bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase behavior of colloidal hard perfect tetragonal parallelepipeds
Authors: John Bettina S. , Juhlin Carol , Escobedo Fernando A.
Published: January 2008

The phase behavior of suspensions of colloidal hard tetragonal parallelepipeds (“TPs”) (also known as rectangular nanorods or nanobars) was studied by using Monte Carlo simulations to gain a detailed understanding of the effect of flat-faceted particles on inducing regular local packing and long range structural order. A TP particle has orthogonal sides with lengths a, b, and c, such that a=b and its aspect ratio is r=c∕a. The phase diagram for such perfect TPs was mapped out for particle aspect ratios ranging from 0.125 to 5.0. Equation of state curves, order parameters, particle distribution functions, and snapshots were used to analyze the resulting phases. Given the athermal nature of the systems studied, it is the interplay of purely entropic forces that drives phase transitions amongst the structures observed that include crystal, columnar, smectic, parquet, and isotropic phases. In the parquet phase that occurs for 0.54<r⩽3.2, for example, the particles possess some translational entropy (mobility) but reduced orientational entropy; particles arrange in stacks oriented perpendicular to one another, so that all particle axes are aligned along three common directors. Multicanonical-type simulations were used to study in more detail the isotropic-parquet phase transition. Both similarities and differences were identified between the results for these perfect TPs and those unveiled in our previous study of approximate (polybead) TPs.
Eliminating fast reactions in stochastic simulations of biochemical networks: A bistable genetic switch
Authors: Morelli Marco J. , Allen Rosalind J. , Tănase-Nicola Sorin , ten Wolde Pieter Rein
Published: January 2008

In many stochastic simulations of biochemical reaction networks, it is desirable to “coarse grain” the reaction set, removing fast reactions while retaining the correct system dynamics. Various coarse-graining methods have been proposed, but it remains unclear which methods are reliable and which reactions can safely be eliminated. We address these issues for a model gene regulatory network that is particularly sensitive to dynamical fluctuations: a bistable genetic switch. We remove protein-DNA and/or protein-protein association-dissociation reactions from the reaction set using various coarse-graining strategies. We determine the effects on the steady-state probability distribution function and on the rate of fluctuation-driven switch flipping transitions. We find that protein-protein interactions may be safely eliminated from the reaction set, but protein-DNA interactions may not. We also find that it is important to use the chemical master equation rather than macroscopic rate equations to compute effective propensity functions for the coarse-grained reactions.
Dissociative recombination of water cluster ions with free electrons: Cross sections and branching ratios
Authors: Öjekull J. , Andersson P. U. , Pettersson J. B. C. , Marković N. , Thomas R. D. , Al Khalili A. , Ehlerding A. , Österdahl F. , af Ugglas M. , Larsson M. , Danared H. , Källberg A.
Published: January 2008

Dissociative recombination (DR) of water cluster ions H+(H2O)n (n=4–6) with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, branching ratios have been determined for the dominating product channels and absolute DR cross sections have been measured in the energy range from 0.001to0.7eV. Dissociative recombination is concluded to result in extensive fragmentation for all three cluster ions, and a maximum number of heavy oxygen-containing fragments is produced with a probability close to unity. The branching ratio results agree with earlier DR studies of smaller water cluster ions where the channel nH2O+H has been observed to dominate and where energy transfer to internal degrees of freedom has been concluded to be highly efficient. The absolute DR cross sections for H+(H2O)n (n=4–6) decrease monotonically with increasing energy with an energy dependence close to E−1 in the lower part of the energy range and a faster falloff at higher energies, in agreement with the behavior of other studied heavy ions. The cross section data have been used to calculate DR rate coefficients in the temperature range of 10–2000K. The results from storage ring experiments with water cluster ions are concluded to partly confirm the earlier results from afterglow experiments. The DR rate coefficients for H+(H2O)n (n=1–6) are in general somewhat lower than reported from afterglow experiments. The rate coefficient tends to increase with increasing cluster size, but not in the monotonic way that has been reported from afterglow experiments. The needs for further experimental studies and for theoretical models that can be used to predict the DR rate of polyatomic ions are discussed.
Optically pumped nuclear magnetic resonance of semiconductors
Authors: Hayes Sophia E. , Mui Stacy , Ramaswamy Kannan
Published: January 2008

Optically pumped NMR (OPNMR) of direct gap and indirect gap semiconductors has been an area of active research interest, motivated by both basic science and technological perspectives. Proposals to enhance and to spatially localize nuclear polarization have stimulated interest in this area. Recent progress in OPNMR has focused on exploring the experimental parameter space in order to elucidate details of the underlying photophysics of optical pumping phenomena. The focus of this review is on recent studies of bulk samples of GaAs and InP, namely, the photon energy dependence, the magnetic field dependence, and the phase dependence of OPNMR resonances. Models for the development of nuclear polarization are discussed.
Revisiting random walks in fractal media: On the occurrence of time discrete scale invariance
Authors: Bab M. A. , Fabricius G. , Albano Ezequiel V.
Published: January 2008

