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  • Other Sources  (86)
  • American Association for the Advancement of Science (AAAS)
  • American Geophysical Union
  • International Union of Crystallography
  • Springer Nature
  • Wiley-Blackwell
  • 2020-2022  (37)
  • 2000-2004  (45)
  • 1980-1984  (4)
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  • 1
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    The History of South American Tropical Precipitation for the Past 25,000 Years (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 291 (5504). pp. 640-643.
    Details
    Publication Date: 2017-01-04
    Description: Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.
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  • 2
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    Microbial Reefs in the Black Sea Fueled by Anaerobic Oxidation of Methane (2002)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 297 (5583). pp. 1013-1015.
    Details
    Publication Date: 2017-07-07
    Description: Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcusgroup). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.
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  • 3
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    Coelacanths: a human responsibility (2001)
    Wiley-Blackwell
    In:  Journal of Fish Biology, 59 . pp. 332-338.
    Details
    Publication Date: 2017-07-06
    Description: The living coelacanth Latimeria chalumnae has a unique position in world biodiversity which raises important questions about conservation and ethics. Some relevant details of coelacanth biology are summarized, including those obtained by direct observation from submersibles. The importance of the coelacanth for evolutionary theory and palaeontology is shown to be paralleled in cultural, literary and artistic areas of human heritage. Threats to the Comoran coelacanths from artisanal fishing are described and conservation measures discussed in relation to local customs and economies as well as the promotion of tourism to spread a new awareness and concern for coelacanths worldwide.
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  • 4
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    Parasite Selection for Immunogenetic Optimality (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 301 (5638). p. 1343.
    Details
    Publication Date: 2017-03-31
    Description: In vertebrates, genes of the major histocompatibility complex (MHC), with their pronounced polymorphism, potentially represent outstanding examples for the selective advantages of genetic diversity (1). Theoretical models predicted that, within an individual, MHC alleles can be subjected to two opposing selective forces, resulting in an optimal number of genes at intermediate individual MHC diversity (2, 3). Diversifying selection increases heterozygosity and enables wider recognition of pathogens (4). This process is opposed by the need to delete T cells that react with self peptide–MHC combinations (5) from the repertoire, which has been proposed as a possible mechanism constraining expansion of MHC genes. Because too high MHC diversity might delimit T cell diversity, it might also impose limitations on the efficiency of pathogen recognition. However, empirical evidence demonstrating fitness benefits in terms of parasite resistance caused by this type of optimal MHC diversity has been lacking. Therefore, we tested whether three-spined sticklebacks (Gasterosteus aculeatus L.) carrying an intermediate level of individual MHC diversity also displayed the strongest level of resistance against parasite infection. Sticklebacks are particularly suited to test MHC optimality, because MHC class II genotypes can differ markedly in the number of MHC class IIB alleles (6). We caught fish from an outbred population and used these to breed six sibships of immunologically naïve fish (i.e., they had no previous contact to parasites). Immunogenetic diversity ranged from three to nine MHC class IIB alleles found in reverse-transcribed messenger RNA (mRNA) [see (6) for details on genotyping]. The MHC genotypes within these sibships segregated above and below the hypothesized optimal number of ∼5 MHC class IIB alleles, which had previously been estimated in an epidemiological field survey (7). In individual infection treatments, fish from all sibships were simultaneously exposed to three of the most abundant parasite species identified in the field (Fig. 1A) (8). After two rounds of infection, separated by an interval of 8 weeks, we found a significant minimal mean infection rate at an intermediate number of individual MHC class IIB variants [i.e., 5.82 expressed alleles (Fig. 1B)]. This result was also confirmed when sibships were considered separately [i.e., 4.96 alleles (Fig. 1C)] (9). The strong pattern only appeared when infection with all three parasites was accounted for simultaneously. This may not be surprising, because single alleles are expected to correlate with single diseases and multiple alleles can contribute to resistance against several infectious agents (2).
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  • 5
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    Parasite Selection for Immunogenetic Optimality (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 301 (5638). p. 1343.
    Details
    Publication Date: 2017-12-14
    Description: In vertebrates, genes of the major histocompatibility complex (MHC), with their pronounced polymorphism, potentially represent outstanding examples for the selective advantages of genetic diversity (1). Theoretical models predicted that, within an individual, MHC alleles can be subjected to two opposing selective forces, resulting in an optimal number of genes at intermediate individual MHC diversity (2, 3). Diversifying selection increases heterozygosity and enables wider recognition of pathogens (4). This process is opposed by the need to delete T cells that react with self peptide–MHC combinations (5) from the repertoire, which has been proposed as a possible mechanism constraining expansion of MHC genes. Because too high MHC diversity might delimit T cell diversity, it might also impose limitations on the efficiency of pathogen recognition. However, empirical evidence demonstrating fitness benefits in terms of parasite resistance caused by this type of optimal MHC diversity has been lacking. Therefore, we tested whether three-spined sticklebacks (Gasterosteus aculeatus L.) carrying an intermediate level of individual MHC diversity also displayed the strongest level of resistance against parasite infection. Sticklebacks are particularly suited to test MHC optimality, because MHC class II genotypes can differ markedly in the number of MHC class IIB alleles (6). We caught fish from an outbred population and used these to breed six sibships of immunologically naïve fish (i.e., they had no previous contact to parasites). Immunogenetic diversity ranged from three to nine MHC class IIB alleles found in reverse-transcribed messenger RNA (mRNA) [see (6) for details on genotyping]. The MHC genotypes within these sibships segregated above and below the hypothesized optimal number of ∼5 MHC class IIB alleles, which had previously been estimated in an epidemiological field survey (7). In individual infection treatments, fish from all sibships were simultaneously exposed to three of the most abundant parasite species identified in the field (Fig. 1A) (8). After two rounds of infection, separated by an interval of 8 weeks, we found a significant minimal mean infection rate at an intermediate number of individual MHC class IIB variants [i.e., 5.82 expressed alleles (Fig. 1B)]. This result was also confirmed when sibships were considered separately [i.e., 4.96 alleles (Fig. 1C)] (9). The strong pattern only appeared when infection with all three parasites was accounted for simultaneously. This may not be surprising, because single alleles are expected to correlate with single diseases and multiple alleles can contribute to resistance against several infectious agents (2).
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  • 6
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    Nautilus Growth and Longevity: Evidence from Marked and Recaptured Animals (1984)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 224 (4652). pp. 990-992.
    Details
    Publication Date: 2019-03-19
    Description: Study of Nautilus belauensis i its natural habitat in Palau, West Caroline Islands, shows that growth is slow (0.1 millimeter of shell per day on the average) and decreases as maturity is approached and that individuals may live at least 4 years beyond maturity. Age estimates for seven animals marked and recaptured between 45 and 355 days after release range from 14.5 to 17.2 years. These data indicate that the life-span of Nautilus may exceed 20 years and that its life strategy is very different from that of other living cephalopods.
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  • 7
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    The Oceanic Sink for Anthropogenic CO〈sub〉2〈/sub〉 (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 305 . pp. 367-371.
    Details
    Publication Date: 2016-09-09
    Description: Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO2) sink for the period from 1800 to 1994 of 118 ± 19 petagrams of carbon. The oceanic sink accounts for ∼48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2 to the atmosphere of about 39 ± 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential.
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  • 8
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    Calcium Carbonate Hexahydrate from Organic-Rich Sediments of the Antarctic Shelf: Precursors of Glendonites (1982)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 216 (4550). pp. 1128-1131.
    Details
    Publication Date: 2018-03-08
    Description: Large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the Bransfield Strait, Antarctic Peninsula, at a water depth of 1950 meters and sub-zero bottom water temperatures. The chemistry, mineralogy, and stable isotope composition of this hydrated calcium carbonate phase, its environment of formation, and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation.
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  • 9
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    Seismic imaging of the downwelling Indian lithosphere beneath Central Tibet (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 300 (5624). pp. 1424-1427.
    Details
    Publication Date: 2016-09-09
    Description: A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from ~ 100- to ~ 400- kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.
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  • 10
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    Propagule banks, herbivory and nutrient supply control population development and dominance patterns in macroalgal blooms (2000)
    Wiley-Blackwell
    In:  Oikos, 85 . pp. 46-58.
