bluuebunny/crossref_metadata_2025 huggingface dataset:
Low power front-end architecture dedicated to the multistandard simultaneous reception
Authors: Burciu Ioan , Villemaud Guillaume , Verdier Jacques , Gautier Matthieu
Published: January 2011

In this paper, we address the architecture of multistandard simultaneous reception receivers and we aim to reduce the complexity and the power consumption of the analog front-end. To this end, we propose an architecture using the double orthogonal translation technique in order to multiplex two signals received on different frequency bands. A study case concerning the simultaneous reception of 802.11 g and Universal Mobile Telecommunications System (UMTS) signals is developed in this article. Theoretical and simulation results show that this type of multiplexing does not significantly influence the evolution of the signal-to-noise ratio of the signals. In the same time a 30% reduction of the power consumption is expected as well as a significant reduction of the complexity.
The multi-antenna code multiplexing front-end: theory and performance
Authors: Gautier Matthieu , Villemaud Guillaume , Burciu Ioan
Published: January 2011

In this paper, we address the architecture of a multi-antenna receiver and we aim at reducing the complexity of the analog front-end. To this end, an innovative architecture is introduced based on code multiplexing. This architecture uses the direct sequence spread spectrum technique in order to multiplex the different antennas contributions through a single In-phase/Quadrature (IQ) demodulator. Simulation and measurement results show that the bit error rate does not increase so much with the multiplexing in both Gaussian and fading environments and with strong radiofrequency (RF) defaults conditions. The complexity evaluation shows that the proposed architecture significantly reduces the chip area and the power consumption of the front-end.
Novel designs of polarization-preserving circular waveguide filters
Authors: Bornemann Jens , Yu Seng Yong
Published: January 2011

Novel designs of circular waveguide components for lowpass, highpass, bandpass, and bandstop applications are presented. The filters are formed by cascaded TM11-mode resonator sections which share a common axis, thus preserving the polarizations of input signals due to rotational symmetry. Moreover, the filters are smaller than standard TE11-mode bandpass filters. Basic design considerations are discussed with respect to the connection of TM11-mode resonators through circular irises. Design principles for all four filter types are presented and their performances computed by the coupled-integral equation technique (CIET). All filter performances are verified by the commercially available software package μWave Wizard, and structural dimensions are provided.
Stream temperature change detection for state and private forests in the Oregon Coast Range
Authors: Groom Jeremiah D. , Dent Liz , Madsen Lisa J.
Published: January 2011

Oregon's forested coastal watersheds support important cold‐water fisheries of salmon and steelhead (Oncorhynchus spp.) as well as forestry‐dependent local economies. Riparian timber harvest restrictions in Oregon and elsewhere are designed to protect stream habitat characteristics while enabling upland timber harvest. We present an assessment of riparian leave tree rule effectiveness at protecting streams from temperature increases in the Oregon Coast Range. We evaluated temperature responses to timber harvest at 33 privately owned and state forest sites with Oregon's water quality temperature antidegradation standard, the Protecting Cold Water (PCW) criterion. At each site we evaluated stream temperature patterns before and after harvest upstream, within, and downstream of harvest units. We developed a method for detecting stream temperature change between years that adhered as closely as possible to Oregon's water quality rule language. The procedure provided an exceedance history across sites that allowed us to quantify background and treatment (timber harvest) PCW exceedance rates. For streams adjacent to harvested areas on privately owned lands, preharvest to postharvest year comparisons exhibited a 40% probability of exceedance. Sites managed according to the more stringent state forest riparian standards did not exhibit exceedance rates that differed from preharvest, control, or downstream rates (5%). These results will inform policy discussion regarding the sufficiency of Oregon's forest practices regulation at protecting stream temperature. The analysis process itself may assist other states and countries in developing and evaluating their forest management and water quality antidegradation regulations.
MicroRNA evolution by arm switching
Authors: Griffiths‐Jones Sam , Hui Jerome H L , Marco Antonio , Ronshaugen Matthew
Published: January 2011

MicroRNAs (miRNAs) modulate transcript stability and translation. Functional mature miRNAs are processed from one or both arms of the hairpin precursor. The miR‐100/10 family has undergone three independent evolutionary events that have switched the arm from which the functional miRNA is processed. The dominant miR‐10 sequences in the insects Drosophila melanogaster and Tribolium castaneum are processed from opposite arms. However, the duplex produced by Dicer cleavage has an identical sequence in fly and beetle. Expression of the Tribolium miR‐10 sequence in Drosophila S2 cells recapitulates the native beetle pattern. Thus, arm usage is encoded in the primary miRNA sequence, but outside the mature miRNA duplex. We show that the predicted messenger RNA targets and inferred function of sequences from opposite arms differ significantly. Arm switching is likely to be general, and provides a fundamental mechanism to evolve the function of a miRNA locus and target gene network.
An evolutionarily acquired genotoxic response discriminates MyoD from Myf5, and differentially regulates hypaxial and epaxial myogenesis
Authors: Innocenzi Anna , Latella Lucia , Messina Graziella , Simonatto Marta , Marullo Fabrizia , Berghella Libera , Poizat Coralie , Shu Chih‐Wen , Wang Jean Y J , Puri Pier Lorenzo , Cossu Giulio
Published: January 2011

