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The gas-to-dust mass ratios found for interstellar dust within the Solar System, versus values determined astronomically for the cloud around the Solar System, suggest that large and small interstellar grains have separate histories, and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and direction of interstellar gas in the cloud surrounding the solar system to derive an in situ value for the gas-to-dust mass ratio, $R_{g/d} = 94^{+46}_{-38}$. Hubble observations of the cloud surrounding the solar system yield a gas-to-dust mass ratio of Rg/d=551+61-251 when B-star reference abundances are assumed. The exclusion of small dust grains from the heliosheath and heliosphere regions are modeled, increasing the discrepancy between interstellar and in situ observations. The shock destruction of interstellar grains is considered, and comparisons are made with interplanetary and presolar dust grains., Comment: 87 pages, 9 figures, 6 tables, accepted for publication in Astrophysical Journal. Uses AASTeX

The solar system is moving through the partially ionized local interstellar cloud (LIC). The ionized matter of the LIC interacts with the expanding solar wind forming the heliospheric interface. The neutral component (interstellar atoms) penetrates through the heliospheric interface into the heliosphere, where it is measured directly "in situ" as pick-up ions and neutral atoms (and as anomalous cosmic rays) or indirectly through resonant scattering of solar Ly-alpha. When crossing the heliospheric interface, interstellar atoms interact with the plasma component through charge exchange. This interaction leads to changes of both neutral gas and plasma properties. The heliospheric interface is also the source of radio emissions which have been detected by the Voyager since 1983. In this paper, we have used a kinetic model of the flow of the interstellar atoms with updated values of velocity, temperature, and density of the circumsolar interstellar hydrogen and calculated how all quantities which are directly associated to the observations vary as a function of the interstellar proton number density. These quantities are the degree of filtration, the temperature and the velocity of the interstellar H atoms in the inner heliosphere, the distances to the bow shock (BS), heliopause, and termination shock, and the plasma frequencies in the LIC, at the BS and in the maximum compression region around the heliosphere which constitutes the "barrier" for radio waves formed in the interstellar medium. Comparing the model results with recent pickup ion data, Ly- alpha measurements, and low-frequencies radio emissions, we have searched for a number density of protons in the local interstellar cloud compatible with all observations., Comment: 14 pages, 5 figures, JGR-Space Physics, accepted, AGU preprint style

We study the production of $c \bar{c}$ pairs and dimuons from hard collisions in nuclear reactions within the covariant transport approach HSD. Adopting 6 mb for the $c \bar{c}$-baryon cross section the data on $J/\Psi$ suppression in p + A reactions are reproduced in line with calculations based on the Glauber model. Furthermore, using $J/\Psi$ absorption cross sections with mesons above the $D\bar{D}$ threshold in the order of 1.5 - 3 mb we find that all data on $J/\Psi$ suppression from NA38/NA50 can be described without assuming the formation of a quark-gluon plasma. Alternatively, we also investigate an 'early'-comover absorption scenario where the $c \bar{c}$ pairs are dissociated in the color electric fields of neighboring strings. Again we find good agreement with the experimental data with an estimate for the string radius of $R_s \approx 0.2-0.25 fm$., Comment: 9 pages, sprocl.tex, 1 .ps-figure, 2.eps-figures, Talk presented at the INT/RHIC workshop `Charmonium Production in Relativistic Nuclear Collisions' Seattle (USA), May 1998

We study systematically the production of strangeness in nuclear reactions from SIS to SPS energies within the covariant hadronic transport approach HSD. Whereas the proton and pion rapidity distributions as well as pion transverse momentum spectra are well described in the hadronic transport model from 2-200 AGeV, the $K^+$ and $K^-$ spectra are noticeably underestimated at AGS energies while the $K^+$ spectra match well at SIS and SPS energies with the experimental data. We conclude that the failure of the hadronic model at AGS energies points towards a nonhadronic phase during the collision of heavy systems around 10 AGeV., Comment: 25 pages, 19 figures

