bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduced intermittency in the magnetic turbulence of reversed field pinch plasmas
Authors: Marrelli L. , Frassinetti L. , Martin P. , Craig D. , Sarff J. S.
Published: February 2005

The statistical temporal properties of broadband magnetic turbulence in the edge of reversed field pinch (RFP) plasmas are significantly altered when global magnetohydrodynamic tearing modes and magnetic relaxation are reduced. Standard RFP plasmas, having relatively large tearing fluctuations, exhibit broadband intermittent bursts of magnetic fluctuations in the bandwidth f<1.5MHz. When the global tearing is reduced via parallel current drive in the edge region, the magnetic turbulence is much less intermittent and has statistical behavior typical of self-similar turbulence (like that expected in self-organized criticality systems). A connection between intermittency and long wavelength plasma instabilities is therefore implied.
Numerical simulation of finite Reynolds number suspension drops settling under gravity
Authors: Bosse Thorsten , Kleiser Leonhard , Härtel Carlos , Meiburg Eckart
Published: February 2005

A suspension drop is a swarm of particles that are suspended in initially still fluid. When settling under the influence of gravity a suspension drop may undergo a complex shape evolution including the formation of a torus and eventual disintegration. In the present work the settling process of initially spherical suspension drops is investigated numerically for low and moderate drop Reynolds numbers Red. In the simulations a pseudospectral method is used for the liquid phase combined with a Lagrangian point-particle model for the particulate phase. In the case of low Reynolds numbers (Red<1) the suspension drop retains a roughly spherical shape while settling. A few particles leak away into a tail emanating from the rear of the drop. Due to the use of periodic boundaries a hindered settling effect is observed: the drop settling velocity is decreased compared to a suspension drop in infinite fluid. In the Reynolds number range 1⩽Red⩽100 the suspension drop deforms into a torus that eventually becomes unstable and breaks up into a number of secondary blobs. This Reynolds number range has not been investigated systematically in previous studies and is the focus of the present work. It is shown that the number of secondary blobs is primarily determined by the Reynolds number and the particle distribution inside the initial drop. An increased number of particles making up the suspension, i.e., a finer drop discretization, may result in a delayed torus disintegration with a larger number of secondary blobs. The influence of the initial particle distribution as a source of (natural) perturbations and the effect of initially imposed (artificial) shape perturbations on the breakup process are examined in detail. To gain a better understanding of the substructural effects (inside the suspension) leading to torus breakup, the particle field is analyzed from a spectral point of view. To this end, the time evolution of the Fourier coefficients associated with the particle distribution in the azimuthal direction of the torus is studied.
Laser wakefield acceleration by petawatt ultrashort laser pulses
Authors: Gorbunov L. M. , Kalmykov S. Yu. , Mora P.
Published: February 2005

An ultrashort (about 30fs) petawatt laser pulse focused with a wide focal spot (about 100μm) in a rarefied plasma (n0∼1017cm−3) excites a nonlinear plasma wakefield which can accelerate injected electrons up to GeV energies without any pulse channeling. Under these conditions, propagation of the laser pulse with an overcritical power for relativistic self-focusing is almost the same as in vacuum. The nonlinear quasiplane plasma wave, whose amplitude and phase velocity vary along the laser path, effectively traps and accelerates injected electrons with a wide range of initial energies. Electrons accelerated over two Rayleigh lengths (about 8cm) can gain energies up to 1Gev. In particular, the electrons trapped from a long (τb∼330fs) nonresonant electron beamlet of 1MeV particles eventually form a low emittance bunch with energies in the range 900±50MeV. These conclusions follow from two-dimensional simulations performed in cylindrical geometry by means of the fully relativistic time-averaged particle code WAKE [P. Mora and T. M. Antonsen, Jr., Phys. Rev. E 53, R2068 (1996); Phys. Plasmas 4, 217 (1997)].
Effects of hot electrons on the stability of a closed field line plasma
Authors: Krasheninnikova Natalia S. , Catto Peter J.
Published: February 2005

Motivated by the electron cyclotron heating being employed on dipole experiments, the effects of a hot species on stability in closed magnetic field line geometry are investigated by considering a Z-pinch plasma. The interchange stability of a plasma of background electrons and ions with a small fraction of hot electrons is considered. The species diamagnetic drift and magnetic drift frequencies are assumed to be of the same order, and the wave frequency is assumed to be much larger than the background, but much less than the hot drift frequencies. An arbitrary total pressure dispersion relation is obtained, with the background plasma treated as a single fluid, while a fully kinetic description is employed for the hot species. The analysis of the dispersion relation shows that two different kinds of resonant hot electron effects modify the simple magnetohydrodynamic interchange stability condition. When the azimuthal magnetic field increases with radius, there is a critical pitch angle above which the magnetic drift of the hot electrons reverses. The interaction of the wave with the hot electrons with pitch angles near this critical value always results in instability. When the magnetic field decreases with radius, magnetic drift reversal is not possible and only low speed hot electrons will interact with the wave. Destabilization by this weaker resonance effect can be avoided by carefully controlling the hot electron density and temperature profiles.
Scaling laws and nonlinear wave dynamics in neon glow discharges
Authors: Wilke C. , Koch B.-P. , Bruhn B.
Published: February 2005

