380 research outputs found
Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO
We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation
Mode locking of vortex matter driven through mesoscopic channels
We investigated the driven dynamics of vortices confined to mesoscopic flow
channels by means of a dc-rf interference technique. The observed mode-locking
steps in the -curves provide detailed information on how the number of rows
and lattice structure in the channel change with magnetic field. Minima in flow
stress occur when an integer number of rows is moving coherently, while maxima
appear when incoherent motion of mixed and row configurations is
predominant. Simulations show that the enhanced pinning at mismatch originates
from quasi-static fault zones with misoriented edge dislocations induced by
disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for
publication in Phys. Rev. Let
London equation studies of thin-film superconductors with a triangular antidot lattice
We report on a study of vortex pinning in nanoscale antidot defect arrays in
the context of the London Theory. Using a wire network model, we discretize the
array with a fine mesh, thereby providing a detailed treatment of pinning
phenomena. The use of a fine grid has enabled us to examine both circular and
elongated defects, patterned in the form of a rhombus. The latter display
pinning characteristics superior to circular defects constructed with the
similar area. We calculate pinning potentials for defects containing zero and
single quanta, and we obtain a pinning phase diagram for the second matching
field, .Comment: 10 pages and 14 figure
Magnetic Interactions and Transport in (Ga,Cr)As
The magnetic, transport, and structural properties of (Ga,Cr)As are reported.
Zincblende GaCrAs was grown by low-temperature molecular beam
epitaxy (MBE). At low concentrations, x0.1, the materials exhibit unusual
magnetic properties associated with the random magnetism of the alloy. At low
temperatures the magnetization M(B) increases rapidly with increasing field due
to the alignment of ferromagnetic units (polarons or clusters) having large
dipole moments of order 10-10. A standard model of
superparamagnetism is inadequate for describing both the field and temperature
dependence of the magnetization M(B,T). In order to explain M(B) at low
temperatures we employ a distributed magnetic moment (DMM) model in which
polarons or clusters of ions have a distribution of moments. It is also found
that the magnetic susceptibility increases for decreasing temperature but
saturates below T=4 K. The inverse susceptibility follows a linear-T
Curie-Weiss law and extrapolates to a magnetic transition temperature
=10 K. In magnetotransport measurements, a room temperature resistivity
of =0.1 cm and a hole concentration of cm
are found, indicating that Cr can also act as a acceptor similar to Mn. The
resistivity increases rapidly for decreasing temperature below room
temperature, and becomes strongly insulating at low temperatures. The
conductivity follows exp[-(T/T)] over a large range of
conductivity, possible evidence of tunneling between polarons or clusters.Comment: To appear in PRB 15 Mar 200
RNA expression of breast cancer resistance protein, lung resistance-related protein, multidrug resistance-associated proteins 1 and 2, and multidrug resistance gene 1 in breast cancer: correlation with chemotherapeutic response
PURPOSE: The aim of this study was to investigate whether expression of
particular drug resistance genes in primary operable breast cancer
correlates with response to first-line chemotherapy in advanced disease.
EXPERIMENTAL DESIGN: We determined mRNA levels of BCRP, LRP, MRP1, MRP2,
and MDR1 in 59 primary breast tumor specimens of patients who
Combined vascular endothelial growth factor and TP53 status predicts poor response to tamoxifen therapy in estrogen receptor-positive advanced breast cancer
PURPOSE: In recent studies, we showed that TP53 gene mutation or high
levels of cytosolic vascular endothelial growth factor (VEGF) in estrogen
receptor (ER)-alpha-positive primary breast tumors predict a poor disease
outcome for patients treated with first-line tamoxifen for advanced
disease. Mutant TP53 may up-regulate VEGF, whereas, on the other hand,
wild-type TP53 may decrease VEGF production. EXPERIMENTAL DESIGN: In the
present study, we aimed to assess the combined predictive value of TP53
gene mutation and VEGF status of 160 advanced breast cancer patients with
ER-positive tumors who were treated with tamoxifen (median follow-up from
start of tamoxifen treatment, 64 months). To assess TP53 gene mutation
status, the entire open reading frame was sequenced; for VEGF status, an
ELISA was used. RESULTS: In univariate analysis, both TP53 gene mutation
(28% of the tumors) and a VEGF level above the median value were
significantly associated with a short progression-free survival,
post-relapse overall survival, and a poor rate of response to tamoxifen.
