bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of cannabinoid CB1 and CB2 receptors suppresses neuropathic nociception evoked by the chemotherapeutic agent vincristine in rats
Authors: Rahn E J , Makriyannis A , Hohmann A G
Published: June 2007

Background and purpose:

The ability of cannabinoids to suppress mechanical hypersensitivity (mechanical allodynia) induced by treatment with the chemotherapeutic agent vincristine was evaluated in rats. Sites of action were subsequently identified.

Experimental approach:

Mechanical hypersensitivity developed over the course of ten daily injections of vincristine relative to groups receiving saline at the same times. Effects of the CB1/CB2 receptor agonist WIN55,212‐2, the receptor‐inactive enantiomer WIN55,212‐3, the CB2‐selective agonist (R,S)‐AM1241, the opiate agonist morphine and vehicle on chemotherapy‐induced neuropathy were evaluated. WIN55,212‐2 was administered intrathecally (i.t.) or locally in the hindpaw to identify sites of action. Pharmacological specificity was established using competitive antagonists for CB1 (SR141716) or CB2 receptors (SR144528).

Key results:

Systemic administration of WIN55,212‐2, but not WIN55,212‐3, suppressed vincristine‐evoked mechanical allodynia. A leftward shift in the dose‐response curve was observed following WIN55,212‐2 relative to morphine treatment. The CB1 (SR141716) and CB2 (SR144528) antagonists blocked the anti‐allodynic effects of WIN55,212‐2. (R,S)‐AM1241 suppressed vincristine‐induced mechanical hypersensitivity through a CB2 mechanism. Both cannabinoid agonists suppressed vincristine‐induced mechanical hypersensitivity without inducing catalepsy. Spinal sites of action are implicated in cannabinoid modulation of chemotherapy‐induced neuropathy. WIN55,212‐2, but not WIN55,212‐3, administered i.t. suppressed vincristine‐evoked mechanical hypersensitivity at doses that were inactive following local hindpaw administration. Spinal coadministration of both the CB1 and CB2 antagonists blocked the anti‐allodynic effects of WIN55,212‐2.

Conclusions and implications:

Cannabinoids suppress the maintenance of vincristine‐induced mechanical allodynia through activation of CB1 and CB2 receptors. These anti‐allodynic effects are mediated, at least in part, at the level of the spinal cord.

British Journal of Pharmacology (2007) 152, 765–777; doi:10.1038/sj.bjp.0707333; published online 18 June 2007
Cholecystokinin CCK2receptors mediate the peptide's inhibitory actions on the contractile activity of human distal colon via the nitric oxide pathway
Authors: Fornai M , Colucci R , Antonioli L , Crema F , Buccianti P , Chiarugi M , Baschiera F , Ghisu N , Tuccori M , Blandizzi C , Del Tacca M
Published: June 2007

Background and purpose:

Cholecystokinin is known to exert stimulant actions on intestinal motility via activation of type 1 cholecystokinin receptors (CCK1). However, the role played by cholecystokinin 2 (CCK2) receptors in the regulation of gut motility remains undetermined. This study was designed to examine the influence of CCK2receptors on the contractile activity of human distal colon.

Experimental approach:

The effects of compounds acting on CCK2receptors were assessedin vitroon motor activity of longitudinal smooth muscle, under basal conditions as well as in the presence of KCl‐induced contractions or transmural electrical stimulation.

Key results:

Cholecystokinin octapeptide sulphate induced concentration‐dependent contractions which were enhanced by GV150013 (CCK2receptor antagonist; +57% at 0.01 μM). These effects were unaffected by tetrodotoxin. The enhancing actions of GV150013 on contractions evoked by cholecystokinin octapeptide sulphate were unaffected by Nω‐propyl‐L‐arginine (NPA, neuronal nitric oxide synthase inhibitor), while they were prevented by Nω‐nitro‐L‐arginine methylester (L‐NAME, non‐selective nitric oxide synthase inhibitor). In the presence of KCl‐induced contractions, cholecystokinin octapeptide sulphate elicited concentration‐dependent relaxations (‐36%), which were unaffected by NPA, but were counteracted by GV150013 or L‐NAME. The application of electrical stimuli evoked phasic contractions which were enhanced by GV150013 (+41 % at 0.01 μM).

Conclusions and implications:

CCK2receptors mediate inhibitory actions of cholecystokinin on motor activity of human distal colon. It is suggested that CCK2receptors exert their modulating actions through a nitric oxide pathway, independent of the activity of the neuronal nitric oxide synthase isoform.

British Journal of Pharmacology(2007)151, 1246–1253; doi:10.1038/sj.bjp.0707339
Verrucotoxin, a stonefish venom, modulates calcium channel activity in guinea‐pig ventricular myocytes
Authors: Yazawa K , Wang J‐W , Hao L‐Y , Onoue Y , Kameyama M
Published: June 2007

Background and purpose:

Stonefish (Synanceia genus) are commonly found in shallow waters of the Pacific and Indian Oceans. The venom of stonefish is stored in the dorsal fine spines and contains a proteinaceous toxin, verrucotoxin (VTX). The stings produced by the spines induce intense pain, respiratory weakness, damage to the cardiovascular system, convulsions and paralysis, sometimes leading to death. Although there are many studies on VTX, the mechanism(s) underlying the VTX‐mediated cardiotoxicity is not yet fully understood. The aim of this study was to investigate the modulation of ion channels in cardiac tissue by VTX.

Experimental approach:

The effects of VTX on changes in the voltage or current in guinea‐pig ventricular myocytes were investigated using a patch clamp method.

