bluuebunny/crossref_metadata_2025 huggingface dataset:
Permafrost distribution from BTS measurements (Sierra de Telera, Central Pyrenees, Spain): assessing the importance of solar radiation in a mid‐elevation shaded mountainous area
Authors: Julián Asunción , Chueca Javier
Published: March 2007

Permafrost distribution was predicted from measurements of basal temperatures of the winter snow cover using a GIS‐based empirical–statistical modelling approach in a mid‐elevation mountainous area, the northern slope of the Sierra de Telera (central Pyrenees, Spain). A total of 223 basal temperature of snow (BTS) measurements were made over 3 years and a multiple linear regression analysis was performed to model the relationship between BTS measurements and three predictor variables: May solar radiation, elevation and snow‐cover persistence. The snow‐cover persistence factor proved non‐significant and was excluded from the final regression analysis. The model used was statistically significant, and predicted permafrost distribution moderately well (K = 0.52) and with an overall accuracy of 0.79. The results show the importance of solar radiation as an explanatory variable for permafrost conditions in a mid‐elevation mountain area with steep topography. Copyright © 2007 John Wiley & Sons, Ltd.
Effects of processing on all‐optical poling characteristics of guest‐host azo‐dye polymer thin films
Authors: Tan Jing , Li Ai‐Dong , Fan Xi‐Zhi , Liu Wen‐Chao , Xu Zu‐Xun , Lin Yang , Wang Hui‐Tian , Wu Di , Ming Naiben
Published: March 2007

Several kinds of azo‐dye polymer films of the guest‐host system were prepared by the spin‐coating method. Four disperse red (DR) dyes of DR1, DR19, DR54 and DR73 were chosen as second order nonlinear optical active chromophores with polymer matrixes such as poly (methyl methacrylate) PMMA or polycarbonate (PC). The processing conditions such as heat‐treatment, substrate, and film storage condition on all‐optical poling characteristics of azopolymers have been investigated. It is found that the second harmonic generation intensity is very sensitive to the chromophores and processing parameters. Some explanations have been proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The vulnerable nanoscale dielectric
Authors: Stoneham Marshall , Gavartin Jacob , Muñoz Ramo David , Shluger Alexander
Published: March 2007

It was the wide‐gap insulating oxide that made silicon the semiconductor of choice, to such a degree that silicon technology has transformed our lives. Its roles of surface passivation and as a lithographic material are essential, but its role as the gate dielectric is especially sophisticated. Even though challenged by newer materials, like HfO2, the silicon dioxide dielectric will be around for some time. We discuss some of the key defect processes in these oxides in materials context. What materials must work alongside silicon? To what extent do silica glasses share properties with the gate dielectric oxide? And are there new phenomena to exploit? To illustrate and partially address some of these issues we present and compare the results of calculations of the properties of oxygen vacancies in SiO2, HfO2 and HfSiO4. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral response of Au–Ti Schottky barrier on semi‐insulating GaAs
Authors: Ghita R. V. , Logofatu C. , Negrila C. , Cotirlan C. , Ghita P. , Manea A. S. , Lazarescu M. F.
Published: March 2007

For the fabrication of the rectifying contact, respectively the Schottky diode structure on semi‐insulating GaAs (100) oriented, Cr‐doped, with a resistivity of ρ ∼ 106–107 Ω cm we have used Au–Ti contact. The Ti contact was deposited on a plasma etched GaAs surface in high vacuum (10–8 torr), Au was deposited in medium vacuum (10–6 torr) and the Au–Ti/GaAs interface was formed by a rapid thermal annealing procedure at T = 320 – 360 °C in low vacuum (10–1 torr). The representative I –V characteristics in dark and under illumination at different power levels are presented. It is worth to mention that we estimate a barrier height of ΦB ∼ 0.84 V (in the frame of thermionic emission model). The spectral response at two operating points and at different temperatures is presented. The signal has a maximum in the Δλ range (850–950) nm, which corresponds to the generation of photo‐carriers due to a band‐to‐band direct transition. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ion beam synthesis of 4H‐(Si1–xC1–y)Gex +y solid solutions
Authors: Pezoldt J. , Kups Th. , Voelskow M. , Skorupa W.
Published: March 2007

4H silicon carbide (Si1–x C1–y )Gex +y solid solutions with an average Ge incorporation on lattice sites ranging from 0.7 to 2.5 percent were formed by ion beam synthesis. RBS and RBS/C investigations revealed a decreasing Ge lattice incorporation with increasing implantation dose above 10%. The carried out rapid thermal annealing at 1300 °C reduces the residual damage, increases the lattice site occupation and led to negligible change in the concentration profiles. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarized far infrared magnetoplasmon reflectivity of doped CdxMn1–xTe semimagnetic semiconductor in the Voigt configuration
Authors: Shayesteh S. Farjami , Hidari M.
Published: March 2007

