64,064 research outputs found
High-Precision Thermodynamics and Hagedorn Density of States
We compute the entropy density of the confined phase of QCD without quarks on
the lattice to very high accuracy. The results are compared to the entropy
density of free glueballs, where we include all the known glueball states below
the two-particle threshold. We find that an excellent, parameter-free
description of the entropy density between 0.7Tc and Tc is obtained by
extending the spectrum with the exponential spectrum of the closed bosonic
string.Comment: 4 pages, 3 figure
Age differences in encoding-related alpha power reflect sentence comprehension difficulties
When sentence processing taxes verbal working memory, comprehension difficulties arise. This is specifically the case when processing resources decline with advancing adult age. Such decline likely affects the encoding of sentences into working memory, which constitutes the basis for successful comprehension. To assess age differences in encoding-related electrophysiological activity, we recorded the electroencephalogram from three age groups (24, 43, and 65 years). Using an auditory sentence comprehension task, age differences in encoding-related oscillatory power were examined with respect to the accuracy of the given response. That is, the difference in oscillatory power between correctly and incorrectly encoded sentences, yielding subsequent memory effects (SME), was compared across age groups. Across age groups, we observed an age-related SME inversion in the alpha band from a power decrease in younger adults to a power increase in older adults. We suggest that this SME inversion underlies age-related comprehension difficulties. With alpha being commonly linked to inhibitory processes, this shift may reflect a change in the cortical inhibition–disinhibition balance. A cortical disinhibition may imply enriched sentence encoding in younger adults. In contrast, resource limitations in older adults may necessitate an increase in cortical inhibition during sentence encoding to avoid an information overload. Overall, our findings tentatively suggest that age-related comprehension difficulties are associated with alterations to the electrophysiological dynamics subserving general higher cognitive functions
Mechanical properties of polycrystalline graphene based on a realistic atomistic model
Graphene can at present be grown at large quantities only by the chemical
vapor deposition method, which produces polycrystalline samples. Here, we
describe a method for constructing realistic polycrystalline graphene samples
for atomistic simulations, and apply it for studying their mechanical
properties. We show that cracks initiate at points where grain boundaries meet
and then propagate through grains predominantly in zigzag or armchair
directions, in agreement with recent experimental work. Contrary to earlier
theoretical predictions, we observe normally distributed intrinsic strength (~
50% of that of the mono-crystalline graphene) and failure strain which do not
depend on the misorientation angles between the grains. Extrapolating for grain
sizes above 15 nm results in a failure strain of ~ 0.09 and a Young's modulus
of ~ 600 GPa. The decreased strength can be adequately explained with a
conventional continuum model when the grain boundary meeting points are
identified as Griffith cracks.Comment: Accepted for Physical Review B; 5 pages, 4 figure
Nucleosynthesis in Fast Expansions of High-Entropy, Proton Rich Matter
We demonstrate that nucleosynthesis in rapid, high-entropy expansions of
proton-rich matter from high temperature and density can result in a wider
variety of abundance patterns than heretofore appreciated. In particular, such
expansions can produce iron-group nuclides, p-process nuclei, or even heavy,
neutron-rich isotopes. Such diversity arises because the nucleosynthesis enters
a little explored regime in which the free nucleons are not in equilibrium with
the abundant alpha particles. This allows nuclei significantly heavier than
iron to form in t he presence of abundant free nucleons early in the expansion.
As the temperature drops, nucleons increasingly assemble into alpha particles
and heavier nuclei. If the assembly is efficient, the resulting depletion of
free neutrons allows disintegrat ion flows to drive nuclei back down to iron
and nickel. If this assembly is inefficient, then the large abundance of free
nucleons prevents the disintegration flows and leaves a distribution of heavy
nuclei after reaction freezeout. For cases in between, an intermediate
abundance distribution, enriched in p-process isotopes, is frozen out. These
last expansions may contribute to the solar system's supply of the p-process
nuclides if mildly proton-rich, high-entropy matter is ejected from
proto-neutron stars winds or other astrophysical sites. Also sign ificant is
the fact that, because the nucleosynthesis is primary, the signature of this
nucleosyn thesis may be evident in metal poor stars.Comment: 11 pages, 2 tables, 1 figure. Submitted to ApJ Letter
Thermomechanical Behavior of the HL-LHC 11 Tesla Nb3Sn Magnet Coil Constituents during Reaction Heat Treatment
The knowledge of the temperature induced changes of the superconductor
volume, and of the thermo-mechanical behaviour of the different coil and
tooling materials is required for predicting the coil geometry and the stress
distribution in the coil after the Nb3Sn reaction heat treatment. In the
present study we have measured the Young's and shear moduli of the HL-LHC 11 T
Nb3Sn dipole magnet coil and reaction tool constituents during in situ heat
cycles with the dynamic resonance method. The thermal expansion behaviours of
the coil components and of a free standing Nb3Sn wire were compared based on
dilation experiments.Comment: 6 pages, 12 figures, presented at MT25 conferenc
Lithological maps of selected Apollo 14 Breccia samples
A booklet of mapped surfaces of some Apollo 14 samples was prepared as an intermediate step towards the preparation of a new Apollo 14 sample catalog. It contains recently obtained observations and pictures of some of the largest and less well documented Apollo breccia samples. Some of the samples (14303, 14305, 14306, and 14311) were chosen because they have large sawn surfaces. These were dusted and mapped using a binocular microscope through the window of the nitrogen cabinet
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