bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between hydrothermal activity and axial magma chamber distribution, depth, and melt content
Authors: Baker Edward T.
Published: June 2009

Hydrothermal activity, especially high‐temperature discharge, is commonly thought to require the presence of an axial magma chamber (AMC), but this association has not been examined systematically. The availability of six lengthy (170–560 km) ridge sections with continuous surveys of both AMCs and hydrothermal plumes now makes it possible to quantitatively compare the distribution and intensity of hydrothermal activity to AMC extent, depth, and, at a few locations, melt content. These six ridge sections span spreading rates from 55 to 145 mm/a and total 20 second‐order segments. At the section (multisegment) scale the linear incidence of hydrothermal plumes increases with AMC incidence (AMCI, r2 = 0.64), excluding the hot spot–affected Galápagos spreading center. For all six sections, plume incidence increases as AMC depth below the seafloor decreases (AMCZ, r2 = 0.66). At the second‐order segment scale, plume incidence is poorly correlated with both AMCI (r2 = 0.12) and AMCZ (r2 = 0.25). Finally, at the subsegment, or local, scale (0.75‐km‐long bins), plume intensity increases as AMCZ shallows (r2 = 0.85). Of bins where plumes are most intense and thus closest to their seafloor sources, 68 ± 13% lie directly over an AMC, as do at least 37 of the 40 known high‐temperature vent fields. The data also allow tests of other hypotheses linking AMC properties and hydrothermal activity. Existing data, though still sparse, do not support the hypothesis that lenses of melt‐rich magma preferentially support vigorous, long‐lasting venting. Also, the suggestion that increased hydrothermal cooling within a segment locally depresses AMCZ finds no support within any ridge section. Evidence for magma bodies is much scarcer on slow spreading ridges, but the data are nevertheless consistent with those from faster ridges. Observations from all spreading rates thus demonstrate that high‐temperature vent fields are almost universally associated with the presence or inference of magma; “hot rock” or other nonmagmatic heat sources are insufficient.
A repeating secondary source of infrasound from the Wells, Nevada, earthquake sequence
Authors: Arrowsmith Stephen J. , Burlacu Relu , Whitaker Rod , Randall George
Published: June 2009

The Wells, Nevada, earthquake of February 21, 2008, generated a complex seismo‐acoustic wavefield. Epicentral infrasound was recorded at 5 seismo‐acoustic arrays in Nevada, Utah, and Wyoming. In addition to epicentral infrasound, the earthquake triggered a secondary source of infrasound at the BGU array in Utah, which was also triggered by subsequent aftershocks. By applying simple constraints on the propagation of seismic and infrasound waves, we show that the secondary source is an isolated peak (‘Floating Island’) that appears to efficiently generate infrasound through the interaction with seismic surface waves. This hypothesized source location is broadly consistent with crosswind directions extracted from the Ground‐to‐Space (G2S) atmospheric model (for the appropriate time and source/receiver locations), although modeling the propagation of infrasound predicts this source location to be within the so‐called ‘zone‐of‐silence’. In contrast to epicentral infrasound, secondary infrasound associated with the Wells, Nevada, earthquake sequence appears to be local to each array (i.e., not observed at multiple arrays). Secondary infrasonic arrivals observed at BGU are much higher in amplitude than epicentral arrivals, highlighting the importance of being able to clearly identify and separate epicentral and secondary arrivals for infrasonic event discrimination.
Extended winter Pacific North America oscillation as a precursor of the Indian summer monsoon rainfall
Authors: Peings Y. , Douville H. , Terray P.
Published: June 2009

In spite of considerable efforts, long‐range forecasting of Indian summer monsoon rainfall (ISMR) is still a challenge for both statistical and dynamical tools. We highlight the winter‐to‐spring Pacific North America (PNA) oscillation as a predictor for the ISMR. A PNA‐related index is proposed that is highly correlated with the following summer precipitation over India and is also a precursor of El Niño‐Southern Oscillation (ENSO) events over recent decades. The PNA index compares well with other predictors used in operational statistical models for ISMR prediction. A multiple linear regression scheme is tested with a cross‐validation hindcast approach and confirms the added value of our predictor, at least over the period 1958–2005. Nevertheless, the predictor shows less skill over the first half of the 20th century. Possible physical mechanisms of this teleconnection are also briefly discussed and could involve both a tropical Pacific sea surface temperature and Eurasian snow cover pathway.
Height resolved ozone hole structure as observed by the Global Ozone Monitoring Experiment–2
Authors: van Peet J. C. A. , van der A R. J. , de Laat A. T. J. , Tuinder O. N. E. , König‐Langlo G. , Wittig J.
Published: June 2009

We present Global Ozone Monitoring Experiment‐2 (GOME‐2) ozone profiles that were operationally retrieved with the KNMI Ozone ProfilE Retrieval Algorithm (OPERA) algorithm for the period September–December 2008. It is shown that it is possible to accurately measure the vertical distribution of stratospheric ozone for Antarctic ozone hole conditions from spectra measured at ultraviolet wavelengths from a nadir viewing instrument. Comparisons with ozone sonde observations from the Neumayer station at the Antarctic coast show a good agreement for various ozone profile shapes representing different phases of the annual recurring ozone hole cycle. A preliminary analysis of the three‐dimensional structure of the ozone hole shows for example that at the vortex edges ozone rich mid‐latitude middle and upper stratospheric layers can be found over ozone depleted lower stratospheric ‘ozone hole’ layers. These Antarctic ozone profile observations combined with the daily global coverage of GOME‐2 enables the monitoring of the three‐dimensional structure of the ozone hole on a daily basis.
Association of phyllosilicates and the inverted channel in Miyamoto crater, Mars
Authors: Marzo G. A. , Roush T. L. , Lanza N. L. , McGuire P. C. , Newsom H. E. , Ollila A. M. , Wiseman S. M.
Published: June 2009