    Details
    Publication Date: 2017-01-31
    Description: Destructive macroalgal mass blooms threaten estuarine and coastal ecosystems worldwide. We asked which factors regulate macroalgal bloom intensity, distribution and species composition. In field experiments in the Baltic Sea, we analyzed the relative effects of nutrients, herbivores and algal propagule banks on population development and dominance patterns in two co-occurring bloom-forming macroalgae, Enteromorpha intestinalis and Pilayella littoralis. Both species were highly affected by the combined effects of a propagule bank, herbivory and nutrients. The magnitude of effects varied with season. The propagule bank was an important overwintering mechanism for both algae, and allowed for recruitment two months earlier than recruitment via freshly dispersed propagules. This provided a seasonal escape from intense herbivory and nutrient limitation later in the year. Favored by massive recruitment from the propagule bank, Enteromorpha was the superior space occupier in early spring, thereby reducing recruitment of Pilayella. Elimination of the propagule bank and recruitment via freshly dispersed propagules favored Pilayella. Strong and selective herbivory on Enteromorpha supported Pilayella in the presence, but not in the absence of the propagule bank. Nutrient enrichment in summer counteracted herbivore pressure on Enteromorpha, thereby negatively affecting Pilayella. Herbivore and nutrient effects were more pronounced for early life stages than adult algae. These results show that recruitment processes and forces affecting early life stages at the beginning of the vegetation period determine development and dominance patterns of macroalgal blooms. Herbivores naturally suppress blooms but increasing nutrient enrichment can override this important control mechanism. The propagule bank plays a previously unrecognized role for population and community dynamics.
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  • 11
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    Prokaryotic Chromosomes and Disease (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 301 (5634). pp. 790-793.
    Details
    Publication Date: 2015-08-27
    Description: Recent insights into bacterial genome organization and function have improved our understanding of the nature of pathogenic bacteria and their ability to cause disease. It is becoming increasingly clear that the bacterial chromosome constantly undergoes structural changes due to gene acquisition and loss, recombination, and mutational events that have an impact on the pathogenic potential of the bacterium. Even though the bacterial genome includes additional genetic elements, the chromosome represents the most important entity in this context. Here, we will show that various processes of genomic instability have an influence on the many manifestations of infectious disease
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  • 12
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    Habitat Selection and Life Cycle Characteristics of Five Species of the Amphipod Genus Gammarus in the Baltic (1981)
    Wiley-Blackwell
    In:  Oikos, 37 (2). p. 173.
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    Publication Date: 2015-10-06
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  • 13
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    Rapid Kimberlite Ascent and the Significance of Ar-Ar Ages in Xenolith Phlogopites (2000)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 289 (5479). pp. 609-611.
    Details
    Publication Date: 2015-11-24
    Description: Kimberlite eruptions bring exotic rock fragments and minerals, including diamonds, from deep within the mantle up to the surface. Such fragments are rapidly absorbed into the kimberlite magma so their appearance at the surface implies rapid transport from depth. High spatial resolution Ar-Ar age data on phlogopite grains in xenoliths from Malaita in the Solomon Islands, southwest Pacific, and Elovy Island in the Kola Peninsula, Russia, indicate transport times of hours to days depending upon the magma temperature. In addition, the data show that the phlogopite grains preserve Ar-Ar ages recorded at high temperature in the mantle, 700°C above the conventional closure temperature.
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  • 14
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    The 2003 European summer heatwaves and drought - synoptic diagnosis and impacts (2004)
    Wiley-Blackwell
    In:  Weather, 59 (8). pp. 209-216.
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    Publication Date: 2020-04-28
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  • 15
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    The central European floods of August 2002: Part 1 – Rainfall periods and flood development (2003)
    Wiley-Blackwell
    In:  Weather, 58 (10). pp. 371-377.
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    Publication Date: 2020-04-28
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  • 16
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    Origin and Migration of the Alpine Iceman (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 302 (5646). pp. 862-866.
    Details
    Publication Date: 2015-11-24
    Description: The Alpine Iceman provides a unique window into the Neolithic-Copper Age of Europe. We compared the radiogenic (strontium and lead) and stable (oxygen and carbon) isotope composition of the Iceman's teeth and bones, as well as 40Ar/39Ar mica ages from his intestine, to local geology and hydrology, and we inferred his habitat and range from childhood to adult life. The Iceman's origin can be restricted to a few valleys within ∼60 kilometers south(east) of the discovery site. His migration during adulthood is indicated by contrasting isotopic compositions of enamel, bones, and intestinal content. This demonstrates that the Alpine valleys of central Europe were permanently inhabited during the terminal Neolithic.
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  • 17
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    The central European floods of August 2002: Part 2 - Synoptic causes and considerations with respect to climatic change (2003)
    Wiley-Blackwell
    In:  Weather, 58 (11). pp. 434-442.
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    Publication Date: 2020-04-28
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  • 18
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    Opposing effects of grazing and nutrients on diversity (2003)
    Wiley-Blackwell
    In:  Oikos (100). pp. 592-600.
    Details
    Publication Date: 2017-01-31
    Description: Conceptual models predict counteractive effects of herbivores and nutrient enrichment on plant diversity and reversed effects of grazers under different nutrient regimes. I tested these hypotheses in 11 field experiments with periphyton communities in three different aquatic habitats (a highly eutrophic lake, an meso-eutrophic lake, and an meso-eutrophic part of the Baltic Sea coast) and in different seasons. Grazer access and nutrient supply were manipulated in a factorial design. Species richness and evenness were chosen as response variables. Both manipulated factors had significant and contrasting effects on diversity, with variable effect strength between sites and seasons. From the two aspects of diversity, evenness well reflected the changes in community composition. Fertilization tended to increase the dominance of few species and thus to decrease evenness, whereas grazers counteracted these effects by removing dominant life forms. The response of species richness was not as expected, since grazers decreased richness throughout, whereas nutrients had weaker effects but tended to increase richness. Species richness rather reflected changes in periphyton architecture. Grazers reduced algal richness presumably by co-consumption of rare species in the tightly connected periphyton assemblages, whereas enrichment may increase richness by providing more structure via increased dominance of filamentous species. Although grazer and nutrient effects on richness and evenness were opposing, there was no change in the effect of one factor by manipulation of the other.
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  • 19
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    The ocean takes a deep breath (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 306 (5700). p. 1377.
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    Publication Date: 2016-09-08
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  • 20
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    Widespread Intense Turbulent Mixing in the Southern Ocean (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 303 . pp. 210-213.
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    Publication Date: 2014-12-02
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  • 21
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    Mitochondrial phylogeny and biogeographic affinities of sea breams of the genus Diplodus (Sparidae) (2001)
    Wiley-Blackwell
    In:  Journal of Fish Biology, 59 . pp. 1638-1652.
    Details
    Publication Date: 2017-09-08
    Description: Phylogenetic analyses, using 482 bp of the mitochondrial 16S rDNA and 461 bp of the control region of 16 Diplodus species and Oblada melanura, Pagellus bogaraveo and Pagellus acarne, all close relatives of Diplodus, identified the two representatives of Pagellus as the sister group of Diplodus. Oblada melanura was confirmed as the sister taxon of D. puntazzo, despite its different dental morphology and ecology. Within the genus Diplodus, three clades were identified, the first containing D. annularis and D. bellottii, the second D. vulgaris and D. prayensis, and the third comprising three subclades. These were formed by O. melanura clustering with D. puntazzo, D. fasciatus with D. cervinus, and by the Diplodus sargus sub-species assemblage which also included the West Atlantic taxa D. argenteus, D. bermudensis, D. holbrooki, and the Red Sea endemic D. noct. All members of the D. sargus assemblage were genetically closely related. Among them, D. sargus lineatus from the Cape Verde islands was resolved as most ancestral branch, pointing to the possibility that the diversification and spread of the D. sargus assemblage originated in this region. The hypothesis of stepwise speciation following colonization events within the D. sargus complex is fully supported by phylogenetic reconstruction.
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  • 22
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    Ventilation of the Glacial Deep Pacific Ocean (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 306 (5699). pp. 1169-1172.
    Details
    Publication Date: 2016-06-15
    Description: Measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial Pacific deep-sea cores suggest that during peak glacial time the radiocarbon age of water at 2-kilometers depth was no greater than that of today. These results make unlikely suggestions that a slowdown in deep-ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon-14 (14C) to carbon in the atmosphere and surface ocean during glacial time. Comparison of 14C ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14C to C ratio difference was not substantially different from today's.
