862 research outputs found
Boundary effects on the scaling of the superfluid density
We study numerically the influence of the substrate (boundary conditions) on
the finite--size scaling properties of the superfluid density in
superfluid films of thickness within the XY model employing the Monte Carlo
method. Our results suggest that the jump at the
Kosterlitz--Thouless transition temperature depends on the boundary
conditions.Comment: 2 pages, 1 Latex file, 1 postscript figure, 2 style file
Red and orange laser operation of Pr:KYF4 pumped by a Nd:YAG/LBO laser at 469.1nm and a InGaN laser diode at 444nm
We report the basic luminescence properties and the continuous-wave (CW) laser operation of a Pr3+-doped KYF4 single crystal in the Red and Orange spectral regions by using a new pumping scheme. The pump source is an especially developed, compact, slightly tunable and intra-cavity frequency-doubled diode-pumped Nd:YAG laser delivering a CW output power up to about 1.4 W around 469.1 nm. At this pump wavelength, red and orange laser emissions are obtained at about 642.3 and 605.5 nm, with maximum output powers of 11.3 and 1 mW and associated slope efficiencies of 9.3% and 3.4%, with respect to absorbed pump powers, respectively. For comparison, the Pr:KYF4 crystal is also pumped by a InGaN blue laser diode operating around 444 nm. In this case, the same red and orange lasers are obtained, but with maximum output powers of 7.8 and 2 mW and the associated slope efficiencies of 7 and 5.8%, respectively. Wavelength tuning for the two lasers is demonstrated by slightly tilting the crystal. Orange laser operation and laser wavelength tuning are reported for the first time
Phenotypically determined resistance of Neisseria gonorrhoeae to normal human serum: environmental factors in subcutaneous chambers in guinea pigs
Some gonococci obtained from human urethral exudate or from subcutaneously implanted chambers in guinea pigs show a resistance to killing by human serum which is lost on subculture in vitro after a few generations. The environmental factors which may influence the phenotypic expression of resistance to serum killing were investigated in guinea pig chambers and in chamber fluid in vitro. The redox potential in chambers before and after infection was lower than that of heart blood but conditions were not anaerobic; H2O2 increased the redox potential but did not decrease gonococcal serum resistance. The chambers were slightly alkaline before and after infection. When the concentration of glucose (depleted in infected chambers by the abundant polymorphonuclear cells) was restored to excess, the serum resistance of the gonococci was unaffected. Concentrations of free amino acids in chambers changed little during infection. Gonococci adapted to growth in chambers and subsequently rendered serum-sensitive by growing once on agar reverted to serum-resistance after 0.5 to 1 h incubation in chamber fluid in vitro at 37°C but not at 25°C or 4°C. After 16 to 24 h growth at 37°C, resistance was again lost. The reversion to serum resistance did not occur in a complex laboratory medium. Examination of the chamber fluid after growth of gonococci in vitro showed depletion of lactate, glutamine and proline
Single-Molecule-Sensitive FRET in Freely-Diffusing Attoliter Droplets
Fluorescence resonance energy transfer (FRET) from individual, dye-labeled
RNA molecules confined in freely-diffusing attoliter-volume aqueous droplets is
carefully compared to FRET from unconfined RNA in solution. The use of
freely-diffusing droplets is a remarkably simple and high-throughput technique
that facilitates a substantial increase in signal-to-noise for
single-molecular-pair FRET measurements. We show that there can be dramatic
differences between FRET in solution and in droplets, which we attribute
primarily to an altered pH in the confining environment. We also demonstrate
that a sufficient concentration of a non-ionic surfactant mitigates this effect
and restores FRET to its neutral-pH solution value. At low surfactant levels,
even accounting for pH, we observe differences between the distribution of FRET
values in solution and in droplets which remain unexplained. Our results will
facilitate the use of nanoemulsion droplets as attoliter volume reactors for
use in biophysical and biochemical assays, and also in applications such as
protein crystallization or nanoparticle synthesis, where careful attention to
the pH of the confined phase is required.Comment: Twenty-three pages, 3 figures, one table, plus supporting information
with additional figures and table
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