The western floor of the Miyamoto crater in Sinus Meridiani on Mars exhibits both geomorphic and spectral evidence for aqueous history. It contains a sinuous and narrow ridge that is interpreted to be an inverted channel and is suggestive of past fluvial activity. Phyllosilicates occur in materials that are proximal to the paleochannel, but are not detected on top the ridge. The simultaneous use of the spectroscopic data, high‐resolution images, and a digital elevation model show that Fe/Mg‐smectites are exposed by erosion. They are associated with polygonally‐fractured bedrock which occurs on the slopes of both sides of the sinuous ridge. The observations provide direct evidence of the presence of water and possibly of multiple aqueous events throughout the area.
Ligand recognition by A‐class Eph receptors: crystal structures of the EphA2 ligand‐binding domain and the EphA2/ephrin‐A1 complex
Authors: Himanen Juha P , Goldgur Yehuda , Miao Hui , Myshkin Eugene , Guo Hong , Buck Matthias , Nguyen My , Rajashankar Kanagalaghatta R , Wang Bingcheng , Nikolov Dimitar B
Published: June 2009

Ephrin (Eph) receptor tyrosine kinases fall into two subclasses (A and B) according to preferences for their ephrin ligands. All published structural studies of Eph receptor/ephrin complexes involve B‐class receptors. Here, we present the crystal structures of an A‐class complex between EphA2 and ephrin‐A1 and of unbound EphA2. Although these structures are similar overall to their B‐class counterparts, they reveal important differences that define subclass specificity. The structures suggest that the A‐class Eph receptor/ephrin interactions involve smaller rearrangements in the interacting partners, better described by a ‘lock‐and‐key’‐type binding mechanism, in contrast to the ‘induced fit’ mechanism defining the B‐class molecules. This model is supported by structure‐based mutagenesis and by differential requirements for ligand oligomerization by the two subclasses in cell‐based Eph receptor activation assays. Finally, the structure of the unligated receptor reveals a homodimer assembly that might represent EphA2‐specific homotypic cell adhesion interactions.
Enhanced Weight Loss With Pramlintide/Metreleptin: An Integrated Neurohormonal Approach to Obesity Pharmacotherapy
Authors: Ravussin Eric , Smith Steven R. , Mitchell Julie A. , Shringarpure Reshma , Shan Kevin , Maier Holly , Koda Joy E. , Weyer Christian
Published: June 2009

The neurohormonal control of body weight involves a complex interplay between long‐term adiposity signals (e.g., leptin), and short‐term satiation signals (e.g., amylin). In diet‐induced obese (DIO) rodents, amylin/leptin combination treatment led to marked, synergistic, fat‐specific weight loss. To evaluate the weight‐lowering effect of combined amylin/leptin agonism (with pramlintide/metreleptin) in human obesity, a 24‐week, randomized, double‐blind, active‐drug‐controlled, proof‐of‐concept study was conducted in obese or overweight subjects (N = 177; 63% female; 39 ± 8 years; BMI 32.0 ± 2.1 kg/m2; 93.3 ± 13.2 kg; mean ± s.d.). After a 4‐week lead‐in period with pramlintide (180 µg b.i.d. for 2 weeks, 360 µg b.i.d. thereafter) and diet (40% calorie deficit), subjects achieving 2–8% weight loss were randomized 1:2:2 to 20 weeks of treatment with metreleptin (5 mg b.i.d.), pramlintide (360 µg b.i.d.), or pramlintide/metreleptin (360 µg/5 mg b.i.d.). Combination treatment with pramlintide/metreleptin led to significantly greater weight loss from enrollment to week 20 (−12.7 ± 0.9%; least squares mean ± s.e.) than treatment with pramlintide (−8.4 ± 0.9%; P < 0.001) or metreleptin (−8.2 ± 1.3%; P < 0.01) alone (evaluable, N = 93). The greater reduction in body weight was significant as early as week 4, and weight loss continued throughout the study, without evidence of a plateau. The most common adverse events with pramlintide/metreleptin were injection site events and nausea, which were mostly mild to moderate and decreased over time. These results support further development of pramlintide/metreleptin as a novel, integrated neurohormonal approach to obesity pharmacotherapy.
Basal and Fasting/Refeeding‐regulated Tissue Levels of Endogenous PPAR‐α Ligands in Zucker Rats
Authors: Izzo Angelo A. , Piscitelli Fabiana , Capasso Raffaele , Marini Pietro , Cristino Luigia , Petrosino Stefania , di Marzo Vincenzo
Published: June 2009

