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

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

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

THE RELATIONSHIP BETWEEN MUSCULOSKELETAL STRENGTH, PHYSIOLOGICAL CHARACTERISTICS, AND KNEE KINESTHESIA FOLLOWING FATIGUING EXERCISE

Fatiguing exercise may result in impaired functional joint stability and increased risk of unintentional injury. While there are several musculoskeletal and physiological characteristics related to fatigue onset, their relationship with proprioceptive changes following fatigue has not been examined. The purpose of this study was to establish the relationship between musculoskeletal and physiological characteristics and changes in proprioception, measured by threshold to detect passive motion (TTDPM), following fatiguing exercise. Twenty, physically active females participated (age: 28.65 ± 5.6 years, height: 165.6 ± 4.3 cm, weight: 61.8 ± 8.0 kg, BMI: 22.5± 2.3 kg/m2, BF: 23.3 ± 5.4%). During Visit 1, subjects completed an exercise history and 24-hour dietary questionnaire, and body composition, TTDPM familiarization, isokinetic knee strength, and maximal oxygen uptake/lactate threshold assessments. During Visit 2, subjects completed TTDPM and isometric knee strength testing prior to and following a fatiguing exercise protocol. Wilcoxon signed rank tests determined TTDPM and isometric knee strength changes from pre- to post- fatigue. Spearman’s rho correlation coefficients determined the relationship between strength and physiological variables with pre- to post-fatigue changes in TTDPM and with pre-fatigue and post-fatigue TTDPM in extension and flexion (α=0.05). No significant differences were demonstrated from pre-fatigue to post-fatigue TTDPM despite a significant decrease in isometric knee flexion strength (P<0.01) and flexion/extension ratio (P<0.05) following fatigue. No significant correlations were observed between strength or physiological variables and changes in TTDPM from pre- to post-fatigue in extension or flexion. Flexion/extension ratio was significantly correlated with pre-fatigue TTDPM in extension (r=-0.231, P<0.05). Peak oxygen uptake was significantly correlated with pre-fatigue (r=-0.500, P<0.01) and post-fatigue (r=-0.520, P<0.05) TTDPM in extension. No significant relationships were demonstrated between musculoskeletal and physiological characteristics and changes in TTDPM following fatigue. The results suggest that highly trained individuals may have better proprioception, and that the high fitness level of subjects in this investigation may have contributed to absence of TTDPM deficits following fatigue despite reaching a high level of perceptual and physiological fatigue. Future studies should consider various subject populations, other musculoskeletal strength characteristics, and different modalities of proprioception to determine the most important contributions to proprioceptive changes following fatigue

Galaxies Probing Galaxies at High Resolution: Co-Rotating Gas Associated with a Milky Way Analog at z=0.4

We present results on gas flows in the halo of a Milky Way-like galaxy at z=0.413 based on high-resolution spectroscopy of a background galaxy. This is the first study of circumgalactic gas at high spectral resolution towards an extended background source (i.e., a galaxy rather than a quasar). Using longslit spectroscopy of the foreground galaxy, we observe spatially extended H alpha emission with circular rotation velocity v=270 km/s. Using echelle spectroscopy of the background galaxy, we detect Mg II and Fe II absorption lines at impact parameter rho=27 kpc that are blueshifted from systemic in the sense of the foreground galaxy's rotation. The strongest absorber EW(2796) = 0.90 A has an estimated column density (N_H>10^19 cm-2) and line-of-sight velocity dispersion (sigma=17 km/s) that are consistent with the observed properties of extended H I disks in the local universe. Our analysis of the rotation curve also suggests that this r=30 kpc gaseous disk is warped with respect to the stellar disk. In addition, we detect two weak Mg II absorbers in the halo with small velocity dispersions (sigma<10 km/s). While the exact geometry is unclear, one component is consistent with an extraplanar gas cloud near the disk-halo interface that is co-rotating with the disk, and the other is consistent with a tidal feature similar to the Magellanic Stream. We can place lower limits on the cloud sizes (l>0.4 kpc) for these absorbers given the extended nature of the background source. We discuss the implications of these results for models of the geometry and kinematics of gas in the circumgalactic medium.Comment: 14 pages, 6 figures, submitted to ApJ, comments welcom

Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs

We advance all optical spin noise spectroscopy (SNS) in semiconductors to detection bandwidths of several hundred gigahertz by employing an ingenious scheme of pulse trains from ultrafast laser oscillators as an optical probe. The ultrafast SNS technique avoids the need for optical pumping and enables nearly perturbation free measurements of extremely short spin dephasing times. We employ the technique to highly n-doped bulk GaAs where magnetic field dependent measurements show unexpected large g-factor fluctuations. Calculations suggest that such large g-factor fluctuations do not necessarily result from extrinsic sample variations but are intrinsically present in every doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure

Price effects of minimum wages: Evidence from the construction sector in East and West Germany

In this paper, the authors present a new approach to estimate the impact of a minimum wage on the labor market of the construction sector in Germany. Instead of estimating the effect on employment, the authors focus on the change of prices on a firm level in order to differentiate between a competitive and a monopsonistic structured labor market. The composition of the sector-specific labor market serves again as a basis to evaluate whether the consequences of the minimum wage can be taken as economically advantageous or disadvantageous. Using firm data monthly conducted by the Ifo Institute for Economic Research, the estimations show that the minimum wage did have a different impact in East and West Germany. In East Germany, we find significant positive price effects of the minimum wage which exclude the possibility of positive employment effects due to monopsonistic structures. On the contrary, our results indicate a competitive sectorspecific labor market and declining employment. In contrast, there was no significant price reaction observed for West Germany. The minimum wage seems too low compared to the wages paid in the West German construction sector. Therefore, the introduction of the minimum wage cannot be assumed to be binding