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  • 23
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    Micro- and macroscopic characters staging gonadal maturation of female Baltic cod (Gadus morhua L.) (2003)
    Wiley-Blackwell
    In:  Journal of Fish Biology, 62 . pp. 253-276.
    Details
    Publication Date: 2017-09-08
    Description: A set of histological characteristics to judge ovarian development was established and used to elaborate morphological criteria of 10 maturity stages of Baltic cod Gadus morhua sampled throughout the annual cycle to represent different macroscopic maturity stages. The applied characteristics confirmed most stages of the macroscopic scale, but the separation of late immature and resting mature females remained imprecise. Atretic vitellogenic oocytes or encapsulated residual eggs identified the resting condition morphologically, but not all ovaries with visible signs of previous spawning showed such features. One ovarian stage that was previously classified as ‘ripening’ was changed to ‘spawning’, owing to the prevalence of hydrated eggs and empty follicles. Ovaries with malfunctions were defined by a separate stage. Macroscopic criteria were revised by comparing the gross anatomy of ovaries with their histology. Female length and gonado-somatic index supported stage definitions, but substantial variation in Fulton's condition factor and the hepato-somatic index rendered these of little use for this purpose. The time of sampling influenced staging accuracy. A female spawner probability function based on the proportion of ripening and ripe specimens in early spring seems to be the most appropriate method to estimate spawner biomass and reproductive potential.
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  • 24
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    Specific gravity and vertical distribution of sprat (Sprattus sprattus) eggs in the Baltic Sea (2003)
    Wiley-Blackwell
    In:  Journal of Fish Biology, 63 . pp. 280-299.
    Details
    Publication Date: 2017-09-13
    Description: During peak spawning of sprat Sprattus sprattus in the Baltic Sea in May–June egg specific gravity averaged ±s.d. 1·00858 ± 0·00116 g cm−3 but was significantly higher in the beginning and significantly lower towards the end of the spawning season. A close relationship was found between egg diameter and egg specific gravity (r2 = 0·71). This relationship, however, changed during the spawning season indicating that some other factor was involved causing the decrease in specific gravity during the spawning period. The vertical egg distribution changed during the spawning season: eggs were distributed mainly in the deep layers early in the season, occurred in and above the permanent halocline during peak spawning, and above the halocline towards the end of the spawning season. Consequently, poor oxygen conditions in the deep layers and low temperatures in layers between the halocline and the developing thermocline may affect egg development. Thus, opportunities for egg development vary over the spawning season and among spawning areas, and depending on frequency of saline water inflows into the Baltic Sea and severity of winters, between years
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  • 25
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    The North Atlantic Oscillation (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 291 (5504). pp. 603-605.
    Details
    Publication Date: 2016-09-09
    Description: The North Atlantic Oscillation (NAO) dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during winter. It strongly affects agricultural yields, water management, fish inventories, and terrestrial ecology. In their Perspective, Hurrell, Kushnir, and Visbeck report recent research into the NAO discussed at an American Geophysical Union Chapman Conference at the end of 2000. Much remains to be learned about the NAO, but it seems increasingly less likely that natural variability is the cause for the recent upward NAO trend.
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  • 26
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    A reflection on Mg, Cd, Ca, Li and Si isotopic measurements and related reference materials (2004)
    Wiley-Blackwell
    In:  Geostandards and Geoanalytical Research, 28 (1). pp. 139-148.
    Details
    Publication Date: 2019-01-22
    Description: This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the “Münster-Cd” and JEPPIM Cd solutions for Cd and the “Big Batch” silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis.
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    Collapse and conservation of shark populations in the Northwest Atlantic (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science (299). pp. 389-392.
    Details
    Publication Date: 2016-09-09
    Description: Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.
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    Temporal trends in deep ocean Redfield ratios (Reply to technical comment by Zhang et al.) (2000)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 289 (5454). p. 1837.
    Details
    Publication Date: 2016-09-09
    Description: The Redfield ratio [carbon:nitrogen:phosphorus (C:N:P)] of particle flux to the deep ocean is a key factor in marine biogeochemical cycling. Changes in oceanic carbon sequestration have been linked to variations in the Redfield ratio on geological time scales, but this ratio generally is assumed to be constant with time in the modern ocean. However, deep-water Redfield ratios in the northern hemisphere show evidence for temporal trends over the past five decades. The North Atlantic Ocean exhibits a rising N:P ratio, which may be related to increased deposition of atmospheric nitrous oxides from anthropogenic N emissions. In the North Pacific Ocean, increasing C:N and C:P ratios are accompanied by rising remineralization rates, which suggests intensified export production. Stronger export of carbon in this region may be due to enhanced bioavailability of aeolian iron. These findings imply that the biological part of the marine carbon cycle currently is not in steady state.
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  • 29
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    Asphalt volcanism and chemosynthetic life, Campeche Knoll, Gulf of Mexico (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 304 . pp. 999-1002.
    Details
    Publication Date: 2016-09-09
    Description: In the Campeche Knolls, in the southern Gulf of Mexico, lava-like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level. Chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt, which chilled and contracted after discharge. The site also includes oil seeps, gas hydrate deposits, locally anoxic sediments, and slabs of authigenic carbonate. Asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the Gulf of Mexico.
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  • 30
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    Effects of macrograzers and light on periphyton stoichiometry (2004)
    Wiley-Blackwell
    In:  Oikos, 106 . pp. 93-104.
    Details
    Publication Date: 2016-05-26
    Description: Ecological stoichiometry describes the biochemical constraints of trophic interactions emerging from the different nutrient content and nutrient demand of producers and consumers, respectively. Most research on this topic originates from well-mixed pelagic food webs, whereas the idea has received far less attention in spatially structured habitats. Here, we test how light as well as grazing and nutrient regeneration by consumers affects growth and biomass of benthic primary producers. In the first laboratory experiment, we manipulated grazer presence (two different snail species plus ungrazed control), in the second experiment we factorially combined manipulation of grazer presence and light intensity. We monitored snail and periphyton biomass as well as dissolved and particulate nutrients (nitrogen and phosphorus) over time. Grazers significantly reduced algal biomass in both experiments. Grazers affected periphyton nutrient content depending on the prevailing nutrient limitation and their own body stoichiometry. In the nitrogen (N-) limited first experiment, grazers increased N both in the periphyton and in the water column. The effect was stronger for grazers with lower N-content. In the phosphorus (P-) limited second experiment, grazers increased the P-content of the periphyton, but the grazer with lower N-content had additionally positive effects on algal N. Light reduction did not affect periphyton biomass, but increased chlorophyll-, N- and P-content of the periphyton. These experiments revealed that the indirect effects of grazers on periphyton were bound by stoichiometric constraints of nutrient incorporation and excretion.
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  • 31
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    Response to Comment on "Parasite Selection for Immunogenetic Optimality" (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 303 (5660). 957b-957.
    Details
    Publication Date: 2013-02-04
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  • 32
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    Detection of Overflow Events in the Shag Rocks Passage, Scotia Ridge (1981)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 213 (4512). pp. 1113-1114.
    Details
    Publication Date: 2019-01-21
    Description: During an almost yearlong period of observations made with a current meter in the fracture zone between the Falkland Islands (Islas Malvinas) and South Georgia, several overflow events were recorded at a depth of 3000 meters carrying cold bottom water from the Scotia Sea into the Argentine Basin. The outflow bursts of Scotia Sea bottom water, a mixing product of Weddell Sea and eastern Pacific bottom water, were associated with typical speeds of more than 28 centimeters per second toward the northwest and characteristic temperatures below 0.6°C. The maximum 24-hour average speed of 65 centimeters per second, together with a temperature of 0.29°C, was encountered on 14 November 1980 at a water depth of 2973 meters, 35 meters above the sea floor.
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  • 33
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    Climate Swings Come into Focus (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 294 (5550). pp. 2308-2309.
    Details
    Publication Date: 2016-06-10
    Description: The last glacial period was far from quiet. During so-called Heinrich events, large armadas of icebergs were shed from the ice sheet that covered much of North America. The tracks of debris left by the melting icebergs can still be seen in sediment cores from the North Atlantic. In their Perspective, Broecker and Hemming report from a recent miniconference that attempted to chart the climatic impacts of these events.
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  • 34
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    Was the Medieval Warm Period Global? (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 291 (5508). pp. 1497-1499.
