bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Astrocyte Glutamine Production by α‐Ketoisocaproic Acid
Authors: Yudkoff Marc , Daikhin Yevgeny , Nissim Ilana , Pleasure David , Stern Janet , Nissim Itzhak
Published: July 2010

Abstract: We have evaluated the effect of α‐ketoisocaproic acid (KIC), the ketoacid of leucine, on the production of glutamine by cultured astrocytes. We used 15NH4Cl as a metabolic tracer to measure the production of both [5‐15N]glutamine, reflecting amidation of glutamate via glutamine synthetase, and [2‐15N]glutamine, representing the reductive amination of 2‐oxoglutarate via glutamate dehydrogenase and subsequent conversion of [15N]‐glutamate to [2‐15N]glutamine. Addition of KIC (1 mM) to the medium diminished the production of [5‐15N]glutamine and stimulated the formation of [2‐15N]glutamine with the overall result being a significant inhibition of net glutamine synthesis. An external KIC concentration as low as 0.06 mM inhibited synthesis of [5‐15N]glutamine and a level as low as 0.13 mM enhanced labeling (atom% excess) of [2‐15N]glutamine. Higher concentrations of KIC in the medium had correspondingly larger effects. The presence of KIC in the medium did not affect flux through glutaminase, which was measured using [2‐15N]glutamine as a tracer. Nor did KIC inhibit the activity of glutamine synthetase that was purified from sheep brain. Addition of KIC to the medium caused no increased release of lactate dehydrogenase from the astrocytes, suggesting that the ketoacid was not toxic to the cells. KIC treatment was associated with an approximately twofold increase in the formation of 14CO2 from [U‐14C]glutamate, indicating that transamination of glutamate with KIC increases intraastrocytic α‐ketoglutarate, which is oxidized in the tricarboxylic acid cycle. KIC inhibited glutamine synthesis more than any other ketoacid tested, with the exception of hydroxypyruvate. The data indicate that KIC diminishes flux through glutamine synthetase by lowering the intraastrocytic glutamate concentration below the Km of glutamine synthetase for glutamate, which we determined to be ∼7 mM.
Photoaffinity Labeling of a Neuronal Octopamine Receptor
Authors: Roeder Thomas , Nathanson James A.
Published: July 2010

Abstract: The invertebrate aminergic neurotransmitter and neuromodulator octopamine (OA) acts at both neuronal and nonneuronal receptors that appear to have distinct pharmacological characteristics. The current work uses a potent and specific OA photoaffinity ligand, tritiated 2(2,6‐diethyl‐4‐azidophenylimino)imidazolidine ([3H]NC‐5Z), to identify and characterize a putative neuronal OA receptor protein in membranes from nerve tissue of the desert locust, Schistocerca gregaria. Under nonphotolyzing conditions, [3H]NC‐5Z demonstrated high‐affinity binding (KD = 2.5 ± 0.3 nM; Bmax = 702 fmol/mg of protein) to a single class of noninteracting sites. The absolute and rank order potency of binding of both agonists and antagonists was highly correlated (r = 0.99) with their known ability to displace [3H]OA binding to locust neuronal membranes and was consistent with the labeling of a class 3 OA receptor. Under photolyzing conditions, [3H]NC‐5Z demonstrated irreversible binding that was resistant to trichloroacetic acid and methanol, displaceable by OA and other octopaminergic agonists and antagonists, soluble in sodium dodecyl sulfate, and only sparingly soluble in nonionic detergents. Membrane‐bound [3H]NC‐5Z, solubilized with Nonidet P‐40, bound specifically only to immobilized concanavalin A or lentil lectin. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of photolyzed proteins under reducing conditions revealed a single peak of radioactivity with a molecular mass of 53 ± 5 kDa. Taken together, these biochemical and pharmacological results support the identity of this protein peak as that of the neuronal OA3 receptor.
Protection and Potentiation of 1‐Methyl‐4‐Phenylpyridinium‐Induced Toxicity by Cytochrome P450 Inhibitors and Inducer May Be Due to the Altered Uptake of the Toxin
Authors: Sriram Krishnan , Pai Karnire S. , Ravindranath Vijayalakshmi
Published: July 2010

Abstract: Earlier studies from our laboratory have demonstrated that 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) toxicity could be modulated by inhibitors and inducer of cytochrome P450 (P450) in an in vitro model consisting of sagittal slices of mouse brain. To understand the molecular mechanisms underlying the role of P450 on MPTP toxicity, it was undertaken to study the effect of the modulators of P450 on the toxicity of the metabolite of MPTP, namely, 1‐methyl‐4‐phenylpyridinium ion (MPP+). Incubation of mouse brain slices with various concentrations of MPP+ (1–100 µM) resulted in dose‐dependent inhibition of mitochondrial enzyme NADH‐dehydrogenase (NADH‐DH) and leakage of the cytosolic enzyme lactate dehydrogenase from the slice into the medium. MPP+‐induced toxicity was abolished by pretreatment of the slices with inhibitors of monoamine oxidase (MAO; pargyline and deprenyl) or inhibitors of P450 (piperonyl butoxide or SKF‐525A) or dopamine uptake blocker (GBR‐12909), as measured by the activity of NADH‐DH in slices and leakage of lactate dehydrogenase from the slice into the medium. Slices prepared from mice pretreated with phenobarbital (an inducer of P450) potentiated the toxic effects of MPP+. Pretreatment of slices with MAO‐inhibitor, P450 inhibitors, or dopamine uptake blocker attenuated the uptake of MPP+ into the slices. In contrast, MPP+ uptake was significantly increased in slices prepared from phenobarbital‐pretreated mice. Thus, both MAO and P450 inhibitors abolish the toxicity of MPP+ in the sagittal slices of mouse brain by altering the uptake of the toxin into the slices.
The Proteins Synaptotagmin and Syntaxin Are Not General Targets of Lambert‐Eaton Myasthenic Syndrome Autoantibody
Authors: Hajela Ravindra K. , Atchison William D.
Published: July 2010

