bluuebunny/crossref_metadata_2025 huggingface dataset:
Cationic diffusion in La2∕3Ca1∕3MnO3 thin films grown on LaAlO3 (001) substrates
Authors: Estradé S. , Arbiol J. , Peiró F. , Abad Ll. , Laukhin V. , Balcells Ll. , Martínez B.
Published: December 2007

Microstructural features of La2∕3Ca1∕3MnO3 layers of various thicknesses grown on top of (001) LaAlO3 substrates are studied by using transmission electron microscopy and electron energy loss spectroscopy. Films are of high microstructural quality but exhibit some structural relaxation and mosaicity both when increasing thickness or after annealing processes. The existence of a cationic segregation process of La atoms toward free surface has been detected, as well as a Mn oxidation state variation through layer thickness. La diffusion would lead to a Mn valence change and, in turn, to reduced magnetization.
Insight into the adsorption competition and the relationship between dissociation and association reactions in ammonia synthesis
Authors: Song Tao , Hu P.
Published: December 2007

Ammonia synthesis on three metal surfaces (Zr, Ru, and Pd) is investigated using density functional theory calculations. In addition to N2 dissociation, all the transition states of the hydrogenation reactions from N to NH3 are located and the reaction energy profiles at both low and high surface coverages are compared and analyzed. The following are found: (i) Surface coverage effect on dissociation reactions is more significant than that on association reactions. (ii) The difference between N and H chemisorption energies, the so-called chemisorption energy gap which is a measure of adsorption competition, is vital to the reactivity of the catalysts. (iii) The hydrogenation barriers can considerably affect the overall rate of ammonia synthesis. A simple model to describe the relationship between dissociation and association reactions is proposed.
The structural and electronic properties of Ag-adsorbed (SiO2)n (n=1–7) clusters
Authors: Zhao Gao-feng , Zhi Li-li , Guo Ling-ju , Zeng Zhi
Published: December 2007

Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO2)n (n=1–7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO2)n (n=1–7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO2)n (n=1–7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au3(SiO2)3 cluster.
Dyson orbitals for ionization from the ground and electronically excited states within equation-of-motion coupled-cluster formalism: Theory, implementation, and examples
Authors: Melania Oana C. , Krylov Anna I.
Published: December 2007

Implementation of Dyson orbitals for coupled-cluster and equation-of-motion coupled-cluster wave functions with single and double substitutions is described and demonstrated by examples. Both ionizations from the ground and electronically excited states are considered. Dyson orbitals are necessary for calculating electronic factors of angular distributions of photoelectrons, Compton profiles, electron momentum spectra, etc, and can be interpreted as states of the leaving electron. Formally, Dyson orbitals represent the overlap between an initial N-electron wave function and the N−1 electron wave function of the corresponding ionized system. For the ground state ionization, Dyson orbitals are often similar to the corresponding Hartree-Fock molecular orbitals (MOs); however, for ionization from electronically excited states Dyson orbitals include contributions from several MOs and their shapes are more complex. The theory is applied to calculating the Dyson orbitals for ionization of formaldehyde from the ground and electronically excited states. Partial-wave analysis is employed to compute the probabilities to find the ejected electron in different angular momentum states using the freestanding and Coulomb wave representations of the ionized electron. Rydberg states are shown to yield higher angular momentum electrons, as compared to valence states of the same symmetry. Likewise, faster photoelectrons are most likely to have higher angular momentum.
A density functional study of YnAl (n=1–14) clusters
Authors: Zhao Gao-feng , Zhang Jun , Jing Qun , Luo You-hua , Wang Yuan-xu
Published: December 2007

The geometries, stabilities, and electronic and magnetic properties of YnAl (n=1–14) clusters have been systematically investigated by using density functional theory with generalized gradient approximation. The growth pattern for different sized YnAl (n=1–14) clusters is Al-substituted Yn+1 clusters and it keeps the similar frameworks of the most stable Yn+1 clusters except for Y9Al cluster. The Al atom substituted the surface atom of the Yn+1 clusters for n<9. Starting from n=9, the Al atom completely falls into the center of the Y-frame. The Al atom substituted the center atom of the Yn+1 clusters to form the Al-encapsulated Yn geometries for n>9. The calculated results manifest that doping of the Al atom contributes to strengthen the stabilities of the yttrium framework. In addition, the relative stability of Y12Al is the strongest among all different sized YnAl clusters, which might stem from its highly symmetric geometry. Mulliken population analysis shows that the charges always transfer from Y atoms to Al atom in all different sized clusters. Doping of the Al atom decreases the average magnetic moments of most Yn clusters. Especially, the magnetic moment is completely quenched after doping Al in the Y13, which is ascribed to the disappearance of the ininerant 4d electron spin exchange effect. Finally, the frontier orbitals properties of YnAl are also discussed.
A group contribution method for associating chain molecules based on the statistical associating fluid theory (SAFT-γ)
Authors: Lymperiadis Alexandros , Adjiman Claire S. , Galindo Amparo , Jackson George
Published: December 2007

