Violent Relaxation of Indistinguishable Objects and Neutrino Hot Dark Matter in Clusters of Galaxies

The statistical mechanical investigation of violent relaxation (Lynden-Bell 1967) is extended to indistinguishable objects. It is found that, coincidentally, the equilibrium distribution is the same as that obtained for classical objects. For massive neutrinos, the Tremaine \& Gunn (1979) phase space bound is revisited and reinterpretated as the limit indicating the onset of degeneracy related to the coarse-grained phase space distribution. In the context of one of the currently most popular cosmological models, the Cold and Hot Dark Matter (CHDM) model (Primack et al. 1995), the onset of degeneracy may be of importance in the core region of clusters of galaxies. Degeneracy allows the neutrino HDM density to exceed the limit imposed by the Tremaine \& Gunn (1979) bound while accounting for the phase space bound.Comment: AASTeX, 16 pages, 2 EPS figures, uses aas2pp4.sty. Accepted by ApJ Letter

Twenty Years of Timing SS433

We present observations of the optical ``moving lines'' in spectra of the Galactic relativistic jet source SS433 spread over a twenty year baseline from 1979 to 1999. The red/blue-shifts of the lines reveal the apparent precession of the jet axis in SS433, and we present a new determination of the precession parameters based on these data. We investigate the amplitude and nature of time- and phase-dependent deviations from the kinematic model for the jet precession, including an upper limit on any precessional period derivative of $\dot P < 5 \times 10^{-5}$. We also dicuss the implications of these results for the origins of the relativistic jets in SS433.Comment: 21 pages, including 9 figures. To appear in the Astrophysical Journa

OAO-3 end of mission tests report

Twelve engineering type tests were performed on several subsystems and experiment(s) of the OAO 3 spacecraft near its end of mission. The systems tested include: Princeton experiment package (PEP), fine error system guidance, inertial reference unit, star trackers, heat pipes, thermal control coatings, command and data handling, solar array; batteries, and onboard processor/power boost regulator. Generally, the systems performed well for the 8 1/2 years life of OAO 3, although some degradation was noted in the sensitivity of PEP and in the absorptivity of the skin coatings. Battery life was prolonged during the life of the mission in large part by carefully monitoring the charge-discharge cycle with careful attention not to overcharge

A statistical-mechanical explanation of dark matter halo properties

Cosmological N-body simulations have revealed many empirical relationships of dark matter halos, yet the physical origin of these halo properties still remains unclear. On the other hand, the attempts to establish the statistical mechanics for self-gravitating systems have encountered many formal difficulties, and little progress has been made for about fifty years. The aim of this work is to strengthen the validity of the statistical-mechanical approach we have proposed previously to explain the dark matter halo properties. By introducing an effective pressure instead of the radial pressure to construct the specific entropy, we use the entropy principle and proceed in a similar way as previously to obtain an entropy stationary equation. An equation of state for equilibrated dark halos is derived from this entropy stationary equation, by which the dark halo density profiles with finite mass can be obtained. We also derive the anisotropy parameter and pseudo-phase-space density profile. All these predictions agree well with numerical simulations in the outer regions of dark halos. Our work provides further support to the idea that statistical mechanics for self-gravitating systems is a viable tool for investigation.Comment: 5 pages, 4 figures, Accepted by A&

Chance long-distance or human-mediated dispersal? How Acacia s.l. farnesiana attained its pan-tropical distribution

Acacia s.l. farnesiana, which originates from Mesoamerica, is the most widely distributed Acacia s.l. species across the tropics. It is assumed that the plant was transferred across the Atlantic to southern Europe by Spanish explorers, and then spread across the Old World tropics through a combination of chance long-distance and human-mediated dispersal. Our study uses genetic analysis and information from historical sources to test the relative roles of chance and human-mediated dispersal in its distribution. The results confirm the Mesoamerican origins of the plant and show three patterns of human- mediated dispersal. Samples from Spain showed greater genetic diversity than those from other Old World tropics, suggesting more instances of transatlantic introductions from the Americas to that country than to other parts of Africa and Asia. Individuals from the Philippines matched a population from South Central Mexico and were likely to have been direct, trans-Pacific introductions. Australian samples were genetically unique, indicating that the arrival of the species in the continent was independent of these European colonial activities. This suggests the possibility of pre-European human- mediated dispersal across the Pacific Ocean. These significant findings raise new questions for biogeographic studies that assume chance or transoceanic dispersal 2 for disjunct plant distributions