Key results:

VTX (10 μg ml−1) prolonged the action potential duration by 2.5‐fold. VTX increased L‐type Ca2+currents (ICa(L)) in a concentration‐dependent manner with a EC50value of 7 μg ml−1and a maximum increase of 3.1‐fold. The non‐selective β‐adrenoceptor antagonist, propranolol (1 μM) and the selective β1‐adrenoceptor antagonist, CGP20712A (10 μM) each abolished the effect of VTX (100 μg ml−1) onICa(L). Furthermore, the protein kinase A (PKA) antagonists H‐89 (10 μM) and Rp‐8‐Br‐cAMPS (30 μM) inhibited the effect of VTX onICa(L).

Conclusions and implications:

VTX modulates Ca2+channel activity through the β‐adrenoceptor‐cAMP‐PKA pathway.

British Journal of Pharmacology(2007)151, 1198–1203; doi:10.1038/sj.bjp.0707340
A cellular and molecular investigation of the action of PMX464, a putative thioredoxin inhibitor, in normal and colorectal cancer cell lines
Authors: Mukherjee A , Huber K , Evans H , Lakhani N , Martin S
Published: June 2007

Background and Purpose:

PMX464 is a novel benzothiazole substituted cyclohexadienone reportedly targeting the thioredoxin (Trx1)/thioredoxin reductase (TrxR1) system. We have previously shown that PMX464 has enhanced hypoxic anti‐proliferative effects in colorectal tumour cells, with some non‐tumour cells (quiescent endothelium and fibroblasts) being relatively resistant. The current study aimed to validate the Trx1 system as a molecular target of PMX464 in tumour cells and to investigate the differential sensitivities of normal cells at the molecular level.

Experimental Approach:

Proliferation, clonogenic survival, protein expression and function, cell cycle and apoptosis assays were conducted using colorectal tumour (HT29), endothelial (HUVEC) and fibroblast (MRCV) cells treated with PMX464 under normoxic and hypoxic (1% O2) conditions.

Key Results:

Protein and enzyme assays showed that PMX464, in HT29, inhibited Trx1 function without altering expression and that inhibition correlated with decreased proliferation and survival, and was more marked under hypoxia. In contrast, although hypoxic HUVEC were sensitive, in terms of proliferation and survival, inhibition of Trx1 function was not observed. Quiescent HUVEC and MRCVs (that have undetectable Trx1 protein) were relatively resistant. The effect on HT29 cells was essentially due to cell cycle inhibition, as apoptosis was modest. Anti‐proliferative effects were lost after a lag period, suggesting a reversible phenomenon.

Conclusions and Implications:

The Trx1 system is an important target in tumour cells and can be inhibited by PMX464. Quiescent HUVEC and fibroblasts are relatively resistant conferring a therapeutic benefit when targeting Trx1.

British Journal of Pharmacology(2007)151, 1167–1175; doi:10.1038/sj.bjp.0707342
Structural basis of functional cooperation of Tim15/Zim17 with yeast mitochondrial Hsp70
Authors: Momose Takaki , Ohshima Chié , Maeda Masahiro , Endo Toshiya
Published: June 2007

Mitochondrial heat‐shock protein 70 (mtHsp70) and its partner proteins drive protein import into the matrix. Tim15/Zim17/Hep1 is a mtHsp70 partner protein on the matrix side of the inner mitochondrial membrane. We determined the nuclear magnetic resonance (NMR) structure of the core domain of Tim15. On the basis of the NMR structure, we created Tim15 mutants and tested their ability to complement the functional defects of Tim15 depletion and to suppress self‐aggregation of mtHsp70 in vivo. A pair of basic residues, Arg 106 and His 107, conserved Asp 111 and flexible loop 133–137, and were important (Arg 106–His 107 pair and Asp 111) or partly important (the loop 133–137) for yeast cell growth, mitochondrial protein import and the suppression of mtHsp70 aggregation. Therefore, the function of Tim15 in yeast cell growth is well correlated with its ability to suppress mtHsp70 aggregation, although it is still unknown whether inhibition of mtHsp70 aggregation is the primary function of Tim15.
Rmi1, a member of the Sgs1–Top3 complex in budding yeast, contributes to sister chromatid cohesion
Authors: Lai Mong Sing , Seki Masayuki , Ui Ayako , Enomoto Takemi
Published: June 2007

The Saccharomyces cerevisiae RecQ‐mediated genome instability (Rmi1) protein was recently identified as the third member of the slow growth suppressor 1–DNA topoisomerase III (Sgs1–Top3) complex, which is required for maintaining genomic stability. Here, we show that cells lacking RMI1 have a mitotic delay, which is partly dependent on the spindle checkpoint, and are sensitive to the microtubule depolymerizing agent benomyl. We show that rmi1 and top3 single mutants are defective in sister chromatid cohesion, and that deletion of SGS1 suppresses benomyl sensitivity and the cohesion defect in these mutant cells. Loss of RAD51 also suppresses the cohesion defect of rmi1 mutant cells. These results indicate the existence of a new pathway involving Rad51 and Sgs1‐Top3‐Rmi1, which leads to the establishment of sister chromatid cohesion.
Mutation in the Scyl1 gene encoding amino‐terminal kinase‐like protein causes a recessive form of spinocerebellar neurodegeneration
Authors: Schmidt Wolfgang M , Kraus Cornelia , Höger Harald , Hochmeister Sonja , Oberndorfer Felicitas , Branka Manuela , Bingemann Sonja , Lassmann Hans , Müller Markus , Macedo‐Souza Lúcia Inês , Vainzof Mariz , Zatz Mayana , Reis André , Bittner Reginald E
Published: June 2007

