Reflection Paths Research Articles

Comparison of nano-structured solar cell anti-reflection coating based on graded-index or mode coupling approach

Solar cell nano-structured anti-reflection coatings based on graded index (GI) and mode coupling are all proposed to significantly reduce the reflection from semiconductor–air interface. In this work, it is shown that purely graded index approach can lead to degradation of long wavelength absorption by eliminating quasi-guided mode excitation. The reason is that the physically graded layer not only provides low reflectance path from air to semiconductor, but also from semiconductor to air, leading to photon escape. This results in out-coupling of photons from the semiconductor to air. On the other hand, anti-reflection coating based on mode coupling does not suffer from degraded long wavelength absorption and it is capable of acting as one-way photon pass coating. It is found that the sidewall thickness of mode coupling anti-reflection coating has significant impact on its effectiveness for anti-reflection, and therefore the selection of process methods is critical for its low reflectance. It is proposed that the purely graded index coating is more suitable for wafer-based photovoltaics where full absorption is possible by two photon traces. The mode coupling coating is suitable for both wafer-based photovoltaics and thin-film photovoltaics since it provides not only low reflectance but also long wavelength quasi-guided mode excitations. In the end, new types of anti-reflection coating and light trapping structure are proposed to further enhance the performance.

Multipeak aniostropic microfacet model for iridescent surfaces

In this paper, we propose an efficient iridescent rendering method. The iridescent colors on a surface is caused by the different reflection paths of rays with different wavelengths. In microfacet-based rendering model, the dominant reflection path of an incident light ray is statistically described by the microfacet-distribution function (MDF) of the surface. Therefore, the iridescent colors on the surface can be produced by applying different MDFs to different light wave channels. However, it is unnatural for a surface to have significantly different reflection properties in accordance with the light waves. Taking those into account, the proposed method employs identical and anisotropic microfacet distribution function(MDF) for each light wave channel, and rotates the identical anisotropic MDF of each channel with its own angle to produce iridescent reflection. The method also employs multi-peak MDF for the simulation of diffraction effects, and can be successfully applied to iridecent surface such as CD-ROM and mother-of-pearl (nacre) furniture. The experimental results demonstrate that the method enables interactive applications such as games or virtual reality softwares to plausibly express various cases of iridescent surfaces.

An Overview of Array Signal Processing and Beam Forming Techniques

For use as hydrophones, projectors and underwater microphones, there is always a need for calibrated sensors. Overview of multi path and effect of reflection on acoustic sound signals due to various objects is required prior to finding applications for different materials as sonar domes, etc. There is also a need to overview multi sensor array processing for many applications like finding direction of arrival and beam forming. Real time data acquisition is also a must for such applications.

Design-Focused Acoustic Analysis of Curved Geometries Using a Differential Raytracing Technique

Curved surfaces have a major influence on the propagation of sound in rooms. Convex surfaces always lead to attenuated reflections spread out over a larger area, while concave surfaces create either amplification or attenuation of reflections, depending on the source and receiver positions relative to the curved surface. Contemporary architecture often involves extensive use of both convex and concave surfaces. Therefore, acoustic consultants need to be able to quickly gain a thorough understanding of a given curved geometry, and judge to what extent the arising focusing will be either benign or problematic (due to focusing, inhomogeneous sound distribution or flutter echoes). The advent of NURBS-based 3D software (e.g. Rhino5) has made it possible to carry out very precise geometrical raytracing on curved surfaces, revealing their geometrical coverage. As a further refinement, a differential raytracing technique is proposed, allowing the straightforward calculation of the amplification or attenuation created by a given curved surface. This purely geometrical technique can also be applied to higher order reflections, in order to help identify flutter echo problems created by multiple reflection paths involving concave surfaces. Practical examples of halls with significant curved geometries will be given to illustrate the use of this approach, including Wigmore Hall, London and Wuxi Grand Theatre.

