Steady-state thermal analysis of an innovative receiver for linear Fresnel reflectors

The study of the performance of an innovative receiver for linear Fresnel reflectors is carried out in this paper, and the results are analyzed with a physics perspective of the process. The receiver consists of a bundle of tubes parallel to the mirror arrays, resulting on a smaller cross section for the same receiver width as the number of tubes increases, due to the diminution of their diameter. This implies higher heat carrier fluid speeds, and thus, a more effective heat transfer process, although it conveys higher pumping power as well. Mass flow is optimized for different tubes diameters, different impinging radiation intensities and different fluid inlet temperatures. It is found that the best receiver design, namely the tubes diameter that maximizes the exergetic efficiency for given working conditions, is similar for the cases studied. There is a range of tubes diameters that imply similar efficiencies, which can drive to capital cost reduction thanks to the flexibility of design. In addition, the length of the receiver is also optimized, and it is observed that the optimal length is similar for the working conditions considered. As a result of this study, it is found that this innovative receiver provides an optimum design for the whole day, even though impinging radiation intensity varies notably. Thermal features of this type of receiver could be the base of a new generation of concentrated solar power plants with a great potential for cost reduction, because of the simplicity of the system and the lower weigh of the components, plus the flexibility of using the receiver tubes for different streams of the heat carrier fluid.

(Table 1) Age and depth of reflectors of the 3.5-kHz and airgun seismic record and their corresponding depth of ash layers, carbonate peaks, and transition zones from DSDP Hole 83-504B

DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504B in a 260 m-thick ooze-chalk-limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW/m**2). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries.

A plea for reflectors : being a description of the new astronomical telescopes with silvered-glass specula and instructions for adjusting and using them /

Mode of access: Internet.

Biological polarized light reflectors in stomatopod crustaceans

Body parts that can reflect highly polarized light have been found in several species of stomatopod crustaceans (mantis shrimps). These polarized light reflectors can be grossly divided into two major types. The first type, usually red or pink in color to the human visual system, is located within an animal’s cuticle. Reflectors of the second type, showing iridescent blue, are located beneath the exoskeleton and thus are unaffected by the molt cycle. We used reflection spectropolarimetry and transmission electron microscopy (TEM) to study the reflective properties and the structures that reflect highly polarized light in stomatopods. For the first type of reflector, the degree of polarization usually changes dramatically, from less than 20% to over 70%, with a change in viewing angle. TEM examination indicates that the polarization reflection is generated by multilayer thin-film interference. The second type of reflector, the blue colored ones, reflects highly polarized light to all viewing angles. However, these reflectors show a slight chromatic change with different viewing angles. TEM sections have revealed that streams of oval-shaped vesicles might be responsible for the production of the polarized light reflection. In all the reflectors we have examined so far, the reflected light is always maximally polarized at around 500 nm, which is close to the wavelength best transmitted by sea water. This suggests that the polarized light reflectors found in stomatopods are well adapted to the underwater environment. We also found that most reflectors produce polarized light with a horizontal e-vector. How these polarized light reflectors are used in stomatopod signaling remains unknown.

Cost-exergy optimisation of linear Fresnel reflectors

This paper presents a new method for the optimisation of the mirror element spacing arrangement and operating temperature of linear Fresnel reflectors (LFR). The specific objective is to maximise available power output (i.e. exergy) and operational hours whilst minimising cost. The method is described in detail and compared to an existing design method prominent in the literature. Results are given in terms of the exergy per total mirror area (W/m2) and cost per exergy (US $/W). The new method is applied principally to the optimisation of an LFR in Gujarat, India, for which cost data have been gathered. It is recommended to use a spacing arrangement such that the onset of shadowing among mirror elements occurs at a transversal angle of 45°. This results in a cost per exergy of 2.3 $/W. Compared to the existing design approach, the exergy averaged over the year is increased by 9% to 50 W/m2 and an additional 122 h of operation per year are predicted. The ideal operating temperature at the surface of the absorber tubes is found to be 300 °C. It is concluded that the new method is an improvement over existing techniques and a significant tool for any future design work on LFR systems

Effect of fibre base and reflectors profile on the efficiency of ultra- long laser cavities

We study the effect of fibre base and grating profile on the efficiency of ultra-long Raman lasers. We show that for the studied parameters, FBG profile does not affect the performance when operating away from the zero-dispersion wavelength.