Abstract: Lambert‐Eaton myasthenic syndrome (LEMS) is an autoimmune neuromuscular disease in which impairment of Ca2+ entry into the nerve ending and consequent impaired release of acetylcholine (ACh) results in muscle weakness. The identity of the primary antigenic target molecule(s) of the autoantibodies is uncertain. Electrophysiological studies and 45Ca2+ uptake studies implicate a direct effect on the Ca2+ channel complex at the motor nerve terminal. Some recent studies, however, suggest a more indirect interference caused by binding of autoantibodies to synaptotagmin or syntaxin, molecules presumed to be involved in docking and/or coupling the synaptic vesicles to the Ca2+ channels in the active zone for vesicle exocytosis and transmitter release. Western blot analyses of rat and human brain membrane proteins and pure recombinant synaptotagmin and syntaxin were used to examine directly the targets of LEMS autoantibodies and determine specifically whether or not synaptotagmin and/or syntaxin were general targets in LEMS. IgG from 14 patients with LEMS was used to probe western blots of gels containing synaptotagmin, syntaxin, rat synaptosomal proteins, and human brain membrane proteins. Several similar immunoreactive bands were observed using both rat and human brain membranes. These include high‐molecular‐weight protein bands whose size would be consistent with being components of Ca2+ channels. No reactive component was observed against either syntaxin or synaptotagmin in IgG of the 14 LEMS patients. However, both human and rat brain membranes contain proteins recognized by antibodies directed against synaptotagmin or syntaxin, indicating their immunologic relatedness and evolutionary conservation. These results suggest that large‐molecular‐weight proteins consistent with being Ca2+ channel subunits rather than syntaxin and synaptotagmin are general targets of LEMS autoantibodies.
Synthesis of Serotonin in Traumatized Rat Brain
Authors: Tsuiki K. , Takada A. , Nagahiro S. , Grdiša M. , Diksic M. , Pappius H. M.
Published: July 2010

Abstract: Previous studies have demonstrated that focal freezing lesions in rats cause a widespread decrease of cortical glucose use in the lesioned hemisphere and this was interpreted as a reflection of depression of cortical activity. The serotonergic neurotransmitter system was implicated in these alterations when it was shown that (1) cortical serotonin metabolism was increased widely in focally injured brain and (2) inhibition of serotonin synthesis prevented the development of cortical hypometabolism. In the present studies we applied an autoradiographic method that uses the accumulation of the 14C‐labeled analogue of serotonin α‐methylserotonin to assess changes in the rate of serotonin synthesis in injured brain. The results confirmed that 3 days after the lesion was made, at the time of greatest depression of glucose use, serotonin synthesis was significantly increased in cortical areas throughout the injured hemisphere. The increase was also seen in the dorsal hippocampus and area CA3, as well as in the medial geniculate and dorsal raphe, but not in any other subcortical structures including median raphe. Present results suggest that the functional changes in the cortex of the lesioned hemisphere are associated with an increased rate of serotonin synthesis mediated by activation of the dorsal raphe. We also documented by α‐[14C]aminoisobutyric acid autoradiography that there was increased permeability of the blood‐brain barrier, but this was restricted to the rim of the lesion.
Dynamic Measurements of Cerebral Pentose Phosphate Pathway Activity In Vivo Using [1,6‐13C2,6,6‐2H2] Glucose and Microdialysis
Authors: Ben‐Yoseph Oded , Camp Dianne M. , Robinson Terry E. , Ross Brian D.
Published: July 2010

Abstract: Cerebral pentose phosphate pathway (PPP) activity has been linked to NADPH‐dependent anabolic pathways, turnover of neurotransmitters, and protection from oxidative stress. Research on this potentially important pathway has been hampered, however, because measurement of regional cerebral PPP activity in vivo has not been possible. Our efforts to address this need focused on the use of a novel isotopically substituted glucose molecule, [1,6‐13C2,6,6‐2H2]glucose, in conjunction with microdialysis techniques, to measure cerebral PPP activity in vivo, in freely moving rats. Metabolism of [1,6‐13C2,6,6‐2H2]glucose through glycolysis produces [3‐13C]lactate and [3‐13C,3,3‐2H2]lactate, whereas metabolism through the PPP produces [3‐13C,3,3‐2H2]lactate and unlabeled lactate. The ratios of these lactate isotopomers can be quantified using gas chromatography/mass spectrometry (GC/MS) for calculation of PPP activity, which is reported as the percentage of glucose metabolized to lactate that passed through the PPP. Following addition of [1,6‐13C2,6,6‐2H2]glucose to the perfusate, labeled lactate was easily detectable in dialysate using GC/MS. Basal forebrain and intracerebral 9L glioma PPP values (mean ± SD) were 3.5 ± 0.4 (n = 4) and 6.2 ± 0.9% (n = 4), respectively. Furthermore, PPP activity could be stimulated in vivo by addition of phenazine methosulfate, an artificial electron acceptor for NADPH, to the perfusion stream. These results show that the activity of the PPP can now be measured dynamically and regionally in the brains of conscious animals in vivo.
Ultrastructure of the 5‐Hydroxytryptamine3 Receptor
Authors: Boess Frank G. , Beroukhim Rameen , Martin Ian L.
Published: July 2010

