bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive gradient search for optimal sidelobe design of hopped‐frequency waveform
Authors: Zhao Dehua , Wei Yinsheng
Published: April 2014

Linear step frequency waveforms can achieve large time‐bandwidth product by uniformly inter‐pulse frequency stepping, but have limited anti‐jamming ability. Hopped‐frequency waveforms overcome the limitation by introducing irregularly or randomly stepped frequency. However, a challenge in hopped‐frequency waveform design is that, given fixed pulse number and time‐bandwidth product, the distribution of its autocorrelation sidelobe varies significantly under different frequency combinations. In this study, the authors propose an adaptive gradient search algorithm for optimal sidelobe design of hopped‐frequency waveform. The method is iterative and applies a negative gradient adjustment adaptively according to sidelobe discrepancy between the current output of the matched filtering and the ideal expectation. As a result, it can be used to find optimal frequency combinations that produce hopped‐frequency pulses with a prescribed sidelobe specification. Experimental evidence suggests that the proposed procedure gives promising results in terms of sidelobe level and it terminates in remarkably little time.
Squared‐root cubature information consensus filter for non‐linear decentralised state estimation in sensor networks
Authors: Yu Liu , You He , Haipeng Wang
Published: April 2014

Distributed analysis of target kinematics captured by a large network of sensors has received significant attention lately. Tracking moving targets in nonlinear systems is one of the most fundamental tasks in this regard and information‐type consensus filters (ICFs) have been applied to this problem. To improve the estimate performance, a squared‐root cubature information filter which can avoid numerically sensitive matrix operations such as matrix square‐rooting and inversion has been developed firstly. And then, based on this filter, a decentralised information filtering algorithm is proposed in an improved consensus framework. Specifically, consensus update at each time‐cycle in the modified consensus scheme is computed in two steps, first towards the predicted value and then towards the final information estimate update, which can improve average estimation accuracy and speed the average consensus. Besides the basic merits of the traditional ICFs, the resulting algorithm is more scalable and robust. Simulation results clearly show the advantage of the proposed algorithm compared with existing ICFs in the considered application scenario.
Direction of arrival estimation with a sparse uniform array of orthogonally oriented and spatially separated dipole‐triads
Authors: Zheng Guimei , Wu Bo , Ma Yan , Chen Baixiao
Published: April 2014

The problem of multiple incident signals’ direction of arrival (DOA) estimation for spatially separated polarisation sensitive array (SS‐PSA) is studied. The proposed SS‐PSA is a sparse uniform array with orthogonally oriented and spatially separated dipole‐triads. The proposed array can reduce the array mutual coupling by using the spatially separated polarised antenna instead of conventional spatially collocated polarised antenna. Moreover, the DOA estimation accuracy can be improved greatly due to the extended aperture offered by sparse array. Computer simulation results verify the effectiveness of the proposed algorithm.
Joint estimation algorithm for multi‐targets’ motion parameters
Authors: Tian Jing , Cui Wei , Lv Xiao‐lei , Wu Shuang , Hou Jian‐gang , Wu Si‐liang
Published: April 2014

When multiple targets are within the same radar antenna beam and cannot be separated in the range dimension, the conventional imaging methods cannot be directly used to obtain a focused radar image. In this study, a new joint estimation algorithm for multi‐targets’ motion parameters is proposed. In this method, the first‐order Keystone transform is first applied to correct the range walk of multiple targets simultaneously, and then the Lv's transform is used to estimate the motion parameters of targets including velocity and acceleration. The signal‐to‐noise ratio threshold for the proposed method is also given. The proposed method is fast and can obtain the accurate parameter estimation without knowing the number of targets and their motion information. Experimental results demonstrate the performance of the proposed algorithm. Comparisons between the proposed method and other methods, the maximum‐likelihood method, fractional Fourier transform and discrete polynomial transform, are performed, which show that the proposed method can efficiently obtain the accurate parameter estimation with low computational burden.
Analytical method for monostatic radar cross section calculation of a perfectly conducting wind turbine model located over dielectric lossy half space
Authors: Makal Yucedag Senem , Mert Yucedag Okan , Serim Huseyin Avni
Published: April 2014

Radar cross section (RCS) of a wind turbine has a key role for determining possible effects of wind farms on radar and navigation systems. Closed form expressions of the physical optics technique are applied to calculate monostatic radar cross section of an electrically large wind turbine model over a dielectric, lossy half space. The model is constructed with perfectly conducting canonical structures. First‐order effects of the half space to the electromagnetic scattering mechanism are approximated with four‐path model. Doppler spectrogram of the turbine model over lossy ground is obtained using short‐time Fourier transform. The closed form expressions provide very‐fast RCS calculations for different broadside directions and blade rotation speeds. Performance of this proposed method shows that it is suitable for real‐time simulations that analyse the effects of the wind farms to the radar and navigation systems performance.
Accounting for randomness in measurement and sampling in studying cancer cell population dynamics
Authors: Ghavami Siavash , Wolkenhauer Olaf , Lahouti Farshad , Ullah Mukhtar , Linnebacher Michael
Published: April 2014

