林冠分配降雨过程的模拟实验分析

实验发现,降雨通过林冠的穿透过程线、树干径流过程线与电感电容电阻串联电路暂态过程线极为相似。由此启发,用此电路暂态方程拟合穿透降雨与树干径流过程并求出了解析解。进而,根据余项法求出截留强度表达式。此举拓宽了森林水文学理论研究思路。     

STIMULATION OF FUNDULUS BY OXALIC AND MALONIC ACIDS AND BREATHING RHYTHM AS FUNCTIONS OF TEMPERATURE

1. Chemical stimulation as a function of temperature was studied by using oxalic acid in fresh and salt water and malonic acid in salt water as stimulating agents on Fundulus. According to the Arrhenius equation the following µ values were obtained for the various acid solutions between 0 and 29°C.: for 0.002N oxalic in fresh water—15,800; 33,000; for 0.0008N oxalic in fresh water—15,800; 33,000; 48,000; for 0.002N oxalic in salt water—19,400; 24,100; 56,500; for 0.004N and 0.002N malonic in salt water—20,600; 65,000. At a critical temperature there is a sharp transition from one thermal increment to another. 2. The chemical processes controlling stimulation do not change with concentration, for different normalities of a single acid yield the same µ values. Distinctly different temperature characteristics were obtained for stimulation by oxalic in salt and fresh water. Likewise stimulation by oxalic and malonic in salt water yielded very different increments. This temperature study indicates that the controlling chemical reactions determining rate of response are different for the same acid in two different environments, or for two dibasic acids in the same environment. Other work indicates, however, that the fundamental stimulation system is the same for all the adds in both environments. Chemical rather than physical processes limit the rate of response since all the values are above 15,000. Stimulation depends upon a series of interrelated chemical reactions, each with its own temperature characteristic. Under varying conditions (e.g. change of temperature, environment, or acid) different chemical reactions may become the slowest or controlling process which determines the rate of response. 3. The variation of response, as measured by the probable error of the mean response time of the fish, is the same function of temperature as reaction time itself. Hence variability is not independent of reaction time and is controlled by the same catenary series of events which determine rate of response to stimulation. 4. Breathing rhythm of Fundulus as related to temperature was studied in both salt and fresh water. In salt water the temperature characteristic is 8,400 while in fresh water it is 16,400 below 9.5°C., and 11,300 above this critical temperature. These µ values are typical of those which have been reported by other workers for respiratory and oxidative biological phenomena. A change in thermal increment with an alteration in environment indicates that different chemical reactions with characteristic velocity constants are controlling the breathing rhythm in salt and fresh water.     

Chemical machines, Maxwell's demon and living organisms

The problem considered in this paper is whether conventional chemical machines can be used in living organisms. I first point out that, due to their molecular nature, living systems pose unique thermodynamic problems, particularly in relation to Maxwell's demon. I then show that these problems may be solved by introducing time into the fundamental statement of the second law so that it becomes valid at the molecular level. This proposal, while clarifying certain logical anomalies in classical thermodynamics, makes no difference to that science in practice. However, I deduce from this statement that there are only two general ways of obtaining useful work from a chemical reaction: the first, a “constrained equilibrium” mechanism, is that employed by conventional chemical engines, but the second, a “molecular energy” mechanism, which depends upon the rapidity of resonant energy-transfer, may not have been suggested before. I then argue that because the former mechanism is essentially macroscopic in character it cannot, in fact, be used in those biological processes, like muscular contraction or active transport, in which useful molecular work is done and that only the latter may be so used. I also suggest reasons why this conclusion has been overlooked. Muscular contraction is used to illustrate these arguments and it is shown that all models of this process so far proposed fall into the first category. Although it is possible to eliminate such models a priori, several examples are finally criticized in detail to clarify the points raised. It is shown that in fact each of these models would have to be a Maxwell's demon machine.     

