41,123 research outputs found

    High density matter

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    The microscopic composition and properties of matter at super-saturation densities have been the subject of intense investigation for decades. The scarcity of experimental and observational data has lead to the necessary reliance on theoretical models. However, there remains great uncertainty in these models, which, of necessity, have to go beyond the over-simple assumption that high density matter consists only of nucleons and leptons. Heavy strange baryons, mesons and quark matter in different forms and phases have to be included to fulfil basic requirements of fundamental laws of physics. In this review the latest developments in construction of the Equation of State (EoS) of high-density matter at zero and finite temperature assuming different composition of the matter are surveyed. Critical comparison of model EoS with available observational data on neutron stars, including gravitational masses, radii and cooling patterns is presented. The effect of changing rotational frequency on the composition of neutron stars during their lifetime is demonstrated. Compatibility of EoS of high-density, low temperature compact objects and low density, high temperature matter created in heavy-ion collisions is discussed.Comment: 10 pages, 6 figures, Invited talk at Nuclei in Cosmos 2012, accepted for publication on PoS. arXiv admin note: text overlap with arXiv:1201.0950 by other author

    Incompressibility in finite nuclei and nuclear matter

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    The incompressibility (compression modulus) K0K_{\rm 0} of infinite symmetric nuclear matter at saturation density has become one of the major constraints on mean-field models of nuclear many-body systems as well as of models of high density matter in astrophysical objects and heavy-ion collisions. We present a comprehensive re-analysis of recent data on GMR energies in even-even 112−124^{\rm 112-124}Sn and 106,100−116^{\rm 106,100-116}Cd and earlier data on 58 ≤\le A ≤\le 208 nuclei. The incompressibility of finite nuclei KAK_{\rm A} is expressed as a leptodermous expansion with volume, surface, isospin and Coulomb coefficients KvolK_{\rm vol}, KsurfK_{\rm surf}, KτK_\tau and KcoulK_{\rm coul}. \textit{Assuming} that the volume coefficient KvolK_{\rm vol} is identified with K0K_{\rm 0}, the KcoulK_{\rm coul} = -(5.2 ±\pm 0.7) MeV and the contribution from the curvature term Kcurv_{\rm curv}A−2/3^{\rm -2/3} in the expansion is neglected, compelling evidence is found for K0K_{\rm 0} to be in the range 250 <K0< < K_{\rm 0} < 315 MeV, the ratio of the surface and volume coefficients c=Ksurf/Kvolc = K_{\rm surf}/K_{\rm vol} to be between -2.4 and -1.6 and KτK_{\rm \tau} between -840 and -350 MeV. We show that the generally accepted value of K0K_{\rm 0} = (240 ±\pm 20) MeV can be obtained from the fits provided c∼c \sim -1, as predicted by the majority of mean-field models. However, the fits are significantly improved if cc is allowed to vary, leading to a range of K0K_{\rm 0}, extended to higher values. A self-consistent simple (toy) model has been developed, which shows that the density dependence of the surface diffuseness of a vibrating nucleus plays a major role in determination of the ratio Ksurf/Kvol_{\rm surf}/K_{\rm vol} and yields predictions consistent with our findings.Comment: 26 pages, 13 figures; corrected minor typos in line with the proof in Phys. Rev.

    On the effects of flight on jet engine exhaust noise

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    Differences between flight data and predictions of jet engine exhaust noise were reconciled by considering the combined effects of jet mixing noise and internally generated engine exhaust noise. The source strength of the internally generated noise was assumed to be unaffected by flight, as experiments demonstrated. The directivity of the internally generated noise was assumed to be the same statically as that given in the NASA interim prediction method for core engine noise. However, it was assumed that in flight internally generated noise is subject to the convective amplification effect of a simple source. The absolute levels of internally generated noise were obtained from an empirical fit of some typical engine data. The static and flight jet noise were predicted using the above prediction method. It was shown that in many cases much of the flyover noise signature is dominated by internally generated noise

