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  • 1
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    An efficient and positivity-preserving layer method for modeling radiation belt diffusion processes (2016)
    Wiley
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    Publication Date: 2016-01-08
    Description: An efficient and positivity-preserving layer method is introduced to solve the radiation belt diffusion equation and is applied to study the bounce resonance interaction between relativistic electrons and magnetosonic waves. The layer method with linear interpolation, denoted by LM-L (layer method-linear), requires the use of a large number of grid points to ensure accurate solutions. We introduce a monotonicity- and positivity-preserving cubic interpolation method to be used with the Milstein-Tretyakov layer method. The resulting method, called LM-MC (layer method-monotone cubic), can be used to solve the radiation belt diffusion equation with a much smaller number of grid points than LM-L, while still being able to preserve the positivity of the solution. We suggest that LM-MC can be used to study long-term dynamics of radiation belts. We then develop a 2D LM-MC code and use it to investigate the bounce resonance diffusion of radiation belt electrons by magnetosonic waves. Using a previously published magnetosonic wave model, we demonstrate that bounce resonance with magnetosonic waves is as important as gyro-resonance; both can cause several orders of magnitude increase of MeV electron fluxes within one day. We conclude that bounce resonance with magnetosonic waves should be taken into consideration together with gyro-resonance.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Turbulent convection and pulsation stability of stars - I. Basic equations for calculations of stellar structure and oscillations (2015)
    Oxford University Press
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    Publication Date: 2015-06-26
    Description: Starting from hydrodynamic equations, we have established a set of hydrodynamic equations for average flow and a set of dynamic equations of auto- and cross-correlations of turbulent velocity and temperature fluctuations, following the classic Reynold's treatment of turbulence. The combination of the two sets of equations leads to a complete and self-consistent mathematical expressions ready for the calculations of stellar structure and oscillations. In this paper, non-locality and anisotropy of turbulent convection are concisely presented, together with defining and calibrating of the three convection parameters ( c 1 , c 2 and c 3 ) included in the algorithm. With the non-local theory of convection, the structure of the convective envelope and the major characteristics of non-adiabatic linear oscillations are demonstrated by numerical solutions. Great effort has been exercised to the choice of convection parameters and pulsation instabilities of the models, the results of which show that within large ranges of all three parameters ( c 1 , c 2 and c 3 ) the main properties of pulsation stability keep unchanged.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Antenna-reactor complexes for photocatalysis [Applied Physical Sciences] (2016)
    National Academy of Sciences
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    Publication Date: 2016-08-11
    Description: Metallic nanoparticles with strong optically resonant properties behave as nanoscale optical antennas, and have recently shown extraordinary promise as light-driven catalysts. Traditionally, however, heterogeneous catalysis has relied upon weakly light-absorbing metals such as Pd, Pt, Ru, or Rh to lower the activation energy for chemical reactions. Here we show that...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 4
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    Long-term engraftment of myogenic progenitors from adipose-derived stem cells and muscle regeneration in dystrophic mice (2015)
    Oxford University Press
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    Publication Date: 2015-10-10
    Description: Stem cell therapy is a promising approach for treating Duchenne muscular dystrophy (DMD); however, its application is hindered by poor cell engraftment. There have been no reports to date describing the efficient generation of myogenic progenitors from adipose-derived stem cells (ADSCs) that can contribute to muscle regeneration. In this study, we examined the in vivo myogenic potential of progenitors differentiated from ADSCs using forskolin, basic fibroblast growth factor, the glycogen synthase kinase 3β inhibitor 6-bromoindirubin-3'-oxime as well as the supernatant of ADSC cultures. The results indicate that a proliferative population of myogenic progenitors can be derived from ADSCs that have characteristics similar to muscle satellite cells and are capable of terminal differentiation into multinucleated myotubes. When transplanted into DMD model mdx mice either by intramuscular injection or systemic delivery, progenitors were successfully engrafted in skeletal muscle for up to 12 weeks, and generated new muscle fibers, restored dystrophin expression and contributed to the satellite cell compartment. These findings highlight the potential application of myogenic progenitors derived from ADSCs to the treatment of muscular dystrophy.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 5
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    P-Rex1 regulates autism-like social behavior [Neuroscience] (2015)
    National Academy of Sciences
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    Publication Date: 2015-12-16
    Description: Autism spectrum disorders (ASDs) are a group of highly inheritable mental disorders associated with synaptic dysfunction, but the underlying cellular and molecular mechanisms remain to be clarified. Here we report that autism in Chinese Han population is associated with genetic variations and copy number deletion of P-Rex1 (phosphatidylinositol-3,4,5-trisphosphate-dependent Rac exchange...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 6
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    Investigation of the emission radii of kHz QPOs for the accreting millisecond X-Ray pulsars, Atoll and Z sources (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-03