STEREOTROPISM AS A FUNCTION OF NEUROMUSCULAR ORGANIZATION

From what has been said concerning the neuromuscular organization of the Asterias ray, it is possible to arrive at certain definite conclusions regarding the nature of the stereotropism of that organ. The righting movements from the start are not haphazard; i.e., they cannot be explained on any hypothesis of "trial and error." The excitation of the sensory cells of the dorsal sheath initiates dorsal flexure of the ray. This movement makes it possible for the tube feet of the tip to touch bottom and start the vigorous action which follows and completes the righting If the "feelers" by chance touch bottom they initiate the reaction de novo. As to the remaining phases, the stereotropic reaction of the ray is referable to the high degree of surface sensitivity of the tube feet disks and the propagation of excitatory and inhibitory impulses, resulting from stimulation, along appropriate paths to the muscles of the ray. In this respect the tube feet may be regarded as playing a role similar to that of tropistic receptors in general. That is, unequal stimulation of the receptors causes a corresponding inequality of tone or of contraction in the musculature which ultimately results in an equilibrium of orientation to the factor involved. It is evident that as a mechanism for righting stereotropism differs in one important respect from other tropisms. The latter depend for their operation upon unilateral effects in organisms which are dynamically bilaterally symmetrical. In stereotropism the sensitivity of the organism is not distributed in bilaterally symmetrical fashion. As a rule only the ventral side is stereosensitive; i.e., the sensitivity is unilaterally distributed. There is a tropistic action in such cases because of the fact that when the sensitive surface is only partially stimulated an unequal contraction of the musculature follows and this as a result brings the sensitive surface into such a position that it is all equally stimulated. Equal muscle tone follows and the organism is in equilibrium with its environment.     

The fundamental processes in ecology: a thought experiment on extraterrestrial biospheres

Ecological science is often organised as a hierarchical series of entities: genes, individuals, populations, species, communities, ecosystems and biosphere. Here, I consider an alternative process‐based approach to ecology, and analyse the nature of the fundamental processes in ecology. These fundamental processes are discussed in the context of the following question:‘for any planet with carbon‐based life, which persists over geological time scales, what are the minimum set of ecological processes that must be present?‘I suggest that the following processes would be present on any such planet: energy flow, multiple guilds, ecological tradeo ffs leading to within‐guild biodiversity, ecological hypercycles, merging of organismal and ecological physiology, carbon sequestration and possibly photosynthesis. Nutrient cycling is described as an emergent property of these fundamental processes. I discuss reasons why a biosphere based on a single species with no nutrient cycling is very unlikely to exist. I also describe the concept of ‘Gaian effect’. This suggests that some processes will always tend to extend the lifespan of a biosphere in which they develop (positive Gaian effect) while others could either increase or decrease (negative Gaian effect) such a lifespan. These ideas are discussed in the context of astrobiology, ecosystem services, conservation biology and Gaia theory.     

INACTIVATION OF CRYSTALLINE TRYPSIN

1. The rate of inactivation of crystalline trypsin solutions and the nature of the products formed during the inactivation at various pH at temperatures below 37°C. have been studied. 2. The inactivation may be reversible or irreversible. Reversible inactivation is accompanied by the formation of reversibly denatured protein. This denatured protein exists in equilibrium with the native active protein and the equilibrium is shifted towards the denatured form by raising the temperature or by increasing the alkalinity. The decrease in the fraction of active enzyme present (due to the formation of this reversibly denatured protein) as the pH is increased from 8.0 to 12.0 accounts for the decrease in the rate of digestion of proteins by trypsin in this range of pH. 3. The loss of activity at high temperatures or in alkaline solutions, just described, is very rapid and is completely reversible for a short time only. If the solutions are allowed to stand the loss in activity becomes gradually irreversible and is accompanied by the appearance of various reaction products the nature of which depends upon the temperature and pH of the solution. 4. On the acid side of pH 2.0 the trypsin protein is changed to an inactive form which is irreversibly denatured by heat. The course of the reaction in this range is monomolecular and its velocity increases as the acidity increases. 5. From pH 2.0 to 9.0 trypsin protein is slowly hydrolyzed. The course of the inactivation in this range of pH is bimolecular and its velocity increases as the alkalinity increases to pH 10.0 and then decreases. As a result of these two reactions there is a point of maximum stability at about pH 2.3. 6. On the alkaline side of pH 13.0 the reaction is similar to that in strong acid solution and consists in the formation of inactive protein. The course of the reaction is monomolecular and the velocity increases with increasing alkalinity. From pH 9.0 to 12.0 some hydrolysis takes place and some inactive protein is formed and the course of the reaction is represented by the sum of a bi- and monomolecular reaction. The rate of hydrolysis decreases as the solution becomes more alkaline than pH 10.0 while the rate of formation of inactive protein increases so that there is a second point at about pH 13.0 at which the rate of inactivation is a minimum. In general the decrease in activity under all these conditions is proportional to the decrease in the concentration of the trypsin protein. Equations have been derived which agree quantitatively with the various inactivation experiments.     

THE RATE OF DECLINE OF MILK SECRETION WITH THE ADVANCE OF THE PERIOD OF LACTATION

It is shown that the course of decline of milk secretion with the advance of the period of lactation may be expressed by the equation of a monomolecular chemical reaction; that is, the percentage decline of milk secretion with the advance of the stage of lactation is constant. This substantiates the idea that milk secretion is limited by a chemical reaction, and, in general, brings lactation into the class of processes the speed of which is determined by the concentration of a limiting substance.     