N‐oleoylethanolamine (OEA) and N‐palmitoylethanolamine (PEA) are endogenous lipids that activate peroxisome proliferator–activated receptor‐α with high and intermediate potency, and exert anorectic and anti‐inflammatory actions in rats, respectively. We investigated OEA and PEA tissue level regulation by the nutritional status in lean and obese rats. OEA and PEA levels in the brainstem, duodenum, liver, pancreas, and visceral (VAT) or subcutaneous (SAT) adipose tissues of 7‐week‐old wild‐type (WT) and Zucker rats, fed ad libitum or following overnight food deprivation, with and without refeeding, were measured by liquid chromatography–mass spectrometry. In WT rats, duodenal OEA, but not PEA, levels were reduced by food deprivation and restored by refeeding, whereas the opposite was observed for OEA in the pancreas, and for both mediators in the liver and SAT. In ad lib fed Zucker rats, PEA and OEA levels were up to tenfold higher in the duodenum, slightly higher in the brainstem, and lower in the other tissues. Fasting/refeeding‐induced changes in OEA levels were maintained in the duodenum, liver, and SAT, and lost in the pancreas, whereas fasting upregulated this compound also in the VAT. The observed changes in OEA levels in WT rats are relevant to the actions of this mediator on satiety, hepatic and adipocyte metabolism, and insulin release. OEA dysregulation in Zucker rats might counteract hyperphagia in the duodenum, but contribute to hyperinsulinemia in the pancreas, and to fat accumulation in adipose tissues and liver. Changes in PEA levels might be relevant to the inflammatory state of Zucker rats.
Eleven‐year Prevalence Trends of Obesity in Greek Children: First Evidence that Prevalence of Obesity Is Leveling Off
Authors: Tambalis Konstantinos D. , Panagiotakos Demosthenes B. , Kavouras Stavros A. , Kallistratos Achilles A. , Moraiti Ioanna P. , Douvis Stavros J. , Toutouzas Pavlos K. , Sidossis Labros S.
Published: June 2009

We examined 11‐year (1997–2007) trends in underweight, overweight, and obesity in Greek children. Population data derived from a yearly, school‐based health survey carried out between 1997 and 2007 in >80% of all Greek schools. Height and weight measurements from 651,582 children, aged 8–9 years (boys: 51.2%) were analyzed. The gender‐ and age‐specific BMI cutoff points by the International Obesity Task Force (IOTF) were used in order to define underweight, normal weight, overweight, and obesity. Trend analysis showed an increase in the prevalence of obesity from 7.2 ± 0.2% in 1997 to 11.3 ± 0.2% in 2004 for girls (P < 0.001) and from 8.1 ± 0.2% in 1997 to 12.3 ± 0.2% in 2004 for boys (P < 0.001). An apparent leveling off in obesity rates was observed during 2004–2007 for both boys and girls. The prevalence of overweight rose between 1997 and 2007 from 20.2 ± 0.2% to 26.7 ± 0.2% for girls (P < 0.001) and from 19.6 ± 0.2% to 26.5 ± 0.2% for boys (P < 0.001). The overall prevalence of thinness in the same period remained constant in both sexes. The presented population‐based data revealed that the prevalence of overweight and obesity among 8‐ to 9‐year‐old Greek children is alarmingly elevated, with the overweight rates rising continuously. However, an apparent leveling off in obesity rates for the past 4 consecutive years was documented for the first time in both genders.
Structural and Functional Alterations of Subcutaneous Small Resistance Arteries in Severe Human Obesity
Authors: Grassi Guido , Seravalle Gino , Scopelliti Francesco , Dell'Oro Raffaella , Fattori Luca , Quarti‐Trevano Fosca , Brambilla Gianmaria , Schiffrin Ernesto L. , Mancia Giuseppe
Published: June 2009

Obese persons are at increased cardiovascular risk and exhibit increased arterial stiffness and impaired endothelial function of large‐ and medium‐size arteries. We hypothesized that normotensive subjects suffering from severe obesity would also present remodeling and endothelial dysfunction of small resistance arteries. A total of 16 lean (age: 49.6 ± 2.9 years, BMI: 22.9 ± 0.3 kg/m2, mean ± s.e.m.) and 17 age‐matched severely obese (BMI: 41.1 ± 2.3 kg/m2) normotensive subjects were investigated. None had glucose or lipid metabolic abnormalities except for insulin resistance. Resistance arteries, dissected from abdominal subcutaneous tissue, were assessed on a pressurized myograph. For superimposable blood pressure, the media thickness, media cross‐sectional area (CSA), and media‐to‐lumen ratio values of resistance arteries were markedly and significantly greater in obese compared to lean subjects (media thickness 26.3 ± 0.6 vs. 16.2 ± 0.6 µm, CSA 22,272 ± 1,339 vs. 15,183 ± 1,186 µm2, and media‐to‐lumen ratio 0.113 ± 0.006 vs. 0.059 ± 0.001, respectively, P < 0.01). Acetylcholine‐induced relaxation was impaired in vessels from obese subjects compared to the lean individuals (−40.4 ± 1.3%, P < 0.01), whereas endothelium‐independent vasorelaxation was similar in all groups. Stiffness of small arteries as assessed by the stress/strain relationship was similar in lean and severely obese subjects. We conclude that severe human obesity is associated with profound alterations in structural and functional characteristics of small arteries, which may be responsible for the presence of elevated cardiovascular risk and increased incidence of coronary, cerebrovascular and renal events reported in obesity.
Skeletal muscle metabolic recovery following submaximal exercise in chronic heart failure is limited more by O2 delivery than O2 utilization
Authors: Kemps Hareld M.C. , Prompers Jeanine J. , Wessels Bart , De Vries Wouter R. , Zonderland Maria L. , Thijssen Eric J.M. , Nicolay Klaas , Schep Goof , Doevendans Pieter A.F.M.
Published: June 2009

