bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraluminal Thread Model of Focal Stroke in the Non-Human Primate
Authors: Freret Thomas , Bouet Valentine , Toutain Jérôme , Saulnier Romaric , Pro-Sistiaga Palma , Bihel Ebeline , MacKenzie Eric T , Roussel Simon , Schumann-Bard Pascale , Touzani Omar
Published: November 2007

The common marmoset ( Callithrix jacchus), a New World monkey, has recently been used as a model of focal cerebral ischaemia. Here, we sought to develop a stroke model in this species using an intraluminal approach to occlude the middle cerebral artery (MCA). This technically simple procedure allows both transient and permanent ischaemia with minimal morbidity. Ten common marmosets underwent either transient (3 h) or permanent ischaemia by the insertion of a nylon filament through the external carotid artery up to the origin of the MCA. Cerebral blood flow (CBF) was monitored by the laser-Doppler flowmetry technique. Sensorimotor functions were regularly evaluated, and histologic, immunohistochemical, and magnetic resonance imaging analyses were performed 8 days after the occlusion. The surgical procedure was achieved straightforwardly without postoperative mortality or cerebral haemorrhage. All animals displayed a consistent decrease in CBF that remained stable over 3 h. Infarction affected both cortical and subcortical structures. Although not statistically significant, the volume of infarction was smaller in marmosets subjected to transient ischaemia compared to those permanently occluded (237±139 and 358±118 mm3, respectively). In all the behavioural tests used, reperfused marmosets exhibited fewer neurologic and functional impairments compared to permanently occluded ones. We show the feasibility of the induction of permanent or transient focal cerebral ischaemia in the marmoset using an intraluminal approach with minimal invasion. This model could be suitable as an advanced screening for potential stroke therapies in which behavioural, imaging, and histologic analyses can be compared.
Fortilin binds Ca2+ and blocks Ca2+-dependent apoptosisin vivo
Authors: Graidist Potchanapond , Yazawa Michio , Tonganunt Moltira , Nakatomi Akiko , Lin Curtis Chun-Jen , Chang Jui-Yoa , Phongdara Amornrat , Fujise Ken
Published: November 2007

Fortilin, a 172-amino-acid polypeptide present both in the cytosol and nucleus, possesses potent anti-apoptotic activity. Although fortilin is known to bind Ca2+, the biochemistry and biological significance of such an interaction remains unknown. In the present study we report that fortilin must bind Ca2+ in order to protect cells against Ca2+-dependent apoptosis. Using a standard Ca2+-overlay assay, we first validated that full-length fortilin binds Ca2+ and showed that the N-terminus (amino acids 1–72) is required for its Ca2+-binding. We then used flow dialysis and CD spectropolarimetry assays to demonstrate that fortilin binds Ca2+ with a dissociation constant (Kd) of approx. 10 μM and that the binding of fortilin to Ca2+ induces a significant change in the secondary structure of fortilin. In order to evaluate the impact of the binding of fortilin to Ca2+in vivo, we measured intracellular Ca2+ levels upon thapsigargin challenge and found that the lack of fortilin in the cell results in the exaggerated elevation of intracellular Ca2+ in the cell. We then tested various point mutants of fortilin for their Ca2+ binding and identified fortilin(E58A/E60A) to be a double-point mutant of fortilin lacking the ability of Ca2+-binding. We then found that wild-type fortilin, but not fortilin(E58A/E60A), protected cells against thapsigargin-induced apoptosis, suggesting that the binding of fortilin to Ca2+ is required for fortilin to protect cells against Ca2+-dependent apoptosis. Together, these results suggest that fortilin is an intracellular Ca2+ scavenger, protecting cells against Ca2+-dependent apoptosis by binding and sequestering Ca2+ from the downstream Ca2+-dependent apoptotic pathways.
Effect of glycation on α-crystallin structure and chaperone-like function
Authors: Kumar P. Anil , Kumar M. Satish , Reddy G. Bhanuprakash
Published: November 2007

The chaperone-like activity of α-crystallin is considered to play an important role in the maintenance of the transparency of the eye lens. However, in the case of aging and in diabetes, the chaperone function of α-crystallin is compromized, resulting in cataract formation. Several post-translational modifications, including non-enzymatic glycation, have been shown to affect the chaperone function of α-crystallin in aging and in diabetes. A variety of agents have been identified as the predominant sources for the formation of AGEs (advanced glycation end-products) in various tissues, including the lens. Nevertheless, glycation of α-crystallin with various sugars has resulted in divergent results. In the present in vitro study, we have investigated the effect of glucose, fructose, G6P (glucose 6-phosphate) and MGO (methylglyoxal), which represent the major classes of glycating agents, on the structure and chaperone function of α-crystallin. Modification of α-crystallin with all four agents resulted in the formation of glycated protein, increased AGE fluorescence, protein cross-linking and HMM (high-molecular-mass) aggregation. Interestingly, these glycation-related profiles were found to vary with different glycating agents. For instance, CML [Nϵ-(carboxymethyl)lysine] was the predominant AGE formed upon glycation of α-crystallin with these agents. Although fructose and MGO caused significant conformational changes, there were no significant structural perturbations with glucose and G6P. With the exception of MGO modification, glycation with other sugars resulted in decreased chaperone activity in aggregation assays. However, modification with all four sugars led to the loss of chaperone activity as assessed using an enzyme inactivation assay. Glycation-induced loss of α-crystallin chaperone activity was associated with decreased hydrophobicity. Furthermore, α-crystallin isolated from glycated TSP (total lens soluble protein) had also increased AGE fluorescence, CML formation and diminished chaperone activity. These results indicate the susceptibility of α-crystallin to non-enzymatic glycation by various sugars and their derivatives, whose levels are elevated in diabetes. We also describes the effects of glycation on the structure and chaperone-like activity of α-crystallin.
Left ventricular hypertrophy induced by aortic banding impairs relaxation of isolated coronary arteries
Authors: McGoldrick Rory B. , Kingsbury Martyn , Turner Mark A. , Sheridan Desmond J. , Hughes Alun D.
Published: November 2007