Here, we show that the murine neurodegenerative disease mdf (autosomal recessive mouse mutant ‘muscle deficient’) is caused by a loss‐of‐function mutation in Scyl1, disrupting the expression of N‐terminal kinase‐like protein, an evolutionarily conserved putative component of the nucleocytoplasmic transport machinery. Scyl1 is prominently expressed in neurons, and enriched at central nervous system synapses and neuromuscular junctions. We show that the pathology of mdf comprises cerebellar atrophy, Purkinje cell loss and optic nerve atrophy, and therefore defines a new animal model for neurodegenerative diseases with cerebellar involvement in humans.
Preparation of corn (Zea mays) peptides and their protective effect against alcohol‐induced acute hepatic injury in NH mice
Authors: Li Hong‐Mei , Guo Ping , Hu Xin , Xu Li , Zhang Xue‐Zhong
Published: June 2007

CPS [corn (Zea mays) peptides] were prepared from corn gluten meal by proteolysis with alcalase, an alkaline protease. The molecular‐mass distribution of CPS is from 200 to 1000 Da as determined by MS. The amino acid composition of CPS was also analysed by HPLC. CPS contains almost no free amino acids. The protective effect of CPS against acute hepatic injuries induced by alcohol was verified in NH mice that were fed with different dosages of CPS for 30 days and subsequently given an acute dose of alcohol orally. As a result, CPS reduced both hepatic malondialdehyde and triacylglycerol levels, along with enhanced hepatic GSH (glutathione) levels, relative to the control. Hepatic histological changes were also observed. The result indicates that CPS is capable of attenuating ethanol‐induced hepatic injury. The effect of CPS on removing superoxide anion in vitro was also studied as an additional proof that CPS is capable of abating hepatic superoxidant stress.
A new method for the determination of haemoglobin concentration using a bromide‐modified silver electrode
Authors: Rezaei‐Zarchi Saeed , Saboury Ali Akbar , Hong Jun , Ghourchian Hedayatollah , Norouzi Parviz , Moosavi‐Movahedi Ali Akbar , Ganjali Mohammad Reza , Javed Aisha
Published: June 2007

A bromide‐mediated silver electrode was applied to the measurement of haemoglobin. Bromide ions showed very good redox behaviour with the silver electrode. The cathodic and anodic peak potentials were related to the concentration of bromide ions involved in making the bromide‐modified silver electrode. The electrode reaction in the bromine solution was a diffusion‐controlled process. In the presence of pure haemoglobin, the modified electrode showed positive shift in cathodic and anodic peaks: −170 to −140 mV for cathodic peak and +30 to +65 mV for anodic peak with a new pair of cathodic and anodic peaks appearing at −58 and 218 mV, which were related to haemoglobin. Redox peak currents increased linearly as haemoglobin concentrations increased from 5 to 70 μM. The correlation coefficient and detection limit were 0.997 and 2 μM respectively. For a real test sample, the correlation coefficient and detection limit of the experiment were 0.993 and 4 μM respectively. The relative S.D. of results was 2.8% for five successive determinations of 20 μM haemoglobin. The modified silver electrode showed very good repeatability and stability for the determination of haemoglobin.
Phage passage after extended processing in small‐virus‐retentive filters
Authors: Lute Scott , Bailey Mark , Combs Jessica , Sukumar Muppalla , Brorson Kurt
Published: June 2007

Retention of a two small phages (ΦX‐174 and pp7) by direct‐flow small‐virus‐retentive filters [Viresolve NFP (normal‐flow parvovirus), Virosart CPV (canine parvovirus), Ultipor DV20 and Planova 20N] was studied using a commercial‐process fluid. Phage passage occurred in each filter type, particularly when overloaded with phage. Clearances of pp7 and ΦX‐174 were similar for any given filter brand, arguing that the two phages are equivalent for testing small‐virus‐retentive filters. The patterns of flux under constant pressure and instantaneous LRV (log reduction value) in relationship to cumulative phage load differed between brands, consistent with the current industry understanding that each brand possesses specific performance attributes. Phages are a powerful and universal tool for evaluating filter performance. Validation of filter performance with phages such as pp7 or ΦX‐174 as models for small mammalian viruses represents an attractive alternative to the current practice.
Stratified rotating Boussinesq equations in geophysical fluid dynamics: Dynamic bifurcation and periodic solutions
Authors: Hsia Chun-Hsiung , Ma Tian , Wang Shouhong
Published: June 2007

The main objective of this article is to study the dynamics of the stratified rotating Boussinesq equations, which are a basic model in geophysical fluid dynamics. First, for the case where the Prandtl number is greater than 1, a complete stability and bifurcation analysis near the first critical Rayleigh number is carried out. Second, for the case where the Prandtl number is smaller than 1, the onset of the Hopf bifurcation near the first critical Rayleigh number is established, leading to the existence of nontrivial periodic solutions. The analysis is based on a newly developed bifurcation and stability theory for nonlinear dynamical systems (both finite and infinite dimensional) by two of the authors [T. Ma and S. Wang, Bifurcation Theory and Applications, World Scientific Series on Nonlinear Sciences Vol. 53 (World Scientific, Singapore, 2005)].
High-frequency noise in nanoscale metal oxide semiconductor field effect transistors
Authors: Navid Reza , Jungemann Christoph , Lee Thomas H. , Dutton Robert W.
Published: June 2007

