Values Of Da Research Articles

Structure and Dynamics of ASC2, a Pyrin Domain-only Protein That Regulates Inflammatory Signaling

Structure and Dynamics of ASC2, a Pyrin Domain-only Protein That Regulates Inflammatory Signaling

Influence of geometry of the discharge interval on distribution of ion and electron streams at surface of the Penning source cathode

In the discharge of oscillating electrons, the mechanism of the processes, which controls the distribution of the ion and electron streams over the cathode surface, is investigated experimentally. The influence of the length of the discharge interval on value and distribution of the ion and electron streams is analyzed. The distribution both of ion and electron streams at the cathode surface is determined at different conditions of the discharge. It is shown that for given values of the anode diameter da=31mm and the gas pressure P=5×10−5Torr, the intensive stream of positive ions falls entirely on the cathode central area in the whole interval of the anode length variation (ℓa=1–11cm). At the cathode, the ion current reaches the maximal value at a certain (optimal) value of the anode length that, in turn, depends on the anode voltage Ua. The intensive stream of longitudinal electrons forms in the short anodes only (ℓa=2.5–3.5cm) and depending on the choice of the discharge regime, may fall both on central and middle parts of the cathode.

Atypical polysaccharide physical gels: structure/property relationships

AbstractChitin and chitosan are polysaccharides produced by the biomass. They have the same general chemical structure and constitute the series of linear copolymers of linked β, (1‐>4) glucosamine and N‐actylglucosamine. We studied the possibility of forming physical gels with all the terms of this series, whatever the proportion of the two kinds of residues included in the polymer chains. We show that physical gelation is still possible through a percolating process when certain important conditions are met. Initially the concentration in polymer must be above C*; a critical value of the balance between hydrophobic and hydrophilic interactions must be achieved and gelation must occur simultaneously everywhere in the medium. These conditions were observed in several situations allowing the formation of different kinds of gels at all values of DA. In view of the rare bio‐active properties of chitin and chitosan, these gels were tested for living tissue regeneration and constitute very interesting examples in illustration of our concept of decoys for biological media.

MIXED SPIN-1 AND SPIN-$\frac{3}{2}$ BLUME–CAPEL ISING FERRIMAGNETIC SYSTEM ON THE BETHE LATTICE

The mixed spin-1 and spin-[Formula: see text] Blume–Capel Ising ferrimagnetic system for the central spin with spin-1 is studied on the Bethe lattice using the exact recursion equations. The exact expressions for the magnetization, the quadrupolar moment, the Curie temperature and the free energy are found and the phase diagrams are constructed on the Bethe lattice with the coordination numbers q = 3, 4 and 6 for the various values of the single-ion anisotropy constants dA = DA/J for spin-1 and dB = DB/J for spin-[Formula: see text]. The existence of a tricritical point is investigated for different values of q and the single-ion anisotropy constants. The phase diagrams in the (kTc/J, dA) plane for the central spin are obtained for two different cases; (1) dA = dB and (2) dA is varied for selected values of dB. The results are compared with those of other approximate methods.

Aerodynamic diameter of conidia of Erynia neoaphidis and other entomophthoralean fungi

The aerodynamic diameter, da, of conidia produced in vivo and in vitro by the entomopathogenic fungus Erynia neoaphidis were estimated using an impaction method. The estimated values of da for conidia produced in vivo were smaller than those produced in vitro: in vivo the values of da for primary and secondary conidia were between 16 and 18 μm (equivalent fall speed, Vs, 0.8–1.0 cm s−1); for in vitro produced conidia da values were between 28 and 31 μm (Vs, 2.4–3 cm s−1). For conidia produced by field collected cadavers the value of da, was estimated to be similar to that for conidia produced in vivo in the laboratory. The aerodynamic diameter of primary conidia of Conidiobolus obscurus (strain X39) and Zoophthora radicans (strain NW250) produced in vivo were also measured using the same method. The values of da for these two species were 45 and 17 μm (Vs, 6.2 and 0.9 cm s−1) respectively. Implications for dispersal of E. neoaphidis are discussed. The physical diameters of the test spores were measured microscopically and compared with the aerodynamic diameters.

