bluuebunny/crossref_metadata_2025 huggingface dataset:
Model of the Transient Neurovascular Response Based on Prompt Arterial Dilation
Authors: Kim Jung Hwan , Khan Reswanul , Thompson Jeffrey K , Ress David
Published: June 2013

Brief neural stimulation results in a stereotypical pattern of vascular and metabolic response that is the basis for popular brain-imaging methods such as functional magnetic resonance imagine. However, the mechanisms of transient oxygen transport and its coupling to cerebral blood flow (CBF) and oxygen metabolism (CMRO2) are poorly understood. Recent experiments show that brief stimulation produces prompt arterial vasodilation rather than venous vasodilation. This work provides a neurovascular response model for brief stimulation based on transient arterial effects using one-dimensional convection-diffusion transport. Hemoglobin oxygen dissociation is included to enable predictions of absolute oxygen concentrations. Arterial CBF response is modeled using a lumped linear flow model, and CMRO2 response is modeled using a gamma function. Using six parameters, the model successfully fit 161/166 measured extravascular oxygen time courses obtained for brief visual stimulation in cat cerebral cortex. Results show how CBF and CMRO2 responses compete to produce the observed features of the hemodynamic response: initial dip, hyperoxic peak, undershoot, and ringing. Predicted CBF and CMRO2 response amplitudes are consistent with experimental measurements. This model provides a powerful framework to quantitatively interpret oxygen transport in the brain; in particular, its intravascular oxygen concentration predictions provide a new model for fMRI responses.
Evidence for High Translational Potential of Mesenchymal Stromal Cell Therapy to Improve Recovery from Ischemic Stroke
Authors: Eckert Mark A , Vu Quynh , Xie Kate , Yu Jingxia , Liao Wenbin , Cramer Steven C , Zhao Weian
Published: June 2013

Although ischemic stroke is a major cause of morbidity and mortality, current therapies benefit only a small proportion of patients. Transplantation of mesenchymal stromal cells (MSC, also known as mesenchymal stem cells or multipotent stromal cells) has attracted attention as a regenerative therapy for numerous diseases, including stroke. Mesenchymal stromal cells may aid in reducing the long-term impact of stroke via multiple mechanisms that include induction of angiogenesis, promotion of neurogenesis, prevention of apoptosis, and immunomodulation. In this review, we discuss the clinical rationale of MSC for stroke therapy in the context of their emerging utility in other diseases, and their recent clinical approval for treatment of graft-versus-host disease. An analysis of preclinical studies examining the effects of MSC therapy after ischemic stroke indicates near-universal agreement that MSC have significant favorable effect on stroke recovery, across a range of doses and treatment time windows. These results are interpreted in the context of completed and ongoing human clinical trials, which provide support for MSC as a safe and potentially efficacious therapy for stroke recovery in humans. Finally, we consider principles of brain repair and manufacturing considerations that will be useful for effective translation of MSC from the bench to the bedside for stroke recovery.
Epigenetic Mechanisms in Cerebral Ischemia
Authors: Schweizer Sophie , Meisel Andreas , Märschenz Stefanie
Published: June 2013

Treatment efficacy for ischemic stroke represents a major challenge. Despite fundamental advances in the understanding of stroke etiology, therapeutic options to improve functional recovery remain limited. However, growing knowledge in the field of epigenetics has dramatically changed our understanding of gene regulation in the last few decades. According to the knowledge gained from animal models, the manipulation of epigenetic players emerges as a highly promising possibility to target diverse neurologic pathologies, including ischemia. By altering transcriptional regulation, epigenetic modifiers can exert influence on all known pathways involved in the complex course of ischemic disease development. Beneficial transcriptional effects range from attenuation of cell death, suppression of inflammatory processes, and enhanced blood flow, to the stimulation of repair mechanisms and increased plasticity. Most striking are the results obtained from pharmacological inhibition of histone deacetylation in animal models of stroke. Multiple studies suggest high remedial qualities even upon late administration of histone deacetylase inhibitors (HDACi). In this review, the role of epigenetic mechanisms, including histone modifications as well as DNA methylation, is discussed in the context of known ischemic pathways of damage, protection, and regeneration.
Copper chaperone Atox1 interacts with the metal-binding domain of Wilson's disease protein in cisplatin detoxification
Authors: Dolgova Nataliya V. , Nokhrin Sergiy , Yu Corey H. , George Graham N. , Dmitriev Oleg Y.
Published: June 2013

