bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of capillary condensation in lattice gas models of confined fluids: A comparison of dynamic mean field theory with dynamic Monte Carlo simulations
Authors: Edison John R. , Monson Peter A.
Published: June 2013

This article addresses the accuracy of a dynamic mean field theory (DMFT) for fluids in porous materials [P. A. Monson, J. Chem. Phys. 128, 084701 (2008)]10.1063/1.2837287. The theory is used to study the relaxation processes of fluids in pores driven by step changes made to a bulk reservoir in contact with the pore. We compare the results of the DMFT to those obtained by averaging over large numbers of dynamic Monte Carlo (DMC) simulation trajectories. The problem chosen for comparison is capillary condensation in slit pores, driven by step changes in the chemical potential in the bulk reservoir and involving a nucleation process via the formation of a liquid bridge. The principal difference between the DMFT results and DMC is the replacement of a distribution of nucleation times and location along the pore for the formation of liquid bridges by a single time and location. DMFT is seen to yield an otherwise qualitatively accurate description of the dynamic behavior.
Molecular dynamics simulation of radiation damage in CaCd6 quasicrystal cubic approximant up to 10 keV
Authors: Chen P. H. , Avchachov K. , Nordlund K. , Pussi K.
Published: June 2013

Due to the peculiar nature of the atomic order in quasicrystals, examining phase transitions in this class of materials is of particular interest. Energetic particle irradiation can provide a way to modify the structure locally in a quasicrystal. To examine irradiation-induced phase transitions in quasicrystals on the atomic scale, we have carried out molecular dynamics simulations of collision cascades in CaCd6 quasicrystal cubic approximant with energies up to 10 keV at 0 and 300 K. The results show that the threshold energies depend surprisingly strongly on the local coordination environments. The energy dependence of stable defect formation exhibits a power-law dependence on cascade energy, and surviving defects are dominated by Cd interstitials and vacancies. Only a modest effect of temperature is observed on defect survival, while irradiation temperature increases lead to a slight increase in the average size of both vacancy clusters and interstitial clusters.
Low-energy electron scattering from the aza-derivatives of pyrrole, furan, and thiophene
Authors: Kossoski F. , Bettega M. H. F.
Published: June 2013

We report elastic integral and differential cross sections for electron scattering from the aza-derivatives of pyrrole, furan, and thiophene, namely, pyrazole, imidazole, isoxazole, oxazole, isothiazole, and thiazole. The calculations were performed within the Schwinger multichannel method with pseudopotentials, with inclusion of static, exchange, and polarization interactions, for energies up to 10 eV. We found two π* shape resonances and a high-lying σ* shape resonance in each system. A sharp low-energy σ* resonance was also identified in isothiazole and thiazole. Pyrazole and imidazole presented yet a broad low-lying σ* resonance. The positions of the resonances agree very well with existing experimental results. We discuss the similarities and differences among the resonances of these compounds.
Hot-spot contributions in shocked high explosives from mesoscale ignition models
Authors: Levesque G. , Vitello P. , Howard W. M.
Published: June 2013

High explosive performance and sensitivity is strongly related to the mesoscale defect densities. Bracketing the population of mesoscale hot spots that are active in the shocked ignition of explosives is important for the development of predictive reactive flow models. By coupling a multiphysics-capable hydrodynamics code (ale3d) with a chemical kinetics solver (cheetah), we can parametrically analyze different pore sizes undergoing collapse in high pressure shock conditions with evolving physical parameter fields. Implementing first-principles based decomposition kinetics, burning hot spots are monitored, and the regimes of pore sizes that contribute significantly to burnt mass faction and those that survive thermal conduction on the time scales of ignition are elucidated. Comparisons are drawn between the thermal explosion theory and the multiphysics models for the determination of nominal pore sizes that burn significantly during ignition for the explosive 1,3,5-triamino-2,4,6-trinitrobenzene.
Electromagnetic instability of thin reconnection layers: Comparison of three-dimensional simulations with MRX observations
Authors: Roytershteyn V. , Dorfman S. , Daughton W. , Ji H. , Yamada M. , Karimabadi H.
Published: June 2013

The influence of current-aligned instabilities on magnetic reconnection in weakly collisional regimes is investigated using experimental observations from Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] and large-scale fully kinetic simulations. In the simulations as well as in the experiment, the dominant instability is localized near the center of the reconnection layer, produces large perturbations of the magnetic field, and is characterized by the wavenumber that is a geometric mean between electron and ion gyroradii k∼(ρeρi)−1/2. However, both the simulations and the experimental observations suggest the instability is not the dominant reconnection mechanism under parameters typical of MRX.
Structural and optical properties of Cu doped SnO2 nanoparticles: An experimental and density functional study
Authors: Chetri Pawan , Saikia Bhamyarswa , Choudhury Amarjyoti
Published: June 2013

