bluuebunny/crossref_metadata_2025 huggingface dataset:
On the longitudinal optimal perturbations to inviscid plane shear flow: formal solution and asymptotic approximation
Authors: Arratia C. , Chomaz J.-M.
Published: November 2013

We study the longitudinal linear optimal perturbations (which maximize the energy gain up to a prescribed time $T$) to inviscid parallel shear flow, which present unbounded energy growth due to the lift-up mechanism. Using the phase invariance with respect to time, we show that for an arbitrary base flow profile and optimization time, the computation of the optimal longitudinal perturbation reduces to the resolution of a single one-dimensional eigenvalue problem valid for all times. The optimal perturbation and its amplification are then derived from the lowest eigenvalue and its associated eigenfunction, while the remainder of the infinite set of eigenfunctions provides an orthogonal base for decomposing the evolution of arbitrary perturbations. With this new formulation we obtain, asymptotically for large spanwise wavenumber ${k}_{z} , $ a prediction of the optimal gain and the localization of inviscid optimal perturbations for the two main classes of parallel flows: free shear flow with an inflectional velocity profile, and wall-bounded flow with maximum shear at the wall. We show that the inviscid optimal perturbations are localized around the point of maximum shear in a region with a width scaling like ${ k}_{z}^{- 1/ 2} $ for free shear flow, and like ${ k}_{z}^{- 2/ 3} $ for wall-bounded shear flows. This new derivation uses the stationarity of the base flow to transform the optimization of initial conditions in phase space into the optimization of a temporal phase along each trajectory, and an optimization among all trajectories labelled by their intersection with a codimension-1 subspace. The optimization of the time phase directly imposes that the initial and final energy growth rates of the optimal perturbation should be equal. This result requires only time invariance of the base flow, and is therefore valid for any linear optimal perturbation problem with stationary base flow.
ALMOST AUTOMORPHIC SOLUTIONS FOR DIFFERENTIAL EQUATIONS WITH PIECEWISE CONSTANT ARGUMENT
Authors: ZHANG LI-LI , LI HONG-XU
Published: November 2013

Using the method of exponential dichotomies, we establish a new existence and uniqueness theorem for almost automorphic solutions of differential equations with piecewise constant argument of the form$$\begin{eqnarray*}{x}^{\prime } (t)= A(t)x(t)+ B(t)x(\lfloor t\rfloor )+ f(t), \quad t\in \mathbb{R} ,\end{eqnarray*}$$where$\lfloor \cdot \rfloor $denotes the greatest integer function, and$A(t), B(t): \mathbb{R} \rightarrow { \mathbb{R} }^{q\times q} $,$f(t): \mathbb{R} \rightarrow { \mathbb{R} }^{q} $are all almost automorphic.
Nitrogen use and food production in European regions from a global perspective
Authors: VAN GRINSVEN H. J. M. , SPIERTZ J. H. J. , WESTHOEK H. J. , BOUWMAN A. F. , ERISMAN J. W.
Published: November 2013

Current production systems for crops, meat, dairy and bioenergy in the European Union (EU) rely strongly on the external input of nitrogen (N). These systems show a high productivity per unit of land. However, the drawback is a complex web of N pollution problems contributing in a major way to degradation of ecosystems. European Union Directives and national policies have improved nutrient management and reduced fertilizer N use in most European countries, which has curbed the N pollution trends particularly in regions with high stocking rates of animals. However, improvement is slowing down and environmental targets for N are not within reach. Building on the 2011 European Nitrogen Assessment, the current paper reviews key features of the complex relationships between N use and food production in Europe in order to develop novel options for a more N-efficient, less N-polluting and secure European food system. One option is to relocate feed and livestock production from Northwestern to Central and Eastern Europe. This would allow a reduction of N rates and N pollution in cereal production in Northwest Europe by 30% (50 kg N/ha), while increasing total cereal production in Europe. Another option is a change towards legume-based cropping systems to produce animal feed, in order to decrease dependence on N fertilizer and feed imports. The greatest challenge for Europe is to decrease the demand for feed commodities, and thus for land and N, by a shift to more balanced (and healthier) diets with less animal protein. These drastic changes can be stimulated by targeted public–private research funding, while the actual implementation can be enhanced by smart payment schemes using, for example money from the Common Agricultural Policy, certification and agreements between stakeholders and players in the food and energy chain. Involving networks of consumers, producers and non-governmental organizations is critical. An effective strategy starts with convincing consumers with a Western diet to eat less meat and dairy by communicating the associated health benefits and smaller ecological footprints. Internalizing the cost of N pollution leading to increased prices for N-intensive food products may also enhance involvement of consumers and provide financial resources to compensate farmers for loss of income and extra costs for stricter N measures.
Partition: The “Pulsing Heart that Grieved”
Authors: Larson Gerald James
Published: November 2013

By way of framing Manan Ahmed Asif's intriguing personal (and poetic) reflection entitled “Idol in the Archive” in this current issue of the Journal of Asian Studies, it must always be remembered that in August 1947, the old British Raj gave birth to not one but two independent nation-states, namely India and Pakistan. India became a “Sovereign Democratic Republic” when its Constitution came into effect on January 26, 1950, following adoption of its draft Constitution by its Constituent Assembly on November 26, 1949. Pakistan took a bit longer, becoming the “Islamic Republic of Pakistan” when its first Constitution came into effect on March 23, 1956. Furthermore, of course, Pakistan underwent secession of its Eastern Province with the founding of the “People's Republic of Bangladesh” in 1971. It is hardly an exaggeration to suggest that partition is the defining event of modern independent India and Pakistan, and, more than that, continues to be the defining event of India and Pakistan even after more than fifty years of independence.
A NOTE ON TRAVELLING WAVES IN COMPETITIVE REACTION SYSTEMS
Authors: FORBES LAWRENCE K.
Published: November 2013