A predictive group-contribution statistical associating fluid theory (SAFT-γ) is developed by extending the molecular-based SAFT-VR equation of state [A. Gil-Villegas et al. J. Chem. Phys. 106, 4168 (1997)] to treat heteronuclear molecules which are formed from fused segments of different types. Our models are thus a heteronuclear generalization of the standard models used within SAFT, comparable to the optimized potentials for the liquid state OPLS models commonly used in molecular simulation; an advantage of our SAFT-γ over simulation is that an algebraic description for the thermodynamic properties of the model molecules can be developed. In our SAFT-γ approach, each functional group in the molecule is modeled as a united-atom spherical (square-well) segment. The different groups are thus characterized by size (diameter), energy (well depth) and range parameters representing the dispersive interaction, and by shape factor parameters (which denote the extent to which each group contributes to the overall molecular properties). For associating groups a number of bonding sites are included on the segment: in this case the site types, the number of sites of each type, and the appropriate association energy and range parameters also have to be specified. A number of chemical families (n-alkanes, branched alkanes, n-alkylbenzenes, mono- and diunsaturated hydrocarbons, and n-alkan-1-ols) are treated in order to assess the quality of the SAFT-γ description of the vapor-liquid equilibria and to estimate the parameters of various functional groups. The group parameters for the functional groups present in these compounds (CH3, CH2, CH3CH, ACH, ACCH2, CH2, CH, and OH) together with the unlike energy parameters between groups of different types are obtained from an optimal description of the pure component phase equilibria. The approach is found to describe accurately the vapor-liquid equilibria with an overall %AAD of 3.60% for the vapor pressure and 0.86% for the saturated liquid density. The fluid phase equilibria of some larger compounds comprising these groups, which are not included in the optimization database and some binary mixtures are examined to confirm the predictive capability of the SAFT-γ approach. A key advantage of our method is that the binary interaction parameters between groups can be estimated directly from an examination of pure components alone. This means that as a first approximation the fluid-phase equilibria of mixtures of compounds comprising the groups considered can be predicted without the need for any adjustment of the binary interaction parameters (which is common in other approaches). The special case of molecular models comprising tangentially bonded (all-atom and united-atom) segments is considered separately; we comment on the adequacy of such models in representing the properties of real molecules.
Unusual refractions in photonic crystals based on polymer-dispersed liquid crystal films
Authors: Wu Shing-Trong , Li Ming Shian , Fuh Andy Ying-Guey
Published: December 2007

This work describes unusual refractive phenomena from a hexagonally close-packed (hcp) photonic crystal (PC) based on a holographic polymer dispersed liquid crystal film. The refracted collimated beams comprise positive and negative refractions and can be switched to exhibit the negative refraction part only by changing the incident angle or the wavelength of the incident beam. The equal frequency surfaces are adopted to analyze the refractions of light both inside and outside the hcp PC.
A simple model to predict the temperature dependence of elastic moduli of bulk metallic glasses
Authors: Zhang Zhiying , Keppens Veerle , Egami Takeshi
Published: December 2007

We report a simple model to predict the temperature dependence of elastic moduli of bulk metallic glasses from room temperature measurements, using the Varshni equation and the basic assumption that between absolute zero and the melting point, the shear and bulk moduli change, respectively, by 45% and 22%. This model has been tested using experimental data obtained on a large variety of bulk metallic glasses, and the predicted values are found to be in very good agreement with the experimental results.
Pressure measurements in laboratory-scale blast wave flow fields
Authors: Rahman S. , Timofeev E. , Kleine H.
Published: December 2007

The present study examines the effects that temporal and spatial averagings due to finite size and finite response time of pressure transducers have on the pressure measurements in blast wave flow fields generated by milligram charges of silver azide. In such applications, the characteristic time and length scales of the physical process are of the same order of magnitude as the temporal and spatial characteristics of the transducer. The measured pressure values will then be spatially and temporally averaged, and important parameters for the assessment of blast effects may not be properly represented in the measured trace. In this study, face-on and side-on pressure transducer setups are considered. In the experiments, face-on and side-on readings at the same distance from the charge as well as time-resolved optical visualization of the whole flow field are obtained simultaneously for the same explosive event. The procedure of data extraction from the experimental pressure traces is revisited and discussed in detail. In the numerical modeling part of the study, numerical blast flow fields are generated using an Euler flow solver. A numerical pressure transducer model is developed to qualitatively simulate the averaging effects. The experimental and numerical data show that the results of pressure measurements in experiments with small charges must be used with great caution. The effective averaging of the pressure signal may lead to a significant underestimation of blast wave intensities. The side-on setup is especially prone to this effect. The face-on setup provides results close to those obtained from optical records only if the pressure transducer is sufficiently remote from the charge.
Epitaxial orientation of Mg2Si(110) thin film on Si(111) substrate
Authors: Wang Y. , Wang X. N. , Mei Z. X. , Du X. L. , Zou J. , Jia J. F. , Xue Q. K. , Zhang X. N. , Zhang Z.
Published: December 2007

Epitaxial Mg2Si(110) thin film has been obtained on Si(111) substrate by thermally enhanced solid-phase reaction of epitaxial Mg film with underlying Si substrate. An epitaxial orientation relationship of Si(111)∥Mg2Si(110) and Si⟨11¯0⟩∥Mg2Si⟨11¯0⟩ has been revealed by transmission electron microscopy. The formation of the unusual epitaxial orientation relationship is attributed to the strain relaxation of Mg2Si film in a MgO∕Mg2Si∕Si double heterostructure.
Configurations of Coulomb clusters in plasma
Authors: Kamimura Tetsuo , Suga Yuta , Ishihara Osamu
Published: December 2007