Despite having distinct expression patterns and phenotypes in mutant mice, the myogenic regulatory factors Myf5 and MyoD have been considered to be functionally equivalent. Here, we report that these factors have a different response to DNA damage, due to the presence in MyoD and absence in Myf5 of a consensus site for Abl‐mediated tyrosine phosphorylation that inhibits MyoD activity in response to DNA damage. Genotoxins failed to repress skeletal myogenesis in MyoD‐null embryos; reintroduction of wild‐type MyoD, but not mutant Abl phosphorylation‐resistant MyoD, restored the DNA‐damage‐dependent inhibition of muscle differentiation. Conversely, introduction of the Abl‐responsive phosphorylation motif converts Myf5 into a DNA‐damage‐sensitive transcription factor. Gene‐dosage‐dependent reduction of Abl kinase activity in MyoD‐expressing cells attenuated the DNA‐damage‐dependent inhibition of myogenesis. The presence of a DNA‐damage‐responsive phosphorylation motif in vertebrate, but not in invertebrate MyoD suggests an evolved response to environmental stress, originated from basic helix–loop–helix gene duplication in vertebrate myogenesis.
Structure and function of BamE within the outer membrane and the β‐barrel assembly machine
Authors: Knowles Timothy J , Browning Douglas F , Jeeves Mark , Maderbocus Riyaz , Rajesh Sandya , Sridhar Pooja , Manoli Eleni , Emery Danielle , Sommer Ulf , Spencer Ashley , Leyton Denisse L , Squire Derrick , Chaudhuri Roy R , Viant Mark R , Cunningham Adam F , Henderson Ian R , Overduin Michael
Published: January 2011

Insertion of folded proteins into the outer membrane of Gram‐negative bacteria is mediated by the essential β‐barrel assembly machine (Bam). Here, we report the native structure and mechanism of a core component of this complex, BamE, and show that it is exclusively monomeric in its native environment of the periplasm, but is able to adopt a distinct dimeric conformation in the cytoplasm. BamE is shown to bind specifically to phosphatidylglycerol, and comprehensive mutagenesis and interaction studies have mapped key determinants for complex binding, outer membrane integrity and cell viability, as well as revealing the role of BamE within the Bam complex.
Inducible SUMO modification of TANK alleviates its repression of TLR7 signalling
Authors: Renner Florian , Saul Vera V , Pagenstecher Axel , Wittwer Tobias , Schmitz Michael Lienhard
Published: January 2011

Adaptor proteins allow temporal and spatial coordination of signalling. In this study, we show SUMOylation of the adaptor protein TANK and its interacting kinase TANK‐binding kinase 1 (TBK1). Modification of TANK by the small ubiquitin‐related modifier (SUMO) at the evolutionarily conserved Lys 282 is triggered by the kinase activities of IκB kinase ε (IKKε) and TBK1. Stimulation of TLR7 leads to inducible SUMOylation of TANK, which in turn weakens the interaction with IKKε and thus relieves the negative function of TANK on signal propagation. Reconstitution experiments show that an absence of TANK SUMOylation impairs inducible expression of distinct TLR7‐dependent target genes, providing a molecular mechanism that allows the control of TANK function.
Temporary Focal Cerebral Ischemia Results in Swollen Astrocytic End-Feet That Compress Microvessels and Lead to Focal Cortical Infarction
Authors: Ito Umeo , Hakamata Yoji , Kawakami Emiko , Oyanagi Kiyomitsu
Published: January 2011

Correction to: Journal of Cerebral Blood Flow & Metabolism (2010) 31, 328–338; doi: 10.1038/jcbfm.2010.97; published online 30 June 2010

1. Following the publication of this article, the authors determined that the article title was inaccurate. The new title is ‘Temporary cerebral ischemia results in swollen astrocytic end-feet that compress microvessels and lead to delayed focal cortical infarction.’

2. Kiyomitsu Oyanagi's institution (3) is in ‘Nagano, Japan’.
Re-entrant kinetic arrest and elasticity of concentrated suspensions of spherical and nonspherical repulsive and attractive colloids
Authors: Kramb Ryan C. , Zhang Rui , Schweizer Kenneth S. , Zukoski Charles F.
Published: January 2011

We have designed and studied a new experimental colloidal system to probe how the weak shape anisotropy of uniaxial particles and variable repulsive (Coulombic) and attractive (van der Waals) forces influence slow dynamics, shear elasticity, and kinetic vitrification in dense suspensions. The introduction of shape anisotropy dramatically delays kinetic vitrification and reduces the shear elastic modulus of colloidal diatomics relative to their chemically identical spherical analogs. Tuning the interparticle interaction from repulsive, to nearly hard, to attractive by increasing suspension ionic strength reveals a nonmonotonic re-entrant dynamical phase behavior (glass–fluid–gel) and a rich variation of the shear modulus. The experimental results are quantitatively confronted with recent predictions of ideal mode coupling and activated barrier hopping theories of kinetic arrest and elasticity, and good agreement is generally found with a couple of exceptions. The systems created may have interesting materials science applications such as flowable ultrahigh volume fraction suspensions, or responsive fluids that can be reversibly switched between a flowing liquid and a solid nonequilibrium state based on in situ modification of suspension ionic strength.
Numerical investigation of closed-loop control for Hall accelerators
Authors: Barral S. , Miedzik J.
Published: January 2011

