Search

Start Over Format bez média Data provider Academy of Sciences Library/Knihovna Akademie věd ČR

6633. Doubting radiocarbon dating from in-slag charcoal: five thousand years of iron production at Wetzlar-Dalheim?

Creator:
Gassmann , Guntram and Schäfer, Andreas
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
radiocarbon dating, methodology, charcoal samples, slag, fossil carbon, radiokarbonové datování, metodika, vzorky uhlíků, struska, and fosilní uhlík
Language:
Czech
Description:
A Roman-Period bloomery smelting site had been excavated in the Lahn valley at Wetzlar-Dalheim in central Germany during 2006–2012. The production unit consisted of a big rectangular workshop pit with 13 slag pit-furnaces, two waste dumps and a small sunken hut. The stratigraphical sequence, along with abundant pottery and small finds, allows the dating of short-lived smelting activity to a time slot around the third quarter of the first century AD. As a first series of radiocarbon measurements from in-slag charcoal samples resulted in a bewildering date range from the Iron Age right back into the Neolithic, a second dating series has been undertaken. This time exclusively charcoal samples taken from the bottom of the furnace pits have been analysed. The resulting dates fit to the archaeologically derived dating. It is clear that the 14C content of the in-slag charcoal samples must have been altered already during the process in antiquity. With none of the analysed dates younger than the archaeologically fixed date of the bloomery production unit, it is obvious that a contamination with fossil carbon must have taken place. The wide and inconsistent date range suggests that fossil carbon has entered the metallurgical system within the furnace in an uncontrollable manner. The observed phenomenon has wide implications for other metallurgical sites with high temperature processes under strongly reducing conditions. Charcoal samples from such sites, especially from inside slags, might be contaminated to an unpredictable degree and produce seemingly older dates. A first review of previously published data series calls for a reconsideration of the reliability of radiocarbon dates from metallurgical slags. and V průběhu let 2006 až 2012 byla v údolí řeky Lahn ve Wetzlar-Dalheimu ve středním Německu odkryta lokalita s doklady výroby železa z doby římské. Výrobní jednotka sestávala z velké dílenské jámy obdélníkového půdorysu se třinácti pecemi se zahloubenou nístějí, dvěma odpadními haldami a malou polozemnicí. Stratigrafická posloupnost spolu s hojně přítomnou keramikou a drobnými nálezy umožňují datovat krátkodobou výrobní činnosti do zhruba 3. čtvrtiny 1. stol. n. l. Jelikož první série radiokarbonových měření provedená na kouscích dřevěného uhlí, které uvízlo ve strusce, vymezila ohromující časový úsek od doby železné až po neolit, byla provedena druhá datovací série. Tentokrát byly analyzovány výlučně vzorky dřevěného uhlí, které byly odebrány z nístějí pecí. Výsledné datování vykazovalo shodu s datováním archeologickým. Vzhledem k tomu, že kontaminaci po exkavaci můžeme vyloučit, je zřejmé, že obsah 14C ve vzorcích dřevěného uhlí musel být změněn už při výrobním procesu v průběhu starověku. Široký a nekonzistentní časový interval naznačuje, že fosilní uhlík vstupuje do metalurgického systému v peci nekontrolovaně. Pozorovaný fenomén má velký dopad na další lokality s doklady metalurgických aktivit, při kterých vysokoteplotní procesy probíhaly za silně redukčních podmínek. Vzorky dřevěného uhlí z takových lokalit, zejména pak uhlíků ze strusek, mohou být kontaminovány nepředvídatelným způsobem a zapříčinit zdánlivě starší datování. První přezkoumání dříve publikovaných datových řad vyzývá k přehodnocení spolehlivosti údajů z radiokarbonového datování metalurgických strusek.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

6637. Down-regulation of photosystem 2 efficiency and spectral reflectance in mango leaves under very low irradiance and varied chilling treatments

Creator:
Weng, J.-H., Jhaung, L.-H., Jiang, J.-Y., Lai, G.-M., and Liao, T.-S.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
chlorophyll fluorescence, dim irrandiance, leaf spectral reflectance, low temperature, and Mangifera indica
Language:
Multiple languages
Description:
In order to elucidate the effects of chilling-stress at night on photosystem 2 (PS2) efficiency under dim irradiance (DI), mango leaves were chilled to varied extent (8-3 °C) and for varied duration (0-12 h) in growth cabinets in the dark, and then exposed to DI (20 μmol m-2 s-1 PPFD) at each chilling-temperature for 1 h. Chilling in the dark had little effect on Fv/Fm of mango leaves. But both the extent and duration of chilling pre-treatments significantly affected Fv'/Fm' when leaves were exposed to DI. This down-regulation of PS2 efficiency was closely related to xanthophyll de-epoxidation, assessed as photochemical reflectance index (PRI) and calculated from leaf spectral reflectance [(R531 - R570)/(R531 + R570)], and non-photochemical quenching (NPQ). The down-regulation of PS2 is a defence mechanism initiated at predawn in winter to alleviate the damage of PS2 by the sudden and strong irradiation at sunrise. Mango leaves, transferred suddenly from warm and dark room to DI and chilling showed a slight down-regulation of PS2 efficiency, in spite of an increased xanthophyll de-epoxidation. This might have been due to the unavailability of some cofactors required for NPQ. and J.-H. Weng ... [et al.].
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

