3,420 research outputs found
Enhancement of reliability in condition monitoring techniques in wind turbines
The majority of electrical failures in wind turbines occur in the semiconductor components (IGBTs) of converters. To increase reliability and decrease the maintenance costs associated with this component, several health-monitoring methods have been proposed in the literature. Many laboratory-based tests have been conducted to detect the failure mechanisms of the IGBT in their early stages through monitoring the variations of thermo-sensitive electrical parameters. The methods are generally proposed and validated with a single-phase converter with an air-cored inductive or resistive load. However, limited work has been carried out considering limitations associated with measurement and processing of these parameters in a three-phase converter. Furthermore, looking at just variations of the module junction temperature will most likely lead to unreliable health monitoring as different failure mechanisms have their own individual effects on temperature variations of some, or all, of the electrical parameters. A reliable health monitoring system is necessary to determine whether the temperature variations are due to the presence of a premature failure or from normal converter operation. To address this issue, a temperature measurement approach should be independent from the failure mechanisms. In this paper, temperature is estimated by monitoring an electrical parameter particularly affected by different failure types. Early bond wire lift-off is detected by another electrical parameter that is sensitive to the progress of the failure. Considering two separate electrical parameters, one for estimation of temperature (switching off time) and another to detect the premature bond wire lift-off (collector emitter on-state voltage) enhance the reliability of an IGBT could increase the accuracy of the temperature estimation as well as premature failure detection
Cantaloupe line CZW-30 containing coat protein genes of cucumber mosaic virus, zucchini yellow mosaic virus, and watermelon mosaic virus-2 is resistant to these three viruses in the field
Cantaloupe line CZW-30 containing coat protein gene constructs of cucumber mosaic cucumovirus (CMV), zucchini yellow mosaic potyvirus (ZYMV), and watermelon mosaic virus 2 potyvirus (WMV-2) was investigated in the field over two consecutive years for resistance to infections by CMV, ZYMV, and/or WMV-2. Resistance was evaluated under high disease pressure achieved by mechanical inoculations and/or natural challenge inoculations by indigenous aphid vectors. Across five different trials, homozygous plants were highly resistant in that they never developed systemic symptoms as did the nontransformed plants but showed few symptomatic leaves confined close to the vine tips. Hemizygous plants exhibited a significant delay (2-3 weeks) in the onset of disease compared to control plants but had systemic symptoms 9-10 weeks after transplanting to the field. Importantly, ELISA data revealed that transgenic plants reduced the incidence of mixed infections. Only 8% of the homozygous and 33% of the hemizygous plants were infected by two or three viruses while 99% of the nontransformed plants were mixed infected. This performance is of epidemiological significance. In addition, control plants were severely stunted (44% reduction in shoot length) and had poor fruit yield (62% loss) compared to transgenic plants, and most of their fruits (60%) were unmarketable. Remarkably, hemizygous plants yielded 7.4 times more marketable fruits than control plants, thus suggesting a potential commercial performance. This is the first report on extensive field trials designed to assess the resistance to mixed infection by CMV, ZYMV, and WMV-2, and to evaluate the yield of commercial quality cantaloupes that are genetically engineere
Criteria for the use of omics-based predictors in clinical trials.