This paper addresses the kinetic behavior of random walks in fractal media. We perform extensive numerical simulations of both single and annihilating random walkers on several Sierpinski carpets, in order to study the time behavior of three observables: the average number of distinct sites visited by a single walker, the mean-square displacement from the origin, and the density of annihilating random walkers. We found that the time behavior of those observables is given by a power law modulated by soft logarithmic-periodic oscillations. We conjecture that logarithmic-periodic oscillations are a manifestation of a time domain discrete scale iNvariance (DSI) that occurs as a consequence of the spatial DSI of the substrate. Our conjecture implies that the logarithmic periods of oscillations in space and time domains are linked by a dynamic exponent z, through z=log(τ)/log(b1), where τ and b1 are the fundamental scaling ratios of the DSI symmetry in the time and space domains, respectively. We use this relationship in order to compute z for different observables and fractals. Furthermore, we check the values obtained with independent measurements provided by the power-law behavior of the mean-square displacement with time [R2(t)∝t2/z]. The very good agreement obtained between both computations of the z exponent gives strong support to the idea of an intimate interplay between spatial and time symmetry properties that we expect will have a quite general scope. We expect that the application of the outlined concepts in the field of dynamic processes in fractal media will stimulate further research.
On the prediction of the crystal and electronic structure of mixed-valence materials by periodic density functional calculations: The case of Prussian Blue
Authors: Wojdeł Jacek C. , de P. R. Moreira Ibério , Bromley Stefan T. , Illas Francesc
Published: January 2008

The consistency of periodic density functional approaches to properly describe the crystal and electronic structure of mixed-valence materials is investigated by taking Prussian Blue as prototypical example. Hybrid B3LYP, GGA, and, GGA+U exchange-correlation potentials have been explored. Localized Gaussian-type orbitals or plane waves have been chosen to expand the valence electron density, and the effect of the core electrons on the electronic structure was accounted for either (i) explicitly by including all electrons in the calculations, (ii) by making use of ultrasoft pseudopotentials, or (iii) by the use of the projected augmented wave method. Comparison to available experimental data shows that all-electron calculations within the hybrid exchange-correlation potential can be taken as appropriate benchmarks. It is also concluded that a proper description of the complex magnetic ground state of Prussian Blue can be reached by using a plane-wave basis set and nonhybrid density functional potentials but only if the electronically distinct iron centers in the material are treated in an independent manner. Physical reasons for such rather unexpected results are given and implications for the description of mixed-valence materials by means of density functional approaches are discussed.
Dynamical dimer method for the determination of transition states with ab initio molecular dynamics
Authors: Poddey Alexander , Blöchl Peter E.
Published: January 2008

A dynamical formulation of the dimer method for the determination of transition states is presented. The method is suited for ab initio molecular dynamics using the fictitious Lagrangian formulation. The method has been applied to the conrotatory ring opening of chlorocyclobutadiene, an example, where the application of the drag method is problematic.
The method of Gaussian weighted trajectories. III. An adiabaticity correction proposal
Authors: Bonnet L.
Published: January 2008

The addition of an adiabaticity correction (AC) to the Gaussian weighted trajectory (GWT) method and its normalized version (GWT-N) is suggested. This correction simply consists in omitting vibrationally adiabatic nonreactive trajectories in the calculations of final attributes. For triatomic exchange reactions, these trajectories satisfy the criterion Ω not much larger than ℏ, where Ω is a vibrational action defined by Ω=∫−∞∞dt(pṙ−p0ṙ0), r being the reagent diatom bond length, p its conjugate momentum, and r0 and p0 the corresponding variables for the unperturbed diatom (Ω∕ℏ bears some analogy with the semiclassical elastic scattering phase shift). The resulting GWT-AC and GWT-ACN methods are applied to the recently studied H++H2 and H++D2 reactions and the agreement between their predictions and those of exact quantum scattering calculations is found to be much better than for the initial GWT and GWT-N methods. The GWT-AC method, however, appears to be the most accurate one for the processes considered, in particular, the H++D2 reaction.
Dispersion due to wall interactions in microfluidic separation systems
Authors: Datta Subhra , Ghosal Sandip
Published: January 2008

The transport of a solute in a straight microchannel of axially variable cross-sectional shape in the presence of an inhomogeneous flow field and an adsorption-desorption process on the wall is studied, motivated by applications to capillary electrophoresis and open-channel capillary electrochromatography. An asymptotic approach based on the long time limit is adopted that reduces the problem to the solution of a one-dimensional transport equation. The reduced model is integrated numerically to study the effects of inhomogeneous electro-osmotic flow and adsorption-desorption kinetics on solute migration and dispersion in a rectangular microchannel. The accuracy of the asymptotic equations is checked by the direct numerical solution of the original three-dimensional transport problem.
Torque magnetometry studies of new low temperature metamagnetic states in ErNi2B2C
Authors: Naugle D. G. , Belevtsev B. I. , Rathnayaka K. D. D. , Lee S.-I. , Yeo S. M.
Published: January 2008

The metamagnetic transitions in single-crystal ErNi2B2C have been studied at 1.9K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [100]. Torque measurements have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) in a wide angular range (more than two quadrants). Sequences of metamagnetic transitions with increasing field are found to be different for the magnetic field along (or close enough to) the easy [100] axis from that near the hard [110] axis. The study have revealed new metamagnetic states in ErNi2B2C, which were not apparent in previous longitudinal-magnetization and neutron studies.
Enhanced adsorption energy of Au1 and O2 on the stoichiometric TiO2(110) surface by coadsorption with other molecules
Authors: Chrétien Steeve , Metiu Horia
Published: January 2008

