Reversing the training effect in exchange biased CoO/Co bilayers

We performed a detailed study of the training effect in exchange biased CoO/Co bilayers. High-resolution measurements of the anisotropic magnetoresistance (AMR) are consistent with nucleation of magnetic domains in the antiferromagnetic CoO layer during the first magnetization reversal. This accounts for the enhanced spin rotation observed in the ferromagnetic Co layer for all subsequent reversals. Surprisingly, the AMR measurements as well as magnetization measurements reveal that it is possible to partially reinduce the untrained state by performing a hysteresis measurement with an in plane external field perpendicular to the cooling field. Indeed, the next hysteresis loop obtained in a field parallel to the cooling field resembles the initial asymmetric hysteresis loop, but with a reduced amount of spin rotation occurring at the first coercive field. This implies that the antiferromagnetic domains, which are created during the first reversal after cooling, can be partially erased.Comment: 4 pages, 4 figure

Geochemical heterogeneity of sand deposits and its implications for the provenance determination of Roman glass

During the production of natron glass most features of the raw materials are lost and only some bulk geochemical characteristics have potential as provenance indicators. To determine the primary origin of archaeological glass artefacts, suitable sand raw materials have to be accurately characterised. In this respect, information about the possible variation in geochemical properties within a silica source is also vital to account for potential (partial) overlap of different sources. In this study, it is shown that the variation in major and minor elemental composition of beach sand on a local scale is smaller than the variation in Roman natron glass. Therefore, a single sand deposit can be seen as a relatively homogeneous source of silica for glass production. Nd isotopic signatures are identical for all samples analysed. The isotopic composition of Sr however varies considerably due to local variations in the relative proportions of carbonates and silicates (mostly feldspar).status: publishe

The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions

We present the results of the largest $L^{\prime}$ ($3.8~\mu$m) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars with spectral types from B to M. Cool planets emit a larger share of their flux in $L^{\prime}$ compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to $\sim20$ au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to $\sim20$ au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or cold-start) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Artificially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii ($\lesssim50$ au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using cold-start models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We find that $\lesssim90\%$ of FGK systems can host a 7 to 10 $M_{\mathrm{Jup}}$ planet from 5 to 50 au. This limit leaves open the possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A

Mineralogy and geochemistry of Mediterranean sand deposits as a raw material for Roman natron glass production.

