bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat generation by electronic current in a quantum dot spin-valve
Authors: Chi Feng , Sun Lian-Liang , Guo Yu
Published: October 2014

Electric-current-induced heat generation in an interacting single-level quantum dot connected to ferromagnetic leads with noncollinear magnetizations is theoretically investigated. We find that when the two leads' spin polarization rates are identical and much smaller than unit, the magnitude of the heat generation is almost monotonously enhanced as the angle between the leads' magnetic moments is varied from zero to π, while the magnitude of the electric current is continuously suppressed. Moreover, the properties of the heat generation depend on the lead's spin polarization rate in different ways when the angle is varied. If at least one of the leads' spin polarization rate approaches to unit, the spin-valve effect of the heat generation is identical to that of the electric current. Now the previously found negative differential of the heat generation disappears when the angle approaches to π. As compared to the current, the heat generation is more sensitive to the system's asymmetry when one of the electrodes is half-metallic in noncollinear configurations.
Proposal for efficient mode converter based on cavity quantum electrodynamics dark mode in a semiconductor quantum dot coupled to a bimodal microcavity
Authors: Li Jiahua , Yu Rong , Ma Jinyong , Wu Ying
Published: October 2014

The ability to engineer and convert photons between different modes in a solid-state approach has extensive technological implications not only for classical communication systems but also for future quantum networks. In this paper, we put forward a scheme for coherent mode conversion of optical photons by utilizing the intermediate coupling between a single quantum dot and a bimodal photonic crystal microcavity via a waveguide. Here, one mode of the photonic crystal microcavity is coherently driven by an external single-frequency continuous-wave laser field and the two cavity modes are not coupled to each other due to their orthogonal polarizations. The undriven cavity mode is thus not directly coupled to the input driving laser and the only way it can get light is via the quantum dot. The influences of the system parameters on the photon-conversion efficiency are analyzed in detail in the limit of weak probe field and it is found that high photon-conversion efficiency can be achieved under appropriate conditions. It is shown that the cavity dark mode, which is a superposition of the two optical modes and is decoupled from the quantum dot, can appear in such a hybrid optical system. We discuss the properties of the dark mode and indicate that the formation of the dark mode enables the efficient transfer of optical fields between the two cavity modes.
Full-dispersion Monte Carlo simulation of phonon transport in micron-sized graphene nanoribbons
Authors: Mei S. , Maurer L. N. , Aksamija Z. , Knezevic I.
Published: October 2014

We simulate phonon transport in suspended graphene nanoribbons (GNRs) with real-space edges and experimentally relevant widths and lengths (from submicron to hundreds of microns). The full-dispersion phonon Monte Carlo simulation technique, which we describe in detail, involves a stochastic solution to the phonon Boltzmann transport equation with the relevant scattering mechanisms (edge, three-phonon, isotope, and grain boundary scattering) while accounting for the dispersion of all three acoustic phonon branches, calculated from the fourth-nearest-neighbor dynamical matrix. We accurately reproduce the results of several experimental measurements on pure and isotopically modified samples [S. Chen et al., ACS Nano 5, 321 (2011);S. Chen et al., Nature Mater. 11, 203 (2012); X. Xu et al., Nat. Commun. 5, 3689 (2014)]. We capture the ballistic-to-diffusive crossover in wide GNRs: room-temperature thermal conductivity increases with increasing length up to roughly 100 μm, where it saturates at a value of 5800 W/m K. This finding indicates that most experiments are carried out in the quasiballistic rather than the diffusive regime, and we calculate the diffusive upper-limit thermal conductivities up to 600 K. Furthermore, we demonstrate that calculations with isotropic dispersions overestimate the GNR thermal conductivity. Zigzag GNRs have higher thermal conductivity than same-size armchair GNRs, in agreement with atomistic calculations.
Observation of localized heating phenomena during microwave heating of mixed powders using in situ x-ray diffraction technique
Authors: Sabelström N. , Hayashi M. , Watanabe T. , Nagata K.
Published: October 2014

In materials processing research using microwave heating, there have been several observations of various phenomena occurring known as microwave effects. One significant example of such a phenomenon is increased reaction kinetics. It is believed that there is a possibility that this might be caused by localized heating, were some reactants would attain a higher than apparent temperature. To examine whether such thermal gradients are indeed possible, mixed powders of two microwave non-absorbers, alumina and magnesia, were mixed with graphite, a known absorber, and heated in a microwave furnace. During microwave irradiation, the local temperatures of the respective sample constituents were measured using an in situ x-ray diffraction technique. In the case of the alumina and graphite sample, a temperature difference of around 100 °C could be observed.
Origin of graphitic filaments on improving the electron field emission properties of negative bias-enhanced grown ultrananocrystalline diamond films in CH4/Ar plasma
Authors: Sankaran K. J. , Huang B. R. , Saravanan A. , Tai N. H. , Lin I. N.
Published: October 2014

