bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivoSerotonin-Sensitive Binding of [11C]CUMI-101: A Serotonin 1A Receptor Agonist Positron Emission Tomography Radiotracer
Authors: Milak Matthew S , Severance Alin J , Prabhakaran Jaya , Kumar JS Dileep , Majo Vattoly J , Ogden R Todd , Mann J John , Parsey Ramin V
Published: June 2010

Positron emission tomography studies of 5-hydroxytryptamine (5-HT)1Areceptors have hitherto been limited to antagonist radiotracers. Antagonists do not distinguish high/low-affinity conformations of G protein-coupled receptors and are less likely to be sensitive to intrasynaptic serotonin levels. We developed a novel 5-HT1Aagonist radiotracer [11C]CUMI-101. This study evaluates the sensitivity of [11C]CUMI-101 binding to increases in intrasynaptic serotonin induced by intravenous citalopram and fenfluramine. Two Papio anubis were scanned, using [11C]CUMI-101 intravenous bolus of 4.5±1.5 mCi. Binding potential (BPF= Bavail/ KD) was measured before ( n=10) and 20 minutes after elevation of intrasynaptic serotonin by intravenous citalopram (2 mg/kg, n=3; 4 mg/kg, n=3) and fenfluramine (2.5 mg/kg, n=3) using a metabolite-corrected arterial input function. Occupancy was also estimated by the Lassen graphical approach. Both citalopram and fenfluramine effects were significant for BPF( P=0.031, P=0.049, respectively). The Lassen approach estimated 15.0, 30.4, and 23.7% average occupancy after citalopram 2 mg/kg, 4 mg/kg, and fenfluramine 2.5 mg/kg, respectively. [11C]CUMI-101 binding is sensitive to a large increase in intrasynaptic serotonin in response to robust pharmacological challenges. These modest changes in BPFmay make it unlikely that this ligand will detect changes in intrasynaptic 5-HT under physiologic conditions; future work will focus on evaluating its utility in measuring the responsiveness of the 5-HT system to pharmacological challenges.
Distribution of Glycylsarcosine and Cefadroxil among Cerebrospinal Fluid, Choroid Plexus, and Brain Parenchyma after Intracerebroventricular Injection is Markedly Different between Wild-Type andPept2Null Mice
Authors: Smith David E , Hu Yongjun , Shen Hong , Nagaraja Tavarekere N , Fenstermacher Joseph D , Keep Richard F
Published: June 2010

The purpose of this study was to define the cerebrospinal fluid (CSF) clearance kinetics, choroid plexus uptake, and parenchymal penetration of PEPT2 substrates in different regions of the brain after intracerebroventricular administration. To accomplish these objectives, we performed biodistribution studies using [14C]glycylsarcosine (GlySar) and [3H]cefadroxil, along with quantitative autoradiography of [14C]GlySar, in wild-type and Pept2 null mice. We found that PEPT2 deletion markedly reduced the uptake of GlySar and cefadroxil in choroid plexuses at 60 mins by 94% and 82% ( P<0.001), respectively, and lowered their CSF clearances by about fourfold. Autoradiography showed that GlySar concentrations in the lateral, third, and fourth ventricle choroid plexuses were higher in wild-type as compared with Pept2 null mice ( P<0.01). Uptake of GlySar by the ependymal–subependymal layer and septal region was higher in wild-type than in null mice, but the half-distance of penetration into parenchyma was significantly less in wild-type mice. The latter is probably because of the clearance of GlySar from interstitial fluid by brain cells expressing PEPT2, which stops further penetration. These studies show that PEPT2 knockout can significantly modify the spatial distribution of GlySar and cefadroxil (and presumably other peptides/mimetics and peptide-like drugs) in brain.
Characterization ofin vivoPharmacokinetic Properties of the Dopamine D1 Receptor Agonist DAR-0100A in Nonhuman Primates Using PET with [11C] NNC112 and [11C] Raclopride
Authors: Slifstein Mark , Suckow Raymond F , Javitch Jonathan A , Cooper Thomas , Lieberman Jeffrey , Abi-Dargham Anissa
Published: June 2010

DAR-0100A, the active enantiomer of dihydrexidine, is a potent dopamine D1 agonist under investigation for treatment of cognitive impairment and negative symptoms of schizophrenia. We measured the dose–occupancy relationship for DAR-0100A at D1 receptors using positron emission tomography (PET) imaging in baboons with [11C] NNC112 and its binding to D2 with [11C] raclopride. Two baboons were scanned with [11C] NNC112 at baseline and after three different doses of DAR-0100A. Two baboons were scanned with [11C] raclopride at baseline and after one dose of DAR-0100A. Occupancy (ΔBPND) was computed in the striatum and cortex. A clear relationship was observed between plasma concentration of DAR-0100A and ΔBPND. ΔBPNDwas larger in the striatum than in the cortex, consistent with reports showing that 25% of [11C] NNC112 BPNDin the cortex is attributed to 5-HT2A. Plasma EC50estimates ranged from 150 to 550 ng/mL according to the constraints on the model. There was no detectable effect of DAR-0100A on [11C] raclopride BPND. These data suggest that at doses likely to be administered to patients, occupancy will not be detectable with [11C] NNC112 PET and binding of DAR-0100A to D2 will be negligible. This is the first demonstration with PET of a significant occupancy by a full D1 agonist in vivo.
Analysis of protein complexes through model‐based biclustering of label‐free quantitative AP‐MS data
Authors: Choi Hyungwon , Kim Sinae , Gingras Anne‐Claude , Nesvizhskii Alexey I
Published: June 2010

