Improving object detection by exploiting semantic relations between objects

En col·laboració amb la Universitat de Barcelona (UB) i la Universitat Rovira i Virgili (URV)Object detection is a fundamental and challenging problem in computer vision. Detecting the objects visible in an image can give us a good understanding and description of the image. The extracted information can later be used to improve the results of other computer vision tasks like activity recognition, content-based image retrieval, scene recognition and more. As technology and internet connection are becoming more accessible, billions of people upload photos and videos every day. In order to make use of this enormous amount of data we need to be able to extract information from these images in a quick and yet reliable way. Convolutional neural networks (CNN) have made possible enormous progresses in object detection and classification in recent years and have already established themself as the state of the art approach for these problems. In this work, we try to improve object detection performances by employing a CNN approach able to exploit object co-occurrences in natural images. Typically, real world scenes often exhibit a coherent composition of object in terms of co-occurrence probability. For instance, in a restaurant we typically see dishes, bottles and glasses. We aim at using this type of knowledge as a cue for disambiguating object labels in a detection task

Probabilistic modelling of gait for robust passive monitoring in daily life

Passive monitoring in daily life may provide valuable insights into a person's health throughout the day. Wearable sensor devices play a key role in enabling such monitoring in a non-obtrusive fashion. However, sensor data collected in daily life reflect multiple health and behavior-related factors together. This creates the need for a structured principled analysis to produce reliable and interpretable predictions that can be used to support clinical diagnosis and treatment. In this work we develop a principled modelling approach for free-living gait (walking) analysis. Gait is a promising target for non-obtrusive monitoring because it is common and indicative of many different movement disorders such as Parkinson's disease (PD), yet its analysis has largely been limited to experimentally controlled lab settings. To locate and characterize stationary gait segments in free-living using accelerometers, we present an unsupervised probabilistic framework designed to segment signals into differing gait and non-gait patterns. We evaluate the approach using a new video-referenced dataset including 25 PD patients with motor fluctuations and 25 age-matched controls, performing unscripted daily living activities in and around their own houses. Using this dataset, we demonstrate the framework's ability to detect gait and predict medication induced fluctuations in PD patients based on free-living gait. We show that our approach is robust to varying sensor locations, including the wrist, ankle, trouser pocket and lower back

Political Participation of Young People: A Comparison between Swedish Students and International Students in Gothenburg

A vast amount of literature has been dedicated to political participation of young people. How do young people perceive the political participation? Some argue that the decreasing participation of young people is balanced with increased political participation outside the traditional methods. Others warn of increase in disinterest in politics, which can affect the functioning of the democratic systems and institutions. Studies have been largely focused only on quantitative methods to try and explain the political participation of young people. This paper presents an analysis of data from three focus groups conducted in Gothenburg with 12 students. The students are European Union citizens from Sweden, Bulgaria, Romania, Lithuania, Spain, Germany and Austria. The study analyzes qualitatively the types of political participation young European Union citizens use, their motivations for political participation, their attitude towards the European Parliament elections and the factors that affect the political participation among young people. The study finds that the participants are engaged in politics and in political participation. Some of the participants use very often issue-oriented participation, such as political consumerism. The empirical data shows that the popular political consumerism among the participants does not link to low trust in government, as has been suggested in the existing literature. In contrast to what some other studies have suggested, I did not find evidence supporting increased focus on online participation than offline political participation among these young people. Regarding the European Parliament elections, the study supports the claims that European elections decrease the political participation. The data suggests that the participants in the discussions are less interested in European elections. However, there is not much support for the theory of European elections as “second-order” elections – theory that links the low political participation with the perceptions of the citizens that the European elections are less important than the national elections and less is at stake. The lack of knowledge and information are new factors that are possible explanations for the low participation in European elections and those factors should be further evaluated

Alternativas en la reconstrucción de la base del cráneo con colgajos libres microvascularizados

