H. Z. Cummins

Light Beating Spectroscopy

During the past decade, light beating spectroscopy has developed into a major new technique for analyzing optical fields with an effective resolution orders of magnitude greater than was available with traditional spectroscopic techniques. In all the early light beating experiments, the optical field under study illuminated a photodetector whose output current was then analyzed with an audio or r.f. spectrum analyzer in order to determine the photocurrent power spectrum.

Rayleigh and Brillouin Scattering in Liquids: The Landau—Placzek Ratio

The classical theory of light scattering in liquids leading to the Landau—Placzek ratio for the intensities of the Rayleigh and Brillouin components is reviewed. A simple modification is proposed in which the effect of dispersion is included by defining a hypersonic compressibility βshs=1/(ρvhs2), where vhs is found from the experimentally measured Brillouin shifts. Further modification is presented to account for dispersion in the electrostriction. A modification of the Landau—Placzek equation due to Fabelinskii is discussed and shown to be essentially equivalent to our equation.The predictions of the ratios are evaluated for 11 common liquids and compared with new experimental values reported in this paper and with other values taken from the literature. It is found that in most cases the dispersion modification leads to ratios in considerably better agreement with the experimental values than does the simple Landau—Placzek equation.We present our measurements of the ratio of the Rayleigh and Brillouin ...

Relaxational dynamics in supercooled liquids: experimental tests of the mode coupling theory

A brief review of the mode coupling theory of the liquid-glass transition is presented. The major experimental techniques that have been used to test its predictions are described. The results of these tests for five glass-forming materials are summarized along with a brief discussion of other materials currently under study.

Fibrin polymerization and release of fibrinopeptide B by thrombin

Abstract Although it is well known that thrombin releases fibrinopeptide A (FPA) more rapidly than fibrinopeptide (FPB) from fibrinogen different opinions have been expressed as to whether fibrin I (FPA release) and II (FPB release) are sequential or simultaneous. Evidence has been presented that FPB release depends on the polymerization of fibrin and the finding that the tetrapeptide gly-pro-arg-pro inhibits fibrin formation provides a new tool to investigate the effect of polymerization. The radioimmunoassay technique which permits the initial rates of the release reactions to be accurately measured at low concentrations of reactants was used to investigate FPB release. In the absence of gly-pro-arg-pro the FPB release pattern showed three phases - an initial slow and a second more rapid phase both of which were at a constant rate and a final phase with decreasing rate as the substrate concentration fell. Gly-pro-arg-pro at appropriate concentrations inhibited fibrin polymerization as indicated by optical density and light scattering techniques as well as by gel filtration on Sephadex G-200. FPA release and the initial rate of FPB release were unaffected. The second phase of rapid FPB release was abolished indicating that this increased rate is entirely dependent on the polymerization of fibrin I. Under one set of specified conditions the initial release rates of FPB by thrombin from different substrates were 15.8 pmol/min (fibrinogen), 14.0 pmol/min (fibrinogen plus gly-pro-arg-pro), 27.4 pmol/min (fibrin I monomer) and 164.4 pmol/min (fibrin I polymer). The data indicate that fibrin I and II formation are not sequential but simultaneous and that it is the more rapid formation of fibrin I which results in the appearance of a sequential reaction. It is suggested that a number of other reactions in the hemostatic system including fibrinolysis which appear to be sequential are also simultaneous.

BRILLOUIN SCATTERING SPECTRA OF CRYSTALLINE QUARTZ, FUSED QUARTZ AND GLASS

The Brillouin scattering spectra of crystalline quartz, fused quartz and Pyrex glass have been observed. The crystalline quartz spectrum contains three doublets corresponding to one longitudinal and two transverse acoustic modes, whereas the spectra of used quartz and Pyrex glass have one longitudinal and one transverse component each, as is expected for isotropic solids. From the lack of observable broadening of any of the Brillouin components, it is concluded that the room temperature attenuation coefficient α of both longitudinal and transverse phonons at 10 to 20 Gc is less than 103 cm−1.

