12,693 research outputs found
How robust is a thermal photon interpretation of the ALICE low-p_T data?
We present a rigorous theoretical analysis of the ALICE measurement of
low-p_T direct-photon production in central lead-lead collisions at the LHC
with a centre-of-mass energy of \sqrt{s_{NN}}=2.76 TeV. Using NLO QCD, we
compute the relative contributions to prompt-photon production from different
initial and final states and the theoretical uncertainties coming from
independent variations of the renormalisation and factorisation scales, the
nuclear parton densities and the fragmentation functions. Based on different
fits to the unsubtracted and prompt-photon subtracted ALICE data, we
consistently find T = 304 \pm 58 MeV and 309 \pm 64 MeV for the effective
temperature of the quark-gluon plasma (or hot medium) at p_T \in [0.8;2.2] GeV
and p_T \in [1.5;3.5] GeV as well as a power-law (p_T^{-4}) behavior for p_T >
4 GeV as predicted by QCD hard scattering.Comment: 18 pages, 7 figures, 1 tabl
Getting the picture : iconicity does not affect representation-referent confusion
Three experiments examined 3- to 5-year-olds' (N = 428) understanding of the relationship between pictorial iconicity (photograph, colored drawing, schematic drawing) and the real world referent. Experiments 1 and 2 explored pictorial iconicity in picture-referent confusion after the picture-object relationship has been established. Pictorial iconicity had no effect on referential confusion when the referent changed after the picture had been taken/drawn (Experiment 1) and when the referent and the picture were different from the outset (Experiment 2). Experiment 3 investigated whether children are sensitive to iconicity to begin with. Children deemed photographs from a choice of varying iconicity representations as best representations for object reference. Together, findings suggest that iconicity plays a role in establishing a picture-object relation per se but is irrelevant once children have accepted that a picture represents an object. The latter finding may reflect domain general representational abilities
Femtosecond pulses and dynamics of molecular photoexcitation: RbCs example
We investigate the dynamics of molecular photoexcitation by unchirped
femtosecond laser pulses using RbCs as a model system. This study is motivated
by a goal of optimizing a two-color scheme of transferring
vibrationally-excited ultracold molecules to their absolute ground state. In
this scheme the molecules are initially produced by photoassociation or
magnetoassociation in bound vibrational levels close to the first dissociation
threshold. We analyze here the first step of the two-color path as a function
of pulse intensity from the low-field to the high-field regime. We use two
different approaches, a global one, the 'Wavepacket' method, and a restricted
one, the 'Level by Level' method where the number of vibrational levels is
limited to a small subset. The comparison between the results of the two
approaches allows one to gain qualitative insights into the complex dynamics of
the high-field regime. In particular, we emphasize the non-trivial and
important role of far-from-resonance levels which are adiabatically excited
through 'vertical' transitions with a large Franck-Condon factor. We also point
out spectacular excitation blockade due to the presence of a quasi-degenerate
level in the lower electronic state. We conclude that selective transfer with
femtosecond pulses is possible in the low-field regime only. Finally, we extend
our single-pulse analysis and examine population transfer induced by coherent
trains of low-intensity femtosecond pulses.Comment: 25 pages, 12 figure
Mechanical properties of polyethylene terephthalate under selected conditions and methods of preparation Semiannual progress report, period ending 31 Oct. 1967
Mechanical properties of polyethylene terephthalate under selected conditions and methods of preparatio
ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde
We aim to directly determine the kinetic temperature and spatial density with
formaldehyde for the 100 brightest ATLASGAL-selected clumps at 870 m
representing various evolutionary stages of high-mass star formation. Ten
transitions ( = 3-2 and 4-3) of ortho- and para-HCO near 211, 218, 225,
and 291 GHz were observed with the APEX 12 m telescope. Using non-LTE models
with RADEX, we derive the gas kinetic temperature and spatial density using the
measured p-HCO 3-2/3-2,
4-3/4-3, and 4-3/3-2
ratios. The gas kinetic temperatures derived from the p-HCO
3-2/3-2 and 4-3/4-3
line ratios are high, ranging from 43 to 300 K with an unweighted average of
91 4 K. Deduced values from the = 3-2 and 4-3
transitions are similar. Spatial densities of the gas derived from the
p-HCO 4-3/3-2 line ratios yield 0.6-8.3
10 cm with an unweighted average of 1.5 (0.1)
10 cm. A comparison of kinetic temperatures derived from p-HCO,
NH, and the dust emission indicates that p-HCO traces a distinctly
higher temperature than the NH (2,2)/(1,1) transitions and the dust,
tracing heated gas more directly associated with the star formation process.
The HCO linewidths are found to be correlated with bolometric luminosity
and increase with the evolutionary stage of the clumps, which suggests that
higher luminosities tend to be associated with a more turbulent molecular
medium. It seems that the spatial densities measured with HCO do not vary
significantly with the evolutionary stage of the clumps. However, averaged gas
kinetic temperatures derived from HCO increase with time through the
evolution of the clumps.Comment: Accepted for publication in A&
Enzyme and Tissue Alterations in Fishes: A Measure of Water Quality
A variety of freshwater fishes were studied by light and electron microscopy, enzyme histochemical and biochemical methods, The objective was to determine normal structure and function in specific target organs and to compare these to altered states in aquatic pollution. The basic question, can fish tissues and enzymes serve as indicators of water quality?, was asked. Microscopic alteration in gill was indicative of copper toxicity at an exposure of 20 parts per billion, Gross and light microscopic alterations were indicative of a single exposure of channel catfish to 15 parts per million of methyl mercuric chloride (CH3HgCl). Microscopic and correlated biochemical study fingerprinted the alterations in cells at an exposure of 0.67 parts per million CH3HgC1. The developments of pathobiological autopsy techniques for the assessment of water quality is discussed
Ink dating using thermal desorption and gas chromatography / mass spectrometry: comparison of results obtained in two laboratories
Recent ink dating methods focused mainly on changes in solvent amounts occurring over time. A promising method was developed at the Landeskriminalamt of Munich using thermal desorption (TD) followed by gas chromatography / mass spectrometry (GC/MS) analysis. Sequential extractions of the phenoxyethanol present in ballpoint pen ink entries were carried out at two different temperatures. This method is applied in forensic practice and is currently implemented in several laboratories participating to the InCID group (International Collaboration on Ink Dating). However, harmonization of the method between the laboratories proved to be a particularly sensitive and time consuming task.
The main aim of this work was therefore to implement the TD-GC/MS method at the Bundeskriminalamt (Wiesbaden, Germany) in order to evaluate if results were comparable to those obtained in Munich. At first validation criteria such as limits of reliable measurements, linearity and repeatability were determined. Samples were prepared in three different laboratories using the same inks and analyzed using two TDS-GC/MS instruments (one in Munich and one in Wiesbaden). The inter- and intra-laboratory variability of the ageing parameter was determined and ageing curves were compared. While inks stored in similar conditions yielded comparable ageing curves, it was observed that significantly different storage conditions had an influence on the resulting ageing curves. Finally, interpretation models, such as thresholds and trend tests, were evaluated and discussed in view of the obtained results. Trend tests were considered more suitable than threshold models. As both approaches showed limitations, an alternative model, based on the slopes of the ageing curves, was also proposed
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