52,685 research outputs found
Response to "The invalidity of a Mach probe model" [Phys. Plasmas 9, 1832 (2002)]
Hutchinson gives a nice analysis of the (in)validity of Hudis and Lidsky’s unmagnetized Mach probe theory.(1) We agree with his main assertions, which are that (1) a one-dimensional model is incapable of properly describing unmagnetized ion collection by a Mach probe and (2) any experimental agreement with theories based on Hudis and Lidsky should not be interpreted as physical validation of their model
Message in the Sky
We argue that the cosmic microwave background (CMB) provides a stupendous
opportunity for the Creator of universe our (assuming one exists) to have sent
a message to its occupants, using known physics. Our work does not support the
Intelligent Design movement in any way whatsoever, but asks, and attempts to
answer, the entirely scientific question of what the medium and message might
be IF there was actually a message. The medium for the message is unique. We
elaborate on this observation, noting that it requires only careful adjustment
of the fundamental Lagrangian, but no direct intervention in the subsequent
evolution of the universe.Comment: 3 pages, revtex; to appear in Mod.Phys.Lett.
A speculative relation between the cosmological constant and the Planck mass
We propose the relation where
, and denote the mass scale associated with the
cosmological constant, the gravitational interaction, and the size of the
universe respectively.Comment: 3 page
Space-time translational gauge identities in Abelian Yang-Mills gravity
We derive and calculate the space-time translational gauge identities in
quantum Yang-Mills gravity with a general class of gauge conditions involving
two arbitrary parameters. These identities of the Abelian group of translation
are a generalization of Ward-Takahasi-Fradkin identities and important for
general discussions of possible renormalization of Yang-Mills gravity with
translational gauge symmetry. The gauge identities in Yang-Mills gravity with a
general class of gauge conditions are substantiated by explicit calculations.Comment: 15 pages. To be published in The European Physical Journal - Plus
(2012
On testing VLSI chips for the big Viterbi decoder
A general technique that can be used in testing very large scale integrated (VLSI) chips for the Big Viterbi Decoder (BVD) system is described. The test technique is divided into functional testing and fault-coverage testing. The purpose of functional testing is to verify that the design works functionally. Functional test vectors are converted from outputs of software simulations which simulate the BVD functionally. Fault-coverage testing is used to detect and, in some cases, to locate faulty components caused by bad fabrication. This type of testing is useful in screening out bad chips. Finally, design for testability, which is included in the BVD VLSI chip design, is described in considerable detail. Both the observability and controllability of a VLSI chip are greatly enhanced by including the design for the testability feature
A Laboratory Plasma Experiment for Studying Magnetic Dynamics of Accretion Discs and Jets
This work describes a laboratory plasma experiment and initial results which
should give insight into the magnetic dynamics of accretion discs and jets. A
high-speed multiple-frame CCD camera reveals images of the formation and
helical instability of a collimated plasma, similar to MHD models of disc jets,
and also plasma detachment associated with spheromak formation, which may have
relevance to disc winds and flares. The plasmas are produced by a planar
magnetized coaxial gun. The resulting magnetic topology is dependent on the
details of magnetic helicity injection, namely the force-free state eigenvalue
alpha_gun imposed by the coaxial gun.Comment: accepted for publication in MNRA
To improve model soil moisture estimation in arid/semi-arid region using in situ and remote sensing information
Soil moisture plays a key role in water and energy exchange in the land hydrologic process. Effective soil moisture information can be used for many applications in weather and hydrological forecasting, water resources, and irrigation system management and planning. However, to accurate modeling of soil moisture variation in the soil layer is still very challenging. In this study, in situ and remote sensing information of near-surface soil moisture is assimilated into the Noah land surface model (LSM) to estimate deep-layer soil moisture variation. The sequential Monte Carlo-Particle Filter technique, being well known for capability of modeling high nonlinear and non-Gaussian processes, is applied to assimilate surface soil moisture measurement to the deep layers. The experiments were carried out over several locations over the semi-arid region of the US. Comparing with in situ observations, the assimilation runs show much improved from the control (non-assimilation) runs for estimating both soil moisture and temperature at 5-, 20-, and 50-cm soil depths in the Noah LSM. © 2012 Springer-Verlag
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Bias adjustment of satellite-based precipitation estimation using artificial neural networks-cloud classification system over Saudi Arabia
Precipitation is a key input variable for hydrological and climate studies. Rain gauges can provide reliable precipitation measurements at a point of observations. However, the uncertainty of rain measurements increases when a rain gauge network is sparse. Satellite-based precipitation estimations SPEs appear to be an alternative source of measurements for regions with limited rain gauges. However, the systematic bias from satellite precipitation estimation should be estimated and adjusted. In this study, a method of removing the bias from the precipitation estimation from remotely sensed information using artificial neural networks-cloud classification system (PERSIANN-CCS) over a region where the rain gauge is sparse is investigated. The method consists of monthly empirical quantile mapping of gauge and satellite measurements over several climate zones as well as inverse-weighted distance for the interpolation of gauge measurements. Seven years (2010–2016) of daily precipitation estimation from PERSIANN-CCS was used to test and adjust the bias of estimation over Saudi Arabia. The first 6 years (2010–2015) are used for calibration, while 1 year (2016) is used for validation. The results show that the mean yearly bias is reduced by 90%, and the yearly root mean square error is reduced by 68% during the validation year. The experimental results confirm that the proposed method can effectively adjust the bias of satellite-based precipitation estimations
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