bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulatory Effect of Histamine on Cyclic AMP Formation in Chick Pineal Gland
Authors: Nowak Jerzy Z. , Sek Barbara
Published: July 2010

Abstract: Histamine (HA) potently stimulated cyclic AMP accumulation in intact pineal glands taken from light‐exposed chicks. The action of HA was stronger in the presence of forskolin and the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX). The effect of HA was mimicked by HA H1‐ and H2‐receptor‐selective agonists in the following order of potency: HA > 4‐methylhistamine (H2) > 2‐methylhistamine (H1) > 2‐thiazolylethylamine (H1) ≫ dimaprit (H2). The HA H3‐receptor‐selective agonist (R)α‐methylhistamine was poorly active. The effect of HA was antagonized by selective H2‐receptor blockers (tiotidine > oxmetidine > cimetidine = ranitidine) and was not significantly affected by the selective H1‐ and H3‐receptor blockers mepyramine and thioperamide. A detailed analysis of an antagonistic action of ranitidine (versus HA) revealed a noncompetitive mode of action of the H2 blocker. The stimulatory action of the H1 agonist 2‐thiazolylethylamine (both under basal conditions and in the presence of forskolin or IBMX) was not significantly influenced by three H1‐receptor‐selective blockers (mepyramine, triprolidine, and diphenhydramine), but it was totally counteracted by ranitidine. Using accepted selective agonists and antagonists of the HA H1, H2, and H3 receptor we were unable to identify clearly the receptor subtype mediating the HA action on the cyclic AMP‐generating system of the chick pineal. It is suggested that the receptor under consideration may represent either an H2‐like (in terms of mammalian criteria) or avian‐specific HA receptor. The data suggest that HA may be considered a modulator of the pineal activity in chicks.
Protein Kinase FA/Glycogen Synthase Kinase‐3α After Heparin Potentiation Phosphorylates τ on Sites Abnormally Phosphorylated in Alzheimer's Disease Brain
Authors: Yang Shiaw‐Der , Yu Jau‐Song , Shiah Shine‐Gwo , Huang Jun‐Jae
Published: July 2010

Abstract: Previously, we identified protein kinase FA/glycogen synthase kinase‐3α (GSK‐3α) as a brain microtubule‐associated τ kinase that phosphorylates Ser235 and Ser404 of τ and causes its electrophoretic mobility shift in gels, a unique property characteristic of paired helical filament‐associated pathological τ (PHF‐τ) in Alzheimer's disease brains. In this study, we found that the activity of kinase FA/GSK‐3α towards phosphorylation of brain τ could be stimulated approximately fourfold by heparin. The phosphorylation molar ratio was increased simultaneously up to 9 mol of phosphates/mol of τ, resulting in a reduced mobility of τ with an apparent molecular mass shift to ∼68 kDa in sodium dodecyl sulfate gels, which is very similar to that observed in Alzheimer‐τ. Tryptic digestion of 32P‐labelled τ, followed by HPLC and two‐dimensional separation on TLC cellulose plates, revealed eight major phosphopeptides. Phosphoamino acid analysis together with sequential manual Edman degradation and protein sequence analysis further revealed that, in addition to Ser235 and Ser404, heparin generated Thr212, Thr231, Ser262, Ser324, and Ser356, the five extra phosphorylation sites in τ. As Ser235, Ser262, Ser324, Ser356, and Ser404 (particularly the site of Ser262) have been identified as five of the most potent sites in τ responsible for reducing microtubule binding possibly involved in neuronal degeneration, and Thr231, Ser235, Ser262, and Ser404 are four of the most well documented sites abnormally phosphorylated in Alzheimer‐τ, the results provide initial evidence that protein kinase FA/GSK‐3α after heparin potentiation may represent one of the most potent systems possibly involved in the abnormal phosphorylation of PHF‐τ in Alzheimer's disease brains.
Characterization of Salt‐Soluble Forms of Acetylcholinesterase from Bovine Brain
Authors: Liao Jian , Boschetti Nicola , Mortensen Vibeke , Jensen Søren Peter , Koch Claus , Nørgaard‐Pedersen Bent , Brodbeck Urs
Published: July 2010

Abstract: The hydrophilic, salt‐soluble (SS) form of acetylcholinesterase (AChE) from bovine brain caudate nucleus exists mainly as a tetramer sedimenting at 10.3S (∼40%), and a monomer sedimenting at 3.4S (∼60%). The enzyme is N‐glycosylated and contains similar HNK‐1 carbohydrates as detergent‐soluble (DS) AChE. No O‐linked carbohydrates could be detected. Amino acid sequencing showed that the N terminus of SS‐AChE is identical to that of DS‐AChE. In tetrameric SS‐AChE, two pairs of disulfide‐linked dimers are associated by hydrophobic forces located in the C terminus. Antibodies were raised against a peptide identical to the last 10 amino acid residues of bovine brain DS‐AChE. The peptide included the sequence of residues 574–583 (H‐Tyr‐Ser‐Lys‐Gln‐Asp‐Arg‐Cys‐Ser‐Asp‐Leu‐OH) of the enzyme. The antibodies cross‐reacted with tetrameric, but not with monomeric, SS‐AChE, showing that in the latter form, the C terminus is truncated. Limited proteolysis of tetrameric SS‐AChE at the C terminus led to the formation of an enzymatically active monomer, which did not react with anti‐C‐terminal antibody. Although the DS form of AChE contains a structural subunit that serves as membrane anchor, no anchor was detected in SS‐AChE. Enzyme antigen immunoassays showed that SS‐AChE reacted with all monoclonal antibodies directed against the catalytic subunit of DS‐AChE, but not with monoclonal antibodies targeting the membrane‐anchored subunits. From our results, we conclude that SS‐AChE utilizes the same alternative splicing pattern as DS‐AChE, leading to tetrameric SS‐AChE devoid of the membrane anchor. The active monomer of SS‐AChE is most likely derived from tetrameric forms by limited postsynthetic proteolysis.
Characterization of [3H]Met‐Enkephalin‐Arg6‐Phe7 Binding to Opioid Receptors in Frog Brain Membrane Preparations
Authors: Wollemann Mária , Farkas Judit , Tóth Géza , Benyhe Sándor
Published: July 2010

