bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuromedin U can exert colon‐specific, enteric nerve‐mediated prokinetic activity, via a pathway involving NMU1 receptor activation
Authors: Dass N B , Bassil A K , North‐Laidler V J , Morrow R , Aziz E , Tuladhar B R , Sanger G J
Published: January 2007

Background and purpose:

The neuromedin U (NMU) receptors, NMU1 and NMU2, are expressed in the gut but their functions are unclear. This study explores the role of NMU in gastrointestinal motility.

Experimental approach:

The effects of NMU were examined in the forestomach and colon isolated from NMU2R wild‐type and NMU2R‐/‐ (knockout) mice, looking for changes in muscle tension and in nerve‐mediated responses evoked by electrical field stimulation (EFS), and in models of peristalsis in mouse colon and faecal pellet transit in guinea‐pig colon.

Key results:

In the mouse forestomach, NMU (1 nM‐10 μM) concentration‐dependently induced muscle contraction, in the presence of tetrodotoxin and atropine, in preparations from both wild‐type and NMU2R‐/‐ mice (pEC50: 7.9, 7.6, Emax: 0.26, 0.20g tension, respectively, n=8 each concentration). The same concentrations of NMU had no consistent effects on the responses to EFS (n=8). In the mouse colon, NMU (0.1 nM‐1 μM) had no significant effect on baseline muscle tension (n=8), but concentration‐dependently potentiated EFS‐evoked contractions in preparations from both wild‐type and NMU2R‐/‐ mice, pEC50: 8.1, 7.8, Emax: 24%, 21%, respectively, n=6‐11. NMU (0.01 nM‐0.1 μM, n=5‐7) concentration‐dependently decreased the interval between waves of peristalsis in the mouse colon (pEC50: 8.8) and increased the rate at which a faecal pellet moved along the guinea‐pig colon.

Conclusions and implications:

These results demonstrate that NMU exerts colon‐specific, nerve‐mediated, prokinetic activity, via a pathway involving activation of NMU1 receptors. This suggests that this receptor may represent a molecular target for the treatment of intestinal motility disorders.

British Journal of Pharmacology (2007) 150, 502–508. doi:10.1038/sj.bjp.0707004
Urotensin‐II Induces Ear Flushing in Rats
Authors: Qi J‐S , Schulingkamp R , Parry T J , Colburn R , Stone D , Haertlein B , Minor L K , Andrade‐Gordon P , Damiano B P
Published: January 2007

Background and purpose:

While investigating the effects of systemic urotensin II (U‐II), a potent vasoactive peptide acting at the UT receptor, we observed ear pinna flushing after systemic administration to conscious rats. In the present study, U‐II‐induced ear flushing was quantified in terms of ear pinna temperature change and potential mechanisms were explored.

Experimental approach:

U‐II‐induced ear flushing was quantified by measuring lateral ear pinna temperature changes and compared to that of calcitonin gene‐related peptide (CGRP), a known cutaneous vasodilator. Further, the effects of a variety of pharmacological agents on U‐II‐induced ear flushing were explored.

Key results:

Subcutaneous injection of U‐II (9 μg kg−1)produced localized ear pinna flushing with an onset of ∼15 min, a duration of ∼30 min and a maximal temperature change of 9°C. In contrast, CGRP caused cutaneous flushing within multiple cutaneous beds including the ear pinna with a shorter onset and greater duration than U‐II. A potent UT receptor antagonist, urantide, blocked U‐II‐induced ear flushing but did not affect CGRP‐induced ear flushing. Pretreatment with indomethacin or L‐N
ω ‐nitroarginine methylester (L‐NAME) abolished U‐II‐induced ear flushing. Mecamylamine or propranolol did not affect this response to U‐II. Direct intracerebroventricular injection studies suggested that the ear flushing response to U‐II was not mediated directly by the CNS.

Conclusion and implications:

Our results suggest that U‐II‐induced ear flushing and temperature increase is mediated by peripheral activation of the UT receptor and involves prostaglandin‐ and nitric oxide‐mediated vasodilation of small capillary beds in the rat ear pinna.

British Journal of Pharmacology (2007) 150, 415–423. doi:10.1038/sj.bjp.0707006
A question of self‐preservation: immunopathology in influenza virus infection
Authors: La Gruta Nicole L , Kedzierska Katherine , Stambas John , Doherty Peter C
Published: January 2007

Influenza A viruses that circulate normally in the human population cause a debilitating, though generally transient, illness that is sometimes fatal, particularly in the elderly. Severe complications arising from pandemic influenza or the highly pathogenic avian H5N1 viruses are often associated with rapid, massive inflammatory cell infiltration, acute respiratory distress, reactive hemophagocytosis and multiple organ involvement. Histological and pathological indicators strongly suggest a key role for an excessive host response in mediating at least some of this pathology. Here, we review the current literature on how various effector arms of the immune system can act deleteriously to initiate or exacerbate pathological damage in this viral pneumonia. Generally, the same immunological factors mediating tissue damage during the anti‐influenza immune response are also critical for efficient elimination of virus, thereby posing a significant challenge in the design of harmless yet effective therapeutic strategies for tackling influenza virus.
Life and death in the granuloma: immunopathology of tuberculosis
Authors: Saunders Bernadette M , Britton Warwick J
Published: January 2007

