El problema de Alhacén

El presente documento es un estudio detallado del problema conocido bajo el título de Problema de Alhacén. Este problema fue formulado en el siglo X por el filósofo y matemático árabe conocido en occidente bajo el nombre de Alhacén. El documento hace una breve presentación del filósofo y una breve reseña de su trascendental tratado de óptica Kitab al-Manazir. A continuación el documento se detiene a estudiar cuidadosamente los lemas requeridos para enfrentar el problema y se presentan las soluciones para el caso de los espejos esféricos (convexos y cóncavos), cilíndricos y cónicos. También se ofrece una conjetura que habría de explicar la lógica del descubrimiento implícita en la solución que ofreció Alhacén. Tanto los lemas como las soluciones se han modelado en los software de geometría dinámica Cabri II-Plus y Cabri 3-D. El lector interesado en seguir dichas modelaciones debe contar con los programas mencionados para adelantar la lectura de los archivos. En general, estas presentaciones constan de tres partes: (i) formulación del problema (se formula en forma concisa el problema); (ii) esquema general de la construcción (se presentan los pasos esenciales que conducen a la construcción solicitada y las construcciones auxiliares que demanda el problema), esta parte se puede seguir en los archivos de Cabri; y (iii) demostración (se ofrece la justificación detallada de la construcción requerida). Los archivos en Cabri II plus cuentan con botones numerados que pueden activarse haciendo “Click” sobre ellos. La numeración corresponde a la numeración presente en el documento. El lector puede desplazar a su antojo los puntos libres que pueden reconocerse porque ellos se distinguen con la siguiente marca (º). Los puntos restantes no pueden modificarse pues son el resultado de construcciones adelantadas y ajustadas a los protocolos recomendados en el esquema general.

Citología de impresión para neoplasias de la superficie ocular

Se estimó la sensibilidad y especificidad de la citología de impresión como prueba diagnóstica en lesiones conjuntivales clínicamente sospechosas de neoplasia usando como patrón de oro la patología. Se estudiaron 60 pacientes, que ingresaron al azar a la Fundación Oftalmológica Nacional, con diagnóstico clínico de neoplasia de superficie ocular o lesión sospechosa de neoplasia, quienes fueron sometidos a citología de impresión y posterior resección quirúrgica completa, más estudio patológico de la lesión. Se realizó un análisis descriptivo, analizando la sensibilidad y la especificidad con el método clásico y análisis bayesiano.

Administrative Structure of the Sovereign State of Boyacá (1857-1886)

The present article has as objectives to show the organization and the functioning of the central administration of the state of Boyacá, as manifested through the President of the state and the secretaries of dispatch, to examine how they operated and which functions were assigned to them during the period of 1857 to 1886. These will be examined through the lenses of the 1857, 1863 and 1869 constitutions and their subsequent normative development as well as through the roles given them by the Legislative Assembly and the State President. Likewise, it will study the progress of the state as seen through the reports presented by the president and the secretaries of dispatch. It must be kept in mind that until now nothing has been written on this topic; the text is innovative in that it allows us to reconstruct a part of our national documentary heritage.

Resultados de la terapia antiangiogenica con Ranibizumab en retinopatia del prematuro: revisión sistemática.

Introducción: La retinopatía del prematuro (ROP) se presenta hasta en el 73% de los neonatos pretérmino por debajo de la semana 27, los agentes antiangiogénicos se presentan como una herramienta para su tratamiento con resultados prometedores. En el presente estudio se pretendió evaluar los resultados de la terapia antiangiogénica con ranibizumab en pacientes con retinopatía del prematuro según la evidencia descrita hasta la fecha. Metodología: se realizó una revisión sistemática de literatura con componente meta-analítico de los datos sociodemográficos y clínicos, incluyendo todos los artículos sobre el tema sin límite de fecha de publicación. Se usó una estrategia de búsqueda en diferentes bases de datos, todos los estudios relacionados con el pronóstico de la enfermedad fueron elegibles. Resultados: Se encontraron un total de 13 artículos que cumplieron criterios de elegibilidad para su inclusión, que incluyeron 75 pacientes en total (133 ojos evaluados). La edad promedio al nacimiento fue 23.6 semanas, la edad al momento de aplicación de tratamiento fue 36.3 semanas. 11/13 artículos reportaron que el tratamiento con ranibizumab fue satisfactorio en términos de resolución completa de la enfermedad sin efectos secundarios (64 pacientes) Discusión: Los resultados de la terapia con ranibizumab para retinopatía del prematuro según la evidencia hasta la fecha permiten recomendar el uso de terapia antiangiogénica con el fin de mejorar la salud visual a mediano y largo plazo y por ende disminución en la prevalencia de ceguera por esta causa.

