped by the liquid squeezed in the gap between the sensor head and the substrate. Force versus distance curves were recorded ranging from 100 μm down to a few microns and are in agreement with the expected power law for the damping curve. The viscosity ratios of different liquids were measured with the sensor and are in accordance with values in the literature. Moreover, the topography of an immersed substrate was recorded with micrometer lateral and vertical resolution by scanning the sensor in constant height mode above the surface.
Greatly reduced leakage current and conduction mechanism in aliovalent-ion-doped BiFeO3
Authors: Qi Xiaoding , Dho Joonghoe , Tomov Rumen , Blamire Mark G. , MacManus-Driscoll Judith L.
Published: February 2005

Transport properties of aliovalent-ion-doped BiFeO3 (BFO) thin films have been studied in order to identify the cause of high leakage currents. Doping of 2at.% Ti4+ ions increased the dc resistivity by more than three orders of magnitude. In contrast, doping of 2+ ions such as Ni2+ reduced the dc resistivity by two orders of magnitude. Current–voltage (I–V) characteristics indicated that the main conduction mechanism for pure and Ni2+ doped BFO was space charge limited, which was associated with the free-carriers trapped by the oxygen vacancies, whereas in the Ti4+ doped BFO, field-assisted ionic conduction was dominant.
Nanometer-scale gaps between metallic electrodes fabricated using a statistical alignment technique
Authors: Steinmann P. , Weaver J. M. R.
Published: February 2005

We describe a fabrication process for the creation of nanoscale gaps between metallic electrodes based on a statistical alignment method. This technique is appropriate for applications in which a sparse array of gaps, connected to macroscopic electrodes and pads, is required, for example the study of single molecule electrical conduction. This process relies on aligning two separate levels of electron beam lithography defining opposing arrays of metallic wires, so that the gap may be defined between wires of two dissimilar materials, such as nickel and gold. Lithographic definition of gaps small enough to permit tunneling was reliable and had high yield. Fitting an analytical model of tunnel conductance to measured electrical characteristics of a typical gap demonstrates a gap spacing of 1.3±0.7nm. The process is compatible with most conventional electron-beam lithography systems and does not require the use of unusually high resolution or accurate pattern placement.
Interface-roughness-induced broadening of intersubband electroluminescence in p-SiGe and n-GaInAs∕AlInAs quantum-cascade structures
Authors: Tsujino S. , Borak A. , Müller E. , Scheinert M. , Falub C. V. , Sigg H. , Grützmacher D. , Giovannini M. , Faist J.
Published: February 2005

The effect of intrasubband interface roughness scattering on intersubband transition linewidths in double-quantum-well and quantum-cascade (QC) structures is studied. In n-GaInAs∕AlInAs structures, the calculated ratios between the linewidths of the spatially vertical and diagonal transitions agree with the experimental values. In p-Si∕Si0.2Ge0.8 QC structures, the experimentally observed linewidth is a factor of 4–7 smaller than the predicted value. However, by assuming a vertical interface correlation between adjacent interfaces separated by less than ∼1.5nm, the theory reproduces the experiment. Transmission electron microscopy of the SiGe QC sample reveals this vertical correlation, supporting the model.
Enhanced optical and structural properties of 1.3μm GaInNAs∕GaAs multiple quantum-well heterostructures with stepped strain-mediating layers
Authors: Liu H. Y. , Soong W. M. , Navaretti P. , Hopkinson M. , David J. P. R.
Published: February 2005

The effects of inserting GaInNAs single or stepped strain-mediating layers between GaInNAs quantum wells and the surrounding matrix on the structural and optical properties of 1.3μm GaInNAs∕GaAs multiple quantum-well (QW) structures have been investigated. Compared to control samples with simple GaInNAs multiple quantum wells, samples with strain-mediating layers exhibit improved optical and structural properties. A further strong enhancement of photoluminescence efficiency at room temperature and a remarkable reduction of emission linewidth of GaInNAs multiple QWs have been observed using a compositionally stepped strain-mediating layer. These results imply that the strain profile between the quantum well and the surrounding matrix has a major effect on the optical and structural qualities of GaInNAs quantum wells.
Parameter for glass forming ability of ternary alloy systems
Authors: Park E. S. , Kim D. H. , Kim W. T.
Published: February 2005

