Oscillatory subglacial drainage in the absence of surface melt

The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from ground water or englacial drainage as a possible explanation for the observed wintertime pressure oscillations

Fiber-Cavity-Based Optomechanical Device

We describe an optomechanical device consisting of a fiber-based optical cavity containing a silicon nitiride membrane. In comparison with typical free-space cavities, the fiber-cavity's small mode size (10 {\mu}m waist, 80 {\mu}m length) allows the use of smaller, lighter membranes and increases the cavity-membrane linear coupling to 3 GHz/nm and quadratic coupling to 20 GHz/nm^2. This device is also intrinsically fiber-coupled and uses glass ferrules for passive alignment. These improvements will greatly simplify the use of optomechanical systems, particularly in cryogenic settings. At room temperature, we expect these devices to be able to detect the shot noise of radiation pressure.Comment: 4 pages, 3 figures; the following article has been submitted to Applied Physics Letter

Description of single and double analog states in the f7/2 shell: The Ti isotopes

The excitation energies of single analog states in even-odd Ti isotopes and double analog states in even-even Ti isotopes are microscopically described in a single j-shell formalism. A projection procedure for generalized BCS states has been used. As an alternative description a particle-core formalism is presented. The latter picture provides a two-parameter expression for excitation energies, which describes fairly well the data in four odd and three even isotopes of Ti.Comment: 14 pages,7 figures, 2 tables. To appear in Phys. Rev.

Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy

The hidden photon model is one of the simplest models which can explain the anomaly of the muon anomalous magnetic moment (g-2). The experimental constraints are studied in detail, which come from the electron g-2 and the hydrogen transition frequencies. The input parameters are set carefully in order to take dark photon contributions into account and to prevent the analysis from being self-inconsistent. It is shown that the new analysis provides a constraint severer by more than one order of magnitude than the previous result.Comment: 18 pages, 2 figures, 1 table. v2: minor correction

Neutrino Pair Bremsstrahlung in Neutron Star Crusts: a Reappraisal

We demonstrate that band-structure effects suppress bremsstrahlung of neutrino pairs by electrons in the crusts of neutron stars at temperatures of the order of $5\times 10^9 \,{\rm K}$ and below. Taking this into account, together with the fact that recent work indicates that the masses of neutron star crusts are considerably smaller than previously estimated, we find neutrino pair bremsstrahlung to be much less important for the thermal evolution of neutron stars than earlier calculations suggested.Comment: 11 plain LaTeX pages, 3 figures available on request, NORDITA-93/72 A/S/

Bring a plate: facilitating experimentation in the Welcome Dinner Project

Drawing on in-depth empirical research, we explore a project called The Welcome Dinner (WDP). The WDP aims to bring together ‘newly arrived’ people and ‘established Australians’ to meet and ‘share stories’ over a potluck meal in ‘the comfort of their own home’. The purpose is to create meaningful connections, new friendships and social solidarities. In this paper, we focus on the micro-contexts of the dinners and the minute activities and techniques that facilitators use in hosting. Our aim is not to analyse the effects of the project but rather the design and meaning of the activities. As a form of ‘designed everyday multiculturalism’, focused on welcoming new arrivals to Australia, it takes effort, skill and labour to manage the contact between different cultural groups over organised meals. Thus, facilitators take over the hosting of the lunches and dinners to run activities, which are imagined to lubricate social dynamics and relations, and produce convivial commensal affects and behaviours. Drawing on theories of training activities as embodied and cognitive experimentations, which enable new knowledge practices and social relations, we analyse field notes and interviews about the facilitation, structure and activities at the WDP home dinners

Nuclear symmetry energy and the r-mode instability of neutron stars

We analyze the role of the symmetry energy slope parameter $L$ on the {\it r}-mode instability of neutron stars. Our study is performed using both microscopic and phenomenological approaches of the nuclear equation of state. The microscopic ones include the Brueckner--Hartree--Fock approximation, the well known variational equation of state of Akmal, Pandharipande and Ravenhall, and a parametrization of recent Auxiliary Field Diffusion Monte Carlo calculations. For the phenomenological approaches, we use several Skyrme forces and relativisic mean field models. Our results show that the {\it r}-mode instability region is smaller for those models which give larger values of $L$. The reason is that both bulk ($\xi$) and shear ($\eta$) viscosities increase with $L$ and, therefore, the damping of the mode is more efficient for the models with larger $L$. We show also that the dependence of both viscosities on $L$ can be described at each density by simple power-laws of the type $\xi=A_{\xi}L^{B_\xi}$ and $\eta=A_{\eta}L^{B_\eta}$. Using the measured spin frequency and the estimated core temperature of the pulsar in the low-mass X-ray binary 4U 1608-52, we conclude that observational data seem to favor values of $L$ larger than $\sim 50$ MeV if this object is assumed to be outside the instability region, its radius is in the range $11.5-12$($11.5-13$) km, and its mass $1.4M_\odot$($2M_\odot$). Outside this range it is not possible to draw any conclusion on $L$ from this pulsar.Comment: 10 pages, 6 figures. Version published in Physical Review

Ion structure factors and electron transport in dense Coulomb plasmas

The dynamical structure factor of a Coulomb crystal of ions is calculated at arbitrary temperature below the melting point taking into account multi-phonon processes in the harmonic approximation. In a strongly coupled Coulomb ion liquid, the static structure factor is split into two parts, a Bragg-diffraction-like one, describing incipient long-range order structures, and an inelastic part corresponding to thermal ion density fluctuations. It is assumed that the diffractionlike scattering does not lead to the electron relaxation in the liquid phase. This assumption, together with the inclusion of multi-phonon processes in the crystalline phase, eliminates large discontinuities of the transport coefficients (jumps of the thermal and electric conductivities, as well as shear viscosity, reported previously) at a melting point.Comment: 4 pages, 2 figures, REVTeX using epsf.sty. Phys. Rev. Lett., in pres

Contribution of the massive photon decay channel to neutrino cooling of neutron stars

We consider massive photon decay reactions via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-antineutrino pairs in the course of neutron star cooling. These reactions may become operative in hot neutron stars in the region of proton pairing where the photon due to the Higgs-Meissner effect acquires an effective mass $m_{\gamma}$ that is small compared to the corresponding plasma frequency. The contribution of these reactions to neutrino emissivity is calculated; it varies with the temperature and the photon mass as $T^{3/2}m_{\gamma}^{7/2} e^{-m_{\gamma}/T}$ for $T < m_{\gamma}$. Estimates show that these processes appear as extra efficient cooling channels of neutron stars at temperatures $T \simeq (10^9-10^{10})$ K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP