bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain-induced magnetization change in patterned ferromagnetic nickel nanostructures
Authors: Bur Alexandre , Wu Tao , Hockel Joshua , Hsu Chin-Jui , Kim Hyungsuk K. D. , Chung Tien-Kan , Wong Kin , Wang Kang L. , Carman Gregory P.
Published: June 2011

We report strain-induced coercive field changes in patterned 300 × 100 × 35 nm3 Ni nanostructures deposited on Si/SiO2 substrate using the magnetoelastic effect. The coercive field values change as a function of the applied anisotropy strain (∼1000 ppm) between 390 and 500 Oe, demonstrating that it is possible to gradually change the coercive field elastically. While the measured changes in coercive field cannot be accurately predicted with simple analytical predictions, fairly good agreement is obtained by using a micromagnetic simulation taking into account the influence of nonuniform strain distribution in the Ni nanostructures. The micromagnetic simulation includes a position dependant strain-induced magnetic anisotropy term that is computed from a finite element mechanical analysis. Therefore, this study experimentally corroborates the requirement to incorporate mechanical analysis into micromagnetic simulation for accurately predicting magnetoelastic effects in patterned ferromagnetic nanostructures.
Branch-point energies and the band-structure lineup at Schottky contacts and heterostrucures
Authors: Mönch Winfried
Published: June 2011

Empirical branch-point energies of Si, the group-III nitrides AlN, GaN, and InN, and the group-II and group-III oxides MgO, ZnO, Al2O3 and In2O3 are determined from experimental valance-band offsets of their heterostructures. For Si, GaN, and MgO, these values agree with the branch-point energies obtained from the barrier heights of their Schottky contacts. The empirical branch-point energies of Si and the group-III nitrides are in very good agreement with results of previously published calculations using quite different approaches such as the empirical tight-binding approximation and modern electronic-structure theory. In contrast, the empirical branch-point energies of the group-II and group-III oxides do not confirm the respective theoretical results. As at Schottky contacts, the band-structure lineup at heterostructures is also made up of a zero-charge-transfer term and an intrinsic electric-dipole contribution. Hence, valence-band offsets are not equal to the difference of the branch-point energies of the two semiconductors forming the heterostructure. The electric-dipole term may be described by the electronegativity difference of the two solids in contact. A detailed analysis of experimental Si Schottky barrier heights and heterostructure valence-band offsets explains and proves these conclusions.
Effect of O2+, H2++ O2+, and N2++ O2+ ion-beam irradiation on the field emission properties of carbon nanotubes
Authors: Acuña J. J. S. , Escobar M. , Goyanes S. N. , Candal R. J. , Zanatta A. R. , Alvarez F.
Published: June 2011

The effect of O2+, H2++ O2+, and N2++ O2+ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H2+ or N2+ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.
Single HeLa and MCF-7 cell measurement using minimized impedance spectroscopy and microfluidic device
Authors: Wang Min-Haw , Kao Min-Feng , Jang Ling-Sheng
Published: June 2011

This study presents an impedance measurement system for single-cell capture and measurement. The microwell structure which utilizes nDEP force is used to single-cell capture and a minimized impedance spectroscopy which includes a power supply chip, an impedance measurement chip and a USB microcontroller chip is used to single-cell impedance measurement. To improve the measurement accuracy of the proposed system, Biquadratic fitting is used in this study. The measurement accuracy and reliability of the proposed system are compared to those of a conventional precision impedance analyzer. Moreover, a stable material, latex beads, is used to study the impedance measurement using the minimized impedance spectroscopy with cell-trapping device. Finally, the proposed system is used to measure the impedance of HeLa cells and MCF-7 cells. The impedance of single HeLa cells decreased from 9.55 × 103 to 3.36 × 103 Ω and the impedance of single MCF-7 cells decreased from 3.48 × 103 to 1.45 × 103 Ω at an operate voltage of 0.5 V when the excitation frequency was increased from 11 to 101 kHz. The results demonstrate that the proposed impedance measurement system successfully distinguishes HeLa cells and MCF-7 cells.
Frequency dependence of spin pumping in Pt/Y3Fe5O12 film
Authors: Harii Kazuya , An Toshu , Kajiwara Yosuke , Ando Kazuya , Nakayama Hiroyasu , Yoshino Tatsuro , Saitoh Eiji
Published: June 2011

The frequency dependence of magnetization precession in spin pumping has been investigated using the inverse spin-Hall effect in a Pt/Y3Fe5O12 bilayer film. We found that the magnitude of a spin current generated by the spin pumping depends weakly on the applied microwave frequency. This weak dependence, which is attributed to the compensation between the frequency change in the spin-pumping cycle and the dynamic magnetic susceptibility, is favorable for making a spin-current-driven microwave demodulator. This behavior is consistent with a model calculation based on the Landau-Lifshitz-Gilbert equation combined with the spin mixing.
Structural and optical properties of rare earth–doped (Ba0.77Ca0.23)1−x(Sm, Nd, Pr, Yb)xTiO3
Authors: Moraes A. P. A. , Filho A. G. Souza , Freire P. T. C. , Filho J. Mendes , M’Peko J. C. , Hernandes A. C. , Antonelli E. , Blair Michael W. , Muenchausen Ross E. , Jacobsohn Luiz G. , Paraguassu W.
Published: June 2011