Abstract: We have determined the ultrastructure of 5‐hydroxytryptamine3 (5‐HT3) serotonin receptors purified from NG108‐15 mouse neuroblastoma × rat glioma cells by electron microscopic examination of receptor particles embedded in uranyl acetate stain and metal replicas of rapidly frozen receptors. The 5‐HT3 receptor can be modelled as a cylinder 11 nm in length and 8 nm in diameter with a closed end and a central cavity 3 nm in diameter. Analysis of the rotational symmetry of single receptor particles indicates that the 5‐HT3 receptor is composed of five subunits arranged symmetrically around a central cavity. Together with evidence obtained for related proteins in other studies using ultrastructural, biochemical, or electrophysiological methods, our observations suggest that all members of the ligand‐gated ion channel superfamily may possess a pentameric quaternary structure.
Dopamine Transporter Cysteine Mutants: Second Extracellular Loop Cysteines Are Required for Transporter Expression
Authors: Wang Jia Bei , Moriwaki Akiyoshi , Uhl George R.
Published: July 2010

Abstract: Studies with thiol‐modifying reagents have suggested that cysteines might play important roles in the function of the dopamine transporter (DAT). To identify DAT cysteines with important thiol groups, we have studied six mutant dopamine transporters in which cysteines were replaced by alanines. Substitutions of cysteines assigned to the DAT's second putative extracellular loop—positions 180 and 189—dramatically decreased the expression of the mutant transporters. Substitutions at positions 90, 242, 305, and 345 had no significant effect in decreasing dopamine uptake, MPP+ uptake, or cocaine analogue binding. Immunostaining COS cells transfected with Cys180 and Cys189 to Ala mutants revealed reduced membrane staining and prominent staining in perinuclear regions consistent with Golgi apparatus. These results suggest that cysteines in the DAT second extracellular loop may provide sulfide residues crucial to full transporter expression, at least in part, through interference with membrane insertion. Conceivably, they might also provide the targets for the influences of thiol‐modifying reagents in modifying the function of the wild‐type DAT expressed in striatal membranes.
Properties of AMPA Receptors Expressed in Rat Cerebellar Granule Cell Cultures: Ca2+ Influx Studies
Authors: Hack N. , Balázs R.
Published: July 2010

Abstract: Cultured cerebellar granule cells become vulnerable to excitatory amino acids, especially to NMDA and kainate, by 9 days in vitro. In the same time, the sensitivity of cells to (RS)‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA), in terms of AMPA‐induced toxicity or 45Ca2+ uptake, was very low. The low AMPA responsiveness was due to receptor desensitization, because agents known to block desensitization, cyclothiazide and the lectins concanavalin A and wheat germ agglutinin, rendered granule cells vulnerable to AMPA and produced a pronounced stimulation of 45Ca2+ accumulation. 45Ca2+ influx was induced specifically by AMPA‐receptor stimulation, because it was blocked virtually completely by 2,3‐dihydroxy‐6‐nitro‐7‐sulfamoylbenzoquinoxaline (NBQX) and the benzodiazepine GYKI 52466 (selective non‐NMDA receptor antagonists). Nevertheless, indirect routes activated by cellular responses to AMPA‐receptor stimulation contributed significantly to the overall 45Ca2+ influx. These included Ca2+ uptake through NMDA‐receptor channels, voltage‐sensitive Ca2+ channels, and via Na+/Ca2+ exchange. However, nearly one‐fifth of the total 45Ca2+ influx remained unaccounted for and this estimate was similar to 45Ca2+ influx observed under Na+‐free conditions. This observation suggested that a significant proportion of the Ca2+ flux passes through the AMPA‐receptor channel proper, a view supported by Co2+ uptake into nearly all granule cells on exposure to AMPA in the presence of cyclothiazide. Results are discussed in light of the reported AMPA receptor‐subunit composition of cerebellar granule cells in vitro.
Comparison of the Neurochemical and Behavioral Effects Resulting from the Inhibition of Kynurenine Hydroxylase and/or Kynureninase
Authors: Chiarugi Alberto , Carpenedo Raffaella , Molina Maria Teresa , Mattoli Luisa , Pellicciari Roberto , Moroni Flavio
Published: July 2010

Abstract: Several kynurenine analogues were synthesized and tested as inhibitors of the enzymes kynurenine hydroxylase and/or kynureninase with the aim of identifying new compounds able to inhibit the synthesis of quinolinic acid (an endogenous excitotoxin) and to increase that of kynurenic acid, an endogenous antagonist of ionotropic glutamate receptors. Among these analogues, we selected m‐nitrobenzoylalanine (mNBA) as an inhibitor of kynurenine hydroxylase and o‐methoxybenzoylalanine (oMBA) as an inhibitor of kynureninase. When administered to rats, mNBA was more potent than oMBA in increasing the content of kynurenine and of kynurenic acid in the brain, blood, liver, and kidney. This confirms that hydroxylation is the main pathway of kynurenine metabolism. Both mNBA and oMBA (50–400 mg/kg i.p.) increased the concentration of kynurenate in hippocampal extracellular spaces (as measured with a microdialysis technique) and, when simultaneously injected, their effects were additive. This biochemical effect was associated with a decrease in locomotor activity in rats and with a protection of audiogenic convulsions in DBA/2 mice. In conclusion, the results of the present experiments indicate the possibility of increasing the neosynthesis of kynurenic acid by inhibiting the enzymes that metabolize kynurenine to 3‐hydroxykynurenine or to anthranilic acid. The increased synthesis of kynurenate is associated with behavioral effects such as sedation and protection from seizures, which suggests a functional antagonism of the excitatory amino acid receptors.
Selective Inhibition of the Tricarboxylic Acid Cycle of GABAergic Neurons with 3‐Nitropropionic Acid In Vivo
Authors: Hassel Bjørnar , Sonnewald Ursula
Published: July 2010