During tuberculosis (TB) infection, the granuloma provides the microenvironment in which antigen‐specific T cells colocate with and activate infected macrophages to inhibit the growth ofMycobacterium tuberculosis. Although the granuloma is the site for mycobacterial killing, virulent mycobacteria have developed a variety of mechanisms to resist this macrophage‐mediated killing. These surviving mycobacteria become dormant, however, if host cellular immunity or the signals maintaining granuloma structure wane, or if mycobacteria resume replication, leading to reactivation of TB. This balance of life and death applies not only to the mycobacterium but also to the host macrophages that may undergo apoptosis or necrosis, leading to the characteristic caseous necrosis within the granuloma, and the potential spread of TB infection. The immunological factors controlling the development and maintenance of the granuloma will be reviewed.
Shigella’s ways of manipulating the host intestinal innate and adaptive immune system: a tool box for survival?
Authors: Phalipon Armelle , Sansonetti Philippe J
Published: January 2007

Shigella, a Gram‐negative invasive enteropathogenic bacterium, causes the rupture, invasion and inflammatory destruction of the human colonic epithelium. This complex and aggressive process accounts for the symptoms of bacillary dysentery. The so‐called invasive phenotype of Shigella is linked to expression of a type III secretory system (TTSS) injecting effector proteins into the epithelial cell membrane and cytoplasm, thereby inducing local but massive changes in the cell cytoskeleton that lead to bacterial internalization into non‐phagocytic intestinal epithelial cells. The invasive phenotype also accounts for the potent pro‐inflammatory capacity of the microorganism. Recent evidence indicates that a large part of the mucosal inflammation is initiated by intracellular sensing of bacterial peptidoglycan by cytosolic leucine‐rich receptors of the NOD family, particularly NOD1, in epithelial cells. This causes activation of the nuclear factor kappa B and c‐JunNH2‐terminal‐kinase pathways, with interleukin‐8 appearing as a major chemokine mediating the inflammatory burst that is dominated by massive infiltration of the mucosa by polymorphonuclear leukocytes. Not unexpectedly, this inflammatory response, which is likely to be very harmful for the invading microbe, is regulated by the bacterium itself. A group of proteins encoded by Shigella, which are injected into target cells by the TTSS, has been recently recognized as a family of potent regulators of the innate immune response. These enzymes target key cellular functions that are essential in triggering the inflammatory response, and more generally defense responses of the intestinal mucosa. This review focuses on the mechanisms employed by Shigella to manipulate the host innate response in order to escape early bacterial killing, thus ensuring establishment of its infectious process. The escape strategies, the possible direct effect of Shigella on B and T lymphocytes, their impact on the development of adaptive immunity, and how they may help explain the limited protection induced by natural infection are discussed.
Relaxor characteristics of layered Ba1−(3∕2)xLaxBi2Nb2O9 ceramics
Authors: Karthik C. , Varma K. B. R. , Maglione Mario , Etourneau J.
Published: January 2007

Barium lanthanum bismuth niobate Ba1−(3∕2)xLaxBi2Nb2O9 (x=0, 0.05, 0.1, and 0.15) powders have been prepared via solid state reaction route. The monophasic layered perovskite nature of each composition of these was confirmed by x-ray diffraction studies. A continuous decrease in the lattice parameter c of parent BaBi2Nb2O9 with increase in La3+ doping level was noteworthy. A decrease in dielectric constant maximum (εm), a shift in dielectric anomaly to lower temperatures (from 488to382K), and an increase in the diffuseness (γ) (from 1.58 to 1.84) of dielectric anomaly were encountered on increasing x from 0 to 0.15. Vogel-Fulcher analyses showed a decrease in freezing temperature (Tf) (from 157to40K) and an increase in the activation energy (0.53to1.12eV) for frequency dispersion with increase in La3+ content. A downward shift in the peak position of the pyroelectric coefficient with increasing La3+ doping level was observed. The observed changes in the above physical properties were attributed to the increase in A-site chemical heterogeneity as a result of aliovalent La3+ doping on Ba2+ sites and associated A-site vacancy formation.
Thermodynamic equilibrium limitations on the growth of SiC by halide chemical vapor deposition
Authors: Fanton M. A. , Weiland B. E. , Snyder D. W. , Redwing J. M.
Published: January 2007

Single crystal SiC for semiconductor applications is commonly produced by physical vapor transport (PVT). Incongruent sublimation of SiC causes the gas phase composition in the PVT growth cell to drift from Si-rich to C-rich as growth proceeds. The change in C/Si ratio in the gas phase causes significant variations in deep center and dopant concentrations along the growth axis of the crystal. Growth of SiC by halide chemical vapor deposition (HCVD) provides direct control over the C/Si ratio by independently metering C and Si precursor gases to the growth environment. Thermally stable Si sources, such as SiCl4, are used instead of SiH4 to eliminate premature decomposition of the Si source. Use of chlorinated precursors, combined with the high precursor concentrations required for growth rates of 50–250 μm/h, impose thermodynamic limits on the maximum C/Si ratio that can be used for deposition of single crystal SiC. A thermodynamic model is provided for predicting the boundary between deposition of SiC and deposition of a mixture of C and SiC. The predicted location of the boundary between SiC and SiC+C, its abrupt nature, and the expected trends in growth rate with precursor flow rates, agree well with the experimental data. Increasing the H2 concentration was predicted to increase the C/Si ratio at which growth of single crystal SiC could be maintained by increasing the equilibrium concentration of C in the gas phase. This was verified experimentally by observing the transition from polycrystalline mixed phase deposits at low H2 concentrations to growth of single crystal SiC at higher H2 concentrations while maintaining constant Si and C precursor input flow rates and concentrations. The transition was characterized using a combination of x-ray diffraction and observations of the growth morphology by optical microscopy.
Investigation of dipolar defects in (1−x)Pb(Zn1∕3Nb2∕3)O3–xPbTiO3 single crystals using different poling methods
Authors: Shen Mingrong , Cao Wenwu
Published: January 2007

