Opaque minerals in Antarctic CO3 carbonaceous chondrites, Yamato-74135, -790992, -791717, -81020, -81025, -82050 and Allan Hills-77307

Metamorphic sequence and mineralogy of opaque minerals of Antarctic seven CO3 chondrites, Yamato (Y)-74135,Y-790992,Y-791717,Y-81020,Y-81025,Y-82050 and Allan Hills (ALH)-77307 was studied by an optical, scanning electron microscope and electron microprobe technique. Based on olivine and chromite compositions, Y-74135,Y-81020 and Y-81025 are classified as least metamorphosed CO3 chondrites. Metamorphic grades of these three chondrites are the same as or less than that of ALH-77307. Whereas metamorphic grades of Y-790992,Y-79171 and Y-82050 are higher than that of ALH-77307. The three least metamorphosed chondrites include cohenite abundantly. Judging from the mode of occurrence of cohenite, cohenite would have formed not by the diffusion of carbon into solid Fe-Ni metal, but by crystallization from Fe-Ni-C melt. Fine-grained tetrataenite within kamacite suggest that precipitation of the tetrataenite occurred under the condition in which Ni movement in kamacite was sluggish extremely (probably below 450℃). In Y-81025,assemblage of spherical magnetite like as framboidal magnetite in CI chondrites was observed. It would be also one of evidences of the low-temperature condition which the least metamorphosed chondrites in this study were situated. In Y-81025 and Y-74135,there are fine-grained perryite and phosphide. Although previous workers have already pointed out that primitive chondrites often have carbides, this study make clear that the existence of cohenite is indeed one of the essential properties in least metamorphosed CO3 chondrites

Chemical composition of Fe-Ni metal and phosphate minerals in Yamato-82094 carbonaceous chondrite

The mineralogy of Fe-Ni metal and associated minerals in the Yamato (Y)-82094 carbonaceous chondrite (CO) have been studied by optical, scanning electron microscope and electron microprobe techniques. There are some characteristic features for the Fe-Ni metal in the Y-82094 : (1) Ni contents in taenite grains are divided into two groups consisting of low-and high-Ni taenite. (2) Partition of Co between coexisting kamacite and taenite shows relatively higher temperatures (approximately 800℃), and their temperature ranges are wide. (3) polycrystalline taenite exists. (4) Fe-Ni metal and troilite form micron-sized intergrowths. (5) The Ni-Co trend of kamacite in chondrule is positive. The high-Ni taenite could have formed through thermal metamorphism on the parent body, while low-Ni taenite might have formed due to reheating caused by shock metamorphism on the parent body or during the colling process of chondrule formation. The positive Ni-Co trend of kamacite in Y-82094 is similar to that of the metal in CR chondrites. This trend may suggest that kamacite in Y-82094 preserves the primitive chemical composition indicating nebula condensation origin. The Fe-Ni metal grains have many phosphate mineral inclusions (whitlockite, brianite and panethite). The mode of occurrence of brianite and panethite indicates that they might have formed simultaneously with the Fe-Ni metal in the nebula

Ultimate low system dark count rate for superconducting nanowire single-photon detector

The dark count rate (DCR) is a key parameter of single-photon detectors. By introducing a bulk optical band-pass filter mounted on a fiber-to-fiber optical bench cooled at 3 K and blocking down to 5 micrometer, we suppressed the DCR of a superconducting nanowire single-photon detector by more than three orders of magnitude. The DCR is limited by the blackbody radiation through a signal passband of 20 nm bandwidth. The figure of merit, system detection efficiency, and DCR were 2.7 x 10^11, 2.3 %, and 0.001 Hz, respectively. Narrowing the bandwidth to 100 GHz suppresses the DCR to 0.0001 Hz and the figure of merit increases to 1.8 x 10^12.Comment: to appear in Optics Letter

U(1) symmetry breaking in one-dimensional Mott insulator studied by the Density Matrix Renormalization Group method

A new type of external fields violating the particle number preservation is studied in one-dimensional strongly correlated systems by the Density Matrix Renormalization Group method. Due to the U(1) symmetry breaking, the ground state has fluctuation of the total particle number, which implies injection of electrons and holes from out of the chain. This charge fluctuation can be relevant even at half-filling because the particle-hole symmetry is preserved with the finite effective field. In addition, we discuss a quantum phase transition obtained by considering the symmetry-breaking fields as a mean field of interchain-hopping.Comment: 7 pages, 4 figure