Human copper transporters ATP7B (Wilson's disease protein) and ATP7A (Menkes' disease protein) have been implicated in tumour resistance to cisplatin, a widely used anticancer drug. Cisplatin binds to the copper-binding sites in the N-terminal domain of ATP7B, and this binding may be an essential step of cisplatin detoxification involving copper ATPases. In the present study, we demonstrate that cisplatin and a related platinum drug carboplatin produce the same adduct following reaction with MBD2 [metal-binding domain (repeat) 2], where platinum is bound to the side chains of the cysteine residues in the CxxC copper-binding motif. This suggests the same mechanism for detoxification of both drugs by ATP7B. Platinum can also be transferred to MBD2 from copper chaperone Atox1, which was shown previously to bind cisplatin. Binding of the free cisplatin and reaction with the cisplatin-loaded Atox1 produce the same protein-bound platinum intermediate. Transfer of platinum along the copper-transport pathways in the cell may serve as a mechanism of drug delivery to its target in the cell nucleus, and explain tumour-cell resistance to cisplatin associated with the overexpression of copper transporters ATP7B and ATP7A.
Controlled invariance‐based fault detection for multisensory control systems
Authors: Stoican Florin , Olaru Sorin , Bitsoris George
Published: June 2013

In this study, set theoretic methods are used to design a fault‐tolerant scheme for a multisensor control application. The basic principle is the separation of the invariant sets for the estimations of the state and tracking error under healthy and faulty functioning. The fault scenario assumes abrupt changes of the observation equations. The main contribution of this paper is the introduction of controlled invariant sets in the fault detection mechanism. The control action is chosen in order to guarantee the closed‐loop positive invariance of a candidate region when the exogenous signals (additive disturbances, noise and reference/set‐points) are bounded.
Exponential synchronisation of hybrid impulsive and switching dynamical networks with time delays
Authors: Yao Jing , Su Yongqing , Guo Yafeng , Zhang Junqi
Published: June 2013

This study formulates and studies a model of hybrid impulsive and switching dynamical networks with time delays. There are two separable switching functions acting on the network. One drives inherent network structures and the other induces finite‐state feedback in the control law. These hybrid networks have both continuous‐time and discrete‐time dynamics. At each moment, the coupling structure changes from one graph to another. At the same time, the continuous state variables may jump from one value to another. Time delays considered in this paper exist in isolated dynamical nodes, interconnections and impulsive noise disturbances. Based on Lyapunov stability theory, some new sufficient criteria are derived for exponential convergence of disagreement dynamics, which implies that network synchronisation of such hybrid‐delayed network is achieved. An illustrative example of a delayed chaotic network with switching topology and impulse effects is used to demonstrate the main results.
Delay‐dependent decentralised H∞ filtering for fuzzy interconnected systems with time‐varying delay based on Takagi–Sugeno fuzzy model
Authors: Zhang Hongbin , Yu Guanjie , Zhou Chenhui , Dang Chuangyin
Published: June 2013

This study focuses on the problem of delay‐dependent H∞ filter design for non‐linear interconnected systems with time‐varying delays via Takagi–Sugeno fuzzy models. Based on the delay‐dependent fuzzy Lyapunov–Krasovskii functional and the fuzzy‐free weighting matrix technique, the delay‐dependent stability and a prescribed H∞ performance index are guaranteed for the overall filtering‐error system. In addition, a sufficient condition for the existence of such a filter is established by using linear matrix inequalities that are numerically feasible. Finally, two examples are given to demonstrate the effectiveness and advantage of the proposed approach.
Coordinated adaptive control for three‐dimensional formation tracking with a time‐varying orbital velocity
Authors: Chen Yang‐Yang , Tian Yu‐Ping
Published: June 2013

This study considers the problem of directing a family of non‐holonomic vehicles to formation tracking a set of closed convex planar orbits in a three‐dimensional (3D) space and approach a time‐varying reference orbital velocity. A novel coordinated adaptive control law based on local neighbour‐to‐neighbour information is proposed to estimate the desired orbital velocity, so that the assumption that every vehicle in the family has access to the reference in the literature is removed. We show how the geometric extension design, projection tracking method and consensus‐based technique can be combined together to construct the formation‐tracking controller under the bidirectional commutation topology. Simulation results demonstrate the effectiveness of the proposed approach.
Diagonal stabilisation of a class of single‐input discrete‐time switched systems
Authors: Zheng Yan , Feng Gang
Published: June 2013

The stabilisation problem for a class of single‐input discrete‐time switched control systems is considered based on common diagonal quadratic Lyapunov functions and switched diagonal quadratic Lyapunov functions, respectively. Sufficient conditions for diagonal stabilisation of the concerned systems are derived in terms of linear inequalities. Numerical examples are finally used to illustrate the effectiveness of the obtained results.
Constrained model predictive control synthesis for uncertain discrete‐time Markovian jump linear systems
Authors: Lu Jianbo , Li Dewei , Xi Yugeng
Published: June 2013

This study is concerned with model predictive control (MPC) for discrete‐time Markovian jump linear systems subject to polytopic uncertainties both in system matrices and in transition probabilities between modes. The multi‐step mode‐dependent state‐feedback control law is utilised to minimise an upper bound on the expected worst‐case infinite horizon cost function. MPC designs for three cases: unconstrained case, constrained case and constrained case with low online computational burden (LOCB) are developed, respectively. All of them are proved to guarantee mean‐square stability. In the constrained case, the minimisation of the expected worst‐case infinite horizon cost function and constraints handling are dealt with in a separate way. The corresponding algorithm is proved to guarantee both the mean‐square stability and the satisfaction of the hard mode‐dependent constraints on inputs and states. To reduce the computational complexity, an algorithm with LOCB is developed by making use of the affine property of the solution to linear matrix inequalities. Finally, a numerical example is given to illustrate the proposed results.
Robust H∞ output feedback control with partly quantised information
Authors: Ge Yang , Wang Jingcheng , Li Chuang , Zhang Langwen
Published: June 2013

