Net Condensation Research Articles

Use of NMR and mass spectrometry to detect and quantify protease-catalyzed peptide bond formation in complex mixtures

Electrospray mass spectroscopy of aqueous solutions containing two different dipeptides, treated with a protease, showed ions corresponding to adducts and new dipeptides, indicating that transpeptidation had occurred. Hydrophobic dipeptides alone mainly gave ions corresponding to oligomers up to the heptamer, indicating that a net condensation reaction had occurred, apparently driven by the insolubility of the oligomers. Nuclear magnetic resonance analysis of 1- 13C-labeled hydrophobic peptides used as markers in plastein-type reactions showed extensive peptide bond formation, indicating that both transpeptidation and condensation had occurred. Extracts of casein hydrolysates, enriched in hydrophobic peptides did not exhibit significant condensation reactions under similar conditions. When hydrophilic di- and tripeptides were used as markers, nuclear magnetic resonance analysis failed to detect transpeptidation reactions catalyzed by endoproteases, even though the dipeptide studies showed that they were possible. Exopeptidases, however, catalyzed transpeptidation of up to 30% of the marker peptide, in both plastein-type reactions and proteolysis of casein, albeit after relatively long reaction times. It is possible that larger, stronger-binding peptides inhibit the transpeptidation of dipeptides by endoproteases but not by exopeptidases. It is likely that transpeptidation is not a significant process under normal industrial proteolysis conditions and causes no ill effects when it does occur, as exopeptidases normally improve protein hydrolysate properties.

Effect of condensation heat on the condensation coefficient

AbstractTo account for the effect of condensation heat on the condensation coefficient (α), a semiempirical model is proposed. The model contains two free parameters: a characteristic size of the “hot spot” where the heat release occurs and its lifetime. At reasonable values of the parameters, the model agrees well with experimental and computer‐simulated data for both simple and associating liquids. For nonequilibrium conditions, the model leads to the Hertz–Knudsen equation with α dependent not only on characteristics of the liquid but also on those of ambient vapor. This offers an explanation for the existing scattering of experimental data in α. Among other things, the expression for α obtained shows that for the net evaporation process α is always higher than that for the net condensation, and moreover, α = 1 for all liquids if evaporation occurs in vacuum. The model also indicates that for complex associating liquids like glycerol α may be quite sensitive to peculiarities of the liquid state under consideration.

Rainfall Distribution over Central and Southern Israel Induced by Large-Scale Moisture Flux

Abstract A map of annual rainfall in Israel was obtained from the real-time calculation of the net condensation in large-scale moisture transport through the eastern Mediterranean, sea surface evaporation, and orographic condensation above the Judean mountain range. The averaged rainfall efficiency of condensation over the rainy season is assumed to be a function of the vertically and time-averaged temperature. The calculated rainfall map correlates well with statistical annual rainfall distribution, correlation coefficient 0.9, and allows the effect of the three sources of precipitation mentioned above to be estimated. The condensation within large-scale moisture transport, the main source of precipitation in the Israel region, yields approximately two-thirds of the bulk rainfall in the Mediterranean Sea shore region. The rest results from the contribution of the sea surface evaporation. Orographic condensation starts near the Mediterranean Sea shore and increases in the direction of the Judean mountains...

Inferring the Diabatic Heat and Moisture Forcing of the Atmosphere from Assimilated Data

Abstract Different estimates of the global-scale diabatic sources and sinks of atmospheric heat and moisture, obtained from a data assimilation system of the ECMWF, are examined. Estimates arrived at using the budget method are compared with those given by the center's forecast model during very short range integrations. Integrations and initialized analyses for February 1979, produced in the mid-1980s in a reassimilation of the final FGGE lIb dataset, are used as a database. The results are specific to the particular assimilation system used in the reassimilation. All estimates yield qualitatively equivalent and meteorologically reasonable vertical integrals. For the moisture forcing, the vertical distributions are also similar. This is not true for the diabatic heating. In the Tropics, the model's physics gives strong cooling in the lower troposphere, where the budget method implies heating. This unrealistic cooling is present even in regions of intense net condensation. Quantitatively, both the heat an...

