258 research outputs found
The sharpness of gamma-ray burst prompt emission spectra
We aim to obtain a measure of the curvature of time-resolved spectra that can
be compared directly to theory. This tests the ability of models such as
synchrotron emission to explain the peaks or breaks of GBM prompt emission
spectra. We take the burst sample from the official Fermi GBM GRB time-resolved
spectral catalog. We re-fit all spectra with a measured peak or break energy in
the catalog best-fit models in various energy ranges, which cover the curvature
around the spectral peak or break, resulting in a total of 1,113 spectra being
analysed. We compute the sharpness angles under the peak or break of the
triangle constructed under the model fit curves and compare to the values
obtained from various representative emission models: blackbody,
single-electron synchrotron, synchrotron emission from a Maxwellian or
power-law electron distribution. We find that 35% of the time-resolved spectra
are inconsistent with the single-electron synchrotron function, and 91% are
inconsistent with the Maxwellian synchrotron function. The single temperature,
single emission time and location blackbody function is found to be sharper
than all the spectra. No general evolutionary trend of the sharpness angle is
observed, neither per burst nor for the whole population. It is found that the
limiting case, a single temperature Maxwellian synchrotron function, can only
contribute up to % of the peak flux. Our results show that even
the sharpest but non-realistic case, the single-electron synchrotron function,
cannot explain a large fraction of the observed GRB prompt spectra. Because of
the fact that any combination of physically possible synchrotron spectra added
together will always further broaden the spectrum, emission mechanisms other
than optically thin synchrotron radiation are likely required in a full
explanation of the spectral peaks or breaks of the GRB prompt emission phase.Comment: 16 pages, 13 figures, 2 tables, accepted for publication in A&
Probing the quantum vacuum with an artificial atom in front of a mirror
Quantum fluctuations of the vacuum are both a surprising and fundamental
phenomenon of nature. Understood as virtual photons flitting in and out of
existence, they still have a very real impact, \emph{e.g.}, in the Casimir
effects and the lifetimes of atoms. Engineering vacuum fluctuations is
therefore becoming increasingly important to emerging technologies. Here, we
shape vacuum fluctuations using a "mirror", creating regions in space where
they are suppressed. As we then effectively move an artificial atom in and out
of these regions, measuring the atomic lifetime tells us the strength of the
fluctuations. The weakest fluctuation strength we observe is 0.02 quanta, a
factor of 50 below what would be expected without the mirror, demonstrating
that we can hide the atom from the vacuum
Synchrotron Cooling in Energetic Gamma-Ray Bursts Observed by the Fermi Gamma-Ray Burst Monitor
We study the time-resolved spectra of eight GRBs observed by Fermi GBM in its
first five years of mission, with 1 keV - 1 MeV fluence
erg cm and signal-to-noise level above 900 keV. We
aim to constrain in detail the spectral properties of GRB prompt emission on a
time-resolved basis and to discuss the theoretical implications of the fitting
results in the context of various prompt emission models. We perform
time-resolved spectral analysis using a variable temporal binning technique
according to optimal S/N criteria, resulting in a total of 299 time-resolved
spectra. We fit the Band function to all spectra and obtain the distributions
for the low-energy power-law index , the high-energy power-law index
, the peak energy in the observed spectrum , and
the difference between the low- and high-energy power-law indices . Using the distributions of and , the
electron population index is found to be consistent with the "moderately
fast" scenario which fast- and slow-cooling scenarios cannot be distinguished.
We also apply a physically motivated synchrotron model, which is a triple
power-law with constrained power-law indices and a blackbody component, to test
for consistency with a synchrotron origin for the prompt emission and obtain
the distributions for the two break energies and ,
the middle segment power-law index , and the Planck function temperature
. A synchrotron model is found consistent with the majority of
time-resolved spectra for these eight energetic Fermi GBM bursts with good
high-energy photon statistics, as long as both the cooling and injection break
are included and the leftmost spectral slope is lifted either by inclusion of a
thermal component or when an evolving magnetic field is accounted for.Comment: 20 pages, 7 figures, 8 tables, accepted for publication in A&
Multimorbidity and its social determinants among older people in southern provinces, Vietnam
Background: Developing countries are poorly equipped for health issues related to ageing populations making multimorbidity challenging. As in Vietnam the focus tends to be on single conditions. Hence little is known about burden of multimorbidity. This study aimed to examine the prevalence and the determinants of multimorbidity among older people in Southern Vietnam. Methods: A cross-sectional study was conducted in two provinces of Southern Vietnam with a sample of 2400 people aged 60 years and older. The presence of chronic disease was ascertained by medical examination done by physicians at commune health stations. Information on social and demographic factors was collected using structured questionnaire. Univariate and multivariable logistic regression analyses were used to examine the factors associated with multimorbidity. Results: Nearly 40 % of older people had multimorbidity. Currently not working, and healthcare utilisation were associated with higher prevalence of multimorbidity. Living in urban areas and being literate were associated with lower prevalence of multimorbidity. Conclusion: The study found a high burden of multimorbidity among illiterate, especially those living in rural areas. This highlights the need for targeted community based programs aimed at reducing the burden of chronic disease
