bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Arginine Vasopressin V1 and V2 Receptors for Brain Damage After Transient Focal Cerebral Ischemia
Authors: Vakili Abedin , Kataoka Hiroharu , Plesnila Nikolaus
Published: March 2005

Brain edema formation is one of the most important mechanisms responsible for brain damage after ischemic stroke. Despite considerable efforts, no specific therapy is available yet. Arginine vasopressin (AVP) regulates cerebral water homeostasis and has been involved in brain edema formation. In the current study, we investigated the role of AVP V1 and V2 receptors on brain damage, brain edema formation, and functional outcome after transient focal cerebral ischemia, a condition comparable with that of stroke patients undergoing thrombolysis. C57/BL6 mice were subjected to 60-min middle cerebral artery occlusion (MCAO) followed by 23 h of reperfusion. Five minutes after MCAO, 100 or 500 ng of [deamino-Pen(1), O-Me-Tyr(2), Arg(8)]-vasopressin (AVP V1 receptor antagonist) or [adamantaneacetyl(1), O-Et-d-Tyr(2), Val(4), Abu(6), Arg(8,9)]-vasopressin (AVP V2 receptor antagonist) were injected into the left ventricle. Inhibition of AVP V1 receptors reduced infarct volume in a dose-dependent manner by 54% and 70% (to 29±13 and 19±10 mm3 versus 63±17 mm3 in controls; P<0.001), brain edema formation by 67% (to 80.4%±1.0% versus 82.7%±1.2% in controls; P<0.001), blood-brain barrier disruption by 75% ( P<0.001), and functional deficits 24 h after ischemia, while V2 receptor inhibition had no effect. The current findings indicate that AVP V1 but not V2 receptors are involved in the pathophysiology of secondary brain damage after focal cerebral ischemia. Although further studies are needed to clarify the mechanisms of neuroprotection, AVP V1 receptors seem to be promising targets for the treatment of ischemic stroke.
Mild to Moderate Hyperthermia Does Not Worsen Outcome after Severe Intracerebral Hemorrhage in Rats
Authors: MacLellan Crystal L , Colbourne Frederick
Published: March 2005

Hyperthermia worsens outcome in clinical and experimental studies of ischemic stroke. Thus, we tested whether hyperthermia aggravates intracerebral hemorrhage (ICH) in rats. A striatal hemorrhage was produced via an infusion of bacterial collagenase. In a preliminary experiment, we compared brain and core temperatures (via telemetry) during heating (infrared lamp). The brain temperature rise exceeded that produced by enforced core hyperthermia, which was used subsequently. In these experiments up to three hyperthermia conditions (versus normothermia) were tested including: hyperthermia (>38.5°C) over the first (HYP-1) or second 24 h period (HYP-2) after ICH and 3 h of 40°C hyperthermia starting 12 h after ICH (HYP-3). The HYP-1, HYP-2, and HYP-3 treatments did not affect functional deficits (e.g., spontaneous forelimb use, skilled reaching) or the volume of injury at 30 days. Furthermore, the HYP-1 treatment did not aggravate injury or deficits at 7 days. Bleeding and inflammation, which contribute to pathology, were not significantly altered by HYP-1 and HYP-3 treatments. Bleeding was assessed at 1 day, and macrophages and neutrophils were counted at 2 and 4 days. Accordingly, hyperthermia, under the present conditions, did not worsen outcome after striatal ICH.
Simultaneous Detection of Blood Volume, Oxygenation, and Intracellular Calcium Changes during Cerebral Ischemia and Reperfusion in vivo Using Diffuse Reflectance and Fluorescence
Authors: Du Congwu , Koretsky Alan P , Izrailtyan Igor , Benveniste Helene
Published: March 2005

We describe an approach to measure changes in intracellular calcium along with changes in blood volume and oxygenation directly from the exposed rat cortex in vivo during cerebral ischemia and reperfusion. Measurements were made using a catheter-based optical system. The endface of a Y-shaped bifurcated fiber optic bundle was mounted on the cortical surface. It delivered the light at three wavelengths of 548, 555, and 572 nm to the brain through a fast monochromator coupled to a xenon lamp, and collected the calcium-dependent fluorescence emission from Rhod2 at 589 nm (excited at 548 nm) along with the diffuse reflections at the wavelengths of 555 and 572 nm to determine the changes in blood volume and hemoglobin oxygenation. The feasibility of this approach was experimentally examined by inducing transient cerebral ischemia and reperfusion in the rat. The ischemia induced an 8.5%±1.7% fluorescence increase compared with the preischemic control values. Blood volume and tissue hemoglobin oxygenation decreased by 57.4%±12.6% and 47.3%±12.5%, respectively. All signals normalized on reperfusion. The ischemia-induced change in Rhod2-Ca2+ fluorescence was blocked using a calcium channel blocker, nimodipine, confirming that intracellular changes in calcium were responsible for the fluorescence changes. Thus, changes in cerebral hemodynamics and intracellular calcium concentration changes were measured simultaneously, facilitating future studies of the interrelationship between neuronal activation and metabolic and vascular processes in normal and diseased brain.
Limitations of the stretched exponential function for describing dynamics in disordered solid materials
Authors: Apitz D. , Johansen P. M.
Published: March 2005

