399,235 research outputs found
It’s Not Just a Game: Contemporary Challenges for Games Research and the Internet
No full textIn this final chapter we will raise a number of issues that we have encountered as we have put this collection of papers together. In doing this, we also reflect upon the seven challenges for video game theory that Bernard Perron and Mark Wolf(2009)put forward in the introduction to the second video game theory reader given it is probably one of the most recent assessments in the area at the time of\ud
writing. These challenges are concerned with Terminology and Accuracy, History, Methodology, Technology, Interactivity, Play and the Integration of Interdisciplinary Approaches. These issues will be brought up throughout this chapter, but not necessarily in mutually exclusive fashion..
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
(2S*)-2-Hydroxy-2- (2S*,5R*)-5-(1-hydroxy-1-methyl-ethyl)tetrahydrofuran -2-yl -1-phenylethanone
No full textThe molecules of the title compound, C15H20O4, link via a single intermolecular hydrogen bond to form chains running along the b axis
Energy transfer in light-harvesting complexes LHCII and CP29 of spinach studied with three pulse echo peak shift and transient grating
No full textThree pulse echo peak shift and transient grating (TG) measurements on the plant light-harvesting complexes LHCII and CP29 are reported. The LHCII complex is by far the most abundant light-harvesting complex in higher plants and fulfills several important physiological functions such as light-harvesting and photoprotection. Our study is focused on the light-harvesting function of LHCII and the very similar CP29 complex and reveals hitherto unresolved excitation energy transfer processes. All measurements were performed at room temperature using detergent isolated complexes from spinach leaves. Both complexes were excited in their Chl b band at 650 nm and in the blue shoulder of the Chl a band at 670 nm. Exponential,: fits to the TG and three pulse echo peak shift decay curves were used to estimate the timescales of the observed energy transfer processes. At 650 nm, the TG decay can be described with time constants of 130 fs and 2.2 ps for CP29, and 300 fs and 2.8 ps for LHCII. At 670 nm, the TG shows decay components of 230 fs and 6 ps for LHCII, and 300 fs and 5 ps for CP29. These time constants correspond to well-known energy transfer processes, from Chl b to Chl a for the 650 nm TG and from blue (670 nm) Chl a to red (680 nm) Chl a for the 670 nm TG. The peak shift decay times are entirely different. At 650 nm we find times of 150 fs and 0.5-1 ps for LHCII, and 360 fs and 3 ps for CP29, which we can associate mainly with Chl b Chl b,energy transfer. At 670 nm we find times of 140 fs and 3 ps for LHCII, and 3 ps for CP29, which we can associate with fast (only in LHCII) and slow transfer between relatively blue Chls a or Chl a states. From the occurrence of both fast Chl b Chl, bland fast Chl b --> Chl a transfer in CP29, we conclude that at least two mixed binding sites are present in this complex. A detailed comparison of our observed rates with exciton calculations on both CP29 and LHCII provides us with more insight in the location of these mixed sites. Most importantly, for CP29, we find that a Chl b pair must be present in some, but not all, complexes, on sites A(3) and B-3. For LHCII, the observed rates can best be understood if the same pair, A(3) and B-3, is involved in both fast Chl b Chl b and fast Chl a Chl a transfer. Hence, it is likely that mixed sites also occur in the native LHCII complex. Such flexibility in chlorophyll binding would agree with the general flexibility in aggregation form and xanthophylli, binding of the LHCII complex and could be of use for optimizing the role of LHCII under specific circumstances, for example under high-light conditions. Our study is the first to provide spectroscopic evidence for mixed binding sites, as well as the first to show their existence in native complexes
Organophosphoryl adducts of tris(pentafluorophenyl)borane; crystal and molecular structure of B(C6F5)(3)·Ph3PO