Affinity purification followed by mass spectrometry (AP‐MS) has become a common approach for identifying protein–protein interactions (PPIs) and complexes. However, data analysis and visualization often rely on generic approaches that do not take advantage of the quantitative nature of AP‐MS. We present a novel computational method, nested clustering, for biclustering of label‐free quantitative AP‐MS data. Our approach forms bait clusters based on the similarity of quantitative interaction profiles and identifies submatrices of prey proteins showing consistent quantitative association within bait clusters. In doing so, nested clustering effectively addresses the problem of overrepresentation of interactions involving baits proteins as compared with proteins only identified as preys. The method does not require specification of the number of bait clusters, which is an advantage against existing model‐based clustering methods. We illustrate the performance of the algorithm using two published intermediate scale human PPI data sets, which are representative of the AP‐MS data generated from mammalian cells. We also discuss general challenges of analyzing and interpreting clustering results in the context of AP‐MS data.
Enhanced luminescence properties of highly threaded conjugated polyelectrolytes with potassium counter-ions upon blending with poly(ethylene oxide)
Authors: Latini Gianluca , Winroth Gustaf , Brovelli Sergio , McDonnell Shane O. , Anderson Harry L. , Mativetsky Jeffrey M. , Samorì Paolo , Cacialli Franco
Published: June 2010

The photophysics and electroluminescence (EL) of thin films of unthreaded and cyclodextrin-encapsulated poly(4,4′-diphenylenevinylene) (PDV) with potassium countercations, blended with poly(ethylene oxide) (PEO) are investigated as a function of the PEO concentration. We show that three main factors contribute to increasing the photoluminescence (PL) quantum efficiency as a result of suppressed intermolecular interactions, namely: the high degree of encapsulation of the polyrotaxanes, the relatively large countercation (e.g., compared to lithium), and the complexation of the rotaxanes with PEO. By facilitating cationic transport to the negative electrodes, PEO also leads to devices with enhanced electron injection and improved charge balance, whose operation therefore resembles that of “virtually unipolar” light-emitting electrochemical cells. This effect, together with the enhanced PL efficiency, leads to higher EL efficiency for both polyrotaxanes and unthreaded polymers, upon addition of the PEO. We show that the concurrent exploitation of the various strategies above lead to an overall EL efficiency that is approximately twice the value previously reported for Li-based PDV. A blueshift of the EL spectrum during the devices turn-on is also reported and analyzed in terms of interference and doping effects.
Weak antiferromagnetic coupling in molecular ring is predicted correctly by density functional theory plus Hubbard U
Authors: Gangopadhyay Shruba , Masunov Artëm E. , Poalelungi Eliza , Leuenberger Michael N.
Published: June 2010

We apply density functional theory with empirical Hubbard U parameter (DFT+U) to study Mn-based molecular magnets. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to π-back bonding, inverting spin polarization of the acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect the performance of the models that assume strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology to Mn12 molecular wheel and find antiparallel spin alignment for the weakly interacting fragments Mn6, in agreement with experimental observations. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single molecule magnets for molecular spintronics and quantum computing applications.
High-density excitation effect on photoluminescence in ZnO nanoparticles
Authors: Suzuki Keigo , Inoguchi Masashi , Fujita Koji , Murai Shunsuke , Tanaka Katsuhisa , Tanaka Nobuhiko , Ando Akira , Takagi Hiroshi
Published: June 2010

In this study, photoluminescence (PL) under high excitation intensity as a function of crystalline size was systematically investigated through ZnO nanocrystalline films prepared by spin-coating a colloidal solution of ZnO nanoparticles obtained using the microemulsion method. Annealing of the films at 723, 633, and 593 K allowed us to tune the crystalline radius R. PL studies distinguished different regimes of crystalline size according to the ratio of R to the effective Bohr radius aB(R/aB). For the sample annealed at 723 K (R/aB=7.2), the peak of stimulated emission due to the exciton-exciton collisions appeared on the low-energy side of the exciton emission with an increase in excitation intensity. A further increase in excitation intensity eventually resulted in the occurrence of an electron-hole plasma (EHP) accompanied by consequent band gap renormalization, which indicates that high excitation intensity provokes the dissociation of excitons. For the sample annealed at 633 K (R/aB=4.7), the stimulated emission was observed while the transition to EHP was obscure. For the sample annealed at 593 K (R/aB=2.1), only emissions due to the recombination of the electron-hole pair were observed, and stimulated emission did not appear even when the excitation intensity was increased. The transition from free-exciton emission to donor-bound exciton emission was observed in temperature dependence of PL only for the sample with R/aB=7.2. The origin of annihilation of the stimulated emission with a size reduction is discussed based on nonradiative Auger recombination.
Initiation of a passivated interface between hafnium oxide and In(Ga)As(  1)−(4×2)
Authors: Clemens Jonathon B. , Bishop Sarah R. , Lee Joon Sung , Kummel Andrew C. , Droopad Ravi
Published: June 2010