Around the glass transition temperature, relaxation dynamics in glass-forming materials follows a strong nonexponential behavior. It is widely accepted that an empirically based stretched exponential function, known as the Kohlrausch–Williams–Watts (KWW) function, ϕ(t)=e−(t∕τ)β, describes universally a broad variety of experimental data. Using intuitive pictures and ellipsometric measurements, we show that (1) in order to describe the dynamics in disordered materials such as in polymers using a KWW function, the response has to be considered over a specific region of time, (2) a single KWW function is not sufficient for correctly describing more than one relaxation processes, and (3) in certain cases, stretching exponents depending on temperature do not cover the ranges previously suggested (from 0 to 1, e.g., as a sigmoid function). As an example, we show that the temperature dependence of the stretching exponent β(T) depends highly on how the curve fits with the KWW function are performed.
Ground state and constrained domain walls in Gd∕Fe multilayers
Authors: Van Aken Bas B. , Prieto José L. , Mathur Neil D.
Published: March 2005

The magnetic ground state of antiferromagnetically coupled Gd∕Fe multilayers and the evolution of in-plane domain walls is modeled with micromagnetics. The twisted state is characterized by a rapid decrease of the interface angle with increasing magnetic field. We found that for certain ratios MFe:MGd, the twisted state is already present at low fields. However, the magnetic ground state is not only determined by the ratio MFe:MGd but also by the thicknesses of the layers; that is by the total moments of the layer. The dependence of the magnetic ground state is explained by the amount of overlap of the domain walls at the interface. Thicker layers suppress the Fe-aligned and the Gd-aligned state in favor of the twisted state. On the other hand, ultrathin layers exclude the twisted state, since wider domain walls cannot form in these ultrathin layers.
Approaching the basis set limit for transition metal compounds with highly polar bonds: A benchmark coupled-cluster study of the ScF3 and FeF3 molecular structures and spectra
Authors: Solomonik Victor G. , Stanton John F. , Boggs James E.
Published: March 2005

The molecular equilibrium geometries, quadratic and cubic force constants, vibrational frequencies, and infrared intensities of scandium and iron trifluorides are determined ab initio with a sequence of atomic natural orbital basis sets using the CCSD(T) treatment of electron correlation. The largest basis set of spdfghi quality contains 462 contracted Gaussian functions. Relativistic corrections are applied to compute the equilibrium geometries and vibrational frequencies. The cubic force constants are used to estimate vibrational corrections to the effective rg internuclear distances determined in the gas electron diffraction experiments. The computed molecular properties are extrapolated to the complete basis-set limit. The predicted values are compared to the available experimental data; uncertainties and inconsistencies in these data are then discussed.
Unified model of secondary electron cascades in diamond
Authors: Ziaja Beata , London Richard A. , Hajdu Janos
Published: March 2005

In this article we present a detailed and unified theoretical treatment of secondary electron cascades that follow the absorption of x-ray photons. A Monte Carlo model has been constructed that treats in detail the evolution of electron cascades induced by photoelectrons and by Auger electrons following inner shell ionizations. Detailed calculations are presented for cascades initiated by electron energies between 0.1 and 10keV. The present article expands our earlier work [B. Ziaja, D. van der Spoel, A. Szöke, and J. Hajdu, Phys. Rev. B 64, 214104 (2001), Phys. Rev. B 66, 024116 (2002)] by extending the primary energy range, by improving the treatment of secondary electrons, especially at low electron energies, by including ionization by holes, and by taking into account their coupling to the crystal lattice. The calculations describe the three-dimensional evolution of the electron cloud, and monitor the equivalent instantaneous temperature of the free electron gas as the system cools. The dissipation of the impact energy proceeds predominantly through the production of secondary electrons whose energies are comparable to the binding energies of the valence (40–50eV) and of the core electrons (300eV). The electron cloud generated by a 10keV electron is strongly anisotropic in the early phases of the cascade (t⩽1fs). At later times, the sample is dominated by low energy electrons, and these are scattered more isotropically by atoms in the sample. Our results for the total number of secondary electrons agree with available experimental data, and show that the emission of secondary electrons approaches saturation within about 100fs following the primary impact.
Infrared overtone spectroscopy and unimolecular decay dynamics of peroxynitrous acid
Authors: Konen Ian M. , Pollack Ilana B. , Li Eunice X. J. , Lester Marsha I. , Varner Mychel E. , Stanton John F.
Published: March 2005

Peroxynitrous acid (HOONO) is generated in a pulsed supersonic expansion through recombination of photolytically generated OH and NO2 radicals. A rotationally resolved infrared action spectrum of HOONO is obtained in the OH overtone region at 6971.351(4)cm−1 (origin), providing definitive spectroscopic identification of the trans-perp (tp) conformer of HOONO. Analysis of the rotational band structure yields rotational constants for the near prolate asymmetric top, the ratio of the a-type to c-type components of the transition dipole moment for the hybrid band, and a homogeneous linewidth arising from intramolecular vibrational energy redistribution and/or dissociation. The quantum state distribution of the OH (ν=0,JOH) products from dissociation is well characterized by a microcanonical statistical distribution constrained only by the energy available to products, 1304±38cm−1. This yields a 5667±38cm−1 [16.2(1)kcalmol−1] binding energy for tp-HOONO. An equivalent available energy and corresponding binding energy are obtained from the highest observed OH product state. Complementary high level ab initio calculations are carried out in conjunction with second-order vibrational perturbation theory to predict the spectroscopic observables associated with the OH overtone transition of tp-HOONO including its vibrational frequency, rotational constants, and transition dipole moment. The same approach is used to compute frequencies and intensities of multiple quantum transitions that aid in the assignment of weaker features observed in the OH overtone region, in particular, a combination band of tp-HOONO involving the HOON torsional mode.
Measurement of stiffness and damping constant of self-assembled monolayers
Authors: Devaprakasam D. , Biswas S. K.
Published: March 2005

