Thermal study of the fossilization processes of the extinct fishes in Araripe Geopark

The study of fossil materials is very important in the geological and biological researches. They can involve ancient past, evolution or extinction of species, oil prospecting and the understanding of different areas such as: paleoclimate, paleoecology, paleogeography, in addition of climate, environmental changes and life. Araripe Geopark is located in the south area of the Ceará state in the Northeast of Brazil and it provides a general overview of the Earth’s History. In this study the vertebral column extinct fish, Cladocyclus ferox and its nodule from Santana Formation, Northeast of Brazil, calcite and apatite minerals, and vertebral column of recent fish, Opisthonema oglinum were investigated by means of thermal analysis. TG/DTG and DTA curves showed decomposition processes, suggesting water evolution, calcium carbonate and phosphate decomposition and thermal transitions indicated that fossilization processes of fish, carbonaceous material involved the fossil after its death and the organic substance was replaced by inorganic compounds.     

Thermodynamics of deformation and swelling of crosslinked polymers under small deformations

A system of equations and physical relationships that show the quasi-static processes of deformation and swelling of crosslinked polymers in solvents under small deformations of the polymer matrix is proposed. The system is obtained via linearization of the respective equations of the nonlinear theory. This makes it possible to reveal the relationship between the constants of the linear theory and the parameters that characterize the elastic and thermodynamic properties of a solvent-swollen crosslinked polymer under finite deformations. Different types of problems that describe the stress-strain state of inhomogeneously swollen crosslinked polymers, as well as the thermodynamics of their deformation and swelling in a solvent medium, are discussed in terms of the linear theory.     

Mechanical structures in polymer melts. II. Roles of entanglements in viscosity and elastic turbulence

Current theories of polymer flow processes often sacrifice realistic molecular models for simplicity of their mathematical equations. An analysis of what might happen to molecules of more realistic sizes and shapes under shear flow, shows the importance of the rapid Brownian motion of chain segments, the elastic deformations of polymer random coils, and the dissipation of this elastic random coil energy by the relatively slow slippage of the chains past each other at a few entanglements where steric hindrance causes long relaxation times. This makes the energy loss depend on the time at each local deformation, and not on the overall shear rate. At high shear rates this model leads to “cluster flow” and low loss cyclic deformations, rather than the high loss processes of steady-state shear. This model gives reasonable qualitative explanations for many anomalous flow properties, and it has predicted new effects that have since been observed.     

Linearized non-equilibrium and non-isothermal two-dimensional model of liquid chromatography for studying thermal effects in cylindrical columns

A non-equilibrium and non-isothermal two-dimensional lumped kinetic model (2?D-LKM) is formulated and analytically solved to study the influence of temperature variations along the axial and radial coordinates of a liquid chromatographic column. The model includes convection-diffusion partial differential equations for mass and energy balances in the mobile phase coupled with differential equations for mass and energy in the stationary phase. The solutions are derived analytically through sequential implementation of finite Hankel and Laplace transformations using the Dirichlet inlet boundary conditions. The coupling between the thermal waves and concentration fronts is demonstrated through numerical simulations and important parameters are recognized that influence the column performance. For a more comprehensive study of the considered model, numerical temporal moments are obtained from the derived solutions. Several case studies are conducted and validity ranges of the derived analytical solutions are identified. The current analytical results will play a major role in the improvements of non-equilibrium and non-isothermal liquid chromatographic processes.     

Determination of thermal expansion coefficient of a monofilament polyamide fiber using digital image correlation

Coiled polymer actuators are a type of artificial muscles that are a promising development in the field of smart materials. The coefficient of thermal expansion of monofilament polyamide fibers is a crucial parameter for understanding the actuation of coiled fibers. The main purpose of this work is to develop a new methodology for estimating the coefficient of thermal expansion and the transition temperature of monofilament polymer fibers. In the experimental procedure, axial deformations of monofilament polyamide fiber samples were induced by temperature variations using a controlled thermal system. These deformations were determined from images of polyamide samples using the digital image correlation method. Two different approaches based on distinct temperature conditions were conducted. An alternative model with three parameters, including the coefficient of thermal expansion, was introduced to describe the thermal-mechanical behavior of monofilament polyamide fibers. Moreover, polyamide samples were also characterized using four conventional methodologies. Results indicated that the coefficient of thermal expansion changed of a modest negative value to a large negative value and this transition occurred around the glass transition temperature of the polyamide. The thermal expansion curves demonstrate good repeatability and all estimated parameters were in accordance with literature, indicating that the proposed approach can be suitable for the proposed study. This investigation may help in understanding of the intrinsic thermal-mechanical behavior of polymeric monofilaments employed as actuators.     