Hafnium oxide interfaces were studied on two related group III rich semiconductor surfaces, InAs(0 0 1)−(4×2) and In0.53Ga0.47As(0 0 1)−(4×2), via two different methods: reactive oxidation of deposited Hf metal and electron beam deposition of HfO2. The interfaces were investigated with scanning tunneling microscopy and spectroscopy (STS). Single Hf atom chemisorption sites were identified that are resistant to oxidation by O2, but Hf islands are reactive to O2. After e− beam deposition of ⪡1 ML of HfO2, single chemisorption sites were identified. At low coverage (<1 ML), the n-type and p-type HfO2/InGaAs(0 0 1)−(4×2) interfaces show p-type character in STS, which is typical of clean InGaAs(0 0 1)−(4×2). After annealing below 200 °C, full coverage HfO2/InGaAs(0 0 1)−(4×2) (1–3 ML) has the surface Fermi level shifted toward the conduction band minimum for n-type InGaAs, but near the valence band maximum for p-type InGaAs. This is consistent with the HfO2/InGaAs(0 0 1)−(4×2) interface being at least partially unpinned, i.e., a low density of states in the band gap. The partially unpinned interface results from the modest strength of the bonding between HfO2 and InGaAs(0 0 1)−(4×2) that prevents substrate atom disruption. The fortuitous structure of HfO2 on InAs(0 0 1)−(4×2) and InGaAs(0 0 1)−(4×2) allows for the elimination of the partially filled dangling bonds on the surface, which are usually responsible for Fermi level pinning.
Magnetization suppression in Co/Pd and CoCrPt by nitrogen ion implantation for bit patterned media fabrication
Authors: Sato Kenji , Ajan Antony , Aoyama Nobuhide , Tanaka Tsutomu , Miyaguchi Yusuke , Tsumagari Kanako , Morita Tadashi , Nishihashi Tsutomu , Tanaka Atsushi , Uzumaki Takuya
Published: June 2010

We propose a bit patterned media fabrication method based on low energy nitrogen ion implantation. Nitrogen ion implantation of fcc-Co/Pd multilayer or hcp-CoCrPt single layer suppresses their magnetizations at room temperature. Ion implantation reduces the Curie temperature from 600 to 400 K (or lower) as a result of lattice expansion and reduced exchange interaction between the magnetic atoms in the magnetic layer. We have made media with magnetic dots of 190 to 30 nm in diameter by nitrogen ion doping through resist patterns. Writing and reading of the signal from individual dots were performed with a commercial perpendicular magnetic recording head.
Excess entropy scaling of diffusion in room-temperature ionic liquids
Authors: Malvaldi Marco , Chiappe Cinzia
Published: June 2010

Excess entropy scaling relationships for diffusivity of ions in room-temperature ionic liquids are tested using molecular dynamics simulations for a model ionic liquid, dimethyl imidazolium chloride. The thermodynamic excess entropy of the single ions (estimated from the ion-ion pair correlation functions) is shown to be very strongly correlated with the diffusivity. An essential feature of these systems, the fact that the heavier and larger cation has a greater diffusivity with respect to the anion, is correctly captured by the excess entropy calculations, which estimates the diffusivity ratio between the two ions with noticeable precision.
The nth root of sequential effect algebras
Authors: Shen Jun , Wu Junde
Published: June 2010

In 2005, Gudder [Int. J. Theor. Phys. 44, 2219 (2005)] presented 25 problems of sequential effect algebras, the 20th problem asked: In a sequential effect algebra, if the square root of some element exists, is it unique? In this paper, we show that for each given positive integer n>1, there is a sequential effect algebra such that the nth root of its some element c is not unique, and the nth root of c is not the kth root of c (k<n). Thus, we answer the problem negatively.
Negative and positive ion trapping by isotopic molecules in cryocrystals in case of solid parahydrogen containing electrons and H6+ radical cations
Authors: Shimizu Yuta , Inagaki Makoto , Kumada Takayuki , Kumagai Jun
Published: June 2010

We performed electron spin resonance studies of trapped electrons and H6+ radical cations produced by radiolysis of solid parahydrogen (p-H2), p-H2−ortho-D2 (o-D2), and p-H2−HD mixtures. Yields of trapped electrons, H6+ radical cations, and its isotopic analogs H6−nDn+ (4≥n≥1) increased with increasing o-D2 and HD concentrations in solid p-H2. Electrons were found trapped near an o-D2 or an HD in solid p-H2 due to the long-range charge-induced dipole and quadrupole interactions between electrons and isotopic hydrogen molecules. H6+ radical cations diffuse in solid p-H2 by repetition of H6++H2→H2+H6+ and are trapped by ortho-D2 or HD to form H6−nDn+ (4≥n≥1) as isotope condensation reactions. Decay behaviors of these cations by the repetition, isotope condensation, and geminate recombination between electrons and H6−nDn+ (4≥n≥0) were reproduced by determining the corresponding reaction rate constants k1, k2, and k3. Values of 0.045 and 0.0015 L mol−1 min−1 were obtained for k1 (H6++D2→H2+H4D2+) and k2 (H4D2++D2→H2+H2D4+), respectively, and the value was quasinull for k3 (H2D4++D2→H2+D6+). These rate constants suggest that hole mobility drastically decreased in the repetition reaction when H6+ radical cations acting as hole carriers formed H4D2+ or H2D4+. HD and D2 molecules, therefore, act as electron and hole acceptors in irradiated solid p-H2−o-D2 and p-H2−HD mixtures.
Anisotropic properties of periodically polarity-inverted zinc oxide structures
Authors: Park J. S. , Minegishi T. , Lee J. W. , Hong S. K. , Song J. H. , Lee J. Y. , Yoon E. , Yao T.
Published: June 2010

We report on the anisotropic structural properties of periodically polarity-inverted (PPI) ZnO structures grown on patterned templates. The etching and growth rates along ⟨112¯0⟩ direction of ZnO structures are higher than those of ⟨101¯0⟩ direction of ZnO films. From the strain evaluation by Raman spectroscopy, compressive strains are observed in all PPI ZnO samples with different stripe pattern size and the smaller pattern size is more effective to residual stress relaxation. The detailed structures at transition region show relationship with the anisotropic crystal quality.
Controllable deformation of silicon nanowires with strain up to 24%
Authors: Walavalkar Sameer S. , Homyk Andrew P. , Henry M. David , Scherer Axel
Published: June 2010

