bluuebunny/crossref_metadata_2025 huggingface dataset:
Peroxynitrite: in vivo cardioprotectant or arrhythmogen?
Authors: Eaton P , Clements‐Jewery H
Published: September 2008

The factors that determine susceptibility to lethal ventricular arrhythmias during myocardial ischaemia and reperfusion in vivo are complex, but the balance between proarrhythmic and antiarrhythmic endogenous substances is likely to be important. However, in this context, it is not well established what effect endogenously produced peroxynitrite has on arrhythmias that develop during ischaemia/reperfusion in vivo. The study by Kiss et al., published in this issue of the BJP, provides some insights to this problem. We discuss the wider implications of this study as well as issues that still require resolution.

British Journal of Pharmacology (2008) 155, 972–973; doi:fn1; published online 22 September 2008
Protective action of doxycycline against diabetic cardiomyopathy in rats
Authors: Yaras N , Sariahmetoglu M , Bilginoglu A , Aydemir‐Koksoy A , Onay‐Besikci A , Turan B , Schulz R
Published: September 2008

Background and purpose:

Reactive oxygen and nitrogen species play an important role in the development of diabetic cardiomyopathy. They can activate matrix metalloproteinases (MMPs), and MMP‐2 in particular is known to mediate early consequences of oxidative stress injury in the heart. Therefore, we investigated the role of MMP‐2 and the effect of the MMP inhibitor doxycycline on the changes of heart function caused by diabetes.

Experimental approach:

Using streptozotocin‐induced diabetic rats, we evaluated the effect of doxycycline on both mechanical and electrical function of isolated hearts, papillary muscle and cardiomyocytes.

Key results:

Doxycycline abolished the diabetes‐induced depression in left ventricular developed pressure and the rates of changes in developed pressure in isolated hearts and normalized the prolongation of the action potential in papillary muscles. In cardiomyocytes isolated from doxycycline‐treated diabetic rats, the altered kinetic parameters of Ca2+ transients, depressed Ca2+ loading of sarcoplasmic reticulum and basal intracellular Ca2+ level, and the spatio‐temporal properties of Ca2+ sparks were significantly restored. Gelatin zymography and western blot data indicated that the diabetes‐induced alterations in MMP‐2 activity and protein level, level of tissue inhibitor of matrix metalloproteinase‐4 and loss of troponin I were restored to control levels with doxycycline.

Conclusions and implications:

Our data suggest that these beneficial effects of doxycycline on the mechanical, electrical and biochemical properties of the diabetic rat heart appear, at least in part, to be related to inhibition of MMP activity, implying a role for MMPs in the development of diabetic cardiomyopathy.

British Journal of Pharmacology (2008) 155, 1174–1184; doi:10.1038/bjp.2008.373; published online 22 September 2008
On the relationship between pinning control effectiveness and graph topology in complex networks of dynamical systems
Authors: Wu Chai Wah
Published: September 2008

This paper concerns pinning control in complex networks of dynamical systems, where an external forcing signal is applied to the network in order to align the state of all the systems to the forcing signal. By considering the control signal as the state of a virtual dynamical system, this problem can be studied as a synchronization problem. The main focus of this paper is to study how the effectiveness of pinning control depends on the underlying graph. In particular, we look at the relationship between pinning control effectiveness and the complex network asymptotically as the number of vertices in the network increases. We show that for vertex balanced graphs, if the number of systems receiving pinning control does not grow as fast as the total number of systems, then the strength of the control needed to effect pinning control will be unbounded as the number of vertices grows. Furthermore, in order to achieve pinning control in systems coupled via locally connected graphs, as the number of systems grows, both the pinning control and the coupling among all systems need to increase. Finally, we give evidence to show that applying pinning control to minimize the distances between all systems to the pinned systems can lead to a more effective pinning control.
Synchronization in networks of chaotic systems with time-delay coupling
Authors: Oguchi Toshiki , Nijmeijer Henk , Yamamoto Takashi
Published: September 2008

In this paper, we consider synchronization of N identical nonlinear systems unidirectionally or bidirectionally coupled with time delay. First we show, using the small-gain theorem, that trajectories of coupled strictly semi-passive systems converge to a bounded region. Next, we consider the network structure under which the synchronization error dynamics has a trivial solution at zero and derive a necessary condition for synchronization with respect to the network structure. Using these facts, we then derive sufficient conditions for synchronization of the systems in terms of linear matrix inequalities via the Lyapunov–Krasovskii functional approach. The obtained results are illustrated on networks of Lorentz systems with coupling delay.
Synchronization properties of network motifs: Influence of coupling delay and symmetry
Authors: D’Huys O. , Vicente R. , Erneux T. , Danckaert J. , Fischer I.
Published: September 2008