Microstructural evolution of bias-enhanced grown (BEG) ultrananocrystalline diamond (UNCD) films has been investigated using microwave plasma enhanced chemical vapor deposition in gas mixtures of CH4 and Ar under different negative bias voltages ranging from −50 to −200 V. Scanning electron microscopy and Raman spectroscopy were used to characterize the morphology, growth rate, and chemical bonding of the synthesized films. Transmission electron microscopic investigation reveals that the application of bias voltage induced the formation of the nanographitic filaments in the grain boundaries of the films, in addition to the reduction of the size of diamond grains to ultra-nanosized granular structured grains. For BEG-UNCD films under −200 V, the electron field emission (EFE) process can be turned on at a field as small as 4.08 V/μm, attaining a EFE current density as large as 3.19 mA/cm2 at an applied field of 8.64 V/μm. But the films grown without bias (0 V) have mostly amorphous carbon phases in the grain boundaries, possessing poorer EFE than those of the films grown using bias. Consequently, the induction of nanographitic filaments in grain boundaries of UNCD films grown in CH4/Ar plasma due to large applied bias voltage of −200 V is the prime factor, which possibly forms interconnected paths for facilitating the transport of electrons that markedly enhance the EFE properties.
Oxygen-vacancy-induced room-temperature magnetization in lamellar V2O5 thin films
Authors: Cezar A. B. , Graff I. L. , Varalda J. , Schreiner W. H. , Mosca D. H.
Published: October 2014

In this work, we study the local atomic and electronic structures as well as oxygen-vacancy-induced magnetic properties of electrodeposited V2O5 films. Unlike stoichiometric V2O5, which is a diamagnetic lamellar semiconductor, our oxygen-defective V2O5 films are ferromagnetic at room-temperature and their saturation magnetization decreases with air exposure time. X-ray absorption spectroscopy was used to monitor the aging effect on these films, revealing that freshly-made samples exhibit only local crystalline order, whereas the aged ones undoubtedly show an enhancement of crystallinity and coordination symmetry. The mean number of oxygen atoms around V tends to increase, indicating a decrease of oxygen vacancies with time. Concurrently with the decrease of oxygen vacancies, a loss of saturation magnetization is also observed. Hence, it can be concluded that the ferromagnetism of the V2O5 films originates from a vacancy-induced mechanism, confirming the universality of this class of ferromagnetism.
Probing the limits of Si:P δ-doped devices patterned by a scanning tunneling microscope in a field-emission mode
Authors: Rudolph M. , Carr S. M. , Subramania G. , Ten Eyck G. , Dominguez J. , Pluym T. , Lilly M. P. , Carroll M. S. , Bussmann E.
Published: October 2014

Recently, a single atom transistor was deterministically fabricated using phosphorus in Si by H-desorption lithography with a scanning tunneling microscope (STM). This milestone in precision, achieved by operating the STM in the conventional tunneling mode, typically utilizes slow (∼102 nm2/s) patterning speeds. By contrast, using the STM in a high-voltage (>10 V) field-emission mode, patterning speeds can be increased by orders of magnitude to ≳104 nm2/s. We show that the rapid patterning negligibly affects the functionality of relatively large micron-sized features, which act as contacting pads for these devices. For nanoscale structures, we show that the resulting electrical transport is consistent with the donor incorporation chemistry constraining the electrical dimensions to a scale of 10 nm even though the pattering spot size is 40 nm.
The mean flow and long waves induced by two-dimensional internal gravity wavepackets
Authors: van den Bremer T. S. , Sutherland B. R.
Published: October 2014

Through theory supported by numerical simulations, we examine the induced local and long range response flows resulting from the momentum flux divergence associated with with a two-dimensional Boussinesq internal gravity wavepacket in a uniformly stratified ambient. Our theoretical approach performs a perturbation analysis that takes advantage of the separation of scales between waves and the amplitude envelope of a quasi-monochromatic wavepacket. We first illustrate our approach by applying it to the well-studied case of deep water surface gravity waves, showing that the induced flow, UDF, resulting from the divergence of the horizontal momentum flux is equal to the Stokes drift. For a localized surface wavepacket, UDF is itself a divergent flow and so there is the well-known non-local response manifest in the form of a deep return flow beneath the wavepacket. For horizontally periodic and vertically localized internal wavepackets, the divergent-flux induced flow, uDF, is found from consideration of the vertical gradient of the vertical flux of horizontal momentum associated with the waves. Because uDF is itself a non-divergent flow field, this accounts entirely for the wave-induced flow; there is no response flow. Our focus is upon internal wavepackets that are localized in the horizontal and vertical. We derive a formula for the divergent-flux induced flow that, as in this case of surface wavepackets, is itself a divergent flow. We show that the response is a horizontally long internal wave that translates vertically with the wavepacket at its group velocity. Scaling relationships are used to estimate the wavenumber, horizontal extent, and amplitude of this induced long wave. At higher order in perturbation theory we derive an explicit integral formula for the induced long wave. Thus, we provide validation of Bretherton's analysis of flows induced by two-dimensional internal wavepackets [F. P. Bretherton, “On the mean motion induced by gravity waves,” J. Fluid Mech. 36, 785–803 (1969)] and we provide further analyses that give intuitive insights into the physics governing the properties of the induced long wave. In particular, consistent with momentum conservation, we show that the horizontally-integrated horizontal flow associated with the long wave is given exactly by the horizontal integral of uDF. However, qualitatively different from horizontally periodic internal waves, the vertical profile of the induced horizontal flow across the horizontally localized wavepacket is positive at the leading edge and negative at the trailing edge. These results are validated by the results of numerical simulations of a Gaussian wavepacket initialized in an otherwise stationary ambient.
Single crystal diamond for infrared sensing applications
Authors: Majdi S. , Kolahdouz M. , Moeen M. , Kovi K. K. , Balmer R. S. , Radamson H. H. , Isberg J.
Published: October 2014

