bluuebunny/crossref_metadata_2025 huggingface dataset:
Principal Component Analysis and the Scaled Subprofile Model Compared to Intersubject Averaging and Statistical Parametric Mapping: I. “Functional Connectivity” of the Human Motor System Studied with [15O]Water PET
Authors: Strother Stephen C. , Anderson Jon R. , Schaper Kirt A. , Sidtis John J. , Liow Jeih-San , Woods Roger P. , Rottenberg David A.
Published: April 2011

Using [15O]water PET and a previously well studied motor activation task, repetitive finger-to-thumb opposition, we compared the spatial activation patterns produced by (1) global normalization and intersubject averaging of paired-image subtractions, (2) the mean differences of ANCOVA-adjusted voxels in Statistical Parametric Mapping, (3) ANCOVA-adjusted voxels followed by principal component analysis (PCA), (4) ANCOVA-adjustment of mean image volumes (mean over subjects at each time point) followed by F-masking and PCA, and (5) PCA with Scaled Subprofile Model pre- and postprocessing. All data analysis techniques identified large positive focal activations in the contralateral sensorimotor cortex and ipsilateral cerebellar cortex, with varying levels of activation in other parts of the motor system, e.g., supplementary motor area, thalamus, putamen; techniques 1–4 also produced extensive negative areas. The activation signal of interest constitutes a very small fraction of the total nonrandom signal in the original dataset, and the exact choice of data preprocessing steps together with a particular analysis procedure have a significant impact on the identification and relative levels of activated regions. The challenge for the future is to identify those preprocessing algorithms and data analysis models that reproducibly optimize the identification and quantification of higher-order sensorimotor and cognitive responses.
Inhibition of Neuronal Nitric Oxide Synthase by 7-Nitroindazole: Effects upon Local Cerebral Blood Flow and Glucose Use in the Rat
Authors: Kelly Paul A. T. , Ritchie Isobel M. , Arbuthnott Gordon W.
Published: April 2011

The novel nitric oxide synthase inhibitor 7-nitroindazole (7-NI) is relatively specific for the neuronal isoform of the enzyme and in this study we have used this compound to investigate the physiological role of perivascular nitric oxide-containing nerves in the cerebrovascular bed. Following injection of 7-NI (25 or 50 mg/kg, i.p.), cerebral blood flow and glucose utilization were measured in the conscious rat using the fully quantitative [14C]iodoantipyrine and 2-[14C]deoxyglucose techniques, respectively. Neither dose of the drug produced any change in arterial blood pressure, confirming a lack of effect upon the endothelial isoform of the enzyme, although there was a pronounced decrease in heart rate (−28% by 10 min postinjection). Throughout the brain 25 mg/kg 7-NI i.p. resulted in decreases in blood flow of between −20% in the hippocampus and −58% in the substantia nigra. Increasing the dose to 50 mg/kg resulted in a further generalized decrease, to almost −60% in parts of the thalamus and hippocampus, but in every animal this higher dose of 7-NI also produced randomly distributed areas of relative hyperaemia, which were most commonly found in those areas where the most intense hypoperfusion was otherwise in evidence. Despite these changes in blood flow, in all but a very few areas of the brain no significant decrease in glucose use was measured at either of the two doses of 7-NI. Thus despite the greater specificity of 7-NI for neuronal nitric oxide synthase, the cerebrovascular effects of the drug in vivo are very similar to that reported for the arginine analogues. However, these data do suggest that nitric oxide-releasing neurones in the brain may have an important role to play in the regulation of cerebral blood flow.
The Role of Neuronal Nitric Oxide Synthase in Regulation of Cerebral Blood Flow in Normocapnia and Hypercapnia in Rats
Authors: Wang Qiong , Pelligrino Dale A. , Baughman Verna L. , Koenig Heidi M. , Albrecht Ronald F.
Published: April 2011

The nitric oxide synthase (NOS) inhibitors, nitro-L-arginine, its methyl ester, and N-monomethyl-L-arginine, have been shown to attenuate resting CBF and hypercapnia-induced cerebrovasodilation. Those agents nonspecifically inhibit the endothelial and neuronal NOS (eNOS and nNOS). In the present study, we used a novel nNOS inhibitor, 7-nitroindazole (7-NI) to examine the role of nNOS in CBF during normocapnia and hypercapnia in fentanyl/N2O-anesthetized rats. CBF was monitored using laser-Doppler flowmetry. Administration of 7-NI (80 mg kg−1 i.p.) reduced cortical brain NOS activity by 57%, the resting CBF by 19–27%, and the CBF response to hypercapnia by 60%. The 60% reduction was similar in magnitude to the CBF reductions observed in previous studies in which nonspecific NOS inhibitors were used. In the present study, 7-NI did not increase the MABP. Furthermore, the CBF response to oxotremorine, a blood–brain barrier permeant muscarinic agonist that induces cerebrovasodilation via endothelium-derived NO, was unaffected by 7-NI. These results confirmed that 7-NI does not influence eNOS; they also indicated that the effects of 7-NI on the resting CBF and on the CBF response to hypercapnia in this study were solely related to its inhibitory action on nNOS. The results further suggest that the NO synthesized by the action of nNOS participates in regulation of basal CBF and is the major, if not the only, category of NO contributing to the hypercapnic CBF response.
Serotonin 5HT2 Receptor Imaging in the Human Brain Using Positron Emission Tomography and a New Radioligand, [18F]Altanserin: Results in Young Normal Controls
Authors: Sadzot B. , Lemaire C. , Maquet P. , Salmon E. , Plenevaux A. , Degueldre C. , Hermanne J. P. , Guillaume M. , Cantineau R. , Comar D. , Franck G.
Published: April 2011

