An experimental study on effects of solid concentration and ζ-potential on pseudoplastic flow of suspensions

The pseudoplastic flow of suspensions, alumina or styrene-acrylamide copolymer particles in water or an aqueous solution of glycerin has been studied by the step-shear-rate method. The relation between the shear rate,D, and the shear stress,0322415l257t05/xxlarge964.gif" alt="tau" align="BASELINE" BORDER="0">, in the step-shear-rate measurements, where the state of dispersion was considered to be constant, was expressed as0322415l257t05/xxlarge964.gif" alt="tau" align="BASELINE" BORDER="0"> = AD ^1/2 +CD. The effective solid volume fraction,ø _F, andA were dependent on the shear rate and expressed byø _F =aD ^b andA = 0322415l257t05/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">D ^{0322415l257t05/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">}. Combining the above relations, the steady flow curve was expressed by0322415l257t05/xxlarge964.gif" alt="tau" align="BASELINE" BORDER="0"> = 0322415l257t05/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">D ^{1/2 + 0322415l257t05/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">} +0322415l257t05/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"> ₀ (1 013; a D ^b/0.74)^013;1.85 D, where0322415l257t05/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"> ₀ is the viscosity of the medium.With an increase in solid volume fraction and a decreases in the absolute value of the0322415l257t05/xxlarge950.gif" alt="zeta" align="MIDDLE" BORDER="0">-potential, the flow behavior of the suspensions changed from Newtonian (0322415l257t05/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"> = 0322415l257t05/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = b = 0), slightly pseudoplastic (0322415l257t05/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = b = 0), pseudoplastic (0322415l257t05/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = 0) to a Bingham-like behavior.The change in viscosity of the medium had an effect on the change in the effective volume fraction.     

Thermoelastoplastic axisymmetric stress-strain state of laminated orthotropic shells

A method is proposed for the numerical analysis of the thermoelastoplastic stress-strain state of laminated shells of revolution, made of isotropic and orthotropic materials, under axisymmetric loading. The method is based on the Kirchhoff-Love hypotheses for a layer stack, the theory of deformation along paths of small curvature for isotropic materials, and Hill01618/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s theory of flow with isotropic hardening for orthotropic materials. The problem is solved by the method of successive approximations. A numerical example is given.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 84013;91, December 2004.     

Asymptotic Modeling of Nonlinear Wave Processes in Shock‐Loaded Elastoplastic Materials

Nonlinear wave processes in shock08.gif" alt="dash" align="MIDDLE" BORDER="0">loaded elastoplastic materials are modeled. A comparison of the results obtained with experimental data and numerical solutions of exact systems of dynamic equations shows that the model equations proposed qualitatively describe the stress08.gif" alt="dash" align="MIDDLE" BORDER="0">distribution evolution in both the elastic08.gif" alt="dash" align="MIDDLE" BORDER="0">flow and plastic08.gif" alt="dash" align="MIDDLE" BORDER="0">flow regions and can be used to solve one08.gif" alt="dash" align="MIDDLE" BORDER="0"> and two08.gif" alt="dash" align="MIDDLE" BORDER="0">dimensional problems of pulsed deformation and fracture of elastoplastic media.     

Mixed Formulations of Bending Problems for Homogeneous Elastic Plates and Beams

Mixed formulations of bending problems for homogeneous plates (beams) are proposed, whose essence is that the deformation of a plate (beam) near its fixed boundary is described by the three0056/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">dimensional elasticity equations, and the remaining part by the conventional equations of plate (beam) bending. At the interface between these regions, the solutions of these equations are joined. The mixed formulation allows one to describe the three0056/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">dimensional stress state in the neighborhood of the fixed boundaries of plates (beams) and take into account the complex nature of the fixing conditions. Finite0056/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">element implementation is more efficient for the mixed formulations of plate (beam) bending problems than for the well0056/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">known three0056/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">dimensional formulations.     

First- and second-order sensitivities of beams with respect to cross-sectional cracks

This paper deals with a variational formulation for the sensitivity problem of beam systems in the context of deformable solids with cracks. Natural frequencies are defined as state variables involved in the energy functional of the system, while the crack0j01n16/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s length and position are treated as system parameters. The hierarchical equation system is formed and solved for the first and second derivatives of the natural frequency functions with respect to the crack0j01n16/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s length and position. An analytical procedure for calculations of the second-order sensitivities of natural frequencies is proposed for the non-symmetrical equation system operator. Numerical algorithms are worked out and implemented computationally. Analytical and numerical aspects of the problem are discussed in detail through a number of illustrative results.The support of this work by the State Committee for Scientific Research (KBN) under Grant No. 4-050-0148/17-98-00 is gratefully acknowledged.     