Abstract: A tritiated heptapeptide, [3H]Tyr‐Gly‐Gly‐Phe‐Met‐Arg‐Phe ([3H]Met‐enkephalin‐Arg6‐Phe7), with high specific radioactivity has been synthesized in order to characterize its opioid binding activity to frog brain membrane fractions. The apparent KD value of the radioligand calculated from homologous displacement experiments was 3.4 nM, and the maximal number of specific binding sites was 630 fmol/mg of protein. The KD determined from equilibrium saturation binding studies was found to be 3.6 nM. However, the Hill coefficient was far below unity (nH = 0.43), which suggests the presence of a second, lower affinity binding site. The presence of this binding component is strengthened by the displacement experiments performed with levorphanol and some other ligands. It is assumed that the lower affinity site has no opiate character. The rank order of potency of the applied ligands in competing reversibly with [3H]Met‐enkephalin‐Arg6‐Phe7 binding reflects a κ2‐ and/or δ‐subtype specificity of the heptapeptide. Binding to a κ1 and/or μ site of opioid receptors is excluded, but the existence of a novel endogenous opiate receptor subtype for Met‐enkephalin‐Arg6‐Phe7 in frogs cannot be ruled out. The [3H]Met‐enkephalin‐Arg6‐Phe7 binding was inhibited by both sodium ions and GppNHp, which suggests the opioid agonist character of the heptapeptide.
Age‐Related Changes of GABA‐Activated Chloride Channel Properties in Brain Cortex Synaptic Plasma Membrane: Evidence for Phospholipase Involvement
Authors: Samochocki Marek , Strosznajder Joanna
Published: July 2010

Abstract: Brain aging decreases binding of tert‐butylbicyclophosphorothionate (TBPS), a specific ligand for Cl− channels, but has no effect on Cl− influx. Detailed studies on the kinetics of TBPS dissociation allowed the characterization of Cl− channel properties. Aging lowers, exclusively in the presence of GABA agonist, muscimol, the half‐life of the fast phase of TBPS dissociation, indicating an opening time of receptor‐dependent Cl− channels shorter than that in adult brain. The half‐life of the slow phase of TBPS dissociation is significantly lower in aged brain in the presence and absence of muscimol. These results suggest a sustained Cl− current, including also the other channel(s) not connected with GABAA receptor activation. The analysis of biphasic TBPS dissociation demonstrates a lowered number of binding sites resulted in the reduction of the number of Cl− channels in the “open” state. This may explain an observed decrease of TBPS binding in aged brain. One of the possible factors involved in modification of GABAA receptor behavior during aging may be arachidonic acid or diacylglycerol, known to be accumulated in aged brain. The action of these compounds on the Cl− channel, observed in this study, correlates well with the effect of aging.
Tyrosine Hydroxylase Phosphorylation in Bovine Adrenal Chromaffin Cells: The Role of Intracellular Ca2+ in the Histamine H1 Receptor‐Stimulated Phosphorylation of Ser8, Ser19, Ser31, and Ser40
Authors: Bunn Stephen J. , Sim Alistair T. R. , Herd Lynn M. , Austin Leone M. , Dunkley Peter R.
Published: July 2010

Abstract: Tyrosine hydroxylase (TOH), the rate‐limiting enzyme in catecholamine biosynthesis, is regulated by phosphorylation. Activation of histaminergic H1 receptors on cultured bovine adrenal chromaffin cells stimulated a rapid increase in TOH phosphorylation (within 5 s) that was sustained for at least 5 min. The initial increase in TOH phosphorylation (up to 1 min) was essentially unchanged by the removal of extracellular Ca2+. In contrast, the H1‐mediated response was abolished by preloading the cells with BAPTA acetoxymethyl ester (50 µM) and significantly reduced by prior exposure to caffeine (10 mM for 10 min) to deplete intracellular Ca2+. Trypticphosphopeptide analysis by HPLC revealed that the H1 response in the presence or absence of extracellular Ca2+ resulted in a major increase in the phosphorylation of Ser19 with smaller increases in that of Ser40 and Ser31. In contrast, although a brief stimulation with nicotine (30 µM for 60 s) also resulted in a major increase in Ser19 phosphorylation, this response was abolished in the absence of extracellular Ca2+. These data indicate that the mobilization of intracellular Ca2+ plays a crucial role in supporting H1‐mediated TOH phosphorylation and may thus have a potentially important role in regulating catecholamine synthesis.
Hydroxyl Radical‐Mediated Oxidation of Serotonin: Potential Insights into the Neurotoxicity of Methamphetamine
Authors: Wrona Monika Z. , Yang Zhaoliang , McAdams Michelle , O'Connor‐Coates Susan , Dryhurst Glenn
Published: July 2010