The structures of Coulomb clusters formed by dust particles in a plasma are studied by numerical simulation. The present study reveals the presence of various types of self-organized structures of clusters confined in an electrostatic potential. The stable configurations depend on the number of dust particles in a cluster as well as on the form of the confining potential. One-dimensional strings, two-dimensional Coulomb lattices, and three-dimensional Coulomb crystals found in the simulation agree well with the observation in the laboratory dust plasma experiments. Elongated axisymmetric Coulomb clusters are found to be composed of a few fundamental configurations. The dynamical features of Coulomb clusters are also studied by the simulation.
Schottky barriers to colloidal quantum dot films
Authors: Clifford Jason P. , Johnston Keith W. , Levina Larissa , Sargent Edward H.
Published: December 2007

We elucidate experimentally a quantitative physical picture of the Schottky barrier formed at the junction between a metallic contact and a semiconducting colloidal quantum dot film. We used a combination of capacitance-voltage and temperature-dependent current-voltage measurements to extract the key parameters of the junction. Three differently processed Al∕PbS colloidal quantum dot junction devices provide rectification ratios of 104, ideality factors of 1.3, and minimal leakage currents at room temperature. The Schottky barrier height is 0.4eV and the built-in potential 0.3V. The depletion width ranges from 90to150nm and the acceptor density ranges from 2×1016to7×1016cm−3.
Dopant-site effect in superconducting diamond (111) studied by atomic stereophotography
Authors: Kato Yukako , Matsui Fumihiko , Shimizu Tatsuya , Daimon Hiroshi , Matsushita Tomohiro , Guo Fang Zhun , Tsuno Takashi
Published: December 2007

We studied the cause of high TC of superconducting boron-doped diamond (111) when compared with that of (001) even at the same boron concentration. The atomic stereophotograph revealed that a disproportionate boron concentration is located at one of the two sites in (111). The distinction of the dopant site exists only in (111) surface and does not exist in (001) surface. Furthermore, there is a theoretical prediction of high density of state at Fermi level in ordered dopant diamonds. Therefore, this configuration should be the origin of the higher TC of (111) as compared with that of (001).
Characterization of the dielectric properties and alternating current conductivity of the SrBi5−xLaxTi4FeO18 (x=, 0.2) compound
Authors: Almodovar N. S. , Portelles J. , Raymond O. , Heiras J. , Siqueiros J. M.
Published: December 2007

Lanthanum-doped bismuth layer-structured ferroelectric ceramics SrBi5−xLaxTi4FeO18 (x=0,0.2) were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phases were formed. Hysteresis loops at room temperature (20 °C) show that the La-doped ceramic presents a slightly lower spontaneous polarization than the undoped compound. Measurements of relative permittivity and dielectric loss versus temperature were performed from room temperature to 700 °C in the 100 Hz–1 MHz frequency range. Three anomalies were observed in the thermal behavior of the relative permittivity in both samples. Anomalies around the temperatures of 465 and 430 °C have been identified as the ferroelectric-paraelectric transition temperatures for the x=0 and 0.2 compounds, respectively. The sizable shift of the transition temperatures toward lower temperatures with the La doping is interpreted as a manifestation of the La ion incorporation into the crystal structure. From the conductivity studies, the activation energies as functions of frequency for three different temperature zones are obtained. It is found that activation energies are strongly frequency dependent, particularly in the low-frequency region. The frequency dependence of the conductivity at different temperatures was analyzed using Jonscher’s power law and the Almond-West conductivity formalism.
Structural modification of a multiply twinned nanoparticle by ion irradiation: A molecular dynamics study
Authors: Järvi T. T. , Kuronen A. , Nordlund K. , Albe K.
Published: December 2007

We study the possibility of modifying the structure of a multiply twinned nanoparticle by ion irradiation. Molecular dynamics simulations are carried out for the prototypic case of a metastable icosahedral Pt particle bombarded with He and Xe ions in the energy range of 0.1–10keV. A single xenon impact can be used to melt the particle. It can also induce partial melting, which causes a collapse of the twin boundary structure in the solid part and transformation to single crystalline morphology. Under He irradiation, we observe a saturation of the vacancy concentration, but no untwinning.
Effects of plasma loss on the luminous efficacy in a full high definition alternating current plasma display panel
Authors: Bae Hyun Sook , Kim Joong Kyun , Jung Hae Yoon , Lim Jong Keun , Whang Ki-Woong
Published: December 2007

We have investigated the effect of cell resolution change on the luminous efficacy of an alternating current plasma display panel with the three-dimensional plasma simulation. The luminous efficacy decreased and the minimum sustain voltage increased as the resolution increased from VGA to full high definition (HD) resolution, due to the increased particle loss to the enclosing surfaces. A simple increase of the Xe content to realize the high luminous efficacy resulted in a much enhanced luminous efficacy decremental ratio as the cell resolution increases because of the increased plasma loss and decreased electron heating efficacy. We are proposing some effective ways of realizing high luminous efficacy in the high resolution 50-in. full HD cell, such as the increase of the sustain electrode gap, the adoption of a segmented electrode in delta color arrayed, enclosed subpixel, type cell with 4:3 aspect ratio, and the optimization of the barrier rib height. Because the adoption of those geometrical parameters causes the reduced plasma loss, the transport efficacy of visible light from phosphor through the front plate in a full HD cell resulted in much increased improvement with the increase of Xe content.
Germanium-rich silicon-germanium films epitaxially grown by ultrahigh vacuum chemical-vapor deposition directly on silicon substrates
Authors: Cannon Douglas D. , Liu Jifeng , Danielson David T. , Jongthammanurak Samerkhae , Enuha Uchechukwu U. , Wada Kazumi , Michel Jurgen , Kimerling Lionel C.
Published: December 2007