Modeling the Martian seasonal CO 2 cycle 2. Interannual variability

A diurnal and seasonal thermal model that can successfully fit seasonal pressure variations observed at the Viking 1 landing site and observed retreat rates of the seasonal polar caps is used to investigate the sensitivity of Martian seasonal pressure curves to interannual variations in the heat balance of the north and south seasonal polar caps. Year-to-year differences between measured surface pressures at the Viking landing sites as a function of season are used as upper limits on the potential magnitudes of interannual variations in the mass of the Martian atmosphere. There are compared with model-calculated interannual pressure variations which we obtain by temporarily altering model input parameter values. The results show that uniform, year-long interannual variations in the albedos or emissivities of the north or south seasonal polar cap of greater than ∼2% absolute would be quite apparent in the Viking Lander data. A brief cessation of net frost condensation within the north seasonal polar cap due to elevated atmospheric temperatures during the 1977B global dust storm would have caused interannual pressure variations later in the year that are larger than those observed. Simulations are performed which show that the dust layers deposited onto the condensing north seasonal polar cap during global dust storms can substantially darken sublimating seasonal frost deposits when they become uncovered during the following spring, and yet have relatively minor effects on seasonal pressure variations. For the case of the 1977B global dust storm, the interannual repeatability of the Viking Lander pressure data could be compatible with a 10% decrease in the albedo of the north seasonal polar cap. This result leaves open the possibility that the asymmetric behavior of CO 2 frost at the north and south residual polar caps could be due to differential dust contamination of accumulating north polar seasonal CO 2 deposits during global dust storms.

A diagnostic study of winter diabatic heating in the Mediterranean in relation to cyclones

Diabatic heating and net condensation rates during winter are calculated over the Mediterranean and surrounding areas from the 1982-88 ECMWF initialized analyses using the residual method for the heat and moisture budgets. The steady-state contributions over the Mediterranean are found to be prominent as in the tropics, but contrary to the case of the tropics the transients contributions in the Mediterranean, attributed to cyclonic activity, are not at all negligible. A composite Cyprus low was constituted from 67 typical cyclones in the eastern Mediterranean. The diabatic heating and net condensation distribution indicate vigorous sea fluxes especially in the lee of the Turkish mountains over the Aegean Sea where the air-sea contrast is maximized. In contrast with other regions, the maximum in the vertical profile of diabatic heating due to latent heat release is found at a lower altitude of about 850 hPa. It is suggested that this fact has important implications in modelling Mediterranean cyclones.

A diagnostic study of winter diabatic heating in the Mediterranean in relation to cyclones

AbstractDiabatic heating and net condensation rates during winter are calculated over the Mediterranean and surrounding areas from the 1982‐88 ECMWF initialized analyses using the residual method for the heat and moisture budgets. The steady‐state contributions over the Mediterranean are found to be prominent as in the tropics, but contrary to the case of the tropics the transients contributions in the Mediterranean, attributed to cyclonic activity, are not at all negligible.A composite Cyprus low was constituted from 67 typical cyclones in the eastern Mediterranean. The diabatic heating and net condensation distribution indicate vigorous sea fluxes especially in the lee of the Turkish mountains over the Aegean Sea where the air‐sea contrast is maximized. In contrast with other regions, the maximum in the vertical profile of diabatic heating due to latent heat release is found at a lower altitude of about 850 hPa. It is suggested that this fact has important implications in modelling Mediterranean cyclones.