During heterogeneous catalysis the surface is simultaneously covered by several adsorbed molecules. The manner in which the presence of one kind of molecule affects the adsorption of a molecule of another kind has been of interest for a long time. In most cases the presence of one adsorbate does not change substantially the binding energy of another adsorbate. The calculations presented here show that the stoichiometric rutile TiO2(110) surface, on which one of the compounds –OH, Au3, Au5, Au7, Na, K, or Cs or two different gold strips was preadsorbed, behaves differently: the binding energy of Au1 or O2 to such a surface is much stronger than the binding to the clean stoichiometric TiO2(110) surface. Moreover, the binding energy of Au1 or O2 and the amount of charge they take from the surface when they adsorb are the same, regardless of which of the above species is preadsorbed. The preadsorbed species donate electrons to the conduction band of the oxide, and these electrons are used by Au1 or O2 to make stronger bonds with the surface. This suggests that adding an electron to the conduction band of the clean stoichiometric TiO2(110) slab used in the calculation will affect similarly the adsorption energy of Au1 or O2. Our calculations show that it does. We have also studied how the preadsorption of Au4 or Au6 affects the binding of Au1 or O2 to the surface. These two gold clusters do not donate electrons to the surface when they bind to it and therefore should not influence substantially the binding energy of Au1 or O2 to the surface. However, adsorbing O2 or Au1 on the surface forces the clusters to change their structure into that of isomers that donate charge to the oxide. This charge is used by Au1 or O2 to bind to the surface and the energy of this bond exceeds the isomerization energy. As a result the surface with the isomerized cluster is the lowest energy state of the system. We believe that these results can be generalized as follows. The molecules that we coadsorbed with Au1 or O2 donate electrons to the oxide and are Lewis bases. By giving the surface high energy electrons, they turn it into a Lewis base and this increases its ability to bind strong Lewis acids such as Au1 and O2. We speculate that this kind of interaction is general and may be observed for other oxides and for other coadsorbed Lewis base–Lewis acid pairs.
Vortices and antivortices as harmonic oscillators
Authors: Krüger Benjamin , Drews André , Bolte Markus , Merkt Ulrich , Pfannkuche Daniela , Meier Guido
Published: January 2008

It is shown that the current- and field-induced gyration of magnetic vortices and antivortices follows the analytical model of a two-dimensional harmonic oscillator. Quantities of the harmonic oscillator, i.e., resonance frequency, damping constant, gyration amplitude, and phase, can be linked to material parameters and sample dimensions. This description is useful for the investigation of vortex-switching and vortex-antivortex annihilation processes.
Ultrafast laser excitation of spin waves and the permanent modification of the exchange bias interaction in IrMn∕Co
Authors: Seu Keoki A. , Reilly Anne C.
Published: January 2008

Single mode coherent magnetization oscillations are observed in exchange biased IrMn∕Co thin films by the pump-probe time-resolved magneto-optical Kerr effect, using moderate intensity pump pulses. Unlike past experiments on exchange biased systems, the oscillations produced can be excited when the Co magnetization is saturated along the pinning axis. The oscillation frequencies correspond to ferromagnetic resonance measurements and can be described using a FMR equation. It is also demonstrated that ultrafast laser pulses can induce pinning along the direction of the applied magnetic field.
The effect of element doping and heat treatment on the impact resistance of Nd–Fe–B sintered magnets
Authors: Wang Huijie , Li Anhua , Guo Yongquan , Zhu Minggang , Li Wei
Published: January 2008

The effects of rare-earth contents, substitutions, and heat treatment parameters on the impact resistance of the Nd–Fe–B sintered magnets were investigated. Analysis shows that the impact resistance increases linearly with increasing plastic rare-earth-rich phase in the investigated magnets. Heavy rare-earth Dy substitutions for Nd help us to improve the impact resistance. The bending strength and impact resistance during annealing process was investigated. It is found that the annealing process affects the bending strength and impact resistance remarkably. Both the bending strength and the intrinsic coercivity are poor in the as-sintered specimen. In the postsintering annealing process, both of them get improved and the change of intrinsic coercivity is similar to that of the bending strength. Study showed that the optimized heat treatment parameters help us to improve the bending strength and impact resistance of the sintered Nd–Fe–B magnets. Study shows that the sintered Nd–Fe–B magnets with improved impact resistance can be produced by the adjustment of compositions and heat treatment parameters.
Ferromagnetic resonance and spin momentum exchange in crystalline magnetic ultrathin films in noncollinear configuration
Authors: Mosendz O. , Kardasz B. , Heinrich B.
Published: January 2008

Au ∕ Fe ∕ Au ∕ Fe ∕ Ga As ( 001 ) ultrathin film structures were grown by molecular beam epitaxy on 4×6 reconstructed GaAs(001) substrates. Measurements were carried out using a network microwave analyzer in the range of frequencies from 1to12GHz allowing one to determine both the in-phase and out-of-phase components of the rf magnetic susceptibility. The ferromagnetic resonance (FMR) results indicate that the ultrathin Fe films are of high crystalline quality. The bottom Fe film [Au∕Fe∕GaAs(001)] has its magnetic hard axis along the [1−10] direction due to a strong in-plane uniaxial interface anisotropy. This leads to a unique behavior of the FMR in noncollinear configuration. Beside the 2 two FMR peaks expected an additional FMR peak was observed in a narrow microwave frequency range. This peak can be explained as a “ghost resonance” which was driven purely by magnetic losses. The FMR linewidth is mostly given by the bulk intrinsic Gilbert damping and spin pumping, and is only weakly affected by small local variations of the internal anisotropy fields. An accidental crossover of the collinear FMR branch of the top Fe layer (Au∕Fe∕Au) with the noncollinear branch of the bottom (Au∕Fe∕GaAs) layer was used to investigate nonlocal spin pumping and spin sink effects in a noncollinear configuration of magnetic moments.
Current-induced magnetization random switching under oblique offset field in MgO-based magnetic tunnel junctions
Authors: Lee Ching-Ming , Weng M. C. , Lee J. M. , Wu Te-Ho
Published: January 2008

