Neurons in striate cortex limit the spatial and temporal resolution for detecting disparity modulation.

Stereopsis is the process of seeing depth constructed from binocular disparity. The human ability to perceive modulation of disparity over space (Tyler, 1974; Prince and Rogers, 1998; Banks et al., 2004a) and time (Norcia and Tyler, 1984) is surprisingly poor, compared with the ability to detect spatial and temporal modulation of luminance contrast. In order to examine the physiological basis of this poor spatial and temporal resolution of stereopsis, I quantified responses to disparity modulation in disparity selective V1 neurons from four awake behaving monkeys. To study the physiological basis of the spatial resolution of stereopsis, I characterized the three-dimensional structure of 55 V1 receptive fields (RF) using random dot stereograms in which disparity varied as a sinusoidal function of vertical position (“corrugations”). At low spatial frequencies, this produced a modulation in neuronal firing at the temporal frequency of the stimulus. As the spatial frequency increased, the modulation reduced. The mean response rate changed little, and was close to that produced by a uniform stimulus at the mean disparity of the corrugation. In 48/55 (91%) of the neurons, the modulation strength was a lowpass function of spatial frequency. These results suggest that the neurons have fronto-parallel planar receptive fields, no disparity-based surround inhibition and no selectivity for disparity gradients. This scheme predicts a relationship between RF size and the high frequency cutoff. Comparison with independent measurements of RF size was compatible with this. All of this behavior closely matches the binocular energy model, which functionally corresponds to cross-correlation: the disparity modulated activity of the binocular neuron measures the correlation between the filtered monocular images. To examine the physiological basis of the temporal resolution of stereopsis, I measured for 59 neurons the temporal frequency tuning with random dot stereograms in which disparity varied as a sinusoidal function of time. Temporal frequency tuning in response to disparity modulation was not correlated with temporal frequency tuning in response to contrast modulation, and had lower temporal frequency high cutoffs on average. The temporal frequency high cut for disparity modulation was negatively correlated with the response latency, the speed of the response onset and the temporal integration time (slope of the line relating response phase and temporal frequency). Binocular cross-correlation of the monocular images after bandpass filtering can explain all these results. Average peak temporal frequency in response to disparity modulation was 2Hz, similar to the values I found in four human observers (1.5-3Hz). The mean cutoff spatial frequency, 0.5 cpd, was similar to equivalent measures of decline in human psychophysical sensitivity for such depth corrugations as a function of frequency (Tyler, 1974; Prince and Rogers, 1998; Banks et al., 2004a). This suggests that the human temporal and spatial resolution for stereopsis is limited by selectivity of V1 neurons. For both, space and time, the lower resolution for disparity modulation than for contrast modulation can be explained by a single mechanism, binocular cross-correlation of the monocular images. The findings also represent a significant step towards understanding the process by which neurons solve the stereo correspondence problem (Julesz, 1971)

Sinopsis del estado de arte de la climatización mediante energía solar térmica

En el presente trabajo se presenta una sinopsis del estado de arte de la refrigeración o climatización a base de energía solar térmica. Teniendo en cuenta dicho objetivo se efectuó una extensa revisión de literatura sobre la temática en cuestión. El trabajo contiene una introducción sobre las tecnologías disponibles en el mercado para la refrigeración. Por lo demás se resume la tecnología de sistemas inclusive pautas para el diseño. A continuación se señala tanto el potencial de la tecnología como los problemas por resolver, que se deben mayormente a la complejidad del sistema. El trabajo concluye con una visión general de los sistemas instalados: lugares, rango de potencia y tecnologías empleadas.The present essay provides a comprehensive overview of the state of the art of solar cooling and air-conditioning technology. This objective is met by an extensive literature review. The document contains an introduction to the market available thermally driven cooling technologies. This section is followed by a close insight into the relevant system technology with rules of thumb for the dimensioning. In the next part the market potential is reviewed and problems to be solved – mostly linked to the complexity of the systems – are presented. The article ends with an overview on existing solar cooling systems including the places of installation, ranges of cooling power and used technologies.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Sinopsis del estado de arte de la climatización mediante energía solar térmica

En el presente trabajo se presenta una sinopsis del estado de arte de la refrigeración o climatización a base de energía solar térmica. Teniendo en cuenta dicho objetivo se efectuó una extensa revisión de literatura sobre la temática en cuestión. El trabajo contiene una introducción sobre las tecnologías disponibles en el mercado para la refrigeración. Por lo demás se resume la tecnología de sistemas inclusive pautas para el diseño. A continuación se señala tanto el potencial de la tecnología como los problemas por resolver, que se deben mayormente a la complejidad del sistema. El trabajo concluye con una visión general de los sistemas instalados: lugares, rango de potencia y tecnologías empleadas.The present essay provides a comprehensive overview of the state of the art of solar cooling and air-conditioning technology. This objective is met by an extensive literature review. The document contains an introduction to the market available thermally driven cooling technologies. This section is followed by a close insight into the relevant system technology with rules of thumb for the dimensioning. In the next part the market potential is reviewed and problems to be solved – mostly linked to the complexity of the systems – are presented. The article ends with an overview on existing solar cooling systems including the places of installation, ranges of cooling power and used technologies.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Sinopsis del estado de arte de la climatización mediante energía solar térmica

