826 research outputs found

    The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables

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    The temperatures of electrons and ions in the post-shock accretion region of a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass flow rates or for sufficiently weak magnetic fields. At lower mass flow rates or in stronger magnetic fields, efficient cyclotron cooling will cool the electrons faster than the electrons can cool the ions and a two-temperature flow will result. Here we investigate the differences in polarized radiation expected from mCV post-shock accretion columns modeled with one- and two-temperature hydrodynamics. In an mCV model with one accretion region, a magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along with a relatively generic geometric orientation of the system, we find that in the ultraviolet either a single linear polarization pulse per binary orbit or two pulses per binary orbit can be expected, depending on the accretion column hydrodynamic structure (one- or two-temperature) modeled. Under conditions where the physical flow is two-temperature, one pulse per orbit is predicted from a single accretion region where a one-temperature model predicts two pulses. The intensity light curves show similar pulse behavior but there is very little difference between the circular polarization predictions of one- and two-temperature models. Such discrepancies indicate that it is important to model some aspect of two-temperature flow in indirect imaging procedures, like Stokes imaging, especially at the edges of extended accretion regions, were the specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc

    Use of Contingent Valuation to Assess Farmer Preference for On-farm Conservation of Minor Millets: Case from South India

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    Smallholder farmers all over the world, particularly in regions of rich agro-biodiversity contribute to on-farm conservation. Past and present agricultural progress could not have happened neither without these genetic resources nor the associated farmer knowledge. Six species of minor millets are grown in India on more than 2 million hectares. The Kolli Hills in Tamil Nadu has been a region where five of these millet species have been under cultivation over the last several hundred years. These minor millets are currently under threat due to high competition from tapioca (cassava) as well as easy access to PDS rice at low cost. Over last three decades there has been decline in the millet area and number of farmers cultivating these species. It is in this context that this study attempts to examine the role of farmer incentive mechanisms to conserve minor millets in Kolli Hills. The millet varieties existing in the study area were classified either as most preferred varieties (MPVs) or least preferred varieties (LPVs) by the farmer respondents based on their yield and consumption preferences. The farmer willingness to accept compensation to participate in the conservation programme is estimated using a contingent valuation method (CVM). Seemingly unrelated bivariate probit regression was used to estimate the determinants of willing to participate in on-farm conservation of minor millets. The result shows that the impact of bid value is significant and positive to participate in the on-farm millet conservation of MPVs. The farmers participating is millet related organization are willing to accept lower compensation for MPVs and higher for LPVs compared to farmers who are not participating in such organization

    Generation of arbitrary two dimensional motional state of a trapped ion

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    We present a scheme to generate an arbitrary two-dimensional quantum state of motion of a trapped ion. This proposal is based on a sequence of laser pulses, which are tuned appropriately to control transitions on the sidebands of two modes of vibration. Not more than (M+1)(N+1)(M+1)(N+1) laser pulses are needed to generate a pure state with upper phonon number MM and NN in the xx and yy direction respectively.Comment: to appear in PR

    Efficacy of beta radiation in prevention of post-angioplasty restenosis

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    Restenosis remains a major limitation of coronary angioplasty in spite of major advances in techniques and technology. Recent studies have demonstrated that ionizing radiation may limit the degree of this problem. Gamma radiation has been shown to be effective in reducing in stent restenosis in humans, and beta radiation following encouraging results in animals has been shown to be feasible in humans. The objective of this study was to assess the feasibility of a 5 F non-centered catheter to deliver beta radiation emitting seeds to the lesion site post angioplasty and its effect on restenosis. Following successful angioplasty, patients were randomized to treatment with 12, 14 or 16 Gy at the angioplasty site. This was delivered with a 5 F non-centered catheter. Twelve beta radiation emitting seeds (90Sr/Y) were delivered to an area 3 cm in length to cover the angioplasty site. Angiographic follow-up was performed at 6 months. Baseline and follow-up angiograms were performed by blinded investigators at a core laboratory. This interim report comprises the first 35 patients to complete 6-month angiographic follow-up. There were no major radiation incidents. Four patients had evidence of angiographic restenosis. The MLD (mm) and percent stenosis were 0.77 +/- 0.27/72.5 +/- 8.6 pre angioplasty, 2.08 +/- 0.4/25.7 +/- 9.8 post angioplasty and radiation and 2.05 +/- 0.59/25.7 +/- 19.8 at follow-up respectively. CONCLUSION: Beta radiation can be feasibly and safely delivered post coronary angioplasty with a very encouraging reduction of restenosis

    Five Dimensional Rotating Black Hole in a Uniform Magnetic Field. The Gyromagnetic Ratio

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    In four dimensional general relativity, the fact that a Killing vector in a vacuum spacetime serves as a vector potential for a test Maxwell field provides one with an elegant way of describing the behaviour of electromagnetic fields near a rotating Kerr black hole immersed in a uniform magnetic field. We use a similar approach to examine the case of a five dimensional rotating black hole placed in a uniform magnetic field of configuration with bi-azimuthal symmetry, that is aligned with the angular momenta of the Myers-Perry spacetime. Assuming that the black hole may also possess a small electric charge we construct the 5-vector potential of the electromagnetic field in the Myers-Perry metric using its three commuting Killing vector fields. We show that, like its four dimensional counterparts, the five dimensional Myers-Perry black hole rotating in a uniform magnetic field produces an inductive potential difference between the event horizon and an infinitely distant surface. This potential difference is determined by a superposition of two independent Coulomb fields consistent with the two angular momenta of the black hole and two nonvanishing components of the magnetic field. We also show that a weakly charged rotating black hole in five dimensions possesses two independent magnetic dipole moments specified in terms of its electric charge, mass, and angular momentum parameters. We prove that a five dimensional weakly charged Myers-Perry black hole must have the value of the gyromagnetic ratio g=3.Comment: 23 pages, REVTEX, v2: Minor changes, v3: Minor change
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