286 research outputs found

    Comparative aspects of pegmatitic and pneumatolytic evolution in Cornish granites

    Get PDF
    Imperial Users onl

    Raman fingerprint of semi-metal WTe2 from bulk to monolayer

    Get PDF
    Tungsten ditelluride (WTe2), a layered transition-metal dichalcogenide (TMD), has recently demonstrated an extremely large magnetoresistance effect, which is unique among TMDs. This fascinating feature seems to be correlated with its special electronic structure. Here, we report the observation of 6 Raman peaks corresponding to the A_2^4, A_1^9, A_1^8, A_1^6, A_1^5 and A_1^2 phonons, from the 33 Raman-active modes predicted for WTe2. This provides direct evidence to distinguish the space group of WTe2 from that of other TMDs. Moreover, the Raman evolution of WTe2 from bulk to monolayer is clearly revealed. It is interesting to find that the A_2^4 mode, centered at ~109.8 cm-1, is forbidden in a monolayer, which may be attributable to the transition of the point group from C2v (bulk) to C2h (monolayer). Our work characterizes all observed Raman peaks in the bulk and few-layer samples and provides a route to study the physical properties of two-dimensional WTe2.Comment: 19 pages, 4 figures and 2 table

    Postglacial sea-level change: novel insights from physical and statistical modelling

    Get PDF
    Developing accurate projections of future sea-level change is a key challenge for the entire science community under the current warming climate. Due to the fact that modern instrumental sea-level observations are only available since the 19-20th century, sea-level projections based on them can only capture short-term effects, leaving physical processes that dominate over longer timescales underestimated. Therefore, an essential step towards accurate and robust long-term sea-level projections is to investigate the physical processes that impact the spatio-temporal evolution of sea-level change over centennial to millennial timescales. Due to sometimes scarce and often noisy palaeo sea-level observations, mechanisms of sea-level change over geological timescales are still not well-understood, with many outstanding questions to be resolved. This thesis develops novel physical and statistical models to better understand the mechanisms behind postglacial sea-level change. Specifically, this thesis focuses on three outstanding problems that are not only important in postglacial sea-level change but also in understanding past ice sheet dynamics and palaeoclimate change. Firstly, a statistical framework is developed to invert the sources of meltwater pulse 1A, the largest and most rapid global sea-level rise event of the last deglaciation, with sophisticated treatment of uncertainties associated with sea-level reconstructions and geophysical modelling. The results suggest there were contributions from North America, 12.0 m (5.6-15.4 m; 95% probability), Scandinavia, 4.6 m (3.2-6.4 m), and Antarctica, 1.3 m (0-5.9 m), giving a total global mean sea-level rise of 17.9 m (15.7-20.2 m) in 500 years. Secondly, the missing ice problem (distinctive imbalance between observed global mean sea-level rise and the reconstructed amount of ice-sheet melt) is revisited by including an extra physical process (sediment isostatic adjustment, SIA) which has not been considered in this problem before. In particular, this thesis investigates the impact of SIA on local RSL variation across the Great Barrier Reef (GBR), the world's largest mixed carbonate-siliciclastic sediment system. Based on a Bayesian calibration method, SIA can contribute up to 1.1 m relative sea-level rise in the outer shelf of the southern central GBR from 28 ka to present. Because the SIA-induced RSL rise is unrelated to ice mass loss, failing to correct for this signal will lead to systematic overestimation of grounded ice volume. Therefore, incorporating the SIA process will reduce the global grounded ice volume estimate for the Last Glacial Maximum (LGM), which can help to mitigate the missing ice problem. Lastly, robust global barystatic sea-level maps with minimum dependency on the detailed geometry of past ice sheet change are reconstructed. Estimating such maps requires physical simulation of relative sea-level corresponding to thousands of different ice histories, which is computationally prohibitive. To improve this situation, this thesis develops a statistical emulator which can mimic the behaviour of a physics-based model and is computationally much cheaper to evaluate. The results highlight the Seychelles as an exceptionally good place to map barystatic sea level throughout the last deglaciation because RSL at this location only slightly departs from global barystatic sea level, with minor dependency on the assumed ice history. Together, these physical and statistical models present powerful tools to yield novel insights into postglacial sea-level change mechanisms and hence they have the potential to yield more robust, accurate and trust-worthy sea-level change projections

    Compressing Context to Enhance Inference Efficiency of Large Language Models

    Full text link
    Large language models (LLMs) achieved remarkable performance across various tasks. However, they face challenges in managing long documents and extended conversations, due to significantly increased computational requirements, both in memory and inference time, and potential context truncation when the input exceeds the LLM's fixed context length. This paper proposes a method called Selective Context that enhances the inference efficiency of LLMs by identifying and pruning redundancy in the input context to make the input more compact. We test our approach using common data sources requiring long context processing: arXiv papers, news articles, and long conversations, on tasks of summarisation, question answering, and response generation. Experimental results show that Selective Context significantly reduces memory cost and decreases generation latency while maintaining comparable performance compared to that achieved when full context is used. Specifically, we achieve a 50\% reduction in context cost, resulting in a 36\% reduction in inference memory usage and a 32\% reduction in inference time, while observing only a minor drop of .023 in BERTscore and .038 in faithfulness on four downstream applications, indicating that our method strikes a good balance between efficiency and performance.Comment: EMNLP 2023. arXiv admin note: substantial text overlap with arXiv:2304.12102; text overlap with arXiv:2303.11076 by other author

