bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphatidylinositol 3-phosphate 5-kinase (PIKfyve) is an AMPK target participating in contraction-stimulated glucose uptake in skeletal muscle
Authors: Liu Yang , Lai Yu-Chiang , Hill Elaine V. , Tyteca Donatienne , Carpentier Sarah , Ingvaldsen Ada , Vertommen Didier , Lantier Louise , Foretz Marc , Dequiedt Franck , Courtoy Pierre J. , Erneux Christophe , Viollet Benoît , Shepherd Peter R. , Tavaré Jeremy M. , Jensen Jørgen , Rider Mark H.
Published: August 2013

PIKfyve (FYVE domain-containing phosphatidylinositol 3-phosphate 5-kinase), the lipid kinase that phosphorylates PtdIns3P to PtdIns(3,5)P2, has been implicated in insulin-stimulated glucose uptake. We investigated whether PIKfyve could also be involved in contraction/AMPK (AMP-activated protein kinase)-stimulated glucose uptake in skeletal muscle. Incubation of rat epitrochlearis muscles with YM201636, a selective PIKfyve inhibitor, reduced contraction- and AICAriboside (5-amino-4-imidazolecarboxamide riboside)-stimulated glucose uptake. Consistently, PIKfyve knockdown in C2C12 myotubes reduced AICAriboside-stimulated glucose transport. Furthermore, muscle contraction increased PtdIns(3,5)P2 levels and PIKfyve phosphorylation. AMPK phosphorylated PIKfyve at Ser307 both in vitro and in intact cells. Following subcellular fractionation, PIKfyve recovery in a crude intracellular membrane fraction was increased in contracting versus resting muscles. Also in opossum kidney cells, wild-type, but not S307A mutant, PIKfyve was recruited to endosomal vesicles in response to AMPK activation. We propose that PIKfyve activity is required for the stimulation of skeletal muscle glucose uptake by contraction/AMPK activation. PIKfyve is a new AMPK substrate whose phosphorylation at Ser307 could promote PIKfyve translocation to endosomes for PtdIns(3,5)P2 synthesis to facilitate GLUT4 (glucose transporter 4) translocation.
CRAC channel inhibition produces greater anti-inflammatory effects than glucocorticoids in CD8 cells from COPD patients
Authors: Grundy Seamus , Kaur Manminder , Plumb Jonathan , Reynolds Sophie , Hall Simon , House David , Begg Malcolm , Ray David , Singh Dave
Published: August 2013

There are increased numbers of pulmonary CD8 lymphocytes in COPD (chronic obstructive pulmonary disease). CRAC (calcium release-activation calcium) channels play a central role in lymphocyte activation though the regulation of the transcription factor NFAT (nuclear factor of activated T-cells). We studied the expression of NFAT in lungs from COPD patients compared with controls, and evaluated the effects of CRAC channel inhibition compared with corticosteroids on NFAT activation and cytokine production in CD8 cells from COPD patients. The effects of the corticosteroid dexamethasone, the calcineurin inhibitor cyclosporin and the CRAC channel inhibitor Synta 66 were studied on cytokine production and NFAT activation using peripheral blood and isolated pulmonary CD8 cells. NFAT1 and CD8 co-expression in the lungs was compared in COPD patients and controls using combined immunohistochemistry and immunofluorescence. NFAT inhibition with either cyclosporin or Synta 66 resulted in significantly greater maximal inhibition of cytokines than dexamethasone in both peripheral blood and pulmonary CD8 cells [e.g. >95% inhibition of IFNγ (interferon γ) production from pulmonary CD8 cells using cyclosporin and Synta 66 compared with <50% using dexamethasone]. The absolute number of pulmonary CD8 cells co-expressing NFAT1 was significantly raised in lungs from COPD patients compared with controls, but the percentage of CD8 cells co-expressing NFAT1 was similar between COPD patients and controls (80.7% compared with 78.5% respectively, P=0.3). Inhibition of NFAT using the CRAC channel Synta 66 produces greater anti-inflammatory effects on CD8 cells from COPD patients than corticosteroids. NFAT is expressed at a high level in pulmonary CD8 cells in COPD.
Randomness of finite‐state sequence machine over GF(4) and quality of hopping turbo codes
Authors: De Micco Luciana , Petruzzi David , Larrondo Hilda A. , Castiñeira Moreira Jorge
Published: August 2013

In this study, the authors study a turbo‐coding (TC) scheme, whose constituent codes are designed using convolutional encoders. These encoders are finite‐state sequence machines (FSSMs) operating over the Galois Field, GF(4). The scheme includes encryption polynomials whose coefficients are selected every L steps, from the set of optimal polynomials of GF(4). Two cases are considered for the polynomial selection: periodical and random. This kind of encoder was studied in a previous study and a correspondence between the randomness of the encoded sequence and performance of the TC was conjectured. The main contribution of this study is to systematically confirm this correspondence, by analysing the randomness of the output and performance of the TC using several randomness quantifiers. Three of the quantifiers are defined on the basis of recurrence plots. Other two quantifiers are defined on the basis of the information theory. All the quantifiers allow one to justify why the proposed TC works better with random selection of the optimal polynomials and with small values of L. In summary, it is shown that a random selection of polynomials and a small L produce FSSMs with enhanced randomness properties and it is also shown that they produce the best quality of the TC, measured by means of the corresponding bit error rate.
Development of rain attenuation model for Southeast Asia equatorial climate
Authors: Nalinggam Renuka , Ismail Widad , Jit Singh Mandeep , Islam Mohammad Tariqul , Menon P. Susthitha
Published: August 2013