We present the experimental results of current-induced magnetization random switching of MgO-based magnetic tunnel junctions (MTJs) with elliptical-shaped cell of dimension 178×133nm2. The R-H loop measurements show that the offset field acting on the free layer is oblique, and magnetoresistance change contains both reversible and irreversible portions. The spin-transfer effect was measured with pulsed current of width 10ms under bias field along easy-axis direction. For bias field equal to or slightly larger than the easy-axis offset field, the MTJ shows random oscillation between the high and low resistance states; however, as the field increases further, a typical R-I hysteresis loop is obtained. The phenomenon may be related to the residue hard-axis offset field.
Switching behavior of La1−xCaxMnO3 thin films grown on SrTiO3 substrates
Authors: Hu F. X. , Sun J. R. , Shen B. G. , Rong C. B. , Gao J.
Published: January 2008

We report the switching behavior of resistive states induced by current flowing in La1−xCaxMnO3 films. The transport behavior upon treatments by applying a large dc current has been investigated in the absence of magnetic field. A switching from low to high resistive state was found upon applying a large dc current for the both compositions. The critical currents for the switching are 10.5mA (density of 2.3×103A∕cm2) and 6.7mA (density of 1.6×103A∕cm2) for compositions x=0.2 and 0.3, respectively. Our repeated measurements indicate that the high resistive state appeared in the film x=0.2 is much stable. Exposing the sample in air and room temperature does not cause any change of the transport properties. However, for the film with x=0.3, the induced high resistive state behaves with unstable characteristics. Keeping the sample at a low temperature of 20K, a relaxation to a higher resistive state takes place. The mechanism of phase separation was taken into account in the interpretation of the observed phenomena.
Magnetic and structural properties of ultrathin epitaxial Fe3Si films on GaAs(001)
Authors: Herfort J. , Schönherr H.-P. , Jenichen B.
Published: January 2008

We have studied the thickness dependence of the structural and magnetic properties of ultrathin Fe3Si films grown on GaAs(001). The onset of ferromagnetism is found to be at about 3 ML at low temperatures. Furthermore, a reorientation of the uniaxial in-plane magnetic anisotropy takes place when the thickness of the films is reduced. This is due to a competition between a volume term and an interface contribution, which have opposite sign. Whereas the origin of the volume term remains unclear, the interface contribution is attributted to an anisotropic bonding at the Fe3Si∕GaAs(001) interface, similar to other ferromagnet/semiconductor hybrid structures.
Regimes of the interactions of high-intensity plane electromagnetic waves with electron-ion plasmas
Authors: Shiryaev O. B.
Published: January 2008

A set of fully nonlinear equations is derived from the Maxwell equations and the electron and ion fluid dynamics in one-dimensional geometry as a model of the interactions of extremely intense plane electromagnetic waves with cold locally non-neutral electron-ion plasmas. The problem is solved for phase velocities close to the speed of light numerically and with the help of asymptotic techniques. Depending on the field magnitudes, three nonlinear regimes are found to occur in the system. At plane-wave intensities inducing relativistic electron fluid dynamics but insufficient to cause significant ion motions, the model reverts to the classic Akhiezer–Polovin problem and yields its solutions describing the nonlinear self-modulation of the electromagnetic fields in plasmas. The types of regimes sustained at field strengths entailing substantial ion dynamics are the self-modulation with a splitting of the plane-wave field spectrum into a set of closely spaced bands, and the harmonics generation with a spectrum comprising broadly distanced bands. The latter two regimes correspond to a subcritical and an overcritical range of the plasma longitudinal field potentials.
Quantum wave kinetics of high-gain free-electron lasers
Authors: Serbeto A. , Mendonça J. T. , Tsui K. H , Bonifacio R.
Published: January 2008

A wave kinetic equation equivalent to the Schrodinger-like equation for the electrons is derived from relativistic theory in the eikonal approximation. This equation is used to study the interaction of the relativistic electron beam in a wiggler field in the quantum regime, i.e., when the normalized quantum free-electron laser parameter ρ¯⩽1. A general quantum dispersion relation and an expression for free-electron laser instabilities are derived. Conditions for kinetic instability, which takes into account the Landau damping effect, are established.
Development of a magetnetostrictive transducer for nondestructive testing of concrete structures
Authors: Jammalamadaka S. Narayana , Markandeyulu G. , Kannan Elankumaran , Balasubramaniam Krishnan
Published: January 2008