This study is concerned with the stability and stabilisability problems of networked control systems (NCSs) with partly quantised information. More precisely, the remote state variables transported from other sub‐systems experience different network‐induced time delays and quantisation errors, whereas the local state variables do not. This consideration is much more natural in NCSs because of the distributive nature of sensors and controllers, even systems. Network‐induced time delays are introduced as a Markov chain and quantisation errors are represented as convex polytopic uncertainties. Based on the Lyapunov–Krasovskii functional approach, sufficient conditions for the existence of a quantised robust H∞ output feedback controller for NCSs are presented. Such conditions are obtained in terms of bilinear matrix inequalities (BMIs). Furthermore, a cone complementarity algorithm is utilised to convert these BMIs into a convex optimisation problem. Finally, a simulation example is provided to demonstrate the efficiency of proposed theorems.
A game‐based control design for discrete‐time Markov jump systems with multiplicative noise
Authors: Hou Ting , Zhang Weihai , Ma Hongji
Published: June 2013

This study is devoted to investigating the inherent relationship among the H2, H∞ and H2 /H∞ control designs for discrete‐time Markov jump systems with multiplicative noise. From a new perspective of non‐zero‐sum Nash game, we show that the Nash equilibrium solution may present a unified treatment approach for these three types of control design problems by taking adequate parameters in the quadratic performance indices. Moreover, a numerical example is supplied to illustrate the proposed results.
Time–time‐transform‐based fault location algorithm for three‐terminal transmission lines
Authors: Ahmadimanesh Alireza , Shahrtash Seyyed Mohammad
Published: June 2013

In this study, time–time transformation is employed to reveal the time of arrival of the fault‐generated travelling waves, where these time instants are then used in a fault location algorithm for three‐terminal single‐ and double‐circuit transmission lines. The performance of the proposed fault location algorithm under different line lengths and fault conditions such as fault types, faulted sections, fault locations, fault resistances and fault inception angles are investigated and the high accuracy of the proposed method is approved in all these conditions even, in fault inception angle of zero and for faults on tap point.
Comparing reliability insurance scheme to performance‐based regulation in terms of consumers’ preferences
Authors: Abedi Seyyed Mostafa , Haghifam Mahmoud Reza
Published: June 2013

Reliability insurance contracts enable consumers to cover fully or partially the financial risk, which they face as a result of outages. These contracts allow consumers to determine their coverage levels according to their value for reliability service (i.e. cost incurred for outages), and pay corresponding premiums to the utility. The utility is then required to reimburse consumers for outages according to their outage cost. Consumer's outage cost is extremely dependent on the duration of outages and this dependency is well defined by function known as customer damage function (CDF). To enable consumers to fully cover reliability risks, utility should provide consumers with contracts, which allow them to select coverage levels according to their CDF. In this study, primarily, CDF‐based insurance contracts are designed, and in following, with respect to these contracts, investment incentives provided by reliability insurance scheme are calculated and compared to incentives provided by performance‐based regulation, especially in terms of consumers’ preferences. Finally, by a numerical example, the effects of these incentives on the utility investment are illustrated.
Eigenvalue‐optimisation‐based optimal power flow with small‐signal stability constraints
Authors: Li Peijie , Wei Hua , Li Bin , Yang Yude
Published: June 2013

The occasional oscillation in large interconnected power system can cause the small‐signal stability problem. As a complement to the damping controllers, the small‐signal stability constrained‐optimal power flow (SSSC‐OPF) model has been used to obtain the required stability margin. Applying the approximate technique to SSSC‐OPF may not only increase the value of the objective function, but also suffer the oscillation of the iterations during the solving process. In this study, an eigenvalue‐optimisation‐based non‐linear semi‐definite programming (NLSDP) model and algorithm is proposed for the small‐signal stability constraints. It is a significant challenge to model the SSSC‐OPF directly because of the implicit and non‐Lipschitz property for the spectral abscissa of the system state matrix. Based on the Lyapunov theorem, the positive definite constraints can express the small‐signal stability accurately and equivalently, so that SSSC‐OPF can be modelled as NLSDP. Afterward, the NLSDP model is transformed into a non‐linear programming problem by formulating the positive definite constraints into non‐linear ones, which can be solved by the interior point method finally. Numerical simulations for two systems confirm the validity of the model and the robustness of the algorithm.
Hybrid methodology for fault distance estimation in series compensated transmission line
Authors: Ray Papia , Panigrahi Bijaya Ketan , Senroy Nilanjan
Published: June 2013

