bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal production of gaseous mercury in the alpine snowpack before snowmelt
Authors: Faïn Xavier , Grangeon Sylvain , Bahlmann Enno , Fritsche Johannes , Obrist Daniel , Dommergue Aurélien , Ferrari Christophe P. , Cairns Warren , Ebinghaus Ralf , Barbante Carlo , Cescon Paolo , Boutron Claude
Published: November 2007

In March 2005, an extensive mercury study was performed just before snowmelt at Col de Porte, an alpine site close to Grenoble, France. Total mercury concentration in the snowpack ranged from 80 ± 08 to 160 ± 15 ng l−1, while reactive mercury was below detection limit (0.2 ng l−1). We observed simultaneously a production of gaseous elemental mercury (GEM) in the top layer of the snowpack and an emission flux from the snow surface to the atmosphere. Both phenomena were well correlated with solar irradiation, indicating photo‐induced reactions in the snow interstitial air (SIA). The mean daily flux of GEM from the snowpack was estimated at ∼9 ng m−2 d−1. No depletion of GEM concentrations was observed in the SIA, suggesting no occurrence of oxidation processes. The presence of liquid water in the snowpack clearly enhanced GEM production in the SIA. Laboratory flux chamber measurements enabled us to confirm that GEM production from this alpine snowpack was first driven by solar radiation (especially UVA and UVB radiation), and then by liquid water in the snowpack. Finally, a large GEM emission from the snow surface occurred during snowmelt, and we report total mercury concentrations in meltwater of about 72 ng l−1.
Remote‐sensing measurements in the polar vortex: Comparison to in situ observations and implications for the simultaneous retrievals and analysis of the NO2 and OClO species
Authors: Berthet G. , Renard J.‐B. , Catoire V. , Chartier M. , Robert C. , Huret N. , Coquelet F. , Bourgeois Q. , Rivière E. D. , Barret B. , Lefèvre F. , Hauchecorne A.
Published: November 2007

Nighttime remote‐sensing balloon observations conducted by the SALOMON instrument in the arctic polar vortex in January 2006 reveal high amounts of stratospheric NO2 in the lower stratosphere similarly to previously published profiles. NO2 concentration enhancements are also present in the vertical profiles observed by the GOMOS instrument on board the Envisat satellite and obtained coincidently to the balloon measurements. Such quantities are not present in in situ observations obtained by the SPIRALE instrument in similar geophysical conditions. While OClO amounts are acceptably reproduced by Chemistry Transport Model (CTM) calculations, NO2 simulated values are well below the observed quantities. The examination of the slant column densities of NO2 obtained at float altitude highlights unexpected strong enhancements with respect to the elevation angle and displacement of the balloon. It is shown that these fluctuations result from NO2 spatial inhomogeneities located above the balloon float altitude. Potential vorticity maps reveal the presence of midlatitude NO2‐rich air in the upper stratosphere or lower mesosphere as a result of the perturbed dynamical situation of the vortex. The presence of spatial inhomogeneities crossed by the lines of sight leads to artificial high concentration values of NO2 in the vertical profile retrieved from the slant column densities assuming spatial homogeneity. A direct implication is that the differences previously observed between measurements of NO2 and OClO and model results are probably mostly due to the improper inversion of NO2 in the presence of perturbed dynamical conditions or when mesospheric NOx production events occur. The dynamical situation will have to be systematically analyzed in future studies involving remote‐sensing observations.
Impacts of the agricultural Green Revolution–induced land use changes on air temperatures in India
Authors: Roy Shouraseni Sen , Mahmood Rezaul , Niyogi Dev , Lei Ming , Foster Stuart A. , Hubbard Kenneth G. , Douglas Ellen , Pielke Roger
Published: November 2007

India has one of the most intensive and spatially extensive irrigation systems in the world developed during the1960s under the agricultural Green Revolution (GR). Irrigated landscapes can alter the regional surface energy balance and its associated temperature, humidity, and climate features. The main objective of this study is to determine the impacts of increased irrigation on long‐term temperature trends. An analysis of the monthly climatological surface data sets at the regional level over India showed that agriculture and irrigation can substantially reduce the air temperature over different regions during the growing season. The processes associated with agriculture and irrigation‐induced feedback are further diagnosed using a column radiation‐boundary layer model coupled to a detailed land surface/hydrology scheme, and 3‐D simulations using a Regional Atmospheric Modeling System. Both the modeling and observational analysis provide evidence that during the growing season, irrigation and agricultural activity are significantly modulating the surface temperatures over the Indian subcontinent. Therefore irrigation and agricultural impacts, along with land use change, and aerosol feedbacks need to be considered in regional and global modeling studies for climate change assessments.
Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars
Authors: Montmessin F. , Gondet B. , Bibring J.‐P. , Langevin Y. , Drossart P. , Forget F. , Fouchet T.
Published: November 2007