    Details
    Publication Date: 2016-06-10
    Description: During the Medieval Warm Period (800 to 1200 A.D.), the Vikings colonized Greenland. In his Perspective, Broecker discusses whether this warm period was global or regional in extent. He argues that it is the last in a long series of climate fluctuations in the North Atlantic, that it was likely global, and that the present warming should be attributed in part to such an oscillation, upon which the warming due to greenhouse gases is superimposed.
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  • 35
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    Does the Trigger for Abrupt Climate Change Reside in the Ocean or in the Atmosphere? (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 300 (5625). pp. 1519-1522.
    Details
    Publication Date: 2016-06-15
    Description: Two hypotheses have been put forward to explain the large and abrupt climate changes that punctuated glacial time. One attributes such changes to reorganizations of the ocean's thermohaline circulation and the other to changes in tropical atmosphere-ocean dynamics. In an attempt to distinguish between these hypotheses, two lines of evidence are examined. The first involves the timing of the freshwater injections to the northern Atlantic that have been suggested as triggers for the global impacts associated with the Younger Dryas and Heinrich events. The second has to do with evidence for precursory events associated with the Heinrich ice-rafted debris layers in the northern Atlantic and with the abrupt Dansgaard-Oeschger warmings recorded in the Santa Barbara Basin.
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  • 36
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    Glacial-to-Holocene Redistribution of Carbonate Ion in the Deep Sea (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 294 (5549). pp. 2152-2155.
    Details
    Publication Date: 2016-06-10
    Description: We have reconstructed the glacial-age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and Holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western Atlantic's Ceara Rise and the western Pacific's Ontong Java Plateau. The results suggest that unlike today's ocean, sizable vertical gradients in the carbonate ion concentration existed in the glacial-age deep ocean. In the equatorial Pacific, the concentration increased with depth, and in the Atlantic, it decreased with depth. In addition, the contrast between the carbonate ion concentration in deep waters produced in the northern Atlantic and deep water in the Pacific appears to have been larger than in today's ocean.
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  • 37
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    Calcium isotopic composition of various standards and seawater (2003)
    Wiley-Blackwell
    In:  Geostandards Newsletter, 27 (1). pp. 13-19.
    Details
    Publication Date: 2019-01-22
    Description: A compilation of δ44/40Ca (δ44/40Ca) data sets of different calcium reference materials is presented, based on measurements in three different laboratories (Institute of Geological Sciences, Bern; Centre de Géochimie de la Surface, Strasbourg; GEOMAR, Kiel) to support the establishment of a calcium isotope reference standard. Samples include a series of international and internal Ca reference materials, including NIST SRM 915a, seawater, two calcium carbonates and a CaF2 reference sample. The deviations in δ44/40Ca for selected pairs of reference samples have been defined and are consistent within statistical uncertainties in all three laboratories. Emphasis has been placed on characterising both NIST SRM 915a as an internationally available high purity Ca reference sample and seawater as representative of an important and widely available geological reservoir. The difference between δ44/40Ca of NIST SRM 915a and seawater is defined as -1.88 O.O4%o (δ44/42CaNISTSRM915a/Sw= -0.94 0.07%o). The conversion of values referenced to NIST SRM 915a to seawater can be described by the simplified equation δ44/40CaSa/Sw=δ44/40CaSa/NIST SRM 915a - 1.88 (δ44/42CaSa/Sw=δ44/42CaSa/NIST SRM 915a - 0.94). We propose the use of NIST SRM 915a as general Ca isotope reference standard, with seawater being defined as the major reservoir with respect to oceanographic studies.
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  • 38
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    Impacts of multiple stressors on biodiversity and ecosystem functioning: The role of species co-tolerance (2004)
    Wiley-Blackwell
    In:  Oikos, 104 . pp. 451-457.
    Details
    Publication Date: 2019-09-23
    Description: Ecosystem resistance to a single stressor relies on tolerant species that can compensate for sensitive competitors and maintain ecosystem processes, such as primary production. We hypothesize that resistance to additional stressors depends increasingly on species tolerances being positively correlated (i.e. positive species co-tolerance). Initial exposure to a stressor combined with positive species co-tolerance should reduce the impacts of other stressors, which we term stress-induced community tolerance. In contrast, negative species co-tolerance is expected to result in additional stressors having pronounced additive or synergistic impacts on biologically impoverished functional groups, which we term stress-induced community sensitivity. Therefore, the sign and strength of the correlation between species sensitivities to multiple stressors must be considered when predicting the impacts of global change on ecosystem functioning as mediated by changes in biodiversity.
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  • 39
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    The challenge of long-term climate change (2003)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 302 . pp. 1923-1925.
    Details
    Publication Date: 2016-09-09
    Description: Climate policy needs to address the multidecadal to centennial time scale of climate change. Although the realization of short-term targets is an important first step, to be effective climate policies need to be conceived as long-term programs that will achieve a gradual transition to an essentially emission-free economy on the time scale of a century. This requires a considerably broader spectrum of policy measures than the primarily market-based instruments invoked for shorter term mitigation policies. A successful climate policy must consist of a dual approach focusing on both short-term targets and long-term goals
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  • 40
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    Biodiversity effects on ecosystem function: emerging issues and their experimental test in aquatic communities (2004)
    Wiley-Blackwell
    In:  Oikos, 104 . pp. 423-436.
    Details
    Publication Date: 2017-01-31
    Description: Recent experiments, mainly in terrestrial environments, have provided evidence of the functional importance of biodiversity to ecosystem processes and properties. Compared to terrestrial systems, aquatic ecosystems are characterised by greater propagule and material exchange, often steeper physical and chemical gradients, more rapid biological processes and, in marine systems, higher metazoan phylogenetic diversity. These characteristics limit the potential to transfer conclusions derived from terrestrial experiments to aquatic ecosystems whilst at the same time provide opportunities for testing the general validity of hypotheses about effects of biodiversity on ecosystem functioning. Here, we focus on a number of unique features of aquatic experimental systems, propose an expansion to the scope of diversity facets to be considered when assessing the functional consequences of changes in biodiversity and outline a hierarchical classification scheme of ecosystem functions and their corresponding response variables. We then briefly highlight some recent controversial and newly emerging issues relating to biodiversity-ecosystem functioning relationships. Based on lessons learnt from previous experimental and theoretical work, we finally present four novel experimental designs to address largely unresolved questions about biodiversity-ecosystem functioning relationships. These include (1) investigating the effects of non-random species loss through the manipulation of the order and magnitude of such loss using dilution experiments; (2) combining factorial manipulation of diversity in interconnected habitat patches to test the additivity of ecosystem functioning between habitats; (3) disentangling the impact of local processes from the effect of ecosystem openness via factorial manipulation of the rate of recruitment and biodiversity within patches and within an available propagule pool; and (4) addressing how non-random species extinction following sequential exposure to different stressors may affect ecosystem functioning. Implementing these kinds of experimental designs in a variety of systems will, we believe, shift the focus of investigations from a species richness-centred approach to a broader consideration of the multifarious aspects of biodiversity that may well be critical to understanding effects of biodiversity changes on overall ecosystem functioning and to identifying some of the potential underlying mechanisms involved.
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    Microbes, Molecules, and Marine Ecosystems (2004)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 303 (5664). pp. 1622-1624.
    Details
    Publication Date: 2019-03-06
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  • 42
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    Metapopulation ecology in the sea: from Levins' model to marine ecology and fisheries science (2004)
    Wiley-Blackwell
    In:  Fish and Fisheries, 5 (2). pp. 131-140.
    Details
    Publication Date: 2016-11-25
    Description: Marine and fisheries scientists are increasingly using metapopulation concepts to better understand and model their focal systems. Consequently, they are considering what defines a metapopulation. One perspective on this question emphasizes the importance of extinction probability in local populations. This view probably stems from the focus on extinction in Levins' original metapopulation model, but places unnecessary emphasis on extinction–recolonization dynamics. Metapopulation models with more complex structure than Levins' patch-occupancy model and its variants allow a broader range of population phenomena to be examined, such as changes in population size, age structure and genetic structure. Analyses along these lines are critical in fisheries science, where presence–absence resolution is far too coarse to understand stock dynamics in a meaningful way. These more detailed investigations can, but need not, aim to assess extinction risk or deal with extinction-prone local populations. Therefore, we emphasize the coupling of spatial scales as the defining feature of metapopulations. It is the degree of demographic connectivity that characterizes metapopulations, with the dynamics of local populations strongly dependent upon local demographic processes, but also influenced by a nontrivial element of external replenishment. Therefore, estimating rates of interpopulation exchange must be a research priority. We contrast metapopulations with other spatially structured populations that differ in the degree of local closure of their component populations. We conclude with consideration of the implications of metapopulation structure for spatially explicit management, particularly the design of marine protected area networks.
