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Vapour Pressure (vapour + pressure)

Distribution by Scientific Domains

Chemistry	37%
Earth and Environmental Science	29%
Physics and Astronomy	14%
Engineering	11%
2 Other Domains	9%

Terms modified by Vapour Pressure

vapour pressure deficit

Selected Abstracts

High temperature arsenic doping of CdHgTe epitaxial layers

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2004
A. Vlasov
Abstract Experimental results on solid-state arsenic doping of the n-type bulk and ISOVPE epitaxial CdXHg1- XTe (X = 0.19 ÷ 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1- xTe films (nAs , 5 · 1016 ÷ 1 · 1020 cm -3; d = 2 ÷ 5 ,m) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 ÷ 600 °C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Comparison of soil moisture and meteorological controls on pine and spruce transpiration

ECOHYDROLOGY, Issue 3 2008
Eric E. Small
Abstract Transpiration is an important component of the water balance in the high elevation headwaters of semi-arid drainage basins. We compare the importance of soil moisture and meteorological controls on transpiration and quantify how these controls are different at a ponderosa pine site and a spruce site in the Jemez river drainage basin of northern New Mexico, a sub-basin of the Rio Grande. If only soil moisture controls fluctuations in transpiration, then simple hydrologic models focussed only on soil moisture limitations are reasonable for water balance studies. If meteorological controls are also critical, then more complex models are required. We measured volumetric water content in the soil and sap velocity, and assumed that transpiration is proportional to sap velocity. Ponderosa sap velocity varies with root zone soil moisture. Nearly all of the scatter in the ponderosa sap velocity,soil moisture relationship can be predicted using a simple model of potential evapotranspiration (ET), which depends only on measured incident radiation and air temperature. Therefore, simple hydrologic models of ponderosa pine transpiration are warranted. In contrast, spruce sap velocity does not clearly covary with soil moisture. Including variations in potential evapotranspiration does not clarify the relationship between sap velocity and soil moisture. Likewise, variations in radiation, air temperature, and vapour pressure do not explain the observed fluctuations in sap velocity, at least according to the standard models and parameters for meteorological restrictions on transpiration. Both the simple and more complex models commonly used to predict transpiration are not adequate to model the water balance in the spruce forest studied here. Copyright © 2008 John Wiley & Sons, Ltd. [source]

New Developments in Vertical Gradient Freeze Growth,

ADVANCED ENGINEERING MATERIALS, Issue 7 2004
O. Pätzold
The Vertical Gradient Freeze (VGF) technique is an important method for growing high quality compound semiconductors such as GaAs. Results obtained with a novel VGF set-up developed for the growth under influence of a rotating magnetic field (RMF) and under vapour pressure control are presented in this paper. The RMF is shown to be a powerful tool to affect the heat and mass transport within the melt in a definite way. In GaAs:Si growth, RMF induced flow results in a decreased curvature of a nominally concave-shaped interface, i.e., it contributes to an axial heat transfer at the solid-liquid interface. The axial dopant segregation of Ga in Ge is found to be improved under continuous RMF action due to better mixing of the melt. The set-up also allowed to determine the influence of carbon and the arsenic vapour pressure on the dopant incorporation and crystal quality. [source]

Constant vapour pressure evaporation from a fragrance emulsion,effect of solubility of surfactant in the fragrance compound

FLAVOUR AND FRAGRANCE JOURNAL, Issue 1 2009
Lingling Ge
Abstract The algebraic system to extract information from phase diagrams was used to establish some of the conditions for an emulsion to evaporate under constant vapour pressure. The model system for the calculations was an emulsion characterized by virtually no solubility in water by either the surfactant or the fragrance and the same condition for the water in the oil. The surfactant and the fragrance, on the other hand, were assumed to be mutually completely soluble and this solution was presupposed to be close to ideal. The results showed a surprisingly strong dependence of the times for evaporation under constant vapour pressure on the surfactant concentration in the oil phase, at which the two-phase equilibrium between the aqueous and the oil phases is replaced by a three-phase equilibrium: aqueous phase, oil phase and liquid crystal phase. The lower this concentration, the more extended the times for evaporation under constant vapour pressure. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Liquid,vapour partition of ethanol in bakery products

