Scaling forces to asteroid surfaces: The role of cohesion

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.Comment: 54 pages, 7 figure

Microwave Remote Sensing of Ocean Surface Wind Speed and Rain Rates over Tropical Storms

The value of using narrowly spaced frequencies within a microwave band to measure wind speeds and rain rates over tropical storms with radiometers is reviewed. The technique focuses on results obtained in the overflights of Hurricane Allen during 5 and 8 of August, 1980

Time-Resolved X-Ray Diffraction Investigation of Superheating-Melting of Crystals under Ultrafast Heating

The maximum superheating of a solid prior to melting depends on the effective dimensionless nucleation energy barrier, heterogeneities such as free surfaces and defects, and heating rates. Superheating is rarely achieved with conventional slow heating due to the dominant effect of heterogeneous nucleation. In present work, we investigate the superheating-melting behavior of crystals utilizing ultrafast heating techniques such as exploding wire and laser irradiation, and diagnostics such as time-resolved X-ray diffraction combined with simultaneous measurements on voltage and current (for exploding wire) and particle velocity (for laser irradiation). Experimental designs and preliminary results are presented

On the Properties of Plastic Ablators in Laser-Driven Material Dynamics Experiments

Radiation hydrodynamics simulations were used to study the effect of plastic ablators in laser-driven shock experiments. The sensitivity to composition and equation of state was found to be 5-10% in ablation pressure. As was found for metals, a laser pulse of constant irradiance gave a pressure history which decreased by several percent per nanosecond. The pressure history could be made more constant by adjusting the irradiance history. The impedance mismatch with the sample gave an increase o(100%) in the pressure transmitted into the sample, for a reduction of several tens of percent in the duration of the peak load applied to the sample, and structured the release history by adding a release step to a pressure close to the ablation pressure. Algebraic relations were found between the laser pulse duration, the ablator thickness, and the duration of the peak pressure applied to the sample, involving quantities calculated from the equations of state of the ablator and sample using shock dynamics.Comment: Typos fixe

Domain Coarsening in Systems Far from Equilibrium

The growth of domains of stripes evolving from random initial conditions is studied in numerical simulations of models of systems far from equilibrium such as Rayleigh-Benard convection. The scaling of the size of the domains deduced from the inverse width of the Fourier spectrum is studied for both potential and nonpotential models. The morphology of the domains and the defect structures are however quite different in the two cases, and evidence is presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende

Perceived age discrimination across age in Europe: from an ageing society to a society for all ages

Ageism is recognized as a significant obstacle to older people's well-being, but age discrimination against younger people has attracted less attention. We investigate levels of perceived age discrimination across early to late adulthood, using data from the European Social Survey (ESS), collected in 29 countries (N = 56,272). We test for approximate measurement invariance across countries. We use local structural equation modeling as well as moderated nonlinear factor analysis to test for measurement invariance across age as a continuous variable. Using models that account for the moderate degree of noninvariance, we find that younger people report experiencing the highest levels of age discrimination. We also find that national context substantially affects levels of ageism experienced among older respondents. The evidence highlights that more research is needed to address ageism in youth and across the life span, not just old adulthood. It also highlights the need to consider factors that differently contribute to forms of ageism experienced by people at different life stages and ages.info:eu-repo/semantics/acceptedVersio

Phase Changes in Ni-Ti Under Laser Shock Loading

Near-equiatomic Ni-Ti, known for its shape memory behavior, can decompose to martensitic phases and/or second phase compounds. This phase competition is investigated in NixTi100-x (494Ti3 but no martensite in the AQ state, consistent with resistivity and dilatometry results which showed no hysteresis indicative of first order phase changes over 1.9 K4Ti3 amounts (present in the AQ state) did change upon loading, indicating the importance of shock-induced heating. A thermodynamically complete equation of state (EOS) for NiTi in its B2 (CsCl) structure was generated by ab initio quantum mechanical calculations. This was tested by performing laser-launched flyer experiments, which showed consistency with the theoretical EOS, validating its use in the prediction of dynamic loading histories in the samples during direct drive loading

Subjective social status of older people across countries: the role of modernization and employment

Objectives. To test and expand upon modernization theory's account of subjective social status (SSS) of older people in society. It was hypothesized that perceptions of older people's social status should be higher in more modernized countries and that the proportion of older people in employment should moderate the relationship between modernization and SSS of older people. Methods. Data were from the "Experiences and Expressions of Ageism" module in the fourth round of the European Social Survey. The sample analyzed included 45,706 individuals from 25 countries in the European region. Multilevel modeling was used to test the hypotheses. Results. The SSS of older people (aged 70 years and older) was perceived to be higher in countries with very high levels of modernization and in countries with a higher proportion of older people in employment. The positive association between modernization and SSS of older people was stronger within countries with a lower proportion of older people in employment. Discussion. The proportion of older people who are employed is an important factor that is related to perceptions of the social status of older people in less modern societies. The individual and societal implications are discussed, specifically in relation to policies promoting active aging.info:eu-repo/semantics/acceptedVersio