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  • 43
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    Cephalopod Hox genes and the origin of morphological novelties (2003)
    Springer Nature
    In:  Nature, 424 (6952). pp. 1061-1065.
    Details
    Publication Date: 2021-07-14
    Description: Cephalopods are a diverse group of highly derived molluscs, including nautiluses, squids, octopuses and cuttlefish. Evolution of the cephalopod body plan from a monoplacophoran-like ancestor1 entailed the origin of several key morphological innovations contributing to their impressive evolutionary success2. Recruitment of regulatory genes3, or even pre-existing regulatory networks4, may be a common genetic mechanism for generating new structures. Hox genes encode a family of transcriptional regulatory proteins with a highly conserved role in axial patterning in bilaterians5; however, examples highlighting the importance of Hox gene recruitment for new developmental functions are also known6,7. Here we examined developmental expression patterns for eight out of nine Hox genes8 in the Hawaiian bobtail squid Euprymna scolopes, by whole-mount in situ hybridization. Our data show that Hox orthologues have been recruited multiple times and in many ways in the origin of new cephalopod structures. The manner in which these genes have been co-opted during cephalopod evolution provides insight to the nature of the molecular mechanisms driving morphological change in the Lophotrochozoa, a clade exhibiting the greatest diversity of body plans in the Metazoa.
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  • 44
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    Worldwide Observations of Remarkable Deep-Sea Squids (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 294 (5551). p. 2505.
    Details
    Publication Date: 2021-07-05
    Type: Article , PeerReviewed
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  • 45
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    Control of octopus arm extension by a peripheral motor program (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 293 (5536). pp. 1845-1848.
    Details
    Publication Date: 2021-07-07
    Description: For goal-directed arm movements, the nervous system generates a sequence of motor commands that bring the arm toward the target. Control of the octopus arm is especially complex because the arm can be moved in any direction, with a virtually infinite number of degrees of freedom. Here we show that arm extensions can be evoked mechanically or electrically in arms whose connection with the brain has been severed. These extensions show kinematic features that are almost identical to normal behavior, suggesting that the basic motor program for voluntary movement is embedded within the neural circuitry of the arm itself. Such peripheral motor programs represent considerable simplification in the motor control of this highly redundant appendage.
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    Trans-European Suture Zone (2020)
    Springer Nature
    In:  In: Encyclopedia of Solid Earth Geophysics. , ed. by Gupta, H. Encyclopedia of Earth Sciences Series . Springer Nature, Cham, Switzerland, , 11 pp. ISBN 978-3-030-10475-7
    Details
    Publication Date: 2021-02-10
    Description: The Trans-European Suture Zone (TESZ) is the transition zone from the Precambrian East European Craton in the north and east to the younger Phanerozoic mobile belts to the south and west. It is the most prominent lithospheric tectonic feature of Europe. The term Trans-European Suture Zone was only adapted around year 2000 during the Pan-European EUROPROBE program of the European Science Foundation. Until then, parts of the zone were termed Teisseyre-Tornquist Zone, Sorgenfrei-Tornquist Zone, Trans-European Fault, and Tornquist Fan.
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  • 47
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    92Nb-92Zr and the early differentation history of planetary bodies (2000)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 289 (5484). pp. 1538-1542.
    Details
    Publication Date: 2016-09-09
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    The Ocean's Role in Atlantic Climate Variability (2002)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 297 . pp. 2223-2224.
    Details
    Publication Date: 2016-09-09
    Description: Atlantic climate variability is an important driving force of climate in the surrounding land areas. In his Perspective, Visbeck explores recent advances toward understanding and predicting climate variability in the tropical Atlantic and the North Atlantic, and elucidating the role played by the ocean's circulation.
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  • 49
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    Keep it simple: three indicators to deal with overfishing (2004)
    Wiley-Blackwell
    In:  Fish and Fisheries, 5 (1). pp. 86-91.
    Details
    Publication Date: 2017-02-02
    Description: Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, with 100% as target; (ii) percent of specimens with optimum length in catch, with 100% as target; and (iii) percentage of ‘mega-spawners‘ in catch, with 0% as target, and 30–40% as representative of reasonable stock structure if no upper size limit exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Epinephelus aeneus demonstrate their usefulness. It is argued that such simple indicators have the potential to allow more stakeholders such as fishers, fish dealers, supermarket managers, consumers and politicians to participate in fisheries management and eventually hold and reverse the global pattern of convenience overfishing, which is defined here as deliberate overfishing sanctioned by official bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts.
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  • 50
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    Tropical Origins for Recent North Atlantic Climate Change (2001)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 292 (5514). pp. 90-92.
    Details
    Publication Date: 2016-02-18
    Description: Evidence is presented that North Atlantic climate change since 1950 is linked to a progressive warming of tropical sea surface temperatures, especially over the Indian and Pacific Oceans. The ocean changes alter the pattern and magnitude of tropical rainfall and atmospheric heating, the atmospheric response to which includes the spatial structure of the North Atlantic Oscillation (NAO). The slow, tropical ocean warming has thus forced a commensurate trend toward one extreme phase of the NAO during the past half-century.
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    Facilitated crystal handling using a simple device for evaporation reduction in microtiter plates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: In the past two decades, most of the steps in a macromolecular crystallography experiment have undergone tremendous development with respect to speed, feasibility and increase of throughput. The part of the experimental workflow that is still a bottleneck, despite significant efforts, involves the manipulation and harvesting of the crystals for the diffraction experiment. Here, a novel low‐cost device is presented that functions as a cover for 96‐well crystallization plates. This device enables access to the individual experiments one at a time by its movable parts, while minimizing evaporation of all other experiments of the plate. In initial tests, drops of many typically used crystallization cocktails could be successfully protected for up to 6 h. Therefore, the manipulation and harvesting of crystals is straightforward for the experimenter, enabling significantly higher throughput. This is useful for many macromolecular crystallography experiments, especially multi‐crystal screening campaigns.
    Description: A simple and low‐cost device has been developed to minimize evaporation in microtiter plates for easy crystal handling and harvesting. image
    Keywords: 548 ; evaporation reduction ; crystal handling ; crystal harvesting ; crystallographic fragment screening
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    Cation distribution in Cu2ZnSnSe4, Cu2FeSnS4 and Cu2ZnSiSe4 by multiple‐edge anomalous diffraction (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order–disorder. However, Cu+, Zn2+ and Fe2+ have very similar scattering factors and are all but indistinguishable in usual X‐ray diffraction experiments. Anomalous diffraction utilizes the dependency of the atomic scattering factors f′ and f′′ of the energy of the radiation, especially close to the element‐specific absorption edges. In the MEAD technique, individual Bragg peaks are tracked over an absorption edge. The intensity changes depending on the structure factor can be highly characteristic for Miller indices selected for a specific structural problem, but require very exact measurements. Beamline KMC‐2 at synchrotron BESSY II, Berlin, has been recently upgraded for this technique. Anomalous X‐ray powder diffraction and XAFS compliment the data. Application of this technique confirmed established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS). In contrast to the literature, cation distribution in Cu2ZnSiSe4 (CZSiSe) is shown to adopt a highly ordered wurtz‐kesterite structure type.
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Application of this technique confirms established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS), but in Cu2ZnSiSe4 (CZSiSe) the cation distribution is shown to adopt a highly ordered wurtz‐kesterite structure type in contrast to the literature. image
    Keywords: 548 ; synchrotron ; anomalous diffraction ; semiconductor ; MEAD
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    The copper(II)‐binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The growth of diffraction‐quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high‐affinity copper(II)‐binding tripeptide GHK was fused to the N‐terminus of a GFP variant and an MBP‐FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square‐pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S‐atom positions could also be located in log‐likelihood‐gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR‐SAD phasing.
    Description: A novel three‐residue tag containing the residues GHK that can be used to promote crystallization and in SAD phasing experiments using its tightly bound copper ion is described. image
    Keywords: 548 ; phasing ; crystallization ; GHK ; SAD
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    Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.