Statistical distribution of rain attenuation is essential for development of microwave and millimeter‐wave communication links. Therefore rain‐related statistics are very important for a commercialisation system designer. This study proposes modifications to the International Telecommunication Union (ITU‐R P.618‐10) model and an appropriate rain attenuation prediction model for tropical countries. The model was developed based on data obtained from tropical and equatorial regions. The proposed model uses rainfall rate and rain attenuation at 0.01% of the time, R0.01 and A0.01, elevation angle θ and altitude of site hs, respectively, as input parameters. The proposed model showed remarkable agreement with existing rain attenuation measured data in terms of prediction errors for mean square, standard deviation and root‐mean square. The proposed rain attenuation model was used for validation by comparing the model with measured data collected from Nigeria, Kenya and Papua New Guinea, whereby the proposed model gave a percentage error below 12%.
Joint sector identity and integer part of carrier frequency offset detection by phase‐difference in Long Term Evolution cell search process
Authors: Su Szu‐Lin , Lin Yung‐Chuan , Fan Yun‐Jhen
Published: August 2013

In the Long Term Evolution (LTE) system, the initial cell search needs not only to achieve the timing synchronisations of symbols, slots and frames, but also to detect the sector identity (ID), the cell ID group and the carrier frequency offset (CFO), which includes an integer part (ICFO) and a fractional part. To accomplish this cell search process, two synchronisation signals, the primary synchronisation signal (PSS) and the secondary synchronisation signal, are periodically broadcasted from base stations in the LTE system. The PSS is mainly used for sector ID detection. In this study, an innovative algorithm for detecting the sector ID and ICFO together via the PSS‐matching process is presented. In the proposed scheme, the phases of the differential correlation instead of the absolute values are adopted to determine the ICFO. Furthermore, a new set of PSS is proposed in order to improve the success probability of ICFO detection. Compared with conventional schemes, the proposed scheme can detect both the sector ID and ICFO with higher accuracy and much lower complexity.
Joint signal‐to‐noise ratio‐based transceiver design for amplify‐and‐forward multiple‐input multiple‐output relay systems
Authors: Bao Wei , Zhang Jianhua , Zhang Ping
Published: August 2013

In this study, the authors address the problem of transceiver design in an amplify‐and‐forward multiple‐input multiple‐output relay system with full or partial channel state information (CSI), where linear processing is applied to maximise the average received signal‐to‐noise ratio (SNR) at source, relay and destination, respectively. This joint design problem is a non‐convex optimisation problem, so the authors convert it into a scalar problem and derive the optimal unitary decoder under average power constraint. The precoder at source and relay can be obtained by employing generalised Rayleigh quotient method. Specifically, two CSI assumptions are considered: (i) the authors first derive the precoder and decoder with full CSI; (ii) assumimg the statistical independence between the channel estimated value and channel estimation errors, the problem with partial CSI can be solved as the same way as full CSI case. Numerical results show a great improvement on the average received SNR by applying the proposed scheme. On the other hand, the authors also illustrate the impact on received SNR arose by the channel estimation errors.
Relay selection in cognitive radio networks with interference constraints
Authors: Seyfi Mehdi , Muhaidat Sami , Liang Jie
Published: August 2013

In this study, the authors investigate the outage probability of underlay cognitive radio systems with relay selection. In particular, they consider a secondary multi‐relay network operating in the amplify‐and‐forward (AF) mode and only the ‘best’ relay is selected, which satisfies an index of merit. The proposed selection strategy takes into consideration the effect of primary user (PU) interference. That is, the authors assume that the secondary multi‐relay network is exposed to unwanted interference from a neighboring PU network. They derive a closed‐form outage probability expression and further present a thorough asymptotic diversity order analysis of the underlying scenario. A simulation study is presented to corroborate the analytical results and to have further insight into the performance of the proposed selection strategy.
Impact of interference power constraint on multi‐hop cognitive amplify‐and‐forward relay networks over Nakagami‐m fading
Authors: Phan Hoc , Zepernick Hans‐Jürgen , Tran Hung
Published: August 2013

In this article, the authors study the effect of peak interference power constraint given by the primary receiver on the performance of multi‐hop cognitive amplify‐and‐forward (AF) relay networks. The athours assume that all involved channels are subject to independent, not necessarily identically distributed Nakagami‐m fading and the secondary multi‐hop relay network operates in channel state information‐assisted AF mode. An analysis of the system performance in terms of outage probability and symbol error rate (SER) is presented. Accordingly, closed‐form expressions for the tightly bounded outage probability and SER are formulated which are used for quantifying the impact of the fading channels, the interference power constraint and the number of hops on system performance. More importantly, an asymptotic performance analysis, which intuitively reveals benefits of cooperative diversity of the secondary relay network, is established. The analysis shows that the diversity gain of the considered cognitive relay networks is equal to the minimum of the fading severity parameters of all relaying hops. Also, the interference power constraint imposed by the primary receiver only affects the coding gain of the secondary relay network.
Approximate distribution of log2(A + χ2) and its applications
Authors: Qi Yuan , Qian Rongrong , Peng Tao , Wang Wenbo
Published: August 2013

