Optimal Calibration of PET Crystal Position Maps Using Gaussian Mixture Models

A method is developed for estimating optimal PET gamma-ray detector crystal position maps, for arbitrary crystal configurations, based on a binomial distribution model for scintillation photon arrival. The approach is based on maximum likelihood estimation of Gaussian mixture model parameters using crystal position histogram data, with determination of the position map taken from the posterior probability boundaries between mixtures. This leads to minimum probability of error crystal identification under the assumed model

Impact of Home Field Advantage: Analyzed Across Three Professional Sports

We examined the impact of home-field advantage in the NFL, NBA, and MLB. We defined home-field advantage as winning more than 50% of the home games. Additionally, we took into consideration how season length could act as a moderator and influence the impact of home-field advantage. We collected data from the 2015 NBA and MLB seasons and the 2015 and 2016 NFL seasons to determine statistical significance. In total, we got data from 4,141 games to analyze. We found that there is statistical significance that the home team has a better chance of winning than the away team across the NFL, NBA, and MLB. We also found that season length has a significant impact on home team winning percentage

Cryogenic Microwave Imaging of Metal-Insulator Transition in Doped Silicon

We report the instrumentation and experimental results of a cryogenic scanning microwave impedance microscope. The microwave probe and the scanning stage are located inside the variable temperature insert of a helium cryostat. Microwave signals in the distance modulation mode are used for monitoring the tip-sample distance and adjusting the phase of the two output channels. The ability to spatially resolve the metal-insulator transition in a doped silicon sample is demonstrated. The data agree with a semi-quantitative finite-element simulation. Effects of the thermal energy and electric fields on local charge carriers can be seen in the images taken at different temperatures and DC biases.Comment: 10 pages, 5 Figures, Accepted to Review of Scientific Instrumen

Simple model of ocean-atmosphere interactions in the topical climate system

May 1999.Includes bibliographical references.The tropical sea surface temperature (SST) distribution strongly modulates the global atmospheric circulation. Although the mechanisms which generate SST anomalies have been the subject of intense scrutiny in recent years [see Neelin et al. (1998) for a review], the steady tropical climate has received much less attention. As a consequence, the dominant physical processes which maintain the steady tropical climate remain poorly under­ stood. The goal ;)f this report is to construct and use a simple, mechanistic box model of the tropical ocean-atmosphere climate system to develop ideas about the interactions among various physical processes which can be tested against observations and results from more sophisticated models. Efforts to study the steady tropical climate have been aided by the recent emergence of box models. Pierrehumbert (1995) developed a two-box model of the tropical climate in which one box represents the ascending branch of the Hadley/Walker circulation, and the second box represents the subsiding branch. Pierrehumbert used the model to demonstrate the importance of a low-water-vapor region in exporting to space excess heat that is generated by the ascending branch. Later studies using box models have demonstrated the im­portance of ocean dynamics (Sun and Liu 1996) and low-level stratus clouds (Miller 1997) for regulating ST and the SST gradient. Despite their success in simulating the tropical climate, simplifying assumptions in these box models make conclusions derived from them less than robust. None of these box models include a momentum budget for the ocean or atmosphere. Each of the box models emphasizes either the ocean or the atmosphere and settles for a highly simplified representation of the other. We have developed a simple coupled ocean-atmosphere model of the Walker circulation which has separate boxes for the ascending and descending branches of the atmospheric circulation and separate boxes for the Cold Pool, Warm Pool, and undercurrent. This is the first box model to include explicit momentum budgets for the atmosphere and ocean components and to calculate the fractional width of the Warm Pool. The atmospheric model contains an explicit hydrologic cycle, a simplified but physically based radiative transfer parameterization, and interactive clouds. We first explored the conditions under which the Warm Pool can establish a radiative-convective equilibrium. Under clear skies, quasi-tropical equilibria occur for realistic prescribed SSTs and wind speeds, but realistic clear-sky equilibria of the tropical ocean-atmosphere system do not occur. If the surface temperature is allowed to vary, the model runs away. When cloud radiative effects are incorporated, the model reaches an unrealistically warm, dry radiative-convective equilibrium. For simulations in which cloud radiative effects are incorporated and realistic, lateral transports of energy and moisture are specified, equilibrium of the ocean-atmosphere system occurs for an SST of 300 K and precipitable water of 40 kg m-2, which is quite realistic. We also demonstrated the sensitivity of the tropopause height and temperature to cloud radiative effects. The tropopause height and temperature are calculated based on the requirement of temperature continuity at the bottom of a two-layer stratosphere in radiative equilibrium. As the cloud optical depth or cloud fraction increase, the upward longwave flux across the tropopause decreases, and so the tropopause temperature decreases and tropopause height increases. Our results from the fully coupled model indicate that the intensity of the tropical circulation is crucially dependent on the specified cloud fraction in the Warm-Pool region and on the amount and distribution of water vapor above the Cold-Pool boundary layer (CPBL). In response to increasing the cloud fraction above the Warm Pool, a feedback involving the tropopause height slows the Walker circulation. As the cloud fraction over the Warm Pool increases, the altitude of the tropopause increases, and so air is advected to the Cold-Pool region from higher, drier altitudes. The effects of the drier air are to reduce the radiative cooling rate above the CPBL and, therefore, to reduce the subsidence rate. Since the width of the Cold Pool remains approximately constant, a decreased subsidence rate implies a weaker Walker circulation. In order to maintain energy balance in spite of a weaker circulation, the precipitable water over the Warm Pool must increase. The radiative effect of the precipitable water contributes to an increase of SST in the Warm Pool. Our "wet troposphere" experiment shows that the Walker circulation intensifies if air which is advected to the subsiding region originates from a lower altitude in the Warm-Pool region. Because the circulation is more intense, the SST and precipitable water of the Warm Pool must decrease in order to balance the energy and moisture budgets. Experiments using our ocean model reveal that cold-water upwelling is the dominant mechanism for regulating SST in the Cold Pool. Although the radiative effect of stratus clouds further depress SST, ocean dynamics prevent the mixed-layer temperature from warming by more than 4 K beyond the temperature of the undercurrent.Sponsored by the National Atmospheric and Space Administration under grant number NAG1-1266 and the National Science Foundation under grant number ATM-92149

