Slow Relaxation Process in Ising like Heisenberg Kagome Antiferromagnets due to Macroscopic Degeneracy in the Ordered State

We study relaxation phenomena in the ferromagnetically ordered state of the Ising-like Heisenberg kagome antiferromagnets. We introduce the "weathervane loop" in order to characterize macroscopic degenerate ordered states and study the microscopic mechanism of the slow relaxation from a view point of the dynamics of the weathervane loop configuration. This mechanism may give a possible origin of the slow relaxation reported in recent experiments.Comment: 6pages, 4figures, HFM2006 proceeding

Pseudogap Formation in Models for Manganites

The density-of-states (DOS) and one-particle spectral function $\rm A({\bf k}, \omega)$ of the one- and two-orbital models for manganites, the latter with Jahn-Teller phonons, are evaluated using Monte Carlo techniques. Unexpectedly robust pseudogap (PG) features were found at low- and intermediate-temperatures, particularly at or near regimes where phase-separation occurs as $\rm T$$\to$0. The PG follows the chemical potential and it is caused by the formation of ferromagnetic metallic clusters in an insulating background. It is argued that PG formation should be generic of mixed-phase regimes. The results are in good agreement with recent photoemission experiments for $\rm La_{1.2} Sr_{1.8} Mn_2 O_7$.Comment: Accepted for publication in Phys. Rev. Lett., 4 pages, Revtex, with 4 figures embedde

Structural and phylogenetic analysis of a conserved actinobacteria-specific protein (ASP1; SCO1997) from Streptomyces coelicolor

<p>Abstract</p> <p>Background</p> <p>The Actinobacteria phylum represents one of the largest and most diverse groups of bacteria, encompassing many important and well-characterized organisms including <it>Streptomyces, Bifidobacterium, Corynebacterium </it>and <it>Mycobacterium</it>. Members of this phylum are remarkably diverse in terms of life cycle, morphology, physiology and ecology. Recent comparative genomic analysis of 19 actinobacterial species determined that only 5 genes of unknown function uniquely define this large phylum <abbrgrp><abbr bid="B1">1</abbr></abbrgrp>. The cellular functions of these actinobacteria-specific proteins (ASP) are not known.</p> <p>Results</p> <p>Here we report the first characterization of one of the 5 actinobacteria-specific proteins, ASP1 (Gene ID: SCO1997) from <it>Streptomyces coelicolor</it>. The X-ray crystal structure of ASP1 was determined at 2.2 Ǻ. The overall structure of ASP1 retains a similar fold to the large NP-1 family of nucleoside phosphorylase enzymes; however, the function is not related. Further comparative analysis revealed two regions expected to be important for protein function: a central, divalent metal ion binding pore, and a highly conserved elbow shaped helical region at the C-terminus. Sequence analyses revealed that ASP1 is paralogous to another actinobacteria-specific protein ASP2 (SCO1662 from <it>S. coelicolor</it>) and that both proteins likely carry out similar function.</p> <p>Conclusion</p> <p>Our structural data in combination with sequence analysis supports the idea that two of the 5 actinobacteria-specific proteins, ASP1 and ASP2, mediate similar function. This function is predicted to be novel since the structures of these proteins do not match any known protein with or without known function. Our results suggest that this function could involve divalent metal ion binding/transport.</p

Multifrequency Polarimetry of the Nrao 140 Jet: Possible Detection of a Helical Magnetic Field and Constraints on its Pitch Angle

We present results from multifrequency polarimetry of NRAO 140 using the Very Long Baseline Array. These observations allow us to reveal the distributions of both the polarization position angle and the Faraday rotation measure (RM). These distributions are powerful tools to discern the projected and line-of-sight components of the magnetic field, respectively. We find a systematic gradient in the RM distribution, with its sign being opposite at either side of the jet with respect to the jet axis. The sign of the RM changes only with the direction of the magnetic field component along the line of sight, so this can be explained by the existence of helical magnetic components associated with the jet itself. We derive two constraints for the pitch angle of the helical magnetic field from the distributions of the RM and the projected magnetic field; the RM distribution indicates that the helical fields are tightly wound, while that of the projected magnetic field suggests they are loosely wound around the jet axis. This inconsistency may be explained if the Faraday rotator is not cospatial with theemitting region. Our results may point toward a physical picture in which an ultra-relativistic jet (spine) with a loosely wound helical magnetic field is surrounded by a sub-relativistic wind layer (sheath) with a tightly wound helical magnetic field.Comment: 12 pages, 4 figures, ApJ, in pres

Cosmological test of gravity with polarizations of stochastic gravitational waves around 0.1-1 Hz

In general relativity, a gravitational wave has two polarization modes (tensor mode), but it could have additional polarizations (scalar and vector modes) in the early stage of the universe, where the general relativity may not strictly hold and/or the effect of higher-dimensional gravity may become significant. In this paper, we discuss how to detect extra-polarization modes of stochastic gravitational wave background (GWB), and study the separability of each polarization using future space-based detectors such as BBO and DECIGO. We specifically consider two plausible setups of the spacecraft constellations consisting of two and four clusters, and estimate the sensitivity to each polarization mode of GWBs. We find that a separate detection of each polarization mode is rather sensitive to the geometric configuration and distance between clusters and that the clusters should be, in general, separated by an appropriate distance. This seriously degrades the signal sensitivity, however, for suitable conditions, space-based detector can separately detect scalar, vector and tensor modes of GWBs with energy density as low as ~10^-15.Comment: 16 pages, 11 figure

