912 research outputs found
Different characteristics of char and soot in the atmosphere and their ratio as an indicator for source identification in Xi'an, China
2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Solar influenced late Holocene temperature changes on the northern Tibetan Plateau
Considerable efforts have been made to extend temperature records beyond the instrumental period through proxy reconstructions, in order to further understand the mechanisms of past climate variability. Yet, the global coverage of existing temperature records is still limited, especially for some key regions like the Tibetan Plateau and for earlier times including the Medieval Warm Period (MWP). Here we present decadally-resolved, alkenone-based, temperature records from two lakes on the northern Tibetan Plateau. Characterized by marked temperature variability, our records provide evidence that temperatures during the MWP were slightly higher than the modern period in this region. Further, our temperature reconstructions, within age uncertainty, can be well correlated with solar irradiance changes, suggesting a possible link between solar forcing and natural climate variability, at least on the northern Tibetan Plateau. Š 2013 The Author(s).published_or_final_versio
Radio-loud Quasars above Redshift 4: VLBI Imaging of an Extended Sample
High-redshift radio sources provide plentiful opportunities for studying the
formation and evolution of early galaxies and supermassive black holes.
However, the number of known radio-loud active galactic nuclei (AGN) above
redshift 4 is rather limited. At high redshifts, it appears that blazars, with
relativistically beamed jets pointing towards the observer, are in majority
compared to radio-loud sources with jets misaligned with respect to the line of
sight. To find more of these misaligned AGN, milliarcsec-scale imaging studies
carried out with very long baseline interferometry (VLBI) are needed, as they
allow us to distinguish between compact core--jet radio sources and those with
more extended emission. Previous high-resolution VLBI studies revealed that
some of the radio sources among blazar candidates in fact show unbeamed radio
emission on milliarcsecond scales. The most accurate optical coordinates
determined with the Gaia astrometric space mission are also useful in the
classification process. Here, we report on dual-frequency imaging observations
of 13 high-redshift (4 < z < 4.5) quasars at 1.7 and 5 GHz with the European
VLBI Network. This sample increases the number of z>4 radio sources for which
VLBI observations are available by about a quarter. Using structural and
physical properties, such as radio morphology, spectral index, variability,
brightness temperature, as well as optical coordinates, we identified six
blazars and six misaligned radio AGNs, with the remaining one tentatively
identified as blazar
Characterization of airborne carbonate over a site near Asian dust source regions during spring 2002 and its climatic and environmental significance
Author name used in this publication: Lee, S. C.2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Why do dogs (Canis familiaris) select the empty container in an observational learning task?
Many argue that dogs show unique susceptibility to human communicative signals that make them suitable for being engaged in complex co-operation with humans. It has also been revealed that socially provided information is particularly effective in influencing the behaviour of dogs even when the humanâs action demonstration conveys inefficient or mistaken solution of task. It is unclear, however, how the communicative nature of the demonstration context and the presence of the human demonstrator affect the dogsâ object-choice behaviour in observational learning situations. In order to unfold the effects of these factors, 76 adult pet dogs could observe a communicative or a non-communicative demonstration in which the human retrieved a tennis ball from under an opaque container while manipulating another distant and obviously empty (transparent) one. Subjects were then allowed to choose either in the presence of the demonstrator or after she left the room. Results showed a significant main effect of the demonstration context (presence or absence of the humanâs communicative signals), and we also found some evidence for the response-modifying effect of the presence of the human demonstrator during the dogsâ choice. That is, dogs predominantly chose the baited container, but if the demonstration context was communicative and the human was present during the dogsâ choice, subjectsâ tendency to select the baited container has been reduced. In agreement with the studies showing sensitivity to humanâs communicative signals in dogs, these findings point to a special form of social influence in observational learning situations when it comes to learning about causally opaque and less efficient (compared to what comes natural to the dog) action demonstrations
Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China
