735 research outputs found
Planar ion trap (retarding potential analyzer) experiment for atmosphere explorer
The retarding potential analyzer and drift meter were carried aboard all three Atmosphere Explorer spacecraft. These instruments measure the total thermal ion concentration and temperature, the bulk thermal ion velocity vector and some limited properties of the relative abundance of H(+), He(+), O(+) and molecular ions. These instruments functioned with no internal failures on all the spacecraft. On AE-E there existed some evidence for external surface contamination that damaged the integrity of the RPA sweep grids. This led to some difficulties in data reduction and interpretation that did not prove to be a disastrous problem. The AE-D spacecraft functioned for only a few months before it re-entered. During this time the satellite suffered from a nutation about the spin axis of about + or - 2 deg. This 2 deg modulation was superimposed upon the ion drift meter horizontal ion arrival angle output requiring the employment of filtering techniques to retrieve the real data
Evaluation of the hazard from exposure to electron irradiation simulating that in the synchronous orbit
The electron spectrum predicted for the synchronous orbit was simulated to determine the effects that might occur to astroscientists exposed to such irradiation while on a prolonged space station mission in that region. Miniature pigs were exposed to monoenergetic and spectral-fractionated irradiations with 0.5 to 2.1 MeV electrons. Clinical and pathological alterations observed in biopsies were correlated with depth-dose pattern and length of post irradiation period up to one year. With monoenergetic electrons, the lowest dose causing a recognizable lesion was 1450 rad and with increasing dose lesions appeared earlier and were more severe. At the highest dose given, 2650 rad, ulceration extending into the dermis was present by twenty one days and required about four months for complete healing. Spectral-fractionated irradiations, in which the total dose range was essentially comparable to that of the monoenergetic series, resulted in very minimal outer dermis edema at 1790 rad and at no dose employed did necrosis of epidermis or ulceration into dermis occur
Calibration of liquid argon and neon detectors with
We report results from tests of Kr, as a calibration
source in liquid argon and liquid neon. Kr atoms are
produced in the decay of Rb, and a clear Kr
scintillation peak at 41.5 keV appears in both liquids when filling our
detector through a piece of zeolite coated with Rb. Based on this
scintillation peak, we observe 6.0 photoelectrons/keV in liquid argon with a
resolution of 6% (/E) and 3.0 photoelectrons/keV in liquid neon with a
resolution of 19% (/E). The observed peak intensity subsequently decays
with the Kr half-life after stopping the fill, and we
find evidence that the spatial location of Kr atoms in
the chamber can be resolved. Kr will be a useful
calibration source for liquid argon and neon dark matter and solar neutrino
detectors.Comment: 7 pages, 12 figure
THE EFFECTS OF 2.0-Bev PROTONS IN MICE
The biological effects of proton beams of 2.0 to 2.2 Bev were studied in mice. Physical studies of particle distribution and depth dosimetry are described. Data are presented on lethal dosage measurements and studies of light element activation in tissues through proton reactions (p,pn) as determined by whole-body counting of gamma activity. (C.H.
Hybrid simulations of lateral diffusion in fluctuating membranes
In this paper we introduce a novel method to simulate lateral diffusion of
inclusions in a fluctuating membrane. The regarded systems are governed by two
dynamic processes: the height fluctuations of the membrane and the diffusion of
the inclusion along the membrane. While membrane fluctuations can be expressed
in terms of a dynamic equation which follows from the Helfrich Hamiltonian, the
dynamics of the diffusing particle is described by a Langevin or Smoluchowski
equation. In the latter equations, the curvature of the surface needs to be
accounted for, which makes particle diffusion a function of membrane
fluctuations. In our scheme these coupled dynamic equations, the membrane
equation and the Langevin equation for the particle, are numerically integrated
to simulate diffusion in a membrane. The simulations are used to study the
ratio of the diffusion coefficient projected on a flat plane and the
intramembrane diffusion coefficient for the case of free diffusion. We compare
our results with recent analytical results that employ a preaveraging
approximation and analyze the validity of this approximation. A detailed
simulation study of the relevant correlation functions reveals a surprisingly
large range where the approximation is applicable.Comment: 12 pages, 9 figures, accepted for publication in Phys. Rev.
