Brownian flocculation of polymer colloids in the presence of a secondary minimum

Most analyses of Brownian flocculation apply to conditions where London–van der Waals attractive forces cause particles to be strongly bound in a deep interparticle potential well. In this paper, results are reported that show the interaction between primary- and secondary-minimum flocculation when the interparticle potential curve reflects both attractive and electrostatic repulsive forces. The process is highly time-dependent because of transfer of particles from secondary- to primary-minimum flocculation. Essential features of the analysis are corroborated by experiments with 0.80-μm polystyrene spheres suspended in aqueous solutions of NaCl over a range of ionic strengths. In all cases, experiments were restricted to the initial stage of coagulation, where singlets and doublets predominate.

Kinetics and thermodynamics of T cell receptor– autoantigen interactions in murine experimental autoimmune encephalomyelitis

In the current study, cellular and molecular approaches have been used to analyze the biophysical nature of T cell receptor (TCR)–peptide MHC (pMHC) interactions for two autoreactive TCRs. These two TCRs recognize the N-terminal epitope of myelin basic protein (MBP1–11) bound to the MHC class II protein, I-Au, and are associated with murine experimental autoimmune encephalomyelitis. Mice transgenic for the TCRs have been generated and characterized in other laboratories. These analyses indicate that the mice either develop encephalomyelitis spontaneously (172.10 TCR) or only if immunized with autoantigen in adjuvant (1934.4 TCR). Here, we show that the 172.10 TCR binds MBP1–11:I-Au with a 4–5-fold higher affinity than the 1934.4 TCR. Consistent with the higher affinity, 172.10 T hybridoma cells are significantly more responsive to autoantigen than 1934.4 cells. The interaction of the 172.10 TCR with cognate ligand is more entropically unfavorable than that of the 1934.4 TCR, indicating that the 172.10 TCR undergoes greater conformational rearrangements upon ligand binding. The studies therefore suggest a correlation between the strength and plasticity of a TCR–pMHC interaction and the frequency of spontaneous disease in the corresponding TCR transgenic mice. The comparative analysis of these two TCRs has implications for understanding autoreactive T cell recognition and activation.

Large electrostatic differences in the binding thermodynamics of a cationic peptide to oligomeric and polymeric DNA.

Results presented here demonstrate that the thermodynamics of oligocation binding to polymeric and oligomeric DNA are not equivalent because of long-range electrostatic effects. At physiological cation concentrations (0.1-0.3 M) the binding of an oligolysine octacation KWK6-NH2 (+8 charge) to single-stranded poly(dT) is much stronger per site and significantly more salt concentration dependent than the binding of the same ligand to an oligonucleotide, dT(pdT)10 (-10 charge). These large differences are consistent with Poisson-Boltzmann calculations for a model that characterizes the charge distributions with key preaveraged structural parameters. Therefore, both the experimental and the theoretical results presented here show that the polyelectrolyte character of a polymeric nucleic acid makes a large contribution to both the magnitude and the salt concentration dependence of its binding interactions with simple oligocationic ligands.

Activation of polymer blend carbon nanofibres by alkaline hydroxides and their hydrogen storage performances

In the present work we study the hydroxide activation (NaOH and KOH) of phenol-formaldehyde resin derived CNFs prepared by a polymer blend technique to prepare highly porous activated carbon nanofibres (ACNFs). Morphology and textural characteristics of these ACNFs were studied and their hydrogen storage capacities at 77 K (at 0.1 MPa and at high pressures up to 4 MPa) were assessed, and compared, with reported capacities of other porous carbon materials. Phenol-formaldehyde resin derived carbon fibres were successfully activated with these two alkaline hydroxides rendering highly microporous ACNFs with reasonable good activation process yields up to 47 wt.% compared to 7 wt.% yields from steam activation for similar surface areas of 1500 m2/g or higher. These nano-sized activated carbons present interesting H2 storage capacities at 77 K which are comparable, or even higher, to other high quality microporous carbon materials. This observation is due, in part, to their nano-sized diameters allowing to enhance their packing densities to 0.71 g/cm3 and hence their resulting hydrogen storage capacities.

The Problem Sensitization Robotic Complex Drilling and Milling of Sandwich Shells of Polymer Composites

In clause is given robotic a complex for drilling and milling sandwich shells from polymeric composites. The machining of polymeric composite materials has technological problems. At drilling sandwich shells there is a probability of destruction of a drill from hit of the tool in a partition. The system sensibilization robotic complex for increase of reliability of work of the cutting tool of the small size is offered.

Variational and Lagrangian thermodynamics of thermal convection-- fundamental shortcomings of the heat-transfer coefficient.

Mode of access: Internet.

Interim report on the thermodynamics of chemical species important to rocket technology..

Mode of access: Internet.

Thermodynamics of small systems.

Bibliographical footnotes.

Dynamics and thermodynamics of planetary entry.

Includes bibliography.

Operation of polymer electrolyte membrane fuel cells with dry feeds: Design and operating strategies

The operation of polymer electrolyte membrane fuel cells (PEMFCs) with dry feeds has been examined with different fuel cell flow channel designs as functions of pressure, temperature and flow rate. Auto-humidified (or self-humidifying) PEMFC operation is improved at higher pressures and low gas velocities where axial dispersion enhances back-mixing of the product water with the dry feed. We demonstrate auto-humidified operation of the channel-less, self-draining fuel cell, based on a stirred tank reactor; data is presented showing auto-humidified operation from 25 to 115 degrees C at 1 and 3 atm. Design and operating requirements are derived for the auto-humidified operation of the channel-less, self-draining fuel cell. The auto-humidified self-draining fuel cell outperforms a fully humidified serpentine flow channel fuel cell at high current densities. The new design offers substantial benefits for simplicity of operation and control including: the ability to self-drain reducing flooding, the ability to uniformly disperse water removing current gradients and the ability to operate on dry feeds eliminating the need for humidifiers. Additionally, the design lends itself well to a modular design concept. (c) 2005 Elsevier B.V. All rights reserved.

Nanotrapping and the thermodynamics of optical tweezers

Particles that can be trapped in optical tweezers range from tens of microns down to tens of nanometres in size. Interestingly, this size range includes large macromolecules. We show experimentally, in agreement with theoretical expectations, that optical tweezers can be used to manipulate single molecules of polyethylene oxide suspended in water. The trapped molecules accumulate without aggregating, so this provides optical control of the concentration of macromolecules in solution. Apart from possible applications such as the micromanipulation of nanoparticles, nanoassembly, microchemistry, and the study of biological macromolecules, our results also provide insight into the thermodynamics of optical tweezers.