1,721,071 research outputs found
A concept for switchable, energy-generating ‘smart’ windows
No full textSmart’ windows, mostly based on chromogenic events triggered chemically, electrically or otherwise, are able to variably control the amount of light that passes into a room space, but make no use of the rejected light. Photovoltaic ‘windows’ such as those based on thin films or tiled photovoltaic cells, on the other hand, may used absorbed light to generate electricity, but are incapable of adjusting transparency. I propose to use fluorescent dye guests in a liquid crystal host sandwiched between glass panels as a new type of ‘smart’ window. The dye material absorbs a variable amount of light depending on its orientation, which may be altered at will by aligning the liquid crystal host through application of an electric field. The absorbed light, rather than being lost, is re-emitted by the fluorescent molecules. A significant fraction of this light becomes trapped in the glass window panels by total internal reflection, and becomes concentrated along the edges of the device. To the edges of the glass waveguides may be attached small photovoltaic cells for generation of electricity. In this work I discuss preliminary results on model ‘smart’ window systems. I demonstrate that there is a variation of absorption upon adjusting the voltage applied to the cell. While there is a concurrent decrease in the amount of light emitted from the edge as the transmission of the window is increased, the variation in edge output is less than the variation in transmission, due to enhanced efficiency of light transport as the dye molecules alter their alignments
Thermally stable sites for electron capture in directly ionized DNA : free radicals produced by the net gain of hydrogen at C5/C6 of cytosine and thymine in crystalline oligodeoxynucleotides
No full textElectron paramagnetic resonance (EPR) spectroscopy is used to study radical trapping in crystalline oligodeoxynucleotides exposed to 70 keV x-irradiation at 4 K and annealed to 240 K. The four oligomers studied were the Z form d(CGCACG:GCGTGC), two A forms, d(CCCTAGGG)2 and d(GTGCGCAC)2, and the B form d(CGCGAATTCGCG)2. In each of these oligomers, evidence was found for trapping of a cytosine radical formed by the net gain of a hydrogen at C6 and a proton at N3 (the Cyt(C6+H, N3+H+)+• radical). The data are consistent with the trapping of another cytosine radical formed by the net gain of hydrogen at C5 (the Cyt(C5+H, N3+H)+• or Cyt(C5+H)• radical). The well-known thymine radical formed by the net gain of hydrogen at C5 (Thy(C6+H)• radical) was observed in the Z- and B-form duplexes but not in the A-form duplexes. The relative yields of these three reduction species indicate that cytosine is comparable to, or better than, thymine as a stable trapping site for reductive damage. These three radicals, Cyt(C6+H, N3+H+)+•, Cyt(C5+H, N3+H)+•, and Thy(C6+H)•, account for 85% of the total irreversibly trapped electrons in samples irradiated at 4 K and annealed to 240 K. Extrapolation of these results to B-form DNA hydrated to 9 waters per nucleotide, x-irradiated at 4 K, and warmed to room temperature predicts end product yields of 0.04-0.06 µmol/J for 5,6-dihydrouracil and 0.03-0.05 µmol/J for 5,6-dihydrothymine
Solar power from plastics?
No full textColorful plastic panels collect and focus sunlight onto small solar cells, offering architects great design freedom in integrating solar-energy systems into the built environment
Using liquid crystals to improve the performance of luminescent solar concentrators
No full textThe luminescent solar concentrator (LSC) has been proposed as a cost-effective solution to bring electricity generation from sunlight into the built environment. The basic LSC design consists of a plastic plate containing or topped by a thin layer of fluorescent dyes. The dyes absorb sunlight and re-emit it at a longer wavelength. A fraction of this light is trapped by total internal reflection and becomes concentrated along the edges of the waveguide, where one can place small photovoltaic cells to convert the emitted light into electrical current. With its flexibility in color, shape, and size, it would appear ideally suited for exploitation by the architect for use in façades and other structures in the urban surroundings. However, limitations in performance have hindered widespread adoption of the devices. In this work I present modifications to the standard LSC using liquid crystals to assist in collecting, directing, and controlling both the incoming and emitted light in the device, as well as describing additional features to allow on-demand adjustment of transparency
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Free radical yields in crystalline DNA x-irradiated at 4 K
No full textThe objective of this work is to determine the extent to which various structural factors influence the yield of trapped free radicals, G(tfr), in DNA irradiated at 4 K. G(tfr) was measured in a series of 13 different oligodeoxynucleotides using electron paramagnetic resonance (EPR) spectroscopy. Each sample consisted of crystalline duplex DNA for which the crystal structure was verified to be that reported in the literature. We find that the G(tfr) of these samples is remarkably high, ranging from 0.55 to 0.75 micromol/J. The standard deviation in G(tfr) for a given crystal structure is generally small, typically less than +/-10%. Furthermore, G(tfr) does not correlate with DNA base sequence, conformation, counterion or length of base stacking. Two observations point to the importance of DNA packing: (1) The radical yields in crystalline DNA are greater than those determined previously for DNA films (0.2 to 0.5 micromol/J); and (2) the variability in G(tfr) is less in DNA crystals than in DNA films. We conclude that closely packed DNA maximizes radical trapping by minimizing the interhelical solvent space. Furthermore, the high efficiency of electron and hole trapping at 4 K is not consistent with DNA possessing properties of a metallic conductor. Indeed, it behaves as an insulator, whether it is in A-, B-, or Z-form and whether base stacking is short- (8 bp) or long-range (>1000 bp)
Electron and hole transfer induced by thermal annealing of crystalline DNA X-irradiated at 4 K
No full textRecent models for long range (>2 nm) transfer of electrons and holes through DNA suggest a mechanism that is neither a single long distance tunneling event nor a mechanism strictly due to hopping, but a mixture of the two. From results reported here we argue that any complete model of electron or hole transfer in DNA should include the effects of reversible proton transfer. Reversible proton transfer (primarily between guanine-cytosine base pairs) influences the ability of DNA to trap free radicals, which in turn affects the migration of holes and electrons. We present the annealing characteristics of electrons and holes trapped in crystalline oligodeoxynucleotides irradiated at 4 K and annealed stepwise to room temperature (RT). The annealing profiles are relatively insensitive to DNA conformation, sequence, or base stacking continuity. The packing of the DNA duplexes is known, and it is readily shown that electron and/or hole transfer must be intermolecular. The distances required for tunneling between separate molecules are found to be comparable to the distances required for tunneling within a DNA duplex. The annealing characteristics of DNA are considerably different than those found in crystals of a-Me-mannoside, 5‘dCMP, and 1-Methylcytosine:5-Fluorouracil. This difference is ascribed to a mechanism wherein reversible proton transfer is a rate-limiting step for electron/hole transfer. Reversible proton transfer is, thereby, a "gate" for electron/hole transfer (via tunneling). Because reversible proton transfer is thermally activated, it is proposed that the energetics of this transfer is a dominant factor in determining the thermal annealing profile of DNA. The competing reactions that govern electron/hole migration created by annealing samples irradiated at 4 K are applicable to electron/hole migration at RT. Evidence for this comes from the observation that, in a number of DNA crystals, the free radical species and radical yields are very similar to crystals irradiated at RT compared to those irradiated at 4 K followed by annealing to RT. The proposed mechanism for electron and hole migration through DNA is one where short transfers (=1 nm) occur by tunneling, and tunneling is gated by reversible proton-transfer
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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