Knowing the expected temporal evolution of the proportion of different cell types in sample tissues gives an indication about the progression of the disease and its possible response to drugs. Such systems have been modelled using Markov processes. We here consider an experimentally realistic scenario in which transition probabilities are estimated from noisy cell population size measurements. Using aggregated data of FACS measurements, we develop MMSE and ML estimators and formulate two problems to find the minimum number of required samples and measurements to guarantee the accuracy of predicted population sizes. Our numerical results show that the convergence mechanism of transition probabilities and steady states differ widely from the real values if one uses the standard deterministic approach for noisy measurements. This provides support for our argument that for the analysis of FACS data one should consider the observed state as a random variable. The second problem we address is about the consequences of estimating the probability of a cell being in a particular state from measurements of small population of cells. We show how the uncertainty arising from small sample sizes can be captured by a distribution for the state probability.
Overshoot in biological systems modelled by Markov chains: a non‐equilibrium dynamic phenomenon
Authors: Jia Chen , Qian Minping , Jiang Daquan
Published: April 2014

A number of biological systems can be modelled by Markov chains. Recently, there has been an increasing concern about when biological systems modelled by Markov chains will perform a dynamic phenomenon called overshoot. In this study, the authors found that the steady‐state behaviour of the system will have a great effect on the occurrence of overshoot. They showed that overshoot in general cannot occur in systems that will finally approach an equilibrium steady state. They further classified overshoot into two types, named as simple overshoot and oscillating overshoot. They showed that except for extreme cases, oscillating overshoot will occur if the system is far from equilibrium. All these results clearly show that overshoot is a non‐equilibrium dynamic phenomenon with energy consumption. In addition, the main result in this study is validated with real experimental data.
Controllable synthesis and optical properties of SnO2 core‐shell microspheres
Authors: Chen Haitao , Zhang Dan , Chen Guoshuai , Zhu Jun , Chen Xiaobing , Zeng Xianghua
Published: April 2014

SnO2 core‐shell microspheres were synthesised via a hydrothermal method with hexamethylenetetramine as a surfactant. The structure and the morphology of the products were characterised by X‐ray diffraction, field‐emission scanning electron microscopy and transmission electron microscopy. The results indicated that the overall dimension of the core‐shell microspheres and the diameter of the spherical nuclei could be adjusted by changing the concentration of NaOH and hexamethylenetetramine or the reaction time. Based on the time dependent reactions, a possible growth mechanism is proposed. It is believed that the Kirkendall effect plays an important role in the formation of the core‐shell structure. The optical properties of the core‐shell structure microspheres were also studied through the photoluminescence and the Raman spectra.
Current–voltage characteristics of Nb–carbon–Nb junctions
Authors: Nevirkovets I. P. , Shafranjuk S. E. , Chernyashevskyy O. , Masilamani N. , Ketterson J. B.
Published: April 2014

We report on properties of Nb(/Ti)–carbon–(Ti/)Nb junctions fabricated on graphite flakes using e-beam lithography. The devices were characterized at temperatures above 1.8 K where a Josephson current was not observed, but the differential conductivity revealed features below the critical temperature of Nb, and overall metallic conductivity, in spite of a high-junctions resistance. Since the conductivity of graphite along the planes is essentially two-dimensional (2D), we use a theoretical model developed for metal/graphene junctions for interpretation of the results. The model involves two very different graphene “access” lengths. The shorter length characterizes ordinary tunneling between the three-dimensional Nb(/Ti) electrode and 2D graphene, while the second, much longer length, is associated with the Andreev reflections (AR) inside the junction and involves also “reflectionless” AR processes. The relevant transmission factors are small in the first case and much larger in the second, which explains the apparent contradiction of the observed behaviors.
Low-temperature 1H NMR spectroscopic study of hydration properties of a hybrid system based on nanosilica, DNA and doxorubicin in the presence of C60 fullerene
Authors: Turov V. V. , Prylutskyy Yu. I. , Ugnivenko A. P. , Barvinchenko V. N. , Krupskaya T. V. , Tsierkezos N. G. , Ritter U.
Published: April 2014

The structure of hydrate cover layers of SiO2-DNA-Dox (where Dox: doxorubicin) and SiO2-DNA-Dox-C60 fullerene hybrids was studied by means of low-temperature 1H NMR spectroscopy in tetrachloromethane. The hydration properties of SiO2-DNA-Dox nanomaterials combined with fullerenes and their derivatives are extremely important for their further use as therapeutics in cancer treatment and for safety reasons. The findings reveal that the hydration properties of the hybrids differ from those of the solid DNA particulates or SiO2-DNA systems due to the existence of different types of water clusters, namely the weakly (WAW) and strongly associated water (SAW) clusters. For SAW clusters the radial distributions as well as the distributions of change in Gibbs free energy due to adsorptive interactions at the surfaces of the investigated systems were obtained.
Gaussian approximations for stochastic systems with delay: Chemical Langevin equation and application to a Brusselator system
Authors: Brett Tobias , Galla Tobias
Published: April 2014