This study proposes an accurate hybrid fault location technique, with wavelet transform (WT) and wavelet packet transform (WPT) combining artificial neural network (ANN) in series compensated transmission line. Proposed method uses single end measurement of current and voltage signal of one cycle duration from the inception of fault. Thereafter features of collected signal are extracted by discrete WT and WPT and optimal feature is selected using forward feature selection algorithm. Selected features are then fed as input to ANN for fault location. Feasibility of the proposed method has been tested for all ten types of fault on two different test systems. Testing of the proposed method is done for varying fault resistance and fault inception angle over different fault location for each type of fault. Performance of the proposed method is evaluated in terms of absolute error and mean error which is found to be quite satisfactory. Simulation result shows that maximum error of less than 0.35% and mean error of less than 0.25% is achieved, which demonstrate high accuracy and robustness of the proposed technique. Results are compared with other different feature selection techniques.
Multi‐FPGA digital hardware design for detailed large‐scale real‐time electromagnetic transient simulation of power systems
Authors: Chen Yuan , Dinavahi Venkata
Published: June 2013

Large‐scale electromagnetic transient simulation of power systems in real‐time using detailed modelling is computationally very demanding. This study introduces a multi‐field programmable gate array (FPGA) hardware design for this purpose. A functional decomposition method is proposed to map FPGA hardware resources to system modelling. This systematic method lends itself to fully pipelined and parallel hardware emulation of individual component models and numerical solvers, while preserving original system characteristics without the need for extraneous components to partition the system. Proof‐of‐concept is provided in terms of a 3‐FPGA and 10‐FPGA real‐time hardware emulation of a three‐phase 42‐bus and 420‐bus power systems using detailed modelling of various system components and iterative non‐linear solution on a 100 MHz FPGA clock. Real‐time results are compared with offline simulation results, and conclusions are derived on the performance and scalability of this multi‐FPGA hardware design.
Probabilistic load flow computation with polynomial normal transformation and Latin hypercube sampling
Authors: Cai Defu , Shi Dongyuan , Chen Jinfu
Published: June 2013

A probabilistic load flow method based on polynomial normal transformation (PNT) and Latin hypercube sampling (LHS) is proposed. The correlation between input random variables has been taken into consideration. The proposed method uses the statistical moments and correlation matrix of input random variables instead of their marginal distribution functions and joint distribution functions, which are very difficult to be obtained, to establish their probability distribution models by PNT and LHS. The statistical moments and probability distribution functions of node voltage and line flow are calculated by Monte Carlo simulation method. Performance of the proposed method is investigated using IEEE 14‐bus and IEEE 118‐bus test systems. The impacts of correlation factor on the statistical moments of power injections and system operation are analysed. Finally, conclusions are duly drawn.
Active islanding detection method using d‐axis disturbance signal injection with intelligent control
Authors: Lin Faa‐Jeng , Huang Yi‐Sheng , Tan Kuang‐Hsiung , Chiu Jian‐Hsing , Chang Yung‐Ruei
Published: June 2013

An active islanding detection method using d‐axis disturbance signal injection with intelligent control is proposed in this study. The proposed active islanding detection method is based on injecting a new disturbance signal into the system through the d‐axis current that leads to a frequency deviation at the terminal of the resistance inductance and capacitance (RLC) load when the grid is disconnected. The feasibility of the proposed method is evaluated under the UL1741 anti‐islanding test configuration. The proposed d‐axis disturbance signal‐injection method is intended to achieve a reliable detection with quasi‐zero non‐detection zone, minimum effects on power quality and easy implementation without additional sensing devices or equipments. Moreover, in order to achieve accurate tracking control of active and reactive power and rapid response of the islanding detection of the distributed generator (DG) system, a wavelet fuzzy neural network (WFNN) intelligent controller is proposed to replace the conventional proportional–integral controller for the control of the DG system. Furthermore, the network structure and the online learning algorithm of the WFNN are introduced in detail. Finally, the feasibility and effectiveness of the proposed d‐axis disturbance signal‐injection method are verified with experimental results.
Robust, fast and optimal solution of practical economic dispatch by a new enhanced gradient‐based simplified swarm optimisation algorithm
Authors: Azizipanah‐Abarghooee Rasoul , Niknam Taher , Gharibzadeh Masihallah , Golestaneh Faranak
Published: June 2013

Nowadays, the rising concern about the costs of fuel and operation of generating units in the energy control centre deserve progress of solution methodologies for the practical economic dispatch (ED) problems. ED aims to schedule the committed units’ output power while satisfying practical constraints and load demand. The generator ramp rate limits, non‐convex and discontinuous nature of prohibited operating zones, non‐smooth characteristic of valve‐point effects, multi‐fuel type of generation units, transmission line losses and the large number of units in practical power plants make this problem very hard to solve. In this study, a new solution method of integrating the classical gradient‐based optimisation technique and a new enhanced simplified swarm optimisation algorithm is comprehensively presented and successfully applied to determine the feasible, robust, fast and globally or near‐globally optimal solution within a rapid timeframe for the ED problems. The simulations are carried out on four‐test systems, including 10‐, 15‐, 40‐ and 80‐units using the proposed optimisation technique in the Fortran Power Station 4.0 software. The current proposal outperforms other methods showcased in the recent state‐of‐the art literature in the area.
Theoretical analysis on the relationship between left ventricular energetic efficiency and acute infarct size
Authors: Shimayoshi Takao , Hasegawa Yuki , Mishima Mitsuharu , Matsuda Tetsuya
Published: June 2013

