15,996 research outputs found
Surface-sensitive NMR in optically pumped semiconductors
We present a scheme of surface-sensitive nuclear magnetic resonance in
optically pumped semiconductors, where an NMR signal from a part of the surface
of a bulk compound semiconductor is detected apart from the bulk signal. It
utilizes optically oriented nuclei with a long spin-lattice relaxation time as
a polarization reservoir for the second (target) nuclei to be detected. It
provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond.
14, 1635 (2004)], which is a polarization reservoir at a surface of the
optically pumped semiconductor that polarizes nuclear spins in a target
material in contact through the nanostructured interfaces.Comment: 4 pages, 5 figure
Optical pumping NMR in the compensated semiconductor InP:Fe
The optical pumping NMR effect in the compensated semiconductor InP:Fe has
been investigated in terms of the dependences of photon energy (E_p), helicity
(sigma+-), and exposure time (tau_L) of infrared lights. The {31}P and {115}In
signal enhancements show large sigma+- asymmetries and anomalous oscillations
as a function of E_p. We find that (i) the oscillation period as a function of
E_p is similar for {31}P and {115}In and almost field independent in spite of
significant reduction of the enhancement in higher fields. (ii) A
characteristic time for buildup of the {31}P polarization under the light
exposure shows strong E_p-dependence, but is almost independent of sigma+-.
(iii) The buildup times for {31}P and {115}In are of the same order (10^3 s),
although the spin-lattice relaxation times (T_1) are different by more than
three orders of magnitude between them. The results are discussed in terms of
(1) discrete energy spectra due to donor-acceptor pairs (DAPs) in compensated
semiconductors, and (2) interplay between {31}P and dipolar ordered indium
nuclei, which are optically induced.Comment: 8 pages, 6 figures, submitted to Physical Review
Superconductivity in La1-xCexOBiSSe: carrier doping by mixed valence of Ce ions
We report the effects of Ce substitution on structural, electronic, and
magnetic properties of layered bismuth-chalcogenide La1-xCexOBiSSe (x = 0-0.9),
which are newly obtained in this study. Metallic conductivity was observed for
x > 0.1 because of electron carriers induced by mixed valence of Ce ions, as
revealed by bond valence sum calculation and magnetization measurements. Zero
resistivity and clear diamagnetic susceptibility were obtained for x = 0.2-0.6,
indicating the emergence of bulk superconductivity in these compounds.
Dome-shaped superconductivity phase diagram with the highest transition
temperature (Tc) of 3.1 K, which is slightly lower than that of F-doped
LaOBiSSe (Tc = 3.7 K), was established. The present study clearly shows that
the mixed valence of Ce ions can be utilized as an alternative approach for
electron-doping in layered bismuth-chalcogenides to induce superconductivity
Requirement of the FATC domain of protein kinase Tel1 for localization to DNA ends and target protein recognition
Two large phosphatidylinositol 3-kinase-related protein kinases (PIKKs), ATM and ATR, play a central role in the DNA damage response pathway. PIKKs contain a highly conserved extreme C-terminus called the FRAP-ATM-TRRAP-C-terminal (FATC) domain. In budding yeast, ATM and ATR correspond to Tel1 and Mec1, respectively. In this study, we characterized functions of the FATC domain of Tel1 by introducing substitution or truncation mutations. One substitution mutation, termed tel1-21, and a truncation mutation, called tel1- Î"C, did not significantly affect the expression level. The tel1-21 mutation impaired the cellular response to DNA damage and conferred moderate telomere maintenance defect. In contrast, the tel1-Î"C mutation behaved like a null mutation, conferring defects in both DNA damage response and telomere maintenance. Tel1-21 protein localized to DNA ends as effectively as wild-type Tel1 protein, whereas Tel1-Î"C protein failed. Introduction of a hyperactive TEL1-hy mutation suppressed the tel1-21 mutation but not the tel1-Î"C mutation. In vitro analyses revealed that both Tel1-21 and Tel1-Î"C proteins undergo efficient autophosphorylation but exhibit decreased kinase activities toward the exogenous substrate protein, Rad53. Our results show that the FATC domain of Tel1 mediates localization to DNA ends and contributes to phosphorylation of target proteins. © 2015 Ogi, Goto, Ghosh, et al
Green's function of fully anharmonic lattice vibration
Motivated by the discovery of superconductivity in beta-pyrochlore oxides, we
study property of rattling motion coupled with conduction electrons. We derive
the general expression of the Green's function of fully anharmonic lattice
vibration within the accuracy of the second order perturbation of electron-ion
interaction by introducing self-energy, vertex-correction, and normalization
factor for each transition. Using the expression, we discuss the characteristic
properties of the spectral function in the entire range from weakly anharmonic
potential to double-well case, and calculate NMR relaxation rate due to the two
phonon Raman process
Collinear-to-Spiral Spin Transformation without Changing Modulation Wavelength upon Ferroelectric Transition in Tb1-xDyxMnO3
Lattice modulation and magnetic structures in magnetoelectric compounds
Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature
T_C by x-ray and neutron diffraction. Temperature-independent modulation
vectors through T_C are observed for the compounds with 0.50< x < 0.68. This
indicates that ferroelectricity with a polarization (P) along the c axis in the
RMnO3 series cannot be ascribed to such an incommensurate-commensurate
transition of an antiferromagnetic order as was previously anticipated. Neutron
diffraction study of a single crystal with x=0.59 shows that the FE transition
is accompanied by the transformation of the Mn-spin alignment from sinusoidal
(collinear) antiferromagnetism into a transverse spiral structure. The observed
spiral structure below T_C is expected to produce P along the c axis with the
`inverse' Dzialoshinski-Moriya interaction, which is consistent with the
observation.Comment: 9 pages, 4 figure
Cosmological evolution of cosmic strings with time-dependent tension
We discuss the cosmological evolution of cosmic strings with time-dependent
tension. We show that, in the case that the tension changes as a power of time,
the cosmic string network obeys the scaling solution: the characteristic scale
of the string network grows with the time. But due to the time dependence of
the tension, the ratio of the energy density of infinite strings to that of the
background universe is {\it not} necessarily constant.Comment: 9 pages, to appear in Phys. Rev.
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