We present a heuristic derivation of Gaussian approximations for stochastic chemical reaction systems with distributed delay. In particular, we derive the corresponding chemical Langevin equation. Due to the non-Markovian character of the underlying dynamics, these equations are integro-differential equations, and the noise in the Gaussian approximation is coloured. Following on from the chemical Langevin equation, a further reduction leads to the linear-noise approximation. We apply the formalism to a delay variant of the celebrated Brusselator model, and show how it can be used to characterise noise-driven quasi-cycles, as well as noise-triggered spiking. We find surprisingly intricate dependence of the typical frequency of quasi-cycles on the delay period.
Investigation of channel width-dependent threshold voltage variation in a-InGaZnO thin-film transistors
Authors: Liu Kuan-Hsien , Chang Ting-Chang , Wu Ming-Siou , Hung Yi-Syuan , Hung Pei-Hua , Hsieh Tien-Yu , Chou Wu-Ching , Chu Ann-Kuo , Sze Simon M. , Yeh Bo-Liang
Published: April 2014

This Letter investigates abnormal channel width-dependent threshold voltage variation in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors. Unlike drain-induced source barrier lowering effect, threshold voltage increases with increasing drain voltage. Furthermore, the wider the channel, the larger the threshold voltage observed. Because of the surrounding oxide and other thermal insulating material and the low thermal conductivity of the IGZO layer, the self-heating effect will be pronounced in wider channel devices and those with a larger operating drain bias. To further clarify the physical mechanism, fast IV measurement is utilized to demonstrate the self-heating induced anomalous channel width-dependent threshold voltage variation.
Role of size and defects in ultrafast broadband emission dynamics of ZnO nanostructures
Authors: Appavoo Kannatassen , Liu Mingzhao , Sfeir Matthew Y.
Published: April 2014

As wide bandgap materials are nanostructured for optoelectronics and energy technologies, understanding how size and defects modify the carrier dynamics becomes critical. Here, we examine broadband ultraviolet-visible subpicosecond emission dynamics of prototypical ZnO in bulk, nanowire and nanosphere geometries. Using a high-sensitivity transient emission Kerr-based spectrometer, we probe exciton dynamics in the low fluence regime to determine how defects states impact thermalization and recombination rates. In contrast to steady-state measurements, we transiently identify low-energy emission features that originate from localized excitonic states rather than mid-gap states, characterized by distinct recombination kinetics, and correlate to longer thermalization times. These states are critical for understanding the overall excited state lifetime of materials in this size regime, where crystallinity rather than dimensionality plays a primary role in dictating recombination dynamics.
Simulation of polyethylene glycol and calcium-mediated membrane fusion
Authors: Pannuzzo Martina , De Jong Djurre H. , Raudino Antonio , Marrink Siewert J.
Published: April 2014

We report on the mechanism of membrane fusion mediated by polyethylene glycol (PEG) and Ca2+ by means of a coarse-grained molecular dynamics simulation approach. Our data provide a detailed view on the role of cations and polymer in modulating the interaction between negatively charged apposed membranes. The PEG chains cause a reduction of the inter-lamellar distance and cause an increase in concentration of divalent cations. When thermally driven fluctuations bring the membranes at close contact, a switch from cis to trans Ca2+-lipid complexes stabilizes a focal contact acting as a nucleation site for further expansion of the adhesion region. Flipping of lipid tails induces subsequent stalk formation. Together, our results provide a molecular explanation for the synergistic effect of Ca2+ and PEG on membrane fusion.
L-asparagine crystals with wide gap semiconductor features: Optical absorption measurements and density functional theory computations
Authors: Zanatta G. , Gottfried C. , Silva A. M. , Caetano E. W. S. , Sales F. A. M. , Freire V. N.
Published: April 2014

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p–carboxyl, C 2p–side chain, and C 2p–carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.
Mechanical energy dissipation induced by sloshing and wave breaking in a fully coupled angular motion system. I. Theoretical formulation and numerical investigation
Authors: Bouscasse B. , Colagrossi A. , Souto-Iglesias A. , Cercos-Pita J. L.
Published: April 2014