Energetic efficiency is an important indicator of cardiac function in acute myocardial infarction. However, the relationship between cardiac energetic efficiency and infarct size is not perfectly elucidated. In this study, the relationship is analysed by means of simulation using a theoretical model of the guinea pig left ventricle. In simulation with varied ratios of infarct area, pressure–volume area (PVA), which is an index of total mechanical energy by ventricular contraction, and myocardial oxygen consumption (MVO2) are calculated for each infarct ratio. Then, change of PVA when MVO2 alters (PVA/MVO2) as a well‐known index of energy conversion efficiency is evaluated. In addition, PVA/VO2, which represents a ratio of PVA change to alteration of mean oxygen consumption of myocytes except for infarct myocytes, is introduced as an index for real energetic efficiency. In simulation results, PVA/MVO2 increases but PVA/VO2 decreases as infarct area expands, because with expansion of infarct area PVA decreases but VO2 remains almost unchanged because of larger shortening of myocytes. This implies that the enlargement of shortening of noninfarcted myocyte to compensate for depression of cardiac output is a potential cause of myocardial remodelling.
Synthesis and characterisation of polymethylmethacrylate/nanosilica and nanosilica/polymethylmethacrylate core–shell structure composite microspheres
Authors: Lin Tao , Zheng Yuying
Published: June 2013

The nanosilica/polymethylmethacrylate (SiO2/PMMA) and polymethylmethacrylate/nanosilica (PMMA/SiO2) core–shell structure composite microspheres were fabricated by dispersion polymerisation under similar reaction conditions. These two kinds of microspheres are different to each other by their opposite core–shell structure. The composite mircospheres were characterised by infrared spectra, transmission electron microscopy and thermal gravimetric analysis (TGA). The diameter of SiO2/PMMA particles is about 50 nm. The average diameters of PMMA/SiO2 particles are in the range of 60–70 nm as KH570 was added after methyl methacrylate polymerisation reaction for 2 h. The TGA curves show that the thermal stability of SiO2/PMMA is better than PMMA/SiO2.
Formation of thin tubular ZnO nanostructure through spontaneously formed porous Zn/ZnO nanoparticles
Authors: Ma Pei , Jie Yanni , Jin Guang Yin , Xu Xin Long , Ren Zhao Yu , Fan Hai Ming
Published: June 2013

The diverse morphology of ZnO nanostructure demonstrates attractive applications and allows an insight into the interesting mechanism for synthesis of other nanomaterials. However, synthesis of an ultrathin ZnO nanotube is still challenging by conventional solution methods at low temperature. Here, inspired by the nanoscale Kirkendall effect on the nanoporous formation, sub‐50 nm nanotubular ZnO were synthesised by a facile low‐temperature hydrothermal treatment using Zn nanoparticles as precursor and seed. The present tiny nanotubes were recognised with the comparable size of spontaneously formed Zn/ZnO seed nanoparticles at an early stage, which hints at the clue to synthesise the tubular nanostructure in controllable dimensions. Moreover, the success of hierarchical tubular ZnO superstructures illustrates the possibility to achieve more complex and well‐ordered superstructures by self‐assembly of Zn/ZnO seeds.
Formation of hierarchical LiMn2O4 dual‐porous nanostructures by pyrolysis of gel precursor
Authors: Tong Yanhua , Li Yingying , Lv Wanyu , Zhao Zhenzhen , Zhang Min
Published: June 2013

A precursor‐pyrolysing route to fabricate hierarchical LiMn2O4 porous nanostructures is presented. The product was characterised by X‐ray powder diffraction, scanning electron microscopy, a transmission electron microscope, a high‐resolution transmission electron microscope and a micromeritics analyser. The results show that the resulting material is a honeycomb‐like dual‐porous structure. One is quasi‐hemispherical macropores of several hundred nanometres and the other is slit mesopores of several nanometres. This dual‐porous nanostructure is composed of many ultrafine nanocrystallines whose size mainly falls into the range from 3 to 10 nm. Moreover, it has a large Brunauer–Emmett‐Teller‐specific surface area of 116 m2/g. The formation of such dual pores should be attributed to the Kirkendall effect and surface diffusion.
Photodissociation of carbon dioxide in singlet valence electronic states. I. Six multiply intersecting ab initio potential energy surfaces
Authors: Grebenshchikov Sergy Yu.
Published: June 2013