First measurement of discrimination between helium and electron recoils in liquid xenon for low-mass dark matter searches
We report the first measurement of discrimination between low-energy helium
recoils and electron recoils in liquid xenon. This result is relevant to
proposed low-mass dark matter searches which seek to dissolve light target
nuclei in the active volume of liquid-xenon time projection chambers.
Low-energy helium recoils were produced by degrading particles from
Po with a gold foil situated on the cathode of a liquid xenon
time-projection chamber. The resulting population of helium recoil events is
well separated from electron recoils and is also offset from the expected
position of xenon nuclear recoil events.Comment: 4 pages, 3 figure
System for the measurement of oscillator instability
System for measuring phase and frequency fluctuations of high precision oscillator
PROGRESSIVE EPITHELIAL DYSPLASIA IN MOUSE SKIN IRRADIATED WITH 10 Mev PROTONS
Up to 6 months after proton irradiation at 600 and 1200 rad epithelial hyperplasia persisted in the exposed mouse skin. Hydropic degeneration of mandy epithelial cells occurred with intra-epithelial cyst formation with hemorrhage. Focal areas of basement membrane degenerated. Interruption of and fragmentation of underlying collagen fibers was prominent. Of interest is the paramount observation that with this degree of cellular alteration and with complete breakdown of basement membrane the epithelial cells did not invade into the dermis. This suggests that the sltered epithelial cells must actually be definitely neoplastic for true invasion to occur and that a single exposure at these doses did not alter the cells sufficiently to render then andaplastic. It is possible however that larger single doses with subsequent time interval elapse might provoke the formation of neoplastic cells. This and the effect of repeated small doses and with longer periods after irradiation before sacrifice of the animal are now being investigated. (auth
Observation of the Dependence of Scintillation from Nuclear Recoils in Liquid Argon on Drift Field
We have exposed a dual-phase Liquid Argon Time Projection Chamber (LAr-TPC)
to a low energy pulsed narrowband neutron beam, produced at the Notre Dame
Institute for Structure and Nuclear Astrophysics to study the scintillation
light yield of recoiling nuclei in a LAr-TPC. A liquid scintillation counter
was arranged to detect and identify neutrons scattered in the LAr-TPC target
and to select the energy of the recoiling nuclei.
We report the observation of a significant dependence on drift field of
liquid argon scintillation from nuclear recoils of 11 keV. This observation is
important because, to date, estimates of the sensitivity of noble liquid TPC
dark matter searches are based on the assumption that electric field has only a
small effect on the light yield from nuclear recoils.Comment: v3 updated to reflect published version, including a set of plots for
49.9 keV dat
Curvature-coupling dependence of membrane protein diffusion coefficients
We consider the lateral diffusion of a protein interacting with the curvature
of the membrane. The interaction energy is minimized if the particle is at a
membrane position with a certain curvature that agrees with the spontaneous
curvature of the particle. We employ stochastic simulations that take into
account both the thermal fluctuations of the membrane and the diffusive
behavior of the particle. In this study we neglect the influence of the
particle on the membrane dynamics, thus the membrane dynamics agrees with that
of a freely fluctuating membrane. Overall, we find that this curvature-coupling
substantially enhances the diffusion coefficient. We compare the ratio of the
projected or measured diffusion coefficient and the free intramembrane
diffusion coefficient, which is a parameter of the simulations, with analytical
results that rely on several approximations. We find that the simulations
always lead to a somewhat smaller diffusion coefficient than our analytical
approach. A detailed study of the correlations of the forces acting on the
particle indicates that the diffusing inclusion tries to follow favorable
positions on the membrane, such that forces along the trajectory are on average
smaller than they would be for random particle positions.Comment: 16 pages, 8 figure
- …