Rhyolitic tephra horizons in northwestern Europe and Iceland from the AD 700s-800s: a potential alternative for dating first human impact

The distribution and geochemistry of four rhyolitic tephra horizons from Iceland dated to the ad 700s–800s is assessed. These include the rhyolitic phase of the Landnám tephra (ad 870s), the ad 860 layer, a previously unrecorded tephra called the GA4–85 layer (c. ad 700–800) and the Tjïrnuvík tephra (c. ad 800s). The ad 860 and GA4–85 layers were first found in peat bogs in north Ireland. They are here correlated with equivalent horizons on Iceland which were found below the Landnám tephra (c. ad 870s). This time period is considered important in the North Atlantic region, because it coincides with a phase of human settlement in Iceland and the Faroe Islands. The establishment of a detailed tephrochronology may provide a tool for exact dating of sediment successions and sediments associated with archaeological excavations. Caution must be taken especially on Iceland where the Landnám tephra is often used for dating archaeological sites. This investigation show that several rhyolitic tephra horizons occur close in time to the Landnám tephra, and that mistakes can be made if detailed geochemical analyses are not carried out, especially in areas which are distal to the source of the Landnám tephra (the Veidivötn and Torfajökull volcanic systems, southern Iceland)

Background Components of a Liquid Scintillation Counter in the 14

From the 19th International Radiocarbon Conference held in Keble College, Oxford, England, April 3-7, 2006.We present a broad and detailed study of the background components of a liquid scintillation (LS) detector, using a simple laboratory-built system, ICELS. It was specifically designed for radiocarbon dating and is compact and easily transportable (total weight 35 kg). Its flexible LS detector unit has a dome-shaped vial with 3 mL benzene to which 45 mg butyl-PBD is added. The vial sits on the top of a vertical 28-mm-diameter phototube. The gamma radiation, to which the benzene is exposed under varying conditions, was measured by replacing the vial with a 38-mm-diameter NaI crystal. The pulse-height spectra of the 14C LS background and the NaI gamma background were measured in a surface laboratory and in a deep underground counting room with: 1) a lead shield of varying thickness; 2) lead of normal and low 210Pb concentration; 3) phototubes of 2 different types; and 4) varying benzene volume. The beta emission from the face of the tubes was measured with a low-level Geiger counter.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Balanced-Energy Counting Window for Stable Liquid Scintillation Radiocarbon Dating

This paper describes an optimal radiocarbon counting window for liquid scintillation (LS) 14C dating that secures for unquenched as well as for heavily quenched dating samples maximal stability of 14C counting efficiency and theoretically minimal quench correction. In high-precision dating, a balanced counting window with fixed channel limits is frequently used, where about 3% of the highest part of the 14C spectrum is sacrificed for high 14C counting stability. The stability is, however, diminished for quenched samples. Therefore, this window is here replaced by a balanced fixed-energy 14C counting window where the channel limits depend on the quench level. The LS system used must have a linear amplifier and a multichannel analyzer. All samples are measured at a fixed high voltage. For energy calibration and determination of the quench level, the channel number of the middle of the 59.5-keV peak from an external 241Am gamma source is determined before and after measuring each sample. This counting mode is valuable in high-precision dating. It could be widely applied if adapted to systems with a logarithmic amplifier, generally used in LS dating.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

A Simple, Extremely Stable Single-Tube Liquid Scintillation System for Radiocarbon Dating

This paper describes a simple and compact liquid scintillation radiocarbon dating system, ICELS, and demonstrates its long-term stability and reproducibility to a precision level rarely presented before, better than 0.04% (3 14C yr). Inexpensive systems of this kind may, in the future, help to meet increasing demand for high precision (+/16 to +/20 14C yr) and strict quality control. ICELS comprises a compact detector unit, where a 3-mL dome-shaped vial, with an optimal light reflector, sits on the top of a vertical 30-mm photomultiplier tube. Sample changing is manual. The high voltage is set at the balance point for each sample, securing maximal counting stability. The quench correction method used (spectrum restoration) corrects with 0.04% precision for all parameters that can normally shift the 14C spectrum. For 3 mL of benzene at 71% 14C counting efficiency (recent carbon 23 cpm), the background is 1.72 cpm behind a 5-cm-thick shield of lead (27 kg) and 1.53 cpm behind 10 cm of lead. The background count rate corrected for atmospheric pressure variations was completely stable over 47and 57-d testing periods for the 2 systems.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Simultaneously Measuring 14

After benzene synthesis, radiocarbon dating samples are usually stored for 34 weeks before counting to allow an eventual radon contamination to decay to a negligible level. This paper presents a technique that can minimize, and often eliminate, this delay by using a simple single-phototube liquid scintillation counting system, specifically designed for 14C dating. Radon contamination is assessed by pulses of 214Po (a 222Rn decay product, half-life 0.16 microseconds), identified through pulse-time analysis. For each 214Po pulse, 0.49 beta particle pulses of 214Pb and 214Bi fall in the 14C counting window, and the 214Po pulses are used to correct the 14C count rate. A 14C sample (count rate 11.6 cpm) was measured continuously for 16 days. It was then doped with radon, which increased the first 24-hr count rate in the 14C channel by 3.8 cpm, and the sample was measured for 27 more days. Radon did not measurably affect the 14C-corrected count rate. Counting a sample for 2 min reveals whether it needs storing. If the radon concentration is low, the sample can be measured immediately without degrading accuracy.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Radiometric 14C Dating: New Background Analysis, Basis of Improved Systems