A dynamical system involving a driven pendulum filled with liquid is analyzed in the present paper series. The study of such a system is conducted in order to understand energy dissipation resulting from the shallow water sloshing and induced wave breaking. This analysis is relevant for the design of Tuned Liquid Damper devices. The complexity and violence of the flow generated by the roll motion results in the impossibility of using an analytical approach, requiring in turn the use of a suitable numerical solver. In this paper, the coupled dynamical system is thoroughly described, revealing its nonlinear features associated with the large amplitude of the forcing, both in terms of mechanical and fluid dynamical aspects. A smoothed particle hydrodynamics model, largely validated in literature, is used to calculate the frequency behavior of the whole system. For small rotation angles, a semi-analytical model of the energy dissipated by the fluid, based on a hydraulic jump solution, is developed; the energy transfer is numerically calculated in order to extend the analysis to large oscillation angles. The experimental part of the investigation is carried out in Paper II [B. Bouscasse, A. Colagrossi, A. Souto-Iglesias, and J. L. C. Pita, “Mechanical energy dissipation induced by sloshing and wave breaking in a fully coupled angular motion system. II. Experimental investigation,” Phys. Fluids 26, 033104 (2014)] of this work.
Loop subdivision surface boundary integral method simulations of vesicles at low reduced volume ratio in shear and extensional flow
Authors: Spann Andrew P. , Zhao Hong , Shaqfeh Eric S. G.
Published: April 2014

Using an unstructured boundary integral method with curvature determination via Loop subdivision surfaces, we explore a region of moderate reduced volume vesicles in flow that includes prolate, biconcave, and stomatocyte shapes. We validate our Loop subdivision code against previously published spectral method simulations. In shear flow, we report dynamic phase diagrams at reduced volumes ranging from 0.65 to 0.95 and determine the critical viscosity ratio at which the vesicle moves away from tank treading. We examine biconcave shapes and find the elimination of the trembling regime and a tumbling that includes significant stretch in the vorticity direction, as well as a general reduction in shear and normal stresses versus a prolate shape. Finally, we re-examine over a wider range of reduced volume the shape instability originally reported by Zhao and Shaqfeh [“The shape stability of a lipid vesicle in a uniaxial extensional flow,” J. Fluid Mech. 719, 345–361 (2013)] of a vesicle placed in an extensional flow. At sufficiently low reduced volume and high capillary number, we find the steady elongated dumbbell shape is unstable to odd perturbations and the vesicle's dumbbell ends become unequal in size. We also find that the critical capillary number as a function of reduced volume is similar between uniaxial and planar extensional flow.
Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H2O)n≤5]H+: Evidence for ground-state proton transfer to solvent for n ≥ 3
Authors: Dopfer Otto , Patzer Alexander , Chakraborty Shamik , Alata Ivan , Omidyan Reza , Broquier Michel , Dedonder Claude , Jouvet Christophe
Published: April 2014

Vibrational and electronic photodissociation spectra of mass-selected protonated benzaldehyde-(water)n clusters, [BZ-(H2O)n]H+ with n ≤ 5, are analyzed by quantum chemical calculations to determine the protonation site in the ground electronic state (S0) and ππ* excited state (S1) as a function of microhydration. IR spectra of [BZ-(H2O)n]H+ with n ≤ 2 are consistent with BZH+-(H2O)n type structures, in which the excess proton is localized on benzaldehyde. IR spectra of clusters with n ≥ 3 are assigned to structures, in which the excess proton is located on the (H2O)n solvent moiety, BZ-(H2O)nH+. Quantum chemical calculations at the B3LYP, MP2, and ri-CC2 levels support the conclusion of proton transfer from BZH+ to the solvent moiety in the S0 state for hydration sizes larger than the critical value nc = 3. The vibronic spectrum of the S1 ← S0 transition (ππ*) of the n = 1 cluster is consistent with a cis-BZH+-H2O structure in both electronic states. The large blueshift of the S1 origin by 2106 cm−1 upon hydration with a single H2O ligand indicates that the proton affinity of BZ is substantially increased upon S1 excitation, thus strongly destabilizing the hydrogen bond to the solvent. The adiabatic S1 excitation energy and vibronic structure calculated at the ri-CC2/aug-cc-pVDZ level agrees well with the measured spectrum, supporting the notion of a cis-BZH+-H2O geometry. The doubly hydrated species, cis-BZH+-(H2O)2, does not absorb in the spectral range of 23 000–27 400 cm−1, because of the additional large blueshift of the ππ* transition upon attachment of the second H2O molecule. Calculations predict roughly linear and large incremental blueshifts for the ππ* transition in [BZ-(H2O)n]H+ as a function of n. In the size range n ≥ 3, the calculations predict a proton transfer from the (H2O)nH+ solvent back to the BZ solute upon electronic ππ* excitation.
Two dimensional electron transport in modulation-doped In0.53Ga0.47As/AlAs0.56Sb0.44 ultrathin quantum wells
Authors: Huang Cheng-Ying , Law Jeremy J. M. , Lu Hong , Jena Debdeep , Rodwell Mark J. W. , Gossard Arthur C.
Published: April 2014