Abstract: When incubated with a hydroxyl radical (HO•)‐generating system (ascorbic acid/Fe2+‐EDTA/O2/H2O2), 5‐hydroxytryptamine (5‐HT; serotonin) is rapidly oxidized initially to a mixture of 2,5‐, 4,5‐, and 5,6‐dihydroxytryptamine (DHT). The major reaction product is 2,5‐DHT, which at physiological pH exists as its keto tautomer, 5‐hydroxy‐3‐ethylamino‐2‐oxindole (5‐HEO). Rapid autoxidation of 4,5‐DHT gives tryptamine‐4,5‐dione (T‐4,5‐D), which reacts with the C(3)‐centered carbanion of 5‐HEO to give 3,3′‐bis(2‐aminoethyl)‐5‐hydroxy‐[3,7′‐bi‐1H‐indole]‐2,4′,5′‐3H‐trione (7). The latter slowly cyclizes to 3′‐(2‐aminoethyl)‐1′,6′,7′,8′‐tetrahydro‐5‐hydroxyspiro[3H‐indole‐3,9′‐[9H]pyrrolo[2,3‐f]quinoline]‐2,4′,5′(1H)‐ trione (9). A minor amount of T‐4,5‐D dimerizes to give 7,7′‐bi‐(5‐hydroxytryptamine‐4‐one) (7,7′‐D). In the presence of GSH, the reaction of T‐4,5‐D with 5‐HEO is diverted and, in the presence of sufficient concentrations of this tripeptide, completely blocked. This is because GSH preferentially reacts with T‐4,5‐D to give 7‐S‐glutathionyltryptamine‐4,5‐dione (11). The results of this investigation suggest that 5,6‐DHT, 5‐HEO, 7, and 9 are products unique to the HO•‐mediated oxidation of 5‐HT. Thus, the observation of other investigators that 5,6‐DHT is formed in the brains of rats following a large dose of methamphetamine (MA) suggests that this drug might evoke HO• formation. However, the present in vitro study indicates that 5,6‐DHT is a rather minor, unstable product of the HO•‐mediated oxidation of 5‐HT and suggests that detection of 5‐HEO, 7/9, and 11 in rat brain following MA administration could provide additional support for HO• formation. Furthermore, one or more of the intermediates and major products of oxidation of 5‐HT by HO• might, in addition to 5,6‐DHT, contribute to the MA‐induced degeneration of serotonergic neurons.
Effects of Arachidonic Acid on Dopamine Synthesis, Spontaneous Release, and Uptake in Striatal Synaptosomes from the Rat
Authors: L'hirondel M. , Chéramy A. , Godeheu G. , Glowinski J.
Published: July 2010

Abstract: Arachidonic acid (AA) markedly stimulated, in a dose‐dependent manner, the spontaneous release of [3H]dopamine ([3H]DA) continuously synthesized from [3H]tyrosine in purified synaptosomes from the rat striatum. As estimated by simultaneous measurement of the rate of [3H]H2O formation (an index of [3H]tyrosine conversion into [3H]DOPA), the AA response was associated with a progressive and dose‐dependent reduction of [3H]DA synthesis. In contrast to AA, arachidic acid, oleic acid, and the methyl ester of AA (all at 10−4M) did not modify [3H]DA release. The AA (3 × 10−5M)‐evoked release of [3H]DA was not affected by inhibiting AA metabolism, with either 5,8,11,14‐eicosatetraynoic acid or metyrapone, suggesting that AA acts directly and not through one of its metabolites. AA also inhibited in a dose‐dependent manner [3H]DA uptake into synaptosomes, with a complete blockade observed at 10−4M. However, AA (10−4M) still stimulated [3H]DA spontaneous release in the presence of either nomifensine or other DA uptake inhibitors, indicating that AA both inhibits DA reuptake and facilitates its release process. Finally, the AA (10−4M)‐evoked release of [3H]DA was not affected by protein kinase A inhibitors (H‐89 or Rp‐8‐Br‐cAMPS) but was markedly reduced in the presence of protein kinase C inhibitors (Ro 31‐7549 or chelerythrine).
Effects of Non‐NMDA Receptor Modulators on [3H]Dopamine Release from Rat Mesencephalic Cells in Primary Culture
Authors: Petitet François , Blanchard Jean‐Charles , Doble Adam
Published: July 2010

Abstract: The effects of AMPA and kainate on [3H]dopamine release from fetal (embryonic day 15) rat mesencephalic neurons in primary culture were enhanced markedly in a dose‐dependent fashion by cyclothiazide, a recently described inhibitor of AMPA receptor desensitization. The EC50 value for cyclothiazide was 2.2 ± 0.8 µM. The release of [3H]dopamine induced by both AMPA (or kainic acid) and the combination of AMPA (or kainic acid) with cyclothiazide was antagonized by specific antagonists like 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione or the noncompetitive benzodiazepine GYKI 52466. Unlike cyclothiazide, the lectin concanavalin A did not stimulate [3H]dopamine release. These results established the involvement of AMPA‐preferring receptors on [3H]dopamine release from rat mesencephalic neurons in primary culture and provided further evidence for the existence of regulatory allosteric sites on AMPA receptor subunits.
Dopamine D4‐Like Receptor Elevation in Schizophrenia: Cloned D2 and D4 Receptors Cannot Be Discriminated by Raclopride Competition Against [3H]Nemonapride
Authors: Seeman Philip , Van Tol Hubert H. M.
Published: July 2010

Abstract: Three independent studies have found that the density of dopamine D4‐like receptors is elevated in postmortem brain striata in schizophrenia. This elevation has been questioned by a fourth study that used a different method and failed to detect a biphasic component when raclopride was used to compete against the binding of 1 nM [3H]nemonapride to schizophrenia tissue. To test whether this competition method could distinguish between dopamine D2 and D4 receptors, the present study used mixtures of only these two cloned receptors, free of all other receptors. Using combinations of cloned dopamine D2 and D4 receptors, this competition method could not resolve these components up to a level of 48% D4 receptors. Thus, the objections raised by the findings of the fourth study, mentioned above, do not appear valid. Furthermore, the present results indicate that the data using such a competition method actually mask a manyfold marked elevation in the density of dopamine D4‐like receptors in schizophrenia.
Detection of DNA Binding Activities of Transcription Factors with Different Protein Motifs in Nuclear Extracts of Murine Brain by Using Gel‐Retardation Electrophoresis
Authors: Ogita Kiyokazu , Yoneda Yukio
Published: July 2010