This note considers an established reaction–diffusion model for a combustion system, in which there are competing endothermic and exothermic reaction pathways. A combustion front is assumed to move at constant speed through the medium. An asymptotic theory is presented for solid fuels in which material diffusion is ignored, and it allows a simple and complete analysis of the approximate system in the phase plane. Both the adiabatic and nonadiabatic cases are discussed.
Nicotinamide phosphoribosyltransferase (NAMPT) activity is essential for survival of resting lymphocytes
Authors: Pittelli Maria , Cavone Leonardo , Lapucci Andrea , Oteri Claudia , Felici Roberta , Niccolai Elena , Amedei Amedeo , Chiarugi Alberto
Published: November 2013

NAD biosynthesis is emerging as a key regulator of immune cell functions. Accordingly, inhibitors of the NAD‐synthesizing enzyme nicotinamide phosphoribosyltransferase (NAMPT) have anti‐inflammatory effects, counteract hematological malignancies and are being tested in clinical trials. Still, their effect on different cell types still waits to be fully investigated. Here we show that the NAMPT inhibitor FK866 induces NAD depletion in various mouse organs but selectively causes dramatic atrophy of the spleen red pulp. Accordingly, in cultured mouse lymphocytes exposed to FK866, NAD contents drop to 50% of basal values within 2 days, a condition sufficient to prompt complete cell death. Cultures of human lymphocytes are more resistant to FK866 and sustain a 50% NAD reduction for 5 days before dying. Death of both cell types can be prevented by different NAD precursors, indicating critical NAD homeostasis in lymphocytes. Indeed, inhibition of the NAD‐consuming enzyme poly(ADP‐ribose) polimerase‐1 suffices to prevent FK866‐induced NAD depletion and death of both lymphocyte types. Poly(ADP‐ribose) polymerase‐1‐null lymphocytes also undergo lower NAD depletion and reduced cell death when exposed to the drug. At variance with other cell types, neither apoptosis nor autophagy are exclusively responsible for lymphocyte death by FK866, consistent with a general impairment of lymphocyte homeostasis following NAD depletion. Data demonstrate a unique sensitivity of resting lymphocytes to NAD‐depleting agents, providing new hints of relevance to lymphocyte biology and therapeutic interventions with NAMPT inhibitors.
Transcriptional regulation is insufficient to explain substrate‐induced flux changes in Bacillus subtilis
Authors: Chubukov Victor , Uhr Markus , Le Chat Ludovic , Kleijn Roelco J , Jules Matthieu , Link Hannes , Aymerich Stephane , Stelling Jörg , Sauer Uwe
Published: November 2013

One of the key ways in which microbes are thought to regulate their metabolism is by modulating the availability of enzymes through transcriptional regulation. However, the limited success of efforts to manipulate metabolic fluxes by rewiring the transcriptional network has cast doubt on the idea that transcript abundance controls metabolic fluxes. In this study, we investigate control of metabolic flux in the model bacterium Bacillus subtilis by quantifying fluxes, transcripts, and metabolites in eight metabolic states enforced by different environmental conditions. We find that most enzymes whose flux switches between on and off states, such as those involved in substrate uptake, exhibit large corresponding transcriptional changes. However, for the majority of enzymes in central metabolism, enzyme concentrations were insufficient to explain the observed fluxes—only for a number of reactions in the tricarboxylic acid cycle were enzyme changes approximately proportional to flux changes. Surprisingly, substrate changes revealed by metabolomics were also insufficient to explain observed fluxes, leaving a large role for allosteric regulation and enzyme modification in the control of metabolic fluxes.
Soluble expression of proteins correlates with a lack of positively-charged surface
Authors: Chan Pedro , Curtis Robin A. , Warwicker Jim
Published: November 2013

Prediction of protein solubility is gaining importance with the growing use of protein molecules as therapeutics and ongoing requirements for high level expression. We have investigated protein surface features that correlate with insolubility. Non-polar surface patches associate to some degree with insolubility, but this is far exceeded by the association with positively-charged patches. Negatively-charged patches do not separate insoluble/soluble subsets. The separation of soluble and insoluble subsets by positive charge clustering (area under the curve for a ROC plot is 0.85) has a striking parallel with the separation that delineates nucleic acid-binding proteins, although most of the insoluble dataset are not known to bind nucleic acid. Additionally, these basic patches are enriched for arginine, relative to lysine. The results are discussed in the context of expression systems and downstream processing, contributing to a view of protein solubility in which the molecular interactions of charged groups are far from equivalent.
Simultaneous determination of caffeine, gallic acid, theanine, (−)-epigallocatechin and (−)-epigallocatechin-3-gallate in green tea using quantitative1H-NMR spectroscopy
Authors: Yuan Yunfei , Song Yuelin , Jing Wanghui , Wang Yitao , Yang Xiaoyun , Liu Deyun
Published: November 2013

1H-NMR spectroscopy is utilized for chemical characterization along with simultaneous determination of caffeine, gallic acid, theanine and tea polyphenols, in commercial green tea.
An indirect competitive enzyme-linked immunosorbent assay for the determination of 3,4-dichlorobiphenyl in sediment using a specific polyclonal antibody
Authors: Yang Guangxin , Zhuang Huisheng , Chen Hanyu , Ping Xianyin
Published: November 2013