Calculations of the p‐polarized far infrared magnetoplasmon reflectivity of semimagnetic semiconductor Cdx Mn1–x Te doped ternary alloy in the presence of a magnetic field parallel to the surface of the sample (the Voigt geometry) are used to investigate magnetoplasmon and zone center optical phonon frequencies. It is assumed that the sample is characterized by a dielectric tensor in which the optical phonon contribution and free carriers (plasmon and cyclotron response) are included. The results show that the transverse optical phonon mode is sensitive to the alloy composition, x, and can be used to determine the value of x. The longitudinal optical phonon frequencies are shifted due to phonon‐plasmon coupling in doped samples. Also, the influence of composition on the vibrational modes in zinc blende Cdx Mn1–x Te is described within a modified random element isodisplacement (MREI) approach. By indicating the plasmon and cyclotron frequencies from p‐polarized reflectivity spectra and the Voigt permittivity, we calculated the carrier concentration and the effective masses of the carriers. Furthermore, we indicate the frequencies of the phonons at the Γ, K, X and L high symmetry points of the Brillouin zone based on a microscopic second‐neighbor rigid ion model (RIM). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of fretting corrosion in machine elements
Authors: Kowal A. , Strzelecki S.
Published: March 2007

Heavy duty machines, which are applied in coal mines, operate at extremely heavy environmental conditions. Their technological process of operation is characterised by variable loads during mining or transport which makes it necessary for these machines to have very high durability. In some cases, the operation of machine elements can be interrupted by failure. The reasons for such failures may be various.

The machine's vibration generates relative micro displacements. After a comparatively short period of operation, the wear occurs on the surfaces of connected machine elements. This type of wear results from the occurrence of a complex phenomenon called fretting.

There are different types of fretting, such as fretting‐fatigue, fretting‐wear, fretting‐adhesion and fretting‐corrosion. The last one is a special kind of machine element damage occurring on the surfaces of contacting elements loaded by pressure and simultaneously subjected to relative and small oscillation movements. Fretting is generated on condition that there exists a displacement between two contacting surfaces, the amplitude of which ranges from a few to tens of micrometres. Furthermore, some number of slip cycles and the normal load are indispensable. It is possible to find the expression for the dependence determining the amplitude of oscillation movements in the joint between two machine elements.

The paper describes the mechanism and analysis of fretting corrosion, gives some examples of surface destruction and presents the amplitude of oscillation movements as well as the results of investigations into fretting in the cylindrical joints, e.g. pin joints applied in heavy duty conditions in coal mines such as in the case of suspension of hoisting devices. Copyright © 2007 John Wiley & Sons, Ltd.
Influence of cylinder‐on‐plate or block‐on‐ring sliding configurations on friction and wear of pure and filled engineering polymers
Authors: Samyn P. , De Baets P. , Keresztes R. , Zsidai L. , Kalacska G. , Kislinder E. , Kozma M.
Published: March 2007

Polyamides, polyesters and polyacetals are often used in line contacts under reciprocating or continuous sliding. These contacts are simulated on cylinder‐on‐plate (COP) or block‐on‐ring (BOR) tribotests. Comparative tests for pure, oil‐filled and solid lubricated polymers at 100N and 0.3m/s are presented for relative material classification. Differences are discussed according to the sliding geometries. Thermal effects dominate friction and wear behaviour: the polymer glass transition temperature is exceeded in COP tests while the temperature is lower in BOR tests. Thick and brittle films are observed for pure polymers in BOR tests, promoting higher friction. The test configuration is mainly important for evaluation of internal lubricants. The efficiency of oil‐lubricated polymers is not demonstrated in COP tests, while solid lubricants are not efficient in BOR tests. Deformation restricts the diffusion of oil lubricants in COP tests while solid lubricants are deposited on the polymer surface rather than being incorporated in the transfer film in BOR tests. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of Sirolimus Treatment on Gene Expression in Renal Transplant Patients
Authors: Vickers Kasey , Mitra Rahul , Kapoor Mini , Kahan Barry , Morrisett Joel D.
Published: March 2007

Background

Sirolimus (rapamycin), a strong immunosuppressive agent, is administered to renal transplant patients to prevent rejection. The rapamycin signaling pathway [mammalian target of rapamycin (mTOR)] has been implicated in transcriptional regulation.

Methods

We used high‐density oligonucleotide human microarrays to evaluate the effects of sirolimus treatment on gene expression in renal transplant patients. With this technique, we assessed selected genes in the rapamycin signaling, immunosuppression, insulin signaling, and triglyceride metabolism pathways.

Results

Filtered data from both treated and untreated patients showed variability within each group. Significant fold changes were observed in genes from the immunosuppression and insulin signaling pathways but not the rapamycin signaling pathway. The triglyceride metabolism pathway revealed a significant reduction of message levels in lipoprotein and triglyceride synthesis genes.

Conclusions

These results show that using oligonucleotide microarrays to analyze the effects of sirolimus treatment in patients with renal transplant is an effective way to evaluate gene message levels in multiple pathways.
Ultra violet sensors based on nanostructured ZnO spheres in network of nanowires: a novel approach
Authors: Hullavarad SS , Hullavarad NV , Karulkar PC , Luykx A , Valdivia P
Published: March 2007

The ZnO nanostructures consisting of micro spheres in a network of nano wires were synthesized by direct vapor phase method. X-ray Photoelectron Spectroscopy measurements were carried out to understand the chemical nature of the sample. ZnO nanostructures exhibited band edge luminescence at 383 nm. The nanostructure based ZnO thin films were used to fabricate UV sensors. The photoresponse measurements were carried out and the responsivity was measured to be 50 mA W−1. The rise and decay time measurements were also measured.
Histone deacetylase inhibitors suppress natural killer cell cytolytic activity
Authors: Ogbomo Henry , Michaelis Martin , Kreuter Jörg , Doerr Hans Wilhelm , Cinatl Jindrich
Published: March 2007

Treatment of transformed cells from leukemia or solid tumors with histone deacetylase inhibitors (HDACi) was shown to increase their sensitivity to NK cell lysis. In this study, treatment of IL‐2‐activated NK cells with HDACi including suberoylanilide hydroxamic acid and valproic acid was studied. Both drugs at therapeutic concentrations inhibited NK cell cytotoxicity on human leukemic cells. This inhibition was associated with decreased expression and function of NK cell activating receptors NKp46 and NKp30 as well as impaired granule exocytosis. NFκB activation in IL‐2‐activated NK cells was inhibited by both HDACi. Pharmacologic inhibition of NFκB activity resulted in similar effects on NK cell activity like those observed for HDACi. These results demonstrate for the first time that HDACi prevent NK cytotoxicity by downregulation of NK cell activating receptors probably through the inhibition of NFκB activation.
Upregulation of the TGFβ signalling pathway by Bcr‐Abl: Implications for haemopoietic cell growth and chronic myeloid leukaemia
Authors: Møller Gigi M.O. , Frost Victoria , Melo Junia V. , Chantry Andrew
Published: March 2007

Chronic myeloid leukaemia (CML) is a myeloproliferative disorder characterized by uncontrolled growth of progenitor cells expressing the tyrosine kinase fusion gene product, Bcr‐Abl. At present, little is known regarding how TGFβ, and downstream Smad transcription factors, influence CML cell proliferation in the context of Bcr‐Abl expression. Here we show that ectopic Bcr‐Abl expression dramatically increases TGFβ/Smad‐dependent transcriptional activity in Cosl cells, and that this may be due to enhancement of Smad promoter activity. Bcr‐Abl expressing TF‐1 myeloid cells are more potently growth arrested by TGFβ compared to the parental TF‐1 cell line. Additionally, growth of Bcr‐Abl‐expressing CD34+ cells from chronic phase CML patients is inhibited by TGFβ and, interestingly, treatment of a non‐proliferating CD34+ CML cell sub‐population with the TGFβ kinase inhibitor SB431542 enhanced cell death mediated by the Bcr‐Abl inhibitor imatinib. Our data suggest that the expression of Bcr‐Abl leads to hyper‐responsiveness of myeloid cells to TGFβ, and we hypothesise that this novel cross‐regulatory mechanism might play an important role in maintaining the transformed progenitor cell population in CML.
STAT1 regulates p73‐mediated Bax gene expression
Authors: Soond Surinder M. , Carroll Christopher , Townsend Paul A. , Sayan Emre , Melino Gerry , Behrmann Iris , Knight Richard A. , Latchman David S. , Stephanou Anastasis
Published: March 2007

Although signal transducer and activator of transcription 1 (STAT1) mediated regulation of p53 transcription and apoptosis has been previously reported, modulation of other members of the p53 family of transcription factors remains poorly understood. In this study, we found that STAT1 and TA‐p73 can interact directly and that p73‐mediated Bax promoter activity was observed to be reduced by STAT1 expression in a p53‐independent manner for which STAT1 Tyrosine‐701 and Serine‐727 are key residues. This study presents the first report physically linking STAT1 and TA‐p73 signalling and highlights the modulation of the Bax promoter in the context of IFN‐γ stimulation.
(−)‐Epigallocatechin gallate suppresses endothelin‐1‐induced interleukin‐6 synthesis in osteoblasts: Inhibition of p44/p42 MAP kinase activation
Authors: Tokuda Haruhiko , Takai Shinji , Hanai Yoshiteru , Matsushima-Nishiwaki Rie , Hosoi Takayuki , Harada Atsushi , Ohta Toshiki , Kozawa Osamu
Published: March 2007

We previously showed that endothelin‐1 (ET‐1) stimulates the synthesis of interleukin‐6 (IL‐6), a potent bone resorptive agent, in osteoblast‐like MC3T3‐E1 cells, and that protein kinase C (PKC)‐dependent p44/p42 mitogen‐activated protein (MAP) kinase plays a part in the IL‐6 synthesis. In the present study, we investigated the effect of (−)‐epigallocatechin gallate (EGCG), one of the major flavonoids containing in green tea, on ET‐1‐induced IL‐6 synthesis in osteoblasts and the underlying mechanism. EGCG significantly reduced the synthesis of IL‐6 stimulated by ET‐1 in MC3T3‐E1 cells as well primary cultured mouse osteoblasts. SB203580, a specific inhibitor of p38 MAP kinase, but not SP600125, a specific SAPK/JNK inhibitor, suppressed ET‐1‐stimulated IL‐6 synthesis. ET‐1‐induced phosphorylation of p38 MAP kinase was not affected by EGCG. On the other hand, EGCG suppressed the phosphorylation of p44/p42 MAP kinase induced by ET‐1. Both the IL‐6 synthesis and the phosphorylation of p44/p42 MAP kinase stimulated by 12‐O‐tetradecanoylphorbol 13‐acetate (TPA), a direct activator of PKC, were markedly suppressed by EGCG. The phosphorylation of MEK1/2 and Raf‐1 induced by ET‐1 or TPA were also inhibited by EGCG. These results strongly suggest that EGCG inhibits ET‐1‐stimulated synthesis of IL‐6 via suppression of p44/p42 MAP kinase pathway in osteoblasts, and the inhibitory effect is exerted at a point between PKC and Raf‐1 in the ET‐1 signaling cascade.
Midwives in the UK: An Exploratory Study of Providing Newborn Feeding Support for Postpartum Mothers in the Hospital
Authors: Furber Christine M. , Thomson Ann M.
Published: March 2007

