bluuebunny/crossref_metadata_2025 huggingface dataset:
The utility of blood glucose meters in biotechnological applications
Authors: FitzGerald Jennifer , Vermerris Wilfred
Published: November 2007

Most methods used to measure glucose concentrations in biotechnological settings are labour‐intensive and/or expensive. With this in mind we have investigated the possibility of employing blood glucose meters, the use of which has the benefit of being fast, convenient and inexpensive, for this purpose. Accu‐Chek® Advantage® (Roche Diagnostics, Indianapolis, IN, U.S.A.) and Precision QID® (Medisense, Abbott Laboratories, Indianapolis, IN, U.S.A.) meters were tested using glucose samples of known concentration, at pH 7.5 and 4.8. The Accu‐Chek® Advantage® meter uses strips containing the enzyme glucose dehydrogenase. This meter showed a linear response for glucose concentrations between 0.50 and 6.0 g/litre, and the effect of pH was small. The Precision QID® meter uses strips containing the enzyme glucose oxidase and is more sensitive to pH. The displayed glucose concentrations at low pH values were consistently lower than at higher pH values. At both pH values the response curve reached a plateau, which limited the effective range of this meter to a range of 0.30–2.5 g/litre. Unlike the Precision QID® meter, the Accu‐Chek® Advantage® meter also responded to xylose and arabinose. A synergistic effect of combining sugars was observed when a mixture of sugars consisting of glucose and arabinose, or glucose and xylose, was applied: the displayed concentrations were consistently higher than was expected on the basis of the individual calibration curves. The use of glucose meters is a fast and convenient alternative to existing methods and may be of particular use for screening purposes where a high degree of accuracy is not crucial. The choice of meter should depend on the application, and in this respect the pH, expected concentration range and the presence of other sugars are among the factors that should be considered.
Pollen‐mediated transformation of Sorghum bicolor plants
Authors: Wang Weiquan , Wang Jingxue , Yang Cuiping , Li Yonghu , Liu Li , Xu Jun
Published: November 2007

Pollen from sorghum (Sorghum bicolor L. Moench) were transformed by a novel genetic transformation approach using mild ultrasonication. The plasmid pBI121 contained the NPT II gene encoding NPT II (neomycin phosphotransferase II) and a GUS (β‐glucuronidase) reporter gene. Plasmid DNA and pollen from sorghum A2V4B were submerged in a 0.3 mol/l sucrose solution and then subjected to ultrasonication. The treated pollen was then used for pollination of stigmas from the male sterile line A2V4A. Detection of transient and stable GUS activity confirmed that the GUS gene was expressed in transgenic plants. PCR amplification and Southern‐blot analysis of transgenic plants confirmed that the NPT II gene had been integrated into the sorghum genome. These results indicate that direct gene transfer to pollen can be mediated by mild ultrasonication.
Enhancing methacrylate‐monolith‐based downstream processes to champion plasmid DNA production
Authors: Danquah Michael K. , Forde Gareth M.
Published: November 2007

Increasing numbers of preclinical and clinical studies are utilizing pDNA (plasmid DNA) as the vector. In addition, there has been a growing trend towards larger and larger doses of pDNA utilized in human trials. The growing demand on pDNA manufacture leads to pressure to make more in less time. A key intervention has been the use of monoliths as stationary phases in liquid chromatography. Monolithic stationary phases offer fast separation to pDNA owing to their large pore size, making pDNA in the size range from 100 nm to over 300 nm easily accessible. However, the convective transport mechanism of monoliths does not guarantee plasmid purity. The recovery of pure pDNA hinges on a proper balance in the properties of the adsorbent phase, the mobile phase and the feedstock. The effects of pH and ionic strength of binding buffer, temperature of feedstock, active group density and the pore size of the stationary phase were considered as avenues to improve the recovery and purity of pDNA using a methacrylate‐based monolithic adsorbent and Escherichia coli DH5α‐pUC19 clarified lysate as feedstock. pDNA recovery was found to be critically dependent on the pH and ionic strength of the mobile phase. Up to a maximum of approx. 92% recovery was obtained under optimum conditions of pH and ionic strength. Increasing the feedstock temperature to 80 °C increased the purity of pDNA owing to the extra thermal stability associated with pDNA over contaminants such as proteins. Results from toxicological studies of the plasmid samples using endotoxin standard (E. coli 0.55:B5 lipopolysaccharide) show that endotoxin level decreases with increasing salt concentration. It was obvious that large quantities of pure pDNA can be obtained with minimal extra effort simply by optimizing process parameters and conditions for pDNA purification.
Water drinking improves orthostatic tolerance in patients with posturally related syncope
Authors: Claydon Victoria E. , Schroeder Christoph , Norcliffe Lucy J. , Jordan Jens , Hainsworth Roger
Published: November 2007