Frecuencia de neoplasia escamosa de la superficie ocular coexistente con pterigio

Introducción: En la literatura, han aparecido reportes de neoplasia escamosa de superficie ocular (NESO) asociado con pterigio en un mismo paciente. Sin embargo, Colombia no cuenta con una estadística para ninguna de estas patologías. Objetivos: Determinar la frecuencia de NESO en pterigios resecados, en la Fundación Oftalmológica Nacional. Identificar factores de riesgo y características clínicas que predispongan a su aparición. Metodología: Estudio descriptivo de corte transversal. Se realizó una clasificación prequirúrgica y estudio histopatológico de los pterigios resecados en 93 pacientes, para confirmar su coexistencia con NESO. Se efectuó un análisis de frecuencias para datos demográficos y factores de riesgo asociados su aparición. Resultados: La frecuencia de NESO asociado a pterigio fue 7,07%. De estos, 28,5% identificados como sospechosos en la evaluación preoperatoria. La mayoría se presentaron en mujeres (71,4%), las ocupaciones con mayor frecuencia: labores domésticas (42,8%) y el comercio (28.5%). La exposición a derivados del petróleo y tabaquismo fue del 14,28%. No se presentaron casos asociados a infección por VIH. No hubo diferencias estadísticamente significativas sobre la presencia de NESO al comparar los casos en edad (p=0,8), procedencia (p=0,6) tabaquismo (p=0,4), leucoplaquia (p=1,0), queratinización (p=0,137), o vasos amputados (p=0,137). Conclusiones: De los pacientes con diagnóstico histopatológico de NESO, un porcentaje mínimo es sospechado clínicamente. Además se encontró este diagnóstico en pacientes más jóvenes que lo reportado en la literatura. Se recomienda realizar estudios con mayor número de pacientes para una mejor identificación de factores de riesgo. Palabras clave:

Efectos del ejercicio en la fisiología ocular.

Monográfico con el título: 'Visión y deporte'. Resumen tomado de la publicación

Neutralización y protección ocular en el deporte.

Monográfico con el título: 'Visión y deporte'. Resumen tomado de la publicación

Interference filters and coatings for mid-infrared astronomy (8-30µm)

The VISIR instrument for the European Southern Observatory (ESO) Very Large Telescope (VLT) is a thermal-infrared imager and spectrometer currently being developed by the French Service d'Astrophysique of CEA Saclay, and Dutch NFRA ASTRON Dwingeloo consortium. This cryogenic instrument will employ precision infrared bandpass filters in the N-( =7.5-14µm) and Q-( =16-28µm) band mid-IR atmospheric windows to study interstellar and circumstellar environments crucial for star and planetary formation theories. As the filters in these mid-IR wavelength ranges are of interest to many astronomical cryogenic instruments, a worldwide astronomical filter consortium was set up with participation from 12 differing institutes, each requiring instrument specific filter operating environments and optical metrology. This paper describes the design and fabrication methods used to manufacture these astronomical consortium filters, including the rationale for the selection of multilayer coating designs, temperature-dependant optical properties of the filter materials and FTIR spectral measurements showing the changes in passband and blocking performance on cooling to <50K. We also describe the development of a 7-14µm broadband antireflection coating deposited on Ge lenses and KRS-5 grisms for cryogenic operation at 40K

Spectral design and verification of HIRDLS filters and antireflection coatings using an integrated system performance approach

The HIRDLS instrument contains 21 spectral channels spanning a wavelength range from 6 to 18mm. For each of these channels the spectral bandwidth and position are isolated by an interference bandpass filter at 301K placed at an intermediate focal plane of the instrument. A second filter cooled to 65K positioned at the same wavelength but designed with a wider bandwidth is placed directly in front of each cooled detector element to reduce stray radiation from internally reflected in-band signals, and to improve the out-of-band blocking. This paper describes the process of determining the spectral requirements for the two bandpass filters and the antireflection coatings used on the lenses and dewar window of the instrument. This process uses a system throughput performance approach taking the instrument spectral specification as a target. It takes into account the spectral characteristics of the transmissive optical materials, the relative spectral response of the detectors, thermal emission from the instrument, and the predicted atmospheric signal to determine the radiance profile for each channel. Using this design approach an optimal design for the filters can be achieved, minimising the number of layers to improve the in-band transmission and to aid manufacture. The use of this design method also permits the instrument spectral performance to be verified using the measured response from manufactured components. The spectral calculations for an example channel are discussed, together with the spreadsheet calculation method. All the contributions made by the spectrally active components to the resulting instrument channel throughput are identified and presented.

