J C Earnshaw

The application of laser light scattering to the study of biological motion

Physical Principles of Light Scattering.- Structure and Movement in Cells.- Applications of Laser Light Scattering to Biological Systems.- Techniques and Instrumentation.- Correlation Function Profile Analysis in Laser Light Scattering I. General Review on Methods of Data Analysis.- Correlation Function Profile Analysis in Laser Light Scattering II. A Hybrid Photon Correlation Spectrometer.- Electrophoretic Light Scattering: Modern Methods and Recent Applications to Biological Membranes and Polyelectrolytes.- Laser Doppler Velocimetry in a Biological Context.- Implementation of Two Different Techniques for Measuring Lateral Diffusion and Optimisation of the Fluorescence Correlation Spectroscopy Concept.- Laser Doppler Microscopy: Especially as a Method for Studying Brownian Motion and Flow in the Sieve Tubes of Plants.- Studies of Neurotransmitter Receptor Interactions Using Quantitative Video Intensification Microscopy (V.I.M.).- Macromolecules and Gels.- Analysis of Diffusion of Biological Materials by Quasielastic Light Scattering.- The Diffusion of Compact Macromolecules Through Biological Gels.- Correlation Spectroscopy and Structural Properties of Macromolecular Solutions.- Depolarized Rayleigh Spectra of DNA in Solution.- Double Scattering in a Structured System of Particles.- Membranes and Amphiphilic Systems.- Fluorescence Techniques for the Study of Biological Motion.- Light Scattering by Model Membranes.- The Movement of Molecules Across Membranes: the Thermodynamic Analysis of the Dependence on Structure, Pressure and Temperature.- Light Scattering and Phase Transitions in GMO Membranes.- Photon Correlatior Studies of Phase Transitions in Lipid Monolayers.- Light Scattering from Micellar Solutions - Proposal for a Light Scattering Standard.- Laser Light Scattering Study of the Fractionation of Casein Micelles in Skim Milk by Controlled Pore Glass Chromotography.- Structural Studies on Bovine Casein Micelles by Laser Light Scattering.- Piological Applications.- Vesicles.- Structure and Dynamics of Disk Membrane Vesicles.- Vesicle Dynamics in Pollen Tubes.- A Preliminary Rheological Investigation of Living Physarum Endoplasm.- Muscles and Muscle Proteins.- The Application of Quasi-Elastic Light Scattering to the Study of Muscular Contraction.- Dynamic Light Scattering Study of Muscle F-Actin in Solution.- Further Evidence of Cross-Bridge Motion in Limulus Thick Myofilament Suspensions.- Stretch-Induced Transparency Change Associated With Cross-Bridge Deformation in Active Frogs Muscle.- Actin Polymerization in Cell Cytoplasm.- Ctyoplasmic Streaming.- Dynamic Cellular Phenomena in Physarum Possibly Accessible to Laser Techniques.- Amoeboid Movement in Chaoscarolinensis.- Cytoplasmic Streaming in Plant Cells and Its Relation to the Cytoskeleton.- The Rotation Model for Filament Sliding as Applied to the Cytoplasmic Streaming.- Motility.- Motility of Living Cells and Micro-organisms.- Chemotaxis and Band Formation of Escherichia coli Studied by Light Scattering.- A Comparison of Models Used in the Analysis of Quasi-Elastic Light Scattering Data from Two Motile Systems: Spermatozoa and Chlamydomonasreinhardtii.- Light Scattering Studies of Biological Populations and Biological Structures.- Systematic Assessment of Sperm Motility.- The Application of Laser Light Scattering to the Study of Photo-Responses of Unicellular Motile Algae.- Concluding Statements.- A Biologist Sums Up.- Epilogue.- Participants.

Inter-cluster scaling in two-dimensional colloidal aggregation

Cluster-cluster aggregation has been studied experimentally in two-dimensional colloidal systems of moderately high area fraction. In the diffusion limited regime the system spontaneously exhibits ordering beyond the scale of the fractal aggregates, which persists into the gelled state. This ordering arises from an effective inter-cluster repulsion due to the mutually exclusive depletion zones surrounding each cluster. Various metrical and topological properties of the system indicate that this long-range order is stationary, apart from the inherent change of scale as the clusters grow. Topological correlations show that the inter-cluster self-organization is compatible with maximum entropy: the non-equilibrium system behaves as if it were in statistical equilibrium, and no physical forces are involved in the long-range order. For the reaction-limited case no such inter-cluster ordering is evident at any stage, the system is nonstationary, and the aggregation is governed by specific physical forces.

Viscoelasticity of monolayers of n-pentadecanoic acid: a light scattering study

The viscoelastic properties of monolayers of n-pentadecanoic acid at the air-water interface have been studied using surface light scattering. The monolayers displayed first-order liquid-condensed to liquid-expanded transitions: the surface properties reported are those of well defined, reproducible monolayer states. Two viscoelastic moduli were determined: for shear transverse to the surface and for uniaxial dilation in the surface. For experiments both above and below the triple point the surface viscoelasticity was found to depend upon the monolayer phase in a complex fashion. Both moduli displayed viscoelastic relaxation, the strength and timescales being different for the two moduli, as well as depending upon the monolayer state. At one point in the phase diagram it was shown that the high-frequency dilational viscosity measured by light scattering could be identified with the conventional surface shear viscosity. The results confirm the complexity of the viscoelastic behaviour of molecular films which is not adequately represented by a single surface viscosity.

