Particulate Backscattering Ratio at Leo 15 and Its Use to Study Particle Composition and Distribution

Particulate scattering and backscattering are two quantities that have traditionally been used to quantify in situ particulate concentration. The ratio of the backscattering by particles to total scattering by particles (the particulate backscattering ratio) is weakly dependent on concentration and therefore provides us with information on the characteristics of the particulate material, such as the index of refraction. The index of refraction is an indicator of the bulk particulate composition, as inorganic minerals have high indices of refraction relative to oceanic organic particles such as phytoplankton and detrital material that typically have a high water content. We use measurements collected near the Rutgers University Long-term Ecosystem Observatory in 15 m of water in the Mid-Atlantic Bight to examine application of the backscattering ratio. Using four different instruments, the HOBILabs Hydroscat-6, the WETLabs ac-9 and EcoVSF, and a prototype VSF meter, three estimates of the ratio of the particulate backscattering ratio were obtained and found to compare well. This is remarkable because these are new instruments with large differences in design and calibration. The backscattering ratio is used to map different types of particles in the nearshore region, suggesting that it may act as a tracer of water movement. We find a significant relationship between the backscattering ratio and the ratio of chlorophyll to beam attenuation. This implies that these more traditional measurements may be used to identify when phytoplankton or inorganic particles dominate. In addition, it provides an independent confirmation of the link between the backscattering ratio and the bulk composition of particles.

Analyzing diffuse scattering with supercomputers

Two new approaches to quantitatively analyze diffuse diffraction intensities from faulted layer stacking are reported. The parameters of a probability-based growth model are determined with two iterative global optimization methods: a genetic algorithm (GA) and particle swarm optimization (PSO). The results are compared with those from a third global optimization method, a differential evolution (DE) algorithm [Storn & Price (1997). J. Global Optim. 11, 341–359]. The algorithm efficiencies in the early and late stages of iteration are compared. The accuracy of the optimized parameters improves with increasing size of the simulated crystal volume. The wall clock time for computing quite large crystal volumes can be kept within reasonable limits by the parallel calculation of many crystals (clones) generated for each model parameter set on a super- or grid computer. The faulted layer stacking in single crystals of trigonal three-pointedstar- shaped tris(bicylco[2.1.1]hexeno)benzene molecules serves as an example for the numerical computations. Based on numerical values of seven model parameters (reference parameters), nearly noise-free reference intensities of 14 diffuse streaks were simulated from 1280 clones, each consisting of 96 000 layers (reference crystal). The parameters derived from the reference intensities with GA, PSO and DE were compared with the original reference parameters as a function of the simulated total crystal volume. The statistical distribution of structural motifs in the simulated crystals is in good agreement with that in the reference crystal. The results found with the growth model for layer stacking disorder are applicable to other disorder types and modeling techniques, Monte Carlo in particular.

Mesopelagic fish abundance and particle size spectrum analysis from Maria S. Merian cruise MSM26, spring 2013

One of the goals of EU BASIN is to understand variability in production across the Atlantic and the impact of this variability on higher trophic levels. One aspect of these investigations is to examine the biomes defined by Longhurst (2007). These biomes are largely based on productivity measured with remote sensing. During MSM 26, mesopelagic fish and size-spectrum data were collected to test the biome classifications of the north Atlantic. In most marine systems, the size-spectrum is a decay function with more, smaller organisms and fewer larger organisms. The intercept of the size-spectrum has been linked to overall productivity while the slope represents the "rate of decay" of this productivity (Zhou 2006, doi:10.1093/plankt/fbi119). A Laser In-Situ Scattering Transmissometer was used to collect size-spectrum data and net collections were made to capture mesopelagic fish. The relationship among the mesopelagic fish size and abundance distributions will be compared to the estimates of production from the size-spectrum data to evaluate the biomes of the stations occupied during MSM 26.