The noise characteristics of today’s short-channel devices are shown to have a better resemblance to ballistic devices than to long-channel metal oxide semiconductor field effect transistors (MOSFETs). Therefore the noise characteristics of these devices are best modeled using a ballistic-MOSFET-based noise model. Extensive hydrodynamic device simulations are presented in support of this hypothesis and a simple compact model is introduced. This model is used for predicting the noise behavior of future nanoscale devices. Most of the findings of this work can also be applied to carbon nanotubes and nanowires because of their similarities to MOSFETs.
Reduced models for fluid flows with strong constraints
Authors: Julien Keith , Knobloch Edgar
Published: June 2007

The presence of a dominant balance in the equations for fluid flow can be exploited to derive an asymptotically exact but simpler set of governing equations. These permit semianalytical and/or numerical explorations of parameter regimes that would otherwise be inaccessible to direct numerical simulation. The derivation of the resulting reduced models is illustrated here for (i) rapidly rotating convection in a plane layer, (ii) convection in a strong magnetic field, and (iii) the magnetorotational instability in accretion disks and the results used to extend our understanding of these systems in the strongly nonlinear regime.
Plasma wake inhibition at the collision of two laser pulses in an underdense plasma
Authors: Rechatin C. , Faure J. , Lifschitz A. , Malka V. , Lefebvre E.
Published: June 2007

An electron injector concept for a laser-plasma accelerator was developed by E. Esarey et al. [Phys. Rev. Lett. 79, 2682 (1997)] and G. Fubiani et al. [Phys. Rev. E 70, 016402 (2004)]; it relies on the use of counterpropagating ultrashort laser pulses. In the latter work, the scheme is as follows: the pump laser pulse generates a large-amplitude laser wakefield (plasma wave). The counterpropagating injection pulse interferes with the pump laser pulse to generate a beatwave pattern. The ponderomotive force of the beatwave is able to inject plasma electrons into the wakefield. In this paper, this injection scheme is studied using one-dimensional Particle-in-Cell simulations. The simulations reveal phenomena and important physical processes that were not taken into account in previous models. In particular, at the collision of the laser pulses, most plasma electrons are trapped in the beatwave pattern and cannot contribute to the collective oscillation supporting the plasma wave. At this point, the fluid approximation fails and the plasma wake is strongly inhibited. Consequently, the injected charge is reduced by one order of magnitude compared to the predictions from previous models.
Measurement of the kinetic dust temperature of a weakly coupled dusty plasma
Authors: Williams Jeremiah D. , Thomas Edward
Published: June 2007

Measurements of the kinetic velocity space distribution function of 3.11μm diam melamine and 1.51μm diam silica particles in an argon dc glow discharge dusty plasma are made through the use of stereoscopic particle image velocimetry. These distribution functions are then used to determine the kinetic temperature of the dust component. These measurements show that the kinetic temperature of the dust component is significantly larger than the other plasma components (electrons, ions, and background neutrals).
Statistical modeling of sequential collision-induced dissociation thresholds
Authors: Armentrout P. B.
Published: June 2007

Thermochemistry determined from careful analysis of the energy dependence of cross sections for collision-induced dissociation (CID) reactions has primarily come from the primary dissociation channel. Higher order dissociations generally have thresholds measured to be higher than the thermodynamic limit because of the unknown internal and kinetic energy distributions of the primary products. A model that utilizes statistical theories for energy-dependent unimolecular decomposition to estimate these energy distributions is proposed in this paper. This permits a straightforward modeling of the cross sections for both primary and secondary dissociation channels. The model developed here is used to analyze data for K+(NH3)x, x=2–5, complexes, chosen because the thermochemistry previously determined by threshold CID studies agrees well with values from theory and equilibrium high pressure mass spectrometry. The model is found to reproduce the cross sections with high fidelity and the threshold values for secondary processes are found to be in excellent agreement with literature values. Furthermore, relative thresholds for higher order dissociation processes appear to provide accurate thermodynamic information as well.
A causal look into the quantum Talbot effect
Authors: Sanz A. S. , Miret-Artés S.
Published: June 2007

A well-known phenomenon in both optics and quantum mechanics is the so-called Talbot effect. This near field interference effect arises when infinitely periodic diffracting structures or gratings are illuminated by highly coherent light or particle beams. Typical diffraction patterns known as quantum carpets are then observed. Here the authors provide an insightful picture of this nonlocal phenomenon as well as its classical limit in terms of Bohmian mechanics, also showing the causal reasons and conditions that explain its appearance. As an illustration, theoretical results obtained from diffraction of thermal He atoms by both N-slit arrays and weak corrugated surfaces are analyzed and discussed. Moreover, the authors also explain in terms of what they call the Talbot-Beeby effect how realistic interaction potentials induce shifts and distortions in the corresponding quantum carpets.
Nonlinear relative rotations in liquid crystalline elastomers
Authors: Menzel Andreas M. , Pleiner Harald , Brand Helmut R.
Published: June 2007

Relative rotations between the coupled subsystems of a complex material can become crucial in continuum modeling. In this paper the authors focus on the macroscopic description of side-chain liquid crystalline elastomers, where relative rotations between the polymer network and the director orientation associated with the liquid crystalline component are decisive. They extend the known expression for relative rotations to the nonlinear regime, within the framework of a continuum characterization of the materials. This allows the investigation of qualitatively different nonlinear effects determined by relative rotations, and they give an illustrative example. The formalism can easily be transferred to the macroscopic description of magnetic gels and will certainly be helpful in the characterization of other complex systems.
Modular microdrop generator
Authors: Schäfer J. , Mondia J. P. , Sharma R. , Lu Z. H. , Wang L. J.
Published: June 2007