LVH (left ventricular hypertrophy) is associated with impaired coronary vascular reserve. In the present study, we examined the effect of pressure-overload hypertrophy on vasorelaxant responses of guinea-pig isolated coronary small arteries and compared them with mesenteric small arteries. Pressure-overload was induced by banding the ascending aorta of guinea-pigs. Haemodynamics, and ventricular, atrial and lung weights were measured 168 days after banding. Isolated coronary and mesenteric small arteries were contracted with a thromboxane mimetic (U46619) and relaxation to ACH (acetylcholine), ISO (isoprenaline), FSK (forskolin) and SNP (sodium nitroprusside) was examined. Arterial wall morphology was examined by light microscopy. Aortic banding reduced cardiac output and increased systemic vascular resistance; atrial, ventricular and lung weights were increased. Coronary artery adventitial and medial thickness were increased, but mesenteric arterial wall morphology was unaffected. Coronary artery relaxation to ACH, ISO, FSK and SNP were reduced in banded animals. In contrast, relaxation of mesenteric arteries to ACH, FSK and SNP were unaffected by banding, although ISO-induced relaxation was reduced. A COX (cyclo-oxygenase) inhibitor, indomethacin, had no effect on coronary artery responses to ACH in banded or sham animals, but the differences in relaxation of coronary arteries between banded and sham animals were no longer significant following pre-incubation with the NO inhibitors L-NMMA (NG-monomethyl-L-arginine) and oxyhaemoglobin. In conclusion, pressure-overload-induced LVH causes impaired relaxation of small coronary arteries to endothelium-dependent and -independent relaxants. These findings are indicative of alterations in vascular smooth muscle responsiveness to vasodilators. Impairment of coronary arterial vasodilation may contribute to the reduced coronary vascular reserve seen in LVH.
The Role of Tissue Factor Pathway Inhibitor in Tumor Growth and Metastasis
Authors: Amirkhosravi Ali , Meyer Todd , Amaya Mildred , Davila Monica , Mousa Shaker A. , Robson Theresa , Francis John L.
Published: November 2007

Clotting activation occurs frequently in cancer. Tissue factor (TF), the most potent initiator of coagulation, is expressed aberrantly in many types of malignancy and is involved not only in tumor-associated hypercoagulability but also in promoting tumor angiogenesis and metastasis via coagulation-dependent and coagulation-independent (signaling) mechanisms. Tissue factor pathway inhibitor (TFPI) is the natural inhibitor of TF coagulant and signaling activities. Studies have shown that TFPI exhibits antiangiogenic and antimetastatic effects in vitro and in vivo. In animal models of experimental metastasis, both circulating and tumor cell-associated TFPI are shown to significantly reduce tumor cell-induced coagulation activation and lung metastasis. Heparins and heparin derivatives, which induce the release of TFPI from the vascular endothelium, also exhibit antitumor effects, and TFPI may contribute significantly to those effects. Indeed, a non-anticoagulant low-molecular-weight heparin with intact TFPI-releasing capacity has been shown to have significant antimetastatic effect in a similar experimental mouse model. The evidence supporting the dual inhibitory functions on TF-driven coagulation and signaling strengthen the rationale for considering TFPI as a potential anticancer agent. This article primarily summarizes the evidence for antiangiogenic and antimetastatic effects of TFPI and describes its potential mechanisms of action. The possible application of TFPI and other inhibitors of TF as potential anticancer agents is described, and information regarding potential antitumor properties of TFPI-2 (which has structural similarities to TFPI) is also included.
The effects of a diffusion controlled surfactant on a viscous drop injected into a viscous medium
Authors: Jin Fang , Stebe Kathleen J.
Published: November 2007