Water drinking improves OT (orthostatic tolerance) in healthy volunteers; however, responses to water in patients with PRS (posturally related syncope) are unknown. Therefore the aim of the present study was to examine whether water would improve OT in patients with PRS. In a randomized controlled cross-over fashion, nine patients with PRS ingested 500 ml and 50 ml (control) of water 15 min before tilting on two separate days. OT was determined using a combined test of head-up tilting and lower body suction and expressed as the time required to induce presyncope. We measured blood pressure and heart rate (using Portapres®) and middle cerebral artery velocity (using transcranial Doppler). SV (stroke volume) and TPR (total peripheral resistance) were calculated using the Modelflow® method. OT was significantly (P<0.02) greater after drinking 500 ml of water than after 50 ml (25.4±1.5 compared with 19.8±2.3 min respectively). After ingestion of 500 ml of water, blood pressure during tilting was higher, the tiltinduced reduction in SV was smaller and the increase in TPR was greater (all P<0.05). The correlation coefficient of the relationship between cerebral blood flow velocity and pressure was lower after 500 ml of water (0.43±0.1 compared with 0.73±0.1; P<0.05), indicating better autoregulation. In conclusion, drinking 500 ml of water increased OT and improved cardiovascular and cerebrovascular control during orthostasis. Patients with PRS should be encouraged to drink water before situations likely to precipitate a syncopal attack.
Expression of adrenomedullin mRNA is altered with gestation and labour in human placenta and fetal membranes
Authors: Al-Ghafra Alfia , Brennecke Shaun P. , King Roger G. , Gude Neil M.
Published: November 2007

The aim of the present study was to investigate whether placental and fetal membrane AdM (adrenomedullin) mRNA expression changes with gestation and human labour, as we have previously found labour-associated changes in AdM content in fetal membranes [Al-Ghafra, Gude, Brennecke and King (2003) Clin. Sci. 105, 419–423]. Placentas and fetal membranes were collected either at term or pre-term from women either in-labour or not-in-labour, and AdM mRNA abundance was measured in tissue extracts by Northern blot analysis. Increases were found in the relative abundance of amniotic tissue AdM mRNA in both in-labour and not-in-labour groups at term compared with those at pre-term, and there were positive correlations with gestational age. Relative abundance of choriodecidual tissue AdM mRNA was also significantly elevated in the not-in-labour groups between pre-term and term tissues, although there was no significant correlation with gestational age. However, placental AdM mRNA expression was neither significantly increased at term (compared with pre-term) nor correlated with gestational age. In addition, there were significant increases in AdM mRNA in amnion and choriodecidua in the in-labour group compared with the not-in-labour group for both pre-term and term gestations. There was no difference in AdM mRNA in placental tissues between labour groups. In conclusion, the present study provides evidence that AdM production by fetal membranes is increased in amniotic and choriodecidual tissues at term, compared with pre-term, and in response to labour.
ACE2 overexpression inhibits hypoxia-induced collagen production by cardiac fibroblasts
Authors: Grobe Justin L. , Der Sarkissian Shant , Stewart Jillian M. , Meszaros J. Gary , Raizada Mohan K. , Katovich Michael J.
Published: November 2007

Cardiac remodelling is a key risk factor for the development of heart failure in the chronic phase following myocardial infarction. Our previous studies have shown an anti-remodelling role of ACE2 (angiotensin-converting enzyme 2) in vivo during hypertension and that these protective effects are mediated through increased circulating levels of Ang-(1–7) [angiotensin-(1–7)]. In the present study, we have demonstrated that cardiac myocytes have modest ACE2 activity, whereas cardiac fibroblasts do not exhibit any endogenous activity. As fibroblasts are the major cell type found in an infarct zone following a myocardial infarction, we examined the effects of ACE2 gene delivery to cultured cardiac fibroblasts after acute hypoxic exposure. Cardiac fibroblasts from 5-day-old Sprague–Dawley rat hearts were grown to confluence and transduced with a lentiviral vector containing murine ACE2 cDNA under transcriptional control by the EF1α (elongation factor 1α) promoter (lenti-ACE2). Transduction of fibroblasts with lenti-ACE2 resulted in a viral dose-dependent increase in ACE2 activity. This was associated with a significant attenuation of both basal and hypoxia/re-oxygenation-induced collagen production by the fibroblasts. Cytokine production, specifically TGFβ (transforming growth factor β), by these cells was also significantly attenuated by ACE2 expression. Collectively, these results indicate that: (i) endogenous ACE2 activity is observed in cardiac myocytes, but not in cardiac fibroblasts; (ii) ACE2 overexpression in the cardiac fibroblast attenuates collagen production; and (iii) this prevention is probably mediated by decreased expression of cytokines. We conclude that ACE2 expression, limited to cardiac fibroblasts, may represent a novel paradigm for in vivo therapy following acute ischaemia.
Study on the nature of interaction of furan with various hydrides
Authors: Wu Jun-Yong , Zhang Jing-Chang , Wang Zhao-Xu , Cao Wei-Liang
Published: November 2007

The nature of interactions of furan with various hydrides (Y) (Y=HF,HCl,H2O,H2S,NH3,PH3) is investigated using ab initio calculations. The contribution of attractive (electrostatic, inductive, and dispersive) and repulsive (exchange) components to the interactions energy is analyzed. HF, H2O, and NH3 favor σo-type H bonding, while HCl, H2S, and PH3 favor π-type H bonding. Interaction energy decomposition reveals that σo-type complexes interactions are predominantly electrostatic in nature, while the dispersion and electrostatic interactions dominate the π-type complexes.
Plasma confinement by circularly polarized electromagnetic field in toroidal geometry
Authors: Svidzinski Vladimir A.
Published: November 2007

