Brightness reduction as a function of the angular position of a glare source

El efecto de difusión intraocular de luz generada por una fuente deslumbrante periférica se cuantifica mediante un modelo formulado empíricamente en términos de la luminancia de velo. Esta luminancia es directamente proporcional a la iluminancia generada en el ojo por dicha fuente e inversamente proporcional al cuadrado del ángulo de excentricidad subtendido por la fuente con el eje visual. En artículos previos se analiza el efecto de reducción de claridad en presencia de una fuente deslumbrante a 10º y se obtiene que el efecto aumenta al crecer la iluminancia generada por la fuente. En el presente trabajo se investiga la dependencia de la reducción de claridad con el ángulo de excentricidad de una fuente deslumbrante transitoria que genera 60lux en el ojo. Se usa un método de comparación de magnitudes en el que la claridad percibida de un estimulo de luminancia variable presentado sin deslumbramiento se compara con la de uno de referencia presentado en sincronía con el deslumbramiento. Para 5 adultos jóvenes emétropes resulta que, al disminuir el ángulo de 15º a 7.5º, la luminancia de igualación se reduce como lo predice el modelo de luminancia de velo. Esto indicaría que el fenómeno de reducción de claridad es fuertemente dependiente del velo producido por la fuente deslumbrante. Los resultados obtenidos se comparan con los de otros autores hallados bajo condiciones de deslumbramiento estable.The effect of intraocular scattering of light generated at a peripheral glare source is quantified using a model empirically formulated in terms of the veiling luminance. This luminance is directly proportional to the illuminance generated at the eye by this source and inversely proportional to the square of the eccentricity angle subtended by the source with the visual axis. In previous articles the effect of brightness reduction due to the presence of a glare source subtending 10º is analyzed and it results that this effect increases when the illuminance generated by the source increases. In the present paper the dependence of brightness reduction on the eccentricity angle of a transient glare source generating 60lux at the eye is investigated. A method of magnitudes comparison, consisting in comparing the perceived brightness of a stimulus of variable luminance presented without glare to that of a reference stimulus presented simultaneously with glare, is employed. For 5 emmetropic young adults it results that, when the angle decreases from 15º to 7.5º, the matching luminance decreases as predicted by the veiling luminance model. This would indicate that the brightness reduction phenomenon is strongly dependent on the veil produced by the glare source. The results obtained are compared to those of other authors found under stable glare conditions.Fil: Issolio, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; ArgentinaFil: Juliana Matranga. No especifica;Fil: Pablo Barrionuevo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; ArgentinaFil: Comastri, Silvia Ana Elva. No especifica;Fil: Gabriel Martin. No especifica;Fil: Colombo, Elisa Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentin

Both Strands of siRNA Have Potential to Guide Posttranscriptional Gene Silencing in Mammalian Cells

Despite the widespread application of RNA interference (RNAi) as a research tool for diverse purposes, the key step of strand selection of siRNAs during the formation of RNA-induced silencing complex (RISC) remains poorly understood. Here, using siRNAs targeted to the complementary region of Survivin and the effector protease receptor 1 (EPR-1), we show that both strands of the siRNA duplex can find their target mRNA and are equally eligible for assembly into Argonaute 2 (Ago2) of RISC in HEK293 cells. Transfection of the synthetic siRNA duplexes with different thermodynamic profiles or short hairpin RNA (shRNA) vectors that generate double-stranded RNAs (dsRNAs), permitting processing specifically from either the 5′ or 3′ end of the incipient siRNA, results in the degradation of the respective target mRNAs of either strand of the siRNA duplex with comparable efficiencies. Thus, while most RNAi reactions may follow the thermodynamic asymmetry rule in strand selection, our study suggests an exceptional mode for certain siRNAs in which both strands of the duplex are competent in sponsoring RNAi, and implies additional factors that might dictate the RNAi targets

Thinning Algorithms for Remote Sensing Observations in Support of Ocean Data Assimilation

