A study of shock impacts and vibration dose values onboard highspeed marine craft

The shocks and impacts encountered on small high-speed craft exceed the limits set for safe working practice according to current standards. European legislation regarding the exposure to vibration will have far reaching effects on the operators of such craft with respect to the safety of their employees. This paper sets out to highlight the vibration dose values that can be expected during typical transits onboard high-speed craft and attempts to clarify some of the controversy currently surrounding vibration dose measurement in such circumstances. In order to relate vibration dosage to the impacts encountered and to boat motion, an algorithm was developed that identifies the timing and magnitude of impacts

Cosmic String Cusps with Small-Scale Structure: Their Forms and Gravitational Waveforms

We present a method for the introduction of small-scale structure into strings constructed from products of rotation matrices. We use this method to illustrate a range of possibilities for the shape of cusps that depends on the properties of the small-scale structure. We further argue that the presence of structure at cusps under most circumstances leads to the formation of loops at the size of the smallest scales. On the other hand we show that the gravitational waveform of a cusp remains generally unchanged; the primary effect of small-scale structure is to smooth out the sharp waveform emitted in the direction of cusp motion.Comment: RevTeX, 8 pages. Replaced with version accepted for publication by PR

Evolution of cosmic string configurations

We extend and develop our previous work on the evolution of a network of cosmic strings. The new treatment is based on an analysis of the probability distribution of the end-to-end distance of a randomly chosen segment of left-moving string of given length. The description involves three distinct length scales: $\xi$, related to the overall string density, $\bar\xi$, the persistence length along the string, and $\zeta$, describing the small-scale structure, which is an important feature of the numerical simulations that have been done of this problem. An evolution equation is derived describing how the distribution develops in time due to the combined effects of the universal expansion, of intercommuting and loop formation, and of gravitational radiation. With plausible assumptions about the unknown parameters in the model, we confirm the conclusions of our previous study, that if gravitational radiation and small-scale structure effects are neglected, the two dominant length scales both scale in proportion to the horizon size. When the extra effects are included, we find that while $\xi$ and $\bar\xi$ grow, $\zeta$ initially does not. Eventually, however, it does appear to scale, at a much lower level, due to the effects of gravitational back-reaction.Comment: 61 pages, requires RevTex v3.0, SUSSEX-TH-93/3-4, IMPERIAL/TP/92-93/4

Scaling property and peculiar velocity of global monopoles

We investigate the scaling property of global monopoles in the expanding universe. By directly solving the equations of motion for scalar fields, we follow the time development of the number density of global monopoles in the radiation dominated (RD) universe and the matter dominated (MD) universe. It is confirmed that the global monopole network relaxes into the scaling regime and the number per hubble volume is a constant irrespective of the cosmic time. The number density $n(t)$ of global monopoles is given by $n(t) \simeq (0.43\pm0.07) / t^{3}$ during the RD era and $n(t) \simeq (0.25\pm0.05) / t^{3}$ during the MD era. We also examine the peculiar velocity $v$ of global monopoles. For this purpose, we establish a method to measure the peculiar velocity by use of only the local quantities of the scalar fields. It is found that $v \sim (1.0 \pm 0.3)$ during the RD era and $v \sim (0.8 \pm 0.3)$ during the MD era. By use of it, a more accurate analytic estimate for the number density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.

Cosmic Rays From Cosmic Strings

It has been speculated that cosmic string networks could produce ultra-high energy cosmic rays as a by-product of their evolution. By making use of recent work on the evolution of such networks, it will be shown that the flux of cosmic rays from cosmologically useful, that is GUT scale strings, is too small to be used as a test for strings with any foreseeable technology.Comment: 11, Imperial/TP/93-94/2

