Intensity Fluctuation Spectroscopy Research Articles

X-ray intensity fluctuation spectroscopy observations of critical dynamics in Fe3Al.

We have carried out intensity fluctuation spectroscopy measurements using coherent x rays to study the dynamics of critical fluctuations in a binary alloy at equilibrium. An intense coherent hard x-ray beam, produced from an undulator source, was scattered from a single crystal of ${\mathrm{Fe}}_{3}\mathrm{Al}$ held at temperatures near the $B2\ensuremath{-}{\mathrm{DO}}_{3}$ order-disorder transition. A speckle pattern was observed at the $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ superlattice reflection. Below ${T}_{c}$ it was essentially static, while above ${T}_{c}$ it fluctuated in time. The behavior of the normalized time correlation function is consistent with predictions of theory.

A low cost correlator employing a personal computer

The intention of this paper is to describe the design of a 16-bit correlation setup employing a personal computer (PC) used in intensity fluctuation spectroscopy. It is based on a hardware acquisition board which counts the photons detected in the selected sampling time. The calculation of the correlation coefficients is achieved with a PC by means of a suitable software program. This arrangement permits one to obtain various kinds of information from the recorded data, i.e., it is possible to evaluate other statistical estimators instead of the usual correlation function. Experimental tests of the apparatus have been obtained by measuring the light scattered by a liquid suspension of polystyrene latex spheres.

Observation of speckle by diffraction with coherent X-rays

REFLECTED light from a coherent light source such as a laser shows a graininess known as speckle. In general, a speckle pattern is produced whenever randomly distributed regions of a material introduce different phase shifts into the scattering of coherent incident light. If the arrangement of the regions evolves with time, the speckle pattern will also change. Observation of the intensity fluctuations at a single point in the speckle pattern provides a direct measure of the time correlation function of the inhomogeneity. This leads to a technique1,2, alternatively called light-beating spectroscopy, dynamic light scattering or intensity fluctuation spectroscopy, which has been widely used with visible light to study processes such as critical fluctuations near phase transitions in fluids and the diffusion of particles in liquids. But it is not possible to study processes involving length scales less than about 200 nm, or those in opaque materials, using visible light. If intensity fluctuation spectroscopy could be carried out using coherent X-rays, however, one could probe the dynamics of processes involving atomic length scales in a wide range of materials. Here we show that by using a high-brilliance X-ray source it should be possible to perform this type of measurement using radiation of wavelength ∼0.15nm. Specifically, we have observed a speckle pattern in the diffraction of coherent X-rays from randomly arranged antiphase domains in a single crystal of the binary alloy Cu3Au.

Direct measurement of orientation correlations in a two-dimensional liquid-crystal system.

The behavior of a two-dimensional orientation field has been studied directly in space and time. In a freely suspended thin film of tilted smectic liquid crystal the local projection onto the film plane of the molecular orientation averaged through the film forms a two-dimensional (2D) vector field C^(x,y) with local orientation \ensuremath{\Phi}(x,y). This orientation field was imaged in real space by depolarized reflection microscopy. By probing the light at two distinct (x,y) locations in the image and employing cross-correlation intensity-fluctuation spectroscopy, we have measured the space-time behavior of ${\ensuremath{\sigma}}^{2}$(\ensuremath{\rho},\ensuremath{\tau})\ensuremath{\equiv}〈\ensuremath{\Vert}\ensuremath{\Phi}(0,0) -\ensuremath{\Phi}(\ensuremath{\rho},\ensuremath{\tau})${\ensuremath{\Vert}}^{2}$〉. At large \ensuremath{\tau}, \ensuremath{\sigma} increases logarithmically with \ensuremath{\tau}, consistent with the expected diffusional dynamics and thermally excited fluctuation spectrum of \ensuremath{\Phi}. This logarithmic (Landau-Peierls) divergence confirms that this 2D orientational system is at its lower marginal dimensionality. In addition, by fitting the behavior of ${\ensuremath{\sigma}}^{2}$(\ensuremath{\rho},\ensuremath{\tau}), we extract the 2D orientational diffusion constants for splay and bend in both the smectic-C and smectic-I phases.