Data assimilation is a method to combine the numerical solutions calculated by circulation models with observations from different platforms in order to obtain an optimal estimate of the state of the system. The computational and numerical difficulties associated with processing the increasing number of observations necessitate the use of thinning techniques to reduce the number of data assimilated. In this thesis the impact of thinning two types of particularly voluminous data sets on the overall performance of an ocean data assimilation system were evaluated. In particular, an analysis of the ocean circulation along the U.S. West Coast with a 10 km resolution grid was performed, spanning a period of one year. Two different thinning methods were tested: an intelligent data thinning (IDT) algorithm to thin gridded satellite sea surface temperature (SST) and a simple thinning algorithm to reduce the volume of radial sea surface velocity measured by a network of coastal high frequency radars. The SST data were thinned by discarding data in regions with low spatial variability while retaining data in regions of high spatial variability. Conversely, the radar observations were averaged to create “super observations” consistent with the resolution of the model grid and prior assumptions about observation errors. The full and thinned data sets were assimilated using a 4-dimensional variational (4D-Var) data assimilation algorithm in the Regional Ocean Modeling System (ROMS). A statistical analysis of the diagnosed background and observation errors showed that the thinning experiments were well-behaved. Furthermore, the innovation and residual vectors (i.e. the difference between each observation and its prior and posterior model counterpart) in all cases generally satisfied the assumption of Gaussian distributions. Additionally, the topology of a the total error covariance matrix of the data assimilation system was explored via its eigen space. The thinning experiments amplified the eigen spectrum, modified the condition number, and in particular thinning SST changed the aspect ratio of the hyperellipse defined by the covariance matrix to change. Lastly the impact of each type of observation on the analyses was quantified for the different thinning methods, suggesting that the radial velocities thinning was perhaps too severe, while the thinning of SST levelled the impact different observations had on the DA analysis. Overall results showed that the thinning did not significantly degrade the analysis, hence the next step will be to test these algorithms in a near-real time forecasting system

Thinning Algorithms for Remote Sensing Observations in Support of Ocean Data Assimilation

Data assimilation is a method to combine the numerical solutions calculated by circulation models with observations from different platforms in order to obtain an optimal estimate of the state of the system. The computational and numerical difficulties associated with processing the increasing number of observations necessitate the use of thinning techniques to reduce the number of data assimilated. In this thesis the impact of thinning two types of particularly voluminous data sets on the overall performance of an ocean data assimilation system were evaluated. In particular, an analysis of the ocean circulation along the U.S. West Coast with a 10 km resolution grid was performed, spanning a period of one year. Two different thinning methods were tested: an intelligent data thinning (IDT) algorithm to thin gridded satellite sea surface temperature (SST) and a simple thinning algorithm to reduce the volume of radial sea surface velocity measured by a network of coastal high frequency radars. The SST data were thinned by discarding data in regions with low spatial variability while retaining data in regions of high spatial variability. Conversely, the radar observations were averaged to create “super observations” consistent with the resolution of the model grid and prior assumptions about observation errors. The full and thinned data sets were assimilated using a 4-dimensional variational (4D-Var) data assimilation algorithm in the Regional Ocean Modeling System (ROMS). A statistical analysis of the diagnosed background and observation errors showed that the thinning experiments were well-behaved. Furthermore, the innovation and residual vectors (i.e. the difference between each observation and its prior and posterior model counterpart) in all cases generally satisfied the assumption of Gaussian distributions. Additionally, the topology of a the total error covariance matrix of the data assimilation system was explored via its eigen space. The thinning experiments amplified the eigen spectrum, modified the condition number, and in particular thinning SST changed the aspect ratio of the hyperellipse defined by the covariance matrix to change. Lastly the impact of each type of observation on the analyses was quantified for the different thinning methods, suggesting that the radial velocities thinning was perhaps too severe, while the thinning of SST levelled the impact different observations had on the DA analysis. Overall results showed that the thinning did not significantly degrade the analysis, hence the next step will be to test these algorithms in a near-real time forecasting system

