2,339 research outputs found
Deformations of calibrated subbundles of Euclidean spaces via twisting by special sections
We extend the "bundle constructions" of calibrated submanifolds, due to
Harvey--Lawson in the special Lagrangian case, and to
Ionel--Karigiannis--Min-Oo in the cases of exceptional calibrations, by
"twisting" the bundles by a special (harmonic, holomorphic, parallel) section
of a complementary bundle. The existence of such deformations shows that the
moduli space of calibrated deformations of these "calibrated subbundles"
includes deformations which destroy the linear structure of the fibre.Comment: 16 pages, no figures. Version 2: Only minor cosmetic and
typographical revisions. To appear in "Annals of Global Analysis and
Geometry.
Perturbative Solutions of the Extended Constraint Equations in General Relativity
The extended constraint equations arise as a special case of the conformal
constraint equations that are satisfied by an initial data hypersurface in
an asymptotically simple spacetime satisfying the vacuum conformal Einstein
equations developed by H. Friedrich. The extended constraint equations consist
of a quasi-linear system of partial differential equations for the induced
metric, the second fundamental form and two other tensorial quantities defined
on , and are equivalent to the usual constraint equations that satisfies
as a spacelike hypersurface in a spacetime satisfying Einstein's vacuum
equation. This article develops a method for finding perturbative,
asymptotically flat solutions of the extended constraint equations in a
neighbourhood of the flat solution on Euclidean space. This method is
fundamentally different from the `classical' method of Lichnerowicz and York
that is used to solve the usual constraint equations.Comment: This third and final version has been accepted for publication in
Communications in Mathematical Physic
Two cases of fungal keratitis caused by Metarhizium anisopliae
We present two cases of keratitis due to Metarhizium anisopliae in geographically separated areas of the United States. The isolates were microscopically similar but morphologically different and were identified by ribosomal DNA sequencing. Both isolates had low minimum inhibitory concentration (MIC) values to caspofungin and micafungin, but high MIC values to amphotericin B. The morphologic and antifungal susceptibility differences between the two isolates indicate possible polyphylogeny of the group. Keywords: Metarhizium, Fungal keratitis, Keratomycosis, Antifungal susceptibilit
Spectral and Spin Measurement of Two Small and Fast-Rotating Near-Earth Asteroids
In May 2012 two asteroids made near-miss "grazing" passes at distances of a
few Earth-radii: 2012 KP24 passed at nine Earth-radii and 2012 KT42 at only
three Earth-radii. The latter passed inside the orbital distance of
geosynchronous satellites. From spectral and imaging measurements using NASA's
3-m Infrared Telescope Facility (IRTF), we deduce taxonomic, rotational, and
physical properties. Their spectral characteristics are somewhat atypical among
near-Earth asteroids: C-complex for 2012 KP24 and B-type for 2012 KT42, from
which we interpret the albedos of both asteroids to be between 0.10 and 0.15
and effective diameters of 20+-2 and 6+-1 meters, respectively. Among B-type
asteroids, the spectrum of 2012 KT42 is most similar to 3200 Phaethon and 4015
Wilson-Harrington. Not only are these among the smallest asteroids spectrally
measured, we also find they are among the fastest-spinning: 2012 KP24 completes
a rotation in 2.5008+-0.0006 minutes and 2012 KT42 rotates in 3.634+-0.001
minutes.Comment: 4 pages, 3 figures, accepted for publication in Icaru
Temperature and Pressure Dependent Kinetics of QOOH Decomposition and Reaction with O2: Experimental and Theoretical Investigations of QOOH Radicals Derived from Cl + (CH3)3COOH