The effects of a diffusion controlled surfactant on the evolution of a buoyant viscous drop injected into a viscous fluid are studied numerically for the case of finite bulk convection to resolve neck dynamics and detaching drop volumes. When the drop is formed, its interface initially expands. The surfactant adsorbs and depletes a region around the drop. When the drop is sufficiently elongated, a neck begins to form. The surface contracts rapidly above the neck, driving the surface concentration above its equilibrium value. The surfactant subsequently desorbs into the region adjacent to the interface that had previously been depleted of the surfactant. This creates diffusion fluxes away from the neck that are larger than suggested by an a priori scaling of the governing equations. The rapid flux removes the surfactant effectively from the contracting neck, preventing the occurrence of strong local reductions in the surface tension. Through this mechanism, neck dynamics are altered only weakly for surface coverages x=Γeq∕Γ∞ less than or equal to 0.9. For surface coverages close enough to maximum packing (x=0.92) and for diffusion fluxes that are sufficiently slow, surfactant accumulation can reduce the local surface tension sufficiently to prevent drops from detaching. A phase diagram summarizing neck shapes and regimes where drops fail to detach is presented as a function of Ψ, the ratio of surfactant diffusion rate (between the interface and the bulk) to the rate of surface contraction.
Microwave spectra and ab initio studies of Ar-propane and Ne-propane complexes: Structure and dynamics
Authors: Peterson Karen I. , Pullman David , Lin Wei , Minei Andrea J. , Novick Stewart E.
Published: November 2007

Microwave spectra in the 7–26MHz region have been measured for the van der Waals complexes, Ar–CH3CH2CH3, Ar–C13H3CH2CH3, Ne20–CH3CH2CH3, and Ne22–CH3CH2CH3. Both a- and c-type transitions are observed for the Ar-propane complex. The c-type transitions are much stronger indicating that the small dipole moment of the propane (0.0848D) is aligned perpendicular to the van der Waals bond axis. While the 42 transition lines observed for the primary argon complex are well fitted to a semirigid rotor Hamiltonian, the neon complexes exhibit splittings in the rotational transitions which we attribute to an internal rotation of the propane around its a inertial axis. Only c-type transitions are observed for both neon complexes, and these are found to occur between the tunneling states, indicating that internal motion involves an inversion of the dipole moment of the propane. The difference in energy between the two tunneling states within the ground vibrational state is 48.52MHz for Ne20–CH3CH2CH3 and 42.09MHz for Ne22–CH3CH2CH3. The Kraitchman substitution coordinates of the complexes show that the rare gas is oriented above the plane of the propane carbons, but shifted away from the methylene carbon, more so in Ne propane than in Ar propane. The distance between the rare gas atom and the center of mass of the propane, Rcm, is 3.823Å for Ar-propane and 3.696Å for Ne-propane. Ab initio calculations are done to map out segments of the intermolecular potential. The global minimum has the rare gas almost directly above the center of mass of the propane, and there are three local minima with the rare gas in the plane of the carbon atoms. Barriers between the minima are also calculated and support the experimental results which suggest that the tunneling path involves a rotation of the propane subunit. The path with the lowest effective barrier is through a C2v symmetric configuration in which the methyl groups are oriented toward the rare gas. Calculating the potential curve for this one-dimensional model and then calculating the energy levels for this potential roughly reproduces the spectral splittings in Ne-propane and explains the lack of splittings in Ar-propane.
Laser induced fluorescence spectroscopy of the C3N radical
Authors: Hoshina Kennosuke , Endo Yasuki
Published: November 2007

Electronic spectra of the C3N radical have been observed for the first time in the near ultraviolet wavelength region by laser induced fluorescence (LIF) spectroscopy. Seventeen vibronic bands of the B̃Πi2–X̃Σ+2 electronic transition system of C3N were identified in LIF spectra of products in a discharge of HC3N. The origin of the B̃Πi2 state was determined to be 27929.985(1)cm−1 from rovibrational analyses. It was found that observations of two types of Σ2 vibronic levels, which have Σ+2 and Σ(±)2 symmetries originated from excitations of the ν4 trans-bending mode (ω4=369.1(20)cm−1) with a large Renner-Teller (RT) interaction (ε4=−0.1549(50)), and the ν5 cis-bending mode (ω5=163.24(84)cm−1) with a small Renner-Teller interaction (ε5=−0.0503(68)), respectively. Vibronic levels, with excitations of the C–C stretching (ω3=869.7cm−1) mode, were also identified. The spin-orbit interaction constant was determined to be Aso=−36.7(50)cm−1 from the RT analysis. In dispersed fluorescence spectra from B̃Πi2, vibrational structures of the low-lying electronically excited ÃΠi2 state were clearly observed with a strong progression due to the ν3′ mode, together with those of the X̃Σ+2 state with weak intensities. The origin of ÃΠi2, T0=1844(3)cm−1, and the vibrational frequencies, ω3′=883(3)cm−1 and ω5′=121(3)cm−1 for ÃΠi2, and ω3″=1054(3)cm−1, ω4″=405(3)cm−1, and ω5″=131(3)cm−1 for X̃Σ+2, were determined. Time profiles of fluorescence from B̃Πi2 have short (50–200ns) and long (>1μs) decay components with quantum beats, indicating that there is a competition between radiative decay and the nonradiative internal conversion to vibrationally highly excited ÃΠi2 and X̃Σ+2.
Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes
Authors: Seo Dong-Kyun
Published: November 2007