During the Late Roman and Byzantine period, natron glass was made from its raw materials in a limited number of primary production centres in Egypt and Syro-Palestine. For the earlier Hellenistic and Roman period, no primary furnaces have been found and the location of primary production during this era remains unclear. Ancient authors such as Strabo and Pliny the Elder suggest that glassmaking sands were found near the River Belus (Israel), in Egypt, near the mouth of the Volturno River (Italy) and also in Spain and France. However, primary production in the western part of the Mediterranean is not supported by any direct archaeological evidence and possible sand raw materials from these regions have never been evaluated for their suitability to produce glass.In this study the possible existence of a Roman primary glass industry in the western Mediterranean is investigated, based on the occurrence of suitable sand raw materials. 178 beach sands from Spain, France and Italy are evaluated for their suitability for glass production by calculating the composition of hypothetical glasses made from these sands and comparing them to Roman natron glass. The results show that good glassmaking sands are far from common. Only a very limited number of the 178 beach sands analysed would produce a glass with major and minor elemental compositions within the ranges of Roman imperial natron glass. The rest of the sands analysed are unsuitable for glass production in their present form due to their insufficient SiO2, high Al2O3 and Fe2O3, and either too low or too high CaO contents. If the sand raw material was too low in CaO, extra lime could be added to the glass batch in the form of shell or limestone. This was taken into account in a second calculation.Overall, six limited areas could be define where suitable sand raw materials would have been available to the Roman glassmaker. Good glassmaking sands occur in the Basilicata and Puglia Regions (SE Italy), and Tuscany (W Italy). After the addition of an extra source of lime, sands from the Huelva Province (SW Spain), the Murcia Region (SE Spain) and from the Provence (SE France) would also produce glasses with a typical Roman composition. The suitability of the suggested sands was checked by performing a series of melting experiments, which provide further insights in the way Roman glass makers would have had to prepare their raw materials and the used batch recipes.Because of the complex nature of Roman natron glass, the provenance determination of this material remains one of the most challenging problems in the field of archaeometry. In the past decades, several attempts have been made to determine the provenance of ancient glass based on major, minor and trace elemental compositions, rare earth element patterns and isotopic signatures of O, Pb, Sr and Nd. Unfortunately, the major elemental composition of natron glass is relatively uniform and specific objects can almost never be uniquely assigned to their origin. Although the use of Sr and Nd isotope ratios and trace element signatures as an indication of provenance has proven promising, there are still unknown factors.The bulk of the Sr in natron glass is believed to have been incorporated with the lime bearing material. Where the lime was derived from Holocene seashell, the Sr isotopic composition of the glass would reflect that of modern seawater. Where the lime was derived from geologically aged limestone, the signature would reflect that of seawater at the time the limestone was deposited, possibly modified by diagenesis. However, also other minerals in the sand, such as feldspar and mica, can influence the Sr budget of the glass batch.Nd in natron based glass originates from the non-quartz mineral fraction of the silica raw material, which is most probably sand. It is well known that the εNd value of deep-sea sediments in the eastern Mediterranean varies significantly due to the varying sediment influx from the Nile (fluvial), the Sahara (eolian) and the European continent (fluvial) and shows a pronounced E-W gradient from as high as -1 at the mouth of the River Nile and the coasts of Egypt and Israel, to -12 south of Sicily. In the western Mediterranean, the distribution of the Nd isotopic composition is less well known. Only very few results for river particulates and deep sea sediments are published and they all show rather low εNd value of around -10. Although it is not possible to directly compare the Nd isotopic signature of glass to sea-floor sediment, such significant differences between the easternmost part of the Mediterranean Sea and the rest of the basin offer a great potential in tracing the origins of sand raw materials used in primary glass production.Trace elements in raw natron glass are related to the accessory minerals in the glassmaking sand. The mineralogy of the heavy mineral fraction of a sand deposit is determined by the composition of the source rocks and is often a good indication of its origin. However, also the other raw materials, such as the natron and the lime, introduce traces of specific elements to the glass batch. Especially the transition metals, such as Mn, Co, Cu, Sb and Pb, are strongly influenced by the addition of colouring or decolouring agents. Recycling of glass cullet, including small quantities of coloured glass, results in elevated concentrations of these elements.In this study, the applicability of Sr and Nd isotopes and trace elemental analysis for provenancing natron glass is evaluated. A database of Sr and Nd isotopic compositions of possible sand raw materials from the western Mediterranean is presented, as a means of comparison for the growing number of isotopic studies on ancient glass. It is shown that the 87Sr/86Sr ratio in natron glass is significantly influenced by the silicate fraction of the sand used and does not always provide a clear indication of the lime source used. The 143Nd/144Nd isotope ratio and εNd value of sands is a good indicator for their geological (and sometimes geographical) provenance.The variation of the isotopic composition of Nd in beach sands along the Mediterranean coasts of Spain, France and Italy is presented, and the relation between the Nd isotopic signatures and geologically distinct regions is explained. The use of the isotopic signature of Nd as a proxy for the source of silica in glass is, however, not always straightforward because of the possible overlap of signatures from different suppliers. However, when used in combination with trace element geochemistry, raw natron glass and sand raw materials from the known production centres in the Levant can be readily distinguished from the suitable glassmaking sands identified in the western part of the Mediterranean. Ti, Cr, Sr, Zr and Ba are shown to be the most useful elements for provenancing natron glass.A comparison between the range of the Nd isotope ratios of suitable glassmaking sands and archaeological natron glass from around the Mediterranean, indicates primary production in both the east and west. Hellenistic and Roman (2nd century BC to 4th century AD) natron glasses show a wide range of Nd isotopic compositions. This may suggest raw glass production all around the Mediterranean Sea but can also reflect intense recycling of glass from a few big glass producers scattered around the Mediterranean. During the Late Roman, Byzantine and Early Islamic period (5th to 7th century AD) large scale raw glass production appears to be restricted to the eastern Mediterranean.nrpages: 148status: publishe

