Variable Dissipation Research Articles

Warm inflation in the DGP brane-world model

Warm inflationary universe models on a warped Dvali–Gabadadze–Porrati brane are studied. General conditions required for these models to be realizable are derived and discussed. By using an effective exponential potential we develop models for constant and variable dissipation coefficient ratio r = Γ 3 H . We use recent astronomical observations for constraining the parameters appearing in our models.

Modified energy dissipation algorithm for seismic structures using magnetorheological damper

A simple modified energy dissipation algorithm is presented for seismic response reduction. The magnetorheological (MR) damper, an efficient semiactive device is controlled using a maximum energy dissipation algorithm (MEDA), as well as a newly proposed modified variable energy dissipation algorithm (VEDA) that supplies continuously varying command voltages. For MEDA, the command voltage is either zero or the maximum value. In some situations when the dominant frequencies of the system under control are low, large changes in the forces applied to the structure may result in high local acceleration values. The VEDA is proposed as a modification to the original MEDA to reduce this effect. Also the applicability of the VEDA-based semiactive control system using MR dampers is investigated through numerical simulation of a three-story shear building.

Modelling of turbulent scalar flux in turbulent premixed flames based on DNS databases

A transport equation for scalar flux in turbulent premixed flames was modelled on the basis of DNS databases. Fully developed turbulent premixed flames were obtained for three different density ratios of flames with a single-step irreversible reaction, while the turbulent intensity was comparable to the laminar burning velocity. These DNS databases showed that the countergradient diffusion was dominant in the flame region. Analyses of the Favre-averaged transport equation for turbulent scalar flux proved that the pressure related terms and the velocity–reaction rate correlation term played important roles on the countergradient diffusion, while the mean velocity gradient term, the mean progress variable gradient term and dissipation terms suppressed it. Based on these analyses, modelling of the combustion-related terms was discussed. The mean pressure gradient term and the fluctuating pressure term were modelled by scaling, and these models were in good agreement with DNS databases. The dissipation terms and the velocity–reaction rate correlation term were also modelled, and these models mimicked DNS well.

Classes of Variable Dissipation Systems with Nonzero Mean in the Dynamics of a Rigid Body

Classes of Variable Dissipation Systems with Nonzero Mean in the Dynamics of a Rigid Body

NEW INTEGRABLE CASES AND FAMILIES OF PORTRAITS IN THE PLANE AND SPATIAL DYNAMICS OF A RIGID BODY INTERACTING WITH A MEDIUM

The purpose of the paper is to elaborate qualitative methods for studying the dynamics of rigid bodies interacting with a resisting medium under quasistationarity conditions. This material refers to the qualitative theory of ordinary differential equations, as well as to the dynamics of rigid bodies. In this paper, we use the properties of motion of a body in a medium under conditions of a jet flow past this body. We study the plane and three-dimensional model problems of motion of a body in a resisting medium. New families of phase portraits of variable dissipation systems on twoand three-dimensional manifolds are obtained, and their absolute or relative roughness (i.e., structural stability) is demonstrated. The Jacobi integrable cases of equations of motion of rigid bodies are found, including those in the problem of motion of a spherical pendulum placed in the incoming flow of a medium.

Characterization of P700 as a photochemical quencher in isolated Photosystem I particles using simultaneous measurements of absorbance changes at 830 nm and photoacoustic signal.

The relationship between the redox state of P700, the primary donor of PS I, monitored using absorbance changes at 830 nm and photochemical energy storage in PS I reaction centers assayed with the photoacoustic method (PA) was studied in isolated PS I submembrane particles aspirated onto nitrocellulose filters. Several donors have been used to support the electron transport through PS I. NADPH and NADH demonstrated low rates of electron donation to PS I, while ascorbate and ascorbate plus 2,6-dichlorophenolindophenol (DCIP) couple have been found more effective in both P700(+) reduction and stimulation of the variable component of the PA signal. A linear relationship was found in isolated PS I particles between the (A(830,max) - A(830,steady))/A(830,max) and (PA(max) - PA(steady))/PA(max) ratios, which characterized the relative amount of P700 in the reduced state and the relative magnitude of the variable PA component, respectively. That linear relationship was obtained independently from the nature of electron donor used for the reduction of P700(+). Such linear relationship was also obtained at various wavelengths of modulated light in the range of 660 to 720 nm, only the slope of the linear fits varied with wavelength. It is concluded that reduced P700 act as a photochemical quencher of absorbed energy. Variable thermal dissipation in PS I reaction centers of isolated submembrane particles linearly depends on the amount of reduced P700 and thus constitutes an appropriate indicator of the redox pressure applied to PS I.

