7,573 research outputs found
Ultra-Scalable Spectral Clustering and Ensemble Clustering
This paper focuses on scalability and robustness of spectral clustering for
extremely large-scale datasets with limited resources. Two novel algorithms are
proposed, namely, ultra-scalable spectral clustering (U-SPEC) and
ultra-scalable ensemble clustering (U-SENC). In U-SPEC, a hybrid representative
selection strategy and a fast approximation method for K-nearest
representatives are proposed for the construction of a sparse affinity
sub-matrix. By interpreting the sparse sub-matrix as a bipartite graph, the
transfer cut is then utilized to efficiently partition the graph and obtain the
clustering result. In U-SENC, multiple U-SPEC clusterers are further integrated
into an ensemble clustering framework to enhance the robustness of U-SPEC while
maintaining high efficiency. Based on the ensemble generation via multiple
U-SEPC's, a new bipartite graph is constructed between objects and base
clusters and then efficiently partitioned to achieve the consensus clustering
result. It is noteworthy that both U-SPEC and U-SENC have nearly linear time
and space complexity, and are capable of robustly and efficiently partitioning
ten-million-level nonlinearly-separable datasets on a PC with 64GB memory.
Experiments on various large-scale datasets have demonstrated the scalability
and robustness of our algorithms. The MATLAB code and experimental data are
available at https://www.researchgate.net/publication/330760669.Comment: To appear in IEEE Transactions on Knowledge and Data Engineering,
201
Resonant Tidal Excitations of Inertial Modes in Coalescing Neutron Star Binaries
We study the effect of resonant tidal excitation of inertial modes in neutron
stars during binary inspiral. For spin frequencies less than 100 Hz, the phase
shift in the gravitational waveform associated with the resonance is small and
does not affect the matched filtering scheme for gravitational wave detection.
For higher spin frequencies, the phase shift can become significant. Most of
the resonances take place at orbital frequencies comparable to the spin
frequency, and thus significant phase shift may occur only in the
high-frequency band (hundreds of Hertz) of gravitational wave. The exception is
a single odd-paity mode, which can be resonantly excited for misaligned
spin-orbit inclinations, and may occur in the low-frequency band (tens of
Hertz) of gravitational wave and induce significant (>> 1 radian) phase shift.Comment: Minor changes. 6 pages. Phys. Rev. D. in press (volume 74, issue 2
Dynamical Tides in Eccentric Binaries and Tidally-Excited Stellar Pulsations in KEPLER KOI-54
Recent observation of the tidally-excited stellar oscillations in the
main-sequence binary KOI-54 by the KEPLER satellite provides a unique
opportunity for studying dynamical tides in eccentric binary systems. We
develop a general theory of tidal excitation of oscillation modes of rotating
binary stars, and apply our theory to tidally excited gravity modes (g-modes)
in KOI-54. The strongest observed oscillations, which occur at 90 and 91 times
the orbital frequency, are likely due to prograde m=2 modes (relative to the
stellar spin axis) locked in resonance with the orbit. The remaining flux
oscillations with frequencies that are integer multiples of the orbital
frequency are likely due to nearly resonant m=0 g-modes; such axisymmetric
modes generate larger flux variations compared to the m=2 modes, assuming that
the spin inclination angle of the star is comparable to the orbital inclination
angle. We examine the process of resonance mode locking under the combined
effects of dynamical tides on the stellar spin and orbit and the intrinsic
stellar spindown. We show that KOI-54 can naturally evolve into a state in
which at least one m=2 mode is locked in resonance with the orbital frequency.
Our analysis provides an explanation for the fact that only oscillations with
frequencies less than 90-100 times the orbital frequency are observed. We have
also found evidence from the published KEPLER result that three-mode nonlinear
coupling occurs in the KOI-54 system. We suggest that such nonlinear mode
coupling may explain the observed oscillations that are not harmonics of the
orbital frequency.Comment: 15 pages, 5 figures, accepted by MNRA
Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems: II. Warped Discs
Magnetic interactions between a protostar and its accretion disc tend to
induce warping in the disc and produce secular changes in the stellar spin
direction, so that the spin axis may not always be perpendicular to the disc.