Scaling laws that are obtained from a hydrodynamic model of the positive column in neon gas discharges are checked in experiments. In contrast to previous investigations, most experiments were performed in parameter regions where nonlinear phenomena are dominant. The results show that the predicted scaling laws are also fulfilled in these cases with satisfactory accuracy.
Lateral and transverse wakes due to moving charged particles
Authors: Bose Anirban , Janaki M. S.
Published: February 2005

The wake structure of a charged particle moving in a dusty plasma is analyzed for the cases where the charge speed is greater or less than the dust-acoustic speed. In the case of M<1, where the Mach number M is the ratio of the test particle speed to the dust acoustic speed, constructive interference of acoustic oscillations leads to both lateral and transverse wakes, while in the case of M>1, only lateral wakes are obtained.
nlinImproving spatial resolution of convergent beam electron diffraction strain mapping in silicon microstructures
Authors: Armigliato A. , Balboni R. , Frabboni S.
Published: February 2005

Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical ⟨110⟩ direction. We demonstrate that it is possible to improve this resolution by using the ⟨340⟩ zone axis, instead of the ⟨230⟩ one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported.
Identifying materials with low friction and adhesion for nanotechnology applications
Authors: Tambe Nikhil S. , Bhushan Bharat
Published: February 2005

The advent of micro/nanostructures and the subsequent miniaturization of moving components for various nanotechnology applications have ascribed paramount importance to tribology and mechanics on the nanoscale. Materials with low friction and adhesion are desirable for avoiding premature failures. We present the coefficient of friction and adhesion dependence on the Young’s modulus over a range of sliding velocities for an array of materials. A contour map is developed to identify tribologically suitable materials. This approach provides a fundamental insight into the mechanical property dependence of friction and adhesion and simplifies the material selection process for nanotechnology applications.
3
ω
-scanning thermal microscope
Authors: Lefèvre Stéphane , Volz Sebastian
Published: February 2005

We present the theoretical and experimental calibrations of a scanning thermal microscope (SThM) based on a hot anemometer wire probe. Under ac heating and due to the linear dependence of the probe electrical resistance to temperature, the third harmonic of the tip voltage is also linear to the temperature. This method called “3-ω” is currently used to estimate the thermal properties with a hot strip deposited on the sample surface. However, in this last technique, the sensor size allows one to reach the sample transient thermal behavior whereas the SThM tip does not. We propose a thermal model showing what information can in fact be obtained by using the microscope under the 3ω mode. We finally report an experimental calibration providing the tip/sample contact thermal parameters.
Two-dimensional tracking of a motile micro-organism allowing high-resolution observation with various imaging techniques
Authors: Oku H. , Ogawa N. , Ishikawa M. , Hashimoto K.
Published: February 2005

In this article, a micro-organism tracking system using a high-speed vision system is reported. This system two dimensionally tracks a freely swimming micro-organism within the field of an optical microscope by moving a chamber of target micro-organisms based on high-speed visual feedback. The system we developed could track a paramecium using various imaging techniques, including bright-field illumination, dark-field illumination, and differential interference contrast, at magnifications of 5 times and 20 times. A maximum tracking duration of 300s was demonstrated. Also, the system could track an object with a velocity of up to 35 000μm∕s (175diameters∕s), which is significantly faster than swimming micro-organisms.
Two-dimensional growth of continuous Cu2O thin films by magnetron sputtering
Authors: Yin Z. G. , Zhang H. T. , Goodner D. M. , Bedzyk M. J. , Chang R. P. H. , Sun Y. , Ketterson J. B.
Published: February 2005

We present results on the in situ, two-dimensional growth (as opposed to the more commonly encountered island-coalescence mechanism) of continuous epitaxial Cu2O films on MgO(011) using dc facing-magnetron sputtering from metallic Cu targets in an oxygen/argon atmosphere. Film growth was studied as a function of deposition time and the dc power applied to the guns. Control of the latter leads to either continuous or island-/rodlike film morphologies.
Optically-pumped long-wavelength vertical-cavity surface-emitting laser with high modulation bandwidth
Authors: Ramana Murty M. V. , Xu D. , Lin C.-C. , Shieh C.-L. , Tsao J. Y. , Cheng Julian
Published: February 2005

Optically-pumped long-wavelength vertical-cavity surface-emitting lasers (VCSELs) have been fabricated exhibiting more than 2mW over 20–70°C, and 1.25mW at 85°C. Small-signal modulation measurements on the VCSEL at 20°C indicate a 3dB bandwidth of 14.8GHz at an output power of 2mW. The VCSELs have a narrow spectral width suitable for data transmission over single-mode fiber. The good temperature performance of the VCSEL is maintained in a suspended configuration that would allow monolithic integration.
X-ray absorption spectroscopy in MnxGe1−x diluted magnetic semiconductor: Experiment and theory
Authors: Picozzi S. , Ottaviano L. , Passacantando M. , Profeta G. , Continenza A. , Priolo F. , Kim M. , Freeman A. J.
Published: February 2005