Evolution of topography on comets II. Icy craters and trenches

We model the heating and sublimation of ice from topographical features to determine the effect of topography on sublimation rates on comets and other icy bodies. We solve the energy balance equation for cylindrical trenches and spherical craters. The model includes shadowing, solar heating, trapping of thermal radiation, trapping of sublimed gas molecules, and reflection of sunlight within the cavity. We solve for the mass loss rate from the topographical feature for a variety of shapes, solar distances, and albedos, and for both water and methane ice. We have improved the analysis over an earlier paper ( J. E. Colwell and B. M. Jakosky, 1987, Icarus 72, 128–134), by treating more realistic geometries, accounting for reflection, and calculating the true net sublimation rate. We also correct an error in the model of secondary heating within a cavity. We find in general an enhancement in the net sublimation rate for trenches and craters farther from the Sun than some critical distance which depends on the albedo. In some cases there is a net condensation of ice onto the rim of a crater or trench, and craters tend to elongate in the direction of the Sun's path. The three-dimensional model of a spherical crater shows significant enhancement of mass loss at the bottom of the crater relative to the rim. The focusing caused by topography will tend to form jets from icy craters that are actively subliming. Methane ice in the outer solar system behaves qualitatively similar to water ice at R ∼ 3 AU. The net effect on topographic evolution depends on the detailed shape of the topography as well as on albedo and solar distance.

Thiolase from Clostridium acetobutylicum ATCC 824 and Its Role in the Synthesis of Acids and Solvents

Thiolase (acetyl-coenzyme A [CoA] acetyltransferase, E.C. 2.3.1.19) from Clostridium acetobutylicum ATCC 824 has been purified 70-fold to homogeneity. Unlike the thiolase in Clostridium pasteurianum, this thiolase has high relative activity throughout the physiological range of internal pH of 5.5 to 7.0, indicating that change in internal pH during acid production is not an important factor in the regulation of this thiolase. In the condensation direction, the thiolase is inhibited by micromolar levels of CoA, and this may be an important factor in modulating the net condensation of acetyl-CoA to acetoacetyl-CoA. Other cofactors and metabolites that were tested and shown to be inhibitors are ATP and butyryl-CoA. The native enzyme consists of four 44,000-molecular-weight subunits. The kinetic binding mechanism is ping-pong. The K(m) value for acetyl-CoA is 0.27 mM at 30 degrees C and pH 7.4. The K(m) values for sulfhydryl-CoA and acetoacetyl-CoA are, respectively, 0.0048 and 0.032 mM at 30 degrees C and pH 8.0. The active site apparently contains a sulfhydryl group, but unlike other thiolases, this thiolase is relatively stable in the presence of 5,5'-dithiobis(2-nitrobenzoic acid). Studies of thiolase specific activity under various types of continuous fermentations show that regulation of this enzyme at both the genetic and enzyme levels is important.

A STUDY ON MODELING OF SNOWMELT DISTRIBUTION

In this paper a model for estimation of snowmelt distribution using insolation, air temperature and precipitation is presented. This model includes net radiation, degreehour approach and condensation and convection in a rainy day. At first the model is determined at the observational base. And it is applied to the slopes and the forested area. The results of the application of the model to the base, the slopes and the forested area are in good agreement with observed data.

The effects of thermal distillation on the performance of differential-contact distillation columns

It is shown for a differential-contact distillation column that when there is net evaporation or net condensation within the column the height of a transfer unit should be lower than it is for adiabatic conditions. However, this improvement in efficiency, which is due to thermal distillation occurring in addition to contact distillation, is detected experimentally only for net condensation. It is also shown that, for the same reflux ratio at the top of the column, when there is thermal distillation fewer transfer units are needed, seemingly giving a further improvement in the performance. However, operating under the more realistic criterion of the same heat load per unit of throughput, implying a higher reflux ratio for adiabatic conditions, a column gives about the same separation whether there is thermal distillation or not.