We have investigated the growth and electron transport in In0.53Ga0.47As/AlAs0.56Sb0.44 two dimensional electron gases (2DEG) and compared their properties with In0.53Ga0.47As/In0.52Al0.48As 2DEGs. For 10 nm thick InGaAs wells, the electron mobility of InGaAs/AlAsSb 2DEGs is comparable to that of InGaAs/InAlAs 2DEGs. Upon thinning the wells to 3 nm, the 2DEG mobility is degraded quickly and stronger interface roughness scattering is observed for InGaAs/AlAsSb heterointerfaces than for InGaAs/InAlAs heterointerfaces. Changing the group-V exposure between As and Sb during growth interruptions at the InGaAs/AlAsSb interfaces did not significantly change the 2DEG mobility. With the insertion of a two monolayer InAlAs at the InGaAs/AlAsSb interfaces, the interface roughness scattering is reduced and the mobility greatly increased. The room temperature 2DEG mobility shows 66% improvement from 1.63 × 103 cm2/V·s to 2.71 × 103 cm2/V·s for a 3 nm InGaAs well.
Acoustic modulation of droplet size in a T-junction
Authors: Schmid Lothar , Franke Thomas
Published: April 2014

We introduce an approach and describe the process of acoustically driven formation of droplets in a microfluidic T-junction. Our system allows for fast and precise control of drop volume over a wide range that is fully electrically triggered. We exploit the interaction of a surface acoustic wave (SAW) excited on a piezoelectric, transparent substrate with the fluid to adjust the size of drops in a continuous microflow in real time and relate SAW intensity and drop size. Our device operates in the squeezing regime at low capillary numbers. We describe the mechanism of SAW modulated formation of a monodisperse microemulsion that forms the basis for the integration of more complex operations useful for droplet fluidic systems.
Time-dependent potential-functional embedding theory
Authors: Huang Chen , Libisch Florian , Peng Qing , Carter Emily A.
Published: April 2014

We introduce a time-dependent potential-functional embedding theory (TD-PFET), in which atoms are grouped into subsystems. In TD-PFET, subsystems can be propagated by different suitable time-dependent quantum mechanical methods and their interactions can be treated in a seamless, first-principles manner. TD-PFET is formulated based on the time-dependent quantum mechanics variational principle. The action of the total quantum system is written as a functional of the time-dependent embedding potential, i.e., a potential-functional formulation. By exploiting the Runge-Gross theorem, we prove the uniqueness of the time-dependent embedding potential under the constraint that all subsystems share a common embedding potential. We derive the integral equation that such an embedding potential needs to satisfy. As proof-of-principle, we demonstrate TD-PFET for a Na4 cluster, in which each Na atom is treated as one subsystem and propagated by time-dependent Kohn-Sham density functional theory (TDDFT) using the adiabatic local density approximation (ALDA). Our results agree well with a direct TDDFT calculation on the whole Na4 cluster using ALDA. We envision that TD-PFET will ultimately be useful for studying ultrafast quantum dynamics in condensed matter, where key regions are solved by highly accurate time-dependent quantum mechanics methods, and unimportant regions are solved by faster, less accurate methods.
Transport characteristics of a superconductor–ferromagnet composite
Authors: Kononenko V. V. , Tarenkov V. Yu. , D’yachenko A. I. , Varyuhin V. N.
Published: April 2014

The transport properties of a composite consisting of the microparticles of superconductor MgB2 and nanopowder of manganite La0.7Sr0.3MnO3 (LSMO) were studied. It was found that when the amount of the ferromagnet component in the composite was above 10% by volume, a sharp increase in the resistivity of the composite occurred. This is caused by the disruption of percolation paths through the magnesium diboride microparticles, thus leading to the formation of a network of superconductor-ferromagnet-superconductor junctions. As a result, a significant broadening of the superconducting transition of the composite was observed while its ferromagnetic properties were maintained. The obtained data indicate that Cooper pairs can pass through the layer of a half-metal ferromagnet with high (about 100%) spin polarization of the charge carriers and thickness d > 10 nm.
Low-temperature micromechanical properties of annealed and hydrostatically extruded Al–3.8 at. % Li alloy
Authors: Rusakova A. V. , Lubenets S. V. , Fomenko L. S. , Zabrodin P. A.
Published: April 2014

The structural state of as-received course-grained (CG) and extruded ultrafine-grained (UFG) billets of Al–3.8 at. % Li substitutional alloy as well as that of the samples of the same alloy subjected to tensile deformation until fracture at 4.2, 77, 295, and 350 K were studied by the microindentation method. The temperature dependence of microhardness was investigated in the temperature range of 77 to 295 K. The measurements revealed anisotropy of the micromechanical properties of the UFG samples due to the texture formed during the extrusion. It was shown that the samples which were pulled until failure exhibit correlation between the microhardness, which is a measure of local strain-hardening, and the magnitude of the local plastic shear deformation. This correlation breaks down for the UFG samples deformed at 295 and 350 K. In this case the microhardness was found to be independent on the magnitude of plastic shear deformation. The temperature dependences of microhardness for the CG and UFG samples were analyzed within the framework of thermally activated motion of dislocations through the network of local obstacles. Impurity atoms, small complexes of them, as well as forest dislocations represent the most probable energy barriers to the motion of dislocations in the alloy under investigation. Intensive plastic deformation in the process of hydrostatic extrusion produced no qualitative effect on the energy parameters of the obstacle spectrum.
Generation of high pressure shocks relevant to the shock-ignition intensity regime
Authors: Batani D. , Antonelli L. , Atzeni S. , Badziak J. , Baffigi F. , Chodukowski T. , Consoli F. , Cristoforetti G. , De Angelis R. , Dudzak R. , Folpini G. , Giuffrida L. , Gizzi L. A. , Kalinowska Z. , Koester P. , Krousky E. , Krus M. , Labate L. , Levato T. , Maheut Y. , Malka G. , Margarone D. , Marocchino A. , Nejdl J. , Nicolai Ph. , O'Dell T. , Pisarczyk T. , Renner O. , Rhee Y. J. , Ribeyre X. , Richetta M. , Rosinski M. , Sawicka M. , Schiavi A. , Skala J. , Smid M. , Spindloe Ch. , Ullschmied J. , Velyhan A. , Vinci T.
Published: April 2014