Fabricated silicon nanostructures demonstrate mechanical properties unlike their macroscopic counterparts. Here we use a force mediating polymer to controllably and reversibly deform silicon nanowires. This technique is demonstrated on multiple nanowire configurations, which undergo deformation without noticeable macroscopic damage after the polymer is removed. Calculations estimate a maximum of nearly 24% strain induced in 30 nm diameter pillars. The use of an electron activated polymer allows retention of the strained configuration without any external input. As a further illustration of this technique, we demonstrate nanoscale tweezing by capturing 300 nm alumina beads using circular arrays of these silicon nanowires.
A two-dimensional modeling of the warm-up phase of a high-pressure mercury discharge lamp
Authors: Araoud Z. , Ben Ahmed R. , Ben Hamida M. B. , Franke St. , Stambouli M. , Charrada K. , Zissis G.
Published: June 2010

The main objective of this work is to provide a better understanding of the warm-up phase of high-intensity discharge lamps. As an example of application, we chose the high-pressure mercury lamp. Based on two-dimensional fluid model parameters, such as the electric current, the length and the diameter of the burner are modified and the effect of the convective transport is studied. This allows us to obtain a thorough understanding of the physics of these lamps in their transitory phase. The simulation of the warm-up phase is a must for the proper predictions of the lamp behavior and can be conducted by solving the energy balance, momentum, and Laplace’s equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall.
Titanium silicide islands on atomically clean Si(100): Identifying single electron tunneling effects
Authors: Tedesco J. L. , Rowe J. E. , Nemanich R. J.
Published: June 2010

Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (<2 nm) on atomically clean Si(100) substrates followed by annealing to ∼800 °C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET. Some of the islands formed are small enough (diameter <10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did not do so, and the reasons for the absence of observable SET are evaluated. The most likely reasons for the absence of SET are determined to be a wide depletion region in the substrate and Schottky barrier lowering due to Fermi level pinning by surface states of the clean silicon near the islands. The results establish that although the Schottky barrier can act as an effective tunnel junction in a DBTJ structure, the islands may be unreliable in future nanoelectronic devices. Therefore, methods are discussed to improve the reliability of future devices.
An efficient iterative grand canonical Monte Carlo algorithm to determine individual ionic chemical potentials in electrolytes
Authors: Malasics Attila , Boda Dezső
Published: June 2010

Two iterative procedures have been proposed recently to calculate the chemical potentials corresponding to prescribed concentrations from grand canonical Monte Carlo (GCMC) simulations. Both are based on repeated GCMC simulations with updated excess chemical potentials until the desired concentrations are established. In this paper, we propose combining our robust and fast converging iteration algorithm [Malasics, Gillespie, and Boda, J. Chem. Phys. 128, 124102 (2008)] with the suggestion of Lamperski [Mol. Simul. 33, 1193 (2007)] to average the chemical potentials in the iterations (instead of just using the chemical potentials obtained in the last iteration). We apply the unified method for various electrolyte solutions and show that our algorithm is more efficient if we use the averaging procedure. We discuss the convergence problems arising from violation of charge neutrality when inserting/deleting individual ions instead of neutral groups of ions (salts). We suggest a correction term to the iteration procedure that makes the algorithm efficient to determine the chemical potentials of individual ions too.
Ni–Mn–Ga ferromagnetic shape memory wires
Authors: Gómez-Polo C. , Pérez-Landazábal J. I. , Recarte V. , Sánchez-Alarcos V. , Badini-Confalonieri G. , Vázquez M.
Published: June 2010

Ni–Mn–Ga ferromagnetic shape memory wires (Ni2.10Mn0.98Ga0.92, mean diameter 170 μm) are obtained by the rotating water bath melt spinning technique. The compositional heterogeneity linked to its dendritelike structure gives rise to a complex and broad martensitic transformation (MT). The reduced value of magnetization in the as-spun sample is ascribed to Mn–Mn antiferromagnetic interactions at structural defects as atomic disorder, vacancies, and antiphase boundaries structures. Moreover, the observed low temperature magnetic relaxation process is characterized by a splitting in the zero-field-cooled/field-cooled magnetization curves and the frequency shift in the ac magnetic susceptibility. The results are interpreted in terms of the coexistence of a reduced magnetization state and nearly noninteracting magnetic clusters. A high temperature treatment optimizes both the MT and the magnetic characteristics (i.e., decrease in the hysteresis of the MT and magnetization recovery, respectively).
Multiple-peak structure in porous Si photoluminescence
Authors: Xu Yan Kai , Adachi Sadao
Published: June 2010

Photoluminescence (PL) measurements have been carried out on anodic porous silicon (PSi) at temperatures between T=20 and 300 K. He–Ne laser (1.96 eV), green laser diode (2.33 eV), and He–Cd laser (3.81 eV) are used as excitation light sources. Low-temperature (T≤250 K) PL spectra show a multiple-peak structure even when laser excitation is far from resonance with the red PL band. The configurational-coordinate model explains such unique multiple-peak structure very well. Fourier transform (FT) technique is used for the analysis of the measured multiple-peak structure. The FT frequency is determined to be ∼64 meV, which is in exact agreement with the bulk long-wavelength optical phonon energy in crystalline Si. Although the origin of the multiple-peak structure is bulk-related, its strength is very sensitive to the presence of surface oxide.
Surface- and bulk-sensitive x-ray absorption study of the valence states of Mn and Co ions in Zn1−2xMnxCoxO nanoparticles
Authors: Kataoka T. , Yamazaki Y. , Sakamoto Y. , Fujimori A. , Chang F.-H. , Lin H.-J. , Huang D. J. , Chen C. T. , Tanaka A. , Mandal S. K. , Nath T. K. , Karmakar D. , Dasgupta I.
Published: June 2010

