bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle
Authors: Syracuse Ellen M. , Abers Geoffrey A. , Fischer Karen , MacKenzie Laura , Rychert Catherine , Protti Marino , González Víctor , Strauch Wilfried
Published: July 2008

The Central American subduction zone exhibits large variations in geochemistry, downgoing plate roughness and dip, and volcano locations over a short distance along the arc. Results from joint inversions for Vp, Vp/Vs, and hypocenters from the Tomography Under Costa Rica and Nicaragua (TUCAN) experiment give insight into its geometry and structure. In both Costa Rica and Nicaragua, the intermediate‐depth seismic zone is a single layer no more than 10 to 20 km thick. Tomographic images show that throughout Nicaragua and Costa Rica the slowest mantle P wave velocities appear below and behind the volcanic front, indicating likely zones of highest temperature extending 80 to 120 km depth. A sheet of high Vp/Vs, thought to be caused by melt, is imaged directly beneath the Nicaraguan volcanoes, whereas a weaker, broader anomaly is imaged beneath the Costa Rican volcanoes, potentially indicating a greater extent of melting beneath Nicaragua. Within the downgoing plate, anomalously low velocities occur at least 20–30 km below Wadati‐Benioff zone seismicity, to depths of 140 km beneath Nicaragua and to 60 km depth beneath Costa Rica. They indicate 10–20% serpentinized upper mantle of the downgoing plate beneath Nicaragua, similar to that inferred from refraction seaward of the trench, but continuing to subarc depths. This unusually hydrated lithosphere may introduce more water into the Nicaraguan mantle, initiating increased amount of melting and fluid flux to the arc.
Comparative genomics of two ecotypes of the marine planktonic copiotroph Alteromonas macleodii suggests alternative lifestyles associated with different kinds of particulate organic matter
Authors: Ivars-Martinez Elena , Martin-Cuadrado Ana-Belen , D'Auria Giuseppe , Mira Alex , Ferriera Steve , Johnson Justin , Friedman Robert , Rodriguez-Valera Francisco
Published: July 2008

Alteromonas macleodii is a common marine heterotrophic γ-proteobacterium. Isolates from this microbe cluster by molecular analysis into two major genotypic groups or ecotypes, one found in temperate latitudes in the upper water column and another that is for the most part found in the deep water column of the Mediterranean. Here, we describe the genome of one strain of the ‘deep ecotype’ (AltDE) isolated from 1000 m in the Eastern Mediterranean and compare this genome with that of the type strain ATCC 27126, a representative of the global ‘surface’ ecotype. The genomes are substantially different with DNA sequence similarity values that are borderline for microbes belonging to the same species, and a large differential gene content, mainly found in islands larger than 20 kbp, that also recruit poorly to the Global Ocean Sampling project (GOS). These genomic differences indicate that AltDE is probably better suited to microaerophilic conditions and for the degradation of recalcitrant compounds such as urea. These, together with other features, and the distribution of this genotypic group, indicate that this microbe colonizes relatively large particles that sink rapidly to meso and bathypelagic depths. The genome of ATCC 27126 on the other hand has more potential for regulation (two component systems) and degrades more sugars and amino acids, which is consistent with a more transient particle attachment, as would be expected for lineages specialized in colonizing smaller particulate organic matter with much slower sinking rates. The genomic data are also consistent with a picture of incipient speciation driven by niche specialization.
Glucokinase and molecular aspects of liver glycogen metabolism
Authors: Agius Loranne
Published: July 2008

Conversion of glucose into glycogen is a major pathway that contributes to the removal of glucose from the portal vein by the liver in the postprandial state. It is regulated in part by the increase in blood-glucose concentration in the portal vein, which activates glucokinase, the first enzyme in the pathway, causing an increase in the concentration of glucose 6-P (glucose 6-phosphate), which modulates the phosphorylation state of downstream enzymes by acting synergistically with other allosteric effectors. Glucokinase is regulated by a hierarchy of transcriptional and post-transcriptional mechanisms that are only partially understood. In the fasted state, glucokinase is in part sequestered in the nucleus in an inactive state, complexed to a specific regulatory protein, GKRP (glucokinase regulatory protein). This reserve pool is rapidly mobilized to the cytoplasm in the postprandial state in response to an elevated concentration of glucose. The translocation of glucokinase between the nucleus and cytoplasm is modulated by various metabolic and hormonal conditions. The elevated glucose 6-P concentration, consequent to glucokinase activation, has a synergistic effect with glucose in promoting dephosphorylation (inactivation) of glycogen phosphorylase and inducing dephosphorylation (activation) of glycogen synthase. The latter involves both a direct ligand-induced conformational change and depletion of the phosphorylated form of glycogen phosphorylase, which is a potent allosteric inhibitor of glycogen synthase phosphatase activity associated with the glycogen-targeting protein, GL [hepatic glycogen-targeting subunit of PP-1 (protein phosphatase-1) encoded by PPP1R3B]. Defects in both the activation of glucokinase and in the dephosphorylation of glycogen phosphorylase are potential contributing factors to the dysregulation of hepatic glucose metabolism in Type 2 diabetes.
Microwave rectification by a carbon nanotube Schottky diode
Authors: Cobas Enrique , Fuhrer Michael S.
Published: July 2008