Model and experimental studies of gravitational convection in an electromembrane cell

The model and experimental studies of the effect of gravitational convection on transport processes in an electromembrane cell are carried out. A model of an unsteady process of binary electrolyte transfer in moderately dilute solutions in an electromembrane cell for underlimiting current modes with allowance made for the natural and forced convection is built in the form of a system of two-dimensional equations of Navier-Stokes, Nernst-Planck, thermal conductivity, and electric current continuity. The dynamics of the appearance and development of vortex structures that arise in response to operation of gravitational archimedian forces is considered as well as their effect on the transfer of salt ions. Chronoampero- and chronopotentiograms obtained in an experimental study of desalination channels in electromembrane systems are interpreted.     

An Insoluble Surfactant Model for a Vertical Draining Free Film

A mathematical model is constructed to study the evolution of a vertically oriented thin liquid film draining under gravity when there is an insoluble surfactant with finite surface viscosity on its free surface. Lubrication theory for this free film results in three coupled nonlinear partial differential equations describing the free surface shape, the surface velocity, and the surfactant transport at leading order. We will show that in the limit of large surface viscosity, the evolution of the free surface is that obtained for the tangentially immobile case. For mobile films with small surface viscosity, transition from a mobile to an essentially immobile film is observed for large Marangoni effects. It is verified that increasing surface viscosity and the Marangoni effect retard drainage, thereby enhancing film stability. The theoretical results are compared with experiment; the purpose of both is to act as a model problem to evaluate the effectiveness of surfactants for potential use in foam-fabrication processes. Copyright 2000 Academic Press.     

Optimizing fitting parameters in thermogravimetry

This study presents an alternative to simple estimation of parametric fitting models used in thermal analysis. The addressed problem consists in performing an alternative optimization method to fit thermal analysis curves, specifically TG curves and their first derivatives. This proposal consists in estimating the optimal parameters corresponding to fitting kinetic models applied to thermogravimetric (TG) curves, using evolutionary algorithms: differential evolution (DE), simulated annealing and covariance matrix adapting evolutionary strategy. This procedure does not need to include a vector with the initial values of the parameters, as is currently required. Despite their potential benefits, the application of these methods is by no means usual in the context of thermal analysis curve’s estimation. Simulated TG curves are obtained and fitted using a generalized logistic mixture model, where each logistic component represents a thermal degradation process. The simulation of TG curves in four different scenarios taking into account the extent of processes overlapping allows us to evaluate the final results and thus to validate the proposed procedure: two degradation processes non-overlapped simulated using two generalized logistics, two processes overlapped, four processes non-overlapped and four processes overlapped two by two. The mean square error function is chosen as objective function and the above algorithms have been applied separately and together, i.e., taking the final solution of the DE algorithm is the initial solution of the remaining. The results show that the evolutionary algorithms provide a good solution for adjusting simulated TG curves, better than that provided by traditional methods.     

Kinetic Aspects and Heats of Reaction between Components in Thermal Decomposition of Ammonium Nitrate-Calcium (Magnesium) Carbonate Mixtures

The kinetics of heat absorption in thermal decomposition of commercial ammonium nitrate-calcium (magnesium) carbonate mixture and a model mixture of ammonium nitrate and calcium carbonate was studied. Rate equations of the processes and temperature dependences of constants in these equations were determined. The heats of these reactions were calculated.     