Mixing Layer on the Lee Side of an Obstacle

Two0330311p8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">layer miscible flow above an uneven bottom is considered. A mathematical model in the shallow0330311p8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">water approximation is constructed for the development of a turbulent layer between homogeneous layers of different density in a two0330311p8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">layer channel flow over a local obstacle. The influence of the mixing process on the formation of an initial segment of the steady0330311p8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">state density0330311p8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">stratified flow on the leeward side of the obstacle is studied.     

Molecular Dynamics Simulations of a β-Hairpin Fragment of Protein G by Means of Atom-Bond Electronegativity Equalization Method Fused into Molecular Mechanics (ABEEMσπ/MM)

There are some controversial opinions about the origin of folding β‐hairpin stability in aqueous solution. In this study, the structural and dynamic behavior of a 16‐residue β‐hairpin from B1 domain of protein G has been investigated at 280, 300, 350 and 450 K using molecular dynamics (MD) simulations by means of Atom‐Bond Electronegativity Equalization Method Fused into Molecular Mechanics i.e., ABEEMδπ/MM and the explicit ABEEM‐7P water solvent model. In addition, a 300 K simulation of one mutant having the aromatic residues substituted with alanines has been performed. The hydrophobic surface area, hydrophilic surface area and some structural properties have been used to measure the role of the hydrophobic interactions. It is found that the aromatic residues substituted with alanines have shown an evident destabilization of the structure and unfolding started after 1.5 ns. It is also found that the number of the main chain hydrogen bonds have different distributions through three different simulations. All above demonstrate that the hydrophobic interactions and the main chain hydrogen bonds play an important role in the stability of the folding structure of β‐hairpin in solution. Furthermore, through the structural analyses of the β‐hairpin structures from four temperature simulations and the comparison with other MD simulations of β‐hairpin peptides, the new ABEEMδπ force field can reproduce the structural data in good agreement with the experimental data.     

Theoretical Studies on the Halogen Bond between Propargyl Radical and Dihalogen Molecules

MP2/aug‐cc‐pVDZ calculations are carried out on the geometries, vibrational frequencies, interaction energies and topological properties for the π‐type halogen‐bonded complexes between propargyl radical and dihalogen molecules ClF, BrF and BrCl. There are two kinds of geometries: complex ( a ) involves the interaction between the X (X=Cl, Br) atom and the midpoint of C(1) –C(2) bond, complex ( b ) involves the interaction between the X atom and C(3) atom. The lengths of the halogen bond, the frequencies of the halogen bond, the elongation extent of the X–Y (XY=ClF, BrF, BrCl) bond, topological parameters at the BCPs of the halogen bond and X–Y bond are all well consistent with the interaction energies. The interaction of complex ( a ) is stronger than that of complex ( b ); the interaction of propargyl···BrF is stronger than that of propargyl···ClF and propargyl···BrCl. For the complexes ( a ) and ( b ), the charge transfer is observed from propargyl radical to XY, the atomic energy, the dipolar polarization, and the volume of the halogen atom X decrease upon complex formation.     

Design and synthesis of a new series of amphiphilic peptide-β-cyclodextrins as phase transfer carriers for glucosamine

A new series of amphiphilic β-cyclodextrins were designed and synthesized by grafting peptide chains on to all primary hydroxyl groups via ester bond formation. The desired amphiphilic structures have been produced from ester connection between the C-6 of β-cyclodextrin and the carboxyl group of N-acetylated resides: H₂N-Leu-COOH, H₂N-Leu-Gly-COOH, H₂N-Leu-Gly-Leu-COOH, and H₂N-Leu-Gly-Leu-Gly-COOH (3a-d). The synthetic pathway involves selective bromination of all primary hydroxyls of β-cyclodextrins and then substitution with the carboxylate moiety of the mentioned N-acetyl residues in the presence of DBU (1,8-diazabicyclo[5,4,0]undec-7-ene). The ability of the synthetic compounds for extraction and phase transfer of glucosamine, as a hydrophilic organic compound, was then studied. The results showed a considerable ability of these amphiphilic compounds for extraction and a selective tendency of 3c for phase transfer of glucosamine.