A parameter (σ parameter) for glass forming ability (GFA) of the ternary bulk metallic glasses is proposed, taking into consideration the relative thermodynamic stability and atomic configuration of the liquid phase. The σ parameter, defined by ΔT*×P′, combines the effects of melting temperature depression (ΔT*) and effective atomic size mismatch between constituting elements (P′). The parameter shows better correlation with GFA than previously proposed parameters. The relationship between σ and GFA can be expressed as Dmax=2.0×10−1exp(20.01σ), where Dmax is the maximum thickness for glass formation. Since σ can be calculated simply using data on melting temperature and atomic size, the GFA can be easily estimated using this parameter.
Tuning of electron injections for n-type organic transistor based on charge-transfer compounds
Authors: Takahashi Y. , Hasegawa T. , Abe Y. , Tokura Y. , Nishimura K. , Saito G.
Published: February 2005

A high mobility (∼1.0cm2∕Vs) n-type organic field-effect transistor is devised in terms of the combination of semiconducting and metallic charge-transfer (CT) compounds, namely, DBTTF-TCNQ crystals as channels and TTF-TCNQ thin films as electrodes for carrier injections on top of the crystals. Comparison of the field-effect properties for devices with conventional electrode materials indicates the successful demonstration of the interface band engineering with use of the CT materials.
Tuning of NiSi∕Si Schottky barrier heights by sulfur segregation during Ni silicidation
Authors: Zhao Q. T. , Breuer U. , Rije E. , Lenk St. , Mantl S.
Published: February 2005

The Schottky barrier height (SBH) of NiSi on Si(100) was tuned in a controlled manner by the segregation of sulfur (S) to the silicide∕silicon interface. S was implanted into silicon prior to silicidation. During subsequent Ni silicidation, the segregation of S at the NiSi∕Si interface leads to the change of the SBH. The SBH of NiSi decreased gradually on n-Si(100) from 0.65eV to 0.07eV and increased correspondingly on p-Si(100).
Negative differential resistance and electroluminescence from InAs light-emitting diodes grown by liquid-phase epitaxy
Authors: Krier A. , Huang X. L.
Published: February 2005

Negative differential resistance has been observed from InAs homojunction light-emitting diodes grown using liquid-phase epitaxy at 455°C. The devices were characterized using current–voltage (I–V) and electroluminescence spectroscopy measurements to obtain information about structure defects in InAs. Two distinct negative differential resistance regions were observed in the forward bias I–V characteristic, consistent with carriers tunnelling into defect levels within the InAs band gap. At large forward bias, carrier injection into the defect levels resulted in electroluminescence peaking at 372meV and then at 392meV with increasing current. Analysis based on a native lattice complex defect indicates that carriers recombine via the defect levels at temperatures up to 175K.
The predictive power of zero intelligence in financial markets
Authors: Farmer J. Doyne , Patelli Paolo , Zovko Ilija I.
Published: February 2005

Standard models in economics stress the role of intelligent agents who maximize utility. However, there may be situations where constraints imposed by market institutions dominate strategic agent behavior. We use data from the London Stock Exchange to test a simple model in which minimally intelligent agents place orders to trade at random. The model treats the statistical mechanics of order placement, price formation, and the accumulation of revealed supply and demand within the context of the continuous double auction and yields simple laws relating order-arrival rates to statistical properties of the market. We test the validity of these laws in explaining cross-sectional variation for 11 stocks. The model explains 96% of the variance of the gap between the best buying and selling prices (the spread) and 76% of the variance of the price diffusion rate, with only one free parameter. We also study the market impact function, describing the response of quoted prices to the arrival of new orders. The nondimensional coordinates dictated by the model approximately collapse data from different stocks onto a single curve. This work is important from a practical point of view, because it demonstrates the existence of simple laws relating prices to order flows and, in a broader context, suggests there are circumstances where the strategic behavior of agents may be dominated by other considerations.
Angiostatic peptides use plasma fibronectin to home to angiogenic vasculature
Authors: Åkerman Maria E. , Pilch Jan , Peters David , Ruoslahti Erkki
Published: February 2005

