Changing food webs in Lake Michigan: Dreissena and the microbial loop

U.S. Department of the InteriorU.S. Geological SurveyOpe

Master of Science

thesisDiscrimination of delayed emissions from photonuclear fission events provides the necessary information for the detection of nuclear materials. The time and energy characteristics of signature signals provide unique fingerprints which can be used for the identification and quantification of fissionable isotopes using γ-ray spectroscopy. This investigation explores measurement results of β-delayed γ-rays from photofission events. During the experiment, spectroscopy measurements were taken using two high-purity germanium detectors while three separate signal processing units were used for data acquisition. Interrogation of 238U, 239Pu, and 232Th was performed using a 22 MeV pulsed bremsstrahlung photon beam. Fission fragments with energies above 3 MeV were identified as delayed-fission γ-rays unique to the fissionable materials. A numerical model of the experimental setup is also proposed as part of this research. This model is based on the Monte Carlo radiation transport code MCNPX. The data from the experiment were used to validate the numerical models. Additionally, photonuclear data libraries were tested in the numerical model for consistency and accuracy. The numerical results showed a good agreement with the experimental data, specifically the comparison of 238U. Discrepancies between the numerical results and experimental data of 232Th were observed. A new photonuclear data library from TENDL/ACE was then implemented for 232Th and the numerical results were improved. One of the main contributions of this work is the development of a reliable computational model that gives almost the same results that could be performed on a physical experimentation as a less expensive option to examine the factors that could fall behind the spectroscopy measurements

Reallocating Multiple Facilities on the Line

We study the multistage $K$-facility reallocation problem on the real line, where we maintain $K$ facility locations over $T$ stages, based on the stage-dependent locations of $n$ agents. Each agent is connected to the nearest facility at each stage, and the facilities may move from one stage to another, to accommodate different agent locations. The objective is to minimize the connection cost of the agents plus the total moving cost of the facilities, over all stages. $K$-facility reallocation was introduced by de Keijzer and Wojtczak, where they mostly focused on the special case of a single facility. Using an LP-based approach, we present a polynomial time algorithm that computes the optimal solution for any number of facilities. We also consider online $K$-facility reallocation, where the algorithm becomes aware of agent locations in a stage-by-stage fashion. By exploiting an interesting connection to the classical $K$-server problem, we present a constant-competitive algorithm for $K = 2$ facilities

Pulsed photofission delayed gamma ray detection for nuclear material identification

pre-printInnovative systems with increased sensitivity and resolution are in great demand to detect diversion and to prevent misuse in support of nuclear materials management for the U.S. fuel cycle. Nuclear fission is the most important multiplicative process involved in non-destructive active interrogation. This process produces the most easily recognizable signature for nuclear materials. High-energy gamma rays can also excite a nucleus and cause fission through a process known as photofission. After photofission reactions, delayed signals are easily distinguishable from the interrogating radiation. LINAC-based, advanced inspection techniques utilizing the fission signals after photofission have been extensively studied for homeland security applications. Previous research also showed that a unique delayed gamma ray energy spectrum exists for each fissionable isotope. Isotopic composition measurement methods based on delayed gamma ray spectroscopy will be the primary focus of this work

Left main reconstruction as an alternative method to CABG after primary PCI complication

AbstractLeft main coronary artery disease is rare, accounting for 1% of all coronary artery disease and traditionally, is treated by coronary artery bypass grafting. We report our experience and five years follow up, after a coronary osteal surgical plasty in a young man who referred to our center with an anterior myocardial infarction

Hemangioma of penile urethra—treatment with simple transurethral excision: a case report

Urethral hemangiomas are rare benign vascular tumors with varying size and usually present as urethral bleeding and/ or hematuria. Treatment depends on the size and site of the lesion. We present a 27 year old male with a two year history of intermittent episodes of urethral bleeding. Cystourethroscopy showed a solitary hemangioma in the penile urethra. The patient was treated with simple transurethral excision with the biopsy forceps. The catheter was removed 48 hours later. He remains symptom free four months later. Simple excision of small hemangiomas may be an effective treatment especially for young patients in order to avoid the side effects of diathermy and when facilities such is laser are not available