    An empirical model for inverted-velocity-profile jet noise prediction

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    An empirical model for predicting the noise from inverted-velocity-profile coaxial or coannular jets is presented and compared with small-scale static and simulated flight data. The model considered the combined contributions of as many as four uncorrelated constituent sources: the premerged-jet/ambient mixing region, the merged-jet/ambient mixing region, outer-stream shock/turbulence interaction, and inner-stream shock/turbulence interaction. The noise from the merged region occurs at relatively low frequency and is modeled as the contribution of a circular jet at merged conditions and total exhaust area, with the high frequencies attenuated. The noise from the premerged region occurs at high frequency and is modeled as the contribution of an equivalent plug nozzle at outer stream conditions, with the low frequencies attenuated

    Flight effects on exhaust noise for turbojet and turbofan engines: Comparison of experimental data with prediction

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    It was demonstrated that static and in flight jet engine exhaust noise can be predicted with reasonable accuracy when the multiple source nature of the problem is taken into account. Jet mixing noise was predicted from the interim prediction method. Provisional methods of estimating internally generated noise and shock noise flight effects were used, based partly on existing prediction methods and partly on recent reported engine data

    Effects of geometric and flow-field variables on inverted-velocity-profile coaxial jet noise

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    Relationships between the noise generation characteristics and the flow field characteristics for inverted-velocity-profile coaxial jets are discussed. Noise measurements were made at four different sideline distances in order to determine the apparent noise source locations, and flow field characteristics were determined from jet plume pressure/temperature surveys. These relationships are based on a published NASA Lewis prediction model, the basic assumptions of which are shown to be consistent with the experimental data reported herein. Improvements to the noise prediction procedure, on the basis of the present study, are included, which increase the accuracy of the high frequency noise prediction

    On the use of relative velocity exponents for jet engine exhaust noise

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    The effect of flight on jet engine exhaust noise has often been presented in terms of a relative velocity exponent, n, as a function of radiation angle. The value of n is given by the OASPL reduction due to relative velocity divided by 10 times the logarithm of the ratio of relative jet velocity to absolute jet velocity. In such terms, classical subsonic jet noise theory would result in a value of n being approximately 7 at 90 degree angle to the jet axis with n decreasing, but remaining positive, as the inlet axis is approached and increasing as the jet axis is approached. However, flight tests have shown a wide range of results, including negative values of n in some cases. In this paper it is shown that the exponent n is positive for pure subsonic jet mixing noise and varies, in a systematic manner, as a function of flight conditions and jet velocity

    Subcooled- and net-boiling heat transfer to low-pressure water in electrically heated tubes

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    Experimental data on subcooled and net-quality boiling heat transfer to low pressure water in electrically heated tube

    The Skyrme Interaction in finite nuclei and nuclear matter

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    Self-consistent mean-field models are a powerful tool in the investigation of nuclear structure and low-energy dynamics. They are based on effective energy-density functionals, often formulated in terms of effective density-dependent nucleon-nucleon interactions. The free parameters of the functional are adjusted to empirical data. A proper choice of these parameters requires a comprehensive set of constraints covering experimental data on finite nuclei, concerning static as well as dynamical properties, empirical characteristics of nuclear matter, and observational information on nucleosynthesis, neutron stars and supernovae. This work aims at a comprehensive survey of the performance of one of the most successful non-relativistic self-consistent method, the Skyrme-Hartree-Fock model (SHF), with respect to these constraints. A full description of the Skyrme functional is given and its relation to other effective interactions is discussed. The validity of the application of SHF far from stability and in dense environments beyond the nuclear saturation density is critically assessed. The use of SHF in models extended beyond the mean field approximation by including some correlations is discussed. Finally, future prospects for further development of SHF towards a more consistent application of the existing and promisingly newly developing constraints are outlined.Comment: 71 pages, 22 figures. Accepted for publication in Prog.Part.Nucl.Phy
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