Climate response to physiological forcing of carbon dioxide simulated by the coupled Community Atmosphere Model (CAM3.1) and Community Land Model (CLM3.0)

Increasing concentrations of atmospheric CO2 decrease stomatal conductance of plants and thus suppress canopy transpiration. The climate response to this CO2-physiological forcing is investigated using the Community Atmosphere Model version 3.1 coupled to Community Land Model version 3.0. In response to the physiological effect of doubling CO2, simulations show a decrease in canopy transpiration of 8%, a mean warming of 0.1K over the land surface, and negligible changes in the hydrological cycle. These climate responses are much smaller than what were found in previous modeling studies. This is largely a result of unrealistic partitioning of evapotranspiration in our model control simulation with a greatly underestimated contribution from canopy transpiration and overestimated contributions from canopy and soil evaporation. This study highlights the importance of a realistic simulation of the hydrological cycle, especially the individual components of evapotranspiration, in reducing the uncertainty in our estimation of climatic response to CO2-physiological forcing. Citation: Cao, L., G. Bala, K. Caldeira, R. Nemani, and G.Ban-Weiss (2009), Climate response to physiological forcing of carbon dioxide simulated by the coupled Community Atmosphere Model (CAM3.1) and Community Land Model (CLM3.0).

Fluctuation phenomena in electrochemistry part I. The formalism

A unified approach to the problem of electrochemical fluctuations is presented. On the basis of the Langevin procedure, primary noise sources are introduced in the basic phenomenological equations and a discussion of the secondary noise sources arising in the expressions for the power spectra of currents is given.

Fluctuation phenomena in electrochemistry part II. Modelling the noise sources

A discussion of the modelling of the primary and secondary noise sources introduced in the formalism of fluctuation phenomena in a previous report is presented. It is illustrated that the generalisation of the modelling of noise sources in mass transport as given by Tyagai is limited in its applicability. A general procedure for the same is discussed in detail.

Generation of H2O2 in biomembranes

Knowledge of the generation of H202 in cellular oxidations has existed for many years. It has been assumed that H202 is tOxiC tO cells and the presence of catalase is indicative of a detoxication mechanism. Other radicals of oxygen were recently recognized to be more potent destructive agents of biological material than H202. Also catalase and other peroxidases utilize H202 in some cellular oxidation processes leading to several important metabolites. Thus, the generation of H202 in cellular processes seems to be purposeful and H202 can not be dismissed as a mere undesirable byproduct. Biological formation of H202 is not limited to the previously known flavoproteins and some copper enzymes, but other redox systems, particularly heme and non-heme iron proteins, are now found to undergo auto-oxidation yielding H202. The capacity for generation of H202 is now found to be widespread in a variety of organisms and in the organdies of the cells. The reduction of oxygen to H20 by mitochondrial cytochrome oxidase being the predominant oxygen-utilizing reaction had over-shadowed the importance of the quantitatively minor pathways. Under aerobic conditions generation of H202 by a Variety of biomembranes has now been found to be a physiological event interlinked with phenomena such as phagocytosis, transport processes and thermogenesis in some as yet unidentified way. The underlying mechanisms of these processes seem to involve generation and utilization of H202 in mitochondria, microsomes, peroxisomes or plasma membranes. This review gives an account of the potential of biomembranes to generate H202 and its implication in the cellular processes.

Mesospheric influences on linkages between solar activity and lower atmospheric phenomena

Analyses of rocket data at mid- and high-latitude locations over the American Continent show a solar activity-dependent mesospheric heating effect in the 60 to 90 km altitude region. A study of the altitude dependence of the effect shows that the heating and associated processes propagating downwards through the mesosphere do not cause discernible effects, below the 50 to 60 km layer. At Thumba, a significant short-term heating effect attributable to varying solar ultraviolet fluxes causing variable heating of atmospheric ozone is observed. This effect does not seem to propagate downwards into the upper stratosphere.