A magnetostrictive transducer operating at 100kHz using rare earth transition metal giant magnetostrictive material for nondestructive testing (NDT) applications was designed and fabricated. The giant magnetostrictive Tb0.3Dy0.7Fe2 material was chosen as the active element for the present purpose. From the impedance measurements, the resonant frequency of the transducer is found to be 100kHz. The performance of the transducer was validated by carrying out NDT on a test concrete block with delaminated regions, using the ultrasonic through-transmission technique and the pitch-catch method.
Magnetic phase diagram of Ce(Mn1−xCux)2Si2
Authors: Liang G. , Yen F.
Published: January 2008

The magnetic structure of mixed valence-Kondo-heavy fermion series Ce(Mn1−xCux)2Si2 (0⩽x⩽1) is reported. The magnetic susceptibility results indicate that for 0⩽x⩽0.3, Mn moments are antiferromagnetically (AFM) ordered and the Neel temperature TN decreases rapidly with decreasing x. For 0.4⩽x⩽0.7, ferromagnetic (FM) phase is observed below 140K and both the ordering temperature Tc and Curie–Weiss temperature θp decrease with increasing x, showing the weakening of in-plane FM magnetic coupling between Mn moments due to the substitution of Mn by nonmagnetic Cu. For 0.8⩽x⩽1, samples exhibit only paramagnetic behavior. The types of magnetic order in this series are basically consistent with the criterion that FM (AFM) phase is favored when intralayer Mn–Mn spacing RMn–Mna is greater (smaller) than a critical value of 2.865Å. A magnetic phase diagram is constructed for this compound series.
Exchange coupling in nanocomposite FePtB thin film magnets
Authors: Kaushik Neelam , Sharma Parmanand , Kimura Hisamichi , Inoue Akihisa , Makino Akihiro
Published: January 2008

The nature of coupling among the L10 FePt hard and FexB (x=2,3) soft magnetic phases in FePtB nanocomposite thin film magnets is investigated by measuring the hysteresis loops and δM (Henkel) plots. The FePtB thin films deposited under optimized sputtering conditions are shown to have almost fully exchange-coupled soft and hard magnetic phases, which resulted in good hard magnetic properties [in-plane Hc∼604kA∕m and (BH)max∼95.6kJ∕m3].
Investigation of water-soluble x-ray luminescence nanoparticles for photodynamic activation
Authors: Liu Yuanfang , Chen Wei , Wang Shaopeng , Joly Alan G.
Published: January 2008

In this letter, we report the synthesis of LaF3:Tb3+–meso-tetra(4-carboxyphenyl) porphine (MTCP) nanoparticle conjugates and investigate the energy transfer as well as singlet oxygen generation following x-ray irradiation. Our observations indicate that LaF3:Tb3+-MTCP nanoparticle conjugates are efficient photodynamic agents that can be initiated by x-rays at a reasonably low dose. The addition of folic acid to facilitate targeting to folate receptors on tumor cells has no effect on the quantum yield of singlet oxygen production in the nanoparticle-MTCP conjugates. Our pilot studies indicate that water-soluble scintillation nanoparticles can potentially be used to activate photodynamic therapy as a promising deep cancer treatment modality.
Growth of Si nanorods in honeycomb and hexagonal-closed-packed arrays using glancing angle deposition
Authors: Patzig Christian , Rauschenbach Bernd , Fuhrmann Bodo , Leipner Hartmut S.
Published: January 2008

Regular arrays of Si nanorods with a circular cross section in hexagonal-closed-packed and triangular cross section in honeycomblike arrangements were grown using glancing angle deposition on Si(100) and fused silica substrates that were patterned with Au dots using self-assembled mono- and double layers of polystyrene nanospheres as an evaporation mask. The Au dots were used as an etching mask for the underlying silica substrates in a reactive ion beam etching process, which greatly enhanced the height of the seeding spaces for the subsequent glancing angle deposition. An elongated shadowing length l of the prepatterned nucleation sites and less growth of Si structures between the surface mounds could be achieved this way. Differences in form, height, and diameter of the Si nanorods grown on either hcp or honeycomb arrays are explained by purely geometrical arguments. Different seed heights and interseed distances are found to be the main reasons for the strong distinctions between the grown nanorod arrays.
Magnetization reversal and magnetic anisotropy in patterned Co/Pd multilayer thin films
Authors: Smith Darren , Parekh Vishal , E Chunsheng , Zhang Shishan , Donner Wolfgang , Lee T. Randall , Khizroev Sakhrat , Litvinov Dmitri
Published: January 2008

( Co / Pd ) N multilayers exhibit high vertical magnetic anisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In this work, (Co/Pd)N multilayers are deposited by magnetron sputtering and patterned into large periodic arrays of 200 nm islands to enable controlled domain wall injection for quantitative comparison of magnetic anisotropy energies. Magnetic properties are correlated with x-ray photoelectron spectroscopy data, an approach commonly used to probe the binding energies and valence band positions. Confirming theoretical predictions, it is demonstrated that the degree of d-shell hybridization at Co/Pd interfaces directly correlated with the magnitude of magnetic anisotropy.
Comparison of air gap breakdown and substrate injection as mechanisms to induce dielectric charging in microelectromechanical switches
Authors: Molinero D. , Castañer L.
Published: January 2008

Experiments show that air breakdown and substrate carrier conduction can be responsible of the dielectric charging of microelectromechanical devices after electrical stress. Test conducted under vacuum allows us to isolate the two mechanisms. It is also shown that the relative importance of the two mechanisms depends on the dielectric nature and technology.
Surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor with 14:1 continuous tuning range
Authors: Lee Chuang-Yuan , Pang Wei , Chen Shih-Jui , Chi Derrick , Yu Hongyu , Kim Eun Sok
Published: January 2008