We investigate the effect of coupling delays on the synchronization properties of several network motifs. In particular, we analyze the synchronization patterns of unidirectionally coupled rings, bidirectionally coupled rings, and open chains of Kuramoto oscillators. Our approach includes an analytical and semianalytical study of the existence and stability of different in-phase and out-of-phase periodic solutions, complemented by numerical simulations. The delay is found to act differently on networks possessing different symmetries. While for the unidirectionally coupled ring the coupling delay is mainly observed to induce multistability, its effect on bidirectionally coupled rings is to enhance the most symmetric solution. We also study the influence of feedback and conclude that it also promotes the in-phase solution of the coupled oscillators. We finally discuss the relation between our theoretical results on delay-coupled Kuramoto oscillators and the synchronization properties of networks consisting of real-world delay-coupled oscillators, such as semiconductor laser arrays and neuronal circuits.
Traveling waves and compactons in phase oscillator lattices
Authors: Ahnert Karsten , Pikovsky Arkady
Published: September 2008

We study waves in a chain of dispersively coupled phase oscillators. Two approaches—a quasicontinuous approximation and an iterative numerical solution of the lattice equation—allow us to characterize different types of traveling waves: compactons, kovatons, solitary waves with exponential tails as well as a novel type of semicompact waves that are compact from one side. Stability of these waves is studied using numerical simulations of the initial value problem.
Synchronization phenomena in mixed media of passive, excitable, and oscillatory cells
Authors: Kryukov A. K. , Petrov V. S. , Averyanova L. S. , Osipov G. V. , Chen W. , Drugova O. , Chan C. K.
Published: September 2008

We study collective phenomena in highly heterogeneous cardiac cell culture and its models. A cardiac culture is a mixture of passive (fibroblasts), oscillatory (pacemakers), and excitable (myocytes) cells. There is also heterogeneity within each type of cell as well. Results of in vitro experiments are modelled by Luo–Rudy and FitzHugh–Nagumo systems. For oscillatory and excitable media, we focus on the transitions from fully incoherent behavior to partially coherent behavior and then to global synchronization as the coupling strength is increased. These regimes are characterized qualitatively by spatiotemporal diagrams and quantitatively by profiles of dependence of individual frequencies on coupling. We find that synchronization clusters are determined by concentric and spiral waves. These waves arising due to the heterogeneity of medium push covered cells to oscillate in synchrony. We are also interested in the influence of passive and excitable elements on the oscillatory characteristics of low- and high-dimensional ensembles of cardiac cells. The mixture of initially silent excitable and passive cells shows the transitions to oscillatory behavior. In the media of oscillatory and passive or excitable cells, the effect of oscillation death is observed.
Cluster synchronization in oscillatory networks
Authors: Belykh Vladimir N. , Osipov Grigory V. , Petrov Valentin S. , Suykens Johan A. K. , Vandewalle Joos
Published: September 2008

Synchronous behavior in networks of coupled oscillators is a commonly observed phenomenon attracting a growing interest in physics, biology, communication, and other fields of science and technology. Besides global synchronization, one can also observe splitting of the full network into several clusters of mutually synchronized oscillators. In this paper, we study the conditions for such cluster partitioning into ensembles for the case of identical chaotic systems. We focus mainly on the existence and the stability of unique unconditional clusters whose rise does not depend on the origin of the other clusters. Also, conditional clusters in arrays of globally nonsymmetrically coupled identical chaotic oscillators are investigated. The design problem of organizing clusters into a given configuration is discussed.
Efficient rewirings for enhancing synchronizability of dynamical networks
Authors: Rad Ali Ajdari , Jalili Mahdi , Hasler Martin
Published: September 2008

In this paper, we present an algorithm for optimizing synchronizability of complex dynamical networks. Starting with an undirected and unweighted network, we end up with an undirected and unweighted network with the same number of nodes and edges having enhanced synchronizability. To this end, based on some network properties, rewirings, i.e., eliminating an edge and creating a new edge elsewhere, are performed iteratively avoiding always self-loops and multiple edges between the same nodes. We show that the method is able to enhance the synchronizability of networks of any size and topological properties in a small number of steps that scales with the network size. For numerical simulations, an optimization algorithm based on simulated annealing is used. Also, the evolution of different topological properties of the network such as distribution of node degree, node and edge betweenness centrality is tracked with the iteration steps. We use networks such as scale-free, Strogatz–Watts and random to start with and we show that regardless of the initial network, the final optimized network becomes homogeneous. In other words, in the network with high synchronizability, parameters, such as, degree, shortest distance, node, and edge betweenness centralities are almost homogeneously distributed. Also, parameters, such as, maximum node and edge betweenness centralities are small for the rewired network. Although we take the eigenratio of the Laplacian as the target function for optimization, we show that it is also possible to choose other appropriate target functions exhibiting almost the same performance. Furthermore, we show that even if the network is optimized taking into account another interpretation of synchronizability, i.e., synchronization cost, the optimal network has the same synchronization properties. Indeed, in networks with optimized synchronizability, different interpretations of synchronizability coincide. The optimized networks are Ramanujan graphs, and thus, this rewiring algorithm could be used to produce Ramanujan graphs of any size and average degree.
Clustering behaviors in networks of integrate-and-fire oscillators
Authors: Mauroy Alexandre , Sepulchre Rodolphe
Published: September 2008