Multiple steady states in reactive distillation: kinetic effects

A model is developed to describe kinetic effects in reactive distillation. A Damköhler number ( Da), the ratio of a characteristic residence time to a characteristic reaction time, is the key parameter. A comprehensive picture of solutions is found with arc length continuation methods that trace solution branches as functions of Da, reboil ratio, or reflux ratio. For methyl tert-butyl ether (MTBE) synthesis in the Jacobs–Krishna column configuration, the model reproduces known solution multiplicities in the limit of reaction equilibrium. In addition to these previously known equilibrium solutions, we report new results concerning the effect of kinetics on solution multiplicity. In particular, isolated solutions branches are found at several values of Da; the isola shrinks and disappears below a critical value of Da. Results for tert-amyl methyl ether (TAME) synthesis in a model for the test column of Mohl et al. [Chem. Eng. Sci. 54 (1999) 1029] are in sharp contrast; multiplicities present in the kinetic regime disappear above a critical value of Da for all values of reflux ratio.

Numerical prediction of air core diameter, coefficient of discharge and spray cone angle of a swirl spray pressure nozzle

Abstract Theoretical predictions of air core diameter, coefficient of discharge and spray cone angle of a swirl spray pressure nozzle have been made from numerical computations of flow within the nozzle. The diameter of central air core that stabilizes inside the nozzle has been predicted from a hydrodynamic situation that yields the minimum resistance to the liquid flow in the nozzle at given operating conditions. The coefficient of discharge and spray cone angle have been evaluated from the distributions of the different velocity components of liquid flow at the nozzle orifice. It has been observed that the coefficient of discharge Cd decreases, while the air core diameter da and spray cone angle ψ increase with the increase in nozzle flow in its lower range. However, all these parameters Cd, da and ψ finally become independent of nozzle flow. Predicted values of da, Cd and ψ for different geometrical dimensions of the nozzle have been compared with the empirical data available in the literature.

Natural convection in a cylindrical porous cavity with internal heat source: a numerical study with Brinkman-extended Darcy model

Natural convection in a 2-D vertical cylinder containing an isotropic porous media with internal heat generation was studied numerically for assessing the effect of Darcy’s law with and without the Brinkman extension on the streamlines, isotherms and Nusselt numbers. Two cases were analyzed: (1) insulated walls at the top and bottom of the cylinder and cooled external walls; (2) isothermally cooled walls at all external surfaces. The effect of the Brinkman extension was significant for high values of Da (10 −4–10 −1). In addition, the Nusselt number increases asymptotically as Da decreases. Also, four correlations for the average Nusselt number were derived.

Ignition and extinction fronts in counterflowing premixed reactive gases

We describe two-dimensional steady propagating flame fronts in the stagnation mixing layer between two opposed streams of the same reactive mixture, the propagation taking place in the direction perpendicular to the plane of strain. The front, which is curved by the nonuniform flow field, separates a chemically frozen region from a region with a twin-flame configuration. The front velocity is calculated in terms of the Lewis number, Le F , and the Damköhler number, Da. Da, equal to the inverse of the Karlovitz number, is defined as the ratio of the strain time to the transit time through the planar unstrained flame. For the cases corresponding to large Da, difficult to tackle numerically, analytical expressions are given, characterizing the flame shape, and the variation of the burning rate along the flame front from the nose up to the planar trailing branches. For moderately large and low values of Da, the study is carried out numerically, yielding, in particular, the propagation velocity in terms of Da, for different values of Le F . Different combustion regimes are thus described including flames propagating toward the unburnt mixture, or ignition fronts, standing flames and retreating flames, or extinction fronts. We also describe stationary cylindrical flames of finite-extent, or 2D burning spots. In particular, a critical Lewis number is found, below which negative propagation speeds do not exist while the 2D burning spots mentioned may be encountered. Typically, these exist only for sufficiently small Le F if the Da is within a range [ Da min , Da max ], depending on Le F . For Da < Da min , the 2D spots are quenched, whereas as Da is increased, they grow in size, tending to give birth to propagating (ignition) fronts; Da max is indeed found to be the smallest Da allowing for ignition fronts. We notice that the range of existence of the 2D spots, for a given Le F , can overlap with that of retreating (extinction) fronts, and possibly with that of 3D spots, or flame balls, in this flow. However, the 3D case is not addressed in this work.

Protein mobility in the cytoplasm of Escherichia coli.