System performance in IR atmospheric radiometry

System aspects of filter radiometer optics used to sense planetary atmospheres are described. Thus the lenses, dichroic beamsplitters and filters in longwave channels of the Mars Observer PMIRR Pressure Modulator Infrared radiometer instrument are assessed individually, and as systems at 20.7µm, 31.9µm, 47.2µm wavelength. A window filter and a longwave calibration filter of the SCARAB earth observer instrument are assessed similarly.

Optical thin films

Optical thin films are coatings of amorphous, crystalline or polymerized materials, in single or multiple layers, on surfaces of optical components such as lenses and mirrors. These thin film coatings are used in optics to reduce reflections from optical parts (antireflection coatings) or to provide highly reflective surfaces (dielectric mirrors), as well as to protect components against abrasion and ambient moisture.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

Purpose. This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Methods. 19 distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2m and 33cm. Stimulus and response AC/A and CA/C ratios were calculated. Results. Accommodation responses for near targets (p=0.017) response gains (p=0.026) were greater in the exotropes than the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p=0.02), but significantly higher CA/C ratios (p=0.02). All the exotropes, whether the angle changed most with lenses (“controlled by accommodation”) or on occlusion (“controlled by fusion”), used binocular disparity not blur as their main cue to target distance. Conclusions. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting over-accommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

Political economy of state-building: power after peace

The purpose of this volume is to examine and evaluate the impact of international state-building interventions on the political economy of post-conflict countries over the last 20 years. It analyses how international interventions have shaped political and economic dynamics and structures – both formal and informal – and what kind of state, and what kind of state-society relations have been created as a result, through three different lenses: first, through the approaches taken by different international actors like the UN, the International Financial Institutions, or the European Union, to state-building; second, through detailed analysis of key state-building policies; and third, through a wide range of country case studies. Amongst the recurring themes that are highlighted by the book’s focus on the political economy of state-building, and that help to explain why international state-building interventions have tended to fall short of the visions of interveners and local populations alike are evidence of important continuities between war-time and “post-conflict” economies and authority structures, which are often consolidated as a consequence of international involvement; tensions arising from what are often the competing interests and values held by different interveners and local actors; and, finally, the continuing salience of economic and political violence in state-building processes and war-to-peace transitions. The book aims to offer a more nuanced understanding of the complex impact of state-building practices on post-conflict societies, and of the political economy of post-conflict state-building.

Corruption and state-building

The chapter examines the compex roles of corruption in state-buioding environments. The first section briefly outlines how statebuilding is conceptualized in this discussion. The second section examines the concept of corruption,and argues that the organization, rather than the scale of corruption, offers a better lens through which its impact can be analyzed. The third section examines the complex relationship between corruption and statebuilding through the lenses of two key aspects of statebuilding – elite settlements, and the provision of public services – and briefly discusses both the complex relationship between corruption and security, and the impact of aid on corruption in statebuilding environments. The fourth section concludes the chapter with a reflection on the implications of the analysis for understanding contemporary statebuilding efforts and policy.

‘Low carbon’ scenarios, roadmaps, transitions and pathways: an overview and discussion

There are a range of studies based in the low carbon arena which use various ‘futures’- based techniques as ways of exploring uncertainties. These techniques range from ‘scenarios’ and ‘roadmaps’ through to ‘transitions’ and ‘pathways’ as well as ‘vision’-based techniques. The overall aim of the paper is therefore to compare and contrast these techniques to develop a simple working typology with the further objective of identifying the implications of this analysis for RETROFIT 2050. Using recent examples of city-based and energy-based studies throughout, the paper compares and contrasts these techniques and finds that the distinctions between them have often been blurred in the field of low carbon. Visions, for example, have been used in both transition theory and futures/Foresight methods, and scenarios have also been used in transition-based studies as well as futures/Foresight studies. Moreover, Foresight techniques which capture expert knowledge and map existing knowledge to develop a set of scenarios and roadmaps which can inform the development of transitions and pathways can not only help potentially overcome any ‘disconnections’ that may exist between the social and the technical lenses in which such future trajectories are mapped, but also promote a strong ‘co-evolutionary’ content.