Clustering behavior is studied in a model of integrate-and-fire oscillators with excitatory pulse coupling. When considering a population of identical oscillators, the main result is a proof of global convergence to a phase-locked clustered behavior. The robustness of this clustering behavior is then investigated in a population of nonidentical oscillators by studying the transition from total clustering to the absence of clustering as the group coherence decreases. A robust intermediate situation of partial clustering, characterized by few oscillators traveling among nearly phase-locked clusters, is of particular interest. The analysis complements earlier studies of synchronization in a closely related model.
Electron transport in back contact dye-sensitized solar cells
Authors: Fuke Nobuhiro , Fukui Atsushi , Islam Ashraful , Komiya Ryoichi , Yamanaka Ryohsuke , Han Liyuan , Harima Hiroshi
Published: September 2008

The electron transport properties of a back contact dye-sensitized solar cell (BCDSC) were investigated in comparison with a conventional DSC. It was found that the BCDSC had a lower short circuit current density (JSC) at the same thickness of TiO2 film and that JSC was not proportional to the thickness of the TiO2 film. Calculation of electron transport length in the TiO2 film suggested that the injected electron travels a longer distance to the electrode in the BCDSC than in the DSC. TiCl4 treatment of the TiO2 film produced a marked improvement of the JSC value in the BCDSC due to an increase in the electron diffusion coefficient of the TiO2 film, whereas the JSC of the DSC remained almost unchanged. It is clear that the value of JSC in the BCDSC is more dependent on the electron transport properties of the TiO2 film than in the DSC. Under standard AM 1.5 irradiation (100 mW cm−2), a BCDSC with N719 dye yielded an overall conversion efficiency of 8.0%.
Rewiring networks for synchronization
Authors: Hagberg Aric , Schult Daniel A.
Published: September 2008

We study the synchronization of identical oscillators diffusively coupled through a network and examine how adding, removing, and moving single edges affects the ability of the network to synchronize. We present algorithms which use methods based on node degrees and based on spectral properties of the network Laplacian for choosing edges that most impact synchronization. We show that rewiring based on the network Laplacian eigenvectors is more effective at enabling synchronization than methods based on node degree for many standard network models. We find an algebraic relationship between the eigenstructure before and after adding an edge and describe an efficient algorithm for computing Laplacian eigenvalues and eigenvectors that uses the network or its complement depending on which is more sparse.
High efficient two color white phosphorescent organic light emitting diode
Authors: Seidel S. , Krause R. , Hunze A. , Schmid G. , Kozlowski F. , Dobbertin T. , Winnacker A.
Published: September 2008

We report on high efficient white organic light emitting diodes comprising the two phosphorescent emitter materials platinum(II)[2-(4′,6′-difluorophenyl)pyridinato-N,C2′)](2,4-pentanedionato) (FPt1) and iridium(III)bis[∼4,6-difluorophenyl-pyridinato N, C2′]picolinate (FIrpic). Investigating the influence of the dopants in the emission layers on the device performance, a series of devices with different FIrpic and FPt1 concentrations have been processed. After optimizing the device with respect to efficiency and white color coordinates the influence of a thickness variation of the emission layers was investigated. The experiments revealed that the device performance is more sensitive to the parameters of the emission layer containing FPt1. Additional optical simulations showed that interference effects play a crucial role in this device setup. The optimized device resulted in an external quantum efficiency of 10%, a power efficiency of 16 lm/W, near warm white color coordinates of 0.39/.41, and a color rendering index of 81 at 1000 cd/m2.
Changes in ferroelectric properties of ceramics in lead magnesium niobate–lead titanate system with compressive stress
Authors: Unruan Muangjai , Wongmaneerung Rewadee , Ngamjarurojana Athipong , Laosiritaworn Yongyut , Ananta Supon , Yimnirun Rattikorn
Published: September 2008

Effects of compressive stress on the ferroelectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) ceramics were investigated. The ceramics with the formula (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 or (1−x)PMN−(x)PT (x=0.1–0.5) were prepared by a conventional mixed-oxide method. Dense perovskite-phase PMN-PT ceramics with a uniform microstructure were obtained. The ferroelectric properties were measured under compressive stress (0–75 MPa) using a homebuilt compressometer in conjunction with a modified Sawyer–Tower circuit. The experimental results revealed that the superimposed compression stress significantly reduced both the dissipation energy and the polarizations of the near morphotropic phase boundary compositions, i.e., 0.8PMN-0.2PT, 0.7PMN-0.3PT, and 0.6PMN-0.4PT, while the stress influence was much less in other compositions. On the contrary, the applied compressive stress showed little or no influence on the coercive field. These results were interpreted through the non-180° ferroelastic domain switching processes and the stress induced decrease in the switchable part of domains.
Laser-induced nuclear magnetic resonance splitting in hydrocarbons
Authors: Ikäläinen Suvi , Lantto Perttu , Manninen Pekka , Vaara Juha
Published: September 2008