Low frequency discharge current oscillations in Hall accelerators are conventionally damped with external inductor-capacitor (LC) or resistor-inductor-capacitor (RLC) networks. The role of such network in the stabilization of the plasma discharge is investigated with a numerical model and the potential advantages of proportional-integral-derivative (PID) closed-loop control over RLC networks are subsequently assessed using either discharge voltage or magnetic field modulation. Simulations confirm the reduction of current oscillations in the presence of a RLC network, but suggest that PID control could ensure nearly oscillation-free operation with little sensitivity toward the PID settings.
Optimization of Monte Carlo trial moves for protein simulations
Authors: Betancourt Marcos R.
Published: January 2011

Closed rigid-body rotations of residue segments under bond-angle restraints are simple and effective Monte Carlo moves for searching the conformational space of proteins. The efficiency of these moves is examined here as a function of the number of moving residues and the magnitude of their displacement. It is found that the efficiency of folding and equilibrium simulations can be significantly improved by tailoring the distribution of the number of moving residues to the simulation temperature. In general, simulations exploring compact conformations are more efficient when the average number of moving residues is smaller. It is also demonstrated that the moves do not require additional restrictions on the magnitude of the rotation displacements and perform much better than other rotation moves that do not restrict the bond angles a priori. As an example, these results are applied to the replica exchange method. By assigning distributions that generate a smaller number of moving residues to lower temperature replicas, the simulation times are decreased as long as the higher temperature replicas are effective.
Study of dielectric relaxations of anhydrous trehalose and maltose glasses
Authors: Kwon Hyun-Joung , Seo Jeong-Ah , Kim Hyung Kook , Hwang Yoon-Hwae
Published: January 2011

We investigated the frequency dependent dielectric relaxation behaviors of anhydrous trehalose and maltose glasses in the temperature range which covers a supercooled and glassy states. In addition to the α-, Johari-Goldstein (JG) β-, and γ-relaxations in a typical glass forming system, we observed an extra relaxation process between JG β- and γ-relaxations in the dielectric loss spectra. We found that the unknown extra relaxation is a unique property of disaccharide which might originate from the intramolecular motion of flexible glycosidic bond. We also found that the temperature dependence of the JG β-relaxation time changes at 0.95Tg and it might be universal.
Plastic hardening in cubic semiconductors by nanoscratching
Authors: Caldas P. G. , Prioli R. , Almeida C. M. , Huang J. Y. , Ponce F. A.
Published: January 2011

The effect of scratch proximity on the resistance to plastic deformation in InP (100) crystals under low normal loads has been studied using atomic force microscopy (AFM) and transmission electron microscopy. Plastic flow has been observed for scratches performed with an atomic force microscope along ⟨110⟩ and ⟨100⟩ crystallographic directions. Plastic hardening has been determined from AFM measurements of the scratch depth and width, as a function of the distance between parallel scratches. For relatively low loads, hardening is found to be independent of the crystallographic direction of the scratch. Significant hardening takes place for scratch separations of less than ∼80 nm. Analysis of the microstructure indicates that hardening occurs due to the interaction of dislocations generated at adjacent scratches and acting on different slip planes.
Ions in solutions: Determining their polarizabilities from first-principles
Authors: Molina John J. , Lectez Sébastien , Tazi Sami , Salanne Mathieu , Dufrêche Jean-François , Roques Jérôme , Simoni Eric , Madden Paul A. , Turq Pierre
Published: January 2011

Dipole polarizabilities of a series of ions in aqueous solutions are computed from first-principles. The procedure is based on the study of the linear response of the maximally localized Wannier functions to an applied external field, within density functional theory. For most monoatomic cations (Li \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}+, Na \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}+, K \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}+, Rb \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}+, Mg \documentclass[12pt]{minimal}\begin{document}$^{2+}$\end{document}2+, Ca \documentclass[12pt]{minimal}\begin{document}$^{2+}$\end{document}2+ and Sr \documentclass[12pt]{minimal}\begin{document}$^{2+}$\end{document}2+) the computed polarizabilities are the same as in the gas phase. For Cs \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}+ and a series of anions (F \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}−, Cl \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}−, Br \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}− and I \documentclass[12pt]{minimal}\begin{document}$^-$\end{document}−), environmental effects are observed, which reduce the polarizabilities in aqueous solutions with respect to their gas phase values. The polarizabilities of H \documentclass[12pt]{minimal}\begin{document}$^+_{\rm (aq)}$\end{document}( aq )+, OH \documentclass[12pt]{minimal}\begin{document}$^-_{\rm (aq)}$\end{document}( aq )− have also been determined along an ab initio molecular dynamics simulation. We observe that the polarizability of a molecule instantaneously switches upon proton transfer events. Finally, we also computed the polarizability tensor in the case of a strongly anisotropic molecular ion, UO \documentclass[12pt]{minimal}\begin{document}$_2^{2+}$\end{document}22+. The results of these calculations will be useful in building interaction potentials that include polarization effects.
Efficient multiple time scale molecular dynamics: Using colored noise thermostats to stabilize resonances
Authors: Morrone Joseph A. , Markland Thomas E. , Ceriotti Michele , Berne B. J.
Published: January 2011