A group of angiogenesis inhibitors are derived from fragments of extracellular matrix or blood proteins. Endostatin, antithrombin, and anastellin are members of this group of substances. The plasma adhesion proteins fibronectin and vitronectin serve as cofactors for these three antiangiogenic proteins. Anginex is a synthetic 33-amino acid peptide that was originally modeled to reproduce the β-sheet structure of antiangiogenic proteins. Here, we show that anginex initiates fibronectin polymerization and is inactive in mice that lack plasma fibronectin. Anginex shares these characteristics with anastellin. Fluorescein-labeled anginex and anastellin specifically localized in angiogenic vessels
in vivo
. This localization was dependent on plasma fibronectin and inhibited by an Arg-Gly-Asp peptide. Thus, anginex shares with several physiological angiogenesis inhibitors a dependence on plasma adhesion proteins. The role of the adhesion protein interaction apparently is to form integrin-binding complexes that deliver the antiangiogenic proteins to sites of angiogenesis. This functional convergence of several antiangiogenic factors has important implications for antiangiogenic therapies.
Mono-(2-ethylhexyl) Phthalate (MEHP) Induces Spermatogenic Cell Apoptosis in Guinea Pig Testes at Prepubertal Stage In Vitro
Authors: Awal M. A. , Kurohmaru M. , Ishii M. , Andriana B. B. , Kanai Y. , Hayashi Y.
Published: February 2005

The effects of mono-(2-ethylhexyl) phthalate (MEHP), an active metabolite of di-(2-ethylhexyl) phthalate (DEHP), on prepubertal guinea pig testes in vitro were investigated. The testes of 35-day-old guinea pigs were surgically excised. They were seeded in a defined medium containing antibiotics and administered MEHP at concentrations of 1, 10, and 100 nmol/ml, respectively. The control groups were administered a similar volume of corn oil vehicle. The tissues were incubated for 3, 6, and 9 h. The specimens were collected at 3, 6, and 9 h after treatment. They were fixed in 4%paraformaldehyde or 5% glutaraldehyde. For quantitation of the apoptotic spermatogenic cells, the terminal dUTP nick end-labeling (TUNEL) staining was performed by light microscopy. Detachment and displacement of spermatogenic cells, thin seminiferous epithelia, and Sertoli cell vacuolization were observed. Maximal testicular damage was recognized at 100 nmol/ml 9 h after MEHP treatment. The percentage (%) of apoptotic spermatogenic cells significantly increased at 3, 6, and 9 h after treatment, compared to the control groups. Because the loss of spermatogenic cells by MEHP treatment varies among species, the present study, using guinea pigs, was designed and conducted to obtain further information.
Interface acoustic waves in piezoelectric bi-crystalline structures of specific types
Authors: Darinskii A. N , Weihnacht M
Published: February 2005

The paper discusses the properties of the acoustic waves guided by an interface inside piezoelectric media. The interfaces of two types have been considered: (i) an infinitesimally thin metallic layer inserted into homogeneous piezoelectric crystal of arbitrary symmetry; (ii) rigidly bonded crystals whose piezoelectric coefficients differ by sign while the other material constants are identical. Several general theorems have been proved regarding the existence of interface acoustic waves (IAWs) propagating more slowly than bulk waves. In particular, a sufficient condition for the existence of such ‘slow’ IAWs has been derived. The propagation of leaky IAWs has been studied. Special attention has been paid to the analysis of the situation when the imaginary component of the leaky IAW velocity vanishes, resulting in the appearance of non-attenuating IAWs travelling faster than the slow transverse bulk wave. The computations performed for LiNbO
3
and LiTaO
3
illustrate general conclusions.
Sperm influences female hibernation success, survival and fitness in the bumble–beeBombus terrestris
Authors: Baer Boris , Schmid-Hempel Paul
Published: February 2005

We present evidence that in the absence of the transfer of male gland compounds in the ejaculate as well as of behavioural male traits, such as mate guarding or harming of females, sperm itself affects female life–history traits such as hibernation success, female longevity and female fitness. Using the bumble–beeBombus terrestris, we artificially inseminated queens (females) with sperm from one or several males and show that sire groups (groups of brother males) vary in their effects on queen hibernation survival, longevity and fitness. In addition, multiply inseminated queens always had a lower performance as compared to singly inseminated queens. Apart from these main effects, sire groups (in situations of multiple insemination) affected queen longevity and fitness not independently of each other, i.e. certain sire group combinations were more harmful to queens than others. So far, the cause(s) of these effects remain(s) elusive. Harmful male traits as detected here are not necessarily expected to evolve in social insects because males depend on females for a successful completion of a colony cycle and thus have strong convergent interests with their mates.
A single mutation alters production and discrimination ofDrosophilasex pheromones
Authors: Marcillac Fabrice , Grosjean Yaël , Ferveur Jean-François
Published: February 2005

