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

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

Technical approach for the design of a high-resolution spectral model on a sphere: Application to decaying turbulence

International audienceSeveral technical suggestions to construct a high-resolution spectral model on a sphere (the T682 barotropic model) are presented and their implementation of FORTRAN77 libraries is provided as a free software package ISPACK (http://www.gfd-dennou.org/arch/ispack/). A test experiment on decaying turbulence is conducted to demonstrate the ability of the model

A further experiment on two-dimensional decaying turbulence on a rotating sphere

A series of numerical experiments on the two-dimensional decaying turbulence is performed for a non-divergent barotropic fluid on a rotating sphere by using a high-resolution spectral model. Time variations of the energy spectrum and the flow field are highly dependent on the rotation rate. In non-rotational cases, isolated coherent vortices emerge in the course of time development as in the planar two-dimensional turbulence. As the rotation rate increases, however, the evolution of the flow field changes drastically, and a westward circumpolar vortex appears in high-latitudes as well as zonal band structures in mid- and low-latitudes. The dependence of these features on the initial energy spectrum is investigated and the dynamics of such pattern formations is discussed

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

CANGAROO-III Observation of TeV Gamma Rays from the vicinity of PSR B1 706-44

Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov Telescope has detected extended emission of TeV gamma rays in the vicinity of the pulsar PSR B1706$-$44. The strength of the signal observed as gamma-ray-like events varies when we apply different ways of emulating background events. The reason for such uncertainties is argued in relevance to gamma-rays embedded in the "off-source data", that is, unknown sources and diffuse emission in the Galactic plane, namely, the existence of a complex structure of TeV gamma-ray emission around PSR B1706$-$44.Comment: 10 pages, 13 figures, to be published in Ap

Multiple time scales in cataclysmic binaries. The low-field magnetic dwarf nova DO Draconis

We study the variability of the cataclysmic variable DO Dra, on time-scales of between minutes and decades. The characteristic decay time dt/dm=0.902(3) days/mag was estimated from our 3 nights of CCD R observations. The quiescent data show a photometric wave with a cycle about 303(15)d. We analyzed the profile of the composite (or mean) outburst. We discovered however, that a variety of different outburst heights and durations had occurred, contrary to theoretical predictions. With increasing maximum brightness, we find that the decay time also increases; this is in contrast to the model predictions, which indicate that outbursts should have a constant shape. This is interpreted as representing the presence of outburst-to-outburst variability of the magnetospheric radius. A presence of a number of missed weak narrow outbursts is predicted from this statistical relationship. A new type of variability is detected, during 3 subsequent nights in 2007: periodic (during one nightly run) oscillations with rapidly-decreasing frequency from 86 to 47 cycles/day and a semi-amplitude increasing from 0.06 to 0. 10, during a monotonic brightness increase from 14. 27 to 14. 13. This phenomenon was observed only during an unusually prolonged event of about 1 mag brightening in 2007 (lasting till autumn), during which no (expected) outburst was detected. We refer to this behaviour as to the transient periodic oscillations (TPO). To study this new and interesting phenomenon, new regular photometric and spectral (in a target of opportunity mode) observations are required.Comment: 12pages, 8figures, accepted in Astronomy and Astrophysic

CANGAROO-III observation of TeV gamma rays from the unidentified gamma-ray source HESS J1614-518

We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov telescope array, of a very high energy gamma-ray signal from the unidentified gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9 sigma level during an effective exposure of 54 hr from 2008 May to August. The spectrum can be represented by a power-law: 8.2+-2.2_{stat}+-2.5_{sys}x10^{-12}x (E/1TeV)^{-Gamma} cm^{-2} s^{-1} TeV^{-1} with a photon index Gamma of 2.4+-0.3_{stat}+-0.2_{sys}, which is compatible with that of the H.E.S.S. observations. By combining our result with multi-wavelength data, we discuss the possible counterparts for HESS J1614-518 and consider radiation mechanisms based on hadronic and leptonic processes for a supernova remnant, stellar winds from massive stars, and a pulsar wind nebula. Although a leptonic origin from a pulsar wind nebula driven by an unknown pulsar remains possible, hadronic-origin emission from an unknown supernova remnant is preferred.Comment: 9 pages, 7 figures, accepted for publication in Ap