Relationship between the redox state of P700 and variable thermal dissipation in isolated photosystem I particles

The relationship between the redox state of P700 monitored using absorbance changes at 830 nm and photochemical energy storage in PSI reaction centers assayed with the photoacoustic method (PA) was studied in isolated PSI submembrane particles aspirated onto nitrocellulose filters. Several donors have been used to support the electron transport through PSI. NADPH and NADH demonstrated low rates of electron donation to PSI, while ascorbate and ascorbate plus 2,6-dichlorophenolindophenol (DCIP) couple have been found more effective in both P700+ reduction and stimulation of the variable component of the PA signal. A linear relationship was found in isolated PSI particles between the (A830, max - A830, steady)/A830, max and (PAmax - PAsteady)/PAmax ratios, which characterized the relative amount of P700 in the reduced state and the relative magnitude of the variable PA component, respectively. That linear relationship was independent on the nature of electron donor used for the reduction of P700+. Such linear relationship were obtained at various wavelength of modulated light used for the measurements of the PA signal in the range of 660 to 720 nm. Only the slope of the linear fits varied with wavelength. It is concluded that in isolated submembrane particles the photochemical energy storage in PSI reaction centers linearly depends on the amount of reduced P700.

ATRAZINE AND CARBOFURAN TRANSPORT THROUGH THE VADOSE ZONE IN THE CLAIBORNE AQUIFER RECHARGE AREA<

A 1-ha field plot with a sandy surface soil, located near Plains, Georgia, was studied for three years (from1993 to 1995) to evaluate pesticide transport in the vadose zone. Vadose zone soil samples were collected 23 times: priorto the initial 1993 pesticide application, each year at approximately 1, 3, 7, 14, 28, and 44 days after pesticideapplication, each fall after harvest, and in the spring of 1995 prior to planting. The samples were analyzed for atrazine,carbofuran, deethylatrazine (DEA), and deisopropylatrazine (DIA). Atrazine and carbofuran in the active root zone(< 100 cm) degraded rapidly. Overall, the higher concentration levels of atrazine, DEA, DIA, and carbofuran werelimited to the top 25 cm of the profile and to the period from 1 to 30 days after application. On the average, by 30 daysafter application 83% of the atrazine and 96% of the carbofuran had degraded. By 44 days after application, virtually allof the pesticides in the top 250 cm of the soil had degraded. Atrazine was found to be more persistent than wascarbofuran with a half life approximately twice that for carbofuran. A two-stage model with a variable dissipation ratefor the period up to 44 days after pesticide application and a second dissipation rate for periods greater than that wasfound to fit the data better than a single stage model. For the first 44 days after application, the first-order decay ratewith a half life of 12 days was found to fit the field data for atrazine within the soil profile. A first-order decay rate with ahalf life of approximately 6 days fit the observed carbofuran data best. The dissipation rate decreased rapidly after thefirst 44 days. When a two-stage dissipation process was assumed, the dissipation rate coefficient decreased from 0.059 to0.006 (days 1 ) for atrazine, while for carbofuran it decreased from 0.110 to 0.018 (days 1 ). Observed levels of theatrazine metabolites DIA and DEA were highest in the top 1 cm of the soil. There appeared to be some movement orcreation of the metabolites at lower depths in the profile later in the growing season, but not at large concentrations.

MIXED TIME FINITE ELEMENTS FOR VIBRATION RESPONSE ANALYSIS

This paper presents a mixed time finite element method for vibration response analysis. The underlying variational formulation is developed from the principle of virtual work. Conventional spatial discretization techniques are adopted. Time discretization is implemented by using mixed time finite elements. The proposed formulation not only forms a unified variational basis for spatial and temporal discretization; it also derives many other robust time step integration algorithms. Unconditionally stable and high order accurate algorithms with variable numerical dissipation can be constructed systematically. Moreover, the proposed formulations can be used to solve linear as well as non-linear problems. The accuracy and stability of the derived algorithms are presented.

Application of modulated photoacoustic spectroscopy to measurement of photochemical quenching of variable thermal emission in thylakoid membranes during heat or light stress

The application of photoacoustic spectroscopy to the study of photosynthesis in thylakoid membranes is well documented in the literature. We use various parameters to compare the quenching of variable fluorescence with the energy storage measured by photoacoustic spectroscopy to gain more information about their interrelationship. The use of thylakoid membranes and photosystem II (PSII) enriched submembrane fractions pretreated at various temperatures or exposed to photoinhibitory illumination indicates that there is a strong correlation between the photochemical quenching of variable fluorescence and that of variable thermal dissipation. However, some differences also exist that are likely due to the involvement of cyclic electron transport in both photosystem I and PSII during the formation of energy storage and to the fact that energy storage is more influenced by the reduction of the plastoquinone pool, whereas variable fluorescence depends solely on the redox state of the primary photosystem II acceptor QA .