Laser-Cluster-Interaction in a Nanoplasma-Model with Inclusion of Lowered Ionization Energies

The interaction of intense laser fields with silver and argon clusters is investigated theoretically using a modified nanoplasma model. Single pulse and double pulse excitations are considered. The influence of the dense cluster environment on the inner ionization processes is studied including the lowering of the ionization energies. There are considerable changes in the dynamics of the laser-cluster interaction. Especially, for silver clusters, the lowering of the ionization energies leads to increased yields of highly charged ions.Comment: 10 pages, 11 figure

Phase transitions in self-gravitating systems. Self-gravitating fermions and hard spheres models

We discuss the nature of phase transitions in self-gravitating systems both in the microcanonical and in the canonical ensemble. We avoid the divergence of the gravitational potential at short distances by considering the case of self-gravitating fermions and hard spheres models. Three kinds of phase transitions (of zeroth, first and second order) are evidenced. They separate a ``gaseous'' phase with a smoothly varying distribution of matter from a ``condensed'' phase with a core-halo structure. We propose a simple analytical model to describe these phase transitions. We determine the value of energy (in the microcanonical ensemble) and temperature (in the canonical ensemble) at the transition point and we study their dependance with the degeneracy parameter (for fermions) or with the size of the particles (for a hard spheres gas). Scaling laws are obtained analytically in the asymptotic limit of a small short distance cut-off. Our analytical model captures the essential physics of the problem and compares remarkably well with the full numerical solutions.Comment: Submitted to Phys. Rev. E. New material adde

General-Relativistic Thomas-Fermi model

A system of self-gravitating massive fermions is studied in the framework of the general-relativistic Thomas-Fermi model. We study the properties of the free energy functional and its relation to Einstein's field equations. A self-gravitating fermion gas we then describe by a set of Thomas-Fermi type self-consistency equations.Comment: 7 pages, LaTex, to appear in Gen. Rel. Gra

Density profiles of dark matter haloes: diversity and dependence on environment

(Abridged) We study the outer density profiles of dark matter haloes predicted by a generalized secondary infall model and observed in a N-body cosmological simulation of a \Lambda CDM model. We find substantial systematic variations in shapes and concentrations of the halo profiles as well as a strong correlation of the profiles with the environment. In the N-body simulation, the average outer slope of the density profiles, \beta (\rho\propto r^{-\beta}), of isolated haloes is \approx 2.9; 68% of these haloes have values of \beta between 2.5 and 3.8. Haloes in dense environments of clusters are more concentrated and exhibit a broad distribution of \beta with values larger than for isolated haloes . Contrary to what one may expect, the haloes contained within groups and galaxy systems are less concentrated and have flatter outer density profiles than the isolated haloes. The concentration decreases with M_h, but its scatter for a given mass is substantial. The mass and circular velocity of the haloes are strongly correlated: M_h \propto V_m^{\alpha} with \alpha ~ 3.3 (isolated) and ~3.5 (haloes in clusters). For M_h=10^12M_sun the rms deviations from these relations are \Delta logM_h=0.12 and 0.18, respectively. Approximately 30% of the haloes are contained within larger haloes or have massive companions (larger than ~0.3 the mass of the current halo) within 3 virial radii. The remaining 70% of the haloes are isolated objects. The distribution of \beta as well as the concentration-mass and M_h-V_m relations for the isolated haloes agree very well with the predictions of our seminumerical approach which is based on a generalization of the secondary infall model and on the extended Press-Schechter formalism.Comment: 14 pages, 11 figures included, uses mn.sty, accepted by MNRAS. Minor modifications, new and updated reference