8,927 research outputs found
Physical picture for the anomalous progagation of ordinary electromagnetic waves in a plasma
It is shown that the physical mechanism for the anomalous propagation of electromagnetic waves at frequencies below the plasma frequency is due to the deflection of particle thermal motions by the wave magnetic field, leading to a density perturbation which can be large when enhanced by some resonance. In presence of an external magnetic field, cyclotron resonance provides the enhancement for ordinary waves. A waveparticle resonance gives rise to anomalous propagation if the velocity distribution is anisotropic with respect to the wave vector, which allows slow electromagnetic waves, with phase velocity less than the velocity of light
Alternating groups and moduli space lifting Invariants
Main Theorem: Spaces of r-branch point 3-cycle covers, degree n or Galois of
degree n!/2 have one (resp. two) component(s) if r=n-1 (resp. r\ge n). Improves
Fried-Serre on deciding when sphere covers with odd-order branching lift to
unramified Spin covers. We produce Hurwitz-Torelli automorphic functions on
Hurwitz spaces, and draw Inverse Galois conclusions. Example: Absolute spaces
of 3-cycle covers with +1 (resp. -1) lift invariant carry canonical even (resp.
odd) theta functions when r is even (resp. odd). For inner spaces the result is
independent of r. Another use appears in,
http://www.math.uci.edu/~mfried/paplist-mt/twoorbit.html, "Connectedness of
families of sphere covers of A_n-Type." This shows the M(odular) T(ower)s for
the prime p=2 lying over Hurwitz spaces first studied by,
http://www.math.uci.edu/~mfried/othlist-cov/hurwitzLiu-Oss.pdf, Liu and
Osserman have 2-cusps. That is sufficient to establish the Main Conjecture: (*)
High tower levels are general-type varieties and have no rational points.For
infinitely many of those MTs, the tree of cusps contains a subtree -- a spire
-- isomorphic to the tree of cusps on a modular curve tower. This makes
plausible a version of Serre's O(pen) I(mage) T(heorem) on such MTs.
Establishing these modular curve-like properties opens, to MTs, modular
curve-like thinking where modular curves have never gone before. A fuller html
description of this paper is at
http://www.math.uci.edu/~mfried/paplist-cov/hf-can0611591.html .Comment: To appear in the Israel Journal as of 1/5/09; v4 is corrected from
proof sheets, but does include some proof simplification in \S
Effect of a surface tension imbalance on a partly submerged cylinder
We perform a static analysis of a circular cylinder that forms a barrier
between surfactant-laden and surfactant-free portions of a liquidgas
interface. In addition to determining the general implications of the balances
for forces and torques, we quantify how the imbalance
between the uniform surface tension
of the surfactant-free portion of the interface and the uniform surface tension
of the surfactant-laden portion of the interface influences the
load-bearing capacity of a hydrophobic cylinder. Moreover, we demonstrate that
the difference between surface tensions on either side of a cylinder with a
cross-section of arbitrary shape induces a horizontal force component
equal to in magnitude, when measured per unit length of the
cylinder. With an energetic argument, we show that this relation also applies
to rod-like barriers with cross-sections of variable shape. In addition, we
apply our analysis to amphiphilic Janus cylinders and we discuss practical
implications of our findings for Marangoni propulsion and surface pressure
measurements
Proton network flexibility enables robustness and large electric fields in the ketosteroid isomerase active site
Hydrogen bond networks play vital roles in biological functions ranging from
protein folding to enzyme catalysis. Here we combine electronic structure
calculations and ab initio path integral molecular dynamics simulations, which
incorporate both nuclear and electronic quantum effects, to show why the
network of short hydrogen bonds in the active site of ketosteroid isomerase is
remarkably robust to mutations along the network and how this gives rise to
large local electric fields. We demonstrate that these properties arise from
the network's ability to respond to a perturbation by shifting proton positions
and redistributing electronic charge density. This flexibility leads to small
changes in properties such as the partial ionization of residues and
isotope effects upon mutation of the residues, consistent with recent
experiments. This proton flexibility is further enhanced when an extended
hydrogen bond network forms in the presence of an intermediate analog, which
allows us to explain the chemical origins of the large electric fields in the
enzyme's active site observed in recent experiments.Comment: 13 pages, 10 figures (7 main text and 3 SI
Superwind-driven Intense H Emission in NGC 6240 II: Detailed Comparison of Kinematical and Morphological Structures of the Warm and Cold Molecular Gas
We report on our new analysis of the spatial and kinematical distribution of
warm and cold molecular gas in NGC 6240, which was undertaken to explore the
origin of its unusually luminous H emission. By comparing three-dimensional
emission-line data (in space and velocity) of CO (J=2-1) in the radio and H
in the near infrared, we are able to study the H emitting efficiency,
defined in terms of the intensity ratio of H to CO [(H)/(CO)], as
a function of velocity. The integrated H emitting efficiency is calculated
by integrating the velocity profile of H emitting efficiency in blue, red,
and total (blue + red) velocity regions of the profile. We find that (1) both
the total H emitting efficiency and the blue-to-red ratio of the efficiency
are larger in regions surrounding the CO and H intensity peaks, and (2) the
H emitting efficiency and the kinematical conditions in the warm molecular
gas are closely related to each other. A collision between the molecular gas
concentration and the external superwind outflow from the southern nucleus
seems plausible to explain these characteristics, since it can reproduce the
enhanced emitting efficiency of blueshifted H around the molecular gas
concentration, if we assume that the superwind blows from the southern nucleus
toward us, hitting the entire gas concentration from behind. In this model,
internal cloud-cloud collisions within the molecular gas concentration are
enhanced by the interaction with the superwind outflow, and efficient and
intense shock-excited H emission is expected as a result of the
cloud-crushing mechanism.Comment: 12 pages, 6 figures, accepted for publication in A
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