An experiment was performed using the PALS laser to study laser-target coupling and laser-plasma interaction in an intensity regime ≤1016 W/cm2, relevant for the “shock ignition” approach to Inertial Confinement Fusion. A first beam at low intensity was used to create an extended preformed plasma, and a second one to create a strong shock. Pressures up to 90 Megabars were inferred. Our results show the importance of the details of energy transport in the overdense region.
Thermocapillar instability of a two-dimensional viscoelastic planar liquid sheet in surrounding gas
Authors: Tong Ming-Xi , Yang Li-Jun , Fu Qing-Fei
Published: April 2014

A two-dimensional viscoelastic planar liquid sheet subjected to a considerable temperature gradient perpendicular to the surfaces, moving in a gas medium, was investigated in a linear scope. The sheet instability was explored by solving the dispersion relation in the sinuous mode. Results suggested that the viscoelastic liquid sheet could behave with greater stability than its Newtonian counterpart when the temperature difference was sufficiently large. Thermal effects improved sheet instability, while the liquid elasticity had a dual effect when considering the temperature difference. It should be noted that thermal effects could retard the breakup process of viscoelastic planar liquid sheets at a large liquid Weber number. Deformation retardation time was a destabilizing factor when there were great temperature differences, which was polar to the case without thermal effects. However, the effects of liquid viscosity, liquid velocity, gas-to-liquid density ratio, and surface tension were analogous, whether or not there existed a difference in temperature. Finally, the competition between thermocapillar and aerodynamic instabilities on sheet instability was examined.
Instability of a polymeric thread
Authors: Eggers J.
Published: April 2014

When a liquid containing a dilute solution of long, flexible polymers breaks up under the action of surface tension, it forms long threads of nearly uniform thickness. However, at a thickness in the order of microns, the thread becomes unstable to the formation of a non-uniform “blistering” pattern: tiny drops separated by threads of highly concentrated polymer solution. We show that standard models for the coupling between stress and polymer concentration lead to a linear instability, which exhibits very strong transient growth of the free surface perturbation. A high concentration of polymer remains in the thread part of the structure.
Enhanced magnetization and improved insulating character in Eu substituted BiFeO3
Authors: Durga Rao T. , Ranjith R. , Asthana Saket
Published: April 2014

The polycrystalline Bi1−xEuxFeO3 (x = 0, 0.05, and 0.1) ceramics were synthesized by conventional solid-state route. X-ray diffraction studies and Raman measurements revealed that the compounds crystallized in rhombohedral structure with R3c space group. In addition, a nominal percentage of orthorhombic phase was observed in 10 mol. % Eu substituted BiFeO3. Appearance of weak ferromagnetism and significant increase in Néel temperature TN in the substituted compounds were discussed on the basis of structural distortions. Enhanced remnant magnetization of 75 memu/g and large coercive field of 6.4 kÖe were observed in 10 mol. % Eu substituted BiFeO3. Equivalent circuit model was employed to estimate the grain and grain boundary contributions towards the electrical parameters such as resistance and conductivity. Non-Debye type of relaxation was confirmed from impedance and electric modulus studies. The obtained frequency variation of ac conductivity at different temperature obeys Jonscher's power law and is consistent with the correlated barrier hopping model. Temperature variations of ac conductivity explained that electronic hopping, oxygen vacancies movement, and/or creation of defects contribute to conduction in all the compounds.
Tunable states of interlayer cations in two-dimensional materials
Authors: Sato K. , Numata K. , Dai W. , Hunger M.
Published: April 2014

The local state of cations inside the Ångstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of 23Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and 23Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed.
On the ordinary mode and whistler mode instabilities in the degenerate anisotropic plasmas
Authors: Iqbal Z. , Hussain A. , Murtaza G. , Tsintsadze N. L.
Published: April 2014