Abstract: The effects of 3‐nitropropionic acid (3‐NPA), an inhibitor of succinate dehydrogenase, on cerebral metabolism were investigated in mice by NMR spectroscopy. 3‐NPA, 180 mg/kg, caused a dramatic buildup of succinate. Succinate was labeled 5.5 times better from [1‐13C]glucose than from [2‐13C]acetate, showing a predominantly neuronal accumulation. [1‐13C]Glucose labeled GABA in the C‐2 position only, compatible with inhibition of the tricarboxylic acid (TCA) cycle associated with GABA formation, at the level of succinate dehydrogenase. Aspartate was not labeled by [1‐13C]glucose in 3‐NPA‐intoxicated animals. In contrast, [1‐13C]glucose labeled glutamate in the C‐2, C‐3, and C‐4 positions showing uninhibited cycling of label in the TCA cycle associated with the large, neuronal pool of glutamate. The labeling of glutamine, and hence GABA, from [2‐13C]acetate showed that the TCA cycle of glial cells was unaffected by 3‐NPA and that transfer of glutamine from glia to neurons took place during 3‐NPA intoxication. The high 13C enrichment of the C‐2 position of glutamine from [1‐13C]glucose showed that pyruvate carboxylation was active in glia during 3‐NPA intoxication. These findings suggest that 3‐NPA in the initial phase of intoxication fairly selectively inhibited the TCA cycle of GABAergic neurons; whereas the TCA cycle of glia remained uninhibited as did the TCA cycle associated with the large neuronal pool of glutamate, which includes glutamatergic neurons. This may help explain why the caudoputamen, which is especially rich in GABAergic neurons, selectively undergoes degeneration both in humans and animals intoxicated with 3‐NPA. Further, the present results may be of relevance for the study of basal ganglia disorders such as Huntington's disease.
Excess Extracellular and Low Intracellular Glutamate in Poorly Differentiating Wobbler Astrocytes and Astrocyte Recovery in Glutamine‐Depleted Culture Medium
Authors: Hantaz‐Ambroise D. , Cambier D. , Aït‐Ikhlef A. , Parvy Ph. , Murawsky M. , Rieger F.
Published: July 2010

Abstract: The wobbler mouse develops an inherited motoneuronal degeneration of unknown origin in the spinal cord. Primary cultures of adult wobbler spinal cord astrocytes display abnormal morphological characteristics with fewer processes and paucity of cell‐cell contacts. We have searched for a possible involvement of glutamate and glutamine intra‐ and extracellular accumulations in vitro in the abnormal differentiation of mutant astrocytes. We have found significantly higher glutamate and glutamine concentrations in the culture media of mutant astrocytes over a 3‐day period compared with normal control astrocytes. Moreover, intracellular glutamate concentrations decreased substantially in mutant astrocytes, but intracellular glutamine concentrations remained unchanged. Furthermore, decreasing initial glutamine concentrations in the culture medium (glutamine‐depleted medium) led to the recovery of normal extra‐ and intracellular concentrations of glutamate and recovery of quasi‐normal morphological differentiation and increased cell‐cell contacts, leading to an essentially normal looking astrocyte network after 3 days of culture. Under these conditions, which lead to recovery, the only remaining abnormality was the higher glutamine extracellular concentration attained in the originally depleted glutamine media. These findings suggest that mechanisms regulating glutamate/glutamine synthesis and/or influx/efflux are defective in wobbler astrocytes, leading to metabolic imbalance and possible cytotoxic effects characterized by disturbed intercellular networks and poor differentiation.
Whittaker–Hill equation and semifinite-gap Schrödinger operators
Authors: Hemery A. D. , Veselov A. P.
Published: July 2010

A periodic one-dimensional Schrödinger operator is called semifinite gap if every second gap in its spectrum is eventually closed. We construct explicit examples of semifinite-gap Schrödinger operators in trigonometric functions by applying Darboux transformations to the Whittaker–Hill equation. We give a criterion for the regularity of the corresponding potentials and investigate the spectral properties of the new operators.
Real-time fracture detection of individual boron nitride nanotubes in severe cyclic deformation processes
Authors: Ghassemi H. M. , Lee C. H. , Yap Y. K. , Yassar R. S.
Published: July 2010

Real-time deformation of individual multiwalled boron nitride nanotubes (BNNTs) was investigated using an atomic force microscopy (AFM) stage installed inside the chamber of a transmission electron microscopy (TEM) system. These in situ AFM-TEM experiments were conducted in following two deformation regimes: a small-angle (∼65°) and a large-angle (∼120°) cyclic bending process. BNNTs survived from the low-angle test and their modulus was determined as ∼0.5 TPa. Fracture failure of individual BNNTs was discovered in the large-angle cyclic bending. The brittle failure mechanism was initiated from the outermost walls and propagated toward the tubular axis with discrete drops of applied forces.
Effects of deposition temperature on the effectiveness of hydrogen doping in Ga-doped ZnO thin films
Authors: Kim Dong-Ho , Lee Sung-Hun , Lee Gun-Hwan , Kim Hyun-Bum , Kim Kwang Ho , Lee Yoon-Gyu , Yu Tae-Hwan
Published: July 2010