A novel plasma confinement concept based on plasma confinement by electromagnetic pressure of circularly polarized electromagnetic fields is proposed. Practical implementation of this concept in a toroidal device is suggested. In this concept the confining field frequency is in the lower range such that the size of the device is much smaller than the vacuum wavelength. Most of the previous radio-frequency (rf) confinement concepts of unmagnetized plasma were related to confinement in rf cavities which operated at high frequency for which the size of the cavity is comparable to the wavelength. Operation at lower frequencies simplifies rf design, reduces Ohmic losses in the conducting walls and probably makes application of superconductors for wall materials more feasible. It is demonstrated that circular (or nearly circular) polarization of the electromagnetic field is required for confinement from both the equilibrium and stability considerations. Numerical analysis of plasma confinement for magnetohydrodynamic plasma model in two-dimensional toroidal geometry is performed. Within this model plasma is confined by the applied rf fields and its equilibrium is stable. Technically feasible compact and medium size toroidal plasma confinement devices based on this concept are proposed. Application of this approach to the fusion reactor requires use of superconducting materials for the toroidal shell to reduce the Ohmic losses. Further theoretical and experimental studies are required for a more reliable conclusion about the attractiveness of this plasma confinement concept.
Ultrafast charge transfer and atomic orbital polarization
Authors: Deppe M. , Föhlisch A. , Hennies F. , Nagasono M. , Beye M. , Sánchez-Portal D. , Echenique P. M. , Wurth W.
Published: November 2007

The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4×2)S∕Ru(0001) the charge transfer times between the sulfur 2s−13p*+1 antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p⊥* state along the surface normal and the 3p‖* state in the surface plane. The charge transfer times are determined as 0.18±0.07 and 0.84±0.23fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.
Local hybrid functionals based on density matrix products
Authors: Janesko Benjamin G. , Scuseria Gustavo E.
Published: November 2007

We present a novel similarity metric comparing exact and semilocal density functional theory (DFT) exchange holes in real space. This metric is obtained from the product of the one-particle density matrix and the uniform electron gas model density matrix. The metric is bound between 0 and 1, 1 in the uniform electron gas, 0 in regions asymptotically far from finite systems, and can detect delocalization of the exact exchange hole and effective fractional occupations. We also present a parameter-free local hybrid functional that uses this similarity metric to locally mix exact and semilocal DFT exchange energy densities. The resulting functional gives better thermochemistry and reaction barrier heights than our original local hybrids [Jaramillo et al., J. Chem. Phys. 118, 1068 (2003)], while retaining moderate accuracy for symmetric radical cation dimers.
Phenol-water1⩽n⩽3 revisited: An ab initio study on the photophysics of these clusters at the level of coupled cluster response theory
Authors: Schemmel Dominik , Schütz Martin
Published: November 2007

The S1(π*←π) state surfaces of the phenol-water1⩽n⩽3 clusters are reexplored at the level of coupled cluster response theory. The global minima for n=2 and n=3 so obtained are qualitatively different from those reported so far, which were obtained with methods such as configuration interaction singles or complete active space self-consistent field lacking dynamical electron correlation effects. Furthermore, the minimum-energy points on the conical intersection seams were located in this work. The results of these calculations offer a qualitative explanation for the anomalous photophysical behavior (broad congested absorption band structure, low quantum yield, short lifetime) of n=2 and the observed predissociation of n=3 at excess energies beyond ≈100cm−1, resolving a disagreement between theory and experiment which persisted for almost a decade.
Temperature control algorithms in dual control volume grand canonical molecular dynamics simulations of hydrogen diffusion in palladium
Authors: Sun Jianwei , Zhang Lucy T.
Published: November 2007

The effectiveness of five temperature control algorithms for dual control volume grand canonical molecular dynamics is investigated in the study of hydrogen atom diffusion in a palladium bulk. The five algorithms, namely, Gaussian, generalized Gaussian moment thermostat (GGMT), velocity scaling, Nosé-Hoover (NH), and its enhanced version Nosé-Hoover chain (NHC) are examined in both equilibrium and nonequilibrium simulation studies. Our numerical results show that Gaussian yields the most inaccurate solutions for the hydrogen-palladium system due to the high friction coefficient generated from the large velocity fluctuation of hydrogen, while NHC, NH, and GGMT produce the most accurate temperature and density profiles in both equilibrium and nonequilibrium cases with their feedback control mechanisms. However, this feedback control also overestimates the self-diffusion coefficients in equilibrium systems and the diffusion coefficient in nonequilibrium systems. Velocity scaling thermostat produces slight inhomogeneities in the temperature and density profiles, but due to the dissipated heat accumulated in the control volumes it still yields accurate self-diffusion coefficients that are in good agreement with the experimental data at a wide range of temperatures while others tend to deviate.
Scaling of asymmetric magnetic reconnection: General theory and collisional simulations
Authors: Cassak P. A. , Shay M. A.
Published: November 2007

