2,659 research outputs found
Torsion matrices over commutative integral group rings
Let ZA be the integral group ring of a finite abelian group A, and n a positive integer greater than 5. We provide conditions on n and A under which every torsion matrix U, with identity augmentation, in GLn(ZA) is conjugate in GLn(QA) to a diagonal matrix with group elements on the diagonal. When A is infinite, we show that under similar conditions, U has a group trace and is stably conjugate to such a diagonal matrix
Doping Dependence of Thermal Oxidation on n-type 4H-SiC
The doping dependence of dry thermal oxidation rates in n-type 4H-SiC was
investigated. The oxidation was performed in the temperature range 1000C to
1200C for samples with nitrogen doping in the range of 6.5e15/cm3 to
9.3e18/cm3, showing a clear doping dependence. Samples with higher doping
concentrations displayed higher oxidation rates. The results were interpreted
using a modified Deal-Grove model. Linear and parabolic rate constants and
activation energies were extracted. Increasing nitrogen led to an increase in
linear rate constant pre-exponential factor from 10-6m/s to 10-2m/s and the
parabolic rate constant pre-exponential factor from 10e9m2/s to 10e6m2/s. The
increase in linear rate constant was attributed to defects from doping-induced
lattice mismatch, which tend to be more reactive than bulk crystal regions. The
increase in the diffusion-limited parabolic rate constant was attributed to
degradation in oxide quality originating from the doping-induced lattice
mismatch. This degradation was confirmed by the observation of a decrease in
optical density of the grown oxide films from 1.4 to 1.24. The linear
activation energy varied from 1.6eV to 2.8eV, while the parabolic activation
energy varied from 2.7eV to 3.3eV, increasing with doping concentration. These
increased activation energies were attributed to higher nitrogen content,
leading to an increase in effective bond energy stemming from the difference in
C-Si (2.82eV) and Si-N (4.26eV) binding energies. This work provides crucial
information in the engineering of SiO2 dielectrics for SiC MOS structures,
which typically involve regions of very different doping concentrations, and
suggests that thermal oxidation at high doping concentrations in SiC may be
defect mediated.Comment: 13 pages. 9 figures, accepted as a transiction in IEEE electron
device. TED MS#8035
Restoration of Equalization and Aeration Tanks of Effluent Treatment Plant at the Mysugar Factory, Mandya, Karnataka, India
This paper deals with the restoration measures resorted to strengthen the structure and prevent the leakage of the equalization and aeration tanks of effluent treatment plant in a sugar factory. These tanks showed distress at the hydraulic test itself before commissioning due to the failure of the reinforced concrete floor and bund lining on account of loss of support due to excessive deformation of the substratum. Extensive sand piling was resorted to strengthen the substratum before recasting the reinforced concrete floor and bund lining to ensure structural stability and prevent leakage. These tanks are functioning satisfactorily since two years after restoration serving the intended functions of the eflluent treatment
Lorentz transformations that entangle spins and entangle momenta
Simple examples are presented of Lorentz transformations that entangle the
spins and momenta of two particles with positive mass and spin 1/2. They apply
to indistinguishable particles, produce maximal entanglement from finite
Lorentz transformations of states for finite momenta, and describe entanglement
of spins produced together with entanglement of momenta. From the entanglements
considered, no sum of entanglements is found to be unchanged.Comment: 5 Pages, 2 Figures, One new paragraph and reference adde
Completely Positive Maps and Classical Correlations
We expand the set of initial states of a system and its environment that are
known to guarantee completely positive reduced dynamics for the system when the
combined state evolves unitarily. We characterize the correlations in the
initial state in terms of its quantum discord [H. Ollivier and W. H. Zurek,
Phys. Rev. Lett. 88, 017901 (2001)]. We prove that initial states that have
only classical correlations lead to completely positive reduced dynamics. The
induced maps can be not completely positive when quantum correlations
including, but not limited to, entanglement are present. We outline the
implications of our results to quantum process tomography experiments.Comment: 4 pages, 1 figur
Unital quantum operators on the Bloch ball and Bloch region
For one qubit systems, we present a short, elementary argument characterizing
unital quantum operators in terms of their action on Bloch vectors. We then
show how our approach generalizes to multi-qubit systems, obtaining
inequalities that govern when a ``diagonal'' superoperator on the Bloch region
is a quantum operator. These inequalities are the n-qubit analogue of the