Characterization of protoporphyrin as the physiological regulator of delta-aminolevulinate dehydratase in Neurospora crassa

In Neurospora crassa, the activity of δ-aminolevulinate dehydratase, the second and rate-limiting enzyme of the heme-biosynthetic pathway, is low in normal cells compared to the activity detected in plants, animals and bacteria. The activity is almost undetectable when Neurospora crassa is grown under iron-deficient conditions. The enzyme activity increases strikingly on addition of iron to iron-deficient cultures. This increase can be blocked by the addition of protoporphyrin, the penultimate product of the heme-biosynthetic pathway, to the cultures. The question whether iron directly acts at the genetic level or acts merely by removing protoporphyrin, converting the latter into heme prosthetic groups of hemoproteins, has been investigated by studying the effect of inhibition of heme synthesis on the induction of δ-aminolevulinate dehydratase. It has been found that treatments with levulinic acid or cyanide which inhibit the formation of the porphyrin moiety, induce δ-aminolevulinate dehydratase, whereas treatments which inhibit at a step after protoporphyrin formation (iron-deficiency and cobalt treatment) repress the enzyme. The endogenous levels of protoporphyrin are strictly controlled: a decrease below the optimum level causing induction and an increase above the optimum level leading to repression of δ-aminolevulinate dehydratase. Levulinic acid and cyanide can induce the enzyme in iron-deficient cultures in the absence of added iron, indicating that the metal iron acts only by converting protoporphyrin to heme fixed in hemoproteins in Neurospora crassa. Therefore it is suggested that protoporphyrin is the physiological regulator of δ-aminolevulinate dehydratase in Neurospora crassa.

Sequence generator for periodic sampling of transient phenomena

A simple instrument that can provide a sequence of timed pulses for first initiating a transient process and then enabling sampling and recording periodically during the course of the transient event is described. The time delay between the first of these sampling pulses and the start of the transient event is adjustable. This sequence generator has additional features that make it ideal for use in acquiring the waveforms when a storage oscilloscope is used as the recording device. For avoiding the clutter caused by many waveforms being recorded at the same place on an oscilloscope screen such features as displacements of waveforms in the X and Y directions and trace blanking at places where the waveform is not required, have been incorporated. This sequence generator has been employed to acquire a sequence of Raman scattered radiation signals from an adiabatically expanding saturated vapour probed by a flashlamp-pumped dye laser.

Critical point phenomena in the electrical resistivity of binary liquid systems: Cs2 + CH3CN and CS2 + CH3NO2

Electrical resistance measurements are reported on the binary liquid mixtures CS2 + CH3CN and CS2 + CH3NO2 with special reference to the critical region. Impurity conduction seems to be the dominant mechanism for charge transport. For the liquid mixture filled at the critical composition, the resistance of the system aboveT c follows the relationR=R c−A(T−T c) b withb=0·6±0·1. BelowT c the conductivities of the two phases obey a relation σ2−σ1=B(T c−T)β with β=0·34±0·02, the exponent of the transport coefficient being the same as the exponent of the order parameter, an equilibrium property.

Studies on transport phenomena during solidification of an aluminum alloy in the presence of linear electromagnetic stirring

Numerical and experimental studies on transport phenomena during solidification of an aluminum alloy in the presence of linear electromagnetic stirring are performed. The alloy is electromagnetically stirred to produce semisolid slurry in a cylindrical graphite mould placed in the annulus of a linear electromagnetic stirrer. The mould is cooled at the bottom, such that solidification progresses from the bottom to the top of the cylindrical mould. A numerical model is developed for simulating the transport phenomena associated with the solidification process using a set of single-phase governing equations of mass. momentum, energy. and species conservation. The viscosity variation of the slurry, used in the model, is determined experimentally using a rotary viscometer. The set of governing equations is solved using a pressure-based finite volume technique, along with an enthalpy based phase change algorithm. The numerical study involves prediction of temperature, velocity, species and solid fraction distribution in the mould. Corresponding solidification experiments are performed, with time-temperature history recorded at key locations. The microstructures at various temperature measurement locations in the solidified billet are analyzed. The numerical predictions of temperature variations are in good agreement with experiments, and the predicted flow field evolution correlates well with the microstructures observed at various locations.

