1,334 research outputs found
Observation of Collective Excitations of the Dilute 2D Electron System
We report inelastic light scattering measurements of dispersive spin and
charge density excitations in dilute 2D electron systems reaching densities
less than 10^{10} cm^{-2}. In the quantum Hall state at nu=2, roton critical
points in the spin inter--Landau level mode show a pronounced softening as r_s
is increased. Instead of a soft mode instability predicted by Hartree--Fock
calculations for r_s ~ 3.3, we find evidence of multiple rotons in the
dispersion of the softening spin excitations. Extrapolation of the data
indicates the possibility of an instability for r_s >~ 11.Comment: Submitted to Physical Review Letter
Gene and protein expression of glucose transporter 1 and glucose transporter 3 in human laryngeal cancer—the relationship with regulatory hypoxia-inducible factor-1α expression, tumor invasiveness, and patient prognosis
Increased glucose uptake mediated by glucose
transporters and reliance on glycolysis are common features
of malignant cells. Hypoxia-inducible factor-1α supports the
adaptation of hypoxic cells by inducing genes related to
glucose metabolism. The contribution of glucose transporter
(GLUT) and hypoxia-inducible factor-1α (HIF-1α) activity to
tumor behavior and their prognostic value in head and neck
cancers remains unclear. The aim of this study was to examine
the predictive value of GLUT1, GLUT3, and HIF-1α messenger
RNA (mRNA)/protein expression as markers of tumor
aggressiveness and prognosis in laryngeal cancer. The level of
hypoxia/metabolic marker genes was determined in 106 squamous
cell laryngeal cancer (SCC) and 73 noncancerous
matched mucosa (NCM) controls using quantitative realtime
PCR. The related protein levels were analyzed by
Western blot. Positive expression of SLC2A1, SLC2A3, and
HIF-1α genes was noted in 83.9, 82.1, and 71.7 % of SCC
specimens and in 34.4, 59.4, and 62.5 % of laryngeal cancer
samples. Higher levels of mRNA/protein for GLUT1 and
HIF-1α were noted in SCC compared to NCM (p<0.05).
SLC2A1 was found to have a positive relationship with grade,
tumor front grading (TFG) score, and depth and mode of
invasion (p<0.05). SLC2A3 was related to grade and invasion
type (p<0.05). There were also relationships of HIF-1α with
pTNM, TFG scale, invasion depth and mode, tumor recurrences,
and overall survival (p<0.05). In addition, more advanced
tumors were found to be more likely to demonstrate
positive expression of these proteins. In conclusion, the
hypoxia/metabolic markers studied could be used as molecular
markers of tumor invasiveness in laryngeal cancer.This work was supported, in part, by the statutory
fund of the Department of Cytobiochemistry, University of Łódź, Poland
(506/811), and by grant fromtheNational Science Council, Poland (N403
043 32/2326)
Probing the Intermediate-Age Globular Clusters in NGC 5128 from Ultraviolet Observations
We explore the age distribution of the globular cluster (GC) system of the
nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from Galaxy
Evolution Explorer (GALEX) observations, with UV - optical colors used as the
age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and
Milky Way in UV - optical color-color diagram, which indicates that the
majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31
and Milky Way. A large fraction of spectroscopically identified
intermediate-age GC (IAGC) candidates with ~ 3-8 Gyr are not detected in the
FUV passband. Considering the nature of intermediate-age populations being
faint in the far-UV (FUV) passband, we suggest that many of the
spectroscopically identified IAGCs may be truly intermediate in age. This is in
contrast to the case of M31 where a large fraction of spectroscopically
suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but
rather older GCs with developed blue horizontal branch stars. Our UV photometry
strengthens the results previously suggesting the presence of GC and stellar
subpopulation with intermediate age in NGC 5128. The existence of IAGCs
strongly indicates the occurrence of at least one more major star formation
episode after a starburst at high redshift.Comment: 8 pages, 3 figures, accepted for ApJ Lette
Why are Prices Sticky? Evidence from Business Survey Data
This paper offers new insights on the price setting behaviour of German retail firms using a novel dataset that
consists of a large panel of monthly business surveys from 1991-2006. The firm-level data allows matching changes
in firms' prices to several other firm-characteristics. Moreover, information on price expectations allow analyzing