Carbon nanotube Schottky diodes have been fabricated in an all-photolithographic process using dissimilar contact metals on high-frequency compatible substrates (quartz and sapphire). Diodes show near-ideal behavior and rectify currents of up to 100nA and at frequencies of up to 18GHz. The voltage and frequency dependence is used to estimate the junction capacitance of ∼10−18F and the intrinsic device cutoff frequency of ∼400GHz.
A note on dust wave excitation in a plasma with warm dust: Comparison with experiment
Authors: Rosenberg M. , Thomas E. , Merlino R. L.
Published: July 2008

Ion-dust streaming instability in a plasma containing dust grains with large thermal speeds is considered using kinetic theory. The results are compared with experimental measurements of the dispersion relation of dust acoustic waves performed at the University of Iowa and Auburn University.
A new approach to electron-spin resonance absorption line shape function
Authors: Kang Nam Lyong , Choi Sang Don
Published: July 2008

We derive a new electron-spin resonance spectrum formula utilizing a quantum-statistical projection technique. The line shape factor appearing in the susceptibility tensor contains the many-body effects for electrons more realistically. It thus becomes possible to explain, in an organized way, all electron transitions including spin conserved processes and spin flipped processes.
Pulse compression radar reflectometry to measure electron density in plasma with parasitic reflections
Authors: Li Bin , Li Hong , Chen Zhipeng , Luo Chen , Wang Huihui , Geng Song , Feng Lei , Liu Qiuyan , Liu Wandong
Published: July 2008

Pulse compression radar reflectometry is used to obtain electron density profile in plasma with parasitic reflections in this article. The pulse compression radar relies on the relation between the temporal width of a pulse and the frequency bandwidth of this pulse: Δt∝1∕Δf. So a set of sweep-frequency microwaves within a bandwidth Δf can be introduced sequentially into the plasma to obtain the same information as the one obtained by a real pulse. By applying a Fourier transform to the data of reflectivity array in the frequency domain, the temporal response in the time domain is obtained. The limitation of the parasitic reflections on measurement can be eliminated from the temporal response by the method of time gate. This is a prominent advantage when this method is compared to the traditional reflectometry. For this method, an appropriate compromise between the spatial resolution and the electron density resolution is important. Experimental results show that the profile obtained from pulse compression radar reflectometry is similar to that from a double Langmuir probe.
Harmonic oscillator chains as Wigner quantum systems: Periodic and fixed wall boundary conditions in gl(1|n) solutions
Authors: Lievens S. , Stoilova N. I. , Van der Jeugt J.
Published: July 2008

We describe a quantum system consisting of a one-dimensional linear chain of n identical harmonic oscillators coupled by a nearest neighbor interaction. Two boundary conditions are taken into account: periodic boundary conditions (where the nth oscillator is coupled back to the first oscillator) and fixed wall boundary conditions (where the first oscillator and the nth oscillator are coupled to a fixed wall). The two systems are characterized by their Hamiltonian. For their quantization, we treat these systems as Wigner quantum systems (WQSs), allowing more solutions than just the canonical quantization solution. In this WQS approach, one is led to certain algebraic relations for operators (which are linear combinations of position and momentum operators) that should satisfy triple relations involving commutators and anti-commutators. These triple relations have a solution in terms of the Lie superalgebra gl(1|n). We study a particular class of gl(1|n) representations V(p), the so-called ladder representations. For these representations, we determine the spectrum of the Hamiltonian and of the position operators (for both types of boundary conditions). Furthermore, we compute the eigenvectors of the position operators in terms of stationary states. This leads to explicit expressions for position probabilities of the n oscillators in the chain. An analysis of the plots of such position probability distributions gives rise to some interesting observations. In particular, the physical behavior of the system as a WQS is very much in agreement with what one would expect from the classical case, except that all physical quantities (energy, position, and momentum of each oscillator) have a finite spectrum.
Electrostatic modes in multi-ion and pair-ion collisional plasmas
Authors: Vranjes J. , Petrovic D. , Pandey B. P. , Poedts S.
Published: July 2008

The physics of plasmas containing positive and negative ions is discussed with special attention to the recently produced pair-ion plasma containing ions of equal mass and opposite charge. The effects of the density gradient in the direction perpendicular to the ambient magnetic field vector are discussed. The possible presence of electrons is discussed in the context of plasma modes propagating at an angle with respect to the magnetic field vector. It is shown that the electron plasma mode may become a backward mode in the presence of a density gradient, and this behavior may be controlled either by the electron number density or the mode number in the perpendicular direction. In plasmas with hot electrons an instability may develop, driven by the combination of electron collisions and the density gradient, and in the regime of a sound ions’ response. In the case of a pure pair-ion plasma, for lower frequencies and for parameters close to those used in the recent experiments, the perturbed ions may feel the effects of the magnetic field. In this case the plasma mode also becomes backward, resembling features of an experimentally observed but yet unexplained backward mode.
Enhanced photoluminescence from germanium-based ring resonators
Authors: Lim Peng Huei , Kobayashi Yosuke , Takita Shinya , Ishikawa Yasuhiko , Wada Kazumi
Published: July 2008

