Experimental assessment of bi-directional transmission distribution functions using digital imaging techniques

Many daylighting applications require a precise knowledge of the directional transmission features of advanced fenestration materials. These photometric properties are described by a bi-directional transmission distribution function (BTDF), whose experimental assessment requires an appropriate equipment. A novel bi-directional photogoniometer, based on digital imaging techniques, has been designed and developed for that purpose. The main advantages of this device are the significant reduction of the time required for data measurement and its capability to assess an almost continuous BTDF function. These features can be achieved only through detailed and accurate calibration procedures of the bi-directional photogoniometer, which are described in this paper, together with digital image and data processing. Several experimental results, obtained for different fenestration materials, are used to illustrate the capabilities of this novel equipment

Bi-directional Photogoniometer for the Assessment of the Luminous Properties of Fenestration Systems

Most energy saving applications of advanced fenestration systems (solar blinds, novel types of glazing and daylight redirecting devices) require a precise knowledge of their directional light transmission features. These photometric properties can be described by a Bi-directional Transmission Distribution Function (BTDF) whose experimental assessment requires appropriate equipment. A novel bi-directional transmission photogoniometer, based on digital imaging techniques, was designed and set up for that purpose. The apparatus takes advantage of a modern video image capturing device (CCD digital camera) as well as of powerful image analysis software (pattern recognition) to considerably reduce the scanning time of a BTDF measurement, in comparison to existing devices that use a conventional approach (mobile photometer). A detailed calibration and validation procedure was used to obtain optimal experimental accuracy for the device during the assessment of BTDF data. It included a spectral, a photometric and a geometrical calibration of the digital video system, as well as several additional corrections, leading to an overall relative accuracy better than 11% for BTDF data. A special effort was made to improve the user-friendliness of BTDF measurement by facilitating the data acquisition and treatment (definition of a data acquisition and electronic data format) and by offering different possibilities of BTDF visualisation (hemispherical representation, axonometric view of photometric solids, C-planes). Overall, the photometric equipment was used to assess the BTDFs of more than 20 novel fenestration products of the industrial partner of the project (Baumann-Hüppe Storen AG). The experimental data produced was successfully used by the company to optimise the visual and energy saving performance of their products, which confirms the adequacy of the novel bi-directional photogoniometer for practical building applications

Innovative bidirectional video-goniophotometer combining transmission and reflection measurements

To assess the daylighting performances of a building, one of the most commonly used quantities is the Daylight factor, which is defined for a given surface element inside the analysed room as the ratio of the inside and outside illuminances under a CIE overcast sky. The Daylight factor consists of three components: the sky component, due to light flux reaching the surface element directly from the sky, the externally and the internally reflected components, respectively due to light flux reflected on external and internal surfaces. To estimate the direct sky component (also called sky factor), analytical methods can be used, based on the luminance distribution of the sky and the window’s geometric properties (dimensions and position in regard to the considered surface element). However, such methods have always been restricted to vertical (lateral) and horizontal (zenithal) windows, requiring heavy approximations to be applied whenever a tilted rectangular opening was considered. In this paper, a generalized method for assessing the sky component is proposed, extending it to rectangular windows of any tilt angle. As a purely analytical approach was found to be inapplicable, it is based on an optimised combination of vertical and horizontal windows situations. To validate the developed methodology, scale model measurements were performed with a sky simulator for two rectangular openings of varying tilt angle (every 15° from vertical to horizontal): the experimental results proved to be in very good agreement with the calculation-based approach

Measurement of bi-directional photometric properties of advanced glazing based on digital imaging techniques

Many daylighting applications require a precise knowledge of the transmission properties of fenestration materials, called bi-directional transmission distribution functions (BTDF), which necessitate systematic and accurate measurements. A new type of bi-directional photogoniometer, based on advanced imaging techniques, has been developed to this end; its mechanical concept, the calibration procedures and the first results are presented here

The configuration of the seismic zone and the downgoing slab in southern Peru

Using data from temporary networks of portable seismographs in southern Peru, we located 888 shallow and intermediate depth events near a proposed discontinuity in the seismic zone there. These events reveal a prominent contortion, instead of a discontinuity, that trends approximately N80°E, parallel to the direction of relative plate motion. North of about 15°S, the seismic zone beneath Peru is nearly horizontal, but south of about 15.5°S, it dips at about 25°. Volcanoes lie above the more steeply dipping zone where earthquakes occur between 120 and 140 km, and the volcanic line in southern Peru stops abruptly at the contortion