    Description: A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image
    Keywords: 548 ; polyhydroxybutyrates ; mixed tacticity ; paracrystallinity ; Rietveld refinement ; thermal factors
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    Concepts for nondestructive and depth‐resolved X‐ray residual stress analysis in the near‐surface region of nearly single crystalline materials with mosaic structure (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Two evaluation concepts for nondestructive depth‐resolved X‐ray residual stress analysis in the near‐surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice‐spacing depth profiles along the ⟨hkl⟩ poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain‐free lattice parameter a0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.
    Description: Two data evaluation concepts are proposed for nondestructive and depth‐resolved X‐ray residual stress analysis by means of energy‐dispersive diffraction on materials featuring cubic symmetry and a nearly single crystalline structure. image
    Keywords: 548 ; residual stress ; X‐ray diffraction ; depth‐resolved analysis ; mosaic crystals
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    X‐ray dichroism in polyimide caused by non‐resonant scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-30
    Description: Dichroism is one of the most important optical effects in both the visible and the X‐ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.
    Description: Aligned molecules, for example in polyimide foils, lead to small dichroism even far from resonances, which can be revealed by high‐precision X‐ray polarimetry. image
    Keywords: 548 ; polyimide ; polarization ; X‐ray polarimetry ; wide‐angle scattering ; X‐ray dichroism
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    Elastic stiffness coefficients of thiourea from thermal diffuse scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-27
    Description: The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high‐energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X‐ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high‐energy photons extends the applicability of the TDS‐based approach to organic compounds which would suffer from radiation damage at lower photon energies.
    Description: The elastic stiffness coefficients of thiourea are determined from thermal diffuse scattering. image
    Keywords: 548 ; thermal diffuse scattering ; elastic stiffness ; thiourea
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    Fast fitting of reflectivity data of growing thin films using neural networks (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-03
    Description: X‐ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α‐sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8–18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.
    Description: Artificial neural networks trained with simulated data are shown to correctly and quickly determine film parameters from experimental X‐ray reflectivity curves.
    Keywords: 548 ; X‐ray reflectivity ; machine learning ; organic semi‐conductors ; neural networks
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    Numerically stable form factor of any polygon and polyhedron (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals.
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image
    Keywords: 548 ; form factors ; polyhedra ; Fourier shape transform
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    ROBL‐II at ESRF: a synchrotron toolbox for actinide research (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
    Description: ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry.
    Keywords: 549 ; actinides ; EXAFS ; XANES ; HERFD‐XANES ; XAS ; XES ; RIXS ; XRD ; CTR ; RAXR ; surface diffraction
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    ATSAS 3.0: expanded functionality and new tools for small‐angle scattering data analysis (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-30
    Description: The ATSAS software suite encompasses a number of programs for the processing, visualization, analysis and modelling of small‐angle scattering data, with a focus on the data measured from biological macromolecules. Here, new developments in the ATSAS 3.0 package are described. They include IMSIM, for simulating isotropic 2D scattering patterns; IMOP, to perform operations on 2D images and masks; DATRESAMPLE, a method for variance estimation of structural invariants through parametric resampling; DATFT, which computes the pair distance distribution function by a direct Fourier transform of the scattering data; PDDFFIT, to compute the scattering data from a pair distance distribution function, allowing comparison with the experimental data; a new module in DATMW for Bayesian consensus‐based concentration‐independent molecular weight estimation; DATMIF, an ab initio shape analysis method that optimizes the search model directly against the scattering data; DAMEMB, an application to set up the initial search volume for multiphase modelling of membrane proteins; ELLLIP, to perform quasi‐atomistic modelling of liposomes with elliptical shapes; NMATOR, which models conformational changes in nucleic acid structures through normal mode analysis in torsion angle space; DAMMIX, which reconstructs the shape of an unknown intermediate in an evolving system; and LIPMIX and BILMIX, for modelling multilamellar and asymmetric lipid vesicles, respectively. In addition, technical updates were deployed to facilitate maintainability of the package, which include porting the PRIMUS graphical interface to Qt5, updating SASpy – a PyMOL plugin to run a subset of ATSAS tools – to be both Python 2 and 3 compatible, and adding utilities to facilitate mmCIF compatibility in future ATSAS releases. All these features are implemented in ATSAS 3.0, freely available for academic users at https://www.embl‐hamburg.de/biosaxs/software.html.
    Description: ATSAS is a comprehensive software suite for the processing, visualization, analysis and modelling of small‐angle scattering data. This article describes developments in the ATSAS 3.0 release, including new programs for data simulation and for the structural modelling of lipids, nucleic acids and polydisperse systems. image
    Keywords: 548 ; small‐angle scattering ; data analysis ; biological macromolecules ; structural modelling ; ATSAS
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    XGANDALF – extended gradient descent algorithm for lattice finding (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Serial crystallography records still diffraction patterns from single, randomly oriented crystals, then merges data from hundreds or thousands of them to form a complete data set. To process the data, the diffraction patterns must first be indexed, equivalent to determining the orientation of each crystal. A novel automatic indexing algorithm is presented, which in tests usually gives significantly higher indexing rates than alternative programs currently available for this task. The algorithm does not require prior knowledge of the lattice parameters but can make use of that information if provided, and also allows indexing of diffraction patterns generated by several crystals in the beam. Cases with a small number of Bragg spots per pattern appear to particularly benefit from the new approach. The algorithm has been implemented and optimized for fast execution, making it suitable for real‐time feedback during serial crystallography experiments. It is implemented in an open‐source C++ library and distributed under the LGPLv3 licence. An interface to it has been added to the CrystFEL software suite.
    Description: A description and evaluation are given of XGANDALF, extended gradient descent algorithm for lattice finding, an algorithm developed for fast and accurate indexing of snapshot diffraction patterns. image
    Keywords: 548 ; indexing ; XGANDALF ; CrystFEL ; multiple lattices ; serial crystallography
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    pinkIndexer – a universal indexer for pink‐beam X‐ray and electron diffraction snapshots (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink‐beam X‐ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit‐cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink‐beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi‐monochromatic X‐rays and with electrons the algorithm indexed more patterns than other programs tested.
    Description: pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink‐beam X‐rays, monochromatic X‐rays and electrons, is described and its use evaluated. image
    Keywords: 548 ; indexing ; pinkIndexer ; CrystFEL ; pink X‐ray beam ; serial electron diffraction
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    Crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-17
    Description: CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal‐binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine‐dependent inhibitor compounds.
    Description: The covalent modification of human CRM1 by 2‐mercaptoethanol interferes with the characterization of cysteine‐dependent inhibitor compounds. image
    Keywords: 548 ; nuclear export ; cancer ; exportin 1 ; cysteine modification
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    Staircase array of inclined refractive multi‐lenses for large field of view pixel super‐resolution scanning transmission hard X‐ray microscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: Owing to the development of X‐ray focusing optics during the past decades, synchrotron‐based X‐ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X‐ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster‐scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi‐lenses (RMLs), fabricated by deep X‐ray lithography and electroplating to generate a large number of long X‐ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X‐rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X‐ray line foci were generated with a length in the centimetre range and constant intervals in the sub‐micrometre range. The capability of this new X‐ray focusing device was first confirmed using ray‐tracing simulations and then using synchrotron radiation at BL20B2 of SPring‐8, Japan. Taking account of the fact that the refractive lens is effective for focusing high‐energy X‐rays, the experiment was performed with 35 keV X‐rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy (PSR‐STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR‐STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super‐resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.
    Description: A new X‐ray focusing device generates hundreds of thousands of line foci, periodically spaced in the sub‐micrometre range, with centimetre length. It enables to achieve large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy. image
    Keywords: 502.82 ; inclined refractive X‐ray multi‐lens array ; pixel super‐resolution ; scanning transmission hard X‐ray microscopy ; deep X‐ray lithography and electroplating
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    A new concept for temporal gating of synchrotron X‐ray pulses (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-02
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of 〉30% and 10−5, respectively. The full efficiency of the pulse picker has not been reached yet due to a long‐range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented.