We design and fabricate an apparatus which uses two dual double cantilever flexures to probe mechanical properties of self-assembled monolayers (SAM) under compression. The cantilevers were designed to give stiffness of the same order as the SAM. One of the cantilevers carrying the probe is vibrated sinusoidally at subresonance frequency and subnanometric amplitude while the dynamic response of the other carrying the SAM is recorded in the contact mode to yield data which could be deconvoluted to give stiffness and damping constant of the SAM under compression using a model of viscoelasticity. We validate the apparatus as well as the method of deconvolution by indenting bulk polytetrafluoroethylene and estimate mechanical properties of SAMs of different chain length and head group. The approach adopted here is able to distinguish in terms of mechanical properties a bulk polymer from a SAM and also between two SAMs of similar but subtly different structure.
Describing static correlation in bond dissociation by Kohn–Sham density functional theory
Authors: Fuchs M. , Niquet Y.-M. , Gonze X. , Burke K.
Published: March 2005

We show that density functional theory within the RPA (random phase approximation for the exchange-correlation energy) provides a correct description of bond dissociation in H2 in a spin-restricted Kohn–Sham formalism, i.e., without artificial symmetry breaking. We present accurate adiabatic connection curves both at equilibrium and beyond the Coulson–Fisher point. The strong curvature at large bond length implies important static (left–right) correlation, justifying modern hybrid functional constructions but also demonstrating their limitations. Although exact at infinite separation and accurate near the equilibrium bond length, the RPA dissociation curve displays unphysical repulsion at larger but finite bond lengths. Going beyond the RPA by including the exact exchange kernel (RPA+X), we find a similar repulsion. We argue that this deficiency is due to the absence of double excitations in adiabatic linear response theory. Further analyzing the H2 dissociation limit we show that the RPA+X is not size consistent, in contrast to the RPA.
Quantum transition state theory for the full three-dimensional H+H2 reaction
Authors: Zheng Yujun
Published: March 2005

A recently developed quantum transition state theory (QTST) [E. Pollak and J. L. Liao, J. Chem. Phys. 108, 2733 (1998)] for calculating thermal rate constants of chemical reactions is applied to the full three-dimensional hydrogen exchange reaction. Results are compared with other numerical results, for temperatures ranging from T=300KtoT=1500K. The QTST rate is almost exact at high temperature and is 20% greater than the exact rate at T=300K, where there is extensive tunneling.
Homogeneous nucleation of n-propanol, n-butanol, and n-pentanol in a supersonic nozzle
Authors: Gharibeh Murad , Kim Yoojeong , Dieregsweiler Uta , Wyslouzil Barbara E. , Ghosh David , Strey Reinhard
Published: March 2005

We have measured the nucleation conditions of n-propanol, n-butanol, and n-pentanol in a supersonic Laval nozzle, and estimated that the maximum nucleation rate J is 5×1016cm−3s−1 with an uncertainty factor of 2. Plotting the vapor pressures pJmax and temperatures TJmax corresponding to the maximum nucleation rate as ln(p) versus 1∕T, produces a series of well separated straight lines. When these values are scaled by their respective critical parameters, pc and Tc, the data lie close to a single straight line. Comparing the experimental data to the predictions of classical nucleation theory reveals much higher experimental rates, and the deviation increases with increasing alcohol chain length and decreasing temperature. A scaling analysis in terms of Hale’s scaled nucleation model [Phys. Rev. A 33, 4156 (1986); Metall. Trans. A 23, 1863 (1992)], clearly shows that our data are consistent with experimental nucleation rates measured using other devices that have characteristic rates many orders of magnitude lower.
Photoelectron spectroscopy of fullerene dianions C762−, C782−, and C842−
Authors: Ehrler Oli T. , Furche Filipp , Mathias Weber J. , Kappes Manfred M.
Published: March 2005

We report laser photoelectron spectra of the doubly negatively charged fullerenes C762−, C782−, and C842− at 2.33, 3.49, and 4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment energies, as well as estimates for the repulsive Coulomb barriers are obtained. These results are discussed in the context of electrostatic models. They reveal that fullerenes are similar to conducting spheres, with electronic properties scaling with their size. The experimental spectra are compared with the accessible excited states of the respective singly charged product ions calculated in the framework of time dependent density functional theory.
The effect of zero-point energy differences on the isotope dependence of the formation of ozone: A classical trajectory study
Authors: Schinke Reinhard , Fleurat-Lessard Paul
Published: March 2005