We have grown device quality germanium-rich silicon-germanium films on silicon substrates using a two-step ultrahigh vacuum chemical-vapor deposition growth process. The films have thermally induced tensile strain, resulting in a direct band gap reduction of ∼30meV, in agreement with what we observe for similarly grown pure germanium films. Our data suggest that alloying of silicon increases the band gap reduction with strain at the high germanium end of the composition range. Annealing of the films allows for reduction in the dislocation density to 2×107∕cm2, comparable to what we achieve in pure germanium films and showing that alloying small amounts of silicon does not inhibit dislocation motion. p-i-n diodes fabricated from these films using a silicon compatible process exhibit reverse leakage currents of ∼10mA∕cm2 at 0.5V reverse bias. The responsivity of a Si0.04.8Ge0.952 diode was measured at 0.23A∕W at 1280nm, demonstrating the high quality of these epitaxial films.
Magnetic field-dependent photoluminescence linewidths as a probe of disorder length scales in quantum wells
Authors: Bansal Bhavtosh , Hayne M. , Arora B. M. , Moshchalkov V. V.
Published: December 2007

Photoluminescence from highly disordered GaAs quantum wells is studied in magnetic fields up to 50T. The monotonic decrease of the photoluminescence linewidth with increasing quantum well thickness indicates that interface roughness is the primary source of line broadening. The magnetic field-dependent exciton linewidth shows an unexpected behavior. We observe not only just a monotonic increase in linewidth but also a field-dependent decreasing linewidth in thicker quantum wells. These observations are understood by postulating the existence of two correlation lengths for the interface fluctuations, one much smaller than the exciton size and the other one of the order of the exciton size.
Self-focusing of spin waves in Permalloy microstripes
Authors: Demidov Vladislav E. , Demokritov Sergej O. , Rott Karsten , Krzysteczko Patryk , Reiss Guenter
Published: December 2007

Excitation and propagation of spin waves in Permalloy microstripes magnetized in their plane perpendicularly to the axis have been investigated by means of microfocus Brillouin light scattering spectroscopy with high spatial resolution. We show that the spatial profile of the spin-wave beam demonstrates a focusing at a certain distance from the excitation source depending on the stripe width. A model connecting the observed phenomenon with an interference of different spin-wave modes existing in the stripe due to the finite-size effect is proposed.
Analyzer-based phase contrast imaging and phase retrieval using a rotating anode x-ray source
Authors: Vine D. J. , Paganin D. M. , Pavlov K. M. , Kräußlich J. , Wehrhan O. , Uschmann I. , Förster E.
Published: December 2007

We have performed an analyzer crystal based phase contrast imaging (ABI) experiment using a rotating anode x-ray source. The use of such an incoherent source demonstrates the potential of ABI as a quantitative characterization tool for the laboratory environment. A phase contrast image of a plastic phantom was recorded on high resolution x-ray film and the projected thickness was retrieved from a single image. The projected thickness recovered from the phase contrast image was shown to quantitatively agree with a reference optical microscope measurement.
Negative index of refraction observed in a single layer of closed ring magnetic dipole resonators
Authors: Hao Zhao , Martin Michael C. , Harteneck Bruce , Cabrini Stefano , Anderson Erik H.
Published: December 2007

We report the results of a spectroscopic study of a single layer of metallic single closed ring resonators on freestanding thin membrane at near normal and grazing angles of incidence. When the magnetic component of the light is perpendicular to the ring plane, we observe a negative index of refraction down to −1 around 150THz, attributed to a strong magnetic dipolar resonance and a broad electric resonance in this metamaterial. We experimentally identify the different resonance modes and the spectral region of negative refractive index on a series of samples with different feature and lattice sizes, comparing to electromagnetic simulations.
Dielectric and nonlinear electrical behaviors observed in Mn-doped CaCu3Ti4O12 ceramic
Authors: Cai Jingnan , Lin Yuan-Hua , Cheng Bo , Nan Ce-Wen , He Jinliang , Wu Yongjun , Chen Xiangming
Published: December 2007

We present a remarkable effect of Mn doping on the dielectric and nonlinear electric properties of CaCu3Ti4O12 ceramics. The results indicate that only 2.5at.% Mn doping can suppress the dielectric permitivity in CaCu3Ti4O12 by up to two orders of magnitude (from 104 to 102), and the nonlinear varistor characteristics disappear completely, which should be mainly ascribed to the decrease of potential barrier height at the grain boundary and charge compensation for the conduction electrons caused by the Mn doping.
10
ns
pulsed atmospheric air plasma for uniform treatment of polymeric surfaces
Authors: Walsh J. L. , Kong M. G.
Published: December 2007