The global potential energy surfaces of the first six singlet electronic states of CO2, 1—31A′, and 1—31A″ are constructed using high level ab initio calculations. In linear molecule, they correspond to \documentclass[12pt]{minimal}\begin{document}$\tilde{X}^1\Sigma _g^+$\end{document}X̃1Σg+, 11Δu, \documentclass[12pt]{minimal}\begin{document}$1^1\Sigma _u^-$\end{document}11Σu−, and 11Πg. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true intersections, both conical and glancing. Near degeneracies can be found for each pair of six states and many intersections involve more than two states. In particular, a fivefold intersection dominates the Franck-Condon zone for the ultraviolet excitation from the ground electronic state. The seam of this intersection traces out a closed loop. All states are diabatized, and a diabatic 5 × 5 potential matrix is constructed, which can be used in quantum mechanical calculations of the absorption spectrum of the five excited singlet valence states.
Volumetric measurements and simulations of the vortex structures generated by low aspect ratio plunging wings
Authors: Calderon D. E. , Wang Z. , Gursul I. , Visbal M. R.
Published: June 2013

Volumetric three-component velocimetry measurements have been performed on low aspect ratio wings undergoing a small amplitude pure plunging motion. This study focuses on the vortex flows generated by rectangular and elliptical wings set to a fixed geometric angle of attack of α = 20°. An investigation into the effect of Strouhal number illustrates the highly three-dimensional nature of the leading edge vortex as well as its inherent ability to improve lift performance. Computational simulations show good agreement with experimental results, both demonstrating the complex interaction between leading, trailing, and tip vortices generated in each cycle. The leading edge vortex, in particular, may deform significantly throughout the cycle, in some cases developing strong spanwise undulations. These are at least both Strouhal number and planform dependent. One or two arch-type vortical structures may develop, depending on the aspect ratio and Strouhal number. At sufficiently high Strouhal numbers, a tip vortex ring may also develop, propelling itself away from the wing in the spanwise direction due to self-induced velocity.
Recombination luminescence of LaPO4-Eu and LaPO4-Pr nanoparticles
Authors: Malyy T. S. , Vistovskyy V. V. , Khapko Z. A. , Pushak A. S. , Mitina N. E. , Zaichenko A. S. , Gektin A. V. , Voloshinovskii A. S.
Published: June 2013

The study of the spectral-luminescence parameters of LaPO4-Eu and LaPO4-Pr nanoparticles upon excitation by the synchrotron radiation with photon energies 4–40 eV was performed. The differences of the luminescence intensity dependence on the size for LaPO4-Eu and LaPO4-Pr nanoparticles excited at the range of matrix transparency, the range of band-to-band transitions, and the range of electronic excitation multiplication were revealed. The observed regularities are explained in terms of the electron-phonon and electron-electron scattering, surface losses, and exciton diffusion. The ratio between the length of thermalization and electron mean free path and the size of nanoparticle is determinative for the luminescence intensity upon excitation in the range of fundamental absorption of matrix and X-ray excitation.
Lattice mismatch accommodation via oxygen vacancy ordering in epitaxial La0.5Sr0.5CoO3-δ thin films
Authors: Gazquez J. , Bose Shameek , Sharma M. , Torija M. A. , Pennycook S. J. , Leighton C. , Varela M.
Published: June 2013

The properties of complex oxide films depend sensitively on epitaxial strain. This strain affects bond lengths and angles, and defect types and densities, thus impacting physical properties. In this work we perform detailed characterization of depth-dependent strain in epitaxial La0.5Sr0.5CoO3-δ (LSCO) films on SrTiO3(001), SrTiO3(110), and LaAlO3(001) substrates, combining high resolution x-ray diffraction and scanning transmission electron microscopy, in addition to geometric phase analysis. We elucidate a fundamental link between strain state and O vacancy ordering in LSCO films, where lattice mismatch and crystallographic orientation can be used to manipulate the modulation vector of the long-range vacancy order, thus providing a new approach to tailor the properties of such films.
Preparation of bionic nanostructures from butterfly wings and their low reflectivity of ultraviolet
Authors: Han Z. W. , Niu S. C. , Li W. , Ren L. Q.
Published: June 2013

This letter presents a bionic study on Parnassius butterfly wings with a prominent ultraviolet (UV)-selective antireflection effect. An accurate SiO2 inverse replica of the nanostructure with a unique optical function from butterfly wings is prepared in multiscale by combining a sol-gel process and subsequent selective etching. It is found that the original nanostructures of biotemplate are well inherited and the excellent UV-antireflection function could be modulated by tunable parameters such as the replica spacing, width, distribution, and shape as well as formation.
An effective network reduction approach to find the dynamical repertoire of discrete dynamic networks
Authors: Zañudo Jorge G. T. , Albert Réka
Published: June 2013