The seasonal and global behavior of water vapor in the Mars atmosphere: Complete global results of the Viking Atmospheric Water Detector Experiment

The water vapor content of the Mars atmosphere was measured from the Viking Orbiter Mars Atmospheric Water Detectors (MAWD) for a period of more than 1 Martian year, from June 1976 through April 1979. Results are presented in the form of global maps of column abundance for 24 periods throughout each Mars year. The data reduction incorporates spatial and seasonal variations in surface pressure and supplements earlier published versions of less complete data. Column abundances vary between 0 and about 100 precipitable microns (pr μm), depending on location and season, while the entire global abundance varies seasonally between an equivalent of about 1 and 2 km3 of ice. The first appearance of vapor at nonpolar latitudes as northern summer approaches and the drop in abundance at mid‐latitudes as summer ends both strongly imply the existence of a seasonal reservoir for water within the regolith. There appear to be no net annual sources away from the poles that contribute significant amounts of water. However, the strong annual gradient of vapor from north to south implies a net annual flow of vapor toward the south. This southward flow may be balanced by a northward flow during the global dust storms, by transport in the form of clouds or adsorbed onto dust grains, or during other years. The perenially cold nature of the south polar residual cap, along with the relatively large summertime vapor abundances over the cap, implies a net annual condensation of vapor onto the cap. Comparison with earlier (Earth‐based) observations of vapor in the south during the local summer indicates that all of the seasonal CO2 cap may sublime away in some years to reveal the water ice cap which must lie underneath, with corresponding large southern summer vapor abundances. The global distribution of the annual average abundance of vapor correlates well with Martian topography, as might be expected for a uniform constant atmospheric mixing ratio. If this topographic effect is divided out, the resulting residual map correlates well with maps of surface albedo and thermal inertia; this correlation may be related to the control exerted by the surface and subsurface temperatures on the adsorption/desorption process and on the atmospheric temperature profile and, hence, the vapor holding capacity of the atmosphere.

A Diagnostic Study of the Diurnal Rainfall Variation in the GATE B-Scale Area

Abstract Heat and moisture budgets are used to compute net condensation rates in the GATE B-scale network for four hours of the day: 0000, 0600, 1200 and 1800 GMT. Budgets are presented for all phases combined, for selected periods of enhanced convection and for selected periods of suppressed convection. Computations are based on fitted values of the meteorological sounding data for the center of the B-scale ship array, on surface heat flux and evaporation measurements for seven ships in the array and on Cox and Griffith's (1979) radiation measurements for Phase III. Results are also presented for the diurnal variation of the basic variables. Main findings are as follows: 1) Temperature variations are small, of the order of a few tenths of a degree, with a daytime maximum and nighttime minimum. There is evidence of possible radiation error above 400 mb where the amplitude is largest. 2) The atmosphere appears to be relatively dry during the day, when convection is most active, and relatively moist at nigh...

Individual Time Period Analyses over the GATE Ship Array

Abstract Diagnostic moisture and dry static energy budgets for the GATE A/B-scale area are performed for individual time periods using rawinsonde and satellite data. The data are sufficiently accurate to permit quantitative analysis of that area with 3–6 h time resolution. Each budget is used to estimate the net condensation rate for every time period. The budget condensation rates slightly exceed radar rainfall estimates for the GATE master array and the radar values lag the budget condensation by 4–6 h during major rainfall episodes. Storage of liquid water and unsampled vapor in clouds can account for a large portion of the observed lag. The present results indicate that observed 3–6 h lags between, low-level mass convergence and echo growth during GATE result primarily from the lag between condensation and precipitation during convective system evolution. The release of latent heat in a tropical convective system appears to be closely related to the instantaneous mass convergence below 700 mb. Budget-...

Kinetic theory approach to the vapor-phase phenomena in a nonequilibrium condensation process

The phenomenon of one-dimensional steady condensation of pure vapor at the plane surface of a liquid is considered from the kinetic theory viewpoint. The vapor is treated as a perfect gas without internal degrees of freedom. For the description of this problem the full nonlinear BGK model equation is used. For the solution of the BGK model equation the method of discrete ordinates is applied. The calculations are carried out for water vapor. As a result the temperature and density distributions in the vapor phase are obtained and also for a given temperature difference the net condensation molecular flux rate is determined, depending on the condensation and evaporation coefficients which are treated as parameters.