This letter reports an experimental study of a 10ns pulsed dielectric barrier discharge in atmospheric air, excited with a train of 65ns voltage pulses at a repetition frequency of 5kHz. It is shown that these ultrashort pulses produce a homogenous discharge with very high electron density in excess of 1013cm−3 and low gas temperature, which are particularly desirable for uniform treatment of thermally sensitive polymer films. Their treatment of polypropylene films is found to introduce microscale surface patterns as well as various carbon-oxygen bonds, both useful for improving the hydrophilic properties of polymeric materials.
From Dirac spinor fields to eigenspinoren des ladungskonjugationsoperators
Authors: da Rocha R. , Hoff da Silva J. M.
Published: December 2007

Dual-helicity eigenspinors of the charge conjugation operator [eigenspinoren des ladungskonjugationsoperators (ELKO) spinor fields] belong—together with Majorana spinor fields—to a wider class of spinor fields, the so-called flagpole spinor fields, corresponding to the class (5), according to Lounesto spinor field classification based on the relations and values taken by their associated bilinear covariants. There exists only six such disjoint classes: the first three corresponding to Dirac spinor fields, and the other three, respectively, corresponding to flagpole, flag-dipole, and Weyl spinor fields. This paper is devoted to investigate and provide the necessary and sufficient conditions to map Dirac spinor fields to ELKO, in order to naturally extend the standard model to spinor fields possessing mass dimension 1. As ELKO is a prime candidate to describe dark matter, an adequate and necessary formalism is introduced and developed here, to better understand the algebraic, geometric, and physical properties of ELKO spinor fields, and their underlying relationship to Dirac spinor fields.
Experiments on single event electrospraying
Authors: Stachewicz Urszula , Dijksman J. Frits , Yurteri Caner U. , Marijnissen Jan C. M.
Published: December 2007

In order to use electrospraying as an on demand deposition method, well defined and reproducible single electrospraying events have been studied. To generate a single electrospraying event, rectangular voltage pulses superimposed on a constant bias voltage were applied, and optimum settings of the bias dc voltage for starting such an event were found. This onset point is related to a critical value of the effective surface tension before dripping starts.
Response of a laterally vibrating nanotip to surface forces
Authors: Yurtsever Ayhan , Gigler Alexander M. , Macias Eduardo , Stark Robert W.
Published: December 2007

The torsional eigenmodes of atomic force microscope (AFM) cantilevers are highly sensitive toward in-plane material properties of the sample. We studied the effect of viscosity and lateral contact stiffness on the detuning, amplitude, and phase response numerically. To verify the theoretical considerations, a torsion mode AFM was operated in frequency modulation. During approach and retract cycles, we observed a negative detuning of the torsional resonant frequency close to the sample surface depending on the tilt angle between the tip and the sample. Thus, the tilt has a significant effect on the imaging process in torsional resonance mode.
Terahertz pulse generation from noble gases
Authors: Chen Yunqing , Yamaguchi Masashi , Wang Mingfeng , Zhang X.-C.
Published: December 2007

Terahertz pulse generation in the laser-induced plasma from a series of noble gases (He, Ne, Ar, Kr, and Xe) was systematically investigated. Femtosecond laser pulses consisting of both a fundamental and its second-harmonic frequency were used for the terahertz generation. Experimental results reveal that terahertz generation efficiency of these noble gases increases with decreasing ionization potential.
Making a field effect transistor on a single graphene nanoribbon by selective doping
Authors: Huang Bing , Yan Qimin , Zhou Gang , Wu Jian , Gu Bing-Lin , Duan Wenhui , Liu Feng
Published: December 2007

Using first-principles electronic structure calculations, we show a metal-semiconductor transition of a metallic graphene nanoribbon with zigzag edges induced by substitutional doping of nitrogen or boron atoms at the edges. A field effect transistor consisting of a metal-semiconductor-metal junction can then be constructed by selective doping of the ribbon edges. The current-voltage characteristics of such a prototype device is determined by the first-principles quantum transport calculations.
Enhancement of piezoelectric and pyroelectric properties of composite films using polymer electrolyte matrix
Authors: Chau K. H. , Wong Y. W. , Shin F. G.
Published: December 2007

Composite films consisting of lead zirconate titanate (PZT) inclusions dispersed in a matrix of polymer electrolyte the polyethylene oxide were fabricated. Their piezoelectric coefficients d33 and pyroelectric coefficients p are increased almost proportional to the volume fraction of the ferroelectric ceramic phase. For 34% PZT composite, d33 and p are 170pC∕N and 120μC∕m2K, respectively, they are much larger than PZT/polyvinylidene fluoride-trifluoroethylene composite with similar ceramics content. It is believed that the enhancement of the measured coefficients is due to the relatively high electrical conductivity of polymer electrolyte matrix. This is confirmed by theoretical models which consider the conductivity of matrix.
Fetal gender screening by ultrasound at 11 to 13+6 weeks
Authors: HSIAO C.H. , WANG H.C. , HSIEH C.F. , HSU J.J.
Published: December 2007