Outras vozes da política: memória e imaginação

The text aims to present the relation between reason and sensibility through a brief path of literary and poetic reflection, trying to think about the nexus between politics and imagination. Taking the relational analysis of the poem “El sur también existe” by Mario Benedetti as a reference and inviting the reader to read poems by Octavio Paz, Martha Nélida Ruiz, Gregory Bateson and Etienne Samain, it also suggests that the social scientist should take into consideration the relations between fiction and socio-historical reality and memory as connections that aim at the web of life which we conventionally call society.Keywords: society, politics, imagination, memory, poetry.

Simulating the effect of acoustic treatment types for residential balconies with road traffic noise

Development of design guides to estimate the difference in speech interference level due to road traffic noise between a reference position and balcony position or façade position is explored. A previously established and validated theoretical model incorporating direct, specular and diffuse reflection paths is used to create a database of results across a large number of scenarios. Nine balcony types with variable acoustic treatments are assessed to provide acoustic design guidance on optimised selection of balcony acoustic treatments based on location and street type. In total, the results database contains 9720 scenarios on which multivariate linear regression is conducted in order to derive an appropriate design guide equation. The best fit regression derived is a multivariable linear equation including modified exponential equations on each of nine deciding variables, (1) diffraction path difference, (2) ratio of total specular energy to direct energy, (3) distance loss between reference position and receiver position, (4) distance from source to balcony façade, (5) height of balcony floor above street, (6) balcony depth, (7) height of opposite buildings, (8) diffusion coefficient of buildings and (9) balcony average absorption. Overall, the regression correlation coefficient, R2, is 0.89 with 95% confidence standard error of ±3.4dB.

The Power Delay Profile of the Single-Antenna Full-Duplex Self-Interference Channel in Indoor Environments at 2.6 GHz

In this letter, the power delay profile (PDP) of the single-antenna full-duplex self-interference channel (SIC) is investigated in the indoor environments. The measurements are performed at the center frequency of 2.6 GHz with 200 MHz bandwidth. We find that the PDP can be decomposed into three components: leakage path, antenna reflection path, and space multipath. The major effects in determining the leakage path and the antenna reflection path are analyzed. Furthermore, the model of the profiles of the leakage path and the antenna reflection path is derived. The space multipath can be modeled as a power-law decay plus a random variable with lognormal statistics.

MODELING AND ANALYSIS OF AN ACOUSTIC CHANNEL WITH A MOVING SURFACE

A ray tracing algorithm for moving surfaces is derived to enable the analysis of surface movement effects. For this, a ray tracing algorithm for frozen surface is modified. By comparing the results from frozen and moving surface ray models allows effects of a moving surface to be investigated. The surface movement effects can be seen with the difference between channel impulse responses from the frozen and moving surface ray models. For an investigation of ray path dependence of the surface movement effects, delay times of surface reflective paths from the two ray models are observed according to transmitted ping time. As the ray path from the source to surface gets longer, difference of travel time results from the two ray models increase. This fact indicates that surface movement effects depend on ray path, in particular travel time until a ray meets a surface.

Pesquisas com os cotidianos: devir-filosofia e devir-arte na ciência

Com este texto, proponho que a tendência em pesquisas que vêm se afirmando no Brasil como pesquisas nos/dos/com os cotidianos configura o atravessamento do devir-filosofia e do devir-arte na ciência da Educação. Com esse propósito, traço um caminho de pensamento que consiste em uma articulação entre ideias defendidas por Deleuze e Guattari sobre filosofia, ciência e arte e os pressupostos epistemológicos, teóricos e metodológicos defendidos por pesquisadores que se filiam a essa tendência. Por fim, indico que as pesquisas nos/dos/com os cotidianos problematizam a pureza das linguagens científica, filosófica e artística historicamente construída, transbordando as fronteiras estipuladas entre esses três modos de pensar o mundo.

