Increase In Collision Frequency Research Articles

Euler/Lagrange computations of pneumatic conveying in a horizontal channel with different wall roughness

The present study is related to the particle behaviour and the pressure drop in a particle-laden six meter long horizontal channel with rectangular cross-section from both experimental and numerical perspectives. Experiments and calculations are carried out for different spherical glass beads with diameters between 60 and 625 μm and mass loadings up to 1.0 (kg particles/kg gas). Additionally, stainless steel walls with different wall roughness are considered. In all experiments the air volume flow rate is constant in order to maintain a fixed gas average velocity of 20 m/s. As a result, the pressure drop in the channel is strongly influenced by wall roughness. Higher wall roughness implies higher pressure drop because of the increase in wall collision frequency, whereby momentum is extracted from the fluid due to two-way coupling. The numerical computations were performed by the Euler/Lagrange approach accounting for two-way and four-way coupling. For the calculation of the particle motion all relevant forces (i.e. drag, transverse lift and gravity), inter-particle collisions and wall collisions with wall roughness were considered. The agreement of the computations with the experiments was found to be very good for the gas and particle velocities as well as the pressure drop.

Influence of damping on proton energy loss in plasmas of all degeneracies

The purpose of the present paper is to describe the effects of electron-electron collisions on the stopping power of plasmas of any degeneracy. Plasma targets are considered fully ionized so electronic stopping is only due to the free electrons. We focus our analysis on plasmas which electronic density is around solid values n(e) approximately = 10(23) cm(-3) and which temperature is around T approximately = 10 eV ; these plasmas are in the limit of weakly coupled plasmas. This type of plasma has not been studied extensively though it is very important for inertial confinement fusion. The electronic stopping is obtained from an exact quantum mechanical evaluation, which takes into account the degeneracy of the target plasma, and later it is compared with common classical and degenerate approximations. Differences are around 30% in some cases which can produce bigger mistakes in further energy deposition and projectile range studies. Then we consider electron-electron collisions in the exact quantum mechanical electronic stopping calculation. Now the maximum stopping occurs at velocities smaller than for the calculations without considering collisions for all kinds of plasmas analyzed. The energy loss enhances for velocities smaller than the velocity at maximum while decreases for higher velocities. Latter effects are magnified with increasing collision frequency. Differences with the same results for the case of not taking into account collisions are around 20% in the analyzed cases.

Decomposition Characteristic of Carbon Tetrafluoride Using 2.45GHz Microwave at Various Gases

The decomposition characteristics of CF4 with Argon or oxygen in 2.45GHz microwave has been investigated by using a Langmuir probe with variation of the microwave power and chamber pressure. For CF4/Ar and CF4/O2/Ar discharges, the ion density and the electron density decrease with increasing microwave power. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. Also with increasing pressure, the electron temperature increase, and ion and electron density decrease by increase of inelastic collision frequency and of collision with the walls in the chamber. The electron temperature is 13.6 ~ 5.9 [eV], the electron density is 4.4×1010 ~ 2.2×1010 [cm-3] and ion density is 5.2×1011 ~ 4×1010 [cm-3]. According as add oxygen, ion and electron density increased relatively comparing to CF4/Ar discharge. The electron temperature is 8.5 ~ 6.2 [eV], the electron and ion density is 5.1×1010 ~ 2.1×1010 [cm-3] and 3.7×1011 ~ 7.3×1010 [cm-3], respectively.

CYP2C9 Protein Interactions with Cytochromeb5: Effects on the Coupling of Catalysis

