9,260 research outputs found
Schools Transition Outdoor Project Report of schools transition research project including One in a Million Free School, Bradford, Leeds Beckett University, Nell Bank Adventure Education Centre and Bradford Adventure Development Unit, Bradford Metropolitan District Council
Stochastic models for atomic clocks
For the atomic clocks used in the National Bureau of Standards Time Scales, an adequate model is the superposition of white FM, random walk FM, and linear frequency drift for times longer than about one minute. The model was tested on several clocks using maximum likelihood techniques for parameter estimation and the residuals were acceptably random. Conventional diagnostics indicate that additional model elements contribute no significant improvement to the model even at the expense of the added model complexity
X-Ray-Induced Cell Death by Apoptosis in the Immature Rat Cerebellum
The cells of the external granular layer (EGL) of the developing cerebellum are known to be particularly sensitive to radiation. In the past, changes induced in this layer by irradiation have been referred to by non-specific terms such as pyknotic cells and the mode of cell death has been assumed to be necrosis. However, in published light micrographs of these dying cells, the appearance is suggestive of apoptosis, a distinctive mode of cell death which occurs spontaneously in normal adult and embryonic tissues and can also be triggered by certain pathological stimuli.
This light and transmission electron microscopic study of control and irradiated (7 h post-irradiation) rat cerebellum from 18 day fetuses and 5 day-old neonates showed that the cell death was effected by apoptosis. The apoptosis was markedly enhanced by x-irradiation and quantification of the cell death in the EGL of 5 day-old rats exposed to 4, 8, 25, 100, and 400 cGy x-irradiation demonstrated that there was a positive dose response relationship. The extent of cell death by apoptosis which was 0.2% in control, ranged from 0.8% after 4 cGy to 62.3% after 400cGy x-irradiation.
The recognition that cell death by apoptosis can be a major component of x-irradiation damage has important implications for radiobiological studies
The Morphologic Categorization of Cell Death Induced by Mild Hyperthermia and Comparison with Death Induced by Ionizing Radiation and Cytotoxic Drugs
This paper presents 1. a summary of the morphological categorization of cell death, 2. results of two in vivo studies on the cell death induced by mild hyperthermia in rat small intestine and mouse mastocytoma, and 3. a comparison of the cell death induced by hyperthermia, radiation and cytotoxic drugs.
Two distinct forms of cell death, apoptosis and necrosis, can be recognized on morphologic grounds. Apoptosis appears to be a process of active cellular self-destruction to which a biologically meaningful role can usually be attributed, whereas necrosis is a passive degenerative phenomenon that results from irreversible cellular injury.
Light and transmission electron microscopic studies showed that lower body hyperthermia (43°C for 30 min) induced only apoptosis of intestinal epithelial cells, and of lymphocytes, plasma cells, and eosinophils. In the mastocytoma, hyperthermia (43°C for 15 min) produced widespread tumor necrosis and also enhanced apoptosis of tumor cells.
