549 research outputs found
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Hydrogen/lithium interdiffusion in a lithium aluminosilicate glass studied by NRA and RBS
Samples of a lithium aluminosilicate (LAS) glass, a model glass for technical LAS glass used in the production of glass ceramics, were treated in hot sulfuric acid and analyzed using Nuclear Reaction Analysis (NRA) techniques for determining hydrogen and lithium depth profiles in the surface layer. It was found that the depth profiles of these two elements are fully complementary, showing that H⁺/Li⁺ ion exchange takes place during the treatment. As revealed by Rutherford Backscattering Spectrometry (RBS) measurements the other glass constituents were not affected by the treatment
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Composition of titania coatings deposited by different techniques
Quantitative dement concentrations in titania films produced by different deposition techniques (evaporation, sputtering, ion-assisted deposition, ion plating and dip coating) have been determined by means of Rutherford Backscattering Spectrometry and Nuclear Reaction Analysis with the reaction ¹H(¹⁵N, αγ)¹²C. Large differences of the hydrogen content are found for the various production techniques and the related deposition parameters, which correlate with the refractive index of the respective film. In dependence on the deposition conditions the oxygen/titanium ratio of the investigated titania films varies between 1.95 and 2.09. The impurities detected in the films (tantalum, molybdenum, silicon, argon, carbon, sodium) can be related to specific deposition conditions. Three multilayer interference systems containing TiO₂ and SiO₂ show large variations in hydrogen content resembling those found for single TiO₂ films
Glutamic Acid Residues in HIV-1 p6 Regulate Virus Budding and Membrane Association of Gag
The HIV-1 Gag p6 protein regulates the final abscission step of nascent
virions from the cell membrane by the action of its two late (l-) domains,
which recruit Tsg101 and ALIX, components of the ESCRT system. Even though p6
consists of only 52 amino acids, it is encoded by one of the most polymorphic
regions of the HIV-1 gag gene and undergoes various posttranslational
modifications including sumoylation, ubiquitination, and phosphorylation. In
addition, it mediates the incorporation of the HIV-1 accessory protein Vpr
into budding virions. Despite its small size, p6 exhibits an unusually high
charge density. In this study, we show that mutation of the conserved glutamic
acids within p6 increases the membrane association of Pr55 Gag followed by
enhanced polyubiquitination and MHC-I antigen presentation of Gag-derived
epitopes, possibly due to prolonged exposure to membrane bound E3 ligases. The
replication capacity of the total glutamic acid mutant E0A was almost
completely impaired, which was accompanied by defective virus release that
could not be rescued by ALIX overexpression. Altogether, our data indicate
that the glutamic acids within p6 contribute to the late steps of viral
replication and may contribute to the interaction of Gag with the plasma
membrane
Multiple scattering of matter waves: an analytic model of the refractive index for atomic and molecular gases
We present an analytic model of the refractive index for matter waves
propagating through atomic or molecular gases. The model, which combines a WKB
treatment of the long range attraction with the Fraunhofer model treatment of
the short range repulsion, furnishes a refractive index in compelling agreement
with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)]
on Li atom matter waves passing through dilute noble gases. We show that the
diffractive contribution, which arises from scattering by a two dimensional
"hard core" of the potential, is essential for obtaining a correct imaginary
part of the refractive index.Comment: 5 pages, 1 figure, 2 table
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Practical IR extinction coefficients for water in commercial glasses determined by nuclear reaction analysis
For a number of commercial glasses with different chemical compositions the water contents were determined by nuclear reaction analysis (NRA) measurements. These results were used to deduce practical extinction coefficients by comparison with the measured IR absorbance values at 2.8 μm. For aluminosilicate and television glasses the practical molar extinction coefficients are given for the first time. Practical extinction coefficients are dependent upon glass composition. With increasing basicity of the glasses studied they decrease from 182 to 24 l/(mol cm)
On the well posedness of the Baumgarte-Shapiro-Shibata-Nakamura formulation of Einstein's field equations
We give a well posed initial value formulation of the
Baumgarte-Shapiro-Shibata-Nakamura form of Einstein's equations with gauge