    Keywords: 548 ; synchrotron ; time‐resolved ; thermal deformation ; transient grating ; pulse picking
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    The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP at BESSY II (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-06-06
    Description: The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP for optical pump/X‐ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four‐circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non‐linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time‐resolution of 17 ps is achieved with the `low‐α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X‐ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time‐resolved detection of the diffracted hard X‐ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
    Description: The KMC‐3 XPP endstation of the synchrotron BESSY II is dedicated to time‐resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X‐ray diffraction with an accessible time range from 17 ps to several microseconds. image
    Keywords: 548 ; beamline instrumentation ; time‐resolved X‐ray diffraction ; optical excitation ; thermal transport ; ferroelectric switching
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    Disordered sodium alkoxides from powder data: crystal structures of sodium ethoxide, propoxide, butoxide and pentoxide, and some of their solvates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n‐propoxide (sodium n‐propanolate, NaOnPr), sodium n‐butoxide (sodium n‐butanolate, NaOnBu) and sodium n‐pentoxide (sodium n‐amylate, NaOnAm) were determined from powder X‐ray diffraction data. NaOEt crystallizes in space group P421m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space‐group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti‐PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n‐propoxide n‐propanol disolvate (NaOnPr·2nPrOH), sodium isopropoxide isopropanol pentasolvate (NaOiPr·5iPrOH) and sodium tert‐amylate tert‐amyl alcohol monosolvate (NaOtAm·tAmOH, tAm = 2‐methyl‐2‐butyl). Their crystal structures were determined by single‐crystal X‐ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen‐bond networks diverge widely among the solvate structures. The hydrogen‐bond topology of the iPrOH network in NaOiPr·5iPrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline iPrOH.
    Description: The crystal structures of NaOEt, NaOPr, NaOBu and NaOAm (Am = amyl = pentyl) were determined from powder data. These compounds crystallize in an anti‐PbO structure in the space groups P21m and P4/nmm. Additionally, solvates with the composition NaOEt·2EtOH, NaOPr·2PrOH, NaOiPr·5iPrOH and NaOtAm·tAmOH were synthesized, and their structures were determined from single crystals. They form interesting chain structures of different compositions and topologies. image
    Keywords: 548 ; sodium alkoxide ; powder data ; solvate ; isopropanol ; Bärnighausen tree ; PXRD
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    Small‐angle X‐ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-27
    Description: Small‐angle X‐ray scattering from GaN nanowires grown on Si(111) is measured in the grazing‐incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q−4. The intensity depends on the orientation of the side facets with respect to the incident X‐ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root‐mean‐square roughness of 0.9 nm, which is the height of just 3–4 atomic steps per micrometre‐long facet, already gives rise to a strong intensity reduction.
    Description: The intensity of small‐angle X‐ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre‐long side facet notably changes the intensity curves. image
    Keywords: 548 ; nanowires ; Porod's law ; facet truncation rods ; small‐angle X‐ray scattering ; SAXS ; grazing‐incidence small‐angle X‐ray scattering ; GISAXS
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    The accuracy of protein models automatically built into cryo‐EM maps with ARP/wARP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-06-28
    Description: Recent developments in cryogenic electron microscopy (cryo‐EM) have enabled structural studies of large macromolecular complexes at resolutions previously only attainable using macromolecular crystallography. Although a number of methods can already assist in de novo building of models into high‐resolution cryo‐EM maps, automated and reliable map interpretation remains a challenge. Presented here is a systematic study of the accuracy of models built into cryo‐EM maps using ARP/wARP. It is demonstrated that the local resolution is a good indicator of map interpretability, and for the majority of the test cases ARP/wARP correctly builds 90% of main‐chain fragments in regions where the local resolution is 4.0 Å or better. It is also demonstrated that the coordinate accuracy for models built into cryo‐EM maps is comparable to that of X‐ray crystallographic models at similar local cryo‐EM and crystallographic resolutions. The model accuracy also correlates with the refined atomic displacement parameters.
    Keywords: 548 ; ARP/wARP ; model building ; cryo‐EM ; model accuracy ; sequence assignment
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    Synthesis, crystal structure and structure–property relations of strontium orthocarbonate, Sr2CO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-06-05
    Description: Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
    Description: A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image
    Keywords: 548 ; orthocarbonates ; crystal structure ; single‐crystal X‐ray diffraction ; high pressure ; Sr2CO4
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  • 72
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    Anomalous SAXS at P12 beamline EMBL Hamburg: instrumentation and applications (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-28
    Description: Small‐angle X‐ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element‐specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X‐rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
    Keywords: 548 ; ASAXS ; biological SAXS ; metalloproteins ; gold nanoparticles ; anomalous scattering ; beamline development
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  • 73
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    Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc21 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-27
    Description: Binary III–V nitrides such as AlN, GaN and InN in the wurtzite‐type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower‐symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non‐existence of compounds crystallizing in Pmc21, formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 74
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    Comparison and evaluation of pair distribution functions, using a similarity measure based on cross‐correlation functions (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-20
    Description: An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross‐correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross‐correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical Rwp values as representative of the comparison based on pointwise differences as well as with the Pearson product‐moment correlation coefficient, using polymorph IV of barbituric acid as an example.
    Description: A novel approach to the quantification of the agreement between pair distribution functions by a similarity measure based on cross‐correlation functions is introduced and evaluated. image
    Keywords: 548 ; pair distribution functions ; similarity measures ; total scattering techniques ; cross‐correlation functions ; R values
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  • 75
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    Novel experimental setup for megahertz X‐ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser (EuXFEL) (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The high‐precision X‐ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X‐ray Free‐Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X‐ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X‐ray heating and diffraction of Bi under pressure, obtained using 20 fs X‐ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.
    Description: The high‐precision X‐ray diffraction (XRD) setup for work with diamond anvil cells (DACs) in Interaction Chamber 2 of the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser is described. image
    Keywords: 548 ; diamond anvil cells ; X‐ray free‐electron lasers ; high‐precision X‐ray diffraction ; finite element modeling
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  • 76
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    The anisotropy in the optical constants of quartz crystals for soft X‐rays (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from orientation‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed. The anisotropy in the optical constants reconstructed from these data is also confirmed by ab initio Bethe–Salpeter equation calculations for the O K edge. This new experimental data set expands the existing literature data for quartz crystal optical constants significantly, particularly in the near‐edge regions.
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from polarization‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. The reconstructed anisotropy in the optical constants is also confirmed by ab initio Bethe–Salpeter equation calculations of the O K edge. image
    Keywords: 548 ; optical constants ; quartz ; anisotropy ; soft X‐ray reflectometry
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  • 77
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    Unravelling the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ mixed ionic electronic conductors (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-05
    Description: Mixed ionic electronic conducting ceramics Nd6−yWO12−δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost‐efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6−yWO12−δ, the ionic/electronic transport mechanism in Nd6−yWO12−δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12−δ and molybdenum‐substituted Nd5.7W0.75Mo0.25O12−δ prepared by the citrate complexation route. High‐resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit‐cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4a and 48h and is evenly distributed, in contrast with La6−yWO12−δ. X‐ray absorption spectroscopy as a function of partial pressure pO2 in the near‐edge regions excludes oxidation state changes of Nd (Nd3+) and W (W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo‐substituted Nd6−yWO12−δ is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.
    Description: The crystal structures of non‐substituted and Mo‐substituted neodymium tungstates are described in detail through neutron diffraction and high‐resolution X‐ray diffraction. Combined X‐ray and neutron diffraction refinements and electron probe micro‐analysis were employed to locate Mo atoms in the crystal structure of Nd6−yW1−zMozO12−δ (z = 0, 0.25), while X‐ray absorption spectroscopy in the near‐edge regions confirmed no changes in the oxidation states of Nd and W.
    Keywords: 548 ; powder diffraction ; mixed conductors ; X‐ray absorption spectroscopy (XAS) ; Nd6−yWO12−δ
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  • 78
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    High‐temperature treatments of niobium under high vacuum, dilute air‐ and nitrogen‐atmospheres as investigated by in situ X‐ray absorption spectroscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: Niobium metal foils were heat‐treated at 900°C under different conditions and in situ investigated with time‐resolved X‐ray absorption fine‐structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high‐vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X‐ray absorption fine‐structure data acquired during treatments in dilute air atmospheres (10−5 mbar to 10−3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre‐conditioning of the studied Nb material for one hour under high‐vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.
    Keywords: 548 ; in situ EXAFS ; high temperature ; time‐resolved EXAFS ; niobium
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  • 79
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    Pressure‐induced Pb–Pb bonding and phase transition in Pb2SnO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.
