A method for estimating the extent of denitrification of Arctic polar vortex air from tracer-tracer scatter plots

A method for estimating the extent of denitrification of Arctic polar vortex air is proposed. Previous estimates of denitrification using tracer-tracer scatter plots have not allowed for mixing-induced changes in tracer-tracer relationships in a sufficiently general way. This difficulty is overcome by constructing an artificial "reference tracer'' from a linear combination of other long-lived tracers. The reference tracer is designed so that, as far as possible, it has a linear canonical relationship with NOy in midlatitudes. A linear relationship is unaffected by mixing, so denitrification is apparent as deviations of vortex measurements from the linear midlatitude relationship. The method is first demonstrated using data from a chemical transport model in which no denitrification processes are present. It is then applied to balloon, aircraft and shuttle-borne measurements made before and during the breakdown of the Arctic vortex in 1992-1993 and 1996-1997. In each case the method indicates that little or no denitrification had occurred in any of the vortex air encountered. When the method is applied to the southern hemisphere vortex in 1994, by contrast, denitrified air is clearly seen to be present around 19-23 km in the vortex

Item banking with Rasch Measurement: An example for primary mathematics in Thailand

This study was conducted in Thailand to create a Mathematics item bank and a Computerized Adaptive Test (CAT) for the students to ‗interrogate‘ the bank. First, 290 multiple-choice test items on mathematical equations were created for an item bank. They consisted of nine aspects: (1) identifying an equation; (2) identifying the true equation; (3) identifying equations with an unknown; (4) finding the value of an unknown that satisfies the equation; (5) identifying a method to solve an equation; (6) finding the solutions to equations; (7) finding a solution to an equation related to a given condition; (8) selecting an equation converted from a verbal problem or a verbal problem related to an equation; and (9) solving an equation problem. Seven papers with 50 items each, containing 40 different items and 10 common items, were administered to 3,062 students of Year 6 (Prathom Suksa 6). There were 409, 413, 412, 400, 410, 408, and 610 students taking part in the 1st to the 7th tests respectively. The data were analysed with the Rasch Unidimensional Measurement Model (RUMM 2010) computer program so that all the item difficulties were linked on the same linear scale along with the student measures of mathematical ability. Ninety-eight test items fitted the measurement model and were installed in the item bank. A computer program for CAT was created, tested, and modified after trialling. A controlled experiment involving the use of CAT with 400 Prathom Suksa 6 students from two primary schools in Ubon Ratchathani province, Thailand, was implemented. Thai students were very supportive of the use of CAT with the mathematical item bank. They showed an interest in CAT and in extending the use of CAT to other subject areas with appropriately developed item banks

A Unified View of Large-scale Zero-sum Equilibrium Computation

The task of computing approximate Nash equilibria in large zero-sum extensive-form games has received a tremendous amount of attention due mainly to the Annual Computer Poker Competition. Immediately after its inception, two competing and seemingly different approaches emerged---one an application of no-regret online learning, the other a sophisticated gradient method applied to a convex-concave saddle-point formulation. Since then, both approaches have grown in relative isolation with advancements on one side not effecting the other. In this paper, we rectify this by dissecting and, in a sense, unify the two views.Comment: AAAI Workshop on Computer Poker and Imperfect Informatio

Modulation of osteoblast cell response through laser surface processing of nylon 6,6

With an ageing population demand on medical facilities is growing, especially for bio-implants. Therefore, there is a need for cheaper, more efficient implants. This paper details how CO2 and KrF excimer lasers can be employed to modulate osteoblast cell growth on nylon 6,6 in relation to laser-modified wettability characteristics. Through patterning the contact angle, θ, increased by up to 19°, indicating the presence of a mixed state wetting regime; whereas θ decreased by up to 20° for the whole area irradiative processed samples. After 24 hours and 4 days incubation the cell cover density and cell count was somewhat modulated over the laser-modified samples compared to the as-received sample. A likely increase in surface toxicity gave rise to a hindered cell response for those samples with high energy densities and high incident pulse numbers. No strong correlations were determined for the laser-induced patterned samples which can be attributed to the likely mixed-state wetting regime. Correlative trends were found between the cell response, θ, polar component and surface oxygen content for the whole area irradiative processed samples. Thus, allowing one to identify the potential for this technology in regenerative medicine

