Kleinberg Navigation in Fractal Small World Networks

We study the Kleinberg problem of navigation in Small World networks when the underlying lattice is a fractal consisting of N>>1 nodes. Our extensive numerical simulations confirm the prediction that most efficient navigation is attained when the length r of long-range links is taken from the distribution P(r)~r^{-alpha}, where alpha=d_f, the fractal dimension of the underlying lattice. We find finite-size corrections to the exponent alpha, proportional to 1/(ln N)^2

Preserved thematic and impaired taxonomic categorisation: a case study

The present paper seeks to understand more about categorisation and its relation to naming. A patient with language impairments (LEW) was examined in a three-part investigation of his ability to make classification decisions. The first part demonstrated LEW's inability to make taxonomic classifications of shape thus confirming his previously documented impaired perceptual categorisation. The second part demonstrated that, despite LEW's inability to perform simple taxonomic classifications, he could reason analogically as well as a 4/5 year-old child. It is therefore argued that taxonomic classifications cannot be driven by the development of analogical reasoning. The third part more directly contrasted thematic and taxonomic classification. LEW showed a preference for thematic classification. In fact, there was no evidence of any substantial ability to make taxonomic colour classifications despite evidence for good preservation of the associated object-colour knowledge

Evaluation of an ATP Assay to Quantify Bacterial Attachment to Surfaces in Reduced Gravity

Aim: To develop an assay to quantify the biomass of attached cells and biofilm formed on wetted surfaces in variable-gravity environments. Methods and Results: Liquid cultures of Pseudomonas aeruginosa were exposed to 30-35 brief cycles of hypergravity (< 2-g) followed by free fall (i.e., reduced gravity) equivalent to either lunar-g (i.e., 0.17 normal Earth gravity) or micro-g (i.e., < 0.001 normal Earth gravity) in an aircraft flying a series of parabolas. Over the course of two days of parabolic flight testing, 504 polymer or metal coupons were exposed to a stationary-phase population of P. aeruginosa strain ERC1 at a concentration of 1.0 x 10(exp 5) cells per milliliter. After the final parabola on each flight test day, half of the material coupon samples were treated with either 400 micro-g/L ionic silver fluoride (microgravity-exposed cultures) or 1% formalin (lunar-gravity-exposed cultures). The remaining sample coupons from each flight test day were not treated with a fixative. All samples were returned to the laboratory for analysis within 2 hours of landing, and all biochemical assays were completed within 8 hours of exposure to variable gravity. The intracellular ATP luminescent assay accurately reflected cell physiology compared to both cultivation-based and direct-count microscopy analyses. Cells exposed to variable gravity had more than twice as much intracellular ATP as control cells exposed only to normal Earth gravity

Lunar Soil Erosion Physics for Landing Rockets on the Moon

To develop a lunar outpost, we must understand the blowing of soil during launch and landing of the new Altair Lander. For example, the Apollo 12 Lunar Module landed approximately 165 meters from the deactivated Surveyor Ill spacecraft, scouring its surfaces and creating numerous tiny pits. Based on simulations and video analysis from the Apollo missions, blowing lunar soil particles have velocities up to 2000 m/s at low ejection angles relative to the horizon, reach an apogee higher than the orbiting Command and Service Module, and travel nearly the circumference of the Moon [1-3]. The low ejection angle and high velocity are concerns for the lunar outpost

