Improving separation capability of regenerated cellulose ultrafiltration membrane by surface modification

In this study we introduced dialdehyde groups to a commercial regenerated cellulose (RC) ultrafiltration membrane by periodate oxidation. They were further converted to nitrogen-containing derivatives by Schiff base reaction with diethylenetriamine (DETA). The modified membrane was challenged with aqueous solution containing Pb(II) metal ions. The different variables affecting the rejection of lead ion by membrane including oxidization time, concentration of DETA, initial metal ion concentration and pH of the solution were elucidated. The membranes were characterized by FTIR-ATR, SEM, EDAX and elemental analyses. The process efficiency was enhanced by improving the oxidization time up to a certain period. In our case this was diminished after 9 h due to deterioration in the membrane integrity. The Pb²⁺ removal was facilitated by increasing feed pH and DETA concentration. This was diminished for more concentrated metal ion in the feed. Membrane regeneration was successfully utilized using 0.1 M HNO₃ solution. The removal capability of the regenerated membranes was maintained even after four cycles.     

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800 MHz ¹H/¹⁵N and ¹H/¹³C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.     

Numerical modeling of nonlinear deformation and buckling of composite plate-shell structures under pulsed loading

Nonlinear three-dimensional problems of dynamic deformation, buckling, and posteritical behavior of composite shell structures under pulsed loads are analyzed. The structure is assumed to be made of rigidly joined plates and shells of revolution along the lines coinciding with the coordinate directions of the joined elements. Individual structural elements can be made of both composite and conventional isotropic materials. The kinematic model of deformation of the structural elements is based on Timoshenko-type hypotheses. This approach is oriented to the calculation of nonstationary deformation processes in composite structures under small deformations but large displacements and rotation angles, and is implemented in the context of a simplified version of the geometrically nonlinear theory of shells. The physical relations in the composite structural elements are based on the theory of effective moduli for individual layers or for the package as a whole, whereas in the metallic elements this is done in the framework of the theory of plastic flow. The equations of motion of a composite shell structure are derived based on the principle of virtual displacements with some additional conditions allowing for the joint operation of structural elements. To solve the initial boundary-value problem formulated, an efficient numerical method is developed based on the finite-difference discretization of variational equations of motion in space variables and an explicit second-order time-integration scheme. The permissible time-integration step is determined using Neumann's spectral criterion. The above method is especially efficient in calculating thin-walled shells, as well as in the case of local loads acting on the structural element, when the discretization grid has to be condensed in the zones of rapidly changing solutions in space variables. The results of analyzing the nonstationary deformation processes and critical loads are presented for composite and isotropic cylindrical shells reinforced with a set of discrete ribs in the case of pulsed axial compression and external pressure.Scientific Research Institute of Mechanics, Lobachevskii Nizhegorodsk State University, N. Novgorod, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 6, pp. 757–776, November–December, 1999.     

A modified Fourier series solution for vibration analysis of truncated conical shells with general boundary conditions

Free vibration analysis of truncated conical shells with general elastic boundary conditions is presented in this paper. An accurate modified Fourier series solution is developed, in which, regardless of the boundary conditions, each displacement of the conical shell is invariantly expressed as a new form of improved series expansions composed of a standard Fourier series and closed-form auxiliary functions introduced to ensure and accelerate the convergence of the series expansion. All the expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh–Ritz method. By using the present method, conical shells with arbitrary boundary conditions including all classical and elastic end restraints can be solved in a unified form. The accuracy and convergence of the current approach are validated by numerical examples and comparison with FEM results and those from the literature, and excellent accuracy is demonstrated. Comprehensive studies on the effects of elastic restraint parameters, semi-vertex angle and the ratio of length to radius are also reported. Some new results are presented for cases with elastic boundary restraints which may serve as benchmark solution for future researches.     

Elastoplastic stress analysis for cylindrical shell with flat strip imperfection

Based on unequidistant B-spline function, generalized spline subdomain displacement mode of rotational shell is obtained by taking double-direction interpolation of spline. The elastoplastic constitutive equation of shells is established by using the endochronic theory.According to the initial deflection theory of shells, the elastoplastic stress analysis of cylindrical shells with flat strip geometrical imperfection is studied. Numerical results show that the geometrical imperfection has a great effect on the stress distribution of shells.     

Static cylindrical matter shells

Static cylindrical shells composed of massive particles arising from matching of two different Levi–Civita space-times are studied for the shell satisfying either an isotropic or an anisotropic equation of state. We find that these solutions satisfy the energy conditions for certain ranges of the parameters.     

A rapid two-step chromatographic method for the quantitative determination of vitellogenin in fish plasma

By combining anion-exchange membrane purification with high-performance size-exclusion chromatography (HPSEC) analysis, a two-step chromatographic method was developed for the determination of vitellogenin (Vtg) in fish plasma. Most plasma protein interferences can be removed during anion-exchange membrane purification process. Vtg is eluted from the size-exclusion chromatography column with a retention time of about 9 min and is characterized based on the native molecular weight, with a limit of quantification of 20 g Vtg mL^–1 plasma. The spiked recovery and interassay variability were better than 80% and 4.8%. This method was successfully applied to analyze the plasma Vtg levels of loach (Misgurnus angaillicaudatus) and sea catfish (Enchelyopus elongatus). In addition to all the female fish, Vtg is detected in 75% of male loaches and 100% of male sea catfish. The result indicates that some chemicals or unknown factors with estrogenic activity have induced male fish to produce Vtg.     

Torocyte shapes of red blood cell daughter vesicles

The shape of the newly described torocyte red blood cell endovesicles induced by octaethyleneglycol dodecylether (C12E8) is characterized. A possible explanation for the origin and stability of the observed torocyte endovesicles is suggested. Three partly complementary mechanisms are outlined, all originating from the interaction of C12E8 molecules with the membrane. The first is a preferential intercalation of the C12E8 molecule into the inner membrane layer, resulting in a membrane invagination which may finally close, forming an inside-out endovesicle. The second is a preference of the C12E8-induced membrane inclusions (clusters) for small local curvature which would favour torocyte endovesicle shape with large regions of small or even negative membrane mean curvatures, the C12E8 membrane inclusion being defined as a complex composed of the embedded C12E8 molecule and some adjacent phospholipid molecules which are significantly distorted due to the presence of the embedded C12E8 molecule. The preference of the C12E8 inclusions for zero or negative local curvature may also lead to the nonhomogeneous lateral distribution of the C12E8 inclusions resulting in their accumulation in the membrane of torocyte endovesicles. The third possible mechanism is orientational ordering of the C12E8-induced inclusions in the regions of torocyte endovesicles with high local membrane curvature deviator.     

Synthesis of new fluorescently labeled glycosylphosphatidylinositol (GPI) anchors

The borondipyrromethene (BODIPY) labeled new glycosylphosphatidylinositol (GPI) molecules were synthesized as cellular probes to study the chemical basis of microdomain organization of GPI-anchored proteins and cholesterol in plasma membrane. The synthesis enabled by a new stereo-selective glycosylation of myo-d-inositol acceptor led to the preparation of optically pure glucosaminyl-(1-6)-α-phosphatidyl-myo-d-inositol and its unnatural stereoisomer.