THE EFFECTS OF URETHANE AND CHLORAL HYDRATE ON OXYGEN CONSUMPTION AND CELL DIVISION IN THE EGG OF THE SEA URCHIN,ARBACIA PUNCTULATA

The effects of a series of concentrations of the narcotics, ethyl carbamate and chloral hydrate, have been determined on the consumption of oxygen by fertilized and unfertilized eggs of the sea urchin Arbacia punctulata. In the fertilized eggs the effects of the two inhibitors on cell division were also examined. The following observations were made: 1. Assuming that the narcotic acts upon a single catalyst in the unfertilized egg the degree to which the consumption of oxygen is inhibited in this resting cell can be related to the narcotic concentration by an expression derived from the law of mass action. 2. To account for the relation between the concentration of the narcotic and its effect on respiration in the fertilized eggs, it is necessary to conclude that in them the narcotic acts on two parallel respiratory systems. The experimental data can be quantitatively predicted (1) if the reaction of the narcotic on the two systems is governed by the law of mass action and (2) if 40 per cent of the oxygen consumption is mediated by one system, the "activity" system, and the remainder by the other, the "resting" or "basal" system. 3. The mass law constants applying to the resting system in the fertilized egg are similar to those for the single system functioning in the unfertilized egg so that these two respiratory systems are probably identical. 4. The concentrations of the narcotics just sufficient to abolish cell division affect primarily the activity system, the existence of which was inferred from the respiratory experiments. It is concluded that normal cell division requires specifically the normal function of the activity system, that in fact the energy for cell division is made available through that system.     

Theory of sedimentation for ligand-mediated heterogeneous association-dissociation reactions

Theoretical analytical sedimentation patterns have been computed for ligand-mediated heterogeneous association-dissociation reactions between macromolecules. Involvement of either a single kind of ligand or two different ligands acting in a stepwise fashion has been considered. Self-association, mediated in a stepwise fashion by two different ligands, has also been examined. The conclusion reached is that such interactions have the potentiality for exhibiting as many as three or four sedimenting peaks despite rapid rates of reaction. In general, the peaks correspond to different equilibrium compositions and not to individual macromolecular species; that is to say, they constitute a reaction boundary. Their resolution depends upon generation of concentration gradients of ligand(s) along the centrifuge cell by chemical reequilibration during sedimentation of the several macromolecular species. The implications of these findings for fundamental studies on subunit proteins and protein assemblies and for conventional applications of ultracentrifugation are discussed.     

Paradoxical Results in Perturbation-Based Signaling Network Reconstruction

Mathematical models are extensively employed to understand physicochemical processes in biological systems. In the absence of detailed mechanistic knowledge, models are often based on network inference methods, which in turn rely upon perturbations to nodes by biochemical means. We have discovered a potential pitfall of the approach underpinning such methods when applied to signaling networks. We first show experimentally, and then explain mathematically, how even in the simplest signaling systems, perturbation methods may lead to paradoxical conclusions: for any given pair of two components X and Y, and depending upon the specific intervention on Y, either an activation or a repression of X could be inferred. This effect is of a different nature from incomplete network identification due to underdetermined data and is a phenomenon intrinsic to perturbations. Our experiments are performed in an in vitro minimal system, thus isolating the effect and showing that it cannot be explained by feedbacks due to unknown intermediates. Moreover, our in vitro system utilizes proteins from a pathway in mammalian (and other eukaryotic) cells that play a central role in proliferation, gene expression, differentiation, mitosis, cell survival, and apoptosis. This pathway is the perturbation target of contemporary therapies for various types of cancers. The results presented here show that the simplistic view of intracellular signaling networks being made up of activation and repression links is seriously misleading, and call for a fundamental rethinking of signaling network analysis and inference methods.     

Paradoxical Results in Perturbation-Based Signaling Network Reconstruction

Mathematical models are extensively employed to understand physicochemical processes in biological systems. In the absence of detailed mechanistic knowledge, models are often based on network inference methods, which in turn rely upon perturbations to nodes by biochemical means. We have discovered a potential pitfall of the approach underpinning such methods when applied to signaling networks. We first show experimentally, and then explain mathematically, how even in the simplest signaling systems, perturbation methods may lead to paradoxical conclusions: for any given pair of two components X and Y, and depending upon the specific intervention on Y, either an activation or a repression of X could be inferred. This effect is of a different nature from incomplete network identification due to underdetermined data and is a phenomenon intrinsic to perturbations. Our experiments are performed in an in vitro minimal system, thus isolating the effect and showing that it cannot be explained by feedbacks due to unknown intermediates. Moreover, our in vitro system utilizes proteins from a pathway in mammalian (and other eukaryotic) cells that play a central role in proliferation, gene expression, differentiation, mitosis, cell survival, and apoptosis. This pathway is the perturbation target of contemporary therapies for various types of cancers. The results presented here show that the simplistic view of intracellular signaling networks being made up of activation and repression links is seriously misleading, and call for a fundamental rethinking of signaling network analysis and inference methods.     

