Spin melting and refreezing driven by uniaxial compression on a dipolar hexagonal plate

We investigate freezing characteristics of a finite dipolar hexagonal plate by the Monte Carlo simulation. The hexagonal plate is cut out from a piled triangular lattice of three layers with FCC-like (ABCABC) stacking structure. In the present study an annealing simulation is performed for the dipolar plate uniaxially compressed in the direction of layer-piling. We find spin melting and refreezing driven by the uniaxial compression. Each of the melting and refreezing corresponds one-to-one with a change of the ground states induced by compression. The freezing temperatures of the ground-state orders differ significantly from each other, which gives rise to the spin melting and refreezing of the present interest. We argue that these phenomena are originated by a finite size effect combined with peculiar anisotropic nature of the dipole-dipole interaction.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference. To appear in a special issue of J. Phys. Condens. Matte

Quartic Anomalous Couplings in γγ\gamma\gamma Colliders

We study the constraints on the vertices $W^+W^- Z\gamma$, $W^+W^-\gamma\gamma$, and $ZZ\gamma\gamma$ that can be obtained from triple-gauge-boson production at the next generation of linear $e^+e^-$ colliders operating in the $\gamma\gamma$ mode. We analyze the processes $\gamma\gamma \to W^+W^-V$ ($V=Z$, or $\gamma$) and show that these reactions increase the potential of $e^+e^-$ machines to search for anomalous four-gauge-boson interactions.Comment: 15 pages, Latex file using ReVteX, 4 uufiled figures include

Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition

Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011-2012 apparition. We aim to confirm the physical parameters useful for JAXA's Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles. With optical imagers and 1-2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid. We have analyzed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R = 18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure

Neutrino Geophysics at Baksan I: Possible Detection of Georeactor Antineutrinos

J.M. Herndon in 90-s proposed a natural nuclear fission georeactor at the center of the Earth with a power output of 3-10 TW as an energy source to sustain the Earth magnetic field. R.S. Raghavan in 2002 y. pointed out that under certain condition antineutrinos generated in georeactor can be detected using massive scintillation detectors. We consider the underground Baksan Neutrino Observatory (4800 m.w.e.) as a possible site for developments in Geoneutrino physics. Here the intrinsic background level of less than one event/year in a liquid scintillation ~1000 target ton detector can be achieved and the main source of background is the antineutrino flux from power reactors. We find that this flux is ~10 times lower than at KamLAND detector site and two times lower than at Gran Sasso laboratory and thus at Baksan the georeactor hypothesis can be conclusively tested. We also discuss possible search for composition of georector burning nuclear fuel by analysis of the antineutrino energy spectrum.Comment: 7 pages in LaTeX, 3 PS figures, Submitted to Physics of Atomic Nucle

The multilevel trigger system of the DIRAC experiment

The multilevel trigger system of the DIRAC experiment at CERN is presented. It includes a fast first level trigger as well as various trigger processors to select events with a pair of pions having a low relative momentum typical of the physical process under study. One of these processors employs the drift chamber data, another one is based on a neural network algorithm and the others use various hit-map detector correlations. Two versions of the trigger system used at different stages of the experiment are described. The complete system reduces the event rate by a factor of 1000, with efficiency $\geq$95% of detecting the events in the relative momentum range of interest.Comment: 21 pages, 11 figure

Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2_2

We investigate the surface electronic structures of polar 1T'-MoTe2, the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy (ARPES) combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain-dependences, indicating the opposite bulk polarity. For both domains, some segment-like band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side.Comment: 13 pages, 4 figure

Protein design in a lattice model of hydrophobic and polar amino acids

A general strategy is described for finding which amino acid sequences have native states in a desired conformation (inverse design). The approach is used to design sequences of 48 hydrophobic and polar aminoacids on three-dimensional lattice structures. Previous studies employing a sequence-space Monte-Carlo technique resulted in the successful design of one sequence in ten attempts. The present work also entails the exploration of conformations that compete significantly with the target structure for being its ground state. The design procedure is successful in all the ten cases.Comment: RevTeX, 12 pages, 1 figur