39,092 research outputs found
Can the age discrepancies of neutron stars be circumvented by an accretion-assisted torque?
It is found that 1E 1207.4-5209 could be a low-mass bare strange star if its
small radius or low altitude cyclotron formation can be identified. The age
problems of five sources could be solved by a fossil-disk-assisted torque. The
magnetic dipole radiation dominates the evolution of PSR B1757-24 at present,
and the others are in propeller (or tracking) phases.Comment: ApJL accepted, or at
http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.ht
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Source-specific Fine Particulate Using Spatiotemporal Concentration Fields Developed using Chemical Transport Modelling and Data Assimilation
Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies
The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on
superconductivity and electronic properties have been studied. A significant
enhancement of the superconducting transition temperature (TC) up to 21K was
observed in the most Fe deficient film (x=0.8). Based on the observed and
simulated structural variation results, there is a high possibility that Fe
vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows
a strong relationship with the lattice strain effect induced by Fe vacancies.
Importantly, the presence of Fe vacancies alters the charge carrier population
by introducing electron charge carriers, with the Fe deficient film showing
more metallic behavior than the defect-free film. Our study provides a means to
enhance the superconductivity and tune the charge carriers via Fe vacancy, with
no reliance on chemical doping.Comment: 15 pages, 4 figure
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Optimization of cool roof and night ventilation in office buildings: A case study in Xiamen, China
Increasing roof albedo (using a “cool” roof) and night ventilation are passive cooling technologies that can reduce the cooling loads in buildings, but existing studies have not comprehensively explored the potential benefits of integrating these two technologies. This study combines an experiment in the summer and transition seasons with an annual simulation so as to evaluate the thermal performance, energy savings and thermal comfort improvement that could be obtained by coupling a cool roof with night ventilation. A holistic approach integrating sensitivity analysis and multi-objective optimization is developed to explore key design parameters (roof albedo, night ventilation air change rate, roof insulation level and internal thermal mass level) and optimal design options for the combined application of the cool roof and night ventilation. The proposed approach is validated and demonstrated through studies on a six-storey office building in Xiamen, a cooling-dominated city in southeast China. Simulations show that combining a cool roof with night ventilation can significantly decrease the annual cooling energy consumption by 27% compared to using a black roof without night ventilation and by 13% compared to using a cool roof without night ventilation. Roof albedo is the most influential parameter for both building energy performance and indoor thermal comfort. Optimal use of the cool roof and night ventilation can reduce the annual cooling energy use by 28% during occupied hours when air-conditioners are on and reduce the uncomfortable time slightly during occupied hours when air-conditioners are off
X-ray ptychography on low-dimensional hard-condensed matter materials
Tailoring structural, chemical, and electronic (dis-)order in heterogeneous media is one of the transformative opportunities to enable new functionalities and sciences in energy and quantum materials. This endeavor requires elemental, chemical, and magnetic sensitivities at the nano/atomic scale in two- and three-dimensional space. Soft X-ray radiation and hard X-ray radiation provided by synchrotron facilities have emerged as standard characterization probes owing to their inherent element-specificity and high intensity. One of the most promising methods in view of sensitivity and spatial resolution is coherent diffraction imaging, namely, X-ray ptychography, which is envisioned to take on the dominance of electron imaging techniques offering with atomic resolution in the age of diffraction limited light sources. In this review, we discuss the current research examples of far-field diffraction-based X-ray ptychography on two-dimensional and three-dimensional semiconductors, ferroelectrics, and ferromagnets and their blooming future as a mainstream tool for materials sciences
Neutrino-Mixing-Generated Lepton Asymmetry and the Primordial He Abundance
It has been proposed that an asymmetry in the electron neutrino sector may be
generated by resonant active-sterile neutrino transformations during Big Bang
Nucleosynthesis (BBN). We calculate the change in the primordial He yield
resulting from this asymmetry, taking into account both the time evolution
of the and distribution function and the spectral
distortions in these. We calculate this change in two schemes: (1) a lepton
asymmetry directly generated by mixing with a lighter right-handed
sterile neutrino ; and (2) a lepton asymmetry generated by a
or transformation
which is subsequently partially converted to an asymmetry in the
sector by a matter-enhanced active-active neutrino
transformation. In the first scheme, we find that the percentage change in
is between -1% and 9% (with the sign depending on the sign of the asymmetry),
bounded by the Majorana mass limit m_{\nu_e}\la 1 eV. In the second scheme,
the maximal percentage reduction in is 2%, if the lepton number asymmetry
in neutrinos is positive; Otherwise, the percentage increase in is \la 5%
for m^2_{\nu_\mu,\nu_\tau}-m^2_{\nu_s}\la 10^4 eV. We conclude that the
change in the primordial He yield induced by a neutrino-mixing-generated
lepton number asymmetry can be substantial in the upward direction, but limited
in the downward direction.Comment: 15 pages, 7 figures, submitted to PR
Electronic transport in a Cantor stub waveguide network
We investigate theoretically, the character of electronic eigenstates and
transmission properties of a one dimensional array of stubs with Cantor
geometry. Within the framework of real space re-normalization group (RSRG) and
transfer matrix methods we analyze the resonant transmission and extended
wave-functions in a Cantor array of stubs, which lack translational order.
Apart from resonant states with high transmittance we unravel a whole family of
wave-functions supported by such an array clamped between two-infinite ordered
leads, which have an extended character in the RSRG scheme, but, for such
states the transmission coefficient across the lead-sample-lead structure
decays following a power-law as the system grows in size. This feature is
explained from renormalization group ideas and may lead to the possibility of
trapping of electronic, optical or acoustic waves in such hierarchical
geometries
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