Background. To survey the accuracy of fetal gender determination during first trimester screening and scan for congenital anomalies. Methods. A prospective observational study was performed on 496 singleton pregnancies at the first trimester ultrasound screening. The doctor was a certified sonographer of first trimester screening by the Fetal Medicine Foundation (FMF). Ultrasound examination was performed on a GE Voluson 730 Pro, transabdominally, between 11 and 13+6 weeks. Both transverse and mid‐sagittal planes of a section of the fetal genital tubercle were performed to identify the gender. The subsequent gender at birth was obtained from karyotyping reports or hospital birth records. Results. During the study, 496 patients requested gender information at the time of first trimester screening. Of the patients it was possible to determine gender (441 out of 496), the scan achieved an overall success rate of 91.8% in correctly identifying gender. The success rate for correctly identifying fetal gender (where identification was possible) increased with gestational age, from 71.9% at 11 weeks, 92% at 12 weeks, and 98.3% at 13 weeks, respectively, where gestational age was calculated from the crown‐rump length in conjunction with menstrual or ovulation dating (p<0.001). Of the 55 cases where no identification of gender was possible, 39 were in the 11‐week gestational age group, representing 40.6% of this category. The overall fetal gender accuracy rate for male fetus was slightly better than female (92.5 versus 91.2%), but was not statistically significant. Conclusions. This study demonstrated that the gestational age of the fetus has a material effect on the accuracy rate of gender determination. At 12 weeks and over, the average success rate for correctly identifying gender, where gender identification was possible, was 94.8%, with the accuracy at 13 weeks of 98.3% approaching that achieved by invasive testing. Fetal gender identification at 11 weeks (where crown‐rump length is <57 mm) is difficult and liable to high rates of inaccuracy when a determination is made.
Male factor infertility, low fertilisation rate following ICSI and low number of high‐quality embryos are associated with high order recurrent implantation failure in young IVF patientsa
Authors: FARHI JACOB , FARHI JACOB , BEN‐HAROUSH AVI , DRESLER HADAS , PINKAS HAIM , SAPIR ONIT , FISCH BENJAMIN
Published: December 2007

Background. The aim of this study was to characterise the clinical and laboratory parameters in young in vitro fertilisation (IVF) patients with high order recurrent implantation failure (RIF). Methods: The first 3 cycles (n = 141 cycles) of 47 consecutive (age <35 years) couples with RIF (≥6 IVF cycles) were compared with 252 consecutive cycles of 152 couples, treated during the same period, who conceived within the first 3 IVF cycles. Results. The incidence of male factor infertility or of combined male and female factors was significantly higher in the study group than the control group (male factor: 78.7 versus 42.5%, p = 0.002, OR =3.2 (95% CI: 1.5–6.8)). Lower fertilisation rates were noted for the intracytoplasmic sperm injection (ICSI)‐treated oocytes of the study group compared with the control group. The availability of high quality embryos for transfer was significantly lower in the RIF group. On multivariate logistic regression analysis, the significantly different variables between the groups were cause of infertility (male factor or combined male and female factors) (p = 0.03), fertilisation rate (p = 0.038), and semen concentration (p = 0.05). Conclusions. Young IVF patients with high order RIF are characterised by male factor infertility, lower fertilisation rate with ICSI, and fewer high quality embryos available for transfer.
What is the recurrence rate of postmenopausal bleeding in women who have a thin endometrium during a first episode of postmenopausal bleeding?
Authors: VAN DOORN H.C. , TIMMERMANS A. , OPMEER B.C. , KRUITWAGEN R.F.M.P. , DIJKHUIZEN F.P.H.L.J. , KOOI G.S. , VAN DE WEIJER P.H.M. , MOL B.W.J. ,   FOR DUPOMEB (DUTCH STUDY IN POSTMENOPAUSAL BLEEDING)
Published: December 2007

Objective. To determine the incidence and significance of recurrent postmenopausal bleeding among women diagnosed with an endometrial thickness ≤4 mm after a first episode of postmenopausal bleeding. Methods. Consecutive patients not using hormone replacement therapy (HRT) presenting with a first episode of postmenopausal bleeding and an endometrial thickness ≤4 mm at transvaginal ultrasonography (TVU) were managed expectantly. In case of recurrent bleeding, the patient was evaluated according to the hospital's local policy with TVU, office endometrial sampling, hysteroscopy or dilatation and curettage (D&C) or a combination of these tests. We evaluated the incidence of recurrent bleeding, potential risk factors for recurrent bleeding, and the diagnosis made after recurrent bleeding. Results. A total of 607 patients were registered with a first episode of postmenopausal bleeding, of whom 249 had an endometrial thickness ≤4 mm. Follow‐up took place with a median of 174 weeks (range: 4–250 weeks). During follow‐up, 25 of the 249 patients (10%; 95% CI: 6.6–14%) had recurrent bleeding. Median time until recurrence of bleeding was 49 weeks (range: 9–186 weeks). Two patients with recurrent bleeding turned out to have an endometrial carcinoma (8%; 95% CI: 2.2–25%), and 1 patient had a malignant melanoma. Time since menopause, age, body mass index, hypertension, diabetes and anticoagulants were not predictive for recurrent bleeding. Conclusion. The recurrence rate after a first episode of postmenopausal bleeding managed expectantly is low and cannot be predicted by patient characteristics. Patients with recurrent bleeding should be re‐evaluated, as they bear a considerable risk of carcinoma.
Factors influencing pregnancy outcome in women with type 2 versus type 1 diabetes mellitus
Authors: GONZALEZ‐GONZALEZ NIEVES LUISA , RAMIREZ OCTAVIO , MOZAS JUAN , MELCHOR JUAN , ARMAS HONORIO , GARCIA‐HERNANDEZ JOSE ANGEL , CABALLERO AGUEDA , HERNANDEZ MARTA , DIAZ‐GOMEZ MARTA NIEVES , JIMENEZ ALEJANDRO , PARACHE JAVIER , BARTHA JOSE LUIS
Published: December 2007