En el presente trabajo se presenta una sinopsis del estado de arte de la refrigeración o climatización a base de energía solar térmica. Teniendo en cuenta dicho objetivo se efectuó una extensa revisión de literatura sobre la temática en cuestión. El trabajo contiene una introducción sobre las tecnologías disponibles en el mercado para la refrigeración. Por lo demás se resume la tecnología de sistemas inclusive pautas para el diseño. A continuación se señala tanto el potencial de la tecnología como los problemas por resolver, que se deben mayormente a la complejidad del sistema. El trabajo concluye con una visión general de los sistemas instalados: lugares, rango de potencia y tecnologías empleadas.The present essay provides a comprehensive overview of the state of the art of solar cooling and air-conditioning technology. This objective is met by an extensive literature review. The document contains an introduction to the market available thermally driven cooling technologies. This section is followed by a close insight into the relevant system technology with rules of thumb for the dimensioning. In the next part the market potential is reviewed and problems to be solved – mostly linked to the complexity of the systems – are presented. The article ends with an overview on existing solar cooling systems including the places of installation, ranges of cooling power and used technologies.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Caracterización del mercado argentino para calentadores solares de agua mediante una encuesta entre empresas

En este trabajo se busca caracterizar el mercado Argentino para calefones solares con el objetivo de conocer los productos ofrecidos y de evaluar el grado de difusión y se basa en una encuesta de la cual participaron 35 empresas del sector. Los resultados demuestran que el sector consiste principalmente en microempresas, cuyo número aumentó fuertemente en los años recientes. El producto mas comercializado es el colector plano para sistemas pasivos. Se registraron cerca de 2000m² instalados en el 2009. Un tercio de esta superficie fue importado, el resto proviene de producción nacional. Los equipos son instalados principalmente en casas particulares en el norte del país sustituyendo leña y gas en garrafas. La evaluación de las barreras percibidas señala la limitada rentabilidad de la tecnología solar térmica por falta de políticas favorables. Como conclusión, el trabajo presenta un resumen detallado del mercado actual y constituye una valiosa base de información para elaborar medidas de promoción.In this article the Argentinean solar thermal market is characterized in order to determine the available products and to evaluate their diffusion. It is based on a survey which was answered by 35 companies of the sector. The results show that the sector consists mainly of microenterprises, with a strong increase in recent years. The most commercialized product is the flat plate collector for passive systems. For 2009 almost 2000m² of installed collector area were registered. One third of it was imported, the rest produced locally. The systems are mainly installed in family houses in the north of the country substituting fire wood or bottled gas. The perceived barriers point out the limited profitability due to the lack of favorable politics. Concluding, the article gives a detailed overview on the actual state of the market and provides a valuable database for the elaboration of promotive measures.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Caracterización del mercado argentino para calentadores solares de agua mediante una encuesta entre empresas

En este trabajo se busca caracterizar el mercado Argentino para calefones solares con el objetivo de conocer los productos ofrecidos y de evaluar el grado de difusión y se basa en una encuesta de la cual participaron 35 empresas del sector. Los resultados demuestran que el sector consiste principalmente en microempresas, cuyo número aumentó fuertemente en los años recientes. El producto mas comercializado es el colector plano para sistemas pasivos. Se registraron cerca de 2000m² instalados en el 2009. Un tercio de esta superficie fue importado, el resto proviene de producción nacional. Los equipos son instalados principalmente en casas particulares en el norte del país sustituyendo leña y gas en garrafas. La evaluación de las barreras percibidas señala la limitada rentabilidad de la tecnología solar térmica por falta de políticas favorables. Como conclusión, el trabajo presenta un resumen detallado del mercado actual y constituye una valiosa base de información para elaborar medidas de promoción.In this article the Argentinean solar thermal market is characterized in order to determine the available products and to evaluate their diffusion. It is based on a survey which was answered by 35 companies of the sector. The results show that the sector consists mainly of microenterprises, with a strong increase in recent years. The most commercialized product is the flat plate collector for passive systems. For 2009 almost 2000m² of installed collector area were registered. One third of it was imported, the rest produced locally. The systems are mainly installed in family houses in the north of the country substituting fire wood or bottled gas. The perceived barriers point out the limited profitability due to the lack of favorable politics. Concluding, the article gives a detailed overview on the actual state of the market and provides a valuable database for the elaboration of promotive measures.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Caracterización del mercado argentino para calentadores solares de agua mediante una encuesta entre empresas