The rate of protein diffusion in bacterial cytoplasm may constrain a variety of cellular functions and limit the rates of many biochemical reactions in vivo. In this paper, we report noninvasive measurements of the apparent diffusion coefficient of green fluorescent protein (GFP) in the cytoplasm of Escherichia coli. These measurements were made in two ways: by photobleaching of GFP fluorescence and by photoactivation of a red-emitting fluorescent state of GFP (M. B. Elowitz, M. G. Surette, P. E. Wolf, J. Stock, and S. Leibler, Curr. Biol. 7:809-812, 1997). The apparent diffusion coefficient, Da, of GFP in E. coli DH5alpha was found to be 7.7 +/- 2.5 microm2/s. A 72-kDa fusion protein composed of GFP and a cytoplasmically localized maltose binding protein domain moves more slowly, with Da of 2.5 +/- 0.6 microm2/s. In addition, GFP mobility can depend strongly on at least two factors: first, Da is reduced to 3.6 +/- 0.7 microm2/s at high levels of GFP expression; second, the addition to GFP of a small tag consisting of six histidine residues reduces Da to 4.0 +/- 2.0 microm2/s. Thus, a single effective cytoplasmic viscosity cannot explain all values of Da reported here. These measurements have implications for the understanding of intracellular biochemical networks.

The Ignition of Solids: An Asymptotic Analysis

The ignition of a solid exposed to a step in surface temperature, including the effect of the curvature, is analyzed by means of large activation energy asymptotics in the whole range of values of the Damköhler number, Da , which lead to a thermal runaway. For very large values of Da the chemical reaction takes place in a surface boundary layer. The evolution of the temperature in this layer is described by a universal problem. Its solution contains a mathematical singularity, which identifies the ignition event occuring at an ignition time much smaller than the conduction time through the solid. When Da is large but of the same order that the square of the nondimensional activation energy, the ignition time becomes of the order of the conduction time. The structure of the ignition problem is identical to that in the previous case, but its solution depends on the body size and shape. In both cases an initial quasisteady stage is followed by a transition stage in which the nonsteady effects must be retained. Finally, for Da of order unity the chemical reaction extends over the whole solid, and the ignition process can be described in terms of a first inert heating stage and a second reacting stage in which the temperature evolves according a nonsteady Frank-Kamenetskii equation.

Effect of central 5-hydroxytryptamine depletion on performance in the "time-left" procedure: further evidence for a role of the 5-hydroxytryptaminergic pathways in behavioural "switching".

This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on performance in a free-operant timing schedule: the "time-left" procedure. Rats received either injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained in a discrete trials schedule in which reinforcers were provided for responding on either of two levers, A and B. At a random time point, t s after the start of each trial, a response on A resulted in the delivery of one food pellet after dA s, whereas a response on B resulted in the delivery of two pellets after 60-t s. The value of dA was varied between 1 and 8 s in different phases of the experiment. Both groups showed decreasing response rates on lever A and increasing response rates on lever B as a function of time within the trial. An index of timing (T75: the time within the trial at which relative response rate on B attained a value of 75%) was systematically related to the value of dA, but did not differ significantly between lesioned and control rats. However, the lesioned group showed significantly higher rates of switching between response alternatives than the sham-lesioned group at all values of dA. The levels of 5HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not significantly altered. The results provide further evidence that the ascending 5HTergic pathways may contribute to the inhibitory regulation of switching between behavioural states.

Linking modelling and visualisation for natural resources management

Natural resources management typically requires prediction of environmental changes over large areas or long time periods. In the case of forest management, for example, decisions can affect timber production, water catchment properties, recreational values, aesthetic values, energy usage, or employment opportunities. Complex decisions can be assisted by effective presentation of the outcome of systems modelling. In this paper we describe the development of advanced visualisation techniques in combination with a geographic information system and resource modelling. Application potential is illustrated through examples in forest management and visual impact assessment. The emphasis is on provision of visual feedback on the outcome of decision options. The main interactive window allows three-dimensional movement of, or over, the management area based initially on imagery draped on a digital terrain model. Also on screen are menus or sliders which may control time, position along a line, or the values of da...

OSMOTIC DEHYDRATION OF PEAS: I. INFLUENCE OF PROCESS VARIABLES ON MASS TRANSFER

Osmotic dehydration of uniformly sized peas at 30C was studied using different solutions of sucrose, sodium citrate and sucrose+citrate mixture. The influence of various factors such as solution concentration and composition and the effect of agitation on the mass transfer mechanism was investigated. It was shown that the rate of water loss in the sample was increased by increasing concentration of osmosis solution and agitation. The most effective osmotic dehydration was obtained in sucrose+citrate mixed solutions of 60% total solids level for which a dehydration model was proposed. The apparent diffusion coefficient of water Da was determined using the dehydration model. The values of Da were found to be in the range 9.10 ± 10−11-7.63 ± 10−10 m2/s.

