27,046 research outputs found
Distribution of spectral widths and preponderance of spin-0 ground states in nuclei
We use a single j-shell model with random two-body interactions to derive
closed expressions for the distribution of and the correlations between
spectral widths of different spins. This task is facilitated by introducing
two-body operators whose squared spectral widths sum up to the squared spectral
width of the random Hamiltonian. The spin-0 width is characterized by a
relatively large average value and small fluctuations while the width of
maximum spin has the largest average and the largest fluctuations. The
approximate proportionality between widths and spectral radii explains the
preponderance of spin-0 ground states.Comment: 4 pages, 4 eps figure
Instrument for measuring thin-film belt lengths
Instrument consists of base, vernier height gauge, sliding block, and balance-beam assembly with tension weight. Pulley bracket is provided with three pulley mounting holes, 4 inches apart, to accommodate widely different belt lengths. Instrument is accurate to within 0.001 inch and is suitable for commercial production
Inference of the ring current ion composition by means of charge exchange decay
The analysis of the measured ion fluxes during the several day storm recovery period and the assumption that beside hydrogen other ions were present and that the decays were exponential in nature, it was possible to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H(+), O(+), and He(+) in the energy and L-value range of the data. This inference technique, thus, establishes the presence of measurable and appreciable quantities of oxygen and helium ions as well as protons in the storm-time ring current. Indications that He(+) may also be present under these same conditions were found
Motions of charged particles in the Magnetosphere under the influence of a time-varying large scale convection electric field
The motions of charged particles under the influence of the geomagnetic and electric fields were quite complex in the region of the inner magnetosphere. The Volland-Stern type large scale convection electric field was used successfully to predict both the plasmapause location and particle enhancements determined from Explorer 45 measurements. A time dependence in this electric field was introduced based on the variation in Kp for actual magnetic storm conditions. The particle trajectories were computed as they change in this time-varying electric field. Several storm fronts of particles of different magnetic moments were allowed to be injected into the inner magnetosphere from L = 10 in the equatorial plane. The motions of these fronts are presented in a movie format
Learning the Roots of Visual Domain Shift
In this paper we focus on the spatial nature of visual domain shift,
attempting to learn where domain adaptation originates in each given image of
the source and target set. We borrow concepts and techniques from the CNN
visualization literature, and learn domainnes maps able to localize the degree
of domain specificity in images. We derive from these maps features related to
different domainnes levels, and we show that by considering them as a
preprocessing step for a domain adaptation algorithm, the final classification
performance is strongly improved. Combined with the whole image representation,
these features provide state of the art results on the Office dataset.Comment: Extended Abstrac
On the Complexity of Local Search for Weighted Standard Set Problems
In this paper, we study the complexity of computing locally optimal solutions
for weighted versions of standard set problems such as SetCover, SetPacking,
and many more. For our investigation, we use the framework of PLS, as defined
in Johnson et al., [JPY88]. We show that for most of these problems, computing
a locally optimal solution is already PLS-complete for a simple neighborhood of
size one. For the local search versions of weighted SetPacking and SetCover, we
derive tight bounds for a simple neighborhood of size two. To the best of our
knowledge, these are one of the very few PLS results about local search for
weighted standard set problems
Nucleosynthesis in Outflows from the Inner Regions of Collapsars
We consider nucleosynthesis in outflows originating from the inner regions of
viscous accretion disks formed after the collapse of a rotating massive star.
We show that wind-like outflows driven by viscous and neutrino heating can
efficiently synthesize Fe-group elements moving at near-relativistic
velocities. The mass of 56Ni synthesized and the asymptotic velocities attained
in our calculations are in accord with those inferred from observations of
SN1998bw and SN2003dh. These steady wind-like outflows are generally proton
rich, characterized by only modest entropies, and consequently synthesize
essentially nothing heavier than the Fe-group elements. We also discuss
bubble-like outflows resulting from rapid energy deposition in localized
regions near or in the accretion disk. These intermittent ejecta emerge with
low electron fraction and are a promising site for the synthesis of the A=130
r-process peak elements.Comment: 35 pages, 6 figures, added discussion of the influence of nuclear
recombination on wind dynamics, to appear in Ap
Wikitruth Through Wikiorder
How does large-scale social production coordinate individual behavior to produce public goods? Hardin (1968) denied that the creation of public goods absent markets or the State is possible. Benkler (2006), Shirky (2008), Zittrain (2008), and Lessig (2008) recently countered that the needed coordination might emerge though social norms. However, the means to this coordination is under-theorized. Focusing on Wikipedia, we argue that the site’s dispute resolution process is an important force in promoting the public good it produces, i.e., a large number of relatively accurate public encyclopedia articles. We describe the development and shape of Wikipedia’s existing dispute resolution system. Further, we present a statistical analysis based on coding of over 250 arbitration opinions from Wikipedia’s arbitration system. The data show that Wiki-dispute resolution ignores the content of user disputes, instead focusing on user conduct. Based on fairly formalized arbitration findings, we find a high correlation between the conduct found and the remedies ordered. In effect, the system functions not so much to resolve disputes and make peace between conflicting users, but to weed out problematic users while weeding potentially productive users back in to participate. Game theorists have modeled large scale social production as a solution to the herder problem/multi-player prisoner’s dilemma. But we demonstrate that the “weeding in” function reflects dynamics more accurately captured in coordination games instead. In this way, dispute resolution can provide a constitutive function for the community
Wikitruth Through Wikiorder
How does large-scale social production coordinate individual behavior to produce public goods? In 1968, Hardin denied that the creation of public goods absent markets or the State is possible. Benkler, Shirky, Zittrain, and Lessig recently countered that the necessary coordination might emerge though social norms. However, scholars have not fully explained how this coordination is to occur. Game theorists have modeled large-scale social production as a solution to the herder problem/multi-player PrisonerÂżs Dilemma. But we demonstrate that the Âżweeding in function reflects dynamics more accurately captured in coordination games. In this way, dispute resolution can provide a constitutive function for the community
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