Multiple time scale molecular dynamics enhances computational efficiency by updating slow motions less frequently than fast motions. However, in practice, the largest outer time step possible is limited not by the physical forces but by resonances between the fast and slow modes. In this paper we show that this problem can be alleviated by using a simple colored noise thermostatting scheme which selectively targets the high frequency modes in the system. For two sample problems, flexible water and solvated alanine dipeptide, we demonstrate that this allows the use of large outer time steps while still obtaining accurate sampling and minimizing the perturbation of the dynamics. Furthermore, this approach is shown to be comparable to constraining fast motions, thus providing an alternative to molecular dynamics with constraints.
Exploring the possibilities to control the molecular switching properties and dynamics: A field-switchable rotor-stator molecular system
Authors: Petreska Irina , Pejov Ljupčo , Kocarev Ljupčo
Published: January 2011

A bistable, dipolar stator-rotor molecular system-candidate for molecular electronics is investigated. We demonstrate that it is possible to control the intramolecular torsional states and dynamics in this system by applying an appropriate additional electric field (instead of biasing one), achieving fine tuning and modulation of the relevant properties. The electric field effects on the quantities responsible for torsional dynamics (potential energy surface, potential barrier height, quantum and classical transition probabilities, correlation time, HOMO-LUMO gap) are studied from first principles. Our results indicate that it is possible to artificially stabilize the metastable conformational state of the studied molecule. The importance of this is evident, as the current-voltage characteristics of the metastable state are clearly distinguishable from the current-voltage characteristics of the two stable states. We report for the first time exact calculations related to the possibilities to control the thermally induced stochastic switching, and reduce the noise in a practical application. Thus, we believe that the molecule studied in this paper could operate as a field-switchable molecular device under real conditions.
Nanoscale surface modifications and formation of conical structures at aluminum surface induced by single shot exposure of soft x-ray laser pulse
Authors: Ishino Masahiko , Faenov Anatoly Ya. , Tanaka Momoko , Hasegawa Noboru , Nishikino Masaharu , Tamotsu Satoshi , Pikuz Tatiana A. , Inogamov Nail A. , Zhakhovsky Vasily V. , Skobelev Igor Yu. , Fortov Vladimir E. , Khohlov Viktor A. , Shepelev Vadim V. , Ohba Toshiyuki , Kaihori Takeshi , Ochi Yoshihiro , Imazono Takashi , Kawachi Tetsuya
Published: January 2011

We irradiated the soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm, a duration time of 7 ps, and fluences of up to 27 mJ/cm2 to aluminum (Al) surface. After the irradiation process, the modified surface was observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL pulses were clearly seen, and it was found that the conical structures having about 70–150 nm in diameters were formed under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. However, those conical structures were deconstructed under the multiple pulse shots exposure. Thermomechanical modeling of SXRL laser interaction with Al surface, which explains nanostructure surface modification, was provided.
The influence of thermal stresses on the phase composition of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 thick films
Authors: Uršič Hana , Zarnik Marina Santo , Tellier Jenny , Hrovat Marko , Holc Janez , Kosec Marija
Published: January 2011

The influence of thermal stresses versus the phase composition for 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) thick films is being reported. The thermal residual stresses in the films have been calculated using the finite-element method. It has been observed that in 0.65PMN–0.35PT films a compressive stress enhances the thermodynamic stability of the tetragonal phase with the space group P4mm.
Adsorption of carbon adatoms to graphene and its nanoribbons
Authors: Ataca C. , Aktürk E. , Şahin H. , Ciraci S.
Published: January 2011

This paper investigates the adsorption of carbon adatoms on graphene and its nanoribbons using first-principles plane wave calculations within density functional theory. The stability at high carbon adatom coverage, migration, and cluster formation of carbon atoms are analyzed. Carbon adatoms give rise to important changes in electronic and magnetic properties even at low coverage. While bare graphene is nonmagnetic semimetal, it is metallized and acquires magnetic moment upon coverage of carbon adatoms. Calculated magnetic moments vary depending on the coverage of adatoms even for large adatom-adatom distances. Electronic and magnetic properties of hydrogen passivated armchair and zigzag nanoribbons show strong dependence on the adsorption site. We also predict a new type of carbon impurity defect in graphene, which has a small formation energy. Interactions between distant carbon adatoms imply a long ranged interaction.
Dielectric properties of NaNbO3:SrTiO3 interface nanolayer
Authors: Tyunina M. , Oja R. , Plekh M. , Nieminen R. M.
Published: January 2011

NaNbO 3 : SrTiO 3 interface nanolayers are studied by combining first-principles modeling and experimental approach. The nature of NaNbO3:SrTiO3 interface is investigated using density-functional theory calculations. Interface parameters are experimentally estimated using analysis of the dielectric response of SrTiO3 and NaNbO3 epitaxial films and NaNbO3:SrTiO3 superlattices. It is shown that NaNbO3:SrTiO3 interfaces can be approximated by dielectric nanolayers with thickness 1–2 nm and with temperature independent permittivity 25–55. Mechanism responsible for the nanolayer formation is the ionic charge mismatch between constituents.
Optical detection system for probing cantilever deflections parallel to a sample surface
Authors: Labuda A. , Brastaviceanu T. , Pavlov I. , Paul W. , Rassier D. E.
Published: January 2011

