Discovery of 15-second oscillations in Hubble Space Telescope observations of WZ Sagittae following the 2001 outburst

We report the discovery of 15-s oscillations in ultraviolet observations of WZ Sge obtained with the Hubble Space Telescope approximately one month after the peak of the 2001 outburst. This is the earliest detection of oscillations in WZ Sge following an outburst and the first time that a signal near 15 s has been seen to be dominant. The oscillations are quite strong (amplitude about 5%), but not particularly coherent. In one instance, the oscillation period changed by 0.7 s between successive observations separated by less than 1 hour. We have also found evidence for weaker signals with periods near 6.5 s in some of our data. We discuss the implications of our results for the models that have been proposed to account for the 28-s oscillations seen in quiescence. If the periods of the 15-s oscillations can be identified with the periods of revolution of material rotating about the white dwarf, the mass of the white dwarf must satisfy M_WD > 0.71 M_sun. The corresponding limit for the 6.5-s signals is M_WD > 1.03 M_sun.Comment: accepted for publication in ApJ Letters; 13 pages, 4 postscript figures; new version corrects a few typos and matches version that will appear in ApJ

Chiral charge-density-waves

We discovered the chirality of charge density waves (CDW) in 1T-TiSe$_2$ by using scanning tunnelling microscopy (STM) and optical ellipsometry. We found that the CDW intensity becomes $I{a_1}:I{a_2}:I{a_3} = 1:0.7 \pm 0.1:0.5 \pm 0.1$, where $Ia_i$ (i =1, 2, 3) is the amplitude of the tunnelling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease \textit{clockwise} and \textit{anticlockwise} when we index each nesting vector in order of intensity in the Fourier transformation of the STM images. The chirality in CDW results in the three-fold symmetry breaking. Macroscopically, two-fold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H_{CDW} \equiv {\boldmath q_1} \cdot ({\boldmath q_2}\times {\boldmath q_3}), where {\boldmath q_i} are the nesting vectors, which is independent of the symmetry of components. The nonzero $H_{CDW}$ - the triple-{\boldmath q} vectors do not exist in an identical plane in the reciprocal space - should induce a real-space chirality in CDW system.Comment: 12 pages, 4 figure

Equation of motion for dislocations with inertial effects

An approximate equation of motion is proposed for screw and edge dislocations, which accounts for retardation and for relativistic effects in the subsonic range. Good quantitative agreement is found, in accelerated or in decelerated regimes, with numerical results of a more fundamental nature.Comment: 6 pages, 4 figures, LaTe

Isolation of 76Br from irradiated Cu276Se targets using dry distillation: evaluations and improvement for routine production

Introduction 76Br is of interest for in vivo PET imaging applications. Its relatively long half-life (16.1 h) allows use not only on small molecules but also proteins which have slow excretion as carrier molecules. Irradiation using a low energy proton beam (~ 20 MeV) on an enriched Cu276Se target, followed by dry distillation with thermal chromatography, is one of the best methods to obtain sufficient amounts of 76Br for clinical applications1,2. However, the thermal chromatography is plagued by poor reproducibility and appears unsuitable for automation of its production, leading us to remove the thermal chroma-tography from the dry distillation. In this investigation we employed H2O solution to collect 76Br and optimized the distillation condition using a small amount of 77Br (57.0 h). We also produced large amount of 76Br under the optimized conditions to evaluate the dry distillation method. Material and Methods Target preparation and dry distillation were conducted based on the methods described in previous reports1,2. To produce 77Br, Cu2natSe target was irradiated with 20 MeV proton beams (5 µA) accelerated by AVF cyclotron in the Japan Atomic Energy Agency. The following two systems were used in the dry distillation optimization studies; (1) an initial system was composed of two furnaces, a main and an auxiliary furnace. Temperature of each furnace was set at 1050 °C (main) and 200 °C (auxiliary) respectively; (2) the second system was made of one large furnace composed of heating and cooling area. Temperature of the heating area was varied from 1050 to 1120 °C. In both systems PTFE tubing, leading to a H2O solution (15 mL), was inserted into the apparatus. The irradiated target was heated under streaming Ar gas (30 mL/min.). An enriched Cu276Se target (76Se enrichment: 99.67%) was used for 76Br production. Radioactivity was measured on a high-purity germanium (HPGe) detector coupled to a multichannel analyzer. TLC analyses were conducted on Al2O3 plates (Merck) using 7:1 acetone:H2O as the eluting solvent. Results and Conclusion Low efficiency (33 %) of 77Br recovery was ob-served in the initial system. Distribution of radioactivity inside the apparatus showed that 35 % was trapped in the PTFE tube and the quartz tube. The recovery yield was increased up to 54 % when the auxiliary furnace was turned off, indicating that the temperature gradient inside the quartz tube is suitable to carry 77Br effectively to the H2O trap. We initially used a quartz boat to place the irradiated target in the furnace, but found that using a reusable tungsten backing was better. However, we found that recovery yield was dramatically reduced to 18 %. The studies where the temperature was varied showed that releasing efficiency was increased up to 100 % at the temperature of 1120 °C. Good recovery yield (~ 77 %) was achieved after optimizing the temperature gradient (FIG. 1b). Using the optimized setup, 76Br production runs (n = 6) have been conducted, allowing us to recover up to 39.8 MBq/µAh (EOB) of 76Br. High specific activity (~4400 GBq/µmol) was obtained in the final solution. TLC analysis showed that chemical form obtained was bromide. We concluded that the dry distillation using H2O trap is capable of providing enough high purity 76Br for clinical applications