Gallium-doped zinc oxide thin films were prepared on glass substrates by dc magnetron sputtering under various hydrogen contents in sputtering ambient. The carrier concentration of the films deposited at low-temperatures (80 and 160 °C) was increased due to the incorporation of hydrogen atoms, acting as shallow donors. A low resistivity of 4.0×10−4 Ω cm was obtained for the film grown at 160 °C with H2 10%, which has a carrier concentration of 8.2×1020/cm3. The beneficial effect of hydrogen doping was not observed for the films deposited at 270 °C. Both carrier concentration and mobility were decreased by the addition of hydrogen gas in the sputtering ambient. Variations in the electrical transport properties upon vacuum annealing showed that the difference is attributed to the thermal stability of interstitial hydrogen atoms in the films. The hydrogen incorporation was found to induce the lattice expansion and the free carrier absorption in near infrared range. The investigation of the structural and optical properties of the films upon annealing also revealed that the incorporated hydrogen atoms are unstable at high temperature, which is consistent with the results obtained in the electrical properties.
An alternative method to determining optical lever sensitivity in atomic force microscopy without tip-sample contact
Authors: Tourek Christopher J. , Sundararajan Sriram
Published: July 2010

Force studies using atomic force microscopy generally require knowledge of the cantilever spring constants and the optical lever sensitivity. The traditional method of evaluating the optical lever sensitivity by pressing the tip against a hard surface can damage the tip, especially sharp ones. Here a method is shown to calculate the sensitivity without having to bring the tip into contact. Instead a sharpened tungsten wire is used to cause a point contact directly onto the cantilever and cause cantilever bending. Using beam theory, the sensitivity thus found can be converted to the equivalent sensitivity that would be obtained using the tip location. A comparison is presented between sensitivity values obtained from the conventional tip contact method and those derived from the wire-based technique for a range of cantilevers in air. It was found that the difference between the calculated sensitivity from the wire-based technique and the sensitivity obtained conventionally was less than 12%. These measurements indicate the presented method offers a simple alternative approach to obtain optical lever sensitivity without compromising the tip shape.
Temperature-dependent studies of defect-assisted light emission and excitation processes in crystalline ZnO nanowire phosphors
Authors: Omari M. , Gupta A. , Kouklin N.
Published: July 2010

A series of photoluminescence and photoluminescence-excitation spectroscopies have been performed to probe the processes regulating defect-assisted light emission from one-dimensional ZnO nanowire phosphors in a wide temperature range of 123–463 K. The observed nonmonotonic change of the integral defect-photoluminescence intensity as well as its peak position with temperature are explained based on the interplay of competing effects of thermal quenching and carrier redistribution over radiative channels. A temperature-induced broadening of the defect photoluminescence band is observed and attributed to the appearance of ∼2.1 eV band, the intensity of which is also found to quench quickly with the onset of higher temperature. The results of photoluminescence-excitation measurements show that band-to-band excitations remain a primary excitation channel of defects especially at low and moderate temperature range, whereas the role of direct, one-photon absorption channel is found to progress as temperature approaches ∼500 K.
Determining time resolution of microchannel plate detectors for electron time-of-flight spectrometers
Authors: Zhang Qi , Zhao Kun , Chang Zenghu
Published: July 2010

The temporal resolution of a 40 mm diameter chevron microchannel plate (MCP) detector followed by a constant fraction discriminator and a time-to-digital converter was determined by using the third order harmonic of 25 fs Ti:sapphire laser pulses. The resolution was found to deteriorate from 200 to 300 ps as the total voltage applied on the two MCPs increased from 1600 to 2000 V. This was likely due to a partial saturation of the MCP and/or the constant fraction discriminator working with signals beyond its optimum range of pulse width and shape.
Hierarchy of minimal flow units in the logarithmic layer
Authors: Flores Oscar , Jiménez Javier
Published: July 2010

The minimal simulation boxes of the buffer layer of turbulent channels can be extended to the logarithmic and outer regions, where they contain a segment of streamwise velocity streak, and a vortex cluster. Smaller boxes restrict “healthy” turbulence closer to the wall, to a layer whose thickness scales with the spanwise size of the box. These minimal boxes burst quasiperiodically, and the bursting period for a band of wall distances grows linearly away from the wall, independently of the box size within the limits within which turbulence is well represented.
Enhanced room temperature excitonic luminescence in ZnO/polymethyl methacrylate nanocomposites prepared by bulk polymerization
Authors: Paramo J. Antonio , Strzhemechny Yuri M. , Anžlovar Alojz , Žigon Majda , Orel Zorica Crnjak
Published: July 2010

Homogeneous ZnO/polymethyl methacrylate (PMMA) nanocomposites were prepared by incorporating ZnO nanoparticles synthesized in various diols into a PMMA matrix by the free-radical bulk polymerization. Room temperature photoluminescence spectra of the as-grown and PMMA-embedded ZnO nanoparticles exhibit an excitonic band-gap emission at 3.3 eV, a near band-gap emission at ∼3.1 eV and a broad defect band centered at ∼2.4 eV. Relative intensity of the defect versus band-gap luminescence depends on the parameters of ZnO preparation as well as the average particle size. However, PMMA-embedded particles produce a much stronger excitonic luminescence, whereas the ratio of the 3.1 to 2.4 eV remains approximately constant. There is no indication of random lasing threshold pointing to the ZnO/PMMA interfacial origin of the enhanced band-gap emission.
Plane and hemispherical potential structures in magnetically expanding plasmas
Authors: Takahashi Kazunori , Igarashi Yuichi , Fujiwara Tamiya
Published: July 2010

Two-dimensional potential structures are measured for different gas pressure in expanding argon plasma using permanent magnets, where the magnetic field is about 100 G in the source and several gauss in the diffusion chamber. The plane potential drop is observed near the source exit for 0.35 mTorr, while the potential structure becomes hemispherical when increasing up to 1 mTorr; the hemispherical structure results in the radial divergence of the ion beam. It is found that the trajectories of the accelerated ions and the electrons overcoming the potential drop are dominated by the potential structure and magnetic-field lines, respectively.
Web-like domain structure formation in barium titanate single crystals
Authors: Rodriguez B. J. , Eng L. M. , Gruverman A.
Published: July 2010