The synthesis of new materials for thermal infrared (IR) detection has been an intensive research area in recent years. Among new semiconductor materials, synthetic diamond has the ability to function even under very high temperature and high radiation conditions. In the present work, diamond Schottky diodes with boron concentrations in the range of 1014 < B < 1017 cm−3 are presented as candidates for IR thermal sensors with an excellent temperature coefficient of resistance (−8.42%/K) and very low noise levels around 6.6 × 10−15 V2/Hz. This enables huge performance enhancements for a wide variety of systems, e.g., automotive and space applications.
Metal–organic framework thin films with well-controlled growth directions confirmed by x-ray study
Authors: Otsubo Kazuya , Kitagawa Hiroshi
Published: October 2014

Metal–organic frameworks (MOFs) have attracted the attention of a variety of researchers because of their structural diversity and designability, and their varied physical properties based on their uniform microporosity. While MOFs are interesting as bulk materials, future applications in functional nanomaterials will require the use of MOFs as thin films, and to achieve this, several thin-film fabrication techniques have been developed. These techniques have provided rational design of a variety of MOF thin films; however, oriented crystal growth of a MOF thin film, which is mainly confirmed by X-ray diffraction, remains a challenge that should be addressed. In this article, we review thin-film fabrications and characterizations, and structural features of MOF thin films with perfect crystalline orientation.
Systematic prediction of high-pressure melting curves of transition metals
Authors: Hieu Ho Khac
Published: October 2014

The pressure effects on melting temperatures of transition metals have been studied based on the combination of the modified Lindemann criterion with statistical moment method in quantum statistical mechanics. Numerical calculations have been performed for five transition metals including Cu, Pd, Pt, Ni, and Mn up to pressure 100 GPa. Our results are in good and reasonable agreements with available experimental data. This approach gives us a relatively simple method for qualitatively calculating high-pressure melting temperature. Moreover, it can be used to verify future experimental and theoretical works. This research proposes the potential of the combination of statistical moment method and the modified Lindemann criterion on predicting high-pressure melting of materials.
Programmed sample delivery on a pressurized paper
Authors: Shin Joong Ho , Park Juhwan , Kim Seung Hoon , Park Je-Kyun
Published: October 2014

This paper reports a method to control the fluid flow in paper-based microfluidic devices simply by pressing over the channel surface of paper, thereby decreasing the pore size and permeability of a non-woven polypropylene sheet. As a result, fluid resistance is increased in the pressed region and causes flow rate to decrease. We characterize the decrease of flow rate with respect to different amounts of pressure applied, and up to 740% decrease in flow velocity was achieved. In addition, we demonstrate flow rate control in a Y-shaped merging paper and sequential delivery of multiple color dyes in a three-branched paper. Furthermore, sequential delivery of multiple fluid samples is performed to demonstrate its application in multi-step colorimetric immunoassay, which shows a 4.3-fold signal increase via enhancement step.
Microfluidic reactors for visible-light photocatalytic water purification assisted with thermolysis
Authors: Wang Ning , Tan Furui , Wan Li , Wu Mengchun , Zhang Xuming
Published: October 2014

Photocatalytic water purification using visible light is under intense research in the hope to use sunlight efficiently, but the conventional bulk reactors are slow and complicated. This paper presents an integrated microfluidic planar reactor for visible-light photocatalysis with the merits of fine flow control, short reaction time, small sample volume, and long photocatalyst durability. One additional feature is that it enables one to use both the light and the heat energy of the light source simultaneously. The reactor consists of a BiVO4-coated glass as the substrate, a blank glass slide as the cover, and a UV-curable adhesive layer as the spacer and sealant. A blue light emitting diode panel (footprint 10 mm × 10 mm) is mounted on the microreactor to provide uniform irradiation over the whole reactor chamber, ensuring optimal utilization of the photons and easy adjustments of the light intensity and the reaction temperature. This microreactor may provide a versatile platform for studying the photocatalysis under combined conditions such as different temperatures, different light intensities, and different flow rates. Moreover, the microreactor demonstrates significant photodegradation with a reaction time of about 10 s, much shorter than typically a few hours using the bulk reactors, showing its potential as a rapid kit for characterization of photocatalyst performance.
Nanoscale dynamics and aging of fibrous peptide-based gels
Authors: Dudukovic Nikola A. , Zukoski Charles F.
Published: October 2014