Changes in serotonin-2 receptors have been demonstrated in brain autopsy material from patients with various neurodegenerative and affective disorders. It would be desirable to locate a ligand for the study of these receptors in vivo with positron emission tomography (PET). Altanserin is a 4-benzoylpiperidine derivative with a high affinity and selectivity for S2 receptors in vitro. Dynamic PET studies were carried out in nine normal volunteers with high-specific activity (376–1,680 mCi/μmol) [18F]altanserin. Arterial blood samples were obtained and the plasma time–activity curves were corrected for the presence of labeled metabolites. Thirty minutes after injection, selective retention of the radioligand was observed in cortical areas, while the cerebellum, caudate, and thalamus had low radioactivity levels. Specific binding reached a plateau between 30 and 65 min postinjection at 1.8% of the injected dose/L of brain and then decreased, indicating the reversibility of the binding. The total/nonspecific binding ratio reached 2.6 for times between 50 and 70 min postinjection. The graphical analysis proposed by Logan et al. allowed us to estimate the binding potential ( Bmax/ KD). Pretreatment with ketanserin was given to three volunteers and brain activity remained uniformly low. An additional study in one volunteer showed that [18F]altanserin can be displaced from the receptors by large doses of ketanserin. At the end of the study, unchanged altanserin was 57% of the total plasma activity. These results suggest that [18F]altanserin is selective for S2 receptors in vivo as it is in vitro. They indicate that [18F]altanserin is suitable for imaging and quantifying S2 receptors with PET in humans.
Tensile stress induced depolarization in [001]-poled transverse mode Pb(Zn1/3Nb2/3)O3 -(6-7)%PbTiO3 single crystals
Authors: Shukla Rahul , Lim Leong-Chew , Gandhi Prasanna
Published: April 2011

This paper investigates the effects of electrically induced and direct tensile stress on the deformation and dielectric properties of Pb(Zn1/3Nb2/3)O3-(6-7)%PbTiO3 single crystals of [110]L× [001]T cut by using a unimorph sample and a four-point-bend (FPB) sample, respectively. The results show a dip in tip displacement for the unimorph sample at sufficiently high electric field parallel to the poling field direction and a sudden rise in capacitance for the FPB sample at sufficiently high tensile stress in the [110] crystal direction, respectively. These phenomena are attributed to the tensile stress induced rhombohedral-to-orthorhombic phase transition and associated depolarization events in the crystal. For the said crystal cut, the obtained tensile depoling stress is in the range of 15-20 MPa. The present work furthermore shows that the occurrence of tensile stress-induced depolarization is possible even when the direction of the applied electric field is parallel to the poling field direction, as in the unimorph sample examined.
Structures and magnetocaloric effects of Gd65−xRExFe20Al15 (x = 0–20; RE=Tb, Dy, Ho, and Er) ribbons
Authors: Fang Y. K. , Chen H. C. , Hsieh C. C. , Chang H. W. , Zhao X. G. , Chang W. C. , Li W.
Published: April 2011

Gd-based Gd65−xRExFe20Al15 (x = 0–20, RE = Tb, Dy, Ho, and Er) alloys in ribbon form have been prepared by rapid quenching technology. It is found that the Gd65−xTbxFe20Al15 ribbons are in amorphous state. However, for the Gd65−xRExFe20Al15(RE = Dy, Ho, and Er) ribbons, in addition to a diffuse diffraction band, peaks from hexagonal rare-earth-rich phases are present indicating a mixture of amorphous and crystalline phases. This indicates that the heavier rare-earth elements (Dy, Ho, and Er) will decrease glass formability in the Gd-based Gd65−xRExFe20Al15 (RE = Dy, Ho, and Er) ribbons. The magnetic entropy changes of these ribbons increase with increasing the contents of the heavier rare-earth elements. The maximal magnetic entropy changes of the Gd45RE20Fe20Al15 (RE = Tb, Dy, Ho, and Er) ribbons are located in the range of 4.46–5.57 J/kg K under 50 kOe. Refrigerant capacity values are obtained to be about 580–720 J/kg under 50 kOe. These values are comparable to or even higher than those of Gd-based bulk metallic glass alloys.
Field dependence on the molecular ionization potential and excitation energies compared to conductivity models for insulation materials at high electric fields
Authors: Smalø Hans S. , Hestad Øystein , Ingebrigtsen Stian , Åstrand Per-Olof
Published: April 2011

