Kinetic theory of cluster impingement in the framework of statistical mechanics of rigid disks

The paper centres on the evaluation of the function n(theta)=N(theta)/N0, that is the normalized number of islands as a function of coverage 0<theta<1, given N0 initial nucleation centres (dots) having any degree of spatial correlation. A mean field approach has been employed: the islands have the same size at any coverage. In particular, as far as the random distribution of dots is concerned, the problem has been solved by considering the contribution of binary collisions between islands only. With regard to correlated dots, we generalize a method previously applied to the random case only. In passing, we have made use of the exclusion probability reported in [S. Torquato, B. Lu, J. Rubinstein, Phys.Rev.A 41, 2059 (1990)], for determining the kinetics of surface coverage in the case of correlated dots, improving our previous calculation [M. Tomellini, M. Fanfoni, M. Volpe Phys. Rev.B 62, 11300, (2000)].Comment: 10 pages, 3 figure

Alloreactive cytotoxic T lymphocytes generated in the presence of viral- derived peptides show exquisite peptide and MHC specificity

The nature of alloreactivity to MHC molecules has been enigmatic, primarily because of the observation that allogeneic responses are considerably stronger than syngeneic responses. To better determine the specificity potential of allogeneic responses, we have generated alloreactive CTL specific for exogenous, viral-derived peptide ligands. This approach allowed us to critically evaluate both the peptide- and MHC-specificity of these alloreactive T cells. Exploiting the accessibility of the H-2Ld class I molecule for exogenous peptide ligands, alloreactive CTL were generated that are specific for either murine cytomegalovirus (MCMV) or lymphocytic choriomeningitis virus (LCMV) peptides bound by Ld alloantigens. Peptide specificity was initially observed in bulk cultures of alloreactive CTL only when tested on peptide-sensitized T2.Ld target cells that have defective presentation of endogenous peptides. Subsequent cloning of bulk alloreactive CTL lines generated to MCMV yielded CTL clones that had exquisitely specific MCMV peptide recognition requirement. All of the MCMV/Ld alloreactive CTL clones were also exquisitely MHC-specific in that none of the CTL clones lysed targets expressing MCMV/Lq complexes, even though Lq differs from Ld by only six amino acid residues and Lq also binds the MCMV peptide. This observation clearly demonstrates that alloreactive CTL are capable of the same degree of specificity for target cell recognition as are syngeneic CTL in MHC-restricted responses

Theoretical Description of Coulomb Balls - Fluid Phase

A theoretical description for the radial density profile of a finite number of identical charged particles confined in a harmonic trap is developed for application over a wide range of Coulomb coupling (or, equivalently, temperatures) and particle numbers. A simple mean field approximation neglecting correlations yields a density profile which is monotonically decreasing with radius for all temperatures, in contrast to molecular dynamics simulations and experiments showing shell structure at lower temperatures. A more complete theoretical description including charge correlations is developed here by an extension of the hypernetted chain approximation, developed for bulk fluids, to the confined charges. The results reproduce all of the qualitative features observed in molecular dynamics simulations and experiments. These predictions are then tested quantitatively by comparison with new benchmark Monte Carlo simulations. Quantitative accuracy of the theory is obtained for the selected conditions by correcting the hypernetted chain approximation with a representation for the associated bridge functions.Comment: 10 figures, submitted to Physical Review

Structure Functions and Pair Correlations of the Quark-Gluon Plasma

Recent experiments at RHIC and theoretical considerations indicate that the quark-gluon plasma, present in the fireball of relativistic heavy-ion collisions, might be in a liquid phase. The liquid state can be identified by characteristic correlation and structure functions. Here definitions of the structure functions and pair correlations of the quark-gluon plasma are presented as well as perturbative results. These definitions might be useful for verifying the quark-gluon-plasma liquid in QCD lattice calculations.Comment: 9 pages, 1 figure, revised version (new remark on the coupling parameter on page 2), to be published in Phys. Rev.

Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps

A density functional theory for colloidal dynamics is presented which includes hydrodynamic interactions between the colloidal particles. The theory is applied to the dynamics of colloidal particles in an optical trap which switches periodically in time from a stable to unstable confining potential. In the absence of hydrodynamic interactions, the resulting density breathing mode, exhibits huge oscillations in the trap center which are almost completely damped by hydrodynamic interactions. The predicted dynamical density fields are in good agreement with Brownian dynamics computer simulations

Attraction between like-charged colloidal particles induced by a surface a density - functional analysis

We show that the first non-linear correction to the linearised Poisson-Boltzman n (or DLVO) theory of effective pair interactions between charge-stabilised, co lloidal particles near a charged wall leads to an attractive component of entro pic origin. The position and depth of the potential compare favourably with rec ent experimental measurementsComment: 12 pages including 2 figures. submitted to physical review letter

What it takes to measure a fundamental difference between dark matter and baryons: the halo velocity anisotropy

Numerous ongoing experiments aim at detecting WIMP dark matter particles from the galactic halo directly through WIMP-nucleon interactions. Once such a detection is established a confirmation of the galactic origin of the signal is needed. This requires a direction-sensitive detector. We show that such a detector can measure the velocity anisotropy beta of the galactic halo. Cosmological N-body simulations predict the dark matter anisotropy to be nonzero, beta~0.2. Baryonic matter has beta=0 and therefore a detection of a nonzero beta would be strong proof of the fundamental difference between dark and baryonic matter. We estimate the sensitivity for various detector configurations using Monte Carlo methods and we show that the strongest signal is found in the relatively few high recoil energy events. Measuring beta to the precision of ~0.03 will require detecting more than 10^4 WIMP events with nuclear recoil energies greater than 100 keV for a WIMP mass of 100 GeV and a 32S target. This number corresponds to ~10^6 events at all energies. We discuss variations with respect to input parameters and we show that our method is robust to the presence of backgrounds and discuss the possible improved sensitivity for an energy-sensitive detector.Comment: 15 pages, 8 figures, accepted by JCAP. Matches accepted versio

New Green-Kubo formulas for transport coefficients in hard sphere-, Langevin fluids and the likes

We present generalized Green-Kubo expressions for thermal transport coefficients $\mu$ in non-conservative fluid-type systems, of the generic form, $\mu$ $= \mu_\infty$ +\int^\infty_0 dt V^{-1} \av{I_\epsilon \exp(t {\cal L}) I}_0 where $\exp(t{\cal L})$ is a pseudo-streaming operator. It consists of a sum of an instantaneous transport coefficient $\mu_\infty$, and a time integral over a time correlation function in a state of thermal equilibrium between a current $I$ and its conjugate current $I_\epsilon$. This formula with $\mu_\infty \neq 0$ and $I_\epsilon \neq I$ covers vastly different systems, such as strongly repulsive elastic interactions in hard sphere fluids, weakly interacting Langevin fluids with dissipative and stochastic interactions satisfying detailed balance conditions, and "the likes", defined in the text. For conservative systems the results reduce to the standard formulas.Comment: 7 pages, no figures. Version 2: changes in the text and references adde

Ornstein-Zernike equation and Percus-Yevick theory for molecular crystals

We derive the Ornstein-Zernike equation for molecular crystals of axially symmetric particles and apply the Percus-Yevick approximation to this system. The one-particle orientational distribution function has a nontrivial dependence on the orientation and is needed as an input. Despite some differences, the Ornstein-Zernike equation for molecular crystals has a similar structure as for liquids. We solve both equations for hard ellipsoids on a sc lattice. Compared to molecular liquids, the tensorial orientational correlators exhibit less structure. However, depending on the lengths a and b of the rotation axis and the perpendicular axes of the ellipsoids, different behavior is found. For oblate and prolate ellipsoids with b >= 0.35 (units of the lattice constant), damped oscillations in distinct directions of direct space occur for some correlators. They manifest themselves in some correlators in reciprocal space as a maximum at the Brillouin zone edge, accompanied by maxima at the zone center for other correlators. The oscillations indicate alternating orientational fluctuations, while the maxima at the zone center originate from nematic-like orientational fluctuations. For a <= 2.5 and b <= 0.35, the oscillations are weaker. For a >= 3.0 and b <= 0.35, no oscillations occur any longer. For many of the correlators in reciprocal space, an increase of a at fixed b leads to a divergence at the zone center q = 0, consistent with nematic-like long range fluctuations, and for some oblate and prolate systems with b ~< 1.0 a simultaneous tendency to divergence of few other correlators at the zone edge is observed. Comparison with correlators from MC simulations shows satisfactory agreement. We also obtain a phase boundary for order-disorder transitions.Comment: 20 pages, 13 figures, submitted to Phys. Rev.