Accurate first-principles calculations of soft x-ray absorption spectra are compared with experimental data obtained for the ion-implanted MnxGe1−x ferromagnetic semiconductor. The well-defined features in the spectra are recognized as a signature of homogeneous Mn dilution within the Ge host, as demonstrated by comparing the Mn spectra in diluted MnGe alloys with other competing Mn–Ge crystalline phases. Moreover, provided that an efficient Mn dilution is achieved, the nature of the semiconducting host is shown to affect only slightly the Mn absorption spectrum, as shown by the similarity of the present results with those for other magnetic semiconductors. Both these findings establish the relevance of ion-implantation in the dilute magnetic semiconductor framework, emphasizing its potential impact in device technology.
Room temperature tunneling transport through Si nanodots in silicon rich silicon nitride
Authors: Pei Zingway , Su Alex Y. K. , Hwang H. L. , Hsiao H. L.
Published: February 2005

Devices containing Si nanodots (NDs) were made in an α-SiNx:H∕Si NDs∕α-SiNx:H structure to explore the transport characteristics. The Si NDs were embedded in a silicon nitride matrix and were produced by using a plasma enhanced chemical vapor deposition technique. Room temperature Si NDs related electron and hole tunneling transport were observed in these devices. Negative differential resistance in the current–voltage characteristics was observed for the hole tunneling. The peak-to-valley ratio was as high as 13.9. Transmission electron microscopy reveals that only one Si ND exists in the current transport direction. The Si NDs are ∼5nm in diameter. A model with a double barrier band diagram is suggested to explain the Si NDs related transport.
Integration of metal oxide nanobelts with microsystems for nerve agent detection
Authors: Yu Choongho , Hao Qing , Saha Sanjoy , Shi Li , Kong Xiangyang , Wang Z. L.
Published: February 2005

We have assembled tin dioxide nanobelts with low-power microheaters for detecting dimethyl methylphosphonate (DMMP), a nerve agent simulant. The electrical conductance of a heated nanobelt increased for 5% upon exposure to 78 parts per billion DMMP in air. The nanobelt conductance recovered fully quickly after the DMMP was shut off, suggesting that the single-crystal nanobelt was not subject to poisoning often observed in polycrystalline metal oxide sensors. While the sensitivity can be improved via doping nanobelts with catalytic additives, directed assembly or growth of nanobelts on microsystems will potentially allow for the large-scale fabrication of nanosensor arrays.
Cu
-doped indium oxide∕Ag ohmic contacts for high-power flip-chip light-emitting diodes
Authors: Song June-O , Kwak Joon Seop , Seong Tae-Yeon
Published: February 2005

We have investigated Cu-doped In2O3(CIO)(3nm)∕Ag(250nm) schemes for forming high-quality ohmic contacts to p-type GaN for high-power flip-chip light-emitting diodes (FCLEDs). It is shown that the CIO∕Ag contacts produce specific contact resistance of 1.28×10−5Ωcm2 and reflectance of about 90% at a wavelength of 460nm when annealed at 530°C for 1min in air ambient. It is also shown that unlike single Ag contacts, the CIO∕Ag contacts are fairly stable without surface and interface degradation although annealed at 530°C for 1min in air ambient. In addition, blue multiquantum-well InGaN∕GaN LEDs fabricated with the annealed CIO∕Ag contact layers give forward-bias voltages of around 3.0V at an injection current of 20mA. The results strongly indicate that the CIO∕Ag scheme can be a highly promising p-type contact for high-power GaN-based FCLEDs for solid-state lighting application.
Molecular volume dependence of the electronic and ionic polarizabilities in TiO2 and SiO2
Authors: Devine R. A. B. , Busani T.
Published: February 2005

The molecular volume dependence of the ionic and electronic parts of the molecular polarizability in SiO2 and TiO2 polymorphs is examined. It is demonstrated that their variation should not be neglected when using models such as the “additivity rule” to predict multicomponent oxide dielectric constants.
Manipulating the transmission of a two-dimensional electron gas via spatially varying magnetic fields
Authors: Song J.-F. , Bird J. P. , Ochiai Y.
Published: February 2005

We explore how the transmission properties of a two-dimensional electron gas can be modified by manipulating the fringing magnetic fields that emanate from a set of patterned gates, deposited on the top surface of its heterojunction. We propose a multigate device whose conductance is shown to depend sensitively upon the relative magnetization of its gates, and which may therefore be of use as a planar magnetoresistance device, or as a memory structure.
Band alignment at the CdS∕Cu(In,Ga)S2 interface in thin-film solar cells
Authors: Weinhardt L. , Fuchs O. , Groß D. , Storch G. , Umbach E. , Dhere N. G. , Kadam A. A. , Kulkarni S. S. , Heske C.
Published: February 2005

The band alignment at the CdS∕Cu(In,Ga)S2 interface in thin-film solar cells on a stainless steel substrate was investigated using photoelectron spectroscopy and inverse photoemission. By combining both techniques, the conduction and valence band offsets were independently determined. We find an unfavorable conduction band offset of −0.45 (±0.15) eV, accounting for the generally observed low open-circuit voltage and indicating the great importance of the buffer∕absorber conduction band offset for such devices. The surface band gap of the Cu(In,Ga)S2 absorber is 1.76 (±0.15) eV, being increased with respect to the expected bulk value by a copper depletion near the surface.
Vertically integrated optics for ballistic electron emission luminescence microscopy
Authors: Appelbaum Ian , Yi Wei , Russell K. J. , Narayanamurti V. , Hanson M. P. , Gossard A. C.
Published: February 2005

