Current-induced vortex dynamics in Josephson-junction arrays: Imaging experiments and model simulations

We study the dynamics of current-biased Josephson-junction arrays with a magnetic penetration depth smaller than the lattice spacing. We compare the dynamics imaged by low-temperature scanning electron microscopy to the vortex dynamics obtained from model calculations based on the resistively-shunted junction model, in combination with Maxwell's equations. We find three bias current regions with fundamentally different array dynamics. The first region is the subcritical region, i.e. below the array critical current I_c. The second, for currents I above I_c, is a "vortex region", in which the response is determined by the vortex degrees of freedom. In this region, the dynamics is characterized by spatial domains where vortices and antivortices move across the array in opposite directions in adjacent rows and by transverse voltage fluctuations. In the third, for still higher currents, the dynamics is dominated by coherent-phase motion, and the current-voltage characteristics are linear.Comment: 10 pages, with eps figures. To appear in Phys. Rev.

Acclimation to salt modifies the activation of several osmotic stress-activated lipid signalling pathways in <em>Chlamydomonas</em>

Osmotic stress rapidly activates several phospholipid signalling pathways in the unicellular alga Chlamydomonas. In this report, we have studied the effects of salt-acclimation on growth and phospholipid signalling. Growing cells on media containing 100 mM NaCl increased their salt-tolerance but did not affect the overall phospholipid content, except that levels of phosphatidylinositol phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] were reduced by one-third. When these NaCl-acclimated cells were treated with increasing concentrations of salt, the same lipid signalling pathways as in non-acclimated cells were activated. This was witnessed as increases in phosphatidic acid (PA), lyso-phosphatidic acid (L-PA), diacylglycerol pyrophosphate (DGPP), PI(4,5)P2 and its isomer PI(3,5)P2. However, all dose-dependent responses were shifted to higher osmotic-stress levels, and the responses were lower than in non-acclimated cells. When NaCl-acclimated cells were treated with other osmotica, such as KCl and sucrose, the same effects were found, illustrating that they were due to hyperosmotic rather than hyperionic acclimation. The results indicate that acclimation to moderate salt stress modifies stress perception and the activation of several downstream pathways

On Phase Transition and Vortex Stability in the Generalized XY Models

We study a recent generalization proposed for the XY model in two and three dimensions. Using both, the continuum limit and discrete lattice, we obtained the vortex configuration and shown that out-of-plane vortex solutions are deeply jeopardized whenever the parameter of generalization, $L$, is increased. The critical temperature for such models is calculated using the self consistent harmonic approximation. In both, two- and three-dimensional cases, such a temperature decreases with raising $L$. Our results are also compared with other approximated methods available in the literature.Comment: 7 pages, 1 figur

High Precision Renormalization Group Study of the Roughening Transition

We confirm the Kosterlitz-Thouless scenario of the roughening transition for three different Solid-On-Solid models: the Discrete Gaussian model, the Absolute-Value-Solid-On-Solid model and the dual transform of the XY model with standard (cosine) action. The method is based on a matching of the renormalization group flow of the candidate models with the flow of a bona fide KT model, the exactly solvable BCSOS model. The Monte Carlo simulations are performed using efficient cluster algorithms. We obtain high precision estimates for the critical couplings and other non-universal quantities. For the XY model with cosine action our critical coupling estimate is $\beta_R^{XY}=1.1197(5)$. For the roughening coupling of the Discrete Gaussian and the Absolute-Value-Solid-On-Solid model we find $K_R^{DG}=0.6645(6)$ and $K_R^{ASOS}=0.8061(3)$, respectively.Comment: 46 pages, PostScript file (compressed and uuencoded), preprints CERN-TH.7182/94, HU-RI-2/94, and MS-TPI-94-

Theory of concentration depolarization in the presence of orientational correlations

A theory is presented that incorporates the effect of orientational correlations between luminescent molecules on the fluorescence depolarization due to incoherent energy transfer. The luminescent molecules are embedded in a homogeneous two- or three-dimensional medium which is in an axially symmetric phase with the xy plane as a symmetry plane, and consists of axially symmetric molecules. For the general orientational singlet distribution and the general form of orientational correlations consistent with these symmetries, we derive analytical expressions for the anisotropy of fluorescence emission. In a no back transfer model, numerical results are evaluated for a simple choice of correlations that tend to align nearby molecules. In a pure donor system, the anisotropy of fluorescence is found to be strongly dependent on these correlations. By ignoring them, the critical transfer distance, as obtained from depolarization experiments, may be drastically underestimated. In a system where donors are surrounded by a huge majority of traps, the critical transfer distance can be determined from the intensity of trap fluorescence. Its anisotropy also strongly depends on correlations and may thus give an indication of the correlation length scale

The Effect of Large Amplitude Fluctuations in the Ginzburg-Landau Phase Transition

The lattice Ginzburg-Landau model in d=3 and d=2 is simulated, for different values of the coherence length $\xi$ in units of the lattice spacing $a$, using a Monte Carlo method. The energy, specific heat, vortex density $v$, helicity modulus $\Gamma_\mu$ and mean square amplitude are measured to map the phase diagram on the plane $T-\xi$. When amplitude fluctuations, controlled by the parameter $\xi$, become large ($\xi \sim 1$) a proliferation of vortex excitations occurs changing the phase transition from continuous to first order.Comment: 4 pages, 5 postscript (eps) figure

Paraoxonase (PON1) and the risk for coronary heart disease and myocardial infarction in a general population of Dutch women.

Contains fulltext : 71536.pdf (Publisher’s version ) (Open Access)There is strong evidence from both animal- and in vitro-models that paraoxonase (PON1) is involved in the onset of cardiovascular disease. In humans there is no consensus on this issue and therefore we investigated the effect of PON1 genotype and activity on the incidence of coronary heart disease (CHD) and acute myocardial infarction (AMI) in a large prospective cohort of 17,357 middle-aged women. We applied a case-cohort design using the CHD (n=211) and AMI cases (n=71) and a random sample from the baseline cohort (n=1527). A weighted Cox proportional hazards model was used to estimate age- and multivariate-adjusted hazard ratios (HR) for the PON1 genetic variants (192Q > R and -107C > T) and tertiles of the PON1 arylesterase- and paraoxonase activities. Neither the PON1 genetic variants, nor the PON1 activities affected the incidence of CHD in general, but, an increased paraoxonase activity was associated with a higher risk of AMI: the second and third tertile HR were 1.31 and 2.07, respectively (P-trend=0.029, multivariate model). In the subgroup of never-smokers, paraoxonase activity was associated with an increased risk for AMI: the second and third tertile HR were 4.1 and 4.7, respectively (P-trend=0.009, multivariate model). Additionally, when compared to the lowest paraoxonase tertile in never-smokers, the highest paraoxonase tertile in current-smokers showed a 19.2-fold higher risk for AMI (95%CI: 5.3-69.5, P < 0.0001, multivariate model). In conclusion, this study shows that in middle-aged women paraoxonase activity was associated with an increased risk for AMI and that the risk was modified by the effects of smoking

Exactly solvable model of three interacting particles in an external magnetic field

The quantum mechanical problem of three identical particles, moving in a plane and interacting pairwise via a spring potential, is solved exactly in the presence of a magnetic field. Calculations of the pair--correlation function, mean distance and the cluster area show a quantization of these parameters. Especially the pair-correlation function exhibits a certain number of maxima given by a quantum number. We obtain Jastrow pre-factors which lead to an exchange correlation hole of liquid type, even in the presence of the attractive interaction between the identical electrons.Comment: 8 pages 3 figure