Dynamical mechanism of antifreeze proteins to prevent ice growth

The fascinating ability of algae, insects and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water/ice interface thus preventing complete solidification. We propose a new dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, AFP). The free energy density involves two fields: one for the ice phase with a low AFP concentration, and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments

Gender role characteristics and depression.

The current study investigates the relationship between aspects of gender role and differences in depression between men and women. Aspects of gender role investigated are instrumentality/expressivity, silencing the self, and private self-consciousness. It was hypothesized that these aspects of gender role orientation will significantly predict vulnerability/invulnerability to depression on a measure of depressive symptomatology. Specifically, it was hypothesized that individuals adopting a more expressive gender role are likely to show higher scores on private self-consciousness, silencing the self, and depression than individuals socialized into a more instrumental gender role. Additionally, the relationship between silencing the self behaviours and private self-consciousness was examined, as this relationship has not been investigated to date. Results supported a negative relationship between instrumentality and depression for men only. This relationship became nonsignificant when self-esteem was controlled. There was a negative relationship between instrumentality and silencing the self even after controlling for sex, suggesting that higher instrumentality is related to less self-silencing in either sex. Analysis of covariance reveals that silencing the self and private self-consciousness have a significant relation to depression when sex differences are analyzed for the influence of gender role characteristics. Further regression analyses indicate that silencing the self serves as a reliable predictor of depressive symptomatology. It is suggested that private self-consciousness may moderate sex differences in depression and have a link to silencing the self through the influence of self-reflectiveness.Dept. of Psychology. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1999 .T48. Source: Masters Abstracts International, Volume: 40-03, page: 0783. Adviser: Michael Kral. Thesis (M.A.)--University of Windsor (Canada), 1999

Understanding Student Computational Thinking with Computational Modeling

Recently, the National Research Council's framework for next generation science standards highlighted "computational thinking" as one of its "fundamental practices". 9th Grade students taking a physics course that employed the Modeling Instruction curriculum were taught to construct computational models of physical systems. Student computational thinking was assessed using a proctored programming assignment, written essay, and a series of think-aloud interviews, where the students produced and discussed a computational model of a baseball in motion via a high-level programming environment (VPython). Roughly a third of the students in the study were successful in completing the programming assignment. Student success on this assessment was tied to how students synthesized their knowledge of physics and computation. On the essay and interview assessments, students displayed unique views of the relationship between force and motion; those who spoke of this relationship in causal (rather than observational) terms tended to have more success in the programming exercise.Comment: preprint to submit to PERC proceedings 201

Ueber die Reduktion des Cineols

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Electron mobility in surface- and buried- channel flatband In_0.53Ga_0.47As MOSFETs with ALD Al₂O₃ gate dielectric.

In this paper, we investigate the scaling potential of flatband III-V MOSFETs by comparing the mobility of surface and buried In<sub>0.53</sub>Ga<sub>0.47</sub>As channel devices employing an Atomic Layer Deposited (ALD) Al<sub>2</sub>O<sub>3</sub> gate dielectric and a delta-doped InGaAs/InAlAs/InP heterostructure. Peak electron mobilities of 4300 cm<sup>2</sup>/V·s and 6600 cm<sup>2</sup>/V·s at a carrier density of 3×1012 cm<sup>-2</sup> for the surface and buried channel structures respectively were determined. In contrast to similarly scaled inversion-channel devices, we find that mobility in surface channel flatband structures does not drop rapidly with electron density, but rather high mobility is maintained up to carrier concentrations around 4x10<sup>12</sup> cm<sup>-2</sup> before slowly dropping to around 2000 cm<sup>2</sup>/V·s at 1x10M<sup>13</sup> cm<sup>-2</sup>. We believe these to be world leading metrics for this material system and an important development in informing the III-V MOSFET device architecture selection process for future low power, highly scaled CM

Survival-extinction phase transition in a bit-string population with mutation

A bit-string model for the evolution of a population of haploid organisms, subject to competition, reproduction with mutation and selection is studied, using mean field theory and Monte Carlo simulations. We show that, depending on environmental flexibility and genetic variability, the model exhibits a phase transtion between extinction and survival. The mean-field theory describes the infinite-size limit, while simulations are used to study quasi-stationary properties.Comment: 11 pages, 5 figure

The influence of water-conservation messages on reducing household water use

As water crises become severe, the desire to explore alternative strategies that focus on the demand-side of water-conservation increase. Changing behaviour through persuasion (message framing) can be an integral part of providing water demand solutions. In this study, we examined the effectiveness of messages related to household water use on water scarcity and intentions to act. We tested whether relationships between communication and water conservation were mediated via increasing capability, opportunity, and motivation behaviour (COM-B dimensions). We applied two message types related to concern about severe water scarcity and conservation strategies to the behaviour change conditions in two combinations: (1) severe water scarcity and water-saving tips/strategies, and (2) severe water scarcity and no water-saving tips/strategies. There was broad support for the hypothesis that COM-B dimensions would mediate the effect of message type on water scarcity concern and intentions to act in conservation activities. Households that received the message framed in terms of water-saving tips/strategies expressed greater water scarcity concern and higher intention to act than those that received the no water-saving tips/strategies message. Mediation analyses showed that the message framed in terms of specific water-saving tips/strategies was mediated by increasing households' capacity (self-efficacy), opportunity and/or motivation in water-conservation actions. Thus, specific water-conservation strategies made available to households have a stronger impact on water-conservation behaviour because these messages appeal to behavioural change conditions

Resolution of Joint Molecules by RuvABC and RecG Following Cleavage of the Escherichia coli Chromosome by EcoKI

DNA double-strand breaks can be repaired by homologous recombination involving the formation and resolution of Holliday junctions. In Escherichia coli, the RuvABC resolvasome and the RecG branch-migration enzyme have been proposed to act in alternative pathways for the resolution of Holliday junctions. Here, we have studied the requirements for RuvABC and RecG in DNA double-strand break repair after cleavage of the E. coli chromosome by the EcoKI restriction enzyme. We show an asymmetry in the ability of RuvABC and RecG to deal with joint molecules in vivo. We detect linear DNA products compatible with the cleavage-ligation of Holliday junctions by the RuvABC pathway but not by the RecG pathway. Nevertheless we show that the XerCD-mediated pathway of chromosome dimer resolution is required for survival regardless of whether the RuvABC or the RecG pathway is active, suggesting that crossing-over is a common outcome irrespective of the pathway utilised. This poses a problem. How can cells resolve joint molecules, such as Holliday junctions, to generate crossover products without cleavage-ligation? We suggest that the mechanism of bacterial DNA replication provides an answer to this question and that RecG can facilitate replication through Holliday junctions

Strategies for the evolution of sex

We find that the hypothesis made by Jan, Stauffer and Moseley [Theory in Biosc., 119, 166 (2000)] for the evolution of sex, namely a strategy devised to escape extinction due to too many deleterious mutations, is sufficient but not necessary for the successful evolution of a steady state population of sexual individuals within a finite population. Simply allowing for a finite probability for conversion to sex in each generation also gives rise to a stable sexual population, in the presence of an upper limit on the number of deleterious mutations per individual. For large values of this probability, we find a phase transition to an intermittent, multi-stable regime. On the other hand, in the limit of extremely slow drive, another transition takes place to a different steady state distribution, with fewer deleterious mutations within the asexual population.Comment: RevTeX, 11 pages, multicolumn, including 12 figure