We have integrated a photon detector directly into a ballistic electron emission luminescence (BEEL) heterostructure, just below a luminescent quantum well. Results from solid-state metal-base hot-electron transistors fabricated with this collector design indicate that more than 10% of the photons emitted by the quantum well excite photoelectrons in the detector region. The improved photonic coupling and effective collection angle in this scheme improves the BEEL signal by many orders of magnitude as compared to far-field detection with the most sensitive single-photon counters, enabling BEEL microscopy in systems with no optical components.
Transmission electron microscopy and electron energy-loss spectroscopy analysis of manganese oxide nanowires
Authors: Du G. H. , Yuan Z. Y. , Van Tendeloo G.
Published: February 2005

Single-crystalline MnOOH and Mn3O4 nanowires have been prepared by hydrothermal treatment of commercial bulky manganese oxide particles. β-MnO2 and α-Mn2O3 nanowires were prepared by calcination of MnOOH nanowires. Transmission electron microscopy analysis demonstrates that MnOOH nanowires grow directly from MnO2 raw particles. The diameter of the nanowires is 20–70 nm, while the length can reach several micrometers. MnOOH nanowires grow preferentially along the [010] direction and Mn3O4 nanowires prefer to grow along the [001] direction; the long dimension of both β-MnO2 and α-Mn2O3 nanowires is along [001]. Electron energy-loss spectroscopy analysis shows that the position of the prepeak of the oxygen K edge shifts to higher energy and the energy separation between the two main peaks of the oxygen K edge decreases with decreasing manganese oxidation state. The manganese-white-line ratios (L3∕L2) were calculated.
Q
-factor optimization of a tuning-fork/fiber sensor for shear-force detection
Authors: Morville Jérôme , Liu Jinquan , Callegari Andrea , Chergui Majed
Published: February 2005

We present the results of an experimental and theoretical study on the optimum design of shear-force sensors, used in scanning probe microscopes. We have optimized a configuration consisting of a tuning-fork/fiber-tip assembly, achieving quality factors (Q) exceeding 8000, and have presented a theoretical analysis of the design wherein the force holding the fiber and fork in contact is provided solely by elastic mechanical deformation, which allows full control of the performance of the system. On this basis, we constructed a high-quality-factor configuration with the fiber glued onto the tuning fork.
Quantum size effects in n-PbTe∕p-SnTe∕n-PbTe heterostructures
Authors: Rogacheva E. I. , Nashchekina O. N. , Meriuts A. V. , Lyubchenko S. G. , Dresselhaus M. S. , Dresselhaus G.
Published: February 2005

The dependencies of the thermoelectric properties of n-PbTe∕p-SnTe∕n-PbTe heterostructures on the SnTe quantum well width (dSnTe=0.5–6.0nm) at fixed PbTe barrier layers thicknesses were studied. It was established that the thickness dependencies of the Seebeck coefficient, electrical conductivity, the Hall coefficient, charge carrier mobility, and the thermoelectric power factor are distinctly nonmonotonic. The observed effect is attributed to the size quantization of the energy spectrum of the hole gas in a SnTe quantum well.
Direct evidence for compressive elastic strain at ground surfaces of nanocomposite ceramics
Authors: Tanner B. K. , Wu H. Z. , Roberts S. G.
Published: February 2005

High-resolution grazing incidence x-ray powder diffraction has been used to provide direct evidence for the existence of a uniform compressive strain close to the surface of ground alumina∕SiC nanocomposites. No such strain is found in ground surfaces of single-phase alumina or polished surfaces of nanocomposite. The strain in the ground nanocomposite is found to be perpendicular to the grinding direction and disappears on annealing at 1250°C. Such a compressive stress provides a mechanism for enhancing the strength of the nanocomposite, by opposing any tensile loading tending to open surface flaws. The origin of the stresses probably lies in the enhanced grain boundary strength in the nanocomposite alumina–silicon carbide compared to alumina.
Fabrication of self-organized conical microstructures by excimer laser irradiation of cyanoacrylate-carbon nanotube composites
Authors: Liu Yuming , Liu Liang , Fan Shoushan
Published: February 2005

Self-organized conical microstructures are fabricated by 308 nm XeCl excimer laser irradiation of cyanoacrylate-carbon nanotube composites in air. The morphology of the surface on the composite films is studied, varying the total number and fluence of the applied laser pulses. A simple mechanism of the fabrication based on the evaporation of cyanoacrylate and the burning of carbon nanotubes is proposed. The conical peak structures of cyanoacrylate-carbon nanotube composite films show good field-emission properties. Similar structures are also observed on carbon nanotube arrays.
Two-dimensional photonic crystals designed by evolutionary algorithms
Authors: Preble Stefan , Lipson Michal , Lipson Hod
Published: February 2005

We use evolutionary algorithms to design photonic crystal structures with large band gaps. Starting from randomly generated photonic crystals, the algorithm yielded a photonic crystal with a band gap (defined as the gap to midgap ratio) as large as 0.3189. This band gap is an improvement of 12.5% over the best human design using the same index contrast platform.
2
GHz
repetition-rate femtosecond blue sources by second harmonic generation in a resonantly enhanced cavity
Authors: Liu Tzu-Ming , Yu Cheng-Ta , Sun Chi-Kuang
Published: February 2005

