bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics
Authors: Cooper Thomas , Ambrosetti Gianluca , Malnati Fabio , Pedretti Andrea , Steinfeld Aldo 
Published: July 2016

AbstractA new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.
Variability management of plugin‐based systems using feature models
Authors: Santos André L. 
Published: July 2016

SummaryPlugin‐based systems are typically realized with resort to a component framework that offers an infrastructure for assembling plugin components, which can be composed to form system variants. Feature models have been proposed as an abstraction to manage software variability, where feature configurations describe variants of a software system. In this paper, we propose an automated approach to map the artifacts of plugin‐based component frameworks to feature models. We describe a methodology for structuring the architecture of a plugin‐based system, so that the variability space and variants are reflected in a feature model and its configurations. We materialized the proposed approach for the Eclipse Equinox component framework in a tool to visualize the variability of plugin‐based systems in feature diagrams, which can be used to generate system variants. We carried out an experiment where we developed a small plugin‐based product line on top of Equinox in the context of an advanced software development course. Copyright © 2016 John Wiley & Sons, Ltd.
Cooperative amplify‐and‐forward partial relay selection with outdated channel information in spectrum‐sharing systems
Authors: Moualeu Jules Merlin , Hamouda Walaa , Takawira Fambirai 
Published: July 2016

AbstractRecently, cooperative relaying techniques have been integrated into spectrum‐sharing systems in an effort to yield higher spectral efficiency. Many investigations on such systems have assumed that the channel state information between the secondary transmitter and primary receiver used to calculate the maximum allowable transmit secondary user transmit power to limit the interference is known to be perfect. However, because of feedback delay from the primary receiver or the time‐varying properties of the channel, the channel information may be outdated, which is an important scenario to cognitive radio systems. In this paper, we investigate the impact of outdated channel state information for relay selection on the performance of partial relay selection with amplify and forward in underlay spectrum‐sharing systems. We begin by deriving a closed‐form expression for the outage probability of the secondary network in a Rayleigh fading channel along with peak received interference power constraint and maximum allowable secondary user transmit power. We also provide a closed‐form expression for the average bit‐error rate of the underlying system. Moreover, we present asymptotic expressions for both the outage probability and average bit‐error rate in the high signal‐to‐noise ratio regime that reveal practical insights on the achievable diversity gain. Finally, we confirm our results through comparisons with computer simulations. Copyright © 2016 John Wiley & Sons, Ltd.
Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes
Authors: Dong Buwen , Sutton Rowan T. , Chen Wei , Liu Xiaodong , Lu Riyu , Sun Ying 
Published: July 2016

Abstract
This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990s. Observations indicate an abrupt increase in summer mean surface air temperature (SAT) over Northeast Asia since the mid-1990s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature (Tmax), daily minimum temperature (Tmin), annual hottest day temperature (TXx), and annual warmest night temperature (TNx) were observed. There were also increases in the frequency of summer days (SU) and tropical nights (TR). Atmospheric general circulation model experiments forced by changes in sea surface temperature (SST)/sea ice extent (SIE), anthropogenic greenhouse gas (GHG) concentrations, and anthropogenic aerosol (AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes, although the abrupt decrease in precipitation since the mid-1990s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA (through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.
Voltammetric Response and Determination of an Anti‐Inflammatory Drug at a Cationic Surfactant‐Modified Glassy Carbon Electrode
Authors: Nayak Deepti S. , Shetti Nagaraj P. 
Published: July 2016

AbstractElectrochemical oxidation of thiosalicylic acid in the presence of cationic surfactant, cetyl trimethylammonium bromide (CTAB), at a glassy carbon electrode was investigated. The electrochemical response of a modified sensor towards thiosalicylic acid determination was studied by the means of cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry (DPV). The liquid phase oxidation of thiosalicylic acid in the presence of CTAB leads to a notable enhancement in the peak current and a lowering of the peak potential. The electrochemical process was observed to be adsorption‐controlled, irreversible and involves oxidation of one electron. Effects of anodic peak potential (Ep), anodic peak current (Ipa) and heterogeneous rate constant (k0) were calculated. The linear response was obtained in the range of 1.0 µM–1.0 mM with a detection limit of 113 nM.
Mineralogical Studies On Bone Apatite and Their Implications for Radiocarbon Dating
Authors: Hassan Afifa A , Termine John D , Haynes C Vance 
Published: July 2016