The US National Cancer Institute (NCI), in collaboration with scientists representing multiple areas of expertise relevant to 'omics'-based test development, has developed a checklist of criteria that can be used to determine the readiness of omics-based tests for guiding patient care in clinical trials. The checklist criteria cover issues relating to specimens, assays, mathematical modelling, clinical trial design, and ethical, legal and regulatory aspects. Funding bodies and journals are encouraged to consider the checklist, which they may find useful for assessing study quality and evidence strength. The checklist will be used to evaluate proposals for NCI-sponsored clinical trials in which omics tests will be used to guide therapy
Muscle power in basketball and volleyball players: relationship between isokinetic dynamometry and vertical jump
The aims of this study were: 1) to determine the anthropometric characteristics and body compositon of players; 2) to evaluate the maximal muscle power of the knee extensors muscles with the isokinetic dynamometry; 3) to determine the relationships between the test of isokinetic power and the vertical jum p test; 4) to compare the results between sports. A sample of 12 basketball players and 13 volleyball players was evaluated in several anthropometric measures and in two tests of muscle power. Body composition was determined through the equation by Jackson & Pollock (1978). Vertical jum p test was made without the arm movements, and the isokinetic muscle power test of the knee extensors was made in four speeds: 60, 180, 240 and 300°/sec.The results showed that the basketball players were taller, heavier and fatter than the volleyball players. There were no significant diferences in power output. When power was related to body weight, volleyball players showed higher values in the vertical jum p test and the isokinetic power test at 60°/sec. and in the vertical jump test when corrected by lean body mass. Relationships between maximal power tests showed from moderate to high degree between isokinetic power test at 180 and 300°/sec. and the vertical jum p test for basketball players. Volleyball players showed similar results at 180 and 300°/sec. Similar results were found when tests were corrected for body weight and lean body mass for basketball players, but in volleyball players relationships were from low to moderateOs objetivos do estudo foram: 1) determinar as caracterÃsticas antropométricas e a composição corporal dos jogadores, 2) avaliar a potência máxima dos músculos extensores do joelho com a dinamometria isocinética, 3) verificar a relação entre o teste isocinético e o teste de salto vertical e 4) comparar os dois grupos de jogadores. Uma amostra de 12 jogadores de basquetebol e 13 de voleibol foi submetida a uma avaliação antropométrica e dois testes de potência muscular. A composição corporal foi calculada a partir da equação de Jackson & Pollock (1978). O teste de salto vertical foi realizado sem o auxÃlio dos membros superiores e a dinamometria isocinética executada no movimento de extensão do joelho à s velocidades de 60, 180, 240 e 300°/seg. Nos jogadores de basquetebol foram encontrados valores mais altos para estatura peso e quantidade de gordura comparados com os voleibolistas. Os dois grupos apresentaram desempenho neuromuscular semelhante em termos absolutos. Relativo ao peso corporal os voleibolistas foram superiores no salto vertical e na potência à 60°/seg. e também no salto vertical relativo à massa magra. Na relação entre os dois testes em termos absolutos, correlações moderadas para altas foram encontradas à 180 e 300°/seg. para os jogadores de basquete e 180 e 240°/seg. para os de voleibol. Resultados semelhantes ocorreram nos praticantes de basquetebol relativo ao peso corporal e a massa magra, contudo, para os voleibolistas as relações foram de baixas para moderada
Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds
This is an open access article, made available under the terms of the Creative Commons attribution license CC BY 3.0 https://creativecommons.org/licenses/by/3.0/This study reports on the origin of ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the −40 to −60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high ice crystal complexity is dominating the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapour during the crystal growth. Indications were found that the crystal complexity is influenced by unfrozen H2SO4/H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers; the Polar Nephelometer (PN) probe of LaMP and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side- and backward scattering directions resulting in low asymmetry parameters g around 0.78. It was found that these functions have a rather low sensitivity to the crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.Peer reviewedFinal Published versio
Pinning of stripes by local structural distortions in cuprate high-Tc superconductors
We study the spin-density wave (stripe) instability in lattices with mixed
low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) crystal