This letter reports a surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor utilizing a simply supported bridge structure, unlike traditional microelectromechanical-system bridges that use fully clamped boundary condition at the anchors. Through the implementation of a simply supported bridge driven by two 100-μm-long ZnO-actuated cantilevers, a compact tunable capacitor has been fabricated on silicon without any warping and shown to be capable of a 1400% continuous tuning from 0.13to1.82pF.
MicroRNA-126 regulates endothelial expression of vascular cell adhesion molecule 1
Authors: Harris Tamia A. , Yamakuchi Munekazu , Ferlito Marcella , Mendell Joshua T. , Lowenstein Charles J.
Published: January 2008

Adhesion molecules expressed by activated endothelial cells play a key role in regulating leukocyte trafficking to sites of inflammation. Resting endothelial cells normally do not express adhesion molecules, but cytokines activate endothelial cells to express adhesion molecules such as vascular cell adhesion molecule 1 (VCAM-1), which mediate leukocyte adherence to endothelial cells. We now show that endothelial cells express microRNA 126 (miR-126), which inhibits VCAM-1 expression. Transfection of endothelial cells with an oligonucleotide that decreases miR-126 permits an increase in TNF-α-stimulated VCAM-1 expression. Conversely, overexpression of the precursor to miR-126 increases miR-126 levels and decreases VCAM-1 expression. Additionally, decreasing endogenous miR-126 levels increases leukocyte adherence to endothelial cells. These data suggest that microRNA can regulate adhesion molecule expression and may provide additional control of vascular inflammation.
Molecular insights into human daily behavior
Authors: Brown Steven A. , Kunz Dieter , Dumas Amelie , Westermark Pål O. , Vanselow Katja , Tilmann-Wahnschaffe Amely , Herzel Hanspeter , Kramer Achim
Published: January 2008

Human beings exhibit wide variation in their timing of daily behavior. We and others have suggested previously that such differences might arise because of alterations in the period length of the endogenous human circadian oscillator. Using dermal fibroblast cells from skin biopsies of 28 subjects of early and late chronotype (11 “larks” and 17 “owls”), we have studied the circadian period lengths of these two groups, as well as their ability to phase-shift and entrain to environmental and chemical signals. We find not only period length differences between the two classes, but also significant changes in the amplitude and phase-shifting properties of the circadian oscillator among individuals with identical “normal” period lengths. Mathematical modeling shows that these alterations could also account for the extreme behavioral phenotypes of these subjects. We conclude that human chronotype may be influenced not only by the period length of the circadian oscillator, but also by cellular components that affect its amplitude and phase. In many instances, these changes can be studied at the molecular level in primary dermal cells.
Sublingual vaccination with influenza virus protects mice against lethal viral infection
Authors: Song Joo-Hye , Nguyen Huan H. , Cuburu Nicolas , Horimoto Taisuke , Ko Sung-Youl , Park Se-Ho , Czerkinsky Cecil , Kweon Mi-Na
Published: January 2008

We assessed whether the sublingual (s.l.) route would be an effective means of delivering vaccines against influenza virus in mice by using either formalin-inactivated or live influenza A/PR/8 virus (H1N1). Sublingual administration of inactivated influenza virus given on two occasions induced both systemic and mucosal antibody responses and conferred protection against a lethal intranasal (i.n.) challenge with influenza virus. Coadministration of a mucosal adjuvant (mCTA-LTB) enhanced these responses and resulted in complete protection against respiratory viral challenge. In addition, s.l. administration of formalin-inactivated A/PR/8 plus mCTA-LTB induced systemic expansion of IFN-γ-secreting T cells and virus-specific cytotoxic T lymphocyte responses. Importantly, a single s.l. administration of live A/PR/8 virus was not pathogenic and induced protection mediated by both acquired and innate immunity. Moreover, s.l. administration of live A/PR/8 virus conferred heterosubtypic protection against respiratory challenge with H3N2 virus. Unlike the i.n. route, the A/PR/8 virus, whether live or inactivated, did not migrate to or replicate in the CNS after s.l. administration. Based on these promising findings, we propose that the s.l. mucosal route offers an attractive alternative to mucosal routes for administering influenza vaccines.
Reduced social interaction and ultrasonic communication in a mouse model of monogenic heritable autism
Authors: Jamain Stephane , Radyushkin Konstantin , Hammerschmidt Kurt , Granon Sylvie , Boretius Susann , Varoqueaux Frederique , Ramanantsoa Nelina , Gallego Jorge , Ronnenberg Anja , Winter Dorina , Frahm Jens , Fischer Julia , Bourgeron Thomas , Ehrenreich Hannelore , Brose Nils
Published: January 2008

