14,468 research outputs found
Threaded pilot insures cutting tool alignment
Threaded pilot allows machining of a port component, or boss, after the reciprocating hole has been threaded. It is used to align cutting surfaces with the boss threads, thus insuring precision alignment
On the structure of the BBGKY hierarchy for a Boltzmann gas
Structure of BBGKY hierarchy for Boltzmann gas and particle distribution
Quark Delocalization, Color Screening, and Nuclear Intermediate Range Attraction
We consider the effect of including quark delocalization and color screening,
in the nonrelativistic quark cluster model, on baryon-baryon potentials and
phase shifts. We find that the inclusion of these additional effects allows a
good qualitative description of both.Comment: 10 pages, LaTeX, 4 figures in PostScript after text, LA-UR-91-215
Characterizing the Hofstadter butterfly's outline with Chern numbers
In this work, we report original properties inherent to independent particles
subjected to a magnetic field by emphasizing the existence of regular
structures in the energy spectrum's outline. We show that this fractal curve,
the well-known Hofstadter butterfly's outline, is associated to a specific
sequence of Chern numbers that correspond to the quantized transverse
conductivity. Indeed the topological invariant that characterizes the
fundamental energy band depicts successive stairways as the magnetic flux
varies. Moreover each stairway is shown to be labeled by another Chern number
which measures the charge transported under displacement of the periodic
potential. We put forward the universal character of these properties by
comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
Testing the existence of optical linear polarization in young brown dwarfs
Linear polarization can be used as a probe of the existence of atmospheric
condensates in ultracool dwarfs. Models predict that the observed linear
polarization increases withthe degree of oblateness, which is inversely
proportional to the surface gravity. We aimed to test the existence of optical
linear polarization in a sample of bright young brown dwarfs, with spectral
types between M6 and L2, observable from the Calar Alto Observatory, and
cataloged previously as low gravity objects using spectroscopy. Linear
polarimetric images were collected in I and R-band using CAFOS at the 2.2 m
telescope in Calar Alto Observatory (Spain). The flux ratio method was employed
to determine the linear polarization degrees. With a confidence of 3,
our data indicate that all targets have a linear polarimetry degree in average
below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were
observed. We detected significant (i.e. P/ 3) linear polarization
for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of
= 0.81 0.17 %.Comment: Accepted for publication in MNRA
MoodBar: Increasing new user retention in Wikipedia through lightweight socialization
Socialization in online communities allows existing members to welcome and
recruit newcomers, introduce them to community norms and practices, and sustain
their early participation. However, socializing newcomers does not come for
free: in large communities, socialization can result in a significant workload
for mentors and is hard to scale. In this study we present results from an
experiment that measured the effect of a lightweight socialization tool on the
activity and retention of newly registered users attempting to edit for the
first time Wikipedia. Wikipedia is struggling with the retention of newcomers
and our results indicate that a mechanism to elicit lightweight feedback and to
provide early mentoring to newcomers improves their chances of becoming
long-term contributors.Comment: 9 pages, 5 figures, accepted for presentation at CSCW'1
Quantum storage on subradiant states in an extended atomic ensemble
A scheme for coherent manipulation of collective atomic states is developed
such that total subradiant states, in which spontaneous emission is suppressed
into all directions due to destructive interference between neighbor atoms, can
be created in an extended atomic ensemble. The optimal conditions for creation
of such states and suitability of them for quantum storage are discussed. It is
shown that in order to achieve the maximum signal-to-noise ratio the shape of a
light pulse to be stored and reconstructed using a homogeneously broadened
absorbtion line of an atomic system should be a time-reversed regular part of
the response function of the system. In the limit of high optical density, such
pulses allow one to prepare collective subradiant atomic states with near flat
spatial distribution of the atomic excitation in the medium.Comment: V2: considerably revised (title, text). V3: minor changes - final
version as published in PR
Metacognition as Evidence for Evidentialism
Metacognition is the monitoring and controlling of cognitive processes. I examine the role of metacognition in āordinary retrieval casesā, cases in which it is intuitive that via recollection the subject has a justiļ¬ed belief. Drawing on psychological research on metacognition, I argue that evidentialism has a unique, accurate prediction in each ordinary retrieval case: the subject has evidence for the proposition she justiļ¬edly believes. But, I argue, process reliabilism has no unique, accurate predictions in these cases. I conclude that ordinary retrieval cases better support evidentialism than process reliabilism. This conclusion challenges several common assumptions. One is that non-evidentialism alone allows for a naturalized epistemology, i.e., an epistemology that is fully in accordance with scientiļ¬c research and methodology. Another is that process reliabilism fares much better than evidentialism in the epistemology of memory
Phase-space holes due to electron and ion beams accelerated by a current-driven potential ramp
One-dimensional open-boundary simulations have been carried out in a current-carrying plasma seeded with a neutral density depression and with no initial electric field. These simulations show the development of a variety of nonlinear localized electric field structures: double layers (unipolar localized fields), fast electron phase-space holes (bipolar fields) moving in the direction of electrons accelerated by the double layer and trains of slow alternating electron and ion phase-space holes (wave-like fields) moving in the direction of ions accelerated by the double layer. The principal new result in this paper is to show by means of a linear stability analysis that the slow-moving trains of electron and ion holes are likely to be the result of saturation via trapping of a kinetic-Buneman instability driven by the interaction of accelerated ions with unaccelerated electrons
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