A specific polyclonal antibody targeting non-dioxin-like PCB 3,4-dichlorobiphenyl (PCB12) was obtained, and a sensitive ic-ELISA was developed for the determination of PCB12 in sediment samples.
Targeting a c-MYC G-quadruplex DNA with a fragment library
Authors: Nasiri Hamid R. , Bell Neil M. , McLuckie Keith I. E. , Husby Jarmila , Abell Chris , Neidle Stephen , Balasubramanian Shankar
Published: November 2013

A fragment library was screened against the human c-MYC promoter G-quadruplex. Ten fragment hits had a significant concordance between a biophysical assay,in silicomodelling and c-MYC expression inhibition.
Enhanced cellular uptake of amphiphilic gold nanoparticles with ester functionality
Authors: Kobayashi Kenya , Niikura Kenichi , Takeuchi Chie , Sekiguchi Shota , Ninomiya Takafumi , Hagiwara Kyoji , Mitomo Hideyuki , Ito Yoshihiro , Osada Yoshihito , Ijiro Kuniharu
Published: November 2013

Gold nanoparticles (AuNPs) coated with ester-headed or ether-headed PEG ligands were synthesized.
The energy transfer and effect of doped Mg2+ in Ca3Sc2Si3O12:Ce3+, Pr3+ phosphor for white LEDs
Authors: Qiao Jun , Zhang Jiahua , Zhang Xia , Hao Zhendong , Liu Yongfu , Luo Yongshi
Published: November 2013

A white LED is obtained by combining the single CSS:0.05Ce3+, 0.01Pr3+, 0.3Mg2+ phosphor with a blue-emitting InGaN LED chip.
Five metal–organic frameworks from 3,4-dimethylphenyl substituted imidazole dicarboxylate: syntheses, structures and properties
Authors: Jia Hongliang , Li Yanlin , Xiong Zhifang , wang Chengjie , Li Gang
Published: November 2013

Five metal–organic frameworks have been hydrothermally synthesized and structurally characterized.
Mesoporous non-siliceous inorganic–organic hybrids: a promising platform for designing multifunctional materials
Authors: Zhu Yun-Pei , Ren Tie-Zhen , Yuan Zhong-Yong
Published: November 2013

An overview of the recent progress in the designed synthesis, modification and multifunctional applications of mesoporous non-siliceous inorganic–organic hybrid materials including metal phosphonates, carboxylates and sulfonates is presented.
PEGylated aza-BODIPY derivatives as NIR probes for cellular imaging
Authors: Collado Daniel , Vida Yolanda , Najera Francisco , Perez-Inestrosa Ezequiel
Published: November 2013

Neutral water-soluble aza-BODIPYs are synthesized for imaging applications, demonstrating their potential as NIR emitting fluorescent probes.
Phosphorylation of bacterial-type phosphoenolpyruvate carboxylase by a Ca2+-dependent protein kinase suggests a link between Ca2+ signalling and anaplerotic pathway control in developing castor oil seeds
Authors: Hill Allyson T. , Ying Sheng , Plaxton William C.
Published: November 2013

The aim of the present study was to characterize the native protein kinase [BTPC (bacterial-type phosphoenolpyruvate carboxylase)-K (BTPC Ser451 kinase)] that in vivo phosphorylates Ser451 of the BTPC subunits of an unusual Class-2 PEP (phosphoenolpyruvate) carboxylase hetero-octameric complex of developing COS (castor oil seeds). COS BTPC-K was highly purified by PEG fractionation and hydrophobic size-exclusion anion-exchange and affinity chromatographies. BTPC-K phosphorylated BTPC strictly at Ser451 (Km=1.0 μM; pH optimum=7.3), a conserved target residue occurring within an intrinsically disordered region, as well as the protein histone III-S (Km=1.7 μM), but not a COS plant-type PEP carboxylase or sucrose synthase or α-casein. Its activity was Ca2+- (K0.5=2.7 μM) and ATP- (Km=6.6 μM) dependent, and markedly inhibited by trifluoperazine, 3-phosphoglycerate and PEP, but insensitive to calmodulin or 14-3-3 proteins. BTPC-K exhibited a native molecular mass of ~63 kDa and was soluble rather than membrane-bound. Inactivation and reactivation occurred upon BTPC-K's incubation with GSSG and then DTT respectively. Ser451 phosphorylation by BTPC-K inhibited BTPC activity by ~50% when assayed under suboptimal conditions (pH 7.3, 1 mM PEP and 10 mM L-malate). Our collective results indicate a possible link between cytosolic Ca2+ signalling and anaplerotic flux control in developing COS.
Detection of mutations in KLHL3 and CUL3 in families with FHHt (familial hyperkalaemic hypertension or Gordon's syndrome)
Authors: Glover Mark , Ware James S. , Henry Amanda , Wolley Martin , Walsh Roddy , Wain Louise V. , Xu Shengxin , Van’t Hoff William G. , Tobin Martin D. , Hall Ian P. , Cook Stuart , Gordon Richard D. , Stowasser Michael , O’Shaughnessy Kevin M.
Published: November 2013