Relation of modifiable neighborhood attributes to walking

Abstract Background There is a paucity of research examining associations between walking and environmental attributes that are more modifiable in the short term, such as car parking availability, access to transit, neighborhood traffic, walkways and trails, and sidewalks. Methods Adults were recruited between April 2004 and September 2006 in the Minneapolis-St Paul metropolitan area and in Montgomery County, Maryland using similar research designs in the two locations. Self-reported and objective environmental measures were calculated for participants\u27 neighborhoods. Self-reported physical activity was collected through the long form of the International Physical Activity Questionnaire (IPAQ-LF). Generalized estimating equations were used to examine adjusted associations between environmental measures and transport and overall walking. Results Participants (n = 887) averaged 47 years of age (SD = 13.65) and reported 67 min/week (SD = 121.21) of transport walking and 159 min/week (SD = 187.85) of non-occupational walking. Perceived car parking difficulty was positively related to higher levels of transport walking (OR 1.41, 95%CI: 1.18, 1.69) and overall walking (OR 1.18, 95%CI: 1.02, 1.37). Self-reported ease of walking to a transit stop was negatively associated with transport walking (OR 0.86, 95%CI: 0.76, 0.97), but this relationship was moderated by perceived access to destinations. Walking to transit also was related to non-occupational walking (OR 0.85, 95%CI: 0.73, 0.99). Conclusions Parking difficulty and perceived ease of access to transit are modifiable neighborhood characteristics associated with self-reported walking

A Far Green Country : Tolkien, Paradise, and the End of All Things in Medieval Literature

Attempts to explain exactly what Frodo goes to when he sails from the Grey Havens. By looking at paradise, purgatory, and earthly Edens in medieval literature and theology, we gain a better understanding of the spiritual purpose of Tolkien’s “far green country” beyond the bent paths of the world. References “Pearl,” “Sir Orfeo,” mystery play cycles, and Sir John Mandeville’s Travels, among other sources

Diet-induced obesity impairs mammary development and lactogenesis in murine mammary gland

We have developed a mouse model of diet-induced obesity that shows numerous abnormalities relating to mammary gland function. Animals ate 40% more calories when offered a high-fat diet and gained weight at three times the rate of controls. They exhibited reduced conception rates, increased peripartum pup mortality, and impaired lactogenesis. The impairment of lactogenesis involved lipid accumulation in the secretory epithelial cells indicative of an absence of copius milk secretion. Expression of mRNAs for -casein, whey acid protein, and -lactalbumin were all decreased immediately postpartum but recovered as lactation was established over 2–3 days. Expression of acetyl-CoA carboxylase (ACC)- mRNA was also decreased at parturition as was the total enzyme activity, although there was a compensatory increase in the proportion in the active state. By day 10 of lactation, the proportion of ACC in the active state was also decreased in obese animals, indicative of suppression of de novo fatty acid synthesis resulting from the supply of preformed fatty acids in the diet. Although obese animals consumed more calories in the nonpregnant and early pregnant states, they showed a marked depression in fat intake around day 9 of pregnancy before food intake recovered in later pregnancy. Food intake increased dramatically in both lean and obese animals during lactation although total calories consumed were identical in both groups. Thus, despite access to high-energy diets, the obese animals mobilized even more adipose tissue during lactation than their lean counterparts. Obese animals also exhibited marked abnormalities in alveolar development of the mammary gland, which may partially explain the delay in differentiation evident during lactogenesis