This study concerns the approximate distribution of the random variable log2(A + χ2) and its applications in the performance analysis of communication systems where A is 0 or 1 and χ2 a chi‐square distributed random variable. The authors prove that log2(A + χ2) is approximately Gaussian distributed and derive the expressions of the mean and variance of the approximate distribution. The approximate Gaussian distribution provides a new way to simplify the derivation of performance metrics and obtain analytical results. Then the authors utilise the approximate results in two applications, which are the approximation of the Gaussian Q‐function and capacity analysis, respectively. For one thing, the approximate distribution can be explored to deduce a new approximate equivalent expression of the Q‐function on the basis of which an accurate approximation of the Gaussian Q‐function can be developed. For another, the approximate Gaussian distribution provides an intuitive approach to analyse the channel capacity of Rayleigh‐fading multiple antenna systems. The approximate statistical distributions of the channel capacities of orthogonal space‐time block codes, single‐input multiple‐output, multiple‐input single‐output, transmit antenna selection with maximal‐ratio combining and multiple‐input multiple‐output systems are presented. The applicability of the approximate distribution can be demonstrated through simulation results in both applications.
Dual‐antenna‐based blind joint hostile jamming cancellation and multi‐user detection for uplink of asynchronous direct‐sequence code‐division multiple access systems
Authors: Zhang Jiang , Zhang Hang , Cui Zhifu
Published: August 2013

The authors investigate the problem of blind multi‐user detection (MUD) for uplink of asynchronous direct‐sequence code‐division multiple access (DS‐CDMA) systems with hostile jamming. To cope with the lack of prior knowledge of spread signals, hostile jamming and channel state information, the authors propose a scheme based on blind source separation (BSS) to solve this problem. Dual receive antennas are used in the proposed scheme. By exploiting the structure of the two received signals, a BSS model with dependent sources is formed, and then blind hostile jamming cancellation and MUD are obtained by solving this BSS problem. The proposed scheme does not require to know any information about the hostile jamming, and can work well under multiple kinds of hostile jamming. Simulation results further demonstrate that if such proposed approach is used to cancel hostile jamming and make MUD, then the bit‐error‐rate performance can be substantially improved as compared with earlier detectors.
Patientenzufriedenheit bei onkologischen Erkrankungen – Eine differenzierte Betrachtung der Sektoren Hausarzt, Facharzt, Krankenhaus und Krankenkasse
Authors: Degen C. , Möller D. , Schlechter C.
Published: August 2013

Die vorliegende Studie untersucht die Einflussgrößen für Patientenzufriedenheit bei onkologischen Patienten. Hierbei wird einerseits die Zufriedenheit mit den Hausärzten, den Fachärzten, dem Krankenhaus sowie den Krankenkassen betrachtet und andererseits die sektorübergreifende Zusammenarbeit in der gesamten onkologischen Versorgung.

An der Patientenbefragung haben 12 Facharztpraxen in 8 Bundesländern teilgenommen. Insgesamt beteiligten sich 516 Patienten im Untersuchungszeitraum 2011 – 2012 an der empirischen Erhebung. Die Auswertung erfolgt mittels der multiplen Regressionsanalyse.

Die Untersuchung zeigt, dass Patienten mit der sektorübergreifenden Zusammenarbeit zufriedener sind, wenn Zufriedenheit mit der Krankenkasse und der fachärztlichen Versorgung besteht. Die differenzierte Betrachtung der Zufriedenheit mit den Sektoren gibt Aufschluss darüber, dass für den haus- und fachärztlichen Bereich das Vertrauen in den Arzt als wichtigste Komponente wahrgenommen wird. Bei Krankenhäusern ist entscheidend, dass sich die Ärzte ihren Patienten gegenüber interessiert zeigen und Zeit für die Patienten nehmen. Für Krankenkassen wurde die Bereitstellung von genügend Informationen als größter Zufriedenheitstreiber identifiziert.

In der Patientenwahrnehmung der Zufriedenheit mit einzelnen Sektoren spielen vor allem psychosoziale Faktoren eine wichtige Rolle. Hierunter fallen z. B. das Vertrauen in den Arzt oder das Besprechen von Ängsten des Patienten. Diese Faktoren sollten von den beteiligten Akteuren im Umgang mit den Patienten stärker fokussiert werden. Krankenkassen können hierbei als kompetenter Ansprechpartner fungieren, der den Patienten qualitätsgesicherte Informationen im Kontext der onkologischen Erkrankung bereitstellt.
Effects of crystallization mechanism on the electrical characteristics of green continuous-wave-laser-crystallized polycrystalline silicon thin film transistors
Authors: Chou Chia-Hsin , Lee I-Che , Yang Po-Yu , Hu Ming-Jhe , Wang Chao-Lung , Wu Chun-Yu , Chien Yun-Shan , Wang Kuang-Yu , Cheng Huang-Chung
Published: August 2013

