2,103 research outputs found
Relativistic quantum clocks
The conflict between quantum theory and the theory of relativity is
exemplified in their treatment of time. We examine the ways in which their
conceptions differ, and describe a semiclassical clock model combining elements
of both theories. The results obtained with this clock model in flat spacetime
are reviewed, and the problem of generalizing the model to curved spacetime is
discussed, before briefly describing an experimental setup which could be used
to test of the model. Taking an operationalist view, where time is that which
is measured by a clock, we discuss the conclusions that can be drawn from these
results, and what clues they contain for a full quantum relativistic theory of
time.Comment: 12 pages, 4 figures. Invited contribution for the proceedings for
"Workshop on Time in Physics" Zurich 201
Lorentz invariance of entanglement classes in multipartite systems
We analyze multipartite entanglement in systems of spin-1/2 particles from a
relativistic perspective. General conditions which have to be met for any
classification of multipartite entanglement to be Lorentz invariant are
derived, which contributes to a physical understanding of entanglement
classification. We show that quantum information in a relativistic setting
requires the partition of the Hilbert space into particles to be taken
seriously. Furthermore, we study exemplary cases and show how the spin and
momentum entanglement transforms relativistically in a multipartite setting.Comment: v2: 5 pages, 4 figures, minor changes to main body, journal
references update
Diabetes is a Risk Factor for Pulmonary Tuberculosis: A Case-Control Study from Mwanza, Tanzania.
Diabetes and TB are associated, and diabetes is increasingly common in low-income countries where tuberculosis (TB) is highly endemic. However, the role of diabetes for TB has not been assessed in populations where HIV is prevalent. A case-control study was conducted in an urban population in Tanzania among culture-confirmed pulmonary TB patients and non-TB neighbourhood controls. Participants were tested for diabetes according to WHO guidelines and serum concentrations of acute phase reactants were measured. The association between diabetes and TB, and the role of HIV as an effect modifier, were examined using logistic regression. Since blood glucose levels increase during the acute phase response, we adjusted for elevated serum acute phase reactants. Among 803 cases and 350 controls the mean (SD) age was 34.8 (11.9) and 33.8 (12.0) years, and the prevalence of diabetes was 16.7% (95% CI: 14.2; 19.4) and 9.4% (6.6; 13.0), respectively. Diabetes was associated with TB (OR 2.2, 95% CI: 1.5; 3.4, p<0.001). However, the association depended on HIV status (interaction, pâ=â0.01) due to a stronger association among HIV uninfected (OR 4.2, 95% CI: 1.5; 11.6, pâ=â0.01) compared to HIV infected (OR 0.1, 95% CI: 0.01; 1.8, pâ=â0.13) after adjusting for age, sex, demographic factors and elevated serum acute phase reactants. Diabetes is a risk factor for TB in HIV uninfected, whereas the association in HIV infected patients needs further study. The increasing diabetes prevalence may be a threat to TB control
The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
We present the first reported case of the simultaneous metallicity
determination of a gamma-ray burst (GRB) host galaxy, from both afterglow
absorption lines as well as strong emission-line diagnostics. Using
spectroscopic and imaging observations of the afterglow and host of the
long-duration Swift GRB121024A at z = 2.30, we give one of the most complete
views of a GRB host/environment to date. We observe a strong damped Ly-alpha
absorber (DLA) with a hydrogen column density of log N(HI) = 21.88 +/- 0.10, H2
absorption in the Lyman-Werner bands (molecular fraction of log(f)~ -1.4;
fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular
emission lines H-alpha, H-beta, [O II], [O III] and [N II], as well as metal
absorption lines. We find a GRB host galaxy that is highly star-forming (SFR ~
40 solar masses/yr ), with a dust-corrected metallicity along the line of sight
of [Zn/H]corr = -0.6 +/- 0.2 ([O/H] ~ -0.3 from emission lines), and a
depletion factor [Zn/Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400
km/s (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a
fairly massive host, in agreement with the derived stellar mass of
log(M/M_solar ) = 9.9+/- 0.2. We dissect the host galaxy by characterising its
molecular component, the excited gas, and the line-emitting star-forming
regions. The extinction curve for the line of sight is found to be unusually
flat (Rv ~15). We discuss the possibility of an anomalous grain size
distributions. We furthermore discuss the different metallicity determinations
from both absorption and emission lines, which gives consistent results for the
line of sight to GRB 121024A.Comment: 20 pages, 11 figures, accepted by MNRA
Effect of locally produced complementary foods on fat-free mass, linear growth, and iron status among Kenyan infants: A randomized controlled trial.
