11,151 research outputs found
Concentric Permutation Source Codes
Permutation codes are a class of structured vector quantizers with a
computationally-simple encoding procedure based on sorting the scalar
components. Using a codebook comprising several permutation codes as subcodes
preserves the simplicity of encoding while increasing the number of
rate-distortion operating points, improving the convex hull of operating
points, and increasing design complexity. We show that when the subcodes are
designed with the same composition, optimization of the codebook reduces to a
lower-dimensional vector quantizer design within a single cone. Heuristics for
reducing design complexity are presented, including an optimization of the rate
allocation in a shape-gain vector quantizer with gain-dependent wrapped
spherical shape codebook
Exact dynamical structure factor of the degenerate Haldane-Shastry model
The dynamical structure factor of the K-component (K = 2,3,4)
spin chain with the 1/r^2 exchange is derived exactly at zero temperature for
arbitrary size of the system. The result is interpreted in terms of a free
quasi-particle picture which is generalization of the spinon picture in the
SU(2) case; the excited states consist of K quasi-particles each of which is
characterized by a set of K-1 quantum numbers. Divergent singularities of
at the spectral edges are derived analytically. The analytic
result is checked numerically for finite systems.Comment: 4 pages, 1 figure, accepted for publication in Phys. Rev. Let
Assessment of Antioxidant Activities, Total Phenolics, and Flavonoids of Different Extracts of Strobilanthes Schomburgkii Leaves
The main purpose of this work was to assess the antioxidant activities of the n-hexane, ethyl acetate and methanol extracts of Strobilanthes schomburgkii leaves collected in Laocai province, Vietnam. Total phenolic and flavonoid contents were determined. The DPPH, H2O2 radical scavenging activity, and total antioxidant activity via phosphomolybdenum method were investigated. The results showed that the methanol extract concluded a high concentration of phenolics and flavonoids which were 65.42 mg/g and 52.05 mg/g, respectively. There was a significant correlation between total phenolic and flavonoid concentrations and EC50 values of different antioxidant assays. The antioxidant properties of the different extracts from Strobilanthes schomburgkii leaves were reported for the first time
A NICER Discovery of a Low-Frequency Quasi-Periodic Oscillation in the Soft-Intermediate State of MAXI J1535-571
We present the discovery of a low-frequency Hz quasi-periodic
oscillation (QPO) feature in observations of the black hole X-ray binary MAXI
J1535-571 in its soft-intermediate state, obtained in September-October 2017 by
the Neutron Star Interior Composition Explorer (NICER). The feature is
relatively broad (compared to other low-frequency QPOs; quality factor
) and weak (1.9% rms in 3-10 keV), and is accompanied by a weak
harmonic and low-amplitude broadband noise. These characteristics identify it
as a weak Type A/B QPO, similar to ones previously identified in the
soft-intermediate state of the transient black hole X-ray binary XTE J1550-564.
The lag-energy spectrum of the QPO shows increasing soft lags towards lower
energies, approaching 50 ms at 1 keV (with respect to a 3-10 keV continuum).
