263 research outputs found
Instanton and Superconductivity in Supersymmetric CP(N-1) Model
The two dimensional supersymmetric CP(N-1) model has a striking similarity to
the N=2 supersymmetric gauge theory in four dimensions. The BPS mass formula
and the curve of the marginal stability (CMS), which exist in the four
dimensional gauge theory, appears in this two dimensional CP(N-1) model. These
two quntities are derived by a one-dimensional n-vector spin model in the large
n limit for the N=2 case. This mapping is further investigated at the critical
point. An application of the study of the BPS mass formula is proposed to the
phenomena of the spin and charge separations in the Higgs phase.Comment: 6 page
The HI content of star-forming galaxies at z = 0.24
We use observations from the Giant Metrewave Radio Telescope (GMRT) to
measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24
(i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected
from Halpha-emitting field galaxies detected in a narrow-band imaging survey
with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain
precise optical redshifts for these galaxies. We then coadded the HI 21 cm
emission signal for all the galaxies within the GMRT spectral line data cube.
From the coadded signal of 121 galaxies, we measure an average atomic
hydrogen gas mass of (2.26 +- 0.90)*10^9 solar masses. We translate this HI
signal into a cosmic density of neutral gas at z = 0.24 of Omega_gas = (0.91 +-
0.42)*10^-3. This is the current highest redshift at which Omega_gas has been
constrained from 21 cm emission and our value is consistent with that estimated
from damped Lyman-alpha systems around this redshift. We also find that the
correlations between the Halpha luminosity and the radio continuum luminosity
and between the star formation rate and the HI gas content in star-forming
galaxies at z = 0.24 are consistent with the correlations found at z = 0. These
two results suggest that the star formation mechanisms in field galaxies ~3 Gyr
ago were not substantially different from the present, even though the star
formation rate is 3 times higher.Comment: 11 pages, contains 9 figures and 1 table. Accepted for publishing in
MNRAS 2007 January 22. Received 2007 January 22; in original form 2006
November 3
Digging up bulk band dispersion buried under a passivation layer
Atomically controlled crystal growth of thin films has established
foundations of nanotechnology aimed at the development of advanced functional
devices. Crystallization under non-equilibrium conditions allows engineering of
new materials with their atomically-flat interfaces in the heterostructures
exhibiting novel physical properties. From a fundamental point of view,
knowledge of the electronic structures of thin films and their interfaces is
indispensable to understand the origins of their functionality which further
evolves into realistic device application. In view of extreme surface
sensitivity of the conventional vacuum-ultraviolet (VUV) angle-resolved
photoemission spectroscopy (ARPES), with a probing depth of several angstroms,
experiments on thin films have to use sophisticated in-situ sample transfer
systems to avoid surface contamination. In this Letter, we put forward a method
to circumvent these difficulties using soft X-ray (SX) ARPES. A GaAs:Be thin
film in our samples was protected by an amorphous As layer with an thickness of
nm exceeding the probing depth of the VUV photoemission with photon
energy around 100 eV. The increase of the probing depth with increasing
towards the SX region has clearly exposed the bulk band dispersion
without any surface treatment. Any contributions from potential interface
states between the thin film and the amorphous capping layer has been below the
detection limit. Our results demonstrate that SX-ARPES enables the observation
of coherent three-dimensional band dispersion of buried heterostructure layers
through an amorphous capping layer, breaking through the necessity of surface
cleaning of thin film samples. Thereby, this opens new frontiers in diagnostics
of authentic momentum-resolved electronic structure of protected thin-film
heterostructures.Comment: 5 pages, 3 figure
Structure of the Bacillus subtilis 70S ribosome reveals the basis for species-specific stalling
Ribosomal stalling is used to regulate gene expression and can occur in a species-specific manner. Stalling during translation of the MifM leader peptide regulates expression of the downstream membrane protein biogenesis factor YidC2 (YqjG) in Bacillus subtilis, but not in Escherichia coli. In the absence of structures of Gram-positive bacterial ribosomes, a molecular basis for species-specific stalling has remained unclear. Here we present the structure of a Gram-positive B. subtilis MifM-stalled 70S ribosome at 3.5-3.9 angstrom, revealing a network of interactions between MifM and the ribosomal tunnel, which stabilize a non-productive conformation of the PTC that prevents aminoacyl-tRNA accommodation and thereby induces translational arrest. Complementary genetic analyses identify a single amino acid within ribosomal protein L22 that dictates the species specificity of the stalling event. Such insights expand our understanding of how the synergism between the ribosome and the nascent chain is utilized to modulate the translatome in a species-specific manner