Author name used in this publication: Lee, S. C.2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Loess plateau storage of northeastern Tibetan plateau-derived Yellow River sediment
Marine accumulations of terrigenous sediment are widely assumed to accurately record climatic- and tectonic-controlled mountain denudation and play an important role in understanding late Cenozoic mountain uplift and global cooling. Underpinning this is the assumption that the majority of sediment eroded from hinterland orogenic belts is transported to and ultimately stored in marine basins with little lag between erosion and deposition. Here we use a detailed and multi-technique sedimentary provenance dataset from the Yellow River to show that substantial amounts of sediment eroded from Northeast Tibet and carried by the riverâs upper reach are stored in the Chinese Loess Plateau and the western Mu Us desert. This finding revises our understanding of the origin of the Chinese Loess Plateau and provides a potential solution for mismatches between late Cenozoic terrestrial sedimentation and marine geochemistry records, as well as between global CO2 and erosion records
Biophysical and electrochemical studies of protein-nucleic acid interactions
This review is devoted to biophysical and electrochemical methods used for studying protein-nucleic acid (NA) interactions. The importance of NA structure and protein-NA recognition for essential cellular processes, such as replication or transcription, is discussed to provide background for description of a range of biophysical chemistry methods that are applied to study a wide scope of protein-DNA and protein-RNA complexes. These techniques employ different detection principles with specific advantages and limitations and are often combined as mutually complementary approaches to provide a complete description of the interactions. Electrochemical methods have proven to be of great utility in such studies because they provide sensitive measurements and can be combined with other approaches that facilitate the protein-NA interactions. Recent applications of electrochemical methods in studies of protein-NA interactions are discussed in detail
Effects of deposition time and post-deposition annealing on the physical and chemical properties of electrodeposited CdS thin films for solar cell application
CdS thin films were cathodically electrodeposited by means of a two-electrode deposition system
for different durations. The films were characterised for their structural, optical, morphological
and compositional properties using x-ray diffraction (XRD), spectrophotometry, scanning
electron microscopy (SEM) and energy dispersive x-ray (EDX) respectively. The results obtained
show that the physical and chemical properties of these films are significantly influenced by the
deposition time and post-deposition annealing. This influence manifests more in the as-deposited
materials than in the annealed ones. XRD results show that the crystallite sizes of the different
films are in the range (9.4 â 65.8) nm and (16.4 â 66.0) nm in the as-deposited and annealed
forms respectively. Optical measurements show that the absorption coefficients are in the range
(2.7Ă104 â 6.7Ă104) cm-1 and (4.3Ă104 â 7.2Ă104) cm-1 respectively for as-deposited and annealed
films. The refractive index is in the range (2.40 â 2.60) for as-deposited films and come to the
value of 2.37 after annealing. The extinction coefficient varies in the range (0.1 â 0.3) in asdeposited
films and becomes 0.1 in annealed films. The estimated energy bandgap of the films is
in the range (2.48 â 2.50) eV for as-deposited films and becomes 2.42 eV for all annealed films.
EDX results show that all the films are S-rich in chemical composition with fairly uniform Cd/S
ratio after annealing. The results show that annealing improves the qualities of the films and
deposition time can be used to control the film thickness.
Keywords: Electrodeposition; two-electrode system; CdS; annealing; deposition time; thin-film
Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, 87Sr/86Sr) data from Kangankunde, Malawi
This is the final version of the article. Available from Springer Verlag via the DOI in this record.Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and 87Sr/86Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8â15 wt% REE2O3, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The 87Sr/86Sr values (0.70302â0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C (δ18O + 3 to + 5â°VSMOW and δ13C â 3.5 to â 3.2â°VPDB). In contrast, dolomite in the same samples has similar δ13C values but much higher δ18O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar δ18O and 87Sr/86Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: δ18O + 7.7 to + 10.3â° and δ13C â5.2 to â6.0â°; 87Sr/86Sr 0.70296â0.70298) is not directly linked with the REE mineralisation.This project was funded by the UK Natural Environment Research Council (NERC) SoS RARE project (NE/M011429/1) and by NIGL (NERC Isotope Geoscience Laboratory) Project number 20135
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