Irradiation of matter with circularly polarized light (CPL) shifts all nuclear magnetic resonance (NMR) lines. The phenomenon arises from the second-order interaction of the electron cloud with the optical field, combined with the orbital hyperfine interaction. The shift occurs in opposite directions for right and left CPL, and rapid switching between them will split the resonance lines into two. We present ab initio and density functional theory predictions of laser-induced NMR splittings for hydrocarbon systems with different sizes: ethene, benzene, coronene, fullerene, and circumcoronene. Due to the computationally challenging nature of the effect, traditional basis sets could not be used for the larger systems. A novel method for generating basis sets, mathematical completeness optimization, was employed. As expected, the magnitude of the spectral splitting increases with the laser beam frequency and polarizability of the system. Massive amplification of the effect is also observed close to the optical excitation energies. A much larger laser-induced splitting is found for the largest of the present molecules than for the previously investigated noble gas atoms or small molecules. The laser intensity required for experimental detection of the effect is discussed.
Liquid Al80Cu20: Atomic diffusion and viscosity
Authors: Brillo J. , Chathoth S. M. , Koza M. M. , Meyer A.
Published: September 2008

Properties of mass transport in liquid Al80Cu20 were measured over a broad temperature range of more than 500 K by means of oscillating cup viscometry and quasielastic neutron scattering. The shear viscosity and the coefficient of the Cu self-diffusion exhibit an Arrhenius-type temperature dependence. The activation energy for the viscous flow is 2.4 times smaller than that of the Cu self-diffusion. Below 1400 K, the Cu self-diffusion becomes increasingly smaller than expected from the viscosity data rescaled via the Stokes–Einstein relation.
Synchronization of genetic oscillators
Authors: Zhou Tianshou , Zhang Jiajun , Yuan Zhanjiang , Chen Luonan
Published: September 2008

Synchronization of genetic or cellular oscillators is a central topic in understanding the rhythmicity of living organisms at both molecular and cellular levels. Here, we show how a collective rhythm across a population of genetic oscillators through synchronization-induced intercellular communication is achieved, and how an ensemble of independent genetic oscillators is synchronized by a common noisy signaling molecule. Our main purpose is to elucidate various synchronization mechanisms from the viewpoint of dynamics, by investigating the effects of various biologically plausible couplings, several kinds of noise, and external stimuli. To have a comprehensive understanding on the synchronization of genetic oscillators, we consider three classes of genetic oscillators: smooth oscillators (exhibiting sine-like oscillations), relaxation oscillators (displaying jump dynamics), and stochastic oscillators (noise-induced oscillation). For every class, we further study two cases: with intercellular communication (including phase-attractive and repulsive coupling) and without communication between cells. We find that an ensemble of smooth oscillators has different synchronization phenomena from those in the case of relaxation oscillators, where noise plays a different but key role in synchronization. To show differences in synchronization between them, we make comparisons in many aspects. We also show that a population of genetic stochastic oscillators have their own synchronization mechanisms. In addition, we present interesting phenomena, e.g., for relaxation-type stochastic oscillators coupled to a quorum-sensing mechanism, different noise intensities can induce different periodic motions (i.e., inhomogeneous limit cycles).
Photon storage with subnanosecond readout rise time in coupled quantum wells
Authors: Winbow A. G. , Butov L. V. , Gossard A. C.
Published: September 2008

Photon storage with 250 ps rise time of the readout optical signal was implemented with indirect excitons in coupled quantum well (CQW) nanostructures. The storage and release of photons was controlled by the gate voltage pulse. The transient processes in the CQW were studied by measuring the kinetics of the exciton emission spectra after application of the gate voltage pulse. Strong oscillations of the exciton emission wavelength were observed in the transient regime when the gate voltage pulse was carried over an ordinary wire. Gating the CQW via an impedance-matched broadband transmission line has lead to an effective elimination of these transient oscillations and expedient switching of the exciton energy to a required value within a short time, much shorter than the exciton lifetime.
Unsteady nanoscale thermal transport across a solid-fluid interface
Authors: Balasubramanian Ganesh , Banerjee Soumik , Puri Ishwar K.
Published: September 2008

We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar–Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solidlike interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance Rk,av decreases as the imposed wall temperature Tw is increased, as Rk,av∝Tw−4.8. The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity.
Background limited long wavelength infrared type-II InAs/GaSb superlattice photodiodes operating at 110 K
Authors: Nguyen Binh-Minh , Hoffman Darin , Huang Edward Kwei-wei , Delaunay Pierre-Yves , Razeghi Manijeh
Published: September 2008