We have performed x-ray absorption spectroscopy (XAS) measurements on Zn1−2xMnxCoxO nanoparticles. From the XAS results, it seems that the Mn and Co ions are in a mixed-valence (2+, 3+, and 4+) state and the relative concentrations of the high-valence (3+ and 4+) Mn and Co ions are higher in the surface region than in the deep core region. We suggest that this is a distinct trend of nanoparticle diluted magnetic semiconductor (DMS) unlike the case of DMS in film and bulk forms, where the transition-metal ions are expected to be 2+.
Communications: Evaluation of the nondiabaticity of quantum molecular dynamics with the dephasing representation of quantum fidelity
Authors: Zimmermann Tomáš , Vaníček Jiří
Published: June 2010

We propose an approximate method for evaluating the importance of non-Born–Oppenheimer effects on the quantum dynamics of nuclei. The method uses a generalization of the dephasing representation (DR) of quantum fidelity to several diabatic potential energy surfaces and its computational cost is the cost of dynamics of a classical phase space distribution. It can be implemented easily into any molecular dynamics program and also can utilize on-the-fly ab initio electronic structure information. We test the methodology on three model problems introduced by Tully and on the photodissociation of NaI. The results show that for dynamics close to the diabatic limit, the decay of fidelity due to nondiabatic effects is described accurately by the DR. In this regime, unlike the mixed quantum-classical methods such as surface hopping or Ehrenfest dynamics, the DR can capture more subtle quantum effects than the population transfer between potential energy surfaces. Hence we propose using the DR to estimate the dynamical importance of diabatic, spin-orbit, or other couplings between potential energy surfaces. The acquired information can help reduce the complexity of a studied system without affecting the accuracy of the quantum simulation.
Drastic time-dependent decrease in the saturation magnetization observed in Pd/Co/Pd trilayers with perpendicular anisotropy
Authors: Li L. , Wen F. S. , Zhang F. , Lü Y. F. , Lu Y. F. , Liu Z. Y. , Xu B. , Yu D. L. , He J. L. , Tian Y. J.
Published: June 2010

In the Pd/Co/Pd trilayer with magnetic perpendicular anisotropy, it has been found that both the saturation magnetization MS and the coercivity HC demonstrate a drastic time-dependent decrease. The time-dependent effect has been observed to be strongly related to the Co layer thickness. When the Co layer is thinner, the drops of HC and MS become much faster with time. The observed time-dependent effect is attributed to absorption of gaseous elements (for example, hydrogen) during exposure of the sample to the air, which can induce the reduction in Pd-polarization.
First-principles studies for CO and O2 on gold nanocluster
Authors: Xie Yao-Ping , Gong Xin-Gao
Published: June 2010

First-principles calculations are performed to study the interaction of gold nanocluster Au55 with small molecules CO and O2. We find that the adsorption energy of CO on Au55 is among 0.5–0.7 eV at different sites and [CO+O2] can be coadsorbed on Au55. Comparisons between Au55 and Au32 show that the adsorption energy not only depends on the size of the cluster but also on the geometry of the cluster. Similar with smaller cluster (Au8 and Au32), the energy difference between [CO+O2] and [CO2+O] on Au55 is much larger than that in the free gas. Our calculations indicate that the nanocluster Au55 can enhance the reaction process, CO+O2→CO2+O, in which the reaction barrier is only about half electron volts.
Identification of metal-cage coupling in a single metallofullerene by inelastic electron tunneling spectroscopy
Authors: Jiang J. , Gao B. , Hu Z. P. , Lu Wei , Wu Z. Y. , Yang J. L. , Luo Y.
Published: June 2010

We report hybrid density functional theory calculations for inelastic electron tunneling spectroscopy (IETS) of a single metallofullerene Gd@C82. It is found that the metal atom inside the carbon cage can have significant impact on the IETS spectral profiles of the system, by modulating both the vibration and electron density. It is demonstrated that the IETS signals are very sensitive to the changes in the metal position and charge states, so that provide a unique tool for identifying the metal-cage coupling in metallofullerenes.
Tuning the photoluminescence characteristics with curvature for rolled-up GaAs quantum well microtubes
Authors: Chun Ik Su , Bassett Kevin , Challa Archana , Li Xiuling
Published: June 2010

III-V microtubes and nanotubes are formed by a strain-induced self-rolling process. We report room-temperature photoluminescence (PL) characteristics of such microtubes with embedded GaAs quantum-well structures and wall thickness as thin as 38 nm. Rolled-up tubes show dramatic PL intensity enhancement compared to their planar counterparts. Holey tubes, formed using patterned membranes, display further increase in intensity implying better light extraction efficiency with the air holes. Systematic shift of PL peak position as a function of tube curvature, attributed to strain induced band structure change, is established.
InAs/GaSb type-II superlattice structures and photodiodes grown by metalorganic chemical vapor deposition
Authors: Huang Yong , Ryou Jae-Hyun , Dupuis Russell D. , Petschke Adam , Mandl Martin , Chuang Shun-Lien
Published: June 2010

