Analytical applications of photon correlation spectroscopy for size distribution measurements of natural colloidal suspensions: capabilities and limitations

Particles are ubiquitous in all natural systems and play an important role in the control and fate of nutrients and pollutants. Currently, only limited information is available concerning particle number and size distributions, owing to the problems involved in their experimental determination. In the present paper, limitations and optimal conditions for particle size determinations of environmental samples using photon correlation spectroscopy are studied. The detection limit, the effects of polydispersity of the sample and the refractive index value are discussed based on results obtained with synthetic colloids. The photon correlation spectroscopic determination of particle size distributions in real aquatic systems is also presented in the second part of the paper.     

Coherent noise, scale invariance and intermittency in large systems

We introduce a new class of models in which a large number of “agents” organize under the influence of an externally imposed coherent noise. The model shows reorganization events whose size distribution closely follows a power law over many decades, even in the case where the agents do not interact with each other. In addition, the system displays “aftershock” events in which large disturbances are followed by a string of others at times which are distributed according to a t⁻¹ law. We also find that the lifetimes of the agents in the system possess a power-law distribution. We explain all these results using an approximate analytic treatment of the dynamics and discuss a number of variations on the basic model relevant to the study of particular physical systems.     

Properties of a local pairing model of high-Tc superconductivity

A simulation technique is used to study the properties of the “hole modulated hopping” model introduced by Hirsch. The superconducting order parameter, energy gap and pair size have been determined for a range of particle densities and temperatures in the neighbourhood of the superconducting phase transition. Results are consistent with the interpretation of the superconducting transition to be Bose-like at low hole densities and BCS-like at high hole densities, with a crossover near the T_c maximum in the T_c versus hole density curve. This behaviour is related to the existence of small non-overlapping pairs at low hole densities and large strongly interpenetrating pairs at hole densities above the T_c maximum.     

The temperature dependence and anisotropy of the thermal conductivity in polyacetylene

Observations of anisotropic transport in (CH)_x reported to date have been made on stretch-oriented films in the plane of the film. We report the first observations of anisotropy in the thermal conductivity measured parallel and perpendicular to the plane of unstretched films. The room-temperature value measured along the film is $\text{50}\text{mW}\text{cm}\text{?}\text{K}$, and is almost a factor of 20 higher than that observed perpendicular to the film $\text{(}\text{3}\text{mW}\text{cm}\text{?}\text{K}\text{)}$. Finally, the temperature dependences for the parallel and perpendicular thermal conductivities are reported.     

NGR study of pyrrhotites obtained in coal hydroliquefaction

Iron Mössbauer spectroscopy has been performed on 38 residues of hydroliquefaction of the French bituminous Freyming coal, without and with added iron based catalysts. 56 to 94 % of the area of each spectrum was occupied by 2, 3, 4 or 5 sextets of Fe_1?xS, either at 295 K or at 78 K or at 4 K. Values of H at 295 K are proposed: 299, 283, 268, 254, 242 and 228 kOe, ±3 kOe, associated with δ(α-Fe)=0.72±0.02 mm/s. The vacancies responsible for the values of H are likely to be randomly distributed. The best accuracy on the relative intensities cannot ensure a precise determination of the overall stoichiometry, so that a better knowledge of the samples is given by the distribution of the Fe sites.     

Determination of the angular and energy dependence of hard constituent scattering from π0 pair events at the CERN intersecting storage rings

We present data on proton-proton collisions, obtained at the CERN Intersecting Storage Rings, in which two roughly back-to-back π⁰'s of high transverse momentum (p_T) were produced. The angular distribution of the dipion axis relative to the collision axis is found to be independent of both the effective mass m of the dipion system and the centre-of-mass energy √s of the proton-proton collision. The cross-sections $\text{d}\text{σ}\text{d}\text{m}$ at the values of √s satisfy a scaling law of the form $\text{d}\text{σ}\text{d}\text{m}\text{=}\text{G(x)}\text{m}{}^{\mathrm{n}}\text{,}\text{where}\text{x = m(π}{}^0\text{, π}{}^0\text{)//trs}\text{and}\text{n = 6.5 ± 0.5}$. We show from our data that the leading π⁰ carries most of the momentum of the scattered parton. Given this fact, the axis of the dipion system follows closely the direction of the scattered constituents, and we exploit this to determine the angular dependence of the hard-scattering subprocess. We also compare our data with the lowest order QCD predictions using structure functions as determined in deep-inelastic scattering and fragmentation functions from electron-positron annihilation.     

High pT π0 production from αα and αp collisions at the CERN ISR

The invariant cross sections for π⁰ meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of $\text{7}\text{GeV}\text{c}$ and $\text{8}\text{GeV}\text{c}$, respectively. These measurements are compared with π⁰ production in pp collisions at the same values of $\text{s}\text{/}$nucleon, and the variation of the nuclear A-dependence with p_T is determined.     

The general solution of the vacuum einstein equation in the limit of strong gravity

The general solution to the strong coupling limit of the vacuum Einstein field equations is obtained. This limit is related to the theory of symmetric spaces.On leave from the Department of Mathematics, Monash University, Clayton, Victoria, 3168, Australia.On leave from F.A.M.A.F., Laprida 854, University of Cordoba, 5000 Cordoba, Argentina.On leave from the Physics Department, Jamestown Community College, Jamestown, N.Y. 14701.     

Silicon-29 and carbon-13 n.m.r. studies of organosilicon chemistry. VII—trimethylsilylated silicates

Silicon-29 n.m.r. was used to study the products from trimethylsilylation of minerals. Chemical shifts are reported for four model compounds, viz. the monomer, dimer, linear trimer (from natrolite) and cyclic tetramer (from laumontite). Information is then obtained from the products of trimethylsilylation of the anhydrous calcium silicates wollastonite and pseudo-wollastonite. In the latter case it is shown that the principal products are the four model compounds, and percentage yields are obtained for these.     

Temperature dependence of the thermal conductivity for tellurium dioxide

The thermal conductivity of tellurium dioxide is reported as a function of temperature. At 77K, the thermal conductivity is 0.09 W/cm-K and it decreases approximately as the inverse of the temperature to a value of 0.02 W/cm-K at 300K. The anisotropy between the a- and c-axes is less than 20% over the entire experimental temperature range, with the a-axis more conductive than the c-axis. By making some simplifying assumptions, the phonon mean free paths and relaxation times are deduced.