Detection of Near Horizontal Muons with the HAWC Observatory

The HAWC (High Altitude Water Cherenkov) gamma ray observatory is able to observe muons with nearly horizontal trajectories. HAWC is located at an altitude of 4100 meters a.s.l. on the Sierra Negra volcano in Mexico. The HAWC detector is composed of 300 water tanks, each 7.3 m in diameter and 4.5 m tall, densely packed over a physical area of 22,000 m$^{2}$. Previous and current experiments have observed high zenith angle (near horizontal) muons at or near sea level. HAWC operates as a hodoscope able to observe multi-TeV muons at zenith angles greater than 75 degrees. This is the first experiment to measure near horizontal muons at high altitude and with large ($\geq$ 10 m) separations for multiple muons. These muons are distinguishable from extensive air showers by observing near horizontal particles propagating with the speed of light. The proximity of Sierra Negra and Pico de Orizaba volcanoes provides an additional measurement of muons with rock overburdens of several km water equivalent. We will present the angular distribution and rate at which HAWC observes these muon eventsComment: Presented at the 35th International Cosmic Ray Conference (ICRC2017), Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution

Simulation of Near Horizontal Muons and Muon Bundles for the HAWC Observatory with CORSIKA

The HAWC (High Altitude Water Cerenkov) gamma ray observatory observes muons with nearly-horizontal trajectories corresponding to zenith angles greater than $80^{0}$. HAWC is located at an altitude of 4100 meters a.s.l. (70 deg. atmospheric depth of 2400 g/cm$^{2}$) on the extinct volcano, Sierra Negra in Mexico. In this poster, we summarize the CORSIKA and GEANT4 as well as toy-model based simulations performed to determine the effective area of HAWC to muons from high zenith angle cosmic ray primaries. We are developing an updated GEANT4 based detector response simulation that includes a model of the volcanoes that are located near HAWC. These simulations are investigating the capability to use muon multiplicity and rates to differentiate between the primary particle composition (proton or iron) and measure the primary energy.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017), Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution

The Sound of Sonoluminescence

We consider an air bubble in water under conditions of single bubble sonoluminescence (SBSL) and evaluate the emitted sound field nonperturbatively for subsonic gas-liquid interface motion. Sound emission being the dominant damping mechanism, we also implement the nonperturbative sound damping in the Rayleigh-Plesset equation for the interface motion. We evaluate numerically the sound pulse emitted during bubble collapse and compare the nonperturbative and perturbative results, showing that the usual perturbative description leads to an overestimate of the maximal surface velocity and maximal sound pressure. The radius vs. time relation for a full SBSL cycle remains deceptively unaffected.Comment: 25 pages; LaTex and 6 attached ps figure files. Accepted for publication in Physical Review

Bubble Shape Oscillations and the Onset of Sonoluminescence

An air bubble trapped in water by an oscillating acoustic field undergoes either radial or nonspherical pulsations depending on the strength of the forcing pressure. Two different instability mechanisms (the Rayleigh--Taylor instability and parametric instability) cause deviations from sphericity. Distinguishing these mechanisms allows explanation of many features of recent experiments on sonoluminescence, and suggests methods for finding sonoluminescence in different parameter regimes.Comment: Phys. Rev. Lett., in pres

Mechanisms for Stable Sonoluminescence

A gas bubble trapped in water by an oscillating acoustic field is expected to either shrink or grow on a diffusive timescale, depending on the forcing strength and the bubble size. At high ambient gas concentration this has long been observed in experiments. However, recent sonoluminescence experiments show that in certain circumstances when the ambient gas concentration is low the bubble can be stable for days. This paper presents mechanisms leading to stability which predict parameter dependences in agreement with the sonoluminescence experiments.Comment: 4 pages, 3 figures on request (2 as .ps files

Comment on Mie Scattering from a Sonoluminescing Bubble with High Spatial and Temporal Resolution [Physical Review E 61, 5253 (2000)]

