Very High Frequency (very + high_frequency)

Distribution by Scientific Domains


Selected Abstracts


Atmospheric tides over the Pyrenees: observational study and numerical simulation

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 650 2010
J. Díaz de Argandoña
Abstract Barometric tides around the Pyrenees mountain range are analyzed by means of synoptic surface-station data recorded during one year, surface data from the Pyrenees Experiment (PYREX) and the CRA/LA Very High Frequency (VHF) wind profiler installed in the north of the range. Tides are decomposed into their diurnal and semi-diurnal components. Diurnal tides show a strong non-migrating component and are very dependent on local conditions. Semi-diurnal tides are more homogeneous and present a north,south asymmetry, also noted in the Alps. This cross-range asymmetry could be related to some interference effect caused by the mountain range in the migrating semi-diurnal tide wave. The asymmetry of the diurnal component presents a very strong seasonal variation, probably related to local diabatic effects. A three-month long simulation has been carried out with the National Center for Atmospheric Research's Weather Research and Forecasting (WRF) limited-area model to try to reproduce the tide structure. The validation of the results with wind-profiler data shows reasonable agreement with the observed diurnal tide and poorer results for the semi-diurnal component. At surface level, however, the model reproduces some of the features of the observed semi-diurnal tide, and especially the cross-range asymmetry. Copyright © 2010 Royal Meteorological Society [source]


Quantitative structural damage detection using high-frequency piezoelectric signatures via the reverberation matrix method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2007
W. Yan
Abstract High-frequency structural analysis so far has been a major issue in dynamic analysis, for which many conventional methods such as finite element method and transfer matrix method are unable to perform well. Since the electromechanical impedance technique for structural health monitoring (SHM) operates at very high frequencies, the reverberation matrix method (RMM), which was just developed a few years ago, is employed to study dynamics of the monitored structures, which are bonded with piezoelectric lead zirconate titanate (PZT) patches. A piecewisely homogeneous Euler,Bernoulli beam model is introduced to approximate the non-homogeneous beam and only one-dimensional axial vibration of PZT wafers is considered. The imperfect interfacial bonding between PZT patches and the host beam is investigated based on a shear lag model. Using a hybrid technique combining electromechanical impedance method and RMM, an analytical expression of impedance (or admittance) related to the response of the coupled model of PZT patch-bonding layer-host beam system is derived for SHM. The proposed method is examined by comparing with other theoretical methods as well as by means of a test on an intelligent system using a steel beam with two symmetrically installed PZT wafers. It could be further applied to predicting the dynamics of monitored Timoshenko beams, continuous beams, and framed structures as well. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Tail morphology in the Western Diamond-backed rattlesnake, Crotalus atrox

JOURNAL OF MORPHOLOGY, Issue 8 2008
Alan H. Savitzky
Abstract The shaker muscles in the tails of rattlesnakes are used to shake the rattle at very high frequencies. These muscles are physiologically specialized for sustaining high-frequency contractions. The tail skeleton is modified to support the enlarged shaker muscles, and the muscles have major anatomical modifications when compared with the trunk muscles and with the tail muscles of colubrid snakes. The shaker muscles have been known for many years to consist of three large groups of muscles on each side of the tail. However, the identities of these muscles and their serial homologies with the trunk muscles were not previously known. In this study, we used dissection and magnetic resonance imaging of the tail in the Western Diamond-backed Rattlesnake, Crotalus atrox, to determine that the three largest muscles that shake the rattle are the M. longissimus dorsi, the M. iliocostalis, and the M. supracostalis lateralis. The architecture of these muscles differs from their serial homologs in the trunk. In addition, the rattlesnake tail also contains three small muscles. The M. semispinalis-spinalis occurs in the tail, where it is a thin, nonvibratory, postural muscle that extends laterally along the neural spines. An additional muscle, which derives from fusion of the M. interarticularis inferior and M. levator costae, shares segmental insertions with the M. longissimus dorsi and M. iliocostalis. Several small, deep ventral muscles probably represent the Mm. costovertebrocostalis, intercostalis series, and transversohypapophyseus. The architectural rearrangements in the tail skeleton and shaker muscles, compared with the trunk muscles, probably relate to their roles in stabilizing the muscular part of the tail and to shaking the rattle at the tip of the tail. Based on comparisons with the tail muscles of a colubrid snake described in the literature, the derived tail muscle anatomy in rattlesnakes evolved either in the pitvipers or within the rattlesnakes. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source]