The temperature dependence of piezoelectric, pyroelectric, and dielectric properties have been measured for [001] and [111] oriented 0.92Pb(Zn1∕3Nb2∕3)O3–0.08PbTiO3 (PZN-8%PT) and 0.955Pb(Zn1∕3Nb2∕3)O3–0.045PbTiO3 (PZN-4.5%PT) single crystals poled by two different poling methods, i.e., room temperature (RT) poling and poling through field cooling (FC). Compared with the RT poling case, some interesting features have been found in the FC poled [001] oriented crystal but not in the [111] oriented crystal. These features include the enhancement of piezoelectric properties, lowering of the transition temperature from rhombohedral to tetragonal phase, increasing the amplitude of the spontaneous polarization in the tetragonal phase region, and the decrease of the dielectric constants in the tetragonal phase. These results revealed that the dipolar defects in the crystals are formed between the B and O sites in the ABO3 perovskite structure.
Electrical characteristics of Schottky diodes based on semi-insulating CdTe single crystals
Authors: Kosyachenko L. A. , Maslyanchuk O. L. , Sklyarchuk V. M. , Grushko E. V. , Gnatyuk V. A. , Aoki T. , Hatanaka Y.
Published: January 2007

Electrical properties of Schottky diodes fabricated by vacuum evaporation of Al on the surface of semi-insulating p-like CdTe single crystals have been investigated. The current-voltage characteristics (CVCs) of the diodes have an unconventional pattern which is manifested in the absence of rectification at both low forward bias voltages (<5V) and reverse bias in a wide range of voltages. The linear behavior of CVC is shown to be caused by a very high resistance of the CdTe substrate. In order to exclude an influence of the substrate and obtain the real CVC of the Al∕CdTe contacts, the samples were illuminated with low absorption light. A sharp increase in the forward current at higher voltages (>5V) is associated with the injection of minority carriers into the bulk of the crystals.
Effect of oxygen gas and annealing treatment for magnetically enhanced reactive ion etched (Ba0.65,Sr0.35)TiO3 thin films
Authors: Zhang Baishun , Quan Zuci , Zhang Tianjin , Guo Tao , Mo Shaobo
Published: January 2007

Sol-gel-derived (Ba0.65,Sr0.35)TiO3 (BST) thin films were etched in CF4∕Ar and CF4∕Ar∕O2 plasmas using magnetically enhanced reactive ion etching technology. Experimental results show that adding appropriate O2 to CF4∕Ar can better the etching effects of BST films for the increase of etching rate and decrease of etched residues. The maximum etching rate is 8.47nm∕min when CF4∕Ar∕O2 gas-mixing ratio is equal to 9∕36∕5. X-ray photoelectron spectroscopy (XPS) data confirm accumulation of reaction products on the etched surface due to low volatility of reaction products such as Ba and Sr fluorides, and these residues could be removed by annealing treatment. The exact peak positions and chemical shifts of the interested elements were deduced by fitting XPS narrow-scan spectra with symmetrical Gaussian-Lorentzian product function for Ba 3d, Sr 3d, and O 1s peaks, meanwhile asymmetrical Gaussian-Lorentzian sum function was used to fit Ti 2p doublet to adjust the multiple splitting and/or shake-up process of transition-metal Ti cations. Compared to the unetched counterparts, the etched Ba 3d5∕2, Ba 3d3∕2, Sr 3d5∕2, Sr 3d3∕2, Ti 2p3∕2, Ti 2p1∕2, and O 1s peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46, and 0.50eV, respectively. While the etched Ti 2p3∕2 and Ti 2p1∕2 peaks have small chemical shifts for two reasons. One is that Ti fluoride (TiFz) is mostly removed from the etched surface because of its higher volatility in the process of thermal desorption. The other is that there is a shift compensation between TiFz and the etched BST matrix in which Ti4+ cations are partially reduced to form Tix+ (0<x<4) cations in the presence of adequate oxygen vacancies. The simulated formula of each BST surface is obtained to be (Ba0.65,Sr0.35)Ti0.97O2.86, (Ba0.70,Sr0.30)Ti0.24O1.39, and (Ba0.68,Sr0.32)Ti0.95O2.74, and then the average valence of Ti cations is estimated to be +3.84, +3.25, and +3.66 with respect to the electroneutrality principle, respectively. It is inferred that electrical properties of the etched BST film may be partially recovered by postannealed after etched.
Soft nitridation of GaAs(100) by hydrazine sulfide solutions: Effect on surface recombination and surface barrier
Authors: Berkovits V. L. , Paget D. , Karpenko A. N. , Ulin V. P. , Tereshchenko O. E.
Published: January 2007