We report on the characterization and performance of epitaxial structures and photodiodes based on InAs/GaSb type-II superlattices grown by metalorganic chemical vapor deposition. Interfacial layers were introduced at the superlattice interfaces to compensate the tensile strain and hence to improve the overall material quality of the superlattice structures. The optimal morphology and low strain was achieved via a combined interfacial layer scheme with InAsSb+InGaSb layers. Using this scheme, a p-i-n photodiode structure with a 360-period InAs/GaSb superlattice was grown on a GaSb substrate, which operates at 78 K with a cut-off wavelength of ∼8 μm and a peak responsivity of 0.6 A/W at ∼6 μm.
Self-assembled crystalline silicon carbide Y junctions by coalescence of nucleated iron catalysts
Authors: Liu Zhenyu , Srot V. , Yang Judith C.
Published: June 2010

Self-assembled crystalline SiC Y junctions with either parallel or inclined branches have been created via the iron catalyzed vapor-liquid-solid mechanism. These formations are attributed to coalescence of two catalyst droplets that have already each formed a SiC nanowire branch, where the merged catalyst remains catalytically active and catalyzes the stem growth of the Y junction. The SiC Y junction formed by two parallel branches follows the original growth direction and creates a single crystal stem. While the SiC Y junction formed by two inclined branches, the merged catalyst creates a bicrystal stem with a planar grain boundary along the center.
Influence of the GaN barrier thickness on the optical properties of InGaN/GaN multilayer quantum dot heterostructures
Authors: Davies S. C. , Mowbray D. J. , Ranalli F. , Wang T.
Published: June 2010

A study of InGaN/GaN multiple layer quantum dot (QD) structures with varying barrier thicknesses is reported. With increasing barrier thickness both a redshift in the photoluminescence (PL) peak energy and increase in the PL decay lifetime is observed. This is attributed to an increase in the size of the internal electric field and the influence on the electronic structure via the quantum confined Stark effect. Theoretical surface integral potential calculations support this interpretation. A minimum barrier thickness of 4 nm appears to be required for the formation of separate homogeneous QD layers.
Nanoscale domains in strained epitaxial BiFeO3 thin Films on LaSrAlO4 substrate
Authors: Chen Zuhuang , You Lu , Huang Chuanwei , Qi Yajun , Wang Junling , Sritharan Thirumany , Chen Lang
Published: June 2010

BiFeO 3 thin films with various thicknesses were grown epitaxially on (001) LaSrAlO4 single crystal substrates using pulsed laser deposition. High resolution x-ray diffraction measurements revealed that a tetragonal-like phase with c-lattice constant ∼4.65 Å is stabilized by a large misfit strain. Besides, a rhombohedral-like phase with c-lattice constant ∼3.99 Å was also detected at film thickness of ∼50 nm and above to relieve large misfit strains. In-plane piezoelectric force microscopy studies showed clear signals and self-assembled nanoscale stripe domain structure for the tetragonal-like regions. These findings suggest a complex picture of nanoscale domain patterns in BiFeO3 thin films subjected to large compressive strains.
Effects of fluorine incorporation into HfO2 gate dielectrics on InP and In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors
Authors: Chen Yen-Ting , Zhao Han , Wang Yanzhen , Xue Fei , Zhou Fei , Lee Jack C.
Published: June 2010

In this work, the effects of fluorine (F) incorporation on electrical characteristics of HfO2/InP and HfO2/In0.53Ga0.47As gate stack are presented. F had been introduced into HfO2 gate dielectric by postgate CF4 plasma treatment, which was confirmed by x-ray photoelectron spectroscopy analysis and a secondary ion mass spectrometry technique. Compared to the control sample, fluorinated samples had great improvements in subthreshold swing, hysteresis, the normalized extrinsic transconductance, and the normalized drain current. These improvements can be attributed to the reduction in fixed charge in the HfO2 bulk and less interface trap density at the HfO2/III–V interface.
Effects of electrodes and space charges on the tunneling electroresistance in the ferroelectric tunnel junction with a SrTiO3/BaTiO3 composite barrier
Authors: Wu Yin-Zhong , Ju Sheng , Li Zhen-Ya
Published: June 2010

Using the lattice model for strained nanoscale ferroelectric films and quantum tunneling theory, we present a theoretical investigation of tunneling electroresistance (TER) in the ferroelectric tunnel junction (FTJ) with a SrTiO3/BaTiO3 composite barrier. The exact profile of local polarizations within the composite barrier is calculated from first principles. It is found that the TER will sensitively depend on the choice of electrode with the increase in SrTiO3 barrier’s thickness. The space charges, which exist at the interface between the two barriers, will enhance the TER, and provide an effective approach to achieving large TER in FTJs.
Composition, variability, and temporal stability of the intestinal microbiota of the elderly
Authors: Claesson Marcus J. , Cusack Siobhán , O'Sullivan Orla , Greene-Diniz Rachel , de Weerd Heleen , Flannery Edel , Marchesi Julian R. , Falush Daniel , Dinan Timothy , Fitzgerald Gerald , Stanton Catherine , van Sinderen Douwe , O'Connor Michael , Harnedy Norma , O'Connor Kieran , Henry Colm , O'Mahony Denis , Fitzgerald Anthony P. , Shanahan Fergus , Twomey Cillian , Hill Colin , Ross R. Paul , O'Toole Paul W.
Published: June 2010