A Sweet-Parker-type scaling analysis for asymmetric antiparallel reconnection (in which the reconnecting magnetic field strengths and plasma densities are different on opposite sides of the dissipation region) is performed. Scaling laws for the reconnection rate, outflow speed, the density of the outflow, and the structure of the dissipation region are derived from first principles. These results are independent of the dissipation mechanism. It is shown that a generic feature of asymmetric reconnection is that the X-line and stagnation point are not colocated, leading to a bulk flow of plasma across the X-line. The scaling laws are verified using two-dimensional resistive magnetohydrodynamics numerical simulations for the special case of asymmetric magnetic fields with symmetric density. Observational signatures and applications to reconnection in the magnetosphere are discussed.
The weak orthogonality functional in explicitly correlated pair theories
Authors: Tew David P. , Klopper Wim , Manby Frederick R.
Published: November 2007

Recent advances have seen the convergence of the R12 and Gaussian geminal explicitly correlated methods, such that the principal remaining distinction is the way in which the many-electron integrals are handled. Here we examine the weak orthogonality functional and the resolution of the identity and find that the first, although exact in the limit of infinite basis, introduces a conflict between the physical description of the electronic cusp and the satisfaction of the strong orthogonality constraint. This leads us to propose an improved weak orthogonality functional where the explicitly correlated pair functions are almost orthogonal to the occupied orbitals by construction. For applications where 95%-98% accuracy in the total correlation energy is sufficient, we recommend use of the strong orthogonality functional in combination with the resolution of the identity for three- and four-electron integral evaluations.
Importance of spin-orbit effects on the isomerism profile of Au3: An ab initio study
Authors: Rusakov Alexander A. , Rykova Elena , Scuseria Gustavo E. , Zaitsevskii Andréi
Published: November 2007

Two-component relativistic density functional theory combined with high-level ab initio correlation techniques was applied to the study of the electronic structure and isomerism of Au3. All calculations were performed with accurate small-core shape-consistent relativistic pseudopotentials. Density functional theory was used to determine the equilibrium structures of the Au3 isomers and isomerization path and to estimate the contributions of spin-orbit effects to the ground state electronic energy along the path. The reliability of these estimates was verified through independent many-body multipartitioning perturbation theory calculations. Spin-orbit corrections were used to refine the isomerization energy profile computed by spin-orbit-free coupled cluster methods.
Scale-up of spherical tokamak solenoid-free startup by coaxial helicity injection
Authors: Tang X. Z. , Boozer A. H.
Published: November 2007

Current multiplication and flux amplification are two critical measures in assessing the usefulness of magnetic helicity injection for forming the plasma confining magnetic field in laboratory spheromak and spherical tokamak (ST) experiments. While the two concepts are closely related for spheromaks, they are independent for a Taylor-relaxed ST plasma, and negatively correlated for a more realistic, partially relaxed ST plasma. An important application of this understanding leads to the so-called relaxed transient coaxial helicity injection scheme for solenoid-free ST startup, which can deliver reactor-grade high current multiplication and flux amplification.
Calculation of vibrational frequencies through a variational reduced-coupling approach
Authors: Scribano Yohann , Benoit David M.
Published: November 2007

In this study, we present a new method to perform accurate and efficient vibrational configuration interaction computations for large molecular systems. We use the vibrational self-consistent field (VSCF) method to compute an initial description of the vibrational wave function of the system, combined with the single-to-all approach to compute a sparse potential energy surface at the chosen ab initio level of theory. A Davidson scheme is then used to diagonalize the Hamiltonian matrix built on the VSCF virtual basis. Our method is applied to the computation of the OH-stretch frequency of formic acid and benzoic acid to demonstrate the efficiency and accuracy of this new technique.
Dissociative chemisorption of H2 on the Cu(110) surface: A quantum and quasiclassical dynamical study
Authors: Kroes G. J. , Pijper E. , Salin A.
Published: November 2007

Six-dimensional quantum dynamical and quasiclassical trajectory (QCT) calculations are reported for the reaction and vibrationally inelastic scattering of (v=0,1,j=0) H2 scattering from Cu(110), and for the reaction and rovibrationally elastic and inelastic scattering of (v=1,j=1) H2 scattering from Cu(110). The dynamics results were obtained using a potential energy surface obtained with density functional theory using the PW91 functional. The reaction probabilities computed with quantum dynamics for (v=0,1,j=0) were in excellent agreement with the QCT results obtained earlier for these states, thereby validating the QCT approach to sticking of hydrogen on Cu(110). The vibrational de-excitation probability P(v=1,j=0→v=0) computed with the QCT method is in remarkably good agreement with the quantum dynamical results for normal incidence energies En between 0.2 and 0.6eV. The QCT result for the vibrational excitation probability P(v=0,j=0→v=1) is likewise accurate for En between 0.8 and 1eV, but the QCT method overestimates vibrational excitation for lower En. The QCT method gives probabilities for rovibrationally (in)elastic scattering, P(v=1,j=1→v′,j′), which are in remarkably good agreement with quantum dynamical results. The rotationally averaged, initial vibrational state-selective reaction probability obtained with QCT agrees well with the initial vibrational state-selective reaction probability extracted from molecular beam experiments for v=1, for the range of collision energies for which the v=1 contribution to the measured total sticking probability dominates. The quantum dynamical probabilities for rovibrationally elastic scattering of (v=1,j=1) H2 from Cu(110) are in good agreement with experiment for En between 0.08 and 0.25eV.
Modeling the thermal conductivity of exfoliated polymer/clay nanocomposites
Authors: Zhou Hu , Zhang Shimin , Yang Mingshu
Published: November 2007