We report a 2GHz repetition-rate, all-solid-state femtosecond blue source. Pumped by a 740mW femtosecond Ti:sapphire laser with the same repetition rate, 150mW femtosecond pulses at 409nm can be efficiently generated from the external resonant cavity with a lithium triborate crystal.
Effective diffusion coefficient for two-band systems
Authors: Kleinert P. , Bryksin V. V.
Published: February 2005

The effective longitudinal diffusion coefficient for two-band systems is determined. Emphasis is put on the nonlinear transport regime realized at high electric fields. Particular results are obtained for bipolar transport in two-band semiconductors and vertical transport in semiconductor superlattices. An additional contribution to the effective diffusion coefficient is identified, which results from different drift velocities in the respective bands (minibands).
Adiabatic compression of parallel-plate metal waveguides for sensitivity enhancement of waveguide THz time-domain spectroscopy
Authors: Zhang Jiangquan , Grischkowsky D.
Published: February 2005

We demonstrate the efficient coupling of THz pulses into and out of an adiabatically compressed parallel-plate metal waveguide. The plate separation of the 63.5-mm long, compressed waveguide was fixed at 103μm at the entrance and exit ends for efficient coupling, but could be reduced in the middle. The experimental results show strong transmission of the THz signal through the compressed waveguide for a minimum midpoint separation of only 8μm. This technique can be used to achieve efficient coupling together with higher sensitivity for waveguide THz-TDS.
Bismuth telluride nanotubes and the effects on the thermoelectric properties of nanotube-containing nanocomposites
Authors: Zhao X. B. , Ji X. H. , Zhang Y. H. , Zhu T. J. , Tu J. P. , Zhang X. B.
Published: February 2005

Nanotubes of quasilayered bismuth telluride compound were prepared by hydrothermal synthesis. Nanotubes have diameters smaller than 100nm and spiral tube-walls. The low-dimensional morphology and hollow structure enable bismuth telluride nanotubes to be a potential thermoelectric material with a high figure of merit due to the efficient phonon blocking effect. The experimental results show that the addition of nanotubes leads to a remarkable decrease in the thermal conductivity with the electrical conductivity much less affected and thus to an increase in the figure of merit of the Bi2Te3-based material.
Integrated microcircuit on a diamond anvil for high-pressure electrical resistivity measurement
Authors: Han Yonghao , Gao Chunxiao , Ma Yanzhang , Liu Hongwu , Pan Yuewu , Luo Jifeng , Li Ming , He Chunyuan , Huang Xiaowei , Zou Guangtian , Li Yanchun , Li Xiaodong , Liu Jing
Published: February 2005

A multilayer microcircuit on a diamond surface has been developed for high-pressure resistivity measurement in a diamond anvil cell (DAC). Using a film deposition technique, a layer of Mo film was deposited on a diamond anvil as a conductor, topped with a layer of alumina film for insulation. A microelectric circuit was fabricated with a photolithographic shaping method after film encapsulation. With precise control and measurements of all the dimensions of the sample for resistance measurement, including the width of the metallic film and the diameter and thickness of the gasket hole, resistivity of a sample can be accurately determined. This microcircuit can be flexibly fabricated and easily cleaned. It also provides a promising prospect to measure resistivity under in situ high pressure and high temperature. We measured the resistivity of ZnS using this method, and proved the pressure induced phase transition at 13.9–17.9GPa to be a semiconductor to semiconductor transformation.
Displacement current detection of photoconduction in carbon nanotubes
Authors: Mohite A. , Chakraborty S. , Gopinath P. , Sumanasekera G. U. , Alphenaar B. W.
Published: February 2005

Using a capacitive photocurrent measurement technique, we demonstrate the ability of both semiconducting and metallic single wall nanotubes to function as photodetectors over a wide spectral range. We observe clear peaks in the photo induced displacement current of a nanotube-plated capacitor that correspond directly to the semiconducting and metallic transitions in the nanotube absorbance spectrum. The signal increases substantially as the carrier drift velocity is raised with applied bias. A large increase in the photocurrent observed below temperatures of 100K suggests that the nanotube hot carrier relaxation rate decreases substantially at low temperatures.
Electronic structure and magnetic properties of Al-doped Fe3O4 films studied by x-ray absorption and magnetic circular dichroism
Authors: Yang C. K. , Chiou J. W. , Tsai H. M. , Pao C. W. , Jan J. C. , Ray S. C. , Yeh C. L. , Huang K. C. , Hsueh H. C. , Pong W. F. , Tsai M.-H. , Hsieh H. H. , Lin H. J. , Hou T. Y. , Hsu J. H.
Published: February 2005

The electronic structure and magnetic properties of Al-doped Fe3O4 films at various Al concentrations were investigated by Al and OK-edge x-ray absorption near-edge structure (XANES) and FeL3,2-edge magnetic circular dichroism (MCD) measurements. The OK-edge XANES spectra reveal that the intensity of O2p–Fe3d hybridized states decreases linearly as the Al concentration increases, suggesting that nonmagnetic Al substitution reduces couplings of the O2p with Fe3d orbitals. The FeL3-edge MCD spectra show that the intensities of MCD features decrease as the Al concentration increases, which suggests that Al substitution reduces the magnetic moments of Fe ions. The FeL3,2 XANES spectra suggest the absence of mixed valence states in agreement with previous x-ray resonance scattering measurements.
Three-layered organic solar cells incorporating a nanostructure-optimized phthalocyanine:fullerene codeposited interlayer
Authors: Suemori Kouji , Miyata Takahiro , Yokoyama Masaaki , Hiramoto Masahiro
Published: February 2005