A unique feature of the Martian climate is the possibility for carbon dioxide, the main atmospheric constituent, to condense as ice. CO2 ice is usually detected as frost but is also known to exist as clouds. This paper presents the first unambiguous observation of CO2 ice clouds on Mars. These images were obtained by the visible and near‐infrared imaging spectrometer OMEGA on board Mars Express. The data set encompasses 19 different occurrences. Compositional identification is based on the detection of a diagnostic spectral feature around 4.26 μm which is produced by resonant scattering of solar photons by mesospheric CO2 ice particles in a spectral interval otherwise dominated by saturated gaseous absorption. Observed clouds exhibit a strong seasonal and geographic dependence, concentrating in the near‐equatorial regions during two periods before and after northern summer solstice (Ls 45° and 135°). Radiative transfer modeling indicates that the 4.26 μm feature is very sensitive to cloud altitude, opacity, and particle size, thereby explaining the variety of spectra associated with the cloud images. On two orbits, the simultaneous detection of clouds with their shadow provides straightforward and robust estimates of cloud properties. These images confirm the conclusions established from modeling: clouds are thick, with normal opacities greater than 0.2 in the near infrared, and are lofted in the mesosphere above 80 km. The mean radius of CO2 ice crystals is found to exceed 1 μm, an unexpected value considering this altitude range. This finding implies the existence of high‐altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles. This statement is consistent with the cumuliform morphology of the clouds which may be linked to a moist convective origin generated by the latent heat released during CO2 condensation.
Free‐surface visualization of streamwise vortices in a channel flow
Authors: Tamburrino Aldo , Gulliver John S.
Published: November 2007

Visualization of the free surface in an open channel can provide insight into certain characteristics of the flow field, such as the occurrence of low‐frequency, large‐scale eddies. This paper presents some experimental results obtained in a moving‐bed flume constructed for research on free‐surface transport without significant shear at the free surface (without wind). Free‐surface velocities were measured using particle tracer velocimetry (PTV) at bulk Reynolds numbers (UH/ν) between 8500 and 45,500. The PTV streaks were digitized in order to perform a quantitative analysis, allowing determination of spatial velocity autocorrelations. Large, vertical oriented vortices and lateral movement are apparent on the water surface, with a lateral length scale of between 1 and 1.5 times the depth. A relationship between these largest scales of turbulence, large streamwise vortices, and secondary currents in the flow is hypothesized. The large‐scale turbulent eddies with streamwise vorticity that form secondary currents across a movable‐bed, open‐channel flow also exist in a smooth‐bed open‐channel flow but are not fixed in space. They oscillate laterally at low frequencies and form permanent secondary currents only near the wall, where lateral migration is limited. They appear to be a significant transport mechanism in the outer layer, transporting mass, energy, and outer region bursts to the free surface.
A new approach to the spatio-temporal pattern identification in neuronal multi-electrode registrations
Authors: Esposti Federico , Lamanna Jacopo , Signorini Maria Gabriella
Published: November 2007

A lot of methods were created in last decade for the spatio-temporal analysis of multi-electrode array (MEA) neuronal data sets. All these methods were implemented starting from a channel to channel analysis, with a great computational effort and onerous spatial pattern recognition task. Our idea is to approach the MEA data collection from a different point of view, i.e. considering all channels simultaneously. We transform the 2D plus time MEA signal in a mono-dimensional plus time signal and elaborate it as a normal 1D signal, using the Space-Amplitude Transform method. This geometrical transformation is completely invertible and allows to employ very fast processing algorithms.
The NCI-Nature Pathway Interaction Database: A cell signaling resource.
Authors: Krupa Shiva , Anthony Kira , Buchoff Jeffrey , Day Matthew , Hannay Timo , Schaefer Carl
Published: November 2007

The Pathway Interaction Database (*PID*, http://pid.nci.nih.gov) is a freely availablecollection of curated and peer-reviewed signaling pathways composed of humanbiomolecular interactions and cellular processes. Created in a collaboration between theU.S. National Cancer Institute and Nature Publishing Group, the database is a researchtool for cell biologists, biochemists, computational biologists and bioinformaticians.The PID offers a range of tools to facilitate pathway exploration. Users can browse thepre-defi ned set of pathways and also create interaction network maps centered ona single molecule of interest or an extensive list of molecules. In addition, users candownload complete data sets in extensible markup language (XML) and BiologicalPathway Exchange (BioPAX) Level 2 formats. The database is updated every month andsupplemented by a concise editorial section that provides synopses of recent noteworthypapers in cell signaling and specially commissioned articles on the practical uses ofother relevant online tools. Users can sign up for free email alerts or RSS feeds to receivedatabase updates.
The Normal Fetal Heart Rate Study: Analysis Plan
Authors: Daumer Martin , Scholz Michael , Boulesteix Anne-Laure , Pildner von Steinburg Stephanie , Schiermeier Sven , Hatzmann Wolfgang , Schneider K T M
Published: November 2007

