3,051 research outputs found
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
Viral self-assembly as a thermodynamic process
The protein shells, or capsids, of all sphere-like viruses adopt icosahedral
symmetry. In the present paper we propose a statistical thermodynamic model for
viral self-assembly. We find that icosahedral symmetry is not expected for
viral capsids constructed from structurally identical protein subunits and that
this symmetry requires (at least) two internal "switching" configurations of
the protein. Our results indicate that icosahedral symmetry is not a generic
consequence of free energy minimization but requires optimization of internal
structural parameters of the capsid proteins.Comment: pdf file, 13 pages, three figure
Observed Faraday Effects in Damped Lyman-Alpha Absorbers and Lyman Limit Systems: The Magnetised Environment of Galactic Building Blocks at Redshift=2
Protogalactic environments are typically identified using quasar absorption
lines, and these galactic building blocks can manifest as Damped Lyman-Alpha
Absorbers (DLAs) and Lyman Limit Systems (LLSs). We use radio observations of
Faraday effects to test whether DLAs and LLSs host a magnetised medium, by
combining DLA and LLS detections throughout the literature with 1.4 GHz
polarization data from the NRAO VLA Sky Survey (NVSS). We obtain a control, a
DLA, and a LLS sample consisting of 114, 19, and 27 lines-of-sight respectively
- all of which are polarized at to ensure Rician bias is
negligible. Using a Bayesian framework, we are unable to detect either coherent
or random magnetic fields in DLAs: the regular coherent magnetic fields within
the DLAs must be G, and the lack of depolarization is consistent
with the weakly magnetised gas in DLAs being non-turbulent and quiescent.
However, we find mild suggestive evidence that LLSs have coherent magnetic
fields: after controlling for the redshift-distribution of our data, we find a
71.5% probability that LLSs have a higher RM than a control sample. We also
find strong evidence that LLSs host random magnetic fields, with a 95.5%
probability that LLS lines-of-sight have lower polarized fractions than a
control sample. The regular coherent magnetic fields within the LLSs must be
G, and the magnetised gas must be highly turbulent with a typical
scale on the order of -20 pc, which is similar to that of the Milky
Way. This is consistent with the standard dynamo pedagogy, whereby magnetic
fields in protogalaxies increase in coherence and strength as a function of
cosmic time. Our results are consistent with a hierarchical galaxy formation
scenario, with the DLAs, LLSs, and strong magnesium II (MgII) systems exploring
three different stages of magnetic field evolution in galaxies.Comment: Submitted to Ap
The effective potential, critical point scaling and the renormalization group
The desirability of evaluating the effective potential in field theories near
a phase transition has been recognized in a number of different areas. We show
that recent Monte Carlo simulations for the probability distribution for the
order parameter in an equilibrium Ising system, when combined with low-order
renormalization group results for an ordinary system, can be used to
extract the effective potential. All scaling features are included in the
process.Comment: REVTEX file, 22 pages, three figures, submitted to Phys. Rev.
Anderson transition of the plasma oscillations of 1D disordered Wigner lattices
We report the existence of a localization-delocalization transition in the
classical plasma modes of a one dimensional Wigner Crystal with a white noise
potential environment at T=0. Finite size scaling analysis reveals a divergence
of the localization length at a critical eigenfrequency. Further scaling
analysis indicates power law behavior of the critical frequency in terms of the
relative interaction strength of the charges. A heuristic argument for this
scaling behavior is consistent with the numerical results. Additionally, we
explore a particular realization of random-bond disorder in a one dimensional
Wigner lattice in which all of the collective modes are observed to be
localized.Comment: 4 pages, 3 figures, Typo for the localization length corrected.
Should read 1 / \n
High resolution Ge/Li/ spectrometer reduces rate-dependent distortions at high counting rates
Modified spectrometer system with a low-noise preamplifier reduces rate-dependent distortions at high counting rates, 25,000 counts per second. Pole-zero cancellation minimizes pulse undershoots due to multiple time constants, baseline restoration improves resolution and prevents spectral shifts
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