Study of the winter 2005 Antarctica polar vortex

During winter and springtime, the flow above Antarctica at high altitude (upper troposphere and stratosphere) is dominated by the presence of a vortex centered above the continent. It lasts typically from August to November. This vortex is characterized by a strong cyclonic jet centered above the polar high. In a recent study of our group (Hagelin et al., 2008) of four different sites in the Antarctic internal plateau (South Pole, Dome C, Dome A and Dome F), it was made the hypothesis that the wind speed strength in the upper atmosphere should be related to the distance of the site to the center of the Antarctic polar vortex. This high altitude wind is very important from an astronomical point of view since it might trigger the onset of the optical turbulence and strongly affect other optical turbulence parameters. What we are interested in here is to localize the position of the minimum value of the wind speed at high altitude in order to confirm the hypothesis of Hagelin et al. (2008).Comment: 3rd ARENA conference, 11-15 May 2009 EAS Publication Serie

Using UV laser surface treatment to modify the wettability characteristics of polyamide 6,6 and its effects on osteoblast cell activity

Lasers can be used to modify the surface characteristics of a number of different materials for many applications. This paper details the way in which a KrF 248 nm excimer laser can be utilized to surface pattern and whole area irradiate nylon 6,6. 50 and 100 µm dimensioned trench and hatch patterns were induced in addition to the whole area irradiative processing which covered an area of 3.75 cm2 with fluencies ranging from 26 to 70 mJcm-2. The surface topography and roughness were determined with the use of a white light interferometer. From this it was found that the largest roughness, Sa, was 1.53 µm which arose from the 100 µm hatch excimer patterned sample. Wettability characteristics were obtained for each sample using a sessile drop device in which it was observed that the contact angle increased by up to 25° for the patterned samples and decreased by up to 15° for the large area processed samples. It is believed that the observed increase in contact angle can be attributed to the likely existence of a mixed-state wetting regime in which both Wenzel and Cassie-Baxter regimes are present over the liquid-solid interface. As a result of the small variation in surface roughness for the large area processed samples the observed decrease in contact angle can be explained by a modification of the surface chemistry and an increase in polar component (γp) and total surface energy (γT). Osteoblast cell activity was analyzed by carrying out cytotoxicity and alkaline leukocyte phosphatase (ALP) activity experiments, two major factors which are linked to sufficient cell growth and proliferation

Solving Large Extensive-Form Games with Strategy Constraints

Extensive-form games are a common model for multiagent interactions with imperfect information. In two-player zero-sum games, the typical solution concept is a Nash equilibrium over the unconstrained strategy set for each player. In many situations, however, we would like to constrain the set of possible strategies. For example, constraints are a natural way to model limited resources, risk mitigation, safety, consistency with past observations of behavior, or other secondary objectives for an agent. In small games, optimal strategies under linear constraints can be found by solving a linear program; however, state-of-the-art algorithms for solving large games cannot handle general constraints. In this work we introduce a generalized form of Counterfactual Regret Minimization that provably finds optimal strategies under any feasible set of convex constraints. We demonstrate the effectiveness of our algorithm for finding strategies that mitigate risk in security games, and for opponent modeling in poker games when given only partial observations of private information.Comment: Appeared in AAAI 201

Automatic assessment of sequence diagrams

In previous work we showed how student-produced entity-relationship diagrams (ERDs) could be automatically marked with good accuracy when compared with human markers. In this paper we report how effective the same techniques are when applied to syntactically similar UML sequence diagrams and discuss some issues that arise which did not occur with ERDs. We have found that, on a corpus of 100 student-drawn sequence diagrams, the automatic marking technique is more reliable that human markers. In addition, an analysis of this corpus revealed significant syntax errors in student-drawn sequence diagrams. We used the information obtained from the analysis to build a tool that not only detects syntax errors but also provides feedback in diagrammatic form. The tool has been extended to incorporate the automatic marker to provide a revision tool for learning how to model with sequence diagrams