FLAVOUR AND FRAGRANCE JOURNAL, Issue 1 2006
Paola Pittia
Abstract Ethanol is a common ingredient in formulated foods, naturally present or added in liquid form in order to achieve the desired sensorial properties. In many complex foods this volatile compound could also serve interesting technological functions, as well as extending their shelf-lives, owing to its capacity to inhibit or reduce the rate of microbial growth. At the European level there are no known restrictions regarding the use of ethanol in foods as a preservative, while in Italy, current regulations allow its addition as an anti-moulding agent in pre-packed bread, at a maximum concentration of 2% on a dry weight basis. This research studied the effect of water activity (aw) and water content on the ethanol vapour pressure of sliced white bread, previously equilibrated at various aw values and with 2% ethanol added. Different aw values were obtained by both rehydration from previously freeze-dried bread, and dehydration from the fresh product. The results showed that both aw and moisture affected the vapour pressure of ethanol as a consequence of water,solute and ethanol,solute interactions in the matrix. These interactions varied according to the modality of equilibration (desorption or absorption) at a given aw. The results are discussed in terms of ethanol activity (ae), computed as the ratio between the ethanol vapour pressure in bread and the vapour pressure of pure ethanol at the same temperature. This index, analogous to aw, proved to be useful in evaluating the ,freedom' of the ethanol present in a food matrix to be released in the vapour phase. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid,solid interface

GEOFLUIDS (ELECTRONIC), Issue 1 2009
J. HARA
Abstract Hydrothermal water,(pyroclastic) rock interactions were examined using flow-through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75,250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature. Based on the chemistry of analysed solutions, the water,rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock,fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ,surface layer' comprised a 0.5,1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al-rich cation-leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10,4 to 10,7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively. [source]

A spectral-element method for modelling cavitation in transient fluid,structure interaction

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2004
M. A. Sprague
Abstract In an underwater-shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite-element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high-order Legendre-polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non-conformal coupling method for the structure and fluid finite-element models, and (iv) introducing structure,fluid time-step subcycling. Field separation provides flexibility, as it admits non-acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non-conformal coupling affords order-of-magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Climate variability and change in the Greater Alpine Region over the last two centuries based on multi-variable analysis

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2009
Michele Brunetti
Abstract An extensive analysis of the HISTALP database is presented with the aim of giving a comprehensive picture of secular climate variability and change in the Greater Alpine Region (GAR, 4,19 E, 43,49 N). The HISTALP database encompasses 242 sites and concerns temperature, pressure, precipitation, cloudiness, sunshine duration, vapour pressure and relative humidity. The analyses are based on four regional mean records representing different GAR low-level areas and on an additional mean record representing high-level locations. The first goal of the paper is to give an overview of the seasonal and annual records for the different variables, aiming to highlight both variability on decadal time scale and long-term evolution. Then it focuses on trend and correlation analysis. Trends are presented both for the period of common data availability for all regional average series and for moving windows that permit studying the trends over a wide range of timescales. Correlations among the different variables are presented both for the regional average series and for their high-pass-filtered versions. The analyses, beside highlighting a warming that is about twice as large as the global trend, also show that the different variables have responded in different ways to this warming and that the mutual interactions linking the different variables are often present only at specific temporal scales and only in parts of the GAR and in defined seasons. In spite of this complex behaviour, which may also be due to some residual inhomogeneities still affecting the data, the analyses give evidence that the HISTALP database has an excellent internal consistency and show that the availability of a multi-variable database turns out to be very useful in order to evaluate the reliability of the reconstruction of each variable and to better understand the behaviour and the mutual interactions of the different variables. Copyright © 2009 Royal Meteorological Society [source]

Humidity parameters from temperature: test of a simple methodology for European conditions