The evolution of communication is a fundamental biological problem. The genetic control of the signal and its reception must be tightly coadapted, especially in inter–individual sexual communication. However, there is very little experimental evidence for tight genetic linkage connecting the emission of a signal and its reception. We found that a single genomic transposon inserted in thedesat1gene ofDrosophila melanogastersimultaneously affected the emission and the perception of sex–specific signals. This mutation greatly decreased the production of unsaturated hydrocarbons on the cuticle of mature flies of both sexes. These substances represent the sex pheromones necessary for mate discrimination: control males could not discriminate the sex of mutantdesat1flies. Moreover, mutant males were unable to discriminate the sex pheromones of control flies. Expression ofdesat1was found in the peripheral tissues that produce and detect sex pheromones. Excision of the transposon rescued both the production and discrimination phenotypes, but the two effects did not always coincide. This indicates that the emission and perception of pheromones are coded by different products of the same gene, reflecting the pleiotropic activity ofdesat1.
Parasites and mutational load: an experimental test of a pluralistic theory for the evolution of sex
Authors: Cooper Tim F. , Lenski Richard E. , Elena Santiago F.
Published: February 2005

Ecological and mutational explanations for the evolution of sexual reproduction have usually been considered independently. Although many of these explanations have yielded promising theoretical results, experimental support for their ability to overcome a twofold cost of sex has been limited. For this reason, it has recently been argued that a pluralistic approach, combining effects from multiple models, may be necessary to explain the apparent advantage of sex. One such pluralistic model proposes that parasite load and synergistic epistasis between deleterious mutations might interact to create an advantage for recombination. Here, we test this proposal by comparing the fitness functions of parasitized and parasite–free genotypes ofEscherichia colibearing known numbers of transposon–insertion mutations. In both classes, we failed to detect any evidence for synergistic epistasis. However, the average effect of deleterious mutations was greater in parasitized than parasite–free genotypes. This effect might broaden the conditions under which another proposed model combining parasite–host coevolutionary dynamics and mutation accumulation can explain the maintenance of sex. These results suggest that, on average, deleterious mutations act multiplicatively with each other but in synergy with infection in determining fitness.
Global trends in world fisheries: impacts on marine ecosystems and food security
Authors: Pauly Daniel , Watson Reg , Alder Jackie
Published: February 2005

This contribution, which reviews some broad trends in human history and in the history of fishing, argues that sustainability, however defined, rarely if ever occurred as a result of an explicit policy, but as result of our inability to access a major part of exploited stocks. With the development of industrial fishing, and the resulting invasion of the refuges previously provided by distance and depth, our interactions with fisheries resources have come to resemble the wars of extermination that newly arrived hunters conducted 40 000–50 000 years ago in Australia, and 11 000–13 000 years ago against large terrestrial mammals arrived in North America. These broad trends are documented here through a map of change in fish sizes, which displays characteristic declines, first in the nearshore waters of industrialized countries of the Northern Hemisphere, then spread offshore and to the Southern Hemisphere. This geographical extension met its natural limit in the late 1980s, when the catches from newly accessed stocks ceased to compensate for the collapse in areas accessed earlier, hence leading to a gradual decline of global landing. These trends affect developing countries more than the developed world, which have been able to meet the shortfall by increasing imports from developing countries. These trends, however, together with the rapid growth of farming of carnivorous fishes, which consumes other fishes suited for human consumption, have led to serious food security issues. This promotes urgency to the implementation of the remedies traditionally proposed to alleviate overfishing (reduction of overcapacity, enforcement of conservative total allowable catches, etc.), and to the implementation of non–conventional approaches, notably the re–establishment of the refuges (also known as marine reserves), which made possible the apparent sustainability of pre–industrial fisheries.
Sustainability in single–species population models
Authors: Quinn Terrance J. , Collie Jeremy S.
Published: February 2005

In this paper, we review the concept of sustainability with regard to a single–species, age–structured fish population with density dependence at some stage of its life history. We trace the development of the view of sustainability through four periods.

