Constant External Conditions Research Articles

A Test of Lumped-Parameter Methods for the Drying Rate in Fluidized Bed Driers for Bioproducts

ABSTRACT For batch fluidized bed drying of bioproducts the distributed parameter model is presented, in which the internal diffusion equation is coupled to the air balance equations. In practice a large part of the process takes place at high relative humidity of the drying air, equivalent to low driving forces. The results of a number of lumped-parameter methods for the estimation of drying times are compared with those of the full model for the case of constant external conditions around a particle. For low relative humidity of the drying air predictions of drying times with the Regular Regime Power Law method correspond well with the full solution, for higher ambient RH large deviations occur. The other methods are shown to give large deviations in all cases.

Instability and structure of axisymmetric rotating flow

The development of instability in an axisymmetric flow has been experimentally investigated. The evolution of disturbances ranging from high-frequency fluctuations to large-scale ordered structures with wave numbersn=2, 3, 4, 5, 6, and 7 is traced. An experimental diagram of the regions of stable existence of various types of disturbances is constructed. The periodic flop-over cycles of a hydrodynamical system with respect ton are obtained experimentally for constant external conditions in the absence of forcing.

Self-organization in reactions at surfaces

The techniques of surface science provide detailed insights into the microscopic processes underlying catalytic reactions which form, on the other hand, the basis for appropriate modelling of the macroscopic kinetics. For constant external conditions, the rate of a catalytic reaction is, however, not necessarily stationary, but may become oscillatory or even chaotic. These effects are associated with non-uniform distribution of the adsorbed species over the surface on a mesoscopic scale, and their theoretical description is based on the concepts of nonlinear dynamics. Experimental verification of these phenomena of spatio-temporal self-organization is demonstrated with the catalytic CO oxidation on a Pt(110) surface as example.

Changes in the rate of food vacuole formation during early clonal life ofParamecium primaurelia

Abstract The rate of food vacuole formation was shown to vary in Paramecium primaurelia during early clonal life; under constant external environmental conditions, remarkable changes occurred in young cells within a few fissions. Studies on different life span clones showed an increased rate, sometimes gradual and constant, and sometimes interrupted by a decrease, followed first by a reduced, then by a constant number of food vacuoles per unit of time. The decrease in food vacuole number, which was not followed by recovery of the food uptake rate, was related to a decline in fission rate. An explanation of the varying rate of food vacuole formation is discussed in terms of a known change in macronuclear DNA content during clonal life. Cells with a high DNA content were supposed to require less food to complete their cell cycle than cells with a low DNA content.

Endogenous rhythms and chaos in crassulacean acid metabolism

Endogenous free-running regular circadian oscillations of net CO2 exchange in the crassulacean-acidmetabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie under constant external conditions in continuous light have been shown to change to irregular non-predictable (chaotic) time behaviour as irradiance or temperature are raised above a critical level. A model of CAM has been constructed with pools of major metabolites of varying concentrations, flows of metabolites leading to exchange between pools, metabolite transformations determined by chemical reactions, and feedback regulations. The model is described by a system of coupled non-linear differential equations. It shows stable rhythmicity in normal dark-light cycles and in continuous light and, like the K. daigremontiana leaves in the experiments, a change to chaos as irradiance is increased. The maintenance of endogenous oscillations in the model is brought about by a hysteresis switch or beat oscillator between two stable oscillation modes. In CAM these stable modes are vacuolar malate accumulation and remobilization. The model shows that the physical nature of the beat oscillator in the leaves can be explained by the balance between active and passive transport at the tonoplast.

Drying processes in the Antarctic collembolan Cryptopygus antarcticus (Willem)

Live and dead specimens of the Antarctic collembolan Cryptopygus antarcticus (Willem) dry, under constant external conditions of temperature (25 or 35°C) and r.h. (0%), like most hygric soil arthropods. The drying curves of both live and dead specimens have three phases: an initial decrease; a constant rate period and a final falling rate period. The latter is exponential. Cryptopygus dries throughout these phases in a purely physical, passive manner. The constant rate period is not indicative of active metabolic or physiological regulation of water loss. The entire drying curve can be explained using drying theories developed for porous, hygroscopic solids. A similar situation pertains in the Antarctic lichen Umbilicaria antarctica Frey et Lamb. Geometrically, the percentage of water remaining at the onset of the falling rate period is related to the hydrated thickness of the collembolan cuticle or the lichen cortices. For Cryptopygus the hydrated thickness is estimated as 14 μm.