The structural, dielectric, and vibrational properties of pure and rare earth (RE)-doped Ba0.77Ca0.23TiO3 (BCT23; RE = Nd, Sm, Pr, Yb) ceramics obtained via solid-state reaction were investigated. The pure and RE-doped BCT23 ceramics sintered at 1450 °C in air for 4 h showed a dense microstructure in all ceramics. The use of RE ions as dopants introduced lattice-parameter changes that manifested in the reduction of the volume of the unit cell. RE-doped BCT23 samples exhibit a more homogenous microstructure due to the absence of a Ti-rich phase in the grain boundaries as demonstrated by scanning electron microscopy imaging. The incorporation of REs led to perturbations of the local symmetry of TiO6 octahedra and the creation of a new Raman mode. The results of Raman scattering measurements indicated that the Curie temperature of the ferroelectric phase transition depends on the RE ion and ion content, with the Curie temperature shifting toward lower values as the RE content increases, with the exception of Yb3+ doping, which did not affect the ferroelectric phase transition temperature. The phase transition behavior is explained using the standard soft mode model. Electronic paramagnetic resonance measurements showed the existence of Ti vacancies in the structure of RE-doped BCT23. Defects are created via charge compensation mechanisms due to the incorporation of elements with a different valence state relative to the ions of the pure BCT23 host. It is concluded that the Ti vacancies are responsible for the activation of the Raman mode at 840 cm−1, which is in agreement with lattice dynamics calculations.
Strength and elasticity of niobium under high pressure
Authors: Singh Anil K. , Liermann Hanns-Peter
Published: June 2011

High purity polycrystalline niobium contained in boron-epoxy gasket was compressed in a diamond anvil cell (DAC). The pressure was increased in steps of ∼3 GPa and the diffraction patterns recorded at each pressure with the incident x-ray beam perpendicular to the load axis of the DAC (radial diffraction). The maximum pressure reached was 37.6 GPa. The compressive strength (differential stress) derived from the radial diffraction data is 0.44(1) GPa at 2.1 GPa and shows a shallow maximum at ∼5 GPa, and then decreases to 0.35(5) at 12 GPa. At higher pressures, strength increases nearly linearly and the extrapolated value at 40 GPa is 0.94(6) GPa. At any pressure, the single-crystal elastic moduli derived from the diffraction data can be made to match well those obtained from the extrapolation of the elasticity data at ambient pressure by adjusting the weight parameter α that appears in the lattice strain theory. The parameter α is found to decrease from 2.00(8) at 2.1 GPa to 1.35(4) at 37.6 GPa.
Imaging of nanoscale charge transport in bulk heterojunction solar cells
Authors: Hamadani Behrang H. , Gergel-Hackett Nadine , Haney Paul M. , Zhitenev Nikolai B.
Published: June 2011

We have studied the local charge transport properties of organic bulk heterojunction solar cells based on the blends of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester with a photoconductive atomic force microscope (PCAFM). We explore the role of morphology on transport of photogenerated electrons or holes by careful consideration of the sample geometry and the choice of the atomic force microscope (AFM) tip. We then consider the role of the film/tip contact on the local current-voltage characteristics of these structures and present a model based on a drift and diffusion description of transport. We find that our simple 1D model can only reproduce qualitative features of the data using unphysical parameters, indicating that more sophisticated modeling is required to capture all the nonideal characteristics of the AFM transport measurements. Our results show that interpretation of PCAFM contrast and its relation to material morphology or charge transport is not very straightforward.
Existence of steady-state solutions in a nonlinear photonic lattice model
Authors: Chen Shouxin , Lei Yuqiong
Published: June 2011

Many careful experimental observations to nonlinear photonic lattice model have been constructed. In this paper, we use the principle of variational method, mountain pass lemma, fixed point method to develop an existence theorem for the steady-state solutions of a nonlinear photonic lattice model describing the propagation of a light wave in a photo-refractive crystal is established, which demonstrates that there is an amount of continuous energy that allows the existence of steady-state solutions. Our results provide a theoretical principles for a variety of experiments and research on photonic lattices and crystals. Finally, it is straightforward to see that the applicability of the present to constructing arbitrarily small energy solutions is also guaranteed.
Plasma excitations of dressed Dirac electrons in graphene layers
Authors: Roslyak Oleksiy , Gumbs Godfrey , Huang Danhong
Published: June 2011