No full textA series of 1 : 1 adducts of B(C6F5)(3) with the organophosphoryl ligands Et3PO, Ph3PO, (Pr3PO)-P-n, Oct(3)(n)PO, (MeO)(3)PO, (EtO)(3)PO, (PhO)(3)PO, (EtO)(2)(H)PO, ((BuO)-O-n)(2)(H)PO, (PhO)(2)(H)PO, (MeO)(2)MePO, (EtO)(2)MePO, (EtO)(2)PhPO, and (EtO)Me2PO have been synthesized and characterised by elemental analysis, mp, and spectroscopic (H-1, C-13, B-11, F-19, P-31 NMR and IR) methods. B(C6F5)(3). Ph3PO was further characterised in the solid state by a single-crystal X-ray diffraction study. P-31 NMR chemical shifts and nu (PO) IR stretching frequencies are discussed in relation to substituent at phosphorus
Three dimensional structure of the light-harvesting chlorophyll a/b protein complex from plant chloroplasts
No full textThe light-harvesting chlorophyll a/b protein complex (LHC-II) is the major collector of solar energy in all plants and it binds about half of the chlorophyll in green plants. LHCII is a trimer in the photosynthetic membrane; each monomer consists of 232 amino acids, binds and orients a minimum of 12 chlorophyll molecules and three caroteinoids (two luteins and one neoxanthin) for light-harvesting and energy transfer. Although, the structure of LHC-II has been determined at 3.4 Å resolution by electron microscopy of two-dimensional crystals (Kühlbrandt et al., 1994), this is not sufficient to allow a complete understanding of the mechanism of energy transfer from LHC-II to the reaction centre, since the effective resolution in the z dimension is 4.9 Å. In fact, the chemical difference between Chl a and Chl b, which has a formyl group instead of the methyl group at the 7-position in the chlorin ring, is too small to be detected at this level of resolution. In addition, the orientation of the chlorophyll tetrapyrroles have not been determined unambiguously. This information is essential for a detailed understanding of the energy transfer within the complex and to the reaction centres of photosystem II and I (PSII and PSI). X-ray crystallography of three dimensional (3D) crystals may yield a more complete structure at high resolution. 3D crystals have been grown from LHC-II isolated from pea leaves using a standard purification procedure (Burke et al., 1978). The thylakoid membranes are solubilised in Triton X-100 and further purified by sucrose gradient ultra centrifugation. The LHC-II fraction is salt precipitated and pellets resuspended at the chlorophyll a/b ratio 2.8 mg/ml in 0.9 % Nonyl-glucoside. Crystals are currently obtained by vapour diffusion in hanging drops. These crystals are thin hexagonal plates, have a fairly large unit cell and diffract quite weakly. The high level of the background is due both to the detergent, necessary for protein solubilisation, and lipids, required for the trimer and crystals formation. However, three data sets, each from one single crystal have been collected up to 3.2 Å resolution over a rotation range of 135°. The crystals were exposed to a very highly collimated and brilliant beam (ID-14 EH1 at ESRF, Grenoble, France) and were kept under a stream of cold nitrogen to prevent radiation damage. Data were successfully integrated using the program XDS by Kabsch (1993). The crystals were found to belong to the space group P6 22 3 and have unit cell dimensions of a=128.45, b=128.45, c=135.32, a= ß=90º, ?=120. The solution of the phase problem was tackled by molecular replacement using, as a search model, the LHC-II structure solved by electron cryo-microscopy studies of twodimensional crystals (Kühlbrandt et al. 1994). Three different programs were tested: the most used AMoRe (Navaza et al., 1994) and the brute force based program Brute (FujinagaDer Chlorophyll a und b bindende Lichtsammelkomplex II (LHC-II) ist der Hauptantennenkomplex höherer Pflanzen. Er dient der Lichtabsorption und Energieweiterleitung und bindet fast die Hälfte der Chlorophylle in grünen Pflanzen. In der Thylakoidmembran liegt LHC-II als Trimer vor. Jedes Monomer besteht aus 232 Aminosäuren und bindet spezifisch mindestens 12 Chlorophyllmoleküle (Chl) und drei Carotinoide (zwei Luteine und ein Neoxanthin). Die Struktur von LHC-II wurde mittels Elektronenmikroskopie anhand von zweidimensionalen Kristallen mit einer Auflösung von 3.4 Å bestimmt. Diese Auflösung reicht jedoch nicht aus, um den Energieübertragungsmechanismus von LHC-II zu Photosystem II (PSII) zu verstehen, besonders