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008
Yvonne Andersson-Sköld
Abstract Atmospheric water content is important for local and regional climate, and for chemical processes of soluble and solute species in the atmosphere. Further, vapour pressure deficit (D) is one of the key controls on the opening of stomata in plants and is thus an important force for evapotransporation, plant respiration and biomass production and for the uptake of harmful pollutants such as ozone through the stomata. Most meteorological stations typically measure both temperature and relative humidity (RH). However, even if recorded at finer time resolution, it is usually the daily or often monthly means of RH which are published in climate reports. Unfortunately, such data cannot be used to obtain the changes in RH or vapour pressure deficit over the day, as this depends strongly on the diurnal temperature variation during the day and not upon the mean temperature. Although RH typically changes significantly over the day, the ambient vapour pressure is often remarkably constant. Here a simple method to estimate diurnal vapour pressure is evaluated, based upon an assumed constant vapour pressure, and that recorded minimum temperatures approximate dew-point temperatures. With a knowledge of only temperature, we will show that day to day estimates of vapour pressure, humidity and especially D, can be made with reasonable accuracy. This methodology is tested using meteorological data from 32 sites covering a range of locations in Europe. Such a simple methodology may be used to extract approximate diurnal curves of vapour pressures from published meteorological data which contains only minimum temperatures for each day, or where humidity data are not available. Copyright © 2007 Royal Meteorological Society [source]

An improved method of constructing a database of monthly climate observations and associated high-resolution grids

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005
Timothy D. Mitchell
Abstract A database of monthly climate observations from meteorological stations is constructed. The database includes six climate elements and extends over the global land surface. The database is checked for inhomogeneities in the station records using an automated method that refines previous methods by using incomplete and partially overlapping records and by detecting inhomogeneities with opposite signs in different seasons. The method includes the development of reference series using neighbouring stations. Information from different sources about a single station may be combined, even without an overlapping period, using a reference series. Thus, a longer station record may be obtained and fragmentation of records reduced. The reference series also enables 1961,90 normals to be calculated for a larger proportion of stations. The station anomalies are interpolated onto a 0.5° grid covering the global land surface (excluding Antarctica) and combined with a published normal from 1961,90. Thus, climate grids are constructed for nine climate variables (temperature, diurnal temperature range, daily minimum and maximum temperatures, precipitation, wet-day frequency, frost-day frequency, vapour pressure, and cloud cover) for the period 1901,2002. This dataset is known as CRU TS 2.1 and is publicly available (http://www.cru.uea.ac.uk/). Copyright © 2005 Royal Meteorological Society [source]

Precipitation characteristics of the Eurasian Arctic drainage system

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2003
Mark C. Serreze
Abstract This study examines characteristics of precipitation over the major watersheds of the Eurasian Arctic drainage system over the period 1960,92. In addition to the Ob, Yenisey and Lena (the three largest drainage systems), we examine the combined Kolyma,Indigirka in eastern Eurasia. Each basin exhibits approximately symmetric mean annual cycles of monthly total precipitation and daily event size, with winter minima and July maxima. These are strikingly similar to the annual cycles of total column water vapour (precipitable water), which fundamentally reflects the control on saturation vapour pressure by temperature. Effective precipitation mechanisms exist in all seasons. However, because of the long distance from strong moisture sources (continentality), precipitation tends to follow the seasonality in column water vapour. An effective contrast is presented for the Iceland sector. Here, the annual cycle of precipitation is tied not to the seasonality in column water vapour, but to the stronger precipitation-generating mechanisms in winter. Hence, the annual cycles of precipitation and column water vapour in this region oppose each other. Mean winter precipitation over the Eurasian watersheds is primarily driven by a modest convergence of water vapour. Whereas precipitation peaks in summer, the mean flux convergence exhibits a general minimum (negative in the Ob). Summer precipitation is hence primarily associated with surface evaporation. A strong role of convection is supported from consideration of static stability, the fairly weak spatial organization of precipitation totals and results from prior studies. On daily time scales, the largest basin-averaged precipitation events, for both summer and winter, are allied with synoptic-scale forcing. This is seen in relationships with cyclone frequency, and patterns of 500 hPa height, vertical motion and the 700 hPa vapour flux. The relative frequency of four 500 hPa synoptic types captures the basic time series structures of precipitation. Copyright © 2003 Royal Meteorological Society [source]

State transitions and physicochemical aspects of cryoprotection and stabilization in freeze-drying of Lactobacillus rhamnosus GG (LGG)