Theclassicalview of sustainability, prevalent in the 1970s and earlier, developed from deterministic production models, in which equilibrium abundance or biomass is derived as a function of fishing mortality. When there is no fishing mortality, the population equilibrates about its carrying capacity. We show that carrying capacity is the result of reproductive and mortality processes and is not a fixed constant unless these processes are constant. There is usually a fishing mortality,FMSY, which results in MSY, and a higher value,Fext, for which the population is eventually driven to extinction. For eachFbetween 0 andFext, there is a corresponding sustainable population. From this viewpoint, the primary tool for achieving sustainability is the control of fishing mortality.

Theneoclassicalview of sustainability, developed in the 1980s, involved population models with depensation and stochasticity. This view point is in accord with the perception that a population at a low level is susceptible to collapse or to a lack of rebuilding regardless of fishing. Sustainability occurs in a more restricted range from that in the classical view and includes an abundance th reshold. A variety of studies has suggested that fishing mortality should not let a population drop below a threshold at 10–20% of carrying capacity.

Themodernview of sustainability in the 1990s moves further in the direction of precaution. The fishing mortality limit is the former target ofFMSY(or some proxy), and the target fishing mortality is set lower. This viewpoint further reduces the range of permissible fishing mortalities and resultant desired population sizes. The objective has shifted from optimizing long–term catch to preserving spawning biomass and egg production for the future. The use of discount rates in objective functions involving catch is not a suitable alternative to protecting reproductive value.

As we move into thepost–moderntime period, new definitions of sustainability will attempt to incorporate he economic and social aspects of fisheries and/or ecosystem and habitat requirements. These definitions now involve ‘warm and fuzzy’ notions (healthy ecosystems and fishing communities, the needs of future generations, diverse fish communities) and value judgements of desired outcomes. Additional work is needed to make these definitions operational and to specify quantitative objectives to be achieved. In addition, multiple objectives may be incompatible, so trade–offs in what constitutes sustainability must be made. The advances made under the single–species approach should not be abandoned in the post–modern era, but rather enhanced and combined with new approaches in the multi–species and economic realms.
Combining control measures for more effective management of fisheries under uncertainty: quotas, effort limitation and protected areas
Authors: Stefansson Gunnar , Rosenberg Andrew A.
Published: February 2005

We consider combinations of three types of control measures for the management of fisheries when the input information for policy decisions is uncertain. The methods considered include effort controls, catch quotas and area closures. We simulated a hypothetical fishery loosely based on the Icelandic cod fishery, using a simple spatially explicit dynamic model. We compared the performance with respect to conserving the resource and economic return for each type of control measure alone and in combination. In general, combining more than one type of primary direct control on fishing provides a greater buffer to uncertainty than any single form of fishery control alone. Combining catch quota control with a large closed area is a most effective system for reducing the risk of stock collapse and maintaining both short and long–term economic performance. Effort controls can also be improved by adding closed areas to the management scheme. We recommend that multiple control methods be used wherever possible and that closed areas should be used to buffer uncertainty. To be effective, these closed areas must be large and exclude all principal gears to provide real protection from fishing mortality.
Does Social Capital Make You Generous?*
Authors: Brooks Arthur C.
Published: February 2005

Objectives. This article tests the hypothesis that social capital—measured in terms of civic group involvement, social and racial trust, and political engagement—leads to charitable behavior by individuals.

Methods. I introduce measures of the “social capital elasticity of giving,” which facilitate comparisons between the effects on charity of different social capital types. Using data from the 2000 Social Capital Community Benchmark Survey, I estimate these elasticities with tobit regression models.

Results. I find strong links between changes in social capital stocks and changes in giving levels. Furthermore, I find that different social capital types have differing levels of impact on giving.

Conclusions. Charitable giving appears to be a beneficial consequence of some types of social capital.
Causes of Civil War in Asia and Sub‐Saharan Africa: A Comparison*
Authors: Krause Volker , Suzuki Susumu
Published: February 2005

Objectives.This article explores the extent to which economic development, ethnic and religious fractionalization, domestic governance, and international trade openness affect civil war in postcolonial Asia and Sub‐Saharan Africa (SSA) from 1950 through 1992.

Methods.We estimate a set of multivariate logit models with the generalized estimating equation (GEE) method for time‐series cross‐sectional (TSCS) data.

