Simulation of Laser Ablation in Aluminum: The Effectivity of Double Pulses

Lasers are becoming a more and more important tool in cutting and shaping materials. Improving precision and effectivity is an ongoing demand in science and industry. One possibility are double pulses. Here we study laser ablation of aluminum by the two-temperature model. There the laser is modeled as a source in a continuum heat conduction equation for the electrons, whose temperature then is transferred to a molecular dynamics particle model by an electron-phonon coupling term. The melting and ablation effectivity is investigated depending on the relative intensity and the time delay between two Gaussian shaped laser pulses. It turns out that at least for aluminum the optimal pulse shapes are standard Gaussian pulses. For double pulses with delay times up to 200 ps we find a behavior as observed in experiment: the ablation depth decreases beyond a delay of 10 ps even if one does not account for the weakening at the second pulse due to laser-plasma interaction.Comment: 18 pages, 6 figure

Construct Validity, Test-Retest Reliability, and Internal Consistency of the Photo Elicitation Semantic Differential Scale (PESD) in Disability Studies

The Photo Elicitation Semantic Differential scale (PESD), developed to examine the social perception of disability and attitudes towards people with a disability (PwD), comprises six dimensions: communicativeness, competence, attractiveness, intelligence, industriousness, and popularity. This paper aims to assess the construct validity, test-retest reliability, and internal consistency of the PESD. A longitudinal study with 40 participants of the Swiss general population and 2 (test-retest) * 8 (different photographs) measurements per subject was performed. Construct validity was examined via Principal Component Analysis (PCA), test-retest reliability via the Intraclass Correlation Coefficient (ICC) and a frequency analysis of deviations among test-retest scores, and internal consistency via Cronbach's alpha. PCA extracted two factors corresponding to hard and soft skills for the test and a single factor for the retest. ICCs ranged from 0.44 (industriousness) to 0.60 (intelligence). Deviations between tests exceeding +/-1 were rather rare ranging from 6% (intelligence) to 14% (competence). Cronbach's alpha equalled 0.814 and 0.858 for test and retest, respectively. Summarising, in our study the PESD appears to be a valid and reliable tool for the examination of the social perception of disability and attitudes towards Pw

A Note on Ex-Ante Stable Lotteries

We study ex-ante priority respecting (ex-ante stable) lotteries in the context of object allocation under thick priorities. We show that ex-ante stability as a fairness condition is very demanding: Only few agent-object pairs have a positive probability of being matched in an ex-ante stable assignment. We interpret our result as an impossibility result. With ex-ante stability one cannot go much beyond randomly breaking ties and implementing a (deterministically) stable matching with respect to the broken ties

Bethe Ansatz solution of a decagonal rectangle triangle random tiling

A random tiling of rectangles and triangles displaying a decagonal phase is solved by Bethe Ansatz. Analogously to the solutions of the dodecagonal square triangle and the octagonal rectangle triangle tiling an exact expression for the maximum of the entropy is found.Comment: 17 pages, 4 figures, some remarks added and typos correcte

Predicting metapopulation responses to conservation in human-dominated landscapes

Loss of habitat to urbanization is a primary cause of population declines as human-dominated landscapes expand at increasing rates. Understanding how the relative effects of different conservation strategies is important to slow population declines for species in urban landscapes. We studied the wood thrush Hylocichla mustelina, a declining forest-breeding Neotropical migratory species, and umbrella species for forest-breeding songbirds, within the urbanized mid-Atlantic United States. We integrated 40 years of demographic data with contemporary metapopulation model simulations of breeding wood thrushes to predict population responses to differing conservation scenarios. We compared four conservation scenarios over a 30-year time period (2014-2044) representing (A) current observed state (Null), (B) replacing impervious surface with forest (Reforest), (C) reducing brown-headed cowbird Molothrus ater parasitism pressure (Cowbird removal), and (D) simultaneous reforesting and cowbird removal. Compared to the Null scenario, the Reforest scenario increased mean annual population trends by 54%, the Remove cowbirds scenario increased mean annual population trends by 38%, and the scenario combining reforestation and cowbird removal increased mean annual population trends by 98%. Mean annual growth rates (lambda) per site were greater in the Reforest (lambda = 0.94) and Remove cowbirds (lambda = 0.92) compared to the Null (lambda = 0.88) model scenarios. However, only by combining the positive effects of reforestation and cowbird removal did wood thrush populations stop declining (lambda = 1.00). Our results suggest that independently replacing impervious surface with forest habitat around forest patches and removing cowbirds may slow current negative population trends. Furthermore, conservation efforts that combine reforestation and cowbird removal may potentially benefit populations of wood thrushes and other similarly forest-breeding songbird species within urbanized fragmented landscapes that typify the mid-Atlantic United States

Formation rates of iron-acceptor pairs in crystalline silicon

The characteristic association time constant describing the formation of iron-acceptor pairs in crystalline silicon has been measured for samples of various p-type dopant concentrations and species (B, Ga, and In) near room temperature. The results show that the dopant species has no impact on the pairing kinetics, suggesting that the pairing process is entirely limited by iron diffusion. This conclusion was corroborated by measurement of the activation energy of pair formation, which coincides with the migration enthalpy of interstitial iron in silicon. The results also indicate that the pair-formation process occurs approximately twice as fast as predicted by a commonly used expression.This work has been supported by the Australian Research Council and the State of Lower Saxony