Particle size spectrum analysis during Maria S. Merian cruise MSM26, spring 2013

A Laser In-Situ Scattering Transmissometer (LISST) was used to collect vertical distribution data of particles from 2.5 to 500 µm in size. The LISST uses a multi-ring detector to measure scattering light of particles from a laser diode. Particles are classified into 32 log-spaced bins and the concentration of each bin is calculated as micro-liters per liter (µl/l). The instrument is rated to a depth of 300 m, and also records temperature and pressure. The sample interval was set to record every second. The LISST was attached to the LOPC frame to conduct casts and allow for particle-size comparisons between the two instruments. The LOPC is rated to a depth of 2000 m, thus a short deployment to a depth of 300 m was first conducted with both instruments. The instruments were then returned to the deck and the LISST removed via a quick release bracket so deep LOPC casts could be continued at a station. Raw LISST size-spectrum data is presented as concentrations for each of the 32 size bins for every second of the cast.

Calculation Methodology and Fabrication Procedures for Particle Accelerator Strip-Line Kickers: Application to the CTF3 Combiner Ring Extraction Kicker and TL2 Tail Clippers

A particle accelerator is any device that, using electromagnetic fields, is able to communicate energy to charged particles (typically electrons or ionized atoms), accelerating and/or energizing them up to the required level for its purpose. The applications of particle accelerators are countless, beginning in a common TV CRT, passing through medical X-ray devices, and ending in large ion colliders utilized to find the smallest details of the matter. Among the other engineering applications, the ion implantation devices to obtain better semiconductors and materials of amazing properties are included. Materials supporting irradiation for future nuclear fusion plants are also benefited from particle accelerators. There are many devices in a particle accelerator required for its correct operation. The most important are the particle sources, the guiding, focalizing and correcting magnets, the radiofrequency accelerating cavities, the fast deflection devices, the beam diagnostic mechanisms and the particle detectors. Most of the fast particle deflection devices have been built historically by using copper coils and ferrite cores which could effectuate a relatively fast magnetic deflection, but needed large voltages and currents to counteract the high coil inductance in a response in the microseconds range. Various beam stability considerations and the new range of energies and sizes of present time accelerators and their rings require new devices featuring an improved wakefield behaviour and faster response (in the nanoseconds range). This can only be achieved by an electromagnetic deflection device based on a transmission line. The electromagnetic deflection device (strip-line kicker) produces a transverse displacement on the particle beam travelling close to the speed of light, in order to extract the particles to another experiment or to inject them into a different accelerator. The deflection is carried out by the means of two short, opposite phase pulses. The diversion of the particles is exerted by the integrated Lorentz force of the electromagnetic field travelling along the kicker. This Thesis deals with a detailed calculation, manufacturing and test methodology for strip-line kicker devices. The methodology is then applied to two real cases which are fully designed, built, tested and finally installed in the CTF3 accelerator facility at CERN (Geneva). Analytical and numerical calculations, both in 2D and 3D, are detailed starting from the basic specifications in order to obtain a conceptual design. Time domain and frequency domain calculations are developed in the process using different FDM and FEM codes. The following concepts among others are analyzed: scattering parameters, resonating high order modes, the wakefields, etc. Several contributions are presented in the calculation process dealing specifically with strip-line kicker devices fed by electromagnetic pulses. Materials and components typically used for the fabrication of these devices are analyzed in the manufacturing section. Mechanical supports and connexions of electrodes are also detailed, presenting some interesting contributions on these concepts. The electromagnetic and vacuum tests are then analyzed. These tests are required to ensure that the manufactured devices fulfil the specifications. Finally, and only from the analytical point of view, the strip-line kickers are studied together with a pulsed power supply based on solid state power switches (MOSFETs). The solid state technology applied to pulsed power supplies is introduced and several circuit topologies are modelled and simulated to obtain fast and good flat-top pulses.