Effect of oxygen plasma etching on graphene studied with Raman spectroscopy and electronic transport

We report a study of graphene and graphene field effect devices after exposure to a series of short pulses of oxygen plasma. We present data from Raman spectroscopy, back-gated field-effect and magneto-transport measurements. The intensity ratio between Raman "D" and "G" peaks, I(D)/I(G) (commonly used to characterize disorder in graphene) is observed to increase approximately linearly with the number (N(e)) of plasma etching pulses initially, but then decreases at higher Ne. We also discuss implications of our data for extracting graphene crystalline domain sizes from I(D)/I(G). At the highest Ne measured, the "2D" peak is found to be nearly suppressed while the "D" peak is still prominent. Electronic transport measurements in plasma-etched graphene show an up-shifting of the Dirac point, indicating hole doping. We also characterize mobility, quantum Hall states, weak localization and various scattering lengths in a moderately etched sample. Our findings are valuable for understanding the effects of plasma etching on graphene and the physics of disordered graphene through artificially generated defects.Comment: 10 pages, 5 figure

Tectonic deformation of the Andes and the configuration of the subducted slab in central Peru: Results from a micro-seismic experiment

The vast majority of the microearthquakes recorded occurred to the east: on the Huaytapallana fault in the Eastern Cordillera or in the western margin of the sub-Andes. The sub-Andes appear to be the physiographic province subjected to the most intense seismic deformation. Focal depths for the crustal events here are as deep as 50 km, and the fault plane solutions, show thrust faulting on steep planes oriented roughly north-south. The Huaytapallana fault in the Cordillera Oriental also shows relatively high seismicity along a northeast-southwest trend that agrees with the fault scarp and the east dipping nodal plane of two large earthquakes that occurred on this fault in 1969. The recorded microearthquakes of intermediate depth show a flat seismic zone about 25 km thick at a depth of about 100 km. This agrees with the suggestion that beneath Peru the slab first dips at an angle of 30 deg to a depth of 100 km and then flattens following a quasi-horizontal trajectory. Fault plane solutions of intermediate depth microearthquakes have horizontal T axes oriented east-west

Facade Integration of Solar Thermal Collectors:A Breakthrough?

One main barrier to the acceptability of façade use of solar thermal collectors is their black appearance and the visibility of piping or absorber irregularities through the glazing. To facilitate façade integration, a project was set up to develop selective filters reflecting only a small part of the solar spectrum in the visible range while letting the rest of the radiation heat the absorber. These filters were successfully produced and, combined with a diffusing glass treatment, have achieved the desired masking effect with minor impact on the collector efficiency (less than 10%). Glasses of various colours combined with several diffusing finishing (acid etching, structured glass etc…) can be produced that are able to hide the absorber. Such glazings will allow the use of the same product both in front of façade areas equipped with solar absorbers (as collector external glass) and in front of the non exposed areas (as façade cladding), opening the way to a broad variety of active façade designs. The active elements can then be positioned at will on the exposed areas, and their quantity determined only by thermal needs. By freeing the dimension of the façade area that can be clad with this glazing from the thermally needed surface for collectors, a major step to help architects use solar thermal on facades has been taken

Sol-gel deposition of nanostructured low refractive index materials on solar collector glazing

Nanoporous SiO2 and nanocomposite MgF2:SiO2 coatings have been deposited by sol gel dip-coating in a particle-free atmosphere. The refractive index of the prepared nanostructured thin films is determined from spectrophotometric data. In both cases, significantly lower values than for compact SiO2 have been achieved. Highly transparent samples have been produced in a single dip-coating step followed by simple thermal annealing in air. Broad spectral transmittance maxima are observed exceeding values of 98.5% (nanoporous SiO2) and 99.5% (quaternary Mg:F:Si:O films). MgF2:SiO2 nanocomposite thin films can be expected to exhibit a higher aging stability than porous SiO2 films with respect to pore-filling by hydrocarbons and are therefore a promising alternative as well for single-layered anti reflection coatings as for multilayered coulored coatings on solar collector glazing