Resilience Following Trauma: Evidence from a Level 1 Trauma Center

The purpose of this study was to examine longitudinally the trajectories of depression and post-traumatic stress disorder (PTSD) in individuals who survived a potentially traumatic event (PTE) and were admitted to a Level 1 trauma center and explore covariate prediction of classes using mild traumatic brain injury (TBI) status, demographic, and health related quality of life variables. Data were analyzed using latent growth mixture modeling. Participants consists of patients consecutively admitted to a Level 1 trauma center that were approached to complete assessments while hospitalized and then at three, six and 12 months post-discharge. The Patient Health Questionnaire-8 (PHQ-8) and the Primary Care Posttraumatic Stress Disorder Screen (PC-PTSD) were used in the present study to identify the classes of adjustment. The sample (n = 406) was predominantly male, European-American, and high school or less educated. The results indicated that a five-class model was the best fit for the depression data, which included a resilient, a delayed, a recovering, a chronic, and a chronic-worsening class. A three-class model was the best fit for the PTSD data, which included a resilient, a chronic, and a stable, moderately distressed class. Lower pain interference and greater psychological well-being while hospitalized was associated with significantly decreased odds of being in a non-resilient class compared to the resilient class. The resilient class reported the fewest symptoms of depression and PTSD and reported the lowest levels of pain interference and greater psychological well-being than the other classes. In conclusion, a five-class model of depression and a three-class model of PTSD best described the data. The results indicate that most survivors following a PTE experienced minor and transient symptoms of depression and PTSD (i.e., resiliency). This pattern provides additional evidence that resiliency may be the most likely outcome following a PTE. In addition, greater psychological well-being and less pain interference soon after a trauma may be protective factors against the development of depression and PTSD following a PTE. Mild TBI, cause of injury, education, or gender did not predict class membership. Despite surviving a PTE, a large percentage of the sample reported low levels of distress. Clinical and research implications of the results are offered

Latin American Immigration as a Determinant of US Foreign Aid Allocation

This is a thesis that explains how the US allocates foreign aid to Latin America, with a special emphasis on the factor of immigration as an explanatory variable in aid distribution. In an effort to further the academic knowledge of the politics of foreign aid, I have isolated one factor that I believe to be under-examined and unexplored—immigration. There are an estimated 41 million immigrants living in the US, or about 13 percent of the total US population (Migration Policy 2014). In 2013 alone, almost 402,000 people immigrated to the US from Latin America. With a few important exceptions, immigration remains largely unaddressed in the literature on foreign aid allocation,2 but I argue that it is a factor in the United States’ considerations of aid distribution. Politicians are concerned about how to respond to the large numbers of immigrants coming to the US through legal and extralegal means. I contend that since policymakers assume that economic conditions in the country of origin are a push factor for migrants leaving their country of origin, and since a sufficient number of policymakers believe foreign aid sometimes spurs growth, policymakers will utilize economic foreign assistance as a means of decreasing the need for further migration. As such, I expect there to be a statistically significant relationship between the flow of migrants from each Latin American country and aid allocation to that country in the subsequent years. My research fills an important niche in the literature on foreign aid. I use the work of other scholars as a starting point, but I aim to take a multi-method, process-oriented approach that traces the mechanism by which migration and aid are connected. I test my theory through a series of semi-structured elite interviews, an analysis of congressional hearings, and a statistical analysis of US foreign aid to Latin America in the years 1990-2012.Bachelor of Art

Prospective Longitudinal Study of the Pregnancy DNA Methylome: The US Pregnancy, Race, Environment, Genes (PREG) Study

Purpose The goal of the Pregnancy, Race, Environment, Genes study was to understand how social and environmental determinants of health (SEDH), pregnancy-specific environments (PSE) and biological processes influence the timing of birth and account for the racial disparity in preterm birth. The study followed a racially diverse longitudinal cohort throughout pregnancy and included repeated measures of PSE and DNA methylation (DNAm) over the course of gestation and up to 1 year into the postpartum period. Participants All women were between 18 and 40 years of age with singleton pregnancies and no diagnosis of diabetes or indication of assisted reproductive technology. Both mother and father had to self-identify as either African-American (AA) or European-American (EA). Maternal peripheral blood samples along with self-report questionnaires measuring SEDH and PSE factors were collected at four pregnancy visits, and umbilical cord blood was obtained at birth. A subset of participants returned for two additional postpartum visits, during which additional questionnaires and maternal blood samples were collected. The pregnancy and postpartum extension included n=240 (AA=126; EA=114) and n=104 (AA=50; EA=54), respectively. Findings to date One hundred seventy-seven women (AA=89, EA=88) met full inclusion criteria out of a total of 240 who were initially enrolled. Of the 63 participants who met exclusion criteria after enrolment, 44 (69.8%) were associated with a medical reason. Mean gestational age at birth was significantly shorter for the AA participants by 5.1 days (M=272.5 (SD=10.5) days vs M=277.6 (SD=8.3)). Future plans Future studies will focus on identifying key environmental factors that influence DNAm change across pregnancy and account for racial differences in preterm birth