The evolution of ferroelectric domain structure in Remeika-grown BaTiO3 crystals under an inhomogeneous electric field has been investigated using piezoresponse force microscopy. The ac imaging bias was found to affect the metastable polarization state and lead to the formation of a web-like domain structure. It is suggested that this behavior is due to the existence of subsurface domains arising in single crystals with a layered structure.
Impedance spectroscopy on stretchable microelectrode arrays
Authors: Minev I. R. , Lacour S. P.
Published: July 2010

We are reporting on the fabrication and electrical characterization of stretchable polydimethylsiloxane (PDMS) based microelectrode arrays for recording of neuronal action potentials. Electrodes are immersed in phosphate buffered saline solution. Their electrical impedance spectra are recorded as a function of uniaxial macroscopic strain applied using a custom built automated stretcher. We propose a model to account for the physical phenomena responsible for electrical conduction in the bulk electrode and at the metal–electrolyte interface. Electrodes with active area dimensions of 100×140 μm2 maintain an impedance of approximately 1 MΩ at 1 kHz when cycled to 20% strain.
Monolithic n-type conductivity on low temperature grown freestanding ultrananocrystalline diamond films
Authors: Joseph P. T. , Tai N. H. , Lin I. N.
Published: July 2010

We report monolithic n-type conductivity on low-temperature (<570 °C) grown ultrananocrystalline diamond (UNCD) films by Li-diffusion (about 255 nm) from LiNbO3 substrates. Low resistivity of 1.2 Ω cm with carrier concentration of −2×1020 cm−3 is obtained on freestanding UNCD films. The films bonded to Cu-tape show very low turn-on field of 4.2 V/μm with emission current density of above 0.3 mA/cm2 at a low applied filed of 10 V/μm. The n-type conductivity of low-temperature Li-diffused UNCD films overwhelms that of the high-temperature (≥800 °C) nitrogen doped ones and will make a significant impact to diamond-based electronics.
Efficient capacitive transduction of high-frequency micromechanical resonators by intrinsic cancellation of parasitic feedthrough capacitances
Authors: Arcamone Julien , Colinet Eric , Niel Antoine , Ollier Eric
Published: July 2010

Parasitic feedthrough capacitances represent a generic issue for capacitively transduced microelectromechanical resonators. Those parasitic capacitances degrade the output signal’s magnitude and phase by increasing the feedthrough signal and attenuating the resonance peak because of the resulting antiresonance peak. Whereas classical capacitive actuation/detection schemes only partially circumvent this issue, this work presents a specific, balanced, set-up that intrinsically cancels the effects of feedthrough capacitances. The resonator can recover its intrinsic purely RLC behavior thanks to this method which preferentially applies to given bulk modes, such as Lamé for plates and elliptic for disks. It has been experimentally tested on 100 MHz plates and disks.
Subwavelength focusing of light by a tapered microtube
Authors: Fu Jian , Dong Hongtao , Fang Wei
Published: July 2010

We propose a mechanism for subwavelength focusing at optical frequencies based on the use of a tapered microtube fabricated from a glass capillary tube. Using coherent illumination at 671 nm and a near-field scanning optical microscope probe which was mounted on a three-axis piezonanopositioning stage, a sequence of two-dimensional intensity profiles were obtained. Our experimental results reveal the smallest focal spot with a near diffraction-limited full width at half-maximum of ∼435 nm (0.65λ) at a distance of ∼1.47 μm (2.2λ) from the output end face of microtube. The experimental results are in agreement with our numerical simulation.
Spin modulation in semiconductor lasers
Authors: Lee Jeongsu , Falls William , Oszwałdowski Rafal , Žutić Igor
Published: July 2010

We provide an analytic study of the dynamics of semiconductor lasers with injection (pump) of spin-polarized electrons, previously considered in the steady-state regime. Using complementary approaches of quasistatic and small signal analyses, we elucidate how the spin modulation in semiconductor lasers can improve performance, as compared to the conventional (spin-unpolarized) counterparts. We reveal that the spin-polarized injection can lead to an enhanced bandwidth and desirable switching properties of spin-lasers.
Carrier dynamics in isoelectronic ZnSe1−xOx semiconductors
Authors: Lin Y. C. , Chung H. L. , Chou W. C. , Chen W. K. , Chang W. H. , Chen C. Y. , Chyi J. I.
Published: July 2010

This study explores the effects of both Oxygen and temperature on the carrier dynamics of isoelectronic ZnSe1−xOx (x=0.027 and 0.053) semiconductors using photoluminescence (PL) and time-resolved PL spectroscopy. We find that the Kohlrausch law is highly consistent with the complex decay traces induced by isoelectronic O traps, and the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature. Complex recombination processes are clarified using the relaxation model based on various decay channels. These findings are consistent with the initial fall in the stretching exponent β followed by its monotonic increase with increasing temperature.
Voltage tunable photodetecting properties of La0.4Ca0.6MnO3 films grown on miscut LaSrAlO4 substrates
Authors: Li X. M. , Zhao K. , Ni H. , Zhao S. Q. , Xiang W. F. , Lu Z. Q. , Yue Z. J. , Wang F. , Kong Yu-Chau , Wong H. K.
Published: July 2010

We report the voltage tunable photodetecting properties of a La0.4Ca0.6MnO3 film grown on miscut LaSrAlO4 (001) substrates under ultraviolet pulsed laser irradiation at ambient temperature. The photovoltage and photocurrent peak sensitivities can be tuned in the range of 0.295–0.786 V/mJ and 0.172–0.314 A/mJ, respectively, when the applied bias is changed from −20 to +20 V, indicating that the vicinal manganite film can be used as an electric tunable ultraviolet photodetector. A possible mechanism based on the high resolution transmission electron microscopy is introduced to explain the experiment results.
Overcoming Cost-Inefficiencies within Small Municipalities: Improve Financial Condition or Reduce the Quality of Public Services?
Authors: Zafra-Gómez José Luis , Antonio Manuel , Muñiz Pérez
Published: July 2010

