381 research outputs found
Electronic and magnetic properties of GaMnAs: Annealing effects
The effect of short-time and long-time annealing at 250C on the conductivity,
hole density, and Curie temperature of GaMnAs single layers and GaMnAs/InGaMnAs
heterostructures is studied by in-situ conductivity measurements as well as
Raman and SQUID measurements before and after annealing. Whereas the
conductivity monotonously increases with increasing annealing time, the hole
density and the Curie temperature show a saturation after annealing for 30
minutes. The incorporation of thin InGaMnAs layers drastically enhances the
Curie temperature of the GaMnAs layers.Comment: 4 pages, 6 figures, submitted to Physica
Searching for tetraquarks on the lattice
We address the question whether the lightest scalar mesons sigma and kappa
are tetraquarks. We present a search for possible light tetraquark states with
J^PC=0^++ and I=0, 1/2, 3/2, 2 in the dynamical and the quenched lattice
simulations using tetraquark interpolators. In all the channels, we unavoidably
find lowest scattering states pi(k)pi(-k) or K(k)pi(-k) with back-to-back
momentum k=0,2*pi/L,.. . However, we find an additional light state in the I=0
and I=1/2 channels, which may be related to the observed resonances sigma and
kappa with a strong tetraquark component. In the exotic repulsive channels I=2
and I=3/2, where no resonance is observed, we find no light state in addition
to the scattering states.Comment: 3 pages, 1 figure, proceedings of Lepton-Photon 2009, Hambur
Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As
The effect of annealing at 250 C on the carrier depth profile, Mn
distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As
layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low
temperatures, is studied by a variety of analytical methods. The vertical
gradient in hole concentration, revealed by electrochemical capacitance-voltage
profiling, is shown to play a key role in the understanding of conductivity and
magnetization data. The gradient, basically already present in as-grown
samples, is strongly influenced by post-growth annealing. From secondary ion
mass spectroscopy it can be concluded that, at least in thick layers, the
change in carrier depth profile and thus in conductivity is not primarily due
to out-diffusion of Mn interstitials during annealing. Two alternative possible
models are discussed.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Fermion loop simulation of the lattice Gross-Neveu model
We present a numerical simulation of the Gross-Neveu model on the lattice
using a new representation in terms of fermion loops. In the loop
representation all signs due to Pauli statistics are eliminated completely and
the partition function is a sum over closed loops with only positive weights.
We demonstrate that the new formulation allows to simulate volumes which are
two orders of magnitude larger than those accessible with standard methods
Water exchange at a hydrated platinum electrode is rare and collective
We use molecular dynamics simulations to study the exchange kinetics of water
molecules at a model metal electrode surface -- exchange between water
molecules in the bulk liquid and water molecules bound to the metal. This
process is a rare event, with a mean residence time of a bound water of about
40 ns for the model we consider. With analysis borrowed from the techniques of
rare-event sampling, we show how this exchange or desorption is controlled by
(1) reorganization of the hydrogen bond network within the adlayer of bound
water molecules, and by (2) interfacial density fluctuations of the bulk liquid
adjacent to the adlayer. We define collective coordinates that describe the
desorption mechanism. Spatial and temporal correlations associated with a
single event extend over nanometers and tens of picoseconds.Comment: 10 pages, 9 figure
Enhancement of the Curie temperature in GaMnAs/InGaMnAs superlattices
We report on an enhancement of the Curie temperature in GaMnAs/InGaMnAs
superlattices grown by low-temperature molecular beam epitaxy, which is due to
thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced
increase of the Curie temperature is strongly correlated to the In
concentration in the embedded layers. Curie temperatures up to 110 K are
observed in such structures compared to 60 K in GaMnAs single layers grown
under the same conditions. A further increase in T up to 130 K can be
achieved using post-growth annealing at temperatures near the growth
temperature. Pronounced thickness fringes in the high resolution X-ray
diffraction spectra indicate good crystalline quality and sharp interfaces in
the structures.Comment: 4 pages, 4 figures, submitted to Appl. Phys. Let
Entropy production fluctuations encode collective behavior in active matter
We derive a general lower bound on distributions of entropy production in
interacting active matter systems. The bound is tight in the limit that
interparticle correlations are small and short-ranged, which we explore in four
canonical active matter models. In all models studied, the bound is weak where
collective fluctuations result in long-ranged correlations, which subsequently
links the locations of phase transitions to enhanced entropy production
fluctuations. We develop a theory for the onset of enhanced fluctuations and
relate it to specific phase transitions in active Brownian particles. We also
derive optimal control forces that realize the dynamics necessary to tune
dissipation and manipulate the system between phases. In so doing, we uncover a
general relationship between entropy production and pattern formation in active
matter, as well as ways of controlling it
Comparative evaluation of [(99m)tc]tilmanocept for sentinel lymph node mapping in breast cancer patients: results of two phase 3 trials.
