301,911 research outputs found
Harvesting sunshine: solar cells, photosynthesis and the thermodynamics of light
No full textEffective capture of sunlight represents one of the grand challenges of photovoltaics today. This paper looks at the opportunities that exist, at the fundamental level, to manage light as the first step of photovoltaic conversion; in particular, how photonics can improve the efficiency and reduce the cost of solar cells. Starting from the current view of light trapping we shall introduce an additional variable: photon frequency. The example of fluorescent collectors will be used to discuss the principal features of frequency management, leading to a novel form of light trapping and, ultimately, the photonic bandgap solar cell. The discussion will be guided by arguments based on thermodynamics to describe photon transformation as part of the absorption / emission / conversion process. By drawing parallels with the capture of light in photosynthetic organisms we shall briefly discuss another important aspect: light harvesting energy collection, and the oportunity this represents for reducing the materials usage in future generations of solar cell
The invisible ideology of white light
No full textThis paper explores the role of white light in film history. It argues that, though we live our lives immersed in ‘white’ daylight, the historical hegemony of white light within moving images has been far from inevitable. The paper elaborates this claim by focusing on how and why Technicolor Inc. predicated its infamous but influential ‘law of emphasis’ on white balanced lighting, and by foregrounding ways in which subsequent uses of and discourses about colour in film have assumed the presence of full-spectrum light. Having drawn attention to this imperceptible – and so, until now, unnoticed – visual ideology, the paper then explores cinematic challenges to the hegemony of white light in films including South Pacific, Querelle and Chunkging Express
Wavefront shaping of a Bessel light field enhances light sheet microscopy with scattered light
No full textThe project was supported by the UK Engineering and Physical Sciences Research Council, RS MacDonald Charitable Trust, SULSA, and the St. Andrews 600th anniversary BRAINS appeal. K. D. is a Royal Society Wolfson Merit Award holder.Light sheet microscopy has seen a resurgence as it facilitates rapid, high contrast, volumetric imaging with minimal sample exposure. Initially developed for imaging scattered light, this application of light sheet microscopy has largely been overlooked but provides an endogenous contrast mechanism which can complement fluorescence imaging and requires very little or no modification to an existing light sheet fluorescence microscope. Fluorescence imaging and scattered light imaging differ in terms of image formation. In the former the detected light is incoherent and weak whereas in the latter the coherence properties of the illumination source, typically a laser, dictate the coherence of detected light, but both are dependent on the quality of the illuminating light sheet. Image formation in both schemes can be understood as the convolution of the light sheet with the specimen distribution. In this paper we explore wavefront shaping for the enhancement of light sheet microscopy with scattered light. We show experimental verification of this result, demonstrating the use of the propagation invariant Bessel beam to extend the field of view of a high resolution scattered light, light sheet microscope and its application to imaging of biological super-cellular structures with sub-cellular resolution. Additionally, complementary scattering and fluorescence imaging is used to characterize the enhancement, and to develop a deeper understanding of the differences of image formation between contrast mechanisms in light sheet microscopy
Archives and Images as Repositories of Time, Language, and Forms from the Past: A Conversation with Daniel Eisenberg
No full textBill from Carolina Power & Light Company
No full textBill from Carolina Power & Light Company, Jacksonville, NC. Addressed to New Farmers of America, Administration Building, c/o Johnson W. T. A&T College, Greensboro, NC
Bill from Carolina Power & Light Company
No full textBill from Carolina Power & Light Company, Jacksonville, NC, to New Farmers of America Bath House c/o Johnson W. T. Exec. Sec. A&T College Greensboro NC
Surface plasmon polariton modification in top-emitting organic light-emitting diodes for enhanced light outcoupling