Nongyrotropic electron velocity distribution functions near the lunar surface
We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ∼10–100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle-trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic-current systems, lunar-surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient-plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials slightly reduce the size of the forbidden regions, but there are no distinct effects of either the diamagnetic current or perpendicular electric fields. On the dayside in the solar wind, the observations suggest the presence of either the diamagnetic-current or solar wind convection electric field effects, or both. In the terrestrial plasma sheet, all three mechanisms can substantially modify the characteristics of the forbidden regions. The observations imply the presence of a local electric field of at least 5 mV/m although the mechanism responsible for production of such a strong electric field is unknown. Analysis of nongyrotropic VDFs associated with the gyroloss effect near solid surfaces can promote a better understanding of the near-surface plasma environment and of plasma–solid-surface interactions
A Shock-Induced Pair of Superbubbles in the High-Redshift Powerful Radio Galaxy MRC 0406-244
We present new optical spectroscopy of the high-redshift powerful radio
galaxy MRC 0406244 at redshift of 2.429. We find that the two extensions
toward NW and SE probed in the rest-frame ultraviolet image are heated mainly
by the nonthermal continuum of the active galactic nucleus. However, each
extension shows a shell-like morphology, suggesting that they are a pair of
superbubbles induced by the superwind activity rather than by the interaction
between the radio jet and the ambient gas clouds. If this is the case, the
intense starburst responsible for the formation of superbubbles could occur
yr ago. On the other hand, the age of the radio jets may
be of the order of yr, being much shorter than the starburst age.
Therefore, the two events, i.e., the starburst and the radio-jet activities,
are independent phenomena. However, their directions of the expanding motions
could be governed by the rotational motion of the gaseous component in the host
galaxy. This idea appears to explain the alignment effect of MRC 0406244.Comment: 4 pages (emulateapj.sty), Fig. 1 (jpeg) + Fig.2 (eps). Accepted for
publications in ApJ (Letters
Presence of a basic secretory protein in xylem sap and shoots of poplar in winter and its physicochemical activities against winter environmental conditions
XSP25, previously shown to be the most abundant hydrophilic protein in xylem sap of Populus nigra in winter, belongs to a secretory protein family in which the arrangement of basic and acidic amino acids is conserved between dicotyledonous and monocotyledonous species. Its gene expression was observed at the same level in roots and shoots under long-day conditions, but highly induced under short-day conditions and at low temperatures in roots, especially in endodermis and xylem parenchyma in the root hair region of Populus trichocarpa, and its protein level was high in dormant buds, but not in roots or branches. Addition of recombinant PtXSP25 protein mitigated the denaturation of lactate dehydrogenase by drying, but showed only a slight effect on that caused by freeze–thaw cycling. Recombinant PtXSP25 protein also showed ice recrystallization inhibition activity to reduce the size of ice crystals, but had no antifreezing activity. We suggest that PtXSP25 protein produced in shoots and/or in roots under short-day conditions and at non-freezing low temperatures followed by translocation via xylem sap to shoot apoplast may protect the integrity of the plasma membrane and cell wall functions from freezing and drying damage in winter environmental conditions
A Subaru Search for Lyman Emitters at Redshift 5.7
We present the results of a survey for Ly emitters at
based on optical narrow-band ( \AA ~ and \AA), and broad-band (, , , and )
observations of the field surrounding the high redshift quasar, SDSSp
J104433.04012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime
Focus Camera, Suprime-Cam. This survey covers a sky area of
arcmin and a co-moving volume of
Mpc. We have found 20 candidates of Ly emitters at 5.7
with . Two of them have been confirmed star-forming
galaxies at and from our follow-up optical spectroscopy. We
discuss star-formation properties of the 20 objects from a statistical point of
view. Our survey leads to a new estimate of the star formation rate density at
, yr
Mpc.Comment: 18 pages, 19 figures, accepted for A
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