28,409 research outputs found
Compact Central WENO Schemes for Multidimensional Conservation Laws
We present a new third-order central scheme for approximating solutions of
systems of conservation laws in one and two space dimensions. In the spirit of
Godunov-type schemes,our method is based on reconstructing a
piecewise-polynomial interpolant from cell-averages which is then advanced
exactly in time. In the reconstruction step, we introduce a new third-order as
a convex combination of interpolants based on different stencils. The heart of
the matter is that one of these interpolants is taken as an arbitrary quadratic
polynomial and the weights of the convex combination are set as to obtain
third-order accuracy in smooth regions. The embedded mechanism in the WENO-like
schemes guarantees that in regions with discontinuities or large gradients,
there is an automatic switch to a one-sided second-order reconstruction, which
prevents the creation of spurious oscillations. In the one-dimensional case,
our new third order scheme is based on an extremely compact point stencil.
Analogous compactness is retained in more space dimensions. The accuracy,
robustness and high-resolution properties of our scheme are demonstrated in a
variety of one and two dimensional problems.Comment: 24 pages, 5 figure
Antiperiodic dynamical 6-vertex model by separation of variables II: Functional equations and form factors
We pursue our study of the antiperiodic dynamical 6-vertex model using
Sklyanin's separation of variables approach, allowing in the model new possible
global shifts of the dynamical parameter. We show in particular that the
spectrum and eigenstates of the antiperiodic transfer matrix are completely
characterized by a system of discrete equations. We prove the existence of
different reformulations of this characterization in terms of functional
equations of Baxter's type. We notably consider the homogeneous functional
- equation which is the continuous analog of the aforementioned discrete
system and show, in the case of a model with an even number of sites, that the
complete spectrum and eigenstates of the antiperiodic transfer matrix can
equivalently be described in terms of a particular class of its -solutions,
hence leading to a complete system of Bethe equations. Finally, we compute the
form factors of local operators for which we obtain determinant representations
in finite volume.Comment: 52 page
Low-noise microwave polarimeter
Two quarterwave-plate polarizers inserted between rotary waveguide joints transform received signals from arbitrary linear to circular polarizations and then from circular to fixed linear polarizations. Fixed linear polarizations are applied to amplifiers and filters in usual fashion
Measurement of transpiration in Pinus taeda L. and Liquidambar styraciflua L. in an environmental chamber using tritiated water
Transpiration rates of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) were measured at two different atmospheric water vapor pressure deficits (V.P.D.) in a controlled environment growth chamber using tritiated water as a tracer. The trees were maintained in a sealed plant bed containing a hydroponic nutrient solution into which labeled water (spike) was introduced. Samples of leaves, chamber air, spiked nutrient solution and control water were assayed for ratio-activity using liquid scintillation techniques to determine transpiration rates. The transpiration rate of sweetgum in ml./hr./gm. (4.95) was found to be 5 times greater than that of loblolly pine (1.03) at 1.84 V.P.D. and 8 times greater at 6.74 V.P.D. (15.99 for sweetgum vs. 2.19 for pine). Transpiration (based on measurements of leaf radioactivity) in both species rose with increasing deficit; however sweetgum increased its output by 3 times while pine only doubled its rate. Cyclical changes in transpiration rates were noted in both species; the sweetgum cycle required a 6 hour interval whereas the pine cycle required a 9 hour interval
QUASAT: An orbiting very long baseline interferometer program using large space antenna systems
QUASAT, which stands for QUASAR SATELLITE, is the name given to a new mission being studied by NASA. The QUASAT mission concept involves a free flying Earth orbiting large radio telescope, which will observe astronomical radio sources simultaneously with ground radio telescopes. The primary goal of QUASAT is to provide a system capable of collecting radio frequency data which will lead to a better understanding of extremely high energy events taking place in a variety of celestial objects including quasars, galactic nuclei, interstellar masers, radio stars and pulsars. QUASAT's unique scientific contribution will be the increased resolution in the emission brightness profile maps of the celestial objects
Data processing method for a weak, moving telemetry signal
Method of processing data from a spacecraft, where the carrier has a low signal-to-noise ratio and wide unpredictable frequency shifts, consists of analogue recording of the noisy signal along with a high-frequency tone that is used as a clock to trigger a digitizer
Fast Matrix Factorization for Online Recommendation with Implicit Feedback
This paper contributes improvements on both the effectiveness and efficiency
of Matrix Factorization (MF) methods for implicit feedback. We highlight two
critical issues of existing works. First, due to the large space of unobserved
feedback, most existing works resort to assign a uniform weight to the missing
data to reduce computational complexity. However, such a uniform assumption is
invalid in real-world settings. Second, most methods are also designed in an
offline setting and fail to keep up with the dynamic nature of online data. We
address the above two issues in learning MF models from implicit feedback. We
first propose to weight the missing data based on item popularity, which is
more effective and flexible than the uniform-weight assumption. However, such a
non-uniform weighting poses efficiency challenge in learning the model. To
address this, we specifically design a new learning algorithm based on the
element-wise Alternating Least Squares (eALS) technique, for efficiently
optimizing a MF model with variably-weighted missing data. We exploit this
efficiency to then seamlessly devise an incremental update strategy that
instantly refreshes a MF model given new feedback. Through comprehensive
experiments on two public datasets in both offline and online protocols, we
show that our eALS method consistently outperforms state-of-the-art implicit MF
methods. Our implementation is available at
https://github.com/hexiangnan/sigir16-eals.Comment: 10 pages, 8 figure
Protein Structure Prediction Using Basin-Hopping
Associative memory Hamiltonian structure prediction potentials are not overly
rugged, thereby suggesting their landscapes are like those of actual proteins.
In the present contribution we show how basin-hopping global optimization can
identify low-lying minima for the corresponding mildly frustrated energy
landscapes. For small systems the basin-hopping algorithm succeeds in locating
both lower minima and conformations closer to the experimental structure than
does molecular dynamics with simulated annealing. For large systems the
efficiency of basin-hopping decreases for our initial implementation, where the
steps consist of random perturbations to the Cartesian coordinates. We
implemented umbrella sampling using basin-hopping to further confirm when the
global minima are reached. We have also improved the energy surface by
employing bioinformatic techniques for reducing the roughness or variance of
the energy surface. Finally, the basin-hopping calculations have guided
improvements in the excluded volume of the Hamiltonian, producing better
structures. These results suggest a novel and transferable optimization scheme
for future energy function development
Preliminary results of the Mariner IV OCCULATION measurement of the atmosphere of Mars
Mariner IV radio occultation measurement of Mars atmospher
Preliminary results of the Mariner IV radio occultation measurements of the upper atmosphere of Mars
Mariner IV radio occultation measurements of Mars upper atmospher
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