Numerical investigation of the impact of reflectors on spectral performance of Raman fibre laser

Using a cavity mode model we study numerically the impact of bandwidth and spectral response profile of fibre Bragg gratings on four-wave-mixing-induced spectral broadening of radiation generated in 6 km and 22 km SMF-based Raman fibre lasers.

Effect of fibre base and reflectors profile on the efficiency of ultra- long laser cavities

We study the effect of fibre base and grating profile on the efficiency of ultra-long Raman lasers. We show that for the studied parameters, FBG profile does not affect the performance when operating away from the zero-dispersion wavelength.

Computational Method to Determine Reflected Ultrasonic Signals From Arbitrary-Geometry Targets

A computational method based on the impulse response and on the discrete representation computational concept is proposed for the determination of the echo responses from arbitrary-geometry targets. It is supposed that each point of the transducer aperture can be considered as a source radiating hemispherical waves to the reflector. The local interaction with each of the hemispherical waves at the reflector surface can be modeled as a plane wave impinging on a planar surface, using the respective reflection coefficient. The method is valid for all field regions and can be performed for any excitation waveform radiated from an arbitrary acoustic aperture. The effects of target geometry, position, and material on both the amplitude and the shape of the echo response are studied. The model is compared with experimental results obtained using broadband transducers together with plane and cylindrical concave rectangular reflectors (aluminum, brass, and acrylic), as well as a circular cavity placed on a plane surface, in a water medium. The method can predict the measured echoes accurately. This paper shows an improved approach of the method, considering the reflection coefficient for all incident hemispherical waves arriving at each point of the target surface.

Facies architecture of the CRP-3 drillhole, Victoria Land Basin, Antarctica

The Cenozoic Victoria Land Basin (VLB) stratigraphic section penetrated by CRP-3 is mostly of Early Oligocene age. It contains an array of lithofacies comprising fine-grained mudrocks, interlaminated and interbedded mudrocks/sandstones, mud-rich and mud-poor sandstones, conglomerates and diametites that are together interpreted as the products of shallow marine to possibly non-marine environments of deposition, affected by the periodic advance and retreat of tidewater glaciers. This lithofacies assemblage can be readily rationalised using the facies scheme designed originally for CRP-2/2A, and published previously. The uppermost 330 metres below sea floor (mbsf) shows a cyclical arrangement of lithofacies also similar to that recognised throughout CRP-2/2A, and interpreted to reflect cyclical variations in relative sea-level driven by ice volume fluctuations ("Motif A"). Between 330 and 480 mbsf, a series of less clearly cyclical units, generally fining-upward but nonetheless incorporating a significant subset of the facies assemblage, has been identified and noted in the Initial Report as "Motif B. Below 480 mbsf, the section is arranged into a repetitive succession of fining-upward units, each of which comprises dolerite clast conglomerate at the base passing upward into relatively thick intervals of sandstones. The cycles present down 480 mbsf are defined as sequences, each interpreted to record cyclical variation of relative sea-level. The thickness distribution of sequences in CRP-3 provides some insights into the geological variables controlling sediment accumulation in the Early Oligocene section. The uppermost part of the section in CRP-3 comprises two or three thick, complete sequences that show a broadly symmetrical arrangement of lithofacies (similar to Sequences 9-11 in CRP-2/2A). This suggests a period of relatively rapid tectonic subsidence, which allowed preservation of the complete facies cycle. Below Sequence 3, however, is a considerable interval of thin, incomplete and erosionally truncated sequences (4-23), which incorporates both the remainder of Motif A sequences and all Motif B sequences recognised. The thinner and more truncated sequences suggest sediment accumulation under conditions of reduced accommodation, and given the lack of evidence for glacial conditions (see Powell et al., this volume) tends to argue for a period of reduced tectonic subsidence. The section below 480 mbsf consists of a series of fining-upward, conglomerate to sandstone intervals which cannot be readily interpreted in terms of relative sea-level change. A relatively mudrock-rich interval above the basal conglomerate/breccia (782-762 mbsf) may record initial flooding of the basin during early rift subsidence. The lithostratigraphy summarised above has been linked to seismic reflection data using depth conversion techniques (Henrys et al., this volume). The three uppermost reflectors ("o", "p" and "q") correlate to the package of thick sequences 1-3, and several deeper reflectors can also be correlated to sequence boundaries. The package of thick Sequences 1-3 shows a sheet-like cross-sectional geometry on seismic reflection lines, unlike the similar package recognised in CRP-2/2A.

