No description available.

Ceramides are sphingolipids that serve as important second messengers in an increasing number of stress-induced pathways. Ceramide has long been known to affect the mitochondria, altering both morphology and physiology. Lipopolysaccharide (LPS) is a prevalent circulating inflammatory agent in obesity, potentially mediating some of the pathologies associated with weight gain. Given previous findings of TLR4-mediated ceramide accrual and ceramide-mediated mitochondrial disruption, we questioned whether ceramide is necessary for LPS-induced mitochondrial disruption. We found that LPS treatment increased gene transcript levels of ceramide synthesis enzymes and mitochondrial fission proteins and increased ceramide content in cultured myotubes and in mouse tissue. Mitochondrial respiration from permeabilized red gastrocnemius was reduced from animals receiving LPS injections when compared with those receiving vehicle (PBS). However, respiration from mice receiving both LPS and myriocin, a ceramide inhibitor, (0.3 mg/kg) was similar to PBS-injected animals. We treated murine myotubes with similar LPS conditions. These cells demonstrated increased ceramide synthesis and increased levels of mitochondrial fission with LPS treatment; these effects were mitigated with the addition of myriocin. However, in contrast to the whole gastrocnemius response in animals receiving LPS, respiration from myotubes was increased with LPS alone, and even higher with both myriocin alone and myriocin with LPS. We also sought to assess the impact of ceramide on skeletal muscle mitochondrial structure and function. A primary observation was the rapid and dramatic division of mitochondria in ceramide-treated cells. This effect is likely a result of increased Drp1 action, as ceramide increased Drp1 expression and Drp1 inhibition prevented ceramide-induced mitochondrial fission. Further, we found that ceramide treatment reduced mitochondrial O2 consumption (i.e., respiration) in cultured myotubes and permeabilized red gastrocnemius muscle fiber bundles. Ceramide treatment also increased H2O2 levels and reduced Akt/PKB phosphorylation in myotubes. However, inhibition of mitochondrial fission via Drp1 knockdown completely protected the myotubes and fiber bundles from ceramide-induced metabolic disruption, including maintained mitochondrial respiration, reduced H2O2 levels, and unaffected insulin signaling. These data suggest that the forced and sustained mitochondrial fission that results from ceramide accrual may alter metabolic function in skeletal muscle, which is a prominent site not only of energy demand (via the mitochondria), but also of ceramide accrual with weight gain.

Nuclear physics experiments typically involve the collection and analysis of detector signals produced by the interaction of subatomic particles with matter to deduce various quantities. When heavy ions are involved, Si Detector signals are distorted by the formation of a plasma-like cloud from the interaction between the heavy ions and the detector material. The signal amplitude is reduced and delayed, two effects known as Pulse Height Defect (PHD) and Plasma Delay Time (PDT). A recent experiment was performed at the Institut Laue-Langevin(ILL) experimental nuclear reactor facility in Grenoble, using the LOHENGRIN mass spectrometer, to study these walk effects. The purpose of this project is to use a subset of the data to perform pulse shape analysis and develop a parametrization of the pulse waveform in order to better understand the PDT and PHD and how the pulses are affected. Initially, the PDT and PHD are estimated for masses 90, 100, 130 and 143 u using already established methods. The pulse waveforms are then investigated and a suitable parametrization of the pulse waveform is developed. The region around the pulse onset, which is important in extracting the timing characteristics of the pulse, is found to be described rather well by the Landau function. The Landau function parameters are further investigated and correlations with pulse shape characteristics are discussed. Finally, this novel parametrization is used as an alternative approach to estimate the PDT for the same masses as initially. Comparisons between the two methods indicate that the PDT is actually a combined effect of the physical plasma delay and the walk effects introduced by the underlying triggering routine that is used during offline analysis.

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No abstract provided. / Thesis / Master of Science (MSc) / Scope and contents: The probability of fission as a function of primary fragment velocities has been obtained by removing the neutron emission and instrumental dispersions from the velocities determined by Stein with time-of-flight techniques for the thermal neutron fission of u235. Each velocity was increased by 0.69% to make the average kinetic energy per fission agree with the calorimetric value of 167.1 Mev. Excitation energy distributions were obtained by using the primary fragment masses given by Cameron and assuming that the most probable charge distribution for a given mass ratio i s that which leads to the greatest energy release. Evaporation theory was used to determine the number of prompt neutrons emitted. When the excitation energy is divided equally between the fragments and a nuclear temperature of 0.59 Mev is used, the average number of neutrons emitted is 2.95 per fission.

L'étude de la réaction ²³⁸U + ⁶⁴Ni à 6,6 MeV par nucléon nous a permis d'identifier des rayons X caractéristiques de l'élément Z = 120. Ces X caractéristiques ont été trouvés en coïncidence avec des fragments de fission des noyaux composés de 120 protons formés au cours de la réaction. La multiplicité de ces rayonnements rend possible l'extraction des informations sur la probabilité de formation par fusion dans la réaction étudiée du noyau de Z = 120 ainsi que sur le temps de fission de ce noyau.

The core of a BWR constitutes a highly complex radiational and chemical environment. Nuclear fission is utilized to generate power and as a consequence, large quantities of ionizing radiation are produced. Gamma and beta-particles along with neutrons have the sufficient ranges to escape the fuel rods and deposit energy in the reactor coolant. By doing so, radiolysis is initiated. The radiolysis species present in the coolant can interact chemically with the fuel rod cladding and cause corrosion. Different forms of corrosion are found on BWR fuel, with some effects being very local.  This thesis work outlines a method developed to investigate local corrosion phenomena, with a high spatial resolution. The purpose was to study Zircaloy corrosion and more particularly, to investigate an observed jump in corrosion thickness around the lower enrichment step on BWR fuel rod cladding. The corrosion thickness jump is a very local effect, hence the need for high spatial resolution. Monte-Carlo simulations were performed in a GEANT4-model of an inoperation reactor, to study the energy deposited from ionizing radiation in the coolant, around the low enrichment-step of the fuel rods. The energy dose data was then used as input to lwrChem to compute electrochemical potential and equilibrium concentrations of radiolysis species. These are the quantities needed to compute an equivalent corrosion rate on the cladding surface, although this was not performed within this project. The main focus was to successfully develop the two-program method using GEANT4 and lwrChem and this was achieved.  The project was performed Uppsala University with financial contribution from Vattenfall Nuclear Fuel AB and scientific contribution from Studsvik Nuclear AB.

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