Specificity of staphylococcal phage and SaPI DNA packaging as revealed by integrase and terminase mutations

MOLECULAR MICROBIOLOGY, Issue 1 2009
Carles Ubeda
Summary SaPI1 and SaPIbov1 are chromosomal pathogenicity islands in Staphylococcus aureus that carry tst and other superantigen genes. They are induced to excise and replicate by certain phages, are efficiently encapsidated in SaPI-specific small particles composed of phage virion proteins and are transferred at very high frequencies. In this study, we have analysed three SaPI genes that are important for the phage,SaPI interaction, int (integrase) terS (phage terminase small subunit homologue) and pif (phage interference function). SaPI1 int is required for SaPI excision, replication and packaging in a donor strain, and is required for integration in a recipient. A SaPI1 int mutant, following phage induction, produces small SaPI-specific capsids which are filled with partial phage genomes. SaPIbov1 DNA is efficiently packaged into full-sized phage heads as well as into SaPI-specific small ones, whereas SaPI1 DNA is found almost exclusively in the small capsids. TerS, however, determines DNA packaging specificity but not the choice of large versus small capsids. This choice is influenced by SaPIbov1 gene 12, which prevents phage DNA packaging into small capsids, and which is also primarily responsible for interference by SaPIbov1 with phage reproduction. [source]


Combined exposure to anti-androgens causes markedly increased frequencies of hypospadias in the rat

INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 2 2008
S. Christiansen
Summary The incidence of hypospadias is increasing in young boys, but it remains unclear whether human exposure to endocrine disrupting chemicals plays a role. Risk assessment is based on estimation of no-observed-adverse-effect levels for single compounds, although humans are exposed to combinations of several anti-androgenic chemicals. In a mixture (MIX) study with three androgen receptor antagonists, vinclozolin, flutamide and procymidone, rats were gavaged during gestation and lactation with several doses of a MIX of the three chemicals or the chemicals alone. External malformations of the male reproductive organs were assessed on PND 47 using a score from 0 to 3 (normal to marked) for hypospadias. Markedly increased frequencies were observed after exposure to a MIX of the three chemicals compared to administration of the three chemicals alone. Anogenital distance at PND 1, nipple retention at PND 13, and dysgenesis score at PND 16 were highly correlated with the occurrence of hypospadias, and MIX effects were seen at doses where each of the individual chemicals caused no observable effects. Therefore, the results indicate that doses of anti-androgens, which appear to induce no hypospadias when judged on their own, may induce a very high frequency of hypospadias when they interact in concert with other anti-androgens. [source]


A genetic algorithm and the Monte Carlo method for stochastic job-shop scheduling

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 6 2003
Y. Yoshitomi
Abstract This paper proposes a method for solving stochastic job-shop scheduling problems using a hybrid of a genetic algorithm in uncertain environments and the Monte Carlo method. First, the genetic algorithm in uncertain environments is applied to stochastic job-shop scheduling problems where the processing times are treated as stochastic variables. The Roulette strategy is adopted for selecting the optimum solution having the minimum expected value for makespan. Applying crossover based on Giffler and Thompson's algorithm results in two offspring inheriting the ancestor's characteristics as the operation completion times averaged up to the parent's generation. Individuals having very high frequency through all generations are selected as the good solutions. Second, the Monte Carlo method is effectively used for finding out the approximately optimum solution among these good solutions. [source]


Intra Day Bid-Ask Spreads, Trading Volume and Volatility: Recent Empirical Evidence from the London Stock Exchange

JOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 5-6 2004
Charlie X. Cai
With the benefit of very high frequency (25 million 1 minute observations) and recent data (2001) for the UK, this paper explores a number of intra day patterns of stock market behaviour. More specifically, a distinct reverse J shaped bid-ask spread pattern is noted for SETS securities, a declining bid-ask spread pattern for non-SETS securities, a two hump pattern for trading volume and a U-shaped pattern for returns volatility for all securities. In terms of complementing the existing literature, the paper shows that differences in trading systems may affect the bid-ask spread patterns, while differences in market environments (i.e. US and UK markets) seems to affect the trading volume pattern. The paper suggests avenues for future research, in particular, the need to consider what factors are significant in determining intra day patterns for different trading systems and the need for additional cross-market comparisons to identify how institutional factors affect the behaviour of investors on an intra day basis. [source]