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.
Full-dimensional (15-dimensional) quantum-dynamical simulation of the protonated water dimer. I. Hamiltonian setup and analysis of the ground vibrational state
Authors: Vendrell Oriol , Gatti Fabien , Lauvergnat David , Meyer Hans-Dieter
Published: November 2007

Quantum-dynamical full-dimensional (15D) calculations are reported for the protonated water dimer (H5O2+) using the multiconfiguration time-dependent Hartree (MCTDH) method. The dynamics is described by curvilinear coordinates. The expression of the kinetic energy operator in this set of coordinates is given and its derivation, following the polyspherical method, is discussed. The potential-energy surface (PES) employed is that of Huang et al. [J. Chem. Phys. 122, 044308 (2005)]. A scheme for the representation of the PES is discussed which is based on a high-dimensional model representation scheme, but modified to take advantage of the mode-combination representation of the vibrational wave function used in MCTDH. The convergence of the PES expansion used is quantified and evidence is provided that it correctly reproduces the reference PES at least for the range of energies of interest. The reported zero point energy of the system is converged with respect to the MCTDH expansion and in excellent agreement (16.7cm−1 below) with the diffusion Monte Carlo result on the PES of Huang et al. The highly fluxional nature of the cation is accounted for through use of curvilinear coordinates. The system is found to interconvert between equivalent minima through wagging and internal rotation motions already when in the ground vibrational state, i.e., T=0. It is shown that a converged quantum-dynamical description of such a flexible, multiminima system is possible.
Full dimensional (15-dimensional) quantum-dynamical simulation of the protonated water dimer. II. Infrared spectrum and vibrational dynamics
Authors: Vendrell Oriol , Gatti Fabien , Meyer Hans-Dieter
Published: November 2007

The infrared absorption spectrum of the protonated water dimer (H5O2+) is simulated in full dimensionality (15 dimensional) in the spectral range of 0–4000cm−1. The calculations are performed using the multiconfiguration time-dependent Hartree (MCTDH) method for propagation of wavepackets. All the fundamentals and several overtones of the vibrational motion are computed. The spectrum of H5O2+ is shaped to a large extent by couplings of the proton-transfer motion to large amplitude fluxional motions of the water molecules, water bending and water-water stretch motions. These couplings are identified and discussed, and the corresponding spectral lines are assigned. The large couplings featured by H5O2+ do not hinder, however, to describe the coupled vibrational motion by well defined simple types of vibration (stretching, bending; etc.) based on well defined modes of vibration, in terms of which the spectral lines are assigned. Comparison of our results to recent experiments and calculations on the system is given. The reported MCTDH IR spectrum is in very good agreement to the recently measured spectrum by Hammer et al. [J. Chem. Phys. 122, 244301 (2005)].
On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters: Benchmarks approaching the complete basis set limit
Authors: Santra Biswajit , Michaelides Angelos , Scheffler Matthias
Published: November 2007

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Møller-Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the nonhybrid generalized gradient approximation functionals, mPWLYP and PBE1W perform best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.
An application of the turbulent magnetohydrodynamic residual-energy equation model to the solar wind
Authors: Yokoi Nobumitsu , Hamba Fujihiro
Published: November 2007

A magnetohydrodynamic (MHD) turbulence model incorporating the turbulent MHD residual energy (difference between the kinetic and magnetic energies) is applied to solar-wind turbulence. In the model, the dynamics of the turbulent cross-helicity (cross-correlation between the velocity and magnetic field) and the turbulent MHD residual energy, which are considered to describe the degree of Alfvénicity of the MHD turbulence, are solved simultaneously with the dynamics of the turbulent MHD energy and its dissipation rate. The transition of solar-wind turbulence from the Alfvén-wave-like fluctuations near the Sun in the inner heliosphere to the fully developed MHD turbulence in the outer heliosphere is discussed. Magnetic dominance in the solar-wind fluctuations is addressed from the dynamics of the evolution equation of the residual energy. An interpretation of the observed Alfvén ratio (ratio of the kinetic to magnetic energies) of ∼0.5 is proposed from the viewpoint of a stationary solution of the turbulence model.
Three-dimensional localized coherent structures of surface turbulence. I. Scenarios of two-dimensional–three-dimensional transition
Authors: Demekhin E. A. , Kalaidin E. N. , Kalliadasis S. , Vlaskin S. Yu.
Published: November 2007

The evolution of naturally excited disturbances on a thin liquid film falling down an inclined planar substrate undergoes several transitions between different wave regimes starting from two-dimensional (2D, one spatial dimension and height) solitary pulses at small Reynolds numbers to the “surface turbulence” stage for sufficiently large Reynolds numbers where the surface is randomly covered by localized three-dimensional (3D, two spatial dimensions and height) coherent structures. In this study, we analyze for the first time the instability of 2D pulses to 3D disturbances and the transitions of 2D pulses to fully developed 3D waves. The main instability mechanism responsible for the transition to 3D localized patterns is the Rayleigh instability of well-separated (isolated) 2D solitary waves. On the other hand, the physical mechanism for the 3D instability of 2D periodic waves and wave trains of 2D solitary waves sufficiently close to each other is not related to the Rayleigh instability but is due to wave-wave interaction and mass exchange between neighboring waves. These instabilities are characteristic of small inclination angles but under special conditions can be realized also for the vertical flow.
Three-dimensional localized coherent structures of surface turbulence. II. Λ solitons
Authors: Demekhin E. A. , Kalaidin E. N. , Kalliadasis S. , Vlaskin S. Yu.
Published: November 2007