CHF (chronic heart failure) is associated with a prolonged recovery of skeletal muscle energy stores following submaximal exercise, limiting the ability to perform repetitive daily activities. However, the pathophysiological background of this impairment is not well established. The aim of the present study was to investigate whether muscle metabolic recovery following submaximal exercise in patients with CHF is limited by O2 delivery or O2 utilization. A total of 13 stable CHF patients (New York Heart Association classes II–III) and eight healthy subjects, matched for age and BMI (body mass index), were included. All subjects performed repetitive submaximal dynamic single leg extensions in the supine position. Post-exercise PCr (phosphocreatine) resynthesis was assessed by 31P-MRS (magnetic resonance spectroscopy). NIRS (near-IR spectroscopy) was applied simultaneously, using the rate of decrease in HHb (deoxygenated haemoglobin) as an index of post-exercise muscle re-oxygenation. As expected, PCr recovery was slower in CHF patients than in control subjects (time constant, 47±10 compared with 35±12 s respectively; P=0.04). HHb recovery kinetics were also prolonged in CHF patients (mean response time, 74±41 compared with 44±17 s respectively; P=0.04). In the patient group, HHb recovery kinetics were slower than PCr recovery kinetics (P=0.02), whereas no difference existed in the control group (P=0.32). In conclusion, prolonged metabolic recovery in CHF patients is associated with an even slower muscle tissue re-oxygenation, indicating a lower O2 delivery relative to metabolic demands. Therefore we postulate that the impaired ability to perform repetitive daily activities in these patients depends more on a reduced muscle blood flow than on limitations in O2 utilization.
Different Levels of 3D: An Evaluation of Visualized Discrete Spatiotemporal Data in Space-Time Cubes
Authors: Kjellin Andreas , Pettersson Lars Winkler , Seipel Stefan , Lind Mats
Published: June 2009

New technologies and techniques allow novel kinds of visualizations and different types of 3D visualizations are constantly developed. We propose a categorization of 3D visualizations and, based on this categorization, evaluate two versions of a space-time cube that show discrete spatiotemporal data. The two visualization techniques used are a head-tracked stereoscopic visualization (‘strong 3D’) and a static monocular visualization (‘weak 3D’). In terms of effectiveness and efficiency the weak 3D visualization is as good as the strong 3D and thus the need for advanced 3D visualizations in these kinds of tasks may not be necessary.
Generics at the Crossroads: Will Europe Lead the Way Forward?
Authors: Gorka Eric
Published: June 2009

The generics industry is at a crossroads. Fundamental growth drivers remain unchanged, and should result in sustained long-term growth. However, growing cost and pricing pressures mean the industry of the future will look very different and the longer term impact of the financial crisis is still unclear. Future industry structure will also be determined by the extent to which genuine competition is allowed to emerge and to overcome the trend towards nationalist protectionist policies. The companies that succeed will be those that excel in four key areas: launches, differentiation, geographic presence and operational excellence. They will implement variations on three basic strategies: leveraging fixed costs/economies of scale, using new technologies and focusing on value products. Although many questions remain to be answered, including the future role of Europe, several global trends are clear, including ongoing industry consolidation and the growing importance of biosimilars. Otherwise, much will depend on developments in the European Union (EU), the world's largest single market. The EU offers an object lesson in the need for political leadership not only from the top but also at the national level, where varying approaches can have make-or-break importance for generic penetration rates and thus for the industry as a whole.
Access to Medicines, Health and Trade
Authors: Lamy Pascal
Published: June 2009

This paper is the written version of the key opening address to the eleventh International Generic Pharmaceutical Alliance Annual Conference that took place in Geneva, Switzerland on 9-10 December 2008 as submitted by the office of Mr Pascal Lamy, Director-General of the World Trade Organisation.
Malaysian Pharmaceutical Industry: Opportunities and Challenges
Authors: Hassali Mohamed Azmi , Yuen Kah Hay , Ibrahim Mohamed Izham Mohamed , Wong Jia Woei , Ng Bee Hong , Ho David Sue San
Published: June 2009

A sound generic pharmaceutical industry is vital for any country in order to increase the access and affordability of pharmaceuticals to the society at large. In this context, the generic pharmaceutical industry in Malaysia is seen as one of the potential manufacturing sectors that contributes not only to the well-being of the population but also in terms of economic output to the nation. However, the viability of the generic pharmaceutical industry in Malaysia is not free from challenges. In this paper, an overview of the Malaysian pharmaceutical industry together with the opportunities and challenges facing the generic market will be discussed.
Pushing the Limits of IP Protection for Pharmaceuticals via the Special 301 Report: The Israel Experience
Authors: Band Tal
Published: June 2009

The paper provides a critical analysis of certain aspects of the Special 301 Report and process, while focusing on the Israel experience. The main argument raised is that both the Special 301 process and its outcome contain serious flaws. It is suggested that the United States Trade Representative's economic ideology bears an important contribution to the formation of such flaws. Such ideology, in the author's opinion, requires modification.
A Follow-On Biological Drug is not a Biogeneric: Lessons from Omnitrope and Valtropin
Authors: Roth Robert I. , Fleischer Nicholas M.
Published: June 2009