Collective plasma excitations of optically dressed Dirac electrons in single and double graphene layers are calculated in the RPA. The presence of circularly polarized light gives rise to an energy gap Eg between the conduction and valence energy bands. Its value may be adjusted by varying the frequency and intensity of the light, and may reach values of the gap reported for epitaxially grown graphene and far exceeding that caused by spin-orbit coupling. We report plasmon dispersion relations for various energy gaps and separations between graphene layers. For a single graphene sheet, we find that plasmon modes may be excited for larger wave vector and frequency when subjected to light. For double layers, we obtained an optical and phononlike mode and found that the optical mode is not as sensitive as the phononlike mode in the long wavelength limit when the layer separation is varied, for a chosen Eg. The dressed electron plasma—although massive—still has Dirac origin, giving rise to anomalous plasmon behavior upon crossing the ω=ℏνFq cone.
Defect states in epitaxial HfO2 films induced by atomic transport from n-GaAs (100) substrate
Authors: Kim C. Y. , Jeong K. S. , Kang Y. S. , Cho S. W. , Cho M.-H. , Chung K. B. , Ko D.-H. , Yi Y. , Kim H.
Published: June 2011

We investigated the chemical states and nature of the defect states below the conduction band edge of HfO2 films grown on GaAs (100) substrates using high-resolution x-ray photoelectron spectroscopy (HRXPS), x-ray absorption spectroscopy (XAS), and density functional theory calculations. O K1-edge absorption spectra of the HfO2/GaAs film revealed two distinct conduction band edge defect states, located at 1.6 ± 0.2 eV and 3.0 ± 0.2 eV below the conduction band edge in HfO2. The combined XAS and HRXPS results as a function of post-deposition annealing temperature indicated that the changes in defect states below the conduction band edge of HfO2 were correlated with the extent of interfacial chemical reactions between the HfO2 film and the GaAs substrate. Spectroscopic and theoretical results revealed that the two conduction band defect states are caused by (i) diffused Ga–O states, Hf3+ states, and (ii) an O divacancy related to the As–O states, respectively.
Sub-bandgap absorption in Ti implanted Si over the Mott limit
Authors: Olea J. , del Prado A. , Pastor D. , Mártil I. , González-Díaz G.
Published: June 2011

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 × 1020 cm−3, which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm2) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 × 103 and 104 cm−1. These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.
Dynamics of laser-induced phase switching in GeTe films
Authors: Gawelda W. , Siegel J. , Afonso C. N. , Plausinaitiene V. , Abrutis A. , Wiemer C.
Published: June 2011

Phase switching in GeTe thin films (grown using a modified metal organic chemical vapor deposition system) upon pulsed femtosecond and nanosecond laser irradiation has been studied. Two in situ methods, i.e., optical microscopy and real-time reflectivity measurements, have been used in order to compare the optical response before and after phase change and to follow the phase change dynamics with a time resolution close to 400 ps. The results show that cycling is possible under irradiation with both fs and ns pulses using single pulses for amorphization and multiple pulses for crystallization. The use of ns pulses favors the crystalline-to-amorphous phase transformation, with a characteristic transformation time of ∼15 ns. The presence of the liquid phase was identified and temporally resolved, featuring a well-defined transient reflectivity state, in between those of the crystalline and amorphous phases. We have also studied the role of material configuration in the phase change dynamics and the mechanisms involved in the re-crystallization process.
Size effect on thermal desorption of CO from Pt nanostructures on graphite
Authors: Julukian A. , Fadnes T. , Raaen S. , Balci M.
Published: June 2011

Self-assembled Pt nanostructures, which are formed by evaporation and subsequent diffusion limited aggregation of Pt on graphite, have been studied by photoemission and scanning electron microscopy. Adsorption of CO has been studied by temperature programmed desorption. Charge induced Pt 4f core level shifts in the order of 1 eV that depend on the effective dimensions of the nanostructures have been observed, and effective dimensions of the Pt structures have been defined based on the Pt 4f core level shifts. The effective dimensions of the Pt structures have been correlated with changes in the thermal desorption of adsorbed CO. It is observed that smaller effective dimensions in the few nanometer range result in lower desorption temperatures of up to 50 K. The possible role of hot electrons in the adsorption process has been discussed.
Iron oxide nanoparticles coated with gold: Enhanced magnetic moment due to interfacial effects
Authors: Banerjee S. , Raja S. O. , Sardar M. , Gayathri N. , Ghosh B. , Dasgupta A.
Published: June 2011

In this paper, we show that when nanoparticles of Fe3O4 are coated with gold there is a distinct enhancement of magnetization by a factor of six. This increase of magnetization has been attributed to large orbital magnetic moment formation at the magnetic particle/Au (core/shell) interface. Our theoretical analysis indicates that the enhanced magnetism observed in Fe3O4-Au (core-shell) nanoparticles is an interfacial effect. The origin of magnetism in Au as an interfacial phenomenon is supported by the observation of positive magnetization in citrate coated gold nanoparticles. In citrate coated gold nanoparticles, we observe a crossover from positive magnetization value to negative magnetization value upon increasing magnetic field indicating cancellation of interfacial magnetization by the diamagnetic contribution from the bulk. We propose a theoretical formalism which semi-quantitatively explains our experimental results and supports the origin of magnetization in Au as an interfacial effect.
Improved coherence of ultrafast spin-transfer-driven precessional switching with synthetic antiferromagnet perpendicular polarizer
Authors: Vaysset A. , Papusoi C. , Buda-Prejbeanu L. D. , Bandiera S. , Marins de Castro M. , Dahmane Y. , Toussaint J.-C. , Ebels U. , Auffret S. , Sousa R. , Vila L. , Dieny B.
Published: June 2011

