The Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-oxidizing Metal Ions 1: Ferric Ions

Hydroxamic acids (XHAs) are organic compounds with affinities for cations such as Fe³⁺, Np⁴⁺ and Pu⁴⁺ and have been identified as useful reagents in nuclear fuel reprocessing. Acid catalyzed hydrolysis of free XHAs is well known and may impact negatively on reprocessing applications. The hydrolysis of metal-bound XHAs within metal ion-XHA complexes is less understood. With the aid of speciation diagrams, we have modelled UV-visible spectrophotometric kinetic studies of the acid-catalyzed hydrolysis of acetohydroxamic acid (AHA) bound to the model ion Fe(III). These studies have yielded the following information for the hydrolysis of AHA in the Fe(AHA)²⁺ complex at 293 K: (i) the order with respect to [H⁺] during the rate determining step, m=0.97, is the same as for the free ligand, indicating a similarity of mechanisms; and (ii) the kinetic rate parameter, k ₁=1.02×10⁻⁴ dm³⋅mol⁻¹⋅s⁻¹, is greater than that for the free ligand, k ₀=1.84×10⁻⁵ dm³⋅mol⁻¹⋅s⁻¹ for pH>−0.5, a result that is consistent with a Hammett analysis of the system.     

Ultrasonic extraction of veterinary antibiotics from soils and pig slurry with SPE clean-up and LC-UV and fluorescence detection

A simple and rapid analytical method is presented in which the three veterinary antibiotics oxytetracycline (OTC), sulfachloropyridazine (SCP) and tylosin (TYL) are simultaneously extracted and determined in four different soils. Extractions were carried out by a combination of ultrasonic agitation and vortex mixing using a mixture of methanol, EDTA and McIlvaine buffer at pH 7 as the extractant solution. The extracts were then cleaned-up by a tandem solid phase extraction (SPE) method using an Isolute SAX anion exchange cartridge to remove natural organic matter and an Oasis HLB polymeric cartridge to retain the study compounds. Analysis was by HPLC-UV with additional fluorescence detection for SCP. Recoveries were in the range 68-85% for SCP in all soil types, 58-75% for OTC in sandy soils, 27-51% for OTC in clay containing soils, 74-105% for TYL and 47-61% in a clay soil. OTC and SCP were also extracted from liquid pig manure using a mixture of EDTA and McIlvaine buffer at pH 7 with ultrasonic agitation and vortex mixing with SPE clean-up and HPLC-UV analysis. Recoveries were greater than 77% and 58% for OTC and SCP, respectively. Limits of detection were 18 μg kg⁻¹ for OTC and SCP and 40 μg kg⁻¹ for TYL in soils and 70 μg L⁻¹ for OTC and 140 μg L⁻¹ for SCP in pig slurry.     

The micro-optical ring electrode. 3: Transient photocurrent studies of photophysical-electrochemical and photophysical-chemical-electrochemical systems

The micro-optical ring electrode (MORE) is a photoelectrochemical device based on a ring microelectrode that uses the insulating material interior to the ring electrode as a light guide. In this paper, we describe the preparation and characterization of very thin ring MOREs with (ring inner radius)/(ring outer radius) > 0.99. Theoretically, we derive asymptotic analytical expressions for the time dependence of the diffusion-limited transient light-on photocurrent generated by two general types of photoelectrochemical systems: (a) the PE (photophysical-electrochemical) system, wherein the photoexcited species itself is directly detected on the ring; (b) the PCE (photophysical-chemical-electrochemical) system, wherein the photoexcited species undergoes a homogeneous electron transfer reaction prior to electrochemical detection. Experimentally, we establish that it is possible to use such MOREs to study the wavelength dependence of photocurrents derived from photoelectrochemically active systems, such as the Ru(bipy)3 2+/Fe3+ PCE system, demonstrating the potential utility of the MORE as a selective electroanalytical probe. We also use our expressions for the time dependence of photocurrents at the MORE to derive values for the photoelectrochemical kinetic parameters of this system, including the rate coefficient for the back reaction of photogenerated Ru(bipy)3 3+ (0.115 s(-1)) and the quantum efficiency for the primary redox products, Ru(bipy)3 3+ and Fe2+, escaping cage recombination, phi(CE) = 0.099.     

Connected and Disconnected Maps

A new relation between morphisms in a category is introduced—roughly speaking (accurately in the categories Set and Top), f ∥ g iff morphisms w:dom(f)→dom(g) never map subobjects of fibres of f non-constantly to fibres of g. (In the algebraic setting replace fibre with kernel.) This relation and a slight weakening of it are used to define “connectedness” versus “disconnectedness” for morphisms. This parallels and generalises the classical treatment of connectedness versus disconnectedness for objects in a category (in terms of constant morphisms). The central items of study are pairs (F,G)({\mathcal F},{\mathcal G}) of classes of morphisms which are corresponding fixed points of the polarity induced by the ∥-relation. Properties of such pairs are examined and in particular their relation to (pre)factorisation systems is analysed. The main theorems characterise:

5-Torsion Points on Curves of Genus 2

Let C be a smooth proper curve of genus 2 over an algebraicallyclosed field k. Fix a Weierstrass point in C(k) and identifyC with its image in its Jacobian J under the Albanese embeddingthat uses as base point. For any integer N1, we write J_N forthe group of points in J(k) of order dividing N and for the subset of J_N of points oforder N. It follows from the Riemann–Roch theorem thatC(k)J₂ consists of the Weierstrass points of C and that C(k) and C(k) are empty (see [3]). The purpose of this paper is to study curvesC with C(k) non-empty.     

Examples of torsion points on genus two curves

We describe a method that sometimes determines all the torsion points lying on a curve of genus two defined over a number field and embedded in its Jacobian using a Weierstrass point as base point. We then apply this to the examples , , and .

     

Droplet size scaling of water-in-oil emulsions under turbulent flow

The size of droplets in emulsions is important in many industrial, biological, and environmental systems, as it determines the stability, rheology, and area available in the emulsion for physical or chemical processes that occur at the interface. While the balance of fluid inertia and surface tension in determining droplet size under turbulent mixing in the inertial subrange has been well established, the classical scaling prediction by Shinnar half a century ago of the dependence of droplet size on the viscosity of the continuous phase in the viscous subrange has not been clearly validated in experiment. By employing extremely stable suspensions of highly viscous oils as the continuous phase and using a particle video microscope (PVM) probe and a focused beam reflectance method (FBRM) probe, we report measurements spanning 2 orders of magnitude in the continuous phase viscosity for the size of droplets in water-in-oil emulsions. The wide range in measurements allowed identification of a scaling regime of droplet size proportional to the inverse square root of the viscosity, consistent with the viscous subrange theory of Shinnar. A single curve for droplet size based on the Reynolds and Weber numbers is shown to accurately predict droplet size for a range of shear rates, mixing geometries, interfacial tensions, and viscosities. Viscous subrange control of droplet size is shown to be important for high viscous shear stresses, i.e., very high shear rates, as is desirable or found in many industrial or natural processes, or very high viscosities, as is the case in the present study.