The hemoprotein cytochrome b(5) (cyt b5) has been demonstrated to affect the kinetics of drug oxidation by the microsomal cytochromes P450 (P450s). However, the mechanisms through which cyt b5 exerts these effects are variable and P450 isoform-dependent. Whereas the effects of cyt b5 on the major drug-metabolizing enzymes CYP2D6, CYP2E1, and CYP3A4 are well studied, fewer studies conducted over limited ranges of cyt b5 concentrations have been performed on CYP2C9. In the present study with CYP2C9, cyt b5 exerted complex actions upon P450 oxidative reactions by affecting the rate of metabolite formation, the consumption of NADPH by cytochrome P450 reductase, and uncoupling of the reaction cycle to hydrogen peroxide and water. Cytochrome b(5) devoid of the heme moiety (apo-b5) exhibited effects similar to those of native cyt b5. All rates were highly dependent on the cyt b5 to CYP2C9 enzyme ratio, suggesting that the amount of cyt b5 present in an in vitro incubation is an important factor that can have an impact on the reliability of extrapolating in vitro generated data to predict the in vivo condition. The major effects of cyt b5 are hypothesized to result from a cyt b5-induced conformational change in CYP2C9 that results in an increased collision frequency between the iron-oxygen species (Cpd I) and the substrate, and a decrease in the oxidase activity. Together, these findings suggest that cyt b5 can alter multiple steps in the P450 catalytic cycle via complex interactions with P450 and P450 reductase.

Dye-Sensitized TiO2 Solar Cells Using Imidazolium-Type Ionic Liquid Crystal Systems as Effective Electrolytes

A novel ionic liquid crystal (ILC) system (C(12)MImI/I(2)) with a smectic A phase used as an electrolyte for a dye-sensitized solar cell (DSSC) showed the higher short-circuit current density (J(SC)) and the higher light-to-electricity conversion efficiency than the system using the non-liquid crystalline ionic liquid (C(11)MImI/I(2)), due to the higher conductivity of ILC. To investigate charge transport properties of the electrolytes in detail, the exchange reaction-based diffusion coefficients (D(ex)) were evaluated. The larger D(ex) value of ILC supported that the higher conductivity of ILC is attributed to the enhancement of the exchange reaction between iodide species. As a result of formation of the two-dimensional electron conductive pathways organized by the localized I(3)- and I- at S(A) layers, the concentration of polyiodide species exemplified by I(m)- (m = 5, 7, ...) was higher in C(12)MImI/I(2). However, as the increment of the concentration of polyiodide species is less than that of D(ex), the contribution of a two-dimensional structure of the conductive pathway through the increase of collision frequency between iodide species was proposed. Furthermore, a quasi-solid-state ionic liquid crystal DSSC was successfully fabricated by employing a low molecular gelator. Addition of the 5.0 g/L gelator to ILC improved light-to-electricity conversion efficiency through the increase of J(SC) due to the enhancement of the conductivity in C(12)MImI/I(2)-gel.

Predicting the sizes of toluene-diluted heavy oil emulsions in turbulent flow Part 2: Hinze–Kolmogorov based model adapted for increased oil fractions and energy dissipation in a stirred tank

The applicability of several classical size prediction models to predict the Sauter mean diameters d 32 of four volume fractions of toluene-diluted heavy oil in water emulsions was studied. Energy dissipation in a fully baffled cylindrical tank stirred at varied speeds by a Rushton turbine was related to the d 32 measured with a Mastersizer 2000 laser light scattering instrument after 75 min of agitation. At low oil fractions of 0.01 droplet breakage behaviour was in accordance with the breakage dominance assumption of Hinze–Kolmogorov (H–K) theory. At intermediate oil fractions of 0.05 and 0.1, the system behaved similarly with lower rates of breakage than at 0.01. At high oil fractions of 0.3, the droplet sizes were the largest. Here, coalescence may have played a larger role due to increased collision frequency, while turbulence dampening caused larger eddies and reduced breakage. The resilience to breakage due to the surface elasticity was assumed to be constant for all oil fractions. The experimental diameters compared with the diameters calculated from several size-predictive models showed unsatisfactory predictions at higher oil fractions of 0.05–0.3. By modification of existing constants and coefficients of a H–K-based model that accounts for breakage and coalescence and by using iterative techniques, specific predictive equations for each mixing speed and a new averaged equation were developed. Good agreement between measured and predicted sizes was achieved.