Based on the fact that the interfacial scattering of phonons dominates the heat transfer processes in the nanostructures and nanomaterials, a quite simple formula is presented to explain the thermal conductivity of the exfoliated polymer/clay nanocomposites. Our model shows that the thermal conductivity of the exfoliated polymer/clay nanocomposites decreases with increasing the clay volume fraction due to the large surface area of the exfoliated clay layers. Furthermore, the experimental results of the exfoliated polymer/clay nanocomposites recently reported in the literature are explained by using this model.
Detection of pure inverse spin-Hall effect induced by spin pumping at various excitation
Authors: Inoue H. Y. , Harii K. , Ando K. , Sasage K. , Saitoh E.
Published: November 2007

Electric-field generation due to the inverse spin-Hall effect (ISHE) driven by spin pumping was detected and separated experimentally from the extrinsic magnetogalvanic effects in a Ni81Fe19∕Pt film. By applying a sample-cavity configuration in which the extrinsic effects are suppressed, the spin pumping using ferromagnetic resonance gives rise to a symmetric spectral shape in the electromotive force spectrum, indicating that the motive force is due entirely to ISHE. This method allows the quantitative analysis of the ISHE and the spin-pumping effect. The microwave-power dependence of the ISHE amplitude is consistent with the prediction of a direct current-spin-pumping scenario.
Flying mirror model for interaction of a super-intense nonadiabatic laser pulse with a thin plasma layer: Dynamics of electrons in a linearly polarized external field
Authors: Kulagin Victor V. , Cherepenin Vladimir A. , Hur Min Sup , Suk Hyyong
Published: November 2007

Interaction of a high-power laser pulse having a sharp front with a thin plasma layer is considered. General one-dimensional numerical-analytical model is elaborated, in which the plasma layer is represented as a large collection of electron sheets, and a radiation reaction force is derived analytically. Using this model, trajectories of the electrons of the plasma layer are calculated numerically and compared with the electron trajectories obtained in particle-in-cell simulations, and a good agreement is found. Two simplified analytical models are considered, in which only one electron sheet is used, and it moves transversely and longitudinally in the fields of an ion sheet and a laser pulse (longitudinal displacements along the laser beam axis can be considerably larger than the laser wavelength). In the model I, a radiation reaction is included self-consistently, while in the model II a radiation reaction force is omitted. For the two models, analytical solutions for the dynamical parameters of the electron sheet in a linearly polarized laser pulse are derived and compared with the numerical solutions for the central electron sheet (positioned initially in the center) of the real plasma layer, which are calculated from the general numerical-analytical model. This comparison shows that the model II gives better description for the trajectory of the central electron sheet of the real plasma layer, while the model I gives more adequate description for a transverse momentum. Both models show that if the intensity of the laser pulse is high enough, even in the field with a constant amplitude, the electrons undergo not only the transverse oscillations with the period of the laser field, but also large (in comparison with the laser wavelength) longitudinal oscillations with the period, defined by the system parameters and initial conditions of particular oscillation.
Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses
Authors: Kulagin Victor V. , Cherepenin Vladimir A. , Hur Min Sup , Suk Hyyong
Published: November 2007

A self-consistent one-dimensional (1D) flying mirror model is developed for description of an interaction of an ultra-intense laser pulse with a thin plasma layer (foil). In this model, electrons of the foil can have large longitudinal displacements and relativistic longitudinal momenta. An approximate analytical solution for a transmitted field is derived. Transmittance of the foil shows not only a nonlinear dependence on the amplitude of the incident laser pulse, but also time dependence and shape dependence in the high-transparency regime. The results are compared with particle-in-cell (PIC) simulations and a good agreement is ascertained. Shaping of incident laser pulses using the flying mirror model is also considered. It can be used either for removing a prepulse or for reducing the length of a short laser pulse. The parameters of the system for effective shaping are specified. Predictions of the flying mirror model for shaping are compared with the 1D PIC simulations, showing good agreement.
Propagation and damping characteristics of low-frequency waves in field-reversed configuration plasmas
Authors: Inomoto Michiaki , Yamamoto Satoshi , Iwasawa Naotaka , Kitano Katsuhisa , Okada Shigefumi
Published: November 2007

Propagation and damping properties of low-frequency waves in extremely high beta plasmas have been investigated in the field-reversed configuration plasma injection experiment apparatus. Two distinct wave modes were excited by different antenna geometry and the radial structures of their magnetic components were measured in detail. Due to the high beta nature of the plasma, the Alfvén resonance predicted for the cold plasma vanished and the wave with small parallel wave number kz∼2.5m−1 propagated in a broad area across the separatrix. The wave exhibited moderate dissipation, which was suggestive of the resistive damping. The wave with large parallel wave number kz∼7.0m−1, however, underwent quite strong damping inside the separatrix. Transit-time magnetic pumping, which converts the wave energy to the ion parallel kinetic energy, is most likely to be responsible for this strong damping since the wave’s parallel phase velocity is close to the ion thermal velocity.
On the equilibrium calculation of the friction coefficient for liquid slip against a wall
Authors: Petravic Janka , Harrowell Peter
Published: November 2007