    Description: The structure of Pb2SnO4 is found to strongly distort on compression and a structural phase transition with a change of space group from Pbam to Pnam occurs at ∼11 GPa. Our complementary DFT‐based calculations show that at ambient conditions, the channels in the structure host the stereochemically active Pb 6s2 lone electron pairs which form bonds between the Pb2+ ions with increasing pressure. image
    Keywords: 548 ; lead stannate (Pb2SnO4) ; density functional theory ; high‐pressure X‐ray diffraction ; pressure‐induced phase transition ; insulator–semiconductor transition
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  • 80
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    A discussion on `Domain formation and phase transitions in the wurtzite‐based heterovalent ternaries: a Landau theory analysis' (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Heterovalent ternary nitrides are considered one of the promising classes of materials for photovoltaics, combining attractive physical properties with low toxicity and element abundance. One of the front‐runner systems under consideration is ZnSnN2. Although it is nominally a ternary compound, no clear crystallographic evidence for cation ordering has been observed so far. An attempt to elucidate this discrepancy [Quayle (2020). Acta Cryst. A76, 410–420] was the trigger for an intensive discussion between the authors, and an agreement was reached to elaborate on some points in order to set things in perspective. Rather than using a conventional comment–answer scheme, this is published in the form of a joint discussion to celebrate constructive criticism and collegiality.
    Description: A scientific exchange on an earlier paper [Quayle (2020). Acta Cryst. A76, 410–420] has led to the clarification of some of the points. image
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 81
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    X‐SPEC: a 70 eV to 15 keV undulator beamline for X‐ray and electron spectroscopies (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: X‐SPEC is a high‐flux spectroscopy beamline at the KIT (Karlsruhe Institute of Technology) Synchrotron for electron and X‐ray spectroscopy featuring a wide photon energy range. The beamline is equipped with a permanent magnet undulator with two magnetic structures of different period lengths, a focusing variable‐line‐space plane‐grating monochromator, a double‐crystal monochromator and three Kirkpatrick–Baez mirror pairs. By selectively moving these elements in or out of the beam, X‐SPEC is capable of covering an energy range from 70 eV up to 15 keV. The flux of the beamline is maximized by optimizing the magnetic design of the undulator, minimizing the number of optical elements and optimizing their parameters. The beam can be focused into two experimental stations while maintaining the same spot position throughout the entire energy range. The first experimental station is optimized for measuring solid samples under ultra‐high‐vacuum conditions, while the second experimental station allows in situ and operando studies under ambient conditions. Measurement techniques include X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS).
    Description: X‐SPEC is a high‐flux undulator beamline for electron and X‐ray spectroscopy with an energy range from 70 eV to 15 keV. It offers X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS) for in vacuo, in situ and operando sample environments. image
    Keywords: 548 ; undulator beamline ; soft X‐ray ; tender X‐ray ; hard X‐ray ; in situ ; operando ; HAXPES ; RIXS ; XAS ; XES
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  • 82
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    Structure determination of organic compounds by a fit to the pair distribution function from scratch without prior indexing (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF‐Global‐Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross‐correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF‐Global‐Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF‐Global‐Fit is in excellent agreement with the published crystal structure data.
    Keywords: 548 ; pair distribution function analysis ; structure determination ; total scattering technique ; similarity measures ; PDF‐Global‐Fit
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  • 83
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    Structural basis of chitin utilization by a GH20 β‐N‐acetylglucosaminidase from Vibrio campbellii strain ATCC BAA‐1116 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-01
    Description: Vibrio species play a crucial role in maintaining the carbon and nitrogen balance between the oceans and the land through their ability to employ chitin as a sole source of energy. This study describes the structural basis for the action of the GH20 β‐N‐acetylglucosaminidase (VhGlcNAcase) in chitin metabolism by Vibrio campbellii (formerly V. harveyi) strain ATCC BAA‐1116. Crystal structures of wild‐type VhGlcNAcase in the absence and presence of the sugar ligand, and of the unliganded D437A mutant, were determined. VhGlcNAcase contains three distinct domains: an N‐terminal carbohydrate‐binding domain linked to a small α+β domain and a C‐terminal (β/α)8 catalytic domain. The active site of VhGlcNAcase has a narrow, shallow pocket that is suitable for accommodating a small chitooligosaccharide. VhGlcNAcase is a monomeric enzyme of 74 kDa, but its crystal structures show two molecules of enzyme per asymmetric unit, in which Gln16 at the dimeric interface of the first molecule partially blocks the entrance to the active site of the neighboring molecule. The GlcNAc unit observed in subsite −1 makes exclusive hydrogen bonds to the conserved residues Arg274, Tyr530, Asp532 and Glu584, while Trp487, Trp546, Trp582 and Trp505 form a hydrophobic wall around the −1 GlcNAc. The catalytic mutants D437A/N and E438A/Q exhibited a drastic loss of GlcNAcase activity, confirming the catalytic role of the acidic pair (Asp437–Glu438).
    Description: Crystal structures of a GH20 β‐N‐acetylglucosaminidase from V. campbellii reveal substrate specificity in chitin utilization.
    Keywords: 577.14 ; GH20 β‐N‐acetylglucosaminidase ; chitin recycling ; Vibrio spp ; marine bacteria
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  • 84
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    Resolution of a bent‐crystal spectrometer for X‐ray free‐electron laser pulses: diamond versus silicon (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: The resolution function of a spectrometer based on a strongly bent single crystal (bending radius of 10 cm or less) is evaluated. It is shown that the resolution is controlled by two parameters: (i) the ratio of the lattice spacing of the chosen reflection to the crystal thickness and (ii) a single parameter comprising crystal thickness, its bending radius, distance to a detector, and anisotropic elastic constants of the chosen crystal. The results allow the optimization of the parameters of bent‐crystal spectrometers for the hard X‐ray free‐electron laser sources.
    Description: The resolution function of a bent‐crystal spectrometer for pulses of an X‐ray free‐electron laser is evaluated. Under appropriate conditions, the energy resolution reaches the ratio of the lattice spacing to the crystal thickness. image
    Keywords: 548 ; X‐ray free‐electron lasers ; X‐ray spectroscopy ; bent crystals ; diamond crystal optics ; femtosecond X‐ray diffraction
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  • 85
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    Separation of the inelastic and elastic scattering in time‐of‐flight mode on the pinhole small‐angle neutron scattering diffractometer KWS‐2 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: To study and control the incoherent inelastic background in small‐angle neutron scattering, which makes a significant contribution to the detected scattering from hydrocarbon systems, the KWS‐2 small‐angle neutron scattering diffractometer operated by the Jülich Centre for Neutron Science (JCNS) at Heinz‐Maier Leibnitz Zentrum (MLZ), Garching, Germany, was equipped with a secondary single‐disc chopper that is placed in front of the sample stage. This makes it possible to record in time‐of‐flight mode the scattered neutrons in the high‐Q regime of the instrument (i.e. short incoming wavelengths and detection distances) and to discard the inelastic component from the measured data. Examples of measurements on different materials routinely used as standard samples, sample containers and solvents in the experiments at KWS‐2 are presented. When only the elastic region of the spectrum is used in the data‐reduction procedure, a decrease of up to two times in the incoherent background of the experimentally measured scattering cross section may be obtained. The proof of principle is demonstrated on a solution of bovine serum albumin in D2O.
    Description: A new chopper has been installed at the sample position in front of the sample stage at the KWS‐2 small‐angle neutron‐scattering diffractometer of the Jülich Centre for Neutron Science. The pulsed beam and the time‐of‐flight data acquisition enable the separation of elastic and inelastic scattering from hydrogenous samples.
    Keywords: 548 ; TOF‐SANS ; incoherent neutron scattering ; inelastic neutron scattering ; hydrocarbon systems
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  • 86
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    Czochralski growth of mixed cubic sesquioxide crystals in the ternary system Lu2O3–Sc2O3–Y2O3 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: Cubic rare‐earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large‐size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range.
    Description: The phase diagram of the ternary system Lu2O3–Sc2O3–Y2O3 is investigated and compositions with melting points below 2200°C are found. This allows for the first successful growth of the mixed cubic sesquioxide crystal (Er0.07Sc0.50Y0.43)2O3 by the Czochralski method from an iridium crucible. image
    Keywords: 548 ; crystal growth ; optical materials ; phase diagrams ; melting points ; rare earth sesquioxides
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