The effect of nitridation of GaAs(100) by hydrazine sulfide solutions on the surface recombination velocity and surface barrier has been studied using photoluminescence and photoreflectance spectroscopies. Nitridation produces a decrease of surface recombination velocity by a factor of 26. After three years of air exposure, the recombination velocity is still smaller than for the naturally oxidized surface by a factor of 11. The observed effect is caused by a continuous nitride monolayer bonded with the GaAs substrate. The surface Fermi level is still pinned near midgap, which is attributed to residual unpassivated surface defects.
Polarization-dependent effects of refractive index change associated with photoisomerization investigated with Z-scan technique
Authors: Liang Jianchu , Zhao Heping , Zhou Xiaoqing , Wang Hongcheng
Published: January 2007

The Z-scan technique is used to investigate the effects of refractive index change (RIC) associated with photoisomerization for two cases: in which the sample is pumped and probed by the same elliptically polarized light, and in which the sample is pumped by a linearly polarized light and probed by another linearly polarized light. Both experimental and theoretical results show that for the first case, this effect depends upon the polarization of the light; that is, when the polarization changes continuously from circularly polarization to linearly polarization, the effects of RIC becomes stronger. For the second case, the effect is similar to the effects of saturable Kerr effect, whose nonlinear coefficient n2 is measured.
Band structure and intersubband absorption in modulation-doped V-groove quantum wires
Authors: Crnjanski Jasna V. , Gvozdić Dejan M.
Published: January 2007

A self-consistent nonparabolic calculation of the band structure and intersubband absorption in a V-groove-quantum-wire are presented and analyzed with respect to doping concentration, geometry, and temperature. A comparison with a parabolic flatband model shows that both the self-consistency and the nonparabolicity considerably affect subband edges and the intersubband absorption which are studied when both effects are taken into account. The absorption spectra exhibit a prominent peak in the terahertz region (wavelength range λX=55−95 μm) for the polarization in the direction of the weak confinement (X), while for polarization in the direction of the strong confinement (Y), it shows two groups of peaks, one in a slightly lower wavelength range than for the X polarization, and the second for λY=8−13 μm. Technological parameters considered in our analysis can be used to tailor and adjust the absorption spectra for various applications in the terahertz spectral range.
Theoretical investigation of highly excited vibrational states in DFCO: Calculation of the out-of-plane bending states and simulation of the intramolecular vibrational energy redistribution
Authors: Pasin Gauthier , Iung Christophe , Gatti Fabien , Meyer Hans-Dieter
Published: January 2007

A previously developed modified Davidson scheme [C. Iung and F. Ribeiro, J. Chem. Phys. 121, 174105 (2005)] is applied to compute and analyze highly excited (ν2,ν6) eigenstates in DFCO. The present paper is also devoted to the simulations of the intramolecular vibrational energy redistribution (IVR) initiated by an excitation of the out-of-plane bending vibration (nν6, n=2,4,6,…,18, and 20). The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. A comprehensive comparison with experimental data as well as with previous simulations of IVR in HFCO [G. Pasin et al. J. Chem. Phys. 124, 194304 (2006)] is presented.
New implementation of second-order Møller-Plesset perturbation theory with an analytic Slater-type geminal
Authors: Ten-no Seiichiro
Published: January 2007

The author introduces a new method for the exchange commutator integrals in explicitly correlated Møller-Plesset second order perturbation theory. The method is well suited with an analytic Slater-type geminal correlation factor. He also explains the scheme for auxiliary integrals needed for the correlation factor. Based on different Ansätze, he analyzes the performance of the method on correlation energies and reaction enthalpies in detail.
Magnetic and transport properties of Co-doped Fe3O4 films
Authors: Tripathy D. , Adeyeye A. O. , Boothroyd C. B. , Piramanayagam S. N.
Published: January 2007

We present a systematic study of the structural, magnetic, and magnetotransport properties of Co-doped Fe3O4 films deposited on MgO (100) substrates by cosputtering technique. Transmission electron microscopy images suggest that the undoped and Co-doped Fe3O4 films are polycrystalline in nature and consist of a well defined grain boundary network. The temperature dependence of resistance also shows that the transport mechanism in our films is dominated by electron tunneling across antiferromagnetically coupled grain boundaries. We observed that the magnetic properties of the doped films are markedly sensitive to the Co doping concentration, with the magnetization curves showing drastic changes in coercivity with increasing doping concentration. In-plane magnetoresistance curves show linear magnetic field dependence for the undoped Fe3O4 films while a reduction in magnetoresistance and a departure from linear field dependence are observed for the Co-doped films.
Electron photoemission from charged films: Absolute cross section for trapping –5eV electrons in condensed CO2
Authors: Michaud M. , Hébert E. M. , Cloutier P. , Sanche L.
Published: January 2007

The electron trapping or attachment cross section of carbon dioxide (CO2) condensed as thin films on a spacer of Ar is obtained using a simple model for electron trapping in a molecular film and then charge releasing from the same film by photon absorption. The measurements are presented for different electron exposures and impact energies, film thicknesses, and probing photon energies. The cross section for trapping an electron of incident energy between 0 and 5eV reveals three different attachment processes characterized by a maximum at about 0.75eV, a structured feature around 2.25eV, and a shoulder around 3.75eV. From the measurement of their dependence with the probing photon energy, the two lowest processes produce traps having a vertical electron binding energy of ∼3.5eV, whereas the highest one yields a slightly higher value of ∼3.7eV. The 0.75eV maximum corresponds to the formation of vibrational Feshbach resonances in (CO2)n− anion clusters. The 2.25eV feature is attributed to the formation of a vibrationally excited Πu2 anion in (CO2)n− clusters, followed by fast decay into its vibrational ground state without undergoing autodetachment. Finally, 3.75eV shoulder is assigned to the well-known dissociative electron attachment process from Πu2 anion state producing the O− anion in the gas phase and the (CO2)nO− anions in clusters.
Stability of 3C-SiC surfaces under diamond growth conditions
Authors: Arnault J. C. , Delclos S. , Saada S. , Tranchant N. , Bergonzo Ph.
Published: January 2007