We numerically construct Λ solitons as a function of the generalized Reynolds number δ. The numerical scheme is based on an impulse response analysis in which the nonlinear hump region is replaced with a Dirac delta function. We also examine the linear stability of Λ solitons with respect to three-dimensional disturbances. It is shown that the operator of the linearized system has both a discrete and a continuous spectrum. The discrete spectrum is always stable, while the continuous spectrum can be destabilized leading to a convective instability of Λ solitons. We demonstrate that the region of existence and stability of Λ solitons is 0.054<δ<0.51.
Exact solution of a RNA-like polymer model on the Husimi lattice
Authors: Zara Reginaldo A. , Pretti Marco
Published: November 2007

We investigate a two-tolerant polymer model on the square Husimi lattice, which aims at describing the properties of RNA-like macromolecules. We solve the model in a numerically exact way, working out the grand-canonical phase diagram, both with and without taking into account the stacking effect. Besides a nonpolymerized phase, we observe two different polymerized phases characterized by a lower or higher density of doubly visited lattice bonds. The system exhibits three qualitatively different regimes, as a function of the monomer chemical potential. Below some T1 temperature and above some T2 temperature, the transition to the nonpolymerized phase is continuous, whereas, in the (T1,T2) temperature range, the transition is first order. In the dilute-solution limit, the high temperature regime corresponds to a swollen (“coil”) state, the intermediate regime to a moderately collapsed (“molten”) state, with a small fraction of paired segments, and the low temperature regime to an almost fully paired (“native”) state. The molten state ends in a tricritical (Θ-like) transition at high temperature and in a critical end point at low temperature. Upon increasing the stacking energy parameter, the temperature range of the molten state turns out to be progressively reduced but never completely removed.
The effect of jet velocity profile on the characteristics of thickness and velocity of the liquid sheet formed by two impinging jets
Authors: Choo Y. J. , Kang B. S.
Published: November 2007

In this study, the effect of jet velocity profile on the thickness and velocity of the liquid sheet formed by two low-speed impinging jets was investigated. In addition to the constant jet velocity and the Poiseuille parabolic profile, the jet velocity profile measured experimentally was considered to account for the real nonuniform jet velocity profile. For three jet velocity profiles, the distributions of the thickness and velocity of the liquid sheet were analytically predicted by solving conservation equations for mass, momentum, and energy. The predicted results were compared with the previous experimental results. The jet velocity profile affected the resulting thickness and velocity characteristics of the liquid sheet. The distributions of the thickness and velocity of the liquid sheet predicted by using the measured jet velocity profile produced more acceptable results, which agreed better with the experimental observations, than those obtained by using the constant jet velocity, which has been commonly used in previous theoretical works.
Translocation of polymers with folded configurations across nanopores
Authors: Kotsev Stanislav , Kolomeisky Anatoly B.
Published: November 2007

The transport of polymers with folded configurations across membrane pores is investigated theoretically by analyzing simple discrete stochastic models. The translocation dynamics is viewed as a sequence of two events: motion of the folded segment through the channel followed by the linear part of the polymer. The transition rates vary for the folded and linear segments because of different interactions between the polymer molecule and the pore. It is shown that the translocation time depends nonmonotonously on the length of the folded segment for short polymers and weak external fields, while it becomes monotonous for long molecules and large fields. Also, there is a critical interaction between the polymers and the pore that separates two dynamic regimes. For stronger interactions, the folded polymer moves slower, while for weaker interactions, the linear chain translocation is the fastest. In addition, our calculations show that the folding does not change the translocation scaling properties of the polymer. These phenomena can be explained by the interplay between translocation distances and transition rates for the folded and linear segments of the polymer. Our theoretical results are applied for analysis of experimental translocations through solid-state nanopores.
Effect of tensile and compressive strains on the transport properties of SmNiO3 layers epitaxially grown on (001) SrTiO3 and LaAlO3 substrates
Authors: Conchon Florine , Boulle Alexandre , Guinebretière René , Girardot Cécile , Pignard Stéphane , Kreisel Jens , Weiss François , Dooryhée Eric , Hodeau Jean-Louis
Published: November 2007

This paper deals with the role of epitaxial strain on the structure and electronic transport properties of metastable SmNiO3 layers grown by metal-organic chemical vapor deposition onto SrTiO3 and LaAlO3 substrates. The characterization of these layers is carried out by high resolution x-ray diffraction and four-probe resistivity measurements. It is found that the SmNiO3 phase is stabilized by in-plane compressive strain whereas in-plane tensile strain induces the creation of oxygen vacancies that induces an annihilation of the metal-insulator transition and a huge increase of the resistivity.
Electron beam instabilities in unmagnetized plasmas via the Stieltjes transform (linear theory and nonlinear mode coupling)
Authors: Krishan S.
Published: November 2007