Alterations in the human intestinal microbiota are linked to conditions including inflammatory bowel disease, irritable bowel syndrome, and obesity. The microbiota also undergoes substantial changes at the extremes of life, in infants and older people, the ramifications of which are still being explored. We applied pyrosequencing of over 40,000 16S rRNA gene V4 region amplicons per subject to characterize the fecal microbiota in 161 subjects aged 65 y and older and 9 younger control subjects. The microbiota of each individual subject constituted a unique profile that was separable from all others. In 68% of the individuals, the microbiota was dominated by phylum
Bacteroides
, with an average proportion of 57% across all 161 baseline samples. Phylum
Firmicutes
had an average proportion of 40%. The proportions of some phyla and genera associated with disease or health also varied dramatically, including
Proteobacteria
,
Actinobacteria
, and
Faecalibacteria
. The core microbiota of elderly subjects was distinct from that previously established for younger adults, with a greater proportion of
Bacteroides
spp. and distinct abundance patterns of
Clostridium
groups. Analyses of 26 fecal microbiota datasets from 3-month follow-up samples indicated that in 85% of the subjects, the microbiota composition was more like the corresponding time-0 sample than any other dataset. We conclude that the fecal microbiota of the elderly shows temporal stability over limited time in the majority of subjects but is characterized by unusual phylum proportions and extreme variability.
Reverse engineering dynamic temporal models of biological processes and their relationships
Authors: Ramakrishnan Naren , Tadepalli Satish , Watson Layne T. , Helm Richard F. , Antoniotti Marco , Mishra Bud
Published: June 2010

Biological processes such as circadian rhythms, cell division, metabolism, and development occur as ordered sequences of events. The synchronization of these coordinated events is essential for proper cell function, and hence the determination of critical time points in biological processes is an important component of all biological investigations. In particular, such critical time points establish logical ordering constraints on subprocesses, impose prerequisites on temporal regulation and spatial compartmentalization, and situate dynamic reorganization of functional elements in preparation for subsequent stages. Thus, building temporal phenomenological representations of biological processes from genome-wide datasets is relevant in formulating biological hypotheses on: how processes are mechanistically regulated; how the regulations vary on an evolutionary scale, and how their inadvertent disregulation leads to a diseased state or fatality. This paper presents a general framework (GOALIE) to reconstruct temporal models of cellular processes from time-course gene expression data. We mathematically formulate the problem as one of optimally segmenting datasets into a succession of “informative” windows such that time points within a window expose concerted clusters of gene action whereas time points straddling window boundaries constitute points of significant restructuring. We illustrate here how GOALIE successfully brings out the interplay between multiple yeast processes, inferred from combined experimental datasets for the cell cycle and the metabolic cycle.
Practice Makes Perfect? When Does Massed Learning Improve Product Usage Proficiency?
Authors: Lakshmanan Arun , Lindsey Charles D. , Krishnan H. Shanker
Published: June 2010

Previous research has shown that spacing of information (over time) leads to better learning of product information. We develop a theoretical framework to describe how massed or spaced learning schedules interact with different learning styles to influence product usage proficiency. The core finding is that with experiential learning, proficiency in a product usage task is better under massed conditions, whereas with verbal learning, spacing works better. This effect is demonstrated for usage proficiency assessed via speed as well as quality of use. Further, massed learning also results in better usage proficiency on transfer tasks, for both experiential and verbal learning. We also find that massed learning in experiential learning conditions leads not only to better usage proficiency but also to positive perceptions of the product. Overall, the pattern of results is consistent with a conceptual mapping account, with massed experiences leading to a superior mental model of usage and thus to better usage proficiency.
Characteristics of plasma immersion ion implantation with a nanosecond rise-time pulse: particle-in-cell simulations
Authors: Sun Jizhong , Sang Chaofeng , Stirner Thomas , Wang Dezhen
Published: June 2010

Processes of plasma immersion ion implantation are analyszed numerically using a one-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision (1D3V PIC–MCC) model. The behaviour of ions and electrons between the processed target and the source plasma is simulated after a nanosecond rise-time voltage pulse is applied to the target. The simulation results show that electron–neutral ionization collisions play a significant role in determining the magnitudes of the ion and electron densities when the pulse rise time is very short, and that the plasma density can be enhanced many times. The physical mechanism for this phenomenon is explained in terms of the formation of a reverse electric field inside the plasma chamber.
Cantilever dynamics in amplitude modulation AFM: continuous and discontinuous transitions
Authors: Santos Sergio , Barcons Victor , Font Josep , Thomson Neil H
Published: June 2010

Transitions between the attractive and the repulsive force regimes for amplitude modulation atomic force microscopy (AFM) can be either discontinuous, with a corresponding jump in amplitude and phase, or continuous and smooth. During the transitions, peak repulsive and average forces can be up to an order of magnitude higher when these are discrete. Under certain circumstances, for example, when the tip radius is relatively large (e.g. R > 20–30 nm) and for high cantilever free amplitudes (e.g. A
0 > 40–50 nm), the L state can be reached with relatively low set-points only (e.g. A
sp/A
0 < 0.30). We find that these cases do not generally lead to higher resolution but increase the background noise instead. This is despite the fact that the imaging can be non-contact under these conditions. The appearance of background noise is linked to increasing cantilever mean deflection and tip–surface proximity with increasing free amplitude in the L state.
Nonconnected moduli spaces of positive sectional curvature metrics
Authors: Kreck Matthias , Stolz Stephan
Published: June 2010

For a closed manifold

M
M

let

ℜ

sec

+

(
M
)

\Re _{{\text {sec}}}^ + (M)

(resp.