The present study deals with the interaction of C-terminated c(2×2) and Si-rich 3×2 3C-SiC (100) reconstructed surfaces with a microwave plasma chemical vapor deposition used for diamond growth. Pure hydrogen and hydrogen/methane exposures have been carried out. Their effects on the atomic ordering and the stoichiometry within the first planes have been studied in situ using low energy electron diffraction and electron spectroscopies: x-ray photoelectron spectroscopy, x-ray Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy. 5min plasma exposures result in a lost of the initial reconstructions, a postplasma oxygen contamination, and strong modifications of the stoichiometry within the first planes. Indeed, the stability of well defined 3C-SiC surfaces depends strongly on their termination: C-terminated surface exhibits a high inertia while the Si-rich surface undergoes partial etching. The three first silicon atomic planes involved in the 3×2 reconstruction are removed upon pure hydrogen plasma while a monolayer is preserved after hydrogen/methane exposure.
Tilt and dislocations in epitaxial laterally overgrown GaAs layers
Authors: Zytkiewicz Z. R. , Domagala J. Z. , Dobosz D. , Dobaczewski L. , Rocher A. , Clement C. , Crestou J.
Published: January 2007

Transmission electron microscopy (TEM) and high-resolution x-ray diffraction were used to study the crystalline quality of GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2-masked (001) GaAs substrates. A low-angle grain boundary with a well-organized set of dislocations accommodating the misorientation of tilted ELO wings was found at the coalescence front of ELO layers. Similar behavior is often reported for GaN on sapphire ELO structures. Unlike the GaN case, however, no dislocations were found above edges of the mask, which is explained by the much smaller wing tilt angle in our case. The geometry of the dislocation network and analysis of thickness fringes on TEM images were used to measure misorientation of merging ELO wings. The values obtained are in good agreement with those determined by x-ray diffraction.
Self-mode locking in a diode-pumped self-Q-switched green laser
Authors: Yang Kejian , Zhao Shengzhi , Li Ming , Li Guiqiu , Li Dechun , Wang Jing , An Jing
Published: January 2007

Simultaneous self-mode locking and self-Q switching in a diode-pumped intracavity frequency doubled Cr4+:Nd3+:YAG∕KTP green laser operating at 532nm is presented. Nearly 100% modulation depth for self-mode-locked green pulses has been achieved and a maximum average output power of 132mW was obtained at an incident pump power of 5.72W. By using a hyperbolic secant function method, considering the Gaussian spatial distribution of the intracavity photon density and the influences of continuous pump rate, as well as the stimulated radiation lifetime of the active medium and the excited-state lifetime of the saturable absorber, a rate equation model was introduced to reconstruct the Q-switched and mode-locked lasers. The theoretical results are in good agreement with the experimental results, and the width of the self-mode-locked green pulse was estimated to be about 350ps.
Extended weak coupling limit for Friedrichs Hamiltonians
Authors: Dereziński Jan , De Roeck Wojciech
Published: January 2007

We study a class of self-adjoint operators defined on the direct sum of two Hilbert spaces: a finite dimensional one called sometimes a “small subsystem” and an infinite dimensional one called a “reservoir.” The operator, which we call a “Friedrichs Hamiltonian,” has a small coupling constant in front of its off-diagonal term. It is well known that under some conditions in the weak coupling limit the appropriately rescaled evolution in the interaction picture converges to a contractive semigroup when restricted to the subsystem. We show that in this model, the properly renormalized and rescaled evolution converges on the whole space to a new unitary evolution, which is a dilation of the above mentioned semigroup. Similar results have been studied before (Accardi et al., 1990) in more complicated models under the name of “stochastic limit.”
Generalized Dirichlet to Neumann map for moving initial-boundary value problems
Authors: Fokas A. S. , Pelloni B.
Published: January 2007

We present an algorithm for characterizing the generalized Dirichlet to Neumann map for moving initial-boundary value problems. This algorithm is derived by combining the so-called global relation, which couples the initial and boundary values of the problem, with a new method for inverting certain one-dimensional integrals. This new method is based on the spectral analysis of an associated ordinary differantial equation and on the use of the d-bar formalism. As an illustration, the Neumann boundary value for the linearized Schrödinger equation is determined in terms of the Dirichlet boundary value and of the initial condition.
Observation of q-profile dependence in noble gas injection radiative shutdown times in DIII-D
Authors: Hollmann E. M. , Jernigan T. C. , Strait E. J. , Antar G. , Evans T. E. , Gray D. S. , Groth M. , Humphreys D. A. , Parks P. B. , Whyte D. G.
Published: January 2007

Massive injection of argon was used to terminate DIII-D discharges with different radial profiles of the safety factor q. An increasing delay before the onset of the central temperature collapse was observed as the overall (core and edge) q of the target plasma was increased. Additionally, an increase in the length of the current quench time was observed, consistent with reduced magnetohydrodynamic (MHD) mode amplitudes and reduced MHD mixing. These results are supported by measurements of heat and impurity mixing during the thermal collapse which observe that thermal transport and impurity mixing are not smooth functions of time but are accelerated when low-order (n=1) MHD modes are destabilized. These results demonstrate that low-order MHD modes play a central role in gas jet shutdowns and density-limit disruptions in tokamaks.
Direct numerical simulation and the theory of receptivity in a hypersonic boundary layer
Authors: Tumin Anatoli , Wang Xiaowen , Zhong Xiaolin
Published: January 2007