Catalytic Isomerization of Quadricyclane Using Fourier Transform Near-Infrared Absorption Spectroscopy: Diffusion, Conversion, and Temperature Effect

By using Fourier transform near-infrared (NIR) absorption spectroscopy, the kinetic behaviors of quadricyclane isomerization, as catalyzed by anhydrous CuSO(4) in chloroform mixture with and without agitation, are presented. Given the acquired NIR spectra, the concentration decay of quadricyclane with the reaction time is determined with the aid of partial least-squares analysis. When the mixture is not agitated, the diffusion coefficients in chloroform are evaluated to be (3.8 +/- 0.1) x 10(-5) cm(2) s(-1) at 27 degrees C and (4.4 +/- 0.1) x 10(-5) cm(2) s(-1) at 39 degrees C. In the size-dependent experiments of the catalyst, the one-site and two-site coordinated conversion rate constants are further determined to be (8.5 +/- 5.9) x 10(-6) s(-1) A(-1) and (2.2 +/- 0.8) x 10(-8) s(-1) A(-2), respectively, at 27 degrees C and (1.3 +/- 0.8) x 10(-5) s(-1) A(-1) and (1.92 +/- 0.01) x 10(-6) s(-1) A(-2), respectively, at 39 degrees C. A denotes the total catalyst surface area per unit effective volume of solvent. Accordingly, the activation energies for one-site and two-site coordination are evaluated to be 24.8 and 286.2 kJ mol(-1), respectively. The reaction is dominated by one-site coordination (1:1 complex) between the reactant and the catalyst. Unless temperature increases, the two-site coordinated reaction may be ignored. In contrast, when analogous experiments are performed in the stirred solution, the diffusion factor is ignored but the conversion rate constants rise due to the increase of collision frequency. For instance, the one-site and two-site coordinated rate constants are increased to (1.7 +/- 1.4) x 10(-5) s(-1) A(-1) and (1.27 +/- 0.06) x 10(-5) s(-1) A(-2) at 39 degrees C. The two-site coordinated reaction rate is enhanced by a factor of 10. Thus, isomerization may proceed via both 1:1 and 1:2 coordination between the reactant and the catalyst. The Arrhenius plot yields the corresponding activation energies to be 24 +/- 3 and 275 +/- 3 kJ mol(-1). The activation energies remain constant, no matter whether the solution is agitated or not.

Effect of electrojet irregularities on DC current flow

A study is presented of the effect of plasma density irregularities in the auroral and equatorial electrojets on the DC currents giving rise to these irregularities. It is shown that the theory predicts extra dissipation and deviation in the direction of the mean current flow from that of E0 × B0/B2, in general agreement with observations. The average power input to the turbulent plasma, equal to the product of the externally applied electric field and the mean current, can be equated to the power input with that resulting in a plasma devoid of irregularities but with an increased collision frequency. Similarly one can compute the deviation in direction of the current flow due to the irregularities and compare this with the deviation caused in a plasma without irregularities, but with an increased collision frequency, and from this comparison assign an anomalous dissipation in the plasma caused by the irregularities. Our study applies elementary principles and deals with the mean current driven by an external field, including effects of the mean values of second order terms in the perturbed quantities. We do not discuss the elementary processes giving rise to the irregularities in the plasma; only their effect on the mean current flow. The anomalous dissipation or the increased apparent collision frequency, is related directly to the angular power spectrum of plasma density fluctuations. It is shown that the power dissipated by the DC current in these anomalous collisions is exactly the same as the power dissipated through normal collisions by the wave modes making up the power spectrum leading to the anomalous DC current dissipation. The study also suggests that the saturation of the instabilities, giving rise to the electrojet turbulence, is likely to be caused by the control of the current by the anomalous resistivity rather than by local nonlinear effects.

Water-based latex dispersions: 4. Exchange dynamics and residence times of nonylphenol ethoxylate in concentrated latex dispersions