Recording of fetal heart rate via CTG monitoring has been routinely performed as an important part of antenatal and subpartum care for several decades. The current guidelines of the FIGO (ref1) recommend a normal range of the fetal heart rate from 110 to 150 bpm. However, there is no agreement in the medical community whether this is the correct range (ref2). We aim to address this question by computerized analysis (ref 3) of a high quality database (HQDb, ref 4) of about one billion electronically registered fetal heart rate measurements from about 10,000 pregnancies in three medical centres over seven years. In the present paper, we lay out a detailed analysis plan for this evidence-based project in the vein of the validation policy of the Sylvia Lawry Centre for Multiple Sclerosis Research (ref 5) with a split of the database into an exploratory part and a part reserved for validation. We will perform the analysis and the validation after publication of this plan in order to reduce the probability of publishing false positive research findings (ref 6-7).
Gastrointestinal roles for proteinase‐activated receptors in health and disease
Authors: Kawabata A , Matsunami M , Sekiguchi F
Published: November 2007

It has been almost a decade since the molecular cloning of all four members of the proteinase‐activated receptor (PAR) family was completed. This unique family of G protein‐coupled receptors (GPCRs) mediates specific cellular actions of various endogenous proteinases including thrombin, trypsin, tryptase, etc. and also certain exogenous enzymes. Increasing evidence has been clarifying the emerging roles played by PARs in health and disease. PARs, particularly PAR1 and PAR2, are distributed throughout the gastrointestinal (GI) tract, modulating various GI functions. One of the most important GI functions of PARs is regulation of exocrine secretion in the salivary glands, pancreas and GI mucosal epithelium. PARs also modulate motility of GI smooth muscle, involving multiple mechanisms. PAR2 appears to play dual roles in pancreatitis and related pain, being pro‐inflammatory/pro‐nociceptive and anti‐inflammatory/anti‐nociceptive. Similarly, dual roles for PAR1 and PAR2 have been demonstrated in mucosal inflammation/damage throughout the GI tract. There is also fundamental and clinical evidence for involvement of PAR2 in colonic pain. PARs are thus considered key molecules in regulation of GI functions and targets for development of drugs for treatment of various GI diseases.

British Journal of Pharmacology(2008)153, S230–S240; doi:10.1038/sj.bjp.0707491; published online 12 November 2007
Cannabinoid CB2receptors: a therapeutic target for the treatment of inflammatory and neuropathic pain
Authors: Guindon J , Hohmann A G
Published: November 2007

Cannabinoids suppress behavioural responses to noxious stimulation and suppress nociceptive transmission through activation of CB1and CB2receptor subtypes. CB1receptors are expressed at high levels in the central nervous system (CNS), whereas CB2receptors are found predominantly, but not exclusively, outside the CNS. CB2receptors are also upregulated in the CNS and dorsal root ganglia by pathological pain states. Here, we review behavioural, neurochemical and electrophysiological data, which identify cannabinoid CB2receptors as a therapeutic target for treating pathological pain states with limited centrally, mediated side effects. The development of CB2‐selective agonists (with minimal affinity for CB1) as well as mutant mice lacking CB2receptors has provided pharmacological and genetic tools required to evaluate the effectiveness of CB2agonists in suppressing persistent pain states. This review will examine the efficacy of cannabinoid CB2‐selective agonists in suppressing acute, inflammatory and neuropathic nociception following systemic and local routes of administration. Data derived from behavioural, neurochemical and neurophysiological approaches are discussed to better understand the relationship between antinociceptive effects induced by CB2‐selective agonists in behavioural studies and neural mechanisms of pain suppression. Finally, the therapeutic potential and possible limitations of CB2‐based pharmacotherapies for pathological pain states induced by tissue and nerve injury are discussed.

British Journal of Pharmacology(2008)153, 319–334; doi:10.1038/sj.bjp.0707531; published online 12 November 2007
Effect of K201, a novel antiarrhythmic drug on calcium handling and arrhythmogenic activity of pulmonary vein cardiomyocytes
Authors: Chen Y‐J , Chen Y‐C , Wongcharoen W , Lin C‐I , Chen S‐A
Published: November 2007

Background and purpose:

Pulmonary veins are the most important focus for the generation of atrial fibrillation. Abnormal calcium homeostasis with ryanodine receptor dysfunction may underlie the arrhythmogenic activity in pulmonary veins. The preferential ryanodine receptor stabilizer (K201) possesses antiarrhythmic effects through calcium regulation. The purpose of this study was to investigate the effects of K201 on the arrhythmogenic activity and calcium regulation of pulmonary vein cardiomyocytes.