Direct numerical simulation of receptivity in a boundary layer over a sharp wedge of half-angle 5.3degrees is carried out with two-dimensional perturbations introduced into the flow by periodic-in-time blowing-suction through a slot. The freestream Mach number is equal to 8. The perturbation flow field downstream from the slot is decomposed into normal modes with the help of the biorthogonal eigenfunction system. Filtered-out amplitudes of two discrete normal modes and of the fast acoustic modes are compared with the linear receptivity problem solution. The examples illustrate how the multimode decomposition technique may serve as a tool for gaining insight into computational results.
Acousto-optic modulator system for femtosecond laser pulses
Authors: Zeng Shaoqun , Bi Kun , Xue Songchao , Liu Yujing , Lv Xiaohua , Luo Qingming
Published: January 2007

Femtosecond laser pulses have made a revolution in multiphoton excitation microscopy, micromachining, and optical storage for their unprecedented high peak power. However, modulation of their intensity with acousto-optic modulator (AOM) is frustrated by dispersion which results in a significant stretch in pulse width. Here we report a scheme composed of two acousto-optic deflectors (AODs) to modulate the intensity of the femtosecond laser pulses with simultaneous compensation for the temporal dispersion. With commercial AODs, we demonstrated such an AOM system for the femtosecond laser pulses with overall transmission efficiency of around 80%. The pulse width of the exit beam is 115–177fs for an input pulse of 110fs, across the wavelength range of 720–920nm when the temporal dispersion compensation is optimally tuned at 800nm. The fluorescence intensity in a two-photon microscopy experiment performed using this system increased 5.5-fold over that of the uncompensated AOM.
Imaging the photodissociation of CH3SH in the first and second absorption bands: The CH3(X̃A12)+SH(XΠ2) channel
Authors: Amaral G. A. , Ausfelder F. , Izquierdo J. G. , Rubio-Lago L. , Bañares L.
Published: January 2007

The CH3(X̃A12)+SH(XΠ2) channel of the photodissociation of CH3SH has been investigated at several wavelengths in the first 1A″1←X̃A′1 and second 2A″1←X̃A′1 absorption bands by means of velocity map imaging of the CH3 fragment. A fast highly anisotropic (β=−1±0.1) CH3(X̃A12) signal has been observed in the images at all the photolysis wavelengths studied, which is consistent with a direct dissociation process from an electronically excited state by cleavage of the C–S bond in the parent molecule. From the analysis of the CH3 images, vibrational populations of the SH(XΠ2) counterfragment have been extracted. In the second absorption band, the SH fragment is formed with an inverted vibrational distribution as a consequence of the forces acting in the crossing from the bound 2A″1 second excited state to the unbound 1A″1 first excited state. The internal energy of the SH radical increases as the photolysis wavelength decreases. In the case of photodissociation via the first excited state, the direct production of CH3 leaves the SH counterfragment with little internal excitation. Moreover, at the longer photolysis wavelengths corresponding to excitation to the 1A″1 state, a slower anisotropic CH3 channel has been observed (β=−0.8±0.1) consistent with a two step photodissociation process, where the first step corresponds to the production of CH3S(X̃E2) radicals via cleavage of the S–H bond in CH3SH, followed by photodissociation of the nascent CH3S radicals yielding CH3(X̃A12)+S(XP0,1,23).
Exploring the conformational energy landscape of glassy disaccharides by cross polarization magic angle spinning C13 nuclear magnetic resonance and numerical simulations. II. Enhanced molecular flexibility in amorphous trehalose
Authors: Lefort Ronan , Bordat Patrice , Cesaro Attilio , Descamps Marc
Published: January 2007

This paper uses chemical shift surfaces to simulate experimental C13 cross polarization magic angle spinning spectra for amorphous solid state disaccharides, paying particular attention to the glycosidic linkage atoms in trehalose, sucrose, and lactose. The combination of molecular mechanics with density functional theory/gauge invariant atomic orbital ab initio methods provides reliable structural information on the conformational distribution in the glass. The results are interpreted in terms of an enhanced flexibility that trehalose possesses in the amorphous solid state, at least on the time scale of C13 nuclear magnetic resonance measurements. Implications of these findings for the fragility of trehalose glass and bioprotectant action are discussed.
Anisotropic actuation in electroclinic liquid crystal elastomers
Authors: Spillmann Christopher M. , Ratna Banahalli R. , Naciri Jawad
Published: January 2007

The macroscopic mechanical response of a freestanding, electroclinic liquid crystal elastomer to an applied electric field is described. Contraction strains and shearing were observed upon e-field application when 60-μm-thick elastomer films were tested normal and parallel to smectic layers, respectively. The anisotropic response observed in the two orthogonal directions with respect to the smectic layers correlate calculated from mechanical studies with the induced tilt of the molecules. The electrostrictive and electroclinic coefficients agree well with the values calculated from optical tilt angle measurements.
Molecular properties from variational reduced-density-matrix theory with three-particle N-representability conditions
Authors: Gidofalvi Gergely , Mazziotti David A.
Published: January 2007