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008
K.S. Pehkonen
Abstract Aims:, The frozen and dehydrated state transitions of lactose and trehalose were determined and studied as factors affecting the stability of probiotic bacteria to understand physicochemical aspects of protection against freezing and dehydration of probiotic cultures. Methods and Results:,Lactobacillus rhamnosus GG was frozen (,22 or ,43°C), freeze-dried and stored under controlled water vapour pressure (0%, 11%, 23% and 33% relative vapour pressure) conditions. Lactose, trehalose and their mixture (1 : 1) were used as protective media. These systems were confirmed to exhibit relatively similar state transition and water plasticization behaviour in freeze-concentrated and dehydrated states as determined by differential scanning calorimetry. Ice formation and dehydrated materials were studied using cold-stage microscopy and scanning electron microscopy. Trehalose and lactose,trehalose gave the most effective protection of cell viability as observed from colony forming units after freezing, dehydration and storage. Enhanced cell viability was observed when the freezing temperature was ,43°C. Conclusions:, State transitions of protective media affect ice formation and cell viability in freeze-drying and storage. Formation of a maximally freeze-concentrated matrix with entrapped microbial cells is essential in freezing prior to freeze-drying. Freeze-drying must retain a solid amorphous state of protectant matrices. Freeze-dried matrices contain cells entrapped in the protective matrices in the freezing process. The retention of viability during storage seems to be controlled by water plasticization of the protectant matrix and possibly interactions of water with the dehydrated cells. Highest cell viability was obtained in glassy protective media. Significance and Impact of the Study:, This study shows that physicochemical properties of protective media affect the stability of dehydrated cultures. Trehalose and lactose may be used in combination, which is particularly important for the stabilization of probiotic bacteria in dairy systems. [source]

Extent and mechanism of solvation and partitioning of isomers of substituted benzoic acids: A thermodynamic study in the solid state and in solution

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2008
German L. Perlovich
Abstract Temperature dependency of saturated vapour pressure and thermochemical characteristics of fusion processes for 2-, 3- and 4-methoxybenzoic acids (anisic acids) were measured and thermodynamic functions of sublimation, fusion, and evaporation calculated. A new approach to split specific and nonspecific energetic terms in the crystal lattice was developed. For methoxybenzoic acid isomers as well as for a number of analogous molecules, a parameter describing molecular packing density by the ratio of free volume of the molecules in the crystal lattice and van der Waals molecular volume is defined. Its relationship to Gibbs energy of sublimation and to the respective melting points was analysed. Temperature dependencies of solubility in buffers with pH 2.0 and 7.4, n -octanol and n -hexane were measured. The thermodynamic functions of solubility, solvation and transfer processes were deduced. Concentration dependence of partition coefficients for the outlined isomers was measured. Specific and nonspecific solvation terms were distinguished using the transfer from the ,inert' n -hexane to the other solvents. Comparison analysis of specific and nonspecific interactions in the solid state and in solution was carried out. A diagram enabling analysis of the mechanism of the partitioning process was applied. It was found that position of substituents essentially affects the mechanism of partitioning in buffer pH 2.0, however, at pH 7.4, the mechanism is independent of the position of the substituent. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:3883,3896, 2008 [source]

A risk-based approach to establish stability testing conditions for tropical countries,,

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2006
Manuel Zahn
Abstract The external stability risk factors heat and moisture are evaluated with respect to the development of pharmaceutical products intended to be marketed in tropical and subtropical countries. The mean daily temperatures and dewpoints measured four times per day at selected places in Southeast Asia, South America, China, Southern Africa and the Caribbean are used to calculate the daily and monthly fluctuations of temperature and partial water vapour pressure, the mean kinetic temperature and the relative humidity. Based on these data, the hottest and the most humid place in each country or region are identified to reflect the worst case for the specific region. A formula to calculate safety margins for temperature and partial vapour pressure is introduced taking into consideration the difference between measured meteorological parameters and the stability testing conditions. An appropriate long-term stability testing condition is proposed for each selected country, related to the worst case for each specific region and the safety margins, as well as its classification in either Climatic Zone IVA or IVB. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:946,965, 2006 [source]

Use of Physicochemical Property Limits to Develop Rules for Identifying Chemical Substances with no Skin Irritation or Corrosion Potential

