45 research outputs found
Parity nonconservation in Atomic Zeeman Transitions
We discuss the possibility of measuring nuclear anapole moments in atomic
Zeeman transitions and perform the necessary calculations. Advantages of using
Zeeman transitions include variable transition frequencies and the possibility
of enhancement of parity nonconservation effects
Coulomb energy contribution to the excitation energy in Th and enhanced effect of variation
We calculated the contribution of Coulomb energy to the spacing between the
ground and first excited state of Th nucleus as a function of the
deformation parameter . We show that despite the fact that the odd
particle is a neutron, the change in Coulomb energy between these two states
can reach several hundreds KeV.This means that the effect of the variation of
the fine structure constant may be enhanced
times in the 7.6 eV "nuclear clock" transition
between the ground and first excited states in the Th nucleus.Comment: 6 pages,2 figure
A New Option for a Search for Alpha Variation: Narrow Transitions with Enhanced Sensitivity
We consider several transitions between narrow lines that have an enhanced
sensitivity to a possible variation of the fine structure constant, alpha. This
enhancement may allow a search to be performed with an effective suppression of
the systematic sources of uncertainty that are unavoidable in conventional
high-resolution spectroscopic measurements. In the future this may provide the
strongest laboratory constraints on alpha variation
Placenta previa percreta left in situ - management by delayed hysterectomy: a case report
<p>Abstract</p> <p>Introduction</p> <p>Placenta percreta is an obstetric emergency often associated with massive hemorrhage and emergency hysterectomy.</p> <p>Case presentation</p> <p>We present the case of a 30-year-old African woman, gravida 7, para 5, with placenta percreta managed by an alternative approach: the placenta was left <it>in situ</it>, methotrexate was administered, and a delayed hysterectomy was successfully performed.</p> <p>Conclusions</p> <p>Further studies are needed to develop the most appropriate management option for the most severe cases of abnormal placentation. Delayed hysterectomy may be a reasonable strategy in the most severe cases.</p
Cold atom Clocks and Applications
This paper describes advances in microwave frequency standards using
laser-cooled atoms at BNM-SYRTE. First, recent improvements of the Cs
and Rb atomic fountains are described. Thanks to the routine use of a
cryogenic sapphire oscillator as an ultra-stable local frequency reference, a
fountain frequency instability of where
is the measurement time in seconds is measured. The second advance is a
powerful method to control the frequency shift due to cold collisions. These
two advances lead to a frequency stability of at 7\times 10^{-16}^{87}^{133}$Cs fountains.
Finally we give an update on the cold atom space clock PHARAO developed in
collaboration with CNES. This clock is one of the main instruments of the
ACES/ESA mission which is scheduled to fly on board the International Space
Station in 2008, enabling a new generation of relativity tests.Comment: 30 pages, 11 figure
Varying constants, Gravitation and Cosmology
Fundamental constants are a cornerstone of our physical laws. Any constant
varying in space and/or time would reflect the existence of an almost massless
field that couples to matter. This will induce a violation of the universality
of free fall. It is thus of utmost importance for our understanding of gravity
and of the domain of validity of general relativity to test for their
constancy. We thus detail the relations between the constants, the tests of the
local position invariance and of the universality of free fall. We then review
the main experimental and observational constraints that have been obtained
from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites
dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic
microwave background and big bang nucleosynthesis. At each step we describe the
basics of each system, its dependence with respect to the constants, the known
systematic effects and the most recent constraints that have been obtained. We
then describe the main theoretical frameworks in which the low-energy constants
may actually be varying and we focus on the unification mechanisms and the
relations between the variation of different constants. To finish, we discuss
the more speculative possibility of understanding their numerical values and
the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit
Continuous-time random walks on networks with vertex- and time-dependent forcing
We have investigated the transport of particles moving as random walks on the vertices of a network, subject to vertex- and time-dependent forcing. We have derived the generalized master equations for this transport using continuous time random walks, characterized by jump and waiting time densities, as the underlying stochastic process. The forcing is incorporated through a vertex- and time-dependent bias in the jump densities governing the random walking particles. As a particular case, we consider particle forcing proportional to the concentration of particles on adjacent vertices, analogous to self-chemotactic attraction in a spatial continuum. Our algebraic and numerical studies of this system reveal an interesting pair-aggregation pattern formation in which the steady state is composed of a high concentration of particles on a small number of isolated pairs of adjacent vertices. The steady states do not exhibit this pair aggregation if the transport is random on the vertices, i.e., without forcing. The manifestation of pair aggregation on a transport network may thus be a signature of self-chemotactic-like forcing