30,986 research outputs found
The expected background spectrum in NaI dark matter detectors and the DAMA result
Detailed Monte Carlo simulations of the expected radioactive background rates
and spectra in NaI crystals are presented. The obtained spectra are then
compared to those measured in the DAMA/NaI and DAMA/LIBRA experiments. The
simulations can be made consistent with the measured DAMA spectrum only by
assuming higher than reported concentrations of some isotopes and even so leave
very little room for the dark matter signal. We conclude that any
interpretation of the annual modulation of the event rate observed by DAMA as a
dark matter signal, should include full consideration of the background
spectrum. This would significantly restrict the range of dark matter models
capable of explaining the modulation effect.Comment: 17 pages, 6 figure
On the structure of subsets of an orderable group with some small doubling properties
The aim of this paper is to present a complete description of the structure
of subsets S of an orderable group G satisfying |S^2| = 3|S|-2 and is
non-abelian
A Dicke Type Model for Equilibrium BEC Superradiance
We study the effect of electromagnetic radiation on the condensate of a Bose
gas. In an earlier paper we considered the problem for two simple models
showing the cooperative effect between Bose-Einstein condensation and
superradiance. In this paper we formalise the model suggested by Ketterle et al
in which the Bose condensate particles have a two level structure. We present a
soluble microscopic Dicke type model describing a thermodynamically stable
system. We find the equilibrium states of the system and compute the
thermodynamic functions giving explicit formulae expressing the cooperative
effect between Bose-Einstein condensation and superradiance
The H-alpha and Infrared Star Formation Rates for the Nearby Field Galaxy Survey
We investigate the H-alpha and infrared star formation rate (SFR) diagnostics
for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in
our sample, we derive H-alpha fluxes (included here) from integrated spectra.
There is a strong correlation between the ratio of far-infrared to optical
luminosities L(FIR)/L(H-alpha) and the extinction E(B-V) measured with the
Balmer decrement. Before reddening correction, the SFR(IR) and SFR(H-alpha) are
related to each other by a power-law. Correction of the SFR(H-alpha) for
extinction using the Balmer decrement and a classical reddening curve both
reduces the scatter in the SFR(IR)-SFR(H-alpha) correlation and results in a
much closer agreement (within ~10%) between the two SFR indicators. This SFR
relationship spans 4 orders of magnitude and holds for all Hubble types with
IRAS detections in the NFGS. A constant ratio between the SFR(IR) and
SFR(H-alpha) for all Hubble types, including early types (S0-Sab), suggests
that the IR emission in all of these objects results from a young stellar
population.Comment: 23 pages, 5 figures, 1 table. Accepted for publication in the
Astronomical Journal. V2: Important changes: IRAS fluxes updated. Only
moderate and good quality IRAS FIR fluxes are now used, resulting in slight
changes to the equations and figures. The IR and H-alpha SFRs now agree to
within ~10%, rather than ~30% as quoted previousl
Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells
Using laser optical pumping, widths and frequency shifts are determined for
microwave transitions between ground-state hyperfine components of Rb
and Rb atoms contained in vapor cells with alkane anti-relaxation
coatings. The results are compared with data on Zeeman relaxation obtained in
nonlinear magneto-optical rotation (NMOR) experiments, a comparison important
for quantitative understanding of spin-relaxation mechanisms in coated cells.
By comparing cells manufactured over a forty-year period we demonstrate the
long-term stability of coated cells, an important property for atomic clocks
and magnetometers
Adaiabtic theorems and reversible isothermal processes
Isothermal processes of a finitely extended, driven quantum system in contact
with an infinite heat bath are studied from the point of view of quantum
statistical mechanics. Notions like heat flux, work and entropy are defined for
trajectories of states close to, but distinct from states of joint thermal
equilibrium. A theorem characterizing reversible isothermal processes as
quasi-static processes (''isothermal theorem'') is described. Corollaries
concerning the changes of entropy and free energy in reversible isothermal
processes and on the 0th law of thermodynamics are outlined
Chemistry by Mobile Phone (or how to justify more time at the bar)
By combining automatic environment monitoring with Java smartphones a system has been produced for the real-time monitoring of experiments whilst away from the lab. Changes in the laboratory environment are encapsulated as simple XML messages, which are published using an MQTT compliant broker. Clients subscribe to the MQTT stream, and produce a user display. An MQTT client written for the Java MIDP platform, can be run on a smartphone with a GPRS Internet connection, freeing us from the constraints of the lab. We present an overview of the technologies used, and how these are helping chemists make the best use of their time
Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range
Recent work investigating resonant nonlinear magneto-optical rotation (NMOR)
related to long-lived (\tau\ts{rel} \sim 1 {\rm s}) ground-state atomic
coherences has demonstrated potential magnetometric sensitivities exceeding
for small () magnetic
fields. In the present work, NMOR using frequency-modulated light (FM NMOR) is
studied in the regime where the longitudinal magnetic field is in the
geophysical range (), of particular interest for many
applications. In this regime a splitting of the FM NMOR resonance due to the
nonlinear Zeeman effect is observed. At sufficiently high light intensities,
there is also a splitting of the FM NMOR resonances due to ac Stark shifts
induced by the optical field, as well as evidence of alignment-to-orientation
conversion type processes. The consequences of these effects for FM-NMOR-based
atomic magnetometry in the geophysical field range are considered.Comment: 8 pages, 8 figure
Recommended from our members
Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.
Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.
Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by ~0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation
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