Results.Both in Asia and in SSA, civil war is less likely with increased economic development and trade openness, while mixed autocratic‐democratic regimes raise the likelihood that states will experience civil war. Although neither ethnic nor religious fractionalization has any statistically significant effect on civil war in SSA, civil war in Asia is more likely with greater ethnic fractionalization.

Conclusions.Despite cross‐regional variation in causes of civil war, economic development and trade openness seem to play a consistent role in reducing civil war.
Grass, Sweat, and Sun: An Exploratory Study of the Labor Market for Gardeners in South Texas*
Authors: Pisani Michael J. , Yoskowitz David W.
Published: February 2005

Objective. This article takes a first exploratory step in understanding the market for home gardeners in the southwest borderlands (Laredo, Texas).

Methods. A questionnaire was administered by a household member familiar with the present study who employed at least one gardener utilizing the snowball method of sample selection. Usable data (surveys) were collected from 244 individuals: 122 gardeners and 122 employers.

Results. Gardeners in Laredo are almost exclusively male, Hispanic, Spanish speaking, and heads of household. Gardeners tend to be Mexican by birth and nationality, work full time as a gardener, be middle aged, and possess a middle school education. Distinctions between full‐time and part‐time gardeners (employment status) as well as formal and informal gardeners (employment process) are discussed. Cross‐tabulation analyses suggest a strong relationship between employment status and process (relationship) with health insurance coverage, enrollment in Social Security, and year‐around work. Logistic regression results also indicate previous work experience as a gardener, medical insurance, and year‐around work as a gardener are the significant variables in determining full‐time employment as a gardener. For informality, logistic regression results suggest Mexican citizenship, Mexican birthplace, and lack of Social Security are the significant explanatory variables.

Conclusion. Gardening enables a mostly informal workforce from Mexico to work in south Texas in pursuit of the American dream—the ability to make a living in a way of one's own choosing.
Gender and the Internet: Causes of Variation in Access, Level, and Scope of Use*
Authors: Wasserman Ira M. , Richmond‐Abbott Marie
Published: February 2005

Objective.The article examines differences in the use of the Internet by gender, with a consideration of access to the web, use of communication facilities related to email and chat rooms, frequency of use, and types of websites used. The study considers the impact of socioeconomic status and social, geographic, racial, and ethnic variables for explaining variations in the use of the web by men and women, and how these factors are mediated by knowledge of how to use the web.

Methods.The study employs data collected by the General Social Survey (GSS) in 2000, and relates access, communication levels, frequency of use, and types of sites used to gender and other relevant variables. The relevant variables are analyzed by multivariate analysis.

Results.Access to the web was independent of gender, but was related to education, race, income, age, and marital status. Women were less likely than men to chat on the web, but were slightly more likely to use email, and they utilized different types of sites than men.

Conclusions.Women access the web as frequently as men, but they communicate on the Internet differently than men, are online less than men, and utilize different types of websites than men. Knowledge related to web use is an important independent variable that influences Internet use by men and women.
Evaluation of anticoagulant system in Turkish children with Perthes disease
Authors: Yilmaz Deniz , Karapinar Levent , Karapinar Bulent , Ozturk Hasan , Kavakli Kaan
Published: February 2005

Abstract 
Background
: Perthes Disease (PD) is generally a self‐limiting disease of childhood but it causes severe pain and may lead to deformity of the femoral head. Intravascular thrombosis seems to form the main mechanism in the pathogenesis of the disease. The aim of this study was to determine hereditary thrombotic risk factors in Turkish children with PD.

Methods
: In 46 Perthes patients (35 male, 11 female), family history of thrombotic events was investigated, Protein C (PC), free‐Protein S (f‐PS), antithrombin (AT) activities, fibrinogen level, and resistance to activated Protein C (APC) were measured. The results were compared with a healthy control group of 79 children matched by age and sex. The relationship between the severity of disease and coagulation system abnormalities was evaluated.

Results
: While the mean PC and AT activities were significantly lower in the patients than those of the controls, the proprotions of patients with low AT activity, resistance to APC, and a history of hereditary thrombophilia were significantly higher than those of the controls. No difference was observed in coagulation system disorders relative to severity of the disease and bilateral or unilateral disease involvement.

Conclusions
: This study shows that a possible association between PD and inherited hypercoagulability. Determination of thrombotic risk factors in these patients may bring a new approach to the treatment. Most importantly, this may be a stimulant to take precautions for other thrombotic events, which patients may face later in life.