The coherence of the precessional switching was compared in planar spin-valves comprising either an additional simple perpendicular polarizer or a synthetic antiferromagnet perpendicular polarizer. A significant improvement in the precession coherence was observed experimentally in the second type of samples. Micromagnetic simulations were performed to study the effect of the stray field from the perpendicular polarizer. They provide an explanation for the gradual loss of coherence of the precession in terms of vortex formation, which occurs much faster when a simple perpendicular polarizer is used.
Simulation and experimental study on compositional evolution of Li-Co in LiCoO2 thin films during sputter deposition
Authors: Nimisha C. S. , Mohan Rao G.
Published: June 2011

The compositional evolution in sputter deposited LiCoO2 thin films is influenced by process parameters involved during deposition. The electrochemical performance of these films strongly depends on their microstructure, preferential orientation and stoichiometry. The transport process of sputtered Li and Co atoms from the LiCoO2 target to the substrate, through Ar plasma in a planar magnetron configuration, was investigated based on the Monte Carlo technique. The effect of sputtering gas pressure and the substrate-target distance (dst) on Li/Co ratio, as well as, energy and angular distribution of sputtered atoms on the substrate were examined. Stable Li/Co ratios have been obtained at 5 Pa pressure and dst in the range 5−11 cm. The kinetic energy and incident angular distribution of Li and Co atoms reaching the substrate have been found to be dependent on sputtering pressure. Simulations were extended to predict compositional variations in films prepared at various process conditions. These results were compared with the composition of films determined experimentally using x-ray photoelectron spectroscopy (XPS). Li/Co ratio calculated using XPS was in moderate agreement with that of the simulated value. The measured film thickness followed the same trend as predicted by simulation. These studies are shown to be useful in understanding the complexities in multicomponent sputtering.
Fourth-order coupled nonlinear Schrödinger equations for gravity waves on deep water
Authors: Gramstad Odin , Trulsen Karsten
Published: June 2011

We derive a set of two fourth-order coupled nonlinear Schrödinger equations describing the evolution of two two-dimensional systems of deep-water gravity waves with different wavenumbers or directions of propagation. It is shown that the coupled equations can be formulated as a Hamiltonian system and that they conserve the total wave action and momentum of the combined wave field. The modulational instability of two interacting uniform wave trains is considered.
Spectrum generating algebras for the free motion in S3
Authors: Gadella M. , Negro J. , Nieto L. M. , Pronko G. P. , Santander M.
Published: June 2011

We construct the spectrum generating algebra (SGA) for a free particle in the three-dimensional sphere S3 for both classical and quantum descriptions. In the classical approach, the SGA supplies time-dependent constants of motion that allow to solve algebraically the motion. In the quantum case, the SGA includes the ladder operators that give the eigenstates of the free Hamiltonian. We study this quantum case from two equivalent points of view.
The effect of geometry on cluster polarizability: Studies of sodium, copper, and silicon clusters at shape-transition sizes
Authors: Chu Xiang , Yang Mingli , Jackson Koblar A.
Published: June 2011

The electronic properties of Na16, Cu16, and Si20–28 clusters were calculated using density functional theory with the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof. These clusters are special, as transitions in cluster shape occur at these sizes in the Nan, Cun, and Sin cluster systems, respectively. Low-energy isomers that are comparable in stability, but possess distinctly different shapes, exist at each of these sizes, making these sets of isomers useful as probes of geometrical effects on cluster properties. Results for ionization potentials, electron affinities, and polarizabilities are shown to have a characteristic dependence on cluster shape. An analysis of the results reveals a close relationship between polarizability and cluster volume for all the isomers studied, despite the differences in cluster type and geometry. This relationship accounts for variations in polarizabilities among isomers of the same size, but different shapes, whereas previously published rules relating the polarizability to other cluster properties do not.
First principles study of the ground and excited states of FeO, FeO+, and FeO−
Authors: Sakellaris Constantine N. , Miliordos Evangelos , Mavridis Aristides
Published: June 2011

Through a variety of highly correlated methods combined with large basis sets we have studied the electronic structure of FeO, FeO+, and FeO−. In particular, we have constructed complete potential energy curves for 48, 24, and 4 states for the FeO, FeO+, and FeO− species, respectively, at the multireference level of theory. For all states examined we report energetics, common spectroscopic parameters, and dipole moments. Overall our results are in good agreement with experiment, but we have encountered as well interesting differences between experiment and theory deserving further investigation.
Structure of droplet-epitaxy-grown InAs/GaAs quantum dots
Authors: Cohen Eyal , Yochelis Shira , Westreich Ohad , Shusterman Sergey , Kumah Divine P. , Clarke Roy , Yacoby Yizhak , Paltiel Yossi
Published: June 2011