Surface light scattering: a methodological review

The methods used in the application of light scattering to the study of thermally excited capillary waves on liquid surface or interfaces are reviewed. The focus is on the use of photon correlation to determine the spectroscopic information carried by the scattered light. Particular attention is directed to extraction of the maximum amount of information from the data, including surface viscoelastic parameters and intensities.

A light scattering study of phase transitions in monolayers of n-pentadecanoic acid

The phase transitions of monolayers of carefully purified n-pentadecanoic acid at the air/water interface have been investigated using both classical and laser scattering methods. The equilibrium pi -A isotherms showed flat coexistence regions between the liquid-expanded and liquid-condensed states. Such clear first-order transitions appear only to be observable for pure pentadecanoic acid. In transitions at temperatures above the triple point ( approximately 17 degrees C) the light scattering clearly showed up phase separation within the monolayer, again demonstrating the first-order nature of the transitions. The liquid domains in the liquid/vapour transition were about 1 cm across. In the liquid-expanded/liquid-condensed transition the denser phase regions were of the order of 0.4 mm in size. These estimates are compatible with surface potential fluctuations which have been observed for this system. In the condensed/vapour transition below the triple point the monolayer behaved quite differently, no fluctuations being observed. At a surface concentration such that half of the pentadecanoic acid was in each surface phase, the viscoelastic properties of the film changed abruptly from close to those of the clean subphase to those of a viscoelastic medium. It is hypothesized that the molecular aggregates formed in this transition interact, when sufficiently close together, to form some kind of surface superstructure, which acts as a homogeneous surface phase.

Dynamics of water confined in non-ionic amphiphiles supramolecular structures

Light scattering studies of water properties in supramolecular structures of the aqueous solutions of polyoxyethylene non-ionic amphiphiles C10E5 are presented. Raman and Depolarized Rayleigh spectra are studied to obtain the OH stretching vibrational contribution and the rotational relaxational time of water along an isothermal path, crossing the isotropic one-phase region from 0 to 1 amphiphile volume fraction φ, and at the structural phase transitions at relatively large amphiphiles concentrations. Data analysis of the vibrational mode points out that the structure of bound water presents a local fourfold-coordinated environment, whereas the water rotational dynamics evidences a behavior that depends on the packing effects of the amphiphile aggregates.

Dynamic light scattering from colloidal monolayers

Quasi-elastic light scattering has been used to investigate the viscoelastic properties of colloidal monolayers on the surface of water. The frequency shifts, linewidths and intensities of the scattered light demonstrate that it arises from thermally excited capillary waves on the liquid surface. The photon correlation functions are consistent with predictions for a surface monolayer, and have been analysed in terms of the tension and dilational modulus of the surface. The measured values of the associated surface viscosities were compatible with zero. The pi -A variation was in accord with literature data from Wilhelmy plate measurements. However, at small A the light scattering values of the dilational modulus systematically exceeded those derived from the pi -A isotherm. This is as expected for viscoelastic relaxation in the monolayer on time scales much slower than the inverse wave frequencies.

Surface fluctuation spectroscopy: some further considerations

Instrumental effects which have previously been shown to cause systematic errors in laser light scattering studies of liquid surface fluctuations are reexamined. The resulting conclusions about experimental design, while different from those previously published, are entirely compatible with established experimental data. The theory of these instrumental effects is extended to include variation of scattered intensity with surface wave vector. This extension is shown to alter the systematic errors causing them to be much less than previously quoted for the recommended optical system.

Diffusive motions in living cytoplasm probed by laser Doppler microscopy

We have examined cytoplasmic motions in growing pollen tube tips using laser Doppler microscopy, a non‐invasive and non‐destructive technique. The observed correlation functions were consistent with the existence of diffusive motions in the tip cytoplasm. Further analysis of the data revealed the existence of at least two major and a third, minor, diffusing species in the cytoplasm. Information from quantitative electron microscopy and from published literature values of cytoplasmic viscosity was used to tentatively identify the organelles contributing to the observed diffusive motions. It is concluded that motions of mitochondria and secretory vesicles dominate the observed correlation functions with a minor component detected from either ribosomes or the microfilament network. Sources of variation in the observed data are discussed, as are the physical limitations that prevent a more positive analysis of the present data.

Left-sided multifractality of the harmonic measure on 2-D cluster-cluster aggregates

Abstract We characterise the morphology of clusters formed in 2-D cluster-cluster aggregation experiments by examining the scaling of the harmonic measure on their perimeter. The calculated f(α) spectra display behaviour typical of left-sided multifractality. The standard interpretation of multifractal, due to Frisch & Parisi and Halsey et al., is thus inadequate to characterise the scaling of the measure on the aggregates and one has to resort to the original and broader interpretation of Mandelbrot.