The paper investigates, both theoretically and experimentally, the structural and optical changes in SnO2 system brought about by introduction of Cu in a SnO2 system. On the experimental front, a cost effective sol-gel technique is used to prepare hexagonal shaped Cu doped SnO2 nanoparticles. The prepared pristine SnO2 nanoparticle is found to be of random shape by transmission electron microscope (TEM) studies. A structural and morphological study is carried out using X-ray diffraction and TEM techniques. The different phonon interaction in the system is observed by Raman spectroscopy while electron paramagnetic resonance and UV-Visible spectroscopy confirms the presence of Cu in 2+ state. First principle calculations have been performed using “density functional theory”-based MedeA Vienna Ab Initio Simulation package on a SnO2 system where Cu is introduced. The introduction of Cu in the SnO2 system brings distortion which is corroborated by the variation in the corresponding bond lengths. The Density of State calculation of Sn16O32 and CuSn15O32 is also performed. Finally, a correlation is established between the experiment and the theory.
8-channel acquisition system for time-correlated single-photon counting
Authors: Antonioli S. , Miari L. , Cuccato A. , Crotti M. , Rech I. , Ghioni M.
Published: June 2013

Nowadays, an increasing number of applications require high-performance analytical instruments capable to detect the temporal trend of weak and fast light signals with picosecond time resolution. The Time-Correlated Single-Photon Counting (TCSPC) technique is currently one of the preferable solutions when such critical optical signals have to be analyzed and it is fully exploited in biomedical and chemical research fields, as well as in security and space applications. Recent progress in the field of single-photon detector arrays is pushing research towards the development of high performance multichannel TCSPC systems, opening the way to modern time-resolved multi-dimensional optical analysis. In this paper we describe a new 8-channel high-performance TCSPC acquisition system, designed to be compact and versatile, to be used in modern TCSPC measurement setups. We designed a novel integrated circuit including a multichannel Time-to-Amplitude Converter with variable full-scale range, a D/A converter, and a parallel adder stage. The latter is used to adapt each converter output to the input dynamic range of a commercial 8-channel Analog-to-Digital Converter, while the integrated DAC implements the dithering technique with as small as possible area occupation. The use of this monolithic circuit made the design of a scalable system of very small dimensions (95 × 40 mm) and low power consumption (6 W) possible. Data acquired from the TCSPC measurement are digitally processed and stored inside an FPGA (Field-Programmable Gate Array), while a USB transceiver allows real-time transmission of up to eight TCSPC histograms to a remote PC. Eventually, the experimental results demonstrate that the acquisition system performs TCSPC measurements with high conversion rate (up to 5 MHz/channel), extremely low differential nonlinearity (<0.04 peak-to-peak of the time bin width), high time resolution (down to 20 ps Full-Width Half-Maximum), and very low crosstalk between channels.
Biaxial extensional motion of an inertially driven radially expanding liquid sheet
Authors: Smolka Linda B. , Witelski Thomas P.
Published: June 2013

We consider the inertially driven, time-dependent biaxial extensional motion of inviscid and viscous thinning liquid sheets. We present an analytic solution describing the base flow and examine its linear stability to varicose (symmetric) perturbations within the framework of a long-wave model where transient growth and long-time asymptotic stability are considered. The stability of the system is characterized in terms of the perturbation wavenumber, Weber number, and Reynolds number. We find that the isotropic nature of the base flow yields stability results that are identical for axisymmetric and general two-dimensional perturbations. Transient growth of short-wave perturbations at early to moderate times can have significant and lasting influence on the long-time sheet thickness. For finite Reynolds numbers, a radially expanding sheet is weakly unstable with bounded growth of all perturbations, whereas in the inviscid and Stokes flow limits sheets are unstable to perturbations in the short-wave limit.
Rayleigh and parametric thermo-vibrational instabilities in supercritical fluids under weightlessness
Authors: Gandikota G. , Amiroudine S. , Chatain D. , Lyubimova T. , Beysens D.
Published: June 2013

Under the absence of gravity forces, the interaction of vibration with a thermal boundary layer (TBL) can lead to a rich variety of dynamics in a supercritical fluid (SCF). When subjected to vibration, a SCF can display different kinds of instabilities for different relative directions of the TBL and vibration. Rayleigh vibrational instability is formed when the vibration direction is tangential to the TBL. When the direction of vibration is perpendicular to the TBL, instabilities of parametric nature can develop. Two-dimensional finite volume numerical analysis of supercritical H2 filled in a square cell under vibration is carried out. The vibrational amplitudes range from 0.05 to 5 times the side of the cell and frequencies vary between 2.78 Hz and 25 Hz. Three different thermal boundary conditions (isothermal walls, adiabatic vertical/isothermal horizontal walls, and adiabatic horizontal/isothermal vertical walls) have been considered with various temperature proximities to the critical point (10 mK, 100 mK, and 1 K). The results evidence Rayleigh vibrational and parametric instabilities in a thermal field. It is for the first time that the latter type of instability is observed in the thermal field under such conditions. Additionally, the role of the cell corners is highlighted (a “corner” instability is observed). These instabilities are analyzed and quantified. In particular, the stability domains have been plotted.
The B−3/2 diffusion in magnetized plasma
Authors: Hsu Jang-Yu , Wu KaiBang , Kumar Agarwal Sujeet , Ryu Chang-Mo
Published: June 2013