A common finding of studies evaluating cost-efficiency in the provision of local public services is the existence of economies of scale in the production of such services. How can smaller, less efficient local authorities overcome this position of disadvantage? According to economic theory, they should either obtain supplementary funding or otherwise reduce the quality levels of the services provided. The aim of the present study is to evaluate the relations among different dimensions of municipal performance. The above concepts are analysed in a sample composed of 923 local authorities in Spain, each with fewer than 20 000 in habitants, using a data envelopment analysis model adapted for the particular characteristics of the local environment and repeating the analysis for two different periods, 2000 and 2005, in order to increase the consistency of the results obtained. Empirical analysis shows that the financial management and the productive efficiency of small local authorities are not interrelated, with the more cost-efficient bodies (especially for quality-related costs) being the least efficient as regards their financial condition. Moreover, our analysis of cost-efficiency for the smaller municipalities shows that revenues must be increased in order to obtain a similar level of quality to that of larger authorities.
Does Regulation Perform Better Than Self-Regulation? An Analysis of Spanish Environmental Policies
Authors: Camisón-Zornoza Cesar , Boronat-Navarro Montserrat
Published: July 2010

The question of why corporations are subject to different regulatory approaches remains open. In this paper we analyze this problem using Ashbein and Ajzen's theory of planned behavior. We study how management's perception of public environmental policies influences how the corporation acts and the ways in which this environmental approach contributes to environmental performance. This research differentiates among five policy approaches, some of which are focused on mandatory regulation and some on positive and voluntary adjustments made by corporations. An empirical analysis is conducted based on data for 1151 Spanish corporations from 2002 to 2005. We conclude that self-regulation produces the greatest environmental gains, particularly when coupled with a cooperative regulatory approach. These results call into question the public preference for environmental policies based on mandatory standards and technologies (based on either coercion or conciliation) and support recommendations for policies to support self-regulation rather than legal coercion.
Nationalist, heretic or populist?
Authors: Brandenberger David
Published: July 2010

I am grateful to Andreas Umland and David Marples for their thoughtful responses to my piece and appreciate the invitation of the editors of Nationalities Papers to briefly reply. Because “Stalin's Populism” is an essay rather than an article devoted to empirical research, historiography or contemporary politics, some of the objections that Umland and Marples raise are a function of genre more than anything else. Other issues require more detailed engagement, however. As both responses indicate, “Stalin's Populism” elaborates upon an argument that I've advanced in a number of places about the USSR's rehabilitation of Russian historical heroes, imagery and iconography during the 1930s and 1940s. An enduring source of debate over the past half-century, this development has been variously attributed to Stalin's retreat from world revolution, his low confidence in proletarian internationalism, his wavering commitment to Marxism and his insecurity during the Second World War. It's also been seen as evidence of a turn toward nationalism and even fascism. I have long been frustrated by the schematicism of such accounts and offer here a more contingent interpretation situated specifically within the historical contours of the Stalinist 1930s. I have also grown frustrated by the hyperbole of the traditional literature's focus on Stalin's personal failings and ideological apostasy and suggest here that the policy changes in question display all the hallmarks of authoritarian populism, inasmuch as they advanced claims of Soviet state legitimacy and authority rather than Russian political autonomy or self-rule. Indeed, it is this official emphasis on party and state legitimacy and union-wide mobilization that leads me to use terms like “national Bolshevism” and russocentrism rather than Russian nationalism in regard to the Stalinist party line.
Energetic-particle modes driven by suprathermal electrons produced by off-axis second harmonic ECRH in compact helical system (CHS)
Authors: Isobe M. , Toi K. , Yoshimura Y. , Shimizu A. , Akiyama T. , Ida K. , Minami T. , Suzuki C. , Okamura S.
Published: July 2010

Recurrent bursting energetic-particle modes (EPMs) are observed in an l = 2 helical plasma heated by second harmonic electron cyclotron resonance heating (ECRH) without neutral beam injection. The observed instabilities are characterized by a rapid frequency downshift, propagating in the ion-diamagnetic drift direction. Such bursting MHD instabilities are seen only in fairly low-density plasmas with off-axis second harmonic ECRH. A soft x-ray detector operating in the counting mode indicates that there exist suprathermal electrons in low-density ECRH plasmas where EPMs are destabilized. The excitation of EPMs is supposed to be due to the helically trapped suprathermal electrons produced by the second harmonic ECRH.
The dependence of the damping rate of medium-n toroidal Alfvén eigenmodes on the edge plasma elongation in JET*
Authors: Testa D. , Mellet N. , Panis T. , Blanchard P. , Carfantan H. , Fasoli A.
Published: July 2010

This paper reports the first quantitative analysis of the measurements of the damping rate (γ/ω) for stable Alfvén eigenmodes (AEs) with toroidal mode number (n) in the range |n| = 3–15 as a function of the edge plasma elongation (κ95). We find that the damping rate γ/ω versus κ95 for medium-n toroidal AEs (TAEs), with n = 3 and n = 7, increases for increasing elongation, i.e. its scaling versus κ95 follows the same trend previously measured and explained theoretically for the n = 1 and n = 2 TAEs. Theoretical analysis of the measurements for the n = 3 TAEs has been performed using the LEMan code. The results are in good agreement (within a factor of two) for all the magnetic configurations where there is only a very minor up/down asymmetry in the poloidal cross-section of the plasma. These experimental results further confirm the possibility of using the edge shape parameters as a real-time actuator for control of the stability of alpha-particle driven AEs in burning plasma experiments, such as ITER.
Anomalous electron transport due to multiple high frequency beam ion driven Alfvén eigenmodes
Authors: Gorelenkov N.N. , Stutman D. , Tritz K. , Boozer A. , Delgado-Aparicio L. , Fredrickson E. , Kaye S. , White R.
Published: July 2010