Thin film transistors (TFTs) with amorphous silicon films crystallized via continuous-wave green laser at a wavelength of 532 nm exhibit very different electrical characteristics in various crystallization regions, corresponding to the Gaussian energy density distribution of the laser beam. In the center region subjected to the highest energy density, the full melting scheme led to the best crystallinity of the polycrystalline silicon film, resulting in the highest field-effect mobility of 500 cm2 V−1 s−1. In contrast, the edge region that resulted in solid phase crystallization exhibited the worst mobility of 48 cm2 V−1 s−1 for the polycrystalline silicon TFTs.
Attenuation of superconductivity in manganite/cuprate heterostructures by epitaxially-induced CuO intergrowths
Authors: Zhang H. , Gauquelin N. , Botton G. A. , Wei J. Y. T.
Published: August 2013

We examine the effect of CuO intergrowths on the superconductivity in epitaxial La2/3Ca1/3MnO3/YBa2Cu3O7−δ (LCMO/YBCO) thin-film heterostructures. Scanning transmission electron microscopy on bilayer LCMO/YBCO thin films revealed double CuO-chain intergrowths which form regions with the 247 lattice structure in the YBCO layer. These nanoscale 247 regions do not appear in x-ray diffraction, but can physically account for the reduced critical temperature (Tc) of bilayer thin films relative to unilayer films with the same YBCO thickness, at least down to ∼25 nm. We attribute the CuO intergrowths to the bilayer heteroepitaxial mismatch and the Tc reduction to the generally lower Tc seen in bulk 247 samples. These epitaxially-induced CuO intergrowths provide a microstructural mechanism for the attenuation of superconductivity in LCMO/YBCO heterostructures.
Occupation statistics of the 5/7-atom dislocation core structure within n-type indium nitride
Authors: Baghani Erfan , O’Leary Stephen K.
Published: August 2013

Recent density functional calculations by Kalesaki et al. [Appl. Phys. Lett. 98, 072103 (2011)] and by Takei and Nakayama [J. Cryst. Growth 311, 2767 (2009)] have shown that the 5/7-atom dislocation core structure possesses a donor character within intrinsic wurtzite InN. In the present work, we relax the assumption that wurtzite InN is intrinsic and obtain the occupation statistics of the different possible ionization states of the 5/7-atom dislocation defect sites as a function of the bulk doping concentration. An underlying Gibbs factor formalism, similar to that applied earlier to the problem of obtaining the occupation statistics of the dislocation defect sites within n-type gallium nitride, has been employed for the purposes of the present analysis. The occupation statistics results of this analysis suggest that dislocation line densities below 1010 cm−2 are necessary in order to achieve bulk free electron concentrations lower than 1017 cm−3 within wurtzite InN. Our occupation statistics results are shown to be consistent with existing electron mobility measurements from the literature.
Persistent-mode high-temperature superconductor shim coils: A design concept and experimental results of a prototype Z1 high-temperature superconductor shim
Authors: Iwasa Yukikazu , Hahn Seungyong , Voccio John , Keun Park Dong , Kim Youngjae , Bascuñán Juan
Published: August 2013

Design, fabrication, and test results of a type persistent-mode high-temperature superconductor (HTS) shim coil are presented. A prototype Z1 rectangle-loop shim, cut from 46-mm wide Y-Ba-Cu-O tape manufactured by AMSC, was fabricated and tested at 77 K. The HTS shim, much thinner than the conventional NbTi shim, is placed inside the main magnet and immune to its diamagnetic wall effects. Combined with the >12-T and >10-K operation capability, the HTS shim offers a versatile design option for nuclear magnetic resonance (NMR) magnets, liquid-helium-free as well as conventional, and is particularly attractive in the next generation NMR magnets.
The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Neutral atomic zinc and oxygen emission
Authors: Khan Enamul H. , Langford S. C. , Dickinson J. T. , Boatner L. A.
Published: August 2013

We report mass-resolved time-of-flight measurements of neutral particles from the (101¯0) surface of single-crystal ZnO during pulsed 193-nm irradiation at laser fluences below the threshold for avalanche breakdown. The major species emitted are atomic Zn and O. We examine the emissions of atomic Zn as a function of laser fluence and laser exposure. Defects at the ZnO surface appear necessary for the detection of these emissions. Our results suggest that the production of defects is necessary to explain intense sustained emissions at higher fluence. Rapid, clean surface etching and high atomic zinc kinetic energies seen at higher laser fluences are also discussed.
Quantum mechanical force field for water with explicit electronic polarization
Authors: Han Jaebeom , Mazack Michael J. M. , Zhang Peng , Truhlar Donald G. , Gao Jiali
Published: August 2013

A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen- and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 106 self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across biological ion channels through membranes.
Hysteretic response of chemical vapor deposition graphene field effect transistors on SiC substrates
Authors: Cazalas Edward , Childres Isaac , Majcher Amanda , Chung Ting-Fung , Chen Yong P. , Jovanovic Igor
Published: August 2013