The study of families with rare inherited forms of hypo- and hyper-tension has been one of the most successful strategies to probe the molecular pathophysiology of blood pressure control and has revealed dysregulation of distal nephron Na+ reabsorption to be a common mechanism. FHHt (familial hyperkalaemic hypertension; also known as Gordon's syndrome) is a salt-dependent form of hypertension caused by mutations in the regulators of the thiazide-sensitive Na+–Cl− co-transporter NCC [also known as SLC12A3 (solute carrier family 12 member 3)] and is effectively treated by thiazide diuretics and/or dietary salt restriction. Variation in at least four genes can cause FHHt, including WNK1 [With No lysine (=K) 1] and WNK4, KLHL3 (kelch-like family member 3), and CUL3 (cullin 3). In the present study we have identified novel disease-causing variants in CUL3 and KLHL3 segregating in 63% of the pedigrees with previously unexplained FHHt, confirming the importance of these recently described FHHt genes. We have demonstrated conclusively, in two unrelated affected individuals, that rare intronic variants in CUL3 cause the skipping of exon 9 as has been proposed previously. KLHL3 variants all occur in kelch-repeat domains and so probably disrupt WNK complex binding. We have found no evidence of any plausible disease-causing variants within SLC4A8 (an alternative thiazide-sensitive sodium transporter) in this population. The results of the present study support the existing evidence that the CUL3 and KLHL3 gene products are physiologically important regulators of thiazide-sensitive distal nephron NaCl reabsorption, and hence potentially interesting novel anti-hypertensive drug targets. As a third of our non-WNK FHHt families do not have plausible CUL3 or KLHL3 variants, there are probably additional, as yet undiscovered, regulators of the thiazide-sensitive pathways.
Performance analysis of selection‐and‐stay combining for multi‐branch systems
Authors: Song Xin‐Hai , Ge Jianhua , Shi Jingjing , Ding Haiyang
Published: November 2013

Selection‐and‐stay combining for multi‐branch (SSTC‐MB) systems is investigated. The mathematical model is first established. Based on the Markovian property of the received signal‐to‐noise ratio, the outage performance is analysed and the closed‐form expression is obtained. Numerical results validate the theoretical analysis and show that the SSTC‐MB system not only enhances outage performance but also expands the applied scope of a diversity system.
Space alignment for cognitive transmission with multiple primary users
Authors: Bai Xiaojuan
Published: November 2013

A space‐alignment (SA) scheme with K primary users in different cells working in the same frequency band based on K‐symbol extension for cognitive transmission in a multiple‐input multiple‐output system is proposed. The main idea is that the secondary transmitter sends a supersymbol over the K timeslot; meanwhile, the secondary transmitter aligns its transmit directions by precoding to the kth primary channel eigenmodes unused at the kth timeslot, and at the same time adapts its transmit power to satisfy the interference‐power constraints at the other K −1 primary receivers. The simulation results show that the proposed scheme achieves a higher performance compared with both the SA scheme with the single primary user and the scheme of the direct singular value decomposition of the secondary channel with interference‐power constraint.
Experimental demonstration of simultaneous SPM and XPM mitigation using combined techniques of optical compensation and multichannel single‐stage DBP
Authors: Kishikawa H. , Kawai T. , Shibahara K. , Fukutoku M.
Published: November 2013

A novel system mitigating self‐phase and cross‐phase modulation effects simultaneously using optical dispersion compensation at optical nodes and multichannel single‐stage digital backward propagation (DBP) is proposed. Experiments demonstrate 2.4 dB Q‐factor improvements with both self‐phase modulation and cross‐phase modulation compensation.
CMOS low‐power bandwidth‐improved derivative superposition mixer using parasitic NPN BJTs
Authors: Wang Keping , Lei Xuemei
Published: November 2013

A low‐power bandwidth‐improved derivative superposition (DS) mixer in a standard 90 nm CMOS technology is analysed in depth. The negative gm″ in saturated NMOS pseudo‐differential transistor is compensated by the positive gm″ in the parasitic NPN bipolar junction transistor. Compared with the traditional DS mixer using the dual‐NMOS method, the proposed DS mixer shows a wider bandwidth owing to the lower parasitic capacitance at the base. The maximum conversion gain of the DS mixer is 7.2 dB with the 1 dB frequency bandwidth from 0.5 to 6 GHz. Compared with the Gilbert‐type mixer, the third‐order input interception point (IIP3) is improved by about 7.5 dB. The DS mixer consumes a DC power of 3.8 mW under 1 V supply.
Phase‐apodisation technique to extend depth of field for high‐frequency ultrasound imaging
Authors: Jeong J.S.
Published: November 2013

The quality of focusing in high‐frequency ultrasound imaging is significantly affected by the length of the depth of field (DOF). A dual‐concentric transducer combined with a phase‐apodisation scheme is presented to achieve the extended DOF maintaining signal‐to‐noise ratio. As a preliminary study, computational simulation by using a Field‐II program is conducted to demonstrate the feasibility. A dual‐concentric transducer is composed of a disc‐ and a ring‐type element with confocal apertures. When two input signals with 0° and 180° phases are simultaneously applied to the inner and outer elements, a bifocal‐zone is generated in the axial direction. The overall − 6 dB DOF is 40% longer compared with a single element transducer. Thus, the proposed scheme can be a potential approach to increase the DOF for high‐frequency ultrasound imaging.
A two degree of freedom micro-gripper with grasping and rotating functions for optical fibers assembling
Authors: Chen Weihai , Shi Xiaohui , Chen Wenjie , Zhang Jianbin
Published: November 2013