Vapor Condensation in a Shock Tube; Condensation Coefficient for sec-Butyl Alcohol

The condensation of sec-butyl alcohol vapor has been observed in a glass shock tube instrumented to observe the variations in monochromatic light transmittance caused by the growth of a liquid film of sec-butyl alcohol on the shock-tube walls. The film thickness was obtained from the transmittance. The gas pressure during condensation was monitered by strain gages, and the wall temperature and shock-wave velocity were measured with the resistance gages. The observed supersaturation ratios at the liquid—vapor interface ranged from 1.1 to 3.2 and the observed net condensation rates ranged from −0.015 to −0.67 g cm−2·sec−1. The interface temperatures ranged from 25° to 50°C. The condensation process was analyzed in terms of an equilibrium condensation coefficient. The gas at the interface was assumed to be uniform, in motion toward the interface, and have a Maxwellian velocity distribution. Using the measured values of net condensation rate, pressure, and temperature, the calculated condensation coefficients were not constant, but varied linearly with net condensation rate. When extrapolated to zero condensation rate, the condensation coefficient had a most probable value of 0.25 with a 65% probability of lying between 0.02 and 0.08. The value of the condensation coefficient calculated by the method of Mortenson and Eyring is in good agreement with the above value.

Mechanism of Dropwise Condensation

From a study of surface phenomena, information is obtained about conditions under which net condensation can occur. An experimental examination of the surface, using an optical method capable of detecting thin films of molecular dimensions, shows that no film greater than a monolayer in thickness exists on the area between the drops. Wetted pits and grooves in the surface are considered to be the most probable drop nucleation sites. A model for drop growth gives results which are compatible with experimentally observed values, and which show the growth rate to be a function of the vapor pressure.

Water-vapor exchange between a water droplet and its environment

Laboratory experiments in which a small water droplet is supported by a stream of rising saturated air confirm the theoretical predictions of a relatively rapid exchange of deuterium between droplet and environment when neither net condensation nor evaporation takes place. The importance of the result to both deuterium and tritium rainwater measurements is far reaching and suggests that such observations ought to be supplemented with atmospheric water-vapor samples.

The effect of heat transfer between the phases on the performance of countercurrent distillation columns

In distillation processes net evaporation or condensation in the bulk phases or at the interface is called thermal distillation. The causes of thermal distillation, especially mismatch between the rates of heat and mass transfer in and between the phases, are discussed. By taking thermal distillation into account in heat and material balances it is shown that the performance of countercurrent equipment should depend upon composition of the mixture and should have a maximum value, as has been found experimentally in this and in previous work. The experimental results indicate that the efficiency of the equipment is very low when the mixture is dilute, and this is not accounted for by the theory.

Heat and mass transfer between the gaseous and liquid phases of a binary mixture

A rigorous theoretical analysis is presented of the heat and mass transfer occurring at an element of the interface separating the liquid and gaseous phases of a binary mixture. Solutions of the equations are presented for ethanol-water mixtures, three separate cases being considered, namely—(i) the bulk liquid and gas states are not saturated, and both Lewis numbers equal to unity; (ii) the bulk states are saturated and both Lewis numbers equal unity; and (iii) the liquid Lewis number is close to zero, while the gaseous one equals unity, the bulk states being either saturated or not. Results are compared with the predictions of the approximate (equi-molal transfer) treatment conventionally used (e.g. [1]). It is shown that the conventional theory only gives tolerable accuracy for case (ii); in the other cases its prediction bears almost no relation to those of the rigorous theory. The rigorous theory shows that, in the examples considered, either net condensation or net vaporization may occur, depending on the conductance values and the bulk states. In some cases the more volatile component is caused to condense despite having a higher gas-phase concentration at the interface than in the bulk of the gas.