Application of computer techniques to some problems in linear viscoelasticity

Computer solutions in terms of molecular theories of linear viscoelasticit

Inhibition of DNA ejection from bacteriophage by Mg+2 counterions

The problem of inhibiting viral DNA ejection from bacteriophages by multivalent counterions, specifically Mg$^{+2}$ counterions, is studied. Experimentally, it is known that MgSO$_4$ salt has a strong and non-monotonic effect on the amount of DNA ejected. There exists an optimal concentration at which the minimum amount of DNA is ejected from the virus. At lower or higher concentrations, more DNA is ejected from the capsid. We propose that this phenomenon is the result of DNA overcharging by Mg$^{+2}$ multivalent counterions. As Mg$^{+2}$ concentration increases from zero, the net charge of DNA changes from negative to positive. The optimal inhibition corresponds to the Mg$^{+2}$ concentration where DNA is neutral. At lower/higher concentrations, DNA genome is charged. It prefers to be in solution to lower its electrostatic self-energy, which consequently leads to an increase in DNA ejection. By fitting our theory to available experimental data, the strength of DNA$-$DNA short range attraction energies, mediated by Mg$^{+2}$, is found to be $-$0.004 $k_BT$ per nucleotide base. This and other fitted parameters agree well with known values from other experiments and computer simulations. The parameters are also in aggreement qualitatively with values for tri- and tetra-valent counterions.Comment: 17 pages, 4 figures, improved manuscript. Submitted to J. Chem. Phys (2010

Calcium-Rich Gap Transients: Tidal Detonations of White Dwarfs?

We hypothesize that at least some of the recently discovered class of calcium-rich gap transients are tidal detonation events of white dwarfs (WDs) by black holes (BHs) or possibly neutron stars. We show that the properties of the calcium-rich gap transients agree well with the predictions of the tidal detonation model. Under the predictions of this model, we use a follow-up X-ray observation of one of these transients, SN 2012hn, to place weak upper limits on the detonator mass of this system that include all intermediate-mass BHs (IMBHs). As these transients are preferentially in the stellar haloes of galaxies, we discuss the possibility that these transients are tidal detonations of WDs caused by random flyby encounters with IMBHs in dwarf galaxies or globular clusters. This possibility has been already suggested in the literature but without connection to the calcium-rich gap transients. In order for the random flyby cross-section to be high enough, these events would have to be occurring inside these dense stellar associations. However, there is a lack of evidence for IMBHs in these systems, and recent observations have ruled out all but the very faintest dwarf galaxies and globular clusters for a few of these transients. Another possibility is that these are tidal detonations caused by three-body interactions, where a WD is perturbed toward the detonator in isolated multiple star systems. We highlight a number of ways this could occur, even in lower-mass systems with stellar-mass BHs or neutron stars. Finally, we outline several new observational tests of this scenario, which are feasible with current instrumentation.Comment: 10 pages, 1 figure, accepted for publication in MNRA

Weathering Behavior of Dimensionally Stabilized Wood Treated by Heating Under Pressure of Nitrogen Gas

With the goal of improving the weathering behavior of wood by reducing its hygroscopicity and accompanying dimensional changes, samples of spruce and beech were heat-treated under nitrogen pressure at 175 to 195 C and subjected to natural and artificial weathering. Beech had a significantly lower hygroscopicity and improved dimensional stability after heat treatment and was more resistant to weathering than the unheated control. Although the hygroscopicity of spruce was also significantly reduced by heat treatment, weathering resistance was diminished. Heat treatment of either species had small, but measurable effects on the performance and durability of semitransparent and film-forming stains applied to the samples