The aim is to improve the understanding of high-field phenomena (such as preinception currents/conduction, streamer initiation and propagation) in insulating materials in terms of the molecular properties of the substances involved. In high electric fields, ionization is a likely process, and in all such processes, the ionization potential is an important parameter. A fundamental question is how these processes depend on the electric field, and therefore, based on the interaction between a negative point charge and a molecular cation as modeled by density functional theory, a field-dependent model for the ionization potential is developed. In addition, the first excitation energies as a function of the electric field are calculated using time-dependent density functional theory. It is demonstrated that empirical high-field conduction models for cyclohexane and n-tridecane can be explained in terms of the difference between the ionization potential and the first excitation energy. It is also suggested that the reduction of the ionization potential with electric fields, can help explain how fast-mode streamers propagate.
Electron mobility in CdO films
Authors: Vasheghani Farahani S. K. , Veal T. D. , King P. D. C. , Zúñiga-Pérez J. , Muñoz-Sanjosé V. , McConville C. F.
Published: April 2011

Electron mobility in degenerate CdO thin films has been studied as a function of carrier concentration. The “optical” mobility has been determined from infrared reflectance measurements of the conduction band plasmon lifetime. The acquired values vary from ∼209 to ∼1116 cm2 V-1 s-1 for carrier concentrations between 2.5×1020 and 2.6×1019 cm-3. Ionized impurity scattering is shown to be the dominant effect reducing the intra-grain mobility of the electrons at room temperature. The transport mobilities from Hall effect measurements range between ̃20 and ̃124 cm2 V-1 s-1 which are much lower than the optical mobilities. Simulation of grain boundary scattering-limited mobility is commonly based on models that assume a depletion layer at the boundaries which causes an inter-grain potential barrier. These models are found not to be applicable to CdO as it has been previously shown to have surface electron accumulation. Therefore, simulation of the transport mobility has been performed using the Fuchs-Sondheimer and Mayadas-Shatzkes models to take into account the grain boundary and surface scattering mechanisms, in addition to intra-grain scattering. The results indicate that electron scattering at grain boundaries with ̃95 % reflection is the dominant mechanism in reducing the mobility across the layer. The effect of surface scattering plays only a minor role in electron transport.
Orbitally driven spin-singlet state in LiVS2
Authors: Guo Ying , Zhang Guoren , Zhang Xiaoli , Jia Ting , Zeng Zhi
Published: April 2011

Based on first-principles electronic structure calculations with a full-potential linearized augmented plane wave method and the exact diagonalization of a three-site cluster within a degenerate Hubbard model, we study the orbital and spin properties of the transition metal compound LiVS2 with a two-dimensional triangular lattice. It is found that in a triangle of three V3+ ions, the orbital ordering with three t2g orbitals alternately occupied by two electrons on each V3+ ion has developed, which corresponds to the valence-bond solid state of trimerization. The spin-singlet state of the trimer originates from such an orbital ordering and the stronger antiferromagnetic exchange interaction JA, compared with Hund’s rule exchange interaction JH. By conducting comparative studies of LiVO2, LiVS2, and LiVSe2, we find that the significantly large V–V bond length and d-p hybridization negatively impact the formation of orbital ordering.
Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas
Authors: Hershkowitz N. , Yip C.-S. , Severn G. D.
Published: April 2011

Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar–Xe and He–Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.
Mössbauer study 57Fe in ultrathin trilayer films with sharp and rough interfaces
Authors: Pogorily A. N. , Bondarkova G. V. , Razumov O. N. , Shypil E. V.
Published: April 2011

Trilayer thin films Py/57Fe/Gd and Gd/57Fe/Py (Py: Fe20Ni80 permalloy) have been prepared by electron-beam evaporation and investigated using conversion-electron Mössbauer spectroscopy (CEMS), scanning tunneling microscopy (STM), polar magneto-optical Kerr effect (PMOKE), and ferromagnetic resonance (FMR). It was shown that the films deposited in the same vacuum and temperature runs but with the reverse order of the layers gave a different quality of interfaces: sharp (Py/57Fe/Gd) and rough (Gd/57Fe/Py). Different distribution of atoms in sharp and rough interfaces results in different magnetic properties: the Mössbauer spectra, FMR, and PMOKE data show the appearance of perpendicular magnetic anisotropy (PMA) and enhancement of magnetization in the samples with the rough Gd/Py interface.
Magnetization and neutron diffraction studies on Sr2TiMnO6
Authors: Lamsal Jagat , Mondal Rajib , Kumar Anil , Kamala Bharathi K. , Santhosh P. N. , Nirmala R. , Nigam A. K. , Yelon W. B. , Quezado S. , Malik S. K.
Published: April 2011

Magnetic properties of the double perovskite oxide, Sr2TiMnO6, have been studied by means of bulk magnetization and powder neutron diffraction experiments. Low field magnetization data reveal transitions at ∼45 K (TC) and at ∼15 K (TN). A magnetic moment value of only ∼0.23 μB/F.U. is attained at 5 K in the 7 T field. Powder neutron diffraction studies suggest the possible antiferromagnetic order in this compound at 12 K with moments of ∼0.5 μB at the Mn site.
Covariant constitutive relations and relativistic inhomogeneous plasmas
Authors: Gratus J. , Tucker R. W.
Published: April 2011