Employing Vlasov-Maxwell set of equations, we have investigated the O-mode and whistler mode instability in a degenerate anisotropic magnetoplasma environment and compared the results to those reported for classical plasmas. We propose the excitation of a new banded type of instability for the O-mode case, which grows at some particular values of temperature anisotropy and external magnetic field. For the case of whistler wave, we observe instability saturation mechanism similar to the case of classical plasmas. The existence of both O-mode and whistler mode instability has been observed only for some specific range of unstable wavenumbers. The possible excitation of such instabilities in solid state plasma has been discussed, particularly for semiconductor and semimetal plasmas.
Proton conducting sodium alginate electrolyte laterally coupled low-voltage oxide-based transistors
Authors: Liu Yang Hui , Qiang Zhu Li , Shi Yi , Wan Qing
Published: April 2014

Solution-processed sodium alginate electrolyte film shows a high proton conductivity of ∼5.5 × 10−3 S/cm and a high lateral electric-double-layer (EDL) capacitance of ∼2.0 μF/cm2 at room temperature with a relative humidity of 57%. Low-voltage in-plane-gate indium-zinc-oxide-based EDL transistors laterally gated by sodium alginate electrolytes are fabricated on glass substrates. The field-effect mobility, current ON/OFF ratio, and subthreshold swing of such EDL transistors are estimated to be 4.2 cm2 V−1 s−1, 2.8 × 106, and 130 mV/decade, respectively. At last, a low-voltage driven resistor-load inverter is also demonstrated. Such in-plane-gate EDL transistors have potential applications in portable electronics and low-cost biosensors.
Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations
Authors: Akiyama Toru , Nakamura Kohji , Ito Tomonori , Freeman Arthur J.
Published: April 2014

The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal AlxGa1−xP and AlxGa1−xAs alloys, respectively, leads to a direct transition with a gap energy of ∼2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.
Calculation of laser induced impulse based on the laser supported detonation wave model with dissociation, ionization and radiation
Authors: Gan Li , Mousen Cheng , Xiaokang Li
Published: April 2014

In the laser intensity range that the laser supported detonation (LSD) wave can be maintained, dissociation, ionization and radiation take a substantial part of the incidence laser energy. There is little treatment on the phenomenon in the existing models, which brings obvious discrepancies between their predictions and the experiment results. Taking into account the impact of dissociation, ionization and radiation in the conservations of mass, momentum and energy, a modified LSD wave model is developed which fits the experimental data more effectively rather than the existing models. Taking into consideration the pressure decay of the normal and the radial rarefaction, the laser induced impulse that is delivered to the target surface is calculated in the air; and the dependencies of impulse performance on laser intensity, pulse width, ambient pressure and spot size are indicated. The results confirm that the dissociation is the pivotal factor of the appearance of the momentum coupling coefficient extremum. This study focuses on a more thorough understanding of LSD and the interaction between laser and matter.
Correlations among various blood parameters at exsanguination and their relationships to pork quality traits
Authors: Choe J. H. , Choi M. H. , Ryu Y. C. , Lim K. S. , Lee E. A. , Kang J. H. , Hong K. C. , Lee S. K. , Kim Y. T. , Moon S. S. , Lee K. W. , Rhee M. S. , Kim B. C.
Published: April 2014

The objectives of this study were to investigate the correlations between various blood parameters compared with cortisol and lactate levels under the standard pre-slaughter procedure and handling conditions and to assess their potential as indicators of pork quality traits. Despite there being no additional pre-slaughter stress treatment, there is considerable variation in blood parameters at exsanguination. Serum cortisol and blood lactate levels, widely used indicators of stress, were positively correlated with blood glucose and electrolytes, such as calcium, potassium and sodium. Moreover, these parameters were significantly correlated with a rapid rate of early postmortem glycolysis and reduced water-holding capacity. In particular, blood lactate and glucose levels significantly differed between porcine quality classes. However, other blood parameters including electrolytes did not significantly differ between quality classes though they significantly correlated with pork quality traits. Therefore, serum cortisol, blood lactate and glucose have potential as indicators of the rate and extent of postmortem metabolism and ultimate pork quality under the standard procedure and handling conditions of pre-slaughter.
Organic Molecular Crystals: From Non-Porous Structure to Potential Porous Structure Controlled by Reaction Temperature
Authors: Wu Xiao-Liu , Luo Ming-Biao , Li Jian-Qiang , Zhu Yan , Luo Feng
Published: April 2014

Reported here are two novel organic crystals, L 1 and L·(DMF)1.5 2 (DMF = (CH3)2NCHO), showing non-porous and microporous structure, where the formations can be precisely controlled by varying the reaction temperature. The reason for this exciting discovery could be directly related to the various degrees of distortion in the organic molecules as observed in 1 and 2, where detailed structural studies were carried out.
Quantum Coherence and its Impact on Biomimetic Light-Harvesting
Authors: Laos Alistair J. , Curmi Paul M. G. , Thordarson Pall
Published: April 2014