PHOTOTROPIC CIRCUS MOVEMENTS OF LIMAX AS AFFECTED BY TEMPERATURE

1. The theory of animal phototropism requires for particular instances a knowledge of the action of light as exerted through each of two bilaterally located receptors functioning singly. The measurement of "circus movements" which this involves must be concerned with such aspects of the reaction as are demonstrably dependent upon the effect of light. 2. The negatively phototropic slug Limax maximus exhibits very definite and continuous circus movement under vertical illumination when one eye-tentacle has been removed. The amplitude of the circling movement, measured in degrees deflection per cm. of path as an index of maintained differential tonus, is intimately related to the concurrent velocity of creeping. Analysis of the orienting mechanism is facilitated by the fact that in gasteropods such as Limax the animal creeps by means of the pedal organ, but orients (turns) by a totally distinct set of muscles in the dorsal and lateral regions of the body wall. 3. The expression of the phototropic orienting tendency, with illumination constant, is greatly influenced by the temperature. Above a zone centering at 15°, the amplitude of turning (degrees per cm. of path) is determined by the temperature in accurate agreement with Arrhenius'' equation for chemical reaction velocity, with the critical increment µ = 16,820; and the rate of creeping is progressively less as the temperature rises, µ for its reciprocal being 10,900. Below 15°, the velocity of creeping becomes less the the lower the temperature, µ being again 16,800; while the amplitude of orientation is limited merely by the velocity of creeping, its reciprocal being directly proportional thereto. 4. Measurements of Limax circus movements in terms of turning deflection as function of light intensity must therefore be carried out at a temperature well above 15°. 5. The analysis provides a gross physical model of how an end-result may be influenced by temperature according to the effect of temperature upon each of several interconnected processes when the "temperature vs. effect" curves for these processes dynamically intersect. 6. It is pointed out that a certain type of unpredictability (quantative variability) in animal behavior under "normal" natural conditions probably results from dynamic equilibrium there obtaining between diverse mechanisms competing for effector control (in the present case, the creeping mechanism and that for turning, in the range 14–16°C.). It follows that the unraveling of the elements of conduct necessitates experimentation under diverse abnormal conditions favoring individual mechanism of response.     

Ethics,ecology and economics

This paper describes the general structure of an environmental philosophy. There can be many such philosophies, and those with their roots in economic theory have been extensively studied recently. Specific examples cited in the paper include the work of David Pearce and Robert Goodin. Economics-based philosophies can founder on the issue of externalities and a misplaced attempt to provide a comprehensive approach to valuing nature as a bundle of goods and services. It is argued that it is dangerously easy to slide from considering nature as a standing reserve of processes and objects that have the potential to satisfy human desires to the idea that it is nothing more than that. In general, the consequentialist basis of economics limits its usefulness in contributing to informed environmental decisions. But there is room for a sensitive use of institutional environmental economics as a partial guide for our reflections and choices. Any such development should take on board the existence of a plurality of perspectives on fundamental issues and the pluralism of values that can be found within moral theory itself.     

KINETICS OF THROMBIN INACTIVATION AS INFLUENCED BY PHYSICAL CONDITIONS,TRYPSIN, AND SERUM

1. A new technique for studying the progressive inactivation of thrombin is described. 2. Thrombin inactivation follows the kinetics of a first order reaction. 3. The rate constant of the inactivation reaction increases with temperature and pH (5.0 → 10.0), and also with the presence of crystalline trypsin, or serum. The rate varies for different thrombin preparations, even under the same experimental conditions. 4. The temperature characteristics of the reaction indicate that thrombin is associated with protein. 5. Thrombin preparations are most stable at pH 4 to 5, even when trypsin or serum is added. 6. The progressive inactivation is believed to be due to two mechanisms: (1) a major effect, thought to be the action of a "serum-tryptase," which is usually present in the thrombin preparations, and (2) a minor effect, probably attributable to denaturation of thrombin-protein. 7. Sources of the thrombinolytic factor (serum-tryptase) and its implications in the general theory and practical problems of blood coagulation and antithrombic action are briefly discussed.     