Molecular ground-state energies and two-electron reduced density matrices (2-RDMs) have recently been computed without the many-electron wave function by constraining the 2-RDM to satisfy a complete set of three-positivity conditions for N representability [D. A. Mazziotti, Phys. Rev. A 74, 032501 (2006)]. Energies at both equilibrium and nonequilibrium geometries are obtained within 0.3% of the correlation energy. In this paper the authors extend this work to examine the accuracy of molecular properties, including multipole moments and components of the ground-state energy, relative to full configuration interaction (FCI). Comparisons are also made with 2-RDM methods with two-positivity conditions and two-positivity plus the generalized T1T2 conditions as well as several approximate wave function methods. Using the 2-RDM method with three-positivity conditions, the authors obtain dipole, quadrupole, and octupole moments for BeH2, BH, H2O, CO, and NH3 at equilibrium geometries that are within 0.04% of their FCI values. In addition, for the potential energy surface of N2, the 2-RDM method with three-positivity yields not only accurate total ground-state energies but also accurate expectation values of the kinetic energy operator, the electron-nuclei potential, and electron-electron repulsion.
Four-channel magnetic resonance imaging receiver using frequency domain multiplexing
Authors: He Wang , Qin Xu , Jiejing Ren , Gengying Li
Published: January 2007

An alternative technique that uses frequency domain multiplexing to acquire phased array magnetic resonance images is discussed in detail. The proposed method has advantages over traditional independent receiver chains in that it utilizes an analog-to-digital converter and a single-chip multicarrier receiver with high performance to reduce the size and cost of the phased array receiver system. A practical four-channel digital receiver using frequency domain multiplexing was implemented and verified on a home-built 0.3T magnetic resonance imaging system. The experimental results confirmed that the cross talk between each channel was below −60dB, the phase fluctuations were about 1°, and there was no obvious signal-to-noise ratio degradation. It is demonstrated that the frequency domain multiplexing is a valuable and economical technique, particularly for array coil systems where the multichannel receiver is indispensable and dynamic range is not a critical problem.
Surface tension and vapor-liquid phase coexistence of confined square-well fluid
Authors: Singh Jayant K. , Kwak Sang Kyu
Published: January 2007

Phase equilibria of a square-well fluid in planar slit pores with varying slit width are investigated by applying the grand-canonical transition-matrix Monte Carlo (GC-TMMC) with the histogram-reweighting method. The wall-fluid interaction strength was varied from repulsive to attractive such that it is greater than the fluid-fluid interaction strength. The nature of the phase coexistence envelope is in agreement with that given in literature. The surface tension of the vapor-liquid interface is calculated via molecular dynamics simulations. GC-TMMC with finite size scaling is also used to calculate the surface tension. The results from molecular dynamics and GC-TMMC methods are in very good mutual agreement. The vapor-liquid surface tension, under confinement, was found to be lower than the bulk surface tension. However, with the increase of the slit width the surface tension increases. For the case of a square-well fluid in an attractive planar slit pore, the vapor-liquid surface tension exhibits a maximum with respect to wall-fluid interaction energy. We also report estimates of critical properties of confined fluids via the rectilinear diameter approach.
Suppression of Rayleigh-Bénard convection with proportional-derivative controller
Authors: Remillieux Marcel C. , Zhao Hui , Bau Haim H.
Published: January 2007

We study theoretically (linear stability) and experimentally the use of proportional and derivative controllers to postpone the transition from the no-motion state to the convective state in a circular cylinder heated from below and cooled from above. The heating is provided with an array of individually controlled actuators whose power is adjusted in proportion to temperatures measured in the cylinder’s interior. As the proportional controller’s gain increases, so does the critical Rayleigh number for the onset of convection. Relatively large proportional controller gains lead to oscillatory convection. The oscillatory convection can be suppressed with the application of a derivative controller, allowing further increases in the critical Rayleigh number. The experimental observations are compared with theoretical predictions.
Two-dimensional and three-dimensional direct numerical simulation of co-rotating vortices
Authors: Orlandi P.
Published: January 2007

Two-dimensional (2D) and three-dimensional (3D) simulations are presented for co-rotating vortices with distributed vorticity at different values of the separation distance b0. The ratio between the vortices’ radius a0 and b0 is smaller than the critical value a0∕b0≈0.30 for merging in inviscid conditions of blobs of constant vorticity. The dependence of merging on Reynolds number and on a0∕b0 has been investigated in 2D simulations. In 2D the resolution can be increased to perform simulations at Re=30000 when very long filaments are generated. These simulations confirm the findings of Brandt and Nomura [L. K. Brandt and K. K. Nomura, Phys. Fluids 18, 51701 (2006)] that the filaments play a minor role in merging. It has been found that a large increase of ∣P∣max (P is the pressure) indicates merging. Time evolving 3D simulations at Re=3000, are similar to the laboratory experiments by Meunier and Leweke [P. Meunier and T. Leweke, J. Fluid Mech. 533, 125 (2005)]. At the same values of a0∕b0 as used in 2D, 3D simulations demonstrate that the merging is more complex than in 2D, and that it largely depends on the kind of axial disturbances imposed, at t=0, on the two vortices. 3D simulations of vortices evolving in space and time, without disturbances at x1=0, have shown that at Re=3000 the results, in a convective frame, do not differ from those in 2D simulations. This assumption, attempting to reproduce the evolution of the vortices behind aircrafts, demonstrates that, with the present computational resources, DNS at practical Reynolds numbers are not feasible.
Low energy electron energy-loss spectroscopy of CF3X (X=Cl,Br)
Authors: Hoshino M. , Sunohara K. , Makochekanwa C. , Pichl L. , Cho H. , Tanaka H.
Published: January 2007