The notion of a 2-point susceptibility kernel used to describe linear electromagnetic responses of dispersive continuous media in nonrelativistic phenomena is generalized to accommodate the constraints required of a causal formulation in spacetimes with background gravitational fields. In particular the concepts of spatial material inhomogeneity and temporal nonstationarity are formulated within a fully covariant spacetime framework. This framework is illustrated by recasting the Maxwell–Vlasov equations for a collisionless plasma in a form that exposes a 2-point electromagnetic susceptibility kernel in spacetime. This permits the establishment of a perturbative scheme for nonstationary inhomogeneous plasma configurations. Explicit formulae for the perturbed kernel are derived in both the presence and absence of gravitation using the general solution to the relativistic equations of motion of the plasma constituents. In the absence of gravitation this permits an analysis of collisionless damping in terms of a system of integral equations that reduce to standard Landau damping of Langmuir modes when the perturbation refers to a homogeneous stationary plasma configuration. It is concluded that constitutive modeling in terms of a 2-point susceptibility kernel in a covariant spacetime framework offers a natural extension of standard nonrelativistic descriptions of simple media and that its use for describing linear responses of more general dispersive media has wide applicability in relativistic plasma modeling.
Synthesis of ferromagnetic nanoparticles with a core/shell structure by a self-propagating combustion method
Authors: Cho S. G. , Jeon K. W. , Moon K. W. , Kim J. B. , Kim K. H. , Kim J.
Published: April 2011

Ferromagnetic nanoparticles with a core/shell structure were fabricated by a self-propagating combustion method and subsequent hydrogen reduction process. Before the reduction process, synthesized particles were Fe oxide phases. Transmission electron micrographs confirmed that the nanoparticles were composed of α-Fe core and Fe–Al oxide shell after the reduction process. The saturation magnetization of the nanoparticles was measured about 180 emu/g and the permeability kept constant value of about 1.8 up to 10 GHz without any noticeable loss. These microstructural and magnetic analyses showed that the oxide phase changed into α-Fe and then Al atoms diffused out to the surface of the particles during the reduction process.
Influence of sputtering power on the high frequency properties of nanogranular FeCoHfO thin films
Authors: Lu Guangduo , Zhang Huaiwu , Xiao John Q. , Bai Feiming , Tang Xiaoli , Li Yuanxun , Zhong Zhiyong
Published: April 2011

Soft magnetic nanogranular FeCoHfO thin films were fabricated using rf magnetron sputtering in an oxygen/argon ambient. During the deposition process, the partial pressure of oxygen was fixed at 2.5% and sputtering power was used as the control parameter, varying from 50 to 300 W. It was found that the film electrical resistivity (ρ) decreases steeply with the increase of sputtering power, and the saturation magnetization (4πMs) and the natural ferromagnetic resonant frequency fr increase with increasing sputtering power from 50 to 200 W, and then decrease when sputtering power exceeded 200 W. The maximum value of 4πMs and fr were 20.5 kG and 3.2GHz, respectively. The coercivity of films had a contrary trend compared with 4πMs and fr, and its minimum value was about 1 Oe. The physical origin of the influence was suggested to be related to the structure and composition changes in films.
Calculation of individual bit island switching field distribution in perpendicular magnetic bit patterned media
Authors: Li W. M. , Chen Y. J. , Huang T. L. , Xue J. M. , Ding J.
Published: April 2011

Bit patterned media (BPM) is a promising candidate to achieve ultrahigh recording density in magnetic data storage. One of the critical issues for BPM in high-density recording is that the switching field distribution (SFD) needs to be narrow enough to secure exact addressability of individual predefined bits without overwriting adjacent bits. In our work, we observed magnetic reversal of individual islands through magnetic force microscopy and calculated the demagnetization and SFD using the obtained intrinsic SFD to verify if dipole–dipole interactions contribute to the SFD broadening. In simulation, we used the formula in the calculation of critical magnetic field for the reversal of individual islands: Hc = Hc,int − ΣMsVbit/r3, where Hc is the critical field, Hc,int is the initial critical field without dipole–dipole interactions, and Σ represents the dipole–dipole interactions from neighboring islands. Hc,int was generated from the obtained initial SFD (2σ = 1.2 kOe), dipole–dipole interactions cause a significant SFD broadening. The width of 2σ = 1.7 kOe after the calculation with the consideration of the dipole–dipole distribution is in a relatively good agreement with our experimental data (2σ = 2.0 kOe). The calculated demagnetization loop also agrees well with our experimental result.
Transcranial magnetic stimulation: Improved coil design for deep brain investigation
Authors: Crowther L. J. , Marketos P. , Williams P. I. , Melikhov Y. , Jiles D. C. , Starzewski J. H.
Published: April 2011

This paper reports on a design for a coil for transcranial magnetic stimulation. The design shows potential for improving the penetration depth of the magnetic field, allowing stimulation of subcortical structures within the brain. The magnetic and induced electric fields in the human head have been calculated with finite element electromagnetic modeling software and compared with empirical measurements. Results show that the coil design used gives improved penetration depth, but also indicates the likelihood of stimulation of additional tissue resulting from the spatial distribution of the magnetic field.
Searching for the best thermoelectrics through the optimization of transport distribution function
Authors: Fan Zheyong , Wang Hui-Qiong , Zheng Jin-Cheng
Published: April 2011