Material Flaw Sizing by Ultrasonic Multipath Detection

Sizing of material flaw is addressed in the multipath scene, and a method is developed to detect an isolated sized flaw and estimate its height based on imaging theory of different path profiles. A signal model based on the multipath higher order reflections of the flaw is built to detect the sized flaw. Multipaths are predicted and identified on the basis of the direct reflection path, which is relatively easy to be identified using the conventional flaw detection techniques. Direct reflection path and combined path are applied to detect the flaw from the top, and multipath w is to detect its bottom of the flaw. Ultrasonic imaging is formed and synthesized by all the identified multipaths, which shows the size of the material flaw. Simulations and experimentations demonstrate that the flaw sizing can be calculated utilizing the time-of-arrivals of the multipath signals.

Simulation and assessment of stray light effects in infrared cameras using non-sequential ray tracing

In this article, we have evaluated the stray light effects in infrared cameras operating in the 3–5μm waveband having cooled focal plane array detectors. A non-sequential ray tracing method is used to model the multiple reflections from polished lens surfaces as well as diffused scattering from rough mechanical surfaces inside the camera housing. The flux signature on the detector surface due to the self-emission of in-band radiation from the lenses and camera housing is calculated. The flux signature due to sources beyond the nominal field-of-view of the camera is also calculated. Light splitting into multiple diffraction orders from diffractive lens surfaces is taken into account both in the transmission and the reflection paths. The wavelength and angle dependent reflection coefficient of the anti-reflection coatings on the polished lens surfaces is taken into account. The effect of local heating of camera mounts on the stray light signature on the detector surface is also evaluated. The results show that using the non-sequential ray tracing method, useful predictions can be made for the stray light signature in the infrared cameras. Such calculations can be used to identify areas in the camera housing which need to be temperature stabilized to reduce their detrimental stray-light signature.

해면 산란효과에 의한 선박 방사소음 추정치 오차

The ship radiated noise level fluctuates by the interference between direct and reflected paths. The effect of sea surface reflection path on interference depends strongly on sea surface roughness. This paper describes error characteristics of ship acoustic signature estimation by sea surface scattering effect. The coherent reflection coefficient which explains a magnitude of sea surface scattering and its resultant interference acoustic field is analyzed quantitatively as a function of a grazing angle, effective surface height, frequency, source-receiver range and depths of source and receiver. Theoretical interference acoustic field is compared with experimental result for two different sea surfaces and five different frequencies by changing source-receiver range. It is found that both matches well each other and a magnitude of interference acoustic field is decreasing by increasing a grazing angle, effective surface height, frequency, and depths of source and receiver and decreasing source-receiver range. For given experimental conditions, the transmission anomaly which is a bias error of ship acoustic signature estimation, is about a range of 1~3 dB. The bias error of an existing ship radiated noise measurement system is also analyzed considering wind speed, source depth and frequency.

INTERCULTURAL THEOLOGICAL EDUCATION: TOWARDS A NEW FUTURE FOR FACULTIES OF THEOLOGY AT HIGHER EDUCATION INSTITUTIONS IN SOUTH AFRICA

This article is a first attempt in beating a new conceptual path for future and ongoing reflection and action in transforming faculties of theology at higher education institutions in South Africa. The following outline should guide us on our journey of discovery, reflection and participation. Firstly, the background and contextual picture of current transformational attempts at the University of the Free State (UFS) will be noted. Secondly, a local theoretical framework for intercultural theological formation is presented. Thirdly, an international theoretical framework for intercultural practices is provided. Fourthly, intercultural education will be viewed in the light of multicultural educational model. Fifthly, new methods of intercultural theological education will be proposed. The article will conclude with a few suggestions for future theological education.