We report the enhancement of direct bandgap emission from germanium ring resonators based on silicon-on-insulator (SOI). As a consequence of their strong confinement, a record quality factor (Q) of 620 is obtained that is an order of magnitude higher than that previously characterized for crystalline germanium microcavities. We also describe a pump power dependency of Q due to bandedge shifts not previously reported for silicon-or germanium-based emitters. A decline in the relative peak to baseline intensities with lower Qs is attributed to the Purcell effect on account of the wavelength-scale dimensions and high index contrast of our samples.
The large N expansion in hyperbolic sigma models
Authors: Niedermaier M. , Seiler E.
Published: July 2008

Invariant correlation functions for SO(1,N) hyperbolic sigma models are investigated. The existence of a large N asymptotic expansion is proven on finite lattices of dimension d≥2. The unique saddle point configuration is characterized by a negative gap vanishing at least like 1/V with the volume. Technical difficulties compared to the compact case are bypassed using horospherical coordinates and the matrix-tree theorem.
High-performance self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistor with Al2O3∕Ga2O3(Gd2O3) as gate dielectrics
Authors: Lin T. D. , Chiu H. C. , Chang P. , Tung L. T. , Chen C. P. , Hong M. , Kwo J. , Tsai W. , Wang Y. C.
Published: July 2008

Self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors (MOSFETs) using ultrahigh-vacuum deposited Al2O3∕Ga2O3(Gd2O3) (GGO) dual-layer dielectrics and a TiN metal gate were fabricated. For a In0.53Ga0.47As MOSFET using a gate dielectric of Al2O3(2nmthick)∕GGO(5nmthick), a maximum drain current of 1.05A∕mm, a transconductance of 714mS∕mm, and a peak mobility of 1300cm2∕Vs have been achieved, the highest ever reported for III-V inversion-channel devices of 1μm gate length.
Reduction of threading dislocations in ZnO/(0001) sapphire film heterostructure by epitaxial lateral overgrowth of nanorods
Authors: Sun Yuekui , Cherns David , Doherty Rachel P. , Warren James L. , Heard Peter J.
Published: July 2008

Transmission electron microscopy was used to study threading dislocations (TDs) in epitaxial ZnO films on (0001) sapphire substrates produced by a two-step method. First, ZnO was deposited by pulsed laser deposition. It was found that the sample consisted of a continuous buffer layer with a high density, 7×1010/cm2, of TDs, with c-aligned nanorods on its top. The nanorods revealed few, if any, TDs. A further layer of ZnO was then grown under conditions favoring nanorod growth, using either chemical vapor deposition (CVD) or a hydrothermal method. In both cases the nanorods grew laterally and eventually coalesced to form a continuous overgrowth. The nanorods remained mostly free of dislocations until coalescence. New grain boundary dislocations were generated where nanorods coalesced, but many of these dislocations migrated laterally and interacted with other dislocations to form closed loops. The TD density at the top of the continuous film was thereby reduced to 1×109/cm2 and 7×109/cm2 in the cases of hydrothermal and CVD treatments, respectively. The mechanism of growth and the means by which TDs are reduced are explained.
Highly ordered diamond and hybrid triangle-diamond patterns in porous anodic alumina thin films
Authors: Smith Joshua T. , Hang Qingling , Franklin Aaron D. , Janes David B. , Sands Timothy D.
Published: July 2008

Utilizing nonequilibrium formation kinetics in porous anodic alumina (PAA) thin films, diamond and hybrid triangle-diamond pore patterns are achieved. During anodization, the self-compensation abilities of PAA allow diamond-shaped pores to form by omitting certain sites in the surface prepatterning process. The effects of tessellation on cell formation in these arrangements yield elongated, regular, and partially compressed hexagonal cell structures leading to diamond, circular, and triangular pores, respectively. The diamond-shaped porous templates provide a low-cost option for the preparation of scalable nanostructures with diamond-shaped cross sections with utility in a range of nanoscale applications, including enhanced sensing and field emission.
On Padé approximants to virial series
Authors: Guerrero André O. , S. Bassi Adalberto B. M.
Published: July 2008

Padé approximants have long been used to predict virial series coefficients and to provide equations of state for low and high density materials. However, some justified criticism has appeared about this procedure. Although we agree to impose several restrictions on the use of Padé approximants, we indicate that the Padé approximant is still an excellent way to predict the first unknown virial series coefficients. As an example, we report a calculation of the B11=128.6 and B12=155 virial coefficients of the three dimensional hard sphere model that are in excellent agreement with the two most recent estimates. We also consider that the commonly used method to choose among Padé approximants is not completely reliable for this specific application and suggest an alternative new method.
Electrospinning and multiferroic properties of NiFe2O4–Pb(Zr0.52Ti0.48)O3 composite nanofibers
Authors: Xie S. H. , Li J. Y. , Liu Y. Y. , Lan L. N. , Jin G. , Zhou Y. C.
Published: July 2008