Infrared (IR) spectrophotometry and X-ray diffraction (XRD) were conducted on modern and fossil bone material from archaeological sites in the U S to determine post-mortem changes in bone apatite and to evaluate the effect of these changes on radiocarbon dating. IR absorption bands, XRD peak-broadening parameters, and XRD unit cell measurements indicated that during fossilization, bone apatite, a mineral similar to dahllite, was partially or completely recrystallized to francolite. Post-mortem changes involved then removal of some of the endogenous crystal carbonate both at surfaces and at internal OH-sites and introduction of exogenous carbonate into internal crystal PO4sites. Increased fluorine content accompanied carbonate substitution.Both the carbon isotopic composition and the amount of exogenous carbonate introduced into the apatite structure will affect the radiocarbon dating of bone apatite. Special sample pre-treatment may remove most of the substituted carbonate in some cases. Simulated experiments are suggested for a better understanding of the nature and mechanism of carbonate substitution in bone apatite for the removal of the exogenously substituted carbon and the improvement of radiocarbon dates.
An Improved Procedure for Wet Oxidation of the 14C Nbs Oxalic Acid Standard
Authors: Valastro S , Land L S , Varela A G 
Published: July 2016

An improved procedure for wet combustion of 14C NBS oxalic acid standard has been devised which gives consistent high carbon yields and average δ13C values of —19.1‰. The principal cause of fractionation in earlier attempts to prepare CO2 by the wet oxidation method was the inexact nature of the end-point. The new procedure employs a chocolate-brown end-point by adding 5ml more of the sulfuric acid-potassium permanganate solution after the initial reddish brown end-point is reached. The sulfuric acid-potassium permanganate solution is added to the NBS oxalic acid in a steady drop-wise flow, heat is applied to the generating apparatus, and a cycling technique is utilized to collect the CO2.Fifteen samples of the NBS oxalic acid were processed. The per cent carbon yields range from 98.8 to 100.9% with an average of 99.7% and an average δ13C of —19.12‰. The results obtained by this procedure are much more consistent than previous results obtained in several laboratories by direct combustion.
Sample Chemistry for the Oxford High Energy Mass Spectrometer
Authors: Gillespie Richard , Hedges Robert E M 
Published: July 2016

Chemical pretreatment procedures for the decontamination, extraction, and isolation of organic materials for 14C dating using the Oxford accelerator system are described. Specific details are given for the isolation and chromatographic purification of amino acids from bone and tooth collagen, of lipids from sediments, and of cellulose and glucose from wood, paper, and textiles. A description is also given of the apparatus used for the routine preparation of 1 to 5mg graphite samples on tantalum wire, for use in the accelerator ion source.The high energy mass spectrometer (HEMS) approach to 14C dating allows the use of very small samples in the low milligram range. Sample pretreatment and decontamination procedures can be both more vigorous and more selective than those used by conventional dating laboratories. Specific chemical compounds can be isolated from archaeologic or geologic samples; such compounds may be characteristic of particular source materials and, hence, provide more detailed information than is generally possible using bulk organic samples. The Oxford Radiocarbon Unit has concentrated on three sample types that represent the kind of material we expect to work on initially: bone, lake sediment, and wood.
University of Pennsylvania Radiocarbon Dates XXII
Authors: Hurst Barbara J , Lawn Barbara 
Published: July 2016

This date list includes most of the archaeologic and geologic samples dated in this laboratory since publication of our last date list (R, 1981, v 23, p 227–240), as well as some samples dated previously which lacked adequate sample information.All samples were pretreated with 3N HCl and some, where noted, were given additional pretreatment with 2% NaOH for the removal of possible humic acid contaminants.
Radiocarbon Dating of Sediments
Authors: Fowler Alison J , Gillespie Richard , Hedges Robert E M 
Published: July 2016