The Effect of Sea Level Rise on Coastal Plain Estuaries, with Examples from Chesapeake Bay: ABSTRACT

Estuaries are geologically transitory features whose evolution depends on a delicate balance among relative sea level basin geometry, shoreline erosion, fluvial sediment discharge, littoral drift, and tidal exchange. Models of modern estuarine development require specific sea level scenarios; almost all assume a continuation of the decelerating sea level rise of the last few thousand years. However, under constant external conditions, estuaries are ephemeral because they rapidly fill with fluvial and marine sediment. The rate of filling changes with time, but only a few thousand years are required to fill most estuaries. The persistence of estuaries, therefore, requires that relative sea level rises at a rate sufficient to compensate for the inherent tendency of estuaries to fill with sediment. Coastal plain estuaries, of which Chesapeake Bay is a prime example, are often referred to as drowned river valleys. Although this description is appropriate for the first-order morphology of Chesapeake Bay, the implied passivity can be misleading, especially in the high-tidal-energy area of the bay mouth where dramatic spit progradation and channel migration have occurred in the last few thousand years. Holocene sediment accumulation rates are more irregular along the length of the estuary than most models would predict; but in general,more » sediment accumulation has been greater at the mouth and at the head of the bay and less along the middle reaches. If relative sea level were to stabilize, the estuary would fill with sediment from both ends within a few thousand years. Evidence for two previous generations of the bay is preserved as the estuarine fill of major fluvial valleys, demonstrating that estuarine episodes have been closely tied to cyclic sea level changes.« less

EVALUATION OF DIFFUSION EQUATION FOR SIMULATING MOlSTURE MOVEMENT WITHIN AN INDIVIDUAL GRAIN KERNEL

ABSTRACT Drying of agricultural grains by and large takes place in the diffusion controlled falling rate period. Therefore, an understanding of the phenomenon of moisture transfer within an individual particles of material is desirable and should be represented precisely by a mathematical model. This paper describes a numerical solution that has been developed for solving spherical diffusion equation describing moisture movement within a grain kernel for accurately calculating bulk drying rate. All agricultural materials in general, when drying as a single particle under constant external conditions, exhibit a constant rate moisture loss

Drying Behavior of Honey‐Starch Mixtures

ABSTRACTDrying behavior of honey‐starch mixtures at constant external conditions were studied. Mixtures with 0, 10, 20, 30, and 40% starch and the balance in honey were coated on aluminum plates at 0.25 mm thickness and dried in a laboratory oven at 60°, 70°, and 80°C. A mass transfer model with two falling rate periods was developed. In the first falling rate period, mass transfer coefficient was a linear function of moisture content. It was a constant in the second falling rate period. Mass transfer coefficients were also found to be affected by temperature and the starch content of each mixture.

On the variety of cathode craters of vacuum arcs, and the influence of the cathode temperature

Cathode craters of 50 A arcs have been investigated with surfaces of reproducible definition. It was found, under constant external conditions, that the occurrence of various crater types is a secondary effect due to the surface state, and not a primary property of the arc. At high temperatures (up to 2500 K) the cathode mechanism is not essentially changed, but the crater size increases. This increase can be interpreted by the model of ion-impact heating. The occurrence of large craters at high temperatures explains the enhanced cathode erosion at high surface load as well as the production of large droplets.

水産養殖の発展に対する生理学と生化学の貢献(日本水産学会創立50周年記念講演)