We have used a direct x-ray phasing method, coherent Bragg rod analysis, to obtain sub-angstrom resolution electron density maps of the InAs/GaAs dot system. The dots were grown by the droplet heteroepitaxy (DHE) technique and their structural and compositional properties are compared with those of dots grown by the strain-driven Stranski–Krastanov method. Our results show that the Ga diffusion into the DHE-grown dots is somewhat larger; however, other characteristics such as the composition of the dots’ uppermost layers, the interlayer spacing, and the bowing of the atomic layers are similar.
First principles semiclassical calculations of vibrational eigenfunctions
Authors: Ceotto Michele , Valleau Stéphanie , Tantardini Gian Franco , Aspuru-Guzik Alán
Published: June 2011

Vibrational eigenfunctions are calculated on-the-fly using semiclassical methods in conjunction with ab initio density functional theory classical trajectories. Various semiclassical approximations based on the time-dependent representation of the eigenfunctions are tested on an analytical potential describing the chemisorption of CO on Cu(100). Then, first principles semiclassical vibrational eigenfunctions are calculated for the CO2 molecule and its accuracy evaluated. The multiple coherent states initial value representations semiclassical method recently developed by us has shown with only six ab initio trajectories to evaluate eigenvalues and eigenfunctions at the accuracy level of thousands trajectory semiclassical initial value representation simulations.
High power efficiency tandem organic light-emitting diodes based on bulk heterojunction organic bipolar charge generation layer
Authors: Chen Yonghua , Chen Jiangshan , Ma Dongge , Yan Donghang , Wang Lixiang , Zhu Furong
Published: June 2011

The significant enhancement in power efficiency of tandem organic light-emitting diodes (OLEDs) was achieved using bulk heterojunction organic bipolar charge generation layer (CGL), consisted of zinc phthalocyanine (ZnPc): fullerene (C60) blend. In addition to a significant enhancement in luminance and current efficiency this work yielded a maximum power efficiency of 21 lm W−1 for a tandem OLED, notably almost two times higher than that of a single-unit device, with a maximum power efficiency of 10.1 lm W−1. The enhancement in power efficiency at higher luminance is also over 50%. The remarkable enhancement in power efficiency has been attributed to the effective charge generation, transport and extraction due to the presence of interface-modified ZnPc:C60 CGL in tandem OLEDs. Our results demonstrate that the bulk heterojunction, consisting of two matched n- and p-type organic semiconductors, is a promising bipolar CGL for high power efficiency tandem OLEDs.
Amplification and nonlinear mechanisms in plane Couette flow
Authors: Gayme Dennice F. , McKeon Beverley J. , Bamieh Bassam , Papachristodoulou Antonis , Doyle John C.
Published: June 2011

We study the input-output response of a streamwise constant projection of the Navier-Stokes equations for plane Couette flow, the so-called 2D/3C model. Study of a streamwise constant model is motivated by numerical and experimental observations that suggest the prevalence and importance of streamwise and quasi-streamwise elongated structures. Periodic spanwise/wall-normal (z–y) plane stream functions are used as input to develop a forced 2D/3C streamwise velocity field that is qualitatively similar to a fully turbulent spatial field of direct numerical simulation data. The input-output response associated with the 2D/3C nonlinear coupling is used to estimate the energy optimal spanwise wavelength over a range of Reynolds numbers. The results of the input-output analysis agree with previous studies of the linearized Navier-Stokes equations. The optimal energy corresponds to minimal nonlinear coupling. On the other hand, the nature of the forced 2D/3C streamwise velocity field provides evidence that the nonlinear coupling in the 2D/3C model is responsible for creating the well known characteristic “S” shaped turbulent velocity profile. This indicates that there is an important tradeoff between energy amplification, which is primarily linear, and the seemingly nonlinear momentum transfer mechanism that produces a turbulent-like mean profile.
Piezoresistance effect of metallic glassy fibers
Authors: Yi Jun , Bai H. Y. , Zhao D. Q. , Pan M. X. , Wang W. H.
Published: June 2011

Smaller electrical resistance strain gauges (ERSG) are highly expected especially for micro-electro-mechanical systems while the reduction in the size of strain gauge is restricted by the relatively low resistivity and poor processability of conventional piezoresistive alloys. We investigate piezoresistive properties of a Pd40Cu30Ni10P20 metallic glassy fiber (MGF), and find that the resistivity, gage factor, elastic limit, and relative change in resistance of the MGF are superior to that of commercial crystalline ERSG piezoresistors. Combining with high flexibility, uniformity, smoothness, and nanoscale size in diameter, the MGFs are promising for submicroscale ERSGs.
Picosecond response times in GaAs/AlGaAs core/shell nanowire-based photodetectors
Authors: Gallo Eric M. , Chen Guannan , Currie Marc , McGuckin Terrence , Prete Paola , Lovergine Nico , Nabet Bahram , Spanier Jonathan E.
Published: June 2011