In14C dating of sediment, the date of deposition is associated with its C age. Most sediments are complex mixtures containing little organic material frequently derived from several sources. The most conspicuous sources of error result from 1) the incorporation of “fossil” carbon (eg, graphite, lignite, etc) into a more recent sediment. This is particularly important in low carbon sediments (Olsson, 1972); 2) the incorporation of older, ‘reworked’ sedimentary material, eg, from terrigenous sources into a lacustrine environment (Schoute, Mook & Streuerman, 1983); 3) the dating of mainly autochthonous material which has metabolized carbon from dissolved bicarbonate carbonates originating from dissolution of fossil.To provide more information for the14C ages of components of a sediment, we have used the small sample capability (ie, > = 1 mg carbon) of the Oxford Radiocarbon Accelerator to date specific fractions. Within the limitations of the ‘conventional’ method, different fractions insoilshave been the subject of two investigations (Scharpenseel, 1979; Sheppard, Syed & Mehringer, 1979). In general the results show that a measurement on undifferentiated sediment may lead to serious errors in the14C date, that specific fractions do not guarantee a better date for deposition, but nearly always provide valuable information on the particular history of the individual sediment in relation to its specific context. It is usually possible to estimate the occurrence of the first two sources of error listed above, but more difficult to quantify the extent of terrestrial input and “hard water” error.
Radiocarbon Variations in Consecutive Single Rings of A 4000-Year-Old Pine from the British Isles
Authors: Hewson A D , Burleigh Richard 
Published: July 2016

At the Ninth International Radiocarbon Conference a paper was presented concerning possible short-term14C variations in 4000-year-old red deer antlers(Cervus elaphus)found in Neolithic flint mines in Norfolk, England (Burleigh and Hewson, 1980). It was argued, on archaeologic grounds, that the true age of the samples varied by a few years at most. Their radiocarbon ages, however, varied by a considerably greater amount than could be explained by the errors in the measurements. Duplication of the measurements confirmed this unexpected variation.Farmer and Baxter (1972) claimed a significant correlation of atmospheric14C levels in the northern hemisphere with sunspot number based on radiocarbon assay of single tree rings for the period 1829 to 1865. In contrast, Stuiver (1978) stated that a series of single-year Douglas Fir measurements did not show a statistically significant periodicity.This paper reports measurements made on a series of single-year dendrochronologic samples of approximately the same age as the red deer antlers, which have been carried out at the British Museum Research Laboratory. The results show that the variation in14C between rings is not statistically significant; some other explanation must be sought for the anomalous antler measurements.
Temperature Dependent Seasonal Variation of the Background in Counters Used for Radiocarbon Dating
Authors: Håkansson Sören 
Published: July 2016

All background values measured in one of our 14C counters during 1977 were analyzed together with corresponding values for atmospheric pressure, outdoor temperature, and coincidence counting rate for investigation of the possibilities to separate the temperature dependency of the background from the better known atmospheric pressure dependency.The background values were normalized to a common atmospheric pressure and plotted in a time diagram. A seasonal trend with higher background values in winter than in summer shown by this diagram was confirmed by regression analysis.The regression line and the “Standard error of estimate” was calculated for the background values as a function of the atomspheric pressure, on the one hand and as a function of the coincidence counting rate, on the other hand. A comparison showed that the coincidence counting rate in this case was a better parameter than the atmospheric pressure for calculation of the actual background.The approximate consistency of the temperature effects on the background was checked for the years 1976 to 1978.
Copenhagen Radiocarbon Dates VI
Authors: Tauber Henrik 
Published: July 2016

The following list comprises a selected number of measurements made up to November 1963. Age calculations are based on a contemporary value equal to 95% of the activity of the NBS oxalic-acid standard, and on a half life for C14of 5570 ± 30 yr.Results are expressed in years before 1950 and in the b.c.-a.d. scales. Errors quoted include the standard deviations of the count rates for the unknown sample, the contemporary value, and the background. Calculated errors smaller than 100 yr have been increased by rounding to that figure as a minimum. Sample descriptions have been prepared in collaboration with collectors and submitters.
Dublin Radiocarbon Dates III
Authors: Dresser P Q 
Published: July 2016

The dating equipment and operating procedures in the Physical laboratory remained as described previously (R, 1974, v 16, no. 1, p 6-9).Dates were calculated using the 5568-year half-life with 1950 as the reference year, the modern standard being 0.95 of the activity of the NBS oxalic acid standard. When done, δ13C was measured on CO2 produced in the combustion of samples, and results are given relative to the PDB standard. All samples were from Ireland.
The Pursuit of Isotopic and Molecular Fire Tracers in the Polar Atmosphere and Cryosphere
Authors: Currie L. A. , Dibb J. E. , Klouda G. A. , Benner B. A. , Conny J. M. , Biegalski S. R. , Klinedinst D. B. , Cahoon D. R. , Hsu N. C. 
Published: July 2016