En este trabajo se busca caracterizar el mercado Argentino para calefones solares con el objetivo de conocer los productos ofrecidos y de evaluar el grado de difusión y se basa en una encuesta de la cual participaron 35 empresas del sector. Los resultados demuestran que el sector consiste principalmente en microempresas, cuyo número aumentó fuertemente en los años recientes. El producto mas comercializado es el colector plano para sistemas pasivos. Se registraron cerca de 2000m² instalados en el 2009. Un tercio de esta superficie fue importado, el resto proviene de producción nacional. Los equipos son instalados principalmente en casas particulares en el norte del país sustituyendo leña y gas en garrafas. La evaluación de las barreras percibidas señala la limitada rentabilidad de la tecnología solar térmica por falta de políticas favorables. Como conclusión, el trabajo presenta un resumen detallado del mercado actual y constituye una valiosa base de información para elaborar medidas de promoción.In this article the Argentinean solar thermal market is characterized in order to determine the available products and to evaluate their diffusion. It is based on a survey which was answered by 35 companies of the sector. The results show that the sector consists mainly of microenterprises, with a strong increase in recent years. The most commercialized product is the flat plate collector for passive systems. For 2009 almost 2000m² of installed collector area were registered. One third of it was imported, the rest produced locally. The systems are mainly installed in family houses in the north of the country substituting fire wood or bottled gas. The perceived barriers point out the limited profitability due to the lack of favorable politics. Concluding, the article gives a detailed overview on the actual state of the market and provides a valuable database for the elaboration of promotive measures.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Contrast dependence and differential contributions from somatostatin- and parvalbumin-expressing neurons to spatial integration in mouse v1

A characteristic feature in the primary visual cortex is that visual responses are suppressed as a stimulus extends beyond the classical receptive field. Here, we examined the role of inhibitory neurons expressing somatostatin (SOM(+)) or parvalbumin (PV(+)) on surround suppression and preferred receptive field size. We recorded multichannel extracellular activity in V1 of transgenic mice expressing channelrhodopsin in SOM(+) neurons or PV(+) neurons. Preferred size and surround suppression were measured using drifting square-wave gratings of varying radii and at two contrasts. Consistent with findings in primates, we found that the preferred size was larger for lower contrasts across all cortical depths, whereas the suppression index (SI) showed a trend to decrease with contrast. We then examined the effect of these metrics on units that were suppressed by photoactivation of either SOM(+) or PV(+) neurons. When activating SOM(+) neurons, we found a significant increase in SI at cortical depths >400 mum, whereas activating PV(+) neurons caused a trend toward lower SIs regardless of cortical depth. Conversely, activating PV(+) neurons significantly increased preferred size across all cortical depths, similar to lowering contrast, whereas activating SOM(+) neurons had no systematic effect on preferred size across all depths. These data suggest that SOM(+) and PV(+) neurons contribute differently to spatial integration. Our findings are compatible with the notion that SOM(+) neurons mediate surround suppression, particularly in deeper cortex, whereas PV(+) activation decreases the drive of the input to cortex and therefore resembles the effects on spatial integration of lowering contrast

Life cycle assessment of innovative materials for thermal energy storage in buildings

The politically endorsed reduction of greenhouse gas emissions entails the transformation of thermal energy systems towards renewable energies, especially in the building sector. This comes along with a demand in energy storage, as there is a time offset between energy availability and demand. As sensible heat storages induce major losses and have limited energy density, current water-based solutions are only partially sufficient to meet these demands. Within the project “Speicher-LCA” the environmental performance of a variety of innovative materials available for energy storage in buildings is assessed. The project provides the first extensive comparison of environmental profiles of various thermal energy storage materials, including phase change, thermochemical and sorption materials. The specific performances in the storage cycle are taken into account. All results will be publically accessible through a spreadsheet tool including a comprehensive set of materials, components as well as their integration into different building types. This paper discusses the methodological framework of the study and presents the environmental assessment results for selected materials. It highlights the main challenges in the assessment of innovative storage materials on different system levels which require specific definition of functional units accordingly. The first assessment results on material level for selected phase change (PCM) and thermo-chemical materials (TCM) allow an environmental characterization regarding their potential application in thermal storages. In addition, ranges of required numbers of storage cycles for amortization have been calculated for the non-renewable primary energy demand. For PCMs amortization cycles range between ∼20 to 150 cycles for salt hydrates and up to ∼280 cycles for paraffins. Regarding TCM, energetic amortization of silica gel and zeolite 13x is reached after ∼60 and ∼260 cycles respectively. Since the realization of storage components and systems which can actually be used in real applications will further increase the cycle number required for amortization, these storage materials may thus not be suitable for applications with a low number of cycles over lifetime, such as seasonal storage