MOLECULAR INFORMATICS, Issue 9 2004
Ingrid Gerner
Abstract This is believed to be the first paper to promote the use of rules based on (quantitative) structure-activity relationship [(Q)SAR] models for identifying chemicals that are not likely to cause a specific adverse health effect, viz., skin irritation or corrosion. The purpose of this paper is to describe limit values for specific physicochemical properties that are appropriate for identifying chemical substances that have no skin irritation or corrosion potential. These physicochemical properties include melting point, molecular weight, octanol-water partition coefficient, surface tension, vapour pressure, aqueous solubility and lipid solubility. Based on analyses of 1833 chemicals, physicochemical properties for limits were defined to determine that when a chemical's physicochemical properties were either greater or less than these limits that these chemicals would have no skin irritation or corrosion potential. To facilitate classification and labeling, the application domains of these limits were constructed to correspond with the European Union's risk phrases for chemicals classified for skin irritation/corrosion, viz., R 34, R35 or R38. This is the second paper of four companion papers. The first paper discussed mechanisms that can lead to significant skin irritation or corrosion after acute exposures to chemicals. The third paper described the application of structural alerts to identify chemical substances with skin irritation or corrosion potential. The fourth paper described the Skin Irritation Corrosion Rules Estimation Tool (SICRET), a user-friendly tool that allows non-(Q)SAR experts to identify chemical substances with skin irritation or corrosion potential based on physicochemical property limits and structural alerts. [source]

Micropore modification in InP

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008
D. Nohavica
Abstract The structural features and optical properties of microporous InP substrates used for epitaxial overgrowth of thin films have been investigated. Both crystalographically oriented (CO) and current line oriented (CLO) pore networks were created by electrochemical dissolution. Heat treatment of the InP pores converted them into microcavities maintaining the same crystallographic direction. The effect of phosphorus vapour pressure was proved to be crucial for the microcavity formation, since it influences the mass transport during heat treatment. Electron microscopy and photoluminescence experiments revealed the absence of significant extended defects, both after the pore and cavities formation. The capability of improved structural quality homo- and hetero-epitaxial overgrown films on the porous InP, was also demonstrated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

,Bubble chamber model' of fast atom bombardment induced processes

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2003
Marina V. Kosevich
A hypothesis concerning FAB mechanisms, referred to as a ,bubble chamber FAB model', is proposed. This model can provide an answer to the long-standing question as to how fragile biomolecules and weakly bound clusters can survive under high-energy particle impact on liquids. The basis of this model is a simple estimation of saturated vapour pressure over the surface of liquids, which shows that all liquids ever tested by fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS) were in the superheated state under the experimental conditions applied. The result of the interaction of the energetic particles with superheated liquids is known to be qualitatively different from that with equilibrium liquids. It consists of initiation of local boiling, i.e., in formation of vapour bubbles along the track of the energetic particle. This phenomenon has been extensively studied in the framework of nuclear physics and provides the basis for construction of the well-known bubble chamber detectors. The possibility of occurrence of similar processes under FAB of superheated liquids substantiates a conceptual model of emission of secondary ions suggested by Vestal in 1983, which assumes formation of bubbles beneath the liquid surface, followed by their bursting accompanied by release of microdroplets and clusters as a necessary intermediate step for the creation of molecular ions. The main distinctive feature of the bubble chamber FAB model, proposed here, is that the bubbles are formed not in the space and time-restricted impact-excited zone, but in the nearby liquid as a ,normal' boiling event, which implies that the temperature both within the bubble and in the droplets emerging on its burst is practically the same as that of the bulk liquid sample. This concept can resolve the paradox of survival of intact biomolecules under FAB, since the part of the sample participating in the liquid,gas transition via the bubble mechanism has an ambient temperature which is not destructive for biomolecules. Another important feature of the model is that the timescale of bubble growth is no longer limited by the relaxation time of the excited zone (,10,12,s), but rather resembles the timescale characteristic of common boiling, sufficient for multiple interactions of gas molecules and formation of clusters. Further, when the bubbles burst, microdroplets are released, which implies that FAB processes are similar to those in spraying techniques. Thus, two processes contribute to the ion production, namely, release of volatile solvent clusters from bubbles and of non-volatile solute from sputtered droplets. This view reconciles contradictory views on the dominance of either gas-phase or liquid-phase effects in FAB. Some other effects, such as suppression of all other ions by surface-active compounds, are consistent with the suggested model. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The destruction of cometary grains and changes in the luminosity of comets

