A social-cognitive model of trait and state levels of gratitude.

Three studies tested a new model of gratitude, which specified the generative mechanisms linking individual differences (trait gratitude) and objective situations with the amount of gratitude people experience after receiving aid (state gratitude). In Study 1, all participants (N = 253) read identical vignettes describing a situation in which they received help. People higher in trait gratitude made more positive beneficial appraisals (seeing the help as more valuable, more costly to provide, and more altruistically intended), which fully mediated the relationship between trait and state levels of gratitude. Study 2 (N = 113) replicated the findings using a daily process study in which participants reported on real events each day for up to14 days. In Study 3, participants (N = 200) read vignettes experimentally manipulating objective situations to be either high or low in benefit. Benefit appraisals were shown to have a causal effect on state gratitude and to mediate the relationship between different prosocial situations and state gratitude. The 3 studies demonstrate the critical role of benefit appraisals in linking state gratitude with trait gratitude and the objective situation

Discrete Path Planing Strategies for Coverage and Multi-Robot Rendezvous

This thesis addresses the problem of motion planning for autonomous robots, given a map and an estimate of the robot pose within it. The motion planning problem for a mobile robot can be defined as computing a trajectory in an environment from one pose to another while avoiding obstacles and optimizing some objective such as path length or travel time, subject to constraints like vehicle dynamics limitations. More complex planning problems such as multi-robot planning or complete coverage of an area can also be defined within a similar optimization structure. The computational complexity of path planning presents a considerable challenge for real-time execution with limited resources and various methods of simplifying the problem formulation by discretizing the solution space are grouped under the class of discrete planning methods. The approach suggests representing the environment as a roadmap graph and formulating shortest path problems to compute optimal robot trajectories on it. This thesis presents two main contributions under the framework of discrete planning. The first contribution addresses complete coverage of an unknown environment by a single omnidirectional ground rover. The 2D occupancy grid map of the environment is first converted into a polygonal representation and decomposed into a set of convex sectors. Second, a coverage path is computed through the sectors using a hierarchical inter-sector and intra-sector optimization structure. It should be noted that both convex decomposition and optimal sector ordering are known NP-hard problems, which are solved using a greedy cut approximation algorithm and Travelling Salesman Problem (TSP) heuristics, respectively. The second contribution presents multi-robot path-planning strategies for recharging autonomous robots performing a persistent task. The work considers the case of surveillance missions performed by a team of Unmanned Aerial Vehicles (UAVs). The goal is to plan minimum cost paths for a separate team of dedicated charging robots such that they rendezvous with and recharge all the UAVs as needed. To this end, planar UAV trajectories are discretized into sets of charging locations and a partitioned directed acyclic graph subject to timing constraints is defined over them. Solutions consist of paths through the graph for each of the charging robots. The rendezvous planning problem for a single recharge cycle is formulated as a Mixed Integer Linear Program (MILP), and an algorithmic approach, using a transformation to the TSP, is presented as a scalable heuristic alternative to the MILP. The solution is then extended to longer planning horizons using both a receding horizon and an optimal fixed horizon strategy. Simulation results are presented for both contributions, which demonstrate solution quality and performance of the presented algorithms

Evaluation of a PACAP Peptide Analogue Labeled with (68)Ga Using Two Different Chelating Agents.