High-speed metal-semiconductor-metal (MSM) photodetectors based on Schottky-contacted core/shell GaAs/AlGaAs and bare GaAs nanowires were fabricated and characterized. The measured core/shell temporal response has a ∼10 ps full-width at half-maximum and an estimated corrected value less than 5 ps. The bare GaAs devices exhibit a slower response (∼35 ps) along with a slow decaying persistent photocurrent (∼80 s). The core/shell devices exhibit significantly improved dc and high-speed performance over bare nanowires and comparable performance to planar MSM photodetectors. The picosecond temporal response, coupled with picoampere dark current, demonstrate the potential for core/shell nanowires in high-speed imaging arrays and on-chip optical interconnects.
Diamagnetic loop measurement in Korea Superconducting Tokamak Advanced Research machine
Authors: Bak J. G. , Lee S. G. , Kim H. S.
Published: June 2011

Diamagnetic loop (DL), which consists of two poloidal loops inside the vacuum vessel, is used to measure the diamagnetic flux during a plasma discharge in the Korea Superconducting Tokamak Advanced Research (KSTAR) machine. The vacuum fluxes in the DL signal can be compensated up to 0.1 mWb by using the coefficients, which are obtained from experimental investigations, in the vacuum flux measurements during vacuum shots under same operational conditions of magnetic coils for plasma experiment in the KSTAR machine. The maximum error in the diamagnetic flux measurement due to the errors of the coefficients was estimated as ∼0.22 mWb. From the diamagnetic flux measurements for the ohmically heated circular plasmas in the KSTAR machine, the stored energy agrees well with the estimated kinetic energy within the discrepancy of 25%. When the electron cyclotron heating, the neutral beam injection, and the ion cyclotron resonance heating are added to the ohmically heated limiter plasmas, the additional heating effects can be clearly observed from the increase of the stored energy evaluated in the DL measurement.
Adiabatic magnetothermia makes possible the study of the temperature dependence of the heat dissipated by magnetic nanoparticles under alternating magnetic fields
Authors: Natividad Eva , Castro Miguel , Mediano Arturo
Published: June 2011

Determining the low-temperature dependence of the specific absorption rate (SAR) of magnetic nanoparticles under alternating magnetic fields with amplitudes and frequencies similar to those used in applications such as magnetic fluid hyperthermia, becomes essential when theoretical expressions fail to extrapolate the behavior of nanoparticle arrangements. We prove that adiabatic magnetothermia is capable of providing SAR(T) data displaying an excellent continuity with those obtained from magnetic measurements at lower ac-field amplitudes and frequencies.
Maximum near-field radiative heat transfer between thin films
Authors: Basu Soumyadipta , Francoeur Mathieu
Published: June 2011

In this letter, we investigate the maximum near-field radiative heat transfer achievable between two thin films. By using frequency-independent permittivities for the films, we obtain optimum values of the real (εopt′) and imaginary (εopt″) parts of the dielectric function maximizing the heat transfer for different thicknesses. We show that when the ratio D of the film thicknesses tf to the vacuum gap d is equal or less than 0.1, the maximum heat flux becomes independent of D. Based on the analysis performed in this study, it is possible to suitably choose film thicknesses maximizing near-field heat transfer at different vacuum gaps. The results obtained in this work also allow the interpretation of the physical details underlying near-field thermal radiation between films.
Antibiotic susceptibility test based on the dielectrophoretic behavior of elongated Escherichia coli with cephalexin treatment
Authors: Chung Cheng-Che , Cheng I-Fang , Yang Wen-Horng , Chang Hsien-Chang
Published: June 2011

This study reports the use of dielectrophoresis (DEP), which determined the crossover frequency (cof) of antibiotic-induced elongation of Escherichia coli (E. coli) with regard to the rapid antibiotic susceptibility test (AST). Different dielectric properties and elongation rates of E. coli are caused by various concentrations of cephalexin treatment. According to the authors’ results, significant changes in the cof of bacteria treated with 32 μg/ml antibiotic for 60 min can be found by using a quadruple electrode array, and the results of DEP-based AST correspond with that of agar dilution method. Utilizing this approach could greatly reduce the period of bacteria growth, and obtain the minimum inhibition concentration of E. coli to cephalexin.
Calculated and experimental electron energy-loss spectra of La2O3, La(OH)3, and LaOF nanophases in high permittivity lanthanum-based oxide layers
Authors: Calmels L. , Coulon P. E. , Schamm-Chardon S.
Published: June 2011

Using first principles methods, the O K energy-loss near-edge structure of cubic and hexagonal La2O3, La(OH)3, and LaOF phases have been calculated. These calculations support the identification of nanocrystalline phases evidenced experimentally by electron energy-loss spectroscopy (EELS) performed in a transmission electron microscope. The nanocrystals have been observed in atomic layer deposited La2O3 thin films developed for advanced metal-oxide-semiconductor field effect transistor applications. The presence of the nanophases can be explained by the hygroscopicity and the particular reactivity with fluorine of La2O3. These calculations provide a set of EELS fingerprints which will be useful for local phase identification in La2O3-based materials.
Independent tuning of frequency and quality factor of microresonators
Authors: Rasouli Mohammad Amin , Bahreyni Behraad
Published: June 2011