The thermoelectric performance of materials is dependent on the interplay or competition among three key components, the electrical conductivity, thermopower, and thermal conductivity, which can be written as integrals of a single function, the transport distribution function (TDF). Mahan and Sofo [Proc. Natl. Acad. Sci. USA 93, 7436 (1996)] found that, mathematically, the thermoelectric properties could be maximized by a delta-shaped transport distribution, which was associated with a narrow distribution of the energy of the electrons participating in the transport process. In this work, we revisited the shape effect of TDF on thermoelectric figure of merit. It is confirmed both heuristically and numerically that among all the normalized TDF the Dirac delta function leads to the largest thermoelectric figure of merit. Whereas, for the case of TDF being bounded, a rectangular-shape distribution is instead found to be the most favorable one, which could be achieved through nanoroute. Our results also indicate that high thermoelectric figure of merit is associated with appropriate violations of the Wiedemann−Franz law.
Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films
Authors: Resnick Damon A. , McClure A. , Kuster C. M. , Rugheimer P. , Idzerda Y. U.
Published: April 2011

Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1−x thin films.
Ramp-edge Josephson junctions made of Pr2−xCexCuO4±δ electrodes and barriers
Authors: Roberge G. , Charpentier S. , Godin-Proulx S. , Fournier P.
Published: April 2011

We present the fabrication steps and the properties of ramp-edge Josephson junctions using electron-doped high Tc cuprate Pr2-xCexCuO4 (PCCO) for the electrodes and the barrier. The superconducting properties of these PCCO junctions are similar to those fabricated from the hole-doped high temperature superconductors. For superconducting electrodes with x=0.13, 0.15 or 0.17 and a nonsuperconducting barrier with x=0.05 and thicknesses as large as 35 nm, we observe large critical current densities, periodic oscillations of critical current Ic in a magnetic field and Shapiro steps. The temperature dependence of the maximum critical current reveals the junction are of superconducting-normal-superconducting type.
Liquid crystalline thin films as a precursor for polycrystalline thin films aimed at field effect transistors
Authors: Iino Hiroaki , Hanna Jun-ichi
Published: April 2011

We have investigated the availability of liquid crystalline thin films as a precursor of quality polycrystalline thin films for organic field effect transistors (OFETs) by solution process. The experiments of spin-coating at various temperatures proved that the morphology of resulting polycrystalline thin films at room temperature strongly depend on what the films immediately after spin-coating and solvent evaporation at those temperatures were, i.e., crystal, liquid crystal, or isotropic liquid. The polycrystalline films spin-coated at the temperatures for crystal and isotropic liquid phases were much roughened owing to many small crystal flakes and droplets. On the other hand, the thin films spin-coated at liquid crystal temperatures were very uniform in a whole area and showed high FET mobility having a small variation from device to device.
Shock induced damage and damage threshold of optical K9 glass investigated by laser-driven shock wave
Authors: Song Yunfei , Yu Guoyang , Jiang Lilin , Zheng Xianxu , Liu Yuqiang , Yang Yanqiang
Published: April 2011

The shock wave driven by short laser pulse is used to study the damage of brittle material K9 glass. The damage morphology of K9 glass surface indicates that the material has experienced different loading modes, respectively, at the central area and the surrounding area of the shock wave. At the central area of shock wave, the wavefront is plane and has a uniform pressure distribution, the material mainly suffers a longitudinal shock pressure; but on the edge the shock wave, the wavefront is approximately spherical, besides longitudinal pressure, transverse tensile stress will emerge inside the material. In the latter case, the damage threshold of the material is much smaller than that in the case of compressing by longitudinal pressure only. According to the relationship between damage area and shock pressure, an experimental method is proposed to measure the damage threshold of materials under shock loading. The damage threshold of K9 glass under spherical shock wave is measured to be about 1.12 GPa; and the damage threshold under plane shock wave is estimated to be between 1.82 and 1.98 GPa. They are much bigger than the damage threshold under static pressure. This method could also be used to measure the damage threshold of other materials when loaded by dynamic pressure.
Magnetically programmable surface acoustic wave radio frequency identification tags
Authors: Chin Matthew , Buford Benjamin , Dhagat Pallavi
Published: April 2011

A reconfigurable surface acoustic wave reflector using an integrated magnetoresistive bit was fabricated and evaluated for use in programmable radio frequency identification tags. It is shown that two distinct reflectivities can be achieved depending on the magnetic state of the bit. The experimental results are compared with theoretical calculations of optimal reflectivities achievable from resistively loaded surface acoustic wave transducers.
Gauge invariant plane-wave solutions in supersymmetric Yang–Mills quantum mechanics
Authors: Korcyl Piotr
Published: April 2011

We derive the spectra of D = 2, SU(3) supersymmetric Yang–Mills quantum mechanics in all fermionic sectors. Moreover, we provide exact expressions for the corresponding eigenvectors in the sectors with none and one fermionic quantum. We also generalize our results obtained in a cut Fock space to the infinite cut-off limit.
A spatially homogeneous and isotropic Einstein–Dirac cosmology
Authors: Finster Felix , Hainzl Christian
Published: April 2011