We present an overview of recent multidisciplinary, multi-institutional efforts to identify and date major sources of combustion aerosol in the current and paleoatmospheres. The work was stimulated, in part, by an atmospheric particle “sample of opportunity” collected at Summit, Greenland in August 1994, that bore the 14C imprint of biomass burning. During the summer field seasons of 1995 and 1996, we collected air filter, surface snow and snowpit samples to investigate chemical and isotopic evidence of combustion particles that had been transported from distant fires. Among the chemical tracers employed for source identification are organic acids, potassium and ammonium ions, and elemental and organic components of carbonaceous particles. Ion chromatography, performed by members of the Climate Change Research Center (University of New Hampshire), has been especially valuable in indicating periods at Summit that were likely to have been affected by the long range transport of biomass burning aerosol. Univariate and multivariate patterns of the ion concentrations in the snow and ice pinpointed surface and snowpit samples for the direct analysis of particulate (soot) carbon and carbon isotopes. The research at NIST is focusing on graphitic and polycyclic aromatic carbon, which serve as almost certain indicators of fire, and measurements of carbon isotopes, especially 14C, to distinguish fossil and biomass combustion sources.Complementing the chemical and isotopic record, are direct “visual” (satellite imagery) records and less direct backtrajectory records, to indicate geographic source regions and transport paths. In this paper we illustrate the unique way in which the synthesis of the chemical, isotopic, satellite and trajectory data enhances our ability to develop the recent history of the formation and transport of soot deposited in the polar snow and ice.
The Sharp Rise of Δ14Cca. 800 cal BC: Possible Causes, Related Climatic Teleconnections and the Impact on Human Environments
Authors: Van Geel Bas , Van Der Plicht Johannes , Kilian M. R. , Klaver E. R. , Kouwenberg J. H. M. , Renssen H. , Reynaud-Farrera I. , Waterbolk H. T. 
Published: July 2016

In this study we report on accelerator mass spectrometry (AMS) wiggle-match dating of selected macrofossils from organic depositsca. 800 cal bc (ca. 2650 bp). Based on paleological, archaeological and geological evidence, we found that the sharp rise of atmospheric14C between 850 and 760 cal bc corresponds to the following related phenomena:1.In European raised bog deposits, the changing spectrum of peat forming mosses and a sharp decline in decomposition of the peat indicate a sudden change from relatively dry and warm to cool, moist climatic conditions.2.As a consequence of climate change, there was a fast and considerable rise of the groundwater table so that peat growth started in areas that were already marginal from a hydrological point of view.3.The rise of the groundwater table in low-lying areas of the Netherlands resulted in the abandonment of settlement sites.4.The contemporaneous earliest human colonization of newly emerged salt marshes in the northern Netherlands (after loss of cultivated land) may have been related to thermal contraction of ocean water, causing a temporary stagnation in the relative sea-level rise.Furthermore, there is evidence for synchronous climatic change in Europe and on other continents (climatic teleconnections on both hemispheres)ca. 2650 bp. We discuss reduced solar activity and the related increase of cosmic rays as a cause for the observed climatological phenomena and the contemporaneous rise in the14C-content of the atmosphere. Cosmic rays may have been a factor in the formation of clouds and precipitation, and in that way changes in solar wind were amplified and the effects induced abrupt climate change.
14C Ages of Terrestrial Macrofossils from Lago Grande Di Monticchio (Italy)
Authors: Hajdas Irka , Bonani Georges , Zolitschka Bernd , Brauer Achim , Negendank Jörg 
Published: July 2016

Lago Grande di Monticchio (Italy) contains long sedimentary records of >75 ka (Zolitschka and Negendank 1996). In a joint European project (Creer and Thouveny 1996), vegetation history and climatic changes for this part of the Mediterranean have been reconstructed (Watts, Allen and Huntley 1996; Watts et al. 1996). In addition to the time scale based on annual laminations and sedimentation rate, tephra layers and pollen spectra, radiocarbon dating was applied for the last 40 ka. Previous studies have shown that the age of bulk sediment from Lago Grande di Monticchio, which is a maar lake at the flanks of Mt. Vulture, was influenced by “dead carbon” of volcanic origin dissolved in the lake water. Thus, 14C dating of the record is problematic and must be limited to dating macrofossils of terrestrial origin.From a set of sediment samples, macrofossils were selected and dated using accelerator mass spectrometry (AMS). A 14C time scale based on seven data points between 9000 and 24,000 bp is compared with other dating of the record based on varve counting and tephrochronology (Zolitschka 1996).