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81.
This paper combines the data sets available today for 14C-age calibration of the last 60 ka. By stepwise synchronization of paleoclimate signatures, each of these sets of 14C-ages is compared with the U/Th-dated Chinese Hulu Cave speleothem records, which shows global paleoclimate change in high temporal resolution. By this synchronization we have established an absolute-dated Greenland-Hulu chronological framework, against which global paleoclimate data can be referenced, extending the 14C-age calibration curve back to the limits of the radiocarbon method. Based on this new, U/Th-based GreenlandHulu chronology, we confirm that the radiocarbon timescale underestimates calendar ages by several thousand years during most of Oxygen Isotope Stage 3. Major atmospheric 14C variations are observed for the period of the Middle to Upper Paleolithic transition, which has significant implications for dating the demise of the last Neandertals. The early part of “the transition” (with 14C ages > 35.0 ka 14C BP) coincides with the Laschamp geomagnetic excursion. This period is characterized by highly-elevated atmospheric 14C levels. The following period ca. 35.0-32.5 ka 14C BP shows a series of distinct large-scale 14C age inversions and extended plateaus. In consequence, individual archaeological 14C dates older than 35.0 ka 14C BP can be age-calibrated with relatively high precision, while individual dates in the interval 35.0-32.5 ka 14C BP are subject to large systematic age-‘distortions,’ and chronologies based on large data sets will show apparent age-overlaps of up to ca. 5,000 cal years. Nevertheless, the observed variations in past 14C levels are not as extreme as previously proposed (“Middle to Upper Paleolithic dating anomaly”), and the new chronological framework leaves ample room for application of radiocarbon dating in the age-range 45.0-25.0 ka 14C BP at high temporal resolution. 相似文献
82.
Craig R. Halberstadt Bernhard O. Palsson A. Rees Midgley Rane L. Curl 《Biotechnology and Bioprocess Engineering》2002,7(3):163-170
This report describes the use of a transtubular bioreactor to study the relative effects of diffusion versus perfusion of
medium on antibody production by a hybridoma cell line. The study was performed with a high-density cell culture maintained
in a serum-free, low-protein medium for 77 days. It was determined that the reactor possessed a macro-mixing pattern residence
time distribution similar to a continuous stirred tank reactor (CSTR). However, due to the arrangement of the medium lines
in the reactor, the flow patterns for nutrient distribution consist of largely independent medium path lengths ranging from
short to long. When operated with cyclic, reversing, transtubular medium flow, some regions of the reactor (with short residence
times) are more accessible to medium than others (with long residence times). From this standpoint, the reactor can be divided
into three regions: a captive volume, which consists of medium primarily delivered via diffusion; a lapped volume, which provides
nutrients through unilateral convection; and a swept volume, which operates through bilateral convection. The relative sizes
of these three volumes were modified experimentally by changing the period over which the direction of medium flow was reversed
from 15 min (larger captive volume) to 9 h (larger swept volume). The results suggest that antibody concentration increases
as the size of the diffusion-limited (captive) volume is increased to a maximum at around 30 min with a sharp decrease thereafter.
As reflected by changes in measured consumption of glucose and production of lactate, no significant difference in cellular
metabolism occurred as the reactor was moved between these different states. These results indicate that the mode of operation
of the transtubular bioreactor may influence antibody productivity under serum-free, low-protein conditions with minimal effects
on cellular metabolism. 相似文献
83.
84.