In this paper, a two degree of freedom flexure-based micro-gripper is proposed and applied in the complicated assembling process of optical fibers. The design concept is modeled on the manipulation of human fingers. Therefore, the two tips of micro-gripper, just like human fingers, can easily grasp the optical fiber with a controllable force and precisely rotate it by the rubbing operation. In addition, some sensors installed on the micro-gripper can enhance the operating accuracy. In the developing process, pseudo-rigid-body model method and virtual work principle are employed to conduct theoretical design. Then the obtained theoretical model is validated and optimized by the finite element analysis. Fabrication of the micro-gripper adopts wire electro discharge machining technology and material of aluminum alloy (AL-7075). Experimental studies are carried out on the prototype to further validate the performance of micro-gripper. Experimental results indicate that the developed micro-gripper can well satisfy the requirements of our mission, which also means that it can be widely used in micro-manipulation field.
A first look at Weyl anomalies in shape dynamics
Authors: Gomes Henrique
Published: November 2013

One of the more popular objections towards shape dynamics is the suspicion that anomalies in the spatial Weyl symmetry will arise upon quantization. The purpose of this short paper is to establish the tools required for an investigation of the sort of anomalies that can possibly arise. The first step is to adapt to our setting Barnich and Henneaux's formulation of gauge cohomology in the Hamiltonian setting, which serve to decompose the anomaly into a spatial component and time component. The spatial part of the anomaly, i.e., the anomaly in the symmetry algebra itself ([Ω, Ω] ∝ ℏ instead of vanishing) is given by a projection of the second ghost cohomology of the Hamiltonian BRST differential associated to Ω, modulo spatial derivatives. The temporal part, [Ω, H] ∝ ℏ is given by a different projection of the first ghost cohomology and an extra piece arising from a solution to a functional differential equation. Assuming locality of the gauge cohomology groups involved, this part is always local. Assuming locality for the gauge cohomology groups, using Barnich and Henneaux's results, the classification of Weyl cohomology for higher ghost numbers performed by Boulanger, and following the descent equations, we find a complete characterizations of anomalies in 3+1 dimensions. The spatial part of the anomaly and the first component of the temporal anomaly are always local given these assumptions even in shape dynamics. The part emerging from the solution of the functional differential equations explicitly involves the shape dynamics Hamiltonian, and thus might be non-local. If one restricts this extra piece of the temporal anomaly to be also local, then overall no Weyl anomalies, either temporal or spatial, emerge in the 3+1 case.
Numerical power balance and free energy loss analysis for solar cells including optical, thermodynamic, and electrical aspects
Authors: Greulich Johannes , Höffler Hannes , Würfel Uli , Rein Stefan
Published: November 2013

A method for analyzing the power losses of solar cells is presented, supplying a complete balance of the incident power, the optical, thermodynamic, and electrical power losses and the electrical output power. The involved quantities have the dimension of a power density (units: W/m2), which permits their direct comparison. In order to avoid the over-representation of losses arising from the ultraviolet part of the solar spectrum, a method for the analysis of the electrical free energy losses is extended to include optical losses. This extended analysis does not focus on the incident solar power of, e.g., 1000 W/m2 and does not explicitly include the thermalization losses and losses due to the generation of entropy. Instead, the usable power, i.e., the free energy or electro-chemical potential of the electron-hole pairs is set as reference value, thereby, overcoming the ambiguities of the power balance. Both methods, the power balance and the free energy loss analysis, are carried out exemplarily for a monocrystalline p-type silicon metal wrap through solar cell with passivated emitter and rear (MWT-PERC) based on optical and electrical measurements and numerical modeling. The methods give interesting insights in photovoltaic (PV) energy conversion, provide quantitative analyses of all loss mechanisms, and supply the basis for the systematic technological improvement of the device.
Terahertz-induced Kerr effect in amorphous chalcogenide glasses
Authors: Zalkovskij M. , Strikwerda A. C. , Iwaszczuk K. , Popescu A. , Savastru D. , Malureanu R. , Lavrinenko A. V. , Jepsen P. U.
Published: November 2013

We have investigated the terahertz-induced third-order (Kerr) nonlinear optical properties of the amorphous chalcogenide glasses As2S3 and As2Se3. Chalcogenide glasses are known for their high optical Kerr nonlinearities which can be several hundred times greater than those of fused silica. We use high-intensity, single-cycle terahertz pulses with a maximum electrical field strength exceeding 400 kV/cm and frequency content from 0.2 to 3.0 THz. By optical Kerr-gate sampling, we measured the terahertz-induced nonlinear refractive indices at 800 nm to be n2=1.746×10−14cm2/W for As2S3 and n2=3.440×10−14 cm2/W for As2Se3.
Uniaxial cell stretching device for live-cell imaging of mechanosensitive cellular functions
Authors: Shao Yue , Tan Xinyu , Novitski Roman , Muqaddam Mishaal , List Paul , Williamson Laura , Fu Jianping , Liu Allen P.
Published: November 2013

External mechanical stretch plays an important role in regulating cellular behaviors through intracellular mechanosensitive and mechanotransductive machineries such as the F-actin cytoskeleton (CSK) structures and focal adhesions (FAs) anchoring the F-actin CSK to the extracellular environment. Studying the mechanoresponsive behaviors of the F-actin CSK and FAs in response to cell stretch has great importance for further understanding mechanotransduction and mechanobiology. In this work, we developed a novel cell stretching device combining dynamic directional cell stretch with in situ subcellular live-cell imaging. Using a cam and follower mechanism and applying a standard mathematical model for cam design, we generated different dynamic stretch outputs. By examining stretch-mediated FA dynamics under step-function static stretch and the realignment of cell morphology and the F-actin CSK under cyclic stretch, we demonstrated successful applications of our cell stretching device for mechanobiology studies where external stretch plays an important role in regulating subcellular molecular dynamics and cellular phenotypes.
Accurate spring constant calibration for very stiff atomic force microscopy cantilevers
Authors: Grutzik Scott J. , Gates Richard S. , Gerbig Yvonne B. , Smith Douglas T. , Cook Robert F. , Zehnder Alan T.
Published: November 2013

