Hubble Diagram Dispersion From Large-Scale Structure

We consider the effects of large structures in the Universe on the Hubble diagram. This problem is treated non-linearly by considering a Swiss Cheese model of the Universe in which under-dense voids are represented as negatively curved regions of space-time. Exact expressions for luminosity distances and redshifts are used to investigate the non-linear effects of structure on the magnitudes of astrophysical sources. It is found that the intervening voids we consider, between the observer and source, produce changes in apparent magnitude of less than 0.012. Sources inside voids, however, can be affected considerably at redshifts below z~0.5. By averaging observable quantities over many randomly generated distributions of voids we find that the presence of these structures has the effect of introducing a dispersion around the mean, which itself can be displaced the background value. Observers in an inhomogeneous universe, who take averages of observables along many different lines of sight, may then introduce systematic biases, and under-estimate errors, if these effects are not taken into account. Estimates of the potential size of these effects are made using data from simulated large-scale structure.Comment: 16 pages, 26 figures. Major correction

A gas sensor system for harsh environment applications

A novel low power, miniature gas sensor measuring system is presented for application in harsh environmental conditions, i.e. to detect carbon monoxide and oxygen at temperatures of up to +225oC and high relative humidities up to 95%. The gas sensors are fabricated using SOI high temperature technology and two full custom ASICs are embedded into a high-temperature circuit board interfaced to a low-cost general purpose microcontroller. The sensor system has been developed for a CO concentration range of 0 to 300 ppm, O2 concentration range of 0 to 21%, and monitors the humidity and temperature of the gas, as well as operating temperatures of micro-heaters within the two MOX gas sensors. Feedback control is built into the program of the micro-controller to compensate for temperature dependence of gas sensors. Preliminary experiments show promising results for the intended application within domestic boilers

Tracking Shallow Chemical Gradients by Actin-Driven Wandering of the Polarization Site

BACKGROUND: Many cells are remarkably proficient at tracking very shallow chemical gradients, despite considerable noise from stochastic receptor-ligand interactions. Motile cells appear to undergo a biased random walk: spatial noise in receptor activity may determine the instantaneous direction, but because noise is spatially unbiased it is filtered out by time-averaging, resulting in net movement up-gradient. How non-motile cells might filter out noise is unknown. RESULTS: Using yeast chemotropic mating as a model, we demonstrate that a polarized patch of polarity regulators “wanders” along the cortex during gradient tracking. Computational and experimental findings suggest that actin-directed membrane traffic contributes to wandering by diluting local polarity factors. The pheromone gradient appears to bias wandering via interactions between receptor-activated Gβγ and polarity regulators. Artificially blocking patch wandering impairs gradient tracking. CONCLUSIONS: We suggest that the polarity patch undergoes an intracellular biased random walk that enables noise filtering by time-averaging, allowing non-motile cells to track shallow gradients

Role of Polarized G Protein Signaling in Tracking Pheromone Gradients

SummaryYeast cells track gradients of pheromones to locate mating partners. Intuition suggests that uniform distribution of pheromone receptors over the cell surface would yield optimal gradient sensing. However, yeast cells display polarized receptors. The benefit of such polarization was unknown. During gradient tracking, cell growth is directed by a patch of polarity regulators that wanders around the cortex. Patch movement is sensitive to pheromone dose, with wandering reduced on the up-gradient side of the cell, resulting in net growth in that direction. Mathematical modeling suggests that active receptors and associated G proteins lag behind the polarity patch and act as an effective drag on patch movement. In vivo, the polarity patch is trailed by a G protein-rich domain, and this polarized distribution of G proteins is required to constrain patch wandering. Our findings explain why G protein polarization is beneficial and illuminate a novel mechanism for gradient tracking

Aged Human Stored Red Blood Cell Supernatant Inhibits Macrophage Phagocytosis in an HMGB1 Dependent Manner After Trauma in a Murine Model:

Red blood cell transfusions in the setting of trauma is a double edged sword, as it is a necessary component for life-sustaining treatment in massive hemorrhagic shock, but also associated with increased risk for nosocomial infections and immune suppression. The mechanisms surrounding this immune suppression are unclear. Using supernatant from human packed red blood cell (RBC), we demonstrate that clearance of E. coli by macrophages is inhibited both in vitro and in vivo using a murine model of trauma and hemorrhagic shock. We further explore the mechanism of this inhibition by demonstrating that human stored RBCs contain soluble high mobility group box 1 protein (HMGB1) which increases throughout storage. HMGB1 derived from the supernatant of human stored RBCs was shown to inhibit bacterial clearance, as neutralizing antibodies to HMGB1 restored the ability of macrophages to clear bacteria. These findings demonstrate that extracellular HMGB1 within stored RBCs could be one factor leading to immune suppression following transfusion in the trauma setting

Georgia Tech Team Entry for the 2011 AUVSI International Aerial Robotics Competition

Presented at the Third International Aerial Robotics Symposium (IASR), 2011.his paper describes the details of a Quadrotor Unmanned Aerial Vehicle capable of exploring cluttered indoor areas without relying on any external navigational aids. An elaborate Simultaneous Localization and Mapping (SLAM) algorithm is used to fuse information from a laser range sensor, an inertial measurement unit, and an altitude sonar to provide relative position, velocity, and attitude information. A wall-following guidance rule is implemented to ensure that the vehicle explores maximum indoor area in a reasonable amount of time. A model reference adaptive control architecture is used to ensure stability and mitigation of uncertainties. The vehicle is intended to be Georgia Tech Aerial Robotic Team's entry for the 2011 International Aerial Robotics Competition (IARC) Symposium on Indoor Flight Issues

Georgia Tech Team Entry for the 2013 AUVSI International Aerial Robotics Competition

Presented at the Fifth International Aerial Robotics Competition (IARC) Symposium on Indoor Flight Issues, Grand Forks, ND, August, 201

Georgia Tech Team Entry for the 2012 AUVSI International Aerial Robotics Competition

Presented at the Third International Aerial Robotics Symposium (IASR), 2012.This paper describes the details of a Quadrotor Unmanned Aerial Vehicle capable of exploring cluttered indoor areas without relying on any external navigational aids. A Simultaneous Localization and Mapping (SLAM) algorithm is used to fuse information from a laser range sensor, an inertial measurement unit, and an altitude sonar to provide relative position, velocity, and attitude information. A wall avoidance and guidance system is implemented to ensure that the vehicle explores maximum indoor area. A model reference adaptive control architecture is used to ensure stability and mitigation of uncertainties. Finally, an object detection system is implemented to identify target objects for retrieval

Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study: common genetic variants in GCK and TCF7L2 are associated with fasting and postchallenge glucose levels in pregnancy and with the new consensus definition of gestational diabetes mellitus from the International Association of Diabetes and Pregnancy Study Groups.

OBJECTIVE: Common genetic variants in GCK and TCF7L2 are associated with higher fasting glucose and type 2 diabetes in nonpregnant populations. However, their associations with glucose levels from oral glucose tolerance tests (OGTTs) in pregnancy have not been assessed in a large sample. We hypothesized that these variants are associated with quantitative measures of glycemia in pregnancy. RESEARCH DESIGN AND METHODS: We analyzed the associations between variants rs1799884 (GCK) and rs7903146 (TCF7L2) and OGTT outcomes at 24-32 weeks' gestation in 3,811 mothers of European (U.K. and Australia) and 1,706 mothers of Asian (Thailand) ancestry from the HAPO cohort. We also tested associations with offspring birth anthropometrics. RESULTS: The maternal GCK variant was associated with higher fasting glucose in Europeans (P = 0.001) and Thais (P 0.05). In both populations, both variants were associated with higher odds of gestational diabetes mellitus according to the new International Association of Diabetes and Pregnancy Study Groups recommendations (P = 0.001-0.08). CONCLUSIONS: Maternal GCK and TCF7L2 variants are associated with glucose levels known to carry an increased risk of adverse pregnancy outcome in women without overt diabetes. Further studies will be important to determine the variance in maternal glucose explained by all known genetic variants