18,722 research outputs found
On elliptic curves with an isogeny of degree 7
We show that if is an elliptic curve over with a
-rational isogeny of degree 7, then the image of the 7-adic Galois
representation attached to is as large as allowed by the isogeny, except
for the curves with complex multiplication by . The
analogous result with 7 replaced by a prime was proved by the first
author in [7]. The present case has additional interesting
complications. We show that any exceptions correspond to the rational points on
a certain curve of genus 12. We then use the method of Chabauty to show that
the exceptions are exactly the curves with complex multiplication. As a
by-product of one of the key steps in our proof, we determine exactly when
there exist elliptic curves over an arbitrary field of characteristic not 7
with a -rational isogeny of degree 7 and a specified Galois action on the
kernel of the isogeny, and we give a parametric description of such curves.Comment: The revision gives a complete answer to the question considered in
Version 1. Version 3 will appear in the American Journal of Mathematic
The optimization air separation plants for combined cycle MHD-power plant applications
Some of the design approaches being employed during a current supported study directed at developing an improved air separation process for the production of oxygen enriched air for magnetohydrodynamics (MHD) combustion are outlined. The ultimate objective is to arrive at conceptual designs of air separation plants, optimized for minimum specific power consumption and capital investment costs, for integration with MHD combined cycle power plants
Variational Principle in the Algebra of Asymptotic Fields
This paper proposes a variational principle for the solutions of quantum
field theories in which the ``trial functions'' are chosen from the algebra of
asymptotic fields, and illustrates this variational principle in simple cases.Comment: 15 pages, Latex, no figure
High-order optical nonlinearity at low light levels
We observe a nonlinear optical process in a gas of cold atoms that
simultaneously displays the largest reported fifth-order nonlinear
susceptibility \chi^(5) = 1.9x10^{-12} (m/V)^4 and high transparency. The
nonlinearity results from the simultaneous cooling and crystallization of the
gas, and gives rise to efficient Bragg scattering in the form of
six-wave-mixing at low-light-levels. For large atom-photon coupling strengths,
the back-action of the scattered fields influences the light-matter dynamics.
This system may have important applications in many-body physics, quantum
information processing, and multidimensional soliton formation.Comment: 5 pages, 3 figure
Tidal Heating of Extra-Solar Planets
Extra-solar planets close to their host stars have likely undergone
significant tidal evolution since the time of their formation. Tides probably
dominated their orbital evolution once the dust and gas had cleared away, and
as the orbits evolved there was substantial tidal heating within the planets.
The tidal heating history of each planet may have contributed significantly to
the thermal budget that governed the planet's physical properties, including
its radius, which in many cases may be measured by observing transit events.
Typically, tidal heating increases as a planet moves inward toward its star and
then decreases as its orbit circularizes. Here we compute the plausible heating
histories for several planets with measured radii, using the same tidal
parameters for the star and planet that had been shown to reconcile the
eccentricity distribution of close-in planets with other extra-solar planets.
Several planets are discussed, including for example HD 209458 b, which may
have undergone substantial tidal heating during the past billion years, perhaps
enough to explain its large measured radius. Our models also show that GJ 876 d
may have experienced tremendous heating and is probably not a solid, rocky
planet. Theoretical models should include the role of tidal heating, which is
large, but time-varying.Comment: Accepted for publication to Ap
Query Expansion of Zero-Hit Subject Searches: Using a Thesaurus in Conjunction with NLP Techniques
The focus of our study is zero-hit queries in keyword subject searches and the effort of increasing recall in these cases by reformulating and, then, expanding the initial queries using an external source of knowledge, namely a thesaurus. To this end, the objectives of this study are twofold. First, we perform the mapping of query terms to the thesaurus terms. Second, we use the matched terms to expand the user’s initial query by taking advantage of the thesaurus relations and implementing natural language processing (NLP) techniques. We report on the overall procedure and elaborate on key points and considerations of each step of the process
Superfield Realizations of Lorentz and CPT Violation
Superfield realizations of Lorentz-violating extensions of the Wess-Zumino
model are presented. These models retain supersymmetry but include terms that
explicitly break the Lorentz symmetry. The models can be understood as arising
from superspace transformations that are modifications of the familiar one in
the Lorentz-symmetric case.Comment: 10 page
Hanbury-Brown and Twiss Intensity Correlations of Parabosons
This paper shows that in intensity correlation measurements there will be
clear and unambiguous signals that new-physics particles are, or aren't,
parabosons. For a parabosonic field in a dominant single-mode, there is a
diagonal P-representation in the "even and odd coherent states" basis. It is
used to analyze zero-time-interval intensity correlations of parabosons in a
maximum-entropic state. As the mean number of parabosons decreases, there is a
monotonic reduction to (2/p) of the constant bosonic ``factor of two''
proportionality of the second-order versus the squared first-order intensity
correlation function.Comment: 16 pages; version 4 to add simple p-independent recursion relatio
Locating regions in a sequence under density constraints
Several biological problems require the identification of regions in a
sequence where some feature occurs within a target density range: examples
including the location of GC-rich regions, identification of CpG islands, and
sequence matching. Mathematically, this corresponds to searching a string of 0s
and 1s for a substring whose relative proportion of 1s lies between given lower
and upper bounds. We consider the algorithmic problem of locating the longest
such substring, as well as other related problems (such as finding the shortest
substring or a maximal set of disjoint substrings). For locating the longest
such substring, we develop an algorithm that runs in O(n) time, improving upon
the previous best-known O(n log n) result. For the related problems we develop
O(n log log n) algorithms, again improving upon the best-known O(n log n)
results. Practical testing verifies that our new algorithms enjoy significantly
smaller time and memory footprints, and can process sequences that are orders
of magnitude longer as a result.Comment: 17 pages, 8 figures; v2: minor revisions, additional explanations; to
appear in SIAM Journal on Computin
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