The effect of zero-point energy differences (ΔZPE) between the possible fragmentation channels of highly excited O3 complexes on the isotope dependence of the formation of ozone is investigated by means of classical trajectory calculations and a strong-collision model. ΔZPE is incorporated in the calculations in a phenomenological way by adjusting the potential energy surface in the product channels so that the correct exothermicities and endothermicities are matched. The model contains two parameters, the frequency of stabilizing collisions ω and an energy dependent parameter Δdamp, which favors the lower energies in the Maxwell–Boltzmann distribution. The stabilization frequency is used to adjust the pressure dependence of the absolute formation rate while Δdamp is utilized to control its isotope dependence. The calculations for several isotope combinations of oxygen atoms show a clear dependence of relative formation rates on ΔZPE. The results are similar to those of Gao and Marcus [J. Chem. Phys. 116, 137 (2002)] obtained within a statistical model. In particular, like in the statistical approach an ad hoc parameter η≈1.14, which effectively reduces the formation rates of the symmetric ABA ozone molecules, has to be introduced in order to obtain good agreement with the measured relative rates of Janssen et al. [Phys. Chem. Chem. Phys. 3, 4718 (2001)]. The temperature dependence of the recombination rate is also addressed.
Fragmentation dynamics of H2S following S 2p photoexcitation
Authors: Guillemin R. , Stolte W. C. , Dang L. T. N. , Yu S.-W. , Lindle D. W.
Published: March 2005

The fragmentation dynamics of core-excited H2S has been studied by means of partial anion and cation yield measurements around the S L2,3-subshell ionization thresholds. All detectable ionic fragments are reported, and significant differences between partial ion yields are observed. Possible dissociation pathways are discussed by comparison to previous studies of electron spectra.
The principles of infrared-x-ray pump-probe spectroscopy. Applications on proton transfer in core-ionized water dimers
Authors: Felicíssimo V. C. , Guimarães F. F. , Gel’mukhanov F. , Cesar A. , Ågren H.
Published: March 2005

In this paper we derive the basic physics underlying infrared-x-ray pump-probe spectroscopy (IR, infrared). Particular features of the spectroscopy are highlighted and discussed, such as dependence on phase of the infrared pulse, duration and delay time of the x-ray pulse, and molecular orientation. Numerical applications are carried out for the water dimer using wave packet techniques. It is shown that core ionization of the donor oxygen of the water dimer results in a drastic change of the potential with the global minimum placed in the proton transfer region. The results of the modeling indicate that IR-x-ray pump-probe spectroscopy can be used to study the dynamics of proton transfer in this core-ionized state, and that, contrary to conventional core level photoelectron spectroscopy, x-ray core-ionization driven by an IR field is a proper method to explore the proton transfer in a system like the water dimer. We observe that the trajectory of the nuclear wave packet in the ground state potential well is strongly affected by the absolute phase of the IR pulse.
Low-impedance internal linear inductive antenna for large-area flat panel display plasma processing
Authors: Kim K. N. , Jung S. J. , Lee Y. J. , Yeom G. Y. , Lee S. H. , Lee J. K.
Published: March 2005

An internal-type linear inductive antenna, that is, a double-comb-type antenna, was developed for a large-area plasma source having the size of 1020mm×830mm, and high density plasmas on the order of 2.3×1011cm−3 were obtained with 15 mTorr Ar at 5000 W of inductive power with good plasma stability. This is higher than that for the conventional serpentine-type antenna, possibly due to the low impedance, resulting in high efficiency of power transfer for the double-comb antenna type. In addition, due to the remarkable reduction of the antenna length, a plasma uniformity of less than 8% was obtained within the substrate area of 880mm×660mm at 5000 W without having a standing-wave effect.
Influence of stoichiometry of direct plasma-enhanced chemical vapor deposited SiNx films and silicon substrate surface roughness on surface passivation
Authors: De Wolf Stefaan , Agostinelli Guido , Beaucarne Guy , Vitanov Petko
Published: March 2005

In this article, we report on the use of direct plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films deposited at low excitation frequency (440 kHz) on low-resistivity (1.5 Ω cm) p-type Czochralski silicon substrate surfaces with different textures, to elucidate the influence of microroughness of the substrate surface on the surface-passivating properties of thin SiNx films. Whereas flat surfaces get the best passivation from Si-rich SiNx films, the optimum passivation shifts towards stoichiometric nitride as the microroughness increases, which points to the increasing relative importance of a charge-induced field effect. When short high-temperature (firing) treatments are applied upon passivation layer deposition, the process window to yield good surface passivation broadens, although very Si-rich films tend to suffer from blistering.
Magnetotransport properties of ferromagnetic Ga1−xMnxAs layers on a (100) GaAs substrate
Authors: Yoon I. T. , Kang T. W. , Kim K. H. , Kim D. J.
Published: March 2005

The magnetotransport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2%–4.4% were investigated using Hall effect measurements. The temperature-dependent Hall carrier concentration for a metallic sample with x≈2.2% was analyzed assuming an activation energy from two acceptor levels. It was found that the two acceptor levels with activation energies of 129.4 and 31.6 meV at B=0Oe decreased to 87.6 and 30.7 meV, respectively, at B=5kOe. The decrease in acceptor activation energy from 129.6 to 87.6 meV was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for the increase in carrier concentration. From magnetic-field-dependent Hall resistance data, the Curie temperature was estimated to be TC=60 and 70 K for Ga1−xMnxAs samples with x≈2.2 and x≈4.4%, respectively. The magnetoresistance measurements confirmed that the anomalous Hall effect existed in these samples that showed metallic and insulating behavior, respectively.
Propagation of a magnetic domain wall in magnetic wires with asymmetric notches
Authors: Himeno A. , Okuno T. , Kasai S. , Ono T. , Nasu S. , Mibu K. , Shinjo T.
Published: March 2005