We demonstrate that the linear response theory of interface friction presented by Bocquet and Barrat [Phys. Rev. E 49, 3079 (1994)] results in a friction coefficient that is not an intrinsic property of the interface and thus does not correspond to the actual interfacial friction coefficient. We point out that this previous derivation includes an unsubstantiated identification of the velocity field in the nonuniform system with the perturbation applied to the equations of the motion. We present an alternative equilibrium theory of the friction associated with the confined fluid and show how this friction is related to the intrinsic interfacial friction.
On the invariant symmetries of the D-metrics
Authors: Ferrando Joan Josep , Sáez Juan Antonio
Published: November 2007

We analyze the symmetries and other invariant qualities of the D-metrics (type D aligned Einstein-Maxwell solutions with cosmological constant whose Debever null principal directions determine shear-free geodesic null congruences). We recover some properties and deduce new ones about their isometry group and about their quadratic first integrals of the geodesic equation, and we analyze when these invariant symmetries characterize the family of metrics. We show that the subfamily of the Kerr-NUT solutions are those admitting a Papapetrou field aligned with the Weyl tensor.
Configuration interaction based on constrained density functional theory: A multireference method
Authors: Wu Qin , Cheng Chiao-Lun , Van Voorhis Troy
Published: November 2007

Existing density functional theory (DFT) methods are typically very effective in capturing dynamic correlation, but run into difficulty treating near-degenerate systems where static correlation becomes important. In this work, we propose a configuration interaction (CI) method that allows one to use a multireference approach to treat static correlation but incorporates DFT’s efficacy for the dynamic part as well. The new technique uses localized charge or spin states built by a constrained DFT approach to construct an active space in which the effective Hamiltonian matrix is built. These local configurations have significantly less static correlation compared to their delocalized counterparts and possess an essentially constant amount of self-interaction error. Thus their energies can be reliably calculated by DFT with existing functionals. Using a small number of local configurations as different references in the active space, a simple CI step is then able to recover the static correlation missing from the localized states. Practical issues of choosing configurations and adjusting constraint values are discussed, employing as examples the ground state dissociation curves of H2+, H2, and LiF. Excellent results are obtained for these curves at all interatomic distances, which is a strong indication that this method can be used to accurately describe bond breaking and forming processes.
The von Neumann entropy asymptotics in multidimensional fermionic systems
Authors: Farkas S. , Zimborás Z.
Published: November 2007

We study the von Neumann entropy asymptotics of pure translation-invariant quasifree states of d-dimensional fermionic systems. It is shown that the entropic area law is violated by all these states: apart from the trivial cases, the entropy of a cubic subsystem with edge length L cannot grow slower than Ld−1lnL. As for the upper bound of the entropy asymptotics, the zero-entropy-density property of these pure states is the only limit: it is proven that arbitrary fast sub-Ld entropy growth is achievable.
Formation mechanism of critical nucleus during nucleation process of liquid metal sodium
Authors: Hou Zhao-yang , Liu Rang-su , Liu Hai-rong , Tian Ze-an , Wang Xin , Zhou Qun-yi , Chen Zhen-hua
Published: November 2007

To deeply understand the formation mechanism of a critical nucleus during the nucleation process of liquid metal sodium, a system consisting of 10 000 Na atoms has been simulated by using molecular dynamics method. The evolutions of nuclei are traced directly, adopting the cluster-type index method. It is found that the energies of clusters and their geometrical constraints interplay to form the favorable microstructures during the nucleation process. The nucleus can be formed through many different pathways, and the critical size of the nucleus would be different for each pathway. It is also found that the critical nucleus is nonspherical and may include some metastable structures. Furthermore, the size of the cluster and its internal structure both play a crucial role in determining whether it is a critical nucleus, and this is in agreement with the simulations by computing the free energy of the Lennard-Jones system [D. Moroni, P. R. ten Wolde, and P. G. Bolhuis, Phys. Rev. Lett. 94, 235703 (2005)].
Optimized expanded ensembles for simulations involving molecular insertions and deletions. I. Closed systems
Authors: Escobedo Fernando A. , Martínez-Veracoechea Francisco J.
Published: November 2007

Monte Carlo simulation methods that involve the insertion-deletion of molecules are of wide spread use for the study of thermophysical behavior of complex systems; e.g., for the estimation of chemical potentials in closed-system ensembles. In this work, efficient expanded ensemble methods are described to overcome the lack of ergodicity that often plagues such molecular moves, wherein an arbitrary physical parameter Λ is used to gradually couple and decouple a partial molecule to and from the system. In particular, we describe the use of (1) acceptance ratio methods for the robust estimation of free-energy changes associated with transitions between Λ states of the partial molecule, (2) non-Boltzmann sampling of the probability density of Λ states so that one can achieve either a flat histogram or an optimized histogram based on the maximization of round trips between the Λ bounds, and (3) an approach to select suitable intermediate stages of the Λ parameter that maximizes such round trips. The validity of the advocated methods is demonstrated by their application to two model systems, namely, the solvation of large hard spheres into a fluid of small spheres, and the mesophase formation of a block copolymer-homopolymer mixture.
Optimized expanded ensembles for simulations involving molecular insertions and deletions. II. Open systems
Authors: Escobedo Fernando A.
Published: November 2007