No full textWe report on the enhanced light outcoupling efficiency of monochrome top-emitting organic light-emitting diodes (OLEDs). These OLEDs incorporate a hole transport layer (HTL) material with a substantially lower refractive index (∼ 1:5) than the emitter material or the standard HTL material (∼ 1:8) of a reference device. This low-index HTL is situated between the opaque bottom metal contact (anode) and the active emission layer. Compared to an HTL with common refractive index, the dispersion relation of the surface plasmon polariton (SPP) mode from the opaque metal contact is shifted to smaller in-plane wavenumbers. This shift enhances the outcoupling efficiency as it reduces the total dissipated power of the emitter. Furthermore, the excitation of the coupled SPPs at the thin transparent metal top contact (cathode) is avoided by using an ultrathin top electrode. Hence, the coupling of the electroluminescence from the emitter molecules to all non-radiative evanescent modes, with respect to the emitter material, is reduced by at least a factor of two, additionally increasing the outcoupling efficiency. Furthermore, for sufficiently high refractive index contrast the shift of the SPP at the anode/organic interface can lead to in-plane wavenumbers smaller than the wavenumber within the organic emitter layer and outcoupling of all excited modes by high index light extraction structures, e.g. microlens, seems feasible. In accordance to optical simulations, the external quantum efficiency is enhanced by about 20% for monochrome green emitting OLEDs with low refractive index HTL compared to a reference sample
Resonant energy transfer in light harvesting and light emitting applications
No full textThe performance of light emitting and light harvesting devices is improved by utilising resonant energy transfer. In lighting applications, the emission energy of a semiconductor heterostructure and the absorption of organic dyes or colloidal quantum dots (QDs) are engineered so that the excitations in the semiconductor heterostructure can be transferred to the light emitters by means of resonant energy transfer. The emitters subsequently emit colour-tunable light ranging from the visible to the near-infrared. As a result, a twofold enhancement of QD emission is demonstrated in a hybrid QD/semiconductor heterostructure. In light harvesting applications, a hybrid structure of colloidal QDs and a quantum well (QW) p-i-n heterostructure is investigated. After highly absorbing QDs absorb photons, the excitations are efficiently transferred to a QW p-i-n heterostructure via resonant energy transfer. The generated electron-hole pairs in the heterostructure are subsequently separated by the built-in electric held and collected by the corresponding electrodes. In order to increase the energy transfer rate, the donor-acceptor separation distance is minimised by fabricating channel structures on the heterostructure surface penetrating its active layers. Consequently, a sixfold enhancement of photocurrent conversion efficiency is demonstrated. Photocurrent of the hybrid structure is further improved by replacing the QW heterostructure with a bulk p-i-n heterostructure which has higher carrier transport efficiency. Hence, the photocurrent of the hybrid bulk heterostructure is about two orders of magnitude higher than that of the hybrid QW heterostructure. The proposed hybrid structures offer efficient light harvesting devices where high absorption of the colloidal QDs is utilised and their low charge-transfer is overcome
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Synthesis of visible-light-activated yellow amorphous TiO2 photocatalyst
No full textVisible-light-activated yellow amorphous TiO2 (yam-TiO2) was synthesised by a simple and organic-free precipitation method. TiN, an alternative precursor for TiO2 preparation, was dissolved in hydrogen peroxide under acidic condition ( pH similar to 1) adjusted by nitric acid. The yellow precipitate was obtained after adjusting pH of the resultant red brown solution to 2 with NH4OH. The BET surface area of this sample was 261 m(2)/g. The visible light photoactivity was evaluated on the basis of the photobleaching of methylene blue (MB) in an aqueous solution by using a 250 W metal halide bulb equipped with UV cutoff filter (lambda > 420 nm) under aerobic conditions. Yam-TiO2 exhibits an interesting property of being both surface adsorbent and photoactive under visible light. It was assigned to the eta(2)-peroxide, an active intermediate form of the addition of H2O2 into crystallined TiO2 photocatalyst. It can be concluded that an active intermediate form of titanium peroxo species in photocatalytic process can be synthesised and used as a visible-light-driven photocatalyst. Copyright (C) 2008 Chamnan Randorn et al.Peer reviewe
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