There are many atomic force microscopy (AFM) applications that rely on quantifying the force between the AFM cantilever tip and the sample. The AFM does not explicitly measure force, however, so in such cases knowledge of the cantilever stiffness is required. In most cases, the forces of interest are very small, thus compliant cantilevers are used. A number of methods have been developed that are well suited to measuring low stiffness values. However, in some cases a cantilever with much greater stiffness is required. Thus, a direct, traceable method for calibrating very stiff (approximately 200 N/m) cantilevers is presented here. The method uses an instrumented and calibrated nanoindenter to determine the stiffness of a reference cantilever. This reference cantilever is then used to measure the stiffness of a number of AFM test cantilevers. This method is shown to have much smaller uncertainty than previously proposed methods. An example application to fracture testing of nanoscale silicon beam specimens is included.
Incomplete ionization of aluminum in silicon and its effect on accurate determination of doping profiles
Authors: Rauer Michael , Rüdiger Marc , Schmiga Christian , Strutzberg Hartmuth , Bähr Mario , Glatthaar Markus , Glunz Stefan W.
Published: November 2013

We present a detailed study on incomplete ionization (i.i.) of aluminum acceptors in highly aluminum-doped p+ silicon formed by alloying from screen-printed Al pastes. We apply electrochemical capacitance-voltage (ECV) and secondary ion mass spectrometry (SIMS) measurements to detect the Al doping profiles and discuss key aspects necessary for a precise determination of the profiles. The excellent accordance of ECV- and SIMS-measured acceptor profile curves allows for the accurate investigation of Al acceptor ionization. We review the physics of i.i. and verify a simple quantitative model for incomplete Al acceptor ionization by comparing measured and calculated sheet-resistances of Al-doped p+ Si surfaces. We thus show that the electrically active Al doping concentration is nearly two times lower than the total Al concentration, so that i.i. of Al acceptors has to be considered for the correct description of highly Al-doped p+ Si regions. Therefore, our results allow for an improved quantitative analysis of n- and p-type silicon solar cells with Al-alloyed p+ rear emitter or back surface field, respectively.
First-principles study on negative thermal expansion of PbTiO3
Authors: Wang Fangfang , Xie Ying , Chen Jun , Fu Honggang , Xing Xianran
Published: November 2013

It is well known that perovskite-type PbTiO3 behaves negative thermal expansion in a wide temperature range from room temperature to Curie temperature (763 K). The present study reports the first-principles study of the anisotropic thermal expansion of PbTiO3, in the framework of the density-functional theory and the density-functional perturbation theory. The curve of temperature dependence of the unit cell volume is presented from 20 to 520 K through the calculation of the minimum of total free energy at each temperature point. The negative thermal expansion of PbTiO3 is calculated without empirical parameters. Furthermore, the distinctive thermodynamic act of PbTiO3 from expanding to contracting at tetragonal phase is reproduced. The ab-initio calculations reveal that this unique appearance depends on the phonon vibration. The dynamical contributions of various atoms are also calculated to account for the disparate role of Pb-O and Ti-O bond.
Relationship between orientation factor of lead zirconate titanate nanowires and dielectric permittivity of nanocomposites
Authors: Tang Haixiong , Malakooti Mohammad H. , Sodano Henry A.
Published: November 2013

The relationship between the orientation of lead zirconate titanate (PZT) nanowires dispersed in nanocomposites and the resulting dielectric constants are quantified. The orientation of the PZT nanowires embedded in a polymer matrix is controlled by varying the draw ratio and subsequently quantified using Herman's Orientation Factor. Consequently, it is demonstrated that the dielectric constants of nanocomposites are improved by increasing the orientation factor of the PZT nanowires. This technique is proposed to improve the dielectric constant of the nanocomposites without the need for additional filler volume fraction since the nanocomposites are utilized in a wide range of high dielectric permittivity electronic components.
Characteristics of light-induced electron transport from P3HT to ZnO-nanowire field-effect transistors
Authors: Choe Minhyeok , Hoon Lee Byoung , Park Woojin , Kang Jang-Won , Jeong Sehee , Cho Kyungjune , Hong Woong-Ki , Hun Lee Byoung , Lee Kwanghee , Park Seong-Ju , Lee Takhee
Published: November 2013

We fabricated ZnO-nanowire (NW) field-effect transistors (FETs) coated with poly(3-hexylthiophene) (P3HT) and characterized the electron-transfer characteristics from the P3HT to the ZnO NWs. Under irradiation by laser light with a wavelength of 532 nm, photo-induced electrons were created in the P3HT and then transported to the ZnO NWs, constituting a source-drain current in the initially enhancement-mode P3HT-coated ZnO-NW FETs. As the intensity of the light increased, the current increased, and its threshold voltage shifted to the negative gate-bias direction. We estimated the photo-induced electron density and the electron-transfer characteristics, which will be helpful for understanding organic-inorganic hybrid optoelectronic devices.
Ion-assisted phase separation in compound films: An alternate route to ordered nanostructures
Authors: Norris Scott A.
Published: November 2013

