2,868 research outputs found
Size of rings in two dimensions
The authors report enumeration results for the radius of gyration and caliper size distribution of self-avoiding unrooted polygons of up to 28 steps, on the square lattice. The (second moment) radius of gyration series is sufficiently smooth to allow verification of the theoretical prediction v(rings)=v(walks) to 0.2% accuracy
Oscillational instabilities in single mode acoustics levitators
An extention of standard results for the acoustic force on an object in a single-mode resonant chamber yields predictions for the onset of oscillational instabilities when objects are levitated or positioned in these chambers. The authors' results are consistent with those of experimental investigators. The present approach accounts for the effects of time delays in the response of a cavity to the motion of an object inside of it. Quantitative features of the instabilities are investigated. The experimental conditions required for sample stability, saturation of sample oscillations, hysteretic effects, and the loss of ability to levitate are discussed
Live-timer method of automatic dead-time correction for precision counting
Automatic correction for dead time losses in nuclear counting experiments is implemented by a simple live timer arrangement in which each counting interval is extended for compensation for the dead time during that interval. this method eliminates repetitious manual calculations, source of error, and dependence upon paralysis shifts
The First Measurement of Cassiopeia A's Forward Shock Expansion Rate
We have obtained a second epoch observation of the Cassiopeia A supernova
remnant (SNR) with the Chandra X-ray Observatory to measure detailed X-ray
proper motions for the first time. Both epoch observations are 50 ks exposures
of the ACIS-S3 chip and they are separated by 2 years. Measurements of the thin
X-ray continuum dominated filaments located around the edge of the remnant
(that are identified with the forward shock) show expansion rates from 0.02%/yr
to 0.33%/yr. Many of these filaments are therefore significantly decelerated.
Their median value of 0.21%/yr is equal to the median expansion of the bright
ring (0.21%/yr) as measured with Einstein and ROSAT. This presents a conundrum
if the motion of the bright ring is indicative of the reverse shock speed. We
have also re-evaluated the motion of the radio bright ring with emphasis on
angle-averaged emissivity profiles. Our new measurement of the expansion of the
angle-averaged radio bright ring is 0.07 plus or minus 0.03%/yr, somewhat
slower than the previous radio measurements of 0.11%/yr which were sensitive to
the motions of small-scale features. We propose that the expansion of the
small-scale bright ring features in the optical, X-ray, and radio do not
represent the expansion of the reverse shock, but rather represent a
brightness-weighted average of ejecta passing through and being decelerated by
the reverse shock. The motion of the reverse shock, itself, is then represented
by the motion of the angle-averaged emissivity profile of the radio bright
ring.Comment: accepted to Ap
Disorder induced transition into a one-dimensional Wigner glass
The destruction of quasi-long range crystalline order as a consequence of
strong disorder effects is shown to accompany the strict localization of all
classical plasma modes of one-dimensional Wigner crystals at T=0. We construct
a phase diagram that relates the structural phase properties of Wigner crystals
to a plasmon delocalization transition recently reported. Deep inside the
strictly localized phase of the strong disorder regime, we observe
``glass-like'' behavior. However, well into the critical phase with a plasmon
mobility edge, the system retains its crystalline composition. We predict that
a transition between the two phases occurs at a critical value of the relative
disorder strength. This transition has an experimental signature in the AC
conductivity as a local maximum of the largest spectral amplitude as a function
of the relative disorder strength.Comment: 5 pages, revtex. Typo regarding localization length exponent
corrected. Should read 1 / \delt
Measurement of the Integrated Faraday Rotations of BL Lac Objects
We present the results of multi-frequency polarization VLA observations of
radio sources from the complete sample of northern, radio-bright BL Lac objects
compiled by H. Kuhr and G. Schmidt. These were used to determine the integrated
rotation measures of 18 objects, 15 of which had never been measured
previously, which hindered analysis of the intrinsic polarization properties of
objects in the complete sample. These measurements make it possible to correct
the observed orientations of the linear polarizations of these sources for the
effect of Faraday rotation. The most probable origin for Faraday rotation in
these objects is the Galactic interstellar medium. The results presented
complete measurements of the integrated rotation measures for all 34 sources in
the complete sample of BL Lac objects.Comment: 9 pages, 7 figure
Hindsight
As a reflexive practice, hindsight enables a subject to re-observe how moments in the once-present past come to bear on a now-present future. Such observations enable us to make (new) sense of our life\u27s trajectory, re-casting seemingly inconsequential moments as “prophetic” happenings. In this essay, I revisit a series of connected moments in my past to examine how actions I took as a then-heterosexual man influenced the construction of my now-queer identity
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