Autism spectrum conditions (ASCs) are heritable conditions characterized by impaired reciprocal social interactions, deficits in language acquisition, and repetitive and restricted behaviors and interests. In addition to more complex genetic susceptibilities, even mutation of a single gene can lead to ASC. Several such monogenic heritable ASC forms are caused by loss-of-function mutations in genes encoding regulators of synapse function in neurons, including
NLGN4
. We report that mice with a loss-of-function mutation in the murine
NLGN4
ortholog
Nlgn4
, which encodes the synaptic cell adhesion protein Neuroligin-4, exhibit highly selective deficits in reciprocal social interactions and communication that are reminiscent of ASCs in humans. Our findings indicate that a protein network that regulates the maturation and function of synapses in the brain is at the core of a major ASC susceptibility pathway, and establish Neuroligin-4-deficient mice as genetic models for the exploration of the complex neurobiological disorders in ASCs.
A phosphorylated subpopulation of the histone variant macroH2A1 is excluded from the inactive X chromosome and enriched during mitosis
Authors: Bernstein Emily , Muratore-Schroeder Tara L. , Diaz Robert L. , Chow Jennifer C. , Changolkar Lakshmi N. , Shabanowitz Jeffrey , Heard Edith , Pehrson John R. , Hunt Donald F. , Allis C. David
Published: January 2008

Histone variants play an important role in numerous biological processes through changes in nucleosome structure and stability and possibly through mechanisms influenced by posttranslational modifications unique to a histone variant. The family of histone H2A variants includes members such as H2A.Z, the DNA damage-associated H2A.X, macroH2A (mH2A), and H2ABbd (Barr body-deficient). Here, we have undertaken the challenge to decipher the posttranslational modification-mediated “histone code” of mH2A, a variant generally associated with certain forms of condensed chromatin such as the inactive X chromosome in female mammals. By using female human cells as a source of mH2A, endogenous mH2A was purified and analyzed by mass spectrometry. Although mH2A is in low abundance compared with conventional histones, we identified a phosphorylation site, S137ph, which resides within the “hinge” region of mH2A. This lysine-rich hinge is an ≈30-aa stretch between the H2A and macro domains, proposed to bind nucleic acids. A specific antibody to S137ph was raised; by using this reagent, S137 phosphorylation was found to be present in both male and female cells and on both splice variants of the mH2A1 gene. Although mH2A is generally enriched on the inactive X chromosome in female cells, mH2AS137ph is excluded from this heterochromatic structure. Thus, a phosphorylated subpopulation of mH2A appears to play a unique role in chromatin regulation beyond X inactivation. We provide evidence that S137ph is enriched in mitosis, suggestive of a role in the regulation of mH2A posttranslational modifications throughout the cell cycle.
Acupuncture versus subcutaneous injections of sterile water as treatment for labour pain
Authors: MÅRTENSSON LENA , STENER‐VICTORIN ELISABET , WALLIN GUNNAR
Published: January 2008

Background.Two methods for pain relief and relaxation during labour are sterile water injections and acupuncture. In several studies, sterile water injections have been shown to provide good pain relief, particularly for low back pain during labour. The acupuncture studies for pain relief during labour are not as concordant. Therefore, the aim of this study was to explore if there were any differences between acupuncture and sterile water injections regarding pain relief and relaxation during labour.Methods.A randomised controlled trial. Some 128 pregnant women at term were randomly assigned to receive acupuncture (n= 62) or sterile water injections (n= 66). The primary endpoint was to compare the differences between pre‐treatment pain levels and maximum pain in the 2 groups.Results.The main results of this study were that sterile water injections yielded greater pain relief (p<0.001) during childbirth compared to acupuncture. The secondary outcome showed that women in the sterile water group had a higher degree of relaxation (p<0.001) compared to the acupuncture group. The women's own assessment of the effects also favoured sterile water injections (p<0.001). There were no significant differences regarding requirements for additional pain relief after treatment between the 2 groups.Conclusions.Women given sterile water injection experience less labour pain compared to women given acupuncture.
Obstetric outcome of teenage pregnancies compared with adult pregnanciesa
Authors: USTA IHAB M. , ZOOROB DANI , ABU‐MUSA ANTOINE , NAASSAN GEORGES , NASSAR ANWAR H.
Published: January 2008

Background. To compare the obstetric outcome of teenage pregnancies with that of older women. Methods. Retrospective chart review of singleton births ≥24 weeks’ gestational age at the American University of Beirut from 1994 to 2003. Adolescents (<20 years) were compared to subsequently delivered women aged 25–30 years (controls), n = 486 each. Results. Only 131 (27.0%) adolescents were <18 years. More adolescents were nulliparous (79.8 versus 17.9%; p<0.0001). Preterm delivery <37 but not <34 weeks occurred more frequently in cases (11.1 versus 5.8%, p = 0.004). Pre‐eclampsia was more commonly encountered (2.9 versus 0.6%; p = 0.012) and mean predelivery haematocrit was lower in cases (30.6±3.3 versus 33.8±4.3%, p<0.001), but the incidence of gestational diabetes, placenta previa, abruptio placentae, breech presentation, or meconium‐stained amniotic fluid were similar. Caesarean delivery was performed less frequently in cases (9.2 versus 14.0%; p = 0.028), but primary caesarean and operative vaginal delivery rates were similar though vacuum was used more frequently in multiparous controls (0.2 versus 2.7%, p = 0.011). Nulliparous cases had shorter first and second stages of labour (384±304 versus 524±339 min, p<0.0001 and 47±36 versus 63±50 min, p = 0.002), respectively. Mean birth weight was higher in controls (3177±567 versus 3284±511 g, p<0.001), but intrauterine growth restriction, birth weight <2500 g, low Apgar scores, intrauterine fetal death, and stillbirths were similar in both groups. Conclusions. Adolescents are more likely to deliver preterm than older women, and are more likely to suffer from anaemia and pre‐eclampsia. Nulliparous adolescents have a quicker progress of labour while multiparous adolescents require vacuum less frequently compared to their older counterparts. In most other respects, they have comparable maternal and perinatal morbidity.
The incidence of obstetric anal sphincter rupture in primiparous women: a comparison between two European delivery settings
Authors: PRAGER MARTINA , ANDERSSON KARIN L. , STEPHANSSON OLOF , MARCHIONNI MAURO , MARIONS LENA
Published: January 2008