Fluid equations with transport effects have been derived from summing up discrete particle effects in the configuration space. The diffusion coefficient takes a form different from, but equivalent to, the Kubo formula. By taking into account the decoherence along the field lines, the diffusive damping in the perpendicular direction, and the finite Larmor radius effect in the cyclotron resonance, it is shown that the diffusion of magnetized 3d plasma has a regime of B−3/2 scaling which lies between the Bohm diffusion of B−1 and the classical diffusion of B−2.
Fluid management in roll-to-roll nanoimprint lithography
Authors: Jain A. , Bonnecaze R. T.
Published: June 2013

The key process parameters of UV roll-to-roll nanoimprint lithography are identified from an analysis of the fluid, curing, and peeling dynamics. The process includes merging of droplets of imprint material, curing of the imprint material from a viscous liquid to elastic solid resist, and pattern replication and detachment of the resist from template. The time and distances on the web or rigid substrate over which these processes occur are determined as function of the physical properties of the uncured liquid, the cured solid, and the roller configuration. The upper convected Maxwell equation is used to model the viscoelastic liquid and to calculate the force on the substrate and the torque on the roller. The available exposure time is found to be the rate limiting parameter and it is O(Rho/uo), where R is the radius of the roller, ho is minimum gap between the roller and web, and uo is the velocity of the web. The residual layer thickness of the resist should be larger than the gap between the roller and the substrate to ensure complete feature filling and optimal pattern replication. For lower residual layer thickness, the droplets may not merge to form a continuous film for pattern transfer.
Dislocation impact on resistive switching in single-crystal SrTiO3
Authors: Kamaladasa R. J. , Noman M. , Chen W. , Salvador P. A. , Bain J. A. , Skowronski M. , Picard Y. N.
Published: June 2013

Filamentary conduction via dislocations has been considered to be a mechanism driving resistive switching in SrTiO3 single-crystals. This possible mechanism is further investigated by fabricating Pt-SrTiO3-Pt lateral devices on high dislocation density areas as well as dislocation-free areas of single-crystal SrTiO3, and using electron channeling contrast imaging and dislocation-selective wet chemical etching to track pre-existing dislocations and dislocations nucleated during electrical biasing. Device size, compliance levels, and vacancy concentration were observed to impact dislocation formation. The susceptibility of SrTiO3 to dislocation formation and strategies to avoid it by reducing power dissipation are discussed. The presence of dislocations is found to have a negligible effect on the device resistive switching behavior. Dislocation-free resistive switching devices are demonstrated for reduced single-crystalline SrTiO3.
NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure
Authors: Młyńczak E. , Luches P. , Valeri S. , Korecki J.
Published: June 2013

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Mössbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using 57Fe-CEMS. An iron oxide phase (Fe3+4Fe2+1O7), as thick as 31 Å, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.
Chemical disorder effect on orthorhombic-rhombohedral structural transition in La0.7Ca0.3MnO3
Authors: Rozenberg E. , Mogilyansky D. , Mukovskii Ya. M. , Jung G. , Gorodetsky G.
Published: June 2013

High temperature X-ray powder diffraction technique was employed to study the orthorhombic to rhombohedral (O-R) structural transition (ST) in single crystal and ceramics of La0.7Ca0.3MnO3. The data obtained evidence that such ST in both samples occurs in the vicinity of temperature T ∼ 700 K and demonstrates O and R phases coexistence within the T-intervals of about 20 K in crystal and ∼60 K in ceramics. This first order transition is hysteretic on heating and cooling procedures and it is shifted on ΔT ∼ 10 K to higher temperatures in crystal as compared to the ceramics of the same composition. We have described these features in the terms of the difference between “technologically driven” chemical disorder characteristic for considered samples. Thus, it seems that spatial (up to the micron size scale) fluctuations of the Ca-dopant content in crystal and “mesoscopic scale disorder” within grain boundary regions in ceramics are responsible for both: above noted difference of ST parameters and reported earlier difference in magnetic ordering of these samples.
Enhanced ionized impurity scattering in nanowires
Authors: Oh Jung Hyun , Lee Seok-Hee , Shin Mincheol
Published: June 2013

The electronic resistivity in silicon nanowires is investigated by taking into account scattering as well as the donor deactivation from the dielectric mismatch. The effects of poorly screened dopant atoms from the dielectric mismatch and variable carrier density in nanowires are found to play a crucial role in determining the nanowire resistivity. Using Green's function method within the self-consistent Born approximation, it is shown that donor deactivation and ionized impurity scattering combined with the charged interface traps successfully to explain the increase in the resistivity of Si nanowires while reducing the radius, measured by Björk et al. [Nature Nanotech. 4, 103 (2009)].
Conduction mechanisms in doped mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films
Authors: Wienkes L. R. , Blackwell C. , Hutchinson T. , Kakalios J.
Published: June 2013

A detailed description of the microscopic nature of electronic conduction in mixed-phase silicon thin films near the amorphous/nanocrystalline transition is presented. A conduction model utilizing both the conductivity and the reduced activation energy data, involving the parallel contributions of three distinct conduction mechanisms, is shown to describe the data to a high accuracy, providing a clear link between measurement and theory in these complex materials.
Theoretical study on copper's energetics and magnetism in TiO2 polymorphs
Authors: Assadi M. Hussein. N. , Hanaor Dorian A. H.
Published: June 2013

