Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star

Using patterns in the oscillation frequencies of a white dwarf observed by K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy from the SOAR telescope show that the star (SDSSJ0837+1856, EPIC 211914185) is a 13,590(340) K, 0.87(03) solar-mass white dwarf. This is the highest mass measured for any pulsating white dwarf with known rotation, suggesting a possible link between high mass and fast rotation. If it is the product of single-star evolution, its progenitor was a roughly 4.0 solar-mass main-sequence B star; we know very little about the angular momentum evolution of such intermediate-mass stars. We explore the possibility that this rapidly rotating white dwarf is the byproduct of a binary merger, which we conclude is unlikely given the pulsation periods observed.Comment: 5 pages, 4 figure, 1 table; accepted for publication in The Astrophysical Journal Letter

Quantitative analysis of regulatory flexibility under changing environmental conditions

The circadian clock controls 24-h rhythms in many biological processes, allowing appropriate timing of biological rhythms relative to dawn and dusk. Known clock circuits include multiple, interlocked feedback loops. Theory suggested that multiple loops contribute the flexibility for molecular rhythms to track multiple phases of the external cycle. Clear dawn- and dusk-tracking rhythms illustrate the flexibility of timing in Ipomoea nil. Molecular clock components in Arabidopsis thaliana showed complex, photoperiod-dependent regulation, which was analysed by comparison with three contrasting models. A simple, quantitative measure, Dusk Sensitivity, was introduced to compare the behaviour of clock models with varying loop complexity. Evening-expressed clock genes showed photoperiod-dependent dusk sensitivity, as predicted by the three-loop model, whereas the one- and two-loop models tracked dawn and dusk, respectively. Output genes for starch degradation achieved dusk-tracking expression through light regulation, rather than a dusk-tracking rhythm. Model analysis predicted which biochemical processes could be manipulated to extend dusk tracking. Our results reveal how an operating principle of biological regulators applies specifically to the plant circadian clock

Localization Properties of Electronic States in Polaron Model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling are completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small.Comment: 6 pages, 6 figure

Effect of nonlinearity on the dynamics of a particle in dc field-induced systems

Dynamics of a particle in a perfect chain with one nonlinear impurity and in a perfect nonlinear chain under the action of dc field is studied numerically. The nonlinearity appears due to the coupling of the electronic motion to optical oscillators which are treated in adiabatic approximation. We study for both the low and high values of field strength. Three different range of nonlinearity is obtained where the dynamics is different. In low and intermediate range of nonlinearity, it reduces the localization. In fact in the intermediate range subdiffusive behavior in the perfect nonlinear chain is obtained for a long time. In all the cases a critical value of nonlinear strength exists where self-trapping transition takes place. This critical value depends on the system and the field strength. Beyond the self-trapping transition nonlinearity enhances the localization.Comment: 9 pages, Revtex, 6 ps figures include

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Linewidths: Kepler Observations of 27 Pulsating DA White Dwarfs Through K2 Campaign 8

We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs, a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 days) and duty cycle (>90%). The space-based photometry reveals pulsation properties previously inaccessible to ground-based observations. We observe a sharp dichotomy in oscillation mode linewidths at roughly 800 s, such that white dwarf pulsations with periods exceeding 800 s have substantially broader mode linewidths, more reminiscent of a damped harmonic oscillator than a heat-driven pulsator. Extended Kepler coverage also permits extensive mode identification: We identify the spherical degree of 61 out of 154 unique radial orders, providing direct constraints of the rotation period for 20 of these 27 DAVs, more than doubling the number of white dwarfs with rotation periods determined via asteroseismology. We also obtain spectroscopy from 4m-class telescopes for all DAVs with Kepler photometry. Using these homogeneously analyzed spectra we estimate the overall mass of all 27 DAVs, which allows us to measure white dwarf rotation as a function of mass, constraining the endpoints of angular momentum in low- and intermediate-mass stars. We find that 0.51-to-0.73-solar-mass white dwarfs, which evolved from 1.7-to-3.0-solar-mass ZAMS progenitors, have a mean rotation period of 35 hr with a standard deviation of 28 hr, with notable exceptions for higher-mass white dwarfs. Finally, we announce an online repository for our Kepler data and follow-up spectroscopy, which we collect at http://www.k2wd.org.Comment: 33 pages, 31 figures, 5 tables; accepted for publication in ApJS. All raw and reduced data are collected at http://www.k2wd.or