Mixed convection in a vertical parallel-plate channel partially filled with porous media of high permeability

The purpose of the present study is to analyze numerically the developing mixed convection in a vertical parallel-plate channel partially filled with porous medium. The SIMPLEC algorithm combining the techniques of ADI and SOR is used in this study. The diffusion and convection are handled by a hybrid scheme. The non-Darcy model, which includes inertia effect, boundary friction effect and convection, is used in the momentum equations for the porous medium layer. The velocity and temperature distributions, local Nusselt number ( Nu x ), local friction coefficient ( C f), pressure drop and entrance length in a vertical parallel-plate channel partially filled with porous medium are obtained under various parameters, such as different thickness of porous medium ( Rs), Darcy number ( Da), Grashof number ( Gr). The numerical results of this investigation show that (a) the local Nusselt number increases as Rs decreases and Da and Gr increase; (b) the local friction coefficient increases as Da and Gr increase; and (c) the pressure drop in the parallel-plate channel increases as Rs increases and Da decreases. There is a minimum non-zero local friction coefficient where the thickness of the porous medium is about 0.2. Hydrodynamic entrance length is shorter as the value of Rs is increased, and is longer as the values of Da and Gr are increased. Thermal entrance becomes longer as the values of Rs and Da increase and shorter as the values of Gr increase.

Simultaneous, selective detection of catecholaminergic and indolaminergic signals using cyclic voltammetry with treated micro-sensor

Selective and simultaneous voltammetric analysis of catechols and indoles in vivo and in vitro has until now been feasible only by means of ‘slow’ scanning methods (scan speed in tens of seconds) such as differential pulse (DPV) and differential normal pulse voltammetry in conjunction with electrically and/or chemically treated carbon-fiber micro-electrodes (mCFE). Faster electrochemical techniques, such as chronoamperometry and cyclic voltammetry (CV), allow more rapid (seconds or fractions of a second) and frequent measurements of these chemicals. However, these methods show poor sensitivity and selectivity in the presence of different electroactive compounds with similar oxidation potentials. In order to analyze whether the lack of sensitivity and selectivity of the fast voltammetric methods results from the rapidity of the measurement or from the use of untreated sensors, the methods of CV (scan speed: 1000 mV/s) and DPV (scan speed: 10 mV/s) have been applied with either untreated or electrically treated mCFE to analyze the in vitro oxidation potential and current values of DA and 5-HT. When associated with untreated mCFE, neither method was able to separate and selectively detect the two compounds dissolved together in an inert vehicle; the voltammogram recorded resulted in a single broad oxidation signal. In contrast, when these techniques were performed with electrically treated mCFE, oxidation signals for DA (peak A) and 5-HT (peak B) were monitored simultaneously at approximately + 65 mV and + 240 mV, with DPV respectively, and at + 120 mV and + 300 mV with CV, respectively. Additionally, CV with treated mCFE on anesthetized rats, simultaneously monitored two striatal signals at approximately + 100 mV and + 300 mV. The oxidation values ( E m) and current levels (nA) of these peaks remained stable during control recordings. The current levels were selectively increased by peripheral injection of fluphenazine (DA antagonist) or of 5-hydroxytryptophan (precursor of serotonin). The chemical nature of these two peaks may therefore be considered catecholaminergic and indolaminergic, respectively. Hence, this report provides the first evidence for the feasibility of concomitant in vitro analysis of DA and 5-HT using a rapid scanning method such as CV. In addition, the values of current level (nA) obtained with CV-mCFE for DA and 5-HT are comparable to those monitored with DPV-mCFE, supporting the view that treatment of the sensor is a key point for increasing the selectivity and the sensitivity of these voltammetric techniques. The feasibility of using CV with electrically treated mCFE for fast in vivo analysis of catechol and indole activities is also demonstrated.