The equilibrium residence times of the nonionic surfactant nonylphenol ethoxylate (NP100) in a latex dispersion were determined using NMR diffusometry. At 16% w/w particle concentration and 0.12, 0.43 and 0.81% w/w NP100, the residence times of the surfactant were 0.16, 1.02 and 4.73 s in solution ( τ A ) and 0.3, 0.37 and 0.61 s on the surface of the particles ( τ B ), respectively. At even higher particle concentration (>45% w/w), τ A and τ B were 1.47 and 2.2 s. Calculating the number of collisions that ought to result in adsorbed species, at 16% w/w, only 2, 5 and 2 ‰ (corresponding to 0.12, 0.43 and 0.81% w/w NP100) resulted in adsorption, whereas at >45% w/w, only 12 ‰ resulted in adsorption, which suggested that the surfactant was irreversibly adsorbed on the particles. The small increase in collision frequency with increased particle concentration could be a result of a diffusion controlled adsorption, while an energy barrier for desorption controlled the overall exchange dynamics in the dispersion. The slow dynamics in the dispersion was controlled, mainly by the nonylphenol group, which gave NP100 a strong preference to surfaces. In addition, the chain length of the poly(ethylene glycol) (PEG) group changed the solution behavior from being that of a typical surfactant to that of a polymer.

312 金属と水とのメカノケミカル反応による水素製造(大気環境改善技術(3),大気・水保全技術)

New method of hydrogen production by mechano-chemical reaction of various metals (Al, Si, Fe, Ni, Pb, Ti, Cu, Cr and Co) with water was investigated. Capacity of hydrogen production were correlated to the standard free energy (⊿G°) of metal oxides formation. It was revealed that aluminum had the highest hydrogen production capability among various metals. However, there was a long induction period in the reaction of Al with water. This induction period was decreased by the addition of high hardness materials such as SiC and Cr. It was concluded that the oxide layer on Al surface was effectively destroyed by the increase of collision frequency between Al particles and high hardness materials.

Theoretical Study of Catalytic Effects in Micellar Solutions

The catalytic effect of charged micelles as manifested through the increased collision frequency between the counterions of an electrolyte in the presence of such micelles is explored by the Monte Carlo simulation technique and various theoretical approaches. The micelles and ions are pictured as charged hard spheres embedded in a dielectric continuum with the properties of water at 298 K with the charge on micelles varying from zero to z(m) = 50 negative elementary charges. Analytical theories such as (i) the symmetric Poisson-Boltzmann theory, (ii) the modified Poisson-Boltzmann theory, and (iii) the hypernetted-chain integral equation are applied and tested against the Monte Carlo data for micellar ions (m) with up to 50 negative charges in aqueous solution with monovalent counterions (c; z(c) = +1) and co-ions (co; z(co) = -1). The results for the counterion-counterion pair correlation function at contact, g(cc)(sigma(cc)), are calculated in a micellar concentration range from c(m) = 5 x 10(-)(6) to 0.1 mol/dm(3) with an added +1:-1 electrolyte concentration of 0.005 mol/dm(3) (for most cases), and for various model parameters. Our computations indicate that even a small concentration of a highly charged polyelectrolyte added to a +1:-1 electrolyte solution strongly increases the probability of finding two counterions in contact. This result is in agreement with experimental data. For low charge on the micelles (z(m) below -8), all the theories are in qualitative agreement with the new computer simulations. For highly charged micelles, the theories either fail to converge (the hypernetted-chain theory) or, alternatively, yield poor agreement with computer data (the symmetric Poisson-Boltzmann and modified Poisson-Boltzmann theories). The nonlinear Poisson-Boltzmann cell model results yield reasonably good agreement with computer simulations for this system.

전기폭발법에서 SMPS를 이용한 Cu 나노분말의 실시간 입자특성평가

Synthesis and characteristics of Cu nanopowder were considered by in-situ characterization method using SMPS in pulsed wire evaporation process. With increasing pressure in chamber, particle size and degree of agglomeration increased by increase of collision frequency. Also, it was found from the XRD analyses and BET measurements that crystallite size and particle size decreased with elevating applied voltage. However, SMPS measurements and TEM observation revealed the increase of particle size and degree of agglomeration with increase of applied voltage. These results suggested that particle growth and agglomeration depend on overheating factor in chamber at the early stage and thermal coagulation in filtering system during powder formation until collection.