Circadian Programs of Transcriptional Activation, Signaling, and Protein Turnover Revealed by Microarray Analysis of Mammalian Cells

Many aspects of physiology and behavior are temporally organized into daily 24 hr rhythms, driven by an endogenous circadian clock. Studies in eukaryotes have identified a network of interacting genes forming interlocked autoregulatory feedback loops which underlie overt circadian organization in single cells [1, 2]. While in mammals the master oscillator resides in the suprachiasmatic nuclei of the hypothalamus [2], semiautonomous circadian oscillators also exist in peripheral tissues [3–5] and in immortalized fibroblasts, where rhythmicity is induced following a serum shock [6, 7]. We used this model system in combination with high-density cDNA microarrays to examine the magnitude and quality of clock control of gene expression in mammalian cells. Supported by application of novel bioinformatics tools, we find ∼2% of genes, including expected canonical clock genes, to show consistent rhythmic circadian expression across five independent experiments. Rhythmicity in most of these genes is novel, and they fall into diverse functional groups, highlighted by a predominance of transcription factors, ubiquitin-associated factors, proteasome components, and Ras/MAPK signaling pathway components. When grouped according to phase, 68% of the genes were found to peak during estimated subjective day, 32% during estimated subjective night, with a tendency to peak at a phase corresponding to anticipation of dawn or dusk

Frenkel Excitons in Random Systems With Correlated Gaussian Disorder

Optical absorption spectra of Frenkel excitons in random one-dimensional systems are presented. Two models of inhomogeneous broadening, arising from a Gaussian distribution of on-site energies, are considered. In one case the on-site energies are uncorrelated variables whereas in the second model the on-site energies are pairwise correlated (dimers). We observe a red shift and a broadening of the absorption line on increasing the width of the Gaussian distribution. In the two cases we find that the shift is the same, within our numerical accuracy, whereas the broadening is larger when dimers are introduced. The increase of the width of the Gaussian distribution leads to larger differences between uncorrelated and correlated disordered models. We suggest that this higher broadening is due to stronger scattering effects from dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review

Radiographic pseudofracture of the Medtronic bipolar polyurethane pacing lead

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25377/1/0000826.pd

Quantum tunneling Sb-heterostructure millimeter-wave diodes

We have developed a new zero bias millimeter wave diode based on quantum tunneling in an InAs/AlSb/GaSb nanostructure. It is ideal for square law radiometry and passive millimeter wave imaging. Excellent sensitivity has been demonstrated at present up to 110 GHz, with higher bandwidth predicted for smaller area diodes

Structural basis for activation of calcineurin by calmodulin

The highly conserved phosphatase calcineurin plays vital roles in numerous processes including T-cell activation, development and function of the central nervous system, and cardiac growth. It is activated by the calcium sensor calmodulin. Calmodulin binds to a regulatory domain within calcineurin, causing a conformational change that displaces an autoinhibitory domain from the active site, resulting in activation of the phosphatase. This is the same general mechanism by which calmodulin activates calmodulin-dependent protein kinases. Previously published data has hinted that the regulatory domain of calcineurin is intrinsically disordered. In this work we demonstrate that the regulatory domain is unstructured and that it folds upon binding calmodulin, ousting the autoinhibitory domain from the catalytic site. The regulatory domain is 95 residues long, with the autoinhibitory domain attached to its C-terminal end and the 24 residue calmodulin binding region towards the N-terminal end. This is unlike the calmodulin-dependent protein kinases which have calmodulin binding sites and autoinhibitory domains immediately adjacent in sequence. Our data demonstrate that not only does the calmodulin binding region fold, but that an ~25-30 residue region between it and the autoinhibitory domain also folds, resulting in over half of the regulatory domain adopting α-helical structure. This appears to be the first observation of calmodulin inducing folding of this scale outside of its binding site on a target protein