1,853 research outputs found
Ultracold Neutral Plasmas
Ultracold neutral plasmas, formed by photoionizing laser-cooled atoms near
the ionization threshold, have electron temperatures in the 1-1000 kelvin range
and ion temperatures from tens of millikelvin to a few kelvin. They represent a
new frontier in the study of neutral plasmas, which traditionally deals with
much hotter systems, but they also blur the boundaries of plasma, atomic,
condensed matter, and low temperature physics. Modelling these plasmas
challenges computational techniques and theories of non-equilibrium systems, so
the field has attracted great interest from the theoretical and computational
physics communities. By varying laser intensities and wavelengths it is
possible to accurately set the initial plasma density and energy, and
charged-particle-detection and optical diagnostics allow precise measurements
for comparison with theoretical predictions. Recent experiments using optical
probes demonstrated that ions in the plasma equilibrate in a strongly coupled
fluid phase. Strongly coupled plasmas, in which the electrical interaction
energy between charged particles exceeds the average kinetic energy, reverse
the traditional energy hierarchy underlying basic plasma concepts such as Debye
screening and hydrodynamics. Equilibration in this regime is of particular
interest because it involves the establishment of spatial correlations between
particles, and it connects to the physics of the interiors of gas-giant planets
and inertial confinement fusion devices.Comment: 89 pages, 54 image
Bose-Einstein Condensation of Sr Through Sympathetic Cooling with Sr
We report Bose-Einstein condensation of Sr, which has a small,
negative s-wave scattering length (\,). We overcome the poor
evaporative cooling characteristics of this isotope by sympathetic cooling with
Sr atoms. Sr is effective in this role in spite of the fact that
it is a fermion because of the large ground state degeneracy arising from a
nuclear spin of , which reduces the impact of Pauli blocking of
collisions. We observe a limited number of atoms in the condensate
() that is consistent with the value of and the
optical dipole trap parameters.Comment: 4 pages, 4 figure
Degenerate Fermi Gas of Sr
We report quantum degeneracy in a gas of ultra-cold fermionic Sr
atoms. By evaporatively cooling a mixture of spin states in an optical dipole
trap for 10.5\,s, we obtain samples well into the degenerate regime with
. The main signature of degeneracy is a change in the
momentum distribution as measured by time-of-flight imaging, and we also
observe a decrease in evaporation efficiency below .Comment: 4 pages, 3 figure
The Inhibition of Ureteral Motility by Periureteral Adipose Tissue
Perivascular adipose tissue exerts an anticontractile influence on vascular smooth muscle. This study was conducted to determine whether periureteral adipose tissue (PUAT) could exert a similar influence upon ureteral smooth muscle. Acetylcholine-stimulated (10−7 M–10−4 M) contractile responses of ureteral segments obtained from male Wistar rats were recorded in the presence and absence of PUAT. Ureters with PUAT generated phasic contractile responses with significantly lower frequencies (P < 0.001) and magnitudes (P < 0.001) compared with ureters cleared of their periureteral adipose tissue. Removal of PUAT significantly increased the frequency (P < 0.01) and magnitude (P < 0.01) of the contractile responses. Bioassay experiments demonstrated that ureters with PUAT released a transferable factor that significantly reduced frequencies (P < 0.05), but not magnitudes, of the contractile responses of ureters cleared of PUAT. The nitric oxide synthase inhibitor L-NNA (10−4 M) did not significantly influence the anticontractile effect exerted by ureters with PUAT. This is the first study to demonstrate that ureteral motility is influenced by its surrounding adipose tissue. The PUAT has an anticontractile effect which is mediated by a transferable factor released from the PUAT. The identity of the factor is unknown but does not exert its effect through nitric oxide
Runaway evaporation for optically dressed atoms
Forced evaporative cooling in a far-off-resonance optical dipole trap is
proved to be an efficient method to produce fermionic- or bosonic-degenerated
gases. However in most of the experiences, the reduction of the potential
height occurs with a diminution of the collision elastic rate. Taking advantage
of a long-living excited state, like in two-electron atoms, I propose a new
scheme, based on an optical knife, where the forced evaporation can be driven
independently of the trap confinement. In this context, the runaway regime
might be achieved leading to a substantial improvement of the cooling
efficiency. The comparison with the different methods for forced evaporation is
discussed in the presence or not of three-body recombination losses
Ultracold Neutral Plasmas
Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near
the ionization threshold. Through the application of atomic physics techniques
and diagnostics, these experiments stretch the boundaries of traditional
neutral plasma physics. The electron temperature in these plasmas ranges from
1-1000 K and the ion temperature is around 1 K. The density can approach
cm. Fundamental interest stems from the possibility of
creating strongly-coupled plasmas, but recombination, collective modes, and
thermalization in these systems have also been studied. Optical absorption
images of a strontium plasma, using the Sr
transition at 422 nm, depict the density profile of the plasma, and probe
kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum
measures the ion velocity distribution, which gives an accurate measure of the
ion dynamics in the first microsecond after photoionization.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Evolution of Ultracold, Neutral Plasmas
We present the first large-scale simulations of an ultracold, neutral plasma,
produced by photoionization of laser-cooled xenon atoms, from creation to
initial expansion, using classical molecular dynamics methods with open
boundary conditions. We reproduce many of the experimental findings such as the
trapping efficiency of electrons with increased ion number, a minimum electron
temperature achieved on approach to the photoionization threshold, and
recombination into Rydberg states of anomalously-low principal quantum number.