da die tatsächliche Auflösung in der z- Dimension nur 4.9 Å beträgt. Der chemische Unterschied zwischen Chl a und Chl b besteht aus einer Formylgruppe anstelle einer Methylgruppe an der siebten Stelle des Chlorin-Rings und ist zu gering, um bei dieser Auflösung sichtbar zu werden. Zudem ist die Orientierung der Phorphyrinringe der Chlorophylle nicht eindeutig zu bestimmen. Diese Kenntnis ist jedoch wichtig für ein detailliertes Verständnis der Energieübertragung innerhalb des Komplexes und auf die Reaktionszentren von PSI und PSII. Um die Auflösung der Struktur zu verbessern und die EM Daten zu vervollständigen wurde Röntgenkristallographie an dreidimensionalen Kristallen (3D) durchgeführt. LHC-II wurde nach einem Standardprotokoll (Burge et al. 1978) aufgereinigt. Die in Triton X-100 solubilisierten Thylakoidmembranen wurden mittels eines linearen Saccharosegradienten aufgetrennt. Die fluoreszierende LHC-II Bande wurde mit KCl präzipitiert, gewaschen und in Nonyl-glucosid aufgenommen. Die Kristalle wurden mittels Dampfdiffusion in hängenden Tropfen erzeugt. Die Kristalle waren dünne hexagonale Platten, welche eine verhältnismäßig große Einheitszelle aufwiesen und schwach beugten. Die Kristalle waren zwischen 0.3 bis 0.4 mm groß und 10 bis 20 µm dick. Der hohe Hintergrund beruhte sowohl auf der Verwendung von Detergenz zur Solubilisierung des Proteins, als auch auf in der Präparation vorhandenen Lipiden. LHC- II bindet verschiedene Lipide: SQDG, MGDG, DGDG, PG und PC. Wie frühere Arbeiten gezeigt haben sind DGDG und PG für die 3D Kristallisation (Nußberger, 1994) notwendig, weshalb auf eine Entfernung der Lipide vor der Kristallisation verzichtet wurde. Die Datenaufnahme erfolgte an gefrorenen Kristallen um Strahlungsschäden zu verringern. Dies ermöglichte einen kompletten Datensatz über einen Rotationsbereich von 135º von einem einzelnen Kristall aufzunehmen. Insgesamt wurden 3 Datensätze mittels eines hoch kollimierten und brillianten Strahls (ID-14 EH1 am ESRF, Grenoble, Frankreich) mit einer Auflösung bis 3.2 Å aufgenommen. Die Datenanalyse erfolgte mittels des Programms XDS von Kabsch (1993). Dieses Programm verwendet einen R-faktor ( Rmrgd F . ) wie er in Diederich
Domestic lighting
No full textLighting is one of the determinants of quality of life. In most developing countries, households spend a considerable part of their cash income on modern fuels to meet their lighting needs. The average amount of fuel consumed for lighting is much higher in villages without electricity than in villages with it; moreover, people with non-electric light have much lower lighting levels than people with electric lights. Why then do people use non-electric lighting when electricity is available? Mainly because they fit well with poor family spending patterns. The initial cost and per month cost of a wick lamp are low, and kerosene can be bought in small quantities as needed. Households with electricity are accustomed to much higher levels of light, for which they have to finance a connection charge, installation cost and for which they pay more for regular use. It is found that houses with electric lighting typically have lighting in every room, whereas non-electric users tend to use only one lamp for the whole house. Although both kinds of lamp give light, they are not directly comparable; it takes 18 kerosene lamps to give off the light of a single 60 watt incandescent bulb.Energy and Poverty Alleviation,Energy and Environment,Renewable Energy,Energy Demand,Engineering
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
Three-dimensional measurements of heavy and light particle dispersion in shear turbulence
No full textWe present new experimental data concerning the statistics of heavy and light particles dispersed at low concentrations in a homogeneous turbulent shear flow. Information on both the spatial distribution and on the relative velocity of the dispersed phases is obtained by accurate three-dimensional optical measurements, and will allow to comparatively discuss the issues of turbulent clustering and small scale anisotropy by analyzing the scale- and angular dependence of suitable particle observables computed in the two cases
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