No description available.

Made available in DSpace on 2014-10-09T12:50:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:49Z (GMT). No. of bitstreams: 1 00722.pdf: 1035259 bytes, checksum: c3c9dd7bddfbc4d12b362b3cf414a527 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Made available in DSpace on 2014-10-09T12:50:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:49Z (GMT). No. of bitstreams: 1 00722.pdf: 1035259 bytes, checksum: c3c9dd7bddfbc4d12b362b3cf414a527 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

<p> Fission-product bromine was isolated from a uranium target by the hot-atom reaction of the fission recoils with methane to form organic bromides. The organically-bound bromine was shown to be formed preferentially by primary (independently-formed) bromine with little contribution from secondary bromine. </p> <p> The delayed-neutron activity of the short-lived bromine isotopes was analyzed to obtain the relative yields of delayed neutrons from Br8?, Br88 and Br89 produced as primary fission products. The relative delayed-neutron yields are summarized below. (see abstract in text) </p> / Thesis / Doctor of Philosophy (PhD)

For many animals, rapid movements place high power demands on underlying muscles. Storage of muscle energy in elastic structures and the subsequent rapid release of that energy can effectively amplify muscle power. Elastic recoil can also confer thermal robustness to performance in behaviors occurring at variable temperatures. Muscle contractile performance tends to decrease at lower temperatures, but elastic recoil is less affected by temperature. Here I examine the impacts of temperature and scale in systems using elastic recoil and I explore possible interactive effects on movement performance. I explored the role that muscle contractile properties play in the differences in performance and thermal robustness between elastic and non-elastic systems by examining muscles from two species of plethodontid salamanders with elastically powered tongue projection and one with non-elastic tongue projection. These salamanders use tongue projection to capture prey and in species with elastic mechanisms, tongue projection is characterized by higher mechanical power output and thermal robustness compared to tongue projection of closely-related genera with non-elastic mechanisms. In vitro and in situ muscle experiments reveal that species differ in their muscle contractile properties, but these patterns do not predict the performance differences between elastic and non-elastic tongue projection. Overall, salamander tongue muscles are like other vertebrate muscles in contractile performance and thermal sensitivity. I conclude that changes in the tongue-projection mechanism, specifically the elaboration of elastic structures, are responsible for high performance and thermal robustness in species with elastic tongue projection. This suggests that the evolution of high-performance and thermally robust elastic-recoil mechanisms can occur via relatively simple changes to morphology, while muscle contractile properties remain relatively unchanged. The efficacy of elastic recoil in the face of changing temperature depends on the mechanical work done by muscle contraction being unaffected by temperature. In vitro stimulation of Cuban tree frog (Osteopilus septentrionalis) plantaris muscles reveals that interactions between force and temperature affect the mechanical work of muscle. At low temperatures (9 – 17°C), muscle work depends on temperature when shortening at any force, and temperature effects are greater at higher forces. At warmer temperatures (13 – 21°C), muscle work depends on temperature when shortening with intermediate and high forces (≥ 30% peak isometric tetanic force). Shortening velocity is most strongly affected by temperature at low temperatures and high forces. Power is also most strongly affected at low temperature intervals but this effect is minimized at intermediate forces. Effects of temperature on muscle force explain these interactions; force production decreases at lower temperatures, increasing the challenge of moving a constant force relative to the muscle’s capacity. These results suggest that animal performance that requires muscles to do work with low forces relative to a muscle’s maximum force production will be robust to temperature changes, and this effect should be true whether muscle acts directly or through elastic-recoil mechanisms and whether force is prescribed (i.e. internal) or variable (i.e. external). Conversely, performance requiring muscles to shorten with relatively large forces is expected to be more sensitive to temperature changes. How muscle work and power scale determines, in part, the scaling of movement performance. Muscle-mass-specific work is predicted to remain constant across a range of scales, assuming geometric similarity, while muscle-mass-specific power is expected to decrease with increasing scale. I tested these predictions by examining muscle morphology and contractile properties of plantaris muscles from frogs ranging in mass from 1.28 to 20.60 g. Scaling of muscle work and power was examined using both linear regression on log10-transformed data (LR) and non-linear regressions on untransformed data (NLR). In LR, muscle-mass-specific work decreased with increasing scale, but this is counteracted by a positive allometry of muscle mass to predict constant movement performance at all scales. These relationships were non-significant in NLR, though scaling with geometric similarity also predicts constant jump performance across scales. Both intrinsic shortening velocity and muscle-mass-specific power were positively allometric in both types of analysis. However, these differences between methods are caused not by large changes in scaling slopes, but by changing levels of statistical significance using corrections for multiple tests. The dependence of these conclusions on the method of regression, largely because of the setting and adjusting of an arbitrary alpha, demonstrates the importance of careful consideration of statistical methods when analyzing patterns of scaling. Nonetheless, scale accounts for little variation in contractile properties over the range of scales examined, indicating that other sources of intraspecific variation may be more important in determining muscle performance and its effects on movement. Elastic recoil used for power amplification is most often found in smaller animals, suggesting that performance in larger animals using less elastic recoil would be affected more by changing temperatures. To examine the interaction between scale and temperature on performance, I recorded jumps from 1-34 g Cuban tree frogs (Osteopilus septentrionalis) at 10, 20, and 30°C and compared jump performance to predictions based on the effects of temperature and scaling on muscle properties. High muscle-mass-specific power requirements from measured jumps indicate that frogs use elastic recoil at all scales to achieve performance that would be impossible using only muscle, and elastic recoil allows small frogs to achieve the same level of performance as large frogs. Performance that is greater at all temperatures than predictions from models using only muscle power could result from some combination of elastic recoil and power directly from muscle. The relative contributions of muscle power and elastic recoil cannot be discerned by examining temperature effects on performance because these effects are predicted to be so similar. Predicted performance from models of elastic recoil is significantly affected by changing temperature at all scales with temperature coefficient (Q10) values similar to predictions for muscle-powered jumping. Measured Q10 values are similar to those from both predictive models and there is no interaction between temperature and scale. Therefore, elastic recoil allows for jump performance that could not be achieved by muscle power alone at all temperatures and scales, but performance predictions from elastic recoil are not more thermally robust than predictions for muscle-powered jumping.