A key parameter underlying the existence of sonoluminescence (SL)is the time relative to SL at which acoustic energy is radiated from the collapsed bubble. Light scattering is one route to this quantity. We disagree with the statement of Gompf and Pecha that -highly compressed water causes the minimum in scattered light to occur 700ps before SL- and that this effect leads to an overestimate of the bubble wall velocity. We discuss potential artifacts in their experimental arrangement and correct their description of previous experiments on Mie scattering.Comment: 10 pages, 2 figure

Three Dimensional Electrical Impedance Tomography

The electrical resistivity of mammalian tissues varies widely and is correlated with physiological function. Electrical impedance tomography (EIT) can be used to probe such variations in vivo, and offers a non-invasive means of imaging the internal conductivity distribution of the human body. But the computational complexity of EIT has severe practical limitations, and previous work has been restricted to considering image reconstruction as an essentially two-dimensional problem. This simplification can limit significantly the imaging capabilities of EIT, as the electric currents used to determine the conductivity variations will not in general be confined to a two-dimensional plane. A few studies have attempted three-dimensional EIT image reconstruction, but have not yet succeeded in generating images of a quality suitable for clinical applications. Here we report the development of a three-dimensional EIT system with greatly improved imaging capabilities, which combines our 64-electrode data-collection apparatus with customized matrix inversion techniques. Our results demonstrate the practical potential of EIT for clinical applications, such as lung or brain imaging and diagnostic screening

Disordered two-dimensional superconductors: roles of temperature and interaction strength

We have considered the half-filled disordered attractive Hubbard model on a square lattice, in which the on-site attraction is switched off on a fraction $f$ of sites, while keeping a finite $U$ on the remaining ones. Through Quantum Monte Carlo (QMC) simulations for several values of $f$ and $U$, and for system sizes ranging from $8\times 8$ to $16\times 16$, we have calculated the configurational averages of the equal-time pair structure factor $P_s$, and, for a more restricted set of variables, the helicity modulus, $\rho_s$, as functions of temperature. Two finite-size scaling {\it ansatze} for $P_s$ have been used, one for zero-temperature and the other for finite temperatures. We have found that the system sustains superconductivity in the ground state up to a critical impurity concentration, $f_c$, which increases with $U$, at least up to U=4 (in units of the hopping energy). Also, the normalized zero-temperature gap as a function of $f$ shows a maximum near $f\sim 0.07$, for $2\lesssim U\lesssim 6$. Analyses of the helicity modulus and of the pair structure factor led to the determination of the critical temperature as a function of $f$, for $U=3,$ 4 and 6: they also show maxima near $f\sim 0.07$, with the highest $T_c$ increasing with $U$ in this range. We argue that, overall, the observed behavior results from both the breakdown of CDW-superconductivity degeneracy and the fact that free sites tend to "push" electrons towards attractive sites, the latter effect being more drastic at weak couplings.Comment: 9 two-column pages, 14 figures, RevTe

Gauge Theories with Cayley-Klein SO(2;j)SO(2;j) and SO(3;j)SO(3;j) Gauge Groups

Gauge theories with the orthogonal Cayley-Klein gauge groups $SO(2;j)$ and $SO(3;{\bf j})$ are regarded. For nilpotent values of the contraction parameters ${\bf j}$ these groups are isomorphic to the non-semisimple Euclid, Newton, Galilei groups and corresponding matter spaces are fiber spaces with degenerate metrics. It is shown that the contracted gauge field theories describe the same set of fields and particle mass as $SO(2), SO(3)$ gauge theories, if Lagrangians in the base and in the fibers all are taken into account. Such theories based on non-semisimple contracted group provide more simple field interactions as compared with the initial ones.Comment: 14 pages, 5 figure

Sonoluminescence as Quantum Vaccum Radiation

We argue that the available experimental data is not compatible with models of sonoluminescence which invoke dynamical properties of the interface without regard to the compositional properties of the trapped gas inside the bubble.Comment: 2 pages,Revtex,No figures,Submitted to PRL(comments