A discrete time-dependent method for metastable atoms in intense fields

The full-dimensional time-dependent Schrodinger equation for the electronic dynamics of single-electron systems in intense external fields is solved directly using a discrete method. Our approach combines the finite-difference and Lagrange mesh methods. The method is applied to calculate the quasienergies and ionization probabilities of atomic and molecular systems in intense static and dynamic electric fields. The gauge invariance and accuracy of the method is established. Applications to multiphoton ionization of positronium and hydrogen atoms and molecules are presented. At very high intensity above saturation threshold, we extend the method using a scaling technique to estimate the quasienergies of metastable states of the hydrogen molecular ion. The results are in good agreement with recent experiments.Comment: 10 pages, 9 figure, 4 table

Kinematic dynamo action in a sphere: Effects of periodic time-dependent flows on solutions with axial dipole symmetry

Choosing a simple class of flows, with characteristics that may be present in the Earth's core, we study the ability to generate a magnetic field when the flow is permitted to oscillate periodically in time. The flow characteristics are parameterised by D, representing a differential rotation, M, a meridional circulation, and C, a component characterising convective rolls. Dynamo action is sensitive to these flow parameters and fails spectacularly for much of the parameter space where magnetic flux is concentrated into small regions. Oscillations of the flow are introduced by varying the flow parameters in time, defining a closed orbit in the space (D,M). Time-dependence appears to smooth out flux concentrations, often enhancing dynamo action. Dynamo action can be impaired, however, when flux concentrations of opposite signs occur close together as smoothing destroys the flux by cancellation. It is possible to produce geomagnetic-type reversals by making the orbit stray into a region where the steady flows generate oscillatory fields. In this case, however, dynamo action was not found to be enhanced by the time-dependence. A novel approach is taken to solving the time-dependent eigenvalue problem, where by combining Floquet theory with a matrix-free Krylov-subspace method we avoid large memory requirements for storing the matrix required by the standard approach.Comment: 22 pages, 12 figures. Geophys. Astrophys. Fluid Dynam., as accepted (2004

Towards higher order lattice Boltzmann schemes

In this contribution we extend the Taylor expansion method proposed previously by one of us and establish equivalent partial differential equations of DDH lattice Boltzmann scheme at an arbitrary order of accuracy. We derive formally the associated dynamical equations for classical thermal and linear fluid models in one to three space dimensions. We use this approach to adjust relaxation parameters in order to enforce fourth order accuracy for thermal model and diffusive relaxation modes of the Stokes problem. We apply the resulting scheme for numerical computation of associated eigenmodes and compare our results with analytical references

Bogoliubov modes of a dipolar condensate in a cylindrical trap

The calculation of properties of Bose-Einstein condensates with dipolar interactions has proven a computationally intensive problem due to the long range nature of the interactions, limiting the scope of applications. In particular, the lowest lying Bogoliubov excitations in three dimensional harmonic trap with cylindrical symmetry were so far computed in an indirect way, by Fourier analysis of time dependent perturbations, or by approximate variational methods. We have developed a very fast and accurate numerical algorithm based on the Hankel transform for calculating properties of dipolar Bose-Einstein condensates in cylindrically symmetric traps. As an application, we are able to compute many excitation modes by directly solving the Bogoliubov-De Gennes equations. We explore the behavior of the excited modes in different trap geometries. We use these results to calculate the quantum depletion of the condensate by a combination of a computation of the exact modes and the use of a local density approximation

Diffusion with critically correlated traps and the slow relaxation of the longest wavelength mode

We study diffusion on a substrate with permanent traps distributed with critical positional correlation, modeled by their placement on the perimeters of a critical percolation cluster. We perform a numerical analysis of the vibrational density of states and the largest eigenvalue of the equivalent scalar elasticity problem using the method of Arnoldi and Saad. We show that the critical trap correlation increases the exponent appearing in the stretched exponential behavior of the low frequency density of states by approximately a factor of two as compared to the case of no correlations. A finite size scaling hypothesis of the largest eigenvalue is proposed and its relation to the density of states is given. The numerical analysis of this scaling postulate leads to the estimation of the stretch exponent in good agreement with the density of states result.Comment: 15 pages, LaTeX (RevTeX

Variation in Wolbachia cidB gene, but not cidA, is associated with cytoplasmic incompatibility mod phenotype diversity in Culex pipiens