Anmerkungen zum Monopson am Arbeitsmarkt: Der Zeithorizont macht den Unterschied

Ob die Marktform des Monopsons am Arbeitsmarkt vorliegt, ist fur die Frage des Für oder Wider des Mindestlohns von essentieller Bedeutung. Denn in der kurzfristigen Analyse kann, insofern monopsonistische beziehungsweise oligopsonistische Strukturen am Arbeitsmarkt nachgewiesen werden, die Einführung eines Mindestlohns nicht nur zu einer exogenen Lohnerhöhung für die bisher angestellten Arbeitnehmer, sondern auch zu einem positiven Beschäftigungseffekt führen. Wählt man jedoch eine Modellierung jenseits einer kurzfristigen Betrachtung und nimmt fur die mittlere Frist den Faktor Kapital als variabel an, dann gilt fur den Unternehmer mit Marktmacht am Arbeitsmarkt genau dasselbe, was auch fur alle anderen Unternehmer ohne Marktmacht am Arbeitsmarkt gilt: Eine exogene Verteuerung des Faktors Arbeit - wie die Einfuhrung eines Mindestlohns - führt zu einer Substitution von Arbeit durch Kapital. Dieses Ergebnis scheint insbesondere vor dem Hintergrund der politischen Diskussion rund um den Mindestlohn und für die Einordnung der Ergebnisse des oft zitierten Beitrages von Card und Krueger (1994) von Bedeutung zu sein.The market forms of monopsony/oligopsony are about the only ones where the introduction of minimum wages goes along with an extension of employment, production and a likely decrease of prices. Thisfinding contrasts the bad outcomes of minimum wages predicted by the model of full competition in the labour market. However, these results were derived in literature with a short-run perspective, where the capital stock is assumed to be either constant or irrelevant. In this paper, we show in detail how these results are modified when capital is now variable and can serve considerably to substitute - if needed - labour. Hence, if capital intensity is significant and the elasticity of substitution between labour and capital is high - given a monsopsonistic firm vis-à-vis to the labour market -, a minimum wage will not cause so much positive employment effects as calculated under the short-run horizon. We also demonstrate the relevance of the rate of exploitation for the likely effects of the minimum wage on employment and capital intensity. Our results contribute to the discussion raised by the seminal paper of Card und Krueger (1994) and tend to shed a less optimistic light on monopsonies/oligopsonies in conjunction with minimum wages

How do Beveridge and Phillips curves in the euro area behave under the stress of the world economic crisis?

In this paper, the authors present a new concept of the 'modified output gap' based on the New Keynesian Phillips curve and on the Beveridge curve. In the first part of the paper, both mentioned curves are derived analytically. In doing so, we identify key parameters for the shift of the Beveridge curve (up- or downwards) and prove that - fulfilling a minimum of assumptions - the New Keynesian Phillips curve is (also) a falling convex relationship between the inflation rate and the unemployment rate in the tradition of Phillips (1958). Inserting the Phillips curve into the Beveridge curve reveals the explicit positive relationship between the vacancy ratio and the inflation rate. In the second part of the paper, we put all three relationships under an empirical 'stress test' using panel data from eleven of the EA 12 countries for three different samples during the world economic crisis: In all cases, the parameter estimates confirm the presumed existence of the three functions

Development and Longevity: Cellular and Molecular Determinants - A Mini-Review

Across species, development and longevity are tightly linked. We discuss the relevant literature and suggest that the root for this stringent relationship is the rate of development. The basis for the relationship between rate of development and longevity lies in adaptations that have occurred through evolution at multiple levels of biological complexity: organism, organ, cellular, and molecular. Thus, the analysis of the relationship is of interest for multiple fields of biology

Examining the Effects of a Virtual Character on Learning and Engagement in Serious Games

Virtual characters have been employed for many purposes including interacting with players of serious games, with a purpose to increase engagement. These characters are often embodied conversational agents playing diverse roles, such as demonstrators, guides, teachers or interviewers. Recently, much research has been conducted into properties that affect the realism and plausibility of virtual characters, but it is less clear whether the inclusion of interactive agents in serious applications can enhance a user’s engagement with the application, or indeed increase efficacy. In a first step towards answering these questions, we conducted a study where a Virtual Learning Environment was used to examine the effect of employing a virtual character to deliver a lesso