9,751 research outputs found

    Searches For New Bosons Coupling To e-q Pairs At HERA And Other Colliders

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    The early observation at HERA of an excess of events compared to the expectation from the Standard Model in very short distance e+pe^+p deep-inelastic scattering processes has renewed the interest in the search for new physics which could manifest in electroweak-like interactions. New preliminary results from the H1 and ZEUS experiments making use of all available e+pe^+p data are reviewed here, with an emphasis on the search for new bosons possessing Yukawa couplings to lepton-quark pairs. The sensitivity of HERA to leptoquarks, and to squarks of R-parity violating supersymmetry, is confronted to existing indirect constraints from rare and forbidden semi-leptonic decays, atomic parity violation and neutrinoless double-beta decay, as well as to direct constraints from LEP and Tevatron colliders. The HERA and Tevatron colliders are found to offer exciting prospects for new physics, accessing yet unexplored domains of the mass-coupling plane. Possible striking manifestation of explicit lepton flavour violation is also discussed.Comment: 27 pages, 16 figures. Proceedings of the WEIN'98 Symposium (June 1998

    Search for Particles and Forces Beyond the Standard Model at HERA ep and Tevatron p\bar{p} Colliders

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    A review of searches for physics beyond the Standard Model carried out at high energy lepton-hadron and hadron-hadron facilities is presented, with emphasis on topics of interest for future data taking at the upgraded Tevatron ppˉp{\bar p} and HERA epep colliders. The status and discovery prospects are discussed for leptoquarks, Technicolour and supersymmetry, forbidden lepton and quark flavour-changing processes, extra gauge bosons, excited states of composite fermions, generic contact interactions and extra compactified dimensions.Comment: 64 pages, 34 figures, submitted for publication in "Progress in Particle and Nuclear Physics

    High-speed fluorescent thermal imaging of quench propagation in high temperature superconductor tapes

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    Fluorescent Microthermographic Imaging, a method using rare-earth fluorescent coatings with temperature-dependent light emission, was used for quench investigation in high temperature superconductors (HTS). A fluorophore was embedded in a polymer matrix and used as a coating on top of an HTS tape, while being excited with UV light and recorded with a high-speed camera. Simultaneously, the tape was pulsed with high amplitude, short duration DC current, and brought to quench with the help of a localized defect. The joule heating during a quench influences the fluorescent light intensity emitted from the coating, and by recording the local variations in this intensity over time, the heating of the tape can be visualized and the developed temperatures can be calculated. In this paper, the fluorophore Europium tris[3-(trifluoromethylhydroxymethylene)- (+)-camphorate] (EuTFC) provided sufficient temperature sensitivity and a usable temperature range from 77 K to 260 K. With the help of high-speed recordings, the normal zone development was imaged in a 20 \mu m copper stabilized HTS tape held in a liquid nitrogen bath, and using a calibration curve, the temperatures reached during the quench have been calculated

    Self-consistent Modeling of the IcI_c of HTS Devices: How Accurate do Models Really Need to Be?

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    Numerical models for computing the effective critical current of devices made of HTS tapes require the knowledge of the Jc(B,theta) dependence, i.e. of the way the critical current density Jc depends on the magnetic flux density B and its orientation theta with respect to the tape. In this paper we present a numerical model based on the critical state with angular field dependence of Jc to extract the Jc(B,theta) relation from experimental data. The model takes into account the self-field created by the tape, which gives an important contribution when the field applied in the experiments is low. The same model can also be used to compute the effective critical current of devices composed of electromagnetically interacting tapes. Three examples are considered here: two differently current rated Roebel cables composed of REBCO coated conductors and a power cable prototype composed of Bi-2223 tapes. The critical currents computed with the numerical model show good agreement with the measured ones. The simulations reveal also that several parameter sets in the Jc(B,theta) give an equally good representation of the experimental characterization of the tapes and that the measured Ic values of cables are subjected to the influence of experimental conditions, such as Ic degradation due to the manufacturing and assembling process and non-uniformity of the tape properties. These two aspects make the determination of a very precise Jc(B,theta) expression probably unnecessary, as long as that expression is able to reproduce the main features of the angular dependence. The easiness of use of this model, which can be straightforwardly implemented in finite-element programs able to solve static electromagnetic problems, is very attractive both for researchers and devices manufactures who want to characterize superconducting tapes and calculate the effective critical current of superconducting devices

    Identifying Barriers and Supports to Breastfeeding in the Workplace Experienced by Mothers in the New Hampshire Special Supplemental Nutrition Program for Women, Infants, and Children Utilizing the Total Worker Health Framework

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    Variations in the barriers and contributors to breastfeeding across industries have not been well characterized for vulnerable populations such as mothers participating in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). Our study used the Total Worker Health Framework to characterize workplace factors acting as barriers and/or contributors to breastfeeding among women participating in the New Hampshire WIC. Surveys were collected from WIC mothers (n = 682), which asked about employment, industry, and workplace accommodation and supports related to breastfeeding in the workplace. We found workplace policy factors supporting breastfeeding (i.e., having paid maternity leave, other maternity leave, and a breastfeeding policy) varied by industry. Women in specific service-oriented industries (i.e., accommodation and retail) reported the lowest rates of breastfeeding initiation and workplace supports for breastfeeding and pumping. Further, how a woman hoped to feed and having a private pumping space at work were significantly associated with industry, breastfeeding initiation, and breastfeeding duration. A substantial portion of women reported being not sure about their workplace environment, policies, and culture related to breastfeeding. Additional studies with larger sample sizes of women participating in WIC are needed to further characterize the barriers to breastfeeding associated with specific industries

    Fluorescent thermal imaging of a non-insulated pancake coil wound from high temperature superconductor tape

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    We have wound a 157-turn, non-insulated pancake coil with an outer diameter of 85 mm and we cooled it down to 77 K with a combination of conduction and gas cooling. Using high-speed fluorescent thermal imaging in combination with electrical measurements we have investigated the coil under load, including various ramping tests and over-current experiments. We have found found that the coil does not heat up measurably when being ramped to below its critical current. Two over-current experiments are presented, where in one case the coil recovered by itself and in another case a thermal runaway occurred. We have recorded heating in the bulk of the windings due to local defects, however the coil remained cryostable even during some over-critical conditions and heated only to about 82-85 K at certain positions. A thermal runaway was observed at the center, where the highest magnetic field and a resistive joint create a natural defect. The maximum temperature, ~100 K, was reached only in the few innermost windings around the coil former

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