We present the design of a simple, modular, and inexpensive generator for droplets with diameters of 20–150μm. The instrument is based on piezoelectric pressure injection. Its main components, their functionality, and instructions for reliable operation are described in detail. The option of charging microdrops is also discussed.
Simulation of methane oxidation on Pt
Authors: Zhdanov V. P. , Carlsson P.-A. , Kasemo B.
Published: June 2007

The authors present a generic model of CH4 oxidation on Pt with the emphasis on the role of surface-oxide formation. The latter process is treated in terms of the theory of first-order phase transitions. The corresponding Monte Carlo simulations indicate that the surface-oxide formation may result in stepwise features in the reaction kinetics. Specifically, with increasing CH4 pressure and/or decreasing O2 pressure, the model predicts a sharp transition from a low-reactive state with the surface completely covered by oxide to a high-reactive state with the surface covered by chemisorbed oxygen. In the former case, the reaction is first order in CH4 and zero order in O2. In the latter case, both reaction orders are positive. All these findings help in interpreting available experiments.
Computational investigation of TiSin (n=2–15) clusters by the density-functional theory
Authors: Guo Ling-Ju , Liu Xia , Zhao Gao-Feng , Luo You-Hua
Published: June 2007

The geometries, stabilities, and electronic properties of TiSin (n=2–15) clusters with different spin configurations have been systematically investigated by using density-functional theory approach at B3LYP/LanL2DZ level. According to the optimum TiSin clusters, the equilibrium site of Ti atom gradually moves from convex to surface, and to a concave site as the number of Si atom increases from 2 to 15. When n=12, the Ti atom in TiSi12 completely falls into the center of the Si outer frame, forming metal-encapsulated Si cages, which can be explained by using 16-electron rule. On the basis of the optimized geometries, various energetic properties are calculated for the most stable isomers of TiSin clusters, including the average binding energy, the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gap, fragmentation energy, and the second-order difference of energy. It is found that at size n=6,8,12 the clusters are more stable than neighboring ones. According to the Mulliken charge population analysis, charges always transfer from Si atoms to Ti atom. Furthermore, the HOMO-LUMO gaps of the most stable TiSin clusters are usually smaller than those of Sin clusters.
Thermal effusivity measurements for liquids: A self-consistent photoacoustic methodology
Authors: Balderas-López J. A.
Published: June 2007

A self-consistent photoacoustic methodology for the measurement of the thermal effusivity for liquids is presented. This methodology makes use of the analytical solution for the one-dimensional heat diffusion problem for a single layer, assuming a harmonic heat source in the surface absorption limit. The analytical treatment involves fitting procedures over normalized amplitudes and phases, obtained as the ratio of photoacoustic signals in the front configuration with and without the liquid sample, as functions of the modulation frequency. Two values of thermal effusivity for each liquid sample are obtained, one from the analysis of the normalized amplitudes and the other one from the normalized phases. The comparison between the experimental and theoretical phases allows the description of a simple criterion for deciding on the appropriate modulation frequency range for the analysis in each case. This methodology was applied for measuring the thermal effusivity of some pure liquids; a very good agreement between the thermal effusivity values obtained by this methodology and the corresponding ones reported in the literature was obtained.
Measurements of the band gap of wurtzite InAs1−xPx nanowires using photocurrent spectroscopy
Authors: Trägårdh J. , Persson A. I. , Wagner J. B. , Hessman D. , Samuelson L.
Published: June 2007

We report measurements of the band gap of InAs1−xPx nanowires having wurtzite crystal structure as a function of the composition for 0.14<x<0.48. The band gap is measured by photocurrent spectroscopy on single InAs nanowires with a centrally placed InAs1−xPx segment. The photocurrent measurements are performed at a temperature of 5 K. The data fit well with a quadratic dependence of the band gap on the composition. Using a bowing parameter of 0.2 eV the extracted values for the band gaps are 0.54 eV for InAs and 1.65 eV for InP. These values are larger than the corresponding zinc blende band gaps. We attribute this increase to the fact that the crystal structure is wurtzite rather than zinc blende.
Magnetism and magnetocaloric effect in (DyxGd5−x)Si2Ge2 (0⩽x⩽5) compounds
Authors: Nirmala R. , Kundaliya Darshan C. , Shinde S. R. , Joshi Amish G. , Morozkin A. V. , Malik S. K.
Published: June 2007

Temperature and field dependence of magnetization of Dy-substituted Gd5Si2Ge2 compounds has been studied in the temperature range of 5–330K. The (DyxGd5−x)Si2Ge2 compounds with x=0.5, 1.5, 3.0, and 3.5 are found to order ferromagnetically with magnetic ordering temperature TC ranging between ∼270 and 80K. The Dy substitution in Gd5Si2Ge2 leads to a lowering of TC, an increase in coercivity, and also to a loss of the first order magnetic phase transition seen in the parent compound. The magnetic entropy change ΔSM associated with the magnetic transition has been computed using the magnetization-field isotherm data. The maximum magnetic entropy changes of ∼8.8, 13.9, and 6.9J∕kgK are obtained for x=0.5, 3.0, and 5 compounds, respectively, for a field change of 55kOe. The ΔSM is spread around TC over a few tens of Kelvin and this feature makes these materials promising for possible use in Ericsson-cycle magnetic refrigerator applications.
Comparison of models that interconnect point defect parameters in solids with bulk properties
Authors: Varotsos P.
Published: June 2007