Density functional theory calculations were employed to model the electronic structure and the magnetic interactions in copper doped anatase and rutile titanium dioxide in order to shed light on the potential of these systems as magnetic oxides using different density functional schemes. In both polymorphs, copper dopant was found to be most stable in substitutional lattice positions. Ferromagnetism is predicted to be stable well above room temperature with long range interactions prevailing in the anatase phase while the rutile phase exhibits only short range superexchange interaction among nearest-neighbour Cu ions. Additionally, energetic evaluation of dopants in scattered and compact configurations reveals a dopant clustering tendency in anatase TiO2.
Enhanced photocatalytic efficiency in zirconia buffered n-NiO/p-NiO single crystalline heterostructures by nanosecond laser treatment
Authors: Molaei R. , Bayati M. R. , Alipour H. M. , Nori S. , Narayan J.
Published: June 2013

We report the formation of NiO based single crystalline p-n junctions with enhanced photocatalytic activity induced by pulsed laser irradiation. The NiO epilayers were grown on Si(001) substrates buffered with cubic yttria-stabilized zirconia (c-YSZ) by using pulsed laser deposition. The NiO/c-YSZ/Si heterostructures were subsequently laser treated by 5 pulses of KrF excimer laser (pulse duration = 25 × 10−9 s) at lower energies. Microstructural studies, conducted by X-ray diffraction (θ-2θ and φ techniques) and high resolution transmission electron microscope, showed a cube-on-cube epitaxial relationship at the c-YSZ/Si interface; the epitaxial relationship across the NiO/c-YSZ interface was established as NiO⟨111 ⟩||c-YSZ⟨001⟩ and in-plane NiO⟨110⟩||c-YSZ⟨100⟩. Electron microscopy studies showed that the interface between the laser annealed and the pristine region as well as the NiO/c-YSZ interface was atomically sharp and crystallographically continuous. The formation of point defects, namely oxygen vacancies and NiO, due to the coupling of the laser photons with the NiO epilayers was confirmed by XPS. The p-type electrical characteristics of the pristine NiO epilayers turned to an n-type behavior and the electrical conductivity was increased by one order of magnitude after laser treatment. Photocatalytic activity of the pristine (p-NiO/c-YSZ/Si) and the laser-annealed (n-NiO/p-NiO/c-YSZ/Si) heterostructures were assessed by measuring the decomposition rate of 4-chlorophenol under UV light. The photocatalytic reaction rate constants were determined to be 0.0059 and 0.0092 min−1 for the as-deposited and the laser-treated samples, respectively. The enhanced photocatalytic efficiency was attributed to the suppressed charge carrier recombination in the NiO based p-n junctions and higher electrical conductivity. Besides, the oxygen vacancies ease the adsorption of 4-chlorophenol, hydroxyl, and water molecules to the surface. Thus, n-NiO/p-NiO single crystalline catalysts can be introduced as a potent candidate to remediate the environmental pollution.
Diffractive imaging route to sub-wavelength pixels
Authors: Inampudi Sandeep , Podolskiy Viktor A.
Published: June 2013

We propose optical imaging technique that relies on diffractive rather than refractive elements. Our approach takes advantage of metagratings, structures with engineered diffraction properties, and natural materials with sufficiently high refractive indices to achieve significant reduction in pixel size. In contrast to conventional refraction-based imaging, the developed approach essentially produces a digital hologram, a low-dimensional projection of the volumetric optical field. The perspectives of numerical recovery of the optical field and the stability of such recovery are discussed.
A metallic photonic crystal high power microwave mode converter
Authors: Wang Dong , Qin Fen , Xu Sha , Shi Meiyou
Published: June 2013

A compact metallic photonic crystal mode converter that converts TEM to TE11 mode for a high power transmission system is presented. Metallic photonic crystal is partially filled along azimuthal direction in the device to divide a single coaxial transmission line into two different partitions with different phase propagation constants for phase-shifting. A three row structure is designed and simulated by commercial software cst microwave studio. Simulation results show that it has high conversion efficiency and the bandwidth is 4.1%. Far-field measurement experiment is carried out and get a typical TE11 mode pattern. The result confirms the validity of the design.
Growth temperature dependent structural and magnetic properties of epitaxial Co2FeAl Heusler alloy films
Authors: Qiao Shuang , Nie Shuaihua , Zhao Jianhua , Zhang Xinhui
Published: June 2013

The structural and magnetic properties of a series of Co2FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co2FeAl films with an ordered L21 structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L21 structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.
Accurate determination of optical bandgap and lattice parameters of Zn1–xMgxO epitaxial films (≤x≤0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire
Authors: Laumer Bernhard , Schuster Fabian , Stutzmann Martin , Bergmaier Andreas , Dollinger Günther , Eickhoff Martin
Published: June 2013

Zn1–xMgxO epitaxial films with Mg concentrations 0≤x≤0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x≤0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.
Rate dependant heat generation in single cycle of domain switching of lead zirconate titanate via in-situ spontaneous temperature measurement
Authors: Chen Hao-Sen , Pei Yong-Mao , Liu Bin , Fang Dai-Ning
Published: June 2013