the determinants of price updating. Using univariate and bivariate ordered probit specifications, empirical menu
cost models are estimated relating the probability of price adjustment and price updating, respectively, to both
time- and state- dependent variables. First, results suggest an important role for state-dependence; changes in
the macroeconomic and institutional environment as well as firm-specific factors are significantly related to the
timing of price adjustment. These findings imply that price setting models should endogenize the timing of price
adjustment in order to generate realistic predictions concerning the transmission of monetary policy. Second, an
analysis of price expectations yields similar results providing evidence in favour of state-dependent sticky plan
models. Third, intermediate input cost changes are among the most important determinants of price adjustment
suggesting that pricing models should explicitly incorporate price setting at different production stages. However, the results show that adjustment to input cost changes takes time indicating "additional stickiness" at the last stage of processing
The physics of dynamical atomic charges: the case of ABO3 compounds
Based on recent first-principles computations in perovskite compounds,
especially BaTiO3, we examine the significance of the Born effective charge
concept and contrast it with other atomic charge definitions, either static
(Mulliken, Bader...) or dynamical (Callen, Szigeti...). It is shown that static
and dynamical charges are not driven by the same underlying parameters. A
unified treatment of dynamical charges in periodic solids and large clusters is
proposed. The origin of the difference between static and dynamical charges is
discussed in terms of local polarizability and delocalized transfers of charge:
local models succeed in reproducing anomalous effective charges thanks to large
atomic polarizabilities but, in ABO3 compounds, ab initio calculations favor
the physical picture based upon transfer of charges. Various results concerning
barium and strontium titanates are presented. The origin of anomalous Born
effective charges is discussed thanks to a band-by-band decomposition which
allows to identify the displacement of the Wannier center of separated bands
induced by an atomic displacement. The sensitivity of the Born effective
charges to microscopic and macroscopic strains is examined. Finally, we
estimate the spontaneous polarization in the four phases of barium titanate.Comment: 25 pages, 6 Figures, 10 Tables, LaTe
Galaxy Collisions - Dawn of a New Era
The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.Comment: 44 pages, 9 figures, review article in press for Astrophysics Update
Vol.
Deep Wide-Field Spectrophotometry of the Open Cluster M67
We present nine color CCD intermediate-band spectrophotometry of a two square
degree field centered on the old open cluster M67, from 3890 to nearly
1. These observations are taken as a part of the BATC
(Beijing-Arizona-Taipei-Connecticut) Color Survey of the Sky, for both
scientific and calibration reasons. With these data we show that the BATC
survey can reach its goal of obtaining spectrophotometry to a zero point
accuracy of 0.01 mag, and down to V = 21 with 0.3 mag random error. We fit the
color-magnitude diagrams (CMDs) with Worthey's theoretical models. The net
result is the excellent fit of the 4.0 Gyr, [Fe/H] = model to our data,
including a good fit to the main sequence (MS) turn-off. Our data are
consistent with a toy model with 50\% of the stars in M67 being binaries and a
random distribution of binary mass-ratios, although other models with different
mass-ratio distributions cannot be ruled out. The spatial distribution and mass
function (MF) of stars in M67 show marked effects of dynamical evolution and
evaporation of stars from the cluster. Blue stragglers and binary stars are the
most condensed within the cluster, with degree of condensation depending on
mass.We find M67 to have an elongated shape, oriented at an angle of
relative to the galactic plane. Within its tidal radius, the
observed MF of M67 between 1.2 and has a
Salpeter slope . For stars of mass below 0.8 , . It is plausible that the leveling-off of the MF at
lower masses is a result of evaporation of lower mass stars in this mass range
at a rate of one every years. If so, it is plausible that the IMF
of M67 has the canonical field value of .Comment: 74 pages, including 19 ps figures. Accepted for publication in AJ,
Aug, 199
- …