We consider a spatially homogeneous and isotropic cosmological model where Dirac spinors are coupled to classical gravity. For the Dirac spinors we choose a Hartree–Fock ansatz where all one-particle wave functions are coherent and have the same momentum. If the scale function is large, the universe behaves like the classical Friedmann dust solution. If however the scale function is small, quantum effects lead to oscillations of the energy-momentum tensor. It is shown numerically and proven analytically that these quantum oscillations can prevent the formation of a big bang or big crunch singularity. The energy conditions are analyzed. We prove the existence of time-periodic solutions which go through an infinite number of expansion and contraction cycles.
Influence of Mn dopants on InAs/GaAs quantum dot electronic states
Authors: Dasika V. D. , Semichaevsky A. V. , Petropoulos J. P. , Dibbern J. C. , Dangelewicz A. M. , Holub M. , Bhattacharya P. K. , Zide J. M. O. , Johnson H. T. , Goldman R. S.
Published: April 2011

We have investigated the influence of Mn dopants on the electronic states in the vicinity of InAs/GaAs quantum dots (QDs) and the surrounding GaAs matrix. A comparison of cross-sectional scanning tunneling microscopy, scanning tunneling spectroscopy, and tight binding calculations of the local density of states reveals that the Mn dopants primarily influence the electronic states at the QD edges and the surrounding GaAs matrix. These results suggest that the Mn dopants reside at the QD edge, consistent with the predictions of a thermodynamic model for the nanoscale-size dependence of dopant incorporation in nanostructures.
Spin-polarized current and tunneling magnetoresistance in ferromagnetic gate bilayer graphene structures
Authors: Nguyen V. Hung , Bournel A. , Dollfus P.
Published: April 2011

We study spin transport in bilayer graphene structures where gate electrodes are attached to ferromagnetic graphene. Due to the exchange field in the gated regions, the current becomes spin dependent and can be controlled by tuning the gate voltages. It is shown that thanks to strong resonant chiral tunneling inherent in bilayer graphene, very high spin polarization and tunneling magnetoresistance can be achieved in the considered structures. Different possibilities for controlling the spin current are discussed. The study demonstrates the potential of bilayer graphene structures for spintronic applications with significant improvement over previously predicted results in monolayer graphene structures.
Thermal activation and saturation of ion beam sculpting
Authors: Hoogerheide David P. , George H. Bola , Golovchenko Jene A. , Aziz Michael J.
Published: April 2011

We report a material-dependent critical temperature for ion beam sculpting of nanopores in amorphous materials under keV ion irradiation. At temperatures below the critical temperature, irradiated pores open at a rate that soon saturates with decreasing temperature. At temperatures above the critical temperature, the pore closing rate rises rapidly and eventually saturates with increasing temperature. The observed behavior is well described by a model based on adatom diffusion, but is difficult to reconcile with an ion-stimulated viscous flow model.
Equivalent circuit analysis of metamaterial strain-dependent effective medium parameters
Authors: Arritt B. J. , Smith D. R. , Khraishi T.
Published: April 2011

In this paper, we analytically describe the strain-dependent effective medium properties for a metamaterial electric-LC (ELC) resonator, commonly used in metamaterial designs to provide a tailored electric response to electromagnetic waves. Combining an equivalent circuit model of the ELC resonator with existing analytic expressions for the capacitive and inductive regions comprising the structure, we obtain strain-dependent permittivity and permeability curves for the metamaterial. The derived expressions account for the effects of spatial dispersion and losses.
Numerical investigation of the ion temperature effects on magnetized DC plasma sheath
Authors: Khoramabadi Mansour , Ghomi Hamid , Shukla Padma Kant
Published: April 2011

The properties of a magnetized plasma sheath with finite ion temperature is considered. The effects of the external magnetic field and the ion temperature on the sheath parameters are examined. It is found that by increasing the ion temperature and the magnetic field strength there is an increase in the positive space charge and the ion energy and a decrease in the sheath thickness. Furthermore, the ion temperature has a direct effect on the ion flux toward the wall.
Ballistic (precessional) contribution to the conventional magnetic switching
Authors: Bazaliy Ya. B. , Stankiewicz Andrzej
Published: April 2011

We consider a magnetic moment with an easy axis anisotropy energy, switched by an external field applied along this axis. Additional small, time-independent bias field is applied perpendicular to the axis. It is found that the magnet’s switching time is a non-monotonic function of the rate at which the field is swept from “up” to “down.” Switching time exhibits a minimum at a particular optimal sweep time. This unusual behavior is explained by the admixture of a ballistic (precessional) rotation of the moment caused by the perpendicular bias field in the presence of a variable switching field. We derive analytic expressions for the optimal switching time, and for the entire dependence of the switching time on the field sweep time. The existence of the optimal field sweep time has important implications for the optimization of magnetic memory devices.
Two- and three-body photodissociation dynamics of diiodobromide (I2Br−) anion
Authors: Crider Paul E. , Harrison Aaron W. , Neumark Daniel M.
Published: April 2011