Effects of Variable Properties and Viscous Dissipation During Optical Fiber Drawing

The axisymmetric free-surface flow and thermal transport of fused silica during optical fiber drawing was considered with variable properties, prescribed heat flux, and neck shape. Experimental data from previous researchers were adapted or used as the basis for assumptions in order to enable a realistic analysis. The main objectives were to model the neck-down process in order to clarify the effects of the variable properties and the associated viscous dissipation. Due to the large changes in dimension and viscosity, this system poses severe nonlinearities, and a new solution algorithm was necessarily developed. Validation was achieved and several important results were obtained. Among these, it was shown that the viscous dissipation has considerable impact on the fiber temperature due to its localization to a small volume near the fiber section. Also, it was shown that a variable viscosity generated vorticity, which was localized to the region where the preform radius undergoes large changes.

An Implicit Numerical Model for the Closed-Chamber Test

Summary An implicit Lagrangean model is presented for the closed-chamber test (CCT). Pressure drops from 5, 000 to 50 psi are not uncommon during a CCT. High fluid velocities near the wellbore under high pressure gradients may lead to non-Darcy flow in the reservoir. The wellbore and the reservoir are modeled by the scalar-conservation laws of momentum and continuity that describe the physical processes—variable celerity, physical dissipation, and momentum. Rate and pressure are obtained simultaneously for the entire reservoir/wellbore system. The Lagrangean formulation permits use of the appropriate equation of state (EOS) in a given wellbore cell. Solution is by a versatile implicit numerical scheme that allows control of numerical dissipation. The automatic regridding is based on the physics of the problem. The reservoir model shows excellent agreement with the finite radial-source solution in porous media. Attributes of the model include the effects of an initial fluid column, sand failure, and a time-dependent skin. The results are in good agreement with two actual field tests from offshore Gulf of Mexico, and the deduction of transmissibility is straightforward.

Numerical solution of thermal entry length problem with variable viscosities and viscous dissipation

A numerical solution of the thermal entry length problem for circular pipes with constant temperature boundaries and with a prescribed dependence of viscosity on temperature and viscous dissipation of some specified order are presented. The results indicate a significant effect of these factors. The results for both heating and cooling processes are presented and compared with the available analytical results. They are useful in the design of heat exchangers with high Prandtl number fluids as the working media.

Studies on finite amplitude waves in bounded water bodies

The problem treated here is the dynamics of a bay where water is driven through its opening periodically in time. The basic equations are expressed in the two horizontal coordinates and time and they are obtained by an integration of the Navier-Stokes equations in the vertical coordinate. The equations are nonlinear because of the convective terms in the acceleration. The problem of harbor dynamics provides a natural parameter as the ratio of mass of water entering the bay through the waves to the total mass of water in the bay. This small parameter multiplies the nonlinear terms and thus the problem is ideally suited for a perturbation analysis. The nonlinear terms are responsible for the generation of secondary flows and are particularly important near resonant frequences. The analysis further indicates the existence of a time independent flow analogous to acoustic streaming, known from solutions of the Navier-Stokes equations. The question of vorticity is studied and is seen that: a constant dissipation coefficient precludes the generation of vorticity even for the nonlinear case: and that only a weak (second order) vorticity can exist in the case of a variable dissipation term expressed through the Chezy coefficient. The study suggests also a semi analytic-numerical scheme with savings of 0(10 2) for irregular geometries through the separation of the various order harmonics as opposed to the usual integration in time.

Refrigeration capacity of an inspired-air cooling system— A mathematical model

This paper describes the development of a mathematical model to predict the refrigeration capacity required of an inspired-air cooling system for dairy animals. The inspired-air system has been generalized from the standpoint of animal heat dissipation to the system via head, neck and respiratory tract. A duct configuration to accommodate eight cows has been selected to allow a mathematical solution of refrigeration capacity for a specific situation. The heat transfer into the duct, principally by conduction from the outside, has been considered in formulating the model. The model developed considers variable ambient and inspired-air conditions, variable animal heat dissipation to the system as a function of varying ambient conditions and ambient heat dissipation to the system. The predictions of this model compare favourably with the theoretical and experimental results of other research workers. Required refrigeration capacities varied from 0·12 ton/cow to 0·41 ton/cow depending upon the assumed ambient conditions. Equations giving refrigeration capacity as a function of outside and inspired-air conditions are presented.

Generalized couette flow with variable viscosity and dissipation of mechanical energy

We employ the method of a small parameter to solve the problem of a pressure-stabilized Couette flow in which we take into account dissipation of mechanical energy and an exponential temperature dependence of viscosity.