On the structure of a-crystallin: the minimum molecular weight

alpha-crystallin can be isolated in two forms depending on the temperature at which the lens is extracted. At 4 degrees C, alpha c-crystallin is obtained while at 37 degrees C, a smaller molecule, alpha m-crystallin can be isolated. The apparent molecular weight of bovine foetal alpha m- and alpha c-crystallins were determined in 5 different ways using sedimentation velocity, sedimentation equilibrium and intensity fluctuation spectroscopy analyses and the experimentally determined diffusion coefficients, intrinsic viscosity and partial specific volume. Values ranged from 291,000 to 369,000 for alpha m and from 604,000 to 760,000 for alpha c due to the differential effects of the protein's polydispersity on the different methods. Subfractionation of the protein by gel filtration yielded much less polydisperse minimum species populations with molecular weights of 280,000 and 529,000 for alpha m and alpha c respectively. It was concluded that alpha-crystallin is probably synthesized as a symmetrical dodecamer and that the polydispersity of most preparations can be attributed to age-related modification in vivo as well as in vitro supra-aggregation due to variations in experimental conditions.

The active cross-bridge motions of isolated thick filaments from myosin-regulated muscles detected by quasi-elastic light scattering

Intensity fluctuation spectroscopy has been used successfully as a probe that can detect an increase in high-frequency internal motions of isolated thick filaments of Limulus muscle upon the addition of calcium ions. We have attributed such motions to cross-bridge motion instead of to an increase in the flexibility of the filament backbone. Here we show that after cleavage of the S-1 and then the S-2 moieties with papain, cross-linking the myosin heads to the filament backbone, or heat denaturation (42 degrees C, 10 min), the increase in the high frequency internal motions in the thick filaments no longer occurs. Congo Red, which has been shown to induce shortening of isolated myofibrils, also increases the high-frequency motions of the isolated filaments. Furthermore, the increase is suppressed by treating the filaments with a myosin ATPase inhibitor such as vanadate ions (10 mM) or by replacing ATP with either an equimolar CrADP or the nonhydrolyzable ATP analogue beta, gamma-imido-adenine-5'-triphosphate (AMP-PNP). Calcium ions have a similar effect on isolated thick filaments from scallop muscle, where the myosin is known to be regulatory. Calcium ions have no such effect on thick filaments isolated from frog muscle, which is believed not to be regulated by calcium binding to myosin. These results confirm our earlier supposition that the additional high frequency internal motions of the thick filaments isolated from striated muscle of Limulus are related to the energy dependent, active cross-bridge motions.

Direct Measurement of Orientation Correlations: Observation of the Landau-Peierls Divergence in a Freely Suspended Tilted Smectic Film

Cross-correlation intensity-fluctuation spectroscopy is used to exhibit the space-time behavior of fluctuations in the director orientation difference between a pair of points in the two-dimensional nematiclike director field of a freely suspended tilted smectic film. The Landau-Peierls divergence expected with increasing time is observed directly.

Dynamic light scattering studies of gelatin gels

Gels formed from very polydispersive gelatin solutions were studied by intensity fluctuation spectroscopy. Single exponential autocorrelation functions were obtained for gelatin gels with and without a crosslinking agent. The elastic continuum model was found to adequately describe all the observed properties. As the concentration increases the cooperative diffusion coefficient Dc of the polymer network decreases in the solution state, but increases in the gel state. For gels without a crosslinking agent, the decay rate of the correlation function was found to remain constant after it reached a terminal value several hours after its temperature was lowered to 20 °C. However, for gels with a crosslinking agent, the decay rate continuously increased and the spatial correlation length became shorter with time.

Intensity-fluctuation spectroscopy of optical fields with non-Gaussian statistics

Intensity-fluctuation spectroscopy (IPS) is usually considered to be complementary to conventional spectroscopy and capable of removing technical restrictions on the resolving power. However, the information provided by field spectroscopy is identical to that obtained by IFS only for fields with Gaussian statistics. For non-Gaussian fields, IFS yields essentially new information, and the present review is devoted to this aspect of IFS. It surveys experiments concerned with the investigation of the noise spectrum of resonance fluorescence and of coherent forward scattering by an atomic vapor, which provide data on the width and the structure of levels involved in atomic transitions under the conditions of dominant Doppler broadening. Fundamental and technical limitations of the method are examined. Analogous studies of fluctuation spectra of radiation scattered by macroparticles in liquids can be used to determine the time dependence of the particle form factor independently of the characteristics of translational diffusion.