Modeling of Convection and Macrosegregation through Appropriate Consideration of Multiphase/Multiscale Phenomena during Alloy Solidification

Solidification processes are complex in nature, involving multiple phases and several length scales. The properties of solidified products are dictated by the microstructure, the mactostructure, and various defects present in the casting. These, in turn, are governed by the multiphase transport phenomena Occurring at different length scales. In order to control and improve the quality of cast products, it is important to have a thorough understanding of various physical and physicochemical phenomena Occurring at various length scales. preferably through predictive models and controlled experiments. In this context, the modeling of transport phenomena during alloy solidification has evolved over the last few decades due to the complex multiscale nature of the problem. Despite this, a model accounting for all the important length scales directly is computationally prohibitive. Thus, in the past, single-phase continuum models have often been employed with respect to a single length scale to model solidification processing. However, continuous development in understanding the physics of solidification at various length scales oil one hand and the phenomenal growth of computational power oil the other have allowed researchers to use increasingly complex multiphase/multiscale models in recent. times. These models have allowed greater understanding of the coupled micro/macro nature of the process and have made it possible to predict solute segregation and microstructure evolution at different length scales. In this paper, a brief overview of the current status of modeling of convection and macrosegregation in alloy solidification processing is presented.

Anode Phenomena in Triggered Vacuum Gaps

Arc voltage - current characteristics and threshold current densities occuring during the formation of anode spots in triggered vacuum gaps are reported. Single pulses of 1.65 ms arcing time, which correspond to switching surge currents, are used in the study with copper and aluminum anodes. The threshold values are 1.75 times the values reported earlier using the longer, 8 mis, arcing time. They are found to depend upon the duration of arcing time as well as upon electrode material, surface conditions, electrode size and contact separation. Lateral inhomogenity in the electrode geometry appears to reduce the threshold value by promoting early formation of anode spots.

Liquid-liquid critical phenomena. The coexistence curve of n-heptane-acetic anhydride

The coexistence curve of the binary liquid mixture n-heptane-acetic anhydride has been determined by the observation of the transition temperatures of 76 samples over the range of compositions. The functional form of the difference in order parameter, in terms of either the mole fraction or the volume fraction, is consistent with theoretical predictions invoking the concept of universality at critical points. The average value of the order parameter, the diameter of the coexistence curve, shows an anomaly which can be described by either an exponent 1 - a, as predicted by various theories (where a is the critical exponent of the specific heat), or by an exponent 20 (where P is the coexistence curve exponent), as expected when the order parameter used is not the one the diameter of which diverges asymptotically as 1 - a.

Modeling of Freezing Phenomena Induced by Chemical Reactions

Spatial variations in the concentration of a reactive solute in solution are often encountered in a catalyst particle, and this leads to variation in the freezing point of the solution. Depending on the operating temperature, this can result in freezing of the solvent oil a portion of catalyst, rendering that part of the active area ineffective Freezing call occur by formation of a sharp front or it mush that separates the solid and fluid phases. In this paper, we model the extent of reduction in the active area due to freezing. Assuming that the freezing point decreases linearly with solute concentration, conditions for freezing to occur have been derived. At steady state, the ineffective fraction of catalyst pellet is found to be the same irrespective of the mode of freezing. Progress of freezing is determined by both the heat of reaction and the latent heat of fusion Unlike in freezing of alloys where the latter plays a dominant role, the exothermicity of the reaction has a significant effect on freezing in the presence of chemical reactions. A dimensionless group analogous to the Stefan number could be defined to capture the combined effect of both of these.