From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.A recent broad study of the background of all types of low-level beta and gamma detectors has now made it possible to analyze its components more reliably and with greater detail. This general analysis is developed further here for gas proportional and liquid scintillation counters used in radiocarbon dating. The background of gas counters, which is dominated by secondary cosmic gamma radiation, is now well understood and can be described quantitatively. The background of liquid counters is less well understood and can only be described semiquantitatively, its analysis resting partly on estimates. Methods to reduce the background of both types of systems are described and their effectiveness discussed. This analysis may help in evaluating the quality of existing systems as well as in designing better ones.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Áhættustýring og afleiður: Áhættustýring Orkuveitu Reykjavíkur

Áhættur í rekstrarumhverfi fyrirtækja hefur sjaldan verð meiri. Er því mikilvægt fyrir fyrirtæki að gera sér grein fyrir þeim áhættuþáttum sem kunna að leynast í umhverfinu. Áhættustjórn felur það í sér að meta áhættu og finna leiðir til þess að verja fyrirtæki gegn þeim ógnum sem gætu haft neikvæð áhrif á rekstur þeirra og áætlanir. Til þess að verja sig gegn áhættu eru til ýmsar leiðir svo sem tryggingar, dreifð eignarsöfn og afleiður. Afleiðusamningar hafa verið notaðir í gegnum tíðina til varnar gegn óvæntum markaðsbreytingum. Til eru nokkrar tegundir afleiðusamninga, má þar meðal annars nefna framvirka samninga, framtíðarsamninga, skiptisamningar og valréttarsamningar. Orkuveita Reykjavíkur stendur frami fyrir ýmsum áhættuþáttum í sínum daglega rekstri, svo sem kjarnaáhættu, mótaðilaáhættu og markaðsáhættu. Orkuveitan notast við afleiðusamninga til þess að stýra markaðsáhættu fyrirtækisins. Breytilegir vextir eru festir til þess að auka fyrirsjáanleika í rekstri. Gengissveiflur hafa mikil áhrif á rekstur fyrirtækja á Íslandi og er Orkuveitan engin undantekning. Félagið hefur varið sig gegn gengissveiflum með stofnun Orku Náttúrunnar sem er gert upp í Bandaríkjadollurum. Einnig hefur fyrirtækið gert gjaldmiðlaskiptisamninga við innlenda banka þar sem erlendum lánum er breytt í íslenskar krónur. Einnig er að finna innbyggða afleiðu í raforkusamningi við álver, þar tengir Orkuveitan söluverð á raforku við markaðsverð á áli. Heimsmarkaðsverð á áli er mjög breytilegt og getur því haft umtalsverð áhrif á rekstur Orkuveitunnar. Til að bregðast við þessum markaðsbreytingum eru gerðir varnarsamningar um álverð