Recent years have seen the approvals, more so in the EU than the United States, of follow-on biological drugs. These products have been new formulations of recombinant therapeutic proteins, developed to compete with the marketed originator products. Intended to closely mimic the originator products in terms of chemistry and therapeutic properties, these so-called ‘biosimilar’ products were initially conceived to be developed according to abbreviated development programmes, presumably at a substantial cost savings to both the drug developer and the consumer. With several such products now recently approved, however, it has become clear that their development programmes have been quite extensive and not particularly abbreviated. Accordingly, cost savings to consumers appear to be relatively modest.
On the estimation by Kadomtsev of coefficients of turbulent transport in magnetized plasma
Authors: Nedospasov A. V.
Published: June 2009

The behavior of plasma in magnetic field is, as a rule, defined by nonlinear interaction of numerous oscillations and exhibits a complex turbulent pattern. Such state of plasma cannot described by linear and quasilinear theories. This paper reflects on the history of studying turbulence in magnetized plasma. In 1964, Kadomtsev (1928–1998) suggested [B. B. Kadomtsev, Vopr. Teor. Plazmy 4, 188 (1964)] that for estimation of coefficients of turbulent transport of plasma across the magnetic field, only the results of linear approximation of plasma instabilities can be used. Examples of experimental validation of the suggested approach, in particular regarding properties of turbulent positive column of discharge in a strong magnetic field, of ionization turbulence of weakly ionized plasma in crossed E, H, fields, and of turbulence of wall plasma in tokamaks, are discussed.
Studies of chlorine-oxygen plasmas and evidence for heterogeneous formation of ClO and ClO2
Authors: Guha Joydeep , Donnelly Vincent M.
Published: June 2009

Plasma and surface diagnostics of Cl2/O2 mixed-gas inductively coupled plasmas are reported. Using trace rare gas optical emission spectroscopy and Langmuir probe analysis, electron temperatures (Te) and number densities for Cl atoms (nCl), electrons (ne), and positive ions were measured as a function of percent O2 in the feed gas and position in the plasma chamber. Adsorbates on and products desorbing from a rotating anodized aluminum substrate exposed to the plasma were detected with an Auger electron spectrometer and a quadrupole mass spectrometer. Te and ne increased with increasing percent O2 in the plasma, while nCl fell off with O2 addition in a manner reflecting simple dilution. Cl atom recombination probabilities (γCl) were measured and were found to be a nearly constant 0.036±0.007 over the range of Cl2/O2 mixing ratios and Cl coverage. Large yields of ClO and ClO2 were found to desorb from the surface during exposure to the plasma, ascribed predominantly to Langmuir–Hinshelwood reactions between adsorbed O and Cl.
Hugoniot and spall strength measurements of porous aluminum
Authors: Kraus Richard G. , Chapman David J. , Proud William G. , Swift Damian C.
Published: June 2009

Plate impact experiments were performed on 14% porous aluminum samples to measure the principal Hugoniot and the spall strength. The principal Hugoniot was measured by performing multiple experiments at a range of flyer velocities, from 0.25–0.89 km/s, leading to incident shock pressures in the target from 0.6–4.8 GPa. The shock compaction data were compared to a theoretical Hugoniot determined from a Mie–Grüneisen equation of state and was found to agree very well over the stress range investigated. Spall strength measurements were performed on the 14% porous aluminum samples at impactor velocities of 0.224, 0.230, and 0.306 km/s. Spall strengths of 78±8, 55±28, and 36±7 MPa, respectively, were measured for the porous Al samples. This is thought to be the first measurement of spall strength in a shock compacted porous ductile material.
Enhanced field emission of vertically aligned core-shelled carbon nanotubes with molybdenum oxide encapsulation
Authors: Yu J. , Sow C. H. , Wee Andrew T. S. , Chua Daniel H. C.
Published: June 2009

The field emission characteristics of the core-shelled nanostructures obtained by directly coating molybdenum oxide onto vertically aligned multiwalled carbon nanotubes (MWNTs) was investigated. A metal-organic chemical vapor deposition technique was used with Mo(CO)6 as the precursor and films deposited at process temperatures of 200, 400, and 700 °C. X-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray diffraction were used to study and understand the material properties of the deposited coatings. Enhanced field emission performance was observed for molybdenum oxide coated MWNT samples at 400 °C with a turn-on field of 1.33 V μm−1 and a field enhancement factor β estimated to be ∼7000. The enhanced performance may be due to both the shape of the coated emitters and a decrease in the effective barrier height.
Computing the performance of an air bearing in humid conditions
Authors: Kirpekar Sujit , Ruiz Oscar
Published: June 2009

We present a rigorous approach to simulating air bearings in disk drives in the presence of humidity. The approach presented here involves a modification of the Reynolds equation and is fundamentally different from that reported in the literature so far. The current method takes into consideration the condensation of water vapor due to super saturation and subsequent drying of the air as it reaches the trailing end. This approach provides better agreement with experimental data than the previous methods. Results based on drive level tests are presented for air bearing at various temperatures.
Calculation of rovibronic intensities for triatomic molecules in double-Renner-degenerate electronic states: Application to the X̃ A2″ and Ã A2′ electronic states of HO2
Authors: Melnikov Vladlen V. , Jensen Per , Hirano Tsuneo
Published: June 2009