6638. Downhole microseismic monitoring of shale deposits: case study from Northern Poland

Creator:
Święch, Eryk, Wandycz, Paweł, Leo Eisner, Pasternacki, Andrzej, and Maćkowski, Tomasz
Format:
print, bez média, and svazek
Type:
article, články, journal articles, model:article, and TEXT
Subject:
Geologie. Meteorologie. Klimatologie, ložiska břidlice, seizmicita, slate deposits, seismicity, Polsko, Poland, Polish shale gas, downhole microseismic processing, anisotropy, microseismic events, 7, and 551
Language:
English
Description:
Microseismic monitoring has become a standard technique to map the development of hydraulic fracturing. This study is a case study of a downhole monitoring of the hydraulic fracturing in a lateral well in Northern Poland. The downhole monitoring array detected a large number of microseismic events indicating successful development of a hydraulic fracture. We show evidence that some stages interacted with the pre-existing natural fault system also mapped from surface active seismic imaging. The mapped hydraulic fracture shows a slight asymme try of the developed hydraulic fractures. We show that the observed microseismicity is cons istent with microseismicity usually observed in the North American shale gas stimulations., Eryk Święch, Paweł Wandycz, Leo Eisner, Andrzej Pasternacki and Tomasz Maćkowski., and Obsahuje bibliografické odkazy
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

6639. Downregulation of endothelial transient receptor potential vanilloid type 4 channel underlines impaired endothelial nitric oxide-mediated relaxation in the mesenteric arteries of hypertensive rats

Creator:
Boudaka, A. , Al-Suleimani, M., Al-Lawati, I., Baomar, H., Al-Siyabi, S. , and Zadjali, F.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
TRPV4, Hypertension, Endothelium, Nitric oxide, and Spontaneously hypertensive rats
Language:
English
Description:
The endothelium contributes to the maintenance of vasodilator tone by releasing endothelium-derived relaxing factors, including nitric oxide (NO). In hypertension, endothelial nitric oxide synthase (eNOS) produces less NO and could be one of the contributing factors to the increased peripheral vascular resistance. Agonist-induced Ca2+ entry is essential for the activation of eNOS. The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca2+-permeant cation channel, is expressed in the endothelial cells and involved in the regulation of vascular tone. The present study aimed to investigate the role of TRPV4 channel in endothelium-dependent NO-mediated relaxation of the resistance artery in hypertensive rats. Using a wire myograph, relaxation response to the TRPV4 activator, 4α-phorbol-12,13-didecanoate (4αPDD) was assessed in mesenteric arteries obtained from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). Compared to WKY, SHR demonstrated a significantly attenuated 4αPDD-induced endothelium-dependent NO-mediated relaxation. Immunohistochemical analysis revealed positive staining for TRPV4 in the endothelium of mesenteric artery sections in both WKY and SHR. Furthermore, TRPV4 mRNA and protein expressions in SHR were significantly lower than their expression levels in WKY rats. We conclude that 4αPDD-induced endothelium-dependent NO-mediated vasorelaxation is reduced in SHR and downergulation of TRPV4 could be one of the contributing mechanisms.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

6640. Downregulation of HCN1 channels in hippocampus and prefrontal cortex in methamphetamine re-exposed mice with enhanced working memory

Creator:
Zhou, M. , Lin, K. , Si, Y. , Ru, Q. , Chen, L. , Xiao, H. , and Li, C.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
methamphetamine, working memory, HCN channels, hippocampus, and prefrontal cortex
Language:
English
Description:
The hyperpolarization-activated cyclic-nucleotide-gated non-selective cation (HCN) channels play a potential role in the neurological basis underlying drug addiction. However, little is known about the role of HCN channels in methamphetamine (METH) abuse. In the present study, we examined the changes in working memory functions of METH re-exposed mice through Morris water maze test, and investigated the protein expression of HCN1 channels and potential mechanisms underlying the modulation of HCN channels by Western blotting analysis. Mice were injected with METH (1 mg/kg, i.p.) once per day for 6 consecutive days. After 5 days without METH, mice were re-exposed to METH at the same concentration. We found that METH re-exposure caused an enhancement of working memory, and a decrease in the HCN1 channels protein expression in both hippocampus and prefrontal cortex. The phosphorylated extracellular regulated protein kinase 1/2 (p-ERK1/2), an important regulator of HCN channels, was also obviously reduced in hippocampus and prefrontal cortex of mice with METH re-exposure. Meanwhile, acute METH exposure did not affect the working memory function and the protein expressions of HCN1 channels and p-ERK1/2. Overall, our data firstly showed the aberrant protein expression of HCN1 channels in METH re-exposed mice with enhanced working memory, which was probably related to the down-regulation of p-ERK1/2 protein expression.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

Limit your search

Show values starting with
more »

Show values starting with
more »

Show values starting with
more »

Show values starting with
more »

Show values starting with
more »

Show values starting with
more »

View distribution

Current results range from 1711 to 2022

View larger »