To date, commercial atomic force microscopes have been optimized for measurements of forces perpendicular to the sample surface. In many applications, sensitive parallel force measurements are desirable. These can be obtained by positioning the cantilever with its long axis perpendicular to the sample: the so-called pendulum geometry. We present a compact optical beam deflection system which solves the geometrical constraint problems involved in focusing a light beam onto a cantilever in the pendulum geometry. We demonstrate the performance of the system on measurements of forces imparted by a muscle myofibril, which is in-plane to a high-magnification objective of an optical microscope.
Annealing effects on the magnetic dead layer and saturation magnetization in unit structures relevant to a synthetic ferrimagnetic free structure
Authors: Jang Soo Young , You Chun-Yeol , Lim S. H. , Lee S. R.
Published: January 2011

The changes in the magnetic dead layer (MDL) and saturation magnetization of the CoFeB layers are investigated as a function of the annealing temperature for four different unit structures, that are relevant to the synthetic ferrimagnetic free structure in MgO-based magnetic tunnel junctions. The MDL results for these unit structures are then converted into those for the constituent interfaces of the free structure. Most of the changes in the MDL thickness occur during annealing at a low temperature of 150 °C while those in the saturation magnetization occur at a high annealing temperature of 350 °C. These results for the MDL and saturation magnetization are critically tested by using the synthetic ferrimagnetic free structures with various thickness asymmetries. The observed switching properties of these tested structures are in good agreement with those expected from the results for the MDL and saturation magnetization, confirming the accuracy of the present results. The accuracy of the saturation magnetization is further confirmed by ferromagnetic resonance experiments.
Enhanced femtosecond optical nonlinearity of Mn doped Ba0.6Sr0.4TiO3 films
Authors: Ning Tingyin , Chen Cong , Wang Can , Zhou Yueliang , Zhang Dongxiang , Ming Hai , Yang Guozhen
Published: January 2011

We report the third-order optical nonlinearity of ferroelectric thin films of Mn doped Ba0.6Sr0.4TiO3 using Z-scan measurement with femtosecond laser pulses at 800 nm. The nonlinear refraction index and two-photon absorption coefficient are measured to be 3.0×10−4 cm2/GW and 1.7 cm/GW, respectively, which are about one order of magnitude larger than those of the undoped Ba0.6Sr0.4TiO3 thin films. The enhancement is attributed to the acceptor behavior of Mn ions dopant. The figure of merit, T, defined by T=βλ/n2, was calculated to be 0.44, less than 1. The results indicate that the thin films have great potential applications in nonlinear photonic devices.
Fano–Feshbach resonance in structural symmetry broken metamaterials
Authors: Kang Ming , Cui Hai-Xu , Li Yongnan , Gu Bing , Chen Jing , Wang Hui-Tian
Published: January 2011

Metamaterials support optically excitable dark-plasmon modes featured by antisymmetric surface current oscillations, which can be explained by Fano-type resonance and can be tailored by controlling the embedded structural geometry. In this article, we numerically investigate the Fano-type resonance in complex metamaterials, and demonstrate the presence of Fano–Feshbach resonances due to the interaction between two Fano-type resonances in the overlapping region, implemented by breaking and tuning the symmetric properties of the resonant metallic element. Features of the resonance are discussed. This work shows that the domain of dark-plasmon mode based metamaterial system supports rich physics and can lead to various potential applications.
An explanation for laser-induced spallation effect in a-C:H films: Altered phase evolution route caused by hydrogen doping
Authors: Ding Qi , Wang Liping , Hu Litian , Hu Tianchang , Wang Yunfeng , Zhang Yaonan
Published: January 2011

The laser-induced spalling effect has been recognized as a unique phenomenon for amorphous carbon (a-C) films during laser processing. In this work, the origin of spalling effect was investigated by ablating two different types of a-C film: hydrogenated a-C (a-C:H) and nonhydrogenated a-C with an Nd-yttrium aluminum garnet laser system. Comparisons of ablating results demonstrated that the spalling effect only occurred in a-C:H rather than nonhydrogenated a-C. Laser heating simulation indicated that the temperature distributions in both films after laser pulse are similar with a high temperature gradient in depth direction. Annealing test results, Raman spectra and nanoindentation show that with the increase in annealing temperature, a-C film transforms into grassy carbon directly, while a-C:H experiences two subprocess under heating: the hydrogen mobilization and rearrangement of CC network at a relatively low temperature range resulting in a denser CC network and raised film density; the graphitization at high temperature which would lower the film density. We propose that the reason of laser-induced spalling effect in a-C:H might depend on two aspects: (1) the heat source like laser pulse which could produce a high temperature gradient in depth direction within ultrashort time and (2) the unique evolution process of film microstructure under heating. Based on above model, the spalling effect is ascribed to the concentrated stress caused by different structure evolution subprocess at different depth in a-C:H during the laser irradiation. It is remarkable that the conclusions deduced from our model are proven to be in good agreement with our experimental results and the previous articles reported by others.
Chemical response of aldehydes to compression between (0001) surfaces of α-alumina
Authors: Haw Sarah M. , Mosey Nicholas J.
Published: January 2011