Kinetics of photoinduced ordering in azo-dye films: two-state and diffusion models
We study the kinetics of photoinduced ordering in the azo-dye SD1
photoaligning layers and present the results of modeling performed using two
different phenomenological approaches. A phenomenological two state model is
deduced from the master equation for an ensemble of two-level molecular
systems. Using an alternative approach, we formulate the two-dimensional (2D)
diffusion model as the free energy Fokker-Planck equation simplified for the
limiting regime of purely in-plane reorientation. The models are employed to
interpret the irradiation time dependence of the absorption order parameters
extracted from the available experimental data by using the exact solution to
the light transmission problem for a biaxially anisotropic absorbing layer. The
transient photoinduced structures are found to be biaxially anisotropic whereas
the photosteady and the initial states are uniaxial.Comment: revtex4, 34 pages, 9 figure
Quantum wave mixing and visualisation of coherent and superposed photonic states in a waveguide
Superconducting quantum systems (artificial atoms) have been recently
successfully used to demonstrate on-chip effects of quantum optics with single
atoms in the microwave range. In particular, a well-known effect of four-wave
mixing could reveal a series of features beyond classical physics, when a
non-linear medium is scaled down to a single quantum scatterer. Here we
demonstrate a phenomenon of the quantum wave mixing (QWM) on a single
superconducting artificial atom. In the QWM, the spectrum of elastically
scattered radiation is a direct map of the interacting superposed and coherent
photonic states. Moreover, the artificial atom visualises photon-state
statistics, distinguishing coherent, one- and two-photon superposed states with
the finite (quantized) number of peaks in the quantum regime. Our results may
give a new insight into nonlinear quantum effects in microwave optics with
artificial atoms.Comment: 6 pages, 5 figures; accepted versio
A Survey of Numerical Solutions to the Coagulation Equation
We present the results of a systematic survey of numerical solutions to the
coagulation equation for a rate coefficient of the form A_ij \propto (i^mu j^nu
+ i^nu j^mu) and monodisperse initial conditions. The results confirm that
there are three classes of rate coefficients with qualitatively different
solutions. For nu \leq 1 and lambda = mu + nu \leq 1, the numerical solution
evolves in an orderly fashion and tends toward a self-similar solution at large
time t. The properties of the numerical solution in the scaling limit agree
with the analytic predictions of van Dongen and Ernst. In particular, for the
subset with mu > 0 and lambda < 1, we disagree with Krivitsky and find that the
scaling function approaches the analytically predicted power-law behavior at
small mass, but in a damped oscillatory fashion that was not known previously.
For nu \leq 1 and lambda > 1, the numerical solution tends toward a
self-similar solution as t approaches a finite time t_0. The mass spectrum n_k
develops at t_0 a power-law tail n_k \propto k^{-tau} at large mass that
violates mass conservation, and runaway growth/gelation is expected to start at
t_crit = t_0 in the limit the initial number of particles n_0 -> \infty. The
exponent tau is in general less than the analytic prediction (lambda + 3)/2,
and t_0 = K/[(lambda - 1) n_0 A_11] with K = 1--2 if lambda > 1.1. For nu > 1,
the behaviors of the numerical solution are similar to those found in a
previous paper by us. They strongly suggest that there are no self-consistent
solutions at any time and that runaway growth is instantaneous in the limit n_0
-> \infty. They also indicate that the time t_crit for the onset of runaway
growth decreases slowly toward zero with increasing n_0.Comment: 41 pages, including 14 figures; accepted for publication in J. Phys.
Reversed-phase liquid chromatography coupled on-line to estrogen receptor bioaffinity detection based on fluorescence polarization
We describe the development and validation of a high-resolution screening (HRS) platform which couples gradient reversed-phase high-performance liquid chromatography (RP-HPLC) on-line to estrogen receptor α (ERα) affinity detection using fluorescence polarization (FP). FP, which allows detection at high wavelengths, limits the occurrence of interference from the autofluorescence of test compounds in the bioassay. A fluorescein-labeled estradiol derivative (E2-F) was synthesized and a binding assay was optimized in platereader format. After subsequent optimization in flow-injection analysis (FIA) mode, the optimized parameters were translated to the on-line HRS bioassay. Proof of principle was demonstrated by separating a mixture of five compounds known to be estrogenic (17β-estradiol, 17α-ethinylestradiol and the phytoestrogens coumestrol, coumarol and zearalenone), followed by post-column bioaffinity screening of the individual affinities for ERα. Using the HRS-based FP setup, we were able to screen affinities of off-line-generated metabolites of zearalenone for ERα. It is concluded that the on-line FP-based bioassay can be used to screen for the affinity of compounds without the disturbing occurrence of autofluorescence
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