Abstract: DNA binding activities of a variety of transcription factors with different protein motifs were determined in nuclear extracts of mouse brains using radiolabeled double‐stranded oligonucleotides containing the respective consensus core elements as probes in gel‐retardation electrophoresis. DNA binding activities of the transcription factor with a leucine‐zipper motif activator protein 1 (AP1) were markedly modulated by the addition of endogenous monovalent and divalent cations at physiological concentrations. In the presence of both KCl and MgCl2 at maximally effective concentrations, the AP1 binding occurred in a temperature‐dependent manner in brain nuclear extracts. Brain nuclear extracts also contained activities to bind probes for seven other transcription factors with leucine‐zipper, zinc finger, or helix‐turn‐helix motifs under the conditions favorable to detecting the AP1 binding. In contrast to brain nuclear extracts, however, both cations and incubation temperature were ineffective in markedly affecting binding of all eight radioprobes tested in hepatic nuclear extracts. Moreover, the addition of hepatic nuclear extracts eliminated the AP1 binding in brain extracts nearly completely, differentially affecting binding of other probes. Size‐exclusion chromatography on hepatic nuclear extracts revealed two distinct fractions with different molecular sizes that both have an activity to inhibit the AP1 binding in brain nuclear extracts. These results suggest that monovalent and divalent cations may modulate DNA binding activities of particular transcription factors in brain nuclear extracts but not in hepatic nuclear extracts that could contain high molecular weight materials with an inhibitory potency on brain DNA binding activities.
The Third Intracellular Loop of the 5‐Hydroxytryptamine2A Receptor Determines Effector Coupling Specificity
Authors: Oksenberg Donna , Havlik Sona , Peroutka Stephen J. , Ashkenazi Avi
Published: July 2010

Abstract: 5‐Hydroxytryptamine (5‐HT) receptors contain seven putative transmembrane domains and couple via different guanine nucleotide binding proteins to specific effector enzymes. Studies with other receptors identify the second and third intracellular loops or the C‐terminus of the receptor as important for selective effector coupling. However, it is not known which regions of the 5‐HT receptor determine effector coupling specificity. To address this question, we constructed a chimeric 5‐HT receptor in which the third intracellular (i3) loop is derived from the 5‐HT2A receptor, which is coupled to activation of phospholipase C, and the rest of the sequence is derived from the 5‐HT1B receptor, which is coupled to inhibition of adenylyl cyclase. The chimeric receptor exhibited ligand binding properties similar to those of the 5‐HT1B receptor and distinct from those of the 5‐HT2A receptor. This suggests that the i3 loop is not critical for the unique pharmacology of the 5‐HT1B receptor. In contrast, the chimeric receptor exhibited signaling properties similar to those of the 5‐HT2A receptor and distinct from those of the 5‐HT1B receptor. This indicates that the i3 loop determines the effector coupling specificity of the 5‐HT2A receptor.
Identification of GABAA Receptor Subunits in Rat Retina: Cloning of the Rat GABAA Receptor ρ2‐Subunit cDNA
Authors: Ogurusu Tarou , Taira Hideharu , Shingai Ryuzo
Published: July 2010

Abstract: We identified GABAA receptor subunits in rat retina using PCR. The high degree of conservation among previously described members of ligand‐gated anion channels in transmembrane domains was used to design degenerate sense and antisense oligonucleotides. These oligonucleotides were used as primers for PCR, which was applied to the rat retina cDNA. Analysis of clones derived from the PCR amplification identified the GABAAα1, β1, β3, and γ2 subunits and the glycine α1 subunit. In addition, two clones closely related to the human GABAAρ‐subunit class were obtained. Molecular cloning revealed one of them as the rat counterpart of the human ρ2 subunit. Northern blot analysis demonstrated the expression of mRNAs for ρ subunits in retina. These results further support the hypothesis that bicuculline‐insensitive GABA channels in rat retina are comprised of ρ subunits.
Glutamate Receptor Activation Regulates mRNA at Both Transcriptional and Posttranscriptional Levels
Authors: Panchision David M. , Gerwin Claudia M. , DeLorenzo Robert J. , Jakoi Emma R.
Published: July 2010