An algorithm and a computer program implementing it are presented for calculation of the rovibronic intensities for a triatomic molecule in a “double-Renner-degenerate” electronic state. The program has been applied to investigate, by theoretical simulation, the absorption spectrum of HO2 in the X̃ A2″ and Ã A2′ electronic states. The spectrum simulations are based on potential energy functions, electric dipole moment functions, and electric dipole transition moment functions constructed from ab initio values calculated at the core-valence MR-SDCI+Q/[cc-pVQZ (H), aug-cc-pCVQZ (O)] level of theory.
Effects of selenization conditions on densification of Cu(In,Ga)Se2 (CIGS) thin films prepared by spray deposition of CIGS nanoparticles
Authors: Ahn SeJin , Kim Ki Hyun , Yun Jae Ho , Yoon Kyung Hoon
Published: June 2009

Spray deposited porous CIGS nanoparticle-derived thin films were selenized in a two zone rapid thermal annealing furnace and effects of various selenization parameters including Se evaporation temperature, flow rate of carrier gas, and substrate temperature on densification of the CIGS layers were investigated. It was found that higher Se supply to CIGS nanoparticles either by increasing Se evaporation temperature or by increasing the flow rate of carrier gas resulted in larger CIGS grains with higher degree of crystallinity, while it also induced formation of a thicker MoSe2 layer in-between CIGS and Mo which resulted in partial detachment of CIGS/MoSe2/Mo layers from the glass substrate. Densification of CIGS layer by growth of nanoparticles and formation of thick MoSe2 were explained by a liquid Se assisted reaction rather than by a vapor phase Se assisted reaction.
Ferroelectric hysteresis and aging effect analysis in multiferroic Pb(Fe0.5Nb0.5)O3 ceramics
Authors: Font R. , Raymond O. , Martinez E. , Portelles J. , Siqueiros J. M.
Published: June 2009

Ferroelectric hysteresis and aging effects in multiferroic Pb(Fe0.5Nb0.5)O3 ceramics obtained through different precursors are discussed using the hysteresis loop modeling by equivalent circuit. Maximum polarization Pmax, remanent polarization Pr, and coercive field EC as functions of external electric fields are determined. A comparative analysis of Pmax, Pr, and EC parameters obtained from the full and remanent hysteresis loops is presented and correlated with a previous structural, morphological, and small signal dielectric frequency-temperature response study using the impedance spectroscopy technique. Three contributions to the full hysteresis were identified: first, a dipolar contribution; second, space charge movement; and third, orientation of the switchable ferroelectric domains. The smaller contribution of the switchable ferroelectric domains, in contrast to the high polarizability of the compound, is explained by assuming that the grains have a complex inner polydomain structure with a distribution of submicrometric sizes and random orientations. Differences in the dielectric hysteresis and aging behavior between the PFN samples obtained through different precursors are established according to their morphological features and their domain structure inside the grains.
Tuning magnetization dynamic properties of Fe–SiO2 multilayers by oblique deposition
Authors: Phuoc Nguyen N. , Xu Feng , Ong C. K.
Published: June 2009

The static and dynamic magnetic properties of Fe–SiO2 multilayers fabricated onto Si(100) substrates by a radio frequency sputter-deposition system are investigated as functions of deposition angle and Fe thickness. By changing the oblique deposition angle, one can effectively tune the ferromagnetic resonance frequency from 1.7 to 3.5 GHz. In addition, the frequency linewidth is significantly changed with the oblique deposition angle when the Fe layer is thick, but it is almost constant in the case of small Fe thickness.
Effect of Cu contamination on recombination of O atoms on a plasma-oxidized silicon surface
Authors: Guha Joydeep , Khare Rohit , Stafford Luc , Donnelly Vincent M. , Sirard Stephen , Hudson Eric A.
Published: June 2009

In the dual damascene microelectronics integration scheme during the last stage of plasma etching of dielectrics down to underlying Cu layers, Cu is sputtered onto the reactor walls and is believed to cause a drift in etching rates. For photoresist etching in an O2-containing plasma, a drop in etching rate suggests that Cu could cause a decrease in the O-atom concentration in the plasma, due perhaps to an increase in the O recombination rate on the chamber walls. We therefore studied the effects of traces of Cu on O recombination on an oxygen plasma-conditioned surface, using the spinning wall technique. With this method, a cylindrical substrate, here coated in situ with sputter-deposited Si and then oxidized in an O2 plasma, is rotated past skimmers, allowing the surface to be periodically exposed to the plasma and an Auger electron spectrometer with a pressure gauge in a differentially pumped chamber. Between plasma exposures, the sample could also be dosed with Cu from an evaporation source in a differentially pumped chamber. With no Cu on the surface, a pressure rise was observed in the Auger chamber, due to desorption of recombined O2. These measurements were used to derive a Langmuir–Hinshelwood recombination coefficient of γO=0.043 for the steady-state oxidized Si, Cu-free surface. The surface was then coated with a small fraction of a monolayer (roughly ∼0.002 monolayers of Cu with a dose of ∼1.4×1013 cm−2 and an assumed sticking coefficient of 0.3) and γO was found to increase to 0.069. Further dosing with Cu did not produce any further increases in γO. The initial low γO value could not be recovered by coating the surface with sputter Si, apparently due to rapid outdiffusion of Cu through Si at room temperature. Cu catalyzed recombination of O is ascribed to a redox cycling between Cu+ and Cu2+ oxidation states.
Mesoscale description of an asymmetric lamellar phase
Authors: Kumaran V.
Published: June 2009