In the Grand Canonical, osmotic, and Gibbs ensembles, chemical potential equilibrium is attained via transfers of molecules between the system and either a reservoir or another subsystem. In this work, the expanded ensemble (EXE) methods described in part I [F. A. Escobedo and F. J. Martínez-Veracoechea, J. Chem. Phys. 127, 174103 (2007)] of this series are extended to these ensembles to overcome the difficulties associated with implementing such whole-molecule transfers. In EXE, such moves occur via a target molecule that undergoes transitions through a number of intermediate coupling states. To minimize the tunneling time between the fully coupled and fully decoupled states, the intermediate states could be either: (i) sampled with an optimal frequency distribution (the sampling problem) or (ii) selected with an optimal spacing distribution (staging problem). The sampling issue is addressed by determining the biasing weights that would allow generating an optimal ensemble; discretized versions of this algorithm (well suited for small number of coupling stages) are also presented. The staging problem is addressed by selecting the intermediate stages in such a way that a flat histogram is the optimized ensemble. The validity of the advocated methods is demonstrated by their application to two model problems, the solvation of large hard spheres into a fluid of small and large spheres, and the vapor-liquid equilibrium of a chain system.
Perovskite lithium and bismuth modified potassium-sodium niobium lead-free ceramics for high temperature applications
Authors: Du Hongliang , Zhou Wancheng , Luo Fa , Zhu Dongmei , Qu Shaobo , Pei Zhibin
Published: November 2007

[ ( K ( 1 − x ) ∕ 2 Na ( 1 − x ) ∕ 2 Li x ) 1 − 3 y Bi y ] Nb O 3 (abbreviated as KNLBN) ceramics were prepared by conventional solid-state sintering. The addition of Li+ and Bi3+ makes the orthorhombic-tetragonal phase transition temperature (TO-T) decrease from 200°C for pure (K0.5Na0.5)NbO3 ceramics to −10°C for KNLBN ceramics (x=0.06, y=0.005), while maintaining high Curie temperature (TC=455°C) and piezoelectric properties (d33=185pC∕N, kp=0.43, kt=0.45, ε33T∕ε0=1020, and tanδ=0.023) at room temperature. In addition, good temperature stability of electrical properties is obtained in KNLBN ceramics (x=0.06, y=0.005) owing to the decrease of TO-T. These results indicate that KNLBN (x=0.06, y=0.005) ceramic is a promising lead-free piezoelectric candidate material for high temperature applications.
Gradient scaling phenomenon in microsize flexoelectric piezoelectric composites
Authors: Fu John Y. , Zhu Wenyi , Li Nan , Smith Nadine B. , Eric Cross L.
Published: November 2007

The flexoelectric-type piezoelectric composites offer an alternative avenue for the development of piezoelectric ceramics, and since the flexoelectric response is diminished rather than enhanced in lead containing compositions, one of the merits of such composites is that those of highest sensitivity will be lead-free. The composites are fabricated by using certain nonpiezoelectric components with a texture symmetry which breaks up applied uniform fields, leading to the field gradients in the active flexoelectric components of the composites. Since these induced field gradients increase as the composite dimensions decrease, it is logical to expect that the piezoelectric performance of such composites would be enhanced with their reduced sizes. In this letter, we report the experimental studies that confirm such a gradient scaling phenomenon in two flexoelectric piezoelectric composites. The fabrication and measurement of the composites are discussed.
Ultrafast optical switching in distributed feedback polymer laser
Authors: Perissinotto Stefano , Lanzani Guglielmo , Zavelani-Rossi Margherita , Salerno Marco , Gigli Giuseppe
Published: November 2007

We show that polymer distributed feedback lasers can be optically controlled at high bit-rate by using an ultrashort gate pulse. We perform switching-off of the laser emission exploiting the photogeneration of charge carriers from the singlet, emitting state induced, by the gate. We study this resonant non-linear process and we show that the system can in principle work at 500GHz repetition rate. There could be the possibility for our devices to be integrated into plastic waveguides or fibers, to develop plastic, large-scale integrated, ultrafast optical logic.
Energy pathways and directionality in deformation twinning
Authors: Kibey S. , Liu J. B. , Johnson D. D. , Sehitoglu H.
Published: November 2007

We present ab initio density functional theory calculations of twinning energy pathways for two opposite twinning modes, (111)[112¯] and (111)[1¯1¯2], in fcc materials to examine the directional nature of twinning which cannot be explained by classical twin nucleation models or the “twinnability” criterion. By accounting for these energy pathways in a multiscale model, we quantitatively predict the critical twinning stress for the (111)[1¯1¯2] mode to be substantially higher compared to the favorable (111)[112¯] mode (whose predicted stresses are in agreement with experiment), thus, ruling out twinning in the (111)[1¯1¯2] mode.
Copper enhanced (111) texture in silver thin films on amorphous SiO2
Authors: Zoo Yeongseok , Han H. , Alford T. L.
Published: November 2007