This letter reports on a developed approach to control losses in torsional microresonators for applications that require high precision. This methodology is demonstrated through realizing an array of microresonators with independent tuning of both quality factor and resonant frequency. The presented approach enables both boosting and reducing the quality factor of a resonator using proper drive signals to the tuning electrodes. The experimental data demonstrates a tunability of as much as +33% and −37% from the initial quality factor value with negligible frequency change. On the other hand, fine resonant frequency tuning was achieved with a minimal effect on the quality factor.
The effect of film and interface structure on the transport properties of Heusler based current-perpendicular-to-plane spin valves
Authors: Lazarov V. K. , Yoshida K. , Sato J. , Hasnip P. J. , Oogane M. , Hirohata A. , Ando Y.
Published: June 2011

We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L21 but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L21. The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs.
Nitrogen assisted etching of graphene layers in a scanning electron microscope
Authors: Fox D. , O’Neill A. , Zhou D. , Boese M. , Coleman J. N. , Zhang H. Z.
Published: June 2011

We describe the controlled patterning of nanopores in graphene layers by using the low-energy (<10 keV) focused electron beam in a scanning electron microscope. Regular nanometer-sized holes can be fabricated with the presence of nitrogen gas. The effect of the gas pressure, beam current, and energy on the etching process are investigated. Transmission electron microscopy, coupled with plasmon energy loss imaging, reveals the microstructure modification of the etched graphene. A nitrogen-ion assisted etching mechanism is proposed for the controlled patterning.
Improvement of efficiency of GaN-based polarization-doped light-emitting diodes grown by metalorganic chemical vapor deposition
Authors: Zhang L. , Wei X. C. , Liu N. X. , Lu H. X. , Zeng J. P. , Wang J. X. , Zeng Y. P. , Li J. M.
Published: June 2011

Our simulated results [Appl. Phys. Lett. 98, 101110 (2011)] reveal that polarization-doped light-emitting diodes (LEDs) have improved internal quantum efficiency due to the enhanced hole injection caused by the improved hole concentration and smooth valence band. In this letter, in order to verify these calculated results, polarization-doped LEDs grown by metalorganic chemical vapor deposition are investigated. The results show that the polarization-doped LED has the improved electroluminescence intensity and external quantum efficiency (EQE) compared with the conventional LED. The influence of the degree of AlGaN gradation on polarization-doped LEDs is also studied. It is found that the polarization-doped LED has the highest EQE when the Al composition of the graded AlGaN is linearly decreased from 0.2 to 0.
Uniaxial tensile strain and exciton–phonon coupling in bent ZnO nanowires
Authors: Chen Rui , Ye Quan-Lin , He T. C. , Wu T. , Sun H. D.
Published: June 2011

We investigate the optical property of bent ZnO nanowires (NWs) obtained by low energy argon ion milling. At room temperature, the bent NWs demonstrates an enhanced near band edge ultraviolet emission, while the deep level green emission is totally suppressed. Temperature dependent photoluminescence measurements were carried out between 10 and 300 K for both the as-grown and the bent ZnO NWs. It is found that the emission peak energy of the bent NWs systematically shifts to lower energy compared to the as-grown NWs in the whole measured temperature range. Our results indicate that the redshift in the emission peak is related to the uniaxial tensile strain and the enhanced exciton–phonon coupling strength in the bent ZnO NWs.
Amplitude-modulated sinusoidal microchannels for observing adaptability in C. elegans locomotion
Authors: Parashar Archana , Lycke Roy , Carr John A. , Pandey Santosh
Published: June 2011

In this paper, we present a movement-based assay to observe adaptability in Caenorhabditis elegans locomotion behavior. The assay comprises a series of sinusoidal microchannels with a fixed wavelength and modulating (increasing or decreasing) amplitude. The channel width is comparable to the body diameter of the organism. Worms are allowed to enter the channel from the input port and migrate toward the output port. Within channel sections that closely match the worm’s natural undulations, the worm movement is relatively quick and steady. As the channel amplitude increases or decreases along the device, the worm faces difficulty in generating the propulsive thrust, begins to slow down and eventually fails to move forward. A set of locomotion parameters (i.e., average forward velocity, number and duration of stops, range of contact angle, and cut-off region) is defined for worm locomotion in modulated sinusoidal channels and extracted from the recorded videos. The device is tested on wild-type C. elegans (N2) and two mutants (lev-8 and unc-38). We anticipate this passive, movement-based assay can be used to screen nematodes showing difference in locomotion phenotype.
Telomerase regulatory subunit Est3 in two Candida species physically interacts with the TEN domain of TERT and telomeric DNA
Authors: Yen Wei-Feng , Chico Lidia , Lei Ming , Lue Neal F.
Published: June 2011

