The stopping of swift protons in matter and its implication for astrophysical fusion reactions

The velocity dependence of the stopping power of swift protons and deuterons in low energy collisions is investigated. At low projectile energies the stopping is mainly due to nuclear stopping and charge exchange of the electron. The second mechanism dominates after Ep >=200 eV. A dynamical treatment of the charge exchange mechanism based on two-center electronic wavefunctions yields very transparent results for the exchange probability. We predict that the stopping cross sections vary approximately as v to the 1.35 power for projectile protons on hydrogen targets in the 1 keV energy region.Comment: 4 figure

Charge confinement and Klein tunneling from doping graphene

In the present work, we investigate how structural defects in graphene can change its transport properties. In particular, we show that breaking of the sublattice symmetry in a graphene monolayer overcomes the Klein effect, leading to confined states of massless Dirac fermions. Experimentally, this corresponds to chemical bonding of foreign atoms to carbon atoms, which attach themselves to preferential positions on one of the two sublattices. In addition, we consider the scattering off a tensor barrier, which describes the rotation of the honeycomb cells of a given region around an axis perpendicular to the graphene layer. We demonstrate that in this case the intervalley mixing between the Dirac points emerges, and that Klein tunneling occurs.Comment: 11 pages, 5 figure

Visibility Fringe Reduction Due to Noise-Induced Effects: Microscopic Approach to Interference Experiments

Decoherence is the main process behind the quantum to classical transition. It is a purely quantum mechanical effect by which the system looses its ability to exhibit coherent behavior. The recent experimental observation of diffraction and interference patterns for large molecules raises some interesting questions. In this context, we identify possible agents of decoherence to take into account when modeling these experiments and study theirs visible (or not) effects on the interference pattern. Thereby, we present an analysis of matter wave interferometry in the presence of a dynamic quantum environment and study how much the visibility fringe is reduced and in which timescale the decoherence effects destroy the interference of massive objects. Finally, we apply our results to the experimental data reported on fullerenes and cold neutrons.Comment: 14 pages, 5 figures. Version to appear in Mod. Phys.

Emotional Episodes Facilitate Word Recall

Dysphoric and nondysphoric college students described self-generated images of themselves interacting with the referents of neutral nouns; the nouns were paired with adjectives that changed their emotional meaning (e.g., cruise ship, cargo ship, sinking ship). On the subsequent unexpected test, the nouns from emotional pairings were more frequently recalled than were those from neutral pairings, regardless of their valence or congruence with the students\u27 mood. An examination of the initial descriptions revealed that emotional images were more distinctive, but not in a pattern correlated with recall of the corresponding nouns

Constructive Memory for Bizarre and Sensible Sentences

Sensible, interrelated sentences were presented with or without bizarre sentences that could be transformed to fit the context of the sensible sentences. Two experiments examined subjects\u27 ability to recognize or recall both types of sentences, either immediately or after 2 weeks. Bizarre sentences were frequently recognized at immediate testing; they were generally unavailable at delayed recognition and were never recalled verbatim. In addition, results indicated that transformations of bizarre sentences were stored in memory but were not well incorporated within the structure for the sensible material. These findings are consistent with a constructive approach to memory. Finally, the results suggest that processing bizarre information can lead to more accurate recognition and recall of the sensible context

Cognition, Emotion, and Memory: Some Applications and Issues

This chapter describes some ways in which the psychology of cognition, emotion, and memory can or might be applied in several practical settings. Recent years have seen a rapid growth in research on cognition and emotion and this research has been summarized in a variety of sources (e.g., Ellis & Ashbrook, 1988, 1989; Ellis, Varner, & Becker, in press; Fiedler & Forgas, 1988; lsen, 1984; Kuiken, 1989; Williams, Watts, MacLeod, & Mathews, 1988). Moreover, a new journal appeared in 1987, Cognition and Emotion, which is entirely devoted to relations among emotional states and the full range of cognitive processes typically studied by psychologists. Ellis and Ashbrook (1989) noted that although this research area has a much earlier history of activity, it lay relatively dormant until the mid-1970s. However, its growth has accelerated rapidly until it has now become an important and active area of research and theoretical development

The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon (=A0620-00)

We have used NIRSPEC on Keck II to obtain $K$-band spectroscopy of the low mass X-ray binary V616 Mon (= A0620$-$00). V616 Mon is the proto-typical soft x-ray transient containing a black hole primary. As such it is important to constrain the masses of the binary components. The modeling of the infrared observations of ellipsoidal variations in this system lead to a derived mass of 11.0 M_{\sun} for the black hole. The validity of this derivation has been called into question due to the possiblity that the secondary star's spectral energy distribution is contaminated by accretion disk emission (acting to dilute the variations). Our new $K$-band spectrum of V616 Mon reveals a late-type K dwarf secondary star, but one that has very weak $^{\rm 12}$CO absorption features. Comparison of V616 Mon with SS Cyg leads us to estimate that the accretion disk supplies only a small amount of $K$-band flux, and the ellipsoidal variations are not seriously contaminated. If true, the derived orbital inclination of V616 Mon is not greatly altered, and the mass of the black hole remains large. A preliminary stellar atmosphere model for the $K$-band spectrum of V616 Mon reveals that the carbon abundance is approximately 50% of the solar value. We conclude that the secondary star in V616 Mon has either suffered serious contamination from the accretion of supernova ejecta that created the black hole primary, or it is the stripped remains of a formerly more massive secondary star, one in which the CNO cycle had been active.Comment: 20 pages, 5 figure