Laboratory studies of bromide oxidation in the presence of ozone: Evidence for glass-surface mediated reaction

The reaction of sodium bromide particles in the presence of ozone was studied in a flow system both under dark conditions and with 254 nm radiation. We found that there was significant formation of gaseous bromine (probably Br2) in the presence of ozone in the dark, and that bromide deposited to the walls of the Pyrex reaction flask was its source. The observed rate of gaseous bromine formation in these experiments was approximately 100–1000 times faster than expected based on the knownrate constant for aqueous reaction of bromide with ozone. While the mechanism responsible for this enhanced reactivity was not identified, based on previous reports we suggest that the glass surface converted ozone to more reactive species, such as hydroxyl radical, which in turn oxidized bromide. In the presence of 254 nm radiation, rates of gaseous bromine collection were further enhanced, likely as a result of increased radical production in the system, and wall-deposited bromide was also the source of the gaseous bromine. In these `light' experiments, there was a significant decline in ozone mixing ratios, consistent with bromine radical chemistry. These results suggest the possibility that ozone reacting with internally mixed silicate/sea-salt particles might be a significant mechanism for the oxidation of particulate halides, and subsequent release of photoactive halogen species, in the marine boundary layer

A chemical probe technique for the determination of reactive halogen species in aqueous solution: Part 1 ? bromide solutions

International audienceReactive halogen species (X*=X˙, ˙X2?, X2 and HOX, where X=Br, Cl, or I) in seawater, sea-salt particles, and snowpacks play important roles in the chemistry of the marine boundary layer. Despite this, relatively little is known about the steady-state concentrations or kinetics of reactive halogens in these environmental samples. In part this is because there are few instruments or techniques that can be used to characterize aqueous reactive halogens. To better understand this chemistry, we have developed a chemical probe technique that can detect and quantify aqueous reactive bromine and chlorine species (Br*(aq) and Cl*(aq)). This technique is based on the reactions of short-lived X*(aq) species with allyl alcohol (CH2=CHCH2OH) to form stable 3-halo-1,2-propanediols that are analyzed by gas chromatography. Using this technique in conjunction with competition kinetics allows determination of the steady state concentrations of the aqueous reactive halogens and, in some cases, the rates of formation and lifetimes of X* in aqueous solutions. We report here the results of the method development for aqueous solutions containing only bromide (Br?)

A simple Fourier transform-based reconstruction formula for photoacoustic computed tomography with a circular or spherical measurement geometry

Photoacoustic computed tomography (PACT), also known as optoacoustic tomography, is an emerging imaging modality that has great potential for a wide range of biomedical imaging applications. In this Note, we derive a hybrid reconstruction formula that is mathematically exact and operates on a data function that is expressed in the temporal frequency and spatial domains. This formula explicitly reveals new insights into how the spatial frequency components of the sought-after object function are determined by the temporal frequency components of the data function measured with a circular or spherical measurement geometry in two- and three-dimensional implementations of PACT, respectively. The structure of the reconstruction formula is surprisingly simple compared with existing Fourier-domain reconstruction formulae. It also yields a straightforward numerical implementation that is robust and two orders of magnitude more computationally efficient than filtered backprojection algorithms.Comment: http://iopscience.iop.org/0031-9155/57/23/N493

On the nucleon self-energy in nuclear matter

We consider the nucleon self-energy in nuclear matter in the absence of Pauli blocking. It is evaluated using the partial-wave analysis of $NN$ scattering data. Our results are compared with that of a realistic calculation to estimate the effect of this blocking. It is also possible to use our results as a check on the realistic calculations.Comment: 6 pages, 2 figure

A partial-dithering strategy for edge-illumination X-ray phase-contrast tomography enabled by a joint reconstruction method

Edge-illumination X-ray phase-contrast tomography (EIXPCT) is a promising imaging technology where partially opaque masks are utilized with laboratory-based X-ray sources to estimate the distribution of the complex-valued refractive index. EIXPCT resolution is mainly determined by the period of a sample mask, but can be significantly improved by a dithering technique. Here, dithering means that multiple images per tomographic view angle are acquired as the object is moved over sub-pixel distances. Drawbacks of dithering include increased data-acquisition times and radiation doses. Motivated by the flexibility in data-acquisition designs enabled by a recently developed joint reconstruction (JR) method, a novel partial-dithering strategy for EIXPCT data-acquisition is proposed. In this strategy, dithering is implemented at only a subset of the tomographic view angles. The strategy can result in spatial resolution comparable to that of the conventional full-dithering strategy, where dithering is performed at every view angle, but the acquisition time is substantially decreased. Here, the effect of dithering parameters on image resolution are explored

Blast Effects on Structural Elements

Blast loads can represent a great hazard to existing structures. Their effects on structural elements can be decisive for the integrity of both the structure itself and the people within it. The behaviour of the individual elements of a building is totally different due to the heterogeneity of the materials composing them. This fact makes it necessary to carry out tests on each type of structural element in order to correctly evaluate the response of the structure. In addition, the scale effect can produce inaccurate results, making it necessary for tests to be performed on a full scale to validate the results. In this work, the results of several tests with explosives are presented, in different constructive elements, all of them carried out at full scale. These elements range from the structural elements (beams and concrete slabs) to the weak elements of a building (masonry panels)

Single particle spectrum and binding energy of nuclear matter

In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a parabolic approximation is often used in the literature. The variation in the binding energy value introduced by the parabolic approximation is quantitatively analyzed in detail. It is found that the approximation can introduce an uncertainty of 1-2 MeV near the saturation density.Comment: 6 Latex pages, 3 postscript figure

Dielectric susceptibility of the Coulomb-glass

We derive a microscopic expression for the dielectric susceptibility X of a Coulomb glass, which corresponds to the definition used in classical electrodynamics, the derivative of the polarization with respect to the electric field. The fluctuation–dissipation theorem tells us that is a function of the thermal fluctuations of the dipole moment of the system. We calculate X numerically for three–dimensional Coulomb glasses as a function of temperature and frequency.We acknowledge financial support from the DGES project number PB96-1118, SMWK, and DFG (SFB 393). A great part of this work was performed during A. D.-S.’s visit at the IFW Dresden; A. D.-S. thanks the IFW for its hospitality