The utilization of the P+-π-M-N+ photodiode architecture in conjunction with a thick active region can significantly improve long wavelength infrared type-II InAs/GaSb superlattice photodiodes. By studying the effect of the depletion region placement on the quantum efficiency in a thick structure, we achieved a topside illuminated quantum efficiency of 50% for an N-on-P diode at 8.0 μm at 77 K. Both the double heterostructure design and the application of polyimide passivation greatly reduce the surface leakage, giving an R0A of 416 Ω cm2 for a 1% cutoff wavelength of 10.52 μm, a Shot–Johnson detectivity of 8.1×1011 cmHz/W at 77 K, and a background limited operating temperature of 110 K with 300 K background.
The effects of nitrogen profile and concentration on negative bias temperature instability of plasma enhanced atomic layer deposition HfOxNy prepared by in situ nitridation
Authors: Maeng W. J. , Kim Hyungjun
Published: September 2008

We have prepared plasma enhanced atomic layer deposition HfOxNy thin films by in situ nitridation using nitrogen/oxygen mixture plasma and studied the effects of nitrogen contents and profiles on the negative bias temperature instability (NBTI). The nitrogen depth profiles and concentrations were controlled by changing the exposure sequences and the nitrogen to oxygen flow ratio, respectively. The best immunity to NBTI degradations was obtained for the nitrogen to oxygen ratio of 2:1 when nitrogen atoms are incorporated away from the high k/Si interface. We propose a dielectric degradation mechanism based on the reaction-diffusion model in which nitrogen plays a role of hydrogen generator at the interface and diffusion barrier in the bulk film.
Theory and phase-cycling scheme selection principles of collinear phase coherent multi-dimensional optical spectroscopy
Authors: Tan Howe-Siang
Published: September 2008

We present the theory and the selection procedure of phase-cycling schemes for phase coherent multidimension optical spectroscopy. We apply our selection procedure to determine the phase-cycling schemes with the least number of steps needed to measure the two-dimensional spectra of various time resolved four wave mixing optical processes. The phase-cycling scheme selection procedure presented in this paper can be applied to higher order nonlinear optical experiments involving more optical pulses that measure higher dimensional optical spectra.
Intermittent spatio-temporal desynchronization and sequenced synchrony in ECoG signals
Authors: Kozma Robert , Freeman Walter J.
Published: September 2008

Electrocorticographic (ECoG) signals from the brain surface typically exhibit high synchrony across large cortical areas, interrupted by brief periods of desynchronization exhibiting propagating phase discontinuities, across which spatial patterns of phase emerge in selected frequency bands. Experiments with rabbits trained using classical conditioning paradigms indicated that such desynchronization periods demarcate cognitive processing in the subjects; the ECoG in the frames between such periods revealed spatial patterns of amplitude modulation that were classified with respect to sensory stimuli that the rabbits had been trained to recognize. The present work describes intermittent synchrony and desynchronization of ECoG signals measured over the visual cortex. We analyze the analytic amplitude (AA) and analytic phase (AP) of the signals bandpassed over the beta band (12.5–25Hz) and theta band (3–7Hz) using the Hilbert transform. The AP of analytic signals evaluated using a Shannon-based synchronization index in theta band exhibits phase synchronization for varying time periods averaging about 1s, interrupted by desynchronization periods of duration about 0.1s. Synchronization periods in the beta-band last <100ms, with interruptions by desynchronization lasting one-tenth that, in which the analytic amplitude drops drastically. During these “null spikes,” the analytic phase is undefined, and the spatial and temporal phase differences show high dispersion. Detailed examination of the bandpass filtered ECoG confirms the presence of a shared mean frequency in a frame of synchronized oscillation, at which frequency the spatial pattern of the AP has the form of a cone. Between frames the AA approaches zero. The form of the null spike resembles a tornado (a vortex), as shown in sequential frames by a rotating spatial pattern of amplitude in the filtered ECoG.
A critical look at electric field emission of electrons from metallic surfaces
Authors: Sodha Mahendra Singh , Dixit Amrit
Published: September 2008

A critical look at the commonly used Fowler's expression for the transmission coefficient of electrons through the potential barrier leads to the conclusion that this expressions is physically untenable. An expression for the field emission current density, corresponding to the expression for the transmission coefficient obtained from the exact solution of Schrödinger’s equation, has been derived. Numerical results have been expressed in the form of tables and graphs and discussed. It is seen that in the range of 10−4<kT/EF<10−3, the effect of temperature on the field emission current density is negligible.
Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots
Authors: Komarala Vamsi K. , Bradley A. Louise , Rakovich Yury P. , Byrne Stephen J. , Gun’ko Yurii K. , Rogach Andrey L.
Published: September 2008