Mass Diffusion Transport Studies of Lithium Sulfate in Aqueous Solutions Using Raman Spectroscopy

The diffusivity coefficients of lithium sulfate solutions in water and water and silica gels over the concentration range 0.2 to 2.5 molal have been measured for the first time with micro-Raman spectroscopy for a horizontal-tube capillary, conventional 90° Raman scattering for a narrow-bore vertical-tube system, and FT-Raman spectroscopy for the gels. Data were obtained for axial concentration profiles as function of the distance and for time elapse at fixed positions on the tube axis with the use of integrated intensity measurements of the v1 (SO4) symmetric stretching band at 980 cm−1. The use of computer model calculations to fit the experimental data yielded values of DA = 0.4 × 10−5 cm2 s−1 for the vertical system and 0.3 × 10−5 cm−2 s−1 for the gel system. Discrepancies observed for the horizontal system have been ascribed to the presence of convective flow. A convective flow rate of 5.10−2 cm h−1 was calculated in this case with the use of computer simulation and used in the fitting of the experimental data through a general form of the second Fick's law. Under these conditions, a DA value of 0.2 × 10−5 cm2 s−1 was obtained.

Fractal dimension of error sequence dynamics in quantitative modeling of syntheses of short oligonucleotide and single-stranded DNA sequences

Oligonucleotides are becoming more and more important in molecular biomedicine; for example, they are used as defined primers in polymerase chain reaction and as antisense oligonucleotides in gene therapy. In this paper, we model the dynamics of polymer-supported oligonucleotide synthesis to an inverse power law of driven multi-cycle synthesis on fixed starting sites. The mathematical model is employed by presenting the accompanying view of error sequences dynamics. This model is a practical one, and is applicable beyond oligonucleotide synthesis to dynamics of biological diversity. Computer simulations show that the polymer support synthesis of oligonucleotides and single-stranded DNA sequences in iterated cyclic format can be assumed as scale-invariant. This synthesis is quantitatively described by nonlinear equations. From these the fractal dimension Da (N,d) is derived as the growth term (N = number of target nucleotides, d = coupling probability function). Da(N,d) is directly measurable from oligonucleotide yields via high-performance liquid chromatography or capillary electrophoresis, and quantitative gel electrophoresis. Different oligonucleotide syntheses, including those with large-scale products can be directly compared with regard to error sequences dynamics. In addition, for short sequences the fractal dimension Da (N,d) is characteristic for the efficiency with which a polymer support of a given load allows oligonucleotide chain growth. We analyze the results of separations of crude oligonucleotide product from the synthesis of a 30 mer. Preliminary analysis of a 238 mer single-stranded DNA sequence is consistent with a simulated estimate of crude synthesis product, although the target sequence itself is not detectable. We characterize the oligonucleotide support syntheses by simulated and experimentally determined values of the fractal dimension Da (N,d0) within limitations (d0 = constant (average) coupling probability).

Restricted diffusion of an 19F-labelled organic acid in human erythrocytes analyzed by 19F pulsed field gradient NMR.

The diffusion coefficient of an 19F-labelled organic acid (3-trifluoromethylhippurate: TFMH) was measured in intact human red blood cells (RBCs) and sealed right-side-out ghosts at 22.5 +/- 0.05 degrees C. Diffusion coefficients were measured using stimulated echo and spin-echo pulsed field gradient sequences. The apparent diffusion coefficient (Da) of TFMH in the intracellular space was much smaller than in the extracellular medium. This was due to restricted diffusion of intracellular TFMH since i) the intracellular Da decreased when the diffusion time was increased, and ii) the smaller Da component disappeared when the membrane was permeabilized with saponin. From the intracellular Da values obtained over a range of diffusion times, from 5 ms to 1 s, the apparent radius of the diffusion barrier was estimated to be 3 +/- 1.1 micron assuming spherical geometry. Despite the high protein concentration in the intracellular space of the intact RBC, the intracellular values of Da were similar to the values obtained in the ghosts at the same diffusion times. We therefore conclude that the small diffusion coefficient of intracellular TFMH is mainly explained by the restricted diffusion due to the cell boundary.

Apparent diffusivities of reducing sugars in potato strips blanched in water

The mechanism of reducing sugar losses was investigated in potatoes cut into 9.5 × 9.5 mm and 13 × 13 mm strips and blanched for 300–2400s at different temperatures between 70°C and 100°C. Experiments were carried out using large amounts of well‐agitated water. Assuming no chemical reaction and using appropriate solutions of the unsteady state diffusion equation for square parallelpiped geometry, the apparent diffusivities, Da, of reducing sugars in the potato matrix were determined at different temperatures. the incorporation of the dimensions of the strips in the solution of the diffusion equation was sufficient to explain the effect of size on losses. Values of Da were found to be in the range 1.2 × 10‐11 1.7 × 10‐11 m2s‐1 and could be correlated with temperature according to the Arrhenius law.