Safety hazards associated with the charging of lithium/sulfur dioxide cells

A continuing research program to assess the responses of spirally wound, lithium/sulfur dioxide cells to charging as functions of charging current, temperature, and cell condition prior to charging is described. Partially discharged cells that are charged at currents greater than one ampere explode with the time to explosion inversely proportional to the charging current. Cells charged at currents of less than one ampere may fail in one of several modes. The data allows an empirical prediction of when certain cells will fail given a constant charging current

Development of a motorized cryovalve for the control of superfluid liquid helium

Recent advances in the technology of infrared detectors have made possible a wide range of scientific measurements and investigations. One of the requirements for the use of sensitive IR detectors is that the entire instrument be cooled to temperatures approaching absolute zero. The cryogenic cooling system for these instruments is commonly designed as a large dewar containing liquid helium which completely surrounds the apparatus. Thus, there is a need for a remotely controlled, motorized cryovalve that is simple, reliable, and compact and can operate over extended periods of time in cryo-vac conditions. The design, development, and test of a motorized cryovalve with application to a variety of cryogenic systems currently under development is described

Mapping the magic numbers in binary Lennard-Jones clusters

Using a global optimization approach that directly searches for the composition of greatest stability, we have been able to find the particularly stable structures for binary Lennard-Jones clusters with up to 100 atoms for a range of Lennard-Jones parameters. In particular, we have shown that just having atoms of different size leads to a remarkable stabilization of polytetrahedral structures, including both polyicosahedral clusters and at larger sizes structures with disclination lines.Comment: 5 pages, 5 figure

Saving the fourth generation Higgs with radion mixing

We study Higgs-radion mixing in a warped extra dimensional model with Standard Model fields in the bulk, and we include a fourth generation of chiral fermions. The main problem with the fourth generation is that, in the absence of Higgs-radion mixing, it produces a large enhancement in the Higgs production cross-section, now severely constrained by LHC data. We analyze the production and decay rates of the two physical states emerging from the mixing and confront them with present LHC data. We show that the current signals observed can be compatible with the presence of one, or both, of these Higgs-radion mixed states (the $\phi$ and the $h$), although with a severely restricted parameter space. In particular, the radion interaction scale must be quite low, Lambda_\phi ~ 1-1.3 TeV. If m_\phi ~ 125 GeV, the $h$ state must be heavier (m_h>320 GeV). If m_h ~ 125 GeV, the $\phi$ state must be quite light or close in mass (m_\phi ~ 120 GeV). We also present the modified decay branching ratios of the mixed Higgs-radion states, including flavor violating decays into fourth generation quarks and leptons. The windows of allowed parameter space obtained are very sensitive to the increased precision of upcoming LHC data. During the present year, a clear picture of this scenario will emerge, either confirming or further severely constraining this scenario.Comment: 22 pages, 5 figures, 4 table

Origin of the Mosaicity in Graphene Grown on Cu(111)

We use low-energy electron microscopy to investigate how graphene grows on Cu(111). Graphene islands first nucleate at substrate defects such as step bunches and impurities. A considerable fraction of these islands can be rotationally misaligned with the substrate, generating grain boundaries upon interisland impingement. New rotational boundaries are also generated as graphene grows across substrate step bunches. Thus, rougher substrates lead to higher degrees of mosaicity than do flatter substrates. Increasing the growth temperature improves crystallographic alignment. We demonstrate that graphene growth on Cu(111) is surface diffusion limited by comparing simulations of the time evolution of island shapes with experiments. Islands are dendritic with distinct lobes, but unlike the polycrystalline, four-lobed islands observed on (100)-textured Cu foils, each island can be a single crystal. Thus, epitaxial graphene on smooth, clean Cu(111) has fewer structural defects than it does on Cu(100).Comment: Article revised following reviewer comment

On the renormalization group flow of f(R)-gravity

We use the functional renormalization group equation for quantum gravity to construct a non-perturbative flow equation for modified gravity theories of the form $S = \int d^dx \sqrt{g} f(R)$. Based on this equation we show that certain gravitational interactions monomials can be consistently decoupled from the renormalization group (RG) flow and reproduce recent results on the asymptotic safety conjecture. The non-perturbative RG flow of non-local extensions of the Einstein-Hilbert truncation including $\int d^dx \sqrt{g} \ln(R)$ and $\int d^dx \sqrt{g} R^{-n}$ interactions is investigated in detail. The inclusion of such interactions resolves the infrared singularities plaguing the RG trajectories with positive cosmological constant in previous truncations. In particular, in some $R^{-n}$-truncations all physical trajectories emanate from a Non-Gaussian (UV) fixed point and are well-defined on all RG scales. The RG flow of the $\ln(R)$-truncation contains an infrared attractor which drives a positive cosmological constant to zero dynamically.Comment: 55 pages, 7 figures, typos corrected, references added, version to appear in Phys. Rev.

Quantum Error Correction in Spatially Correlated Quantum Noise

We consider quantum error correction of quantum-noise that is created by a local interaction of qubits with a common bosonic bath. The possible exchange of bath bosons between qubits gives rise to spatial and temporal correlations in the noise. We find that these kind of noise correlations have a strong negative impact on quantum error correction.Comment: 4 pages, 1 figure, final version with minor correction

Clues to unveil the emitter in LS 5039: powerful jets vs colliding winds

LS 5039 is among the most interesting VHE sources in the Galaxy. Two scenarios have been put forward to explain the observed TeV radiation: jets vs pulsar winds. The source has been detected during the superior conjunction of the compact object, when very large gamma-ray opacities are expected. In addition, electromagnetic cascades, which may make the system more transparent to gamma-rays, are hardly efficient for realistic magnetic fields in massive star surroundings. All this makes unlikely the standard pulsar scenario for LS 5039, in which the emitter is the region located between the star and the compact object, where the opacities are the largest. Otherwise, a jet-like flow can transport energy to regions where the photon-photon absorption is much lower and the TeV radiation is not so severely absorbed.Comment: 3 pages, 3 Figures, contribution to the "Fourth Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy 2008

Comment on the numerical solutions of a new coupled MKdV system (2008 Phys. Scr. 78 045008)

In this comment we point out some wrong statements in the paper by Inc and Cavlak, Phys. Scr. 78 (2008) 04500

Thermostatistics of overdamped motion of interacting particles

We show through a nonlinear Fokker-Planck formalism, and confirm by molecular dynamics simulations, that the overdamped motion of interacting particles at T=0, where T is the temperature of a thermal bath connected to the system, can be directly associated with Tsallis thermostatistics. For sufficiently high values of T, the distribution of particles becomes Gaussian, so that the classical Boltzmann-Gibbs behavior is recovered. For intermediate temperatures of the thermal bath, the system displays a mixed behavior that follows a novel type of thermostatistics, where the entropy is given by a linear combination of Tsallis and Boltzmann-Gibbs entropies.Comment: 4 pages, 2 figure