Abstract: Previous studies from this laboratory have demonstrated that extracellular calcium entry through the NMDA subtype of glutamate receptors in hippocampal neurons selectively down‐regulated ligatin gene expression in a rapid and long‐lasting manner. Here we investigated the molecular mechanism that underlies this phenomenon. We demonstrate that glutamate receptor activation transiently increased the transcriptional activity of the ligatin gene and simultaneously shortened the half‐life of its message. Using nuclear run‐on assays and northern analyses of total RNA from α‐amanitin‐treated cells, we measured the effects of glutamate on the transcriptional activity and mRNA stability of the ligatin gene. The transcriptional activity of ligatin was found to be transiently increased (1.4‐fold) 20 min after the addition of glutamate, with a return to basal levels by 60 min. Thus, the glutamate‐dependent decrease in ligatin message could not be explained by a decline in its synthesis. Instead, concurrent with transcriptional up‐regulation, glutamate shortened the half‐life of the ligatin message from 10 h to 58 min, leading to a net decrease (0.7‐fold) in its steady‐state levels by 60 min. This posttranscriptional destabilization of ligatin mRNA was mimicked by the translation inhibitor, cycloheximide, but not by puromycin. This finding indicated that the stability of ligatin mRNA was translation independent and distinguished this posttranscriptional regulatory mechanism from those previously described. Moreover, using in situ hybridization and confocal microscopy, we showed that control of message stability occurred both in the cell body and in the dendritic regions distant from the nucleus. The selective glutamate‐induced changes in the synthesis and stability of mRNA indicated that transcriptional and posttranscriptional regulation of gene expression may be part of the normal receptor‐mediated regulatory program of plasticity and may play an important role in local modulation of neuronal phenotype by neurotransmitters. Our results provide the first description of a receptor‐modulated, calcium‐dependent mechanism that rapidly destabilizes mRNA in neurons.
Nitric Oxide‐Induced [3H]GABA Release from Cerebral Cortical Neurons Is Mediated by Peroxynitrite
Authors: Ohkuma Seitaro , Narihara Hidehiko , Katsura Masashi , Hasegawa Takeshi , Kuriyama Kinya
Published: July 2010

Abstract: The functional significance of peroxynitrite in the release of [3H]GABA induced by nitric oxide (NO) liberated from NO generators was investigated using cerebral cortical neurons in primary culture. NO generators such as sodium nitroprusside (SNP) and S‐nitroso‐N‐acetylpenicillamine (SNAP) increased [3H]GABA release in a dose‐dependent manner. These increases in [3H]GABA release were significantly inhibited by hemoglobin, indicating that those NO generators evoke the release of [3H]GABA by the formation of NO. Two types of superoxide scavengers, Cu2+/Zn2+ superoxide dismutase and ceruloplasmin, significantly reduced the increase in [3H]GABA release induced by both SNP and SNAP, which assumes that NO requires superoxide to induce [3H]GABA release from the neurons. In addition, synthesized peroxynitrite induced a dose‐dependent increase in [3H]GABA release from the neurons. These results indicate that NO‐induced [3H]GABA release is mediated by peroxynitrite formed by the reaction of NO with superoxide.
Understanding of large auxetic properties of iron-gallium and iron-aluminum alloys
Authors: Zhang Yan-ning , Wu Ru-qian , Schurter Holly M. , Flatau Alison B.
Published: July 2010

Large auxetic properties of iron-gallium and iron-aluminum alloys have been investigated with both theoretical and experimental approaches. Tensile tests of single-crystal iron-gallium alloys with compositions of 12%–25% gallium were conducted to determine the composition dependent values of the Poisson’s ratio. Systematic density functional calculations revealed a simple correlation between the Poisson’s ratio and tetragonal shear modulus. We attribute the auxetic properties of these intermetallic alloys to the drastic reduction in C′ with the presence of metalloid atoms in the DO3-type structures.
Time dependent behavior of a localized electron at a heterojunction boundary of graphene
Authors: Jang Min Seok , Kim Hyungjun , Atwater Harry A. , Goddard William A.
Published: July 2010

We develop a finite-difference time-domain (FDTD) method for simulating the dynamics of graphene electrons, denoted GraFDTD. We then use GraFDTD to study the temporal behavior of a single localized electron wave packet, showing that it exhibits optical-like dynamics including the Goos–Hänchen effect [F. Goos and H. Hänchen, Ann. Phys. 436, 333 (1947)] at a heterojunction, but the behavior is quantitatively different than for electromagnetic waves. This suggests issues that must be addressed in designing graphene-based electronic devices analogous to optical devices. GraFDTD should be useful for studying such complex time-dependent behavior of a quasiparticle in graphene.
Anomalous thermal expansion and magnetic properties of Tm2Fe17−xCrx compounds
Authors: Hao Yanming , Zhang Xuemin , Wang Bowen , Yuang Yizhe , Wang Fang
Published: July 2010

The structural and magnetic properties of Tm2Fe17−xCrx (x=0, 0.5, 1.0, 1.5, and 2.0) compounds are investigated by means of x-ray diffraction and magnetization measurements. The Tm2Fe17−xCrx compounds have a hexagonal Th2Zi17-type structure. There exist a negative thermal expansion coefficient for Tm2Fe17−xCrx compounds near their Curie temperature and an anisotropic and strong spontaneous magnetostriction in the magnetic states of Tm2Fe17−xCrx compounds. In Tm2Fe17−xCrx compounds, Cr atoms substituting for Fe atoms can increase obviously the Curie temperature and the easy-axis magnetocrystalline anisotropy. The Curie temperature of Tm2Fe16Cr compound is about 160 K higher than that of the mother compound Tm2Fe17. The saturation magnetization of Tm2Fe17−xCrx compounds decreases with increasing Cr content.
Enhancement of Curie temperature in electrochemically prepared crystalline thin films of Prussian blue analogs KjFekII[CrIII(CN)6]l⋅mH2O
Authors: Bhatt Pramod , Yusuf S. M. , Mukadam M. D. , Yakhmi J. V.
Published: July 2010