Elastic network normal modes provide a basis for protein structure refinement

It is well recognized that thermal motions of atoms in the protein native state, the fluctuations about the minimum of the global free energy, are well reproduced by the simple elastic network models (ENMs) such as the anisotropic network model (ANM). Elastic network models represent protein dynamics as vibrations of a network of nodes (usually represented by positions of the heavy atoms or by the C(α) atoms only for coarse-grained representations) in which the spatially close nodes are connected by harmonic springs. These models provide a reliable representation of the fluctuational dynamics of proteins and RNA, and explain various conformational changes in protein structures including those important for ligand binding. In the present paper, we study the problem of protein structure refinement by analyzing thermal motions of proteins in non-native states. We represent the conformational space close to the native state by a set of decoys generated by the I-TASSER protein structure prediction server utilizing template-free modeling. The protein substates are selected by hierarchical structure clustering. The main finding is that thermal motions for some substates, overlap significantly with the deformations necessary to reach the native state. Additionally, more mobile residues yield higher overlaps with the required deformations than do the less mobile ones. These findings suggest that structural refinement of poorly resolved protein models can be significantly enhanced by reduction of the conformational space to the motions imposed by the dominant normal modes.     

Kinetic study of the multistep thermal behaviour of barium titanyl oxalate prepared via chemical precipitation method

This study describes the physico-geometrical mechanism and overall kinetics for the multistep thermal dehydration of barium titanyl oxalate tetrahydrate (BTO). The thermal dehydration kinetics of BTO was studied at four different linear heating rates under non-isothermal conditions. The reaction kinetics was performed using differential scanning calorimetry (DSC) and the curves obtained were analysed using different isoconversional model-free equations and the values are found to be compatible with each other. The kinetic deconvolution principle is used for identifying the partially overlapped kinetic processes of the thermal dehydration of BTO, and it occurs in two stages. The overall reaction kinetics parameters calculated via kinetic deconvolution of the sample indicate the multistep nature of the process and the kinetic analysis of the non-isothermal data of this reaction model shows that the reaction is best described by Sestak–Berggren (m, n) empirical kinetic model. The prepared sample was identified and characterized by means of FT-IR, XRD, SEM, and TEM.

     

Calculating the rigidity of a composite with allowance for flexural deformations of the filler

Models for describing the mechanical properties of inhomogeneous fine-structure polymer systems with marked asymmetry (a large aspect ratio) of one of their components are proposed. Solution of this problem by traditional methods of composite mechanics is limited by two circumstances. The first consists in marked flexural deformations of the fine objects, which are not taken into account in the well-developed analytical techniques based on self-consistency approximations. The second is that the marked structural asymmetry causes significant difficulties in the use of numerical techniques for solving boundary-value problems of composite mechanics because the small thickness of the inclusions (along with their great length) necessitates strong discretization of the continual equations. The backbone deformation model proposed in this study for a composite containing a fine-structure rigid cluster is based on the theory of bending of thin beams. A new numerical technique, which does not require an overly fine partition of the integration domain, is developed as well. An important role of flexural deformations is demonstrated; among other things, they lead to a significant decrease in the elastic moduli of the composites.     

Drying and pyrolysis of wood particles: experiments and simulation

The objective of this study is to develop a flexible and stable numerical method to predict the thermal decomposition of large wood particles due to drying and pyrolysis. At a later stage, this model is applied to each particle of a packed bed and thus, forms the entire packed bed process as a sum of individual particle processes. Therefore, this approach can deal with particles of different sizes, shapes and properties. A general formulation of the conservation equations allows the geometry of a fuel particle to be treated as a plate, cylinder or sphere. The various processes such as heat-up, drying and pyrolysis are described by a set of one-dimensional and transient conservation equations for mass and energy. This allows for simultaneous processes e.g. reactions in time and covers the entire range between transport-limited (shrinking core) and kinetically limited (reacting core) reaction regimes. The particles interact with a gas phase by heat and mass transfer taking into account the Stefan correction due to the gas outflow during conversion. Experiments carried out span a temperature range between T=300 and 900 °C for particle sizes varying between 8 and 17 mm. A comparison between measurements and predictions of drying models yielded satisfactory agreement only for the constant evaporation temperature model and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles. Likewise, predicted results of pyrolysis for the above-mentioned range of temperatures and sizes agreed satisfactorily with measurements.     

