17,206 research outputs found
Two Dimensional Ising Superconductivity in Gated MoS
The Zeeman effect, which is usually considered to be detrimental to
superconductivity, can surprisingly protect the superconducting states created
by gating a layered transition metal dichalcogenide. This effective Zeeman
field, which is originated from intrinsic spin orbit coupling induced by
breaking in-plane inversion symmetry, can reach nearly a hundred Tesla in
magnitude. It strongly pins the spin orientation of the electrons to the
out-of-plane directions and protects the superconductivity from being destroyed
by an in-plane external magnetic field. In magnetotransport experiments of
ionic-gate MoS transistors, where gating prepares individual
superconducting state with different carrier doping, we indeed observe a spin-
protected superconductivity by measuring an in-plane critical field
far beyond the Pauli paramagnetic limit. The
gating-enhanced is more than an order of magnitude larger
compared to the bulk superconducting phases where the effective Zeeman field is
weakened by interlayer coupling. Our study gives the first experimental
evidence of an Ising superconductor, in which spins of the pairing electrons
are strongly pinned by an effective Zeeman field
Global Dynamics of Advection-Dominated Accretion Revisited
We numerically solve the set of dynamical equations describing
advection-dominated accretion flows (ADAF) around black holes, using a method
similar to that of Chakrabarti (1996a). We choose the sonic radius of the flow
and the integration constant in angular momentum equation as free
parameters, and integrate the equations from the sonic point inwards to see if
the solution can extend supersonically to the black hole horizon, and outwards
to see if and where an acceptable outer boundary of the flow can be found. We
recover the ADAF-thin disk solution constructed in Narayan, Kato, & Honma
(1997, NKH97), an representative paper of the previous works on global ADAF
solutions, although in that paper an apparently very different procedure was
adopted. We obtain a complete picture in the form of parameter space
which sums up the situation of ADAF solution at a glance. For comparison we
also present the distribution of global solutions for inviscid flows in the
space, which supports the view that there should be some similarities
between the dynamical behavior of ADAF and that of adiabatic flows, and that
there should be a continuous change from the properties of viscous flows to
those of inviscid ones.Comment: 24 pages with 15 figures, to appear in ApJ Vol. 52
A New Parameter In Accretion Disk Model
Taking optically thin accretion flows as an example, we investigate the
dynamics and the emergent spectra of accretion flows with different outer
boundary conditions (OBCs) and find that OBC plays an important role in
accretion disk model. This is because the accretion equations describing the
behavior of accretion flows are a set of {\em differential} equations,
therefore, accretion is intrinsically an initial-value problem. We argue that
optically thick accretion flow should also show OBC-dependent behavior. The
result means that we should seriously consider the initial physical state of
the accretion flow such as its angular momentum and its temperature. An
application example to Sgr A is presented.Comment: 6 pages, 4 figures, to appear in the Proceeding of "Pacific Rim
Conference on Stellar Astrophysics", Aug. 1999, HongKong, Chin
Design of a AB5-metal hydride cylindrical tank for hydrogen storage
Hydrogen storage in metal hydrides presents distinct challenges which encourage the study of effective heat management strategies. Hydrogen absorption in metal hydrides is an exothermic reaction, consequently the generated heat must be removed effectively to achieve the desired performance. This work presents a mathematical model describing the adsorption of hydrogen in La Ni4.7Co0.3 metal hydride as a storage material. Heat and mass transfer effects are modeled in detail. The effect of heat transfer coefficient is also estimated. Besides, a heat transfer fluid for cooling is incorporated to the model. The problem is mathematically formulated presenting a numerical simulation of a design of a cylindrical tank for hydrogen storage. The alloy is studied by using pressure-composition-temperature curves which are carried out at different temperatures. Thermodynamic parameters and hydrogen storage capacity are determined. For isotherm's kinetics, the Jonhson-Mehl-Avrami-Kolomogorov model is used, from which the kinetic constant of the hydriding process is determined.Agencia Nacional de Investigación e Innovació
An Imaging and Spectral Study of Ten X-Ray Filaments around the Galactic Center
We report the detection of 10 new X-ray filaments using the data from the
{\sl Chandra} X-ray satellite for the inner ( parsec)
around the Galactic center (GC). All these X-ray filaments are characterized by
non-thermal energy spectra, and most of them have point-like features at their
heads that point inward. Fitted with the simple absorbed power-law model, the
measured X-ray flux from an individual filament in the 2-10 keV band is to ergs cm s and the
absorption-corrected X-ray luminosity is ergs s
at a presumed distance of 8 kpc to the GC. We speculate the origin(s) of these
filaments by morphologies and by comparing their X-ray images with the
corresponding radio and infrared images. On the basis of combined information
available, we suspect that these X-ray filaments might be pulsar wind nebulae
(PWNe) associated with pulsars of age yr. The fact
that most of the filament tails point outward may further suggest a high
velocity wind blowing away form the GC.Comment: 29 pages with 7 figures and 3 pages included. Accepted to Ap
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