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An analysis of experimental data from the inverse-kinematics ISODEC experiment on 78Kr+40Ca reaction at a bombarding energy of 10 AMeV has revealed signatures of a hitherto unknown reaction mechanism, intermediate between the classical damped binary collisions and fusion-fission, but also substantially different from what is being termed in the literature as fast fission or quasi fission. These signatures point to a scenario where the system fuses transiently while virtually equilibrating mass asymmetry and energy and, yet, keeping part of the energy stored in a collective shock-imparted and, possibly, angular momentum bearing form of excitation. Subsequently the system fissions dynamically along the collision or shock axis with the emerging fragments featuring a broad mass spectrum centered around symmetric fission, relative velocities somewhat higher along the fission axis than in transverse direction, and virtually no intrinsic spin. The class of massasymmetric fission events shows a distinct preference for the more massive fragments to proceed along the beam direction, a characteristic reminiscent of that reported earlier for dynamic fragmentation of projectile-like fragments alone and pointing to the memory of the initial mass and velocity distribution., Comment: 5 PAGES, 6 FIGURES

In many applications, one has side information, e.g., labels that are provided in a semi-supervised manner, about a specific target region of a large data set, and one wants to perform machine learning and data analysis tasks "nearby" that prespecified target region. For example, one might be interested in the clustering structure of a data graph near a prespecified "seed set" of nodes, or one might be interested in finding partitions in an image that are near a prespecified "ground truth" set of pixels. Locally-biased problems of this sort are particularly challenging for popular eigenvector-based machine learning and data analysis tools. At root, the reason is that eigenvectors are inherently global quantities, thus limiting the applicability of eigenvector-based methods in situations where one is interested in very local properties of the data. In this paper, we address this issue by providing a methodology to construct semi-supervised eigenvectors of a graph Laplacian, and we illustrate how these locally-biased eigenvectors can be used to perform locally-biased machine learning. These semi-supervised eigenvectors capture successively-orthogonalized directions of maximum variance, conditioned on being well-correlated with an input seed set of nodes that is assumed to be provided in a semi-supervised manner. We show that these semi-supervised eigenvectors can be computed quickly as the solution to a system of linear equations; and we also describe several variants of our basic method that have improved scaling properties. We provide several empirical examples demonstrating how these semi-supervised eigenvectors can be used to perform locally-biased learning; and we discuss the relationship between our results and recent machine learning algorithms that use global eigenvectors of the graph Laplacian.

The evolution of the nuclear matter density distribution with excitation energy is studied within the framework of a finite-range interacting Fermi gas model and microcanonical thermodynamics in Thomas-Fermi approximation. It is found that with increasing excitation energy, both infinite and finite systems become unstable against infinitesimal matter density fluctuations, albeit in different ways. In modeling, this instability reveals itself via an apparent negative heat capacity of the system and is seen to result in the volume boiling in the case of infinite matter and surface boiling in the case of finite systems. The latter phenomenon of surface boiling is unique to small systems and it appears to provide a natural explanation for the observed saturation-like patterns in what is commonly termed caloric curves and what represents functional dependence of nuclear temperature on the excitation energy., Comment: 17 pages, 4 figures

The Large Underground Xenon (LUX) dark matter search experiment is currently being deployed at the Homestake Laboratory in South Dakota. We will highlight the main elements of design which make the experiment a very strong competitor in the field of direct detection, as well as an easily scalable concept. We will also present its potential reach for supersymmetric dark matter detection, within various timeframes ranging from 1 year to 5 years or more., Comment: 4 pages, in proceedings of the SUSY09 conference

Based on an extended compound nucleus model, isospin effects in statistical fragment emission from excited nuclear systems are investigated. An experimentally observed scaling behavior of the ratio of isotope yields $Y_i(N,Z)$ from two similar emitting sources with different neutron-to-proton ratios is predicted theoretically, i.e., the relationship of $Y_2/Y_1 \propto exp(\alpha N + \beta Z)$ is demonstrated. The symmetry energy coefficient $C_{sym}$ extracted from the simulation results is $\sim$ 27 MeV which is consistent with realistic theoretical estimates and recent experimental data. The influence of the surface entropy on the isoscaling behavior is discussed in detail. It is found that although the surface entropy increases the numercial values of isoscaling parameters $\alpha$ and $\beta$, it does not affect the isoscaling behavior qualitatively and has only a minor effect on the extracted symmetry energy coefficient., Comment: 10 pages, 6 figures

