1,256 research outputs found
Analytic properties of force-free jets in the Kerr spacetime -- III: uniform field solution
The structure of steady axisymmetric force-free magnetosphere of a Kerr black
hole (BH) is governed by a second-order partial differential equation of
depending on two "free" functions and ,
where is the component of the vector potential of the
electromagnetic field, is the angular velocity of the magnetic field
lines and is the poloidal electric current. In this paper, we investigate
the solution uniqueness. Taking asymptotically uniform field as an example,
analytic studies imply that there are infinitely many solutions approaching
uniform field at infinity, while only a unique one is found in general
relativistic magnetohydrodynamic simulations. To settle down the disagreement,
we reinvestigate the structure of the governing equation and numerically solve
it with given constraint condition and boundary condition. We find that the
constraint condition (field lines smoothly crossing the light surface (LS)) and
boundary conditions at horizon and at infinity are connected via radiation
conditions at horizon and at infinity, rather than being independent. With
appropriate constraint condition and boundary condition, we numerically solve
the governing equation and find a unique solution. Contrary to naive
expectation, our numerical solution yields a discontinuity in the angular
velocity of the field lines and a current sheet along the last field line
crossing the event horizon. We also briefly discuss the applicability of the
perturbation approach to solving the governing equation
Signatures of Self-Interacting Dark Matter in the Matter Power Spectrum and the CMB
We consider a self-interacting dark matter model in which the massive dark
photon mediating the self-interaction decays to light dark fermions to avoid
over-closing the universe. We find that if the model is constrained to explain
the dark matter halos inferred for spiral galaxies and galaxy clusters
simultaneously, there is a strong indication that dark matter is produced
asymmetrically in the early universe. It also implies the presence of dark
radiation, late kinetic decoupling for dark matter, and a suppressed linear
power spectrum due to dark acoustic damping. The Lyman- forest power
spectrum measurements put a strong upper limit on the damping scale and the
model has little room to reduce the abundances of satellite galaxies. Future
observations in the matter power spectrum and the CMB, in tandem with the
impact of self-interactions in galactic halos, makes it possible to measure the
gauge coupling and masses of the dark sector particles even when signals in
conventional dark matter searches are absent.Comment: 5 pages, 7 figures, published version in PL
Bituminous Coal Combustion with New Insights
As one of the most important primary energy, bituminous coal has been widely applied in many fields. The combustion studies of bituminous coal have attracted a lot of attention due to the releases of hazardous emissions. This work focuses on the investigation of combustion characteristics of Shenmu bituminous pulverized coal as a representative bituminous coal in China with a combined TG-MS-FTIR system by considering the effect of particle size, heating rate, and the total flow rate. The combustion products were accurately quantified by normalization and numerical analysis of MS results. The results indicate that the decrease of the particle size, heating rate, and the total flow rate result in lower ignition and burnout temperatures. The activation energy tends to be lower with smaller particle size, faster heating rate, and lower total flow rate. The MS and FTIR results demonstrate that lower concentrations of different products, such as NO, NO2, HCN, CH4, and SO2, were produced with smaller particle size, slower heating rate, and lower total flow rate. This work will guide to understand the combustion kinetics of pulverized coals and be beneficial to control the formation of pollutants
CVD‐Made Spinels: Synthesis, Characterization and Applications for Clean Energy
To reduce emissions and protect environment from pollution caused by volatile organic compounds (VOCs) and CO, catalytic oxidation can be applied as an efficient and promising technique. This review provides a novel and facile strategy to synthesize spinel-type and non-spinel-type transition metal oxides (TMOs). Specifically, single (Co3O4, α-Fe2O3, Mn3O4, CuO, Cu2O and Cr2O3) and binary (Co3-xCuxO4, Co3-xMnxO4 and Co3-xFexO4) TMOs have been prepared using pulsed spray evaporation chemical vapor deposition approach (PSE-CVD). PSE-CVD offers several advantages over conventional methods, such as relatively low cost, simplicity and high throughput, which makes it a promising strategy. Moreover, the PSE delivery system allows using less stable precursors and permits improving the reproducibility of the film properties with tailored compositions. The above listed TMOs prepared by PSE-CVD were successfully tested as catalysts toward the complete oxidation of some real fuels such as CO, C2H2, C3H6, n-C4H8 and C2H6O as representatives of VOCs and industrial exhaust streams. The active TMOs explored in this review could be potential catalysts candidates in one of the research areas that are currently under scrutiny, as the battle for the future of energy and environment involves the generation and application of clean energy
A Deterministic and Storable Single-Photon Source Based on Quantum Memory
A single photon source is realized with a cold atomic ensemble (Rb
atoms). In the experiment, single photons, which is initially stored in an
atomic quantum memory generated by Raman scattering of a laser pulse, can be
emitted deterministically at a time-delay in control. It is shown that
production rate of single photons can be enhanced by a feedback circuit
considerably while the single-photon quality is conserved. Thus our present
single-photon source is well suitable for future large-scale realization of
quantum communication and linear optical quantum computation
Experimental preparation and verification of quantum money
A quantum money scheme enables a trusted bank to provide untrusted users with
verifiable quantum banknotes that cannot be forged. In this work, we report an
experimental demonstration of the preparation and verification of unforgeable
quantum banknotes. We employ a security analysis that takes experimental
imperfections fully into account. We measure a total of states
in one verification round, limiting the forging probability to based
on the security analysis. Our results demonstrate the feasibility of preparing
and verifying quantum banknotes using currently available experimental
techniques.Comment: 12 pages, 4 figure
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