Coalescence during emulsification: 2. Role of small molecule surfactants

An oil-soluble hexadecyl pyrene (HDP) probe is used to monitor coalescence of hexadecane oil-in-water emulsions, during emulsification, in stirred systems and in a high-pressure homogenizer (microfluidizer), when small molecule surfactants are used as emulsifiers. The effect of sodium dodecyl sulfate concentration and salt concentration on the amount of coalescence and final drop size is studied. The behavior of oil-soluble surfactants and mixtures of oil-soluble and water-soluble surfactants on emulsification performance is also discussed. For high-pressure homogenizers, the drop sizes obtained are found to depend mostly on the ability of surfactants to stabilize the drops against coalescence, rather than their ability to reduce the interfacial tension. Increasing oil phase fractions increase the coalescence rate, because of the increase in collision frequency, which, in turn, impacts the drop size of the homogenized emulsion.

Duration of exposure to high fluid shear stress is critical in shear-induced platelet activation-aggregation.

Platelet functions are increasingly measured under flow conditions to account for blood hydrodynamic effects. Typically, these studies involve exposing platelets to high shear stress for periods significantly longer than would occur in vivo. In the current study, we demonstrate that the platelet response to high shear depends on the duration of shear exposure. In response to a 100 dyn/cm2 shear stress for periods less than 10-20 sec, platelets in PRP or washed platelets were aggregated, but minimally activated as demonstrated by P-selectin expression and binding of the activation-dependent alphaIIbbeta3 antibody PAC-1 to sheared platelets. Furthermore, platelet aggregation under such short pulses of high shear was subjected to rapid disaggregation. The disaggregated platelets could be re-aggregated by ADP in a pattern similar to unsheared platelets. In comparison, platelets that are exposed to high shear for longer than 20 sec are activated and aggregated irreversibly. In contrast, platelet activation and aggregation were significantly greater in whole blood with significantly less disaggregation. The enhancement is likely via increased collision frequency of platelet-platelet interaction and duration of platelet-platelet association due to high cell density. It may also be attributed to the ADP release from other cells such as red blood cells because increased platelet aggregation in whole blood was partially inhibited by ADP blockage. These studies demonstrate that platelets have a higher threshold for shear stress than previously believed. In a pathologically relevant timeframe, high shear alone is likely to be insufficient in inducing platelet activation and aggregation, but acts synergistically with other stimuli.

Low-frequency electrostatic waves in self-gravitating dusty plasmas with dust-ion collisions.

The influence of dust-ion collisions on low-frequency modes in a self-gravitating dusty plasma is studied. The stability of the system is easily determined using elementary principles of rootlocus theory. It shows that collisions between ions and dust grains do not change the criteria for gravitational collapse at any value of their collision frequency, but diminish the growth rate of unstable dusty plasmas. Moreover, the rootlocus plots visualize qualitatively the evolution of the real frequencies and damping decrements of the dust-acoustic and ion-acoustic modes as the dust-ion collision frequency increases.

Experimental studies on particle behaviour and turbulence modification in horizontal channel flow with different wall roughness

Detailed measurements in a developed particle-laden horizontal channel flow (length 6 m, height 35 mm, the length is about 170 channel heights) are presented using phase-Doppler anemometry for simultaneous determination of air and particle velocity. The particles were spherical glass beads with mean diameters in the range of 60 µm–1 mm. The conveying velocity could be varied between about 10 m/s and 25 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. For the first time, the degree of wall roughness could be modified by exchanging the wall plates. The influence of these parameters and the effect of inter-particle collisions on the profiles of particle mean and fluctuating velocities and the normalised concentration in the developed flow were examined. It was shown that wall roughness decreases the particle mean velocity and enhances fluctuating velocities due to irregular wall bouncing and an increase in wall collision frequency, i.e. reduction in mean free path. Thereby, the larger particles are mainly more uniformly distributed across the channel, and gravitational settling is reduced. Both components of the particle velocity fluctuation were reduced with increasing mass loading due to inter-particle collisions and the momentum loss involved. Moreover, the effect of the particles on the air flow and the turbulent fluctuations was studied on the basis of profiles in the developed flow and turbulence spectra determined for the streamwise velocity component. In addition to the effect of particle size and mass loading on turbulence modulation, the influence of wall roughness was analysed. It was clearly shown that increasing wall roughness also results in a stronger turbulence dissipation due to two-way coupling.