Algoet-Fujiwara conditions. Our work is facilitated by an analysis of
operator-sum decompositions in which negative summands are allowed.Comment: Revised and corrected, to appear in Physical Review
Microstructural and Mechanical Properties of Al2O3 and Al2O3/TiB2 Ceramics Consolidated by Plasma Pressure Compaction
Alumina oxide ceramics were produced by plasma pressure compaction (P2C) sintering process. Two types of pure α-alumina (Al2O3) and a mixture of alumina and titanium diboride (TiB2) powders were used as starting materials. Microstructure and mechanical properties, namely hardness, elastic modulus, and fracture toughness, were analyzed and correlated to the type of the sintered powders and the adopted manufacturing route. The microstructural development and the chemical composition variation induced by the sintering process were assessed by using scanning electron microscopy and x-ray diffraction. Nano-indentation and Chevron notch beam techniques were adopted to estimate the mechanical properties of the sintered ceramics. The conducted analyses show the capability of P2C technique to produce sound alumina ceramics. Pure alumina bulks exhibit a good level of compaction and mechanical properties close to those achievable with conventional sintering processes, such as hot isostatic pressing or spark plasma sintering. No significant alterations in the chemical composition of the ceramics were observed. The addition of the titanium diboride in the alumina powders caused a moderate increase in the grain size lowering the hardness and Young’s modulus of the sintered alumina and, at the same time, increased its fracture toughness to the occurrence of toughening mechanisms, like crack bridging and crack deflection
Not All Children with Cystic Fibrosis Have Abnormal Esophageal Neutralization during Chemical Clearance of Acid Reflux.
PurposeAcid neutralization during chemical clearance is significantly prolonged in children with cystic fibrosis, compared to symptomatic children without cystic fibrosis. The absence of available reference values impeded identification of abnormal findings within individual patients with and without cystic fibrosis. The present study aimed to test the hypothesis that significantly more children with cystic fibrosis have acid neutralization durations during chemical clearance that fall outside the physiological range.MethodsPublished reference value for acid neutralization duration during chemical clearance (determined using combined impedance/pH monitoring) was used to assess esophageal acid neutralization efficiency during chemical clearance in 16 children with cystic fibrosis (3 to <18 years) and 16 age-matched children without cystic fibrosis.ResultsDuration of acid neutralization during chemical clearance exceeded the upper end of the physiological range in 9 of 16 (56.3%) children with and in 3 of 16 (18.8%) children without cystic fibrosis (p=0.0412). The likelihood ratio for duration indicated that children with cystic fibrosis are 2.1-times more likely to have abnormal acid neutralization during chemical clearance, and children with abnormal acid neutralization during chemical clearance are 1.5-times more likely to have cystic fibrosis.ConclusionSignificantly more (but not all) children with cystic fibrosis have abnormally prolonged esophageal clearance of acid. Children with cystic fibrosis are more likely to have abnormal acid neutralization during chemical clearance. Additional studies involving larger sample sizes are needed to address the importance of genotype, esophageal motility, composition and volume of saliva, and gastric acidity on acid neutralization efficiency in cystic fibrosis children
Complex Energy Spectrum and Time Evolution of QBIC States in a Two-Channel Quantum wire with an Adatom Impurity
We provide detailed analysis of the complex energy eigenvalue spectrum for a
two-channel quantum wire with an attached adatom impurity. The study is based
on our previous work [Phys. Rev. Lett. 99, 210404 (2007)], in which we
presented the quasi-bound states in continuum (or QBIC states). These are
resonant states with very long lifetimes that form as a result of two
overlapping continuous energy bands one of which, at least, has a divergent van
Hove singularity at the band edge. We provide analysis of the full energy
spectrum for all solutions, including the QBIC states, and obtain an expansion
for the complex eigenvalue of the QBIC state. We show that it has a small decay
rate of the order , where is the coupling constant. As a result of
this expansion, we find that this state is a non-analytic effect resulting from
the van Hove singularity; it cannot be predicted from the ordinary perturbation
analysis that relies on Fermi's golden rule. We will also numerically
demonstrate the time evolution of the QBIC state using the effective potential
method in order to show the stability of the QBIC wave function in comparison
with that of the other eigenstates.Comment: Around 20 pages, 50 total figure
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