28,334 research outputs found
Rat mammary carcinogenesis following neutron- or X-radiation
Female 61 to 63 - day - old Sprague-Dawley rats were exposed once to a single dose of either 0.43 - MeV
neutrons or 250 - kVX - rays . For neutrons 23 rats were exposed in plastic tubes rotated around and 31 c m from
a water-cooled tritium impregnated target bombarded with 2.45 - MeV protons from a V a n de Graaff generator.
The mean kerma was measured at the rat location by integrating the response of a rat - sized homogeneous
tissue equivalent ionization chamber of minimum mass. The ratio between absorbed dose and kerma is under
investigation and is anticipated to be approximately 0.7. A compensated GM gamma-ray dosimeter indicated
that the gamma - ray doses were 3.5% of the total dose. All rats were examined weekly for the presence
of breast tumours and these were removed, fixed, stained and verified histologically as mammary neoplasms.
At 10 months after exposure 98<7ο of the rats were a live . The neutron kerma, the per cent of rats with
mammary neoplasia, and the number of rats were, respectively: 0.125 rads, 8.2°}o, 182; 0.5 rads, 9.0^0,
89; 2 rads, 20. 6,68; and 8 rads, 31.1%, 45. The X - ray results were: 30 R, 1.4% 95; 60 R, 27. l°Io, 48;
and 90 R, 35.4%, 48. A 3. O^o incidence was found in 167 control rats. At 10 months after exposure the
mammary neoplastic response after 8 rads of neutrons corresponds approximately to that after 60 - 90 R of
X - rays . Similarly, the response after 2 rads of neutrons was intermediate between 30 and 60 R of X - rays and
the response after 0 . 125 and 0.5 rads of neutrons was similar to that after 30 R of X - rays . This demonstrates
that the RBE for 0.43 - MeV neutrons is much lower at high doses than at low doses. Determination of the
confidence limits for the dose-RBE dependence and dose-incidence relationship will be determined as additional
data are collected
Statistical Geometry in Quantum Mechanics
A statistical model M is a family of probability distributions, characterised
by a set of continuous parameters known as the parameter space. This possesses
natural geometrical properties induced by the embedding of the family of
probability distributions into the Hilbert space H. By consideration of the
square-root density function we can regard M as a submanifold of the unit
sphere in H. Therefore, H embodies the `state space' of the probability
distributions, and the geometry of M can be described in terms of the embedding
of in H. The geometry in question is characterised by a natural Riemannian
metric (the Fisher-Rao metric), thus allowing us to formulate the principles of
classical statistical inference in a natural geometric setting. In particular,
we focus attention on the variance lower bounds for statistical estimation, and
establish generalisations of the classical Cramer-Rao and Bhattacharyya
inequalities. The statistical model M is then specialised to the case of a
submanifold of the state space of a quantum mechanical system. This is pursued
by introducing a compatible complex structure on the underlying real Hilbert
space, which allows the operations of ordinary quantum mechanics to be
reinterpreted in the language of real Hilbert space geometry. The application
of generalised variance bounds in the case of quantum statistical estimation
leads to a set of higher order corrections to the Heisenberg uncertainty
relations for canonically conjugate observables.Comment: 32 pages, LaTex file, Extended version to include quantum measurement
theor
Minimal qubit tomography
We present, and analyze thoroughly, a highly symmetric and efficient scheme
for the determination of a single-qubit state, such as the polarization
properties of photons emitted by a single-photon source. In our scheme there
are only four measured probabilities, just enough for the determination of the
three parameters that specify the qubit state, whereas the standard procedure
would measure six probabilities.Comment: 14 pages, 10 figures; final versio
Hot Core, Outflows and Magnetic Fields in W43-MM1 (G30.79 FIR 10)
We present submillimeter spectral line and dust continuum polarization
observations of a remarkable hot core and multiple outflows in the high-mass
star-forming region W43-MM1 (G30.79 FIR 10), obtained using the Submillimeter
Array (SMA). A temperature of 400 K is estimated for the hot-core using
CHCN (J=19-18) lines, with detections of 11 K-ladder components. The high
temperature and the mass estimates for the outflows indicate high-mass
star-formation. The continuum polarization pattern shows an ordered
distribution, and its orientation over the main outflow appears aligned to the
outflow. The derived magnetic field indicates slightly super-critical
conditions. While the magnetic and outflow energies are comparable, the B-field
orientation appears to have changed from parsec scales to 0.1 pc scales
during the core/star-formation process.Comment: accepted, ApJ Letter
An electron paramagnetic resonance study of Pr_{0.6}Ca_{0.4}MnO_{3} across the charge ordering transition
We report the first electron paramagnetic resonance studies of single
crystals and powders of Pr_{0.6}Ca_{0.4}MnO_{3} in the 300-4.2 K range,
covering the charge ordering transition at ~ 240 K and antiferromagnetic
transition (T_N) at ~ 170 K. The asymmetry parameter for the Dysonian single
crystal spectra shows anomalous increase at T_{co}. Below T_{co} the g-value
increases continuously, suggesting a gradual strengthening of orbital ordering.
The linewidth undergoes a sudden increase at T_{co} and continues to increase
down to T_N. The intensity increases as the temperature is decreased till
T_{co} due to the renormalization of magnetic susceptibility arising from the
build up of ferromagnetic correlations. The value of the exchange constant, J,
is estimated to be 154 K.Comment: Uses Revtex3.
Quasi-stationary waves in the Southern Hemisphere during El Niño and La Niña events
Characteristics of quasi-stationary (QS) waves in the Southern Hemisphere are discussed using 49 years (1950–1998) of NCEP/NCAR reanalysis data. A comparison between the stationary wave amplitudes and phases between the recent data (1979–1998) and the entire 49 years data showed that the differences are not large and the 49 years data can be used for the study. Using the 49 years of data it is found that the amplitude of QS wave&nbsp;1 has two maxima in the upper atmosphere, one at 30°S and the other at 55°S. QS waves 2 and 3 have much less amplitude. Monthly variation of the amplitude of QS wave&nbsp;1 shows that it is highest in October, particularly in the upper troposphere and stratosphere. </p><p style="line-height: 20px;"> To examine the QS wave propagation Plumb's methodology is used. A comparison of Eliassen-Palm fluxes for El Niño and La Niña events showed that during El Niño events there is a stronger upward and equatorward propagation of QS waves, particularly in the austral spring. Higher upward propagation indicates higher energy transport. A clear wave train can be identified at 300hPa in all the seasons except in summer. The horizontal component of wave activity flux in the El Niño composite seems to be a Rossby wave propagating along a Rossby wave guide, at first poleward until it reaches its turning latitude in the Southern Hemisphere midlatitudes, then equatorward in the vicinity of South America. The position of the center of positive anomalies in the austral spring in the El&nbsp;Niño years over the southeast Pacific, near South America, favors the occurrence of blocking highs in this region. This agrees with a recent numerical study by Renwick and Revell (1999).<br><br> <b>Key words.</b> Meteorology and atmospheric dynamics (climatology; general circulation; ocean-atmosphere interactions
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