Our objective was to explore English midwives' views and experiences of supporting mothers with feeding their newborn baby. Grounded theory methodology was used. Data were collected using in‐depth interviews from 30 midwives in the North of England. Data were analyzed using constant comparison techniques. Midwives were theoretically sampled for interview from a pool of volunteers recruited from a poster promoting the study in the clinical areas. Overall, hospital midwives felt that they did not have enough time to support mothers with feeding their neonate. To cope with these time constraints, midwives developed practices of rationing the time that they spent with mothers, and the rationing of resources available to mothers, to help them process mothers through the hospital services. These practices have important implications for the success of breastfeeding in hospitals as the practices by providers who are assigned to help breastfeeding initiation described here may inhibit the breastfeeding process.
Women's Perspectives on Maternity Services in Sweden: Processes, Problems, and Solutions
Authors: Hildingsson Ingegerd , Thomas Jan E.
Published: March 2007

Most measures of health care quality focus on medical outcomes rather than patients' assessments of quality. Drawing on data from a national survey of Swedish women, this study describes women's opinions about what is important to them during pregnancy and birth. This qualitative study is based on responses of 827 pregnant women to an open question completed in the second trimester. In total, 2061 separate statements were analyzed. Using content analysis, these statements were clustered into 4 themes: desirable characteristics of midwife, prenatal care during pregnancy, care during labor and birth, and care after birth. Within those themes, 13 categories were found. Findings suggest areas for improvement in maternity services including: the timing and length of prenatal visits, making parent education classes available to all women, prelabor visits to the maternity ward, continuous information about the progress of labor, flexibility in time of discharge, and postpartum support for families. Women also stated that characteristics of the midwife, such as being supportive, friendly, attentive, respectful, and nonjudgemental, were important. A patient‐centered and individualized approach, with women and their partners as the subjects rather than the objects of care, would increase satisfaction and the overall quality of maternity services in Sweden.
An Update on Vicarious Liability for Certified Nurse‐Midwives/Certified Midwives
Authors: Booth Joseph W.
Published: March 2007

The unique placement of midwives in the health care industry prompts renewed consideration of vicarious liability. Generally, vicarious liability is the liability of an employer for an employee's actions. A review of recent case law over the past decade shows limited case activity and indicates that the certified nurse‐midwife/certified midwife (CNM/CM) roles do not create vicarious liability risks different from any other employee/agent. The lack of case law signals a lack of dispute over vicarious liability, not a lack of liability. Absent unique statutory provisions, which may be in effect in a minority of states, an employer of a CNM/CM is as liable for the midwife's negligence committed in the scope of their employment as employers are generally liable for an employee's negligence. When there is no employment/agency relationship, vicarious liability does not apply. A collaborative practice agreement is a good example of a nonemployment arrangement. Proper contractual documentation of relationships and comprehensive professional liability coverage are necessary to manage this form of liability.
Survey of Connecticut Nurse‐Midwives
Authors: Holland Margaret L. , Holland Eliza S.
Published: March 2007

Descriptive data on nurse‐midwifery income, workload, job definitions, employment benefits, and clinical practices are limited. Information about nurse‐midwifery practice today is important for the growth of the profession and for future policy initiatives. A survey of nurse‐midwives in Connecticut was conducted in 2005. This article reports state‐specific data about income, workload, job definitions, employment benefits, and clinical issues, such as vaginal birth after cesarean. Full‐time midwives in Connecticut worked an average of 77 hours per week, had a mean salary of $79,554, and 87% had on‐call responsibilities. A “typical” Connecticut midwife had an “average” full‐time work week consisting of two 24‐hour call days and three 7‐hour office days, seeing 19 to 24 patients per office day. Most held Master of Science in Nursing degrees, worked in physician‐owned practices, and attended births in hospitals or medical centers. Health insurance, paid sick time, and retirement plans were offered to most respondents. Almost all respondents provide gynecologic, antepartum, and postpartum care, but few offer newborn care. There is significant variation in restrictions on midwives offering vaginal birth after cesarean and on length of scheduled appointments. Data on expanded practices, such as first‐assisting caesarean sections and endometrial biopsies, are reported for the first time.
PARTICIPATION RATES AND THE DIFFERENCE IN PERFORMANCE OF WOMEN AND MEN IN CHESS
Authors: BILALIĆ MERIM , MCLEOD PETER
Published: March 2007

The superiority of men over women in chess has been cited as evidence that there are fundamental differences in male and female intelligence (Howard, 2005a, 2006; Irwing & Lynn, 2005). An alternative interpretation of the difference is that it is due to differential male and female participation rates in chess (Charness & Gerchak, 1996; Bilalić & McLeod, 2006; Chabris & Glickman, in press). This has been dismissed by Howard (2006) on the grounds that changes in the difference in skill level between top male and female players in recent years are not correlated with changing relative participation rates. Here it is shown that Howard’s analysis is misleading. The data are consistent with differential participation rates as the explanation of the gap between the performance of women and men in chess.
Controlled Pilot Development Unit‐Scale Fed‐Batch Cultivation of Yeast on Spruce Hydrolysates
Authors: Rudolf Andreas , Lequeux Gaspard , Lidén Gunnar
Published: March 2007