Synthesis of Bimodal PVC Latexes by Emulsion Polymerization: An Experimental and Modeling Study

The onset and extent of secondary particle formation in the seeded emulsion polymerization of vinyl chloride were investigated by performing a series of seeded polymerizations at different concentrations of seed latex and surfactant. It was found that, in general, both the onset and the extent of secondary particle formation are determined not only by the rate of homogeneous nucleation, but also by the rates of particle coagulation. A comparison of methods to compute the evolution of the particle size distribution in vinyl chloride emulsion polymerization was also carried out. For growth processes, the widely-used pseudo-bulk model gives correct answers. For processes involving particle formation, on the other hand, this model cannot be used because it neglects, among others, the effects of nucleation and coagulation on the radical number distribution. To surmount this problem, we propose to use the zero-one-two model, for which the full population balance equations are given here.     

THE MULTIPLE EQUILIBRIA IN THE COUPLED ATMOSPHERE-OCEAN SYSTEM

In this paper, a topography forced quasi-geostrophic baroclinic model and an SST (sea surface temperature) equation are used to set up a simple coupled atmosphere-ocean model The large-scale ocean current is nearly the Sverdrup flow. Two basic processes are considered in this system, i. e. the SST as a thermal forcing drives the atmospheric circulation and the ocean current produced by the wind redistributes the SST. Highly truncating and multiple scale method are used to simplify the model and obtain a low dimensional dynamic system. In this part, the qualitative vector in the phase space of the system is analysed and two stable equilibria are obtained. These two kinds of equailibria may be used to explain some features of the long-range anomalies of circulation.     

A study on dual solutions for water-based hybrid nanofluids flowing through convergent channel with dissipative heat transport

Over the years, the fluid flows in conjunction with thermal transport between non-parallel surfaces having converging nature is of great significance due to their broad spectrum of applications, which include fluid flows through nozzles in petroleum engineering, blood flow in arteries, lubrication systems, automobile radiators, thermal pumps, and water purification processes. Additionally, hybrid nanofluid is a prolific topic because of its thermal properties and potentials which provide a better performance even compared with common nanofluid in optimizing heat transfer. Therefore, this article presents a numerical simulation to investigate the heat transport characteristics of hybrid nanofluids in Jeffery-Hamel flow through a convergent channel. The considered hybrid nanofluids are composed of Copper (Cu) and Graphene-oxide (Go) as suspended nanoparticles and water as base fluid. This analysis further includes the impacts of viscous dissipation and magnetic field. A mathematical model for fluid flow and heat transfer are constructed with the help of cylindrical polar coordinates. The governing equations are converted into a system of ordinary differential equations (ODEs) by Lie symmetry group transformation. A MATLAB code is exercise to get the numerical solutions for flow and thermal distributions. An interesting phenomenon is that dual solutions are obtained in the computation. Thus, a comprehensive discussion is included on the dual solutions for various involved variables. The current findings may be employed in petroleum science, r biomedical scientists, polymer industry, etc.     

A 2D electrohydrodynamic model for electrorotation of fluid drops

A theoretical analysis of spontaneous electrorotation of deformable fluid drops in a DC electric field is presented with a 2D electrohydrodynamic model. The fluids in the system are assumed to be leaky dielectric and Newtonian. If the rotating flow is dominant over the cellular convection type of electrohydrodynamic flow, closed-form solutions for drops of small deformations can be obtained. Because the governing equations are in general nonlinear even when drop deformations are ignored, the general solution for even undeformed drop takes a form of infinite series and can only be evaluated by numerical means. Both closed-form solutions for special cases and numerical solutions for more general cases are obtained here to describe steady-state field variables and first-order drop deformations. In a DC electric field of strength beyond the threshold value, spontaneous electrorotation of a drop is shown to occur when charge relaxation in the surrounding fluid is faster than the fluid inside the drop. With increasing the strength of the applied electric field from the threshold for onset of electrorotation, the axis of drop contraction deviates from from that of the applied electric field in the direction of the rotating flow with an angle increasing with the field strength.