Graphene field effect transistors (GFETs) fabricated by chemical vapor deposition graphene deposited onto SiC substrates exhibit sensitivity to broadband visible light. The hysteretic nature of this GFET type was studied utilizing a new current-voltage measurement technique in conjunction with current-time measurements. This measurement method accounts for hysteretic changes in graphene response and enables transfer measurements that can be attributed to fixed gate voltages. Graphene hysteresis is shown to be consistent with electrochemical p-type doping, and current-time measurements clearly resolve a hole to electron to hole carrier transition in graphene with a single large change in gate voltage.
Existence and uniqueness, attraction for stochastic age-structured population systems with diffusion and Poisson jump
Authors: Chen Huabin
Published: August 2013

In this paper, the problems about the existence and uniqueness, attraction for strong solution of stochastic age-structured population systems with diffusion and Poisson jump are considered. Under the non-Lipschitz condition with the Lipschitz condition being considered as a special case, the existence and uniqueness for such systems is firstly proved by using the Burkholder-Davis-Gundy inequality (B-D-G inequality) and Itô’s formula. And then by using a novel inequality technique, some sufficient conditions ensuring the existence for the domain of attraction are established. As another by-product, the exponential stability in mean square moment of strong solution for such systems can be also discussed.
Exact transport equation for local eddy viscosity in turbulent shear flow
Authors: Hamba Fujihiro
Published: August 2013

Two-equation models that treat the transport equations for two variables are typical models for the Reynolds-averaged Navier-Stokes equation. Compared to the equation for the turbulent kinetic energy, the equation for the second variable such as the energy dissipation rate has not been validated enough from the theoretical point of view. In this work, the transport equation for the eddy viscosity was derived and examined for better understanding turbulence and improving turbulence models. The local approximation was first applied to the exact nonlocal eddy-viscosity representation for the Reynolds stress. A new length scale was then introduced, which involves the response function for the velocity fluctuation. It was shown that the local eddy viscosity can be expressed as the correlation between the velocity fluctuation and the new length scale. The exact transport equations for the local eddy viscosity and the length-scale variance were derived theoretically. A direct numerical simulation of turbulent channel flow was carried out to evaluate statistics such as terms in the transport equations. In the local eddy-viscosity equation, the production term due to the Reynolds stress shows large positive values, whereas the pressure–strain correlation term plays a role of destructing the eddy viscosity. The transport equation for the length-scale variance was also examined. It is expected that the analysis of the transport equations is helpful in developing better turbulence models.
Poly(vinyl alcohol)-heparin biosynthetic microspheres produced by microfluidics and ultraviolet photopolymerisation
Authors: Young Cara , Rozario Kester , Serra Christophe , Poole-Warren Laura , Martens Penny
Published: August 2013

Biosynthetic microspheres have the potential to address some of the limitations in cell microencapsulation; however, the generation of biosynthetic hydrogel microspheres has not been investigated or applied to cell encapsulation. Droplet microfluidics has the potential to produce more uniform microspheres under conditions compatible with cell encapsulation. Therefore, the aim of this study was to understand the effect of process parameters on biosynthetic microsphere formation, size, and morphology with a co-flow microfluidic method. Poly(vinyl alcohol) (PVA), a synthetic hydrogel and heparin, a glycosaminoglycan were chosen as the hydrogels for this study. A capillary-based microfluidic droplet generation device was used, and by varying the flow rates of both the polymer and oil phases, the viscosity of the continuous oil phase, and the interfacial surface tension, monodisperse spheres were produced from ∼200 to 800 μm. The size and morphology were unaffected by the addition of heparin. The modulus of spheres was 397 and 335 kPa for PVA and PVA/heparin, respectively, and this was not different from the bulk gel modulus (312 and 365 for PVA and PVA/heparin, respectively). Mammalian cells encapsulated in the spheres had over 90% viability after 24 h in both PVA and PVA/heparin microspheres. After 28 days, viability was still over 90% for PVA-heparin spheres and was significantly higher than in PVA only spheres. The use of biosynthetic hydrogels with microfluidic and UV polymerisation methods offers an improved approach to long-term cell encapsulation.
Polarizer design for millimeter-wave plasma diagnostics
Authors: Leipold F. , Salewski M. , Jacobsen A. S. , Jessen M. , Korsholm S. B. , Michelsen P. K. , Nielsen S. K. , Stejner M.
Published: August 2013

Radiation from magnetized plasmas is in general elliptically polarized. In order to convert the elliptical polarization to linear polarization, mirrors with grooved surfaces are currently employed in our collective Thomson scattering diagnostic at ASDEX Upgrade. If these mirrors can be substituted by birefringent windows, the microwave receivers can be designed to be more compact at lower cost. Sapphire windows (a-cut) as well as grooved high density polyethylene windows can serve this purpose. The sapphire window can be designed such that the calculated transmission of the wave energy is better than 99%, and that of the high density polyethylene can be better than 97%.
On-chip terahertz spectroscopic techniques for measuring mesoscopic quantum systems
Authors: Wood C. D. , Mistry D. , Li L. H. , Cunningham J. E. , Linfield E. H. , Davies A. G.
Published: August 2013

