5,921 research outputs found
The Construction of Verification Models for Embedded Systems
The usefulness of verification hinges on the quality of the verification model. Verification is useful if it increases our confidence that an artefact bahaves as expected. As modelling inherently contains non-formal elements, the qualityof models cannot be captured by purely formal means. Still, we argue that modelling is not an act of irrationalism and unpredictable geniality, but follows rational arguments, that often remain implicit. In this paper we try to identify the tacit rationalism in the model construction as performed by most people doing modelling for verification. By explicating the different phases, arguments, and design decisions in the model construction, we try to develop guidelines that help to improve the process of model construction and the quality of models
Enhancement of perfluorooctanoate and perfluorooctanesulfonate activity at acoustic cavitation bubble interfaces
Acoustic cavitation driven by ultrasonic irradiation decomposes and mineralizes the recalcitrant perfluorinated surfactants perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Pyrolytic cleavage of the ionic headgroup is the rate-determining step. In this study, we examine the sonochemical adsorption of PFOX, where X = S for PFOS and A for PFOA, by determining kinetic order and absolute rates over an initial PFOX concentration range of 20 nM to 200 μM. Sonochemical PFOX kinetics transition from pseudo-first-order at low initial concentrations, [PFOX]_i 40 μM, as the bubble interface sites are saturated. At PFOX concentrations below 100 μM, concentration-dependent rates were modeled with Langmuir−Hinshelwood (LH) kinetics. Empirically determined rate maximums, V_(Max)^(−PFOA) = 2230 ± 560 nM min^−1 and V_(Max)^(−PFOS) = 230 ± 60 nM min^−1, were used in the LH model, and sonochemical surface activities were estimated to be K_(Sono)^(PFOS) = 120000 M^−1 and K_(Sono)^(PFOA) = 28500 M^−1, 60 and 80 times greater than equilibrium surface activities, K_(Eq)^(PFOS) and K_(Eq)^(PFOA). These results suggest enhanced sonochemical degradation rates for PFOX when the bubble interface is undersaturated. The present results are compared to previously reported sonochemical kinetics of nonvolatile surfactants
A direct optical method for the study of grain boundary melting
The structure and evolution of grain boundaries underlies the nature of
polycrystalline materials. Here we describe an experimental apparatus and light
reflection technique for measuring disorder at grain boundaries in optically
clear material, in thermodynamic equilibrium. The approach is demonstrated on
ice bicrystals. Crystallographic orientation is measured for each ice sample.
The type and concentration of impurity in the liquid can be controlled and the
temperature can be continuously recorded and controlled over a range near the
melting point. The general methodology is appropriate for a wide variety of
materials.Comment: 8 pages, 8 figures, updated with minor changes made to published
versio
Abrupt grain boundary melting in ice
The effect of impurities on the grain boundary melting of ice is investigated
through an extension of Derjaguin-Landau-Verwey-Overbeek theory, in which we
include retarded potential effects in a calculation of the full frequency
dependent van der Waals and Coulombic interactions within a grain boundary. At
high dopant concentrations the classical solutal effect dominates the melting
behavior. However, depending on the amount of impurity and the surface charge
density, as temperature decreases, the attractive tail of the dispersion force
interaction begins to compete effectively with the repulsive screened Coulomb
interaction. This leads to a film-thickness/temperature curve that changes
depending on the relative strengths of these interactions and exhibits a
decrease in the film thickness with increasing impurity level. More striking is
the fact that at very large film thicknesses, the repulsive Coulomb interaction
can be effectively screened leading to an abrupt reduction to zero film
thickness.Comment: 8 pages, 1 figur
Dynamics of explosive degassing of magma: Observations of fragmenting two-phase flows
Liquid explosions, generated by rapid degassing of strongly supersaturated liquids, have been investigated in the laboratory with a view to understanding the basic physical processes operating during bubble nucleation and growth and the subsequent behavior of the expanding two-phase flow. Experiments are carried out in a shock tube and are monitored by high-speed photography and pressure transducers. Theoretical CO_2 supersaturations up to 455 times the ambient saturation concentration are generated by a chemical reaction; K_2CO_3 solution is suddenly injected into an excess of HCl solution in such a way as to mix the two solutions rapidly. Immediately after the injection event, a bubble nucleation delay of a few milliseconds is followed by rapid nucleation and explosive expansion of CO_2 bubbles forming a highly heterogeneous foam. Enhanced diffusion due to advection in the flow coupled with continuous mixing of the reactants, and hence on-going bubble nucleation after injection, generates an increasingly accelerating flow until the reactants become depleted at peak accelerations of around 150 g and velocities of about 15 m s^(−1). Stretching of the accelerating two-phase mixture enhances the mixing. Liberation of CO_2 vapor is spatially inhomogeneous leading to ductile fragmentation occurring throughout the flow in regions of greatest gas release as the consequence of the collision and stretching of fluid streams. The violence of the eruptions is controlled by using different concentrations of the HCl and K_2CO_3 solutions, which alters the CO_2 supersaturation and yield and also the efficiency of the mixing process. Peak acceleration is proportional to theoretical supersaturation. Pressure measurements at the base of the shock tube