572 research outputs found
Cocycle twisting of E(n)-module algebras and applications to the Brauer group
We classify the orbits of coquasi-triangular structures for the Hopf algebra
E(n) under the action of lazy cocycles and the Hopf automorphism group. This is
applied to detect subgroups of the Brauer group of E(n) that are
isomorphic. For a triangular structure on E(n) we prove that the subgroup
of arising from is isomorphic to a direct
product of , the Brauer-Wall group of the ground field , and
, the group of symmetric matrices under addition. For a
general quasi-triangular structure on E(n) we construct a split short
exact sequence having as a middle term and as a left term a
central extension of the group of symmetric matrices of order (
depending on ). We finally describe how the image of the Hopf automorphism
group inside acts on .Comment: Accidentally an old version of the paper was posted. Main corrections
are in Section 2 and in Section 4.
The X-ray Ridge Surrounding Sgr A* at the Galactic Center
We present the first detailed simulation of the interaction between the
supernova explosion that produced Sgr A East and the wind-swept inner ~ 2-pc
region at the Galactic center. The passage of the supernova ejecta through this
medium produces an X-ray ridge ~ 9'' to 15'' to the NE of the supermassive
black hole Sagittarius A* (Sgr A*). We show that the morphology and X-ray
intensity of this feature match very well with recently obtained Chandra
images, and we infer a supernova remnant age of less than 2,000 years. This
young age--a factor 3--4 lower than previous estimates--arises from our
inclusion of stellar wind effects in the initial (pre-explosion) conditions in
the medium. The supernova does not clear out the central ~ 0.2-pc region around
Sgr~A* and does not significantly alter the accretion rate onto the central
black hole upon passage through the Galactic center.Comment: 10 pages, 3 figures, submitted to ApJ
Visualizing plasmon-exciton polaritons at the nanoscale using electron microscopy
Polaritons are compositional light-matter quasiparticles that have recently
enabled remarkable breakthroughs in quantum and nonlinear optics, as well as in
material science. Despite the enormous progress, however, a direct
nanometer-scale visualization of polaritons has remained an open challenge.
Here, we demonstrate that plasmon-exciton polaritons, or plexcitons, generated
by a hybrid system composed of an individual silver nanoparticle and a
few-layer transition metal dichalcogenide can be spectroscopically mapped with
nanometer spatial resolution using electron energy loss spectroscopy in a
scanning transmission electron microscope. Our experiments reveal important
insights about the coupling process, which have not been reported so far. These
include nanoscale variation of Rabi splitting and plasmon-exciton detuning, as
well as absorption-dominated extinction signals, which in turn provide the
ultimate evidence for the plasmon-exciton hybridization in the strong coupling
regime. These findings pioneer new possibilities for in-depth studies of
polariton-related phenomena with nanometer spatial resolution
Optical and Infrared Photometry of the Unusual Type Ia Supernova 2000cx
We present optical and infrared photometry of the unusual Type Ia supernova
2000cx. With the data of Li et al. (2001) and Jha (2002), this comprises the
largest dataset ever assembled for a Type Ia SN, more than 600 points in
UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B-V
colors as SN 2000cx entered the nebular phase. Its I-band secondary hump was
extremely weak given its B-band decline rate. The V minus near infrared colors
likewise do not match loci based on other slowly declining Type Ia SNe, though
V-K is the least ``abnormal''. In several ways SN 2000cx resembles other slow
decliners, given its B-band decline rate (Delta m_15(B) = 0.93), the appearance
of Fe III lines and weakness of Si II in its pre-maximum spectrum, the V-K
colors and post-maximum V-H colors. If the distance modulus derived from
Surface Brightness Fluctuations of the host galaxy is correct, we find that the
rate of light increase prior to maximum, the characteristics of the bolometric
light curve, and the implied absolute magnitude at maximum are all consistent
with a sub-luminous object with Delta m_15(B) ~ 1.6-1.7 having a higher than
normal kinetic energy.Comment: 46 pages, 17 figures, to be published in Publications of the
Astronomical Society of the Pacifi
A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center
The Ibis/Isgri imager on Integral detected for the first time a hard X-ray
source, IGR J17456-2901, located within 1' of Sgr A* over the energy range
20-100 keV. Here we present the results of a detailed analysis of ~7 Ms of
Integral observations of the GC. With an effective exposure of 4.7 Ms we have
obtained more stringent positional constraints on this HE source and
constructed its spectrum in the range 20-400 keV. Furthermore, by combining the
Isgri spectrum with the total X-ray spectrum corresponding to the same physical
region around SgrA* from XMM data, and collected during part of the Integral
observations, we constructed and present the first accurate wide band HE
spectrum for the central arcmins of the Galaxy. Our complete analysis of the
emission properties of IGR shows that it is faint but persistent with no
variability above 3 sigma contrary to what was alluded to in our first paper.