symmetry. Within an explicit mean-field model it is shown how local LTT regions
act as pinning centers for static stripe formation. We calculate the
modulations in the local density of states near these local stripe regions and
find that mainly the coherence peaks and the van Hove singularity (VHS) are
spatially modulated. Lastly, we use the real-space approach to simulate recent
tunneling data in the overdoped regime where the VHS has been detected by
utilizing local normal state regions.Comment: Conference proceedings for Stripes1
A new Differential Optical Absorption Spectroscopy instrument to study atmospheric chemistry from a high-altitude unmanned aircraft
Observations of atmospheric trace gases in the tropical upper troposphere (UT), tropical tropopause layer (TTL), and lower stratosphere (LS) require dedicated measurement platforms and instrumentation. Here we present a new limb-scanning Differential Optical Absorption Spectroscopy (DOAS) instrument developed for NASA's Global Hawk (GH) unmanned aerial system and deployed during the Airborne Tropical TRopopause EXperiment (ATTREX). The mini-DOAS system is designed for automatic operation under unpressurized and unheated conditions at 14–18 km altitude, collecting scattered sunlight in three wavelength windows: UV (301–387 nm), visible (410–525 nm), and near infrared (900–1700 nm). A telescope scanning unit allows selection of a viewing angle around the limb, as well as real-time correction of the aircraft pitch. Due to the high altitude, solar reference spectra are measured using diffusors and direct sunlight. The DOAS approach allows retrieval of slant column densities (SCDs) of O₃, O₄, NO₂, and BrO with relative errors similar to other aircraft DOAS systems. Radiative transfer considerations show that the retrieval of trace gas mixing ratios from the observed SCD based on O₄ observations, the most common approach for DOAS measurements, is inadequate for high-altitude observations. This is due to the frequent presence of low-altitude clouds, which shift the sensitivity of the O₄ SCD into the lower atmosphere and make it highly dependent on cloud coverage. A newly developed technique that constrains the radiative transfer by comparing in situ and DOAS O₃ observations overcomes this issue. Extensive sensitivity calculations show that the novel O₃-scaling technique allows the retrieval of BrO and NO₂ mixing ratios at high accuracies of 0.5 and 15 ppt, respectively. The BrO and NO₂ mixing ratios and vertical profiles observed during ATTREX thus provide new insights into ozone and halogen chemistry in the UT, TTL, and LS
Radiation Campaign of HPK Prototype LGAD sensors for the High-Granularity Timing Detector (HGTD)
We report on the results of a radiation campaign with neutrons and protons of
Low Gain Avalanche Detectors (LGAD) produced by Hamamatsu (HPK) as prototypes
for the High-Granularity Timing Detector (HGTD) in ATLAS. Sensors with an
active thickness of 50~m were irradiated in steps of roughly 2 up
to a fluence of . As a function of the
fluence, the collected charge and time resolution of the irradiated sensors
will be reported for operation at
Search for Yukawa Production of a Light Neutral Higgs Boson at LEP
Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in
the mass range of 4-12 GeV has been performed in the Yukawa process e+e- -> b
bbar A/h -> b bbar tau+tau-, using the data collected by the OPAL detector at
LEP between 1992 and 1995 in e+e- collisions at about 91 GeV centre-of-mass
energy. A likelihood selection is applied to separate background and signal.
The number of observed events is in good agreement with the expected
background. Within a CP-conserving 2HDM type II model the cross-section for
Yukawa production depends on xiAd = |tan beta| and xihd = |sin alpha/cos beta|
for the production of the CP-odd A and the CP-even h, respectively, where tan
beta is the ratio of the vacuum expectation values of the Higgs doublets and
alpha is the mixing angle between the neutral CP-even Higgs bosons. From our
data 95% C.L. upper limits are derived for xiAd within the range of 8.5 to 13.6
and for xihd between 8.2 to 13.7, depending on the mass of the Higgs boson,
assuming a branching fraction into tau+tau- of 100%. An interpretation of the
limits within a 2HDM type II model with Standard Model particle content is
given. These results impose constraints on several models that have been
proposed to explain the recent BNL measurement of the muon anomalous magnetic
moment.Comment: 24 pages, 9 figures, Submitted to Euro. Phys. J.
Search for the Standard Model Higgs Boson with the OPAL Detector at LEP
This paper summarises the search for the Standard Model Higgs boson in e+e-
collisions at centre-of-mass energies up to 209 GeV performed by the OPAL
Collaboration at LEP. The consistency of the data with the background
hypothesis and various Higgs boson mass hypotheses is examined. No indication
of a signal is found in the data and a lower bound of 112.7GeV/C^2 is obtained
on the mass of the Standard Model Higgs boson at the 95% CL.Comment: 51 pages, 21 figure
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