850 research outputs found
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
Influence of Polyphenol Levels on the Perception of Aroma in Vitis vinifera cv. Malbec wine
The aim of this study was to explore the effect of two ranges of polyphenols naturally present in Malbec wine,high concentrations (4.5-7.2 g/L) and low (1.4-3.2 g/L), on the perception of aroma. Samples with a maximumethanol level of 13.5% were taken from the fermentation tanks before the clarification and filtration process. AQuantitative Descriptive Analysis of wines was assessed by ten trained assessors, and HS-SPME-GC-MS andphysicochemical analyses were performed. The intensities of fruity (P < 0.01), citrus (P < 0.01), strawberry (P< 0.05), cooked fruit (P < 0.01) and floral (P < 0.01) aromas decreased when the level of polyphenols increased.Neither volatile compounds nor physicochemical analyses were significant in the two groups of wines
All-solid-state electrochromic reflectance device for emittance modulation in the far-infrared spectral region
All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission range. Multicycle optical switching and emittance modulation is demonstrated. The measured change in emissivity of the device is to 20%
Equation of State for Helium-4 from Microphysics
We compute the free energy of helium-4 near the lambda transition based on an
exact renormalization-group equation. An approximate solution permits the
determination of universal and nonuniversal thermodynamic properties starting
from the microphysics of the two-particle interactions. The method does not
suffer from infrared divergences. The critical chemical potential agrees with
experiment. This supports a specific formulation of the functional integral
that we have proposed recently. Our results for the equation of state reproduce
the observed qualitative behavior. Despite certain quantitative shortcomings of
our approximation, this demonstrates that ab initio calculations for collective
phenomena become possible by modern renormalization-group methods.Comment: 9 pages, 6 figures, revtex updated version, journal referenc
Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems
Tungsten trioxide adopts a variety of structures which can be intercalated
with charged species to alter the electronic properties, thus forming `tungsten
bronzes'. Similar optical effects are observed upon removing oxygen from WO_3,
although the electronic properties are slightly different. Here we present a
computational study of cubic and hexagonal alkali bronzes and examine the
effects on cell size and band structure as the size of the intercalated ion is
increased. With the exception of hydrogen (which is predicted to be unstable as
an intercalate), the behaviour of the bronzes are relatively consistent. NaWO_3
is the most stable of the cubic systems, although in the hexagonal system the
larger ions are more stable. The band structures are identical, with the
intercalated atom donating its single electron to the tungsten 5d valence band.
Next, this was extended to a study of fractional doping in the Na_xWO_3 system
(0 < x < 1). A linear variation in cell parameter, and a systematic change in
the position of the Fermi level up into the valence band was observed with
increasing x. In the underdoped WO_3-x system however, the Fermi level
undergoes a sudden jump into the conduction band at around x = 0.2. Lastly,
three compounds of a layered WO_4×a,wdiaminoalkane hybrid series were
studied and found to be insulating, with features in the band structure similar
to those of the parent WO_3 compound which relate well to experimental
UV-visible spectroscopy results.Comment: 12 pages, 16 figure
Theory of imaging a photonic crystal with transmission near-field optical microscopy
While near-field scanning optical microscopy (NSOM) can provide optical
images with resolution much better than the diffraction limit, analysis and
interpretation of these images is often difficult. We present a theory of
imaging with transmission NSOM that includes the effects of tip field,
tip/sample coupling, light propagation through the sample and light collection.
We apply this theory to analyze experimental NSOM images of a nanochannel glass
(NCG) array obtained in transmission mode. The NCG is a triangular array of
dielectric rods in a dielectric glass matrix with a two-dimensional photonic
band structure. We determine the modes for the NCG photonic crystal and
simulate the observed data. The calculations show large contrast at low
numerical aperture (NA) of the collection optics and detailed structure at high
NA consistent with the observed images. We present calculations as a function
of NA to identify how the NCG photonic modes contribute to and determine the
spatial structure in these images. Calculations are presented as a function of
tip/sample position, sample index contrast and geometry, and aperture size to
identify the factors that determine image formation with transmission NSOM in
this experiment.Comment: 28 pages of ReVTex, 14 ps figures, submitted to Phys. Rev.
Narrow inhomogeneous and homogeneous optical linewidths in a rare earth doped transparent ceramic
Inhomogeneous and homogeneous linewidth are reported in a Eu3+ doped transparent Y2O3 ceramic for the 7F 0-5D0 transition, using high-resolution coherent spectroscopy. The 8.7-GHz inhomogeneous linewidth is close to that of single crystals, as is the 59-kHz homogeneous linewidth at 3 K (T2 = 5.4 μs). The homogeneous linewidth exhibits a temperature dependence that is typical of a crystalline environment, and additional dephasing observed in the ceramic is attributed to magnetic impurities or defects introduced during the synthesis process. The absence of Eu3+segregation at the grain boundaries, evidenced through confocal microfluorescence, further indicates that the majority of Eu3+ions in the ceramic experience an environment comparable to a single crystal. The obtained results suggest that ceramic materials can be competitive with single crystals for applications in quantum information and spectral hole burning devices, beyond their current applications in lasers and scintillatorsThis work was supported by National Science Foundation under award No. PHY-1212462, the European Union FP7 project QuRep (247743), the Spanish Ministry of Economy
and Competitiveness (MAT2010-17443) and Comunidad de Madrid (S-2009/MAT-1756
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