New,strong cationic hydrogels: Preparation of N,N,N′,N′‐tetraallyl piperazinium dibromide and its copolymers with N,N‐diallyl morpholinium bromide

N,N,N′,N′‐tetraallyl piperazinium dibromide (TAP) has been prepared in high yields by quaternization of N,N′‐diallyl piperazine with allyl bromide. Herein, we have described preparation of nonhydrolysable, strong, cationic hydrogels by copolymerization of TAP with N,N‐diallyl morpholinium bromide (DAM) in the presence of t‐butyl hydroperoxide as initiator in aqueous solutions. Because the monomer and crosslinker involved consist of quaternary amine functions, these hydrogels are fully cationic and do not carry hydrolysable groups. Contrary to expectations, the quaternary amine hydrogels presented do not show any super absorbency, instead dry gel particles in water undergo spontaneous disintegration with an audible bursting of the particles due to instantaneous, high osmotic pressure. Whereas, in KBr or HBr solutions, the swellings are relatively slow. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1006–1013, 2000     

A continuum theory of dense suspensions

A continuum theory is introduced for viscous fluids carrying dense suspensions (such as blood) or emulsions of arbitrary shape and inertia. Suspended particles possess microinertia that make the mixture an anisotropic fluid whose viscosity changes with motion and orientation of suspensions. The microinertia balance law coupled with the equations of motion of an anisotropic fluid govern the ultimate outcome. By means of the second law of thermodynamics, constitutive equations are obtained in terms of the frame-independent tensors. In a special case, a theory of bar-like suspensions is obtained. The field equations, boundary and initial conditions are given for both the arbitrarily-shaped suspensions and the bar-like suspensions. The theory is demonstrated with the solution of the channel flow problem. The mean viscosity of the fluid with suspensions is determined. The motions of suspensions down flow are demonstrated.     

Performance Evaluation Models for Single-item Periodic Pull Production Systems

A number of pull production systems reported in the literature are found to be equivalent to a tandemqueue so that existing accurate tandem-queue approximation methods can be used to evaluate such systems. In this study, we consider developing an exact performance evaluation model for a non-tandemqueue equivalent pull production system using discrete-time Markov processes. It is a periodically controlled serial production system in which a single-item is processed at each stage with an exponential processing time in order to satisfy the Poisson finished product demand. The selected performance measures are throughput, inventory levels, machine utilizations and service level of the system. For large systems, which are difficult to evaluate exactly because of large state-spaces involved, we also propose a computationally feasible approximate decomposition technique together with some numerical experimentations.     

Micromorphic description of turbulent channel flow

The simple microfluid theory of Eringen is employed to determine the velocity profile and microgyrations in a steady flow of viscous fluids between two parallel walls. The shearing stress, microrotations, microinertia and Reynold stresses are determined. The results are compared with the experimental work of Laufer.     

Single Machine Earliness-Tardiness Scheduling Problems Using the Equal—Slack Rule

The purpose of this paper is to analyse a special case of the non-pre-emptive single machine scheduling problem where the distinct due dates for each job are related to processing times according to the Equal–Slack rule. The scheduling objective is to minimize the sum of earliness and tardiness penalties. After determining some properties of the problem, the unrestricted case is shown to be equivalent to a polynomial time solvable problem, whereas the restricted case is shown to be NP-hard, and suggestions are made for further research.     

Preparation of poly(acrylonitrile-co-methyl acrylate)/cellulose composite membranes and their application in wastewater treatment

In this study, new poly(acrylonitrile-co-methyl acrylate)/cellulose composite membranes were prepared firstly and then characterized. Then they were used in the removal of Fe(III) and Co(II) ions from wastewater with a stirred ultrafiltration cell. Also, alginic acid polymer was used as complexing agent to enhance the retention. In the filtration of Fe(III) and Co(II) solutions, the effects of pH, concentration of solutions, and pressure on the retention percentage were examined. Aqueous solutions of Fe(III) and Co(II) were filtrated at the stirred velocity of 400?rpm. The maximum retention percentage was found as 78.66% for Fe(III) solution at the pH of 3.3, concentration of 0.3?×?10^?4 M Fe(III) solution, pressure of 40?psi by using 2.5 (w/v)% Poly(acrylonitrile-co-methyl acrylate)/cellulose composite membranes. For Co(II) solutions the maximum retention percentage was found as 77% at the pH of 6, concentration of 0.3?×?10^?4 M Co(II) solution, pressure of 50?psi by using 2.5 (w/v)%Poly(acrylonitrile-co-methyl acrylate)/cellulose composite membranes.