Solutions of the aromatic dipeptide derivative molecule fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) in dimethyl sulfoxide produce fibrous gels when mixed with water. We study the evolution of density fluctuations of this three-component system using X-ray photon correlation spectroscopy (XPCS) and compare these results to the macroscopic rheology of the gels and optical observations of the microstructure evolution. At the investigated scattering angles, the intensity autocorrelation functions do not follow behavior expected for simple diffusion of individual Fmoc-FF molecules localized within cages of nearest neighbors. Instead, the dynamics are associated with density fluctuations on length scales of ∼10–100 nm arising from disaggregation and reformation of fibers, leading to an increasingly uniform network. This process is correlated with the growth of the elastic modulus, which saturates at long times. Autocorrelation functions and relaxation times acquired from XPCS measurements are consistent with relaxation rates of structures at dynamic equilibrium. This study provides further support to the concept of exploring peptide-based gelators as valence-limited patchy particles capable of forming equilibrium gels.
A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults
Authors: Piluso N. , Camarda M. , La Via F.
Published: October 2014

A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n < 1016 at/cm−3), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phonon-plasmon-coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LO phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to determine the spatial morphology of stacking faults; the obtained morphologies were found to be in excellent agreement with those provided by standard photoluminescence techniques. The results show that the detection of defects via i-LOPC spectroscopy is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0.7 eV, thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Combining the i-LOPC method with the analysis of the transverse optical mode, the micro-Raman characterization can determine the most important properties of unintentionally doped film, including the stress status of the wafer, lattice impurities (point defects, polytype inclusions) and a detailed analysis of crystallographic defects, with a high spectral and spatial resolution.
Parallel heat flux and flow acceleration in open field line plasmas with magnetic trapping
Authors: Guo Zehua , Tang Xian-Zhu , McDevitt Chris
Published: October 2014

The magnetic field strength modulation in a tokamak scrape-off layer (SOL) provides both flux expansion next to the divertor plates and magnetic trapping in a large portion of the SOL. Previously, we have focused on a flux expander with long mean-free-path, motivated by the high temperature and low density edge anticipated for an absorbing boundary enabled by liquid lithium surfaces. Here, the effects of magnetic trapping and a marginal collisionality on parallel heat flux and parallel flow acceleration are examined. The various transport mechanisms are captured by kinetic simulations in a simple but representative mirror-expander geometry. The observed parallel flow acceleration is interpreted and elucidated with a modified Chew-Goldberger-Low model that retains temperature anisotropy and finite collisionality.
Simulation of phosphorene Schottky-barrier transistors
Authors: Wan Runlai , Cao Xi , Guo Jing
Published: October 2014

Schottky barrier field-effect transistors (SBFETs) based on few and mono layer phosphorene are simulated by the non-equilibrium Green's function formalism. It is shown that scaling down the gate oxide thickness results in pronounced ambipolar I-V characteristics and significant increase of the minimal leakage current. The problem of leakage is especially severe when the gate insulator is thin and the number of layer is large, but can be effectively suppressed by reducing phosphorene to mono or bilayer. Different from two-dimensional graphene and layered dichalcogenide materials, both the ON-current of the phosphorene SBFETs and the metal-semiconductor contact resistance between metal and phosphorene strongly depend on the transport crystalline direction.
LiFe2Cln (n = 4–6) clusters: Double-exchange mediated molecular magnets
Authors: Pradhan Kalpataru , Jena Purusottam
Published: October 2014

A systematic study of LiFe2Cln (n = 4–6) clusters, based on gradient corrected density functional theory (DFT), shows that the electron contributed by Li can transform antiferromagnetic Fe2Cln (n = 4 and 6) clusters into ferromagnetic clusters. In Fe2Cl6 (Fe2Cl4) cluster, the Fe atoms in +3 (+2) oxidation states are aligned antiferromagnetically, consistent with the super-exchange model. The extra electron from Li atom creates a charge disproportionation in the LiFe2Cl6 (LiFe2Cl4) cluster that mediates the double-exchange interaction between the Fe atoms. Antiferromagnetic to ferromagnetic transition can also be induced by hole doping as seen to be the case with Fe2Cl5 which has a ferromagnetic ground state. Simultaneous electron and hole doping is also seen to impact on the magnetic properties of LiFe2Cl5 which can be viewed as (Fe2Cl4+LiCl). While Fe2Cl4 is antiferromagnetic and LiCl is nonmagnetic, the ground state of LiFe2Cl5 is ferromagnetic. We also analyzed the results with on-site Coulomb interaction U by performing DFT+U calculations. These results can be useful in the synthesis of functional molecular magnets.
Phase-field modeling of diffusion-induced crack propagations in electrochemical systems
Authors: Liang Linyun , Stan Marius , Anitescu Mihai
Published: October 2014