Isolation and identification of granule-associated proteins relevant for poly(3-hydroxyalkanoic acid) biosynthesis in Chromatium vinosum D 总被引:1,自引:0,他引:1
Matthias Liebergesell Bernhard Schmidt Alexander Steinbüchel 《FEMS microbiology letters》1992,99(2-3):227-232
Abstract Poly(3-hydroxybutyric acid) granules, which harbored only four major granule-associated proteins as revealed by SDS polyacrylamide gel electrophoresis, were isolated from crude cellular extracts of Chromatium vinosum D by centrifugation in a linear sucrose gradient. N-Terminal amino acid sequence determination identified two proteins of M r 41 000 and M r 40 000 as the phaE Cv and phaC Cv translational products, respectively, of C. vinosum D. In a previous study it was shown that both proteins are required for the expression opf poly(3-hydroxyalkanoic acid) synthase activity. The N-terminus of the third protein ( M r 17 000) exhibited no homology to other proteins. Lysozyme, which was during purification of the granules, exhibited a strong affinity to PHB granules and was identified as the fourth protein enriched with the granules. 相似文献
85.
86.
Belowground biodiversity effects of plant symbionts support aboveground productivity 总被引:1,自引:0,他引:1
Soil microbes play key roles in ecosystems, yet the impact of their diversity on plant communities is still poorly understood. Here we demonstrate that the diversity of belowground plant-associated soil fungi promotes plant productivity and plant coexistence. Using additive partitioning of biodiversity effects developed in plant biodiversity studies, we demonstrate that this positive relationship can be driven by complementarity effects among soil fungi in one soil type and by a selection effect resulting from the fungal species that stimulated plant productivity the most in another soil type. Selection and complementarity effects among fungal species contributed to improving plant productivity up to 82% and 85%, respectively, above the average of the respective fungal species monocultures depending on the soil in which they were grown. These results also indicate that belowground diversity may act as insurance for maintaining plant productivity under differing environmental conditions. 相似文献
87.
Ebrahim AM Eltayeb M Benker B Grill P Attahir M Osman A Elsadig M Michalke B 《Biological trace element research》2011,144(1-3):225-233
This study was performed to investigate trace elements and arsenic contents among Sudanese inhabitants living in the north, east, and west of Sudan. Inductively coupled plasma atomic emission spectrometry was used to determine the contents of Zn and Cu. Graphite furnace atomic absorption spectrometry was used to determine Se in serum samples. It was found that Se and Cu are in the normal range. Zinc showed discrepancies among all studied groups. Acute Zn deficiency was detected in the northern and eastern regions of Sudan. Inductively coupled plasma mass spectroscopy was operated in the dynamic reaction cell mode to determine the arsenic content in the nail samples of the northern inhabitants of Sudan. High values of arsenic were found in the northern people compared with the control group. This elevation could be linked to the misuse of insecticides and herbicides which might be associated with the high rate of cancer incidence in this region. 相似文献
88.
Michal Toborek rzej Malecki Rosario Garrido Mark P. Mattson Bernhard Hennig Byron Young 《Journal of neurochemistry》1999,73(2):684-692
Spinal cord trauma can cause a marked release of free fatty acids, in particular, arachidonic acid (AA), from cell membranes. Free fatty acids, and AA by itself, may lead to secondary damage to spinal cord neurons. To study this hypothesis, cultured spinal cord neurons were exposed to increasing concentrations of AA (0.01-10 microM). AA-induced injury to spinal cord neurons was assessed by measurements of cellular oxidative stress, intracellular calcium levels, activation of nuclear factor-KB (NF-kappaB), and cell viability. AA treatment increased intracellular calcium concentrations and decreased cell viability. Oxidative stress increased significantly in neurons exposed to 1 and 10 microM AA. In addition, AA treatment activated NF-kappaB and decreased levels of the inhibitory subunit, IKB. It is interesting that manganese superoxide dismutase protein levels and levels of intracellular total glutathione increased in neurons exposed to this fatty acid for 24 h, consistent with a compensatory response to increased oxidative stress. These results strongly support the hypothesis that free fatty acids contribute to the tissue injury observed following spinal cord trauma. 相似文献
89.
90.
Barbara Messner Johann Kern Dominik Wiedemann Stefan Schwaiger Adrian Türkcan Christian Ploner Alexander Trockenbacher Klaus Aumayr Nikolaos Bonaros Günther Laufer Hermann Stuppner Gerold Untergasser David Bernhard 《PloS one》2013,8(3)