We present the self-aligned fabrication of on-chip devices in which waveguides, incorporating integrated photoconductive switches, are combined with two-dimensional electron systems to allow probing of the ultrafast (terahertz frequency range) properties of confined semiconductor systems, both at cryogenic temperatures and in high magnetic fields. We demonstrate the direct injection of on-chip terahertz pulses into the mesoscopic system by femtosecond, near infra-red laser excitation of in-plane photoconductive switches formed on an epitaxially grown, low-temperature GaAs layer, which is integrated monolithically with a GaAs/AlGaAs heterostructure containing a two-dimensional electron system. Both the input and output terahertz signals of an on-chip waveguide are sampled by altering dynamically the photoconductive excitation/detection arrangement in situ on a single device. We also demonstrate a new method for sub-Kelvin excitation and detection of on-chip terahertz frequency radiation in a 3He/4He dilution refrigerator that allows the photocurrent and detected terahertz transient to be mapped as function of the near-infrared excitation position at the emitter and the detector, respectively. Furthermore, we demonstrate transmission of terahertz transients through a two-dimensional electron system in a coplanar waveguide under magnetic field at temperatures as low as 200 mK.
Van der Waals interactions in density functional theory by combining the quantum harmonic oscillator-model with localized Wannier functions
Authors: Silvestrelli Pier Luigi
Published: August 2013

We present a new scheme to include the van der Waals (vdW) interactions in approximated Density Functional Theory (DFT) by combining the quantum harmonic oscillator model with the maximally localized Wannier function technique. With respect to the recently developed DFT/vdW-WF2 method, also based on Wannier Functions, the new approach is more general, being no longer restricted to the case of well separated interacting fragments. Moreover, it includes higher than pairwise energy contributions, coming from the dipole–dipole coupling among quantum oscillators. The method is successfully applied to the popular S22 molecular database, and also to extended systems, namely graphite and H2 adsorbed on the Cu(111) metal surface (in this case metal screening effects are taken into account). The results are also compared with those obtained by other vdW-corrected DFT schemes.
Room temperature low field magnetoresistance in Sr2FeMoO6/ZnxFe1−xFe2O4 composites
Authors: Kumar Nitu , Khurana Geetika , Gaur Anurag , Kotnala R. K.
Published: August 2013

Double perovskite Sr2FeMoO6/ZnxFe1−xFe2O4 (SFMO/ZFO) composite systems with varying zinc content in nanosized zinc ferrite were synthesized. Composites have been prepared by two phase sintering process of limited intermixing of the SFMO calcined powder and ZFO nanoparticles. The structural analysis confirms the coexistence of both the phases in the composites and revealed that the agglomerated ZFO nanoparticles segregated at the grain boundaries. It was found that the inclusion of low ZFO content (2 wt. %) increases the resistivity, magnetization, and low field magnetoresistance (LFMR), whereas it further decreases with increasing ZFO content. A large room-temperature tunnelling magnetoresistance (Δρ/ρ0) ratio 4.83% and 6.90% was observed for pristine SFMO and SFMO/ZFO (x = 0.7) composite samples respectively at low magnetic field of 2 kOe, which is 1.42 times larger than pure SFMO sample. The enhanced LFMR is highly desirable for room temperature magneto resistive applications.
Modeling of Lorentz forces and radiated wave fields for bulk wave electromagnetic acoustic transducers
Authors: Zhai Guofu , Wang Kaican , Wang Yakun , Su Riliang , Kang Lei
Published: August 2013

Currently, the finite element method (FEM) and analytical calculation are widely employed for the modeling of electromagnetic acoustic transducers (EMATs). However, it takes long time for finite element calculation. Previous analytical models for bulk wave EMATs are generally considered separately and incompletely, and expressions of radiated wave fields contain infinite integrations and multiple singular points, which result in complex numerical computation. A complete model containing the Lorentz force and radiated wave field calculation for the EMAT with a spiral coil and a NdFeB permanent magnet is established. By introducing a current loop instead of the permanent magnet and adopting the truncated region eigenfunction expansion (TREE) method, the distributions of static and dynamic magnetic fields and their generated Lorentz forces are calculated. A series expansion method is proposed for the computation of radiated wave fields, which replaces the integration by series operation and avoids the solutions of singular points effectively. The Lorentz forces and radiated wave fields of a typical transducer are computed. The validity of the model is verified by FEM and experiments. Their good agreements verify the accuracy and validity of the model.
Length-dependent lattice thermal conductivity of graphene and its macroscopic limit
Authors: Park Minkyu , Lee Sun-Chul , Kim Yong-Sung
Published: August 2013

In this paper, we report a non-equilibrium molecular dynamics study on the length-dependent lattice thermal conductivity of graphene with lengths up to 16 μm at room temperature. In the molecular dynamics simulations, whether the non-equilibrium systems reach the steady states is rigorously investigated, and the times to reach the steady states are found to drastically increase with the lengths of graphene. From the ballistic to the diffusive regime, the lattice thermal conductivities are explicitly calculated and found to keep increasing in a wide range of lengths with finally showing a converging behavior at 16 μm. That obtained macroscopic value of the lattice thermal conductivity of graphene is 3200 W/mK.
Structure-based coarse-graining for inhomogeneous liquid polymer systems
Authors: Fukuda Motoo , Zhang Hedong , Ishiguro Takahiro , Fukuzawa Kenji , Itoh Shintaro
Published: August 2013