In recent years, observations of highly ordered, hexagonal arrays of self-organized nanostructures on binary or impurity-laced targets under normal-incidence ion irradiation have excited interest in this phenomenon as a potential route to high-throughput, low-cost manufacture of nanoscale devices or nanostructured coatings. The currently prominent explanation for these structures is a morphological instability driven by ion erosion discovered by Bradley and Shipman; however, recent parameter estimates via molecular dynamics simulations suggest that this erosive instability may not be active for the representative GaSb system in which hexagonal structures were first observed. Motivated by recent experimental and numerical evidence suggesting the likely importance of phase separation during thin-film processing, we here generalize the Bradley-Shipman theory to include the effect of ion-assisted phase separation. The resulting system admits a chemically driven finite-wavelength instability that can explain the order of observed patterns even when the erosive Bradley-Shipman instability is inactive. In a relevant simplifying limit, it also provides an intuitive instability criterion similar to results in thin-film deposition, as well as predictions on pattern wavelengths that agree qualitatively with experimental observations. Finally, we identify a characteristic experimental signature that distinguishes the chemical and morphological instabilities and highlights the need for specific additional experimental data on the GaSb system.
Pyroelectric response of lead zirconate titanate thin films on silicon: Effect of thermal stresses
Authors: Kesim M. T. , Zhang J. , Trolier-McKinstry S. , Mantese J. V. , Whatmore R. W. , Alpay S. P.
Published: November 2013

Ferroelectric lead zirconate titanate [Pb(ZrxTi1-xO)3, (PZT x:1-x)] has received considerable interest for applications related to uncooled infrared devices due to its large pyroelectric figures of merit near room temperature, and the fact that such devices are inherently ac coupled, allowing for simplified image post processing. For ferroelectric films made by industry-standard deposition techniques, stresses develop in the PZT layer upon cooling from the processing/growth temperature due to thermal mismatch between the film and the substrate. In this study, we use a non-linear thermodynamic model to investigate the pyroelectric properties of polycrystalline PZT thin films for five different compositions (PZT 40:60, PZT 30:70, PZT 20:80, PZT 10:90, PZT 0:100) on silicon as a function of processing temperature (25–800 °C). It is shown that the in-plane thermal stresses in PZT thin films alter the out-of-plane polarization and the ferroelectric phase transformation temperature, with profound effect on the pyroelectric properties. PZT 30:70 is found to have the largest pyroelectric coefficient (0.042 μC cm−2 °C−1, comparable to bulk values) at a growth temperature of 550 °C; typical to what is currently used for many deposition processes. Our results indicate that it is possible to optimize the pyroelectric response of PZT thin films by adjusting the Ti composition and the processing temperature, thereby, enabling the tailoring of material properties for optimization relative to a specific deposition process.
Simulations of magnetic vortex dynamics in exchange-biased sub-micron-sized disks
Authors: Parreiras S. O. , Fior G. B. M. , Garcia F. , Martins M. D.
Published: November 2013

In this work we have investigated the influence of exchange bias coupling in the magnetic vortex dynamics of sub-micrometer bilayer disk by means of a series of micromagnetic simulations. The hysteresis simulations showed that the vortex stability increases with the coupling constant. In relaxation simulations, it was observed that the gyrotropic movement has a variable frequency that increases with time, which is not observed when exchange bias is absent. Under a rotating magnetic field acting on the disks, the critical velocity for vortex polarity reversion increases with the coupling constant and frequency. Our results show that the critical velocity can be adjusted in a wide range by selecting the magnetic coupling constant and the oscillating frequency, i.e., it would be possible to control the critical velocity for vortex polarity inversion through the exchange bias coupling.
Ultrasensitive strain sensors of multiwalled carbon nanotube/epoxy nanocomposite using dielectric loss tangent
Authors: Alamusi  , Yuan W. F. , Surina  , Li Y. , Hu N. , Ning H. M. , Liu Y. L. , Wu L. K. , Atobe S. , Fukunaga H.
Published: November 2013

In this work, the dielectric loss tangent (tan δ) of a series of strain sensors, fabricated from an epoxy nanocomposite with multi-wall carbon nanotube (MWCNT) content varying at 1 wt. % – 5 wt. %, was characterized experimentally. The effects of four parameters including frequency, strain of nanocomposite, MWCNT content, and loading voltage were investigated extensively. Moreover, an alternative current gauge factor KAC was developed. The largest value of KAC was found to be 256 for the nanocomposite strain sensor with 1 wt. % MWCNT content at 0.6% tensile strain, which indicates the ultra-sensitivity of the present strain sensor.
Dynamically tunable broadband mid-infrared cross polarization converter based on graphene metamaterial
Authors: Cheng Hua , Chen Shuqi , Yu Ping , Li Jianxiong , Xie Boyang , Li Zhancheng , Tian Jianguo
Published: November 2013

We present a mid-IR highly wavelength-tunable broadband cross polarization conversion composed of a single patterned top layer with L-shaped graphene nanostructures, a dielectric spacer, and a gold plane layer. It can convert linearly polarized light to its cross polarization in the reflection mode. The polarization conversion can be dynamically tuned and realize a broadband effect by varying the Fermi energy without reoptimizing and refabricating the nanostructures. This offers a further step in developing the tunable polarizers and the polarization switchers.
Investigations on correlation between I–V characteristic and internal quantum efficiency of blue (AlGaIn)N light-emitting diodes
Authors: Binder M. , Galler B. , Furitsch M. , Off J. , Wagner J. , Zeisel R. , Katz S.
Published: November 2013