Three-layered organic solar cells incorporating a codeposited interlayer of fullerene and metal-free phthalocyanine, whose nanostructure was optimized by controlling the substrate temperature during coevaporation, showed a photoelectric conversion efficiency of 2.5% under illumination with simulated solar light. The three-layered cells were concluded to have a p-i-n-like energetic structure.
Positive temperature coefficient effect in multiwalled carbon nanotube/high-density polyethylene composites
Authors: He X. J. , Du J. H. , Ying Z. , Cheng H. M. , He X. J.
Published: February 2005

Multiwalled carbon nanotube (MWNT)-filled high-density polyethylene (HDPE) composites were prepared by a solution-precipitation process, and the temperature dependence of electrical conductivity of the MWNT/HDPE composites was studied. An obvious positive temperature coefficient (PTC) effect was found in the MWNT/HDPE composites with a relatively low MWNT concentration. Compared with that of carbon black (CB)/HDPE composite, the negative temperature coefficient (NTC) effect of the MWNT/HDPE composite at temperature above the melting temperature of HDPE was much less obvious and could be further eliminated after 80kGy γ-ray irradiation. The mechanism of the PTC and NTC effects in MWNT/HDPE composites was discussed.
Complex early genes
Authors: Roy Scott W. , Gilbert Walter
Published: February 2005

We use the pattern of intron conservation in 684 groups of orthologs from seven fully sequenced eukaryotic genomes to provide maximum likelihood estimates of the number of introns present in the same orthologs in various eukaryotic ancestors. We find: (
i
) intron density in the plant–animal ancestor was high, perhaps two-thirds that of humans and three times that of
Drosophila
; and (
ii
) intron density in the ancestral bilateran was also high, equaling that of humans and four times that of
Drosophila
. We further find that modern introns are generally very old, with two-thirds of modern bilateran introns dating to the ancestral bilateran and two-fifths of modern plant, animal, and fungus introns dating to the plant–animal ancestor. Intron losses outnumber gains over a large range of eukaryotic lineages. These results show that early eukaryotic gene structures were very complex, and that simplification, not embellishment, has dominated subsequent evolution.
Transcriptional activating regions target attached substrates to a cyclin-dependent kinase
Authors: Ansari Aseem Z. , Ogirala Anuja , Ptashne Mark
Published: February 2005

The yeast cyclin-dependent kinase Srb10 phosphorylates various transcriptional activators as they activate transcription, and acidic transcriptional activating domains found on several activators directly bind Srb10. Here we show that the interaction between Srb10 (with its associated cyclin Srb11) and each of several different activating regions,
in vitro
, leads to the phosphorylation of peptide sequences attached to but outside of the activating regions themselves. In some cases, residues within the activating regions are also phosphorylated. The results define a mechanism by which a kinase is recruited to alternate substrates with diverse physiological consequences.
Neurodevelopmental Disorders Following Thimerosal-Containing Childhood Immunizations: A Follow-Up Analysis
Authors: Geier David A. , Geier Mark R.
Published: February 2005

The authors previously published the first epidemiological study from the United States associating thimerosal from childhood vaccines with neurodevelopmental disorders (NDs) based upon assessment of the Vaccine Adverse Event Reporting System (VAERS). A number of years have gone by since their previous analysis of the VAERS. The present study was undertaken to determine whether the previously observed effect between thimerosal-containing childhood vaccines and NDs are still apparent in the VAERS as children have had a chance to further mature and potentially be diagnosed with additional NDs. In the present study, a cohort of children receiving thimerosal-containing diphtheria-tetanus-acellular pertussis (DTaP) vaccines in comparison to a cohort of children receiving thimerosal-free DTaP vaccines administered from 1997 through 2000 based upon an assessment of adverse events reported to the VAERS were evaluated. It was determined that there were significantly increased odds ratios (ORs) for autism (OR = 1.8, p < .05), mental retardation (OR = 2.6, p < .002), speech disorder (OR = 2.1, p <.02), personality disorders (OR=2.6, p <.01), and thinking abnormality (OR=8.2, p <.01) adverse events reported to the VAERS following thimerosal-containing DTaP vaccines in comparison to thimerosal-free DTaP vaccines. Potential confounders and reporting biases were found to be minimal in this assessment of the VAERS. It was observed, even though the media has reported a potential association between autism and thimerosal exposure, that the other NDs analyzed in this assessment of the VAERS had significantly higher ORs than autism following thimerosal-containing DTaP vaccines in comparison to thimerosal-free DTaP vaccines. The present study provides additional epidemiological evidence supporting previous epidemiological, clinical and experimental evidence that administration of thimerosal-containing vaccines in the United States resulted in a significant number of children developing NDs.
Decompositions of small tensor powers and Larsen’s conjecture
Authors: Guralnick Robert , Tiep Pham
Published: February 2005