show an initial nucleation delay and a pressure pulse related to the onset of explosive bubble formation. These chemically induced explosions differ from liquid explosions created in other experiments. In explosions caused by sudden depressurization of CO_2-saturated water, the bubbles nucleate uniformly throughout the liquid in a single nucleation event. Subsequent bubble growth causes the two-phase mixture to be accelerated upward at nearly constant accelerations. Explosively boiling liquids, in which heterogeneous nucleation is suppressed, experience an evaporation wave which propagates down into the liquid column at constant average velocity. Fragmentation occurs at the sharply defined leading edge of the wavefront. The chemical flows effectively simulate highly explosive volcanic eruptions as they are comparable in terms of flow densities, velocities, accelerations, and in the large range of scales present. The large accelerations cause strong extensional strain and longitudinal deformation. Comparable deformation rates in volcanic systems could be sufficient to approach conditions for brittle fragmentation. Tube pumice is a major component of plinian deposits and ignimbrites and preserves evidence of accelerating flow conditions
How political are national identities? A comparison of the United States, the United Kingdom, and Germany in the 2010s
This is the final version of the article. Available from SAGE Publications via the DOI in this record.Original data supporting this research are available from the UK Data Archive (Study Number 851142): http://dx.doi.org/10.5255/UKDA-SN-851142/Research demonstrates the multi-dimensional nature of American identity arguing that the normative content of American identity relates to political ideologies in the United States, but the sense of belonging to the nation does not. This paper replicates that analysis and extends it to the German and British cases. Exploratory structural equation modeling attests to cross-cultural validity of measures of the sense of belonging and norms of uncritical loyalty and engagement for positive change. In the 2010s, we find partisanship and ideology in all three nations explains levels of belonging and the two content dimensions. Interestingly, those identifying with major parties of the left and right in all three countries have a higher sense of belonging and uncritical loyalty than their moderate counterparts. The relationship between partisanship, ideology, and national identity seems to wax and wane over time, presumably because elite political discourse linking party or ideology to identity varies from one political moment to the next.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Data collection was funded by a grant from the Economic and Social Research Council of the United Kingdom (RES-061-25-0405)
Surface Transitions for Confined Associating Mixtures
Thin films of binary mixtures that interact through isotropic forces and
directionally specific "hydrogen bonding" are considered through Monte Carlo
simulations. We show, in good agreement with experiment, that the single phase
of these mixtures can be stabilized or destabilized on confinement. These
results resolve a long standing controversy, since previous theories suggest
that confinement only stabilizes the single phase of fluid mixtures.Comment: LaTeX document, documentstyle[aps,preprint]{revtex}, psfig.sty,
bibtex, 13 pages, 4 figure
NATO and CSDP: party and public positioning in Germany and France
This is the final version. Available on open access from the NATO Defense College via the link in this recordVolkswagen Foundatio
The Dipole Anisotropy of the 2mass Redshift Survey
We estimate the flux weighted acceleration on the Local Group (LG) from the
near-infrared Two Micron All Sky Redshift Survey (2MRS). The near-infrared flux
weighted dipoles are very robust because they closely approximate a mass
weighted dipole, bypassing the effects of redshift distortions and require no
preferred reference frame. We use this method with the redshift information to
determine the change in dipole with distance. The LG dipole seemingly converges
by 60 Mpc/h. Assuming convergence, the comparison of the 2MRS flux dipole and
the CMB dipole provides a value for the combination of the mass density and
luminosity bias parameters Omega_m^0.6/b_L= 0.40+/-0.09.Comment: 4 pages, 2 figures, Contribution to Rencontres de Moriond: Contents
and Structures of the Universe, March 18-25, 2006, La Thuil
Generalized Interpolation Material Point Approach to High Melting Explosive with Cavities Under Shock
Criterion for contacting is critically important for the Generalized
Interpolation Material Point(GIMP) method. We present an improved criterion by
adding a switching function. With the method dynamical response of high melting
explosive(HMX) with cavities under shock is investigated. The physical model
used in the present work is an elastic-to-plastic and thermal-dynamical model
with Mie-Gr\"uneissen equation of state. We mainly concern the influence of
various parameters, including the impacting velocity , cavity size , etc,
to the dynamical and thermodynamical behaviors of the material. For the
colliding of two bodies with a cavity in each, a secondary impacting is
observed. Correspondingly, the separation distance of the two bodies has a
maximum value in between the initial and second impacts. When the
initial impacting velocity is not large enough, the cavity collapses in a
nearly symmetric fashion, the maximum separation distance increases
with . When the initial shock wave is strong enough to collapse the cavity
asymmetrically along the shock direction, the variation of with
does not show monotonic behavior. Our numerical results show clear indication
that the existence of cavities in explosive helps the creation of ``hot
spots''.Comment: Figs.2,4,7,11 in JPG format; Accepted for publication in J. Phys. D:
Applied Physic
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