In this paper, we report a strategy for hybrid multiferroicity at nanoscale. Multiferroic NiFe2O4–Pb(Zr0.52Ti0.48)O3 composite nanofibers are synthesized by a sol-gel process and electrospinning, with fiber diameters ranging from 100 to 400 nm. Energy dispersive spectroscopy and transmission electron microscopy indicate that nanocrystalline Pb(Zr0.52Ti0.48)O3 and NiFe2O4 grains are randomly distributed in the composite nanofibers, with grain size around 30 nm. The spinel structure of NiFe2O4 and the perovskite structure of Pb(Zr0.52Ti0.48O3) are verified by x-ray diffraction, and multiferroicity of the nanofibers is confirmed by piezoresponse force microscopy and magnetic hysteresis. The structures and properties of the composite nanofibers are also compared with single-phase Pb(Zr0.52Ti0.48)O3 and NiFe2O4 nanofibers. These composite nanofibers could lead to unconventional multiferroic structures and devices.
Temperature dependence of spin-polarized electron transport including electron-electron interaction
Authors: Takahashi Yutaka , Inaba Nobuyuki , Hirose Fumihiko
Published: July 2008

Carrier transport is modified by electron-electron interaction in spin-polarized systems. We numerically investigated transport coefficients in a spin-polarized two-dimensional electron gas in a heterostructure of GaAs from 10 K up to room temperature in the presence of electron-electron interaction caused by the Coulomb force. Transport is modified by the exchange of momentum between spin-up and spin-down electrons through their collisions (spin drag) and also by the electron energy renormalization arising from many-electron correlations. Our calculations show that the mobility is less affected by electron-electron interaction at high temperatures, while the diffusion coefficients show complex temperature dependence caused by both spin drag and energy renormalization.
Room-temperature ferromagnetism in single crystal Fe1.7Ge thin films of high thermal stability grown on Ge(111)
Authors: Jaafar R. , Nehme Y. , Berling D. , Bubendorff J. L. , Mehdaoui A. , Pirri C. , Garreau G. , Uhlaq-Bouillet C.
Published: July 2008

We report on the epitaxial growth of ultrathin ferromagnetic Fe1.7Ge layers on Ge(111) wafer. These single crystal intermetallic layers adopt the InNi2 (B82) crystallographic structure. They are ferromagnetic with a Curie temperature well above room temperature. The interface between the ferromagnet layer and the Ge wafer is of high perfection. Interestingly, the annealing of the sample up to 300°C alters neither the crystallographic structure, nor the interface quality, nor the magnetic properties but leads to a nearly perfect smoothening of the germanide layer surface. This high thermal robustness should open the way for the growth of fully epitaxial iron germanide/Ge hybrid structures.
Studies on the Bi∕Si(100)−(2×1) interface
Authors: Bannani A. , Bobisch C. A. , Möller R.
Published: July 2008

Epitaxial Bi(111) films on the Si(100)−(2×1) surface were studied by two different scanning probe techniques, to obtain information on the buried interface. Ballistic electron emission microscopy reveals that the transmission across the Schottky barrier depends on the type of substrate terrace. The thermovoltage in scanning tunneling microscopy exhibits alternating signals for substrate step edges, which can be related to SA and SB steps, characteristic for the uncovered Si(100)−(2×1) surface. In addition to information about the growth mode of Bi, it was found that typical features of the Si(100)−(2×1) surface reconstruction are maintained.
Direct chemical synthesis of high coercivity air-stable SmCo nanoblades
Authors: Chinnasamy C. N. , Huang J. Y. , Lewis L. H. , Latha B. , Vittoria C. , Harris V. G.
Published: July 2008

Ferromagnetic air-stable SmCo nanoparticles have been produced directly using a one-step chemical synthesis method. X-ray diffraction studies confirmed the formation of hexagonal SmCo5 as a dominant phase. High resolution transmission electron microscopy confirms the presence of uniform, anisotropic bladelike nanoparticles approximately 10nm in width and 100nm in length. Values of the intrinsic coercivity and the magnetization in the as-synthesized particles are 6.1kOe and 40emu∕g at room temperature and 8.5kOe and 44emu∕g at 10K, respectively. This direct synthesis process is environmentally friendly and is readily scalable to large volume synthesis to meet the needs for the myriad of advanced permanent magnet applications.
Near-field radiative heat transfer enhancement via surface phonon polaritons coupling in thin films
Authors: Francoeur Mathieu , Mengüç M. Pinar , Vaillon Rodolphe
Published: July 2008

We investigate near-field thermal radiation between a nanometric film and a bulk SiC using fluctuational electrodynamics. Results show a narrow spectral band enhancement of the radiative flux for nanometric emitters due to coupling of surface phonon polaritons inside the film. For a 10nm thick SiC emitter, the total radiative flux is 2.2 times larger than for a bulk emitter. The total radiative flux is increased by a factor of 3.3 if a dielectric is coated with a 10nm SiC film due to a splitting of the resonant frequency into two distinct ones, which has practical interests for near-field thermophotovoltaic devices.
Complementary metal oxide silicon integrated circuits incorporating monolithically integrated stretchable wavy interconnects
Authors: Kim Dae-Hyeong , Choi Won Mook , Ahn Jong-Hyun , Kim Hoon-Sik , Song Jizhou , Huang Yonggang , Liu Zhuangjian , Lu Chun , Koh Chan Ghee , Rogers John A.
Published: July 2008

Stretchable complementary metal oxide silicon circuits consisting of ultrathin active devices mechanically and electrically connected by narrow metal lines and polymer bridging structures are presented. This layout—together with designs that locate the neutral mechanical plane near the critical circuit layers—yields strain independent electrical performance and realistic paths to circuit integration. A typical implementation reduces the strain in the silicon to less than ∼0.04% for applied strains of ∼10%. Mechanical and electrical modeling and experimental characterization reveal the underlying physics of these systems.
Negative refraction in chiral composite materials
Authors: Dong Wenting , Gao Lei
Published: July 2008