Experimental approach:

The ionic currents and intracellular calcium were studied in isolated single cardiomyocytes from rabbit pulmonary vein before and after the administration of K201, by the whole‐cell patch clamp and indo‐1 fluorimetric ratio techniques.

Key results:

K201 (0.1, 0.3, 1 μM) reduced the firing rates in pulmonary vein cardiomyocytes, decreased the amplitudes of the delayed afterdepolarizations and prolonged the action potential duration. K201 decreased the L‐type calcium currents, Na+/Ca2+ exchanger currents, transient inward currents and calcium transients. K201 (1 μM, but not 0.1 μM or 0.3 μM) also reduced the sarcoplasmic reticulum calcium content. Moreover, both the pretreatment and administration of K201 (0.3 μM) decreased the isoprenaline (10 nM)‐induced arrhythmogenesis in pulmonary veins.

Conclusions and implications:

K201 reduced the arrhythmogenic activity of pulmonary vein cardiomyocytes and attenuated the arrhythmogenicity induced by isoprenaline. These findings may reveal the anti‐arrhythmic potential of K201.

British Journal of Pharmacology (2008) 153, 915–925; doi:10.1038/sj.bjp.0707564; published online 12 November 2007
In vitroandin vivocharacterization of A‐796260: a selective cannabinoid CB2receptor agonist exhibiting analgesic activity in rodent pain models
Authors: Yao B B , Hsieh G C , Frost J M , Fan Y , Garrison T R , Daza A V , Grayson G K , Zhu C Z , Pai M , Chandran P , Salyers A K , Wensink E J , Honore P , Sullivan J P , Dart M J , Meyer M D
Published: November 2007

Background and purpose:

Selective cannabinoid CB2receptor agonists have demonstrated analgesic activity across multiple preclinical pain models. AM1241 is an indole derivative that exhibits high affinity and selectivity for the CB2binding site and broad spectrum analgesic activity in rodent models, but is not an antagonist of CB2in vitrofunctional assays. Additionally, its analgesic effects are μ‐opioid receptor‐dependent. Herein, we describe thein vitroandin vivopharmacological properties of A‐796260, a novel CB2agonist.

Experimental approach:

A‐796260 was characterized in radioligand binding andin vitrofunctional assays at rat and human CB1and CB2receptors. The behavioural profile of A‐796260 was assessed in models of inflammatory, post‐operative, neuropathic, and osteoarthritic (OA) pain, as well as its effects on motor activity. The receptor specificity was confirmed using selective CB1, CB2and μ‐opioid receptor antagonists.

Key results:

A‐796260 exhibited high affinity and agonist efficacy at human and rat CB2receptors, and was selective for the CB2vs CB1subtype. Efficacy in models of inflammatory, post‐operative, neuropathic and OA pain was demonstrated, and these activities were selectively blocked by CB2, but not CB1or μ‐opioid receptor‐selective antagonists. Efficacy was achieved at doses that had no significant effects on motor activity.

Conclusions and implications:

These results further confirm the therapeutic potential of CB2receptor‐selective agonists for the treatment of pain. In addition, they demonstrate that A‐796260 may be a useful new pharmacological compound for further studying CB2receptor pharmacology and for evaluating its role in the modulation of pain.

British Journal of Pharmacology(2008)153, 390–401; doi:10.1038/sj.bjp.0707568; published online 12 November 2007
Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders
Authors: Farré R , Sifrim D
Published: November 2007

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L‐type Ca2+channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co‐transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M3and tachykinin NK2receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro‐oesophageal reflux disease.

British Journal of Pharmacology(2008)153, 858–869; doi:10.1038/sj.bjp.0707572; published online 12 November 2007
Role of NADPH oxidase and iNOS in vasoconstrictor responses of vessels from hypertensive and normotensive rats
Authors: Álvarez Y , Briones A M , Hernanz R , Pérez‐Girón J V , Alonso M J , Salaices M
Published: November 2007

Background and purpose:

To analyse the influence of hypertension in the modulation induced by inducible NOS (iNOS)‐derived NO and superoxide anion (O2
•−) of vasoconstrictor responses and the sources of O2
•− implicated.

Experimental approach:

Vascular reactivity experiments were performed in segments of aorta from normotensive, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR); protein and mRNA expressions were respectively measured by western blot and quantitative reverse transcription‐polymerase chain reaction and O2
•− production was evaluated by ethidium fluorescence.