The photodissociation of gas-phase I2Br− was investigated using fast beam photofragment translational spectroscopy. Anions were photodissociated from 300 to 270 nm (4.13–4.59 eV) and the recoiling photofragments were detected in coincidence by a time- and position-sensitive detector. Both two- and three-body channels were observed throughout the energy range probed. Analysis of the two-body dissociation showed evidence for four distinct channels: Br− + I2, I− + IBr, ${\rm Br} + {\rm I}_2^ - $ Br +I2−, and I + IBr−. In three-body dissociation, Br(2P3/2) + I(2P3/2) + I− and Br− + I(2P3/2) + I(2P3/2) were produced primarily from a concerted decay mechanism. A sequential decay mechanism was also observed and attributed to ${\rm Br}^ - ({}^1S) + {\rm I}_{\rm 2} (B{}^3\Pi _{0u}^ +)$ Br −(1S)+I2(B3Π0u+) followed by predissociation of I2(B).
Green's function for the time-dependent scattering problem in the fractional quantum mechanics
Authors: Dong Jianping
Published: April 2011

We study the Green's function of the time-dependent 3D space-fractional Schrödinger equation for the scattering problem in the fractional quantum mechanics. The Green's function is expressed in terms of Fox's H-function and in a computable series form. We get the asymptotic formula of the Green's function, and apply it to obtain the approximate wave function for the fractional quantum scattering problem.
Slow photoelectron velocity-map imaging spectroscopy of the n-methylvinoxide anion
Authors: Yacovitch Tara I. , Kim Jongjin B. , Garand Etienne , van der Poll Derek G. , Neumark Daniel M.
Published: April 2011

High resolution photoelectron spectra of the n-methylvinoxide anion and its deuterated isotopologue are obtained by slow electron velocity-map imaging. Transitions between the $\tilde X$X̃ 1A′ anion ground electronic state and the radical $\tilde X$X̃ 2A″ and $\tilde A$Ã 2A′ states are observed. The major features in the spectra are attributed to transitions involving the lower energy cis conformers of the anion and neutral, while the higher energy trans conformers contribute only a single small peak. Franck–Condon simulations of the $\tilde X$X̃ 2A″ ← $\tilde X$X̃ 1A′ and $\tilde A$Ã 2A′ ← $\tilde X$X̃ 1A′ transitions are performed to assign vibrational structure in the spectrum and to aid in identifying peaks in the cis-n-methylvinoxy $\tilde X$X̃ 2A″ band that occur only through vibronic coupling. The experimental electron affinity and $\tilde A$Ã state term energy are found to be EA = 1.6106 ± 0.0008 eV and T0 = 1.167 ± 0.002 eV for cis-n-methylvinoxy.
Microspectroscopy of ultrafast laser inscribed channel waveguides in Yb:tungstate crystals
Authors: Bain F. M. , Silva W. F. , Lagatsky A. A. , Thomson R. R. , Psaila N. D. , Kar A. K. , Sibbett W. , Jaque D. , Brown C. T. A.
Published: April 2011

We report microspectroscopy measurements of crystalline channel waveguides fabricated in Yb:KGd(WO4)2 and Yb:KY(WO4)2 using the ultrafast laser inscription technique. From these measurements we find that densification of the WO2W bridge in the double tungstate crystal lattice is responsible for the refractive index increase, which creates the waveguide confinement. We identified that shifts toward lower energies in the ∼760 cm−1 Raman mode indicate regions, which guide light polarized along the crystallographic b axis, while higher energy shifts in the 682 and 898 cm−1 Raman lines correspond to guiding regions for light polarized along the crystallographic a axis.
Integrating diffusion maps with umbrella sampling: Application to alanine dipeptide
Authors: Ferguson Andrew L. , Panagiotopoulos Athanassios Z. , Debenedetti Pablo G. , Kevrekidis Ioannis G.
Published: April 2011

Nonlinear dimensionality reduction techniques can be applied to molecular simulation trajectories to systematically extract a small number of variables with which to parametrize the important dynamical motions of the system. For molecular systems exhibiting free energy barriers exceeding a few kBT, inadequate sampling of the barrier regions between stable or metastable basins can lead to a poor global characterization of the free energy landscape. We present an adaptation of a nonlinear dimensionality reduction technique known as the diffusion map that extends its applicability to biased umbrella sampling simulation trajectories in which restraining potentials are employed to drive the system into high free energy regions and improve sampling of phase space. We then propose a bootstrapped approach to iteratively discover good low-dimensional parametrizations by interleaving successive rounds of umbrella sampling and diffusion mapping, and we illustrate the technique through a study of alanine dipeptide in explicit solvent.
Thermal and effective efficiency based analysis of discrete V-down rib-roughened solar air heaters
Authors: Singh Sukhmeet , Chander Subhash , Saini J. S.
Published: April 2011

A parametric investigation of discrete V-down rib-roughness geometry in the absorber plate of solar air heater has been carried out and results obtained are compared with those of conventional flat plate solar air heater. The thermal and thermohydraulic performance evaluation has been carried out for various values of Reynolds number and roughness parameters of discrete V-down rib-roughness geometry in the absorber plate of solar air heater duct. The performance curves are plotted in terms of Reynolds number and temperature rise parameter. The discrete V-down rib-roughened solar air heater performs better as per thermal efficiency or heat energy gain criteria for the investigated range of Reynolds number and rib-roughness parameters. The thermal efficiency is high for discrete V-down rib-roughened solar air heater due to higher turbulence; however, the pumping power required for air flow also increases. The thermohydraulic performance on the basis of effective efficiency is a more suitable criterion as it takes into account both the heat collected and the pump work required. For Reynolds number range (or temperature rise parameter) generally employed in solar air heaters, the discrete V-down rib-roughened solar air heater gives higher effective efficiency. It was found that there exist optimum roughness parameters of discrete V-down rib for a given Reynolds number (or temperature rise parameter) at which the effective efficiency is the highest. Curves of optimum roughness parameters based on effective efficiency criterion are also plotted.
Modeling three-dimensional network formation with an atomic lattice model: Application to silicic acid polymerization
Authors: Jin Lin , Auerbach Scott M. , Monson Peter A.
Published: April 2011