The propagation of a magnetic domain wall (DW) in a submicron magnetic wire consisting of a magnetic/nonmagnetic/magnetic trilayered structure with asymmetric notches was investigated by utilizing the giant magnetoresistance effect. The propagation direction of a DW was controlled by a pulsed local magnetic field, which nucleates the DW at one of the two ends of the wire. It was found that the depinning field of the DW from the notch depends on the propagation direction of the DW.
Hybrid electronic device based on polyaniline-polyethyleneoxide junction
Authors: Erokhin Victor , Berzina Tatiana , Fontana Marco P.
Published: March 2005

A three-electrode hybrid molecular electronic element based on polyaniline (PANI) emeraldine base–polyethylene oxide∕LiCl was fabricated and tested. Source and drain electrodes were connected to the conducting polymer layer. Solid electrolyte was deposited as a narrow stripe over the PANI film, and the third electrode (gate), maintained at ground potential, was attached to it. Drain and gate currents were measured during a drain voltage sweep. Drain voltage–current characteristics revealed a rectifying behavior, while gate characteristics were similar to those for cyclic voltammograms. Such behavior was attributed to the electrochemical control of the redox state (and hence of conductivity) of PANI area under the solid electrolyte. The device was stable and reproducible with robust electrical characteristics. In particular, an asymmetry in time relaxation due to ion diffusion was found; a possible application of this to the use of this device in adaptive conducting networks is proposed.
Domain-wall dynamics at micropatterned constrictions in ferromagnetic (Ga,Mn)As epilayers
Authors: Honolka J. , Masmanidis S. , Tang H. X. , Roukes M. L. , Awschalom D. D.
Published: March 2005

The influence of sub-μm geometric constrictions on 90° magnetic domain-wall nucleation and propagation in stripes of ferromagnetic (Ga0.95,Mn0.05)As was explored. Measurements of the magnetic switching behavior were performed during ramping of an external magnetic field at constant rate and at constant field in the time domain. Demagnetizing fields are found to play a crucial role in the switching behavior around the region of the constriction. Depending on the sample’s initial magnetization the constriction can either assist domain-wall nucleation or hinder its propagation.
Preisach model and simulation of the converse piezoelectric coefficient in ferroelectric ceramics
Authors: Turik S. A. , Reznitchenko L. A. , Rybjanets A. N. , Dudkina S. I. , Turik A. V. , Yesis A. A.
Published: March 2005

The electric-field dependencies of the elastic strains ξ3(E) and the converse piezoelectric coefficients d33(E) for ferroelectric ceramics of different degree of ferroelectric hardness have been measured. The observed results have been approximated by the Preisach and Rayleigh polynomials. The nonmonotonic d33(E) dependence for ferroelectric ceramics has been established. The interpretation of the observed results based on a substantially different distribution of reoriented domains over the internal and coercive electric fields in the ceramics of different degree of ferroelectric hardness is given.
High coupling KNbO3 width-extensional vibrators with a polar multidomain structure
Authors: Koyama Hirokatsu , Nakamura Kiyoshi , Takano Takehiro
Published: March 2005

The longitudinal piezoelectric coupling factor for the width-extensional mode of a thin KNbO3 plate, k11′, has theoretically been predicted to be as high as 82.4% for the 43.5° rotated Z cut about the Y axis. To experimentally confirm the predicted value we fabricated a width-extensional vibrator using a 45° rotated Z cut plate about the Y axis, which is close to the maximum k11′ cut. However, the measured value of k11′ was 71.3%, appreciably lower than the predicted value. It is clarified that the lower coupling factor can be ascribed to the tilt of the electric-field vector from the major face of the plate, which results from an off-diagonal component of the dielectric tensor. To prevent the electric-field tilt, a polar multidomain structure consisting of two kinds of 90° domains is introduced into the width-extensional vibrator instead of a single-domain structure. It is demonstrated by finite element method simulations that the coupling factor approaches the predicted value (82.4%) as the number of domains formed in the vibrator increases. The measured coupling factor of a width-extensional vibrator with a polar multidomain structure is as high as 79.4%, which is close to the predicted value. An additional advantage of using this domain structure is its lower spurious response.
On the accuracy of the void fraction measurements using optical probes in bubbly flows
Authors: Enrique Juliá J. , Harteveld Wouter K. , Mudde Robert F. , Van den Akker Harrie E. A.
Published: March 2005

The accuracy of the measurement of the void fraction in bubbly flows using an optical probe is investigated. Experiments were performed in tap water with ellipsoidal-shaped air bubbles with equivalent diameters and velocities in the range of 2.8–5.2 mm and 0.22–0.28 m∕s. Comparison of charge coupled devices (CCD) images of dynamic bubble piercing events with optical probe signals shows that for piercing in the area around the bubble side, the so-called low-level criterion gives the best agreement with the actual gas-liquid transition for the undisturbed bubble. In addition, residence time underestimation due to a partial blinding effect is observed in the outer regions of the bubble. Residence times of the probe inside the bubble are obtained from the probe signal and from CCD images of the undisturbed bubble. These are compared to study the relevance of various probe-bubble interaction effects. The crawling effect is found to play an important role. For perpendicular piercing, the experiment shows that in the central area of the bubble deceleration effects induced by the probe lead to local overestimation of residence times. In the outer region of the bubble, large-scale deformation leads to local underestimation of residence times. The larger cross-sectional area associated with the underestimation leads to a net underestimation of the total bubble volume. For nonperpendicular piercing, the probe inclination is found to generate an additional drifting effect, creating an additional source of underestimation.
Kinetic study on the phase transformations in sputter deposited NiMn thin films
Authors: Huang Mianliang
Published: March 2005