Aim. To compare pregnancy outcome and factors related to adverse perinatal outcome in women with type 1 versus type 2 diabetes mellitus (DM). Material and methods. Multicentre retrospective study. Some 404 women were studied, 257 with type 1 DM and 147 with type 2 DM. Main outcome measures were rates of prematurity, macrosomia, instrumental deliveries, congenital malformations, need for neonatal intensive care unit (NICU), and perinatal mortality. Results. There were no significant differences in pregnancy outcome between women with type 1 and type 2 DM, except for an increased rate of instrumental deliveries in women with type 1 DM. In these women, duration of diabetes was a significant predictor of caesarean delivery (OR =1.06 (1.01–1.12); p = 0.02). Chronic hypertension was positively related to prematurity (p = 0.02), and proved to be a significant predictor of birth weight lower than 2,500 g (OR =3.54 (1.4–12.49); p = 0.043) and perinatal mortality (OR =10.6 (1.15–117.6); p = 0.04). In women with type 2 DM, third trimester higher glycosylated haemoglobin was related to both prematurity (OR 4.9 (1.7–14.4; p = 0.004) and low birth weight. Macrosomia was a significant risk factor for caesarean section. First trimester glycosylated haemoglobin was related to congenital malformations and proved to be a significant predictor of perinatal mortality (OR =2.4 (1.02–5.74); p = 0.04). Conclusions. Duration of DM and chronic hypertension were the most influential factors related to adverse perinatal outcomes in women with type 1 DM, and poor metabolic control and macrosomia in women with type 2 DM.
Endometrial thermal balloon ablation has a beneficial long‐term effect on menorrhagia
Authors: AHONKALLIO SARI , MARTIKAINEN HANNU , SANTALA MARKKU
Published: December 2007

Background. More data on the long‐term results of thermal balloon endometrial ablation are needed. Methods. A retrospective observational study of 190 women who underwent endometrial thermal balloon ablation in the treatment of menorrhagia. The mean follow‐up period was 6 years. Results. Of the 172 women analysed after exclusion, 28 (16%) had a hysterectomy during follow‐up. Women with regular menstrual periods had the best outcome. Some 152 (89%) women filled in a questionnaire concerning their satisfaction with the procedure, and 76% were satisfied. Amenorrhoea was reported by 14% and eumenorrhoea by 54% of the women who completed the questionnaire. Conclusion. Endometrial thermal balloon ablation has good long‐term efficacy and can be considered an applicable alternative in the treatment of menorrhagia, especially for women who have regular periods and are over 40 years of age.
Adverse pregnancy outcome in women with mild glucose intolerance: is there a clinically meaningful threshold value for glucose?
Authors: JENSEN DORTE M. , KORSHOLM LARS , OVESEN PER , BECK‐NIELSEN HENNING , MØLSTED‐PEDERSEN LARS , DAMM PETER
Published: December 2007

Background. The diagnostic criteria of gestational diabetes mellitus (GDM) have been based on the risk of future maternal diabetes rather than the short‐term risk of mother and infant. Our aim was to illustrate the relation between various adverse pregnancy outcomes and maternal glucose levels in women with mild glucose intolerance using a graphical approach. Methods. Observational study of 2,885 pregnant women examined with a 2‐h, 75‐g oral glucose tolerance test (OGTT) based on risk indicators. Only women with 2‐h capillary blood glucose <9.0 mmol/l were included, as women with 2‐h values ≥9.0 mmol/l were treated for GDM. Empirical frequencies of adverse outcomes were related to 2‐h values by linear and quadratic logistic models. Adjustments for well‐known confounders were performed by a multiple logistic model. Results. Linear trends were demonstrated for the outcomes: shoulder dystocia, caesarean section rate (univariate analysis only), spontaneous preterm delivery, and macrosomia (large‐for‐gestational age infants). None of the outcomes deviated significantly from linearity. No significant trend was found for hypertension or neonatal hypoglycaemia and jaundice. Conclusions. A gradually increasing risk for a number of adverse pregnancy outcomes was found with increasing glucose levels. No obvious threshold value for GDM was demonstrated for 2‐h values up to 9.0 mmol/l.
The 1918–1919 influenza pandemic in England and Wales: spatial patterns in transmissibility and mortality impact
Authors: Chowell Gerardo , Bettencourt Luís M.A , Johnson Niall , Alonso Wladimir J , Viboud Cécile
Published: December 2007