The relationship between the parameters in a description based on a mesoscale free energy functional for the concentration field and the macroscopic properties, such as the bending and compression moduli and the permeation constant, are examined for an asymmetric lamellar phase where the mass fractions of the hydrophobic and hydrophilic parts are not equal. The difference in the mass fractions is incorporated using a cubic term in the free energy functional, in addition to the usual quadratic and quartic terms in the Landau–Ginsburg formulation. The relationship between the coefficient of the cubic term and the difference in the mass fractions of the hydrophilic and hydrophobic parts is obtained. For a lamellar phase, it is important to ensure that the surface tension is zero due to symmetry considerations. The relationship between the parameters in the free energy functional for zero surface tension is derived. When the interface between the hydrophilic and hydrophobic parts is diffuse, it is found that the bending and compression moduli, scaled by the parameters in the free energy functional, do increase as the asymmetry in the bilayer increases. When the interface between the hydrophilic and hydrophobic parts is sharp, the scaled bending and compression moduli show no dependence on the asymmetry in the bilayer. The ratio of the permeation constant in between the water and bilayer in a molecular description and the Onsager coefficient in the mesoscale description is O(1) for both sharp and diffuse interfaces and it increases as the difference in the mass fractions is increased.
The metal-insulator transition in vanadium dioxide: A view at bulk and surface contributions for thin films and the effect of annealing
Authors: Yin W. , West K. G. , Lu J. W. , Pei Y. , Wolf S. A. , Reinke P. , Sun Y.
Published: June 2009

Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO2 thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition. In the analysis of the VO2 films, bulk-sensitive methods [x-ray diffraction (XRD) and transport measurements] and surface sensitive techniques [photoelectron spectroscopy (PES) and scanning tunneling microscopy and spectroscopy] were employed. The samples were subjected to heating cycles with annealing temperatures of up to 425 and 525K. Prior to annealing the VO2 films exhibit the transition from the monoclinic to the tetragonal phase with the concurrent change in conductivity by more than a factor of 103 and their phase purity is confirmed by XRD. Annealing to 425K and thus cycling across the metal-insulator transition (MIT) temperature has no impact on the bulk properties of the VO2 film but the surface undergoes irreversible electronic changes. The observation of the valence band with PES during the annealing illustrates that the surface adopts a partially metallic character, which is retained after cooling. Annealing to a higher temperature (525K) triggers a modification of the bulk, which is evidenced by a considerable reduction in the MIT characteristics, and a degradation in crystallite morphology. The local measurement of the conductivity with scanning tunneling spectroscopy shows the transition of the surface from predominantly semiconducting surface prior to annealing to a surface with an overwhelming contribution from metallic sections afterward. The spatial distribution of metallic regions cannot be linked in a unique manner to the crystallite size or location within the crystallites. The onset of oxygen depletion at the surface is held responsible for this behavior. The onset of bulk modification at higher temperatures is most likely linked to oxygen loss and effusion along the grain boundaries and concurrent onset of sintering. Our study focuses on the comparison of the MIT in the bulk and at the surface of thin VO2 layers and establishes an irreversible modification of the crystallite structure and surface for temperatures exceeding the MIT. The surface modification impacts on the strategies which will be employed to build the metallic contacts to VO2 layers.
Tunneling transport and spectroscopy in carbon nanotube quantum dots
Authors: Logan David E. , Galpin Martin R.
Published: June 2009

This paper provides a theoretical description of sequential tunneling transport and spectroscopy, in carbon nanotube quantum dots weakly tunnel coupled to metallic leads under a voltage bias. The effects of Coulomb blockade charging, spin-orbit fine structure, and orbital- and spin-Zeeman effects arising from coupling to applied magnetic fields are considered; and the dependence of the conductance upon applied gate voltage, bias voltage, and magnetic fields is determined. The work is motivated by recent experiments on ultraclean carbon nanotube dots [Kuemmeth et al., Nature (London) 452, 448 (2008)], to which comparison is made.
Cyclotron frequency multiplication in Cherenkov backward-wave oscillators
Authors: Savilov A. V.
Published: June 2009

In relativistic Cherenkov backward-wave oscillators, the output radiation is usually formed by a forward wave, which arises due to reflection of the operating backward wave from the input end of the operating waveguide. In this paper, we propose to use the resonant cyclotron absorption of this forward wave as a way to produce the secondary, stimulated cyclotron radiation at a multiplied frequency and a high cyclotron harmonic. Along with the “simple” cyclotron resonance, the high-frequency wave can be emitted also in the regime of a combined resonance caused by nonresonant cyclotron interaction of electrons with the backward low-frequency wave. Existence of combined resonances helps provide the frequency synchronization, as well as to improve the electron-wave interaction at the multiplied frequency.
Virial coefficients of Lennard-Jones mixtures
Authors: Schultz Andrew J. , Kofke David A.
Published: June 2009