We report on the simulations of recently observed correlations of the core electron transport with the sub-thermal ion cyclotron frequency instabilities in low aspect ratio plasmas of the National Spherical Torus Experiment. In order to model the electron transport the guiding centre code ORBIT is employed. A spectrum of test functions of multiple core localized global shear Alfvén eigenmode (GAE) instabilities based on a previously developed theory and experimental observations is used to examine the electron transport properties. The simulations exhibit thermal electron transport induced by electron drift orbit stochasticity in the presence of multiple core localized GAE.
Internal measurements of Alfvén eigenmodes with heavy ion beam probing in toroidal plasmas*
Authors: Melnikov A.V. , Eliseev L.G. , Jiménez-Gómez R. , Ascasibar E. , Hidalgo C. , Chmyga A.A. , Komarov A.D. , Kozachok A.S. , Krasilnikov I.A. , Khrebtov S.M. , Krupnik L.I. , Liniers M. , Lysenko S.E. , Mavrin V.A. , de Pablos J.L. , Pedrosa M.A. , Perfilov S.V. , Ufimtsev M.V. , Ido T. , Nagaoka K. , Yamamoto S. , Taschev Yu.I. , Zhezhera A.I. , Smolyakov A.I.
Published: July 2010

Energetic ion driven Alfvén eigenmodes (AEs) are believed to be an important element disturbing the transport in a future fusion reactor. The studies of the AE properties in modern toroidal devices have made crucial contributions to the reactor relevant physics. AEs are conventionally studied by magnetic probes (MPs), which provide the poloidal m and toroidal n mode numbers and their spectral characteristics. Heavy ion beam probing (HIBP) has become a new tool to study AEs with high spatial and frequency resolution. HIBP in the TJ-II heliac observes locally (∼1 cm) resolved AEs over the whole radial interval. The set of low-m (m < 8) modes, detected with the high-frequency resolution (<5 kHz), present different types of AEs. AEs are pronounced in the local density, electric potential and poloidal magnetic field oscillations, detected simultaneously by HIBP in the frequency range 50 kHz < f
AE < 300 kHz. Various AE modes are visible in the neutral beam injector (NBI)-heated plasma for co-NBI (<450 kW), counter- (<450 kW) and balanced NBI (<900 kW) from the plasma centre to the edge. A high coherence between MP and HIBP data was found for specific AEs. When the density rises, AE frequency decreases,
, and the cross-phase between the plasma density, poloidal magnetic field and potential remains constant. The amplitude of the AE potential oscillations δφAE ∼ 10 V was estimated. Poloidally resolved density and potential measurements may provide information about the AE poloidal wavelength and the AE contribution to the poloidal electric field E
pol and the turbulent particle flux 𝚪

E
×
B

. The typical range of E
pol oscillations for AEs is
. Depending on the δn
e and δE
pol amplitudes and cross-phase, AEs may make a small or a significant contribution to the turbulent particle flux 𝚪

E
×
B

for the observed wavenumbers k
θ < 3 cm−1.
Phenomenology of energetic-ion loss from the DIII-D tokamak
Authors: Zhu Y.B. , Heidbrink W.W. , Pickering L.D.
Published: July 2010

Thin-foil Faraday collectors mounted near the midplane measure energetic-ion loss signals from the DIII-D tokamak. Modulation of the neutral beam sources shows that, under appropriate conditions, prompt losses from every beam line are observed. Prompt losses are usually larger when the plasma current or toroidal field is low. Enhanced losses occur during ion cyclotron heating. Instabilities that produce strong field perturbations at the edge also produce enhanced losses.
Expression of Actin-interacting Protein 1 Suppresses Impaired Chemotaxis ofDictyosteliumCells Lacking the Na+-H+Exchanger NHE1
Authors: Choi Chang-Hoon , Patel Hitesh , Barber Diane L.
Published: July 2010

Increased intracellular pH is an evolutionarily conserved signal necessary for directed cell migration. We reported previously that in Dictyostelium cells lacking H+efflux by a Na+-H+exchanger (NHE; Ddnhe1−), chemotaxis is impaired and the assembly of filamentous actin (F-actin) is attenuated. We now describe a modifier screen that reveals the C-terminal fragment of actin-interacting protein 1 (Aip1) enhances the chemotaxis defect of Ddnhe1−cells but has no effect in wild-type Ax2 cells. However, expression of full-length Aip1 mostly suppresses chemotaxis defects of Ddnhe1−cells and restores F-actin assembly. Aip1 functions to promote cofilin-dependent actin remodeling, and we found that although full-length Aip1 binds cofilin and F-actin, the C-terminal fragment binds cofilin but not F-actin. Because pH-dependent cofilin activity is attenuated in mammalian cells lacking H+efflux by NHE1, our current data suggest that full-length Aip1 facilitates F-actin assembly when cofilin activity is limited. We predict the C-terminus of Aip1 enhances defective chemotaxis of Ddnhe1−cells by sequestering the limited amount of active cofilin without promoting F-actin assembly. Our findings indicate a cooperative role of Aip1 and cofilin in pH-dependent cell migration, and they suggest defective chemotaxis in Ddnhe1−cells is determined primarily by loss of cofilin-dependent actin dynamics.