CRUDE OIL FOULING IN A PILOT-SCALE PARALLEL TUBE APPARATUS

Maya crude oil fouling reveals a seemingly straightforward dependency of initial fouling rate on surface temperature but a maximum is found in the initial fouling rate – velocity relationship which mirrors that found in a model chemical system of styrene polymerization. The linear dependency of the logarithm of the pre-exponential factor on apparent activation energy for the crude oil is also found in the styrene system. The apparent activation energy for the crude oil ranged from 26.4 kJ/mol at 1.0 m/s to 245 kJ/mol at 4.0 m/s. Such strong dependencies of apparent activation energy on velocity, even at high velocity, are consistent with Epstein’s mass transfer-reaction-attachment model. Surface temperatures at which the fouling rate becomes velocity-independent are 274°C and 77°C for Maya crude oil and styrene, respectively. For surface temperatures in excess of this isokinetic temperature, an increase in velocity would lead to an increase in the rate of fouling

Patterned growth and cathodoluminescence of conical boron nitride nanorods

We demonstrate a simple and effective approach for growing large-scale, high-density, and well-patterned conical boron nitride nanorods. A catalyst layer of Fe(NO3)3 was patterned on a silicon substrate by using a copper grid as a mask. The nanorods were grown via annealing milled boron carbide powders at 1300 &deg;C in a flow of nitrogen gas. The as-grown nanorods exhibit uniform morphology and the catalyst pattern precisely defines the position of nanorod deposition. Cathodoluminescence (CL) spectra of the nanorods show two broad emission bands centered at 3.75 and 1.85 eV. Panchromatic CL images reveal clear patterned structure<br /

Patterned growth and cathodoluminescence of conical boron nitride nanorods

We demonstrate a simple and effective approach for growing large-scale, high-density, and well-patterned conical boron nitride nanorods. A catalyst layer of Fe(NO₃)₃ was patterned on a silicon substrate by using a copper grid as a mask. The nanorods were grown via annealing milled boron carbide powders at 1300°C in a flow of nitrogen gas. The as-grown nanorods exhibit uniform morphology and the catalyst pattern precisely defines the position of nanorod deposition. Cathodoluminescence(CL) spectra of the nanorods show two broad emission bands centered at 3.75 and 1.85eV. Panchromatic CL images reveal clear patterned structure.This work is financially supported, in part, by The Australian Research Council under the nanotube program of the Center for Functional Nanomaterials

Hysteresis loops of Co-Pt perpendicular magnetic multilayers

We develop a phenomenological model to study magnetic hysteresis in two samples designed as possible perpendicular recording media. A stochastic cellular automata model captures cooperative behavior in the nucleation of magnetic domains. We show how this simple model turns broad hysteresis loops into loops with sharp drops like those observed in these samples, and explains their unusual features. We also present, and experimentally verify, predictions of this model, and suggest how insights from this model may apply more generally.Comment: 4.5 pages, 5 figure

Excitation spectrum of a two-component Bose-Einstein condensate in a ring potential

A mixture of two distinguishable Bose-Einstein condensates confined in a ring potential has numerous interesting properties under rotational and solitary-wave excitation. The lowest-energy states for a fixed angular momentum coincide with a family of solitary-wave solutions. In the limit of weak interactions, exact diagonalization of the many-body Hamiltonian is possible and permits evaluation of the complete excitation spectrum of the system.Comment: 4 pages, 1 figur

Heat capacity study of BaFe2_{2}As2_{2}: effects of annealing

Heat-capacity, X-ray diffraction, and resistivity measurements on a high-quality BaFe$_{2}$As$_{2}$ sample show an evolution of the magneto-structural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 $\mu\Omega$cm, with a residual resistance ratio $\sim$36; the heat-capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of $\sim$0.15 K, and is unchanged in a magnetic field $\mu_{0}$H = 14 T. The X-ray and heat-capacity data combined suggest that there is a first order jump in the structural order parameter. The entropy of the transition is reported

The Dynamics of Zeroth-Order Ultrasensitivity: A Critical Phenomenon in Cell Biology

It is well known since the pioneering work of Goldbeter and Koshland [Proc. Natl. Acad. Sci. USA, vol. 78, pp. 6840-6844 (1981)] that cellular phosphorylation- dephosphorylation cycle (PdPC), catalyzed by kinase and phosphatase under saturated condition with zeroth order enzyme kinetics, exhibits ultrasensitivity, sharp transition. We analyse the dynamics aspects of the zeroth order PdPC kinetics and show a critical slowdown akin to the phase transition in condensed matter physics. We demonstrate that an extremely simple, though somewhat mathematically "singular" model is a faithful representation of the ultrasentivity phenomenon. The simplified mathematical model will be valuable, as a component, in developing complex cellular signaling network theory as well as having a pedagogic value.Comment: 8 pages, 3 figure

Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O

Thermodynamic critical field curves have been measured for $La_{2-x}Sr_{x}CuO_{4+\delta}$ over the full range of carrier concentrations where superconductivity occurs in order to determine changes in the normal state density of states with carrier concentration. There is a substantial window in the $H-T$ plane where the measurements are possible because the samples are both thermodynamically reversible and the temperature is low enough that vortex fluctuations are not important. In this window, the data fit Hao-Clem rather well, so this model is used to determine $H_c$ and $\kappa_c$ for each temperature and carrier concentration. Using N(0) and the ratio of the energy gap to transition temperature, $\Delta (0)/k_BT_c$, as fitting parameters, the $H_c vs T$ curves give $\Delta (0)/k_BT_c \sim 2.0$ over the whole range of $x$. Values of N(0) remain rather constant in the optimum-doped and overdoped regime, but drops quickly toward zero in the underdoped regime.