9,675 research outputs found
His+ reversions Caused in Salmonella typhimurium by different types of ionizing radiation
The yield of his+ reversions in the Ames Salmonella tester strain TA2638 has been determined for 60Co γ rays, 140 kV X rays, 5.4 keV characteristic X rays, 2.2 MeV protons, 3.1 MeV α particles, and 18 MeV/U Fe ions. Inactivation studies were performed with the same radiations. For both mutation and inactivation, the maximum effectiveness per unit absorbed dose was obtained for the characteristic X rays, which have a dose averaged linear energy transfer (LET) of roughly 10 keV/μm. The ratio of the effectiveness of this radiation to γ rays was 2 for inactivation and about 1.4 for the his+ reversion. For both end points the effectiveness decreases substantially at high LET, i.e., for the α particles and the Fe ions. The composition of the bottom and the top agar was the one recommended by Maron and Ames [Mutat. Res. 113, 173-215 (1983)] for application in chemical mutagenicity tests. The experiments with the less penetrating radiations differed from the usual protocol by utilization of a technique of plating the bacteria on the surface of the top agar. As in an earlier study [Roos et al., Radiat. Res. 104, 102-108 (1985)] greatly enhanced yields of mutations, relative to the spontaneous reversion rate, were obtained in these experiments by performing the irradiations 6 h after plating, which differs from the conventional procedure to irradiate the bacteria shortly after plating
Vacuum Energy: Cosmological Constant or Quintessence?
For a flat universe presently dominated by smooth energy, either cosmological
constant (LCDM) or quintessence (QCDM), we calculate the asymptotic collapsed
mass fraction as function of the present ratio of smooth energy to matter
energy . Identifying the normalized collapsed fraction as a
conditional probability for habitable galaxies, we observe that the observed
present ratio is likely in LCDM, but more likely in QCDM.
Inverse application of Bayes' Theorem makes the Anthropic Principle a
predictive scientific principle: the data implies that the prior probability
for must be essentially flat over the anthropically allowed
range. Interpreting this prior as a distribution over {\em theories} lets us
predict that any future theory of initial conditions must be indifferent to
. This application of the Anthropic Principle does not demand the
existence of other universes.Comment: 17 pages AAS LATEX, including 2 tables, 3 figures (Postscript
From Newton's Laws to the Wheeler-DeWitt Equation
This is a pedagogical paper which explains some ideas in cosmology at a level
accessible to undergraduate students. It does not use general relativity, but
uses the ideas of Newtonian cosmology worked out by Milne and McCrea. The
cosmological constant is also introduced within a Newtonian framework.
Following standard quantization procedures the Wheeler-DeWitt equation in the
minisuperspace approximation is derived for empty and non-empty universes.Comment: 13 pages, 1 figur
Quantum frequency estimation with trapped ions and atoms
We discuss strategies for quantum enhanced estimation of atomic transition
frequencies with ions stored in Paul traps or neutral atoms trapped in optical
lattices. We show that only marginal quantum improvements can be achieved using
standard Ramsey interferometry in the presence of collective dephasing, which
is the major source of noise in relevant experimental setups. We therefore
analyze methods based on decoherence free subspaces and prove that quantum
enhancement can readily be achieved even in the case of significantly imperfect
state preparation and faulty detections.Comment: 5 pages + 6 pages appendices; published versio
Personality traits, brie' recurrent depression and attempted suicide
This study investigated the relationship between attempted suicide, personality factors and brief recurrent depression. Over a period of 1 year, the demographic and psychiatric factors of 307 patients who had attempted suicide and subsequently been hospitalised at H. F. Verwoerd Hospital and referred to its Department of Psychiatry were recorded. Their personality traits were evaluated clinically. After 5 years, 205 respondents were traced to complete a follow-up questionnaire and, where possible, a personality assessment was completed on clinical grounds. They were also evaluated for brief recurrent depression. Among the men, antisocial, dependent and histrionic personality traits, in that order, were most commonly noted and among the women, histrionic, dependent and antisocial traits. A clear relationship between suicidal behaviour and the syndrome of brief recurrent depression was established. The latter was also found to be related to histrionic personality traits in women. This underscores the relationship between suicide attempts and histrionic personality traits
Response of the Ames Test to different Types of ionizing Radiation
Kein Inhaltsverzeichnis, keine Seitenzahl
- …