Yeast production on hydrolysate is a likely process solution in large‐scale ethanol production from lignocellulose. The hydrolysate will be available on site, and the yeast has furthermore been shown to acquire an increased inhibitor tolerance when cultivated on hydrolysate. However, due to over‐flow metabolism and inhibition, efficient yeast production on hydrolysate can only be achieved by well‐controlled substrate addition. In the present work, a method was developed for controlled addition of hydrolysate to PDU (process development unit)‐scale aerobic fed‐batch cultivations of Saccharomyces cerevisiae TMB 3000. A feed rate control strategy, which maintains the ethanol concentration at a low constant level, was adapted to process‐like conditions. The ethanol concentration was obtained from on‐line measurements of the ethanol mole fraction in the exhaust gas. A computer model of the system was developed to optimize control performance. Productivities, biomass yields, and byproduct formation were evaluated. The feed rate control worked satisfactorily and maintained the ethanol concentration close to the setpoint during the cultivations. Biomass yields of 0.45 g/g were obtained on added hexoses during cultivation on hydrolysate and of 0.49 g/g during cultivation on a synthetic medium with glucose as the carbon source. Exponential growth was achieved with a specific growth rate of 0.18 h−1 during cultivation on hydrolysate and 0.22 h−1 during cultivation on glucose.
Cross‐shore sediment transport on natural beaches and its relation to sandbar migration patterns: 2. Application of the field transport parameterization
Authors: Mariño‐Tapia I. J. , O'Hare T. J. , Russell P. E. , Davidson M. A. , Huntley D. A.
Published: March 2007

A cross‐shore sediment transport parameterization (shape function) based on data from intensive field experiments carried out on five European beaches is incorporated into a simple time dependent model to explore its capability for reproducing sandbar generation and evolution in the medium term (O(months)). Model results are compared with bar‐crest migration patterns observed at Duck, North Carolina. The model comprises a simple wave transformation routine that accounts for linear shoaling and assumes a saturation law for wave decay inside the surf zone. Second‐order statistics derived from the cross‐shore distribution of wave heights are used to scale the sediment transport parameterizations which estimate the cross‐shore structure of the third and fourth velocity moments. Cross‐shore gradients in sediment fluxes, calculated with an energetics approach, produce bed elevation changes. The updated morphology affects the wave propagation in the next time step forming a fully coupled model for predicting sandbar evolution. Bar generation close to shore and the details of the sandbar evolution are successfully reproduced (R2 = 0.86) over the 77‐day period of the observations using default values for drag coefficients and efficiency factors. In accordance with the observations, the model shows rapid offshore sandbar migration in response to individual storms, and weak onshore bar movement for lower energy conditions. Owing to its simple nature, the model is not capable of reproducing the whole profile morphology especially in the trough (no trough generation), and it is only valid for replicating bar crest position. The results suggest that a convergence of sediment near the breakpoint (breakpoint hypothesis) combined with morphological feedback, can successfully explain the evolution of bar crest over periods of months from the details of forcing (incident waves and water levels).
Validation of Global Ozone Monitoring Experiment ozone profiles and evaluation of stratospheric transport in a global chemistry transport model
Authors: de Laat A. T. J. , Landgraf J. , Aben I. , Hasekamp O. , Bregman B.
Published: March 2007

This paper presents a validation of Global Ozone Monitoring Experiment (GOME) ozone (O3) profiles which are used to evaluate stratospheric transport in the chemistry transport model (CTM) Tracer Model version 5 (TM5) using a linearized stratospheric O3 chemistry scheme. A comparison of GOME O3 profile measurements with independent O3 sonde measurements at midlatitudes shows an excellent agreement. Differences are smaller than 5%, well within the uncertainty of the O3 sonde measurements. Within the tropics, the GOME O3 profile differences are larger, with a clear lower stratospheric negative O3 bias with compensating positive biases in the troposphere and higher stratosphere. The TM5 model with linearized O3 chemistry simulates realistic lower and middle stratospheric spatial and temporal O3 variations on both short (daily) and long (seasonal) timescales. Model stratospheric O3 is significantly overestimated in the extratropics and slightly underestimated in the tropics, as is also shown in a comparison with Total Ozone Mapping Spectrometer total O3 column measurements. This model bias predominantly occurs in the lower stratosphere and is present throughout the year, albeit with seasonal variations: The bias is larger during local winter compared with local summer. The particular spatial and seasonal variations of the model bias suggest a too fast meridional stratospheric transport in TM5, which agrees with earlier found shortcomings of using winds from data assimilation systems. The model results are very sensitive to the data assimilation method in the numerical weather prediction that provides the model wind fields. A large reduction (up to 50% of the bias) in modeled lower stratospheric midlatitude O3 was found when winds from four‐dimensional instead of three‐dimensional data assimilation were used. Previous work has shown that using different forecast periods was important for improving the age of air. Model results differed with different forecast periods (up to 3 days), although the effect was mainly confined to high‐latitude lower stratospheric O3. Apparently, using different forecast periods is more important for age‐of‐air calculations than for stratospheric O3 calculations. A positive bias in the extratropical lower stratosphere of about 20% remained, possibly related to the lack of heterogeneous polar stratospheric O3 destruction in TM5.
Phase transitions and aging phenomena in dielectriclike polymeric materials investigated by ac measurements
Authors: D’Angelo P. , Barra M. , Nicodemi M. , Cassinese A.
Published: March 2007