Trace Element Analysis in Provenancing Roman Glass-Making

In this study, the use of trace elements as a provenance indicator for Roman natron glass is evaluated. Suitable glass-making sand raw materials are analysed for their trace elemental composition and compared to glass from known production centres. It is shown that the combined use of Nd isotopic and trace element analysis can be efficient for the provenancing of Roman glass. Trace elements associated with (de)colourants of glass are only present in small concentrations in glass-making sands. Background levels introduced to the glass by the sand raw material are defined and a lower threshold for the concentrations influenced by recycling is determined.status: publishe

Western Mediterranean sands for ancient glass making

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The archaeometry of ancient glassmaking: reconstructing ancient technology and the trade of raw materials

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The production of Roman glass with western Mediterranean sand raw materials: preliminary results

Pliny the Elder’s ‘Natural History’ is often cited in studies of ancient natron glass production. Pliny describes the production of glass using sand from the Belus River in Israel and the Volturno River in Italy. He also mentions that glass was similarly made in France and Spain. However, no direct archaeological evidence has ever been found to support glass production in these regions. In this study we investigate the possible existence of a Roman primary glass industry in the western Mediterranean, based on the occurrence of suitable sand raw materials. 178 beach sands from Spain, France and Italy are evaluated for their suitability for glass production by calculating the composition of hypothetical glasses made from these sands and comparing them to Roman natron glass. The results show that good glassmaking sands are far from common. Only six limited areas could be defined where suitable sand raw materials would have been available to the Roman glassmaker. The rest of the sands are unsuitable for glass production in their present form. The suitability of the suggested sands was checked by performing a series of melting experiments, which provide further insights in the way Roman glass makers would have had to prepare their raw materials and the used batch recipes.status: publishe

Sr-Nd isotopic analysis of glass from Sagalassos (SW Turkey)

The Nd isotopic composition of an ancient glass is typical of the (heavy) non-quartz fraction in the silica raw material. The Sr isotopic composition is considered typical for the lime component in the raw material. In the case of natron glass, this is mostly attributed to shell or limestone in the silica sand. In this study, 1st to 5th and 6th to 7th century AD glass from Sagalassos is compared to the typical signature of 4th to 8th century AD primary glass with a known production location in Egypt and Syro-Palestine. The results suggest a difference in glass supply to Sagalassos between both periods, and that glass was produced in the eastern and western Mediterranean area at least before the 6th century AD.status: publishe

Metallogenesis of the Nkana copper–cobalt South Orebody, Zambia

The Central African Copperbelt is one of the largest and richest metallogenic provinces in the world. Despite the many studies, the genesis of the stratiform Cu–Co-mineralization remains a subject of intense discussion. A diagenetic, pre-folding origin is proposed for most ore deposits both in Zambia and the Democratic Republic of Congo. However, later mineralization and/or remobilization seem to be important in the enrichment of the ores. The geological mapping of the South Orebody mine at Nkana (Zambia) indicates a relation between the mineralization and the host rock but also with compressional deformation. The location of the rich ore bodies generally corresponds with the hinge zones of tight to isoclinal folds and with the contact between the sandstones and conglomerates of the Footwall Sandstone Formation and the overlying organic-rich shales of the Ore Formation. The circulation of the mineralizing/remobilizing fluids through the rocks was facilitated by fracturing, especially in the hinge zones of the folds resulting in a structural permeability. A petrographical study demonstrated that, in addition to disseminated sulphides, three successive vein generations occur at Nkana South Orebody, i.e. layer parallel veins, irregular, crosscutting veins and massive veins. These vein generations respectively formed during the initial phase of basin inversion, the main phase of deformation and a late phase of orogenesis or later extensional tensions. Early diagenetic disseminated framboidal pyrites were replaced by Cu–sulphides. The timing of this replacement could not be constrained. Silicification, K-feldspar alteration, albitization, carbonatization and replacement by anhydrite are the main alteration phases.status: publishe