Structural and magnetic properties of electrochemically prepared crystalline films of Prussian blue analogs (PBAs) KjFekII[CrIII(CN)6]l⋅mH2O, with varying deposition time and electrode voltage, which result into change in film thickness and stoichiometry, respectively, have been investigated by using x-ray diffraction (XRD), infrared (IR) spectroscopy, and dc magnetization measurement techniques. An atomic force microscopy (AFM) and XRD study reveal uniform and crystalline nature of all films. As the film thickness increases from 1 μm to 5 μm, the Curie temperature (TC), coercive field, and maximum magnetization increase from 11 K to 21 K, 20 Oe to 160 Oe, and 5.7 μB to 6.5 μB, respectively. For the films prepared with variation in electrode voltage, it has been found that the alkali metal ions are introduced into the films just by using suitable electrode voltage, contrary to usual method where alkali metal ions are intentionally introduced into the lattice by using additional compounds of alkali metals as starting materials. In addition, an enhancement in TC with an increasing electrode voltage has been observed. The film deposited with a lower electrode voltage of −0.6 V shows a TC of ∼21 K, close to the previously reported value of TC. Whereas, for films prepared with an electrode voltage of −0.9 V, an increase in TC(∼65 K) is observed. The rise in TC is attributed to the decrease in FeII/CrIII ratio with an increasing electrode voltage. The ability of tuning TC just by changing the electrode voltage could be useful in designing thin films of new molecule based magnets.
Conduction noise absorption by ITO thin films attached to microstrip line utilizing Ohmic loss
Authors: Kim Sun-Hong , Kim Sung-Soo
Published: July 2010

For the aim of wide-band noise absorbers with a special design for low frequency performance, this study proposes conductive indium-tin oxide (ITO) thin films as the absorbent materials in microstrip line. ITO thin films were deposited on the polyimide film substrates by rf magnetron cosputtering of In2O3 and Sn targets. The deposited ITO films show a typical value of electrical resistivity (∼10−4 Ω m) and sheet resistance can be controlled in the range of 20–230 Ω by variation in film thickness. Microstrip line with characteristic impedance of 50 Ω was used for determining their noise absorbing properties. It is found that there is an optimum sheet resistance of ITO films for the maximum power absorption. Reflection parameter (S11) is increased with decrease in sheet resistance due to impedance mismatch. On the while, transmission parameter (S21) is decreased with decrease in sheet resistance due to larger Ohmic loss of the ITO films. Experimental results and computational prediction show that the optimum sheet resistance is about 100 Ω. For this film, greater power absorption is predicted in the lower frequency region than ferrite thin films of high magnetic loss, which indicates that Ohmic loss is the predominant loss parameter for power absorption in the low frequency range.
Effect of residual attractive interactions in size asymmetric colloidal mixtures: Theoretical analysis and predictions
Authors: Germain Ph.
Published: July 2010

We analyze the influence of residual attractions on the static and some dynamic properties of size asymmetric mixtures of “hard-sphere-like” colloids. These attractions, usually neglected in the theoretical analysis, are characterized by a very short range and a moderate strength reflecting the underlying microscopic structure of the colloidal particles. Their effect on the potentials of mean force is analyzed from analytical expressions obtained from low density expansions. The effective potential of the big particle fluid is next considered. An analytical expression is proposed for estimating the deviation with respect to the hard sphere depletion potential. This case is compared to that of mixtures with noninteracting depletants. The important consequences on the binodals and the glass transition lines of the effective fluid are discussed in both cases. This study is next extended to other properties—the specific heat and the low shear viscosity—which incorporate contributions from the two components of the binary mixture.
High-resolution soft x-ray spectroscopic study on amorphous gallium indium zinc oxide thin films
Authors: Lee Mi Ji , Kang Se Jun , Baik Jae Yoon , Kim Ki-jeong , Kim Hyeong-Do , Shin Hyun-Joon , Chung JaeGwan , Lee Jaecheol , Lee JaeHak
Published: July 2010

Amorphous gallium indium zinc oxide (a-GIZO) thin films of different compositions (Ga2O3:In2O3:ZnO=1:1:1,2:2:1,3:2:1,4:2:1) on Si substrates were investigated by high-resolution x-ray photoelectron spectroscopy and x-ray absorption spectroscopy (XAS) using synchrotron radiation. The O 1s, Ga 3d, In 4d, Zn 3d core, and shallow-core levels as well as the valence band maxima and O K-edge XAS were investigated. Each O 1s spectrum could be deconvoluted by a main component (O1 in the text) representing the Ga–In–Zn–O quaternary system along with two other higher-binding energy (BE) components (O2 and O3 in the text). The O2+O3 intensity increased as the Ga2O3 content increased. For the as-prepared samples, the spectral peak separations between the Ga 3d (∼20 eV) and Zn 3d (∼11 eV) orbitals and between the In 4d (∼18 eV) and Zn 3d orbitals became larger, respectively, as the Ga2O3 content increased. For the surface-cleaned samples, this trend was the same but with smaller increases in their separations. The sputter-cleaning effectively reduced the Zn 3d intensity by ∼30% relative to those of Ga 3d and In 4d. The valence band maximum shifted toward higher BE, up to ∼0.5 eV for the as-prepared samples and ∼0.25 eV for the cleaned samples, and the conduction band minimum (measured at the O K-edge) was measured at photon energies ranging upwards to ∼0.2 eV as the Ga2O3 content increased, demonstrating that the band gap can be tailored by increasing the Ga2O3 content. The effects of increasing Ga2O3 contents on the local chemical states and the corresponding electrical conduction are discussed in this paper.
Effect of forward current stress on low frequency noise in 4H–SiC p-n junctions
Authors: Rumyantsev S. L. , Levinshtein M. E. , Shur M. S. , Palmour J. W. , Agarwal A. K. , Das M. K.
Published: July 2010