Förster resonance energy transfer (FRET) between CdTe quantum dots (QDs) at nanoscale proximity to gold nanoparticle (Au NP) layers is investigated experimentally. We have observed the enhancement in the acceptor QDs’ photoluminescence lifetime intensities. The decrease in donor QDs’ exciton lifetime from 5.74to2.06ns, accompanied by an increase in acceptor QDs’ exciton lifetime from 3.38to7.52ns, provided evidence for enhanced FRET between the QDs near Au NPs. The Au NPs’ surface plasmon dipole fields are assisted to overcome the weak electronic coupling between the emitting (donor) and absorbing (acceptor) transition exciton dipoles in the homogeneous medium.
Single-electron transistors made by chemical patterning of silicon dioxide substrates and selective deposition of gold nanoparticles
Authors: Coskun Ulas C. , Mebrahtu Henok , Huang Paul B. , Huang Jeremy , Sebba David , Biasco Adriana , Makarovski Alex , Lazarides Anne , LaBean Thom H. , Finkelstein Gleb
Published: September 2008

We describe a method to pattern SiO2 surfaces with colloidal gold nanoparticles by e-beam lithography and selective nanoparticle deposition. The simple technique allows us to deposit nanoparticles in continuous straight lines, just one nanoparticle wide and many nanoparticles long. We contact the prepositioned nanoparticles with metal leads to form single electron transistors. The Coulomb blockade pattern surprisingly does not show the parasitic “offset charges” at low temperatures, indicating relatively little surface contamination.
Efficient and robust quantum Monte Carlo estimate of the total and spin electron densities at nuclei
Authors: Håkansson P. , Mella Massimo
Published: September 2008

The computational performance of two different variational quantum Monte Carlo estimators for both the electron and spin densities on top of nuclei are tested on a set of atomic systems containing also third-row species. Complications due to an unbounded variance present for both estimators are circumvented using appropriate sampling strategies. Our extension of a recently proposed estimator [Phys. Rev. A 69, 022701 (2004)] to deal with heavy fermionic systems appears to provide improved computational efficiency, at least an order of magnitude, with respect to alternative literature approaches for our test set. Given the importance of an adequate sampling of the core region in computing the electron density at a nucleus, a further reduction in the overall simulation cost is obtained by employing accelerated sampling algorithms.
Selection of in-phase or out-of-phase synchronization in a model based on global coupling of cells undergoing metabolic oscillations
Authors: Gonze Didier , Markadieu Nicolas , Goldbeter Albert
Published: September 2008

On the basis of experimental observations, it has been suggested that glycolytic oscillations underlie the pulsatile secretion of insulin by pancreatic β cells, with a periodicity of about 13min. If β cells within an islet are synchronized through gap junctions, the question arises as to how β cells located in different islets of Langerhans synchronize to produce oscillations in plasma levels of insulin. We address this question by means of a minimal model that incorporates the secretion of insulin by cells undergoing glycolytic oscillations. Global coupling and synchronization result from the inhibition exerted by insulin on the production of glucose, which serves as the substrate for metabolic oscillations. Glycolytic oscillations are described by a simple two-variable model centered on the product-activated reaction catalyzed by the allosteric enzyme phosphofructokinase. We obtain bifurcation diagrams for the cases in which insulin secretion is controlled solely by the product or by the substrate of the metabolic oscillator. Remarkably, we find that the oscillating cells in these conditions synchronize, respectively, in phase or out of phase. Numerical simulations show that in-phase and out-of-phase synchronization can sometimes coexist when insulin release is controlled by both the substrate and the product of the metabolic oscillator. The results provide an example of a system in which the selection of in-phase or out-of-phase synchronization is governed by the nature of the coupling between the intracellular oscillations and the secretion of the biochemical signal through which the oscillating cells are globally coupled.
Introduction to Focus Issue: Synchronization in Complex Networks
Authors: Suykens Johan A. K. , Osipov Grigory V.
Published: September 2008

Synchronization in large ensembles of coupled interacting units is a fundamental phenomenon relevant for the understanding of working mechanisms in neuronal networks, genetic networks, coupled electrical and laser networks, coupled mechanical systems, networks in social sciences, and others. It relates to mathematical and computational analysis of the existence of different states and its stability, clustering, bifurcations and chaos, robustness and sensitivity analysis, etc., at the intersection between synchronization and pattern formation in complex networks. This interdisciplinary oriented Focus Issue presents recent progress in this area with contributions on generic methods, specific model studies, and applications.
Improving an electret transducer by fully utilizing the implanted charge
Authors: Okamoto Hiroshi , Onuki Teppei , Kuwano Hiroki
Published: September 2008

Most of the countercharge in the conventional electret-based electromechanical transducer, where the electret is formed on a conducting or semiconducting substrate, is induced in the substrate. Here we introduce a type of electret transducer that contains a freestanding electret without a conducting substrate, thereby enhancing the electric field between the electret and the electrodes where the output current is generated. A measurement of the power output from an electromechanical transducer yielded approximately five times larger power when a freestanding electret film was used than when the same electret material was deposited on a conducting substrate.
Integrated electroplated heat spreaders for high power semiconductor lasers
Authors: Fu Jianping , Yang Ronggui , Chen Gang , Fleurial Jean Pierre , Snyder G. Jeffrey
Published: September 2008