We present an atomic lattice model for studying the polymerization of silicic acid in sol-gel and related processes for synthesizing silica materials. Our model is based on Si and O atoms occupying the sites of a body-centered-cubic lattice, with all atoms arranged in SiO4 tetrahedra. This is the simplest model that allows for variation in the Si–O–Si angle, which is largely responsible for the versatility in silica polymorphs. The model describes the assembly of polymerized silica structures starting from a solution of silicic acid in water at a given concentration and pH. This model can simulate related materials—chalcogenides and clays—by assigning energy penalties to particular ring geometries in the polymerized structures. The simplicity of this approach makes it possible to study the polymerization process to higher degrees of polymerization and larger system sizes than has been possible with previous atomistic models. We have performed Monte Carlo simulations of the model at two concentrations: a low density state similar to that used in the clear solution synthesis of silicalite-1, and a high density state relevant to experiments on silica gel synthesis. For the high concentration system where there are NMR data on the temporal evolution of the Qn distribution, we find that the model gives good agreement with the experimental data. The model captures the basic mechanism of silica polymerization and provides quantitative structural predictions on ring-size distributions in good agreement with x-ray and neutron diffraction data.
High voltage pulser with a fast fall-time for plasma immersion ion implantation
Authors: Zhu Zongtao , Gong Chunzhi , Tian Xiubo , Yang Shiqin , Fu Ricky K. Y. , Chu Paul K.
Published: April 2011

A novel high voltage (HV) modulator that offers a short fall time to minimize sputtering effects and allow more precise control of the incident ion fluence in plasma immersion ion implantation is described. The use of 36 insulated-gate bipolar transistors in the 30 kV hard-tube pulser reduces the HV fall time to 3.5 μs, compared to a fall time of 80 μs if a pull-down resister is used. The voltage balance is achieved by a voltage-balancing resistor, clamped capacitance, and the synchronization of drive signals. Compared to the traditional method employing a pull-down resister or an additional hard tube, our design consumes less power and is more economical and reliable.
Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature
Authors: Zhao K. , Xia X. X. , Bai H. Y. , Zhao D. Q. , Wang W. H.
Published: April 2011

We report a high entropy metallic glass of Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.
Al-doped HfO2/In0.53Ga0.47As metal-oxide-semiconductor capacitors
Authors: Hwang Yoontae , Chobpattana Varistha , Zhang Jack Y. , LeBeau James M. , Engel-Herbert Roman , Stemmer Susanne
Published: April 2011

Hafnium oxide gate dielectrics doped with a one to two percent of aluminum are grown on In0.53Ga0.47As channels by codeposition of trimethylaluminum (TMA) and hafnium tertbutoxide (HTB). It is shown that the addition of TMA during growth allows for smooth, amorphous films that can be scaled to ∼5 nm physical thickness. Metal-oxide-semiconductor capacitors (MOSCAPs) with this dielectric have an equivalent oxide thickness of 1 nm, show an unpinned, efficient Fermi level movement and lower interface trap densities than MOSCAPs with HfO2 dielectrics grown by sequential TMA/HTB deposition.
High resolution cathodoluminescence hyperspectral imaging of surface features in InGaN/GaN multiple quantum well structures
Authors: Bruckbauer Jochen , Edwards Paul R. , Wang Tao , Martin Robert W.
Published: April 2011

InGaN/GaN multiple quantum wells (MQWs) have been studied by using cathodoluminescence hyperspectral imaging with high spatial resolution. Variations in peak emission energies and intensities across trenchlike features and V-pits on the surface of the MQWs are investigated. The MQW emission from the region inside trenchlike features is redshifted by approximately 45 meV and more intense than the surrounding planar regions of the sample, whereas emission from the V-pits is blueshifted by about 20 meV and relatively weaker. By employing this technique to the studied nanostructures it is possible to investigate energy and intensity shifts on a 10 nm length scale.
Dry nanogranular materials
Authors: Yuan Chia-Nan , Li Yueh-Feng , Sheng Yu-Jane , Tsao Heng-Kwong
Published: April 2011

Granular materials consisting of macroscopic grains have commercial applications and their flow behavior plays key role in geophysics. However, flow characteristics of nanogranules differ significantly from those of granules. The former can form low-volume fraction (5%) particle gels in air and do not exhibit gravity-driven granular flow easily. It is found that although dry nanogranules possess a high compressibility, close to gases, they are less susceptible to flow than granules due to high yield stress and viscosity. Such differences can be attributed to van der Waals attractions, which support the weight of nanoparticles to form aerogels and resist shearing deformation.