A new method for manipulating transgenes: engineering heat tolerance in a complex, multicellular organism

BACKGROUND: Heat-shock proteins (hsps) are thought to protect cells against stresses, especially due to elevated temperatures. But while genetic manipulation of hsp gene expression can protect microorganisms and cultured metazoan cells against lethal stress, this has so far not been demonstrated in multicellular organisms. Testing whether expression of an hsp transgene contributes to increased stress tolerance is complicated by a general problem of transgene analysis: if the transgene cannot be targeted to a precise site in the genome, newly observed phenotypes may be due to either the action of the transgene or mutations caused by the transgene insertion. RESULTS: To study the relationship between heat tolerance and hsp expression in Drosophila melanogaster, we have developed a novel method for transgene analysis, based upon the site-specific FLP recombinase. The method employs site-specific sister chromatid exchange to create an allelic series of transgene insertions that share the same integration site, but differ in transgene copy number. Phenotypic differences between members of this series can be confidently attributed to the transgenes. Using such an allelic series and a novel thermotolerance assay for Drosophila embryos, we investigated the role of the 70 kD heat-shock protein, Hsp 70, in thermotolerance. At early embryonic stages, Hsp70 accumulation was rate-limiting for thermotolerance, and elevated Hsp70 expression increased survival at extreme temperatures. CONCLUSION: Our results provide an improved method for analyzing transgenes and demonstrate that, in Drosophila, Hsp70 is a critical thermotolerance factor. They show, moreover, that manipulating the expression of a single hsp can be sufficient to improve the stress tolerance of a complex multicellular organism.     

RNA Stability in Human Liver: Comparison of Different Processing Times, Temperatures and Methods

The accuracy of information garnered by real-time quantitative polymerase chain reaction (RT-qPCR), an important technology for elucidating molecular mechanisms of disease, is dependent on tissue quality. Thus, this study aimed to determine the effects of intra-operative manipulation, extended processing times, different temperatures or storage in RNAlater on RNA quality in liver samples for tissue banking. Liver samples, flash-frozen or in RNAlater, were collected over a time course (during surgery before blood arrest up to 1 day after surgery) with samples kept either at room temperature (RT) or on ice. This study showed that at the longest time-point at RT, the RNA quality decreased significantly by 20%. However, relative gene expressions of FOS, GUSB, MYC, HIF1?? and GFER were in general not significantly different when the time-points were compared. In conclusion, samples should be kept on ice during processing, and either RNAlater or snap-freezing should be utilised for storage. Further, intra-operative manipulation and extended postoperative processing time generally does not change relative gene expression levels for the 5 genes studied, making such sampling suitable for RT-qPCR analysis. Thus, if relative gene expression of a gene of interest is stable, these guidelines will lead to increased accrual of samples to the tissue bank.     

STUDIES ON TOXICITY

With yeast subjected to the action of phenol or of phenol and alcohol the curves of survivors as measured by resistance to staining with methylene blue when plotted against time do not in general prove to be logarithmic. It is believed that such resemblances as have been found between such curves and monomolecular reaction or logarithmic curves are superficial and fortuitous. Any method therefore of evaluating disinfecting power based upon such a concept must prove misleading. Variations in resistance of individual cells and the distribution of such variations must be regarded as of fundamental importance in accounting for rates of death of microorganisms.     

THE ULTRAVIOLET ABSORPTION SPECTRUM OF PEPSIN

The ultraviolet absorption spectrum of Northrop''s pure crystalline pepsin has been determined. The curve of calculated molecular extinction coefficients is given. There is noted a general resemblance of the absorption curve for pepsin to that for urease and tyrosine; the absorption band is maximum at 2750–2800 Å.µ., minimum near 2500. A slight hump on either side of the peak of the extinction curve may be significant.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : VIII. THE FORM OF THE FLICKER CONTOUR

Flicker response curves (man) obtained with images formed entirely within the fovea are like those secured with lower animals having only one general class of retinal receptors. They are normal probability integrals (F vs. log I_m), and the properties of their parameters agree with those for visually simplex animals and for the "cone" portions of contours exhibiting visual duplexity. By several different procedures, involving experimental modifications of the "cone" curve, the "rod" part of the typical human duplex curve can be obtained free from overlapping by the extrapolated "cone" curve. It then has the probability integral form which the lower segment does not directly exhibit when combined with "cone" effects. These results are discussed with reference to the statistical nature of the fundamental form of the flicker contour and to the interpretation of duplex curves produced by the neural integration of two independently modifiable groups of sensory effects.