Cyclic electric loading induced heat in ferroelectric materials may affect their applications. In this letter, an in-situ non-contact and full-field experimental method was proposed to monitor temperature with a 50 Hz infrared thermal camera. Test results in one bipolar electric loading cycle showed that the heat generation occurs as soon as polarization reversal finishes and is on the order of 500 × 103 J/m3. Due to the competition between the rate-dependent domain switching and the heat convention, it is interesting to note that under some specific electric loadings, heat generation first slightly increases and then decreases with the frequency, and even approaches zero at 200 Hz.
Influence of magnetic field on the compressive behavior of carbon nanotube with magnetic nanoparticles
Authors: Reddy S. K. , Suri A. , Misra A.
Published: June 2013

Carbon nanotubes (CNT) in their cellular like micro-structure have presented an excellent mechanical energy absorption capacity. Although, several efforts have been progressed to modify the CNT structure for further enhancing their energy absorption capacity but yet no report has revealed the effect of magnetic field on the mechanical behavior of as-grown CNT mat that contains magnetic iron nanoparticles in the form of decorated nanoparticles on the surface or filled inside core of the CNT. We report a significant impact of the presence of magnetic content that modifies the mechanical behavior of the entangled CNT mat in the presence of an external magnetic field. The energy absorption capacity doubles when magnetic field was applied in the radial direction of the CNT mat under uniaxial compression.
Energy dependence of electron effective mass and effect of wave function confinement in a nanoscale In0.53Ga0.47As/In0.52Al0.48As quantum well
Authors: Kotera Nobuo
Published: June 2013

The effective mass in the conduction band was analyzed as a function of the kinetic energy in a 5–20 nm-thick In0.53Ga0.47As/In0.52Al0.48As quantum well (QW). An increase in the effective mass caused by wave function confinement in the QW, which was previously proposed theoretically, was not found to be present in this material under the framework of the energy effective mass. In the direction normal to the QW plane, the mass determined by the interband optical transition at 100-300 K fitted well with the calculated result based on Kane's bulk band theory. In a direction parallel to the QW plane, the cyclotron resonance energy at less than 70 T and the magneto photoluminescence energy at less than 13 T fitted with the calculated result to within an error range of ±2 meV. In the analysis of the magneto-photoluminescence at 1.4 K, the bandgap renormalization was determined and large new peaks appeared above 8 T, possibly because of the interaction of the magneto-exciton states with the ground-state zero-dimensional Landau level.
Tunneling magneto thermocurrent in CoFeB/MgO/CoFeB based magnetic tunnel junctions
Authors: Liebing N. , Serrano-Guisan S. , Krzysteczko P. , Rott K. , Reiss G. , Langer J. , Ocker B. , Schumacher H. W.
Published: June 2013

We study the tunneling magneto thermopower and tunneling magneto thermocurrent of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ). The devices show a clear change of the thermoelectric properties upon reversal of the magnetisation of the CoFeB layers from parallel to the antiparallel orientation. When switching from parallel to antiparallel the thermopower increases by up to 55% whereas the thermocurrent drops by 45%. These observations can be well explained by the Onsager relations taking into account the tunneling magneto resistance of the MTJ. These findings contrast previous studies on Al2O3 based MTJ systems, revealing tunneling magneto thermo power but no tunneling magneto thermocurrent.
High–speed imaging of a bulk metallic glass during uniaxial compression
Authors: Wright Wendelin J. , Byer Rachel R. , Gu Xiaojun
Published: June 2013

High–speed imaging directly correlates the propagation of a particular shear band with mechanical measurements during uniaxial compression of a bulk metallic glass. Imaging shows shear occurs simultaneously over the entire shear plane, and load data, synchronized and time–stamped to the same clock as the camera, reveal that shear sliding is coincident with the load drop of each serration. Digital image correlation agrees with these results. These data demonstrate that shear band sliding occurs with velocities on the order of millimeters per second. Fracture occurs much more rapidly than the shear banding events, thereby readily leading to melting on fracture surfaces.
Suppression of Walker breakdown in magnetic domain wall propagation through structural control of spin wave emission
Authors: Burn David M. , Atkinson Del
Published: June 2013

The control of individual magnetic domain walls has potential for future spintronic memory and data processing applications. The speed and reliability of such devices are determined by the dynamic properties of the domain walls. Typically, spin precession limitations lead to Walker breakdown, limiting wall velocity resulting in low mobility. Here, we show the suppression of Walker breakdown by the careful design of small amplitude periodic nanowire structuring to match the periodicity of domain wall spin structure transformations. This opens up a channel for energy dissipation via spin wave emission, allowing a domain wall to maintain its spin structure during propagation.
Delayed freezing of water droplet on silver nanocolumnar thin film
Authors: Singh Dhruv P. , Singh Jitendra P.
Published: June 2013

