9,723 research outputs found
Wave polarizations for a beam-like gravitational wave in quadratic curvature gravity
We compute analytically the tidal field and polarizations of an exact
gravitational wave generated by a cylindrical beam of null matter of finite
width and length in quadratic curvature gravity. We propose that this wave can
represent the gravitational wave that keep up with the high energy photons
produced in a gamma ray burst (GRB) source.Comment: 5 pages, 3 figures, minor corrections, to appear in CQ
Phase transitions, entanglement and quantum noise interferometry in cold atoms
We show that entanglement monotones can characterize the pronounced
enhancement of entanglement at a quantum phase transition if they are sensitive
to long-range high order correlations. These monotones are found to develop a
sharp peak at the critical point and to exhibit universal scaling. We
demonstrate that similar features are shared by noise correlations and verify
that these experimentally accessible quantities indeed encode entanglement
information and probe separability.Comment: 4 pages 4 figure
Prenatal diagnosis of facial clefts: evaluation of a specialised counselling.
Prenatal diagnosis of cleft lip and palate has raised many questions concerning the best way to inform the parents and offer appropriate support during the remaining pregnancy to help prepare a positive birth experience. Prenatal counselling differs according to who is responsible, and to that person's knowledge of the practical aspects of care and the impact of the malformation on the child's quality of life. The aim of the study was to evaluate our current techniques and modify them when appropriate.
29 couples having experienced prenatal diagnosis were asked to respond retrospectively to a questionnaire. Personal obstetric and family history, timing and quality of information provided and their impressions at birth were considered.
The parents used several sources of information: the obstetrician, the counsel by the cleft team surgeon, the parents support groups and the Internet. 93% of the parents felt well prepared psychologically for the birth of their child and concerning the practical aspects of care. 54% felt relieved that their child was less affected than imagined. 96% considered prenatal diagnosis a benefit.
Basic information should be provided soon after ultrasound confirmation, followed by progressively more detailed technical discussions over the remaining pregnancy
Nonadiabatic electron heat pump
We investigate a mechanism for extracting heat from metallic conductors based
on the energy-selective transmission of electrons through a spatially
asymmetric resonant structure subject to ac driving. This quantum refrigerator
can operate at zero net electronic current as it replaces hot by cold electrons
through two energetically symmetric inelastic channels. We present numerical
results for a specific heterostructure and discuss general trends. We also
explore the conditions under which the cooling rate may approach the ultimate
limit given by the quantum of cooling power.Comment: 4 pages, 3 figures; published version, typos correcte
Postflight analysis of the single-axis acoustic system on SPAR VI and recommendations for future flights
The single axis acoustic levitator that was flown on SPAR VI malfunctioned. The results of a series of tests, analyses, and investigation of hypotheses that were undertaken to determine the probable cause of failure are presented, together with recommendations for future flights of the apparatus. The most probable causes of the SPAR VI failure were lower than expected sound intensity due to mechanical degradation of the sound source, and an unexpected external force that caused the experiment sample to move radially and eventually be lost from the acoustic energy well
Effects of random localizing events on matter waves: formalism and examples
A formalism is introduced to describe a number of physical processes that may
break down the coherence of a matter wave over a characteristic length scale l.
In a second-quantized description, an appropriate master equation for a set of
bosonic "modes" (such as atoms in a lattice, in a tight-binding approximation)
is derived. Two kinds of "localizing processes" are discussed in some detail
and shown to lead to master equations of this general form: spontaneous
emission (more precisely, light scattering), and modulation by external random
potentials. Some of the dynamical consequences of these processes are
considered: in particular, it is shown that they generically lead to a damping
of the motion of the matter-wave currents, and may also cause a "flattening" of
the density distribution of a trapped condensate at rest.Comment: v3; a few corrections, especially in Sections IV and
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