A three-dimensional phase-field model was developed to simulate and predict crack propagations caused by local variations of solute concentrations. Its application to the electrolyte-LiFePO4 cathode nanoparticle system in Li-ion batteries captures the Li chemical reaction-intercalation-induced crack propagation during the cell discharging operations. The inherent mechanism underlying the crack propagation is critical for understanding the degradation mechanism limiting battery life and performance. Complex phenomena such as anisotropic coherence strains, elastic inhomogeneity, anisotropic Li diffusion, and chemical reaction of Li ions are fully incorporated in this model. Results of crack propagation in both the bc-plane and ab-plane are consistent with experimental observations. A calculated fracture phase diagram as a function of different nanoparticle sizes and chemical reaction rates provides a failure criterion that is valid for a large class of brittle electrode materials. The current study provides a direct relation between reaction-diffusion-induced stress fields and the observed structural failure in electrochemical system.
Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state
Authors: Dvornik Mykola , Vansteenkiste Arne , Van Waeyenberge Bartel
Published: October 2014

In this work, a self-consistent thermodynamic approach to micromagnetism is presented. The magnetic degrees of freedom are modeled using the Landau-Lifshitz-Baryakhtar theory, which separates the different contributions to the magnetic damping, and thereby allows them to be coupled to the electron and phonon systems in a self-consistent way. We show that this model can quantitatively reproduce ultrafast magnetization dynamics in Nickel suggesting that in ferromagnetic metals the ultrafast angular momentum transfer happens via the relativistic spin-electron scattering.
Dynamics of fast pattern formation in porous silicon by laser interference
Authors: Peláez Ramón J. , Kuhn Timo , Vega Fidel , Afonso Carmen N.
Published: October 2014

Patterns are fabricated on 290 nm thick nanostructured porous silicon layers by phase-mask laser interference using single pulses of an excimer laser (193 nm, 20 ns pulse duration). The dynamics of pattern formation is studied by measuring in real time the intensity of the diffraction orders 0 and 1 at 633 nm. The results show that a transient pattern is formed upon melting at intensity maxima sites within a time <30 ns leading to a permanent pattern in a time <100 ns upon solidification at these sites. This fast process is compared to the longer one (>1 μs) upon melting induced by homogeneous beam exposure and related to the different scenario for releasing the heat from hot regions. The diffraction efficiency of the pattern is finally controlled by a combination of laser fluence and initial thickness of the nanostructured porous silicon layer and the present results open perspectives on heat release management upon laser exposure as well as have potential for alternative routes for switching applications.
The effect of interface adhesion on buckling and cracking of hard thin films
Authors: Flores-Johnson E. A. , Shen L. , Annabattula R. K. , Onck P. R. , Shen Y. G. , Chen Z.
Published: October 2014

The physics behind the strain-released buckling patterns including telephone cords and straight-sided wrinkles with and without cracks, as experimentally observed in sputter-deposited Ti-Si-N thin films on Si substrates, is investigated with model-based simulations by varying the mechanical properties of the interface. Our calculations reveal that the location of the cracks depends on the normal stiffness, the interfacial toughness, and the normal strength of the cohesive interface. These properties determine the geometrical shape of the buckles such as width, wavelength, and deflection, and hence the local bending-induced tensile stresses. Buckling patterns with cracks at the apexes occur for low-stiffness interfaces as well as for high-stiffness interfaces with high toughness. On the other hand, cracks at the bottom of the buckles are more likely to occur for interfaces with high stiffness and low toughness. By using an elastic material model with a fracture criterion for brittle behavior, we demonstrate that the crack will follow the path where the bending-induced principal stress exceeds the flexural strength of the film.
Microscale mapping of oscillatory flows
Authors: Nedev Spas , Carretero-Palacios S. , Kirchner S. R. , Jäckel F. , Feldmann J.
Published: October 2014

We present an optofluidic method that allows the two-dimensional vectorial near-field mapping of oscillatory flows with micron-scale resolution. An oscillatory flow created by a microsource (an optically trapped silica particle set to oscillate in a dipole-type mode) is detected by another twin silica particle independently trapped and located in the vicinity of the source. Fourier analysis of the motion of the detecting particle at different points in space and time renders the vectorial velocity map around the oscillating microsphere. The method introduced here paves the way for in-situ characterization of fast mixing microscale devices and for new detection methods able to provide location and recognition (due to the field pattern) of moving sources that may be applied to both artificial and living microobjects, including macromolecules, cells, and microorganisms.
Damage induced dissipation in electroactive polymer harvesters
Authors: Colonnelli S. , Saccomandi G. , Zurlo G.
Published: October 2014

Electromechanical harvesters based on dielectric electroactive polymers are promising devices for the production of electrical energy by the conversion of abundant sources of mechanical work available in Nature. However, severe limitations to the performance of these devices arise from various sources of dissipation and failure of the polymeric material. By making use of an energetic approach, we establish a direct and quantitative connection between the Mullins effect taking place in the polymeric material and the harvesting efficiency, showing the prominent role of rate-independent effects in the hysteretic behavior of electromechanical harvesters.
Systematic study of doping dependence on linear magnetoresistance in p-PbTe
Authors: Schneider J. M. , Peres M. L. , Wiedmann S. , Zeitler U. , Chitta V. A. , Abramof E. , Rappl P. H. O. , de Castro S. , Soares D. A. W. , Mengui U. A. , Oliveira N. F.
Published: October 2014