Discrete dynamic models are a powerful tool for the understanding and modeling of large biological networks. Although a lot of progress has been made in developing analysis tools for these models, there is still a need to find approaches that can directly relate the network structure to its dynamics. Of special interest is identifying the stable patterns of activity, i.e., the attractors of the system. This is a problem for large networks, because the state space of the system increases exponentially with network size. In this work, we present a novel network reduction approach that is based on finding network motifs that stabilize in a fixed state. Notably, we use a topological criterion to identify these motifs. Specifically, we find certain types of strongly connected components in a suitably expanded representation of the network. To test our method, we apply it to a dynamic network model for a type of cytotoxic T cell cancer and to an ensemble of random Boolean networks of size up to 200. Our results show that our method goes beyond reducing the network and in most cases can actually predict the dynamical repertoire of the nodes (fixed states or oscillations) in the attractors of the system.
Thermal runaway in multijunction solar cells
Authors: Zimmermann Claus G.
Published: June 2013

A small fraction of GaInP2/GaAs/Ge triple junction solar cells exposed to the 6× concentrated air mass zero spectrum at 523 K for 5 min was found to be severely shunted afterwards. A combination of electroluminescence imaging and focused ion beam cross sectioning revealed that pre-existing top-middle cell shunts were responsible for the observed degradation. Joule heating in the shunt resistance limiting Ge substrate is modeled and exhibits a thermal runaway effect above a critical voltage, in agreement with the experimental observation. The implications for current and future multijunction cells are discussed.
Impact of doping on the ionic conductivity of ceria: A comprehensive model
Authors: Wang Hao , Chroneos Alexander , Schwingenschlögl Udo
Published: June 2013

Doped ceria is considered as an electrolyte for solid oxide fuel cell applications. The introduction of dopants in the ceria lattice will affect its electronic structure and, in turn, its ionic conductivity. Simulation of these issues using density functional theory becomes complicated by the random distribution of the constituent atoms. Here we use the generalized gradient approximation with on-site Coulomb interaction in conjunction with the special quasirandom structures method to investigate 18.75% and 25% Y, Gd, Sm, Pr, and La doped ceria. The calculated lattice constants and O migration energies allow us to explain the behavior of the conductivity as obtained in experiments.
Plasma expansion into a waveguide created by a linearly polarized femtosecond laser pulse
Authors: Lemos N. , Grismayer T. , Cardoso L. , Figueira G. , Issac R. , Jaroszynski D. A. , Dias J. M.
Published: June 2013

We demonstrate the efficient generation of 4 mm and 8 mm long plasma waveguides in hydrogen and helium. These waveguides have matching spots sizes for 13 to 34 μm laser beams. The plasma waveguides are created by ultra-short laser pulses (sub-picosecond) of moderate intensities, ∼1015–1016 W cm−2, that heat the plasma to initial temperatures of tens of eV in order to create a hot plasma column that will expand into a plasma waveguide. We have determined that the main heating mechanism when using fs laser pulses and plasma densities ∼1018–19 cm−3 is Above Threshold Ionization. Detailed time and space electron density measurements are presented for the laser produced plasma waveguides.
Kinetic particle simulation of discharge and wall erosion of a Hall thruster
Authors: Cho Shinatora , Komurasaki Kimiya , Arakawa Yoshihiro
Published: June 2013

The primary lifetime limiting factor of Hall thrusters is the wall erosion caused by the ion induced sputtering, which is predominated by dielectric wall sheath and pre-sheath. However, so far only fluid or hybrid simulation models were applied to wall erosion and lifetime studies in which this non-quasi-neutral and non-equilibrium area cannot be treated directly. Thus, in this study, a 2D fully kinetic particle-in-cell model was presented for Hall thruster discharge and lifetime simulation. Because the fully kinetic lifetime simulation was yet to be achieved so far due to the high computational cost, the semi-implicit field solver and the technique of mass ratio manipulation was employed to accelerate the computation. However, other artificial manipulations like permittivity or geometry scaling were not used in order to avoid unrecoverable change of physics. Additionally, a new physics recovering model for the mass ratio was presented for better preservation of electron mobility at the weakly magnetically confined plasma region. The validity of the presented model was examined by various parametric studies, and the thrust performance and wall erosion rate of a laboratory model magnetic layer type Hall thruster was modeled for different operation conditions. The simulation results successfully reproduced the measurement results with typically less than 10% discrepancy without tuning any numerical parameters. It is also shown that the computational cost was reduced to the level that the Hall thruster fully kinetic lifetime simulation is feasible.
Shock-induced concentric rings in femtosecond laser ablation of glass
Authors: Heins Alan , Guo Chunlei
Published: June 2013

Both the single and multiple pulse ablation of dielectrics with high-intensity femtosecond lasers have been well studied. Additionally, the “pulse-shaping” regime, in which temporal peaks are separated by picoseconds, has also been investigated. In this paper, we show that a “prepulse configuration”—where one pulse is followed several nanoseconds later by a much stronger pulse—is qualitatively different from any of the previously investigated regimes. In particular, it leads to the recently discovered “concentric rings” feature in glass. We show that the damage pattern produced in glass is very different for two pulses separated by nanoseconds than for two pulses separated by either milliseconds or picoseconds. For nanosecond separations, the second pulse interacts with the shock wave created by the first, significantly altering the damage pattern. In addition to producing novel structures, this pump-probe technique provides a new way of studying ablation plume and shockwave dynamics.
Nanomechanical actuation from phase transitions in individual VO2 micro-beams
Authors: Guo Hua , Wang Kevin , Deng Yu , Oh Y. , Syed Asif S. A. , Warren O. L. , Shan Z. W. , Wu J. , Minor A. M.
Published: June 2013