Kvantifiering av statisk och dynamisk stabilitet i amputerade med låg aktivitet

Background: Approximately 67% of lower limb amputees fall once or more every year. It is important for their daily functioning and their social life that their prosthetic device provide them with stability and security. Measuring stability for amputees and their prosthetic devices is challenging, especially for amputees with low activity level. However, it is important for the users and the product designers to know if the products are actually providing the user with more stability. Objective: The aim of the study is to create a measurement protocol to quantify static and dynamic stability with enough sensitivity to differentiate between two prosthetic products for amputees with low activity level. Methods: Ten K2, unilateral transtibial subjects were recruited and 6 of them completed the protocol during a 2-hour visit. They repeated the same protocol for two prosthetic feet, K2C (Össur, Iceland) and K2 Sensation (Össur, Iceland). In order to compare the static and dynamic stability of the subjects and the products, three different tests and one questionnaire were used: Static standing test, Limit of Stability (LOS) test, Walking on level ground, and the Activities-specific Balance Confidence scale (ABC scale). Results: For the static standing test, the K2Sensation showed less range for the center of pressure in the anteroposterior direction while standing in a normal position with the eyes open. However, the participants were able to reach further (LOS test) over their prosthetic side while wearing the K2C foot. For the K2C foot, gait parameters such as ankle power, positive work, self selected walking speed and the range of motion in the prosthetic ankle all increased. The backward margin of stability (BwMOS) only increased for 2 participants who had it in common to both wear ProFlex-XC in daily life. No difference was seen in perceived stability according to the ABC scale. Conclusion: The aim of the study was reached. Static and dynamic stability were quantified and distinguished between the 2 different prosthetic feet. It is concluded that both the static standing test and the LOS test are necessary parts of the protocol as they capture different aspects of static stability. For future studies, a longer adaptation time is suggested for the participants to achieve a stable gait pattern and to answer the ABC scale with more reliabilityBakgrund: Cirka 67% av patienter som amputerat ett eller både ben ramlar minst en gång varje år. En protesfot som förser dem med stabilitet och säkerhet är viktigt för den dagliga funktionen och socialsamvaron. Det är en stor utmaning att mäta protesstabilitet, särskilt för patienter med en relativt låg aktivitetsnivå. Det är dock viktigt för både dem och för tillverkarna med relevant information om huruvida protesen ökar patienternas stabilitet, både objektivt och subjektivt. Syfte: Syftet med studien är att skapa ett experimentellt protokoll för att kvantitativt mäta statisk och dynamisk stabilitet. Protokollet bör vara tillräcklig känsligt för att kunna urskilja mellan två protesdesign hos amputerade med låg aktivitetsnivå. Metoder: Tio st. K2 patienter med unilateral transtibial amputation rekryterades, av dem 6 kunde fullfölja experimentet under ett två timmars besök. Samma experimentell procedur upprepades med två protesfötter, K2C (Össur, Island) och K2 Sensation (Össur, Island), i en randomiserade ordning. Tre experimentella test och ett frågeformulär användes för att jämföra statisk och dynamisk stabilitet: Static standing test, Limit of Stability (LOS)- test, Walking on level ground, samt Activities-specific Balance Conidence scale (ABC-skala). Resultat: Under statiska stående i en normal position med öppna ögon, kunde patienterna nå mindre sina Center of Pressure (COP) i anteroposterior riktningen med K2Sensation än med K2C. Deltagarna kunde dock luta mera (LOStest) över sina K2C-fötter än över sina K2Sensation-fötter. Med K2C-foten ökade temporospatiala gångparametrar såsom fotledseffekt, positivt fotledsarbete, självvald gånghastighet och dynamiskt rörelseomfång hos protesfoten. Backwards Margin of Stability (BwMOS) ökade med K2C-foten enbart hos 2 deltagare, som både använder vanligtvis en ProFlex-XC fot. Ingen skillnad i den subjektiva upplevelsen av stabilitet enligt ABC-skalan har visats. Slutsats: Syftet med studien uppnåddes; statisk och dynamisk stabilitet kunde kvantifieras och urskiljes mellan de två olika protetiska fötter. Slutsatsen är att både statiska test och dynamiska (t.ex LOS-testet) behövs eftersom de fångar olika aspekter av stabilitet när man står. För att öka tillförlitlighet i både experimentella parametrar samt i ABC-skalan, samt för att ge patienterna möjlighet att arbeta fram ett stabilt gångmönster med en ny protesfot, förslås i framtida studier att patienterna får en längre anpassningstid före undersökningen

Veraldlegt innihald fagnaðarerindisins. Siðfræðileg greining á róttækri kristinni friðarstefnu J.H. Yoders

Í þessari ritgerð er framsetning Johns Howards Yoders á róttækri kristinni friðarstefnu tekin til umfjöllunar. Gerð er siðfræðileg greining á guðfræði hans með það fyrir sjónum að varpa ljósi á hvað friðarstefna hans feli í sér. Meginspurningar sem hér er leitast við að svara eru: hver þungamiðja boðskapar Jesú hafi verið að mati Yoders og hvernig hann tengdi þessa tvö þúsund ára gömlu fyrirmynd við breytni í nútímanum. Ritgerðinni er skipt í tvo hluta. Í þeim fyrri er fjallað með almennum hætti um þá grein guðfræðinnar sem kenning Yoders fellur innan en með því að greina frá víðara samhengi orðræðunnar gefst fyllri mynd af tiltekinni kenningu. Þar hefst umfjöllunin á helstu þeirra kenninga sem fram hafa komið um samband kristinnar kirkju og stjórnmála. Því næst er fjallað um hin mismunandi kristnu viðhorf til stríðs og friðar sem skotið hafa upp kollinum í aldanna rás. Þegar því hefur verið komið til skila er kastljósinu beint að kristnum friðarstefnum. Gerð er grein fyrir helstu röksemdarfærslum kristinna friðarsinna. Þá er friðarstefna frumkirkjunnar tekin til umfjöllunar. Í seinni hluta ritgerðarinnar er guðfræði Yoders tekin til ítarlegrar umfjöllunar. Byrjað er á því að lýsa trúarlegum bakgrunni hans, þar sem að útlínurnar að guðfræði hans eru dregnar upp. Því næst er farið yfir þær breytingar sem Yoder taldi hafa orðið á kristinni kirkju vegna breyttrar stöðu hennar í Rómaveldi á 4. öld. Þá eru dregin fram helstu stef bókar Yoders, The Politics of Jesus, með það fyrir sjónum að skýra hvað hafi falist í kristsskilningi hans. Áður en að umfjöllunin er dregin saman og lokaorð lögð fyrir er kenning Yoders greind siðfræðilega og er hún sett í samhengi við víðari orðræðuna, sem lýst er í fyrri hluta ritgerðarinnar