6,670 research outputs found
Dimers on two-dimensional lattices
We consider close-packed dimers, or perfect matchings, on two-dimensional
regular lattices. We review known results and derive new expressions for the
free energy, entropy, and the molecular freedom of dimers for a number of
lattices including the simple-quartic (4^4), honeycomb (6^3), triangular (3^6),
kagome (3.6.3.6), 3-12 (3.12^2) and its dual [3.12^2], and 4-8 (4.8^2) and its
dual Union Jack [4.8^2] Archimedean tilings. The occurrence and nature of phase
transitions are also analyzed and discussed.Comment: Typos corrections in Eqs. (28), (32) and (43
Submillimeter satellite radiometer first semiannual engineering progress report
Development of 560 GHz fourth harmonic mixer and 140 GHz third harmonic generator for use in radiomete
Submillimeter satellite radiometer Final engineering report
All solid-state superheterodyne Dicke radiometer for submillimeter wavelength
A restatement of the normal form theorem for area metrics
An area metric is a (0,4)-tensor with certain symmetries on a 4-manifold that
represent a non-dissipative linear electromagnetic medium. A recent result by
Schuller, Witte and Wohlfarth provides a pointwise normal form theorem for such
area metrics. This result is similar to the Jordan normal form theorem for
(1,1)-tensors, and the result shows that any area metric belongs to one of 23
metaclasses with explicit coordinate expressions for each metaclass. In this
paper we restate and prove this result for skewon-free (2,2)-tensors and show
that in general, each metaclasses has three different coordinate
representations, and each of metaclasses I, II, ..., VI, VII need only one
coordinate representation.Comment: Updated proof of Proposition A.2 (Claim 5). Fixed typo in Theorem 6
(Metaclass XXIII
Cataclysmic Variables and a New Class of Faint UV Stars in the Globular Cluster NGC 6397
We present evidence that the globular cluster NGC 6397 contains two distinct
classes of centrally-concentrated UV-bright stars. Color-magnitude diagrams
constructed from U, B, V, and I data obtained with the HST/WFPC2 reveal seven
UV-bright stars fainter than the main-sequence turnoff, three of which had
previously been identified as cataclysmic variables (CVs). Lightcurves of these
stars show the characteristic ``flicker'' of CVs, as well as longer-term
variability. A fourth star is identified as a CV candidate on the basis of its
variability and UV excess. Three additional UV-bright stars show no photometric
variability and have broad-band colors characteristic of B stars. These
non-flickering UV stars are too faint to be extended horizontal branch stars.
We suggest that they could be low-mass helium white dwarfs, formed when the
evolution of a red giant is interrupted, due either to Roche-lobe overflow onto
a binary companion, or to envelope ejection following a common-envelope phase
in a tidal-capture binary. Alternatively, they could be very-low-mass
core-He-burning stars. Both the CVs and the new class of faint UV stars are
strongly concentrated toward the cluster center, to the extent that mass
segregation from 2-body relaxation alone may be unable to explain their
distribution.Comment: 11 pages plus 3 eps figures; LaTeX using aaspp4.sty; to appear in The
Astrophysical Journal Letter
Temperature Effects on Threshold Counterion Concentration to Induce Aggregation of fd Virus
We seek to determine the mechanism of like-charge attraction by measuring the
temperature dependence of critical divalent counterion concentration
() for the aggregation of fd viruses. We find that an increase in
temperature causes to decrease, primarily due to a decrease in the
dielectric constant () of the solvent. At a constant ,
is found to increase as the temperature increases. The effects of
and on can be combined to that of one parameter:
Bjerrum length (). decreases exponentially as
increases, suggesting that entropic effect of counterions plays an important
role at the onset of bundle formation.Comment: 12 pages, 3 figure
Boolean Models of Bistable Biological Systems
This paper presents an algorithm for approximating certain types of dynamical
systems given by a system of ordinary delay differential equations by a Boolean
network model. Often Boolean models are much simpler to understand than complex
differential equations models. The motivation for this work comes from
mathematical systems biology. While Boolean mechanisms do not provide
information about exact concentration rates or time scales, they are often
sufficient to capture steady states and other key dynamics. Due to their
intuitive nature, such models are very appealing to researchers in the life
sciences. This paper is focused on dynamical systems that exhibit bistability
and are desc ribedby delay equations. It is shown that if a certain motif
including a feedback loop is present in the wiring diagram of the system, the
Boolean model captures the bistability of molecular switches. The method is
appl ied to two examples from biology, the lac operon and the phage lambda
lysis/lysogeny switch
The arctic curve of the domain-wall six-vertex model
The problem of the form of the `arctic' curve of the six-vertex model with
domain wall boundary conditions in its disordered regime is addressed. It is
well-known that in the scaling limit the model exhibits phase-separation, with
regions of order and disorder sharply separated by a smooth curve, called the
arctic curve. To find this curve, we study a multiple integral representation
for the emptiness formation probability, a correlation function devised to
detect spatial transition from order to disorder. We conjecture that the arctic
curve, for arbitrary choice of the vertex weights, can be characterized by the
condition of condensation of almost all roots of the corresponding saddle-point
equations at the same, known, value. In explicit calculations we restrict to
the disordered regime for which we have been able to compute the scaling limit
of certain generating function entering the saddle-point equations. The arctic
curve is obtained in parametric form and appears to be a non-algebraic curve in
general; it turns into an algebraic one in the so-called root-of-unity cases.
The arctic curve is also discussed in application to the limit shape of
-enumerated (with ) large alternating sign matrices. In
particular, as the limit shape tends to a nontrivial limiting curve,
given by a relatively simple equation.Comment: 39 pages, 2 figures; minor correction
Algebras in Higher Dimensional Statistical Mechanics - the Exceptional Partition (MEAN Field) Algebras
We determine the structure of the partition algebra (a generalized
Temperley-Lieb algebra) for specific values of Q \in \C, focusing on the
quotient which gives rise to the partition function of site -state Potts
models (in the continuous formulation) in arbitrarily high lattice
dimensions (the mean field case). The algebra is non-semi-simple iff is a
non-negative integer less than . We determine the dimension of the key
irreducible representation in every specialization.Comment: 4 page
Radiative Reactions and Coherence Modeling in the High Altitude Electromagnetic Pulse
A high altitude nuclear electromagnetic pulse (EMP) with a peak field
intensity of 5 x 10^4 V/m carries momentum that results in a retarding force on
the average Compton electron (radiating coherently to produce the waveform)
with magnitude near that of the geomagnetic force responsible for the coherent
radiation. The retarding force results from a self field effect. The Compton
electron interaction with the self generated magnetic field due to the other
electrons accounts for the momentum density in the propagating wave;
interaction with the self generated electric field accounts for the energy flux
density in the propagating wave. Coherent addition of radiation is also
quantitatively modeled.Comment: 23 pages, 0 figure
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