Laser-derived particle size data from CRP-3, Victoria Land Basin, Antarctica: Implications for sequence and seismic stratigraphy

Seven hundred and nineteen samples from throughout the Cainozoic section in CRP-3 were analysed by a Malvern Mastersizer laser particle analyser, in order to derive a stratigraphic distribution of grain-size parameters downhole. Entropy analysis of these data (using the method of Woolfe and Michibayashi, 1995) allowed recognition of four groups of samples, each group characterised by a distinctive grain-size distribution. Group 1, which shows a multi-modal distribution, corresponds to mudrocks, interbedded mudrock/sandstone facies, muddy sandstones and diamictites. Group 2, with a sand-grade mode but showing wide dispersion of particle size, corresponds to muddy sandstones, a few cleaner sandstones and some conglomerates. Group 3 and Group 4 are also sand-dominated, with better grain-size sorting, and correspond to clean, well-washed sandstones of varying mean grain-size (medium and fine modes, respectively). The downhole disappearance of Group 1, and dominance of Groups 3 and 4 reflect a concomitant change from mudrock- and diamictite-rich lithology to a section dominated by clean, well-washed sandstones with minor conglomerates. Progressive downhole increases in percentage sand and principal mode also reflect these changes. Significant shifts in grain-size parameters and entropy group membership were noted across sequence boundaries and seismic reflectors, as recognised in others studies.

Rapid colour changes in multilayer reflecting stripes in the paradise whiptail, Pentapodus paradiseus

The Paradise whiptail (Pentapodus paradiseus) has distinct reflective stripes on its head and body. The reflective stripes contain a dense layer of physiologically active iridophores, which act as multilayer reflectors. The wavelengths reflected by these stripes can change from blue to red in 0.25 s. Transmission electron microscopy revealed that the iridophore cells contain plates that are, on average, 51.4 nm thick. This thickness produces a stack, which acts as an ideal quarter-wavelength multilayer reflector (equal optical thickness of plates and spaces) in the blue, but not the red, region of the spectrum. When skin preparations were placed into hyposmotic physiological saline, the peak wavelength of the reflected light shifted towards the longer (red) end of the visible spectrum. Hyperosmotic saline reversed this effect and shifted the peak wavelength towards shorter (blue/UV) wavelengths. Norepinephrine (100 mumol l(-1)) shifted the peak wavelength towards the longer end of the spectrum, while adenosine (100 mumol l(-1)) reversed the effects of norepinephrine. The results from this study show that the wavelength changes are elicited by a change of similar to70 nm in the distance between adjacent plates in the iridophore cells.

An interpretation of the deep seismic lines from the Penninic Alps of Valais (Switzerland)

The upper part of three deep seismic lines running across the Penninic Swiss Alps of Valais have been studied. Numerous reflectors illustrate the nappe structure of this internal part of the orogen. These reflectors, even at great depths (20-25 km), can be correlated with outcropping geological features and are most likely produced by lithological boundaries rather than by mylonites zones, which are hardly reflective in such an environment. Our interpretations, largely constrained by projections of the outcropping geology, have improved our knowledge of the deep structure of this segment of the Alpine belt, enhancing the importance of the backfolding and the crustal scale deformation phase which produced the Rawil-Valpelline depression and the Aar-Toce culmination. Furthermore we have here the possibility of correlating seismic patterns produced by ductile folds with the outcropping structures.

Modelado de una cámara de onda milimétrica

En aquest projecte s'ha dissenyat i simulat una càmera d'ones mil·limètriques mitjançant "Spinning Reflectors" amb l'objectiu d'estudiar la qualitat de les imatges obtingudes, així com determinar la configuració de reflectors acceptable per a la nostra càmera. Per al seu disseny, s'ha realitzat el model d'una antena Cassegrain amb botzina alimentadora a FEKO i s'han simulat els diagrames de radiació corresponents als diferents angles de rotació d'ambdós reflectors al voltant de l'eix en el qual estan situats. Finalment, a partir del principi de funcionament de la nostra càmera, s'ha exposat la seva implementació física i s'ha representat en Matlab la seva PSF (Point Spread Function) i la imatge d'un objecte arbitrari d'acord amb les tècniques de formació d'imatges.