ℜ

Ric

+

(
M
)

\Re _{{\text {Ric}}}^ + (M)

) be the space of Riemannian metrics on

M
M

with positive sectional (resp. Ricci) curvature and let

Diff

(
M
)

{\text {Diff}}(M)

be the diffeomorphism group of

M
M

, which acts on these spaces. We construct examples of

7
7

-dimensional manifolds for which the moduli space

ℜ

sec

+

(
M
)

/

Diff

(
M
)

\Re _{{\text {sec}}}^ + (M)/{\text {Diff}}(M)

is not connected and others for which

ℜ

Ric

+

(
M
)

/

Diff

(
M
)

\Re _{{\text {Ric}}}^ + (M)/{\text {Diff}}(M)

has infinitely many connected components. The examples are obtained by analyzing a family of positive sectional curvature metrics on homogeneous spaces constructed by Aloff and Wallach, on which

S
U
(
3
)

SU(3)

acts transitively, respectively a family of positive Einstein metrics constructed by Wang and Ziller on homogeneous spaces, on which

S
U
(
3
)
×
S
U
(
2
)
×
U
(
1
)

SU(3) \times SU(2) \times U(1)

acts transitively.
Hardy spaces and the two-dimensional Euler equations with nonnegative vorticity
Authors: Evans L. C. , Müller S.
Published: June 2010

We prove that certain quadratic expressions involving the gradient of a weakly superharmonic function in

R

2

{\mathbb {R}^2}

belong to a local Hardy space. As an application we provide a new proof of J.-M. Delort’s convergence theorem for solutions of the two-dimensional Euler equations with vorticities of one sign.
Matching theorems and empirical discrepancy computations using majorizing measures
Authors: Talagrand M.
Published: June 2010

We give explicit constructions of certain majorizing measures. These constructions allow us to give a unified proof of deep matching theorems of Ajtai, Komlòs, and Tusnàdy, of Leighton and Shor, and of Shor, as well as of more precise and more general results in a similar spirit.
How many eigenvalues of a random matrix are real?
Authors: Edelman Alan , Kostlan Eric , Shub Michael
Published: June 2010

Let

A
A

be an

n
×
n

n \times n

matrix whose elements are independent random variables with standard normal distributions. As

n
→
∞

n \to \infty

, the expected number of real eigenvalues is asymptotic to

2
n

/

π

\sqrt {2n/\pi }

. We obtain a closed form expression for the expected number of real eigenvalues for finite

n
n

, and a formula for the density of a real eigenvalue for finite

n
n

. Asymptotically, a real normalized eigenvalue

λ

/

n

\lambda /\sqrt n

of such a random matrix is uniformly distributed on the interval [-1, 1]. Analogous, but strikingly different, results are presented for the real generalized eigenvalues. We report on numerical experiments confirming these results and suggesting that the assumption of normality is not important for the asymptotic results.
Asymptotic completeness of 𝑁-particle long-range scattering
Authors: Sigal I. M. , Soffer A.
Published: June 2010

We prove asymptotic completeness for

N
N

-particle long-range system with potentials vanishing as

O
(

|
x
|

−
μ

)

O({\left | x \right |^{ - \mu }})

, where

μ
≥
1
−

2

−
N
−
2

\mu \geq 1 - {2^{ - N - 2}}

, at infinity.
A characterization of Banach spaces containing 𝑐₀
Authors: Rosenthal Haskell
Published: June 2010

A subsequence principle is obtained, characterizing Banach spaces containing

c
0

{c_0}

, in the spirit of the author’s 1974 characterization of Banach spaces containing

ℓ
1

{\ell ^1}

. Definition. A sequence

(

b
j

)

({b_j})

in a Banach space is called strongly summing (s.s.) if

(

b
j

)

({b_j})

is a weak-Cauchy basic sequence so that whenever scalars

(

c
j

)

({c_j})

satisfy

su

p

n

∥

Σ

j
=
1

n

c
j

b
j

∥>
∞

{\text {su}}{{\text {p}}_n}\parallel \Sigma _{j = 1}^n{c_j}{b_j}\parallel > \infty

, then

Σ

c
j

\Sigma {c_j}

converges. A simple permanence property: if

(

b
j

)

({b_j})

is an (s.s.) basis for a Banach space

B
B

and

(

b
j
∗

)

(b_j^ * )

are its biorthogonal functionals in

B
∗

{B^ * }

, then

(

Σ

j
=
1

n

b
j
∗

)

n
=
1

∞

(\Sigma _{j = 1}^nb_j^ * )_{n = 1}^\infty

is a non-trivial weak-Cauchy sequence in

B
∗

{B^ * }

; hence

B
∗

{B^ * }

fails to be weakly sequentially complete. (A weak-Cauchy sequence is called non-trivial if it is non-weakly convergent.) Theorem. Every non-trivial weak-Cauchy sequence in a (real or complex) Banach space has either an (s.s.) subsequence or a convex block basis equivalent to the summing basis. Remark. The two alternatives of the theorem are easily seen to be mutually exclusive. Corollary 1. A Banach space

B
B

contains no isomorph of

c
0

{c_0}

if and only if every non-trivial weak-Cauchy sequence in

B
B

has an (s.s.) subsequence. Combining the

c
0

{c_0}

- and

ℓ
1

{\ell ^1}

-Theorems, we obtain Corollary 2. If

B
B

is a non-reflexive Banach space such that

X
∗

{X^ * }

is weakly sequentially complete for all linear subspaces

X
X

of

B
B

, then

c
0

{c_0}

embeds in

B
B

; in fact,

B
B

has property

(
u
)

(u)

. The proof of the theorem involves a careful study of differences of bounded semi-continuous functions. The results of this study may be of independent interest.