First-principles molecular dynamics simulations are used to investigate the chemical response of acetaldehyde molecules (MeCHO) to compression and decompression between (0001) surfaces of α-alumina (Al2O3), with pressures reaching approximately 40 GPa. The results demonstrate that the MeCHO molecules are transformed into other chemical species through a range of chemical processes involving the formation of C–O and C–C bonds between MeCHO monomers as well as proton transfer. The mechanistic details of a representative set of the observed reactions are elucidated through analysis of maximally localized Wannier functions. Analysis of the changes in structure demonstrates that the main role of compression is to reduce the distances between MeCHO molecules to facilitate the formation of C–O bonds. Additional examination of the electronic structure demonstrates that the surface plays a role in facilitating proton transfer by both rendering hydrogen atoms in adsorbed MeCHO molecules more acidic and by acting as a proton acceptor. In addition, adsorption of the MeCHO molecules on the surface renders the sp2 carbon atoms in these molecules more electrophilic, which promotes the formation of C–C and C–O bonds. It is suggested that the reaction products may be beneficial in the context of wear inhibition. Comparison of the surface structure before compression and after decompression demonstrates that the aldehydes and reaction products are capable of inhibiting irreversible changes in the structure as long as there is at least a monolayer coverage of these species. As a whole, the study sheds light on the chemical behavior of the aldehydes in response to uniaxial compression in nanoscopic contacts that likely applies to other molecules containing carbonyl groups and other metal oxide surfaces.
Manipulation of nuclear spin dynamics in n-GaAs using an on-chip microcoil
Authors: Chen Y. S. , Huang J. , Ludwig A. , Reuter D. , Wieck A. D. , Bacher G.
Published: January 2011

We present an approach for electrically manipulating nuclear spins in n-GaAs using an on-chip microcoil. Optically injected spin-polarized electrons are used to generate a dynamic nuclear polarization via electron-nucleus hyperfine interaction with a characteristic time constant of ∼10 min. The saturated Overhauser field amplitude is on the order of several 10 mT and proportional to the spin polarization degree of the injected electrons. Applying an rf field resonant for the A75s nuclei, complete depolarization of A75s nuclear spins is observed.
Evolving morphotropic phase boundary in lead-free (Bi1/2Na1/2)TiO3–BaTiO3 piezoceramics
Authors: Jo Wook , Daniels John E. , Jones Jacob L. , Tan Xiaoli , Thomas Pamela A. , Damjanovic Dragan , Rödel Jürgen
Published: January 2011

The correlation between structure and electrical properties of lead-free (1−x)(Bi1/2Na1/2)TiO3–xBaTiO3 (BNT-100xBT) polycrystalline piezoceramics was investigated systematically by in situ synchrotron diffraction technique, combined with electrical property characterization. It was found that the morphotropic phase boundary (MPB) between a rhombohedral and a tetragonal phase evolved into a morphotropic phase region with electric field. In the unpoled material, the MPB was positioned at the transition from space group R3m to P4mm (BNT-11BT) with optimized permittivity throughout a broad single-phase R3m composition regime. Upon poling, a range of compositions from BNT-6BT to BNT-11BT became two-phase mixture, and maximum piezoelectric coefficient was observed in BNT-7BT. It was shown that optimized electrical properties are related primarily to the capacity for domain texturing and not to phase coexistence.
Coherent population trapping resonances in Cs–Ne vapor microcells for miniature clocks applications
Authors: Boudot R. , Dziuban P. , Hasegawa M. , Chutani R. K. , Galliou S. , Giordano V. , Gorecki C.
Published: January 2011

We report the characterization of dark line resonances observed in Cs vapor microcells filled with a unique neon (Ne) buffer gas. The impact on the coherent population trapping (CPT) resonance of some critical external parameters such as laser intensity, cell temperature, and microwave power is studied. We show the suppression of the first-order light shift by proper choice of the microwave power. The temperature dependence of the Cs ground state hyperfine resonance frequency is shown to be canceled in the 77–80 °C range for various Ne buffer gas pressures. The necessity to adjust the Ne buffer gas pressure or the cell dimensions to optimize the CPT signal height at the frequency inversion temperature is pointed out. Based on such Cs–Ne microcells, we preliminary demonstrate a 852 nm vertical cavity surface emitted laser (VCSEL)-modulated based CPT atomic clock exhibiting a short term fractional frequency instability σy(τ)=1.5×10−10τ−1/2 until 30 s. These results, similar to those published in the literature by others groups, prove the potential of our original microcell technology in view of the development of high-performance chip scale atomic clocks.
Energy dissipation in a dynamic nanoscale contact
Authors: Santos Sergio , Thomson Neil H.
Published: January 2011

The size of an atomic force microscope tip can vary rapidly during interaction with a surface but this is typically overlooked. Here, we treat the tip radius as a dynamic variable. Comparison with nanoscission of DNA molecules shows that the pressure in the nanoscale contact cannot increase without bound, rather the tip gradually blunts as the energy in the cantilever is increased. We develop a method to stabilize the tip and then reliably calculate the effective area of interaction and dissipation of eV/atom in situ. Tip radius typically stabilizes around 20–30 nm and keeps the maximum pressure below ∼1 GPa.
Electrically assisted drop sliding on inclined planes
Authors: ‘t Mannetje D. J. C. M. , Murade C. U. , van den Ende D. , Mugele F.
Published: January 2011