Key results:

The contractile responses to phenylephrine (1 nM–30 μM) and 5‐hydroxytryptamine (0.1–100 μM) were greater in aortic segments from SHR than WKY. The selective iNOS inhibitor, 1400W (10 μM), increased the phenylephrine contraction only in WKY segments; however, iNOS protein and mRNA expressions were greater in aorta from SHR than WKY. Superoxide dismutase (SOD, 150 U ml−1) reduced phenylephrine and 5‐hydroxytryptamine responses only in aorta from SHR; the NAD(P)H oxidase inhibitor apocynin (0.3 mM) decreased phenylephrine and 5‐hydroxytryptamine responses more in vessels from SHR than WKY. Co‐incubation with SOD plus 1400W potentiated the phenylephrine and 5‐hydroxytryptamine responses more in segments from SHR than WKY. O2
•− production was greater in aorta from SHR than WKY; apocynin abolished this difference.

Conclusions and implications:

Increased O2
•− formation from NADP(H) oxidase in vessels from hypertensive rats contributes to the vasoconstrictor responses and counteract the increase of NO from iNOS and the consequent modulation of these responses.

British Journal of Pharmacology (2008) 153, 926–935; doi:10.1038/sj.bjp.0707575; published online 12 November 2007
Unmixing in random flows
Authors: Wilkinson M. , Mehlig B. , Östlund S. , Duncan K. P.
Published: November 2007

We consider particles suspended in a randomly stirred or turbulent fluid. When effects of the inertia of the particles are significant, an initially uniform scatter of particles can cluster together. We analyze this “unmixing” effect by calculating the Lyapunov exponents for dense particles suspended in such a random three-dimensional flow, concentrating on the limit where the viscous damping rate is small compared to the inverse correlation time of the random flow (that is, the regime of large Stokes number). In this limit Lyapunov exponents are obtained as a power series in a parameter which is a dimensionless measure of the inertia. We report results for the first seven orders. The perturbation series is divergent, but we obtain accurate results from a Padé-Borel summation. We deduce that particles can cluster onto a fractal set and show that its dimension is in satisfactory agreement with previously reported simulations of turbulent Navier-Stokes flows. We also investigate the rate of formation of caustics in the particle flow.
Dynamics of probability density functions for decaying passive scalars in periodic velocity fields
Authors: Camassa Roberto , Martinsen-Burrell Neil , McLaughlin Richard M.
Published: November 2007

The probability density function (PDF) for a decaying passive scalar advected by a deterministic, periodic, incompressible fluid flow is numerically studied using a variety of random and coherent initial scalar fields. We establish the dynamic emergence at large Péclet numbers of a broad-tailed PDF for the scalar initialized with a Gaussian random measure, and further explore a rich parameter space involving scales of the initial scalar field and the geometry of the flow. We document that the dynamic transition of the PDF to a broad-tailed distribution is similar for shear flows and time-varying nonsheared flows with positive Lyapunov exponent, thereby showing that chaos in the particle trajectories is not essential to observe intermittent scalar signals. The role of the initial scalar field is carefully explored. The long-time PDF is sensitive to the scale of the initial data. For shear flows we show that heavy-tailed PDFs appear only when the initial field has sufficiently small-scale variation. We also connect geometric features of the scalar field with the shape of the PDFs. We document that the PDF is constructed by a subtle balance between spatial regions of strong and weak shear in conjunction with the presence of small-scale scalar variation within the weak shear regions. For cellular flows we document a lack of self-similarity in the PDFs when periodic time dependence is present, in contrast to the self-similar decay for time independent flow. Finally, we analyze the behavior of the PDFs for coherent initial fields and the parametric dependence of the variance decay rate on the Péclet number and the initial wavenumber of the scalar field.
A self-adapting turbulence model for flow simulation at any mesh resolution
Authors: Perot J. Blair , Gadebusch Jason
Published: November 2007

A two-equation transport model is used to model turbulence at any mesh resolution, from Reynolds-averaged Navier–Stokes (RANS), to large eddy simulations (LES), to direct numerical simulations. The two-equation model used is a slight modification of the standard k∕ε model that allows the backscatter of energy to resolved scales. A mathematical explanation is provided for why RANS models (such as this two-equation model) are applicable to LES. The model automatically adapts to the mesh resolution provided and no interaction from the user is necessary. This approach is tested on the problem of moderately high Reynolds number isotropic decaying turbulence and gives good predictions at any mesh resolution and with different initial conditions. A detailed analysis shows that at LES resolutions the solution remains fully unsteady and three-dimensional and does not approach a RANS-like solution.
Transformation from chemisorption to physisorption with tube diameter and gas concentration: Computational studies on NH3 adsorption in BN nanotubes
Authors: Li Yafei , Zhou Zhen , Zhao Jijun
Published: November 2007

