Internal stress wave measurements in solids subjected to lithotripter pulses

Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter

A SUSY A4 model for fermion masses and mixings

We study a supersymmetric extension of the Standard Model based on discrete A4xZ3xZ4 flavor symmetry. We obtain quark mixing angles as well as a realistic fermion mass spectrum and we predict tribimaximal leptonic mixing by a spontaneous breaking of A4. The top quark Yukawa interaction is present at the renormalizable level in the superpotential while all the other Yukawa interactions arise only at higher orders. We study the Higgs potential and show that it can potentially solve the so called vacuum alignment problem. The leading order predictions are not spoiled by subleading corrections.Comment: version accepted in JHEP, Z3xZ2 changed in Z3xZ4, typos in table corrected, references adde

Holes in the walls: primordial black holes as a solution to the cosmological domain wall problem

We propose a scenario in which the cosmological domain wall and monopole problems are solved without any fine tuning of the initial conditions or parameters in the Lagrangian of an underlying filed theory. In this scenario domain walls sweep out (unwind) the monopoles from the early universe, then the fast primordial black holes perforate the domain walls, change their topology and destroy them. We find further that the (old vacuum) energy density released from the domain walls could alleviate but not solve the cosmological flatness problem.Comment: References added; Published in Phys. Rev.

Sensitivity studies for the cubic-kilometre deep-sea neutrino telescope KM3NeT

The observation of high-energy neutrinos from astrophysical sources would substantially improve our knowledge and understanding of the non-thermal processes in these sources, and would in particular pinpoint the accelerators of cosmic rays. The sensitivity of different design options for a future cubic-kilometre scale neutrino telescope in the Mediterranean Sea is investigated for generic point sources and in particular for some of the galactic objects from which TeV gamma emmission has recently been observed by the H.E.S.S. atmospheric Cherenkov telescope. The effect of atmospheric background on the source detection probabilities has been taken into account through full simulation. The estimated event rates are compared to previous results and limits from present neutrino telescopes.Comment: 4 pages, 1 figure, contribution of the 30th International Cosmic Ray conferenc

Al Toxicity of Wheat Grown in Acidic Subsoils in Relation to Soil Solution Properties and Exchangeable Cations

Toxic concentrations of soluble A1 in the subsoil decrease the yield of wheat grown on many yellow earths in the eastern wheatbelt of Western Australia. In our previous research (Carr et al. 1991), we observed variable plant response to high concentrations of soluble Al in subsoils of yellow earths in different regions of the wheatbelt. Environmental conditions (e.g. water supply) and/or an unidentified soil mitigating factor may have contributed to the variable plant response to soluble Al in some of the regions studied. We collected ten soils from four regions of the eastern wheatbelt of Western Australia. In a glasshouse experiment using these soils, we studied the effect of soil solution and KCl extract properties on wheat growth under uniform environmental conditions. The concentration of Al in a 0.005 M KCl extract was able to explain 97% of the variation in root fresh weight of wheat grown in the 10 soils, even though the soil solution properties were found to differ markedly between regions. For example, 97% of the variation in root fresh weight (RFW) was explained by the total [Al] in soil solution extracted from soils in one region (Merredin). In comparison, 58% of the variation in RFW was explained by the total [Al] in the soil solution extracted from soils collected from all four regions studied. Ionic strength differences and possibly [SO4] were the major chemical properties that differed between Merredin and the other regions studied. These chemical differences presumably altered the toxic proportion of Al in the soil solution, and hence, the plant response in some regions. The effect of ionic strength on toxic Al appeared to be simulated by extraction of the soil with 0.005 M KCl

Bose-Einstein condensates with attractive interactions on a ring

Considering an effectively attractive quasi-one-dimensional Bose-Einstein condensate of atoms confined in a toroidal trap, we find that the system undergoes a phase transition from a uniform to a localized state, as the magnitude of the coupling constant increases. Both the mean-field approximation, as well as a diagonalization scheme are used to attack the problem.Comment: 4 pages, 4 ps figures, RevTex, typographic errors correcte

Asymptotically Friedmann self-similar scalar field solutions with potential

We investigate self-similar solutions which are asymptotic to the Friedmann universe at spatial infinity and contain a scalar field with potential. The potential is required to be exponential by self-similarity. It is found that there are two distinct one-parameter families of asymptotic solutions,one is asymptotic to the proper Friedmann universe, while the other is asymptotic to the quasi-Friedmann universe, i.e., the Friedmann universe with anomalous solid angle. The asymptotically proper Friedmann solution is possible only if the universe is accelerated or the potential is negative. If the potential is positive, the density perturbation in the asymptotically proper Friedmann solution rapidly falls off at spatial infinity, while the mass perturbation is compensated. In the asymptotically quasi-Friedmann solution, the density perturbation falls off only in proportion to the inverse square of the areal radius and the relative mass perturbation approaches a nonzero constant at spatial infinity. The present result shows that a necessary condition holds in order that a self-gravitating body grows self-similarly due to the constant accretion of quintessence in an accelerating universe.Comment: accepted for publication in Physical Review D, minor correction, typos correcte

Near-Critical Gravitational Collapse and the Initial Mass Function of Primordial Black Holes

The recent discovery of critical phenomena arising in gravitational collapse near the threshold of black hole formation is used to estimate the initial mass function of primordial black holes (PBHs). It is argued that the universal scaling relation between black hole mass and initial perturbation found for a variety of collapsing space-times also applies to PBH formation, indicating the possibility of the formation of PBHs with masses much smaller than one horizon mass. Owing to the natural fine-tuning of initial conditions by the exponential decline of the probability distribution for primordial density fluctuations, sub-horizon mass PBHs are expected to form at all epochs. This result suggests that the constraints on the primordial fluctuation spectrum based on the abundance of PBHs at different mass scales may have to be revisited.Comment: 4 pages, uses revtex, also available at http://bigwhirl.uchicago.edu/jcn/pub_pbh.html . To appear in Phys. Rev. Let