The yeast telomerase regulatory protein Est3 is required for telomere maintenance in vivo, and shares intriguing structural and functional similarities with the mammalian telomeric protein TPP1. Here we report our physical and functional characterizations of Est3 homologues from
Candida parapsilosis
and
Lodderomyces elongisporus
, which bear unique N- and C-terminal tails in addition to a conserved central OB fold. We show that these Est3 homologues form stable complexes with the TEN domain of telomerase reverse transcriptase. Efficient complex formation requires both the N- and C-terminal tails, as well as conserved OB fold residues of Est3. Other Est3 homologues devoid of the tails failed to interact strongly with the cognate TEN domains. Remarkably, the
C. parapsilosis
Est3 alone exhibits no appreciable DNA-binding activity, but can be crosslinked to telomeric DNA in the presence of the TEN domain. A conserved basic residue on the putative DNA-binding surface of
Cp
Est3 is required for efficient crosslinking. Mutating the equivalent residue in
Candida albicans
Est3 caused telomere attrition. We propose that interaction with the TEN domain unmasks a functionally important nucleic acid-binding activity in Est3. Our findings provide insights on the mechanisms and evolution of a widely conserved and functionally critical telomeric/telomerase component.
Major Lineages and Metapopulations in Columbia River Oncorhynchus mykiss Are Structured by Dynamic Landscape Features and Environments
Authors: Blankenship Scott M. , Campbell Matt R. , Hess Jon E. , Hess Maureen A. , Kassler Todd W. , Kozfkay Christine C. , Matala Andrew P. , Narum Shawn R. , Paquin Melanie M. , Small Maureen P. , Stephenson Jeff J. , Warheit Kenneth I. , Moran Paul
Published: June 2011

It is widely recognized that genetic diversity within species is shaped by dynamic habitats. The quantitative and molecular genetic patterns observed are the result of demographics, mutation, migration, and adaptation. The populations of rainbow trout Oncorhynchus mykiss in the Columbia River basin (including both resident and anadromous forms and various subspecies) present a special challenge to understanding the relative roles of those factors. Standardized microsatellite data were compiled for 226 collections (15,658 individuals) from throughout the Columbia and Snake River basins to evaluate the genetic patterns of structure and adaptation. The data were primarily from fish of the anadromous life history form, and we used a population grouping procedure based on principal components and hierarchical k‐means clustering to cluster populations into eight aggregates or groups with similar allele frequencies. These aggregates approximated geographic regions, and the two largest principal components corresponded to ancestral lineages of Sacramento redband trout O. m. stonei, coastal rainbow trout O. m. irideus, and interior Columbia River redband trout O. m. gairdneri. Genetic data were partitioned among primary aggregates (lower Columbia, middle–upper Columbia, and Snake rivers), and the magnitude of genetic divergence relative to genetic diversity was analyzed (per locus) to test for evidence of selection and subsequent signals of adaptation. Two loci showed higher divergence than expected by chance (i.e., positive selection); however, both of these loci were on the fringe of the 99% confidence level and are potential false positives. Genetic patterns were also significantly correlated with certain environmental and habitat parameters (e.g., precipitation), but the extent to which those correlations are causal as opposed to effectual remains unclear. Despite the remaining questions, these data provide a foundation for more detailed investigations of harvest, admixture, and introgression between hatchery‐ and natural‐origin fish and differences in reproductive success among individuals as well as monitoring trends in productivity.
Diminished Reproductive Success of Steelhead from a Hatchery Supplementation Program (Little Sheep Creek, Imnaha Basin, Oregon)
Authors: Berntson Ewann A. , Carmichael Richard W. , Flesher Michael W. , Ward Eric J. , Moran Paul
Published: June 2011

Hatchery supplementation programs are designed to enhance natural production and maintain the fitness of the target population; however, it can be difficult to evaluate the success of these programs. Key to the success of such programs is a relatively high reproductive success of hatchery fish. This study investigated the relative reproductive success (RRS) of steelhead Oncorhynchus mykiss (anadromous rainbow trout) by creating pedigrees for hatchery and natural spawning steelhead. We genotyped adult steelhead that returned to a weir and were released upstream to spawn in Little Sheep Creek, a tributary to the Imnaha River in eastern Oregon. The broodstock for this supplementation program were originally chosen from natural‐origin steelhead returning to the weir and in subsequent years consisted of both natural‐ and hatchery‐origin individuals. Microsatellite analyses showed the broodstock to be genetically similar to the natural population across years. We also genotyped adult resident rainbow trout from multiple locations upstream of the weir and determined the parentage of progeny collected at various life history stages, including returning adults in subsequent years. Analysis of progeny sampled at both the juvenile and adult life stages suggested that the RRS of hatchery‐origin fish was 30–60% that of their natural‐origin counterparts. Using generalized linear models to address the importance of various factors associated with reduced reproductive success, we found that the greatest effects on RRS were origin (natural versus hatchery), length, return date, and the number of same‐sex competitors. Natural parents were less negatively affected by same‐sex competitors. Differential survival of juveniles and the behavior of offspring and/or spawning adults may all contribute to diminished fitness in hatchery‐reared salmon, although it could not be determined to what extent these effects were of a persistent, heritable nature as distinct from an environmental effect associated with hatchery rearing and release strategies.