Using first-principles computations, we studied NH3 adsorption on a series of zigzag (n,0) single-walled BN nanotubes (BNNTs) and the effect of gas coverage. Tube diameter and NH3 coverage play important roles on the tube-NH3 interaction. Chemisorption of a single NH3 molecule on top of B site is energetically preferable for all the tubes studied, but the adsorption energy decreases sharply with increasing tube diameter, and then gradually approaches the value for NH3 physisorption on BN graphene layer. On the sidewall of (10,0) BNNT, NH3 molecules prefer to pair arrangement on top of B and N atoms opposite in the same hexagon. At low coverages, NH3 molecules are partly chemically bound to BNNTs. With the increase of NH3 coverage, hydrogen bonds form between the adsorbed NH3 molecules or between the NH3 molecules and N atoms in BNNTs. When the coverage reaches 25%, the chemisorption of NH3 transforms to physisorption completely. NH3 adsorption does not modify the overall band structures of BNNTs, irrespective of NH3 coverage, but the band gap is narrowed due to the NH3-tube coupling and tube deformation.
Mechanical and electrical properties of CdTe tetrapods studied by atomic force microscopy
Authors: Fang Liang , Park Jeong Young , Cui Yi , Alivisatos Paul , Shcrier Joshua , Lee Byounghak , Wang Lin-Wang , Salmeron Miquel
Published: November 2007

The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with three of its arms. The length of these arms was found to be 130±10nm. A large fraction of the tetrapods had a shortened vertical arm as a result of fracture during sample preparation. Fracture also occurs when the applied load is a few nanonewtons. Compression experiments with the atomic force microscope tip indicate that tetrapods with the shortened vertical arm deform elastically when the applied force was less than 50nN. Above 90nN additional fracture events occurred that further shortened the vertical arm. Loads above 130nN produced irreversible damage to the other arms as well. Current-voltage characteristics of tetrapods deposited on gold revealed a semiconducting behavior with a current gap of ∼2eV at low loads (<50nN) and a narrowing to about 1eV at loads between 60 and 110nN. Atomistic force field calculations of the deformation suggest that the ends of the tetrapod arms are stuck during compression so that the deformations are due to bending modes. Empirical pseudopotential calculation of the electron states indicates that the reduction of the current gap is due to electrostatic effects, rather than strain deformation effects inside the tetrapod.
Study of the quasicanonical localized orbital method based on protein structures
Authors: Nishino-Uemura Noriko , Hirano Toshiyuki , Sato Fumitoshi
Published: November 2007

An initial guess is one of the most important factors in solving self-consistent field (SCF) molecular orbital calculations for large molecules. Recently, the authors reported that the quasicanonical localized orbital (QCLO) method was useful to prove the initial guess for all-electron calculations for proteins. This paper describes a new QCLO method that takes into account protein information derived from protein structures such as salt bridges and the secondary structure of the molecule. In several test calculations using typical models, the difference between the initial guess and final atomic charges was markedly decreased, and the number of SCF iterations was reduced. We suggest that the structure-based QCLO method improves the precision of the initial guess and achievement of automatic all-electron calculations for proteins.
A comparative study of solvation dynamics in room-temperature ionic liquids
Authors: Kobrak Mark N.
Published: November 2007

The solvation dynamics of ionic liquids have been the subject of many experimental and theoretical studies but remain poorly understood. We analyze these dynamics by modeling the time-resolved fluorescence response of coumarin 153 in two room-temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bromide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. Our results demonstrate that phenomena such as electrostatic screening operate significantly differently in the two liquids, and the relative importance of translational and rovibrational components of the ionic response depends significantly on the character of the ions involved. However, collective motion dominates the response of both ionic liquids, and the qualitative features of this collective behavior are strikingly similar in both cases.
Seven dimensional quantum dynamics study of the H2+NH2→H+NH3 reaction
Authors: Yang Minghui , Corchado Jose C.
Published: November 2007

Initial state-selected time-dependent wave packet dynamics calculations have been performed for the H2+NH2→H+NH3 reaction using a seven dimensional model on an analytical potential energy surface based on the one developed by Corchado and Espinosa-García [J. Chem. Phys. 106, 4013 (1997)]. The model assumes that the two spectator NH bonds are fixed at their equilibrium values and nonreactive NH2 group keeps C2v symmetry and the rotation-vibration coupling in NH2 is neglected. The total reaction probabilities are calculated when the two reactants are initially at their ground states, when the NH2 bending mode is excited, and when H2 is on its first vibrational excited state, with total angular momentum J=0. The converged cross sections for the reaction are also reported for these initial states. Thermal rate constants and equilibrium constants are calculated for the temperature range of 200–2000K and compared with transition state theory results and the available experimental data. The study shows that (a) the reaction is dominated by ground-state reactivity and the main contribution to the thermal rate constants is thought to come from this state, (b) the excitation energy of H2 was used to enhance reactivity while the excitation of the NH2 bending mode hampers the reaction, (c) the calculated thermal rate constants are very close to the experimental data and transition state theory results at high and middle temperature, while they are ten times higher than that of transition state theory at low temperature (T=200K), and (d) the equilibrium constants results indicate that the approximations applied may have different roles in the forward and reverse reactions.
Field-resolved measurement of reaction-induced spectral densities by polarizability response spectroscopy
Authors: Moran Andrew M. , Nome Rene A. , Scherer Norbert F.
Published: November 2007

The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute’s electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of reactions that do not satisfy the time-scale separability inherent to nonadiabatic kinetic models.
Reclassifying exciton-phonon coupling in molecular aggregates: Evidence of strong nonadiabatic coupling in oligothiophene crystals
Authors: Spano F. C. , Silvestri L. , Spearman P. , Raimondo L. , Tavazzi S.
Published: November 2007

Exciton-phonon (EP) coupling in molecular aggregates is reexamined in cases where extended intermolecular interactions result in low-energy excitons with high effective masses. The analysis is based on a single intramolecular vibrational mode with frequency ω0 and Huang-Rhys factor λ2. When the curvature Jc at the exciton band bottom is much smaller than the free-exciton Davydov splitting W, the strength of the EP coupling is determined by comparing the nuclear relaxation energy λ2ω0 with the curvature. In this way, weak (λ2ω0⪡4πJc), intermediate I (λ2ω0≈4πJc), and strong I (λ2ω0⪢4πJc) coupling regimes are introduced. The conventional intermediate (λ2ω0≈W) and strong (λ2ω0⪢W) EP coupling regimes originally defined by Simpson and Peterson [J. Chem. Phys. 26, 588 (1957)] are based solely on the Davydov splitting and are referred to here as intermediate II and strong II regimes, respectively. Within the intermediate I and strong I regimes the near degeneracy of the low-energy excitons allows efficient nonadiabatic coupling, resulting in a spectral splitting between the b- and ac-polarized first replicas in the vibronic progression characterizing optical absorption. Such spectral signatures are clearly observed in OT4 thin films and crystals, where splittings for the lowest energy mode with ω0=161cm−1 are as large as 30cm−1 with a small variation due to sample disorder. Numerical calculations using a multiphonon BO basis set and a Hamiltonian including linear EP coupling yield excellent agreement with experiment.
Young’s law and the effects of interfacial energy on the pressure at the solid-fluid interface
Authors: Lunati Ivan
Published: November 2007

In a recent paper [R. Finn, Phys. Fluids 18, 047102 (2006)] the attention has been drawn on the tension component perpendicular to the solid surface that results from Young’s law. Considering the problem of a solid sphere floating in zero gravity, it has been argued that this component yields a spurious net vertical force acting on the sphere, which remains unbalanced. Therefore, the validity of Young’s law has been questioned in favor of an energy argument. The scope of this Brief Communication is to restate the equivalence between the energy and the force descriptions of the problem. It is shown that there is no contradiction in Young’s law if one accounts for the different stress acting on the solid surface in the two fluids. The net force resulting from the latter balances the force resultant associated with the tension component perpendicular to the solid.
Optical bandgap and photoconductance of electrospun tin oxide nanofibers
Authors: Wang Yu , Ramos Idalia , Santiago-Avilés Jorge J.
Published: November 2007

Optical and photoconductive properties of transparent SnO2 nanofibers, made from C22H44O4Sn via electrospinning and metallorganic decomposition, were investigated using Fourier transform infrared and ultraviolet (UV)/visible spectrometry and the two-probe method. Their optical bandgap was determined from their UV absorption edge to be 3.95–4.08eV. Their conductance responds strongly to UV light for a wavelength of 254nm: in air its steady-state on-to-off ratios are 1.31–1.56 (rise) and 1.25–1.33 (fall); its 90% rise and fall times are 76–96 and 71–111s, respectively. In a vacuum of about 10−4torr, its on-to-off ratios are higher than 35.6 (rise) and 3.4 (fall), respectively, and its 90% rise and fall times are longer than 3×104s.
Homology and symmetry breaking in Rayleigh-Bénard convection: Experiments and simulations
Authors: Krishan Kapilanjan , Kurtuldu Huseyin , Schatz Michael F. , Gameiro Marcio , Mischaikow Konstantin , Madruga Santiago
Published: November 2007

Algebraic topology (homology) is used to analyze the state of spiral defect chaos in both laboratory experiments and numerical simulations of Rayleigh-Bénard convection. The analysis reveals topological asymmetries that arise when non-Boussinesq effects are present. The asymmetries are found in different flow fields in the simulations and are robust to substantial alterations to flow visualization conditions in the experiment. However, the asymmetries are not observable using conventional statistical measures. These results suggest homology may provide a new and general approach for connecting spatiotemporal observations of chaotic or turbulent patterns to theoretical models.
Thermodynamic properties of the Mie n-6 fluid: A comparison between statistical associating fluid theory of variable range approach and molecular dynamics results
Authors: Galliero Guillaume , Lafitte Thomas , Bessieres David , Boned Christian
Published: November 2007