Red imported fire ant impacts on the endangered Florida grasshopper sparrow

Red imported fire ants (Solenopsis invicta) invaded peninsular Florida more than 30 years ago. Highlands and Polk counties, Florida, were probably first invaded in the late 1960s. Since then, fire ants have continued both to spread and to increase in abundance. Experimental evidence has shown that red imported fire ants may have a detrimental impact on native species, both invertebrate and vertebrate, and that these impacts may be both direct and indirect. This segment of research was designed to determine if fire ants have a negative impact on Florida grasshopper sparrow (Ammodramus savannarumfloridanus) populations at Avon Park Air Force Bombing Range, Florida. The sampling reported herein was conducted during June and October, 1997, and all analyses are restricted to data collected during those periods. As assessed by baits, fire ants were dominant on about half the sites, and absent from others. In particular, OQ Range sites tended to have fewer fire ants present, while Delta Trail sites were more heavily infested, although there were exceptions. June fire ant abundance was strongly negatively correlated with both native ant abundance (r = -0.743, P = 0.006) and native ant species richness (r = -0.730, P = 0.007). October fire ant abundance was strongly negatively correlated with both native ant abundance (r = -0.690, P = 0.013) and native ant species richness (r = -0.736, P = 0.006). The patterns of fire ant abundance as assessed by pitfalls were very similar to those determined from bait sampling. June fire ant abundance was negatively correlated (p < 0.05) with native ant richness, but other June comparisons were not statistically significant (P > 0.05). October fire ant abundance was negatively correlated (P < 0.05) with native ant richness and abundance, but other comparisons were not statistically significant (P > 0.05). There was no significant correlation between overall insect biomass as assessed by light traps and fire ant abundance as assessed by baits or pitfalls. Total biomass varied considerably among the two sample periods because of changes in overall insect abundance during different seasons. There was a negative spatial correspondence between fire ants and native invertebrates. Over most of the intensive study areas, there was a negative spatial relationship between fire ants and the abundance of native invertebrates. Over about 50% of the intensive study areas, there was a negative spatial relationship between fire ants and the abundance of Florida grasshopper sparrows, although the relationship was not as strong as that between fire ants and native invertebrates. Fire ant and native invertebrates were negatively correlated at grasshopper sparrow count locations (r =0.347, P = 0.03). A multiple regression model was fit to the data, using fire ants and native invertebrates as independent variables, and grasshopper sparrow 100-m population estimates (n = 39) as the dependent variable. The influence of fire ants on grasshopper sparrows was negative while the influence of native invertebrates was positive. However, the overall model, while suggestive, was not significant (r = 0.304, P = 0.17). Fire ant abundance was a better (negative) predictor of sparrow populations (P = 0.13) than was invertebrate abundance (P = 0.59). The overall model and influence of fire ants on sparrow populations was suggestive of a negative influence warranting analyses of data for 1998 and 1999. (Document has 93 pages

On the size of the smallest scales in cosmic string networks

We present a method for the calculation of the gravitational back reaction cutoff on the smallest scales of cosmic string networks taking into account that not all modes on strings interact with all other modes. This results in a small scale structure cutoff that is sensitive to the initial spectrum of perturbations present on strings. From a simple model, we compute the cutoffs in radiation- and matter-dominated universes.Comment: 4 pages, revte

Cosmological Evolution of Global Monopoles

We investigate the cosmological evolution of global monopoles in the radiation dominated (RD) and matter dominated (MD) universes by numerically solving field equations of scalar fields. It is shown that the global monopole network relaxes into the scaling regime, unlike the gauge monopole network. The number density of global monopoles is given by $n(t) \simeq (0.43\pm0.07) / t^{3}$ during the RD era and $n(t) \simeq (0.25\pm0.05) / t^{3}$ during the MD era. Thus, we have confirmed that density fluctuations produced by global monopoles become scale invariant and are given by $\delta \rho \sim 7.2(5.0) \sigma^{2} / t^{2}$ during the RD (MD) era, where $\sigma$ is the breaking scale of the symmetry.Comment: 6 pages, 2 figures, to appear in Phys. Rev. D (R

Comment on "Quantum diffusion of 3-He impurities in solid 4- He"

In this comment I show that the experimental data on quantum diffusion of 3-He impurities in solid 4-He can be explained using the adopted quasiparticle theory. The contention by E.G. Kisvarsanyi and N.S. Sullivan (KS) in Phys.Rev.B v. 48, 16557 (1993) as well as in their Reply (ibid. v. 55, 3989 (1997)) to the Grigor'ev's Comment (Phys.Rev. B v. 55, 3987 (1997)) that "Pushkarov's theory of phonon scattering fails to fit the data by very large factors" is groundless and may result from their bad arithmetical error. This means that the phonon-impurity scattering mechanism of diffusion is consistent with experiment and its neglecting by KS makes their results questionable.Comment: RevTex, 5 pages, no figures, to be published in Phys.Rev.

Lagrangian evolution of global strings

We establish a method to trace the Lagrangian evolution of extended objects consisting of a multicomponent scalar field in terms of a numerical calculation of field equations in three dimensional Eulerian meshes. We apply our method to the cosmological evolution of global strings and evaluate the energy density, peculiar velocity, Lorentz factor, formation rate of loops, and emission rate of Nambu-Goldstone (NG) bosons. We confirm the scaling behavior with a number of long strings per horizon volume smaller than the case of local strings by a factor of $\sim$ 10. The strategy and the method established here are applicable to a variety of fields in physics.Comment: 5 pages, 2 figure