We demonstrate that electrowetting using alternating current (ac) voltage can be used to overcome pinning of small drops due to omnipresent heterogeneities on solid surfaces. By balancing contact angle hysteresis with gravity on inclined planes, we find that the critical electrowetting number for mobilizing drops is consistent with the voltage-dependent reduction in contact angle hysteresis in ac electrowetting. Moreover, the terminal velocity of sliding drops under ac electrowetting is found to increase linearly with the electrowetting number. Based on this effect, we present a prototype of a wiper-free windscreen.
Field-induced crossover from phonon to field assisted hopping conductivity in organic materials
Authors: Bourbie D.
Published: January 2011

Recently the change in temperature dependence of conductivity observed in polythiophene field-effect transistors has been attributed to field-induced metal-insulator transition. Under a high source-drain voltage, the conductivity becomes independent from temperature and depends exponentially on the inverse of the square root of electric field. In this paper we present a theoretical interpretation of this behavior in the framework of hopping mechanism. The ingredient of this model, is the energy gained from the electrical field is always larger than the energy difference between the localized states involved into the charge transitions, which induces a crossover from phonon-assisted hopping to field-assisted hopping.
The transport properties of D-σ-A molecules: A strikingly opposite directional rectification
Authors: Pan J. B. , Zhang Z. H. , Deng X. Q. , Qiu M. , Guo C.
Published: January 2011

We design the A-R rectifier based on the D-σ-A molecules to examine the rectifying performances by the first-principles method. The calculated results show that the electronic structures for all of our systems perfectly match the A-R rectifier, as expected, but their rectifying direction is very strikingly opposite and working mechanism is completely different. This behavior can be rationalized through an asymmetrical shift of molecular levels under bias of different polarities, which is because of always-existing intrinsic asymmetrical coupling effects of molecular levels to electrodes. Detailed analysis demonstrates that the rectifying direction induced by this mechanism is always in opposition to that induced by the A-R mechanism.
Evidence of the defect-induced ferromagnetism in Na and Co codoped ZnO
Authors: Gu Hao , Jiang Yinzhu , Xu Yongbing , Yan Mi
Published: January 2011

The effect of Na concentration on the room-temperature ferromagnetism in Na and Co codoped ZnO diluted magnetic semiconductor (DMSs) was investigated. The ferromagnetic state was found to be stable below 5% doping of Na due to the exchange interaction via electron trapped oxygen vacancies (F-center) coupled with the magnetic Co ions. With large Na doping of up to 10%, a sharp reduction in the magnetization was observed, showing that the oxygen vacancy mediated antiferromagnetic state becomes predominant. The observed correlation between the Na concentration, the carrier concentration, and the magnetization demonstrated the effect of the defect in controlling the ferromagnetism in the ZnO-based DMS system.
Electrochemical restructuring of plasmonic metamaterials
Authors: Ruther M. , Shao L.-H. , Linden S. , Weissmüller J. , Wegener M.
Published: January 2011

Recent electrochemical experiments on gold-based photonic metamaterials have shown reversible optical modulation as well as an irreversible reduction in the plasmonic damping. Here, we systematically study the latter aspect as a possible means of postprocessing plasmonic gold nanoantennae arrays aiming at loss reduction. We characterize the samples by optical spectroscopy, electron microscopy, and atomic-force microscopy. For sub-10 nm gold thicknesses, the measured damping decreases by factors exceeding 3; for 20–30 nm thin structures, the obtained loss reduction still amounts to about 30%.
Circuit approach to the minimal configuration of terahertz anomalous extraordinary transmission
Authors: Beruete M. , Navarro-Cía M. , Kuznetsov S. A. , Sorolla M.
Published: January 2011

In this letter we present an in-depth circuit analysis of anomalous extraordinary transmission (ET) through subwavelength slit and hole arrrays loaded by a dielectric slab. We show the key role played by the thickness of the dielectric slab in order to enhance the transmission for TE-polarized waves (incident electric field parallel to the slits or to the short in-plane period in hole arrays arranged in rectangular lattice) within the cut-off regime of the apertures and to suppress Wood’s anomaly. Analytical and numerical results together with experimental data are presented, showing good agreement among them. This work provides physical insight of the underlying mechanism governing anomalous ET and offers further independent control over orthogonal polarized waves impinging into subwavelength aperture arrays.
Structural and magnetic properties of lithium ferrite (LiFe5O8) thin films: Influence of substrate on the octahedral site order
Authors: Boyraz Cihat , Mazumdar Dipanjan , Iliev Milko , Marinova Vera , Ma Jianxing , Srinivasan Gopalan , Gupta Arunava
Published: January 2011

Structural properties of lithium ferrite [LiFe5O8, (LFO)] thin films are investigated as a function of substrate-induced strain and growth temperature. Through x-ray diffraction and Raman spectroscopy analysis we find LFO films grown on isostructural MgAl2O4 (MAO) are closer to bulk single crystal behavior, whereas the films remain coherently strained on lattice matched MgO substrate. Film texture and surface morphology are enhanced with better lattice match, indicating different growth modes on different substrates. Raman spectra reveal enhanced disorder of Li and Fe ions at the octahedral sites on MgO substrate contrasting with the relatively high degree of octahedral site ordering on MAO.
On solvable Dirac equation with polynomial potentials
Authors: Stachowiak Tomasz
Published: January 2011