Based on the Maxwell–Garnett approximation, we obtain the negative refraction in chiral composites in which electrically small isotropic chiral inclusions are randomly embedded in an isotropic achiral host medium. Numerical results show that there exists negative refraction in high (or low) frequency region for right- (or left-) circular polarized wave, and the region is widened for large volume fraction and small damping factor. In addition, the magnitude of negative refractive index increases with decreasing the dielectric loss. Moreover, it is numerically shown that the negative refraction results from relatively large chirality parameter in chiral composites compared to the corresponding parameters in the components.
Reconfigurable cloak for multiple operating frequencies
Authors: Wang Dongxing , Chen Hongsheng , Ran Lixin , Huangfu Jiangtao , Kong Jin Au , Wu Bae-Ian
Published: July 2008

An invisible cloak based on active metamaterials whose permittivity can be controlled is proposed, and the performances of the cloak are verified in numerical simulations. Because of the tunability of the active metamaterials, the working frequency of the invisible cloak is reconfigurable, which is different from the traditional cloak designs based on passive metamaterials whose working frequencies are fixed.
Single-frequency, Yb-free, resonantly cladding-pumped large mode area Er fiber amplifier for power scaling
Authors: Dubinskii Mark , Zhang Jun , Kudryashov Igor
Published: July 2008

We report results for a single-frequency (SF) resonantly cladding-pumped Yb-free large mode area (LMA) erbium-doped fiber amplifier (EDFA) with nearly 50% slope efficiency based on a commercial 20∕125μm Er-doped double-clad LMA fiber with a core numerical aperture of 0.07. We believe that this is the original demonstration of a SF resonantly cladding-pumped LMA EDFA. We obtained a diffraction-limited SF output of 9.3W, which is also a record power output obtained for resonantly cladding-pumped LMA EDFA.
First-principles study on inversion layer properties of double-gate atomically thin silicon channels
Authors: Kageshima Hiroyuki , Fujiwara Akira
Published: July 2008

The inversion layer properties of double-gate atomically thin silicon channels are studied based on the first-principles enforced Fermi energy difference method. The calculated results indicate that the atomic-scale thickness of the channel significantly affects the inversion layer capacitance as well as the inversion layer carrier properties. They also indicate that the first-principles approach is essential and practical for studying the device physics of the field effect transistors with nanometer-scale channels.
Experimental observation of the inductive electric field and related plasma nonuniformity in high frequency capacitive discharge
Authors: Ahn S. K. , Chang H. Y.
Published: July 2008

To elucidate plasma nonuniformity in high frequency capacitive discharges, Langmuir probe and B-dot probe measurements were carried out in the radial direction in a cylindrical capacitive discharge driven at 90MHz with argon pressures of 50 and 400mTorr. Through the measurements, a significant inductive electric field (i.e., time-varying magnetic field) was observed at the radial edge, and it was found that the inductive electric field creates strong plasma nonuniformity at high pressure operation. The plasma nonuniformity at high pressure operation is physically similar to the E-H mode transition typically observed in inductive discharges. This result agrees well with the theories of electromagnetic effects in large area and/or high frequency capacitive discharges.
Slab waveguides and nanoscale patterning of pulsed laser-deposited Ge0.2Se0.8 chalcogenide films
Authors: Liu W. C. , Hoffman G. , Zhou W. , Reano R. M. , Boolchand P. , Sooryakumar R.
Published: July 2008

Planar slab waveguides were fabricated by pulsed laser deposition from GexSe1−x glass compounds with composition (x∼0.2) that lies very close to the floppy to rigid stiffness transition. These high quality active structures, which were deposited on SiO2 cladding layers above silicon substrates, support several transverse-electric (TE) modes, and a loss of 0.24dB∕cm for the TE0 mode was measured at 632.8nm wavelength. The ability to exploit electron beam writing at these special Ge in Se compositions to create nanoscale surface motifs are promising advances to create unique miniature optical processing devices.
Photoluminescence properties of AlN homoepilayers with different orientations
Authors: Sedhain A. , Nepal N. , Nakarmi M. L. , Al tahtamouni T. M. , Lin J. Y. , Jiang H. X. , Gu Z. , Edgar J. H.
Published: July 2008

AlN homoepilayers and heteroepilayers were grown on polar c-plane and nonpolar a-plane and m-plane orientations of AlN bulk and sapphire substrates by metal organic chemical vapor deposition. A systematic comparative study of photoluminescence properties of these samples revealed that all AlN homoepilayers (c, a and m planes) were strain free with an identical band gap of about 6.099 (6.035)eV at 10 (300)K, which is about 42meV below the band gap of c-plane AlN heteroepilayers grown on sapphire. Also, nonpolar a-plane homoepilayers have the highest emission intensity over all other types of epilayers. We believe that a-plane AlN homoepilayers have the potential to provide orders of magnitude improvement in the performance of new generation deep UV photonic devices.
Superhydrophobic membranes with electrically controllable permeability and their application to “smart” microbatteries
Authors: Lifton V. A. , Taylor J. A. , Vyas B. , Kolodner P. , Cirelli R. , Basavanhally N. , Papazian A. , Frahm R. , Simon S. , Krupenkin T.
Published: July 2008