The Stieltjes transform has been used in place of a more common Laplace transform to determine the time evolution of the self-consistent field (SCF) of an unmagnetized semi-infinite plasma, where the plasma electrons together with a primary and a low-density secondary electron beam move perpendicular to the boundary surface. The secondary beam is produced when the primary beam strikes the grid. Such a plasma system has been investigated by Griskey and Stanzel [M. C. Grisky and R. L. Stenzel, Phys. Rev. Lett. 82, 556 (1999)]. The physical phenomenon, observed in their experiment, has been named by them as “secondary beam instability.” The character of the instability observed in the experiment is not the same as predicted by the conventional treatments—the field amplitude does not grow with time. In the frequency spectrum, the theory predicts peak values in the amplitude of SCF at the plasma frequency of plasma and secondary beam electrons, decreasing above and below it. The Stieltjes transform for functions, growing exponentially in the long time limit, does not exist, while the Laplace transform technique gives only exponentially growing solutions. Therefore, it should be interesting to know the kind of solutions that an otherwise physically unstable plasma will yield. In the high-frequency limit, the plasma has been found to respond to any arbitrary frequency of the initial field differentiated only by the strength of the resulting SCF. The condition required for exponential growth in the conventional treatments, and the condition for maximum amplitude (with respect to frequency) in the present treatment, have been found to be the same. Nonlinear mode coupling between the modes excited by the plasma electrons and the low-density secondary beam gives rise to two frequency-dependent peaks in the field amplitude, symmetrically located about the much stronger peak due to the plasma electrons, as predicted by the experiment.
Dissipation in relativistic pair-plasma reconnection
Authors: Hesse Michael , Zenitani Seiji
Published: November 2007

An investigation into the relativistic dissipation in magnetic reconnection is presented. The investigated system consists of an electron-positron plasma. A relativistic generalization of Ohm’s law is derived. A set of numerical simulations is analyzed, composed of runs with and without guide magnetic field, and of runs with different species temperatures. The calculations indicate that the thermal inertia-based dissipation process survives in relativistic plasmas. For antiparallel reconnection, it is found that the pressure tensor divergence remains the sole contributor to the reconnection electric field, whereas relativistic guide field reconnection exhibits a similarly important role of the bulk inertia terms.
Studies on soliton energy at critical and noncritical densities of negative ions in an inhomogeneous magnetized warm plasma
Authors: Singh Dhananjay K. , Malik Hitendra K.
Published: November 2007

Considering an inhomogeneous plasma having finite-temperature negative and positive ions, and the isothermal electrons in the presence of an external magnetic field, the solitons at noncritical and critical densities of the negative ions are studied through Korteweg–deVries (KdV) and modified Korteweg-deVries (mKdV) equations, respectively. The compressive (rarefactive) KdV solitons are found to propagate when the negative ion concentration is less (greater) than the critical density of the negative ions. At the critical density, both the compressive and the rarefactive solitons of equal amplitudes are found to occur. The energies of the compressive KdV soliton and the mKdV solitons are found to increase and that of the rarefactive KdV soliton is found to decrease with the negative ion density. Soliton energy for both the KdV and the mKdV solitons gets lowered under the effect of stronger magnetic field. The effect of ion temperature is to increase the energy of the compressive KdV soliton, whereas the energy of the rarefactive KdV soliton as well as of the mKdV solitons gets decreased. The variation of the energy with the obliqueness of the magnetic field is different for the KdV and the mKdV solitons.
Self-focusing and cross-focusing of Gaussian electromagnetic beams in fully ionized collisional magnetoplasmas
Authors: Sodha Mahendra Singh , Mishra S. K. , Agarwal Sujeet Kumar
Published: November 2007

This paper presents an analysis and subsequent discussion of the phenomena of self-focusing of single electromagnetic Gaussian beams and cross-focusing of multiple coaxial beams in fully ionized magnetoplasma, taking into account the Ohmic heating of the electrons by the beams and loss of energy by electrons due to collision with the ions and electronic thermal conduction; the energy gained by ions in collision with the electrons has been equated to the energy lost on account of ionic thermal conduction. It is seen that the inclusion of the ionic thermal conduction reduces self/cross-focusing for high values of the magnetic field (νe≪Ωc) and enhances the same for low values of the magnetic field (νe≫ωc); here νe is the electron collision frequency and ωc,Ωc are the cyclotron frequencies of electrons and ions, respectively. The wave frequency is assumed to be much higher than the cyclotron frequency of the electrons. The results lead to the conclusion that considerable error occurs by neglecting ionic thermal conduction in a collisional plasma.
A simple technique to estimate the fully time-resolved x-ray diameter of a z pinch
Authors: Coleman Philip L.
Published: November 2007

