Results 1 - 10 of 5804
Results 1 - 10 of 5804. Search took: 0.03 seconds
|Sort by: date | relevance|
[en] Amphiphilic molecules (surfactants) consist of two opposing parts - a water-soluble moiety and a water-insoluble one - which are chemically bonded. Consequently, above a certain threshold concentration in aqueous solution (critical micellar concentration, cmc) surfactants self-assemble into aggregates. Aqueous solutions containing linear, flexible chain molecules (polymers) and surfactants exhibit self-assembly at much lower surfactant concentrations. This feature offers a delicate control over the physical properties of the solution, which is used in numerous applications. We study theoretically the onset of self-assembly in such polymer-surfactant systems. Focusing on the effect of the surfactant on polymer conformation and using a conjecture of local instability of the polymer at the onset of self-assembly, we obtain several simple predictions: (i) the threshold concentration required for polymer-surfactant self-assembly (critical aggregation concentration, cac) is always lower than the cmc; (ii) in charged systems the cac increases with the concentration of added salt and is almost independent of polymer charge; (iii) in weakly interacting systems the cac follows changes in the cmc roughly linearly. We further use the special case of interactions between surfactants and amphiphilic polymers to demonstrate the crucial role of chain conformation in the self-assembly. The predictions are supported by available experiments
[en] A Failure that happened sometimes ago in the sintering furnace of HR-05 PEBN-BATAN became a driving force of the investigation to find out the reason of the failure and to review its safety system. From the component level analysis of its electrical system, it is concluded that the failure is caused by the gas trapped inside the furnace while its heating system is on and gas outlet is closed, so that a small explosion is occurred to break the filament heater of the furnace. The failure of the outlet to open is caused by the weakness of the triggering instrument to the outlet while the explosion is caused by the weakness of the safety system design. The replacement of the triggering instrument according to the improved design is the best solution. However, an alternative solution is given if it is desired to keep the old triggering instrument still working in the system after being repaired. (author)
[en] We present the design of a contact atomic force microscope (AFM) that can be used to image solid surfaces in aqueous solution up to 150 degree C and 6 atm. The main features of this unique AFM are: (1) an inert gas pressurized microscope base containing stepper motor for coarse advance and the piezoelectric tube scanner; (2) a chemically inert membrane separating these parts from the fluid cell; (3) a titanium fluid cell with fluid inlet-outlet ports, a thermocouple port, and a sapphire optical window; (4) a resistively heated ceramic booster heater for the fluid cell to maintain the temperature of solutions sourced from a hydrothermal bomb; and (5) mass flow control. The design overcomes current limitations on the temperature and pressure range accessible to AFM imaging in aqueous solutions. Images taken at temperature and pressure are presented, demonstrating the unit-cell scale (<1 nm) vertical resolution of the AFM under hydrothermal conditions. copyright 1998 American Institute of Physics
[en] This deals with 6 sigma quality performance introducing company which has 6 sigma quality management, 6 sigma quality activity and customer, secret of success of 6 sigma quality management, what 6 sigma is, 6 sigma quality management propel system 5 propel steps of project like point of 6 sigma, flow of problem solution, tool for propel of project, performance of CTQ and total customer satisfaction, and quality management system and 6 sigma quality.
[en] The electrochemical pretreatment of aqueous solutions of synthetic surfactants in a diaphragm elelctrolyzer was used in order to diminish surfactant interference. The determination of cadmium, lead, and copper by stripping voltammetry with a mercury-film electrode in model solutions of cetylpyriridinium chloride, sodium lauryl sulfate, and OP-10 was taken as an example. It was found that the reproducibility of anodic peaks of the elements was improved, and the linearity of calibration characteristics was recovered; however, the sensitivity was not always as high as the value in the blank experiment
[en] The problem of uniqueness of the low-resolution shape determination from small-angle scattering by isotropic monodisperse systems is considered. The particle shape is represented by the envelope function parameterized using spherical harmonics as described in a previous paper. Computer simulations are made on the model bodies with sharp boundaries exactly represented by spherical harmonics. If the number of independent parameters describing the shape is 1 to 1.5 times the number of Shannon channels covered by the data set, the shape restoration is found to be unique and stable with respect to the random and systematic errors. The resolution limits of the straightforward shape determination are connected to the computational accuracy of the model intensities; with current algorithms, shapes described by 15 to 20 independent parameters can be uniquely determined. The results from a basis for an ab initio low-resolution shape determination in terms of spherical harmonics. (orig.)
[en] The use of linearly or circularly polarized light in the absorption or excitation beam in spectroscopic studies involving lanthanide ions, and the analysis of emitted light polarization has provided useful information concerning molecular structure, excitation state dynamics and energetics. Linear polarization studies may be used to aid in the assignment of crystal field components of electronic transitions, and circular polarization may be employed as a probe of chiral structure and structural changes. Examples of several of the different experimental techniques are presented and discussed. (author)
[en] This book introduces the invention as a tool to overcome IMF crisis. These are the titles of the way to create invention and idea : what is idea? everyone can create something, have a confidence, this is patent, replace or change something, invention is not logical, challenge the normal law, throw away stereotype, movement of idea, original imagination, there are a lot of solutions, there is no expert, have a positive thought, why does inventor invent? necessity is invention of mother, three stage of idea and invention and imitation for invention.
[en] Colloidal suspensions of charge-stabilized polystyrene latex spheres in near-critical mixtures of 2,6-lutidine and water aggregate reversibly on the side of the coexistence curve rich in the nonpreferred liquid. We have used static light scattering and a Zimm analysis to determine the second virial coefficient B2 for this system. Measurements were made as a function of temperature for different solvent compositions. On the aggregation side of the coexistence curve, as the temperature is brought near but not into the aggregation zone, the virial coefficient plunges through zero to large, negative values. On the nonaggregating side of the coexistence curve, the virial coefficient drops to a small negative value very close to coexistence. On the critical trajectory we have observed similar behavior of the virial coefficient to that seen on the aggregating side even though aggregation does not occur on this thermodynamic trajectory. We have also used lower surface charge density particles where the aggregation occurs on the opposite side of the coexistence curve. The results are similar to those just described for the high surface charge density particles. The combined evidence points to a gradual and continuous change in solvent fluctuation-colloidal particle interaction near the solvent coexistence curve, as solvent composition is varied through the critical composition. copyright 1996 The American Physical Society
[en] By using the algebraic Bethe ansatz, we find the exact solution of Perk-Schultz model with general open boundary conditions. The Bethe ansatz equation and the eigenvalue of the transfer matrix are obtained, which depends on two free parameters dominating the different grade boundary. Under the special condition m=1 , the results in present paper give the solution of multichannel t-J model with general boundary condition. Our results also recover those obtained by A. Gonzalez-Ruiz, Nucl. Phys. B 424 [FS] (1994) 468