937 research outputs found
ARPES Study of X-Point Band Overlaps in LaB and SmB - Contrast to SrB and EuB
In contrast to our recent finding of an X-point band gap in divalent
hexaborides, we report here that angle resolved photoemission spectroscopy
(ARPES) data shows that the gap is absent for trivalent LaB and is absent
or nearly so for mixed valent SmB. This finding demonstrates a nontrivial
evolution of the band structure from divalent to trivalent hexaborides.Comment: submitted to SCES '0
The Random-bond Potts model in the large-q limit
We study the critical behavior of the q-state Potts model with random
ferromagnetic couplings. Working with the cluster representation the partition
sum of the model in the large-q limit is dominated by a single graph, the
fractal properties of which are related to the critical singularities of the
random Potts model. The optimization problem of finding the dominant graph, is
studied on the square lattice by simulated annealing and by a combinatorial
algorithm. Critical exponents of the magnetization and the correlation length
are estimated and conformal predictions are compared with numerical results.Comment: 7 pages, 6 figure
Current reversal with type-I intermittency in deterministic inertia ratchets
The intermittency is investigated when the current reversal occurs in a
deterministic inertia ratchet system. To determine which type the intermittency
belongs to, we obtain the return map of velocities of particle using
stroboscopic recording, and numerically calculate the distribution of average
laminar length . The distribution follows the scaling law of , the characteristic relation of type-I
intermittency.Comment: 4 pages, 7 figure
Mathematical results for some models of turbulence with critical and subcritical regularizations
In this paper, we establish the existence of a unique "regular" weak solution
to turbulent flows governed by a general family of models with
critical regularizations. In particular this family contains the simplified
Bardina model and the modified Leray- model. When the regularizations
are subcritical, we prove the existence of weak solutions and we establish an
upper bound on the Hausdorff dimension of the time singular set of those weak
solutions. The result is an interpolation between the bound proved by Scheffer
for the Navier-Stokes equations and the regularity result in the critical case
Targeting Conservation Investments in Heterogeneous Landscapes: A distance function approach and application to watershed management
To achieve a given level of an environmental amenity at least cost, decision-makers must integrate information about spatially variable biophysical and economic conditions. Although the biophysical attributes that contribute to supplying an environmental amenity are often known, the way in which these attributes interact to produce the amenity is often unknown. Given the difficulty in converting multiple attributes into a unidimensional physical measure of an environmental amenity (e.g., habitat quality), analyses in the academic literature tend to use a single biophysical attribute as a proxy for the environmental amenity (e.g., species richness). A narrow focus on a single attribute, however, fails to consider the full range of biophysical attributes that are critical to the supply of an environmental amenity. Drawing on the production efficiency literature, we introduce an alternative conservation targeting approach that relies on distance functions to cost-efficiently allocate conservation funds across a spatially heterogeneous landscape. An approach based on distance functions has the advantage of not requiring a parametric specification of the amenity function (or cost function), but rather only requiring that the decision-maker identify important biophysical and economic attributes. We apply the distance-function approach empirically to an increasingly common, but little studied, conservation initiative: conservation contracting for water quality objectives. The contract portfolios derived from the distance-function application have many desirable properties, including intuitive appeal, robust performance across plausible parametric amenity measures, and the generation of ranking measures that can be easily used by field practitioners in complex decision-making environments that cannot be completely modeled. Working Paper # 2002-01
Women are more likely than men to blame structural factors for women's political under-representation: evidence from 27 countries
Over time, gender and politics research has made progress in identifying those factors that result in low numbers of women in political institutions and in making evidence-informed suggestions about how to ameliorate them. These factors include discrimination in party recruitment processes, male-dominated political culture and broader gender inequalities in society. In contrast, little is known about public opinion regarding these drivers of women's political under-representation, especially whether to who or what women assign blame for the under-representation of women in politics differs from men. This article provides the first discussion and analysis of blame assignment for women's numeric under-representation in politics. In doing so, it outlines and operationalises a framework that distinguishes between meritocratic explanations of women's under-representation, whereby the blame for women not holding political office in greater numbers is assigned to women themselves, and structural explanations, whereby social forces external to women are seen to result in their numeric under-representation. Cross-national data from 27 European countries is used to show that women are significantly more likely than men to assign blame for women's numeric under-representation