El éxito de la reconstrucción de la base de cráneo depende de varios principios fundamentales, destacando el sellado hermético de la duramadre, la barrera entre el tracto aerodigestivo y duramadre, la obliteración del espacio muerto y el buen soporte del cerebro y estructuras vitales. Los colgajos libres microquirúrgicos se han convertido en la técnica de primera elección para la reconstrucción de defectos extensos de la base de cráneo. Los resultados funcionales y estéticos son en general superiores a los obtenidos con los métodos convencionales, incluyendo los colgajos locales que son útiles sólo para pequeños defectos. Objetivo: Demostrar la eficacia y la fiabilidad de la transferencia de tejido libre microvascularizado en la reconstrucción de defectos complejos tridimensionales de la base de cráneo. Métodos: Se ha realizado un estudio retrospectivo descriptivo basado en la revisión de los datos clínicos de pacientes con defectos de la base de cráneo anterior o lateral que fueron sometidos a reconstrucción microquirúrgica en el Hospital General Universitario Gregorio Marañón, Madrid (España) entre enero de 2003 y marzo de 2012. Datos demográficos, patológicos preoperatorios y postoperatorios fueron recogidos y analizados. Resultados: Veintiocho pacientes con defectos de la base de cráneo fueron identificados, entre ellos 15 mujeres (53,6%) y 13 hombres (46,3%) (edad media: 54 años, rango de edad: 16-82 años). De entre los pacientes analizados, uno fue intervenido por colesteatoma y 2 por tumores benignos, mientras que los 25 pacientes restantes fueron intervenidos por tumores malignos, de los cuales el carcinoma epidermoide fue el más común (n=13). Se utilizaron 32 colgajos libres. El más utilizado fue el colgajo de recto abdominal (n=17); fueron utilizados 5 tipos de colgajos, incluyendo colgajo anterolateral del muslo (ALT) (n=6), colgajo de dorsal ancho (n=6), colgajo antebraquial radial (n=2) y colgajo de perforante de arteria epigástrica inferior profunda (DIEP) (n=1). En total, hubo 7 complicaciones relacionadas con el colgajo con 2 pérdidas totales del mismo. La tasa global de complicaciones fue del 56,3% de las cuales las más comunes fueron las complicaciones locales de la herida (n=18) y las complicaciones intracraneales (n=8). La tasa de mortalidad perioperatoria fue del 3,1% y la estancia hospitalaria media fue 22 días (rango, 6-56 días). Conclusiones: La transferencia de tejido libre microvascularizado para reconstrucción de defectos extensos de la base de cráneo ha demostrado ser un método altamente exitoso en la serie presentada en esta Memoria. La versatilidad y la fiabilidad de diferentes colgajos libres se ha presentado y discutido. Se han dado consejos útiles para optimizar la reconstrucción microquirúrgica de la base de cráneo en casos difíciles. [ABSTRACT] Successful skull base reconstruction depends on several key principles, including a watertight dural seal, a barrier between the aerodigestive tract and dura, obliteration of dead space and good support of the brain and vital structures. Microsurgical free flaps have become the gold standard for reconstruction of large skull base defects. The functional and aesthetic results are in general superior to those obtained with conventional methods including local flaps that are useful only for small defects. Objective: To demonstrate the effectiveness and reliability of microvascular free tissue transfer in reconstructing complex three dimensional skull base defects. Methods: A retrospective chart review was conducted identifying patients with anterior or lateral skull base defects who underwent microvascular free flap reconstruction in the General University Hospital Gregorio Marañón in Madrid (Spain) between January 2003 and March 2012. Appropriate demographic, pathological preoperative and postoperative data were collected and analyzed. Results: Twenty-eight patients with skull base defects were identified, including 15 women (53.6%) and 13 men (46.3%) (mean age: 54 y; age range: 16-82 y). Defects were secondary to cholesteatoma in one patient and to benign tumors in two patients, whereas the remaining 25 patients were secondary to ablative procedures for a variety of malignant tumors, of which squamous cell carcinoma was the most common (n=13). 32 free flaps were used. The most commonly used was the rectus abdominis flap (n=17); however, five different flap types were employed, including anterolateral thigh flap (ALT) (n=6), latissimus dorsi flap (n=6), radial forearm flap (n=2) and deep inferior epigastric artery perforator flap (DIEP) (n=1). In all, there were seven flap-related complications and there were two total flap losses. There was a 56.3% overall rate of postoperative complications, with the most common complications being grouped as local wound complications (n=18) and intracranial complications (n=8). The perioperative mortality rate was 3.1%, and the average hospital stay was 22 days (range: 6-56 d). Conclusions: The use of microvascular free tissue transfer for reconstruction of extensive skull base defects has proven highly successful in the series presented in the current study. The versatility and reliability of different free flaps for such reconstruction are shown and discussed. Helpful hints are given to optimize the skull base reconstruction in difficult cases

Improving object detection by exploiting semantic relations between objects

En col·laboració amb la Universitat de Barcelona (UB) i la Universitat Rovira i Virgili (URV)Object detection is a fundamental and challenging problem in computer vision. Detecting the objects visible in an image can give us a good understanding and description of the image. The extracted information can later be used to improve the results of other computer vision tasks like activity recognition, content-based image retrieval, scene recognition and more. As technology and internet connection are becoming more accessible, billions of people upload photos and videos every day. In order to make use of this enormous amount of data we need to be able to extract information from these images in a quick and yet reliable way. Convolutional neural networks (CNN) have made possible enormous progresses in object detection and classification in recent years and have already established themself as the state of the art approach for these problems. In this work, we try to improve object detection performances by employing a CNN approach able to exploit object co-occurrences in natural images. Typically, real world scenes often exhibit a coherent composition of object in terms of co-occurrence probability. For instance, in a restaurant we typically see dishes, bottles and glasses. We aim at using this type of knowledge as a cue for disambiguating object labels in a detection task

Liquid-Crystal Spin-VCSEL with Electro-Optically Controllable Birefringence

We suggest a new construction of spin-VCSEL with an embedded nematic liquid crystal (LC) in a second cavity. We design such a coupled-cavity LC-VCSEL and develop a procedure for calculating its LC-voltage dependent polarization resolved resonant longitudinal modes and their quantum-well confinement factors. Using these characteristics, we are able to slightly modify the spin-flip VCSEL model to include the voltage dependent birefringence and anisotropy. Then, we show that such an LC-VCSEL can reach small signal modulation response with a 3dB cut off frequency of several hundreds of GHz

Liquid-Crystal Spin-VCSEL with Electro-Optically Controllable Birefringence

We suggest a new construction of spin-VCSEL with an embedded nematic liquid crystal (LC) in a second cavity. We design such a coupled-cavity LC-VCSEL and develop a procedure for calculating its LC-voltage dependent polarization resolved resonant longitudinal modes and their quantum-well confinement factors. Using these characteristics, we are able to slightly modify the spin-flip VCSEL model to include the voltage dependent birefringence and anisotropy. Then, we show that such an LC-VCSEL can reach small signal modulation response with a 3dB cut off frequency of several hundreds of GHz