699 research outputs found
Bubble formation in potential
Scalar field theory with an asymmetric potential is studied at zero
temperature and high-temperature for potential. The equations of
motion are solved numerically to obtain O(4) spherical symmetric and O(3)
cylindrical symmetric bounce solutions. These solutions control the rates for
tunneling from the false vacuum to the true vacuum by bubble formation. The
range of validity of the thin-wall approximation (TWA) is investigated. An
analytical solution for the bounce is presented, which reproduces the action in
the thin-wall as well as the thick-wall limits.Comment: 22 pag
Helmholtz's inverse problem of the discrete calculus of variations
International audienceWe derive the discrete version of the classical Helmholtz's condition. Precisely, we state a theorem characterizing second order finite differences equations admitting a Lagrangian formulation. Moreover, in the affirmative case, we provide the class of all possible Lagrangian formulations
Singularities of bi-Hamiltonian systems
We study the relationship between singularities of bi-Hamiltonian systems and
algebraic properties of compatible Poisson brackets. As the main tool, we
introduce the notion of linearization of a Poisson pencil. From the algebraic
viewpoint, a linearized Poisson pencil can be understood as a Lie algebra with
a fixed 2-cocycle. In terms of such linearizations, we give a criterion for
non-degeneracy of singular points of bi-Hamiltonian systems and describe their
types
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
The effect of maternal ketanserin treatment on foetal 5-HT receptor function in umbilical cord artery of pre-eclamptic patients
Background: Maternal treatment with the 5-HT2Areceptor antagonist ketanserin (KT) in pre-eclamptic patients is associated with a high placental transmission of KT, resulting in pharmacologically active levels of KT in the umbilical cord artery (UCA) and the neonate. Prolonged exposure to a 5-HT receptor antagonist may influence the functionality of foetal 5-HT receptors and compromise foetal development. Objective: To study whether exposure to KT influences the characteristics of foetal 5-HT receptors, functional studies were performed on 5-HT2Aand 5-HT1B/1Dreceptors in UCA from pre-eclamptic patients treated with KT. Methods: UCAs were obtained, immediately after delivery, from pre-eclamptic patients (n = 7), treated antenatally with intravenous KT. Pre-eclamptic patients (n = 13), not treated with KT (non-KT), were included as a control group. Segments of UCA were prepared and mounted in tissue baths and isometric force changes were determined. Cumulative concentration response curves to 5-HT and to the 5-HT1B/1Dreceptor agonist sumatriptan were constructed in the absence or presence of the 5-HT2Areceptor antagonist KT or the 5-HT1B/1Dreceptor antagonist GR125743, respectively. Results: All UCA segments showed contractile responses to both 5-HT and sumatriptan, and the concentration response curves showed a rightward shift with increasing concentrations of KT and
A Step Beyond the Bounce: Bubble Dynamics in Quantum Phase Transitions
We study the dynamical evolution of a phase interface or bubble in the
context of a \lambda \phi^4 + g \phi^6 scalar quantum field theory. We use a
self-consistent mean-field approximation derived from a 2PI effective action to
construct an initial value problem for the expectation value of the quantum
field and two-point function. We solve the equations of motion numerically in
(1+1)-dimensions and compare the results to the purely classical evolution. We
find that the quantum fluctuations dress the classical profile, affecting both
the early time expansion of the bubble and the behavior upon collision with a
neighboring interface.Comment: 12 pages, multiple figure
The STAR Silicon Strip Detector (SSD)
The STAR Silicon Strip Detector (SSD) completes the three layers of the
Silicon Vertex Tracker (SVT) to make an inner tracking system located inside
the Time Projection Chamber (TPC). This additional fourth layer provides two
dimensional hit position and energy loss measurements for charged particles,
improving the extrapolation of TPC tracks through SVT hits. To match the high
multiplicity of central Au+Au collisions at RHIC the double sided silicon strip
technology was chosen which makes the SSD a half million channels detector.
Dedicated electronics have been designed for both readout and control. Also a
novel technique of bonding, the Tape Automated Bonding (TAB), was used to
fullfill the large number of bounds to be done. All aspects of the SSD are
shortly described here and test performances of produced detection modules as
well as simulated results on hit reconstruction are given.Comment: 11 pages, 8 figures, 1 tabl
Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2
We have measured the spin structure functions g2p and g2d and the virtual
photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0
< Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons
from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is
significantly smaller than the sqrt{R} positivity limit over the measured
range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We
obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The
Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range
0.02 < x < 0.8.Comment: 12 pages, 4 figures, 1 tabl
Availability of age-appropriate paediatric formulations in the Netherlands: The need in daily clinical practice remains
Objectives: To quantify the availability of authorised, age-appropriate paediatric medicines in clinical practice in the Netherlands and to identify gaps by assessing dispensing practice in a paediatric hospital. Methods: The availability of age-appropriate formulations was assessed by conducting a survey on the use of pharmacy compounded medicines among the paediatric hospitals in the Netherlands, and by analysing dispensing data of oral medication from the inpatient pharmacy of the largest paediatric hospital in the Netherlands. The age-appropriateness of the dispensed formulations was assessed on two aspects: dose-capability and acceptability. Liquid drug products that are unsuitable due to the presence of potentially harmful excipients, were identified based on the dosage in clinical practice. Results: For 129 out of 139 drug substances included in the survey (93%), at least one of the eight respondents stated to use a pharmacy compounded product to meet the needs of their paediatric patients. The age-appropriateness of medicines dispensed from the inpatient pharmacy increased with age, and was higher for non-intensive care unit (ICU) patients than for ICU patients. We identified 15 drug products causing excipient exposure above the European Medicines Agency-recommended values. Conclusions: This study confirms there is still a large need for age-appropriate formu
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