593 research outputs found
Superconductivity and non-metallicity induced by doping the topological insulators Bi2Se3 and Bi2Te3
We show that by Ca-doping the Bi2Se3 topological insulator, the Fermi level
can be fine tuned to fall inside the band gap and therefore suppress the bulk
conductivity. Non-metallic Bi2Se3 crystals are obtained. On the other hand, the
Bi2Se3 topological insulator can also be induced to become a bulk
superconductor, with Tc ~ 3.8 K, by copper intercalation in the van der Waals
gaps between the Bi2Se3 layers. Likewise, an as-grown crystal of metallic
Bi2Te3 can be turned into a non-metallic crystal by slight variation of the Te
content. The Bi2Te3 topological insulator shows small amounts of
superconductivity with Tc ~ 5.5 K when reacted with Pd to form materials of the
type PdxBi2Te3
Acute effects of ambient nitrogen oxides and interactions with temperature on cardiovascular mortality in Shenzhen, China
Background: Though inconsistent, acute effects of ambient nitrogen oxides on cardiovascular mortality have been reported. Whereas, interactive roles of temperature on their relationships and joint effects of different indicators of nitrogen oxides were less studied. This study aimed to extrapolate the independent roles of ambient nitrogen oxides and temperature interactions on cardiovascular mortality.Methods: Data on mortality, air pollutants, and meteorological factors in Shenzhen from 2013 to 2019 were collected. Three indicators including nitric oxide (NO), nitrogen dioxide (NO2), and nitrogen oxides (NOX) were studied. Adjusted generalized additive models (GAMs) were applied to analyse their associations with cardiovascular mortality in different groups.Results: The average daily concentrations of NO, NO2, and NOX were 11.7 mu g/m(3), 30.7 mu g/m(3), and 53.2 mu g/m(3), respectively. Significant associations were shown with each indicator. Cumulative effects of nitrogen oxides were more obvious than distributed lag effects. Males, population under 65 years old, and population with stroke related condition were more susceptible to nitrogen oxides. Adverse effects of nitrogen oxides were more significant at low temperature. Impacts of NO2 on cardiovascular mortality, and NO on stroke mortality were the most robust in the multi-pollutant models, whereas variations were shown in the other relationships.Conclusions: Low levels of nitrogen oxides showed acute and adverse impacts and the interactive roles of temperature on cardiovascular mortality. Cumulative effects were most significant and joint effects of nitrogen oxides required more attention. Population under 65 years old and population with stroke-related health condition were susceptible, especially days at lower temperature
Knotlike Cosmic Strings in The Early Universe
In this paper, the knotlike cosmic strings in the Riemann-Cartan space-time
of the early universe are discussed. It has been revealed that the cosmic
strings can just originate from the zero points of the complex scalar
quintessence field. In these strings we mainly study the knotlike
configurations. Based on the integral of Chern-Simons 3-form a topological
invariant for knotlike cosmic strings is constructed, and it is shown that this
invariant is just the total sum of all the self-linking and linking numbers of
the knots family. Furthermore, it is also pointed out that this invariant is
preserved in the branch processes during the evolution of cosmic strings
Observation of Two New N* Peaks in J/psi -> and Decays
The system in decays of is limited to be
isospin 1/2 by isospin conservation. This provides a big advantage in studying
compared with and experiments which mix
isospin 1/2 and 3/2 for the system. Using 58 million decays
collected with the Beijing Electron Positron Collider, more than 100 thousand
events are obtained. Besides two well known
peaks at 1500 MeV and 1670 MeV, there are two new, clear peaks in
the invariant mass spectrum around 1360 MeV and 2030 MeV. They are the
first direct observation of the peak and a long-sought "missing"
peak above 2 GeV in the invariant mass spectrum. A simple
Breit-Wigner fit gives the mass and width for the peak as MeV and MeV, and for the new peak above 2 GeV
as MeV and MeV, respectively
Carbonaceous nanomaterial reinforced Ti-6Al-4V matrix composites: Properties, interfacial structures and strengthening mechanisms
For conventional titanium matrix composites (TiMCs), there is always a trade-off issue between enhanced strength and ductility of these materials. In this study, we explore a new design methodology by reinforcing titanium alloy matrix with carbonaceous nanomaterials and investigate the mechanisms for achieving a good balance of their strength and ductility. The TiMCs were synthesized through a low-cost powder metallurgy route using pre-mixed Ti-6Al-4V (TC4) powders and various carbon based nanofillers, including graphite powders (GPs), graphene oxide nanosheets (GONs) and graphene nanoplates (GNPs), and were further rolled at a temperature of 1173 K with a deformation of 66.7%. Among these three types of carbon reinforcing sources, the GNPs are more easily reacted with TC4 matrix and form more contents of TiC phases after sintering owing to their larger amounts of defects than those of the GPs and GONs. TiC products are identified to play a bridging role for not only connecting the TC4 matrix but also forming coherent interfaces with the TC4 matrix, thus facilitating a strong interfacial bonding of the composites. The as-rolled GNPs/TC4 composites exhibit a 0.2% yield strength of 1146.36 MPa (with an elongation of ∼8.1%), which is 24.6%, 9.22% and 5.62% higher than those of pure TC4, GPs/TC4 and GONs/TC4 composites. The GNPs/TC4 nanocomposites show a better balance of strength and ductility than those of the other two types of nanocomposites. The synergetic strengthening mechanisms are identified to be Orowan strengthening effect, effective load transfer capability of GNPs, and in-situ formation of interfacial TiC structures, which provide optimum interfacial microstructures to achieve good mechanical properties of the TiMCs