In addition, many of these effects establish themselves very early in the
plasma evolution ( ns) before present experimental observations begin.Comment: 4 pages, 3 figures, submitted to PR
Stable Isotope Analysis of the Inca Mummy from Nevado de Chuscha (Salta, Argentina)
This paper presents the carbon (13C/12C), nitrogen (15N/14N), oxygen (18O/16O), hydrogen (2H/1H) and sulfur (34S/32S) stable isotope values measured in the hair of a female individual from north-western Argentina. The analysis of segments of this tissue allows for the recording of the diet and migratory changes with a short time resolution. The sample is from a mummified young female individual discovered in Chuscha mount, Salta province. It was found at more than 5000 masl, in a mountain sanctuary of the Inca expansion (capacochas). The paper discusses the paleodiet and mobility patterns of this individual in the period before her death, focusing on the isotopic variations in a limited time scale. The results indicate that the individual moved from a different region to the place where she was sacrificed. Furthermore, in the last year the individual was alive, a shift in the isotopic composition of the food consumed is detected: a variation in the importance of C4 over C3 resources is evident. The results are compared with the isotopic estimations for other children and young people recovered in archaeological contexts associated with capacochas to infer variability in the geographical trajectories covered during their last months of life.Fil: Killian Galván, Violeta Anahí. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto Interdisciplinario Tilcara; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tessone, Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Valenzuela, Luciano Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Sociales. Departamento de Arqueología. Laboratorio de Ecología Evolutiva Humana (Sede Quequén); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sharp, Z. D.. Universidad de Nuevo México.; Estados UnidosFil: Panarello, Hector Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentin
Plasma Oscillations and Expansion of an Ultracold Neutral Plasma
We report the observation of plasma oscillations in an ultracold neutral
plasma. With this collective mode we probe the electron density distribution
and study the expansion of the plasma as a function of time. For classical
plasma conditions, i.e. weak Coulomb coupling, the expansion is dominated by
the pressure of the electron gas and is described by a hydrodynamic model.
Discrepancies between the model and observations at low temperature and high
density may be due to strong coupling of the electrons.Comment: 4 pages, 4 figures. Accepted Phys. Rev. Let
Probing Nonlocal Spatial Correlations in Quantum Gases with Ultra-long-range Rydberg Molecules
We present photo-excitation of ultra-long-range Rydberg molecules as a probe
of spatial correlations in quantum gases. Rydberg molecules can be created with
well-defined internuclear spacing, set by the radius of the outer lobe of the
Rydberg electron wavefunction . By varying the principal quantum number
of the target Rydberg state, the molecular excitation rate can be used to
map the pair-correlation function of the trapped gas . We
demonstrate this with ultracold Sr gases and probe pair-separation length
scales ranging from , which are on the order of the
thermal de Broglie wavelength for temperatures around 1 K. We observe
bunching for a single-component Bose gas of Sr and anti-bunching due to
Pauli exclusion at short distances for a polarized Fermi gas of Sr,
revealing the effects of quantum statistics.Comment: 6 pages, 5 figure
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