Silver nanocolumns were grown on Si substrate using glancing angle deposition method. Interestingly, the cold nanocolumnar surface was observed to make a delay of more than 62 s in freezing compared to the conventional silver thin film. The observed delay in freezing on silver nanocolumns is explainable in terms of reduction in effective liquid-solid interface area within the framework of Cassie-Baxter model. This study shows the possibility of using silver nanocolumnar films in ice free coatings and surfaces with tunable freezing properties.
Third-order nonlinear optical response of CuInS2 quantum dots—Bright probes for near-infrared biodetection
Authors: Cichy B. , Wawrzynczyk D. , Bednarkiewicz A. , Samoc M. , Strek W.
Published: June 2013

Nonlinear refraction and nonlinear absorption in stoichiometric colloidal CuInS2 quantum dots, with absorption edge tuned up to the visible spectral region, were investigated. The nonlinear optical response of the quantum dots was measured in a wide range of wavelengths (700–1600 nm) using the Z-scan technique. The measurements revealed the presence of two-photon absorption in the near-infrared range and the negative nonlinear refraction in almost whole spectral range for all the investigated nanoparticles. The cubic nonlinearity of CuInS2 quantum dots is discussed in terms of defect-related optical properties of the material. The results indicate that CuInS2 quantum dots may be an interesting material for the single and multiphoton luminescence bio-detection techniques.
The effect of aqueous ammonia soaking on enzymatic hydrolysis of wheat straw
Authors: Yazici Sonnur , Isci Asli
Published: June 2013

Enzymatic hydrolysis of wheat straw was performed following aqueous-ammonia soaking. The effects of various operating variables including pretreatment temperature (30, 50, and 70 °C), pretreatment time (15, 30, and 45 h), and ammonia concentration (10% and 30%) on the enzymatic digestibility were investigated. Enzymatic hydrolysis were performed at 5% (w/w) solid loading, 50 °C, and 150 rpm for 96 h, using Accellerase 1500 (30 FPU/g dry biomass). The best reaction conditions observed (50 °C, 45 h, and 30% ammonia) resulted in enzymatic hydrolysis yields of 76% for glucose and 81% for xylose. Total reducing sugars released during hydrolysis experiments were also determined. As the severity of the pretreatment was increased, higher reducing sugar release was observed. It was also found that total reducing sugars vary exponentially with the reciprocal of the pretreatment temperature. An empirical model was developed, which relates reducing sugar concentrations to pretreatment time and temperature.
Response surface methodology based prediction of engine performance and exhaust emissions of a diesel engine fuelled with canola oil methyl ester
Authors: Ileri Erol , Karaoglan Aslan Deniz , Atmanli Alpaslan
Published: June 2013

The objective of this study was to investigate the effect of fuel injection timing and engine speed on engine performance and exhaust emission parameters using a diesel engine running on canola oil methyl ester (COME). COME was produced by means of the transesterification method and tested at full load with various engine speeds by changing fuel injection timing (12, 15, and 18 °CA) in a turbocharged direct injection (TDI) diesel engine. The experiments were designed using response surface methodology (RSM), which is one of the well-known design of experiment technique for predicting the responses engine performance and exhaust emission parameters from a second order polynomial equation obtained by modeling the relation between fuel injection timing (t) and engine speed (n) parameters. By using the second order full quadratic RSM models obtained from experimental results, responses brake power, brake torque, brake mean effective pressure, brake specific fuel consumption, brake thermal efficiency, exhaust gas temperature, oxygen (O2), oxides of nitrogen (NOx), carbon dioxide (CO2), carbon monoxide (CO), and light absorption coefficient (K) affected from factors t and n were able to be predicted by 95% confidence interval.
Experimental investigation of a “throatless” downdraft gasifier with palm kernel shell
Authors: Kuhe A. , Iortyer H. A. , Kucha E. I.
Published: June 2013

In the present study, a downdraft biomass gasifier is used to carry out the gasification experiments with palm kernel shells (PKS). The effect of air flow rate on biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the biomass gasifier system is evaluated in terms of equivalence ratio, producer gas composition, lower heating value (LHV), and cold gas efficiency. At an airflow rate of 0.0009 m3/s−1, the producer gas has a combustible fraction of 46.58% v/v. and LHV of 6.32 MJ m−3. From the results obtained, in view of ease of operation, a small-scale throatless downdraft gasifier can make an important contribution to the economy of rural areas where PKS are abundant. It is also suggested that gasification of PKS is a clean alternative to fuel wood and the producer gas can be used for local process heat in the Agro-processing sector.
High efficiency hybrid solid state blended dyes sensitized solar cell based on zinc oxide nanostructures
Authors: Singh R. G. , Gautam Naina , Gautam Subodh K. , Kumar Vinod , Kapoor A. , Singh Fouran
Published: June 2013