The phase transformations of NiMn films were investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The sputter deposited NiMn thin films onto room temperature substrates were observed to possess a metastable, chemically disordered, mixture of amorphous and face centered cubic (fcc) phases. DSC measurements revealed four exothermic peaks. TEM studies determined that the DSC peaks were associated with the oxidation of the Mn, two phase transformation reactions (amorphous to fcc and fcc to L10) and grain growth of L10 phase. Using DSC, the enthalpy (activation energy) for amorphous to fcc and fcc to L10 transformations has been measured yielding values of −1.4, −4.7kJ∕mol (121±25 and 140±25kJ∕mol), respectively. The enthalpy of grain growth has been determined as −1.1kJ∕mol. The kinetics of the reaction was simulated using the Johnson–Mehl–Avrami analysis, where the necessary parameters were determined by the Kissinger method on DSC data and also from XRD data of isothermal annealed samples.
Freezing/melting of Lennard-Jones fluids in carbon nanotubes
Authors: Hung F. R. , Gubbins K. E. , Radhakrishnan R. , Szostak K. , Béguin F. , Dudziak G. , Sliwinska-Bartkowiak M.
Published: March 2005

We report molecular simulation and experimental results for the freezing/melting behavior of Lennard-Jones fluids adsorbed in pores of cylindrical geometry, using simple models for multiwalled carbon nanotubes (MWNTs) of inner diameter 5nm. For cylindrical pores, our results for a D=9.7σff MWNT show no formation of regular three-dimensional crystalline structures. They also suggest that the outer layers experience an increase in the freezing temperature, while the inner layers provoke a depression in the freezing temperature with respect to the bulk freezing point. Dielectric relaxation spectroscopy shows a solid-fluid transition at 234K for CCl4 in these MWNTs that is in qualitative agreement with that determined in our simulations for the inner adsorbed layers.
Using fluorescence lifetime for discriminating detector afterpulsing in fluorescence-correlation spectroscopy
Authors: Enderlein Jörg , Gregor Ingo
Published: March 2005

Fluorescence correlation spectroscopy (FCS) has become an important and widely used technique for many applications in physics, chemistry, and biology. Usually, FCS is measured with sensitive light detectors working in the photon-counting Geiger mode. A common property of such detectors is afterpulsing: the generation of spurious photon detection events after a genuine photon detection. Such afterpulsing causes a significant deviation of the measured autocorrelation function from its true value on a short time scale and can seriously influence derived parameters for fast processes such as triplet-state photophysics. Here, we discuss the impact of afterpulsing on FCS in detail. A new method is developed to eliminate afterpulsing effects by using time-correlated single-photon counting for separating the true fluorescence signal from afterpulsing events.
On the piezoelectric contribution to the photopyroelectric signal
Authors: Salazar A. , Oleaga A.
Published: March 2005

The most important goal of the photopyroelectric (PPE) technique, wherein an opaque sample is periodically illuminated on one face while the other is in contact with the pyroelectric detector, is its ability to measure the thermal properties across phase transitions with high accuracy. For thermally thick samples, the logarithm of the amplitude and the phase of the PPE signal are parallel straight lines when represented as a function of the square root of the modulation frequency. From their slope and from their vertical separation, thermal diffusivity and thermal effusivity are obtained, respectively. However, these linear relations are lost when measuring solid samples below 230 K, the temperature at which the coupling fluid used to guarantee the thermal coupling between the sample and the pyroelectric detector freezes. In this work we demonstrate quantitatively that this loss of linearity is due to the piezoelectric contribution to the pyroelectric signal, which increases with the stiffness of the coupling fluid. Moreover, a multiparametric fitting allows us to retrieve the thermal parameters.
Enhanced magnetic ionization in hydrogen reflex discharge plasma source
Authors: Toader E. I. , Covlea V. N.
Published: March 2005

The effect of enhanced magnetic ionization on the external and internal parameters of a high-density, low pressure reflex plasma source operating in hydrogen is studied. The Langmuir probe method and Druyvesteyn procedure coupled with suitable software are used to measure the internal parameters. The bulk plasma region is free of an electric field and presents a high degree of uniformity. The electron energy distribution function is bi-Maxwellian with a dip∕shoulder structure around 5.5eV, independent of external parameters and radial position. Due to the enhanced hollow cathode effect by the magnetic trapping of electrons, the electron density ne is as high as 1018m−3, and the electron temperature Te is as low as a few tens of an electron volt, for dissipated energy of tens of Watts. The bulk plasma density scales with the dissipated power.
Fabrication and uniaxial magnetic anisotropy of Co nanowires on a Pd(110) surface
Authors: Yan L. , Przybylski M. , Lu Yafeng , Wang W. H. , Barthel J. , Kirschner J.
Published: March 2005