The iterative Boltzmann inversion (IBI) method is used to derive interaction potentials for coarse-grained (CG) systems by matching structural properties of a reference atomistic system. However, because it depends on such thermodynamic conditions as density and pressure of the reference system, the derived CG nonbonded potential is probably not applicable to inhomogeneous systems containing different density regimes. In this paper, we propose a structure-based coarse-graining scheme to devise CG nonbonded potentials that are applicable to different density bulk systems and inhomogeneous systems with interfaces. Similar to the IBI, the radial distribution function (RDF) of a reference atomistic bulk system is used for iteratively refining the CG nonbonded potential. In contrast to the IBI, however, our scheme employs an appropriately estimated initial guess and a small amount of refinement to suppress transfer of the many-body interaction effects included in the reference RDF into the CG nonbonded potential. To demonstrate the application of our approach to inhomogeneous systems, we perform coarse-graining for a liquid perfluoropolyether (PFPE) film coated on a carbon surface. The constructed CG PFPE model favorably reproduces structural and density distribution functions, not only for bulk systems, but also at the liquid-vacuum and liquid-solid interfaces, demonstrating that our CG scheme offers an easy and practical way to accurately determine nonbonded potentials for inhomogeneous systems.
Combinatoric analysis of heterogeneous stochastic self-assembly
Authors: D’Orsogna Maria R. , Zhao Bingyu , Berenji Bijan , Chou Tom
Published: August 2013

We analyze a fully stochastic model of heterogeneous nucleation and self-assembly in a closed system with a fixed total particle number M, and a fixed number of seeds Ns. Each seed can bind a maximum of N particles. A discrete master equation for the probability distribution of the cluster sizes is derived and the corresponding cluster concentrations are found using kinetic Monte-Carlo simulations in terms of the density of seeds, the total mass, and the maximum cluster size. In the limit of slow detachment, we also find new analytic expressions and recursion relations for the cluster densities at intermediate times and at equilibrium. Our analytic and numerical findings are compared with those obtained from classical mass-action equations and the discrepancies between the two approaches analyzed.
Low conductive support for thermal insulation of a sample holder of a variable temperature scanning tunneling microscope
Authors: Hanzelka Pavel , Vonka Jakub , Musilova Vera
Published: August 2013

We have designed a supporting system to fix a sample holder of a scanning tunneling microscope in an UHV chamber at room temperature. The microscope will operate down to a temperature of 20 K. Low thermal conductance, high mechanical stiffness, and small dimensions are the main features of the supporting system. Three sets of four glass balls placed in vertices of a tetrahedron are used for thermal insulation based on small contact areas between the glass balls. We have analyzed the thermal conductivity of the contacts between the balls mutually and between a ball and a metallic plate while the results have been applied to the entire support. The calculation based on a simple model of the setup has been verified with some experimental measurements. In comparison with other feasible supporting structures, the designed support has the lowest thermal conductance.
Nature of the AX center participating persistent photoconductivity effect in As-doped p-ZnO
Authors: Jeong T. S. , Yu J. H. , Mo H. S. , Kim T. S. , Youn C. J. , Hong K. J.
Published: August 2013

The possible nature of metastable capture centers giving rise to persist photoconductivity (PPC) effect in As-doped p-ZnO was investigated using the photoluminescence result. Through the plot of log σph vs. 1/T and temperature-dependent PPC-decay process, the metastable trapping centers were extracted to be 15.1, 178.2, 180.6, and 291.9 meV. The shallow level of 15.1 meV was related to the binding energy of the neutral acceptor bound exciton. Also, the deep levels of 178.2 and 180.6 meV were caused by complex acceptor states of AsZn-2VZn located at 185 meV above the edge of the valence band. Furthermore, the trapping center of 291.9 meV was corresponded to the hole capture barrier of VZn located at 300 meV above the valence band. Therefore, these trapping centers were deeply related to the AX centers originating the native defects due to VZn or defect complexes of the As-implanted dopant in ZnO. Also, these defects, induced by the metastable AX centers, were concluded to be responsible for the PPC effect.
Light absorption and conversion in solar cell based on Si:O alloy
Authors: Scapellato G. G. , Rubino M. , Crupi I. , Di Marco S. , Simone F. , Mirabella S.
Published: August 2013

Thin film Si:O alloys have been grown by plasma enhanced chemical vapor deposition, as intrinsic or highly doped (1 to 5 at. % of B or P dopant) layers. UV-visible/near-infrared spectroscopy revealed a great dependence of the absorption coefficient and of the optical gap (Eg) on the dopant type and concentration, as Eg decreases from 2.1 to 1.9 eV, for the intrinsic or highly p-doped sample, respectively. Thermal annealing up to 400 °C induces a huge H out-diffusion which causes a dramatic absorption increase and a reduction of Eg, down to less than 1.8 eV. A prototypal solar cell has been fabricated using a 400 nm thick, p-i-n structure made of Si:O alloy embedded within flat transparent conductive oxides. Preliminary electrical analyses show a photovoltaic (PV) effect with an open circuit voltage of 0.75 V and a spectral conversion efficiency blue-shifted in comparison to a-Si:H based cell, as expected since the higher Eg in Si:O alloy. These data are presented and discussed, suggesting Si:O alloy as promising material for PV device fabrication.
A simple criterion for predicting multicrystalline Si solar cell performance from lifetime images of wafers prior to cell production
Authors: Wagner H. , Müller M. , Fischer G. , Altermatt P. P.
Published: August 2013

