8,659 research outputs found
Twisted K-theory and K-theory of bundle gerbes
In this note we introduce the notion of bundle gerbe K-theory and investigate
the relation to twisted K-theory. We provide some examples. Possible
applications of bundle gerbe K-theory to the classification of D-brane charges
in non-trivial backgrounds are discussed.Comment: 29 pages, corrected typos, added references, included new section on
twisted Chern character in non-torsion cas
Effects of rf Current on Spin Transfer Torque Induced Dynamics
The impact of radiofrequency (rf) currents on the direct current (dc) driven
switching dynamics in current-perpendicular-to-plane nanoscale spin valves is
demonstrated. The rf currents dramatically alter the dc driven free layer
magnetization reversal dynamics as well as the dc switching level. This occurs
when the frequency of the rf current is tuned to a frequency range around the
dc driven magnetization precession frequencies. For these frequencies,
interactions between the dc driven precession and the injected rf induce
frequency locking and frequency pulling effects that lead to a measurable
dependence of the critical switching current on the frequency of the injected
rf. Based on macrospin simulations, including dc as well as rf spin torque
currents, we explain the origin of the observed effects.Comment: 5 pages, 4 figure
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
Supersymmetry and the Anomalous Anomalous Magnetic Moment of the Muon
The recently reported measurement of the muon's anomalous magnetic moment
differs from the standard model prediction by 2.6 standard deviations. We
examine the implications of this discrepancy for supersymmetry. Deviations of
the reported magnitude are generic in supersymmetric theories. Based on the new
result, we derive model-independent upper bounds on the masses of observable
supersymmetric particles. We also examine several model frameworks. The sign of
the reported deviation is as predicted in many simple models, but disfavors
anomaly-mediated supersymmetry breaking.Comment: 4 pages, 4 figures, version to appear in Phys. Rev. Let
Is the Cepheus E Outflow driven by a Class 0 Protostar?
New early release observations of the Cepheus E outflow and its embedded
source, obtained with the Spitzer Space Telescope, are presented. We show the
driving source is detected in all 4 IRAC bands, which suggests that traditional
Class 0 classification, although essentially correct, needs to accommodate the
new high sensitivity infrared arrays and their ability to detected deeply
embedded sources. The IRAC, MIPS 24 and 70 microns new photometric points are
consistent with a spectral energy distribution dominated by a cold, dense
envelope surrounding the protostar. The Cep E outflow, unlike its more famous
cousin the HH 46/47 outflow, displays a very similar morphology in the near and
mid-infrared wavelengths, and is detected at 24 microns. The interface between
the dense molecular gas (where Cep E lies) and less dense interstellar medium,
is well traced by the emission at 8 and 24 microns, and is one of the most
exotic features of the new IRAC and MIPS images. IRS observations of the North
lobe of the flow confirm that most of the emission is due to the excitation of
pure H2 rotational transitions arising from a relatively cold (Tex~700 K) and
dense (N{H}~9.6E20 cm-2 molecular gas.Comment: 14 pages (pre-print format), including 6 figures. Published in ApJ
Special Spitzer Issue (2004
Experimental data on the single spin asymmetry and their interpretations by the chromo-magnetic string model
An attempt is made to interpret the various existing experimental data on the
single spin asymmetries in inclusive pion production by the polarized proton
and antiproton beams. As the basis of analysis the chromo-magnetic string model
is used. A whole measured kinematic region is covered. The successes and fails
of such approach are outlined. The possible improvements of model are
discussed.Comment: 17 pages, 3 figure
A Sensitive Search for Variability in Late L Dwarfs: The Quest for Weather
We have conducted a photometric monitoring program of three field late L brown dwarfs (DENIS-P J0255-4700, 2MASS J0908+5032, and 2MASS J2244+2043) looking for evidence of nonaxisymmetric structure or temporal variability in their photospheres. The observations were performed using Spitzer IRAC 4.5 and 8 ÎŒm bandpasses and were designed to cover at least one rotational period of each object; 1 Ï rms uncertainties of less than 3 mmag at 4.5 ÎŒm and around 9 mmag at 8 ÎŒm were achieved. Two out of the three objects studied exhibit some modulation in their light curves at 4.5 ÎŒmâbut not 8 ÎŒmâwith periods of 7.4 hr (DENIS 0255) and 4.6 hr (2MA 2244) and peak-to-peak amplitudes of 10 and 8 mmag. Although the lack of detectable 8 ÎŒm variation suggests an instrumental origin for the detected variations, the data may nevertheless still be consistent with intrinsic variability, since the shorter wavelength IRAC bandpasses probe more deeply into late L dwarf atmospheres than the longer wavelengths. A cloud feature occupying a small percentage (1%-2%) of the visible hemisphere could account for the observed amplitude of variation. If, instead, the variability is indeed instrumental in origin, then our nonvariable L dwarfs could be either completely covered with clouds or objects whose clouds are smaller and uniformly distributed. Such scenarios would lead to very small photometric variations. Follow-up IRAC photometry at 3.6 and 5.8 ÎŒm bandpasses should distinguish between the two cases. In any event, the present observations provide the most sensitive search to date for structure in the photospheres of late L dwarfs at mid-IR wavelengths, and our photometry provides stringent upper limits to the extent to which the photospheres of these transition L dwarfs are structured
Cyclic cocycles on twisted convolution algebras
We give a construction of cyclic cocycles on convolution algebras twisted by
gerbes over discrete translation groupoids. For proper \'etale groupoids, Tu
and Xu provide a map between the periodic cyclic cohomology of a gerbe-twisted
convolution algebra and twisted cohomology groups which is similar to a
construction of Mathai and Stevenson. When the groupoid is not proper, we
cannot construct an invariant connection on the gerbe; therefore to study this
algebra, we instead develop simplicial techniques to construct a simplicial
curvature 3-form representing the class of the gerbe. Then by using a JLO
formula we define a morphism from a simplicial complex twisted by this
simplicial curvature 3-form to the mixed bicomplex computing the periodic
cyclic cohomology of the twisted convolution algebras. The results in this
article were originally published in the author's Ph.D. thesis.Comment: 39 page
- âŠ