Cross-correlation intensity fluctuation spectroscopy applied to colloidal suspensions

The method of cross-correlation intensity fluctuation spectroscopy (CCIFS) is presented and contrasted with other scattering techniques. While standard scattering techniques monitor structure factors which are related to particle pair correlation functions, the CCIFS technique is sensitive to higher-order correlation functions and may be used to monitor the local particle order in condensed phases. To demonstrate the CCIFS technique, cross-correlation data for scattering from a two-dimensional colloidal monolayer is presented. These cross-correlation data indicate a local hexagonal structure in the fluid phase. A model calculation is presented which treats the two-dimensional colloidal fluid phase as a randomly oriented hexagonal solid with large lattice vibrations. The results of this calculation are in qualitative agreement with experimental observation.

Spektroskopiya fluktuatsii intensivnosti opticheskikh polei s negaussovoi statistikoi

Спектроскопия флуктуаций интенсивности оптических полей с негауссовой статистикой, Александров Е.Б., Голубев Ю.М., Ломакин А.В., Носкин В.А.

Study of polymerization by intensity fluctuation spectroscopy

Study of polymerization by intensity fluctuation spectroscopy

Hydrodynamic determination of molecular weight, dimensions, and structural parameters of Pf3 virus.

Measurements of the translational, DT, and rotational, DR, diffusion coefficients of Pf3 virus by low-angle polarized intensity fluctuation spectroscopy and field-free transient electric birefringence, respectively, give a length of 720 +/- 25 nm and diameter of 6.5 +/- 1.5 nm upon simultaneous solution of the Broersma equations for rigid rods. Sedimentation coefficient and density increment values obtained under solvent conditions identical with those of DT give a molecular weight of (13.4 +/- 0.8) x 10(6) g mol-1, which gives a mass per length of 18 600 +/- 1300 g mol-1 nm-1. Combining these results with the molecular weight of Pf3 DNA yields a number of protein subunits of 2500 +/- 160 and 2.38 +/- 0.14 nucleotides/protein subunit. Sedimentation coefficient and density increment values of Xf virus when combined with a value for the Xf translational diffusion coefficient [Chen, F. C., Koopmans, G., Wiseman, R. L., Day, L. A., & Swinney, H. L. (1980) Biochemistry 19, 1373] yield a molecular weight of (17.9 +/- 1.0) x 10(6) g mol-1, a number of protein subunits of 3590 +/- 230, 2.07 +/- 0.15 nucleotides/protein subunit, and a mass per length of 18 300 +/- 1200 g mol-1 nm-1. Thus, despite major differences in the DNA-protein packing between these viruses, as well as fd virus, the mass per lengths are surprisingly similar.

Physicochemical characterization of ten fractions of bovine alpha lipoproteins.

With the onset of milk production, serum concentrations of alpha lipoproteins in the dairy cow steadily increase, frequently attaining values greater than 1.5 g/dl. Since these lipoproteins comprise a highly polydisperse system, we have carried out studies to explore differences among bovine alpha lipoproteins in the density interval between 1.05 to 1.21 g/ml. Separation into ten fractions was achieved ultracentrifugally in an isopycnic gradient. Agarose gel electrophoresis showed that all but the bottom fraction contained alpha lipoproteins as either the major or sole lipoprotein class. Compositional analyses revealed an increasing percentage of both protein and phospholipid and a decreasing percentage of cholesterol with increasing fraction density. The esterified to unesterified cholesterol ratio ranged from 3 to 8 from the top to the bottom of the gradient. The densities of the particles obtained from the various fractions were calculated both from sedimentation velocity measurements and from compositional analyses. The resulting density values agreed well with the solution densities of these isopycnic gradient fractions. The major apoprotein of each fraction was apoA-I. Combining diffusion coefficient data obtained by intensity fluctuation spectroscopy with sedimentation velocity data, we were able to calculate molecular weights, frictional ratios, and Einstein-Stokes radii for three of the fractions. Results are discussed in terms of previously published data on bovine lipoproteins as well as other mammalian data.

