3,570 research outputs found
Mortality of Escherichia coli O157:H7 in Two Soils with Different Physical and Chemical Properties
Wild and domesticated animals can harbor a pathogenic Escherichia coli strain designated as O157:H7. Potential health problems could occur if strain O157:H7 is a more robust survivor in defecated waste than commonly used indicator bacteria. A laboratory study was conducted to assess E. coli O157:H7 survival relative to a nonpathogenie E. coli strain in two soils with different physical and chemical characteristics. Bacteria in the inoculated soils were enumerated on a weekly basis for 8 wk using a most probable number (MPN) technique. First-order decay models were used to describe bacteria mortality in the soils. Decay series were described slightly better by a two-stage function than by a single-stage function. Strain O157:H7 exhibited similar mortality patterns to the nonpathogenic E. coli in the same soil environment. Both E. coli strains had greater mortality rates in Pope silt loam (coarse-loamy, mixed, active, mesic Fluventic Dystrudept) than Zanesville silt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalf). Differences in available soil water probably were the overriding factor in E. coli survival. Escherichia coli O157:H7 survival could be modeled in the same way as nonpathogenic E. coli and appears to have a slightly higher mortality rate
\u3cem\u3eEscherichia coli\u3c/em\u3e Pathogen O157:H7 Does Not Survive Longer In Soil Than A Nonpathogenic Fecal Coliform
Survival rates for individual types of fecal organisms are quite different. Although some pathogens may persist as long as 5 years in soil, most fecal pathogens from human and animal waste usually die very quickly. Two to three months is sufficient in most cases to reduce pathogens to negligible numbers once they have been excreted or land-applied in animal wastes.
It is expensive and time- consuming to test for individual pathogens. Consequently, nonpathogenic fecal indicator bacteria, which are easily and inexpensively detected, are often used to study pathogen survival in soil and water. Current methods for rapidly detecting fecal indicator bacteria use the capacity of fecal coliforms (e.g. Escherichia coli) to metabolize a fluorescent indicator compound, 4-methylumbelliferyl ß-D-glucuronide (MUG) as evidence for fecal contamination
Mortality of Escherichia coli O157:H7 in Two Soils with Different Physical and Chemical Properties
Wild and domesticated animals can harbor a pathogenic Escherichia coli strain designated as O157:H7. Potential health problems could occur if strain O157:H7 is a more robust survivor in defecated waste than commonly used indicator bacteria. A laboratory study was conducted to assess E. coli O157:H7 survival relative to a nonpathogenie E. coli strain in two soils with different physical and chemical characteristics. Bacteria in the inoculated soils were enumerated on a weekly basis for 8 wk using a most probable number (MPN) technique. First-order decay models were used to describe bacteria mortality in the soils. Decay series were described slightly better by a two-stage function than by a single-stage function. Strain O157:H7 exhibited similar mortality patterns to the nonpathogenic E. coli in the same soil environment. Both E. coli strains had greater mortality rates in Pope silt loam (coarse-loamy, mixed, active, mesic Fluventic Dystrudept) than Zanesville silt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalf). Differences in available soil water probably were the overriding factor in E. coli survival. Escherichia coli O157:H7 survival could be modeled in the same way as nonpathogenic E. coli and appears to have a slightly higher mortality rate
Uniformly Accelerated Mirrors. Part 1: Mean Fluxes
The Davies-Fulling model describes the scattering of a massless field by a
moving mirror in 1+1 dimensions. When the mirror travels under uniform
acceleration, one encounters severe problems which are due to the infinite blue
shift effects associated with the horizons. On one hand, the Bogoliubov
coefficients are ill-defined and the total energy emitted diverges. On the
other hand, the instantaneous mean flux vanishes. To obtained well-defined
expressions we introduce an alternative model based on an action principle. The
usefulness of this model is to allow to switch on and off the interaction at
asymptotically large times. By an appropriate choice of the switching function,
we obtain analytical expressions for the scattering amplitudes and the fluxes
emitted by the mirror. When the coupling is constant, we recover the vanishing
flux. However it is now followed by transients which inevitably become singular
when the switching off is performed at late time. Our analysis reveals that the
scattering amplitudes (and the Bogoliubov coefficients) should be seen as
distributions and not as mere functions. Moreover, our regularized amplitudes
can be put in a one to one correspondence with the transition amplitudes of an
accelerated detector, thereby unifying the physics of uniformly accelerated
systems. In a forthcoming article, we shall use our scattering amplitudes to
analyze the quantum correlations amongst emitted particles which are also
ill-defined in the Davies-Fulling model in the presence of horizons.Comment: 23 pages, 7 postscript figure
Orientation and symmetries of Alexandrov spaces with applications in positive curvature
We develop two new tools for use in Alexandrov geometry: a theory of ramified
orientable double covers and a particularly useful version of the Slice Theorem
for actions of compact Lie groups. These tools are applied to the
classification of compact, positively curved Alexandrov spaces with maximal
symmetry rank.Comment: 34 pages. Simplified proofs throughout and a new proof of the Slice
Theorem, correcting omissions in the previous versio
Nonnegatively curved homogeneous metrics obtained by scaling fibers of submersions
We consider invariant Riemannian metrics on compact homogeneous spaces G/H
where an intermediate subgroup K between G and H exists, so that the
homogeneous space G/H is the total space of a Riemannian submersion. We study
the question as to whether enlarging the fibers of the submersion by a constant
scaling factor retains the nonnegative curvature in the case that the
deformation starts at a normal homogeneous metric. We classify triples of
groups (H,K,G) where nonnegative curvature is maintained for small
deformations, using a criterion proved by Schwachh\"ofer and Tapp. We obtain a
complete classification in case the subgroup H has full rank and an almost
complete classification in the case of regular subgroups.Comment: 23 pages; minor revisions, to appear in Geometriae Dedicat
Decay of accelerated particles
We study how the decay properties of particles are changed by acceleration.
It is shown that under the influence of acceleration (1) the lifetime of
particles is modified and (2) new processes (like the decay of the proton)
become possible. This is illustrated by considering scalar models for the decay
of muons, pions, and protons. We discuss the close conceptual relation between
these processes and the Unruh effect.Comment: Latex2e, 12 pages, 6 Postscript figures included with epsfig, to
appear in Phys. Rev.
Radiation from a uniformly accelerating harmonic oscillator
We consider a radiation from a uniformly accelerating harmonic oscillator
whose minimal coupling to the scalar field changes suddenly. The exact time
evolutions of the quantum operators are given in terms of a classical solution
of a forced harmonic oscillator. After the jumping of the coupling constant
there occurs a fast absorption of energy into the oscillator, and then a slow
emission follows. Here the absorbed energy is independent of the acceleration
and proportional to the log of a high momentum cutoff of the field. The emitted
energy depends on the acceleration and also proportional to the log of the
cutoff. Especially, if the coupling is comparable to the natural frequency of
the detector () enormous energies are radiated away
from the oscillator.Comment: 26 pages, 1 eps figure, RevTeX, minor correction in grammar, add a
discussio
The Energy-Momentum Tensor in Fulling-Rindler Vacuum
The energy density in Fulling-Rindler vacuum, which is known to be negative
"everywhere" is shown to be positive and singular on the horizons in such a
fashion as to guarantee the positivity of the total energy. The mechanism of
compensation is displayed in detail.Comment: 9 pages, ULB-TH-15/9
- …