239 research outputs found
Interaction of an electron gas with photoexcited electron-hole pairs in modulation-doped GaAs and CdTe quantum wells
The nature of the correlated electron gas and its response to photo-injected
electron-hole pairs in nominally undoped and modulation-doped multiple
quantum-well (MQW) structures was studied by experiment and theory, revealing a
new type of optically-active excitation, magnetoplasmons bound to a mobile
valence hole. These excitations are blue-shifted from the corresponding
transition of the isolated charged magnetoexciton X-. The observed blue-shift
of X- is larger than that of two-electron negative donor D-, in agreement with
theoretical predictions.Comment: 4 pages, 3 figures, EP2DS-14 manuscript, to be published in Physica
Flux-lattice melting in two-dimensional disordered superconductors
The flux line lattice melting transition in two-dimensional pure and
disordered superconductors is studied by a Monte Carlo simulation using the
lowest Landau level approximation and quasi-periodic boundary condition on a
plane. The position of the melting line was determined from the diffraction
pattern of the superconducting order parameter. In the clean case we confirmed
the results from earlier studies which show the existence of a quasi-long range
ordered vortex lattice at low temperatures. Adding frozen disorder to the
system the melting transition line is shifted to slightly lower fields. The
correlations of the order parameter for translational long range order of the
vortex positions seem to decay slightly faster than a power law (in agreement
with the theory of Carpentier and Le Doussal) although a simple power law decay
cannot be excluded. The corresponding positional glass correlation function
decays as a power law establishing the existence of a quasi-long range ordered
positional glass formed by the vortices. The correlation function
characterizing a phase coherent vortex glass decays however exponentially
ruling out the possible existence of a phase coherent vortex glass phase.Comment: 12 pages, 21 figures, final version to appear in Phys. Rev.
A highly divergent Encephalomyocarditis virus isolated from nonhuman primates in Singapore
10.1186/1743-422X-10-248Virology Journal10
Urbanisation affects ecosystem functioning more than structure in tropical streams
Urbanisation poses a clear threat to tropical freshwater streams, yet fundamental knowledge gaps hinder our ability to effectively conserve stream biodiversity and preserve ecosystem functioning. Here, we studied the impact of urbanisation on structural and functional ecosystem responses in low-order streams in Singapore, a tropical city with a mosaic landscape of protected natural forests, managed buffer zones (between forest and open-country habitats), and built-up urban areas. We quantified an urbanisation gradient based on landscape, in-stream, and riparian conditions, and found an association between urbanisation and pollution-tolerant macroinvertebrates (e.g. freshwater snail and worm species) in litter bags. We also found greater macroinvertebrate abundance (mean individuals bag−1; forest: 30.3, buffer: 70.1, urban: 109.0) and richness (mean taxa bag−1; forest: 4.53, buffer: 4.75, urban: 7.50) in urban streams, but similar diversity across habitats. Higher levels of primary productivity (measured from algal accrual on ceramic tiles) and microbial decomposition (measured from litter-mass loss in mesh bags) at urban sites indicate rapid microbial activity at higher light, temperature, and nutrient levels. We found that urbanisation affected function 32% more than structure in the studied tropical streams, likely driven by greater algal growth in urban streams. These changes in ecological processes (i.e. ecosystem functioning) possibly lead to a loss of ecosystem services, which would negatively affect ecology, society, and economy. Our results point to possible management strategies (e.g. increasing vegetation density through buffer park creation) to reduce the impacts of urbanisation, restore vital ecosystem functions in tropical streams, and create habitat niches for native species
DNA metabarcoding unravels unknown diversity and distribution patterns of tropical freshwater invertebrates
Tropical freshwater invertebrate species are becoming extinct without being described, and effective conservation is hampered by a lack of taxonomic and distribution data. DNA metabarcoding is a promising tool for rapid biodiversity assessments that has never been applied to tropical freshwater invertebrates across large spatial and taxonomic scales. Here we use DNA metabarcoding to comprehensively assess the benthic freshwater invertebrate fauna of the Perak River basin, Malaysia. Specific objectives were to: (1) assess performance of two DNA metabarcoding protocols; (2) identify gaps in reference databases; (3) generate new data on species diversity and distribution; and (4) draw conclusions regarding the potential value of DNA metabarcoding in tropical freshwater conservation. Organisms were collected by hand and net at 34 sites and divided into small (retained in 0.5-mm but passing through 1-mm mesh) and large (retained in 1-mm mesh) fractions, and a 313-bp cytochrome c oxidase subunit I fragment amplified and