Influencia de lentes oftálmicas en el ángulo subtendido por un punto fuente periférico

Cuando un ojo miope o hipermétrope utilizando una lente oftálmica mira un estímulo y, además, recibe luz de un punto periférico, la lente modifica el ángulo de excentricidad con el cual la luz originada en dicho punto llega al ojo. En aproximación paraxial, el aumento visual de la lente (cociente entre los ángulos subtendidos en el vértice corneal por el punto y por su imagen a través de lente) puede evaluarse como es usual, considerando o bien lente gruesa o delgada. En el primer caso, el cálculo requiere datos (no siempre disponibles) referentes a ubicación de la fuente, parámetros constructivos de la lente y distancia de vértice mientras que, en el segundo, los resultados son imprecisos para lentes gruesas empleadas por pacientes con hipermetropía severa. Para evitar estos inconvenientes, en el presente artículo obtenemos una formula para el aumento visual promedio de una lente oftálmica estándar de caras esféricas como función solo de su potencia. Proponemos utilizar esta fórmula para estimar de modo sencillo y aproximado el ángulo de excentricidad efectivo correspondiente a un punto fuente lejano o cercano y a cualquier lente oftálmica estándar y distancia de vértice habitual.When a myopic or hyperopic eye wearing an ophthalmic lens looks at a stimulus and also receiveslight from a peripheral point, the lens modifies the eccentricity angle with which light originated at this point reaches the eye. Under paraxial approximation, the lens visual magnification (quotient between the angles subtended at the corneal vertex by the point and by its image through the lens) can be evaluated as usual, either considering thick or thin lens. In the first case, the calculation requires data (not always available) concerning source location, lens construction parameters and vertex distance while, in the second, results are imprecise for thick lenses employed by patients suffering severe hyperopia. To avoid these drawbacks, in the present article we obtain a formula for the mean visual magnification of a standard ophthalmic lens of spherical surfaces as a function only of its power. We propose the use of this formula to estimate in a simple and approximate way the effective eccentricity angle corresponding to a far or near point source and to any standard ophthalmic lens and habitual vertex distance.Fil: Comastri, Silvia Ana Elva. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Issolio, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; ArgentinaFil: Matranga, Juliana. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Colombo, Elisa Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentin

Influence of ophthalmic lenses in the illuminance originated at a peripheral glare source and reaching the eye

To study the influence of glare on the visual performance of a subject wearing an ophthalmic lens, it is useful to know how the lens affects the illuminance reaching the eye. In this paper, considering spherical standard ophthalmic lenses and defining the relative illuminance, Er, as the quotient between the illuminance at the cornea with and without lens, a methodology to evaluate Er in terms of easily determined parameters is developed. Three effects are considered, pupil size variation of the system with and without lens; lateral shifts of rays transmitted through the lens and reflections at the lens. Calculations are experimentally verified employing 5 organic ophthalmic lenses of ±6; ±4 and 0.12 dioptres and 2 glass plane parallel plates 1.95 and 6.6 mm thick. Using a photometer whose sensor is 12 mm apart from the lens and 740 mm apart from a glare source subtending an eccentricity angle of 9.6°, it results Er=1.204 for the 6 dioptres lens and Er=0.803 for the -6 dioptres one if sensor diameter is 10 mm while, for a 719 mm distance and a 10° angle, Er=0.922 for the thin plate and a 30 mm sensor and Er=1.006 for the thick plate and a 10 mm sensor. Experimental and theoretical results differ in less than 3%.Fil: Comastri, Silvia Ana Elva. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: J.Matranga. Universidad de Buenos Aires. Facultad de Ingeniería; ArgentinaFil: Bastida, Karina. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Issolio, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Luminotecnia, Luz y Visión; ArgentinaFil: Colombo, Elisa Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Luminotecnia, Luz y Visión; Argentin