to structural factors. The hierarchical nature of the dataset is exploited using multilevel models and significant differences in levels of structural blame assignment between countries is found as well as between-country variation in the probability of women assigning blame to structural explanations for women's under-representation. Finally, the category of structural explanations is disaggregated in order to assess their relative prominence and to provide strong corroborative evidence that women predominantly assign blame for women's under-representation to political culture over other structural blame factors. The article concludes with a discussion of the implications of the study's findings for policy makers contemplating the pursuit of gender equality policies aimed at increasing women's political representation and makes suggestions for the direction of future research in this area.</p
Evidence for softening of first-order transition in 3D by quenched disorder
We study by extensive Monte Carlo simulations the effect of random bond
dilution on the phase transition of the three-dimensional 4-state Potts model
which is known to exhibit a strong first-order transition in the pure case. The
phase diagram in the dilution-temperature plane is determined from the peaks of
the susceptibility for sufficiently large system sizes. In the strongly
disordered regime, numerical evidence for softening to a second-order
transition induced by randomness is given. Here a large-scale finite-size
scaling analysis, made difficult due to strong crossover effects presumably
caused by the percolation fixed point, is performed.Comment: LaTeX file with Revtex, 4 pages, 4 eps figure
Organic nitrate aerosol formation via NOÂł + biogenic volatile organic compounds in the southeastern United States
Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that a nitrate radical (NOâ) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NOâ to terpenes are correlated with increase in gasand aerosol-organic nitrate concentrations made during the campaign. Correlation of NOâ radical consumption to organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield of aerosol-phase monoterpene nitrates of 23â44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to BVOCs and show CââHââNOâ
, likely a hydroperoxy nitrate, is a major nitrate-oxidized terpene product being incorporated into aerosols. The comparable isoprene product Câ
HâNOâ
was observed to contribute less than 1% of the total organic nitrate in the aerosol phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45% of the NOy budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNOâ uptake produced nitrate aerosol mass loading at a rate comparable to that of organic nitrate produced via NOâ CBVOCs
Domain growth and aging scaling in coarsening disordered systems
Using extensive Monte Carlo simulations we study aging properties of two
disordered systems quenched below their critical point, namely the
two-dimensional random-bond Ising model and the three-dimensional
Edwards-Anderson Ising spin glass with a bimodal distribution of the coupling
constants. We study the two-times autocorrelation and space-time correlation
functions and show that in both systems a simple aging scenario prevails in
terms of the scaling variable , where is the time-dependent
correlation length, whereas is the waiting time and is the observation
time. The investigation of the space-time correlation function for the
random-bond Ising model allows us to address some issues related to
superuniversality.Comment: 8 pages, 9 figures, to appear in European Physical Journal
Accessing the soot-related radiative heat feedback in a flame spreading in microgravity: optical designs and associated limitations
Novel, high-fidelity results related to soot from microgravity flames were obtained by an international topical team on fire safety in space. More specifically, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed. The configuration used a non-buoyant axisymmetric flame propagating in an opposed laminar stream overa Low Density PolyEthylene coating of an electrical wire. Within this context, both the standard Broadband Two Color Pyrometry (B2CP) and its recent extension Broadband Modulated Absorption/Emission (BMAE) technique can be deployed to measure the spatial distribution of soot temperature and volume fraction within the flame. Both fields are then processed to establish the field of local radiative balance attributed to soot within the flame, and ultimately the soot contribution to the radiative flux to the wire. The present study first assesses the consistency of the methodology contrasting an experimental frame and a synthetic one, the latter being produced by a signal modeling that processes fields delivered by a numerical simulation of the configuration as inputs. Using the synthetic signals obtained, the fields of local radiative balance within the flame are then computed and significant discrepancies were disclosed locally between the fields originating from the synthetic BMAE and B2CP inputs. Nevertheless, the subsequent evaluation of the soot-related radiative heat feedback to the wire shows that a weak deviation among the techniques implemented is expected. This finding is corroborated by similar evaluations conducted with experimental BMAE and B2CP measurements obtained in parabolic flights. As BMAE is implemented in an ISS configuration within the SCEM rig, BMAE and B2CP will soon provide long-duration soot observations in microgravity. In order to contrast the upcoming results, this current study quantifies discrepancies originating from the post-processing regarding soot temperature and volume fraction, and shows that the radiative feedback evaluation from both methods should be consistent
- âŠ