We have studied the electrical and optical characteristics of (AlGaIn)N multiple quantum well light-emitting diodes. Minimizing contact effects by utilizing platinum as p-contact metal, ideality factors as low as 1.1 have been achieved. In agreement with basic semiconductor theory, a correlation between ideality factor and small-current efficiency was found. We were able to emulate the experimental current-voltage characteristic over seven orders of magnitude utilizing a two diode model. This model enables a very good prediction of internal quantum efficiency at moderate current densities out of purely electrically derived parameters.
Polarity driven simultaneous growth of free-standing and lateral GaAsP epitaxial nanowires on GaAs (001) substrate
Authors: Sun Wen , Guo Yanan , Xu Hongyi , Gao Qiang , Hoe Tan Hark , Jagadish Chennupati , Zou Jin
Published: November 2013

Simultaneous growth of ⟨111⟩B free-standing and ±[110] lateral GaAsP epitaxial nanowires on GaAs (001) substrates were observed and investigated by electron microscopy and crystallographic analysis. It was found that the growth of both free-standing and lateral ternary nanowires via Au catalysts was driven by the fact that Au catalysts prefer to maintain low-energy {111}B interfaces with surrounding GaAs(P) materials: in the case of free-standing nanowires, Au catalysts maintain {111}B interfaces with their underlying GaAsP nanowires; while in the case of lateral nanowires, each Au catalyst remain their side {111}B interfaces with the surrounding GaAs(P) material during the lateral nanowire growth.
Low threshold for optical damage in AlGaN epilayers and heterostructures
Authors: Saxena Tanuj , Tamulaitis Gintautas , Shatalov Max , Yang Jinwei , Gaska Remis , Shur Michael S.
Published: November 2013

Laser pulses with duration much shorter than the effective carrier lifetime cause permanent photoluminescence (PL) quenching and enhancement of PL decay rate in bare-faceted and capped AlGaN epilayers and multiple quantum wells at pulse energies about an order of magnitude lower than those causing the surface to melt and degrade. In contrast, GaN epilayers exhibit no photomodification in the same excitation intensity range. PL spectra and decay kinetics show that lattice heating is not responsible for the observed changes in AlGaN, which result from the formation of nonradiative recombination centers via recombination-enhanced defect reactions occurring at high nonequilibrium carrier densities.
Communication: Benzene dimer—The free energy landscape
Authors: Kumar Tummanapelli Anil , Vasudevan Sukumaran
Published: November 2013

Establishing the relative orientation of the two benzene molecules in the dimer has remained an enigmatic challenge. Consensus has narrowed the choice of structures to either a T-shape, that may be tilted, or a parallel displaced arrangement, but the relatively small energy differences makes identifying the global minimum difficult. Here we report an ab initio Car-Parrinello Molecular Dynamics based metadynamics computation of the free-energy landscape of the benzene dimer. Our calculations show that although competing structures may be isoenergetic, free energy always favors a tilted T-shape geometry at all temperatures where the bound benzene dimer exist.
Direct acceleration of electrons by a circular polarized laser pulse with phase modulation
Authors: Zhu Lun-Wu , Sheng Zheng-Mao , Yu M. Y.
Published: November 2013

Electron acceleration by transversely echelon phase-modulated (EPM) circularly polarized (CP) intense laser pulse is investigated. Solution of the relativistic electron equations of motion shows that the CP EPM light wave structure can disrupt the harmonic response of a trapped electron not only in the transverse direction but also in the direction of laser propagation. In each laser cycle, there can be a net gain in the electron's transverse momentum, which is promptly converted into the forward direction by the Lorentz force. As a result, the electron can be trapped and accelerated in the favorable phase of the laser for a rather long time. Its momentum gain then accumulates and can eventually reach high levels. It is also found that with the CP EPM laser, the net acceleration of the electron is not sensitive to its initial position and velocity relative to the phase of the laser fields, so that such a laser can also be useful for accelerating thermal electron bunches to high energies.
Investigation on non-exchange spring behaviour and exchange spring behaviour: A first order reversal curve analysis
Authors: Roy Debangsu , Sreenivasulu K. V. , Anil Kumar P. S.
Published: November 2013

The First Order Reversal Curve (FORC) method has been utilised to understand the magnetization reversal and the extent of the irreversible magnetization of the soft CoFe2O4-hard SrFe12O19 nanocomposite in the nonexchange spring and the exchange spring regime. The single peak switching behaviour in the FORC distribution of the exchange spring composite confirms the coherent reversal of the soft and hard phases. The onset of the nucleation field and the magnetization reversal by domain wall movement are also evident from the FORC measurements.
Morphological origin for the stratification of P3HT:PCBM blend film studied by neutron reflectometry
Authors: Keum Jong Kahk , Browning James F. , Xiao Kai , Shao Ming , Halbert Candice E. , Hong Kunlun
Published: November 2013

Understanding the origin for the film stratification of electron donor/acceptor blend is crucial for high efficiency organic photovoltaic cell. In this study, P3HT:PCBM blend is deposited onto hydrophilic and hydrophobic substrate to examine the film stratifications. The neutron reflectivity results show that, on the different surfaces, PCBM diffuses toward the two interfacial regions in an identical fashion during thermal annealing. This evidences that the film stratification is not affected by the substrates. Instead, since P3HT remains more amorphous in the interfacial regions and PCBM is miscible with amorphous P3HT, PCBM preferentially diffuses to the interfacial regions, resulting in the stratification.
Field nano-localization of gas bubble production from water electrolysis
Authors: Hammadi Z. , Morin R. , Olives J.
Published: November 2013

Using a tip shaped electrode and ac voltages, we show that the production of micro bubbles of gas from water electrolysis is localized at the tip apex inside a domain in the voltage frequency phase space. A model taking into account the electrode shape and dimensions explains these results which suggest a field effect control of the electrolysis reaction rate at a nanometer scale.