Occultations are routinely used to derive information about astronomical objects. Here an occultation scheme is used to derive a fully time-resolved estimate of the x-ray emitting diameter of a z pinch. By using different filtrations on the sensors, one could for example, distinguish the size of the K-line emitting region compared to the higher energy K-continuum emitting volume. Or with suitable apertures and detector arrays, the pinch diameter could be axially and temporally resolved.
Random walk of magnetic field-lines for different values of the energy range spectral index
Authors: Shalchi A. , Kourakis I.
Published: November 2007

An analytical nonlinear description of field-line wandering in partially statistically magnetic systems was proposed recently. In this article the influence of the wave spectrum in the energy range onto field-line random walk is investigated by applying this formulation. It is demonstrated that in all considered cases we clearly obtain a superdiffusive behavior of the field-lines. If the energy range spectral index exceeds unity a free-streaming behavior of the field-lines can be found for all relevant length-scales of turbulence. Since the superdiffusive results obtained for the slab model are exact, it seems that superdiffusion is the normal behavior of field-line wandering.
Transient photoelectron spectroscopy of the dissociative Br2(Πu1) state
Authors: Strasser Daniel , Goulay Fabien , Leone Stephen R.
Published: November 2007

Photodissociation of bromine on the Br2(Πu1) state is probed with ultrafast extreme ultraviolet (53.7nm) single-photon ionization. Time-resolved photoelectron spectra show simultaneously the depletion of ground state bromine molecules as well as the rise of Br(P3∕22) products due to 402.5nm photolysis. A partial photoionization cross-section ratio of atomic versus molecular bromine is obtained. Transient photoelectron spectra of a dissociative wave packet on the excited state are presented in the limit of low-power-density, single-photon excitation to the dissociative state. Transient binding energy shifts of “atomic-like” photoelectron peaks are observed and interpreted as photoionization of nearly separated Br atom pairs on the Br2(Πu1) state to repulsive dissociative ionization states.
Ion acceleration by colliding electrostatic shock waves in laser-solid interaction
Authors: Chen Min , Sheng Zheng-Ming , Dong Quan-Li , He Min-Qing , Weng Su-Ming , Li Yu-Tong , Zhang Jie
Published: November 2007

Based on particle-in-cell simulations, ion acceleration by collisionless electrostatic shock waves in the interaction of intense laser pulses with solid targets containing two ion species of different charge-to-mass ratios R is studied. The acceleration processes of the ions with different R and located in different regions of the target have been considered. Simulations also show that ions with larger R can be reflected and accelerated dramatically between two oppositely propagating shocks generated in plasma dominated by ions with smaller R. The studies suggest a new way to generate high energy ions. The involved phenomena may also occur in space and astrophysical plasmas.
An accurate air temperature measurement system based on an envelope pulsed ultrasonic time-of-flight technique
Authors: Huang Y. S. , Huang Y. P. , Huang K. N. , Young M. S.
Published: November 2007

A new microcomputer based air temperature measurement system is presented. An accurate temperature measurement is derived from the measurement of sound velocity by using an ultrasonic time-of-flight (TOF) technique. The study proposes a novel algorithm that combines both amplitude modulation (AM) and phase modulation (PM) to get the TOF measurement. The proposed system uses the AM and PM envelope square waveform (APESW) to reduce the error caused by inertia delay. The APESW ultrasonic driving waveform causes an envelope zero and phase inversion phenomenon in the relative waveform of the receiver. To accurately achieve a TOF measurement, the phase inversion phenomenon was used to sufficiently identify the measurement pulse in the received waveform. Additionally, a counter clock technique was combined to compute the phase shifts of the last incomplete cycle for TOF. The presented system can obtain 0.1% TOF resolution for the period corresponding to the 40kHz frequency ultrasonic wave. Consequently, with the integration of a humidity compensation algorithm, a highly accurate and high resolution temperature measurement can be achieved using the accurate TOF measurement. Experimental results indicate that the combined standard uncertainty of the temperature measurement is approximately 0.39°C. The main advantages of this system are high resolution measurements, narrow bandwidth requirements, and ease of implementation.
A new switched-capacitor frequency modulated driver for light emitting diodes
Authors: Feng Weifeng , Shi Frank G.
Published: November 2007

A new type of drivers for light emitting diodes (LEDs) is introduced based on the switched-capacitor frequency modulation. In contrast to conventional constant dc current drivers, the current pulse is provided by this new switched-capacitor LED driver. In the present driver, the charging capacitor is charged and discharged through a LED and the current flow direction is controlled by a metal oxide semiconductor switch. The input current (and thus the LED brightness) is proportional to the switch clock frequency at relatively low frequencies and becomes saturated at relatively high frequencies. This new driver circuit is simple and robust and maintains high efficiency for a wide range of input powers. In addition, the dimming control is easily realized by modulating clock frequency. Finally, this LED driver consumes no dc current and thus provides inherent protection to LED in standby mode.
Single-step electrochemical method for producing very sharp Au scanning tunneling microscopy tips
Authors: Gingery David , Bühlmann Philippe
Published: November 2007