Ionizing radiation and cytotoxic drugs are also known to induce apoptosis in a variety of tissues. It is attractive to speculate that DNA damage by each agent is the common event which triggers the same process of active cellular self-destruction that characteristically effects selective cell deletion in normal tissue homeostasis
Elastic electron scattering from 3-hydroxytetrahydrofuran: experimental and theoretical studies
We report the results of measurements and calculations for elastic electron scattering from 3-hydroxytetrahydrofuran (C4H8O2). The measurements are performed with a crossed electron-target beam apparatus and the absolute cross-sections are determined using the relative flow technique. The calculations are carried out using the Schwinger multichannel method in the static-exchange plus polarization (SEP) approximation. A set of angular differential cross-sections (DCS) is provided at five incident energies (6.5, 8, 10, 15 and 20 eV) over an angular range of 20–130°, and the energy dependence of the elastic DCS at a scattering angle of 120° is also presented. Integral elastic and elastic momentum transfer cross-sections have also been derived and calculated. The results are compared with those of recent measurements and calculations for the structurally similar molecule tetrahydrofuran (C4H8O)
Path-integral calculation of the third virial coefficient of quantum gases at low temperatures
We derive path-integral expressions for the second and third virial
coefficients of monatomic quantum gases. Unlike previous work that considered
only Boltzmann statistics, we include exchange effects (Bose-Einstein or
Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials
to calculate the third virial coefficient of 3He and 4He in the temperature
range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited
experimental data. Inclusion of exchange effects is necessary to obtain
accurate results below about 7 K.Comment: The following article has been accepted by The Journal of Chemical
Physics. After it is published, it will be found at http://jcp.aip.org/
Version 2 includes the corrections detailed in the Erratu
Beam alignment techniques based on the current multiplication effect in photoconductors Third summary technical progress report, 15 Nov. 1966 - 15 Oct. 1967
Beam alignment techniques developed for infrared sensitive single crystal germanium to study multiplication effect in photoconductor
Non-Gaussian statistics of electrostatic fluctuations of hydration shells
We report the statistics of electric field fluctuations produced by SPC/E
water inside a Kihara solute given as a hard-sphere core with a Lennard-Jones
layer at its surface. The statistics of electric field fluctuations, obtained
from numerical simulations, are studied as a function of the magnitude of a
point dipole placed close to the solute-water interface. The free energy
surface as a function of the electric field projected on the dipole direction
shows a cross-over with the increasing dipole magnitude. While it is a
single-well harmonic function at low dipole values, it becomes a double-well
surface at intermediate dipole moment magnitudes, transforming to a single-well
surface, with a non-zero minimum position, at still higher dipoles. A broad
intermediate region where the interfacial waters fluctuate between the two
minima is characterized by intense field fluctuations, with non-Gaussian
statistics and the variance far exceeding the linear-response expectations. The
excited state of the surface water is found to be lifted above the ground state
by the energy required to break approximately two hydrogen bonds. This state is
pulled down in energy by the external electric field of the solute dipole,
making it readily accessible to thermal excitations. The excited state is a
localized surface defect in the hydrogen-bond network creating a stress in the
nearby network, but otherwise relatively localized in the region closest to the
solute dipole
Urban water security - what does it mean?
This research is focussed on understanding what urban water security means–a surprisingly elusive concept given the global shift from rural to urban living. We first make the case for a distinct urban water security definition. We then identify 25 unique water security definitions, of which three relate to the urban context but all with scope for improvement. Applying novel indices, we assess the prevalence, complexity and evolution of themes and dimensions within all definitions and find a stable spectrum of themes; but note a shifting emphasis towards environmental and social dimensions, away from quality and quantity of supply. Overall the definitions are becoming more comprehensive by simply listing more outcomes to be achieved. Instead of this ‘shopping-list’ approach, we propose a simplified urban water security definition with a focus on agreement of needs with community stakeholders, while using the themes to guide what the objectives might be
Electric field inside a "Rossky cavity" in uniformly polarized water
Electric field produced inside a solute by a uniformly polarized liquid is
strongly affected by dipolar polarization of the liquid at the interface. We
show, by numerical simulations, that the electric "cavity" field inside a
hydrated non-polar solute does not follow the predictions of standard Maxwell's
electrostatics of dielectrics. Instead, the field inside the solute tends, with
increasing solute size, to the limit predicted by the Lorentz virtual cavity.
The standard paradigm fails because of its reliance on the surface charge
density at the dielectric interface determined by the boundary conditions of
the Maxwell dielectric. The interface of a polar liquid instead carries a
preferential in-plane orientation of the surface dipoles thus producing
virtually no surface charge. The resulting boundary conditions for
electrostatic problems differ from the traditional recipes, affecting the
microscopic and macroscopic fields based on them. We show that relatively small
differences in cavity fields propagate into significant differences in the
dielectric constant of an ideal mixture. The slope of the dielectric increment
of the mixture versus the solute concentration depends strongly on which
polarization scenario at the interface is realized. A much steeper slope found
in the case of Lorentz polarization also implies a higher free energy penalty
for polarizing such mixtures.Comment: 9 pages, 8 figure
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