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF2 exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF2 doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.
Extending light-harvesting of poly(3-hexylthiophene) through efficient energy transfer from infra-red absorbing nanocrystals: Single nanoparticle study
Authors: Grzelak Justyna , Ciszak Kamil , Nyk Marcin , Mackowski Sebastian , Piatkowski Dawid
Published: October 2014

We report on single nanocrystal fluorescence microscopy of blends composed of colloidal up-converting NaYF4 nanocrystals doped with rare-earth ions embedded in poly(3-hexylthiophene) (P3HT) polymer. By probing both steady-state and time-resolved fluorescence properties of individual nanocrystals excited with infra-red 980 nm laser, we demonstrate that upon up-conversion to the visible spectral range, the energy is efficiently transferred from the nanocrystals to P3HT. From the analysis of fluorescence lifetimes, the energy transfer efficiency for 550 nm emission of the nanocrystals was estimated to be 60%. This observation renders the up-converting nanocrystals as potential structures for improving light-harvesting efficiency of polymers in the near-infrared spectral region.
Measurement and control of pressure driven flows in microfluidic devices using an optofluidic flow sensor
Authors: Cheri Mohammad Sadegh , Shahraki Hamidreza , Sadeghi Jalal , Moghaddam Mohammadreza Salehi , Latifi Hamid
Published: October 2014

Measurement and control of pressure-driven flow (PDF) has a great potential to enhance the performance of chemical and biological experiments in Lab on a Chip technology. In this paper, we present an optofluidic flow sensor for real-time measurement and control of PDF. The optofluidic flow sensor consists of an on-chip micro Venturi and two optical Fabry-Pérot (FP) interferometers. Flow rate was measured from the fringe shift of FP interferometers resulted from movement fluid in the on-chip micro Venturi. The experimental results show that the optofluidic flow sensor has a minimum detectable flow change of 5 nl/min that is suitable for real time monitoring and control of fluids in many chemical and biological experiments. A Finite Element Method is used to solve the three dimensional (3D) Navier–Stokes and continuity equations to validate the experimental results.
Evolution of structure in Na0.5Bi0.5TiO3 single crystals with BaTiO3
Authors: Ge Wenwei , Luo Chengtao , Zhang Qinhui , Ren Yang , Li Jiefang , Luo Haosu , Viehland D.
Published: October 2014

The structural, dielectric, and piezoelectric properties of Na0.5Bi0.5TiO3-x mol. %BaTiO3 (NBT-x%BT) crystals have been investigated. The dielectric and piezoelectric properties of NBT-x%BT were enhanced near x = 5–7. High resolution synchrotron x-ray powder diffraction studies revealed the presence of a phase boundary between monoclinic (Cc) and tetragonal (P4bm) phases near x = 5–7, where the dielectric and piezoelectric properties were enhanced.
Increased formate-dependent H2 production from xylose in Enterobacter sp. CN1 transformed with a formate hydrogenlyase activator gene
Authors: Qiu Yufeng , Huang Jiang , Nian Dinglan , Zhang Mingming , Long Minnan , Hu Zhong
Published: October 2014

Finding bacterial strains for effective hydrogen production and optimization of the fermentative conditions are two major approaches to promoting commercial application of bio-hydrogen. In the present study, we carried out experiments to examine factors that affected H2 yield in Enterobacter sp. CN1. The result showed that H2 could be produced from formate alone and the yields were positively correlated with formate concentrations. Moreover, the yield of H2 from xylose was significantly increased in the presence of formate, revealing that formate is not only a good carbon source but also promotes H2 production from xylose in strain CN1. The production of H2 from formate was not affected by pH; however, H2 production from xylose at pH 7 was higher than that at pH 6, no matter if formate is presence or absence in the medium. Further, H2 production from pyruvate was inhibited completely when sodium hypophosphate (HPP) was present, but formate-dependent H2 production was mostly not affected. In addition, H2 production from glucose or xylose was dramatically reduced but sill detectable in the presence of HPP, suggesting that formate hydrogenlyase is the main pathway responsible for H2 production from xylose in Enterobacter sp. CN1. To confirm the above hypothesis, the formate hydrogenlyase activator (fhlA) gene was cloned and over-expressed in strain CN1. Compared with the wild-type, recombinant CN1 strain increased H2 production per gram of xylose and per gram of cells by 10.5% and 18.8%, respectively, in the presence of xylose.
The role of the isolated 6s states in BiVO4 on the electronic and atomic structures
Authors: Ma Jie , Wang Lin-Wang
Published: October 2014