Electrically tunable membranes with controllable permeability have been experimentally demonstrated by combining nanostructured and microstructured superhydrophobic surfaces with the phenomenon of electrowetting. Electrowetting allows dynamical tuning of the contact angle that the liquid forms with the membrane nanofeatures and microfeatures, thus controlling the flow of the liquid through the membrane and, therefore, tuning the permeability of the entire structure. “Smart” electrochemical energy storage cells that can be activated on demand have been built by combining these membranes and microfabricated Zn∕MnO2 electrodes. A typical open-circuit voltage of 1.55V and capacity of 200μAh∕cm2 have been demonstrated.
Self-assembly of orthogonal three-axis sensors
Authors: Cho J. H. , Hu S. , Gracias D. H.
Published: July 2008

Conventional planar microfabrication is widely utilized to construct sensors for the measurement of physical or chemical properties. However, in these devices, the information component measured is typically restricted to only one vectorial axis. Here, we describe a self-assembling strategy that can be utilized to construct three dimensional (3D) cubic devices that facilitate measurement along three axes. This 3D measurement is achieved by arranging sensing elements orthogonally; any sensing element that can be lithographically patterned can be utilized. The 3D arrangement of sensors allows for the measurement of angular and orientation parameters. As an example, we describe a three-axis cantilever based sensor and demonstrate measurement of an evaporated analyte using resonant frequency shifts of cantilevers in each of the x, y, and z axes.
Dynamical dislocation emission processes from twin boundaries
Authors: Wang Y. B. , Wu B. , Sui M. L.
Published: July 2008

In situ tensile straining transmission electron microscopy investigation of electrodeposited copper with high density of nanoscale growth twins reveals that twin boundaries (TBs) can serve as dislocation sources. Atomic steps at TBs formed by sessile Frank partial dislocations are beneficial for TBs serving as dislocation sources. The underlying mechanism that includes dislocation reactions with TBs is discussed.
Magnetic properties of the insulating ferromagnetic phase in strained Pr0.6Ca0.4MnO3 thin films
Authors: Mertelj T. , Yusupov R. , Filippi M. , Prellier W. , Mihailovic D.
Published: July 2008

Bulk magnetization in Pr0.6Ca0.4MnO3 thin films with tensile (SrTiO3) and compressive (LaAlO3) substrate-induced strain is compared to the magneto-optical Kerr effect (MOKE) measurements. In the absence of an external magnetic field, in both films, a stable ferromagnetic insulating majority phase coexists with an antiferromagnetic insulating phase below ∼120K. The MOKE measurements indicate that at 5K a metastable ferromagnetic metallic (FM) phase is formed at the surface of the stretched film in a magnetic field below 1.1T already; while in the bulk the FM phase starts to form in the field above ∼4T in both films.
Entangled light beams from four-wave mixing carry spatial information
Authors: Miller Johanna
Published: July 2008

Not only do the beams display correlations in their quantum fluctuations, but so do different parts of them when examined separately.
The effect of repeated applications of phosphorus fertiliser on wheat yields in the Mallee from 1943 to 2006
Authors: Latta R. A. , Mock I. , Smith J.
Published: July 2008

A previous study in 1968 on this long-term experiment reported the cumulative effects of repeated applications of phosphorus (P) and found that residual effects of applied P resulted in increasing grain yields. A re-analysis of most of that dataset (1943–59) confirmed these results over six cycles of a 3-year rotation (fallow–wheat–oats) with superphosphate applied at 0, 3, 6, 9, and 12 kg P/ha. However, continuation of the experiment in the same plots with a 2-year rotation (fallow–wheat or pasture–wheat) found no further cumulative benefit of residual P on grain yields. Over four decades from 1962 to 2001, yields remained generally constant, after adjusting for growing-season rainfall, with the differences in yield between rates of applied superphosphate also remaining constant over the period. On average, adding 3 kg P/ha was estimated to increase yield by 0.45 t/ha (compared with 0 kg P/ha) and adding 6, 9, and 12 kg P/ha resulted in estimated step-wise yield increases of 0.10 t/ha, 0.10 t/ha, and 0.01 t/ha, respectively.
Managing yields of high fruit retention in transgenic cotton (Gossypium hirsutum L.) using sowing date
Authors: Bange Michael P. , Caton Sarah J. , Milroy Stephen P.
Published: July 2008