Small amounts (5at.%) of copper were added to silver thin films to improve adhesion and minimize agglomeration on SiO2 layers. Resistivity measurements from the Ag(Cu) films showed that small Cu additions do not significantly increase the resistivity compared to pure Ag. Texture evolution and surface morphology of Ag and Ag(Cu) thin films on SiO2 were also investigated using x-ray diffraction (XRD) techniques and atomic force microscopy. Normalized (111) θ-2θ XRD intensities increased from 91.6% to 96.8% upon addition of Cu, likely due to enhanced adatom diffusion resulting from the Cu addition. XRD pole figure analysis revealed differences in texture evolution between the Ag and Ag(Cu) thin films. Since high adatom surface diffusion of Cu promotes preferred grain growth of the Ag matrix, Ag(Cu) thin films showed enhanced (111) texture compared to Ag thin films. Glancing angle XRD results confirmed the evolution of (111) texture in the Ag and Ag(Cu) thin films. In the case of Ag, (111) texture was enhanced mainly by recrystallization of disordered regions during annealing. In addition to recrystallization, (111) texture enhancement in Ag(Cu) was attributed to consumption of grains with other non-(111) crystallographic orientations.
Direct observation of amorphous to crystalline phase transitions in nanoparticle arrays of phase change materials
Authors: Raoux Simone , Rettner Charles T. , Jordan-Sweet Jean L. , Kellock Andrew J. , Topuria Teya , Rice Philip M. , Miller Dolores C.
Published: November 2007

We have used time-resolved x-ray diffraction to study the amorphous-crystalline phase transition in 20–80nm particles of the phase change materials Ge2Sb2Te5, nitrogen-doped Ge2Sb2Te5, Ge15Sb85, Sb2Te, and Sb2Te doped with Ag and In. We find that all samples undergo the phase transition with crystallization temperatures close to those of similarly prepared blanket films of the same materials with the exception of Sb2Te that shows the transition at a temperature that is about 40°C higher than that of blanket films. Some of the nanoparticles show a difference in crystallographic texture compared to thick films. Large area arrays of these nanoparticles were fabricated using electron-beam lithography, keeping the sample temperatures well below the crystallization temperatures so as to produce particles that were entirely in the amorphous phase. The observation that particles with diameters as small as 20nm can still undergo this phase transition indicates that phase change solid-state memory technology should scale to these dimensions.
Comparative analysis of internal friction and natural frequency measured by free decay and forced vibration
Authors: Wang Y. Z. , Ding X. D. , Xiong X. M. , Zhang J. X.
Published: November 2007

Relations between various values of the internal friction (tgδ, Q−1, Q−1*, and Λ∕π) measured by free decay and forced vibration are analyzed systemically based on a fundamental mechanical model in this paper. Additionally, relations between various natural frequencies, such as vibration frequency of free decay ωFD, displacement-resonant frequency of forced vibration ωd, and velocity-resonant frequency of forced vibration ω0 are calculated. Moreover, measurement of natural frequencies of a copper specimen of 99.9% purity has been made to demonstrate the relation between the measured natural frequencies of the system by forced vibration and free decay. These results are of importance for not only more accurate measurement of the elastic modulus of materials but also the data conversion between different internal friction measurements.
Harnessing bifurcations in tapping-mode atomic force microscopy to calibrate time-varying tip-sample force measurements
Authors: Sahin Ozgur
Published: November 2007

Torsional harmonic cantilevers allow measurement of time-varying tip-sample forces in tapping-mode atomic force microscopy. Accuracy of these force measurements is important for quantitative nanomechanical measurements. Here we demonstrate a method to convert the torsional deflection signals into a calibrated force wave form with the use of nonlinear dynamical response of the tapping cantilever. Specifically the transitions between steady oscillation regimes are used to calibrate the torsional deflection signals.
Laser output power stabilization for direct laser writing system by using an acousto-optic modulator
Authors: Kim Dong Ik , Rhee Hyug-Gyo , Song Jae-Bong , Lee Yun-Woo
Published: November 2007

We present experimental results on the output power stabilization of an Ar+ laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of ±0.20% for 12min and the relative intensity noise level of 2.1×10−7Hz−1∕2 at 100Hz. In addition, we applied our system to a 2mW internal mirror He–Ne laser. As a consequence, we achieved the output power stability of ±0.12% for 25min.
Three-dimensional aspects of fluid flows in channels. II. Effects of meniscus and thin film regimes on viscous fingers
Authors: Ledesma-Aguilar R. , Pagonabarraga I. , Hernández-Machado A.
Published: November 2007

We perform a three-dimensional study of steady state viscous fingers that develop in linear channels. By means of a three-dimensional lattice-Boltzmann scheme that mimics the full macroscopic equations of motion of the fluid momentum and order parameter, we study the effect of the thickness of the channel in two cases. First, for total displacement of the fluids in the channel thickness direction, we find that the steady state finger is effectively two-dimensional and that previous two-dimensional results can be recovered by taking into account the effect of a curved meniscus across the channel thickness as a contribution to surface stresses. Second, when a thin film develops in the channel thickness direction, the finger narrows with increasing channel aspect ratio in agreement with experimental results. The effect of the thin film renders the problem three-dimensional and results deviate from the two-dimensional prediction.