We study the production of cc~ pairs in nuclear reactions at SPS energies within the covariant transport approach HSD. The production of cc~ is treated perturbatively employing experimental cross sections while the interactions of cc~ pairs with baryons are included by conventional cascade-type two-body collisions. Adopting 6 mb for the cc~-baryon cross sections the data on J/\Psi suppression in p+A reactions are reproduced in line with calculations based on the Glauber model. Additionally the dissociation of the cc~ pairs by strings is included in a purely geometrical way. We find good agreement with experimental data from the NA38 and NA50 collaboration with an estimate for the string radius of ~0.2-0.3 fm., Comment: 9 pages (LaTeX), 5 PS figures

We present first results on the Ca isotopic abundances derived from the high resolution Mass Time-of-Flight (MTOF) spectrometer of the charge, element, and isotope analysis system (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO). We obtain isotopic ratios 40Ca/42Ca = (128+-47) and 40Ca/44Ca = (50+-8), consistent with terrestrial values. This is the first in situ determination of the solar wind calcium isotopic composition and is important for studies of stellar modeling and solar system formation since the present-day solar Ca isotopic abundances are unchanged from their original isotopic composition in the solar nebula., Comment: 14 pages, 3 figures

The tensor-RPA approach developed previously in part I is applied to the Nambu-Jona-Lasinio (NJL) model. As a first step we investigate the structure of Dirac-Hartree-Fock solutions for a rotationally and isospin invariant ground-state density. Whereas vacuum properties can be reproduced, no solitonic configuration for a system with unit baryon number is found. We then solve the tensor-RPA equation employing simple models of the nucleon ground state. In general the ph interaction effects a decrease of the excited states to lower energies. Due to an enhanced level density at low energies the obtained spectra cannot be matched with the experimental data when a standard MIT-bag configuration is used. However, when the size of the nucleon quark core is reduced to approximately 0.3 fm a fair description of the baryon spectrum in the positive-parity channel is achieved. For this purpose the residual interaction turns out to be crucial and leads to a significant improvement compared with the mean-field spectra., Comment: 33 pages, Latex, 9 Postscpript figures, section on the excited states has been completely rewritten after error was detected, results are now much more encouraging

In this paper we develop a theoretical framework which allows us to study excitations of the nucleon. Assuming an effective two-body interaction as a model for low-energy QCD, we derive a relativistic TDHF equation for a many-body system of quarks. To render the Dirac-sea contribution tothe mean field finite, we introduce a symmetry conserving regularization scheme. In the small amplitude limit we derive an RPA equation. The structure of the $ph$ interaction and modifications due to the regularization scheme are discussed. We give a prescription to obtain a nucleon state with good angular momentum (J) and isospin (T) quantum numbers on mean-field level. To study excitations, we develop a tensor-RPA approach, which is an extension of the conventional RPA techniques to systems with a nonscalar ground state. This allows us to construct excited states with good (J/T) quantum numbers. We discuss a method to reduce the overcomplete $ph$-space and compute the tensor-RPA interaction matrix elements. Finally we extend our scheme to include ({3/2}^+, {3/2})-states., Comment: Minor changes

Excited states of the nucleon are described as RPA configurations on a mean--field ground state taken from the MIT bag model. A residual interaction of a structure as in the Nambu--Jona--Lasinio model is used. The particle-hole states are coupled to good total angular momentum and isospin. Valence excitations of particle-hole type and quark--antiquark ($q\overline{q}$) states from the Dirac--sea are included. The dependence of the baryon spectrum and multipole response functions on the coupling constant $G$ is studied. At critical values of $G$ the 3q--ground state becomes degenerate with strongly collective $q\overline{q}$ modes. The model is used to calculate the electric polarizability of the neutron $\alpha_N$. Without residual interaction $\alpha_N=7\cdot 10^{-4}fm^3$ is found. With residual interaction the value increases to $\alpha_N=(7-11)\cdot 10^{-4}fm^3$. The measured value of $\alpha_N$ is reproduced within experimental error bars., Comment: LaTeX, 19 pages, 2 figures