Characteristic signatures of statistical Coulomb fragmentation of highly excited nuclear systems were analyzed. It was found that in some important aspects, they coincide with perceived signatures of phase transitions in confined hypothetical pseudo-microcanonical systems, thus potentially giving rise to a false interpretation of experimental observations in terms of phase transitions. It is demonstrated that the heat capacity as derived based on experimental observations may show domains of faux negative heat capacity for the same fundamental reason a faux negative heat capacity appears in constrained numerical modeling of phase transitions in excited nuclear matter, the reason being an effective truncation of the microcanonical phase space. Similarly, selected experimental data may exhibit bimodality apparently in accordance with the truncated pseudo-microcanonical (but not the true microcanonical) calculations for confined systems., Comment: 23 pages, 7 figures

We propose a new concept for a very low background multi-ton liquid xenon Dark Matter experiment. The detector consists of two concentric spheres and a charge readout device in the centre. Xenon between the two spheres forms a self-shield and veto device. The inner surface of the central sphere is coated with CsI to form an internal photocathode with minimum of 2\pi coverage for any event in the active volume. Photoelectrons from the CsI photocathode drift toward the charge readout micro-structure in the centre of the detector. Both scintillation and ionisation are measured simultaneously for background rejection and 3-D event mapping. In addition to external shielding, the low background is achieved by eliminating PMTs and by using low radioactivity pure materials throughout the detector. We present detailed calculations of the charge readout system and design details. The detector is expected to probe the full SUSY parameter space., Comment: to appear in Proc. 7th UCLA Symposium on Sources and Detection of Dark Matter and Dark Energy in the Universe, 22-24 February, Marina del Rey, USA; Nucl. Phys. B Proc. Suppl., in press; 4 pages, 3 figues

Particle evaporation rates from excited nuclear systems at equilibrium matter density are studied within the Harmonic-Interaction Fermi Gas Model (HIFGM) combined with Weisskopf's detailed balance approach. It is found that thermal expansion of a hot nucleus, as described quantitatively by HIFGM, leads to a significant retardation of particle emission, greatly extending the validity of Weisskopf's approach. The decay of such highly excited nuclei is strongly influenced by surface instabilities.

The caloric curve for mononuclear configurations is studied with a schematic model. We investigate the dependence of the entropy on the density and effective mass profiles. A plateau in the caloric curve is a direct result of decreasing density and the destruction of correlations with increasing excitation. The mononuclear regime is metastable with respect to binary fission at low excitation energy and unstable with respect to multifragmentation at high excitation. The statistical framework presented here is suitable to treat scenarios where experimental conditions are set to favor population of highly excited mononuclear states., Comment: 4 pages, 4 figures, 3 color

The importance of a Coulomb correction to the formalism proposed by Albergo et al. for determining the temperatures of nuclear systems at break-up and the ensities of free nucleon gases is discussed. While the proposed correction has no effect on the temperatures extracted based on double isotope ratios, it becomes non-negligible when such temperatures or densities of free nucleon gases are extracted based on multiplicities of heavier fragments of different atomic numbers.

Experimental joint multiplicity distributions of neutrons and charged particles emitted in complex nuclear reactions provide an important test of theoretical models. The method is applied to test three different theoretical models of nuclear multi-fragmentation, two of which fail the test. The measurement of neutrons is decisive in distinguishing between the Berlin and Copenhagen models of nuclear multi-fragmentation and challenges the interpretation of pseudo- Arrhenius plots. Statistical-model evaporation calculations with GEMINI give a good reproduction first and second moments of the experimental multiplicity correlations., Comment: 12 pages, 3 figures Added GEMINI calculations of multiplicity correlations Added brief discussion of how neutron emission is treated in MMMC

It is found that the total IMF-transverse-energy (E_t) spectra in multi-IMF events are well represented by synthetic spectra obtained by folding of the single-IMF spectrum. Using the experimental IMF multiplicity distribution, the observed trends in the IMF multiplicity distribution for fixed values of E_t are reproduced. The synthetic distributions show binomial reducibility and Arrhenius-like scaling, similar to that reported in the literature. Similar results are obtained when the above folding-type synthesis is replaced with one based on mixing events with different IMF multiplicities. For statistically independent IMF emission, the observed binomial reducibility and Arrhenius-type scaling are merely reflections of the shape of the single-IMF transverse-energy spectrum. Hence, a valid interpretation of IMF distributions in terms of a particular production scenario has to explain independently the observed shape of the single-IMF E_t spectrum., Comment: 13 pages with 8 figure

A novel mechanism of prompt nuclear fragmentation is proposed. Assuming micro-canonical or canonical equilibrium, it is shown that a strong enhancement of the accessible phase space volume, due to the diffuceness of the nuclear surface, leads to dynamical instabilities of hot nuclei and to prompt fragmentation. Equations are derived for the transition temperature T_T, for which the thermodynamical surface tension vanishes, as well as for the thermodynamical fissility parameter chi_td., Comment: 11 pages, 2 figures