OBJECTIVE: The authors have conjugated chelating agents (DOTA and NODAGA) with a peptide (pituitary adenylate cyclase-activating peptide [PACAP] analogue) that has a high affinity for VPAC1 receptors expressed on cancer cells. To determine a suitable chelating agent for labeling with (68)Ga, they have compared the labeling kinetics and stability of these peptide conjugates. METHODS: For labeling, (68)GaCl3 was eluted in 0.1 M HCl from a [(68)Ge-(68)Ga] generator. The influences of peptide concentration, pH, and temperature on the radiolabeling efficiency were studied. The stability was evaluated in saline, human serum, DTPA, transferrin, and metallic ions (FeCl3, CaCl2, and ZnCl2). Cell binding assay was performed using human breast cancer cells (T47D). Tissue biodistribution was studied in normal athymic nude mice. RESULTS: Optimal radiolabeling (\u3e95.0%) of the DOTA-peptide conjugates required a higher (50°C-90°C) temperature and 10 minutes of incubation at pH 2-5. The NODAGA-peptide conjugate needed incubation only at 25°C for 10 minutes. Both radiocomplexes were stable in saline, serum, as well as against transchelation and transmetallation. Cell binding at 37°C for 15 minutes of incubation with (68)Ga-NODAGA-peptide was 34.0% compared to 24.5% for (68)Ga-DOTA-peptide. Tissue biodistribution at 1 hour postinjection of both (68)Ga-labeled peptide conjugates showed clearance through the kidneys. CONCLUSIONS: NODAGA-peptide showed more convenient radiolabeling features than that of DOTA-peptide

VOC chemical climate and O3 variation: impact of emissions on regional O3 increment

Understanding the role of individual volatile organic compounds (VOCs) in the formation of surface ozone is important for the effective targeting of ozone mitigation strategies. The UK operates two European Monitoring and Evaluation Programme (EMEP) monitoring ‘supersites’ where concurrent measurement of 27 VOCs, NOx and ozone allows the relationships between these precursors and ozone to be explored. This work presents the relative contribution of measured VOCs on ozone formation at the ‘supersites’, including spatial variation across the UK, and temporal changes between 1999 and 2012. The study was undertaken using the impact-centred chemical climatology framework (Malley et al 2014) VOC concentrations are made up from both regional and local emissions. Regional components of ozone concentrations are distinguished from hemispheric background ozone and measured ozone concentrations which show depletion due to the local NOx environment. Increased VOC photochemical cycling is observed during periods of regional ozone formation, and the contribution of individual VOCs to this total measured VOC cycling is discussed. The drivers of this photochemical depletion, such as meteorology and emissions are evaluated. Back trajectories are coupled with gridded VOC emission maps to estimate the exposure of trajectories to VOC emissions for the four days prior to their arrival at the receptor site. These emissions are disaggregated into 11 broad source sectors, and their contribution is evaluated. Finally the implications of the level of source disaggregation available are discussed in terms of its limitations on VOC emissions speciation to estimate the exposure of receptor sites to individual VOCs.. Using the SNAP sector and the NFR code sector data, it is demonstrated that a greater level of source sector disaggregation would be beneficial for atmospheric model studies and policy determination

Systematic biases in measurement of urban nitrogen dioxide using passive diffusion samplers

Measurement of nitrogen dioxide using passive diffusion tube over 22 months in Cambridge, U.K. are analysed as a function of sampler exposure time, and compared with NO2 concentrations obtained from a co-located chemiluminescence analyser. The average ratios of passive sampler to analyser NO2 at a city centre site (mean NO2 concentration 22 ppb) are 1.27 (n = 22), 1.16 (n = 34) and 1.11 (n = 7) for exposures of 1, 2 and 4-weeks, respectively. Modelling the generation of extra NO2 arising from chemical reaction between co-diffusing NO and O3 in the tube gave a ratio (modelled/measured) of 1.31 for 1-week exposures. Such overestimation is greatest when NO2 constitutes, on average, about half of total NOx (= NO + NO2) at the monitoring locality. Although 4- week exposures gave concentrations which were not significantly different from analyser NO2, there was no correlation between the datasets. At both the city-centre site and another semi-rural site (mean NO2 concentration 11 ppb) the average of the aggregate of four consecutive 1-week sampler exposures or of two consecutive 2-week sampler exposures was systematically greater than for a single 4-week exposure. The results indicate two independent and opposing systematic biases in measurement of NO2 by passive diffusion sampler: an exposure-time independent chemical overestimation with magnitude determined by local relative concentrations of NO and O3 to NO2, and an exposuretime dependent reduction in sampling efficiency. The impact of these and other potential sources of systematic bias on the application of passive diffusion tubes for assessing ambient concentrations of NO2 in short (1-week) or long (4-week) exposures are discussed in detail