As of writing this thesis there are two detectors at TRIUMF’s DRAGON facility which directly measure the kinetic energy (E) of heavy ions at the focal plane of its recoil separator. These are an ionization chamber and a double-sided-silicon-strip detector (DSSSD). The ionization chamber has in- ferior resolution to the DSSSD but can discriminate isobaric contaminants in a E-∆E spectrum. A DSSSD has superior energy resolution and timing but cannot discriminate isobaric contaminants in many cases. A hybrid ioniza- tion chamber / double-sided-silicon-strip detector has been designed using the GEANT4 simulation package that combines the strengths of both these detec- tor types. This hybrid detector design consists of an ionization chamber set in front of a DSSSD positioned at the end of the beamline of the recoil separator. The design presented here is specific to DRAGON’s needs but can conceiv- ably be re-purposed in other environments requiring heavy ion detection and identification and may be useful in fields such as health physics. / Thesis / Master of Science (MSc)

The nucleus is a mesoscopic system that retains features from both the quantum and macroscopic worlds. A basic property of a macroscopic body is its shape. Nuclear shapes can be deduced from experimental data as they influence the excitation mode of the nucleus and hence the energies and lifetimes of its excited levels. Various short-lived nuclei were created in fusion-evaporation experiments performed at international heavy-ion accelerator facilities. The emitted γ rays and, in some experiments, also the charged particles and neutrons emitted in the reactions were detected. The studied neutron-deficient isotopes were either selected by the type and number of particles emitted in the reactions, or by using their characteristic decays. The excited states of the different isotopes were extracted from the γ-ray analyses. Spectroscopic properties, such as the lifetimes of the excited states or the angular distribution of the emitted γ rays were measured when possible. The experimentally obtained level schemes together with the other spectroscopic information were used to deduce the excitation modes and the shapes of the studied nuclei. The detector systems are described in the first chapter and in the second chapter some techniques used to extract information from the experimental data are explained. Finally, a brief theoretical overview on the nuclear models which were used to interpret the experimental results is given. / QC 20100621