Thermal management of high power semiconductor lasers is challenging due to the low thermal conductivity of the laser substrate and the active device layers. In this work, we demonstrate the use of a microfabricated laser test device to study the thermal management of edge emitting semiconductor lasers. In this device, metallic heat spreaders of high thermal conductivity are directly electroplated on structures that mimic edge-emitting semiconductor lasers. The effects of various structural parameters of the heat spreader on the reduction of the thermal resistance of the laser test device are demonstrated both experimentally and theoretically. Without resolving to computational costive simulations, we developed two independent analytical models to verify the experimental data and further utilized them to identify the dominant thermal resistance under different laser mounting configurations. We believe our approach here of using microfabricated devices to mimic thermal characteristics of lasers as well as the developed analytical models for calculating the laser thermal resistance under different mounting configurations can potentially become valuable tools for thermal management of high power semiconductor lasers.
Axis-encircling electron beam generation using a smooth magnetic cusp for gyrodevices
Authors: He W. , Whyte C. G. , Rafferty E. G. , Cross A. W. , Phelps A. D. R. , Ronald K. , Young A. R. , Robertson C. W. , Speirs D. C. , Rowlands D. H.
Published: September 2008

The generation of an annular-shaped axis-encircling electron beam using a smooth magnetic cusp was studied through numerical simulations and experiments for harmonic operation of a gyrodevice. Two magnetic coils were used to form a magnetic cusp located just downstream from the velvet cathode of an accelerator diode. An electron beam of current 34 A and voltage 130 kV with an adjustable velocity ratio α up to 1.2 was fully transported to the downstream uniform magnetic field region and used to drive a gyrotron traveling wave amplifier into saturation.
Quantitative determination of Ge profiles across SiGe wetting layers on Si (001)
Authors: Brehm M. , Grydlik M. , Lichtenberger H. , Fromherz T. , Hrauda N. , Jantsch W. , Schäffler F. , Bauer G.
Published: September 2008

The peak positions in photoluminescence spectra of Ge wetting layers (WL) deposited at 700 °C were measured versus the Ge coverage with an extremely high relative resolution of 0.025 monolayers. A nearly linear redshift of the peaks with increasing Ge coverage is observed. We derived quantitative WL composition profiles by fitting this shift, and its dependence on the deposition temperature of the capping layer (Tc), to results of band structure calculations. Despite the high growth temperature, the Ge content in the WL exceeds 80%. It is shown that the composition profile is dominated by surface segregation of Ge on Si.
Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations
Authors: Hu Qing-Miao , Li Shu-Jun , Hao Yu-Lin , Yang Rui , Johansson Börje , Vitos Levente
Published: September 2008

The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti–Nb–Zr–Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e∕a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti–Sn alloy.
Plasmonic nanoparticle enhanced light absorption in GaAs solar cells
Authors: Nakayama Keisuke , Tanabe Katsuaki , Atwater Harry A.
Published: September 2008

We demonstrate an improvement in efficiency of optically thin GaAs solar cells decorated with size-controlled Ag nanoparticles fabricated by masked deposition through anodic aluminum oxide templates. The strong scattering by the interacting surface plasmons in densely formed high aspect-ratio nanoparticles effectively increases the optical path of the incident light in the absorber layers resulting in an 8% increase in the short circuit current density of the cell. The nanoparticle array sheet conductivity also reduces the cell surface sheet resistance evidenced by an improved fill factor. This dual function of plasmonic nanoparticles has potential to enable thinner photovoltaic layers in solar cells.
The unsaturated photocurrent controlled by two-dimensional barrier geometry of a single ZnO nanowire Schottky photodiode
Authors: Cheng Gang , Li Zhaohan , Wang Shujie , Gong Hechun , Cheng Ke , Jiang Xiaohong , Zhou Shaomin , Du Zuliang , Cui Tian , Zou Guangtian
Published: September 2008

In this letter, the I-V curve of a single ZnO nanowire assembled by dielectrophoresis was measured, which indicated that a back-to-back Schottky barrier structure was formed. Under ultraviolet light illumination, the photocurrent of the ZnO nanowire Schottky photodiode was unsaturated, and its differential conductivity increased with the increase of bias. A two-dimensional Schottky barrier geometry model was introduced to describe the separation of photogenerated electron-hole pairs in the depletion layer, which can well explain the unsaturated photocurrent property. In addition, the corresponding photocurrent equation was obtained, which was in good agreement with the experimental results.
Efficient termination of vacuolar Rab GTPase signaling requires coordinated action by a GAP and a protein kinase
Authors: Brett Christopher L. , Plemel Rachael L. , Lobingier Braden T. , Vignali Marissa , Fields Stanley , Merz Alexey J.
Published: September 2008