On the charged particle drag acting on LAGEOS

A recent study by the authors points to Charged Particle Drag (CPD) as a contributor to revisit in the LAGEOS non-gravitational perturbations problem. Such perturbations must account for dynamical contributions in the order of pms−2 . The simulated effect takes into account: (i) spatial and temporal variations of the plasmatic parameters (temperature and concentration of the species), (ii) spacecraft potential variations caused by both the eclipse passages and variations in the parameters mentioned above, and (iii) solar and geomagnetic conditions. Furthermore, recent theoretical improvements concerning scattering drag overcome previous limitations allowing for a complete formulation of this effect. For each satellite the lifetime CPD instantaneous acceleration is computed. The plasmatic parameters have been obtained fromthe Sheffield Coupled Thermosphere-Ionosphere-Plasmasphere (SCTIP) semi-empirical model (up to the polar region), as well as alytical/empirical approximations based on spacecraft measurements for the auroral and polar regions. Results show that maximum amplitudes for LAGEOSI are larger than those for LAGEOS-II: −85 pms−2 and −70 pms−2 respectively. This is due to the almost (magnetically) polar orbit configuration of the first, producing larger combinations of plasmatic parameter values. High solar activity has a huge impact in the resulting LAGEOS accelerations: it yields a perfect modulation of the resulting acceleration with maximum amplitudes up to a factor of 10 when comparing low and high activity periods. On the other hand, the impact of the geomagnetic activity results into a reduction of the effect itself, probably due to a decrease in the hydrogen concentration for high energy input periods. The acceleration results will be used in a refined orbit computation in a subsequent investigation.

A Semi-Lagrangian Particle Level Set Finite Element Method for Interface Problems

We present a quasi-monotone semi-Lagrangian particle level set (QMSL-PLS) method for moving interfaces. The QMSL method is a blend of first order monotone and second order semi-Lagrangian methods. The QMSL-PLS method is easy to implement, efficient, and well adapted for unstructured, either simplicial or hexahedral, meshes. We prove that it is unconditionally stable in the maximum discrete norm, � · �h,∞, and the error analysis shows that when the level set solution u(t) is in the Sobolev space Wr+1,∞(D), r ≥ 0, the convergence in the maximum norm is of the form (KT/Δt)min(1,Δt � v �h,∞ /h)((1 − α)hp + hq), p = min(2, r + 1), and q = min(3, r + 1),where v is a velocity. This means that at high CFL numbers, that is, when Δt > h, the error is O( (1−α)hp+hq) Δt ), whereas at CFL numbers less than 1, the error is O((1 − α)hp−1 + hq−1)). We have tested our method with satisfactory results in benchmark problems such as the Zalesak’s slotted disk, the single vortex flow, and the rising bubble.

Fast ignition driven by quasi-monoenergetic ions: Optimal ion type and reduction of ignition energies with an ion beam array

Fast ignition of inertial fusion targets driven by quasi-monoenergetic ion beams is investigated by means of numerical simulations. Light and intermediate ions such as lithium, carbon, aluminum and vanadium have been considered. Simulations show that the minimum ignition energies of an ideal configuration of compressed Deuterium-Tritium are almost independent on the ion atomic number. However, they are obtained for increasing ion energies, which scale, approximately, as Z2, where Z is the ion atomic number. Assuming that the ion beam can be focused into 10 ?m spots, a new irradiation scheme is proposed to reduce the ignition energies. The combination of intermediate Z ions, such as 5.5 GeV vanadium, and the new irradiation scheme allows a reduction of the number of ions required for ignition by, roughly, three orders of magnitude when compared with the standard proton fast ignition scheme.

Developments in the Theory of X-ray Absorption and Compton Scattering.

Thesis (Ph.D.)--University of Washington, 2016-06

Quantitative scattering of melanin solutions

The optical scattering coefficient of a dilute, well-solubilized eumelanin solution has been accurately measured as a function of incident wavelength, and found to contribute < 6% of the total optical attenuation between 210 and 325 nm. At longer wavelengths (325-800 nm), the scattering was less than the minimum sensitivity of our instrument. This indicates that ultraviolet and visible optical density spectra can be interpreted as true absorption with a high degree of confidence. The scattering coefficient versus wavelength was found to be consistent with Rayleigh theory for a particle radius of 38 6 1 nm. Our results shed important light on the role of melanins as photoprotectants.