Two models have been proposed for the interconnection of the defect Gibbs energy gi with bulk properties almost 60 and 30years ago, respectively. The one, proposed by Zener [J. Appl. Phys. 22, 372 (1951)], assumes that gi can account for the work that goes into straining the lattice and hence that it is proportional to the shear modulus of the solid. The other considers that since gi corresponds to an isobaric and isothermal process, it should be proportional to the isothermal bulk modulus and the mean volume per atom. The results of these two models are compared for different processes (defect formation, self-diffusion activation, and heterodiffusion) in a variety of solids including metals (fcc, bcc, and tetragonal) as well as solids that exhibit a superionic behavior. We find that the latter model does better than the former.
Contribution of water dimer absorption to the millimeter and far infrared atmospheric water continuum
Authors: Scribano Yohann , Leforestier Claude
Published: June 2007

We present a rigorous calculation of the contribution of water dimers to the absorption coefficient α(ν¯,T) in the millimeter and far infrared domains, over a wide range (276–310K) of temperatures. This calculation relies on the explicit consideration of all possible transitions within the entire rovibrational bound state manifold of the dimer. The water dimer is described by the flexible 12-dimensional potential energy surface previously fitted to far IR transitions [C. Leforestier et al., J. Chem. Phys. 117, 8710 (2002)], and which was recently further validated by the good agreement obtained for the calculated equilibrium constant Kp(T) with experimental data [Y. Scribano et al., J. Phys. Chem. A. 110, 5411 (2006)]. Transition dipole matrix elements were computed between all rovibrational states up to an excitation energy of 750cm−1, and J=K=5 rotational quantum numbers. It was shown by explicit calculations that these matrix elements could be extrapolated to much higher J values (J=30). Transitions to vibrational states located higher in energy were obtained from interpolation of computed matrix elements between a set of initial states spanning the 0–750cm−1 range and all vibrational states up to the dissociation limit (∼1200cm−1). We compare our calculations with available experimental measurements of the water continuum absorption in the considered range. It appears that water dimers account for an important fraction of the observed continuum absorption in the millimeter region (0–10cm−1). As frequency increases, their relative contribution decreases, becoming small (∼3%) at the highest frequency considered ν¯=944cm−1.
Investigation of the electronic structure at interfaces of crystalline and amorphous Gd2O3 thin layers with silicon substrates of different orientations
Authors: Badylevich M. , Shamuilia S. , Afanas’ev V. V. , Stesmans A. , Laha A. , Osten H. J. , Fissel A.
Published: June 2007

Internal photoemission, photoconductivity, and spectroscopic ellipsometry experiments were carried out to characterize the electronic structure of interfaces of (001) and (111)-oriented Si with crystalline (epitaxially grown) and amorphous Gd2O3 insulators. The energy barriers for electrons and holes (3.2 and 3.9eV, respectively) appear to be sensitive neither to the orientation of the Si crystal surface nor to the oxide phase (crystalline or amorphous). This result indicates that despite the difference in Si–O bond density in going from (001) to (111)Si, the interface dipoles do not ensue any measurable effect on the electronic structure of the interface and the associated band offsets.
Dwell time of a Brownian molecule in a microdomain with traps and a small hole on the boundary
Authors: Taflia Adi , Holcman David
Published: June 2007

We calculate the mean time a Brownian particle spends in a domain with traps and the number of bonds it makes before escaping through a small hole in the boundary. This mean time, called the Dwell time, depends on the backward binding rate (with the trap, e.g., scaffolding molecules), the mean time to reach the trap (forward binding rate), and the size of the hole. We estimate the mean and variance of the number of bonds made prior to exit. In a biochemical context, a quantitative signal occurs when the mean number of bonds exceeds a certain threshold, which may initiate a cascade of chemical reactions that have physiological consequences. We apply the present results to obtain estimates of the mean time a Brownian receptor spends inside a synaptic domain, when it moves freely by lateral diffusion on the membrane of a neuron and interacts at a synapse with scaffolding molecules.
Carrier transport through a dry-etched InP-based two-dimensional photonic crystal
Authors: Berrier A. , Mulot M. , Malm G. , Östling M. , Anand S.
Published: June 2007

The electrical conduction across a two-dimensional photonic crystal (PhC) fabricated by Ar/Cl2 chemically assisted ion beam etching in n-doped InP is influenced by the surface potential of the hole sidewalls, modified by dry etching. Carrier transport across photonic crystal fields with different lattice parameters is investigated. For a given lattice period the PhC resistivity increases with the air fill factor and for a given air fill factor it increases as the lattice period is reduced. The measured current-voltage characteristics show clear ohmic behavior at lower voltages followed by current saturation at higher voltages. This behavior is confirmed by finite element ISE TCAD™ simulations. The observed current saturation is attributed to electric-field-induced saturation of the electron drift velocity. From the measured and simulated conductance for the different PhC fields we show that it is possible to determine the sidewall depletion region width and hence the surface potential. We find that at the hole sidewalls the etching induces a Fermi level pinning at about 0.12 eV below the conduction band edge, a value much lower than the bare InP surface potential. The results indicate that for n-InP the volume available for conduction in the etched PhCs approaches the geometrically defined volume as the doping is increased.
Coulomb-staircase observed in silicon-nanodisk structures fabricated by low-energy chlorine neutral beams
Authors: Kubota Tomohiro , Hashimoto Takeshi , Takeguchi Masaki , Nishioka Kensuke , Uraoka Yukiharu , Fuyuki Takashi , Yamashita Ichiro , Samukawa Seiji
Published: June 2007