BiVO4 is one of the most promising photoanodes for water-splitting applications. Similar to many d10 materials, where the full-shell d electrons are not directly involved in the bonding, the Bi 6s electrons form isolated low-energy bands in BiVO4. By systematically altering the energy of the Bi 6s states, we find direct evidences that the isolated s states, through the s-p coupling, affect the BiVO4 properties, including valence band maximum position, charge density, and atomic structural distortion. We find that many good properties of BiVO4 for water splitting are related to the s-p coupling due to the existence of Bi 6s states. Based on this understanding, we propose that alloying Bi with Sb can enhance these properties, and hence improve the water-splitting efficiency.
Research of least squares support vector regression based on differential evolution algorithm in short-term load forecasting model
Authors: Sun Wei , Liang Yi
Published: October 2014

To improve the accuracy of short-term load forecasting, a differential evolution algorithm (DE) based least squares support vector regression (LSSVR) method is proposed in this paper. Through optimizing the regularization parameter and kernel parameter of the LSSVR by DE, a short-term load forecasting model which can take load affected factors such as meteorology, weather, and date types into account is built. The proposed LSSVR method is proved by implementing short-term load forecasting on the real historical data of Yangquan power system in China. The average forecasting error is less than 1.6%, which shows better accuracy and stability than the traditional LSSVR and Support vector regression. The result of implementation of short-term load forecasting demonstrates that the hybrid model can be used in the short-term forecasting of the power system more efficiently.
Latest development status of offshore wind power in China—The perspective of developers
Authors: Li Wei , Yao Hui , Wang Huanqi , Wang Zhiqun
Published: October 2014

In recent years, Chinese wind power has progressed rapidly, such that most accessible high quality, onshore sites are either operational or at least in some stage of development. Thus, offshore wind power has become the new industry focus. This paper reviews the development of China's offshore wind power and its current status. All aspects of preliminary planning, design, approval, construction, O&M, and electricity pricing policy are discussed from a developer's perspective. Data and key points are introduced, based on current engineering practices. European developments are reviewed briefly to help assess similar problems and issues in China. This study suggests that China's relative lack of experience must be recognized. Nevertheless, the development of this nascent technology is already underway.
An advanced wind speed multi-step ahead forecasting approach with characteristic component analysis
Authors: Zhang Guoyong , Wu Yonggang , Liu Yuqi
Published: October 2014

Accurate wind speed prediction provides essential information for system operation and management with wind power integration. Most existing prediction methods chose to model original data directly without considering the inherent characteristics of wind speed time series. However, the properties of characteristic components can offer better information for prediction. This paper proposes to extract the characteristic components of original data using the ensemble empirical mode decomposition and sample entropy techniques. For the multi-step ahead forecasting of characteristic components, a multiple-input multiple-output (MIMO) based extreme learning machine model is constructed. The effectiveness of the proposed approach is illustrated by applying it to two real wind farm datasets. The extracted characteristic components are shown to be of much lower complexity and the MIMO strategy is found to be better than the common iterated strategy and direct strategy. Moreover, compared to the existing neural networks based methods, the proposed approach has been demonstrated to be a more effective method in both prediction accuracy and computational cost.
Extraordinary induction heating effect near the first order Curie transition
Authors: Barati M. R. , Selomulya C. , Sandeman K. G. , Suzuki K.
Published: October 2014

While materials with a 1st order Curie transition (TC) are known for the magnetic cooling effect due to the reversibility of their large entropy change, they also have a great potential as a candidate material for induction heating where a large loss power is required under a limited alternating magnetic field. We have carried out a proof-of-concept study on the induction heating effect in 1st order ferromagnetic materials where the temperature is self-regulated at TC. LaFe11.57Si1.43H1.75, a well-known magnetocaloric material, was employed in this study because TC of this compound (319 K) resides in the ideal temperature range for hyperthermia treatment of cancerous cells. It is found that the hysteresis loss of LaFe11.57Si1.43H1.75 increases dramatically near TC due to the magnetic phase coexistence associated with the 1st order magnetic transition. The spontaneous magnetization (Ms) shows a very abrupt decrease from 110 Am2kg−1 at 316 K to zero at 319 K. This large Ms immediately below TC along with the enhanced irreversibility of the hysteresis curve result in a specific absorption rate as large as 0.5 kWg−1 under a field of 8.8 kAm−1 at 279 kHz. This value is nearly an order of magnitude larger than that observed under the same condition for conventional iron oxide-based materials. Moreover, the large heating effect is self-regulated at the 1st order TC (319 K). This proof-of-concept study shows that the extraordinary heating effect near the 1st order Curie point opens up a novel alloy design strategy for large, self-regulated induction heating.
A comparative study on converter topologies for maximum power point tracking application in photovoltaic generation
Authors: Bhattacharjee Subhadeep , Saharia Barnam Jyoti
Published: October 2014