Gas and particle dynamics of a contoured shock tube for pre-clinical microparticle drug delivery

We investigate the gas-particle dynamics of a device designed for biological pre-clinical experiments. The device uses transonic/supersonic gas flow to accelerate microparticles such that they penetrate the outer skin layers. By using a shock tube coupled to a correctly expanded nozzle, a quasi-one-dimensional, quasi-steady flow (QSF) is produced to uniformly accelerate the microparticles. The system utilises a microparticle cassette (a diaphragm sealed container) that incorporates a jet mixing mechanism to stir the particles prior to diaphragm rupture. Pressure measurements reveal that a QSF exit period - suitable for uniformly accelerating microparticles - exists between 155 and 220 mus after diaphragm rupture. Immediately preceding the QSF period, a starting process secondary shock was shown to form with its (x,t) trajectory comparing well to theoretical estimates. To characterise the microparticle, flow particle image velocimetry experiments were conducted at the nozzle exit, using particle payloads with varying diameter (2.7-48 mu m), density (600-16,800 kg/m(3)) and mass (0.25-10 mg). The resultant microparticle velocities were temporally uniform. The experiments also show that the starting process does not significantly influence the microparticle nozzle exit velocities. The velocity distribution across the nozzle exit was also uniform for the majority of microparticle types tested. For payload masses typically used in pre-clinical drug and vaccine applications (

Elastic and inelastic scattering of fast neutrons in fusion reactor materials

In this work, the angular distributions for elastic and. inelastic scattering of fast neutrons in fusion .reactor materials have been studied. Lithium and lead material are likely to be common components of fusion reactor wall configuration design. The measurements were performed using an associated particle time-of- flight technique. The 14 and 14.44 Mev neutrons were produced by the T(d,n} 4He reaction with deuterons being accelerated in a 150kev SAMES type J accelerator at ASTON and in.the 3. Mev DYNAMITRON at the Joint Radiation Centre, Birmingham respectively. The associated alpha-particles and fast. neutrons were detected.by means of a plastic scintillator mounted on a fast focused photomultiplier tube. The samples used were extended flat plates of thicknesses up to 0.9 mean-free-path for Lithium and 1.562 mean-free-path for Lead. The differential elastic scattering cross-sections were measured for 14 Mev neutrons for various thicknesses of Lithium and Lead in the angular range from zero to; 90º. In addition, the angular distributions of elastically scattered 14,.44 Mev .neutrons from Lithium samples were studied in the same angular range. Inelastic scattering to the 4.63 Mev state in 7Li and the 2.6 Mev state, and 4.1 Mev state in 208Pb have:been :measured.The results are compared to ENDF/B-IV data files and to previous measurements. For the Lead samples the differential neutron scattering:cross-sections for discrete 3 Mev ranges and the angular distributions were measured. The increase in effective cross-section due to multiple scattering effects,as the sample thickness increased:was found to be predicted by the empirical .relation ....... A good fit to the exoerimental data was obtained using the universal constant............ The differential elastic scattering cross-section data for thin samples of Lithium and Lead were analyzed in terms of optical model calculations using the. computer code. RAROMP. Parameter search procedures produced good fits to the·cross-sections. For the case of thick samples of Lithium and Lead, the measured angular distributions of :the scattered neutrons were compared to the predictions of the continuous slowing down model.