ASTRONOMISCHE NACHRICHTEN, Issue 8 2009
P. Gronkowski
Abstract One explanation of the sudden changes in the brightness of comets is proposed based on the author's earlier suggestions involving the fragmentation of cometary grains. Within the inner coma, a core-mantle model of the structure of grains is assumed. The proposed mechanism is a combination of electrostatic stress and thermodynamical fragmentation of the cometary grains water-ice mantle. It has been shown that the vapour pressure of volatile inclusions placed in the waterice mantle of grains can increase sufficiently to cause their fragmentation. It takes place before grains can completely sublime into the vacuum away. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. The proposed approach yields increases in cometary brightness consistent with observations of typical cometary outbursts. It is concluded that this approach can provide an explanation of the sudden change in activity of comets for a wide range of heliocentric distances (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Beton unter hohen Temperaturen , eine Frage der Tunnelsicherheit

BETON- UND STAHLBETONBAU, Issue 2 2006
Konrad Bergmeister Prof. Dipl.-Ing.
Die Sicherheit in den Tunnels wird einerseits durch das Verhalten der Benützer und andererseits durch die Konstruktion und Ausstattung bestimmt. Neben der Modellierung des Verhaltens und der Anwendung von Sicherheitstheorien in Tunnel gilt es, organisatorische und erzieherische Maßnahmen in der Planungs-, Ausführungs- und Betriebsphase zu setzen. Durch die extreme Hitzeentwicklung können die Einbauten und das Tunneltragwerk beschädigt werden. Dabei kann es zu Betonabplatzungen (spalling) und zum Ablösen von Betonstücken bzw. Verankerungen kommen. In diesem Beitrag werden unterschiedliche Spritzbetone -experimentell unter hohen Temperaturen untersucht. Dabei zeigt sich, daß die Dichte und die Porenverteilung sowie die Zugkapazität der Betonformulierung von ausschlaggebender Bedeutung sind. Concrete exposed to high Temperatures , a safety Issue of tunnels The safety of tunnels is related to the behaviour of the users as well as to the construction and the equipment, which may be damaged due to heat impact. Concrete spalling decreases the effects of corrosion protection and the bonding of the reinforcement, and the load capacity is also diminished. Predictions about possible concrete spalling and failure mechanism often are based on experimental research. The crucial parameters for concrete spalling are the gas pressure in the pores, the physical properties e. g. water absorption at 20 °C and after 1000 °C and the mechanical resistance. In a full scale fire test in a highway tunnel there have been investigated various shotcrete mixtures. Pore size and distribution have been determined with the Mercury Intrusion (MIP) Porosimeter, whereas the permeability was calculated using the results of the MIP at different temperatures. It could be shown, that the moisture in the pore system and the physical and chemical adsorpted water in the matrix as well as in the aggregates evaporates under external increase of temperature and thus leading to higher pressure. Fire resistant shotcrete for use in tunnel shells should exhibit a certain volume of open pores in order to equalize the vapour pressure. [source]

Probing the Local Structure of Pure Ionic Liquid Salts with Solid- and Liquid-State NMR,

CHEMPHYSCHEM, Issue 1 2010
Peter G. Gordon
Abstract Room-temperature ionic liquids (RTILs) are gaining increasing interest and are considered part of the green chemistry paradigm due to their negligible vapour pressure and ease of recycling. Evidence of liquid-state order, observed by IR and Raman spectroscopy, diffraction studies, and simulated by ab initio methods, has been reported in the literature. Here, quadrupolar nuclei are used as NMR probes to extract information about the solid and possible residual order in the liquid state of RTILs. To this end, the anisotropic nature and field dependence of quadrupolar and chemical shift interactions are exploited. Relaxation time measurements and a search for residual second-order quadrupolar coupling were employed to investigate the molecular motions present in the liquid state and infer what kind of order is present. The results obtained indicate that on a timescale of ,10,8 sec or longer, RTILs behave as isotropic liquids without residual order. [source]

Anchoring ,-cyclodextrin to retain fragrances on cotton by means of heterobifunctional reactive dyes