Measurements of molecular weights of low-density lipoprotein (LDL) from homozygotes for familial hypercholesterolemia and controls

Weight average molecular weights ( M r(w)) were determined for LDL and LDL 2 taken from normals and patients who were homozygotic and heterozygotic for familial cholesterolemia (FH). M r(w) were calculated using experimental estimates of S 0 20,w , D 20,w (using intensity fluctuation spectroscopy) and apparent specific volume (Φ), all made on the same samples. The results showed that although there was variability in M r(w) between individuals, these differences could not be related to the FH condition. It was also found that M r(w) for LDL and LDL 2 were surprisingly similar for individuals examined at intervals, and furthermore the values for LDL and LDL 2 were also very similar, showing that the separation into these two fractions was by density only. These findings must be considered alongside the findings that there are observable differences in the LDL between normal and FH patients when examined in the ultracentrifuge. Examination of LDL from a patient before and after plasmapheresis showed a temporal change in the LDL which would be consistent with the view that the FH patients could synthesize normal LDL but they had an abnormal catabolism; this view would also be consistent with the consistency in molecular weights for individuals.

Light Scattering Study of the 12-Hydroxyoctadecanoic Acid and Benzene Mixture in the Gel State

Abstract The structure of the 12-hydroxyoctadecanoic acid-benzene gel was studied by the use of the light scattering spectrometer. The scattering angular dependence of the scattering intensity and the time correlation function of the electric field were measured. It was found that the coarse mesh network and the fine mesh network coexist in this gel. The former was detected by the intensity measurement, while the latter was detected by intensity-fluctuation spectroscopy. The usefulness of the light scattering technique was emphasized.

Diffusion coefficients of hemoglobin by intensity fluctuation spectroscopy: effects of varying pH and ionic strength

Measurements of the mutual diffusion coefficients (D) of the liganded human hemoglobins (Hb) oxy-HbA and oxy-HbS were performed as a function of Hb concentration (CHb), pH, and ionic strength (tau) by intensity fluctuation spectroscopy (IFS). Average diffusion coefficients, (D), and normalized variances, ((D/(D) - 1)2), were recorded. Results are reported and select features are discussed quantitatively. (a) for tau = 0.15 M, the shape of the (d) vs. CHb curve is found to vary with pH. We developed a precise description of this effect in the form of an algebraic relationship between (D), CHb, and Z, the titration charge. (b) only slight differences between the (D) values of oxy-HbS and oxy-HbA are observed, at tau = 0.15 M, for CHb Less Than or Equal To 10 g%. These differences are explained by the theory of part a. (c) No evidence of aggregation is found in solutions of oxy-HbA or oxy-HbS, at tau = 0.15 M, for CHb Less Than or Equal To 10 g%. (d) Indications of aggregation appear in oxy-HbA solutions at very low concentrations of salt. An estimate is made of the extent of aggregation, and the average radius of a cluster is determined.

Determination of Lengths and Diameters of Rod-Like Macromolecules by Intensity Fluctuation Spectroscopy

Abstract This work presents a numerical study on the possibility of identifying the length and the diameter of rod-like macromolecules in diluted solution, when the laser light scattered by the solution is analyzed by means of intensity fluctuation spectroscopy (IFS). This study is made by computer-simulation of the second order normalyzed factorial moment, n(2)(T), of the laser light scattered by the macromolecules. The results are presented and discussed.

A Fast Computer-Simulation Method for Generating Values of n(2) in Intensity Fluctuation Spectroscopy

Abstract In this paper we present a fast method of simulation of the normalized second factorial moment n(2)(T) of the photon-counting distribution obtained in an intensity fluctuation spectroscopy experiment, in order to test the confidence with which one can derive information from such measurements.

Physical measurements on the lipid-containing bacteriophage phi 6.

Bacteriophage phi 6 has been studied by small-angle X-ray scattering intensity-fluctuation spectroscopy, analytical ultracentrifugation, and spectroscopy. The sedimentation coefficient (S(0)0,w) is 375 S, the diffusion coefficient (D(0)20, w) is 2.66 x 10(-8) cm 2/s. Using the Svedberg equation and and an estimate of the partial specific volume, the Mr is 1.49 +/- 0.32 x 10(8). A simple model which describes phi 6, is a central sphere consisting of RNA and protein of radius 330 A and an outer shell of low electron density 40 A thick. The RNA may form five concentric shells in the region r = 140-290 A.