Physiological and biochemical methods and techniques are used to study biological processes at different levels of organization of living matter. Normal physiological processes of marine organisms caught in natural environment or maintained under constant external conditions have been studied in numerous scientific works. Nutrition, respiration, reproduction and metabolism for instance, are physiological functions more or less extensively known in algae, fishes, molluscs and crustaceans, among other phyla, generally depending on their economical interest. Less studied are the physiological variations characterizing these species under different external conditions, systematically fixed, one by noe, or by groups, or under determinde variations of these environmental factors. Ecophysiology provide considerable information on the ecological characteristics of the studied species in nature, where temperature, photophase, light intensity, salinity, etc…, vary simultaneously in a non-programmed manner. The effects and consequences of each of these factors considered individually must be evaluated and measured in order to ascertain the importance of each one in nature and for each physiological function. The scientific information obtained in these studiesins easily made use of in aquaculture, especially with intensive techniques. The normal biochemical characteristics of marine organisms caught in natural environment or maintained under constant external conditions have sometimes been of interest for laboratories specialized in pure or physiological biochemistry. Some descriptive works in structural biochemistry, concerning the detailed composition of marine organisms, are available. The former vary in number and importance, depending on the different phyla. Enzymes characteristic of each physiological function, i. e. digestive enzymes in the nutritional function, and enzymes of intermediary metabolism for instance are much less known than in mammals, and sometimes not known at all in certain enire zoological groups. Biochemical variation of these species under systematically fixed or expermentally varying external conditions have been much less developed and are much less known, especially in marine organisms. This scientific area, which can be called ecobiochemistry, will provide a fundamental explanation of the physiological functions of aquatic species, especially those reared in aquaculture. The physiological and biochemical rhythmicity of these species internal or imposed, circadian, seasonal, annual, or dependingon the molting cycles in arthropods, have to be studeied in detail in order to enhance intensive aquaculture and automatization of the related techniques. The relationship between the variable physiology and biochemistry of the hosts and their parasites, where interesting results have recently been obtained, have to be developed in order to gain an understanding of the processes of infestation, the reciprocal complementarities of the hosts and the parasite, and to improve the prevention and treatment of the hosts. Such a scientific area could be called ecophysioparasitology. Similarly, ecophysiopathology deals with the internal and external conditions of disease apparition. The development of ecophysiology and ecobiochemistry needs interdisciplainary teams made up of marine biologists, physiologists and biochemists, working closely with specialists in aquaculture and development.

Steady states of weakly dissipative systems

The states to which weakly dissipative systems in constant external conditions tend are examined. At vanishing dissipation, several steady states, which are superpositions of steady states of an isolated conservative system, can exist. With increasing dissipation, these states can form clusters. When the correlation time of the conservative motions is finite, a description with a probability density, which is a solution of a Fokker-Planck equation in a coarse grained phase space, seems possible.

Chemical Oscillations

AbstractUnder constant external conditions, chemical reactions may also proceed in a rhythmic manner. The kinetic mechanisms responsible for such oscillations prove to be unexpectedly complicated. It can nevertheless be demonstrated that chemical periodicity is caused by certain kinds of coupling between simultaneous reactions or transport processes. A general survey of the chemistry and phenomenology of the principal chemical oscillations is followed by a discussion of the situations leading to periodic reactions on the basis of the multivariable kinetics of feedback systems. Autocatalysis and autoinhibition play an important role, as also do kinetic instability and spatial propagation.

Some remarks on the statistical character of crystal growth

AbstractThe instantaneous growth rate of KBr crystals growing under constant external conditions in a supersaturated aqueous solution and that of fixing salt crystals growing in an under‐cooled melt show statistical fluctuations. According to our experiments the instantaneous growth rate – as a probability variable – may be described with a good approximation by using a Maxwellian probability density function.

Learned and unlearned components of the rat’s adaptation to water deprivation

Rats were given three successive lO-day adaptation periods on 23.5 h water deprivation with five days of ad lib conditions interpolated between adaptations. Latency to drink, water in­ take, and body weights were measured. Latency to drink de­ creased with repeated testing. indicating a learned component of adaptation behavior. Water intake and body weight, con­ versely, required the same adjustment process during each adaptation, indicating that these components are not in­ fluenced by prior learning. The results are discussed in the context of a prior controversy in the literature. A controversy has resulted from the behavioral studies which have attempted to describe the process of adaptation to water deprivation. Ghent (1957) re­ ported decreasing latency to drink, increasing water intake, and progressively less weight loss during suc­ cessive days of adaptation to 23 h water deprivation. She explained the increased intake on successive days as a learning phenomenon. She reasoned that since there was progressivley less weight loss, the increased intake could not be due to an increased physiological deficit. However, she did not test this explanation with repeated adaptations. Beck (1962) found that rats deprived of water one day and allowed two days on ad lib before being deprived again, showed no progressive increase in intake with repeated deprivations. Beck reasoned that either the rat did not learn to utilize the drinking period in spite of repeated deprivations, or the need for water was less on the first day of deprivation. He concluded that increased water intake with experience on deprivation was due to increased need for water. The present experiment attempted to resolve this controversy by using (a) 10 day adaptation periods within which drinking is known to stabilize, and (b) constant external stimulus conditions during the ad lib recovery periods, which eliminates confounding factors associated with a novel drinking situation. Method The Ss were 11 male albino rats of the Holtzman strain. They were housed in individual wire cages, where Wayne Lab Blox were constantly available. Three days after their arrival in the laboratory, Ss were weighed and the water bottles were removed from their home cages. For the next 10 days, Ss were weighed and given 0.5 h free access to water in individual drinking boxes. These boxes were fixed with 100 ml gas measuring tubes, graduated in 0.2 ml, and had Plexiglas covers for observations of drinking. Latency to drink after being placed in the box and water intake were measured daily. Following the 10th day