QOOH radicals are key species in autoignition, produced by internal isomerisations of RO2 radicals, and are central to chain branching reactions in low temperature combustion. The kinetics of QOOH radical decomposition and reaction with O2 have been determined as a function of temperature and pressure, using observations of OH radical production and decay following H-atom abstraction from tertiary-butyl hydroperoxide ((CH3)3COOH) by Cl atoms to produce QOOH (.CH2(CH3)2COOH) radicals. The kinetics of QOOH decomposition have been investigated as a function of temperature (251 to 298 K), and pressure (10 to 350 Torr), in helium and nitrogen bath gases, and those of the reaction between QOOH and O2 have been investigated as a function of temperature (251 to 304 K), and pressure (10 to 100 Torr) in He and N2. Decomposition of the QOOH radicals was observed to display temperature and pressure dependence, with a barrier height for decomposition of (44.7 ± 4.0) kJ mol-1 determined by master equation fitting to the experimental data. The rate coefficient for the reaction between QOOH and O2 was determined to be (5.6 ± 1.7) × 10-13 cm3 s-1 at 298 K, with no significant dependence on pressure, and can be described by the Arrhenius parameters A = (7.3 ± 6.8) × 10-14 cm3 s-1 and Ea = -(5.4 ± 2.1) kJ mol-1 in the temperature range 251 to 304 K. This work represents the first measurements of any QOOH radical kinetics as a function of temperature and pressure
Comparing postural stability entropy analyses to differentiate fallers and non-fallers
The health and financial cost of falls has spurred research to differentiate the characteristics of fallers and non-fallers. Postural stability has received much of the attention with recent studies exploring various measures of entropy. This study compared the discriminatory ability of several entropy methods at differentiating two paradigms in the center-of-pressure of elderly individuals: (1) eyes open (EO) vs. eyes closed (EC) and (2) fallers (F) vs. non-fallers (NF). Methods were compared using the area under the curve (AUC) of the receiver-operating characteristic curves developed from logistic regression models. Overall, multiscale entropy (MSE) and composite multiscale entropy (CompMSE) performed the best with AUCs of 0.71 for EO/EC and 0.77 for F/NF. When methods were combined together to maximize the AUC, the entropy classifier had an AUC of for 0.91 the F/NF comparison. These results suggest researchers and clinicians attempting to create clinical tests to identify fallers should consider a combination of every entropy method when creating a classifying test. Additionally, MSE and CompMSE classifiers using polar coordinate data outperformed rectangular coordinate data, encouraging more research into the most appropriate time series for postural stability entropy analysis
A Multi-Frequency Radio Study of Supernova Remnant G292.0+1.8 and its Pulsar Wind Nebula
(Abridged) We present a detailed radio study of the young supernova remnant
(SNR) G292.0+1.8 and its associated pulsar PSR J1124-5916, using the Australia
Telescope Compact Array at observing wavelengths of 20, 13 and 6 cm. We find
that the radio morphology of the source consists of three main components: a
polarized flat-spectrum central core coincident with the pulsar J1124-5916, a
surrounding circular steep-spectrum plateau with sharp outer edges and,
superimposed on the plateau, a series of radial filaments with spectra
significantly flatter than their surroundings. HI absorption argues for a lower
limit on the distance to the system of 6 kpc.
The core clearly corresponds to radio emission from a pulsar wind nebula
powered by PSR J1124-5916, while the plateau represents the surrounding SNR
shell. The plateau's sharp outer rim delineates the SNR's forward shock, while
the thickness of the plateau region demonstrates that the forward and reverse
shocks are well-separated. Assuming a distance of 6 kpc and an age for the
source of 2500 yr, we infer an expansion velocity for the SNR of ~1200 km/s and
an ambient density ~0.9 cm^-3. We interpret the flat-spectrum radial filaments
superimposed on the steeper-spectrum plateau as Rayleigh-Taylor unstable
regions between the forward and reverse shocks of the SNR. The flat radio
spectrum seen for these features results from efficient second-order Fermi
acceleration in strongly amplified magnetic fields.Comment: 11 pages of text, plus 7 embedded EPS figures. Accepted to ApJ. Added
missing units on x-axis of Fig
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