A single-step electrochemical method for making sharp gold scanning tunneling microscopy tips is described. 3.0M NaCl in 1% perchloric acid is compared to several previously reported etchants. The addition of perchloric acid to sodium chloride solutions drastically shortens etching times and is shown by transmission electron microscopy to produce very sharp tips with a mean radius of curvature of 15nm.
Active drift compensation applied to nanorod manipulation with an atomic force microscope
Authors: Tranvouez E. , Boer-Duchemin E. , Comtet G. , Dujardin G.
Published: November 2007

We have developed a simple algorithm to overcome the problem of thermal drift in an atomic force microscope (AFM) operating under ambient conditions. Using our method, we demonstrate that the AFM tip remains above a 5-nm-high and 50-nm-long CdSe nanorod for more than 90min despite the thermal drift present (6nm∕min). We have applied our drift compensation technique to the AFM manipulation of CdSe colloidal nanorods lying horizontally on a highly oriented pyrolytic graphite surface. Since we have precise control over the position of the AFM tip relative to the nanorod, we can choose to either translate or rotate the rod by changing the location of the tip-rod interaction point.
A low temperature scanning tunneling microscope for electronic and force spectroscopy
Authors: Smit R. H. M. , Grande R. , Lasanta B. , Riquelme J. J. , Rubio-Bollinger G. , Agraït N.
Published: November 2007

In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision.
Setup for in situ x-ray diffraction study of swift heavy ion irradiated materials
Authors: Kulriya P. K. , Singh F. , Tripathi A. , Ahuja R. , Kothari A. , Dutt R. N. , Mishra Y. K. , Kumar Amit , Avasthi D. K.
Published: November 2007

An in situ x-ray diffraction (XRD) setup is designed and installed in the materials science beam line of the Pelletron accelerator at the Inter-University Accelerator Centre for in situ studies of phase change in swift heavy ion irradiated materials. A high vacuum chamber with suitable windows for incident and diffracted X-rays is integrated with the goniometer and the beamline. Indigenously made liquid nitrogen (LN2) temperature sample cooling unit is installed. The snapshots of growth of particles with fluence of 90MeV Ni ions were recorded using in situ XRD experiment, illustrating the potential of this in situ facility. A thin film of C60 was used to test the sample cooling unit. It shows that the phase of the C60 film transforms from a cubic lattice (at room temperature) to a fcc lattice at around T=255K.
BaHigh-force magnetic tweezers with force feedback for biological applications
Authors: Kollmannsberger Philip , Fabry Ben
Published: November 2007

Magnetic micromanipulation using magnetic tweezers is a versatile biophysical technique and has been used for single-molecule unfolding, rheology measurements, and studies of force-regulated processes in living cells. This article describes an inexpensive magnetic tweezer setup for the application of precisely controlled forces up to 100nN onto 5μm magnetic beads. High precision of the force is achieved by a parametric force calibration method together with a real-time control of the magnetic tweezer position and current. High forces are achieved by bead-magnet distances of only a few micrometers. Applying such high forces can be used to characterize the local viscoelasticity of soft materials in the nonlinear regime, or to study force-regulated processes and mechanochemical signal transduction in living cells. The setup can be easily adapted to any inverted microscope.
Analysis of the validity of the asymptotic techniques in the lower hybrid wave equation solution for reactor applications
Authors: Cardinali A. , Morini L. , Castaldo C. , Cesario R. , Zonca F.
Published: November 2007

Knowing that the lower hybrid (LH) wave propagation in tokamak plasmas can be correctly described with a full wave approach only, based on fully numerical techniques or on semianalytical approaches, in this paper, the LH wave equation is asymptotically solved via the Wentzel-Kramers-Brillouin (WKB) method for the first two orders of the expansion parameter, obtaining governing equations for the phase at the lowest and for the amplitude at the next order. The nonlinear partial differential equation (PDE) for the phase is solved in a pseudotoroidal geometry (circular and concentric magnetic surfaces) by the method of characteristics. The associated system of ordinary differential equations for the position and the wavenumber is obtained and analytically solved by choosing an appropriate expansion parameter. The quasilinear PDE for the WKB amplitude is also solved analytically, allowing us to reconstruct the wave electric field inside the plasma. The solution is also obtained numerically and compared with the analytical solution. A discussion of the validity limits of the WKB method is also given on the basis of the obtained results.
Phase separation in Eu0.58Sr0.42MnO3 under pressure
Authors: Zhang W. , Liu G. J. , Sun J. R. , Yang L. X. , Yao L. D. , Li F. Y. , Liu Z. X. , Jin C. Q. , Yu R. C.
Published: November 2007

Resistivity measurements of Eu0.58Sr0.42MnO3 were carried out at different magnetic fields under ambient pressure and 1 GPa, respectively. The critical temperature TC of the ferromagnetic metallic state is 128.5 K under 1 GPa and 7 T. The antiferromagnetic insulating phase can be transformed into the ferromagnetic metallic phase by either magnetic field or pressure. Different from the effect of the magnetic field, a plateau is observed in the temperature dependence of the resistivity curve in the lower temperature under pressure, which indicates a phase separation. Magnetic phase diagrams at ambient pressure and 1 GPa are established.