3,095,336 research outputs found

    Cooling system for high speed aircraft

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    The system eliminates the necessity of shielding an aircraft airframe constructed of material such as aluminum. Cooling is accomplished by passing a coolant through the aircraft airframe, the coolant acting as a carrier to remove heat from the airframe. The coolant is circulated through a heat pump and a heat exchanger which together extract essentially all of the added heat from the coolant. The heat is transferred to the aircraft fuel system via the heat exchanger and the heat pump. The heat extracted from the coolant is utilized to power the heat pump. The heat pump has associated therewith power turbine mechanism which is also driven by the extracted heat. The power turbines are utilized to drive various aircraft subsystems, the compressor of the heat pump, and provide engine cooling

    Cooper Pairs with Broken Parity and Time-Reversal Symmetries in D-wave Superconductors

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    Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a d-wave superconductor in the absence of impurities. This component, which breaks both parity and time-reversal symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high-Tc, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at H=0 and characterized by singlet-triplet mixed Copper pairs with broken time-reversal symmetry in a vortex phase, is discussed.Comment: 10 pages, 1 figures, Phys. Rev. Lett., submitted (July 25 2005

    The cosmological evolution of p-brane networks

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    In this paper we derive, directly from the Nambu-Goto action, the relevant components of the acceleration of cosmological featureless pp-branes, extending previous analysis based on the field theory equations in the thin-brane limit. The component of the acceleration parallel to the velocity is at the core of the velocity-dependent one-scale model for the evolution of pp-brane networks. We use this model to show that, in a decelerating expanding universe in which the pp-branes are relevant cosmologically, interactions cannot lead to frustration, except for fine-tuned non-relativistic networks with a dimensionless curvature parameter k1k \ll 1. We discuss the implications of our findings for the cosmological evolution of pp-brane networks.Comment: 6 page

    Cosmological Perturbations of Quantum-Mechanical Origin and Anisotropy of the Microwave Background

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    Cosmological perturbations generated quantum-mechanically (as a particular case, during inflation) possess statistical properties of squeezed quantum states. The power spectra of the perturbations are modulated and the angular distribution of the produced temperature fluctuations of the CMBR is quite specific. An exact formula is derived for the angular correlation function of the temperature fluctuations caused by squeezed gravitational waves. The predicted angular pattern can, in principle, be revealed by the COBE-type observations.Comment: 9 pages, WUGRAV-92-17 Accepted for Publication in Phys. Rev. Letters (1993

    Relic Gravitational Waves and Cosmology

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    This is an expanded version of my talk given at the international conference "Zeldovich-90". I start with a brief recollection of interactions with Zeldovich in the context of the study of relic gravitational waves. I then summarise the principles and early results on the quantum-mechanical generation of cosmological perturbations. The expected amplitudes of relic gravitational waves are different in different frequency windows, and therefore the techniques and prospects of their detection are different. One section of the paper describes the present state of efforts in direct detection of relic gravitational waves. Another section is devoted to indirect detection via the anisotropy and polarisation measurements of the cosmic microwave background radiation (CMB). It is emphasized throughout the paper that the conclusions on the existence and expected amount of relic gravitational waves are based on a solid theoretical foundation and the best available cosmological observations. I also explain in great detail what went wrong with the so-called `inflationary gravitational waves', whose amount is predicted by inflationary theorists to be negligibly small, thus depriving them of any observational significance.Comment: 36 pages including 8 figures; expanded version of a talk at the international conference `Zeldovich-90', Moscow, December 2004; http://hea.iki.rssi.ru/Z-90; v.2: additional formulas and explanations in response to remarks of anonymous referee; v.3: extra details about 'scalar' perturbations and T/S ratio, scheduled to appear in Uspekhi Fiz. Nauk v.176 (2006); v.4: matches published paper: Physics-Uspekhi, 48(12) 1235-1247 (2005) [Russian version: Uspekhi Fiz. Nauk, 175(12) 1289-1303 (2005)
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