Site percolation and random walks on d-dimensional Kagome lattices

The site percolation problem is studied on d-dimensional generalisations of the Kagome' lattice. These lattices are isotropic and have the same coordination number q as the hyper-cubic lattices in d dimensions, namely q=2d. The site percolation thresholds are calculated numerically for d= 3, 4, 5, and 6. The scaling of these thresholds as a function of dimension d, or alternatively q, is different than for hypercubic lattices: p_c ~ 2/q instead of p_c ~ 1/(q-1). The latter is the Bethe approximation, which is usually assumed to hold for all lattices in high dimensions. A series expansion is calculated, in order to understand the different behaviour of the Kagome' lattice. The return probability of a random walker on these lattices is also shown to scale as 2/q. For bond percolation on d-dimensional diamond lattices these results imply p_c ~ 1/(q-1).Comment: 11 pages, LaTeX, 8 figures (EPS format), submitted to J. Phys.

Formation of hydrogen-boron complexes in boron-doped silicon treated with a high concentration of hydrogen atoms

The formation of hydrogen (H) related complexes and their effect on boron (B) dopant were investigated in B-ion implanted and annealed silicon (Si) substrates treated with a high concentration of H. Isotope shifts by replacement of 10B with 11B were observed for some H-related Raman peaks, but not for other peaks. This shows proof of the formation of B-H complexes in which H directly bonds to B in Si. This is an experimental result concerning the formation of B-H complexes with H bonded primarily to B. Electrical resistivity measurements showed that the B acceptors are passivated via the formation of the observed B-H complexes, as well as the well-known passivation center in B-doped Si; namely, the H-B passivation center

Ultrafast Electron-Phonon Decoupling in Graphite

We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced non-equilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the non-adiabatic electron-phonon interaction by creating the non-equilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast non-equilibrium electron dynamics.Comment: 4 pages, 4 figure

Measures of insulin sensitivity, leptin, and adiponectin concentrations in cats in diabetic remission compared to healthy control cats

Objectives: Firstly, to compare differences in insulin, adiponectin, leptin, and measures of insulin sensitivity between diabetic cats in remission and healthy control cats, and determine whether these are predictors of diabetic relapse. Secondly, to determine if these hormones are associated with serum metabolites known to differ between groups. Thirdly, if any of the hormonal or identified metabolites are associated with measures of insulin sensitivity. Animals: Twenty cats in diabetic remission for a median of 101 days, and 21 healthy matched control cats. Methods: A casual blood glucose measured on admission to the clinic. Following a 24 h fast, a fasted blood glucose was measured, and blood sample taken for hormone (i.e., insulin, leptin, and adiponectin) and untargeted metabolomic (GC-MS and LC-MS) analysis. A simplified IVGGT (1 g glucose/kg) was performed 3 h later. Cats were monitored for diabetes relapse for at least 9 months (270 days). Results: Cats in diabetic remission had significantly higher serum glucose and insulin concentrations, and decreased insulin sensitivity as indicated by an increase in HOMA and decrease in QUICKI and Bennett indices. Leptin was significantly increased, but there was no difference in adiponectin (or body condition score). Several significant correlations were found between insulin sensitivity indices, leptin, and serum metabolites identified as significantly different between remission and control cats. No metabolites were significantly correlated with adiponectin. No predictors of relapse were identified in this study. Conclusion and clinical importance: Insulin resistance, an underlying factor in diabetic cats, persists in diabetic remission. Cats in remission should be managed to avoid further exacerbating insulin resistance