Rab guanosine triphosphatases (GTPases) are pivotal regulators of membrane identity and dynamics, but the in vivo pathways that control Rab signaling are poorly defined. Here, we show that the GTPase-activating protein Gyp7 inactivates the yeast vacuole Rab Ypt7 in vivo. To efficiently terminate Ypt7 signaling, Gyp7 requires downstream assistance from an inhibitory casein kinase I, Yck3. Yck3 mediates phosphorylation of at least two Ypt7 signaling targets: a tether, the Vps-C/homotypic fusion and vacuole protein sorting (HOPS) subunit Vps41, and a SNARE, Vam3. Phosphorylation of both substrates is opposed by Ypt7-guanosine triphosphate (GTP). We further demonstrate that Ypt7 binds not one but two Vps-C/HOPS subunits: Vps39, a putative Ypt7 nucleotide exchange factor, and Vps41. Gyp7-stimulated GTP hydrolysis on Ypt7 therefore appears to trigger both passive termination of Ypt7 signaling and active kinase-mediated inhibition of Ypt7's downstream targets. We propose that signal propagation through the Ypt7 pathway is controlled by integrated feedback and feed-forward loops. In this model, Yck3 enforces a requirement for the activated Rab in docking and fusion.
Consensus nomenclature for the human ArfGAP domain-containing proteins
Authors: Kahn Richard A. , Bruford Elspeth , Inoue Hiroki , Logsdon John M. , Nie Zhongzhen , Premont Richard T. , Randazzo Paul A. , Satake Masanobu , Theibert Anne B. , Zapp Maria L. , Cassel Dan
Published: September 2008

At the FASEB summer research conference on “Arf Family GTPases”, held in Il Ciocco, Italy in June, 2007, it became evident to researchers that our understanding of the family of Arf GTPase activating proteins (ArfGAPs) has grown exponentially in recent years. A common nomenclature for these genes and proteins will facilitate discovery of biological functions and possible connections to pathogenesis. Nearly 100 researchers were contacted to generate a consensus nomenclature for human ArfGAPs. This article describes the resulting consensus nomenclature and provides a brief description of each of the 10 subfamilies of 31 human genes encoding proteins containing the ArfGAP domain.
Matched Case-Control Analysis of Polymicrobial Bloodstream Infection In A Neonatal Intensive Care Unit
Authors: Bizzarro Matthew J. , Dembry Louise-Marie , Baltimore Robert S. , Gallagher Patrick G.
Published: September 2008

Objective.

To compare and contrast the epidemiology of polymicrobial and monomicrobial bloodstream infections (BSIs) in newborn intensive care unit (NICU) patients.

Design.

Retrospective, matched case-control study.

Setting.

The Yale-New Haven Hospital NICU from 1989 through 2006.

Subjects.

NICU patients with BSIs.

Methods.

Each neonate with polymicrobial BSI (case patient) was matched to one neonate with monomicrobial BSI (control patient), by birth date, weight, and sex; and univariate and multivariate analyses were performed.

Results.

One hundred five cases of polymicrobial BSI were identified in 102 infants, representing 10% of all neonatal BSIs in our institution. Coagulase-negative staphylococci were the most common organisms recovered from culture. Infants with polymicrobial BSI had later onset of infection than infants with monomicrobial BSI (mean day of life, 37.5 vs 24.0;P< .001). Polymicrobial BSI occurred more frequently among infants with a severe underlying condition than in those without such a condition (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.1-3.2) and among infants requiring an indwelling central venous catheter for a prolonged duration (mean, 16.9 days, compared with 9.8 days for infants with monomicrobial BSI;P= .001). Multivariate analysis revealed that later onset of infection (adjusted OR [aOR], 1.02; 95% CI, 1.00-1.04) and presence of a severe underlying condition (aOR, 1.91; 95% CI, 1.12-3.38) were independent risk factors for polymicrobial BSI. No differences in outcome or mortality were observed.

Conclusions.

Changes in the microbiology and epidemiology of NICU-related polymicrobial BSI have occurred since the last North American review. In the present study, although differences were observed, most risk factors and outcomes were similar between monomicrobial BSI and polymicrobial BSI. Epidemiologic surveillance is critical to identify trends associated with neonatal polymicrobial BSI, particularly those that may impact preventative strategies, diagnostic measures, and therapeutic interventions.
Recommendations For Metrics For Multidrug-Resistant Organisms In Healthcare Settings: SHEA/HICPAC Position Paper
Authors: Cohen Adam L. , Calfee David , Fridkin Scott K. , Huang Susan S. , Jernigan John A. , Lautenbach Ebbing , Oriola Shannon , Ramsey Keith M. , Salgado Cassandra D. , Weinstein Robert A. ,   The Society for Healthcare Epidemiology of America and the Healthcare Infection Control Practices Advisory Committee
Published: September 2008

Monitoring multidrug-resistant organisms (MDROs) and the infections they cause in a healthcare setting is important to detect newly emerging antimicrobial resistance profiles, to identify vulnerable patient populations, and to assess the need for and effectiveness of interventions; however, it is unclear which metrics are the best, because most of the metrics are not standardized. This document describes useful and practical metrics and surveillance considerations for measuring MDROs and the infections they cause in the practice of infection prevention and control in healthcare settings. These metrics are designed to aid healthcare workers in documenting trends over time within their facility and should not be used for interfacility comparison.