conditions given by a Bona-Masso like slicing condition for the lapse and a
frozen shift. This is achieved by introducing extra variables and recasting the
evolution equations into a first order symmetric hyperbolic system. We also
consider the presence of artificial boundaries and derive a set of boundary
conditions that guarantee that the resulting initial-boundary value problem is
well posed, though not necessarily compatible with the constraints. In the case
of dynamical gauge conditions for the lapse and shift we obtain a class of
evolution equations which are strongly hyperbolic and so yield well posed
initial value formulations
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Multi-method characterization of soda-lime glass corrosion : Part 2. Corrosion in humidity Report of the International Commissionon Glass (ICG) Subcommittee of Technical Committee 19 "Glass Surface Diagnostics"
As-received and cleaned soda-lime glass surfaces corroded in high relative humidity of 95 % at a temperature of 60 °C for times up to one week are investigated by means of TOF-SIMS, SNMS, XPS, NRA, ERD, RBS, GIXR, AFM, SEM and optical microscopy. Distinct differences in the corrosion behavior are observed for as-received and cleaned glass surfaces. Changes in element concentration in the glass interface and in the topography of the glass surfaces are described for different exposure times in humidity. They are combined with variations in density of the modified surface layer. Cleaning before the corrosion treatment drastically reduces degradation; cleaning after the corrosion treatment can restore the surface
Well-Posed Initial-Boundary Evolution in General Relativity
Maximally dissipative boundary conditions are applied to the initial-boundary
value problem for Einstein's equations in harmonic coordinates to show that it
is well-posed for homogeneous boundary data and for boundary data that is small
in a linearized sense. The method is implemented as a nonlinear evolution code
which satisfies convergence tests in the nonlinear regime and is robustly
stable in the weak field regime. A linearized version has been stably matched
to a characteristic code to compute the gravitational waveform radiated to
infinity.Comment: 5 pages, 6 figures; added another convergence plot to Fig. 2 + minor
change
Theory of decoherence in a matter wave Talbot-Lau interferometer
We present a theoretical framework to describe the effects of decoherence on
matter waves in Talbot-Lau interferometry. Using a Wigner description of the
stationary beam the loss of interference contrast can be calculated in closed
form. The formulation includes both the decohering coupling to the environment
and the coherent interaction with the grating walls. It facilitates the
quantitative distinction of genuine quantum interference from the expectations
of classical mechanics. We provide realistic microscopic descriptions of the
experimentally relevant interactions in terms of the bulk properties of the
particles and show that the treatment is equivalent to solving the
corresponding master equation in paraxial approximation.Comment: 20 pages, 4 figures (minor corrections; now in two-column format
Tetracationic bis-triarylborane 1, 3-butadiyne as a combined fluorimetric and Raman probe for simultaneous and selective sensing of various DNA, RNA and proteins
A new bis-triarylborane tetracation (4-Ar2B-3, 5-Me2C6H2)-C≡C- C≡C-(3, 5-Me2C6H2-4-BAr2 [Ar = (2, 6-Me2-4-NMe3-C6H2)+] (24+) shows distinctly different behaviour in its fluorimetric response than that of our recently published bis-triarylborane 5- (4-Ar2B-3, 5-Me2C6H2)-2, 2’-(C4H2S)2-5’-(3, 5-Me2C6H2-4-BAr2) (34+). Single-crystal X-ray diffraction data on the neutral bis- triarylborane precursor 2N confirm its rod-like dumbbell structure, which is shown to be important for DNA/RNA targeting and also for BSA protein binding. Fluorimetric titrations with DNA/RNA/BSA revealed the very strong affinity of 24+ and indicated the importance of the properties of the linker connecting the two triarylboranes. Using the butadiyne- rather than a bithiophene linker resulted in an opposite emission effect (quenching vs enhancement), and 24+ bound to BSA 100 times stronger than 34+. Moreover, 24+ interacted strongly with ss-RNA, and circular dichroism (CD) results suggest ss- RNA chain-wrapping around the rod-like bis-triarylborane dumbbell structure like a thread around a spindle, a very unusual mode of binding of ss-RNA with small molecules. Furthermore, 24+ yielded strong Raman/SERS signals, allowing DNA or protein detection at ca. 10 nM concentrations. The above observations, combined with low cytotoxicity, efficient human cell uptake and organelle-selective accumulation make such compounds intriguing novel lead structures for bio-oriented, dual fluorescence/Raman-based applications
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