Recently, genetically engineered (transgenic) cottons expressing genes from Bacillis thuringiensis (Bt) have been made available to cotton growers throughout the world. In Australia, cotton growers have access to Bt cotton that contains genes expressing the insecticidal proteins Cry1Ac and Cry2Ab (Bollgard II®). Bollgard II offers significant potential to reduce pesticide use for the control of major Lepidopteran pests (particularly Helicoverpa spp. in Australia). As a consequence of the improved insect control, retention of squares (flower buds) and young bolls is higher in Bollgard II varieties than in non-Bollgard varieties. A concern raised by Australian cotton growers is that in some regions, yield potential for Bollgard II may be limited because the demands of earlier high fruit retention reduce resources for continued growth and fruiting, thus leading to earlier maturity and reduced yield. Non-Bollgard crops with high early retention are known to mature earlier sometimes reducing yield.
Three field experiments over three seasons, which varied sowing date and compared non-Bollgard II and Bollgard II cotton cultivars, were conducted to test the hypothesis that delaying sowing date in Bollgard II will increase canopy size (without delaying crop development) and alleviate the potential concerns for the effect of higher fruit retention reducing canopy size and the time to maturity, limiting the yield of Bollgard II. In non-Bollgard II crops, larger canopies resulting from early loss of fruit or apical meristem damage can support more fruit growth for longer, provided season length allows fruit to mature. Results showed that delayed sowing did not increase the yield of the Bollgard II cultivar through increased leaf area index at flowering compared with normal sowing dates. However, in comparison with the conventional cultivar, which had yields that became lower with later sowings, Bollgard II maintained its yield presumably through the shorter fruiting cycle (because of its consistently higher earlier fruit retention), allowing time to support growth of the same number of bolls as earlier sowings. Improvements in fibre quality were also recorded with later sowings for both cultivars. Varying sowing dates for Bollgard II in different production regions may offer opportunities for Australian growers to help optimise yield, fibre quality, and reduce risks associated with poor crop establishment when crops are sown too early.
Reverse actin sliding triggers strong myosin binding that moves tropomyosin
Authors: Bekyarova T. I. , Reedy M. C. , Baumann B. A. J. , Tregear R. T. , Ward A. , Krzic U. , Prince K. M. , Perz-Edwards R. J. , Reconditi M. , Gore D. , Irving T. C. , Reedy M. K.
Published: July 2008

Actin/myosin interactions in vertebrate striated muscles are believed to be regulated by the “steric blocking” mechanism whereby the binding of calcium to the troponin complex allows tropomyosin (TM) to change position on actin, acting as a molecular switch that blocks or allows myosin heads to interact with actin. Movement of TM during activation is initiated by interaction of Ca
2+
with troponin, then completed by further displacement by strong binding cross-bridges. We report x-ray evidence that TM in insect flight muscle (IFM) moves in a manner consistent with the steric blocking mechanism. We find that both isometric contraction, at high [Ca
2+
], and stretch activation, at lower [Ca
2+
], develop similarly high x-ray intensities on the IFM fourth actin layer line because of TM movement, coinciding with x-ray signals of strong-binding cross-bridge attachment to helically favored “actin target zones.” Vanadate (Vi), a phosphate analog that inhibits active cross-bridge cycling, abolishes all active force in IFM, allowing high [Ca
2+
] to elicit initial TM movement without cross-bridge attachment or other changes from relaxed structure. However, when stretched in high [Ca
2+
], Vi-“paralyzed” fibers produce force substantially above passive response at pCa ∼ 9, concurrent with full conversion from resting to active x-ray pattern, including x-ray signals of cross-bridge strong-binding and TM movement. This argues that myosin heads can be recruited as strong-binding “brakes” by backward-sliding, calcium-activated thin filaments, and are as effective in moving TM as actively force-producing cross-bridges. Such recruitment of myosin as brakes may be the major mechanism resisting extension during lengthening contractions.
An introduced and a native vertebrate hybridize to form a genetic bridge to a second native species
Authors: McDonald David B. , Parchman Thomas L. , Bower Michael R. , Hubert Wayne A. , Rahel Frank J.
Published: July 2008

The genetic impacts of hybridization between native and introduced species are of considerable conservation concern, while the possibility of reticulate evolution affects our basic understanding of how species arise and shapes how we use genetic data to understand evolutionary diversification. By using mitochondrial NADH dehydrogenase subunit 2 (ND2) sequences and 467 amplified fragment-length polymorphism nuclear DNA markers, we show that the introduced white sucker (Catostomus commersoni) has hybridized with two species native to the Colorado River Basin—the flannelmouth sucker (Catostomus latipinnis) and the bluehead sucker (Catostomus discobolus). Hybrids between the flannelmouth sucker and white sucker have facilitated introgression between the two native species, previously isolated by reproductive barriers, such that individuals exist with contributions from all three genomes. Most hybrids had the mitochondrial haplotype of the introduced white sucker, emphasizing its pivotal role in this three-way hybridization. Our findings highlight how introduced species can threaten the genetic integrity of not only one species but also multiple previously reproductively isolated species. Furthermore, this complex three-way reticulate (as opposed to strictly bifurcating) evolution suggests that seeking examples in other vertebrate systems might be productive. Although the present study involved an introduced species, similar patterns of hybridization could result from natural processes, including stream capture or geological formations (e.g., the Bering land bridge).
Environmental influence on primary sex ratio in a dioecious plant
Authors: Stehlik Ivana , Friedman Jannice , Barrett Spencer C. H.
Published: July 2008