Gas Metal Arc Welding (GMAW) is one of the most important welding processes in industrial application. To control metal transfer at given variables is a focus in the field of research and development in welding community. In this dissertation, laser enhanced GMAW is proposed and developed by adding a lower power laser onto the droplet to generate an auxiliary detaching force. The electromagnetic force needed to detach droplets, thus the current that determines this force, is reduced. Wire feed speed, arc voltage, and laser intensity were identified as three major parameters that affect the laser enhanced metal transfer process and a systematic series of experiments were designed and conducted to test these parameters. The behaviors of the laser enhanced metal transfer process observed from high speed images were analyzed using the established physics of metal transfer. In all experiments, the laser was found to affect the metal transfer process as an additional detaching force that tended to change a short-circuiting transfer to drop globular or drop spray, reduce the diameter of the droplet detached in drop globular transfer, or decrease the diameter of the droplet such that the transfer changed from drop globular to drop spray. The enhancement of the laser was found to increase as the laser intensity increased. The larger laser intensity tended to help reduce the size of the droplet detached. The arc voltage affected the metal transfer process through changing the current and changing the gap and possible time interval of the droplet development. A larger arc voltage helped reduce the size of the droplet detached through an increased electromagnetic force. Desired heat input and current/arc pressure waveforms may thus be both delivered and controlled by GMAW through laser enhancement. Laser recoil pressure force was estimated based on the difference of gravitational force with and without laser pulse, and the result was with an acceptable accuracy. Good formation of welds and full penetration of thin plate could be obtained using laser enhanced GMAW. A nonlinear model was established to simulate the dynamic metal transfer in laser enhanced GMAW, and the results agree with the experimental one.

A large acceptance polarimeter has been designed to measure recoil polarisation in pseudoscalar (Jπ=0−) meson photoproduction reactions. The device was installed at the MAMI facility at the Institut für Kernphysik in Mainz, Germany. A racetrack microtron provided a longitudinally polarised 1.5 GeV electron beam, which impinged on a 12 μm copper radiator, producing a beam of circularly polarised Bremsstrahlung photons with energies between 400-1400 MeV. The electrons were then momentum analysed in the Glasgow Photon Tagging Spectrometer to tag the photon energy with a resolution of ~4 MeV. The photons were incident on a liquid hydrogen target, and the reaction products were detected using the Crystal Ball and TAPS detectors. The beam-recoil polarisation observable Cx, which describes the fraction of circular polarisation transferred from the photon beam to the recoiling nucleon, was measured in the reactions γp→pπ0 and γp→pη from data taken in September-October 2008. The results for π0 production give a significant expansion of the world data set and are shown to be consistent with the few previous measurements taken at Jefferson Lab, USA, while the results for the η channel are a world first. The observed values for Cx are compared to the current solutions from the two leading partial wave analyses, SAID and MAID, with wide angular coverage up to a photon beam energy of 1400 MeV. Significant discrepancies in the prediction of Cx can be resolved by the new data.

Studying nuclei beyond the proton dripline can provide valuable information on the structure of nuclei at the limits of stability, where the strong nuclear force starts to be overcome by Coulomb repulsion between protons. Simple experimental observables, such as excitation energies and lifetimes of excited states in these proton-unbound nuclei can provide information on the nuclear wave function. Experimental data, such as that presented in this work, can then be used to improve models of nuclear structure at the proton dripline. This thesis presents data from a recoil-decay tagged differential plunger experiment undertaken at the University of Jyvaskyla in 2014. A fusion-evaporation reaction was used to populate excited states in the deformed ground-state proton emitter 113Cs. The JUROGAM-RITU-GREAT experimental setup was used to correlate gamma rays emitted from these excited states with protons emitted from 113Cs and the differential plunger for unbound nuclear states (DPUNS) was placed at the target position to measure the excited state lifetimes. The lifetime of the (11/2+) state in the most intense rotational band of 113Cs was measured to be tau = 24(6) ps, while a limit of tau is less than or equal to 5 ps was found for the lifetime of the higher energy (15/2+) state. The lifetime of proton emission was measured to be tau = 24.2(2) microseconds. The experimental data were used to test the predictions of a non adiabatic quasi-particle model for proton-emitting nuclei, which was employed to deduce the deformation of the states in 113Cs. Wave functions from the non adiabatic quasi-particle model were used to independently calculate proton-emission rates, gamma-ray transition rates and excited state energies as functions of deformation. The deformation of 113Cs could then be extracted from the intersection of the different theoretical values and experimental observables. A deformation of beta2 = 0.22(6)was extracted from the (11/2+) excitation energy and lifetime. The deformation values taken from the proton-emission rate and the lifetime limit of the (15/2+) state were also consistent with this value. The consistency of the different deformations calculated shows the effectiveness of the non adiabatic quasi-particle method when used to calculate the properties of deformed ground-state proton-emitters.