Interface engineering of graphene/copper matrix composites decorated with tungsten carbide for enhanced physico-mechanical properties
For metal matrix composites (MMCs), introduction of low-dimensional nano-carbon materials (NCMs) into three dimensional metallic matrix is commonly applied to enhance mechanical and physical properties of metals and thus significantly extend their wide range applications. However, the interfaces between the NCMs and metal matrix are always a major issue for achieving the best enhancement effects. In this paper, we investigated interfacial structures of graphene nanoplates (GNPs) reinforced Cu matrix composites fabricated using a simple and industrially scalable strategy, through integration of interface engineering design methodology and a spark plasma sintering (SPS) process. We then systematically evaluated their physico-mechanical properties, interfacial characteristics and strengthening mechanisms. The in-situ formed WxCy nano-layers and carbide nanoparticles on the surfaces of GNPs and near the interfaces of Cu grains promote strong interfacial bonding and improves the cohesive strength of Cu based nanocomposites. The GNPs-W/Cu composites show a good balance between strength and electrical conductivity. Their 0.2% yield strength and ultimate tensile strength have been improved up to 239.13% (112.73%) and 197.76% (72.51%), respectively, when compared with those of pure copper (or GNPs/Cu composites). Electrical conductivity of GNPs-W/Cu composites shows no apparent changes after the addition of the GNPs. The dislocation strengthening, refinement strengthening and load transfer strengthening were achieved simultaneously through the engineered interfaces in GNPs-W/Cu matrix composites. This work has provided a new strategy to fabricate high-performance NCMs enhanced MMCs by using the interface engineering methodology
Search for Invisible Decays of and in and
Using a data sample of decays collected with the BES
II detector at the BEPC, searches for invisible decays of and
in to and are performed.
The signals, which are reconstructed in final states, are used
to tag the and decays. No signals are found for the
invisible decays of either or , and upper limits at the 90%
confidence level are determined to be for the ratio
and for . These are the first
searches for and decays into invisible final states.Comment: 5 pages, 4 figures; Added references, Corrected typo
Experimental NMR Realization of A Generalized Quantum Search Algorithm
A generalized quantum search algorithm, where phase inversions for the marked
state and the prepared state are replaced by phase rotations, is
realized in a 2-qubit NMR heteronuclear system. The quantum algorithm searches
a marked state with a smaller step compared to standard Grover algorithm. Phase
matching requirement in quantum searching is demonstrated by comparing it with
another generalized algorithm where the two phase rotations are and
respectively. Pulse sequences which include non 90 degree pulses are
given.Comment: 12 pages, 2 figures, accepted for publication in Plysics Letters
Colletotrichum species associated with anthracnose of Pyrus spp. in China
Colletotrichum species are plant pathogens, saprobes, and endophytes on a range of economically important hosts. However, the species occurring on pear remain largely unresolved. To determine the morphology, phylogeny and biology of Colletotrichum species associated with Pyrus plants, a total of 295 samples were collected from cultivated pear species (including P. pyrifolia, P. bretschneideri, and P. communis) from seven major pear-cultivation provinces in China. The pear leaves and fruits affected by anthracnose were sampled and subjected to fungus isolation, resulting in a total of 488 Colletotrichum isolates. Phylogenetic analyses based on six loci (ACT, TUB2, CAL, CHS-1, GAPDH, and ITS) coupled with morphology of 90 representative isolates revealed that they belong to 10 known Colletotrichum species, including C. aenigma, C. citricola, C. conoides, C. fioriniae, C. fructicola, C. gloeosporioides, C. karstii, C. plurivorum, C. siamense, C. wuxiense, and two novel species, described here as C. jinshuiense and C. pyrifoliae. Of these, C. fructicola was the most dominant, occurring on P. pyrifolia and P. bretschneideri in all surveyed provinces except in Shandong, where C. siamense was dominant. In contrast, only C. siamense and C. fioriniae were isolated from P. communis, with the former being dominant. In order to prove Koch's postulates, pathogenicity tests on pear leaves and fruits revealed a broad diversity in pathogenicity and aggressiveness among the species and isolates, of which C. citricola, C. jinshuiense, C. pyrifoliae, and C. conoides appeared to be organ-specific on either leaves or fruits. This study also represents the first reports of C. citricola, C. conoides, C. karstii, C. plurivorum, C. siamense, and C. wuxiense causing anthracnose on pear.Earmarked Fundhttps://www.ingentaconnect.com/content/nhn/pimjhj2020BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
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