We report results of calculations of the second through sixth virial coefficients for four prototype Lennard-Jones (LJ) mixtures that have been the subject of previous studies in the literature. Values are reported for temperatures ranging from T=0.6 to T=10.0, where here the temperature is given units of the LJ energy parameter of one of the components. Thermodynamic stability of the mixtures is studied using the virial equation of state (VEOS) with the calculated coefficients, with particular focus on characterizing the vapor-liquid critical behavior of the mixtures. For three of the mixtures, vapor-liquid coexistence and critical data are available for comparison at only one temperature, while for the fourth we can compare to a critical line. We find that the VEOS provides a useful indication of the presence and location of critical behavior, although in some situations we find need to consider “near-miss” critical behavior, where the classical conditions of criticality are nearly but not exactly satisfied.
An exactly solvable model of hierarchical self-assembly
Authors: Dudowicz Jacek , Douglas Jack F. , Freed Karl F.
Published: June 2009

Many living and nonliving structures in the natural world form by hierarchical organization, but physical theories that describe this type of organization are scarce. To address this problem, a model of equilibrium self-assembly is formulated in which dynamically associating species organize into hierarchical structures that preserve their shape at each stage of assembly. In particular, we consider symmetric m-gons that associate at their vertices into Sierpinski gasket structures involving the hierarchical association of triangles, squares, hexagons, etc., at their corner vertices, thereby leading to fractal structures after many generations of assembly. This rather idealized model of hierarchical assembly yields an infinite sequence of self-assembly transitions as the morphology progressively organizes to higher levels of the hierarchy, and these structures coexists at dynamic equilibrium, as found in real hierarchically self-assembling systems such as amyloid fiber forming proteins. Moreover, the transition sharpness progressively grows with increasing m, corresponding to larger and larger loops in the assembled structures. Calculations are provided for several basic thermodynamic properties (including the order parameters for assembly for each stage of the hierarchy, average mass of clusters, specific heat, transition sharpness, etc.) that are required for characterizing the interaction parameters governing this type of self-assembly and for elucidating other basic qualitative aspects of these systems. Our idealized model of hierarchical assembly gives many insights into this ubiquitous type of self-organization process.
Spectroscopic study on the structural isomers of 7-azaindole(ethanol)n (n=1–3) and multiple-proton transfer reactions in the gas phase
Authors: Sakota Kenji , Komure Noriyuki , Ishikawa Wataru , Sekiya Hiroshi
Published: June 2009

The resonance-enhanced two-photon ionization (RE2PI) and laser-induced fluorescence excitation spectra were recorded for the S1-S0(ππ∗) region of the 7-azaindole(ethanol)n (n=1–3) [7AI(EtOH)n (n=1–3)] clusters in the gas phase to investigate the geometrical structures and the multiple-proton/hydrogen atom transfer reaction dynamics. Four and two structural isomers were identified for 7AI(EtOH)2 and 7AI(EtOH)3, respectively. Density functional theory calculations at the B3LYP/6-31++G∗∗/6-31G∗ level predicted four different conformations of the ethyl group for 7AI(EtOH)2, in good agreement with the observation of the four structural isomers in the RE2PI spectra. Visible fluorescence from the tautomeric forms was observed in the S1 states for all isomers of 7AI(EtOH)2, but no sign of double-proton/hydrogen atom transfer and quadruple-proton/hydrogen atom transfer has been obtained in the electronic spectra of 7AI(EtOH)1 and 7AI(EtOH)3, respectively. These results suggest that the multiple-proton transfer reaction is cluster-size selective, and the triple-proton/hydrogen atom transfer potential is dominated by the cyclic hydrogen-bonded network in 7AI(EtOH)2. The excitation of the in-phase intermolecular stretching vibration prominently enhances the excited-state triple-proton/hydrogen atom transfer reaction.
Heat capacities of freely evaporating charged water clusters
Authors: Sundén A. E. K. , Støchkel K. , Panja S. , Kadhane U. , Hvelplund P. , Nielsen S. Brøndsted , Zettergren H. , Dynefors B. , Hansen K.
Published: June 2009

We report on evaporation studies on positively charged water clusters (H+(H2O)N) and negatively charged mixed clusters (X−(H2O)N) with a small core ion X (X=O2, CO3, or NO3), in the size range N=5–300. The clusters were produced by corona discharge in ambient air, accelerated to 50 keV and mass selected by an electromagnet. The loss of monomers during the subsequent 3.4 m free flight was recorded. The average losses are proportional to the clusters’ heat capacities and this allowed the determination of size-dependent heat capacities. The values are found to increase almost linearly with clusters size for both species, with a rate of 6kB–8kB per added molecule. For clusters with N<21 the heat capacities per molecule are lower but the incremental increase higher. For N>21 the values are intermediate between the bulk liquid and the solid water 0 °C values.
Molecular dynamics study of polymer conformation as a function of concentration and solvent quality
Authors: Zhou Zhongwu , Daivis Peter J.
Published: June 2009

A coarse-grained model for molecular dynamics simulations of polymer solutions with variable solvent quality is proposed. This model allows solvent quality to be varied over the whole range from very poor to very good solvent conditions by varying a single parameter. The model has several advantages. All interactions are short ranged and repulsive, making the model very computationally efficient compared with other explicit solvent models that include the long-ranged attractive part of the interactions; the solvent is included explicitly, ensuring that the theta condition corresponds to a genuine cancellation of the solvent-mediated polymer-polymer interactions; and hydrodynamic interactions and entanglement can occur for all solvent conditions. The theta point is determined and the conformational properties of a 50-bead chain system are investigated over the whole concentration range from the dilute limit to the melt as a function of solvent quality.