Chronic Atrophic Gastritis and Metachronous Gastric Cancer in Japanese Alcoholic Men With Esophageal Squamous Cell Carcinoma

ALCOHOLISM, Issue 5 2009
Akira Yokoyama
Background:, The risk of metachronous gastric cancer is high in Japanese with esophageal squamous cell carcinoma (SCC), especially in alcoholic men, suggesting a common background underlying the gastric and esophageal cancers. Methods:, Endoscopic follow-up ranging from 7 to 160 months (median, 47 months) after the initial diagnosis was performed in 99 Japanese gastric-cancer-free alcoholic men (56.8 ± 6.4 years) with esophageal SCC detected by an endoscopic screening examination. Chronic atrophic gastritis (CAG) assessed by the serum pepsinogen test and Helicobacter pylori status was compared between 90 of the 99 esophageal SCC cases and 180 age-matched Japanese gastric- and esophageal-cancer-free alcoholic men. Results:, The serum pepsinogen test showed a higher seroprevalence of severe CAG among the cases than among the age-matched controls (35.4% vs. 14.2% for H. pylori -seropositive, 71.4% vs. 7.7% for H. pylori -indeterminate, and 17.1% vs. 9.8% for H. pylori -negative, respectively; H. pylori status-adjusted p = 0.0008), whereas their H. pylori status was similar. The accelerated progression of severe CAG observed in the Japanese alcoholic men with esophageal SCC suggests the existence of common mechanisms by which both esophageal SCC and H. pylori -related severe CAG develop in this population. Metachronous gastric adenocarcinoma was diagnosed in 11 of the 99 gastric-cancer-free patients, and the cumulative rate of metachronous gastric cancer within 5 years was estimated to be 15% according to the Kaplan,Meier method. The age-adjusted hazard ratios were 7.87 (95% confidence interval: 1.43 to 43.46) and 4.84 (1.16 to 20.21), respectively, in the patients with severe CAG in comparison with those without CAG and those without severe CAG. Inactive heterozygous aldehyde dehydrogenase-2, a very strong risk factor for esophageal SCC in the alcoholics, was not associated with an increased risk of metachronous gastric cancer. Conclusions:, Accelerated development of severe CAG at least partially explained the very high frequency of development of metachronous gastric cancer in this population. [source]


A new method used to control the structure of high rate microcrystalline silicon thin films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010
X. D. Zhang
Abstract We report a systematic study of plasma heating effect on microcrystalline silicon (,c-Si:H) deposition. Normally, substrate surface temperature increases with time during a high rate deposition of ,c-Si:H thin film, especially under a high power and high pressure condition. We deposited ,c-Si:H films using a very high frequency discharge under the high pressure and high power condition at a fixed heater temperature or a profiled heater temperature. Raman spectra with different wavelength excitations showed that a proper heater temperature profiling during ,c-Si:H deposition is an effective method to modify the structure of ,c-Si:H films, which can control the structure evolution to form a uniform crystallinity along the growth direction and reduce the amorphous incubation layer thickness (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


High suicidal ideation in persons testing for Huntington's disease

ACTA NEUROLOGICA SCANDINAVICA, Issue 3 2000
T-B. Robins Wahlin
This study examined the first participants who registered for the Huntington's disease predictive testing program 1990,1995 in Stockholm, Sweden. A psychosocial investigation was performed to evaluate potential effects of the presymptomatic testing. The results showed no significant differences between 13 genecarriers and 21 noncarriers in pretest attitudes, expectations, general well-being, life satisfaction and lifestyle, the need for support, estimated sense of well-being or degree of health. However, both groups showed high suicidal ideation and self-injurious behavior. Noncarriers had a very high frequency of attempted suicide, and both groups had similarly pronounced psychiatric dysfunction. Their relatives also had high frequencies of psychiatric diseases, suicide or suicidal attempts. Most of the participants had a desire to meet a psychologist or a social worker. The need for counseling, using a well designed protocol, and the importance of focusing on suicide risk of participants in predictive testing programs is emphasized. [source]