96,342 research outputs found
Anomalous impurity effect on magnetization in frustrated one-dimensional ferro- and ferrimagnets
Significant decrease of spontaneous magnetization in frustrated
one-dimensional ferro- and ferrimagnets due to non-magnetic impurities is
predicted. Using the density-matrix renormalization group method and the exact
diagonalization method, we confirm that the total spin can vanish due to a
single impurity in finite chains. Introducing the picture of magnetic domain
inversion, we numerically investigate the impurity-density dependence of
magnetization. In particular, we show that even with an infinitesimal density
of impurities the magnetization in the ground state is reduced by about 40%
from that of the corresponding pure system. Conditions for the materials which
may show this anomalous impurity effect are formulated.Comment: 4 pages, 6 figure
Two dimensional thermal and charge mapping of power thyristors
The two dimensional static and dynamic current density distributions within the junction of semiconductor power switching devices and in particular the thyristors were obtained. A method for mapping the thermal profile of the device junctions with fine resolution using an infrared beam and measuring the attenuation through the device as a function of temperature were developed. The results obtained are useful in the design and quality control of high power semiconductor switching devices
The study of plasma-boundary interactions Quarterly report, 1 Sep. - 30 Nov. 1967
Electrode drag force measurements in boundary interactions of pulsed accelerator plasm
Interacting dark energy, holographic principle and coincidence problem
The interacting and holographic dark energy models involve two important
quantities. One is the characteristic size of the holographic bound and the
other is the coupling term of the interaction between dark energy and dark
matter. Rather than fixing either of them, we present a detailed study of
theoretical relationships among these quantities and cosmological parameters as
well as observational constraints in a very general formalism. In particular,
we argue that the ratio of dark matter to dark energy density depends on the
choice of these two quantities, thus providing a mechanism to change the
evolution history of the ratio from that in standard cosmology such that the
coincidence problem may be solved. We investigate this problem in detail and
construct explicit models to demonstrate that it may be alleviated provided
that the interacting term and the characteristic size of holographic bound are
appropriately specified. Furthermore, these models are well fitted with the
current observation at least in the low red-shift region.Comment: 20 pages, 3 figure
Delayed Recombination
Under the standard model for recombination of the primeval plasma, and the
cold dark matter model for structure formation, recent measurements of the
first peak in the angular power spectrum of the cosmic microwave background
temperature indicate the spatial geometry of the universe is nearly flat. If
sources of Lya resonance radiation, such as stars or active galactic nuclei,
were present at z ~ 1000 they would delay recombination, shifting the first
peak to larger angular scales, and producing a positive bias in this measure of
space curvature. It can be distinguished from space curvature by its
suppression of the secondary peaks in the spectrum.Comment: submitted to ApJ
Noise Robust Blind System Identification Algorithms Based On A Rayleigh Quotient Cost Function
A novel approach for the assessment of morphological evolution based on observed water levels in tide-dominated estuaries
Assessing the impacts of both natural (e.g., tidal forcing from the ocean) and human-induced changes (e.g., dredging for navigation, land reclamation) on estuarine morphology is particularly important for the protection and management of the estuarine environment. In this study, a novel analytical approach is proposed for the assessment of estuarine morphological evolution in terms of tidally averaged depth on the basis of the observed water levels along the estuary. The key lies in deriving a relationship between wave celerity and tidal damping or amplification. For given observed water levels at two gauging stations, it is possible to have a first estimation of both wave celerity (distance divided by tidal travelling time) and tidal damping or amplification rate (tidal range difference divided by distance), which can then be used to predict the morphological changes via an inverse analytical model for tidal hydrodynamics. The proposed method is applied to the Lingdingyang Bay of the Pearl River Estuary, located on the southern coast of China, to analyse the historical development of the tidal hydrodynamics and morphological evolution. The analytical results show surprisingly good correspondence with observed water depth and volume in this system. The merit of the proposed method is that it provides a simple approach for understanding the decadal evolution of the estuarine morphology through the use of observed water levels, which are usually available and can be easily measured.National Key R&D of China (Grant No.
2016YFC0402601), National Natural Science Foundation of China (Grant No. 51979296, 51709287,
41706088, 41476073), Fundamental Research Funds for the Central Universities (No.18lgpy29)
and from the Water Resource Science and Technology Innovation Program of Guangdong Province (Grant
No. 2016-20, 2016-21). The work of the second author was supported by FCT research contracts
IF/00661/2014/CP1234.info:eu-repo/semantics/submittedVersio
Analytical Solution of Electron Spin Decoherence Through Hyperfine Interaction in a Quantum Dot
We analytically solve the {\it Non-Markovian} single electron spin dynamics
due to hyperfine interaction with surrounding nuclei in a quantum dot. We use
the equation-of-motion method assisted with a large field expansion, and find
that virtual nuclear spin flip-flops mediated by the electron contribute
significantly to a complete decoherence of transverse electron spin correlation
function. Our results show that a 90% nuclear polarization can enhance the
electron spin time by almost two orders of magnitude. In the long time
limit, the electron spin correlation function has a non-exponential
decay in the presence of both polarized and unpolarized nuclei.Comment: 4 pages, 3 figure
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