One-dimensional Dirac equation is analyzed with regard to the existence of exact (or closed-form) solutions for polynomial potentials. The notion of Liouvillian functions is used to define solvability, and it is shown that except for the linear potentials the equation in question is not solvable.
Ultrasmooth growth of amorphous silicon films through ion-induced long-range surface correlations
Authors: Redondo-Cubero A. , Gago R. , Vázquez L.
Published: January 2011

Ultrasmooth amorphous silicon films with a constant roughness below 0.2 nm were produced for film thickness up to ∼1 μm by magnetron sputtering under negative voltage substrate biasing (100–400 V). In contrast, under unbiased conditions the roughness of the resulting mounded films increased linearly with growth time due to shadowing effects. A detailed analysis of the amorphous film growth dynamics proves that the bias-induced ultrasmoothness is produced by a downhill mass transport process that leads to an extreme surface leveling inducing surface height correlations up to lateral distances close to 0.5 μm.
Compensation-dependence of magnetic and electrical properties in Ga1−xMnxP
Authors: Winkler T. E. , Stone P. R. , Li Tian , Yu K. M. , Bonanni A. , Dubon O. D.
Published: January 2011

We demonstrate the control of the hole concentration in Ga1−xMnxP over a wide range by introducing compensating vacancies. The resulting evolution of the Curie temperature from 51 to 7.5 K is remarkably similar to that observed in Ga1−xMnxAs despite the dramatically different character of hole transport between the two material systems. The highly localized nature of holes in Ga1−xMnxP is reflected in the accompanying increase in resistivity by many orders of magnitude. Based on variable-temperature resistivity data we present a general picture for hole conduction in which variable-range hopping is the dominant transport mechanism in the presence of compensation.
Signal-to-noise ratio in dual-gated silicon nanoribbon field-effect sensors
Authors: Tarasov A. , Fu W. , Knopfmacher O. , Brunner J. , Calame M. , Schönenberger C.
Published: January 2011

Recent studies on nanoscale field-effect sensors reveal the crucial importance of the low-frequency noise for determining the ultimate detection limit. In this letter, the 1/f-type noise of Si nanoribbon field-effect sensors is investigated. We demonstrate that the signal-to-noise ratio can be increased by almost two orders of magnitude if the nanoribbon is operated in an optimal gate voltage range. In this case, the additional noise contribution from the contact regions is minimized, and an accuracy of 0.5‰ of a pH shift in 1 Hz bandwidth can be reached.
A polymorphism at the melatonin receptor 1A (MTNR1A) gene in Sarda ewes affects fertility after AI in the spring
Authors: Carcangiu Vincenzo , Luridiana Sebastiano , Vacca Giuseppe Massimo , Daga Cinzia , Mura Maria Consuelo
Published: January 2011

The effect of MTNR1A gene polymorphisms on the fertility rate after AI in Sarda sheep was evaluated in 600 lactating adult ewes. Genomic DNA was subjected to amplification of the MTNR1A gene exon II. Amplicons were digested with restriction endonuclease MnlI. Ten samples from each genotype were sequenced. A polymorphism was detected (A612G) and ewes were determined to be +/+, +/– or –/– for the allele. Allelic frequency was 0.77 for the + allele and 0.23 for the – allele. The frequency of the +/+, +/– and –/– genotypes was 68, 19 and 13%, respectively. On 16 May 2009, 60 ewes from each genotype group were synchronised using intravaginal sponges containing 40 mg fluorogestone acetate for 14 days. At sponge removal, the ewes were administered 350 IU pregnant mare’s serum gonadotropin and were then inseminated, 54–56 h later, with 400 × 106 spermatozoa. Pregnancies were confirmed 50 days after AI using transabdominal ultrasonography. Lambing dates and the number of newborn lambs were recorded within 155 days after AI. Conception and lambing rate were higher for ewes with the +/+ and +/– genotypes compared with those with the –/– genotype (P < 0.01). In conclusion, there was a positive correlation between MTNR1A allele polymorphisms the reproductive response following synchronisation and AI in the spring.
Anti-inflammatory therapy in an ovine model of fetal hypoxia induced by single umbilical artery ligation
Authors: Bertucci Micka C. , Loose Jan M. , Wallace Euan M. , Jenkin Graham , Miller Suzanne L.
Published: January 2011

Perinatal morbidity and mortality are significantly higher in pregnancies complicated by chronic hypoxia and intrauterine growth restriction (IUGR). Clinically, placental insufficiency and IUGR are strongly associated with a fetoplacental inflammatory response. To explore this further, hypoxia was induced in one fetus in twin-bearing pregnant sheep (n = 9) by performing single umbilical artery ligation (SUAL) at 110 days gestation. Five ewes were administered the anti-inflammatory drug sulfasalazine (SSZ) daily, beginning 24 h before surgery. Fetal blood gases and inflammatory markers were examined. In both SSZ- and placebo-treated ewes, SUAL fetuses were hypoxic and growth-restricted at 1 week (P < 0.05). A fetoplacental inflammatory response was observed in SUAL pregnancies, with elevated pro-inflammatory cytokines, activin A and prostaglandin E2. SSZ did not mitigate this inflammatory response. It is concluded that SUAL induces fetal hypoxia and a fetoplacental inflammatory response and that SSZ does not improve oxygenation or reduce inflammation. Further studies to explore whether alternative anti-inflammatory treatments may improve IUGR outcomes are warranted.