18,155 research outputs found
Hierarchical solutions of the Sherrington-Kirkpatrick model: Exact asymptotic behavior near the critical temperature
We analyze the replica-symmetry-breaking construction in the
Sherrington-Kirkpatrick model of a spin glass. We present a general scheme for
deriving an exact asymptotic behavior near the critical temperature of the
solution with an arbitrary number of discrete hierarchies of the broken replica
symmetry. We show that all solutions with finite-many hierarchies are unstable
and only the scheme with infinite-many hierarchies becomes marginally stable.
We show how the solutions from the discrete replica-symmetry-breaking scheme go
over to the continuous one with increasing the number of hierarchies.Comment: REVTeX4, 11 pages, no figure
On-Chip Microwave Quantum Hall Circulator
Circulators are non-reciprocal circuit elements integral to technologies
including radar systems, microwave communication transceivers, and the readout
of quantum information devices. Their non-reciprocity arises from the
interference of microwaves over the centimetre-scale of the signal wavelength
in the presence of bulky magnetic media that break time-reversal symmetry. Here
we realize a completely passive on-chip microwave circulator with size
one-thousandth the wavelength by exploiting the chiral, slow-light response of
a 2-dimensional electron gas (2DEG) in the quantum Hall regime. For an
integrated GaAs device with 330 um diameter and 1 GHz centre frequency, a
non-reciprocity of 25 dB is observed over a 50 MHz bandwidth. Furthermore, the
direction of circulation can be selected dynamically by varying the magnetic
field, an aspect that may enable reconfigurable passive routing of microwave
signals on-chip
Absence of anomalous negative lattice-expansion for polycrystalline sample of Tb2Ti2O7
High resolution X-ray powder-diffraction experiments on a well-characterized
polycrystalline sample of the spin liquid Tb2Ti2O7 reveal that it shows normal
positive thermal-expansion above 4 K, which does not agree with the intriguing
anomalous negative thermal-expansion due to a magneto-elastic coupling reported
for a single crystal sample below 20 K. We also performed a Rietveld profile
refinement of a powder-diffraction pattern taken at a room temperature, and
confirmed that it is consistent with the fully ordered cubic pyrochlore
structure.Comment: 2 pages, 3 figure
Two 2MASS-Selected Young Stellar Clusters: Photometry, Spectroscopy, and the IMF
We present near-infrared J, H, and K_s images and K-band spectroscopy of two
newly discovered stellar clusters at different stages of evolution. Our spectra
suggest the presence of massive YSOs in the heavily embedded cluster in the
star-forming region near radio source G353.4-0.4 and an O5-O6V star in the
cluster near radio source G305+00.2. We determine a K-band luminosity function
(KLF) for both clusters and an initial mass function (IMF) for the cluster near
G305+00.2. The derived IMF slope is -1.5 if the KLF is used to derive the IMF
and is -0.98 if the color-magnitude diagram and spectra are used. The more
reliable CMD-based slope is flatter than the Salpeter value usually found for
stellar clusters. We find that using the KLF alone to derive an IMF is likely
to produce an overly steep slope in stellar clusters subject to variable
extinction.Comment: 16 pages, 18 figures, accepted to A
Magnetic Ordering in the Spin-Ice Candidate HoRuO
Neutron scattering measurements on the spin-ice candidate material
HoRuO have revealed two magnetic transitions at T 95 K and T
1.4 K to long-range ordered states involving the Ru and Ho sublattices,
respectively. Between these transitions, the Ho moments form
short-ranged ordered spin clusters. The internal field provided by the ordered
S=1 Ru moments disrupts the fragile spin-ice state and drives the
Ho moments to order. We have directly measured a slight shift in the
Ho crystal field levels at 95 K from the Ru ordering.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Letter
A Deep Multicolor Survey. VI. Near-Infrared Observations, Selection Effects, and Number Counts
I present near-infrared J (1.25um), H (1.65um), and K (2.2um) imaging
observations of 185 square arcminutes in 21 high galactic latitude fields.
These observations reach limiting magnitudes of J ~ 21 mag, H ~ 20 mag and K ~
18.5 mag. The detection efficiency, photometric accuracy and selection biases
as a function of integrated object brightness, size, and profile shape are
quantified in detail. I evaluate several popular methods for measuring the
integrated light of faint galaxies and show that only aperture magnitudes
provide an unbiased measure of the integrated light that is independent of
apparent magnitude. These J, H, and K counts and near-infrared colors are in
best agreement with passive galaxy formation models with at most a small amount
of merging (for Omega_M = 0.3, Omega_Lambda = 0.7).Comment: AJ Accepted (Feb 2001). 28 pages, 7 embedded ps figures, AASTEX5.
Minor changes to submitted version. Also available at
http://www.astronomy.ohio-state.edu/~martini/pubs
Optimal static and dynamic recycling of defective binary devices
The binary Defect Combination Problem consists in finding a fully working
subset from a given ensemble of imperfect binary components. We determine the
typical properties of the model using methods of statistical mechanics, in
particular, the region in the parameter space where there is almost surely at
least one fully-working subset. Dynamic recycling of a flux of imperfect binary
components leads to zero wastage.Comment: 14 pages, 15 figure
A Search for Molecular Gas in GHz Peaked Spectrum Radio Sources
We present searches for molecular gas (CO, OH, CS, and Ammonia) in six GHz
Peaked Spectrum (GPS) radio sources. We do not detect gas in any source and
place upper limits on the mass of molecular gas which are generally in the
range 1E9 to a few times 1E10 solar masses. These limits are consistent with
the following interpretations: (1) GPS sources do not require very dense gas in
their hosts, and (2) The GPS sources are unlikely to be confined by dense gas
and will evolve to become larger radio sources
Symmetries of Differential Equations via Cartan's Method of Equivalence
We formulate a method of computing invariant 1-forms and structure equations
of symmetry pseudo-groups of differential equations based on Cartan's method of
equivalence and the moving coframe method introduced by Fels and Olver. Our
apparoach does not require a preliminary computation of infinitesimal defining
systems, their analysis and integration, and uses differentiation and linear
algebra operations only. Examples of its applications are given.Comment: 15 pages, LaTeX 2.0
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