The proximity of mates can influence mating opportunities and the quantity and quality of offspring, especially in dioecious plant species. Progeny sex ratios modulated by environmental conditions is one of the most radical ways in which offspring quality may be influenced, yet it has rarely been reported in plants. A mechanism proposed to influence progeny sex ratios in dioecious plants involves competition between female- and male-determining microgametophytes (certation) as a result of variation in pollination intensity. However, the role of selective fertilization in dioecious plants is controversial and has not been demonstrated under field conditions. Here we investigate whether natural variation in the spatial arrangement of females and males influences pollination intensity and progeny sex ratios in the wind-pollinated herbRumex nivalis. Based on previous experimental manipulation of pollination intensity in this species, we predicted that maternal parents in close proximity to males would produce more strongly female-biased progeny sex ratios. We tested this prediction in six alpine populations in Switzerland by measuring the distance between focal females and neighboring males and assessing pollen loads and seed sex ratios of maternal parents. In four of the six populations, females positioned in close proximity to males captured more pollen and exhibited more female-biased sex ratios. Our results demonstrate that demographic aspects of the maternal mating environment can influence progeny sex ratios. The most probable explanation for biased primary sex ratios inRumexis selective fertilization resulting from pollen tube competition.
Active control of ultrasonic hearing in frogs
Authors: Gridi-Papp Marcos , Feng Albert S. , Shen Jun-Xian , Yu Zu-Lin , Rosowski John J. , Narins Peter M.
Published: July 2008

Vertebrates can modulate the sound levels entering their inner ears in the face of intense external sound or during their own vocalizations. Middle ear muscle contractions restrain the motion of the middle ear ossicles, attenuating the transmission of low-frequency sound and thereby protecting the hair cells in the inner ear. Here we show that the Chinese concave-eared torrent frog,
Odorrana tormota
, can tune its ears dynamically by closing its normally open Eustachian tubes. Contrary to the belief that the middle ear in frogs permanently communicates with the mouth,
O. tormota
can close this connection by contraction of the submaxillary and petrohyoid muscles, drastically reducing the air volume behind the eardrums. Mathematical modeling and laser Doppler vibrometry revealed that the reduction of this air volume increases the middle ear impedance, resulting in an up to 20 dB gain in eardrum vibration at high frequencies (10–32 kHz) and 26 dB attenuation at low frequencies (3–10 kHz). Eustachian tube closure was observed in the field during calling and swallowing. Besides a potential role in protecting the inner ear from intense low-frequency sound and high buccal air pressure during calling, this previously unrecognized vertebrate mechanism may unmask the high-frequency calls of this species from the low-frequency stream noise which dominates the environment. This mechanism also protects the thin tympanic membranes from injury during swallowing of live arthropod prey.
Hopping of a processivity factor on DNA revealed by single-molecule assays of diffusion
Authors: Komazin-Meredith Gloria , Mirchev Rossen , Golan David E. , van Oijen Antoine M. , Coen Donald M.
Published: July 2008

Many DNA-interacting proteins diffuse on DNA to perform their biochemical functions. Processivity factors diffuse on DNA to permit unimpeded elongation by their associated DNA polymerases, but little is known regarding their rates and mechanisms of diffusion. The processivity factor of herpes simplex virus DNA polymerase, UL42, unlike “sliding clamp” processivity factors that normally form rings around DNA, binds DNA directly and tightly as a monomer, but can still diffuse on DNA. To investigate the mechanism of UL42 diffusion on DNA, we examined the effects of salt concentration on diffusion coefficient. Ensemble studies, employing electrophoretic mobility shift assays on relatively short DNAs, showed that off-rates of UL42 from DNA depended on DNA length at higher but not lower salt concentrations, consistent with the diffusion coefficient being salt-dependent. Direct assays of the motion of single fluorescently labeled UL42 molecules along DNA revealed increased diffusion at higher salt concentrations. Remarkably, the diffusion coefficients observed in these assays were ≈10
4
-fold higher than those calculated from ensemble experiments. Discrepancies between the single-molecule and ensemble results were resolved by the observation, in single-molecule experiments, that UL42 releases relatively slowly from the ends of DNA in a salt-dependent manner. The results indicate that UL42 “hops” rather than “slides,” i.e., it microscopically dissociates from and reassociates with DNA as it diffuses rather than remaining so intimately associated with DNA that cation condensation on the phosphate backbone does not affect its motion. These findings may be relevant to mechanisms of other processivity factors and DNA-binding proteins.
Benefits of cooperation with genetic kin in a subsocial spider
Authors: Schneider J. M. , Bilde T.
Published: July 2008

Interaction within groups exploiting a common resource may be prone to cheating by selfish actions that result in disadvantages for all members of the group, including the selfish individuals. Kin selection is one mechanism by which such dilemmas can be resolved This is because selfish acts toward relatives include the cost of lowering indirect fitness benefits that could otherwise be achieved through the propagation of shared genes. Kin selection theory has been proved to be of general importance for the origin of cooperative behaviors, but other driving forces, such as direct fitness benefits, can also promote helping behavior in many cooperatively breeding taxa. Investigating transitional systems is therefore particularly suitable for understanding the influence of kin selection on the initial spread of cooperative behaviors. Here we investigated the role of kinship in cooperative feeding. We used a cross-fostering design to control for genetic relatedness and group membership. Our study animal was the periodic social spider
Stegodyphus lineatus
, a transitional species that belongs to a genus containing both permanent social and periodic social species. In
S. lineatus
, the young cooperate in prey capture and feed communally. We provide clear experimental evidence for net benefits of cooperating with kin. Genetic relatedness within groups and not association with familiar individuals directly improved feeding efficiency and growth rates, demonstrating a positive effect of kin cooperation. Hence, in communally feeding spiders, nepotism favors group retention and reduces the conflict between selfish interests and the interests of the group.