The mechanical response due to structural phase transitions in individual VO2 nanowires was quantitatively investigated in situ in a transmission electron microscope. The electron beam was employed to locally heat the nanowire, and stress-strain was measured in situ using a microfabricated push-to-pull device. Tensile loading was found to increase the metal-insulator transition temperature and decrease the insulator-insulator transition temperature, consistent with the phase diagram of VO2. These phase transitions resulted in an axial mechanical response of the VO2 nanowires, an effect that can potentially be used to actuate nanostructures or gauge the local temperature change induced by electron beam irradiation.
The effect of nanocomposite polymeric layer on the radiation of antisymmetric zero-order Lamb wave in a piezoelectric plate contacting with liquid
Authors: Kuznetsova I. E. , Zaitsev B. D. , Borodina I. A. , Shikhabudinov A. M. , Teplykh A. A. , Manga E. , Feuillard G.
Published: June 2013

A nanocomposite polymeric layer is proposed to be used for increasing the efficiency of ultrasound radiation into the liquid by antisymmetric zero-order (A0) Lamb waves propagating in piezoelectric plates. The theoretical and experimental investigations of the influence of the nanocomposite polymeric layers on the efficiency and radiation angle of acoustic wave into liquid were carried out. It has been theoretically shown that the use of the layer of the polyethylene of low density with nanoparticles of cadmium sulfide of concentration 25% between the plate of 128YX LiNbO3 and water medium allows to increase the radiation attenuation on ∼1 dB/λ if the ratio of the thicknesses of the layer and plate is equal to 0.16 at the frequency of 1.3 MHz. The experimental data were in a good agreement with theoretical results. It has been also shown that the presence of nanocomposite film leads to the increase of the radiation angle of bulk acoustic wave in liquid and allows the effective operation of the radiator not only in the sweet water but also in salt one. The obtained results may be used for the development of effective radiators/receivers of acoustic waves in liquids for flow meters and for underwater communication systems.
Identifying different mechanisms of circular photogalvanic effect in GaAs/Al0.3Ga0.7As two dimensional electron gas by photo-modulation technique
Authors: Ma Hui , Jiang Chongyun , Liu Yu , Zhu Laipan , Qin Xudong , Chen Yonghai
Published: June 2013

We investigate the circular photogalvanic effect (CPGE) excited by sub-bandgap radiation in a GaAs/Al0.3Ga0.7As two dimensional electron gas and tune its amplitude by synchronously imposing an above-bandgap unpolarized light at normal incidence. With this photo-modulation technique, we identify two microscopic mechanisms of CPGE according to the dramatic change of apparent Rashba and Dresselhaus effects. We suggest the optical transitions to be Franz-Keldysh and intraband regime, respectively. Both regimes coexist in conventional CPGE and the intraband regime dominates at sufficient modulation power.
A flexible high potential printed battery for powering printed electronics
Authors: Gaikwad Abhinav M. , Steingart Daniel A. , Nga Ng Tse , Schwartz David E. , Whiting Gregory L.
Published: June 2013

Mechanically flexible arrays of alkaline electrochemical cells fabricated using stencil printing onto fibrous substrates are shown to provide the necessary performance characteristics for driving ink-jet printed circuits. Due to the dimensions and material set currently required for reliable low-temperature print processing of electronic devices, a battery potential greater than that sourced by single cells is typically needed. The developed battery is a series interconnected array of 10 low resistance Zn-MnO2 alkaline cells, giving an open circuit potential of 14 V. This flexible battery is used to power an ink-jet printed 5-stage complementary ring oscillator based on organic semiconductors.
A review of pressure anisotropy caused by electron trapping in collisionless plasma, and its implications for magnetic reconnection
Authors: Egedal Jan , Le Ari , Daughton William
Published: June 2013

From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, βe∞, the pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for electron acceleration.
Structural and dielectric properties of sputtered SrxZr(1−x)Oy
Authors: Grube Matthias , Martin Dominik , Weber Walter M. , Mikolajick Thomas , Riechert Henning
Published: June 2013

Over the past years, high-k dielectrics have been incorporated into modern semiconductor devices. One example is ZrO2, which has been introduced in memory applications. This paper elucidates some difficulties with pure ZrO2 like unintended crystallization during the growth of the dielectric and the evolution of the monoclinic phase, which reduces the k-value. The admixture of Sr is shown as a solution to circumvent those issues. A detailed structural analysis for a varying stoichiometry ranging from pure ZrO2 to the perovskite SrZrO3 is given. The detected crystal structures are correlated to our observations of the dielectric properties obtained by an electrical characterization.