74 research outputs found
Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
We have studied how 2- and 3- dimensional systems made up of particles
interacting with finite range, repulsive potentials jam (i.e., develop a yield
stress in a disordered state) at zero temperature and applied stress. For each
configuration, there is a unique jamming threshold, , at which
particles can no longer avoid each other and the bulk and shear moduli
simultaneously become non-zero. The distribution of values becomes
narrower as the system size increases, so that essentially all configurations
jam at the same in the thermodynamic limit. This packing fraction
corresponds to the previously measured value for random close-packing. In fact,
our results provide a well-defined meaning for "random close-packing" in terms
of the fraction of all phase space with inherent structures that jam. The
jamming threshold, Point J, occurring at zero temperature and applied stress
and at the random close-packing density, has properties reminiscent of an
ordinary critical point. As Point J is approached from higher packing
fractions, power-law scaling is found for many quantities. Moreover, near Point
J, certain quantities no longer self-average, suggesting the existence of a
length scale that diverges at J. However, Point J also differs from an ordinary
critical point: the scaling exponents do not depend on dimension but do depend
on the interparticle potential. Finally, as Point J is approached from high
packing fractions, the density of vibrational states develops a large excess of
low-frequency modes. All of these results suggest that Point J may control
behavior in its vicinity-perhaps even at the glass transition.Comment: 21 pages, 20 figure
Taxonomic studies of Amanita muscaria (L.) Lam (Amanitaceae, Agaricomycetes) and its infraspecific taxa in Brazil
Fungos conidiais associados ao folhedo de Clusia melchiorii Gleason e C. nemorosa G. Mey. (Clusiaceae) em fragmento de Mata AtlĂąntica, BA, Brasil
Efeito de prĂ©-cultivos sobre o potencial de inĂłculo de fungos micorrĂzicos arbusculares e produção da mandioca
Colonisation par les mycorhizes arbusculaires dans des plantes vasculaires des forĂȘts des Yungas, Argentine
Exploring Cosmic Origins with CORE: Cluster Science
We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission. Using realistic simulations of the millimeter sky, produced with the latest version of the Planck Sky Model, we characterize the CORE cluster catalogues as a function of the main mission performance parameters. We pay particular attention to telescope size, key to improved angular resolution, and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade. A possible CORE mission concept with a 150 cm diameter primary mirror can detect of the order of 50,000 clusters through the thermal Sunyaev-Zeldovich effect (SZE). The total yield increases (decreases) by 25% when increasing (decreasing) the mirror diameter by 30 cm. The 150 cm telescope configuration will detect the most massive clusters (> 1014 M) at redshift z > 1.5 over the whole sky, although the exact number above this redshift is tied to the uncertain evolution of the cluster SZE flux-mass relation; assuming self-similar evolution, CORE will detect ⌠500 clusters at redshift z > 1.5. This changes to 800 (200) when increasing (decreasing) the mirror size by 30 cm. CORE will be able to measure individual cluster halo masses through lensing of the cosmic microwave background anisotropies with a 1-Ï sensitivity of 4 Ă 1014M, for a 120 cm aperture telescope, and 1014M for a 180 cm one. From the ground, we estimate that, for example, a survey with about 150,000 detectors at the focus of 350 cm telescopes observing 65% of the sky from Atacama would be shallower than CORE and detect about 11,000 clusters, while a survey from the South Pole with the same number of detectors observing 25% of sky with a 10 m telescope is expected to be deeper and to detect about 70,000 clusters. When combined with such a South Pole survey, CORE would reach a limiting mass of M500 ⌠2 â 3 Ă 1013Mand detect 220,000 clusters (5 sigma detection limit). Cosmological constraints from CORE cluster counts alone are competitive with other scheduled large scale structure surveys in the 2020âs for measuring the dark energy equation-of-state parameters w0 and wa (Ïw0 = 0.28, Ïwa = 0.31). In combination with primary CMB constraints, CORE cluster counts can further reduce these error bars on w0 and wa to 0.05 and 0.13 respectively, and constrain the sum of the neutrino masses, ÎŁmÎœ, to 39 meV (1 sigma). The wide frequency coverage of CORE, 60 - 600 GHz, will enable measurement of the relativistic thermal SZE by stacking clusters. Contamination by dust emission from the clusters, however, makes constraining the temperature of the intracluster medium difficult. The kinetic SZE pairwise momentum will be extracted with S/N = 70 in the foreground-cleaned CMB map. Measurements of TCMB(z) using CORE clusters will establish competitive constraints on the evolution of the CMB temperature: (1+z) 1âÎČ , with an uncertainty of ÏÎČ . 2.7Ă10â3 at low redshift (z . 1). The wide frequency coverage also enables clean extraction of a map of the diffuse SZE signal over the sky, substantially reducing contamination by foregrounds compared to the Planck SZE map extraction. Our analysis of the one-dimensional distribution of Compton-y values in the simulated map finds an order of magnitude improvement in constraints on Ï8 over the Planck result, demonstrating the potential of this cosmological probe with CORE
Exploring cosmic origins with CORE: Cosmological parameters
We forecast the main cosmological parameter constraints achievable with the
CORE space mission which is dedicated to mapping the polarisation of the Cosmic Microwave
Background (CMB). CORE was recently submitted in response to ESAâs fifth call for mediumsized mission proposals (M5). Here we report the results from our pre-submission study of the
impact of various instrumental options, in particular the telescope size and sensitivity level,
and review the great, transformative potential of the mission as proposed. Specifically, we
assess the impact on a broad range of fundamental parameters of our Universe as a function
of the expected CMB characteristics, with other papers in the series focusing on controlling
astrophysical and instrumental residual systematics. In this paper, we assume that only a
few central CORE frequency channels are usable for our purpose, all others being devoted
to the cleaning of astrophysical contaminants. On the theoretical side, we assume ÎCDM as
our general framework and quantify the improvement provided by CORE over the current
constraints from the Planck 2015 release. We also study the joint sensitivity of CORE and
of future Baryon Acoustic Oscillation and Large Scale Structure experiments like DESI and
Euclid. Specific constraints on the physics of inflation are presented in another paper of the
series. In addition to the six parameters of the base ÎCDM, which describe the matter content
of a spatially flat universe with adiabatic and scalar primordial fluctuations from inflation, we
derive the precision achievable on parameters like those describing curvature, neutrino physics,
extra light relics, primordial helium abundance, dark matter annihilation, recombination
physics, variation of fundamental constants, dark energy, modified gravity, reionization and
cosmic birefringence. In addition to assessing the improvement on the precision of individual
parameters, we also forecast the post-CORE overall reduction of the allowed parameter space
with figures of merit for various models increasing by as much as ⌠107 as compared to Planck
2015, and 105 with respect to Planck 2015 + future BAO measurements
Desert Truffles of the Australian Outback: Ecology, Ethnomycology, and Taxonomy
The Aborigines of central Australia have traditionally used desert truffles as food. Truffle hunting in the desert requires substantial ecological knowledge, as truffles occur sporadically and only with adequate and properly distributed rainfall as well as the presence of necessary soil conditions and mycorrhizal hosts. Truffles are hunted primarily by women, who look for cracks or humps in the soil caused by expansion of the truffles, which are then extracted with digging sticks. The truffles are typically eaten raw or baked or roasted in ashes. Seven truffle species are recorded from the Australian Outback, including three that have been only recently described
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