A study of the scattering of fast neutrons in large samples

In the present work, the elastic scattering of fast neutrons from iron and concrete samples were studied at incident neutron energies of 14.0 and 14.4 Mev, using a neutron spectrometer based on the associated particle time-of-flight technique. These samples were chosen because of their importance in the design of fusion reactor shielding and construction. Using the S.A.M.E.S. accelerator and the 3 M v Dynamitron accelerator at the Radiation Centre, 14.0 and 14.4 Mev neutrons were produced by the T(d, n)4He reaction at incident deuteron energies of 140 keV and 900 keV mass III ions respectively. The time of origin of the neutron was determined by detecting the associated alpha particles. The samples used were extended flat plates of thicknesses up to 1.73 mean free paths for iron and 2.3 mean free paths for concrete. The associated alpha particles and fast neutrons were detected by means of a plastic scintillator mounted on a fast focused photomultiplier tube. The differential neutron elastic scattering cross-sections were measured for 14 Mev neutrons in various thicknesses of iron and concrete in the angular range from zero to 90°. In addition, the angular distributions of 14.4 Mev neutrons after passing through extended samples of iron were measured at several scattering angles in the same angular range. The measurements obtained for the thin sample of iron were compared with the results of Coon et al. The differential cross-sections for the thin iron sample were also analyzed on the optical model using the computer code RAROMP. For the concrete sample, the angular distribution of the thin sample was compared with the cross-sections calculated from the major constituent elements of concrete, and with the predicted values of the optical model for those elements. No published data could be found to compare with the results of the concrete differential cross-sections. In the case of thick samples of iron and concrete, the number of scattered neutrons were compared with a phenomological calculation based on the continuous slowing down model. The variation of measured cross-sections with sample thickness were found to follow the empirical relation σ = σ0 eαx. By using the universal constant "K", good fits were obtained to the experimental data. In parallel with the work at 14.0 and 14.4 Mev, an associated particle time-of-flight spectrometer was investigated which used the 2H(d,n)3He reaction for 3.02 Mev neutron energy at the incident deuteron energy of 1 Mev.

Gamma rays associated with neutron scattering in fusion reactor materials

The gamma-rays produced by the inelastic scattering of 14 MeV neutrons. in fusion reactor materials have been studied using a gamma-ray spectrometer employing a sodium iodide scintillation detector. The source neutrons are produced by the T(d,n)4He reaction using the SAMES accelerator at the University of Aston in Birmingham. In order to eliminate the large gamma-ray background and neutron signal due to the sensitivity of the sodium iodide detector to neutrons, the gamma-ray detector is heavily shielded and is used together with a particle time of flight discrimination system based on the associated particle time of flight method. The instant of production of a source neutron is determined by detecting the associated alpha-particle enabling discrimination between the neutrons and gamma-rays by their different time of flight times. The electronic system used for measuring the time of flight of the neutrons and gamrna-rays over the fixed flight path is described. The materials studied in this work were Lithium and Lead because of their importance as fuel breeding and shielding materials in conceptual fusion reactor designs. Several sample thicknesses were studied to determine the multiple scattering effects. The observed gamma-ray spectra from each sample at several scattering angles in the angular range Oº - 90° enabled absolute differential gamma-ray production cross-sections and angular distributions of the resolved gamma-rays from Lithium to be measured and compared with published data. For the Lead sample, the absolute differential gamma-ray production cross-sections for discrete 1 MeV ranges and the angular distributions were measured. The measured angular distributions of the present work and those on Iron from previous work are compared to the predictions of the Monte Carlo programme M.O.R.S.E. Good agreement was obtained between the experimental results and the theoretical predictions. In addition an empirical relation has been constructed which describes the multiple scattering effects by a single parameter and is capable of predicting the gamma-ray production cross-sections for the materials to an accuracy of ± 25%.

First-principles investigation of the alloy scattering potential in dilute Si1-xCx

A first-principles method is applied to find the intra and intervalley n-type carrier scattering rates for substitutional carbon in silicon. The method builds on a previously developed first-principles approach with the introduction of an interpolation technique to determine the intravalley scattering rates. Intravalley scattering is found to be the dominant alloy scattering process in Si1-xCx, followed by g-type intervalley scattering. Mobility calculations show that alloy scattering due to substitutional C alone cannot account for the experimentally observed degradation of the mobility. We show that the incorporation of additional charged impurity scattering due to electrically active interstitial C complexes models this residual resistivity well.