On the stretch factor of the Theta-4 graph

In this paper we show that the \theta-graph with 4 cones has constant stretch factor, i.e., there is a path between any pair of vertices in this graph whose length is at most a constant times the Euclidean distance between that pair of vertices. This is the last \theta-graph for which it was not known whether its stretch factor was bounded

Flawed Currency Areas and Viable Currency Areas: External Imbalances and Public Finance in the Time of the Euro

The main problem discussed in this paper is whether a balance of payments constraint exists within the Euro area. It is argued that the question of a member state’s foreign position is still relevant, at difference from what happens in successful currency areas like the USA, where persistent imbalances in the payments from one dis- trict to another are acceptable and are made sustainable by financial transfers revolving around the system of taxes and transfers and the public debt. Persistent imbalances in payments between regions within the area are to be settled in either the common currency or (which is basically the same thing) the public debt. But while this is acceptable in the USA, it is far from acceptable in the Euro area, where creditor countries (Germany being by far the most important) clamour for a settlement in ‘hard assets’, like, e.g. state-owned real estate, if not gold. This means that a balance of payments constraint still binds state members of the Euro area, and is a serious threat to its survival

Optometría Deportiva. Tiro Olímpico con Arma Corta

En este trabajo de fin de grado de revisión se recogerán aquellos aspectos más importantes que todo Óptico Optometrista debería conocer para poder llevar a cabo una atención completa que requiere una ayuda óptica para la práctica deportiva, ya sea profesional o amateur, del tiro olímpico en la modalidad de arma corta. Recogeremos así, los puntos más importantes para entender esta modalidad, las pruebas que será necesario relizar a esta persona que acude a nuestro centro óptico, y por último, cómo serán las posibiidades de ayuda y cómo deberemos adaptarlas a cada caso.Grado en Óptica y Optometrí

First results from SAM-FP: Fabry-Perot observations with ground-layer adaptive optics - the structure and kinematics of the core of 30 Doradus

The aim of this paper is to present the first data set obtained with SOAR Adaptive Module-Fabry-Parot (SAM-FP), a Fabry-Perot instrument mounted inside the SOAR telescope Adaptive-Optics Module. This is the only existing imaging Fabry-Perot interferometer using laser-assisted ground-layer adaptive optics. SAM-FP was used to observe the ionized gas, traced by Halpha, in the centre of the 30 Doradus starburst (the Tarantula Nebula) in the Large Magellanic Cloud, with high spatial (~0.6" or 0.15 pc) and spectral (R=11200) resolution. Radial velocity, velocity dispersion and monochromatic maps were derived. The region displays a mix of narrow, sigma ~ 20 km/s profiles and multiple broader profiles with sigma ~ 70-80 km/s, indicating the complex nature of the nebula kinematics. A comparison with previously obtained VLT/FLAMES spectroscopy demonstrates that the data agree well in the regions of overlap, but the Fabry-Perot data are superior in spatial coverage. A preliminary analysis of the observations finds a new expanding bubble south of R136, with a projected radius of r=5.6 pc and an expansion velocity of 29 +/- 4 km/s. In addition, the first-time detailed kinematic maps derived here for several complexes and filaments of 30 Doradus allow identification of kinematically independent structures. These data exemplify the power of the combination of a high-order Fabry-Perot with a wide-field imager (3' x 3' GLAO-corrected field of view) for high-resolution spatial and spectral studies. In particular, SAM-FP data cubes are highly advantageous over multifibre or long-slit data sets for nebula structure studies and to search for small-scale bubbles, given their greatly improved spatial coverage. For reference, this paper also presents two appendices with detailed descriptions of the usage of Fabry-Perot devices, including formulae and explanations for understanding Fabry-Perot observations.Comment: 22 pages, 9 figures, 1 tabl

ANALYZING ALGEBRAIC THINKING USING “GUESS MY NUMBER” PROBLEMS

The purpose of this study was to assess student knowledge of numeric, visual and algebraic representations. A definite gap between arithmetic and algebra has been documented in the research. The researchers’ goal was to identify a link between the two. Using four “Guess My Number problems, seventh and tenth grade students were asked to write numeric, visual, and algebraic representations. Seventh-grade students had significantly higher scores than tenth-grade students on visual representation responses. There were no significant differences between the seventh and tenth grade students’ responses on the numeric and algebraic representation. The researchers believed that the semi-concrete and visual models, such as used in this study, may provide the link between numeric and algebraic concepts for many students