This paper reports on the development of high efficiency hybrid solid state blended dye sensitized solar cell (HssBDSSC) using ultrasonification process. Cell synthesized using conducting organic polymer as organic hole-transporting material together with BDs, while Poly (3-Octylthiopehene) (P3OT) and zinc oxide nanostructures (ns-ZnO) as electron-transporting material. BD is made in a composition, so that it can absorbed light in the entire visible region and provided the high electron injection. The HssBDSSC device structure such as indium tin oxide (ITO)/PEDOT:PSS/ns-ZnO+P3OT/BDs/Electrode is developed and an ultrathin layer of PEDOT:PSS is deposited on ITO for making Schottky contact. Device shows a very high conversion efficiency of 4.67%, Fill Factor (FF) 52.9%, open-circuit photo voltages 0.58 V and short-circuit photocurrents 15.1 mA/cm2 under 100 mW/cm2 visible band illumination. We propose an energy level alignment diagram to understand the photophysics of hybrid nanocomposites, which include charge carriers generation, separation, and transfer processes.
Electronic structure of Ce3+ multicenters in yttrium aluminum garnets
Authors: Przybylińska H. , Ma Chong-Geng , Brik M. G. , Kamińska A. , Sybilski P. , Wittlin A. , Berkowski M. , Zorenko Yu. , Gorbenko V. , Wrzesinski H. , Suchocki A.
Published: June 2013

Low temperature, infrared, and visible-ultraviolet absorption spectra of yttrium aluminum garnet (YAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f–4f transitions, the spectra of the bulk YAG crystals exhibit existence of at least two different Ce3+ related centers, a major one associated with Ce in regular positions substituting yttrium and also additional center, due to so called antisite positions in the garnet host, i.e., ions in the Al positions. Crystal field analysis based on exchange charge model exhibit excellent agreement with the experimental data for major Ce3+ center.
On the asymptotic balance between electric and magnetic energies for hydromagnetic relativistic flows
Authors: Núñez Manuel
Published: June 2013

In the equations of classical magnetohydrodynamics, the displacement current is considered vanishingly small due to low plasma velocities. For velocities comparable to the speed of light, the full relativistic electromagnetic equations must be used. In the absence of gravitational forcings and with an isotropic Ohm's law, it is proved that for poloidal magnetic field and velocity and toroidal electric field, the electric and magnetic energies tend to be equivalent in average for large times. This represents a partial extension of Cowling's theorem for axisymmetric fields.
282-nm AlGaN-based deep ultraviolet light-emitting diodes with improved performance on nano-patterned sapphire substrates
Authors: Dong Peng , Yan Jianchang , Wang Junxi , Zhang Yun , Geng Chong , Wei Tongbo , Cong Peipei , Zhang Yiyun , Zeng Jianping , Tian Yingdong , Sun Lili , Yan Qingfeng , Li Jinmin , Fan Shunfei , Qin Zhixin
Published: June 2013

We first report AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) grown on nano-patterned sapphire substrates (NPSS) prepared through a nanosphere lithography technique. The AlN coalescence thickness on NPSS is only 3 μm due to AlN's nano-scaled lateral growth, which also leads to low dislocation densities in AlN and epi-layers above. On NPSS, the light-output power of a 282-nm UV-LED reaches 3.03 mW at 20 mA with external quantum efficiency of 3.45%, exhibiting 98% better performance than that on flat sapphire. Temperature-dependent photoluminescence reveals this significant enhancement to be a combination of higher internal quantum efficiency and higher light extraction efficiency.
Interaction of two plasmon modes in the organic photovoltaic devices with patterned back-electrode
Authors: Lu D. , Rengnath E. , Cui Y. , Wang Z. , Ding Y. , Park W.
Published: June 2013

We designed and fabricated silver grating structures on the back-electrodes of organic photovoltaic (OPV) devices to achieve absorption enhancement. The observed enhancement is attributed to several effects, including scattering through corrugated grating surface and surface plasmon modes generated by periodic plasmonic structure. Two plasmon modes are identified in our structure: localized surface plasmon (LSP) and surface plasmon polariton (SPP) modes. The former exists near the absorption edge of the active material and extends the absorption band while the latter provides an absorption pathway in the sub-gap region. Also, LSP is insensitive to active layer thickness and grating period, while the SPP which is excited whenever the momentum matching condition is satisfied shows strong dependence on active layer thickness and grating period. The two modes also exhibit strong interaction as indicated by anti-crossing behavior and thus the interplay between the two modes must be considered for back-electrode design.
Magnetic properties of gadolinium substituted Bi2Te3 thin films
Authors: Li S. , Harrison S. E. , Huo Y. , Pushp A. , Yuan H. T. , Zhou B. , Kellock A. J. , Parkin S. S. P. , Chen Y.-L. , Hesjedal T. , Harris J. S.
Published: June 2013

Thin film GdBiTe3 has been proposed as a candidate material in which to observe the quantum anomalous Hall effect. As a thermal non-equilibrium deposition method, molecular beam epitaxy (MBE) has the ability to incorporate large amounts of Gd into Bi2Te3 crystal structures. High-quality rhombohedral (GdxBi1−x)2Te3 films with substitutional Gd concentrations of x ≤ 0.4 were grown by MBE. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact up to the highest Gd concentration. Magnetoresistance measurements show weak antilocalization, indicating strong spin orbit interaction. Magnetometry reveals that the films are paramagnetic with a magnetic moment of 6.93 μB per Gd3+ ion.
Population dynamics in epitaxial Er2O3 thin films grown on Si(111)
Authors: Tawara T. , Omi H. , Hozumi T. , Kaji R. , Adachi S. , Gotoh H. , Sogawa T.
Published: June 2013