We study the glassy phase of a thin polydimethylsiloxane film by high sensitivity dielectric measurements. We can locate its glass and melting transition temperatures and discuss its aging properties and frequency dependencies. Our data are framed into the general picture of glassy phenomena and compared, in particular, to the so called universal dielectric response model of frequency dispersion. The effect of a dc bias is also analyzed.
Physics of internal transport barrier of toroidal helical plasmas
Authors: Itoh K. , Toda S. , Fujisawa A. , Itoh S.-I. , Yagi M. , Fukuyama A. , Diamond P. H. , Ida K.
Published: March 2007

The role of zonal flows (ZFs) in the formation of an internal transport barrier in a toroidal helical plasma is analyzed. The turbulent transport coefficient is shown to be suppressed when the plasma state changes from the branch of a weak negative radial electric field to the strong positive one. This new transition of turbulent transport is caused by the change of the damping rate of the ZFs. It is clearly demonstrated, theoretically and experimentally, that the damping rate of the ZFs governs the global confinement of toroidal plasmas.
New 2+1 dimensional nonisospectral Toda lattice hierarchy
Authors: Gordoa P. R. , Pickering A. , Zhu Z. N.
Published: March 2007

We give a new 2+1 dimensional nonisospectral generalization of the Toda lattice hierarchy. Reductions yield a variety of new integrable hierarchies along with their underlying linear problems, including new 1+1 dimensional differential-delay hierarchies (nonisospectral and isospectral), new ordinary differential-delay hierarchies, and new discrete Painlevé hierarchies. We also show that a reduction in components yields our previously obtained 2+1 dimensional nonisospectral Volterra lattice hierarchy.
Remote transfer of ultrastable frequency references via fiber networks
Authors: Foreman Seth M. , Holman Kevin W. , Hudson Darren D. , Jones David J. , Ye Jun
Published: March 2007

Three distinct techniques exist for distributing an ultrastable frequency reference over optical fibers. For the distribution of a microwave frequency reference, an amplitude-modulated continuous wave (cw) laser can be used. Over kilometer-scale lengths this approach provides an instability at 1 s of ∼3×10−14 without stabilization of the fiber-induced noise and ∼1×10−14 with active noise cancellation. An optical frequency reference can be transferred by directly transmitting a stabilized cw laser over fiber and then disseminated to other optical and microwave regions using an optical frequency comb. This provides an instability at 1 s of 2×10−14 without active noise cancellation and 3×10−15 with active noise cancellation [Recent results reduce the instability at 1 s to 6×10−18.] Finally, microwave and optical frequency references can be simultaneously transmitted using an optical frequency comb, and we expect the optical transfer to be similar in performance to the cw optical frequency transfer. The instability at 1 s for transfer of a microwave frequency reference with the comb is ∼3×10−14 without active noise cancellation and <7×10−15 with active stabilization. The comb can also distribute a microwave frequency reference with root-mean-square timing jitter below 16 fs integrated over the Nyquist bandwidth of the pulse train (∼50 MHz) when high-bandwidth active noise cancellation is employed, which is important for remote synchronization applications.
Nonlinear perpendicular propagation of ordinary mode electromagnetic wave packets in pair plasmas and electron-positron-ion plasmas
Authors: Kourakis I. , Verheest F. , Cramer N. F.
Published: March 2007

The nonlinear amplitude modulation of electromagnetic waves propagating in pair plasmas, e.g., electron-positron or fullerene pair-ion plasmas, as well as three-component pair plasmas, e.g., electron-positron-ion plasmas or doped (dusty) fullerene pair-ion plasmas, assuming wave propagation in a direction perpendicular to the ambient magnetic field, obeying the ordinary (O-) mode dispersion characteristics. Adopting a multiple scales (reductive perturbation) technique, a nonlinear Schrödinger-type equation is shown to govern the modulated amplitude of the magnetic field (perturbation). The conditions for modulation instability are investigated, in terms of relevant parameters. It is shown that localized envelope modes (envelope solitons) occur, of the bright- (dark-) type envelope solitons, i.e., envelope pulses (holes, respectively), for frequencies below (above) an explicit threshold. Long wavelength waves with frequency near the effective pair plasma frequency are therefore unstable, and may evolve into bright solitons, while higher frequency (shorter wavelength) waves are stable, and may propagate as envelope holes.
Role of electron temperature on charging of dust grains
Authors: Kausik S. S. , Chakraborty M. , Saikia B. K.
Published: March 2007

Dust grains are produced by evaporation of silver in an experimental setup consisting of a dust chamber, a plasma chamber, and a deflection chamber. Due to differential pressure between the dust and plasma chambers, the dust grains move upward and after passing through plasma they become negatively charged. These charged dust grains are then deflected by a dc field applied across a pair of deflector plates in the deflection chamber. Both from the amount of deflection and also from the floating potential, the number of charges collected on the dust grains is calculated. As the gas pressure is changed, the plasma density and the electron temperature changes. Dust charge is then calculated at each value of pressure from the deflection and floating potential. It is found that the electron temperature has a profound effect in the accumulation of charge on dust grains.
Nonmagnetic indenter-type high-pressure cell for magnetic measurements
Authors: Kobayashi T. C. , Hidaka H. , Kotegawa H. , Fujiwara K. , Eremets M. I.
Published: March 2007

