9,366 research outputs found
Identifying prognostic indicators for electrical treeing in solid insulation through pulse sequence analysis
Predictive maintenance attempts to evaluate the condition of equipment and predict the future trend of the equipment's aging, in order to reduce costs when compared to the two traditional approaches: corrective and preventive maintenance. This prediction requires an accurate prognostic model of aging. In solid insulation, the ultimate goal of prognostics is to predict the advent of failure, i.e., insulation breakdown, in terms of remaining useful life (RUL). One fault is electrical treeing, which is progressive thus leading to potentially catastrophic failure. Research has shown that diagnosis of faults can be achieved based on partial discharge (PD) monitoring [1], i.e., phase-resolved and pulse sequence analysis (PSA). This work will explore the extension of this concept towards predicting evolution of the defect: moving beyond diagnostics towards prognostics. To do this, there is a need for further investigation of prognostic features within PD characteristics leading up to breakdown. In this work, a needle-plane test arrangement was set up using a hypodermic needle and pre-formed silicone rubber as test samples. The visual observations and tree growth measurements were made using a digital microscope. PD data was captured using a radio frequency (RF) sensor and analysed using PSA. The main idea of the PSA approach is the strong relationship between two consecutive pulses caused by PD activities, which can give an understanding of the local degradation processes [1]. As for electrical treeing, a breakdown indicator in PSA is the appearance of heavily clustered data points that lie diagonally in scatter plots of the differential ratio of voltage and time of consecutive charges (Un = Δun/Δtn) [2,3]. Figure 1 shows an example of a plot that changed to a diagonal line after 14 hours of aging time. This paper investigates the formation of the diagonal line based on the distribution of the plot from the start of electrical treeing until breakdown occurs. Finally, statistical features of the PSA plot are given and will be used for lifetime prediction of insulation samples in future work
Asymmetries in top quark pair production at hadron colliders
We review the asymmetries in top quark pair production at the Tevatron and
the LHC. We summarize the experimental measurements and the interpretations of
a possible excess in terms of new physics. We also review other top quark
properties-emphasizing effects related to the asymmetries-as well as
other collider signals.Comment: RevTeX 40 pages. Final version to be published in Reviews of Modern
Physics, with several addition
Feasibility and Acceptability of an English-as-a-Second Language Curriculum on Hepatitis B for Older Chinese American Immigrants
Asian immigrants to the U.S. have an increased prevalence of hepatitis B virus (HBV) infection compared to native born individuals; an estimated 10 percent of Chinese immigrants are infected with HBV. Using qualitative data from focus groups, we developed an English-as-a-Second Language (ESL) curriculum that aimed to improve knowledge about key hepatitis B facts. The curriculum was pilot-tested among 56 students aged 50 and older from intermediate-level ESL classes at a community-based organization that serves Chinese immigrants. Post-curriculum data showed increases in knowledge that hepatitis B can cause liver cancer (73% at pre-test vs. 91% at post-test; p value = 0.01) and that individuals can be infected with hepatitis B for life (34% vs. 81%; p valu
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the Magnetar Candidate 1E 1048.1-5937
We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.Comment: 24 pages, 4 figures, submitted to the Astrophysical Journa
Electroweak Precision Observables and the Unhiggs
We compute one-loop corrections to the S and T parameters in the Unhiggs
scenario. In that scenario, the Standard Model Higgs is replaced by a non-local
object, called the Unhiggs, whose spectral function displays a continuum above
the mass gap. The Unhiggs propagator has effectively the same UV properties as
the Standard Model Higgs propagator, which implies that loop corrections to the
electroweak precision observables are finite and calculable. We show that the
Unhiggs is consistent with electroweak precision tests when its mass gap is at
the weak scale; in fact, it then mimics a light SM Higgs boson. We also argue
that the Unhiggs, while being perfectly visible to electroweak precision
observables, is invisible to detection at LEP.Comment: 13 pages; v2: references added, discussion of production
cross-section expande
Probing Relativity using Space-Based Experiments
An overview of space tests searching for small deviations from special
relativity arising at the Planck scale is given. Potential high-sensitivity
space-based experiments include ones with atomic clocks, masers, and
electromagnetic cavities. We show that a significant portion of the coefficient
space in the Standard-Model Extension, a framework that covers the full
spectrum of possible effects, can be accessed using space tests. Some remarks
on Lorentz violation in the gravitational sector are also given.Comment: 12 pages, invited talk at International Workshop, From Quantum to
Cosmos, Warrenton, VA, USA, May 22-24, 200
The silent burden of anaemia in Tanzania children:a community-based study
Objective was to document the prevalence, age-distribution, and risk factors for anaemia in Tanzanian children less than 5 years old,thereby assisting in the development of effective strategies for controlling anaemia.\ud
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Cluster sampling was used to identify 2417 households at random from four contiguous districts in south-eastern\ud
United Republic of Tanzania in mid-1999. Data on various social and medical parameters were collected and analysed.\ud
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Blood haemoglobin concentrations (Hb) were available for 1979 of the 2131 (93%) children identified and ranged from 1.7 to 18.6 g/dl. Overall, 87% (1722) of children had an Hb <11 g/dl, 39% (775) had an Hb <8 g/dl and 3% (65) had an Hb <5 g/dl. The highest prevalence of anaemia of all three levels was in children aged 6–11 months, of whom 10% (22/226) had an Hb <5 g/dl. However, the prevalence of anaemia was already high in children aged 1–5 months (85% had an Hb <11 g/dl, 42% had an Hb <8 g/dl, and 6% had an Hb <5 g/dl). Anaemia was usually asymptomatic and when symptoms arose they were nonspecific and rarely identified as a serious illness by the care provider. A recent history of treatment with antimalarials and iron\ud
was rare. Compliance with vaccinations delivered through the Expanded Programme of Immunization (EPI) was 82% and was notassociated with risk of anaemia.\ud
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Anaemia is extremely common in south-eastern United Republic of Tanzania, even in very young infants. Further implementation of the Integrated Management of Childhood Illness algorithm should improve the case management of anaemia. However, the asymptomatic nature of most episodes of anaemia highlights the need for preventive strategies. The EPI has good coverage of the target population and it may be an appropriate channel for delivering tools for controlling anaemia and malaria
A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS Radio Sources
We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz
radio survey catalogs for radio pulsations at 610 MHz. The selected radio
sources are bright, have no identification with extragalactic objects, are
point-like and are more than 5% linearly polarized. Our search was sensitive to
sub-millisecond pulsations from pulsars with dispersion measures (DMs) less
than 500 pc cm-3 in the absence of scattering. We have detected no pulsations
from these sources and consider possible effects which might prevent detection.
We conclude that as a population, these sources are unlikely to be pulsars.Comment: 8 pages, including 2 tables and 1 figure. Accepted for publication in
A
Technical Supplement for the article A Meta-Analysis of the Correlations Among Broad Intelligences: Understanding their Relations
This technical supplement was developed by the author along with their report, “A eta analysis of the correlations among broad intelligences: Understanding their relations” as part of a single, ongoing research project. The original report provides the general purpose and theoretical overview of the project, as well as the key analyses. This supplement also includes pieces of that material where relevant but focuses on detailing the programming and data analyses of the project to a far greater extent
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