Spin-Wave Excitations of Half-Filled Kondo Lattice Model

The spin excitations in the antiferromagnetic phase of half-filled Kondo lattice model are studied by means of the decoupling approximation for spin Green's function. The spin-wave spectrum is calculated as a function of Kondo coupling, and this is used to calculate the thermodynamic quantities at low temperatures. The N\'{e}el temperature of the form $T_{\rm N}=0.087{J}^2\ln{(1/J)}$ is obtained for the 3-dimensional case in the weak-coupling limit. It is pointed out that the ratio of the spin-wave velocity to the N\'{e}el temperature $v_s/T_{\rm N}$ is enhanced as the Kondo coupling becomes small, reflecting the long-range nature of effective interactions between localized spins.Comment: 6 pages, LaTeX, 2 figure

Wideband MgB2 Hot-Electron Bolometer Mixers: IF Impedance Characterisation and Modeling

In this paper we present a method for low signal S11 parameter vector measurements of a cryogenic device in the microwave frequency range. In particular, the intermediate frequency (IF) impedance of MgB2 Hot-electron Bolometer (HEB) mixers was investigated over a frequency range of 100 MHz to 10 GHz. A new cryogenic calibration technique, which employs the HEB as a calibration kitandrequires two consecutive thermal cycles, was developed for this purpose.The real part of measured IF impedance showed a strong correlationwith the differential resistance (dV/dI) obtained from the dc I-V curves while the imaginary partwas capacitive for almost the entire frequency range

Numerical Study on Spin Torque Switching in Thermally Activated Region

We studied the spin torque switching of the single free layer in the thermally activated region by numerically solving the Landau-Lifshitz-Gilbert equation. We found that the temperature dependence of the switching time of the in-plane magnetized system is nonlinear, which means $b \neq 1$. Here, $b$ is the exponent of the current term in the switching rate formula and has been widely assumed to be unity. This result enables us to evaluate the thermal stability of spintronics devices.Comment: 3 pages, 4 figure

Role of KIT-Positive Interstitial Cells of Cajal in the Urinary Bladder and Possible Therapeutic Target for Overactive Bladder

In the gastrointestinal tract, interstitial cells of Cajal (ICCs) act as pacemaker cells to generate slow wave activity. Interstitial cells that resemble ICCs in the gastrointestinal tract have been identified by their morphological characteristics in the bladder. KIT is used as an identification marker of ICCs. ICCs in the bladder may be involved in signal transmission between smooth muscle bundles, from efferent nerves to smooth muscles, and from the urothelium to afferent nerves. Recent research has suggested that not only the disturbance of spontaneous contractility caused by altered detrusor ICC signal transduction between nerves and smooth muscle cells but also the disturbance of signal transduction between urothelial cells and sensory nerves via suburothelial ICC may induce overactive bladder (OAB). Recent reports have suggested that KIT is not only a detection marker of these cells, but also may play a crucial role in the control of bladder function. Research into the effect of a c-kit receptor inhibitor, imatinib mesylate, on bladder function implies that KIT-positive ICCs may be therapeutic target cells to reduce bladder overactivity and that the blockage of c-kit receptor may offer a new therapeutic strategy for OAB treatment, although further study will be needed

Exportin-5 orthologues are functionally divergent among species

Exportin-5, an evolutionarily conserved nuclear export factor belonging to the importin-β family of proteins, is known to play a role in the nuclear export of small noncoding RNAs such as precursors of microRNA, viral minihelix RNA and a subset of tRNAs in mammalian cells. In this study, we show that the exportin-5 orthologues from different species such as human, fruit fly and yeast exhibit diverged functions. We found that Msn5p, a yeast exportin-5 orthologue, binds double-stranded RNAs and that it prefers a shorter 22 nt, double-stranded RNA to ∼80 nt pre-miRNA, even though both of these RNAs share a similar terminal structure. Furthermore, we found that Drosophila exportin-5 binds pre-miRNAs and that amongst the exportin-5 orthologues tested, it shows the highest affinity for tRNAs. The knockdown of Drosophila exportin-5 in cultured cells decreased the amounts of tRNA as well as miRNA, whereas the knock down of human exportin-5 in cultured cells affected only miRNA but not tRNA levels. These results indicate that double-stranded RNA binding ability is an inherited functional characteristic of the exportin-5 orthologues and that Drosophila exportin-5 functions as an exporter of tRNAs as well as pre-miRNAs in the fruit fly that lacks the orthologous gene for exportin-t