BackgroundSentinel lymph node (SLN) surgery is used worldwide for staging breast cancer patients and helps limit axillary lymph node dissection. [(99m)Tc]Tilmanocept is a novel receptor-targeted radiopharmaceutical evaluated in 2 open-label, nonrandomized, within-patient, phase 3 trials designed to assess the lymphatic mapping performance.MethodsA total of 13 centers contributed 148 patients with breast cancer. Each patient received [(99m)Tc]tilmanocept and vital blue dye (VBD). Lymph nodes identified intraoperatively as radioactive and/or blue stained were excised and histologically examined. The primary endpoint, concordance (lower boundary set point at 90 %), was the proportion of nodes detected by VBD and [(99m)Tc]tilmanocept.ResultsA total of 13 centers contributed 148 patients who were injected with both agents. Intraoperatively, 207 of 209 nodes detected by VBD were also detected by [(99m)Tc]tilmanocept for a concordance rate of 99.04 % (p < 0.0001). [(99m)Tc]tilmanocept detected a total of 320 nodes, of which 207 (64.7 %) were detected by VBD. [(99m)Tc]Tilmanocept detected at least 1 SLN in more patients (146) than did VBD (131, p < 0.0001). In 129 of 131 patients with ≥1 blue node, all blue nodes were radioactive. Of 33 pathology-positive nodes (18.2 % patient pathology rate), [(99m)Tc]tilmanocept detected 31 of 33, whereas VBD detected only 25 of 33 (p = 0.0312). No pathology-positive SLNs were detected exclusively by VBD. No serious adverse events were attributed to [(99m)Tc]tilmanocept.Conclusion[(99m)Tc]Tilmanocept demonstrated success in detecting a SLN while meeting the primary endpoint. Interestingly, [(99m)Tc]tilmanocept was additionally noted to identify more SLNs in more patients. This localization represented a higher number of metastatic breast cancer lymph nodes than that of VBD
Calibration Of The Johnson–Cook Model At High Temperatures For An Ultra-High Strength CrNiMoV Steel
This paper presents a study on the thermo-mechanical behavior of an ultra-high strength CrNiMoV steel at high temperatures and medium strain rates through hot tensile tests. The material was examined in two conditions: as-cast/heat-treated (AC/HT) and as-rolled (AR). Tensile tests were conducted at temperatures of 800,900,1000,1100, and 1200°C, and strain rates of 0.1,1, and 10s−1. Inclusion and porosity analysis was also performed on the tensile specimens. The results revealed that the flow stress decreased by approximately 70% on average from 800°C to 1200°C, while increasing by approximately 32% on average from 0.1s−1 to 10s−1 in strain rate. The elongation exhibited an increase from 16.5% at 800°C to 33% at 1200°C. However, the ductility transition was slower than expected, particularly for the AC/HT conditions. The AC/HT samples exhibited higher levels of inclusions and porosity compared to the AR samples, with porosity significantly affecting the elongation to failure and ultimate tensile strength (UTS) at a strain rate of 1s−1. Furthermore, calibrated Johnson–Cook parameters were reported and compared, demonstrating excellent agreement between predicted and experimental values with less than 20% variation. The calibrated Johnson–Cook model can be effectively employed for modeling purposes within the studied temperature range, and its application can even be extrapolated for higher strain rates
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