This may help explain the recently observed spin-orbit misalignment in a number
of exoplanetary systems. We study the dynamics of warped protoplanetary discs
under the combined effects of magnetic warping/precession torques and internal
stresses in the disc, including viscous damping of warps and propagation of
bending waves. We show that when the outer disc axis is misaligned with the
stellar spin axis, the disc evolves towards a warped steady-state on a
timescale that depends on the disc viscosity or the bending wave propagation
speed, but in all cases is much shorter than the timescale for the spin
evolution (of order of a million years). Moreover, for the most likely physical
parameters characterizing magnetic protostars, circumstellar discs and their
interactions, the steady-state disc has a rather small warp, such that the
whole disc lies approximately in a single plane determined by the outer disc
boundary conditions, although more extreme parameters may give rise to larger
disc warps. In agreement with our recent analysis (Lai et al. 2010) based on
flat discs, we find that the back-reaction magnetic torques of the slightly
warped disc on the star can either align the stellar spin axis with the disc
axis or push it towards misalignment, depending on the parameters of the
star-disc system. This implies that newly formed planetary systems may have a
range of inclination angles between the stellar spin axis and the symmetry axis
of the planetary orbits.Comment: 18 pages, 20 figures, Accepted by MNRA
The Effects of a Non-Ferroelectric Slab on the Polarization and the Susceptibility of the Ferroelectric Multilayer
The polarization and the susceptibility of a ferroelectric multilayer with a
non-ferroelectric slab are investigated within the framework of transverse
Ising model with a four-spin interaction term. The effect of the thickness and
the position of the non-ferroelectric slab are investigated in this paper. We
find that the increase of the thickness of the non-ferroelectric will decrease
the polarization and the susceptibility of the film. If the position of the
non-ferroelcetric slab shifts from the center of the film to the surface, the
number of the peaks of the susceptibility will change. And a step-like
polarization curve is found.Comment: 15 pages, 4 figure
Tidal Excitation of Oscillation Modes in Compact White Dwarf Binaries: I. Linear Theory
We study the tidal excitation of gravity modes (g-modes) in compact white
dwarf binary systems with periods ranging from minutes to hours. As the orbit
of the system decays via gravitational radiation, the orbital frequency
increases and sweeps through a series of resonances with the g-modes of the
white dwarf. At each resonance, the tidal force excites the g-mode to a
relatively large amplitude, transferring the orbital energy to the stellar
oscillation. We calculate the eigenfrequencies of g-modes and their coupling
coefficients with the tidal field for realistic non-rotating white dwarf
models. Using these mode properties, we numerically compute the excited mode
amplitude in the linear approximation as the orbit passes though the resonance,
including the backreaction of the mode on the orbit. We also derive analytical
estimates for the mode amplitude and the duration of the resonance, which
accurately reproduce our numerical results for most binary parameters. We find
that the g-modes can be excited to a dimensionless (mass-weighted) amplitude up
to 0.1, with the mode energy approaching of the gravitational binding
energy of the star. This suggests that thousands of years prior to the binary
merger, the white dwarf may be heated up significantly by tidal interactions.
However, more study is needed since the physical amplitudes of the excited
oscillation modes become highly nonlinear in the outer layer of the star, which
can reduce the mode amplitude attained by tidal excitation.Comment: 10 pages, 8 figure
Protective Effect of Anthocyanins Extract from Blueberry on TNBS-Induced IBD Model of Mice
This study was carried out to evaluate the protective effect of anthocyanins extract of blueberry on trinitrobenzene sulfonic acid (TNBS)-induced inflammatory bowel disease (IBD) model of mice. The study employed female C57BL/6 mice (n = 50), and colitis was induced by intracolonic injection of 0.5 mg of TNBS dissolved in 50% ethanol–phosphate buffered solution. The mice were divided into five groups (n = 10): vehicle, TNBS control and anthocyanins groups that received different doses of anthocyanins extract (10, 20 and 40 mg kg−1) daily for 6 days. Both increase in body weight and diarrhea symptoms were monitored each day. After 6 days, the animals were killed, and the following parameters were assessed: colon length, morphological score, histological score and biochemical assay (NO, myeloperoxidase (MPO), interleukin (IL)-12, IL-10, tumor necrosis factor (TNF)-α and interferon (IFN)-γ). The results showed that the anthocyanins extract of blueberry rendered strong protection against TNBS-induced colonic damage at a dosage of 40 mg kg−1. When compared with the control, anthocyanins extract significantly prevented loss of body weight and ameliorated the scores of diarrhea, morphology and histology. Treatment with anthocyanins extract restored IL-10 excretion, as well as caused reduction in the levels of NO, MPO, IL-12, TNF-α and IFN-γ. Our research revealed the protective effect of anthocyanins extract from blueberry on TNBS-induced experimental colitis in mice, as well as examined whether high levels of dietary blueberries would lower the risk or have protective effects on human IBD, which may require further investigation
Effect of beraprost sodium on renal function and p38MAPK signaling pathway in rats with diabetic nephropathy
Purpose: To investigate the effect of beraprost sodium (BPS) on renal function and P38MAPK pathway in diabetic nephropathy (DN) rats.Methods: Sprague Dawley (SD) rats (n = 30) were randomly divided into three groups, viz, normal control (NC), diabetic nephropathy (DN) and beraprost sodium (BPS). Creatinine (Cr), blood urea nitrogen (BUN) and fasting blood glucose (FBG), were determined by Hitachi 7020 automatic biochemical analyzer, while low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG) and total cholesterol (TC) were measured by Olympus 400 automatic biochemical analyzer. Western blot analysis was performed to examine protein expression. Interleukin-6 (IL-6), hs-CRP, and TNF-α levels were evaluated using enzyme linked immunosorbent assay (ELISA).Results: After 8 weeks of treatment, renal function indices (urine output, KW/BW, UAlb/24 h, Cr and BUN), blood lipid indices (FBG, LDL-C, TG and TC) and inflammatory factors levels (IL-6, hs-CRP and TNF-α) in DN group were higher than NC group (p < 0.05). In BPS group, renal function and blood lipid indices and inflammatory factor levels decreased when compared to DN group (p < 0.05). Furthermore, BPS inhibited the protein expression of p-P38MAPK, TGF-β1 and COX-2.Conclusion: Beraprost sodium improves renal function in DN rats by inhibiting P38MAPK signalingpathway
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