A silicon-nanodisk structure, a nanometer-scale silicon disk on extremely thin SiO2 film, was fabricated by etching a 3.5–4-nm-thick polycrystalline silicon (poly-Si) thin film/1.4–3-nm-thick underlying oxide layer/Si substrate structure with a 7-nm-diameter ferritin iron-core mask and Cl neutral beam etching (NBE). The degree of etching was precisely controlled by detecting its depth using x-ray photoelectron spectroscopy. Cross-sectional scanning transmission electron microscopy (STEM) with elemental mapping by electron energy-loss spectroscopy (EELS) revealed that the underlying oxide layer remained while the Si layer was accurately etched. The STEM-EELS observation also revealed that there was an Si layer about 1–2-nm thick even in the nanodisk, while the nanodisk’s surface region was covered by native oxide. Removing the surface oxide layer prior to the NBE process could decrease the nanodisk diameter. Irradiation by Cl NB of the underlying 1.4-nm-thick SiO2 film increased the thickness of the SiO2 film and drastically decreased the SiO2 leakage current. This worked as self-aligned isolation in the space between the nanodisks when measuring their current-voltage (I−V). This may also be useful for fabricating future quantum-effect devices using nanodisks. Coulomb staircases could be observed by measuring the I−V of nanodisks even at room temperature. These results indicated that the nanodisks fabricated in this research have a precise quantum-effect structure and they attained single-electron properties. This research has great potential for the development of practical and robust fabrication processes for future quantum-effect devices.
Nanospot welding and contact evolution during cycling of a model microswitch
Authors: Doelling Christopher M. , Kyle Vanderlick T. , Song Jun , Srolovitz David
Published: June 2007

The useful lifetime of microelectromechanical system switches is shortened during repetitive contact when the continual making and breaking of an electrical circuit accelerates damage done to the metallic contact points in the switch. In this study the interfacial force microscope is used as a model switch, and we explore the fundamental processes involved in switch failure. We find that repeated indentation (cyclic contact) causes protective coatings (in the form of self-assembled monolayers) to fail allowing metal-metal intimacy and formation of a malleable “nanospot weld.” The weld is stretched during separation of the contacting surfaces, leading to the development of nanoasperities. With the help of atomistic simulations, which provide insight into material transfer and consequential roughening of the surfaces, we show that asperity length grows with continued repetition, drastically changing the resistance of the contact over the lifetime of the switch. Controlling the amount of current passed through the contact influences the extent of weld stretching and arcing observed during contact separation.
Morphotropic phase diagram and dielectric and ferroelectric properties of (1−x)Ba(Zn1∕3Nb2∕3)O3−xPbTiO3 solid solution
Authors: Long Xifa , Ye Zuo-Guang
Published: June 2007

A new solid solution of (1−x)Ba(Zn1∕3Nb2∕3)O3−xPbTiO3 [(1−x)BZN−xPT] has been synthesized in the form of ceramics by solid state reactions and characterized by means of x-ray diffraction, dielectric spectroscopy, and ferroelectric measurements. A partial solid state phase diagram of the binary system is established. It exhibits a morphotropic phase boundary region in the composition range between x=0.58 and 0.61. The dielectric permittivity of BZN has been greatly enhanced by the substitution of PT. The ceramics with compositions x=0.5−0.58 show typical relaxor ferroelectric behavior with the diffuse maximum of high permittivity shifting to higher temperature with increasing frequencies. With further increase of the PT content, the permittivity peaks become frequency-independent, indicating a normal ferroelectric phase transition, the temperature of which (TC) increases with x. Thus a composition-induced transformation from a simple dielectric to relaxor and to ferroelectric phase has been realized in this solid solution system.
Observations of nanoporous foam arising from impact and rapid solidification of molten Ni droplets
Authors: Qu Meng , Wu Yuhong , Srinivasan Vasudevan , Gouldstone Andrew
Published: June 2007

The authors report highly nanoporous surfaces on the underside of impacted, rapidly quenched Ni droplets (splats) removed from substrates. The formation mechanism is interpreted as nucleation of gas bubbles during rapid postimpact depressurization, and subsequent freezing to a porous solid. Good agreement is found between experimental observations and predictions from bubble nucleation theory. Results from experimental variations suggest the potential for control of pore size and distribution.
Helically corrugated waveguide gyrotron traveling wave amplifier using a thermionic cathode electron gun
Authors: Cross A. W. , He W. , Phelps A. D. R. , Ronald K. , Whyte C. G. , Young A. R. , Robertson C. W. , Rafferty E. G. , Thomson J.
Published: June 2007

Experimental operation of a gyrotron traveling wave amplifier with a helically corrugated waveguide using a thermionic cathode electron gun is presented. The coupling between the second harmonic cyclotron mode of the gyrating electron beam and the radiation occurred in the region of near infinite phase velocity over a broad frequency band. With an axis-encircling electron beam of pitch factor of ∼1.2, energy of 185keV, and current of 6.0A, the amplifier achieved an output power of 220kW, saturated gain of 24dB, saturated bandwidth of 8.4to10.4GHz, and an interaction efficiency of 20%.
Real time structural modification of epitaxial FePt thin films under x-ray rapid thermal annealing using undulator radiation
Authors: Skuza J. R. , Lukaszew R. A. , Dufresne E. M. , Walko D. A. , Clavero C. , Cebollada A. , Cionca C. N. , Clarke R.
Published: June 2007

Modification of chemical order in epitaxial FePt binary alloy thin films deposited on MgO (100) substrates was induced and investigated in real time using x-ray rapid thermal annealing (XRTA). This is possible because synchrotron undulator radiation has sufficient power density to induce significant structural modifications in thin films and its energy can be tuned to optimize absorption in the sample. A monochromatic portion of the pink beam diffracted from the epitaxial FePt sample was used to probe microstructure evolution in real time and significant changes in chemical order were observed. In particular, the relative amount of L10 phase remained practically unchanged whereas the amount of L12 phase was significantly decreased in the FePt thin film sample during XRTA.
Structural stability in the Al–Li–Si system
Authors: Pisch A. , Jakse N. , Pasturel A. , Harvey J. P. , Chartrand P.
Published: June 2007