An indenter-type high-pressure cell has been developed for electric and magnetic measurements in low-temperature and high-magnetic-field environments. The maximum pressure achieved at low temperatures is more than 4.5GPa, which is higher than that of a conventional piston-cylinder cell. The typical sample space at maximum pressure is 1.6mm in diameter and approximately 0.7mm in depth, and magnetic measurements such as ac-susceptibility and nuclear magnetic resonance can be performed using a miniature coil. All the components of the indenter cell are made of nonmagnetic materials that have enough thermal conductivity for low-temperature experiments using a He3∕He4 dilution refrigerator. Another indenter-type cell designed for a commercial superconducting quantum interference device magnetometer is also reported.
Collective rotational dynamics in ionic liquids: A computational and experimental study of 1-butyl-3-methyl-imidazolium tetrafluoroborate
Authors: Schröder C. , Wakai C. , Weingärtner H. , Steinhauser O.
Published: March 2007

The aim of this study is the analysis of the rotational motion in ionic liquids, in particular, 1-butyl-3-methyl-imidazolium tetrafluoroborate. By comparing single-particle and collective motion it is found that the Madden-Kivelson relation is fairly fulfilled in long-term simulation studies (>100 ns), i.e., the collective reorientation can be predicted by the corresponding single-particle property and the static dipolar correlation factor, GK. Furthermore, simulated reorientation is in accordance with hydrodynamic theories yielding hydrodynamic radii comparable to van der Waals radii. Since viscosity is the central quantity entering hydrodynamic formulas, we calculated and measured the viscosity of our system in order to have two independent cycles of hydrodynamic evaluation, a computational and an experimental one. While the static dielectric constant agrees with dielectric reflectance experiment, the hydrodynamic radii derived from the experiments are much lower as a consequence of enhanced rotational motion. Even more, a considerable dynamic broadening is observed in the experiments.
Phase diagram and adsorption-desorption kinetics of CO on Ru(0001) from first principles
Authors: McEwen J.-S. , Eichler A.
Published: March 2007

A kinetic lattice gas model is used to study the equilibrium properties and the desorption kinetics of CO on Ru(0001). The authors compute all relevant on-site binding and interaction energies of CO molecules within density functional theory and import them in two different models. The first model allows the CO molecules to adsorb upright on top and hollow sites. The authors calculate the phase diagram, coverage isobars, and temperature programed desorption spectra. Up to a coverage of 1∕3 ML, very good agreement is obtained between theory and experiment when considering top sites only. For coverages beyond 1∕3 ML, hollow sites are included and disagreement between theory and experiment occurs. The second model allows adsorption on top sites only but allows them to tilt and shift from their upright positions. The authors show that this model resolves many of the deficiencies of their first one. Furthermore, the authors demonstrate that this model is more consistent with experiment since it is the only model that is able to explain the results from IR-spectroscopy experiments.
Fragmentation of methyl chloride studied by partial positive and negative ion-yield spectroscopy
Authors: Céolin D. , Piancastelli M. N. , Guillemin R. , Stolte W. C. , Yu S.-W. , Hemmers O. , Lindle D. W.
Published: March 2007

The authors present partial-ion-yield experiments on the methyl chloride molecule excited in the vicinity of the Cl2p and C1s inner shells. A large number of fragments, cations produced by dissociation or recombination processes, as well as anionic species, have been detected. Although the spectra exhibit different intensity distributions depending on the core-excited atom, general observations include strong site-selective fragmentation along the C–Cl bond axis and a strong intensity dependence of transitions involving Rydberg series on fragment size.
Electromagnetic strong plasma turbulence
Authors: Melatos A. , Jenet F. A. , Robinson P. A.
Published: March 2007

The first large-scale simulations of continuously driven, two-dimensional electromagnetic strong plasma turbulence are performed, for electron thermal speeds 0.01c⩽v⩽0.57c, by integrating the Zakharov equations for coupled Langmuir and transverse (T) waves near the plasma frequency. Turbulence scalings and wave number spectra are calculated, a transition is found from a mix of trapped and free T eigenstates for v⩾0.1c to just free eigenstates for v⩽0.1c, and wave energy densities are observed to undergo slow quasiperiodic oscillations.
Simplified self-consistent model for emittance growth in charged beams with mismatched envelopes
Authors: Nunes R. P. , Pakter R. , Rizzato F. B.
Published: March 2007

This paper analyzes the envelope dynamics of magnetically focused, high-intensity charged particle beams. As known, mismatched envelopes decay into equilibrium with simultaneous emittance growth. To describe the emittance growth we develop a simplified self-consistent macroscopic model: emittance is evaluated in a partially analytical way which invokes the beam profile, with self-consistency resulting from the inclusion of the emittance growth into the envelope equation. The model is then compared with full N-particle beam simulations and the agreement is shown to be quite reasonable. The model helps to understand the physics of the problem and is computationally faster than full simulations. Other aspects are discussed in the paper.
Optimization of Fe doping at the regrowth interface of GaN for applications to III-nitride-based heterostructure field-effect transistors
Authors: Lee W. , Ryou J.-H. , Yoo D. , Limb J. , Dupuis R. D. , Hanser D. , Preble E. , Williams N. M. , Evans K.
Published: March 2007