We report on the effect of forward current stress on the low frequency noise in the 4H–SiC rectifier p+-n diodes rated at 20 and 10 kV. The 4H–SiC diodes with 20 kV blocking voltage were the most sensitive to the forward current stress. Even the stress by the current density j=13 A/cm2 for 30 min led to a noticeable increase in the forward voltage drop and changes in the noise spectra. The stress decreased the level of the 1/f noise but led to the appearance of the burst noise. Stress at higher current densities (50 A/cm2) led to the disappearance of the burst noise and to a further increase in the forward voltage drop. Diodes with 10 kV blocking capability were more resistant to the forward current stress. However, they also demonstrated a decrease in the 1/f noise as a result of the 60 min stress at j=100 A/cm2.
Real-time observation of anisotropic strain relaxation by three-dimensional reciprocal space mapping during InGaAs/GaAs (001) growth
Authors: Suzuki Hidetoshi , Sasaki Takuo , Sai Akihisa , Ohshita Yoshio , Kamiya Itaru , Yamaguchi Masafumi , Takahasi Masamitu , Fujikawa Seiji
Published: July 2010

Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In0.12Ga0.88As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [1¯10] directions caused by α and β misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by α-MDs is higher than that caused by β-MDs, and therefore crystal quality along [110] is worse than that along [1¯10]. Rapid relaxation along both [110] and [1¯10] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [1¯10] direction, presumably due to β-MDs, becomes better that along [110] direction and the ratio does not decay with thickness.
Morphology and electronic states of chemically treated CdZnTe surfaces
Authors: Egan C. K. , Choubey A. , Brinkman A. W.
Published: July 2010

The morphology and electronic structure of chemically treated CdZnTe surfaces has been studied using atomic force microscopy and scanning tunneling microscopy/spectroscopy. Studies have been performed on wet chemically etched and passivated surfaces. Etching in bromine methanol solutions effectively removes surface damage after polishing and produces a hillock like structure. A number of surface electronic states are introduced, both donor-like and acceptor-like, and are attributed to various surface defects. Because of the amorphous nature of the surface, these states have tails that extend into the band gap and produces a very narrow surface band. Charge hopping across the narrow band gap is proposed to explain the high surface conductivity. Surfaces passivated in hydrogen peroxide show increased roughness and using atomic force microscopy, the evolution of the formation of an oxide layer has been observed. Additional acceptor-like surface states of higher energy are introduced and the surface band gap is found to increase, reducing the surface conductivity.
Free energy calculation using molecular dynamics simulation combined with the three dimensional reference interaction site model theory. I. Free energy perturbation and thermodynamic integration along a coupling parameter
Authors: Miyata Tatsuhiko , Ikuta Yasuhiro , Hirata Fumio
Published: July 2010

This article proposes a free energy calculation method based on the molecular dynamics simulation combined with the three dimensional reference interaction site model theory. This study employs the free energy perturbation (FEP) and the thermodynamic integration (TDI) along the coupling parameters to control the interaction potential. To illustrate the method, we applied it to a complex formation process in aqueous solutions between a crown ether molecule 18-Crown-6 (18C6) and a potassium ion as one of the simplest model systems. Two coupling parameters were introduced to switch the Lennard-Jones potential and the Coulomb potential separately. We tested two coupling procedures: one is a “sequential-coupling” to couple the Lennard-Jones interaction followed by the Coulomb coupling, and the other is a “mixed-coupling” to couple both the Lennard-Jones and the Coulomb interactions together as much as possible. The sequential-coupling both for FEP and TDI turned out to be accurate and easily handled since it was numerically well-behaved. Furthermore, it was found that the sequential-coupling had relatively small statistical errors. TDI along the mixed-coupling integral path was to be carried out carefully, paying attention to a numerical behavior of the integrand. The present model system exhibited a nonmonotonic behavior in the integrands for TDI along the mixed-coupling integral path and also showed a relatively large statistical error. A coincidence within a statistical error was obtained among the results of the free energy differences evaluated by FEP, TDI with the sequential-coupling, and TDI with the mixed-coupling. The last one is most attractive in terms of the computer power and is accurate enough if one uses a proper set of windows, taking the numerical behavior of the integrands into account. TDI along the sequential-coupling integral path would be the most convenient among the methods we tested, since it seemed to be well-balanced between the computational load and the accuracy. The numerical results reported in this article qualitatively agree with the experimental data for the potassium ion recognition by the 18C6 in aqueous solution.
A system for measuring bubble voidage and frequency around tubes immersed in a fluidized bed of particles
Authors: Whitty Kevin J. , Siddoway Michael
Published: July 2010

Gas-solid fluidized beds are common in chemical processing and energy production industries. These types of reactors frequently have banks of tubes immersed within the bed to provide heating or cooling, and it is important that the fluid dynamics within these bundles is efficient and uniform. This paper presents a simple, low-cost method for quantitatively analyzing the behavior of gas bubbles within banks of tubes in a fluidized bed cold flow model. Two probes, one containing an infrared emitter and one containing an infrared (IR) detector, are placed into adjacent glass tubes such that the emitter and detector face each other. As bubbles pass through the IR beam, the detector signal increases due to less solid material blocking the path between the emitter and detector. By calibrating the signal response to known voidage of the material, one can measure the bubble voidage at various locations within the tube bundle. The rate and size of bubbles passing through the beam can also be determined by high frequency data collection and subsequent analysis. This technique allows one to develop a map of bubble voidage within a fluidized bed, which can be useful for model validation and system optimization.
Electrostatic origins of polyelectrolyte adsorption: Theory and Monte Carlo simulations
Authors: Wang Lei , Liang Haojun , Wu Jianzhong
Published: July 2010