We classify all pairs

(
G
,
V
)

(G,V)

with

G
G

a closed subgroup in a classical group

G

\mathcal G

with natural module

V
V

over

C

\mathbb C

, such that

G

\mathcal G

and

G
G

have the same position factors on

V

⊗
k

V^{\otimes k}

for a fixed

k
∈
{
2
,
3
,
4
}

k\in \{2,3,4\}

. In particular, we prove Larsen’s conjecture stating that for

dim
⁡
(
V
)
>
6

\dim (V)>6

and

k
=
4

k=4

there are no such

G
G

aside from those containing the derived subgroup of

G

\mathcal G

. We also find all the examples where this fails for

dim
⁡
(
V
)
≤
6

\dim (V)\le 6

. As a consequence of our results, we obtain a short proof of a related conjecture of Katz. These conjectures are used in Katz’s recent works on monodromy groups attached to Lefschetz pencils and to character sums over finite fields. Modular versions of these conjectures are also studied, with a particular application to random generation in finite groups of Lie type.
A bioeconomic analysis of bushmeat hunting
Authors: Damania R. , Milner-Gulland E. J. , Crookes D. J.
Published: February 2005

Unsustainable bushmeat hunting is a major threat to mammal species, particularly in West/Central Africa. We developed a multispecies dynamic simulation model of hunter behaviour, parameterized using data from the Ashanti region, Ghana. The model distinguishes between two hunting techniques, snaring and gun hunting. We analyse the impact of key economic parameters on off–takes. Economic incentives determine the effort devoted to hunting, the choice of hunting technique, and the species that are consumed domestically or traded in markets. These factors, together with the growth rates and catchabilities of hunted species, determine the ecological impact of hunting. The results suggest that increased bushmeat prices are likely to lead to a switch from snaring, which is cheaper but less efficient, to gun hunting, with a consequent impact on vulnerable species. Increases in agricultural prices have an ambiguous effect on hunter behaviour, depending on the balance between incentives to invest in agriculture and increased consumption as incomes improve. Penalties are more effective if they target bushmeat sales, rather than the act of hunting. This model represents a step forward because it explicitly considers bushmeat as a component of the household economy. This has important implications as regards the development of policies to conserve species hunted for bushmeat.
Managing to harvest? Perspectives on the potential of aquaculture
Authors: Muir James
Published: February 2005

Aquaculture has been one of the most rapid and technically innovative of food production sectors globally, with significant investment, scientific and technical development and production growth in many parts of the world over the past two decades. While this has had a significant effect on the global supply of aquatic food products and had an important impact in rural and urban food supply and employment in many developing economies, growth and increasing internationalization has not been without concern for natural resource use, environmental impact and social disruption. The expectations for production and diversification are now significant and while the scientific and technical means are already available to meet much of the intended targets, practical constraints of investment, profitability, resource access and system efficiency are likely to become far more important constraints for the future. This review offers a contemporary perspective on the ways in which the sector might develop, its interactions with constraints and the strategies that may be required to ensure that future development is both positive and sustainable.
Back–to–the–future: a fresh policy initiative for fisheries and a restoration ecology for ocean ecosystems
Authors: Pitcher Tony J.
Published: February 2005

‘Back–to–the–future’ (BTF) is an integrative approach to a restoration ecology of the oceans that attempts to solve the fisheries crisis. To this end, it harnesses the latest understanding of ecosystem processes developments in whole ecosystem simulation modelling, and insight into the human dimension of fisheries management. BTF includes new methods for describing past ecosystems, designing fisheries that meet criteria for sustainability and responsibility, and evaluating the costs and benefits of fisheries in restored ecosystems. Evaluation of alternative policy choices, involving trade–offs between conservation and economic values, employs a range of economic, social and ecological measures. Automated searches maximize values of objective functions, and the methodology includes analyses of model parameter uncertainty. Participatory workshops attempt to maximize compliance by fostering a sense of ownership among all stakeholders. Some challenges that have still to be met include improving methods for quantitatively describing the past, reducing uncertainty in ecosystem simulation techniques and in making policy choices robust against climate change. Critical issues include whether past ecosystems make viable policy goals, and whether desirable goals may be reached from today's ecosystem. Examples from case studies in British Columbia, Newfoundland and elsewhere are presented.
Social Capital and the Growth of the Nonprofit Sector*
Authors: Saxton Gregory D. , Benson Michelle A.
Published: February 2005

Objectives. This article examines the extent to which nonprofit organizational foundings are determined by various forms of social capital. Our hypothesis is that, controlling for other relevant social, political, and economic factors, communities with higher levels of social capital should experience more extensive growth in their nonprofit sectors.

Methods. Using data derived from the Social Capital Community Benchmark Survey and the IRS “charitable organization” Business Master Files, we test our hypothesis using a negative binomial event count regression on nonprofit organization foundings in 284 U.S. counties in the year 2001.

Results. We find that two core dimensions of social capital—political engagement and “bridging” social ties—have a significant impact on county‐level nonprofit foundings. Surprisingly, a key element of social capital in the literature, the level of interpersonal trust, does not lead to an increase in foundings of new not‐for‐profit organizations.