The authors have studied the effects of Fe doping at the interface between GaN epitaxial layers for heterostructure field-effect transistors grown by metal-organic chemical vapor deposition and the corresponding impact on the device characteristics. The epitaxial structures were grown with different Fe-doped GaN layers at the layer-template interface. Analysis of the measured electron and interface charge distributions in the heterostructures demonstrated the important role of Fe doping at the regrowth interface. No charge at the regrowth interface was observed in transistor structures with a thick Fe-doped layer. Characterization of the electrical properties of the transistor structures revealed the presence of high sheet carrier concentrations and improved mobilities with increasing thickness of the Fe-doped GaN layer at the regrowth interface.
Weibel instability with non-Maxwellian distribution functions
Authors: Zaheer S. , Murtaza G.
Published: March 2007

The Weibel instability in an unmagnetized plasma is investigated for non-Maxwellian distribution functions. In particular, analytical expressions are derived for the real and imaginary parts of the dielectric constant for the Maxwellian, kappa (κ), and (r,q) distribution functions under the conditions of ξ=ω∕k‖θ‖⪢1 and ⪡1. The real frequency and the growth rate of the instability now depend upon the values of the spectral indices of the distribution functions. In general, the growth rate is suppressed for small values of κ and q (keeping r fixed) and for negative values of r (keeping q fixed) instability transforms into damping. In the limiting cases (i) κ→∞ and (ii) r=0, q→∞, the results approach to the Maxwellian situation.
Ion-acoustic solitary waves in a relativistic plasma
Authors: Lee Nam C. , Choi Cheong Rim
Published: March 2007

The possibility of an ion-acoustic solitary wave in a relativistic plasma comprised of hot electrons and cold ions is investigated by Sagdeev’s pseudopotential method using a set of fully relativistic two-fluid equations. In the nonrelativistic limit, the general relativistic conditions for the existence of solitary waves found in the present study reduces exactly to the well known expressions for the nonrelativistic conditions. It is found by a graphical method that as the flow velocity of the plasma increases, the shape of the solitary wave becomes sharper and more prominent if the flow velocity is larger than the solitary-wave velocity. In the case in which the flow velocity is smaller than the solitary-wave velocity, however, the solitary wave is more pronounced for smaller flow velocity. It is also found that, for a fixed flow velocity, the sharpness and the height of the solitary wave decrease as the temperature increases as in nonrelativistic plasmas. Unlike in nonrelativistic plasmas, the present study predicts the existence of nonmoving soliton-like electrostatic structures.
Novel quantum mechanical/molecular mechanical method combined with the theory of energy representation: Free energy calculation for the Beckmann rearrangement promoted by proton transfers in the supercritical water
Authors: Takahashi Hideaki , Tanabe Kohsuke , Aketa Masataka , Kishi Ryohei , Furukawa Shin-ichi , Nakano Masayoshi
Published: March 2007

The Beckmann rearrangement of acetone oxime promoted by proton transfers in the supercritical water has been investigated by means of the hybrid quantum mechanical/molecular mechanical approach combined with the theory of energy representation (QM/MM-ER) recently developed. The transition state (TS) structures have been explored by ab initio calculations for the reaction of hydrated acetone oxime on the assumption that the reaction is catalyzed by proton transfers along the hydrogen bonds connecting the solute and the solvent water molecules. Up to two water molecules have been considered as reactants that take part in the proton transfers. As a result of the density functional theory calculations with B3LYP functional and aug-cc-pVDZ basis set, it has been found that participation of two water molecules in the reaction reduces the activation free energy by −12.3kcal∕mol. Furthermore, the QM/MM-ER simulations have revealed that the TS is more stabilized than the reactant state in the supercritical water by 2.7kcal∕mol when two water molecules are involved in the reaction. Solvation free energies of the reactant and the TS have been decomposed into terms due to the electronic polarization of the solute, electron density fluctuation, and others to elucidate the origin of the stabilization of the TS as compared with the reactant. It has been revealed that the promotion of the chemical reaction due to the hydration mainly originates from the interaction between the nonpolarized solute and the solvent water molecules at the supercritical state.
On the use of local diffusion models for path ensemble averaging in potential of mean force computations
Authors: Calderon Christopher P.
Published: March 2007

We use a constant velocity steered molecular dynamics (SMD) simulation of the stretching of deca-alanine in vacuum to demonstrate a technique that can be used to create a surrogate processes approximation (SPA) using the time series that come out of SMD simulations. In this article, the surrogate processes are constructed by first estimating a sequence of local parametric diffusion models along a SMD trajectory and then a single global model is constructed by piecing the local models together through smoothing splines (estimation is made computationally feasible by likelihood function approximations). The SPAs are then “bootstrapped” in order to obtain a plausible range of work values associated with a particular SMD realization. This information is then used to assist in estimating a potential of mean force constructed by appealing to the Jarzynski equality. When this procedure is repeated for a small number of SMD paths, it is shown that the global models appear to come from a single family of closely related diffusion processes. Possible techniques for exploiting this observation are also briefly discussed. The findings of this paper have potential relevance to computationally expensive computer simulations and experimental works involving optical tweezers where it is difficult to collect a large number of samples, but possible to sample accurately and frequently in time.