The survival of all photosynthetic organisms relies on the initial light harvesting step, and thus, after ~3 billion years of evolution energy capture and transfer has become a highly efficient and effective process. Here we examine the latest developments on understanding light harvesting, particularly in systems that exhibit an ultrafast energy transfer mechanism known as quantum coherence. With increasing knowledge of the structural and function parameters that produce quantum coherence in photosynthetic organisms, we can begin to replicate this process through biomimetic systems providing a faster and more efficient approach to harvesting and storing solar power for the worlds energy needs. Importantly, synthetic systems that display signs of quantum coherence have also been created and the first design principles for synthetic systems utilising quantum coherence are beginning to emerge. Recent claims that quantum coherence also plays a key role in ultrafast charge-separation highlights the importance for chemists, biologists, and material scientists to work more closely together to uncover the role of quantum coherence in photosynthesis and solar energy research.
Bcl2L13 is a ceramide synthase inhibitor in glioblastoma
Authors: Jensen Samuel A. , Calvert Andrea E. , Volpert Giora , Kouri Fotini M. , Hurley Lisa A. , Luciano Janina P. , Wu Yongfei , Chalastanis Alexandra , Futerman Anthony H. , Stegh Alexander H.
Published: April 2014

Significance

Molecular mechanisms of therapy (apoptosis) resistance in cancer are poorly understood. Here, we have identified Bcl2-like 13 (Bcl2L13) as a ceramide synthase inhibitor that is overexpressed in glioblastoma (GBM) and other malignancies. Bcl2L13 inhibits therapy-induced apoptosis and promotes GBM tumor growth in vivo. Mechanistically, Bcl2L13 binds to proapoptotic ceramide synthases 2 (CerS2) and 6 (CerS6) and blocks CerS2/6 complex formation and activity. Correspondingly, CerS2/6 activity and Bcl2L13 abundance are inversely correlated in GBM tumors, thereby providing a molecular explanation for the low levels of proapoptotic ceramide species in high-grade gliomas, which are associated with poor survival. To our knowledge, this work provides the first evidence of direct regulation of CerS activity by a Bcl-2 family member and establishes the Bcl2L13–CerS axis as a target for therapeutic intervention.
From a structural average to the conformational ensemble of a DNA bulge
Authors: Shi Xuesong , Beauchamp Kyle A. , Harbury Pehr B. , Herschlag Daniel
Published: April 2014

Significance

Obtaining the conformational ensembles of biological macromolecules, beyond average structures, is extremely challenging but necessary for a complete understanding of their folding and functions. Such insights may also lead to the rational design of therapeutics that can target less-ordered macromolecules and may advance the design of nanostructures and nanomachines from nucleic acids. We have applied X-ray interferometry to estimate the conformational ensemble of a small-model macromolecule, a DNA bulge, representative of helix–junction–helix building blocks of natural RNAs and designed DNA nanostructures. The measured ensemble, in combination with molecular dynamics simulations, provides testable atomic-level models. X-ray interferometry is extremely sensitive and can detect changes in the ensemble arising from different bulge sequences and solution salt conditions.
Methanogenic burst in the end-Permian carbon cycle
Authors: Rothman Daniel H. , Fournier Gregory P. , French Katherine L. , Alm Eric J. , Boyle Edward A. , Cao Changqun , Summons Roger E.
Published: April 2014

Significance

The end-Permian extinction is the most severe biotic crisis in the fossil record. Its occurrence has been attributed to increased CO2levels deriving from massive Siberian volcanism. However, such arguments have been difficult to justify quantitatively. We propose that the disruption of the carbon cycle resulted from the emergence of a new microbial metabolic pathway that enabled efficient conversion of marine organic carbon to methane. The methanogenic expansion was catalyzed by nickel associated with the volcanic event. We support this hypothesis with an analysis of carbon isotopic changes leading up to the extinction, phylogenetic analysis of methanogenic archaea, and measurements of nickel concentrations in South China sediments. Our results highlight the sensitivity of the Earth system to microbial evolution.
Systemic Activin signaling independently regulates sugar homeostasis, cellular metabolism, and pH balance in
Drosophila melanogaster
Authors: Ghosh Arpan C. , O’Connor Michael B.
Published: April 2014

Significance

Deciphering the systemic signaling mechanisms that modulate metabolic activity has important implications owing to the central role that metabolism plays in regulating organismal adaptability and survival. Here, we show that loss of
Drosophila
TGF-β/Activin-like ligand Dawdle (Daw) causes major alterations in larval metabolic activity, including accumulation of tricarboxylic acid cycle intermediates, acidification of hemolymph pH, and misregulation of insulin signaling and nuclear-encoded mitochondrial gene expression. These metabolic defects lead to a food-dependent lethality phenotype, suggesting that Daw likely influences environmental adaptability via its modulation of several central metabolic processes. These observations, coupled with previous findings in mammals and
Caenorhabditis elegans
, highlight a potentially conserved role for TGF-β/Activin signaling in regulating important metabolic processes across the animal kingdom and may have clinical implications.