324 research outputs found
Dual equilibrium in a finite aspect ratio tokamak
A new approach to high pressure magnetically-confined plasmas is necessary to
design efficient fusion devices. This paper presents an equilibrium combining
two solutions of the Grad-Shafranov equation, which describes the
magnetohydrodynamic equilibrium in toroidal geometry. The outer equilibrium is
paramagnetic and confines the inner equilibrium, whose strong diamagnetism
permits to balance large pressure gradients. The existence of both equilibria
in the same volume yields a dual equilibrium structure. Their combination also
improves free-boundary mode stability
Formation of ultracold RbCs molecules by photoassociation
The formation of ultracold metastable RbCs molecules is observed in a double
species magneto-optical trap through photoassociation below the
^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous
emission. The molecules are detected by resonance enhanced two-photon
ionization. Using accurate quantum chemistry calculations of the potential
energy curves and transition dipole moment, we interpret the observed
photoassociation process as occurring at short internuclear distance, in
contrast with most previous cold atom photoassociation studies. The vibrational
levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^-
electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation
limit. The computed vibrational distribution of the produced molecules shows
that they are stabilized in deeply bound vibrational states of the lowest
triplet state. We also predict that a noticeable fraction of molecules is
produced in the lowest level of the electronic ground state
Optimal trapping wavelengths of Cs molecules in an optical lattice
The present paper aims at finding optimal parameters for trapping of Cs
molecules in optical lattices, with the perspective of creating a quantum
degenerate gas of ground-state molecules. We have calculated dynamic
polarizabilities of Cs molecules subject to an oscillating electric field,
using accurate potential curves and electronic transition dipole moments. We
show that for some particular wavelengths of the optical lattice, called "magic
wavelengths", the polarizability of the ground-state molecules is equal to the
one of a Feshbach molecule. As the creation of the sample of ground-state
molecules relies on an adiabatic population transfer from weakly-bound
molecules created on a Feshbach resonance, such a coincidence ensures that both
the initial and final states are favorably trapped by the lattice light,
allowing optimized transfer in agreement with the experimental observation
Relativistic Landau resonances
The possible interactions between plasma waves and relativistic charged particles are considered. An electromagnetic perturbation in the plasma is formulated as an elliptically polarized wave, and the collisionless plasma is described by a distribution in phase space, which is realized in cylindrical coordinates. The linearized Vlasov equation is solved in the semi-relativistic limit, to obtain the distribution function in the rest frame of the observer. The perturbed currents supported by the ionized medium are then calculated, so that an expression can be written for the total amount of energy available for transfer through the Landau mechanism. It is found that only certain modes of the perturbed current are available for this energy transfer. The final expressions are presented in terms of Stokes parameters, and applied to the special cases of a thermal as well as a nonthermal plasma. The thermal plasma is described by a Maxwellian distribution, while two nonthermal distributions are considered: the kappa distribution and a generalized Weibull distribution
Resonant Coupling in the Heteronuclear Alkali Dimers for Direct Photoassociative Formation of X(0,0) Ultracold Molecules
Promising pathways for photoassociative formation of ultracold heteronuclear
alkali metal dimers in their lowest rovibronic levels (denoted X(0,0)) are
examined using high quality ab initio calculations of potential energy curves
currently available. A promising pathway for KRb, involving the resonant
coupling of the and states just below the lowest excited
asymptote (K()+Rb()), is found to occur also for RbCs and less
promisingly for KCs as well. The resonant coupling of the and
states, also just below the lowest excited asymptote, is found to be
promising for LiNa, LiK, LiRb, and less promising for LiCs and KCs. Direct
photoassociation to the state near dissociation appears promising in
the final dimers, NaK, NaRb, and NaCs, although detuning more than 100
cm below the lowest excited asymptote may be required.Comment: 20 pages, 12 figures, Submitted to Journal of Physical Chemistry
Tamoxifen mechanically deactivates hepatic stellate cells via the G protein-coupled estrogen receptor
Tamoxifen has been used for many years to target estrogen receptor signalling in breast cancer cells. Tamoxifen is also an agonist of the G protein-coupled estrogen receptor (GPER), a GPCR ubiquitously expressed in tissues that mediates the acute response to estrogens. Here we report that tamoxifen promotes mechanical quiescence in hepatic stellate cells (HSCs), stromal fibroblast-like cells whose activation triggers and perpetuates liver fibrosis in hepatocellular carcinomas. This mechanical deactivation is mediated by the GPER/RhoA/myosin axis and induces YAP deactivation. We report that tamoxifen decreases the levels of hypoxia-inducible factor-1 alpha (HIF-1α) and the synthesis of extracellular matrix proteins through a mechanical mechanism that involves actomyosin-dependent contractility and mechanosensing of tissue stiffness. Our results implicate GPER-mediated estrogen signalling in the mechanosensory-driven activation of HSCs and put forward estrogenic signalling as an option for mechanical reprogramming of myofibroblast-like cells in the tumour microenvironment. Tamoxifen, with half a century of safe clinical use, might lead this strategy of drug repositioning.Peer reviewe
Collisional and thermal ionization of sodium Rydberg atoms I. Experiment for nS and nD atoms with n=8-20
Collisional and thermal ionization of sodium nS and nD Rydberg atoms with
n=8-20 has been studied. The experiments were performed using a two-step pulsed
laser excitation in an effusive atomic beam at atom density of about 2 10^{10}
cm^{-3}. Molecular and atomic ions from associative, Penning, and thermal
ionization processes were detected. It has been found that the atomic ions were
created mainly due to photoionization of Rydberg atoms by photons of blackbody
radiation at the ambient temperature of 300K. Blackbody ionization rates and
effective lifetimes of Rydberg states of interest were determined. The
molecular ions were found to be from associative ionization in Na(nL)+Na(3S)
collisions. Rate constants of associative ionization have been measured using
an original method based on relative measurements of Na_{2}^{+} and Na^{+} ion
signals.Comment: 23 pages, 10 figure
Formation of ultracold dipolar molecules in the lowest vibrational levels by photoassociation
We recently reported the formation of ultracold LiCs molecules in the
rovibrational ground state X1Sigma+,v''=0,J''=0 [J. Deiglmayr et al., PRL 101,
133004 (2008)]. Here we discuss details of the experimental setup and present a
thorough analysis of the photoassociation step including the photoassociation
line shape. We predict the distribution of produced ground state molecules
using accurate potential nergy curves combined with an ab-initio dipole
transition moment and compare this prediction with experimental ionization
spectra. Additionally we improve the value of the dissociation energy for the
X1Sigma+ state by high resolution spectroscopy of the vibrational ground state.Comment: Submitted to Faraday Discussions 142: Cold and Ultracold Molecules 18
pages, 8 figure
Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
We present the design, implementation and characterization of a dual-species
magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom
numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9
40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a
2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s
and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies
collisions of ~65% were observed and could be minimized to ~10% by using low
magnetic field gradients and low light powers in the repumping light of both
atomic species. The described system represents the starting point for the
production of a large-atom number quantum degenerate Fermi-Fermi mixture
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