3,310 research outputs found
Sampling atmospheric sea-salt nuclei over the ocean
Atmospheric hygroscopic nuclei are of primary interest to meteorologists in studies of haze, fog, clouds, etc. (Simpson, 1941; Middleton, 1941; Sheppard, 1947). The sea surface is presumed to be an important source of these nuclei in the form of drops of concentrated sea water arising from spray
Relationships between giant sea salt particles and clouds inferred from aircraft physicochemical data
Cumulative and Differential Effects of Early Child Care and Middle Childhood Out-of-School Time on Adolescent Functioning.
Effects associated with early child care and out-of-school time (OST) during middle childhood were examined in a large sample of U.S. adolescents (N = 958). Both higher quality early child care AND more epochs of organized activities (afterschool programs and extracurricular activities) during middle childhood were linked to higher academic achievement at age 15. Differential associations were found in the behavioral domain. Higher quality early child care was associated with fewer externalizing problems, whereas more hours of early child care was linked to greater impulsivity. More epochs of organized activities was associated with greater social confidence. Relations between early child care and adolescent outcomes were not mediated or moderated by OST arrangements in middle childhood, consistent with independent, additive relations of these nonfamilial settings
Equilibrium Simulation of the Slip Coefficient in Nanoscale Pores
Accurate prediction of interfacial slip in nanoscale channels is required by
many microfluidic applications. Existing hydrodynamic solutions based on
Maxwellian boundary conditions include an empirical parameter that depends on
material properties and pore dimensions. This paper presents a derivation of a
new expression for the slip coefficient that is not based on the assumptions
concerning the details of solid-fluid collisions and whose parameters are
obtainable from \textit{equilibrium} simulation. The results for the slip
coefficient and flow rates are in good agreement with non-equilibrium molecular
dynamics simulation.Comment: 11 pages, 4 figures, submitted to Phys Rev Let
Testing refinements by refining tests
One of the potential benefits of formal methods is that they offer the possibility of reducing the costs of testing. A specification acts as both the benchmark against which any implementation is tested, and also as the means by which tests are generated. There has therefore been interest in developing test generation techniques from formal specifications, and a number of different methods have been derived for state based languages such as Z, B and VDM. However, in addition to deriving tests from a formal specification, we might wish to refine the specification further before its implementation. The purpose of this paper is to explore the relationship between testing and refinement. As our model for test generation we use a DNF partition analysis for operations written in Z, which produces a number of disjoint test cases for each operation. In this paper we discuss how the partition analysis of an operation alters upon refinement, and we develop techniques that allow us to refine abstract tests in order to generate test cases for a refinement. To do so we use (and extend existing) methods for calculating the weakest data refinement of a specification
Velocity Statistics in the Two-Dimensional Granular Turbulence
We studied the macroscopic statistical properties on the freely evolving
quasi-elastic hard disk (granular) system by performing a large-scale (up to a
few million particles) event-driven molecular dynamics systematically and found
that remarkably analogous to an enstrophy cascade process in the decaying
two-dimensional fluid turbulence. There are four typical stages in the freely
evolving inelastic hard disk system, which are homogeneous, shearing (vortex),
clustering and final state. In the shearing stage, the self-organized
macroscopic coherent vortices become dominant. In the clustering stage, the
energy spectra are close to the expectation of Kraichnan-Batchelor theory and
the squared two-particle separation strictly obeys Richardson law.Comment: 4 pages, 4 figures, to be published in PR
Measuring the flow properties of small powder samples using an avalanche tester
The feasibility of using a small-scale avalanche tester to measure the flow properties of pharmaceutical lactose powders was examined. The modes of behaviour observed in larger systems were displayed and showed a clear distinction between angular, free-flowing particles and more spherical particles of similar flow characteristics. Angular Lactohale LH100 particles showed slumping behaviour at a rotational frequency of 0.33Hz which disappeared at higher frequencies. Spherical lactose powder with a similar flow function to LH100 only showed rolling behaviour under the same conditions, as did more cohesive powders LH200 and LH300. Further investigation of the LH100 data using Fast Fourier analysis showed that the slumping frequency was 1/10th of the rotational frequency
Impact of flood disasters on Taiwan in the last quarter century
Copyright © Springer 2006. The final publication is available at Springer via http://dx.doi.org/10.1007/s11069-005-4667-7The increasing natural disasters, especially floods during the last quarter century, are raising the economic losses in Taiwan. The most severe hazard in Taiwan is flooding induced by typhoons and storms in summer and autumn. By comparing the rivers around the world, the ones in Taiwan have the steepest slopes, the largest discharge per unit drainage area, and the shortest time of concentrations. Rapid urbanization without proper land uses managements usually worsen the flood problems. Consequently, flood hazards mitigation has become the most essential task for Taiwan to deal with. Although the government keeps improving flood defense structures, the flood damage grows continuously. In this article, possible flood mitigation strategies are identified for coping with complex environmental and social decisions with flood risk involved.National Science and Technology Center
for Disaster ReductionNational Science Council, RO
Entropic Origin of the Growth of Relaxation Times in Simple Glassy Liquids
Transitions between ``glassy'' local minima of a model free-energy functional
for a dense hard-sphere system are studied numerically using a
``microcanonical'' Monte Carlo method that enables us to obtain the transition
probability as a function of the free energy and the Monte Carlo ``time''. The
growth of the height of the effective free energy barrier with density is found
to be consistent with a Vogel-Fulcher law. The dependence of the transition
probability on time indicates that this growth is primarily due to entropic
effects arising from the difficulty of finding low-free-energy saddle points
connecting glassy minima.Comment: Four pages, plus three postscript figure
Time Scales for transitions between free energy minima of a hard sphere system
Time scales associated with activated transitions between glassy metastable
states of a free energy functional appropriate for a dense hard sphere system
are calculated by using a new Monte Carlo method for the local density
variables. We calculate the time the system,initially placed in a shallow
glassy minimum of the free energy, spends in the neighborhood of this minimum
before making a transition to the basin of attarction of another free energy
minimum. This time scale is found to increase with the average density. We find
a crossover density near which this time scale increases very sharply and
becomes longer than the longest times accessible in our simulation. This scale
shows no evidence of dependence on sample size.Comment: 25 pages, Revtex, 6 postscript figures. Will appear in Phys Rev E,
March 1996 or s
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