    Metaphor Detection via Explicit Basic Meanings Modelling

    Full text link
    One noticeable trend in metaphor detection is the embrace of linguistic theories such as the metaphor identification procedure (MIP) for model architecture design. While MIP clearly defines that the metaphoricity of a lexical unit is determined based on the contrast between its \textit{contextual meaning} and its \textit{basic meaning}, existing work does not strictly follow this principle, typically using the \textit{aggregated meaning} to approximate the basic meaning of target words. In this paper, we propose a novel metaphor detection method, which models the basic meaning of the word based on literal annotation from the training set, and then compares this with the contextual meaning in a target sentence to identify metaphors. Empirical results show that our method outperforms the state-of-the-art method significantly by 1.0\% in F1 score. Moreover, our performance even reaches the theoretical upper bound on the VUA18 benchmark for targets with basic annotations, which demonstrates the importance of modelling basic meanings for metaphor detection.Comment: ACL 202

    Taxonomic review of the Asian Trogloneta species (Araneae, Mysmenidae)

    Get PDF
    Five Trogloneta species from Southwest China and Japan are reviewed that two new combinations and a new synonymy are proposed in the current paper: T. nojimai (Ono, 2010), comb. n. is transferred from Mysmena, T. yunnanense (Song & Zhu, 1994), comb. n. (= T. denticocleari Lin & Li, 2008, syn. n.) is transferred from Pholcomma of the Theridiidae, T. speciosum Lin & Li, 2008, T. uncata Lin & Li, 2013, and T. yuensis Lin & Li, 2013. The female of T. yuensis is described for the first time. An identification key and diagnoses are provided for these species, as well as new photographs or illustrations of the genital organs and habitus of T. yuensis and T. yunnanense

    Inhibition of Bacterial Ammonia Oxidation by Organohydrazines in Soil Microcosms

    Get PDF
    Hydroxylamine oxidation by hydroxylamine oxidoreductase (HAO) is a key step for energy-yielding in support of the growth of ammonia-oxidizing bacteria (AOB). Organohydrazines have been shown to inactivate HAO from Nitrosomonas europaea, and may serve as selective inhibitors to differentiate bacterial from archaeal ammonia oxidation due to the absence of bacterial HAO gene homolog in known ammonia-oxidizing archaea (AOA). In this study, the effects of three organohydrazines on activity, abundance, and composition of AOB and AOA were evaluated in soil microcosms. The results indicate that phenylhydrazine and methylhydrazine at the concentration of 100 μmol g−1 dry weight soil completely suppressed the activity of soil nitrification. Denaturing gradient gel electrophoresis fingerprinting and sequencing analysis of bacterial ammonia monooxygenase subunit A gene (amoA) clearly demonstrated that nitrification activity change is well paralleled with the growth of Nitrosomonas europaea-like AOB in soil microcosms. No significant correlation between AOA community structure and nitrification activity was observed among all treatments during the incubation period, although incomplete inhibition of nitrification activity occurred in 2-hydroxyethylhydrazine-amended soil microcosms. These findings show that the HAO-targeted organohydrazines can effectively inhibit bacterial nitrification in soil, and the mechanism of organohydrazine affecting AOA remains unclear

    Phylogenetic placement of eight poorly known spiders of Microdipoena (Araneae, Mysmenidae), with descriptions of five new species

    Get PDF
    Ten species of the spider genus Microdipoena Banks, 1895 are reported from China, Laos, Indonesia, Georgia, and Seychelles. DNA sequences of the eight species are obtained to confirm their correct identification. The molecular phylogenetic analysis based on five gene fragments (16S, 18S, 28S, COI, and H3) were used to test the relationships and taxonomic placements of eight Microdipoena species, of which five species are documented as new to science: i.e., M. huisun sp. nov. (♀, China), M. lisu sp. nov. (♀, China), M. shenyang sp. nov. (♂♀, China), M. thatitou sp. nov. (♀, Laos), and M. zhulin sp. nov. (♂♀, China). Five known species are redescribed: M. elsae Saaristo, 1978 (♂♀, Seychelles), M. gongi (Yin, Peng & Bao, 2004) (♂♀, China), M. menglunensis (Lin & Li, 2008) (♂♀, China), M. jobi (Kraus, 1967) (♂♀, Georgia), and M. yinae (Lin & Li, 2013) (♂♀, China). All but M. menglunensis are diagnosed and illustrated. The family Mysmenidae is also the first recorded from Laos and Georgia
    corecore