Preparation and characterization of monodisperse unilamellar phospholipid vesicles with selected diameters of from 300 to 600 nm

A method has been developed for making large unilamellar vesicles (LUV) with low polydispersity. The LUV, constituted of dioleoylphosphatidic acid (DOPA), 300 nm in diameter are made by a modification of the pH adjustment technique (Hauser, H. and Gains, N. (1982) Proc. Natl. Acad. Sci. USA 79, 1683-1687). This size is 10 times that (30 nm) of vesicles prepared by prolonged sonication. Vesicle size is increased stepwise by adding cholesterol (to a maximum of 40 mol% cholesterol) to form vesicles in 0.15 M KCl with up to 600 nm diameter. The vesicle size is measured by photon correlation spectroscopy, electron microscopy, and by measurement of the internal volume with cyanocobalamin while calculating the number of DOPA molecules per vesicle. Vesicles are stable for at least three weeks. Sepharose 4B column chromatography of the preparation yields a peak of fractions with the same polydispersity as the original sample and shows that 30 to 40% of the original lipid in a sample is recovered as LUV. Less than 2% of the sample forms small unilamellar vesicles (SUV) (diameter = 30 nm), which emerge from the column in a separate peak. Since the remaining lipid is not suspended in the buffer during vesicle formation, for most purposes the vesicles may be used immediately after titration so that they can be prepared in less than 40 min.

The liquid-glass transition: a mode-coupling perspective

We review the dynamics of supercooled liquids approaching the liquid-glass transition, starting with the conventional generalized hydrodynamics formulation. Empirical models for the memory function are discussed, as are empirical models for the self-energy function for phonons in crystals. Two examples of microscopic analyses based on non-linear interactions are then described, the anharmonic lattice dynamics model for structural phase transitions, and Kawasakis mode-mode-coupling approach for critical dynamics. We then review the mode-coupling theory of the liquid-glass transition, emphasizing its relation to generalized hydrodynamics with the memory function derived from a microscopic theory of non-linear interactions. We discuss the major predictions of this theory, particularly the asymptotic expansion results, which provide specific formulae for analysing experimental data.

Brillouin-scattering study of propylene carbonate: An evaluation of phenomenological and mode coupling analyses

Brillouin-scattering spectra of the molecular glass-forming material propylene carbonate (PC) in the temperature range 140 K to 350 K were analyzed using both the phenomenological Cole-Davidson memory function and a hybrid memory function consisting of the Cole-Davidson function plus a power-law term representing the critical decay part of the fast beta relaxation. The spectra were also analyzed using the extended two-correlator schematic mode-coupling theory (MCT) model recently employed by Götze and Voigtmann to analyze depolarized light backscattering, dielectric, and neutron-scattering spectra of PC [Phys. Rev. E 61, 4133 (2000)]. We assess the ability of the phenomenological and MCT fits, each with three free fitting parameters, to simultaneously describe the spectra and give reasonable values for the alpha-relaxation time tau(alpha).

Time dependence of the soliton density in K2ZnCl4: Dielectric evidence for pair annihilation in the intrinsic chaotic state

Abstract The excess dielectric constant or dielectric tail below T c has been investigated in K 2 ZnCl 4 . With decreasing impurity content the tail becomes longer, and its relaxation at constant temperature becomes slower, indicating that the metastable chaotic soliton state is intrinsic rather than impurity induced. Observation of the decay at different temperatures in a well-annealed crystal suggests that once the soliton density decays below a critical value n s * , it then follows a square-law curve characteristic of pair-annihilation mediated decay.

Raman scattering and fluorescence in calcium fluoride

Abstract Raman scattering from a high purity calcium fluoride crystal excited by a 6328 A He-Ne laser has been observed. Contrary to results reported by Russell, no Raman structure was observed except for the first order line at 322 cm -1 . The strong spectrum, reported by Russell as second order Raman scattering, is found to closely resemble the fluorescence spectrum of erbium in calcium fluoride.