Accuracy of a mechanical single electron shuttle

Motivated by recent experiments, we calculate both the average current and the current fluctuations for a metallic island which oscillates between two symmetric electrodes. Electrons can only tunnel on or off the island when it is close to one of the electrodes. Using a Master equation we investigate the accuracy of such an electron shuttle both analytically and numerically. It is shown that optimum operation is reached when the contact time is much larger than the RC-time.Comment: RevTeX, 8 pages, 5 figure

Scaling and data collapse for the mean exit time of asset prices

We study theoretical and empirical aspects of the mean exit time of financial time series. The theoretical modeling is done within the framework of continuous time random walk. We empirically verify that the mean exit time follows a quadratic scaling law and it has associated a pre-factor which is specific to the analyzed stock. We perform a series of statistical tests to determine which kind of correlation are responsible for this specificity. The main contribution is associated with the autocorrelation property of stock returns. We introduce and solve analytically both a two-state and a three-state Markov chain models. The analytical results obtained with the two-state Markov chain model allows us to obtain a data collapse of the 20 measured MET profiles in a single master curve.Comment: REVTeX 4, 11 pages, 8 figures, 1 table, submitted for publicatio

Integrability of a Generalized Ito System: the Painleve Test

It is shown that a generalized Ito system of four coupled nonlinear evolution equations passes the Painleve test for integrability in five distinct cases, of which two were introduced recently by Tam, Hu and Wang. A conjecture is formulated on integrability of a vector generalization of the Ito system.Comment: LaTeX, 5 page

Pulsation models for the roAp star HD 134214

Precise time-series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD 134214. We have fitted the observed frequencies with theoretical frequencies of axisymmetric modes in a grid of stellar models with dipole magnetic fields. We find that, among models with a standard composition of $(X,Z) = (0.70,0.02)$ and with suppressed convection, eigenfrequencies of a $1.65\,{\rm M}_\odot$ model with $\log T_{\rm eff} = 3.858$ and a polar magnetic field strength of 4.1kG agree best with the observed frequencies. We identify the observed pulsation frequency with the largest amplitude as a deformed dipole ($\ell = 1$) mode, and the four next-largest-amplitude frequencies as deformed $\ell = 2$ modes. These modes have a radial quasi-node in the outermost atmospheric layers ($\tau \sim 10^{-3}$). Although the model frequencies agree roughly with observed ones, they are all above the acoustic cut-off frequency for the model atmosphere and hence are predicted to be damped. The excitation mechanism for the pulsations of HD 134214 is not clear, but further investigation of these modes may be a probe of the atmospheric structure in this magnetic chemically peculiar star.Comment: 9 pages, 6 figures; accepted for publication in MNRA

A parabolic free boundary problem with Bernoulli type condition on the free boundary

Consider the parabolic free boundary problem $$\Delta u - \partial_t u = 0 \textrm{in} \{u>0\}, |\nabla u|=1 \textrm{on} \partial\{u>0\} .$$ For a realistic class of solutions, containing for example {\em all} limits of the singular perturbation problem $$\Delta u_\epsilon - \partial_t u_\epsilon = \beta_\epsilon(u_\epsilon) \textrm{as} \epsilon\to 0,$$ we prove that one-sided flatness of the free boundary implies regularity. In particular, we show that the topological free boundary $\partial\{u>0\}$ can be decomposed into an {\em open} regular set (relative to $\partial\{u>0\}$) which is locally a surface with H\"older-continuous space normal, and a closed singular set. Our result extends the main theorem in the paper by H.W. Alt-L.A. Caffarelli (1981) to more general solutions as well as the time-dependent case. Our proof uses methods developed in H.W. Alt-L.A. Caffarelli (1981), however we replace the core of that paper, which relies on non-positive mean curvature at singular points, by an argument based on scaling discrepancies, which promises to be applicable to more general free boundary or free discontinuity problems

Non-Markovian master equation for a damped oscillator with time-varying parameters