Conclusions. This study provides further evidence of the strength of political engagement and bridging ties for the vitality of the community. It also shows that the different dimensions of social capital do not manifest a uniform effect on nonprofit sector growth. These results further demonstrate that the growth of a community's not‐for‐profit sector is dependent on a mix of ecological and environmental factors, especially preexisting organizational density, median household income, unemployment, and levels of governmental spending. Overall, social capital can usefully be seen as another key “environmental” factor in explanations of organizational foundings.
A Meta‐Analysis of Campaign Contributions' Impact on Roll Call Voting*
Authors: Roscoe Douglas D. , Jenkins Shannon
Published: February 2005

Objectives. Conventional wisdom about the link between campaign contributions and roll call votes is that contributions rarely matter because groups tend to give to like‐minded legislators. This meta‐analysis examines the conventional wisdom by analyzing published research on this topic.

Methods. More than 30 studies are pooled to produce more than 350 individual tests of the contributions‐roll call link. Extending meta‐regression (Stanley and Jarrell, 1989), a logit meta‐analysis is conducted to summarize the literature and assess the importance of various modeling choices.

Results. We find that some, but not all, model specifications have an impact on whether significant results are present. Models that control for friendly giving by including a measure of legislators' ideology and that include more than one contributions variable are less likely to produce significant results.

Conclusions. After considering the impact of model choice on study results, we conclude that one‐third of roll call votes exhibit the impact of campaign contributions.
When Southern Symbolism Meets the Pork Barrel: Opportunity for Executive Leadership*
Authors: Bullock Charles S. , Hood M. V.
Published: February 2005

Objectives. Many empirical studies have sought to explain executive‐legislative relations at the federal level; however, much less research on this topic is available at the state level. This article examines legislative‐gubernatorial relations in Georgia using the highly visible, emotion‐laden, and politically costly issue of changing the state flag.

Methods. Using probit models, estimated probabilities for various sets of hypothetical legislators are constructed to explain the vote in each house of the Georgia General Assembly.

Results. In the absence of executive pressure, constituency characteristics, specifically district racial composition, dominated legislative decision making on the governor's initiative. In the Senate, where there was adequate time for lobbying before the vote, the carrot of additional school construction funding weighed heavily in legislators' vote calculus.

Conclusions. This study demonstrates that governors can, and do, use district‐specific benefits as a tool to help ensure the success of their legislative agendas.
Public Opinion and Dynamic Representation in the American States: The Case of Environmental Attitudes*
Authors: Johnson Martin , Brace Paul , Arceneaux Kevin
Published: February 2005

Objective. We investigate causal processes linking environmental conditions, attitudes, and policies in the American states: Is public opinion about ecology shaped by environmental conditions? Are state policymakers responsive to environmental opinions? Does public opinion respond to policy adoption?

Methods. Using public opinion data from the DDB Worldwide Life Style Survey to measure aggregate state attitudes about the environment, as well as measures of water quality and policy intervention, we capture the dynamics of representation in the American states on the environment during the late 1980s and early 1990s.

Results. Our findings support a thermostatic model of representation—state environmental opinions are influenced by environmental conditions and are responsive to policy outputs alongside improved environmental conditions.

Conclusions. This model of the opinion‐policy linkage refines our understanding of representation and focuses us not just on the passage of public policy to address public desires, but the effectiveness of that policy as well.
A New Right? Moral Issues and Partisan Change in Canada*
Authors: Lusztig Michael , Wilson J. Matthew
Published: February 2005

Objective. Beginning with the 1993 election, Canada's Progressive Conservative Party was replaced as the dominant force on the political right by the more ideological Reform Party/Canadian Alliance. This article examines what specific issues most centrally motivated this seismic shift among conservative Canadians.

Method. Using data from the 1993, 1997, and 2000 Canadian Election Studies, we employ bivariate analyses and multinomial logit voting models to determine whether constitutional, economic, nativist, or moral issues most clearly differentiate PC supporters from R/A voters.

Results. Regional concerns are important and other issues have sporadic impacts, but moral traditionalism is the most consistent and powerful factor distinguishing supporters of the new party from supporters of the old one.

Conclusions. Although existing studies have focused primarily on other sources of R/A support, moral traditionalism is clearly a key factor in explaining the party's ascendancy. This phenomenon, we contend, is part of a larger trend toward postmaterial politics in Western democracies.
Strategic and Sincere Voting in a One‐Sided Election: The Canadian Federal Election of 1997*
Authors: Justice J. W. , Lanoue David J.
Published: February 2005

Objective. We are interested in whether and how voters make strategic decisions in a race that is, according to the polls, expected to be very one sided. Looking specifically at the choices available to ideologically right‐of‐center voters in the 1997 Canadian federal election, we argue that strategic considerations will be filtered by voters' assessments of the competitiveness of the race both locally and nationally.

Methods. We estimate logistic regression models measuring support for the two right‐of‐center Canadian political parties. Our models focus on the relationship between assessments of district‐ and national‐level party prospects on voting for the Progressive Conservative Party.

Results. We find that voters who consider the race competitive emphasize district‐level data in their strategic calculations. However, those who consider the election to be all but over look more closely at national‐level concerns when deciding which right‐wing party to support.

Conclusions. We conclude that earlier understandings of tactical voting should be updated to take into consideration the circumstances under which voters will use national‐level evaluations of relative party viability in casting their ballots.