We grow single crystal erbium-oxide (Er2O3) epitaxially on a Si (111) substrate by using molecular beam epitaxy and investigate the population dynamics in Er3+ ions for the coherent manipulation of the population in Er2O3. Sharp and discrete Stark energy levels of the 4I13/2 manifold as small as 200 μeV are observed with inhomogeneous broadening caused by the uniform crystal field of the epitaxial Er2O3. We also experimentally determine the time constant of the resonant population transfer between spatially distant Er3+-ion sites, which is limited to the manipulation time of the population in the Er2O3 crystals. Using selective excitation of the Stark level in the 4I13/2 manifold, we obtain the energy transfer times between spatially distant Er3+ ions, and they are about 2 μs between sites whose crystallographic symmetry is different and 10 μs between sites whose symmetry is the same.
Angular velocity response of nanoparticles dispersed in liquid crystal
Authors: Huang Pin-Chun , Shih Wen-Pin
Published: June 2013

A hybrid material of nanoparticles dispersed in liquid crystal changed capacitance after spinning beyond threshold angular velocity. Once the centrifugal force of nanoparticles overcomes the attractive force between liquid crystals, the nanoparticles begin to move. The order of highly viscous liquid crystals is disturbed by the nanoparticles' penetrative movement, and the dielectric constant of the liquid crystal cell changes as a result. We found that the angular velocity response of nanoparticles dispersed in liquid crystal with higher working temperature and nanoparticles' density provided higher sensitivity. The obtained results are important for the continuous improvement of liquid-crystal-based inertial sensors or nano-viscometers.
Predator threat assessment in Daphnia magna: the role of kairomones versus conspecific alarm cues
Authors: Pestana J. L. T. , Baird D. J. , Soares A. M. V. M.
Published: June 2013

Studying the finely tuned mechanism of predation risk assessment allows for a better understanding of how prey organisms make key decisions under different levels of predation pressure. We studied the relative importance of conspecific alarm cues and fish kairomones as initiators of D. magna antipredator defences. By exposing a clone of D. magna to different infochemicals that simulated the presence of an active fish predator, we observed cue-specific responses in terms of altered feeding behaviour, respiration and life-history traits. Results agreed with the hypothesis that D. magna processes information from alarm cues from macerated conspecifics and from predator kairomones to assess the level of predation risk, adjusting the magnitude of their responses to the different levels of threat perceived. Results support the findings of other investigations and further show that single cues (fish kairomones or alarm cues) triggered feeding reduction and increased oxygen consumption, whereas fish kairomones only elicited D. magna life-history responses. Prey-specific alarm cues can thus modify the response of Daphnia to trout kairomones and this combination of both chemical cues appears to be necessary to trigger the full deployment of antipredator responses and avoid unnecessary costs arising from maladaptive responses.
Juvenile Coho Salmon in the Elwha River Estuary Prior to Dam Removal: Seasonal Occupancy, Size Distribution, and Comparison to Nearby Salt Creek
Authors: Quinn Thomas P. , Harris Nicole , Anne Shaffer J. , Byrnes Chris , Crain Patrick
Published: June 2013

In addition to the downstream migration of smolts in spring, Coho Salmon Oncorhynchus kisutch also enter estuaries throughout the year but especially in the spring as fry and in the fall as parr. The removal of two large dams on the Elwha River, Washington, has increased the area accessible to salmon and is affecting many aspects of the system. For comparison with the postdam period, when the Elwha River estuary will likely expand in size and complexity, monthly sampling was conducted in the estuary during 2007–2011 to determine patterns of Coho Salmon presence and size prior to dam removal; Salt Creek, a nearby undammed stream, was also sampled to allow comparison of fish size and seasonal timing patterns. The spring smolt migration in the Elwha River included a large fraction of unmarked fish (primarily of natural origin) as well as marked fish from the Lower Elwha Klallam Tribe Fish Hatchery. Subyearlings entered both estuaries during much of the year, exhibiting a peak in September. Coho Salmon from the Elwha River (including wild and hatchery‐origin fish) were larger and more heavily represented in the fall relative to the spring smolt migration compared to those from Salt Creek. Future patterns in the Elwha River may include reduced presmolt use of the estuary if the center of distribution is farther upriver, but improved estuarine habitat may make it more suitable for presmolts.
Is U.S. Agricultural Productivity Growth Slowing?
Authors: Ball Eldon , Schimmelpfennig David , Wang Sun Ling
Published: June 2013

This paper uses statistics on agricultural productivity compiled by the U.S. Department of Agriculture's Economic Research Service to test the productivity slowdown hypothesis. The indexes of productivity growth span the years 1948 to 2009. In our analysis, we apply econometric techniques that allow for multiple structural breaks at unknown points in time and in various forms. The tests identify a break in trend in 1974 and an intercept shift in 1985. These results point to slower productivity growth in agriculture beginning in 1974. Prior to 1974, productivity grew at an annual rate of 1.71%, but this slowed to 1.56% after 1974. This slower rate of productivity growth persisted after the intercept shift in 1985 but from a higher absolute level of productivity.