This large phase shift has similar amplitude but opposite sign to that seen in
Rossi X-ray Timing Explorer data for a Type B QPO from the transient black hole
X-ray binary GX 339-4. Previous phase-resolved spectroscopy analysis of the
Type B QPO in GX 339-4 pointed towards a precessing jet-like corona
illuminating the accretion disk as the origin of the QPO signal. We suggest
that this QPO in MAXI J1535-571 may have the same origin, with the different
lag sign depending on the scale height of the emitting region and the observer
inclination angle.Comment: Accepted for publication in ApJ Letter
Absence of stable collinear configurations in Ni(001)ultrathin films: canted domain structure as ground state
Brillouin light scattering (BLS) measurements were performed for (17-120)
Angstrom thick Cu/Ni/Cu/Si(001) films. A monotonic dependence of the frequency
of the uniform mode on an in-plane magnetic field H was observed both on
increasing and on decreasing H in the range (2-14) kOe, suggesting the absence
of a metastable collinear perpendicular ground state. Further investigation by
magneto-optical vector magnetometry (MOKE-VM) in an unconventional canted-field
geometry provided evidence for a domain structure where the magnetization is
canted with respect to the perpendicular to the film. Spin wave calculations
confirm the absence of stable collinear configurations.Comment: 6 pages, 3 figures (text, appendix and 1 figure added
Large asymptomatic Left Atrial Myxoma with ossification: case report
<p>Abstract</p> <p>Background</p> <p>Atrial myxomas are the most common primary cardiac tumors. They are usually small or moderate in size by the time of the diagnosis, exhibiting non specific cardiac or systemic symptoms, and are most frequently soft and friable without microscopic signs of ossification. We describe herein an extremely rare case of an asymptomatic giant left atrial myxoma with angiographic neovascularization and ossification.</p> <p>Case presentation</p> <p>An asymptomatic 58-year-old male with a giant left atrial tumor, was transferred to our Unit for surgical treatment. The tumor was an incidental finding during a work-up for hemoptysis due to bronchectasis. The coronary angiogram showed tumor vessels originating from the RCA. The tumor macroscopically did not resemble a myxoma, considering its dimensions (12 × 10 cm) and its solid substance. The mass was excised together with the interatrial septum and the right lateral LA wall close to the right pulmonary veins orifices. The defect was closed with Dacron patches in order to prevent malformation of both atria. The pathology study revealed a benign myxoma with excessive osteoid (mature bone) content.</p> <p>Conclusion</p> <p>We consider our case as extremely rare because of the asymptomatic course despite the large size of the tumor, the blood supply from the right coronary artery and the bone formation.</p
Frame Permutation Quantization
Frame permutation quantization (FPQ) is a new vector quantization technique
using finite frames. In FPQ, a vector is encoded using a permutation source
code to quantize its frame expansion. This means that the encoding is a partial
ordering of the frame expansion coefficients. Compared to ordinary permutation
source coding, FPQ produces a greater number of possible quantization rates and
a higher maximum rate. Various representations for the partitions induced by
FPQ are presented, and reconstruction algorithms based on linear programming,
quadratic programming, and recursive orthogonal projection are derived.
Implementations of the linear and quadratic programming algorithms for uniform
and Gaussian sources show performance improvements over entropy-constrained
scalar quantization for certain combinations of vector dimension and coding
rate. Monte Carlo evaluation of the recursive algorithm shows that mean-squared
error (MSE) decays as 1/M^4 for an M-element frame, which is consistent with
previous results on optimal decay of MSE. Reconstruction using the canonical
dual frame is also studied, and several results relate properties of the
analysis frame to whether linear reconstruction techniques provide consistent
reconstructions.Comment: 29 pages, 5 figures; detailed added to proof of Theorem 4.3 and a few
minor correction
Novel cyclic di-GMP effectors of the YajQ protein family control bacterial virulence
Bis-(3 ',5 ') cyclic di-guanylate (cyclic di-GMP) is a key bacterial second messenger that is implicated in the regulation of many critical processes that include motility, biofilm formation and virulence. Cyclic di-GMP influences diverse functions through interaction with a range of effectors. Our knowledge of these effectors and their different regulatory actions is far from complete, however. Here we have used an affinity pull-down assay using cyclic di-GMP-coupled magnetic beads to identify cyclic di-GMP binding proteins in the plant pathogen Xanthomonas campestris pv. campestris (Xcc). This analysis identified XC_3703, a protein of the YajQ family, as a potential cyclic di-GMP receptor. Isothermal titration calorimetry showed that the purified XC_3703 protein bound cyclic di-GMP with a high affinity (K-d similar to 2 mu M). Mutation of XC_3703 led to reduced virulence of Xcc to plants and alteration in biofilm formation. Yeast two-hybrid and far-western analyses showed that XC_3703 was able to interact with XC_2801, a transcription factor of the LysR family. Mutation of XC_2801 and XC_3703 had partially overlapping effects on the transcriptome of Xcc, and both affected virulence. Electromobility shift assays showed that XC_3703 positively affected the binding of XC_2801 to the promoters of target virulence genes, an effect that was reversed by cyclic di-GMP. Genetic and functional analysis of YajQ family members from the human pathogens Pseudomonas aeruginosa and Stenotrophomonas maltophilia showed that they also specifically bound cyclic di-GMP and contributed to virulence in model systems. The findings thus identify a new class of cyclic di-GMP effector that regulates bacterial virulence
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