In Cox multivariate regression analysis including the traditional
predictive factors, the addition of TP53 gene mutation and VEGF status,
alone or in combination, significantly predicted a poor efficacy of
tamoxifen treatment. When the two factors were combined, a significantly
decreased odds ratio was seen for the rate of response (odds ratio, 0.27).
Similarly, an increased hazard ratio (HR) was seen for progression-free
survival (HR, 2.32) and post-relapse overall survival (HR, 1.68) in the
group with mutant TP53 and high VEGF compared with the group with both
risk factors absent. CONCLUSIONS: Combined TP53 gene mutation status and
high VEGF levels of ER-positive primary breast tumors independently
predict a poor course of the disease of patients with advanced breast
cancer treated with tamoxifen. These patients, having unfavorable tumor
characteristics, might benefit more from other types of (individualized)
treatment protocols
Structure and Magnetization of Two-Dimensional Vortex Arrays in the Presence of Periodic Pinning
Ground-state properties of a two-dimensional system of superconducting
vortices in the presence of a periodic array of strong pinning centers are
studied analytically and numerically. The ground states of the vortex system at
different filling ratios are found using a simple geometric argument under the
assumption that the penetration depth is much smaller than the spacing of the
pin lattice. The results of this calculation are confirmed by numerical studies
in which simulated annealing is used to locate the ground states of the vortex
system. The zero-temperature equilibrium magnetization as a function of the
applied field is obtained by numerically calculating the energy of the ground
state for a large number of closely spaced filling ratios. The results show
interesting commensurability effects such as plateaus in the B-H diagram at
simple fractional filling ratios.Comment: 12 pages, 19 figures, submitted for publicatio
The urokinase system of plasminogen activation and prognosis in 2780 breast cancer patients
The antigen levels of components of the urokinase-type plasminogen
activator (uPA) system of plasminogen activation are correlated with
prognosis in several types of cancers, including breast cancer. In the
present study involving 2780 patients with primary invasive breast cancer,
we have evaluated the prognostic importance of the four major components
of the uPA system [uPA, the receptor uPAR (CD87), and the inhibitors PAI-1
and PAI-2]. The antigen levels were determined by ELISA in cytosols
prepared from primary breast tumors. The levels of the four factors
significantly correlated with each other; the Spearman rank correlation
coefficients (r(s)) ranged from 0.32 (between PAI-2 and PAI-1 or uPAR) to
0.59 (between uPA and PAI-1). The median duration of follow-up of patients
still alive was 88 months. In the multivariate analyses for relapse-free
survival (RFS) and overall survival (OS), we defined a basic model
including age, menopausal status, tumor size and grade, lymph node status,
adjuvant therapy, and steroid hormone receptor status. uPA, uPAR, PAI-1,
and PAI-2 were considered as categorical variables, each with two cut
points that were established by isotonic regression analysis. Compared
with tumors with low levels, those with intermediate and high levels
showed a relative hazard rate (RHR) and 95% confidence interval (95% CI)
of 1.22 (1.02-1.45) and 1.69 (1.39-2.05) for uPA, and 1.32 (1.14-1.54) and
2.17 (1.74-2.70) for PAI-1, respectively, in multivariate analysis for RFS
in all patients. Compared with tumors with high PAI-2 levels, those with
intermediate and low levels showed a poor RFS with a RHR (95% CI) of 1.30
(1.14-1.48) and 1.76 (1.38-2.24), respectively. Similar results were
obtained in the multivariate analysis for OS in all patients. Furthermore,
uPA and PAI-1 were independent predictive factors of a poor RFS and OS in
node-negative and node-positive patients. PAI-2 also added to the
multivariate models for RFS in node-negative and node-positive patients,
and in the analysis for OS in node-negative patients. uPAR did not further
contribute to any of the multivariate models. A prognostic score was
calculated based on the estimates from the final multivariate model for
RFS. Using this score, the difference between the highest and lowest 10%
risk groups was 66% in the analysis for RFS at 10 years and 61% in the
analysis for OS. Moreover, separate prognostic scores were calculated for
node-negative and node-positive patients. In the 10% highest risk groups,
the proportion of disease-free patients was only 27 +/- 6% and 9 +/- 3% at
10 years for node-negative and node-positive patients, respectively. These
proportions were 86 +/- 4% and 61 +/- 6% for the corresponding 10% lowest
risk groups of relapse. We conclude that several components of the uPA
system are potential predictors of RFS and OS in patients with primary
invasive breast cancer. Knowledge of these factors could be helpful to
assess the individual risk of patients, to select various types of
adjuvant treatment and to identify patients who may benefit from targeted
therapies that are currently being developed
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