Density functional theory calculations are performed to theoretically interpret the structural stability of different ternary phases in the Al–Li–Si system. The stability of the already well-known AlLiSi compound is determined and found to be in excellent agreement with calorimetric measurements. The authors also study the stability of different phases reported in the literature. It is found that the ternary Al3Li7Si4, AlLi5Si2, and AlLi9Si3 compounds display much higher negative formation energies than that of the Al3Li8Si5 compound, giving new insights in understanding phase stabilities of compounds in the ternary Al–Li–Si system.
Fermi level shift in La1−xSrxMO3 (M=Mn, Fe, Co, and Ni) probed by Schottky-like heteroepitaxial junctions with SrTi0.99Nb0.01O3
Authors: Sawa A. , Yamamoto A. , Yamada H. , Fujii T. , Kawasaki M. , Matsuno J. , Tokura Y.
Published: June 2007

The authors have studied electrical properties of perovskite heteroepitaxial junctions consisting of transition metal oxides La1−xSrxMO3 (LSMO: M=Mn, Fe, Co, and Ni) and an n-type semiconductor SrTi0.99Nb0.01O3 (Nb:STO). The junctions showed rectifying current-voltage characteristics that could be analyzed by taking into account a Schottky-like barrier formed in the Nb:STO at the interfaces. As the doping level x is increased, the Schottky barrier height and built-in potential increase as ∼x (eV), indicating the downward shift of the Fermi level position in the LSMO. The Fermi level position in the LSMO with the same doping level x tends to be deepened with increasing the atomic number of M, in the order of Mn, Fe, Co, and Ni.
Microwave frequency characterization of undoped and p-doped quantum dot lasers
Authors: Martinez Anthony , Li Yan , Lester Luke F. , Gray Allen L.
Published: June 2007

The maximum relaxation frequency of directly modulated p-type doped quantum dot (QD) lasers decreases monotonically from 4.6 to 3.6GHz with p-doping levels in the range of 20–40 holes/dot. Modulation efficiencies decrease as well with these p-type concentrations. These results are shown to originate from significantly larger internal losses in the p-doped QD devices that, despite an increased maximum ground state modal gain, causes increased gain compression and decreased differential gain for constant cavity length lasers.
On the through-thickness critical current density of an YBa2Cu3O7−x film containing a high density of insulating, vortex-pinning nanoprecipitates
Authors: Kim S. I. , Kametani F. , Chen Z. , Gurevich A. , Larbalestier D. C. , Haugan T. , Barnes P.
Published: June 2007

Using sequential ion milling the authors have studied the thickness dependence of the critical current density Jc(H) of a single crystal 1μm thick YBa2Cu3O7−x thin film containing ∼5vol% of insulating Y2BaCuO5 (Y211) nanoparticles in order to better understand how to obtain high critical currents in thick films. Except very near the interface where the defect density was enhanced, Jc(H) in the body of the film was uniform and independent of thickness with a high maximum pinning force of 8.8GN∕m3 at 77K. The authors conclude that the nanoscale Y211 precipitates result in strong, three-dimensional pinning characterized by a pin spacing of ∼30nm, much smaller than the film thickness.
Transient gain spectroscopy of (GaIn)As quantum wells: Experiment and microscopic analysis
Authors: Lange C. , Chatterjee S. , Schlichenmaier C. , Thränhardt A. , Koch S. W. , Rühle W. W. , Hader J. , Moloney J. V. , Khitrova G. , Gibbs H. M.
Published: June 2007

Transient gain measurements are performed for (GaIn)As quantum well structures. Gain up to gL=2×10−3 per quantum well is observed on a time scale of several hundred picoseconds. A microscopic theory quantitatively provides theoretical support and yields the carrier density as a function of time by matching the spectral shapes and intensities to the experiment. The decay rate of the population density is found to be proportional to the carrier density, which underlines the importance of monomolecular recombination processes.
Comprehensive analysis of hydrogen sensing properties of a Pd-gate metal-semiconductor high electron mobility transistor
Authors: Tsai Yan-Ying , Lin Kun-Wei , Chen Huey-Ing , Hung Ching-Wen , Chen Tzu-Pin , Liu Wen-Chau
Published: June 2007

The electric and hydrogen sensing properties of an interesting Pd-gate metal-semiconductor-type high electron mobility transistor are comprehensively studied. The dipolar layer formed by adsorbed hydrogen atoms at the semiconductor of Pd–AlGaAs interface is equivalent to a two-dimensional layer. The concentration of available hydrogen adsorption sites at the metal-semiconductor interface ni and the effective distance d from the Pd–AlGaAs interface to adsorbed hydrogen atoms are 9.5×1013cm−2 and 3Å, respectively. Furthermore, the simulated curves are in excellently agreement with the experimental results.
Reversible strain induced by martensite variant rearrangement under magnetic field and mechanical loading of Fe–Pd single crystals
Authors: Yamamoto Tokujiro , Taya Minoru
Published: June 2007

Reversible and repeatable strain without external bias stress was induced by applied magnetic field-induced martensite variant rearrangement (VR) and compressive stress-induced martensite VR for Fe–Pd single crystals. The amounts of the reversible strain induced by the magnetic field and the compressive stress were 0.4% and 5.0%, respectively, where the Fe–Pd specimen was martensitically transformed from austenite to martensite which consist of two large correspondence variants (CVs). The motion of the twinning boundary between the two CVs moved by applying the magnetic field or the compressive stress, and its movement was found to be reversible and repeatable.