Electrostatic interactions may promote or abate polyelectrolyte adsorption onto a charged surface depending on a number of interrelated factors including the surface and polymer charge densities, the salt concentration, and nonelectrostatic interactions such as van der Waals and hydrophobic forces. Even without the nonelectrostatic interactions, the electrostatic behavior of polyelectrolyte systems is often counterintuitive and cannot be explained with conventional theories of polymers or simple electrolytes. In this work, a nonlocal density functional theory (NLDFT) and Monte Carlo simulations are used together to investigate polyelectrolyte adsorption at both oppositely charged and like-charged surfaces (one due to the direct electrostatic attraction and the other due to counterion correlations). The simulation results provide a stringent test of the numerical performance of the NLDFT, in particular for systems containing multivalent counterions where electrostatic correlations are important. A systematic study of the effects of ion valence, salt concentration, and polyion chain length reveals that polyelectrolyte attraction to an oppositely charged surface is nearly a neutralization effect, little influenced by the polyion chain length and counterion valence. Neither the surface mean electrostatic potential nor the integrated local charge density shows no significant sign of charge inversion. Both theory and simulation predict polyelectrolyte adsorption onto a like-charged surface when the system contains multivalent counterions. In that case, the surface excess is sensitive to the surface charge density, the counterion valence, and the salt concentration. The surface mean electrostatic potential shows a clear evidence of charge inversion when two layers of like charges are mediated by multivalent counterions. The theoretical investigations indicate that most likely, the electrostatic correlation mediated by multivalent counterions is responsible for the layer-by-layer assembly of oppositely charged polyelectrolyte films.
Design and fabrication of microcavity-array superhydrophobic surfaces
Authors: Salvadori M. C. , Cattani M. , Oliveira M. R. S. , Teixeira F. S. , Brown I. G.
Published: July 2010

We have modeled, fabricated, and characterized superhydrophobic surfaces with a morphology formed of periodic microstructures which are cavities. This surface morphology is the inverse of that generally reported in the literature when the surface is formed of pillars or protrusions, and has the advantage that when immersed in water the confined air inside the cavities tends to expel the invading water. This differs from the case of a surface morphology formed of pillars or protrusions, for which water can penetrate irreversibly among the microstructures, necessitating complete drying of the surface in order to again recover its superhydrophobic character. We have developed a theoretical model that allows calculation of the microcavity dimensions needed to obtain superhydrophobic surfaces composed of patterns of such microcavities, and that provides estimates of the advancing and receding contact angle as a function of microcavity parameters. The model predicts that the cavity aspect ratio (depth-to-diameter ratio) can be much less than unity, indicating that the microcavities do not need to be deep in order to obtain a surface with enhanced superhydrophobic character. Specific microcavity patterns have been fabricated in polydimethylsiloxane and characterized by scanning electron microscopy, atomic force microscopy, and contact angle measurements. The measured advancing and receding contact angles are in good agreement with the predictions of the model.
Symmetric miniaturized heating system for active microelectronic devices
Authors: McCracken Michael , Mayer Michael , Jourard Isaac , Moon Jeong-Tak , Persic John
Published: July 2010

To qualify interconnect technologies such as microelectronic fine wire bonds for mass production of integrated circuit (IC) packages, it is necessary to perform accelerated aging tests, e.g., to age a device at an elevated temperature or to subject the device to thermal cycling and measure the decrease of interconnect quality. There are downsides to using conventional ovens for this as they are relatively large and have relatively slow temperature change rates, and if electrical connections are required between monitoring equipment and the device being heated, they must be located inside the oven and may be aged by the high temperatures. Addressing these downsides, a miniaturized heating system (minioven) is presented, which can heat individual IC packages containing the interconnects to be tested. The core of this system is a piece of copper cut from a square shaped tube with high resistance heating wire looped around it. Ceramic dual in-line packages are clamped against either open end of the core. One package contains a Pt100 temperature sensor and the other package contains the device to be aged placed in symmetry to the temperature sensor. According to the temperature detected by the Pt100, a proportional-integral-derivative controller adjusts the power supplied to the heating wire. The system maintains a dynamic temperature balance with the core hot and the two symmetric sides with electrical connections to the device under test at a cooler temperature. Only the face of the package containing the device is heated, while the socket holding it remains below 75 °C when the oven operates at 200 °C. The minioven can heat packages from room temperature up to 200 °C in less than 5 min and maintain this temperature at 28 W power. During long term aging, a temperature of 200 °C was maintained for 1120 h with negligible resistance change of the heating wires after 900 h (heating wire resistance increased 0.2% over the final 220 h). The device is also subjected to 5700 thermal cycles between 55 and 195 °C, demonstrating reliability under thermal cycling.
Observation of spin-glass behavior in antiperovskite compound SnCFe3
Authors: Wang B. S. , Tong P. , Sun Y. P. , Zhu X. B. , Yang Z. R. , Song W. H. , Dai J. M.
Published: July 2010

We investigated the physical properties of antiperovskite compound SnCFe3 by comprehensive magnetic measurements. The strong irreversibility is clearly observed from zero-field-cooled and field-cooled magnetizations. The peaks of ac susceptibility display strong dependences on the frequency and magnetic field. Both the magnetic relaxation effects and related analysis indicate a typical spin-glass (SG) behavior in SnCFe3. The corresponding characteristic parameters are obtained: the freezing temperature T0=20.3 K, the dynamical exponent zν=9.441, and the flipping time τ0=2.42×10−11 s. Furthermore, the Sn deficiency affects significantly the SG behavior and results in a sharp decrease in T0.
Engineering the band gap of SiC nanotubes with a transverse electric field
Authors: Alfieri G. , Kimoto T.
Published: July 2010

The effects of a transverse electric field, of intensities ranging from 0 to 0.20 V/Å, on the band gap width of SiC nanotubes (SiCNTs) are investigated by means of density functional theory. A decrease in the band gap width, as a function of the electric field, is observed and the mechanism for such reduction, as well as its dependence on the nanotube diameter, is analyzed. An empirical model to describe the field dependence of the band gap is also proposed.