WE‐E‐134‐05: Noncontact Ultrasound Applied to Osteroporosis Diagnostics Updated to Include Broadband Ultrasonic Attenuation and Offline Data Analysis

Purpose: The purpose was to push forward our efforts on applying noncontact ultrasound to quantitative imaging of cortical bone as described in our recent paper on speed of sound and attenuation, and integrated response to ultrasound spectroscopy including Broadband ultrasound attenuation (BUA) and to replace our noisy piezoelectric transducers with much quieter velocity correcting capacitive transducers at frequencies of 500 kHz and 850kHz. Methods: An NCU imaging system, a pair of broadband capacitive .500 and .850 MHz, non‐contact transducers, and cortical bone phantoms were used to determine bone mineral density (BMD), speed of sound (SOS), integrated acoustical response (IR), and ultrasonic transmittance. Air gaps of greater than 3 cm, two transmission and reflection paths, and a digital signal processor were used to collect data from phantoms of nominal mass density and (BMD) from 1.17 g/cm3 to 2.25 g/cm3 and from 0 g/cm3 to 1.7 g/cm3. Spectra were analyzed offline using Matlab, including its signal processing and Simulink tool boxes as well as customized Matlab based files, therefore providing much more detailed methods then online approaches, as used in our initial paper. Results: Good correlations between known BMD and measured SOS, IR, and transmittance were obtained for all 14 phantoms obtained in the original studies were complimented with spectroscopic and BUA measurements obtained with capacitive transducers that had much better stability then the original measurements and provided strong correlations with the known BMD of phantoms. Conclusion: The results suggest that the usage of capacitive transducers, offline analysis with Matlab including customized simulations and data analysis algorithms yields much better results than those in our original paper. The new results give us all the more impetus to extend the NCU methods to bone phantoms that more closely mimic human cortical bone and to subsequently apply our methods in vivo.

Enhanced spatial analysis of room acoustics using acoustic multiple-input multiple-output systems

Standard acoustic measurements in enclosures typically employ single-input single-output (SISO) acoustic systems. The parameters obtained from these measurements describe features of energy decay and do not characterize spatial attributes of the enclosure. Directional analysis of enclosures became popular with the introduction of microphone and loudspeaker arrays. In particular, spherical arrays have been shown to be highly beneficial for spatial analysis. Spherical microphone arrays facilitate the estimation of the arrival direction of the direct and reflected sound, while the use of both loudspeaker and microphones arrays can support the estimation of both radiation and arrival directions, with the application of conventional beamforming methods. However, when several reflections are attributed to the same time bin in a discrete impulse response, reflection paths may not be uniquely determined by existing beamforming techniques. We present a new method to uniquely determine source and receiver directions for multiple reflections when time separation is unfeasible. The paper presents the formulation of the proposed method, also showing a simulation study to demonstrate the performance of the proposed method.

The uncertainty in layered models from wide-angle seismic data

The analytical method of estimating the uncertainty in layered models is addressed to models obtained using a layer-stripping modeling strategy or forward modeling. It is based on a simple principle of small error propagation. There are two variants of the method: a simplified one that includes refraction and vertical reflections and one that also includes wide-angle reflections. Both give a quantitative estimation for the existing models. To allow for a simple analytical estimation, refracted waves are described using a head-wave approximation in constant velocity layers; wide angle reflection paths are also simplified. In the case of trial and error forward modeling, this method can help determine how well the used parameterization is reflected in the data and avoid over-fitting the structures. This is especially important because the forward modeling is very subjective and there is no method to assess the parameterization without generating alternative models. For inversion problems using the layer-stripping method, the analysis allows for a correct propagation of errors and will help to evaluate the effect of including a priori information with known uncertainty. As a result, the layer-stripping modeling strategy is worse than simultaneous inversion for layered models because it gives larger uncertainties.