Karakterisasi Film Tipis Cu-c60/mgo Akibat Penuaan(ageing)dengan Teknik Hamburan Raman

KARAKTERISASI FILM TIPIS Cu-C60/MgO AKIBAT PENUAAN(AGEING)DENGAN TEKNIK HAMBURAN RAMAN. Film tipis campuran antara Cu dan C60 telah dianalisis dengan menggunakan spektroskopi Raman. Campuran secara atomik dideposit pada substrat Mg(001). Pengujian topografi dengan mikroskop optik menunjukkan bahwa warna film di sebagian besar sisi luar adalah coklat muda dan berubah menjadi coklat tua pada bagian tengah film. Terjadinya Perubahan warna dapat diatributkan dengan baberapa jenis interaksi kimia antara Cu-Cu, Cu-C60, C60-C60 dan Perubahan alotrop molekul C60. Dari analisis spektroskopik Raman dapat disimpulkan bahwa ciri spektrum secara kuat berkorelasi dengan variasi warna yang bergantung pada daerah pengamatan. Pada tepi filmdengan warna coklat terang (ditunjukkan pada daerah 2 dan 3) atom-atom Cu berinteraksi secara kimia dengan fullerene (Cu-C60). Pada iteraksi ini terjadi pergeseran puncak kira-kira 6 cm-1dari puncak pristine C60 yang diamati untuk puncak-puncak Ag(2) dan Hg(8). Pada pusat film dengan warna coklat gelap (ditunjukkan pada daerah 3, daerah 4 dan daerah 5) terlihat sebagai puncak baru yanang secara tipikal seperti puncak D dan G yang secara umum berkaitan dengan formasi disordered graphite melalui konversi kimia dari C60 dibawah pengaruh oksidasi

Where is the best site on Earth? Domes A, B, C and F, and Ridges A and B

The Antarctic plateau contains the best sites on earth for many forms of astronomy, but none of the existing bases was selected with astronomy as the primary motivation. In this article, we try to systematically compare the merits of potential observatory sites.We include South Pole, Domes A, C, and F, and also Ridge B (running northeast from Dome A), and what we call "Ridge A" (running southwest from Dome A). Our analysis combines satellite data, published results, and atmospheric models, to compare the boundary layer, weather, aurorae, airglow, precipitable water vapor, thermal sky emission, surface temperature, and the free atmosphere, at each site. We find that all Antarctic sites are likely to be compromised for optical work by airglow and aurorae. Of the sites with existing bases, Dome A is easily the best overall; but we find that Ridge A offers an even better site. We also find that Dome F is a remarkably good site. Dome C is less good as a thermal infrared or terahertz site, but would be able to take advantage of a predicted "OH hole" over Antarctica during spring.Comment: Revised version. 16 pages, 21 figures (22 in first version). Submitted to PASP 16/05/09, accepted 13/07/09; published 20/08/0

Pengaruh Iluminasi Laser Pada Film Campuran Emas-fullerene (Auc60) Dalam Analisis Spectroskopi Raman

PENGARUH ILUMINASI LASER PADA FILM CAMPURAN EMAS-FULLERENE (AUC60) DALAM ANALISIS SPECTROSKOPI RAMAN. Analisis Raman secara rinci pada campuran antara emas danfullerene (C60) telah dilakukan dengan cara mengubah intensitas laser secara sistematik untuk mempelajari pengaruh agitasi termal pada campuran. Analisis pergeseran Raman menunjukkan bahwa Perubahan secara sistematik daya laser menyebabkan pergeseran dan penyempitan puncak Raman. Kenaikan daya laser dari 0,5 miliwatt ke 3 miliwatt akan menyebabkan pergeseran-penurunan frekuensi Raman. Besarnya pergeseran frekuensi Raman kira-kira 2 cm" dan 5,4 cm", masing-masing untuk mode Ag(2) dan Hg(8). Penurunan pergeseran yang diamati berkaitan dengan beberapa macam interaksi antara atom Au dan molekul C60, seperti Au dan C60 ,,softly bound'' yang peka pada suhu sehingga kemungkinan terjadi difusi Au dalam campuran, Nano-kristal Au menunjukkan sifat kimia yang bergantung ukuran (tergantung jumlah atom Au) dan hal penting dari nano-Au adalah kemungkinan penggunaan untuk penandaan DNA, dan posisi-sensitif spektroskopi Raman memberikan kita kesempatan untuk menganalisis reaksi bio-kimia dalam ruang topologi. Kenaikan daya iluminasi menyebabkan pergeseran frekswensi teramati. Iluminasi 0,5 miliwatt dipilih sebagai satu kondisi moderat

ALMA polarimetry measures magnetically aligned dust grains in the torus of NGC 1068

The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, is not thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations ($0.07"$, $4.2$ pc; 348.5 GHz, $860$ $\mu$m). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of $3.7\pm0.5$\% and position angle of $109\pm2^{\circ}$ (B-vector) at $\sim8$ pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 $\mu$m continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from 1) an inhomogeneous optical depth, and 2) a variation of the velocity dispersion, i.e. variation of the magnetic field turbulence at sub-pc scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few pc contribute to the accretion flow onto the active nuclei.Comment: 19 pages, 11 figures (Accepted for Publication to ApJ