    Description: We infer the emission positions of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs) based on the Alfvén wave oscillation model (AWOM). For most sources, the emission radii of kHz QPOs cluster around a region of 16–19 km with the assumed NS radii of 15 km. Cir X-1 has the larger emission radii of 23 ~ 38 km than those of the other sources, which may be ascribed to its large magnetosphere-disc radius or strong NS surface magnetic field. SAX J1808.4–3658 is also a particular source with the relative large emission radii of kHz QPOs of 20 ~ 23 km, which may be due to its large inferred NS radius of 18 ~ 19 km. The emission radii of kHz QPOs for all the sources are larger than the NS radii, and the possible explanations of which are presented. The similarity of the emission radii of kHz QPOs (~16–19 km) for both the low/high luminosity Atoll/Z sources is found, which indicates that both sources share the similar magnetosphere-disc radii.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Turbulent convection and pulsation stability of stars - II. Theoretical instability strip for {delta} Scuti and {gamma} Doradus stars (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-22
    Description: By using a non-local and time-dependent convection theory, we have calculated radial and low-degree non-radial oscillations for stellar evolutionary models with M  = 1.4–3.0 M . The results of our study predict theoretical instability strips for  Scuti and  Doradus stars, which overlap with each other. The strip of  Doradus is slightly redder in colour than that of  Scuti. We have paid great attention to the excitation and stabilization mechanisms for these two types of oscillations, and we conclude that radiative mechanism plays a major role in the excitation of warm  Scuti and  Doradus stars, while the coupling between convection and oscillations is responsible for excitation and stabilization in cool stars. Generally speaking, turbulent pressure is an excitation of oscillations, especially in cool  Scuti and  Doradus stars and all cool Cepheid- and Mira-like stars. Turbulent thermal convection, on the other hand, is a damping mechanism against oscillations that actually plays the major role in giving rise to the red edge of the instability strip. Our study shows that oscillations of  Scuti and  Doradus stars are both due to the combination of mechanism and the coupling between convection and oscillations, and they belong to the same class of variables at the low-luminosity part of the Cepheid instability strip. Within the  Scuti– Doradus instability strip, most of the pulsating variables are very likely hybrids that are excited in both p and g modes.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Chronic stress promotes cancer [Genetics] (2012)
    National Academy of Sciences
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    Publication Date: 2012-05-02
    Description: Epidemiological studies strongly suggest that chronic psychological stress promotes tumorigenesis. However, its direct link in vivo and the underlying mechanisms that cause this remain unclear. This study provides direct evidence that chronic stress promotes tumorigenesis in vivo; chronic restraint, a well-established mouse model to induce chronic stress, greatly promotes ionizing radiation (IR)-induced tumorigenesis in p53+/− mice. The tumor suppressor protein p53 plays a central role in tumor prevention. Loss or attenuation of p53 function contriubutes greatly to tumorigenesis. We found that chronic restraint decreases the levels and function of p53 in mice, and furthermore, promotes the growth of human xenograft tumors in a largely p53-dependent manner. Our results show that glucocorticoids elevated during chronic restraint mediate the effect of chronic restraint on p53 through the induction of serum- and glucocorticoid-induced protein kinase (SGK1), which in turn increases MDM2 activity and decreases p53 function. Taken together, this study demonstrates that chronic stress promotes tumorigenesis in mice, and the attenuation of p53 function is an important part of the underlying mechanism, which can be mediated by glucocortcoids elevated during chronic restraint.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Constraints on kilohertz quasi-periodic oscillation models and stellar equations of state from SAX J1808.4-3658, Cyg X-2 and 4U 1820-30 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: We test the relativistic precession model (RPM) and the magnetohydrodynamics Alfvén wave oscillation model (AWOM) for the kilohertz (kHz) quasi-periodic oscillations (QPOs) from sources with measured neutron star (NS) masses and twin kHz QPO frequencies. For the RPM, the derived NS masses of Cyg X-2, SAX J1808.4–3658 and 4U 1820–30 are 1.96 ± 0.10, 2.83 ± 0.04 and 1.85 ± 0.02 M , respectively. These are, respectively, ~30, 100 and 40 per cent higher than the measured results 1.5 ± 0.3, 〈1.4 and $1.29^{+0.19}_{-0.07}$ M . For the AWOM, where the free parameter of the model is the density of the star, we infer the NS radii to be around 10–20 km for the above three sources. Based on this, we can infer the matter compositions inside the NSs with the help of the equations of state. In particular, for SAX J1808.4–3658, the AWOM shows a lower mass density for its NS than those of the other known kHz QPO sources, with a radius range of 17–20 km, which excludes the strange quark matter inside its star.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Pentacene/Cu(110) interface formation monitored by in situ optical spectroscopy (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-01-25
    Description: Author(s): L. Zhang, C. Y. Liu, X. Fu, L. D. Sun, and P. Zeppenfeld The adsorption of pentacene on the Cu(110) surface has been investigated by reflectance difference spectroscopy (RDS) and spot profile analysis low energy electron diffraction (SPA-LEED). The sensitivity of RDS to electronic transitions involving both surface states and intramolecular transitions al... [Phys. Rev. B 89, 035428] Published Fri Jan 24, 2014
    Keywords: Surface physics, nanoscale physics, low-dimensional systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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