Dispersion, measurement

Blanton S A ef a/1997 Dielectric dispersion measurements of CdSe nanocrystals colloids observations of a permanent dipole moment Phys. Rev. Lett. 79 865... 

Both phases are siibstantiaUy in plug flow. Dispersion measurements of the hquid phase usuaUy report Peclet numbers, Uid /D, less than 0.2. With the usual smaU particles, the waU effect is negligible in commercial vessels of a meter or so in diameter, but may be appreciable in lab units of 50 mm (1.97 in) diameter. Laboratory and commercial units usuaUy are operated at the same space velocity, LHSy but for practical reasons the lengths of lab units may be only 0.1 those of commercial units. 

In addition to the expected 2,2-dimethyl- and 2a-methyl- compounds (7) and (8) the 2 -methyl-3-ketone (9) is obtained. Chemical evidence and optical rotatory dispersion measurements indicate that ring A in (7) and (9) is in the boat conformation. 

Olaj et /.124 proposed that termination of S polymerization involves substantial disproportionation. They analyzed the molecular weight distribution of PS samples prepared with either BPO or AIBN as initiator at temperatures in the range 20-90 °C and estimated kJkK to be ca 0.2. In a more recent study, Olaj et a/.149 determined the molecular weight distribution of PS samples prepared with photoinitiation at 60 and 85 °C and estimated values of kxproblems associated with estimating k-.vk , on the basis of dispersity measurements and determined that kxiiklc should be "substantially smaller" than suggested by Olaj et til.m... 

Stemerding (S16) has reported dispersion measurements in a column filled with 13-mm Raschig rings with water and air in countercurrent flow. The dispersion coefficient was observed to be essentially independent of the water flow rate and dependent on the air flow rate only. For increasing air flow rates, the dispersion coefficient passed through a maximum. 

Shang, H.-T., 1981, Chromatic dispersion measurement by white light interferometry on meter-length single-mode optical fiber, J. Opt. Soc. Am., 71, 1587... 

Figure 4. Platinum Agglomeration and Dispersion Measured by Ion Scattering.

The effectiveness of a number of crude oil dispersants, measured using a variety of evaluation procedures, indicates that temperature effects result from changing viscosity, dispersants are most effective at a salinity of approximately 40 ppt (parts per thousand), and concentration of dispersant is critical to effectiveness. The mixing time has little effect on performance, and a calibration procedure for laboratory dispersant effectiveness must include contact with water in a manner analogous to the extraction procedure otherwise, effectiveness may be inflated [587]. Compensation for the coloration produced by the dispersant alone is important only for some dispersants. 

Fig. 2.6.10 Specialized experimental set-up for microfluidic flow dispersion measurements. Fluid is supplied from the top, flows via a capillary through the microfluidic device to be profiled and exits at the bottom. The whole apparatus is inserted into the bore of a superconducting magnet. Spatial information is encoded by MRI techniques, using rf and imaging gradient coils that surround the microfluidic device. They are symbolized by the hollow cylinder in the figure. After the fluid has exited the device, it is led through a capillary to a microcoil, which is used to read the encoded information in a time-resolved manner. The flow rate is controlled by a laboratory-built flow controller at the outlet [59, 60].

In case of unsymmetric distributed measured values, the dispersion factor v can be used to estimate a relative dispersion measure that has the character... 

Useful measures of precision could be derived from relative dispersion measures, namely by their differences from 1, e.g., the precision of an analytical procedure... 

Fig. 1. Comparison of amide V VCD for an identical sample of poly-L-lysine in D20 as measured on the UIC dispersive instrument (top) and on the ChirallRFT-VCD instrument (at Vanderbilt University, kindly made available by Prof. Prasad Polavarapu). Sample spectra were run at the same resolution for the same total time ( 1 h) in each case. The FTIR absorbance spectrum of the sample is shown below. VCD spectra are offset for sake of comparison. Each ideal baseline is indicated by a thin line, the scale providing a measure of amplitude. Noise can be estimated as the fluctuation in the baseline before and after the amide V, which indicates the S/N advantage of the single band dispersive measurement.

Recent applications of relaxation dispersion measurements to concrete or cement-based materials are promising for characterizing reactive nanopor-ous materials, the structure of which may evolve over time (75-78). The MRD profiles have provided, for the first time, a direct means for characterizing the specific surface area, Sp, of a hydrated cement-based material (79), without exposing the sample to extremes of temperature or pressure (80-83). The interest in such a surface area is to provide information on the microsctruc-ture and its impact on macroscopic or structural properties. The method is based on a clear separation of surface and bulk contributions of the overall... 

For this reason, a detailed description of the console in this paper is superfluous, except for a brief list of those features which, in our opinion, any research-grade FFC console should possess in order to guarantee maximum versatility of NMR dispersion measurements. 

From the H/M values for the catalysts NiSn-BM (Sn/Ni = 0.29) and PtSn-BM (Sn/Pt = 0.71), and the H/M values for the corresponding monometallic ones, it can be inferred that Sn blocks about 70% of the originally accessible M atoms. For these systems, based on the dispersion measured for Pt and Ni, the atomic ratios Sn/M correspond to values higher than 1. Notably, even in these cases, an important portion of the metallic surface has sites accessible to hydrogen dissociative adsorption, which is essential for the phase to be active in hydrogenation reactions. 

The physical and chemical properties of the AChR have been elucidated. Optical rotatory dispersion measurements indicate that the receptor consists of about 34% helix and 28-30% P-sheet structure—a high proportion of ordered secondary structure. Some carbohydrates are part of the molecule. The DNA encoding the receptor has been cloned and sequenced, revealing the complete amino acid sequence of the subunits. 

Chapter E is devoted to the mean-square dipole moment and mean rotational relaxation time derived from dielectric dispersion measurements. Typical data, both in helieogenic solvents and in the helix-coil transition region, are presented and interpreted in terms of existing theories. At thermodynamic equilibrium, helical and randomly coiled sequences in a polypeptide chain are fluctuating from moment to moment about certain averages. These fluctuations involve local interconversions of helix and random-coil residues. Recently, it has been shown that certain mean relaxation times of such local processes can be estimated by dielectric dispersion experiment. Chapter E also discusses the underlying theory of this possibility. 

Helical fraction is the only quantity that can be estimated experimentally among the various quantities characterizing the conformation of polypeptides. There are several means of estimating helical fraction (15,16). The most commonly used is based on the assumption that the Moffitt-Yang parameter b0 derived from optical rotatory dispersion measurement is a linear function of fN. Thus... 

Dielectric dispersion measurements also provide a means of determining rotational diffusion coefficients or mean rotational relaxation times of solute molecules. In principle, data for these hydrodynamic quantities can be used for a... 

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