Dissipative electrostatic waves associated with the dust grain density in a nonequilibrium plasma

A new nonlinear dissipative equation associated with the gravitational effect of dust grains is derived in a nonequilibrium plasma. Temporal evolution of the solution of this equation is shown by numerical calculation. It is shown that the nonlinear term of this equation forms the steepening and the dissipative effect damps the wave amplitude. Damping of the wave grows as the collision frequency increases. In the very low collision frequency, when the gravitational force becomes comparatively larger than the electrostatic force, the wave becomes somewhat unstable. On the other hand, when the collision frequency increases, i.e., the acceleration for the grains is comparatively larger, the behavior of the nonlinear wave becomes mild.

Study on Crystallinity of Tin-Doped Indium Oxide Films Deposited by DC Magnetron Sputtering

Tin-doped indium oxide (ITO) films were deposited by dc magnetron sputtering using oxide (ITO) or alloy (IT) targets. The ITO films sputter-deposited using Ar at total pressure (Ptot) lower than 1.2 Pa showed polycrystalline structure, whereas entirely amorphous films were deposited at Ptot higher than 1.4 Pa, indicating that the crystallinity of the ITO films were heavily affected by Ptot. This was quantitatively explained in terms of the kinetic energy of sputtered particles reaching to the substrate surface, which decreased due to an increase in collision frequency between the sputtered particles and sputtering gas molecules. ITO films were also deposited using Xe or He as sputtering gases, where amorphous films were deposited at Ptot higher than 0.7 Pa (Xe) and 12 Pa (He), respectively. Based on a hard sphere collision model, the energy loss rates of the sputtered particles due to collision with sputtering gas molecules were estimated to be consistent with the experimental results for the case of using He, Ar or Xe gases.

Electron transport fluxes in potato plateau regime

Electron transport fluxes in the potato plateau regime are calculated from the solutions of the drift kinetic equation and fluid equations. It is found that the bootstrap current density remains finite in the region close to the magnetic axis, although it decreases with increasing collision frequency. This finite amount of the bootstrap current in the relatively collisional regime is important in modeling tokamak startup with 100% bootstrap current.

Formation of inhomogeneity in drop concentration induced by the inertia of drops falling in a turbulent flow, and the influence of the inhomogeneity on the drop‐spectrum broadening

AbstractThe mechanisms of drop‐concentration inhomogeneity formation are studied using both a numerical simulation with a model of isotropic and homogeneous turbulence, and analytical methods. It is shown that atmospheric turbulence can create a significant drop‐concentration inhomogeneity due to the effects of drop inertia. Two types of area in the turbulent flow are revealed. Drops tend to leave the areas of ‘drop vortices’ and collect within the zones out of the vortices. As a result, the zones of drop‐track collection turn out to be the zones of enhanced drop concentration. the rate of concentration enhancement is studied for drops of different sizes using the Monte Carlo method. It is shown that the drop flux velocity divergence and droplet‐concentration variations reach their maximum at 100 μm drop radius. Zones of enhanced drop concentrations are stretched along the drop tracks. Characteristic scales of drop‐concentration fluctuations along the drop tracks are of the order of several metres or even a few tens of metres. Across the drop tracks, the characteristic scale of concentration pulsations is of the order of a few centimetres.The existence of the areas of drop‐concentration enhancement and the areas of decreased concentration means that drop collisions are not distributed uniformly, but are concentrated within the areas with greater drop concentration. the possible effects of droplet inhomogeneity is simulated by solving a stochastic coalescence equation for the water drop‐size‐distribution function in areas of enhanced and decreased droplet concentration with the subsequent mixing of the corresponding spectra at each 10 s. It is shown that due to the nonlinear nature of collision processes the effects of the increase of collision frequency in the areas of enhanced concentration dominate over those of its decrease. the effects of the drop‐concentration inhomogeneity are accumulated with time and lead to substantial acceleration of droplet spectrum broadening. It is supposed that the inhomogeneity of rain rates with time and space can be attributed to these turbulence effects determining drop‐track collection and drop‐concentration inhomogeneity. These turbulence effects can contribute to the formation of inhomogeneity of ice and aerosol particles as well.