Search results for "Pressure"
showing 10 items of 4493 documents
Natural optical anisotropy of h-BN: Highest giant birefringence in a bulk crystal through the mid-infrared to ultraviolet range
2018
The giant birefringence of layered h-BN was demonstrated by analyzing the interference patterns in reflectance and transmittance measurements in the mid-infrared to the deep ultraviolet energy range. The refractive index for polarization perpendicular to the c axis is much higher than the refractive index for polarization parallel to the c axis, and it displays a strong increase in the ultraviolet range that is attributed to the huge excitonic effects arising from the unique electronic structure of h-BN. Thus, h-BN is shown to exhibit a giant negative birefringence that ranges from -0.7 in the visible to -2 in the deep ultraviolet close to the band gap. The electronic dielectric constants f…
Organic solvent vapor effects on phase transition of α and β tegafur upon grinding with solvent additives.
2012
Abstract Solvent effects on α tegafur (5-fluoro-1-(tetrahydro-2-furyl)uracil) phase transition to β tegafur during grinding with solvent additive, as well as phase transition in samples exposed to 95% relative solvent vapor pressure has been studied in this research. Samples containing 0.5% and 0.1% of β tegafur in α and β tegafur mixture, as well as samples of pure α tegafur were ground with different solvent additives, and conversion degrees depending on the solvent were determined using PXRD method. Samples with α and β tegafur weight fraction of 1:1 were exposed to 95% relative solvent vapor pressure, and phase transition rates were determined. Solubility of α tegafur, solvent sorption …
Electronic structure of adsorbed organic molecules
1997
We report on investigations of chiral organic molecules in the gas phase and physisorbed on graphite. The measurements were carried out by means of angle-resolving VUV photoelectron spectroscopy. The emission from specific orbitals in oriented molecules can be forbidden because of dipole selection rules. Due to the lack of certain features in the spectra, it was possible to determine the adsorption geometry of cyclohexanone and camphor as being with their ring system parallel to the surface. By comparison of gas-phase and adsorbate spectra of ethyl benzene derivatives, adsorption could be proved to be molecular without decomposition. For amino acids on graphite, the occurrence of characteri…
Is the formation of a zeolite from a dry powder via a gas phase transport process possible?
1994
Abstract ZSM-5 was synthesized by four methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in the form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO2·A2O3 gels at 650°C were transformed into zeolites in the presence of dried NH4F and TPABr. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure under the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF4 as the mobile species between the solid phase, which contains the amorphous Si/Al pre…
Low-temperature molecular layer deposition using monifunctional aromatic precursors and ozone-based ring-opening reactions
2017
Molecular layer deposition (MLD) is an increasingly used deposition technique for producing thin coatings consisting of purely organic or hybrid inorganic-organic materials. When organic materials are prepared, low deposition temperatures are often required to avoid decomposition, thus causing problems with low vapor pressure precursors. Monofunctional compounds have higher vapor pressures than traditional bi- or trifunctional MLD precursors, but do not offer the required functional groups for continuing the MLD growth in subsequent deposition cycles. In this study, we have used high vapor pressure monofunctional aromatic precursors in combination with ozone-triggered ring-opening reactions…
Water Adsorption in Flexible Gallium-Based MIL-53 Metal–Organic Framework
2014
Understanding the adsorption of water in metal–organic frameworks (MOF), and particularly in soft porous crystals, is a crucial prerequisite before considering MOFs for industrial applications. We report here a joint experimental and theoretical study on the behavior of a gallium-based breathing MOF, Ga-MIL-53, upon water adsorption. By looking at the energetics and thermodynamics of Ga-MIL-53, we demonstrate why it behaves differently from its sibling Al-MIL-53, showing a different phase at room temperature (a nonporous phase) and the presence of a hydrated narrow-pore structure at gas saturation pressure. Moreover, we present a complete water vapor pressure vs temperature phase diagram of…
Use of the Weibull model to describe inactivation of dry harvested conidia of different Penicillium species by ethanol vapours
2010
Aims: This study aimed at modelling the effect of ethanol vapours, in the range 0·7–7·5 kPa, on the inactivation of dry-harvested conidia of Penicillium chrysogenum, Penicillium digitatum and Penicillium italicum. Methods and Results: Survival curves were modelled by a Weibull model: log (N/N0) = −1/2·303 (t/α)β. The shape parameter β was different from one in all cases, indicating that the classical first-order kinetics approach is the exception rather than the rule. Survival curves exhibited upward concavity (β < 1) with the notable exception of P. chrysogenum at ethanol vapour pressures 0·7 and 1·5 kPa. The scale parameter α (h) varied greatly depending on the ethanol vapour pressure a…
(Vapour + liquid) equilibria of (water + dimethylformamide): application of the headspace-gas chromatography for the determination of thermodynamic i…
1998
Abstract Isothermal measurements of the partial vapour pressures have been carried out on {water + dimethylformamide (DMF)} at temperatures betweenT=305.15 K andT=323.15 K using an apparatus composed of a headspace sampler and a normal gas chromatograph. These data were simultaneously evaluated in one step with respect to the (composition dependent, integral) Flory-Huggins interaction parametergby means of a new method which minimizes the Gibbs energy of mixing and does not require chemical potentials. The expression forggiven by Koningsveld and Kleintjens, originally designed for polymer solutions, describes the present results best.
Advance in Vascular Phenotype Assessment in Children and Adolescents
2010
Cardiovascular damage occurring in adults finds its roots in risk factors operating early in life. Among the factors influencing cardiovascular risk, blood pressure values represent an important measurable marker of the level of potential cardiovascular risk in children and adolescents. Indeed, there is growing evidence that mild blood pressure elevations are much more common than was thought in the past in a pediatric population. Furthermore, hypertension in childhood has gained ground in cardiovascular medicine thanks to the progress made in several areas of pathophysiological and clinical research.1 It is not uncommon for high blood pressure in the young to be accompanied by evidence of …
Quantitative Bestimmung der Hirnperfusion mit Hilfe der digitalen Subtraktionsangiographie (DSA)
1990
In a search for a reliable and relatively non-invasive method for quantifying cerebral perfusion, we examined the possible role of DSA. By using special software, it is possible to demonstrate vascular morphology and obtain functional data concerning blood flow. Regions of interest are used for obtaining time-density curves and these are evaluated by a formula designed by Meier and Zierler. Perfusion through the arterial territory in both cerebral hemispheres was correlated with the clinical symptoms of the patients and with the morphological findings. Difficulties and problems are described and discussed.