The impact of quality complementary food products on infant growth and body composition has not been adequately investigated. This study evaluated the effect on fat-free mass (FFM) accrual, linear growth, and iron status of locally produced complementary food products comparing to a standard product. In a randomized, double-blind trial, 499 infants at 6 months received nine monthly rations of (a) WinFood Classic (WFC) comprising germinated amaranth (71%), maize (10.4%), small fish (3%), and edible termites (10%); (b) WinFood Lite (WFL) comprising germinated amaranth (82.5%), maize (10.2%), and multimicronutrient premix; or (c) fortified corn-soy blend plus (CSB+). Primary outcomes were changes in FFM, length, and plasma ferritin and transferrin receptors (TfR). FFM was determined using deuterium dilution. Analysis was by intention to treat, based on available cases. Compared with CSB+, there were no differences in change from 6 to 15 months in FFM for WFC 0.0 kg (95% CI [-0.30, 0.29]) and WFL 0.03 kg (95% CI [-0.25, 0.32]) and length change for WFC -0.3 cm (95% CI [-0.9, 0.4]) and WFL -0.3 cm (95% CI [-0.9, 0.3]). TfR increased in WFC group 3.3 mg L-1 (95% CI [1.7, 4.9]) and WFL group 1.7 mg L-1 (95% CI [0.1, 3.4]) compared with CSB+. Compared with the increase in Hb in CSB+ group, there was a reduction in Hb in WFC of -0.9 g dl-1 (95% CI [-1.3, -0.5]) and a lower increase in WFL -0.4 g dl-1 (95% CI [-0.8, 0.0]). In conclusion, the tested WinFoods had the same effect on FFM and length as CSB+, whereas Hb and iron status decreased, suggesting inhibited iron bioavailability from the amaranth-based WinFoods
Modeling the high-energy emission in GRB 110721A and implications on the early multiwavelength and polarimetric observations
GRB 110721A was detected by the Gamma-ray Burst Monitor and the Large Area
Telescope (LAT) onboard the Fermi satellite and the Gamma-ray Burst Polarimeter
onboard the IKAROS solar mission. Previous analysis done of this burst showed:
i) a linear polarization signal with position angle stable () and high degree of , ii) an extreme peak
energy of a record-breaking at 152 MeV, and iii) a subdominant prompt
thermal component observed right after the onset of this burst. In this paper,
the LAT data around the reported position of GRB 110721A are analysed with the
most recent software and then, the LAT light curve above 100 MeV was obtained.
The LAT light curve is modelled in terms of adiabatic early-afterglow external
shocks when the outflow propagates into a stellar wind. Additionally, we
discuss the possible origins and also study the implications of the
early-afterglow external shocks on the extreme peak energy observed at 152
MeV, the polarization observations and the subdominant prompt thermal
component.Comment: 9 pages and one figure. Accepted for publication in Ap
The mysterious optical afterglow spectrum of GRB140506A at z=0.889
Context. Gamma-ray burst (GRBs) afterglows probe sightlines to star-forming
regions in distant star-forming galaxies. Here we present a study of the
peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim
is to understand the origin of the very unusual properties of the absorption
along the line-of-sight. Methods. We analyse spectroscopic observations
obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs
8.8 h and 33 h after the burst as well as imaging from the GROND instrument. We
also present imaging and spectroscopy of the host galaxy obtained with the
Magellan telescope. Results. The underlying afterglow appears to be a typical
afterglow of a long-duration GRB. However, the material along the line-of-
sight has imprinted very unusual features on the spectrum. Firstly, there is a
very broad and strong flux drop below 8000 AA (4000 AA in the rest frame),
which seems to be variable between the two spectroscopic epochs. We can
reproduce the flux-drops both as a giant 2175 AA extinction bump and as an
effect of multiple scattering on dust grains in a dense environment. Secondly,
we detect absorption lines from excited H i and He i. We also detect molecular
absorption from CH+ . Conclusions. We interpret the unusual properties of these
spectra as reflecting the presence of three distinct regions along the
line-of-sight: the excited He i absorption originates from an H ii-region,
whereas the Balmer absorption must originate from an associated
photodissociation region. The strong metal line and molecular absorption and
the dust extinction must originate from a third, cooler region along the
line-of-sight. The presence of (at least) three separate regions is reflected
in the fact that the different absorption components have different velocities
relative to the systemic redshift of the host galaxy.Comment: 8 pages, 4 figures. Accepted for publications in A&
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