Divine Passibility in Light of Two Pictures of Intercession

AbstractThe New Testament's two pictures of divine intercession, that of the risen Christ interceding at the right hand of God (Rom 8:34; Heb 7:25) and that of the Holy Spirit interceding from within believers’ hearts (Rom 8:26–7), offer additional perspective on the difficult issue of how God comes in touch with human suffering. Romans 8:26–7 connects the Spirit's intercession with the experience of human suffering, and through its reference to groaning implies that the Spirit communicates something of the believer's felt experience of weakness to God. Hebrews links Christ's high priestly work, including his intercessory activity, with his experience of struggle, thereby implying that he brings the needs of weak and pressured believers to God with an empathy born of direct experience of suffering. These scriptural pictures open a fruitful path for theological reflection, suggesting that God comes to know human suffering not simply by unmediated divine knowledge, or even by the bare fact of the divine Son's incarnation, but also in a mediated fashion, through complementary actions of Christ and the Spirit best described as acts of intercession.Applying a model of thought which emphasises the intercessory activities of Christ and the Spirit to the problem of divine passibility has a number of advantages. First, it coheres well with New Testament patterns for describing the roles of Father, Son and Holy Spirit: Christ's intercession is rooted in his incarnation and distinctive redemptive mission, while the Spirit's intercession emerges from his redemptive indwelling. Second, its picture of God knowing human suffering through the mediated process of intercession suggests that God maintains his freedom and holiness even as he gets in touch with human suffering. Third, the intercession model may shed additional light on how the sufferings of the incarnate Son touch or otherwise relate to the Father. Fourth, the Bible's pictures of divine intercession suggest that God is brought in touch with two dimensions of human suffering: the objective reality of human affliction (mediated through Christ's intercession) and the subjective experiences of afflicted people (mediated through the Spirit's intercession). Finally, these scriptural pictures of intercession orient our thoughts about the question of passibility in a pastoral direction.

Identification of the lateral position of a virtual object based on echoes by humans

Echolocation offers a promising approach to improve the quality of life of people with blindness although little is known about the factors influencing object localisation using a ‘searching’ strategy. In this paper, we describe a series of experiments using sighted and blind human listeners and a ‘virtual auditory space’ technique to investigate the effects of the distance and orientation of a reflective object and the effect of stimulus bandwidth on ability to identify the right-versus-left position of the object, with bands of noise and durations from 10–400 ms. We found that performance reduced with increasing object distance. This was more rapid for object orientations where mirror-like reflection paths do not exist to both ears (i.e. most possible orientations); performance with these orientations was indistinguishable from chance at 1.8 m for even the best performing listeners in other conditions. Above-chance performance extended to larger distances when the echo was artificially presented in isolation, as might be achieved in practice by an assistive device. We also found that performance was primarily based on information above 2 kHz. Further research should extend these investigations to include other factors that are relevant to real-life echolocation.

Quantitative evaluation of multipath rejection capabilities of GNSS antennas

Multipath error remains the largest error source in many high precision GPS applications. To counteract this problem, solutions at both software and hardware level have been studied. Software processing by means of measurement redundancy or error predictability can be used in order to mitigate the multipath effects. In general, these techniques work properly only when the length of a reflection path exceeds that of the direct path by more than 10---20 m. Unfortunately, in most cases, reflections are generated in the area near the receiving antenna. For this reason, multipath rejection actuated at the antenna level is one of the most valid means to improve the accuracy of GPS systems. The scope of this work is twofold. First, a review of low-multipath reception requirements will be proposed for comparing different classes of high precision GNSS antennas. Based on this discussion, we introduce a quantitative evaluation of multipath rejection capabilities of a GNSS antenna. The proposed assessment technique is focused on the antenna pattern, but, in contrast to other parameters evaluating the antenna radiation characteristics, it is specifically conceived to capture the effects of multipath signals.

Low Complexity Codebook-Based Beam Switching for 60 GHz Anti-Blockage Communication

A low complexity solution to the 60 GHz link- blockage problem is proposed based on the codebook beam switching technique. The directional link is easily blocked by a moving person, which is regarded as one of the severe problems in 60 GHz communication. Codebook based beam switching is a feasible technique to resolve the link-blockage by switching the beams from the blocked path to a backup reflection path. Typically, the selection of the best reflection path is crucial. Based on beam training mechanism, an ordered beam pair list (OBPL) of reflection paths is proposed for more accurate path selection and rapid link switching. Based on the OBPL, a complete and closed-form beam switching process is developed, which can apply for blockages of both LOS path and reflection NLOS paths. The link-blockage detection and LOS link- recovery detection are investigated. Theoretical analysis and numerical results show that for IEEE 802.15.3c indoor channel model, the proposed scheme has a good performance in complexity, applicability and system throughput. 