COLORATION TECHNOLOGY, Issue 1 2004
Wang Chao-Xia
Cyclodextrins are cyclic oligosaccharides which are able to form complexes with a wide range of organic compounds, including fragrance oils. As a result of the complexation, the vapour pressure of the volatile substance is reduced and its release is better controlled. To achieve this, ,-cyclodextrin can be anchored to cellulose by means of a chemical linkage provided by heterobifunctional reactive dyes. [source]

Compositional effects accompanying near equilibrium vapour growth of solid solution crystals of the types IV-VI and II-VI

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2010
A. Szczerbakow
Abstract Near equilibrium evaporation-condensation in a sealed ampoule leads to almost full compositional reproduction of a solid solution if it consists of components having comparable vapour pressures; this can be qualitatively interpreted by domination of entropy increase. Nevertheless, even vestigial separation requires closer characteristics, since it may prove crucial , particularly for properties of semiconducting solid solutions. Maximum component separation allowed by a small temperature difference is described here in terms of thermodynamics and kinetics of solid-vapour and vapour-solid phase transitions. Theoretical models of the determining effects having different character are shortly described, and their applicability areas are determined. Experimental data collected for crystal growth of numerous semiconducting solid solutions of the II-VI and IV-VI type support the conclusion drawn from the models that the near equilibrium crystal growth from the vapour in a closed system ensures the highest degree of compositional uniformity. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A comparison between the experimental and estimated evaporation paths from emulsions

FLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2009
Abeer Al-Bawab
Abstract The evaporation paths in linalool emulsions were experimentally determined using a rotary evaporator coupled to a vacuum pump and calculated from vapour pressures for a series of emulsions with varied oil/water (O/W) ratios. The evaporation paths were comparable to an acceptable degree, suggesting that determination of the evaporation path under reduced pressure, combined with a straightforward calculation using vapour pressures, can be used to estimate the evaporation under different relative humilities. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Effect of snowpack removal on energy balance, melt and runoff in a small supraglacial catchment

HYDROLOGICAL PROCESSES, Issue 14 2002
Ian C. Willis
Abstract Modelling melt and runoff from snow- and ice-covered catchments is important for water resource and hazard management and for the scientific study of glacier hydrology, dynamics and hydrochemistry. In this paper, a distributed, physically based model is used to determine the effects of the up-glacier retreat of the snowline on spatial and temporal patterns of melt and water routing across a small (0·11 km2) supraglacial catchment on Haut Glacier d'Arolla, Switzerland. The melt model uses energy-balance theory and accounts for the effects of slope angle, slope aspect and shading on the net radiation fluxes, and the effects of atmospheric stability on the turbulent fluxes. The water routing model uses simplified snow and open-channel hydrology theory and accounts for the delaying effects of vertical and horizontal water flow through snow and across ice. The performance of the melt model is tested against hourly measurements of ablation in the catchment. Calculated and measured ablation rates show a high correlation (r2 = 0·74) but some minor systematic discrepancies in the short term (hours). These probably result from the freezing of surface water at night, the melting of the frozen layer in the morning, and subsurface melting during the afternoon. The performance of the coupled melt/routing model is tested against hourly discharge variations measured in the supraglacial stream at the catchment outlet. Calculated and measured runoff variations show a high correlation (r2 = 0·62). Five periods of anomalously high measured discharge that were not predicted by the model were associated with moulin overflow events. The radiation and turbulent fluxes contribute c. 86% and c. 14% of the total melt energy respectively. These proportions do not change significantly as the surface turns from snow to ice, because increases in the outgoing shortwave radiation flux (owing to lower albedo) happen to be accompanied by decreases in the incoming shortwave radiation flux (owing to lower solar incidence angles) and increases in the turbulent fluxes (owing to higher air temperatures and vapour pressures). Model sensitivity experiments reveal that the net effect of snow pack removal is to increase daily mean discharges by c. 50%, increase daily maximum discharges by >300%, decrease daily minimum discharges by c. 100%, increase daily discharge amplitudes by >1000%, and decrease the lag between peak melt rates and peak discharges from c. 3 h to c. 50 min. These changes have important implications for the development of subglacial drainage systems. Copyright © 2002 John Wiley & Sons, Ltd. [source]