This paper makes a comparative investigation of the three basic non-isolated dc-dc converters used as interface for maximum power point tracking (MPPT) application in photovoltaic generators using the direct duty ratio control tracking algorithm. Analysis of the buck, boost, and buck–boost converters has been undertaken to study the behavior of the converter's performance with respect to the changing atmospheric conditions and in-turn duty ratio variation (as a result of MPPT) and the tracking efficiency of each converter. Effect of different resistive loads on the output of the converter side has also been considered for the three topologies and it has been observed that the buck-boost converter is the only converter which is able to track the maximum power point under variation of insolation, temperature, and loading effect, with the highest tracking efficiency.
Oxygen-vacancy-related relaxation and conduction behavior in (Pb1-xBax)(Zr0.95Ti0.05)O3 ceramics
Authors: Zhang Tian-Fu , Tang Xin-Gui , Liu Qiu-Xiang , Lu Sheng-Guo , Jiang Yan-Ping , Huang Xian-Xiong , Zhou Qi-Fa
Published: October 2014

(Pb1-xBax)(Zr0.95Ti0.05)O3 (x = 0, 0.025, 0.05, 0.075 and 0.1) ceramics were prepared via a solid-state reaction route. Low-frequency (20 ∼ 2 × 107 Hz) dielectric properties were investigated in the temperature region of 25-650 °C. Ba2+ doping can slightly reduce the phase transition temperature of ferroelectric to paraelectric. The dielectric diffuse anomaly in the dielectric relaxation was found in the high temperature region of 400-650 °C. Activation energy, calculated from the impedance and conductivity data of samples, suggests that the dielectric relaxation is due to oxygen vacancies generated during the sintering process. Ba2+ doping can reduce significantly the concentration of oxygen vacancies, and slightly enhance activation energy for the migration of oxygen vacancies. Results of activation energy calculated from impedance and conductance suggest that the dielectric relaxation is due to the short-range hopping of oxygen vacancies, and the conduction due to the movement of doubly-ionized oxygen vacancies.
A laminate of ferromagnetic films with high effective permeability at high frequencies
Authors: Iakubov I. T. , Lagarkov A. N. , Osipov A. V. , Maklakov S. A. , Rozanov K. N. , Ryzhikov I. A. , Starostenko S. N.
Published: October 2014

The paper reports on development of magnetodielectric material with high microwave permeability. The material is a laminate of multi-layer permalloy films deposited onto a thin mylar substrate by magnetron sputtering. The deposited films are arranged into a stack and glued together under pressure to obtain the laminate. With the content of ferromagnetic component in the laminate being 22 % vol., its measured quasistatic permeability is 60. The peak value of imaginary permeability attains 50 and the peak is located near 1 GHz. As compared with the multi-layer films, which the laminate is made of, it exhibits lower magnetic loss tangent at frequencies below the magnetic loss peak and may therefore be useful for many technical applications. Lower low-frequency loss may be attributed to pressing of the glued sample. This rectifies wrinkling appearing due to sputtering of rigid multi-layer film onto flexible mylar substrate and, therefore, makes the magnetic structure of the film more uniform.
Dynamic characterization of hydrophobic and hydrophilic solutes in oleic-acid enhanced transdermal delivery using two-photon fluorescence microscopy
Authors: Tseng Te-Yu , Yang Chiu-Sheng , Tsai Tsung-Hua , Chen Yang-Fang , Dong Chen-Yuan
Published: October 2014

In this letter, we propose an efficient methodology of investigating dynamic properties of sulforhodamine B and rhodamine B hexyl ester molecules transporting across ex-vivo human stratum corneum with and without oleic acid enhancement. Three-dimensional, time-lapse fluorescence images of the stratum corneum can be obtained using two-photon fluorescence microscopy. Furthermore, temporal quantifications of transport enhancements in diffusion parameters can be achieved with the use of Fick's second law. Dynamic characterization of solutes transporting across the stratum corneum is an effective method for understanding transient phenomena in transdermal delivery of probe molecules, leading to improved delivery strategies of molecular species for therapeutic purposes.
Graphitization of polymer surfaces by scanning ion irradiation
Authors: Koval Yuri
Published: October 2014

Graphitization of polymer surfaces was performed by low-energy Ar+ and He+ ion irradiation. A method of scanning irradiation was implemented. It was found that by scanning ion irradiation, a significantly higher electrical conductivity in the graphitized layers can be achieved in comparison with a conventional broad-beam irradiation. The enhancement of the conductance becomes more pronounced for narrower and better collimated ion beams. In order to analyze these results in more detail, the temperature dependence of conductance of the irradiated samples was investigated. The results of measurements are discussed in terms of weak localization corrections to conductance in disordered metals. The observed effects can be explained by enlargement of graphitic patches, which was achieved with the scanning ion irradiation method.
Experimental observation of disorder induced self-focusing in optical fibers
Authors: Leonetti Marco , Karbasi Salman , Mafi Arash , Conti Claudio
Published: October 2014

We observed disorder induced focusing nonlinearity activated by a monochromatic light beam in optical fibers composed by two kinds of plastics. The two materials, arranged in disordered fashion, support modes with a degree of localization which increases with the intensity of the optical beam. The temporal response of the optical fiber demonstrates the thermal origin of this nonlinearity. Measurements of the localization length as a function of the input power with broadband and monochromatic inputs show the effectiveness of focusing action with respect to the case of homogeneous fibers.