We have fabricated Co atomic chains and nanowires on a Pd(110) surface oriented along the [1-10] direction. This is possible due to high diffusion anisotropy of the Co adatom on the Pd(110) surface. The Co nanowires on Pd(110) exhibit a strong uniaxial in-plane magnetic anisotropy, in which the easy axis is along [1-10], i.e., nanowire direction.
Growth and characterization of single quantum dots emitting at 1300 nm
Authors: Alloing B. , Zinoni C. , Zwiller V. , Li L. H. , Monat C. , Gobet M. , Buchs G. , Fiore A. , Pelucchi E. , Kapon E.
Published: March 2005

We have optimized the molecular-beam epitaxy growth conditions of self-organized InAs∕GaAs quantum dots (QDs) to achieve a low density of dots emitting at 1300 nm at low temperature. We used an ultralow InAs growth rate, lower than 0.002ML∕s, to reduce the density to 2dots∕μm2 and an InGaAs capping layer to achieve longer emission wavelength. Microphotoluminescence spectroscopy at low-temperature reveals emission lines characteristic of exciton-biexciton behavior. We also study the temperature dependence of the photoluminescence, showing clear single QD emission up to 90 K. With these results, InAs∕GaAs QDs appear as a very promising system for future applications of single photon sources in fiber-based quantum cryptography.
Isomer selective infrared spectroscopy of neutral metal clusters
Authors: Fielicke André , Ratsch Christian , von Helden Gert , Meijer Gerard
Published: March 2005

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80–400cm−1 region. The observed spectra for Nb9Arn (n=1–4) are different for different values of n. This is explained by the presence of two isomers of Nb9 that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.
Extremely low surface recombination velocity in GaInAsSb∕AlGaAsSb heterostructures
Authors: Wang C. A. , Shiau D. A. , Donetsky D. , Anikeev S. , Belenky G. , Luryi S.
Published: March 2005

Low surface recombination velocity is critical to the performance of minority carrier devices. Minority carrier lifetime in double heterostructures (DHs) of 0.53-eV p-GaInAsSb confined with 1.0-eV p-AlGaAsSb, and grown lattice-matched to GaSb, was measured by time-resolved photoluminescence. The structures were designed to be dominated by the heterointerface while minimizing the contribution of photon recycling to minority carrier lifetime. Surface recombination velocity as low as 30cm∕s for DHs was achieved. This value is over an order of magnitude lower than that reported in previous studies.
Pressure-dependent thermopower of individual Bi nanowires
Authors: Gitsu D. , Konopko L. , Nikolaeva A. , Huber T. E.
Published: March 2005

The 240–620nm diameter nanowires were freely suspended and thermopower measurements were carried out over the temperature range 4–300K and for stresses as high as 1GPa. The peaks of up to 80μV∕K that are observed around 40K are interpreted in terms of a model of diffusion thermopower under strong electron and hole-boundary scattering. The partial Seebeck coefficients are calculated from the stress-dependent carrier Fermi energies obtained from magnetoresistance measurements. The prospect of Bi nanowire arrays achieving high thermoelectric figure of merit is discussed.
High mobility two-dimensional electron gas in AlGaN∕GaN heterostructures grown on bulk GaN by plasma assisted molecular beam epitaxy
Authors: Skierbiszewski C. , Dybko K. , Knap W. , Siekacz M. , Krupczyński W. , Nowak G. , Boćkowski M. , Łusakowski J. , Wasilewski Z. R. , Maude D. , Suski T. , Porowski S.
Published: March 2005

The results on growth and magnetotransport characterization of AlGaN∕GaN heterostructures obtained by plasma assisted molecular beam epitaxy on dislocation-free (below 100cm−2) GaN high pressure synthesized bulk substrates are presented. The record mobilities of the two dimensional electron gas (2DEG) exceeding 100000cm2∕Vs at liquid helium temperature and 2500cm2∕Vs at room temperature are reported. An analysis of the high field conductivity tensor components allowed us to discuss the main electron scattering mechanisms and to confirm unambiguously the 2DEG room temperature mobility values.
Plastic flow localization in bulk tungsten with ultrafine microstructure
Authors: Wei Q. , Ramesh K. T. , Ma E. , Kesckes L. J. , Dowding R. J. , Kazykhanov V. U. , Valiev R. Z.
Published: March 2005

Shear localization is demonstrated in bulk tungsten (W) of commercial purity under dynamic uniaxial compression. Microstructure refinement via severe plastic deformation was the strategy used to induce this unusual deformation mode for W. The ultrafine microstructure achieved in bcc materials leads to elevated strength and ductility, as well as reduced strain hardening and strain rate hardening, thus enhancing the propensity for adiabatic plastic flow localization.
Mixed host organic light-emitting devices with low driving voltage and long lifetime
Authors: Lee Jiun-Haw , Wu Chih-I. , Liu Shun-Wei , Huang Ching-An , Chang Yih
Published: March 2005

In this letter, we present and analyze the device performance of the mixed host (MH) organic light-emitting devices (OLEDs). The host of the emitting layer (EML) material in this device consists of a hole transport layer (HTL) and an electron transport layer (ETL) fabricated by coevaporation. The bipolar transport characteristic of the MH layer helps to reduce the driving voltage. Device lifetime is increased due to the elimination of the sharp boundary of the HTL/EML interface. Combining the MH structure with a high mobility electron ETL material, bis(10-hydroxybenzo[h]qinolinato)beryllium, the OLED has shown a brightness of 27600cd∕m2 at a driving voltage of 5 V, and a lifetime four times longer than that of a conventional OLED.
Dynamically focused optical coherence tomography for endoscopic applications
Authors: Divetia Asheesh , Hsieh Tsung-Hsi , Zhang Jun , Chen Zhongping , Bachman Mark , Li Guann-Pyng
Published: March 2005