Background. During the last years, the incidence of obstetric anal sphincter rupture (OASR) has increased markedly in Sweden, and significantly less frequently in Italy. Our objective was to explore if different delivery management may explain the variation in OASR incidences. Methods. In a retrospective study, data from 2,000 primiparous women in a Swedish and an Italian delivery unit were compared with respect to OASR, maternal age, gestational length, birth weight, labour induction, use of epidural analgesia (EDA) and oxytocin, vacuum extraction, episiotomy, and duration of the second stage of labour. Results. Incidences of OASR were 9.2 and 0.4% in the Swedish and Italian centres, respectively. Other significant differences were noticed in maternal age, birth weight, gestational length, use of EDA, oxytocin, vacuum extraction, episiotomy, and frequency of induction. Further analysis of the Swedish population revealed a significant association between OASR and birth weight as well as vacuum extraction. The association with gestational age and duration of the second stage of labour approached significance level. However, no association could be found between OASR and maternal age, EDA, episiotomy or induction of labour. Conclusion. Women delivering in the Swedish setting had a 23 times higher risk of OASR. An association between OASR and birth weight, gestational age, instrumental vaginal deliveries and duration of second stage was found. These factors varied between the settings and could possibly explain the differences in OASR incidence. The importance of alternative management, such as constant midwife support and perineal protection during delivery, may be a subject for further studies.
Dinoprostone vaginal slow‐release system (Propess®) compared to expectant management in the active treatment of premature rupture of the membranes at term: impact on maternal and fetal outcomes
Authors: LARRAÑAGA‐AZCÁRATE CARLOS , CAMPO‐MOLINA GEMA , FELICITAS PÉREZ‐RODRÍGUEZ ANA , EZCURDIA‐GURPEGUI MIGUEL
Published: January 2008

Background. Retrospective study of 744 women at the Virgen del Camino Hospital in Pamplona concerning two variants for the active treatment of premature rupture of the membranes (PROM). The main purpose of the study was to assess the differences between two variants for the active treatment of PROM at term in pregnant women with negative vaginal‐rectal culture screening for Group B Streptococci, and a Bishop test of 4 or less on admission. Methods. Retrospective study of 744 patients with single pregnancy at term, PROM, and Bishop test <4. The patients, who were not randomised, were treated with dinoprostone (Propess®) or expectant therapy, according to the physician's choice. Induction with oxytocin was started 12 h after PROM. Qualitative data were analysed using the χ2 test, while quantitative data were analysed using the Student's t‐test or the Mann–Whitney U‐test according to the distribution of the variables. Regression models were applied to correct the biases caused by confounding variables. Results. Of the 744 patients, the cervix of 13% was maturated with pericervical dinoprostone, while 87% were subject to expectant management until 12 h after rupture of the membranes. The time of dilation and the time until labour were significantly shorter in the dinoprostone group (p = 0.0). The rate of caesarean sections was also lower in the dinoprostone group at 9.3% compared to 17.6% in the expectant management group, reaching statistical significance (p = 0.04). There were no differences in the parameters of fetal well being (Apgar and pH). Conclusions. The use of therapy with dinoprostone in patients with PROM could be a safe method and more effective than expectant management.
Determinants of the choice for single or double embryo transfer in twin prone couples
Authors: VAN PEPERSTRATEN A.M. , KREUWEL I.A.M. , HERMENS R.P.M.G. , NELEN W.L.D.M. , VAN DOP P.A. , GROL R.P.T.M. , KREMER J.A.M.
Published: January 2008

Background. Some 84% of all European in vitro fertilisation (IVF) and intracytoplasmatic sperm injection (ICSI) cycles is performed with the transfer of more than 1 embryo, with 22% resulting in twin pregnancies. At many centres, the choice for one or more embryos is made through a shared decision‐making process. To reduce the twin rate in a twin prone population by increasing the use of elective single embryo transfer (eSET), it is important to identify which objective patient factors are related to the choice for double embryo transfer (DET) and eSET. Therefore, the aim of this study was to identify determinants related to the choice for the transfer of eSET or DET in a twin prone population. Methods. A retrospective study was performed on 477 twin prone couples at 2 Dutch IVF centres. We collected data on possible objective patient determinants, and a multivariate logistic regression analysis was performed to determine the impact of these determinants on the decision for DET. Results. Of the twin prone couples, 61% opted for DET in their first IVF/ICSI cycle. Within the multivariate analysis, two objective patient determinants acted as a risk factor for the choice of DET – a lower number of available embryos (p = 0.03) and a previous ongoing pregnancy after IVF/ICSI (p = 0.04). The explained variance of the determinants was 3%. Conclusions. In twin prone couples, 61% still opted for DET in their first IVF/ICSI cycle. We identified 2 objective patient determinants for DET, but with an explained variance of only 3%. Therefore, further research is necessary to identify barriers and facilitators for eSET at both the level of the couples and clinicians.