Endosymbiotic Wolbachia bacteria are, to date, considered the most widespread symbionts in arthropods and are the cornerstone of major biological control strategies. Such a high prevalence is based on the ability of Wolbachia to manipulate their hosts' reproduction. One manipulation called cytoplasmic incompatibility (CI) is based on the death of the embryos generated by crosses between infected males and uninfected females or between individuals infected with incompatible Wolbachia strains. CI can be seen as a modification-rescue system (or mod-resc) in which paternal Wolbachia produce mod factors, inducing embryonic defects, unless the maternal Wolbachia produce compatible resc factors. Transgenic experiments in Drosophila melanogaster and Saccharomyces cerevisiae converged towards a model where the cidB Wolbachia gene is involved in the mod function while cidA is involved in the resc function. However, as cidA expression in Drosophila males was required to observe CI, it has been proposed that cidA could be involved in both resc and mod functions. A recent correlative study in natural Culex pipiens mosquito populations has revealed an association between specific cidA and cidB variations and changes in mod phenotype, also suggesting a role for both these genes in mod diversity. Here, by studying cidA and cidB genomic repertoires of individuals from newly sampled natural C. pipiens populations harbouring wPipIV strains from North Italy, we reinforce the link between cidB variation and mod phenotype variation fostering the involvement of cidB in the mod phenotype diversity. However, no association between any cidA variants or combination of cidA variants and mod phenotype variation was observed. Taken together our results in natural C. pipiens populations do not support the involvement of cidA in mod phenotype variation

Markov chain analysis of random walks on disordered medium

We study the dynamical exponents $d_{w}$ and $d_{s}$ for a particle diffusing in a disordered medium (modeled by a percolation cluster), from the regime of extreme disorder (i.e., when the percolation cluster is a fractal at $p=p_{c}$) to the Lorentz gas regime when the cluster has weak disorder at $p>p_{c}$ and the leading behavior is standard diffusion. A new technique of relating the velocity autocorrelation function and the return to the starting point probability to the asymptotic spectral properties of the hopping transition probability matrix of the diffusing particle is used, and the latter is numerically analyzed using the Arnoldi-Saad algorithm. We also present evidence for a new scaling relation for the second largest eigenvalue in terms of the size of the cluster, $|\ln{\lambda}_{max}|\sim S^{-d_w/d_f}$, which provides a very efficient and accurate method of extracting the spectral dimension $d_s$ where $d_s=2d_f/d_w$.Comment: 34 pages, REVTEX 3.

Lupin Peptide T9 (GQEQSHQDEGVIVR) Modulates the Mutant PCSK9D374Y Pathway : in vitro Characterization of its Dual Hypocholesterolemic Behavior

GQEQSHQDEGVIVR (T9) is a peptide originated by the tryptic digestion of lupin \u3b2-conglutin that is absorbed in human intestinal Caco-2 cells. A previous study has shown that T9 impairs the protein-protein interaction between mutant D374Y Proprotein Convertase Subtilisin/Kexin 9 (PCSK9D374Y) and the low-density lipoprotein receptor (LDLR), thus exerting a hypocholesterolemic effect. Moreover, a bioinformatic study predicting that T9 may potentially act as an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCoAR), has suggested a complementary cholesterol-lowering activity. The present study demonstrates that T9 inhibits in vitro the HMGCoAR functionality with an IC50 value of 99.5 \ub1 0.56 \ub5M. Through the inhibition of either HMGCoAR or PCSK9D374Y activities, T9 enhances the LDLR protein levels leading to an improved ability of HepG2 cells transfected with the mutant PCSK9D374Y-FLAG plasmid to uptake extracellular LDL with a final cholesterol-lowering effect. In addition, T9 modulates the PCSK9D374Y signaling pathway in transfected HepG2 cells leading to a decrease of PCSK9D374Y and HNF-1\u3b1 protein levels. All these results indicate that the hypocholesterolemic effects of T9 are due to a dual mechanism of action involving either the modulation of the PCSK9D374Y or LDLR pathways. This may represent an added value from a therapeutic point of view

Lupin Peptides Lower Low-Density Lipoprotein (LDL) Cholesterol through an Up-regulation of the LDL Receptor/Sterol Regulatory Element Binding Protein 2 (SREBP2) Pathway at HepG2 Cell Line

Previous experiments in suitable animal models and in mild hypercholesterolemic individuals have shown that the consumption of lupin proteins may be useful for controlling total and low-density lipoprotein (LDL) cholesterol levels. With the objective of providing evidence that peptides deriving from the hydrolysis of lupin proteins may be responsible of the observed activities and for investigating the mechanism of action, HepG2 cells were treated with lupin peptides obtained by either pepsin (P) or trypsin (T) hydrolysis, and molecular and functional investigations were performed on the LDL receptor/SREBP2 pathway. For the first time, this paper provides experimental evidence that lupin peptides are able to interfere with the HMGCoAR activity, up-regulating the LDL receptor (136 and 84% vs the control for P and T peptides, respectively, at 1 mg/mL) and SREBP2 proteins (148 and 73% vs the control for P and T peptides, respectively, at 1 mg/mL) via the activation of PI3K/Akt/GSK3\u3b2 pathways and increasing the LDL uptake at HepG2 cell line (40 and 50% vs the control for P and T peptides, respectively, at 1 mg/mL). These results may be useful in explaining the activities observed in vivo in animals and humans treated with lupin protein