We report a demonstration of a small liquid-filled polymer lens that may be used to dynamically provide scanning depth focus for endoscopic optical coherence tomography (OCT) applications. The focal depth of the lens is controlled by changing the hydraulic pressure within the lens, enabling dynamic focal depth control without the need for articulated parts. The 1 mm diameter lens is shown to have resolving power of 5 μm, and can enable depth scans of 2.5 mm, making it suitable for use with OCT-enabled optical biopsy applications.
Flow actuation using radio frequency in partially ionized collisional plasmas
Authors: Roy Subrata
Published: March 2005

We present a multidimensional theoretical model for a better understanding and the design of the dielectric barrier discharge-induced momentum exchange. Specifically, the formulation is used to predict surface discharge using two-dimensional asymmetric electrode configurations. Model predictions for charge densities, the electric field, and gas velocity distributions are shown to mimic trends reported in the experimental literature. We also predict the electron charge accumulation on the dielectric surface self-limiting the discharge.
Highly efficient polymer light-emitting devices using ambipolar phosphorescent polymers
Authors: Suzuki Mitsunori , Tokito Shizuo , Sato Fumio , Igarashi Takeshi , Kondo Kunio , Koyama Tamami , Yamaguchi Tetsuhiko
Published: March 2005

We report on highly efficient polymer light-emitting devices (PLEDs) achieved using a phosphorescent polymer, which is a copolymer that has bis(2-phenylpyridine)iridium (acetylacetonate) [Ir(ppy)2(acac)], N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a side group. The phosphorescent polymer has an ambipolar charge-transport ability. An increase in PBD unit concentration allows an improvement in the efficiency of the PLEDs. Ba and Cs were used for electron-injection layers as well as Ca, to improve the electron injection. An external quantum efficiency of 11.8% and a power efficiency of 38.6lm∕W were obtained by using Cs. The results indicate that this can be attributed to an improvement in the charge balance of electrons and holes.
Compact wavelength monitoring by lateral outcoupling in wedged photonic crystal multimode waveguides
Authors: Viasnoff-Schwoob E. , Weisbuch C. , Benisty H. , Cuisin C. , Derouin E. , Drisse O. , Duan G-H. , Legouézigou L. , Legouézigou O. , Pommereau F. , Golka S. , Heidrich H. , Hensel H. J. , Janiak K.
Published: March 2005

A device concept for laterally extracting selected wavelengths from an optical signal traveling along a waveguide, for operation in metropolitan area networks, is presented. The signal on the fundamental mode of a multimode photonic crystal waveguide is coupled to a higher-order mode, at a center frequency that spatially depends on the slowly varying guide parameters. The device is compact, intrinsically fault tolerant, and can split any desired fraction of the signal for monitoring purpose. Characterizations by the internal light source technique validate the optical concept whereas an integrated device with four photodiodes qualifies its potential with respect to real-world applications.
Formation mechanism of fivefold deformation twins in nanocrystalline face-centered-cubic metals
Authors: Zhu Y. T. , Liao X. Z. , Valiev R. Z.
Published: March 2005

Fivefold deformation twins have been recently observed in nanocrystalline face-centered-cubic (fcc) metals and alloys synthesized by severe plastic deformation techniques. However, numerous molecular dynamics simulations in the literature have not observed fivefold deformation twins in nanocrystalline fcc metals. The discrepancy between experimental observations and molecular dynamics simulations has raised an issue on their formation mechanism and conditions. Here we propose a sequential twinning mechanism that provides a clear path for the formation of fivefold deformation twins. The mechanism requires an orientation change of applied stresses, which explains why molecular dynamics simulations under a constant load orientation do not produce fivefold deformation twins.
Role of the microstructure on the magnetic properties of Co-doped ZnO nanoparticles
Authors: Martínez B. , Sandiumenge F. , Balcells Ll. , Arbiol J. , Sibieude F. , Monty C.
Published: March 2005

We report on the magnetic and structural properties of Co-doped ZnO nanoparticles prepared by the vaporization-condensation method in a solar reactor. X-ray diffraction data and high-resolution electron microscopy (HREM) confirm the total absence of metallic Co clusters or any other phase different from würtzite-type ZnO. Electron energy loss spectroscopy analyses performed on several particles indicate that the oxidation state of Co is +2 and yield an average Co concentration of 4.5at.%, in good agreement with the nominal composition. Transmission electron microscopy micrographs show that shape and size of the particles are strongly dependent on the preparation conditions, as well as the microstructure as evidenced by HREM. Ferromagnetism is only found in samples prepared in vacuum revealing a close correlation between microstructure and magnetic properties.
Emissivity — a remote sensor of giant magnetoresistance
Authors: Stirk S. M. , Thompson S. M. , Matthew J. A. D.
Published: March 2005

The link between emissivity in the mid-to-far-infrared regime and electrical conductivity is used to probe magnetoresistance. A direct relationship between the change in radiated flux and giant magnetoresistance is confirmed by experiment. The potential for spatially resolved measurements is also considered.