Mathematical Study of the First Stage of Drying of a Moist Soil

AbstractIn the classical “first stage of drying” of a moist soil, constant external conditions produce a constant evaporation rate. The exponential dependence of moisture diffusivity on water content, suggested by W. R. Gardner, has been used for working out the changing soil moisture profiles in homogeneous soil columns, initially uniformly moistened, with gravity neglected. The characteristic parameter for the process is (βq0L/DI), where q0 is the evaporation rate [cm.3/(cm.2sec.)], β is a constant in the diffusivity equation D = γ · exp (β θ), L is the length of the column, and DI(cm.2/sec.) is diffusivity at initial moisture content θ1(cm.3/cm.3). If (β q0L/DI) is > 5, then the column behaves as an infinitely long column throughout the first stage of drying, and a newly‐computed universal relationship holds: β(θI − θ) = F [(βq0 x/DI), (β2 q02 t/DI)], where x is distance from evaporation surface and t is time. If (βq0L/DI) is < 5, then finiteness of length becomes important within the first stage of drying. The variable β(θI − θ) has been computed as a function of (x/L), (βq0t/L), and (βq0L/DI) for selected values of the latter. These new mathematical functions facilitate theoretical studies and the determination of desorption parameters from observations.

A Temperature-dependent Endogenous Rhythm in the Rate of Carbon Dioxide Output of Periplaneta americana

Ball, Dyke and Wilkins1 and Wilkins2 developed an apparatus, incorporating an infra-red gas analyser (Grubb-Parsons, S.B.1), for continuously estimating the rate of carbon dioxide metabolism of plant tissue maintained under constant external conditions for 5–10 days. Using this apparatus the rate of carbon dioxide output of individual adult cockroaches was determined. The insects were kept in 12 : 12 hr. alternations of light and darkness and, at the commencement of an experiment., were transferred to a small flask which was placed in darkness and at a constant temperature at the end of a light period. The records presented here were derived from one insect, but five other cockroaches gave closely similar results.

A method of determining variance in the presence of a linear systematic error

1. The determination of the variance of a series of measuring instrument readings is possible not only with constant external conditions but also in the presence of a systematic error. 2. The method here developed provides the determination of the variance of instrument readings in the presence of a systematic progressive linear error. 3. The determination of the variance by this method is possible both by calculation and graphically. 4. The definition of the term “variance” adopted in metrology is a particular case of the general variation in which the readings are affected by a systematic error.

Geisselmodelle und adenosintriphosphat (ATP)

Flagella of spermatozoa and trypanosomes extracted in glycerine-water (flagellum models), undulate in the presence of ATP. These movements correspond in all respects to the contraction of fibroblast- and muscle-models, but it is a peculiarity of the contractile system of the flagella to alternate between contraction and relaxation under constant external conditions. This spontaneity must be attributed to the contractile apparatus itself, because it occurs even in separated parts of the flagellum and because the cell membranes and their selective permeability are destroyed in the preparation of the models. ATP has a double function in flagellar movement. It works specifically to cause contraction and unspecifically as a plasticiser. Since the plasticity of the models determines the speed of their movement, the ATP concentration controls the frequency of the beat. Germanin is an extremely effective inhibitor of the movement of trypanosome models.

Colour Change in the Echinoid, Diadema antillarum, Philippi

PHYSIOLOGICAL colour change has been but rarely reported in echinoderms1. Mortensen2, in a footnote, makes cautious reference to the possibility of such changes occurring in Diadema antillarum; but it is clear that he was not aware of the striking manifestation of the phenomenon reported here, which occurs in young forms of this species. Indications of the existence of a rhythmic change in colour persisting under constant external conditions do not appear to have been reported previously in this form, nor indeed, so far as I am aware, in any other echinoderm.