This result, in conjunction with the spectral characteristics of the X-ray
emission from this region, suggests that the source is most likely not
point-like but, rather, that it is a compact, yet diffuse, non-thermal emission
region. The centroid of IGR is estimated to be R.A.=17h45m42.5,
decl.=-28deg59'28'', offset by 1' from the radio position of Sgr A* and with a
positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x10^35
erg/sec. Very recently, Hess detected of a source of ~TeV g-rays also located
within 1' of Sgr A*. We present arguments in favor of an interpretation
according to which the photons detected by Integral and Hess arise from the
same compact region of diffuse emission near the central BH and that the
supernova remnant Sgr A East could play an important role as a contributor of
very HE g-rays to the overall spectrum from this region.Comment: 14 pages, 11 figures, Accepted for publication in Ap
Preparation of low cost SERS-substrates for virus characterization
Raman spectroscopy is a technique that allows the characterization and detection of a wide range of molecules. The characterization of biomolecules and viruses has been a novel application in the last decades. A relevant problem for applying this technique is the low intensity of the Raman signal and the low concentration of the analyte, which makes the identification of molecules and viruses quite difficult. An alternative to overcome this problem is the use of surface- enhanced Raman spectroscopy (SERS). This involves the use of SERS-substrates that generally are very expensive and can only be used once. In this work, we report the preliminary results of virus detection by SERS using low-cost homemade substrates and commercially available substrates. Characteristic Raman peaks associated with the influenza virus were detected. The results obtained with the homemade SERS-substrates are comparable to the obtained by using the comercial ones.Preparación de sustratos SERS de bajo coste para caracterización de virus
La espectroscopia Raman es una técnica que permite la caracterización y detección de una amplia gama de moléculas. La caracterización de biomoléculas y virus ha sido una aplicación novedosa en las últimas décadas. Un problema relevante para aplicar esta técnica es la baja intensidad de la señal de Raman y la baja concentración de analito, lo que dificulta bastante la identificación de moléculas y virus. Una alternativa para superar este problema es el uso de SERS (surface-enhanced Raman spectroscopy). Esto implica el uso de sustratos SERS que generalmente cuestan una cantidad considerable de dinero y solo se pueden usar una vez. En este trabajo, reportamos resultados preliminares de la detección de virus por SERS utilizando sustratos caseros de bajo costo y sustratos disponibles comercialmente. Se detectaron picos característicos Raman asociados a virus de la influenza. Los resultados obtenidos con los sustratos SERS caseros son comparables a los obtenidos utilizando los comerciales
Impact of Exercise Partner Attractiveness on Mood, Enjoyment, and Exertion
Social comparison theory was used to examine if males exercising with a female research confederate posing as either attractive or unattractive would alter their exercise mood, exertion, and enjoyment. A total of 101 college students (51 males and 51 females) were randomly assigned to one of three conditions: biking alone, biking with an attractive female confederate, or biking with the same female confederate appearing unattractive. All participants were instructed to complete 20 minutes of exercise at 60%-70% of their maximum target heart rate. Standard exercise mood measures (e.g., Activation-Deactivation Adjective Check List) were administered immediately prior to and immediately following exercise. Pulse rate and exercise work load (i.e., bike speed and RPMs) were assessed throughout the exercise experience and exercise enjoyment was measured following exercise. In the attractive condition, the confederate dressed fashionably in form fitting and stylish work-out clothes and wore make-up and jewelry while the same confederate in the unattractive condition wore baggie casual sweat clothes and no make-up or jewelry. Results indicated that female participants were more relaxed while males were less relaxed when they were in the unattractive confederate condition (p \u3c .05). However, no exertion differences emerged between experimental conditions (p’s \u3e .05). Participants reported the most enjoyment while in the control condition exercising alone and the least enjoyment in the attractive confederate condition (p \u3c .05). Social comparison theory predicts exercise outcome such that participants report less enjoyment yet more relaxation for females but less for males when exercising with an attractive female confederate thus altering their exercise experience based on those around them
Transition metal dichalcogenide nanodisks as high-index dielectric Mie nanoresonators
Monolayer transition metal dichalcogenides (TMDCs) have recently been
proposed as a unique excitonic platform for advanced optical and electronic
functionalities. However, in spite of intense research efforts, it has been
largely overlooked that, in addition to displaying rich exciton physics, TMDCs
also possess a very high refractive index. This opens a possibility to utilize
these materials for constructing resonant nanoantennas based on subwavelength
geometrical modes. Here we show that nanodisks fabricated from exfoliated
multilayer WS support distinct Mie resonances and so-called anapole states
that can be easily tuned in wavelength over the visible and near-infrared
spectral range by varying the nanodisks' size and aspect ratio. We argue that
the TMDC material anisotropy and the presence of excitons substantially enrich
nanophotonics by complementing traditional approaches based on plasmonics and
well-known high-index materials such as silicon. As a proof-of-concept, we
demonstrate a novel regime of light-matter interaction, anapole-exciton
polaritons, which we realize within a single WS nanodisk. Our results thus
suggest that nanopatterned TMDCs are promising materials for high-index
nanophotonics applications with enriched functionalities and superior
prospects
Is there really a debris disc around ?
The presence of a debris disc around the Gyr-old solar-type star
was suggested by the infrared
excess detection. Follow-up observations with /PACS revealed
a double-lobed feature, that displayed asymmetries both in brightness and
position. Therefore, the disc was thought to be edge-on and significantly
eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which
unambiguously reveal that these lobes show no common proper motion with
. In these observations, no flux has been detected
around that exceeds the levels. We
conclude that surface brightness upper limits of a debris disc around
are at 1.3 mm, and
at 870 microns. Our results overall demonstrate
the capability of the ALMA/ACA to follow-up observations of
debris discs and clarify the effects of background confusion.Comment: 6 pages, 2 figures, 2 table
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