Bacterial GDGTs in Holocene sediments and catchment soils of a high Alpine lake: application of the MBT/CBT-paleothermometer

A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.

Safety of Active Implantable Devices during MRI Examinations: A Finite Element Analysis of an Implantable Pump

The goal of this study was to propose a general numerical analysis methodology to evaluate the magnetic resonance imaging (MRI)-safety of active implants. Numerical models based on the finite element (FE) technique were used to estimate if the normal operation of an active device was altered during MRI imaging. An active implanted pump was chosen to illustrate the method. A set of controlled experiments were proposed and performed to validate the numerical model. The calculated induced voltages in the important electronic components of the device showed dependence with the MRI field strength. For the MRI radiofrequency fields, significant induced voltages of up to 20 V were calculated for a 0.3T field-strength MRI. For the 1.5 and 3.0T MRIs, the calculated voltages were insignificant. On the other hand, induced voltages up to 11 V were calculated in the critical electronic components for the 3.0T MRI due to the gradient fields. Values obtained in this work reflect to the worst case situation which is virtually impossible to achieve in normal scanning situations. Since the calculated voltages may be removed by appropriate protection circuits, no critical problems affecting the normal operation of the pump were identified. This study showed that the proposed methodology helps the identification of the possible incompatibilities between active implants and MR imaging, and can be used to aid the design of critical electronic systems to ensure MRI-safety

The Rasikajy civilization in northeast Madagascar: a pre-European Chinese community?

Archaeological excavations in northern Madagascar during the first half of the 20th century have revealed the presence of a former prosperous civilisation known as the Rasikajy civilisation. Little is known about the origin of this civilisation and how and when they first arrived in Madagascar. The most striking evidence for the Rasikajy civilisation comes from excavations at a necropolis in Vohemar located along the northeast coast, where more than 600 tombs containing spectacular objects were unearthed in the 1940s (Vernier & Millot 1971). The findings in the tombs included, amongst others, Chinese ceramics, silver and gold jewellery, iron weapons, glassware, bronze mirrors and chlorite-schist objects (ibid.). The latter objects were produced from chlorite schist mined at quarries in northern and eastern Madagascar and there is evidence that jewellery and iron objects were also produced by the Rasikajy from locally available raw material. Chlorite-schist objects have not only been found in coastal sites in Madagascar, but also in the Comores and eastern Africa suggesting an active engagement of the Rasikajy in western Indian Ocean trade. Our re-evaluation of published literature on archaeological sites in northern Madagascar indicates that the majority of Chinese ceramics found in the tombs at Vohemar dates from the 15th and first half of the 16th century with some dating back to the 14th century or earlier. Our comparative analysis of burial objects at Vohemar shows that locally produced chlorite-schist tripod vessels exhibit remarkable resemblances to ancient Chinese bronze ritual tripod vessels. The objects encountered in the tombs and their positions with respect to the body indicate that the Rasikajy practiced burial rites similar to those practised in the past in China. Our re-evaluation of the literature suggests that communities with Chinese roots were present in northeastern Madagascar prior to the arrival of the first Europeans in 1500 and participated in the Indian Ocean trade network. The demise of the Rasikajy civilisation seems to have occurred in the second half of the 16th century when production of chlorite-schist objects ceased. It is still unclear why this occurred.