Spatial variations in disease patterns of the 1918–1919 influenza pandemic remain poorly studied. We explored the association between influenza death rates, transmissibility and several geographical and demographic indicators for the autumn and winter waves of the 1918–1919 pandemic in cities, towns and rural areas of England and Wales. Average measures of transmissibility, estimated by the reproduction number, ranged between 1.3 and 1.9, depending on model assumptions and pandemic wave and showed little spatial variation. Death rates varied markedly with urbanization, with 30–40% higher rates in cities and towns compared with rural areas. In addition, death rates varied with population size across rural settings, where low population areas fared worse. By contrast, we found no association between transmissibility, death rates and indicators of population density and residential crowding. Further studies of the geographical mortality patterns associated with the 1918–1919 influenza pandemic may be useful for pandemic planning.
Nanotribology, nanomechanics and nanomaterials characterization
Authors: Bhushan Bharat
Published: December 2007

Nanotribology and nanomechanics studies are needed to develop fundamental understanding of interfacial phenomena on a small scale and to study interfacial phenomena in magnetic storage devices, nanotechnology and other applications. Friction and wear of lightly loaded micro/nanocomponents are highly dependent on the surface interactions (a few atomic layers). These structures are generally coated with molecularly thin films. Nanotribology and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures and provide a bridge between science and engineering. An atomic force microscope (AFM) tip is used to simulate a single-asperity contact with a solid or lubricated surface. AFMs are used to study the various tribological phenomena that include surface roughness, adhesion, friction, scratching, wear and boundary lubrication.In situsurface characterization of local deformation of materials and thin coatings can be carried out using a tensile stage inside an AFM. Mechanical properties such as hardness, Young's modulus of elasticity and creep/relaxation behaviour can be determined on micro- to picoscales using a depth-sensing indentation system in an AFM.
Controlled exchange of chromosomal arms reveals principles driving telomere interactions in yeast
Authors: Schober Heiko , Kalck Véronique , Vega-Palas Miguel A. , Van Houwe Griet , Sage Daniel , Unser Michael , Gartenberg Marc R. , Gasser Susan M.
Published: December 2007

The 32 telomeres in the budding yeast genome cluster in three to seven perinuclear foci. Although individual telomeres and telomeric foci are in constant motion, preferential juxtaposition of some telomeres has been scored. To examine the principles that guide such long-range interactions, we differentially tagged pairs of chromosome ends and developed an automated three-dimensional measuring tool that determines distances between two telomeres. In yeast, all chromosomal ends terminate in TG1–3 and middle repetitive elements, yet subgroups of telomeres also share extensive homology in subtelomeric coding domains. We find that up to 21 kb of >90% sequence identity does not promote telomere pairing in interphase cells. To test whether unique sequence elements, arm length, or chromosome territories influence juxtaposition, we reciprocally swapped terminal domains or entire chromosomal arms from one chromosome to another. We find that the distal 10 kb of Tel6R promotes interaction with Tel6L, yet only when the two telomeres are present on the same chromosome. By manipulating the length and sequence composition of the right arm of chr 5, we confirm that contact between telomeres on opposite chromatid arms of equal length is favored. These results can be explained by the polarized Rabl arrangement of yeast centromeres and telomeres, which promote to telomere pairing by allowing contact between chromosome arms of equal length in anaphase.
Genome-wide discovery and verification of novel structured RNAs inPlasmodium falciparum
Authors: Mourier Tobias , Carret Celine , Kyes Sue , Christodoulou Zoe , Gardner Paul P. , Jeffares Daniel C. , Pinches Robert , Barrell Bart , Berriman Matt , Griffiths-Jones Sam , Ivens Alasdair , Newbold Chris , Pain Arnab
Published: December 2007

We undertook a genome-wide search for novel noncoding RNAs (ncRNA) in the malaria parasitePlasmodium falciparum. We used the RNAz program to predict structures in the noncoding regions of theP. falciparum3D7 genome that were conserved with at least one of seven otherPlasmodiumspp. genome sequences. By using Northern blot analysis for 76 high-scoring predictions and microarray analysis for the majority of candidates, we have verified the expression of 33 novel ncRNA transcripts including four members of a ncRNA family in the asexual blood stage. These transcripts represent novel structured ncRNAs inP. falciparumand are not represented in any RNA databases. We provide supporting evidence for purifying selection acting on the experimentally verified ncRNAs by comparing the nucleotide substitutions in the predicted ncRNA candidate structures inP. falciparumwith the closely related chimp malaria parasiteP. reichenowi. The high confirmation rate within a single parasite life cycle stage suggests that many more of the predictions may be expressed in other stages of the organism’s life cycle.
Laparoscopic Findings in Senescent Patients with Primary Biliary Cirrhosis
Authors: KUROSE Kiyotaka , MASUMOTO Toshikazu , AKBAR S. M. Fazle , MICHITAKA Kojiro , HORIIKE Norio , ONJI Morikazu
Published: December 2007

Abstract: Fifty ‐two patients with primary biliary cirrhosis (PBC), 10 of whom were 65 years or older at the time of diagnosis, were investigated by laparo‐scopy. Laparoscopic findings in these 10 patients were evaluated and compared with those in younger patients. The 10 cases were composed of nine females and one male, and two had been diagnosed as having symptomatic PBC with skin itching, while the remaining eight had asymptomatic PBC. Two, seven and one case were in Scheuer's stage I, II and III, respectively, and eight had chronic non‐suppurative destructive cholangitis (CNSDC) on liver biopsy specimens. The majority of senescent PBC patients had typical findings of the early stage of PBC on the liver surface; mild undulations in nine and reddish patches in eight. The laparoscopic findings in senescent PBC were relatively mild.