10,607 research outputs found

    A gas-dynamic calculation of type 2 shock propagation through the corona

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    An approximate analytic theory of acoustic shock propagation in nonuniform media is used to determine the motion of a flare-generated shock wave in the corona. The shock is followed from the time it strikes the chromosphere-corona transition region (density interface) out to 5 solar radii under the assumption that the corona in this region is approximately in hydrostatic equilibrium. The strength of the shock incident on the transition region from below determines the ejection velocity of eruptive prominence material, as well as the initial velocity of the coronal shock. The calculation is applied to one well-documented case of a related flare spray, moving type 4 isolated source, and type 2 burst. It is shown that a chromospheric shock of the appropriate strength to produce the observed prominence and type 4 velocities strengthens as it moves out in the corona by an amount sufficient to account for the observed high velocity of the type 2 burst

    Large-scale electric fields resulting from magnetic reconnection in the corona

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    The method of Forbes and Priest (2-D model) is applied to the large two-ribbon flare of July 29, 1973, for which both detailed H observations and magnetic data are available. For this flare the ribbons were long, nearly straight, and parallel to each other, and the 2-D model for the coronal field geometry may be adequate. The temporal profile E(t) is calculated and indicates that reconnection sets in at the beginning of the decay phase. From this time the electric field grows rapidly to a maximum value of about 2 V/cm within just a few minutes. Thereafter it decreases monotonically with time

    Magnetic field re-arrangement after prominence eruption

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    It has long been known that magnetic reconnection plays a fundamental role in a variety of solar events. Although mainly invoked in flare problems, large scale loops interconnecting active regions, evolving coronal hole boundaries, the solar magnetic cycle itself, provide different evidence of phenomena which involve magnetic reconnection. A further example might be given by the magnetic field rearrangement which occurs after the eruption of a prominence. Since most often a prominence reforms after its disappearance and may be observed at about the same position it occupied before erupting, the magnetic field has to undergo a temporary disruption of relax back, via reconnection, to a configuration similar to the previous one. The above sequence of events is best observable in the case of two ribbon (2-R) flares but most probably is associated with all filament eruptions. Even if the explanation of the magnetic field rearrangement after 2-R flares in terms of reconnection is generally accepted, the lack of a 3-dimensional model capable of describing the field reconfiguration, has prevented, up to now, a thorough analysis of its topology as traced by H alpha/x ray loops. A numerical technique is presented which enables oneto predict and visualize the reconnected configuration, at any time, and therefore allows one to make a significant comparison of observations and model predictions throughout the whole process

    Light Z' Bosons at the Tevatron

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    New gauge bosons with Standard Model-like couplings to leptons are constrained by collider searches to be heavier than approximately ~1 TeV. A Z' boson with suppressed couplings to leptons, however, could be much lighter and possess substantial couplings to Standard Model quarks. In this article, we consider a new leptophobic Z' gauge boson as a simple and well motivated extension of the Standard Model, and discuss several of its possible signatures at the Tevatron. We find that three of the recent anomalies reported from the Tevatron - in particular the top-quark forward-backward asymmetry and excesses in the 3b and W + 2 jets final states - could be explained by a new Z' with a mass of approximately 150 GeV, relatively large couplings to quarks, and suppressed couplings to electrons and muons. Moreover, we find that such a particle could also mediate the interactions of dark matter, leading to potentially interesting implications for direct detection experiments.Comment: 12 pages, 7 figures. v2, v3: updated references. v4: updated to match published version, including minor revisions to figures 1 and

    Clinical relevance of soluble c-erbB-2 for patients with metastatic breast cancer predicting the response to second-line hormone or chemotherapy

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    Concentrations of soluble c-erbB-2 were determined in the sera of 64 patients with distant metastasis from advanced breast cancer receiving second-line hormone or chemotherapy in comparison to 35 breast cancer patients without detectable recurrent disease and 17 healthy blood donors. The sera of non-metastatic breast cancer patients contained s-erbB-2 concentrations similar to those of healthy blood donors. Patients with distant metastasis from advanced breast cancer had significantly higher values of s-erbB-2 in comparison to patients with non-disseminated disease (mean: 59.6 vs. 11.6 U/ml; p = 0.022). A significant correlation was observed between s-erbB-2 serum levels and serum LDH concentrations (p < 0.001), levels of alkaline phosphatase (p < 0.001), and the presence of hepatic metastasis (p = 0.001). Time to tumor progression was significantly shorter in patients with s-erbB-2 levels above 40 U/ml (mean: 23.4 vs. 56.7 months; p = 0.002). Furthermore, breast cancer patients with hepatic metastasis and those with elevated s-erbB-2 serum levels above 40 U/ml had limited response to hormone or chemotherapy. Non-responders had significantly higher s-erbB-2 levels (mean: 270.3, range: 42-500 U/ml;) compared with the responder group (mean: 23.1, range: 0-149 U/ml; p < 0.001). Logistic regression analysis indicated that elevated s-erbB-2 serum levels above 40 U/ml independently predicted an unfavorable response to second-line hormone or chemotherapy in patients with advanced metastatic breast cancer. Copyright (C) 2002 S. KargerAG, Basel

    Semiclassical transport in nearly symmetric quantum dots II: symmetry-breaking due to asymmetric leads

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    In this work - the second of a pair of articles - we consider transport through spatially symmetric quantum dots with leads whose widths or positions do not obey the spatial symmetry. We use the semiclassical theory of transport to find the symmetry-induced contributions to weak localization corrections and universal conductance fluctuations for dots with left-right, up-down, inversion and four-fold symmetries. We show that all these contributions are suppressed by asymmetric leads, however they remain finite whenever leads intersect with their images under the symmetry operation. For an up-down symmetric dot, this means that the contributions can be finite even if one of the leads is completely asymmetric. We find that the suppression of the contributions to universal conductance fluctuations is the square of the suppression of contributions to weak localization. Finally, we develop a random-matrix theory model which enables us to numerically confirm these results.Comment: (18pages - 9figures) This is the second of a pair of articles (v3 typos corrected - including in equations

    Stellar Wakes from Dark Matter Subhalos

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    We propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way's dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses ∼107 M⊙\sim 10^7\,M_\odot or below. The detection of such subhalos would have implications for dark-matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.Comment: 6 + 3 pages, 1 + 2 figures, code available at: https://github.com/bsafdi/stellarWake

    Recent Enhancements to Determine Flow Stress Data in High Speed Compression Tests

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    The accuracy in numerical simulation and physical models is increasing continually. For this reason, the attention to the measurement of flow stress fields at hot forming conditions rises presently. The determination of flow curves at small and middle strain rates up to 100/s has become a standard procedure. In the wide range between strain rates of 100/s up to 500/s no accurate experimental data of compression tests by the use of servo-hydraulic testing systems exists to date. In this context, the IBF investigated how compression tests especially on servo hydraulic testing-machines can be developed in order to expand the range of flow-curve fields clearly above 100/s with strains up to phi = 0.7. The maximum tool speed of the IBF testing machine is 3000 mm/s. This presentation shows the advances realised in this field. During the research activities, the existing servo-hydraulic high-speed testing machine has been optimised and new post processing techniques have been developed. Hence, valid flow stress values can now be determined up to strain rates of 300/s in compression tests on the utilised servo hydraulic testing system. Present investigations have the aim to determine absolutely reliably flow stress data even for strain rates up to 500 /s
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