We derive an exact non-Markovian master equation that generalizes the previous work [Hu, Paz and Zhang, Phys. Rev. D {\bf 45}, 2843 (1992)] to damped harmonic oscillators with time-varying parameters. This is achieved by exploiting the linearity of the system and operator solution in Heisenberg picture. Our equation governs the non-Markovian quantum dynamics when the system is modulated by external devices. As an application, we apply our equation to parity kick decoupling problems. The time-dependent dissipative coefficients in the master equation are shown to be modified drastically when the system is driven by $\pi$ pulses. For coherence protection to be effective, our numerical results indicate that kicking period should be shorter than memory time of the bath. The effects of using soft pulses in an ohmic bath are also discussed

Allelic variation in HLA-B and HLA-C sequences and the evolution of the HLA-B alleles

Several new HLA-B (B8, B51, Bw62)- and HLA-C (Cw6, Cw7)-specific genes were isolated either as genomic cosmid or cDNA clones to study the diversity of HLA antigens. The allele specificities were identified by sequence analysis in comparison with published HLAB and -C sequences, by transfection experiments, and Southern and northern blot analysis using oligonucleotide probes. Comparison of the classical HLA-A, -B, and -C sequences reveals that allele-specific substitutions seem to be rare events. HLA-B51 codes only for one allelespecific residue: arginine at position 81 located on the cd helix, pointing toward the antigen binding site. HLA-B8 contains an acidic substitution in amino acid position 9 on the first central/3 sheet which might affect antigen binding capacity, perhaps in combination with the rare replacement at position 67 (F) on the Alpha-l helix. HLA-B8 shows greatest homology to HLA-Bw42, -Bw41, -B7, and -Bw60 antigens, all of which lack the conserved restriction sites Pst I at position 180 and Sac I at position 131. Both sites associated with amino acid replacements seem to be genetic markers of an evolutionary split of the HLA-B alleles, which is also observed in the leader sequences. HLA-Cw7 shows 98% sequence identity to the JY328 gene. In general, the HLA-C alleles display lower levels of variability in the highly polymorphic regions of the Alpha 1 and Alpha 2 domains, and have more distinct patterns of locusspecific residues in the transmembrane and cytoplasmic domains. Thus we propose a more recent origin for the HLA-C locus

Sparse polynomial space approach to dissipative quantum systems: Application to the sub-ohmic spin-boson model

We propose a general numerical approach to open quantum systems with a coupling to bath degrees of freedom. The technique combines the methodology of polynomial expansions of spectral functions with the sparse grid concept from interpolation theory. Thereby we construct a Hilbert space of moderate dimension to represent the bath degrees of freedom, which allows us to perform highly accurate and efficient calculations of static, spectral and dynamic quantities using standard exact diagonalization algorithms. The strength of the approach is demonstrated for the phase transition, critical behaviour, and dissipative spin dynamics in the spin boson modelComment: 4 pages, 4 figures, revised version accepted for publication in PR

CLONING OF THE 1.4-kb mRNA SPECIES OF HUMAN COMPLEMENT FACTOR H REVEALS A NOVEL MEMBER OF THE SHORT CONSENSUS REPEAT FAMILY RELATED TO THE CARBOXY TERMINAL OF THE CLASSICAL 150-kDa MOLECULE

Three factor H mRNA species of 4.3 kb, 1.8 kb, and 1.4 kb are constitutively expressed in human liver. Having previously characterized full-length cDNA clones derived from the 4.3-kb and 1.8-kb factor mRNA, we report here the isolation and eucaryotic expression of full-length cDNA clones coding for the 1.4-kbm RNA species. The 1266-bp cDNA codes for a polypeptide of 330 amino acids and contains two polyadenylation signals and a short poly(A)+tailT. he protein is composed of a leader peptide followed by five short consensus repeat domains. It shows a hybrid structure with the last three domains being almost identical to the carboxy- terminal of thcel assical 1 BO-kDa factor H molecule and the two first domains representing unique short consensus repeat structures. Eucaryotic expression in COS7 cells revealed two polypeptides derived from one cDNA clone that area lso found in human serum. Differences between the cDcNloAn es within the last three domains indicate two distinct, possibly allelic sequences that, in addition, differ from the authentic 150-kDa factor H sequence. Southern blot results support the notion that the 4.3-kb factor H and the 1.4-kb factor H-related mRNA are transcribed from two separate but highly homologous genes. Factor H, a glycoprotein of 150,00