We report threshold electron energy-loss spectra for the fluorohalomethanes CF3X (X=Cl,Br). Measurements were made at incident electron energies of 30 and 100eV in energy-loss range of 4–14eV, and at scattering angles of 4° and 15°. Several new electronic transitions are observed which are ascribable to excitation of low-lying states as well as are intrinsically overlapped in the molecules themselves. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-section measurements, high-energy scattering spectra, and ab initio molecular orbital calculations. The calculated potential curves along the C–X bond show repulsive nature, suggesting that these transitions may lead to dissociation of the C–X bond. The present results are also compared with the previous ones for CF3H, CF4, and CF3I.
Femtosecond multichannel photodissociation dynamics of CH3I from the A band by velocity map imaging
Authors: de Nalda R. , Izquierdo J. G. , Durá J. , Bañares L.
Published: January 2007

The reaction times of several well-defined channels of the C–I bond rupture of methyl iodide from the A band, which involves nonadiabatic dynamics yielding ground state I(P3∕22) and spin-orbit excited I*(P1∕22) and ground and vibrationally excited CH3 fragments, have been measured by a combination of a femtosecond laser pump-probe scheme and velocity map imaging techniques using resonant detection of ground state CH3 fragments. The reaction times found for the different channels studied are directly related with the nonadiabatic nature of this multidimensional photodissociation reaction.
Narrow UV emission from homogeneous GaN∕AlGaN quantum wells
Authors: Feltin E. , Simeonov D. , Carlin J.-F. , Butté R. , Grandjean N.
Published: January 2007

The authors report on the achievement of narrow ultraviolet emission using GaN∕AlGaN quantum wells grown by metal organic vapor phase epitaxy. The origin of the inhomogeneous broadening of the emission is explained by means of micro-photoluminescence and atomic force microscopy measurements. The effect of the well/barrier interface roughness on the linewidth is found to be marginal, while the impact of Al composition fluctuations of the barriers is highly critical. Emission linewidths as small as 5meV at 10K are obtained by decreasing the aluminum concentration fluctuations in the AlGaN barrier.
Screw dislocation assisted martensitic transformation of a bcc Cu precipitate in bcc Fe
Authors: Shim Jae-Hyeok , Cho Young Whan , Kwon Sang Chul , Kim Whung Whoe , Wirth Brian D.
Published: January 2007

Molecular dynamics simulations of the interaction between a screw dislocation and a coherent bcc Cu precipitate in bcc Fe indicate that the screw dislocation stress field assists a martensitic transformation into a close-packed structure for precipitate diameters larger than 1.8nm, resulting in a stronger obstacle to dislocation glide. The observed martensitic transformation mechanism agrees with the Nishiyama-Kajiwara [Jpn. J. Appl. Phys. 2, 478 (1963)] model. For coherent bcc Cu precipitates with diameter larger than 2.5nm, the screw dislocation bypass mechanism becomes Orowan looping due to the coherency loss of the precipitates during the transformation.
Interfacial viscoelasticity of thin polymer films studied by nanoscale dynamic mechanical analysis
Authors: Zhou J. , Komvopoulos K.
Published: January 2007

The interfacial viscoelastic behavior of thin polymer films deposited on silicon substrate was investigated by nanoscale dynamic mechanical analysis involving modulation of the nanoindentation load in the frequency range of 10–200Hz. Significant differences were observed between interfacial and bulk viscoelastic properties. Both the storage modulus and the loss modulus increased with the indentation depth due to the effect of the substrate stiffness. In the low-frequency range, the interfacial viscous behavior was greatly suppressed, presumably due to changes in the molecular chain conformation at the film/substrate interface and/or dynamic confinement of the molecular chains between the indenter and the substrate. Both effects significantly restricted small-scale mobility of the main chains. In the high-frequency range, main chain rearrangement was inhibited and short-range side group relaxation was the dominant mode.
Onset of stacking faults in InP nanowires grown by gas source molecular beam epitaxy
Authors: Cornet D. M. , Mazzetti V. G. M. , LaPierre R. R.
Published: January 2007

InP nanowires (NWs) were grown by gas source molecular beam epitaxy on InP (111)B substrates, using Au nanoparticles as a growth catalyst. The rod-shaped NWs exhibited hexagonal sidewall facets oriented along the {−211} family of crystal planes for all NW diameters, indicating minimal sidewall growth. Stacking faults, when present, were concentrated near the NW tips, while NWs with lengths less than 300nm were completely free of stacking faults.
Use of ultrasound for metal cluster engineering in ion implanted silicon oxide
Authors: Romanyuk Andriy , Oelhafen Peter , Kurps Rainer , Melnik Viktor
Published: January 2007

This letter presents an approach to metal cluster engineering in silicon oxide that uses ultrasound vibration applied in situ during implantation. Analysis by transmission electron microscopy has demonstrated that in situ applied acoustic vibrations result in a lowering of the clustering threshold and an increase in cluster size after subsequent annealing. The results are interpreted in terms of the interaction between ultrasonic vibrations and point defects leading to the formation of vacancy-rich regions, as determined by deuterium decoration method. The excess of vacancies in the precipitation region facilitates nucleation and stimulates cluster growth due to enhanced diffusion of metal species.