Canine cutaneous mast cell tumor. The importance of prognostic factors in the determination of surgical margins

PòsterJun

Continuous Yao Graphs

In this paper, we introduce a variation of the well-studied Yao graphs. Given a set of points $S\subset \mathbb{R}^2$ and an angle $0 < \theta \leq 2\pi$, we define the continuous Yao graph $cY(\theta)$ with vertex set $S$ and angle $\theta$ as follows. For each $p,q\in S$, we add an edge from $p$ to $q$ in $cY(\theta)$ if there exists a cone with apex $p$ and aperture $\theta$ such that $q$ is the closest point to $p$ inside this cone. We study the spanning ratio of $cY(\theta)$ for different values of $\theta$. Using a new algebraic technique, we show that $cY(\theta)$ is a spanner when $\theta \leq 2\pi /3$. We believe that this technique may be of independent interest. We also show that $cY(\pi)$ is not a spanner, and that $cY(\theta)$ may be disconnected for $\theta > \pi$.Comment: 7 pages, 7 figures. Presented at CCCG 201

Béns i serveis associats als ecosistemes de fanerògames marines i estimacions de pèrdues causades per la seva degradació

Les praderies de posidònia de la costa catalana són ecosistemes d'alta importància, ja que tenint en compte la seva poca extensió, ens aporten una gran multiplicitat de béns i serveis ecosistèmics. No obstant, els danys observats en els prats en les últimes dècades, tant pel que fa a la regressió en superfície com a la pèrdua d'integritat ecològica, ens indiquen que aquests ecosistemes s'estan enfrontant a una crisi causada principalment per les pressions de les activitats antròpiques a les zones costaneres. En aquest projecte es pretenen identificar tots els béns i serveis que ens proporcionen aquests herbeis, així com també dictaminar quina és la importància de cada un d'ells en el context de la costa catalana. D'altra banda, es pretenen avaluar els impactes i conseqüències de la seva degradació i també quantificar, de manera relativa, la pèrdua d'aquests béns i serveis a la costa catalana, partint de la base que, segons els resultats obtinguts, la pèrdua d'abundància en els prats ha estat d'aproximadament el 60% des d'un hipotètic estat "pre-industrial" fins l'actualitat.Las praderas de posidonia presentes en la costa catalana son ecosistemas de alta importancia; aunque no son muy extensas, nos aportan una gran multiplicidad de bienes y servicios ecosistémicos. Sin embargo, en las últimas décadas se ha observado un deterioro generalizado, tanto en lo que respecta a su regresión en superficie ocupada, como en lo que respecta a la pérdida de integridad ecológica. Ello nos indica que estos ecosistemas se están enfrentando a una crisis causada principalmente por las presiones de las actividades humanas en las zonas costeras. En este proyecto se pretenden identificar todos los bienes y servicios que nos proporcionan los ecosistemas de fanerógamas marinas, así como también dictaminar cuál es la importancia de cada uno de ellos en el contexto de la costa catalana. Asimismo, se pretenden evaluar los impactos que causan la degradación y sus consecuencias, así como cuantificar, en términos relativos, la pérdida de estos bienes y servicios en la costa catalana, partiendo del dato de que la pérdida en abundancia, según los resultados, ha sido de aproximadamente del 60% desde un hipotético estado "pre-industrial" hasta la actualidad.The posidonia oceanica seagrass meadows of the Catalan Coast are ecosystems of high importance, because taking into account their little extension, they provide a great multiplicity of ecosystem goods and services. Nevertheless, the damages observed in the seagrass meadows in the last decades, not only in terms of surface regression, but also regarding the loss of ecological integrity, indicate that these ecosystems are facing a crisis caused mainly by the pressure of the anthropic activities at the coastlines. This project aims to identify all the goods and services provided by these seagrass meadows, and also determine the importance of each of them in the context of the Catalan Coast. On the other hand, it aims to evaluate the impacts and consequences of their degradation, and to quantify, in a relative way, the loss of these goods and services in the Catalan Coast, given the fact that, from the results obtained, since a hypothetical "pre-industrial" state, there has been a loss in the meadow abundance of around 60%