The aim of this paper is to clarify which mean value can be used to predict multicrystalline Si (mc-Si) solar cell performance from lifetime distributions on wafers prior to production. Therefore, a numerical device simulation model is presented that predicts cell performance very precisely from lifetime distributions. This model is used to derive a simple lifetime averaging procedure, which can be used as a criterion for excluding low-quality wafers from production. Compared with standard mean values such as the arithmetic, harmonic, or geometric mean, the criterion derived here significantly reduces the number of mistakenly rejected wafers prior to cell production. In an exemplary case study where 1000 different lifetime distributions were analyzed, our new procedure misjudged only 13 wafers, in contrast with 158 wafers when using the arithmetic mean, 109 wafers when using the geometric mean, and 78 when using the harmonic mean. Further, the influence of lower lifetime regions on mc-cell performance is quantified, showing that low lifetime regions cannot be overcompensated with higher lifetimes in general.
Optimization of force sensitivity in Q-controlled amplitude-modulation atomic force microscopy
Authors: Kim Jongwoo , Sung Baekman , Kim Byung I. , Jhe Wonho
Published: August 2013

We present control of force sensitivity in Q-controlled amplitude-modulation atomic force microscopy (AM-AFM) that is based on the high-Q quartz tuning-fork. It is found that the phase noise is identical to the amplitude noise divided by oscillation amplitude in AM-AFM. In particular, we observe that while Q-control does not compromise the signal-to-noise ratio, it enhances the detection sensitivity because the minimum detectable force gradient is inversely proportional to the effective quality factor for large bandwidths, which is due to reduction of frequency noise. This work demonstrates Q-control in AM-AFM is a useful technique for enhancement of the force sensitivity with increased Q or improvement of the scanning speed with decreased Q.
Contactless electroreflectance studies of surface potential barrier for N- and Ga-face epilayers grown by molecular beam epitaxy
Authors: Kudrawiec R. , Janicki L. , Gladysiewicz M. , Misiewicz J. , Cywinski G. , Boćkowski M. , Muzioł G. , Chèze C. , Sawicka M. , Skierbiszewski C.
Published: August 2013

Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band for N- and Ga-face GaN surface, respectively.
A qubit coupled with confined phonons: The interplay between true and fake decoherence
Authors: Pouthier Vincent
Published: August 2013

The decoherence of a qubit coupled with the phonons of a finite-size lattice is investigated. The confined phonons no longer behave as a reservoir. They remain sensitive to the qubit so that the origin of the decoherence is twofold. First, a qubit-phonon entanglement yields an incomplete true decoherence. Second, the qubit renormalizes the phonon frequency resulting in fake decoherence when a thermal average is performed. To account for the initial thermalization of the lattice, the qua- ntum Langevin theory is applied so that the phonons are viewed as an open system coupled with a thermal bath of harmonic oscillators. Consequently, it is shown that the finite lifetime of the phonons does not modify fake decoherence but strongly affects true decoherence. Depending on the values of the model parameters, the interplay between fake and true decoherence yields a very rich dynamics with various regimes.
Improvement in plasma illumination properties of ultrananocrystalline diamond films by grain boundary engineering
Authors: Sankaran K. J. , Srinivasu K. , Chen H. C. , Dong C. L. , Leou K. C. , Lee C. Y. , Tai N. H. , Lin I. N.
Published: August 2013

Microstructural evolution of ultrananocrystalline diamond (UNCD) films as a function of substrate temperature (TS) and/or by introducing H2 in Ar/CH4 plasma is investigated. Variation of the sp2 and sp3 carbon content is analyzed using UV-Raman and near-edge X-ray absorption fine structure spectra. Morphological and microstructural studies confirm that films deposited using Ar/CH4 plasma at low TS consist of a random distribution of spherically shaped ultra-nano diamond grains with distinct sp2-bonded grain boundaries, which are attributed to the adherence of CH radicals to the nano-sized diamond clusters. By increasing TS, adhering efficiency of CH radicals to the diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nano-sized diamond grains break, whereas the addition of 1.5% H2 in Ar/CH4 plasma at low TS induces atomic hydrogen that preferentially etches out the t-PA attached to ultra-nano diamond grains. Both cases make the sp3-diamond phase less passivated. This leads to C2 radicals attaching to the diamond lattice promoting elongated clustered grains along with a complicated defect structure. Such a grain growth model is highly correlated to explain the technologically important functional property, namely, plasma illumination (PI) of UNCD films. Superior PI properties, viz. low threshold field of 0.21 V/μm with a high PI current density of 4.10 mA/cm2 (at an applied field of 0.25 V/μm) and high γ-coefficient (0.2604) are observed for the UNCD films possessing ultra-nano grains with a large fraction of grain boundary phases. The grain boundary component consists of a large amount of sp2-carbon phases that possibly form interconnected paths for facilitating the transport of electrons and the electron field emission process that markedly enhance PI properties.