Comparison of the action of primary alcohols as inhibitors of a soluble and a membrane-bound cytochrome P450 hydroxylase.

This thesis describes the development of a procedure for comparing the manner in which organic solvents inhibit biocatalysts. The research compared the effect of a series of primary alcohols on a membrane bound and a soluble cytochrome P450 hydroxylase. The effect of alkanes and primary alcohols on the bioluminescence of luciferase (EC 1.13.12.7) was developed as the basis of a fast and stable bioassay for measuring the aqueous concentration of a primary alcohol or an alkane (Franks and Lieb, 1984). This was then used to determine the concentration of organic solvents in the aqueous phase of a mixture of biological membranes and water. The bioassay was used in a study of the effect of primary alcohols on two cytochrome P450 hydroxylases. The first was a purified and soluble cytochrome P450, derived from Bacillus megaterium (recombinant P450 BM3 engineered for high expression in Escherichia coli (kindly supplied by Dr Munro at the University of Edinburgh)) and the second a membrane associated enzyme present in Rhizopus stolonifer (formally known as R. nigricans). The effect of the solvents in the reaction mixture was characterised by their IC50 value, that is, the concentration of the solvent that caused a 50 % inhibition of the enzyme activity. The soluble enzyme from B. megaterium was found to be more strongly inhibited by short chain alcohols (IC50 for methanol = 0.71 M) than the enzyme from R. stolonifer (IC50 for methanol =1.63 M). The inhibition of both enzymes by the primary alcohols becomes more extreme as their molecular weight increased, and they were almost equally inhibited by pentanol (IC50 =62 mM and 46 mM respectively). Hexanol inhibited the enzyme from R. nigricans (IC50 =25 mM) but was not sufficiently soluble in water (solubility limit is 50.1 M at 25 C,Bell, 1972) to inhibit the enzyme from B. megaterium. The aqueous concentration of various primary alcohols and alkanes in the presence of the cells of R. stolonifer suggested that at 50 % inhibition the molar concentration of the solvent in the membranes of the cells was the same for all the alcohols studied. The log IC50 (the logarithm of the concentration of the alcohols that caused a 50 % inhibition of the enzyme activity) was found to be a linear function of the carbon chain length of the alcohol and decreased regularly as the chain length increased. A multiple regression analysis showed that the effect of the series of primary alcohols on the two hydroxylases studies was significantly different

Lattice Boltzmann Method for Electromagnetic Wave Propagation

We present a new Lattice Boltzmann (LB) formulation to solve the Maxwell equations for electromagnetic (EM) waves propagating in a heterogeneous medium. By using a pseudo-vector discrete Boltzmann distribution, the scheme is shown to reproduce the continuum Maxwell equations. The technique compares well with a pseudo-spectral method at solving for two-dimensional wave propagation in a heterogeneous medium, which by design contains substantial contrasts in the refractive index. The extension to three dimensions follows naturally and, owing to the recognized efficiency of LB schemes for parallel computation in irregular geometries, it gives a powerful method to numerically simulate a wide range of problems involving EM wave propagation in complex media.Comment: 6 pages, 3 figures, accepted Europhysics letter

Three-dimensional central-moments-based lattice Boltzmann method with external forcing: A consistent, concise and universal formulation

The cascaded or central-moments-based lattice Boltzmann method (CM-LBM) is a robust alternative to the more conventional BGK-LBM for the simulation of high-Reynolds number flows. Unfortunately, its original formulation makes its extension to a broader range of physics quite difficult. To tackle this issue, a recent work [A. De Rosis, Phys. Rev. E 95, 013310 (2017)] proposed a more generic way to derive concise and efficient three-dimensional CM-LBMs. Knowing the original model also relies on central moments that are derived in an adhoc manner, i.e., by mimicking those of the Maxwell-Boltzmann distribution to ensure their Galilean invariance a posteriori, a very recent effort [A. De Rosis and K. H. Luo, Phys. Rev. E 99, 013301 (2019)] was proposed to further generalize their derivation. The latter has shown that one could derive Galilean invariant CMs in a systematic and a priori manner by taking into account high-order Hermite polynomials in the derivation of the discrete equilibrium state. Combining these two approaches, a compact and mathematically sound formulation of the CM-LBM with external forcing is proposed. More specifically, the proposed formalism fully takes advantage of the D3Q27 discretization by relying on the corresponding set of 27 Hermite polynomials (up to the sixth order) for the derivation of both the discrete equilibrium state and the forcing term. The present methodology is more consistent than previous approaches, as it properly explains how to derive Galilean invariant CMs of the forcing term in an a priori manner. Furthermore, while keeping the numerical properties of the original CM-LBM, the present work leads to a compact and simple algorithm, representing a universal methodology based on CMs and external forcing within the lattice Boltzmann framework.Comment: Published in Phys. Fluids as Editor's Pic

High speed video capture for mobile phone cameras

We consider an electromechanical model for the operation of a voice coil motor in a mobile phone camera, with the aim of optimizing how a lens can be moved to a desired focusing motion. Although a methodology is developed for optimizing lens shift, there is some concern about the experimentally-determined model parameters that are at our disposal. Central to the model is the value of the estimated magnetic force constant, Kf: its value determines how far it is actually possible to move lens, but it appears that, from the value given, it would not be possible to shift the lens through the displacements desired. Furthermore, earlier experiments have also estimated the value of the back EMF constant, Kg , to be roughly five times greater than Kf, even though we present two theoretical arguments that show that Kf = Kg: a conclusion supported by readily-available manufacturers’ data

Ground State Energy of the One-Component Charged Bose Gas

The model considered here is the `jellium' model in which there is a uniform, fixed background with charge density $-e\rho$ in a large volume $V$ and in which $N=\rho V$ particles of electric charge $+e$ and mass $m$ move --- the whole system being neutral. In 1961 Foldy used Bogolubov's 1947 method to investigate the ground state energy of this system for bosonic particles in the large $\rho$ limit. He found that the energy per particle is $-0.402 r_s^{-3/4} {me^4}/{\hbar^2}$ in this limit, where $r_s=(3/4\pi \rho)^{1/3}e^2m/\hbar^2$. Here we prove that this formula is correct, thereby validating, for the first time, at least one aspect of Bogolubov's pairing theory of the Bose gasComment: 38 pages latex. Typos corrected.Lemma 6.2 change

Spatial stochasticity and non-continuum effects in gas flows

We investigate the relationship between spatial stochasticity and non-continuum effects in gas flows. A kinetic model for a dilute gas is developed using strictly a stochastic molecular model reasoning, without primarily referring to either the Liouville or the Boltzmann equations for dilute gases. The kinetic equation, a stochastic version of the well-known deterministic Boltzmann equation for dilute gas, is then associated with a set of macroscopic equations for the case of a monatomic gas. Tests based on a heat conduction configuration and sound wave dispersion show that spatial stochasticity can explain some non-continuum effects seen in gases