Molecular dynamics (MD) simulations of direct and derivative thermodynamic properties of the Mie n-6 fluid (n=8, 10, and 12) have been performed for liquid to supercritical states. Using the results, an in depth test of the monomer-monomer interaction estimation of a recently derived statistical associating fluid theory of variable range (SAFT-VR) equation of state [Lafitte et al., J. Chem. Phys., 124, 024509 (2006)] has been carried out based on the Mie n-6 potential. For pure fluids, using an appropriate scaling, MD simulations show that density and isometric heat capacity are nearly independent of n, whereas sound velocity and thermal pressure coefficient tend to increase with n. In addition, the results show that predictions provided by the equation of state are consistent with those coming from MD and catch correctly the trends of each property with n except for the heat capacity. The comparison is next extended to binary mixtures with components differing only in the value of the n parameter and which demonstrate the reliability of the scheme (MX1b) used by Lafitte et al. to deal with this parameter in the SAFT-VR equation of state. In addition, a new empirical one-fluid approximation of the n parameter is proposed thanks to MD simulations, which very favorably compare with the one-fluid model on n previously proposed in the literature. The consistency of this approximation is addressed by making use of it in combination with the SAFT-VR Mie equation of state. It is shown that using such an approach, which is easier to handle than the MX1b one, yields slightly improved results compared to those of the MX1b.
Nonhomogeneous shear flow in concentrated liquid-crystalline solutions
Authors: Green Micah J. , Brown Robert A. , Armstrong Robert C.
Published: November 2007

The dynamics of concentrated solutions of rodlike molecules in nonhomogeneous shear flow are explored using a consistent numerical simulation of the Doi diffusion equation and the nonhomogeneous Onsager model of excluded-volume rod interactions. Simulations of planar, wall-driven shear flow show that out-of-plane structure instabilities occur when nematic anchoring constraints at the boundaries are removed. A new composite state with misaligned logrolling and flow-aligning domains is observed for pressure-driven flow in a planar channel. These results mark the first use of the Doi diffusion equation to show how a nonhomogeneous flow field generates sharp inter-domain interfaces analogous to those observed in rheological experiments.
Realization of Π-type attenuator using Ti(N) thin films for the fourth generation of mobile telecommunications
Authors: Cuong Nguyen Duy , Yoon Soon-Gil , Kim Dong-Jin
Published: November 2007

The performances of 20dB and 25W Π-type attenuators prepared using Ti(N) thin film resistors on AlN substrates were investigated at applied frequencies of 3 and 6GHz. An attenuation and voltage standing wave ratio (VSWR) were significantly improved by a design of L∕W (length/width) ratios of main resistor R2. The chip design with L∕W ratio of 3.0 was observed as an optimal condition for the attenuators. The attenuator prepared at L∕W of 3.0 shows the attenuation tolerance of 1.10dB and VSWR of 1.21 at an applied frequency of 6GHz.
High quality factor gigahertz frequencies in nanomechanical diamond resonators
Authors: Gaidarzhy Alexei , Imboden Matthias , Mohanty Pritiraj , Rankin Janet , Sheldon Brian W.
Published: November 2007

We report actuation and detection of gigahertz-range resonance frequencies in nanocrystalline diamond mechanical resonators. High order transverse vibration modes are measured in coupled-beam resonators exhibiting frequencies up to 1.441GHz. The cantilever-array design of the resonators translates the gigahertz-range resonant motion of micron-long cantilever elements to the displacement of the central supporting structure. Use of nanocrystalline diamond further increases the frequency compared to single crystal silicon by a factor of 3. High clamping losses usually associated with micron-sized straight beams are suppressed in the periodic geometry of our resonators, allowing for high quality factors exceeding 20 000 above 500MHz.
Resistive internal kink modes in a differentially rotating cylindrical plasma
Authors: Mikhailovskii A. B. , Lominadze J. G. , Galvão R. M. O. , Churikov A. P. , Erokhin N. N. , Konovalov S. V. , Smolyakov A. I. , Tsypin V. S.
Published: November 2007

The resistive internal kink modes in a differentially rotating cylindrical plasma column are studied. It is shown that the Velikhov effect, which causes the magnetorotational instability in astrophysics, contributes to the magnetic hill/well and thereby enhances or suppresses these modes, depending on the character of radial profile of the rotation frequency. It is pointed out that, in the case of unfavorable rotation frequency profile, such a rotation-induced magnetic hill can exceed the hill effect due to the plasma pressure gradient. Under this condition, there appears a new variety of resistive-interchange modes, which are referred to as rotational modes. On the other hand, for a favorable rotation frequency profile, the Velikhov effect suppresses the resistive-interchange modes. These results concern the m>1 modes, where m is the poloidal mode number. In the case of perturbations with m=1, the favorable rotation frequency profile leads to decreasing the growth rate of the reconnecting mode.