5,125 research outputs found
Conditions for resistivity from electron-electron scattering
Many complex oxides (including titanates, nickelates and cuprates) show a
regime in which resistivity follows a power law in temperature (). By analogy to a similar phenomenon observed in some metals at low
temperature, this has often been attributed to electron-electron (Baber)
scattering. We show that Baber scattering results in a power law only
under several crucial assumptions which may not hold for complex oxides. We
illustrate this with sodium metal () and
strontium titanate (). We conclude that an
observation of is not sufficient evidence for
electron-electron scattering.Comment: 5 pages, 4 figure
Crystal vs glass formation in lattice models with many coexisting ordered phases
We present here new evidence that after a quench the planar Potts model on
the square lattice relaxes towards a glassy state if the number of states q is
larger than four. By extrapolating the finite size data we compute the average
energy of these states for the infinite system with periodic boundary
conditions, and find that it is comparable with that previously found using
fixed boundary conditions. We also report preliminary results on the behaviour
of these states in the presence of thermal fluctuationsComment: 7 pages with 5 figure
Why are Rural People Vulnerable to Famine?
It is now generally accepted by researchers (although not by governments) that famines are caused as much by act of man as by act of god. But our understanding of famine is still quite rudimentary, and what little we know is rarely translated into policies to prevent or control famine. Few people would argue that we clearly understand what makes people vulnerable to famine, or that we can predict that one group will be vulnerable while another will not.European Research Council (ERC
The response of neotropical dragonflies (Insecta: Odonata) to local and regional abiotic factors in small streams of the Amazon
Since the relative role of local and regional abiotic factors on the Odonata diversity in rainforest streams is still poorly understood, we evaluated the effects of these factors on adult Odonata (Insecta) from preserved and altered streams in the Amazonian region. Adult Odonata were sampled in 98 streams in the Eastern Amazon, Pará, Brazil. Six variables were used to measure local environmental factors: habitat integrity index; mean canopy over the channel; and four physical and chemical descriptors of the water. To measure regional environmental factors, six variables were also used: altitude gradient, three bioclimatic variables and two percentage forest variables. In partial redundancy analysis, both abiotic factors (local and regional) were important to explain the variation in the Odonata community. The Odonata community can be influenced by regional and local factors. The relationship between Odonata and the local (e.g., integrity, canopy cover, and physical and chemical descriptors of the water) and regional (e.g., bioclimatic and forest cover variables) environmental variables recorded in this study has important implications for the use of these organisms to monitor small streams of the Eastern Amazon. The scale at which habitat is measured is an important issue in community structuring studies considering the rapid environmental changes. It is of great importance to consider the different scales in studies assessing community structure, once an adequate habitat must meet the ecological needs of all stages of the life of the Odonata.Funding Agency
National Council for Scientific and Technological Development (CNPq)
CNPq Amazonian Biodiversity and Land Use project
CNPq 574008/2008-0
Brazilian Agricultural Research Company-EMBRAPA
SEG: 02.08.06.005.00
Darwin Initiative, United Kingdom
17-023
Nature Conservancy and Natural Environment Research Council (NERC)
NE/F01614X/1
NE/G000816/1
National Council for Scientific and Technological Development (CNPq)
307597/2016-4
Portuguese Foundation for Science and Technology
UID/Multi/04326/2019
PROPESP/UFPA through Edital 01/2018 (Programa de Apoio a Publicacao Qualificada-PAPQ)info:eu-repo/semantics/publishedVersio
A 2MASS Analysis of the Stability of Southern Bok Globules
We used near-infrared 2MASS data to construct visual extinction maps of a
sample of Southern Bok globules utilizing the NICE method. We derived radial
extinction profiles of dense cores identified in the globules and analyzed
their stability against gravitational collapse with isothermal Bonnor-Ebert
spheres. The frequency distribution of the stability parameter xi_max of these
cores shows that a large number of them are located in stable states, followed
by an abrupt decrease of cores in unstable states. This decrease is steeper for
globules with associated IRAS point sources than for starless globules.
Moreover, globules in stable states have a Bonnor-Ebert temperature of T = 15
+- 6 K, while the group of critical plus unstable globules has a different
temperature of T = 10 +- 3 K. Distances were estimated to all the globules
studied in this work and the spectral class of the IRAS sources was calculated.
No variations were found in the stability parameters of the cores and the
spectral class of their associated IRAS sources. On the basis of 13CO J = 1-0
molecular line observations, we identified and modeled a blue-assymetric line
profile toward a globule of the sample, obtaining an upper limit infall speed
of 0.25 km/s.Comment: 53 pages, 15 figures, accepted for publication in Ap
Pattern Selection in a Phase Field Model for Directional Solidification
A symmetric phase field model is used to study wavelength selection in two
dimensions. We study the problem in a finite system using a two-pronged
approach. First we construct an action and, minimizing this, we obtain the most
probable configuration of the system, which we identify with the selected
stationary state. The minimization is constrained by the stationary solutions
of stochastic evolution equations and is done numerically. Secondly, additional
support for this selected state is obtained from straightforward simulations of
the dynamics from a variety of initial states.Comment: 7 pages, 6 figures, to appear in Physica
Immediate performance of self-etching versus system adhesives with multiple light-activated restoratives
Objectives: The purpose of this study was to evaluate the performance of both single and double applications of (Adper Prompt L-Pop) self-etching dental adhesive, when used with three classes of light-activated restorative materials, in comparison to the performance of each restorative system adhesive. Evaluation parameters to be considered for the adhesive systems were (a) immediate marginal adaptation (or gap formation) in tooth cavities, (b) free setting shrinkage-strain determined by the immediate marginal gap-width in a non-bonding Teflon cavity, and (c) their immediate shear bond-strengths to enamel and to dentin.
Methods: The maximum marginal gap-width and the opposing-width (if any) in the tooth cavities and in the Teflon cavities were measured immediately (3 min) after light-activation. The shear bond-strengths to enamel and to dentin were also measured at 3 min.
Results: For light-activated restorative materials during early setting (<3 min), application of Adper Prompt L-Pop exhibited generally superior marginal adaptation to most system adhesives. But there was no additional benefit from double application. The marginal-gaps in tooth cavities and the marginal-gaps in Teflon cavities were highly correlated (r=0.86–0.89, p<0.02–0.01). For enamel and dentin shear bond-strengths, there were no significant differences between single and double applications, for all materials tested except Toughwell and Z 250 with enamel.
Significance: Single application of a self-etch adhesive was a feasible and beneficial alternative to system adhesives for several classes of restorative. Marginal gap-widths in tooth cavities correlated more strongly with free shrinkage-strain magnitudes than with bond-strengths to tooth structure.</p
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