sequenced using general Metazoa primers. Bioinformatic analysis resulted in 468 operational taxonomic units (~species) from 12 phyla. Only 29% of species could be assigned binominal names through matches to public sequence libraries, indicating varying levels of library completeness across Orders. Extraction of small-fraction DNA with a soil kit resulted in a significantly higher species count than with a general kit, but this was not even across taxa. Metabarcoding (amplification) success rate, estimated via comparison to morphological identifications of the large-fraction specimens, was high in most taxa analysed but low, for example, in ampullariid and viviparid gastropods. Conversely, a large proportion of species-site records for Decapoda and Bivalvia came from metabarcoding only. Species richness averaged 29 ± 16 species per site, dominated by Diptera, Annelida, and Odonata, and was particularly high in tributaries of the mountainous Titiwangsa Range. At least eight species are new records for Malaysia, including the non-natives Ferrissia fragilis (Gastropoda) and Dugesia notogaea (Platyhelminthes). Our study showed that DNA metabarcoding is generally more effective in detecting tropical freshwater invertebrate species than traditional morphological approaches, and can efficiently improve knowledge of distribution patterns and ranges of native and non-native species. However, current gaps in reference databases, particularly for bioindicator taxa, such as the Plecoptera, Ephemeroptera, and Coleoptera, need to be addressed urgently
DNA metabarcoding unravels unknown diversity and distribution patterns of tropical freshwater invertebrates
Tropical freshwater invertebrate species are becoming extinct without being described, and effective conservation is hampered by a lack of taxonomic and distribution data. DNA metabarcoding is a promising tool for rapid biodiversity assessments that has never been applied to tropical freshwater invertebrates across large spatial and taxonomic scales. Here we use DNA metabarcoding to comprehensively assess the benthic freshwater invertebrate fauna of the Perak River basin, Malaysia. Specific objectives were to: (1) assess performance of two DNA metabarcoding protocols; (2) identify gaps in reference databases; (3) generate new data on species diversity and distribution; and (4) draw conclusions regarding the potential value of DNA metabarcoding in tropical freshwater conservation. Organisms were collected by hand and net at 34 sites and divided into small (retained in 0.5-mm but passing through 1-mm mesh) and large (retained in 1-mm mesh) fractions, and a 313-bp cytochrome c oxidase subunit I fragment amplified and sequenced using general Metazoa primers. Bioinformatic analysis resulted in 468 operational taxonomic units (~species) from 12 phyla. Only 29% of species could be assigned binominal names through matches to public sequence libraries, indicating varying levels of library completeness across Orders. Extraction of small-fraction DNA with a soil kit resulted in a significantly higher species count than with a general kit, but this was not even across taxa. Metabarcoding (amplification) success rate, estimated via comparison to morphological identifications of the large-fraction specimens, was high in most taxa analysed but low, for example, in ampullariid and viviparid gastropods. Conversely, a large proportion of species-site records for Decapoda and Bivalvia came from metabarcoding only. Species richness averaged 29 ± 16 species per site, dominated by Diptera, Annelida, and Odonata, and was particularly high in tributaries of the mountainous Titiwangsa Range. At least eight species are new records for Malaysia, including the non-natives Ferrissia fragilis (Gastropoda) and Dugesia notogaea (Platyhelminthes). Our study showed that DNA metabarcoding is generally more effective in detecting tropical freshwater invertebrate species than traditional morphological approaches, and can efficiently improve knowledge of distribution patterns and ranges of native and non-native species. However, current gaps in reference databases, particularly for bioindicator taxa, such as the Plecoptera, Ephemeroptera, and Coleoptera, need to be addressed urgently
Diagnosis of biliary tract and ampullary carcinomas
Diagnostic methods for biliary tract carcinoma and the efficacy of these methods are discussed. Neither definite methods for early diagnosis nor specific markers are available in this disease. When this disease is suspected on the basis of clinical symptoms and risk factors, hemato-biochemical examination and abdominal ultrasonography are performed and, where appropriate, enhanced computed tomography (CT) and/or magnetic resonance cholangiopancreatography (MRCP) is carried out. Diagnoses of extrahepatic bile duct cancer and ampullary carcinoma are often made based on the presence of obstructive jaundice. Although rare, abdominal pain and pyrexia, as well as abnormal findings of the hepatobiliary system detected by hemato-biochemical examination, serve as a clue to making a diagnosis of these diseases. On the other hand, the early diagnosis of gallbladder cancer is scarcely possible on the basis of clinical symptoms, so when this cancer is found with the onset of abdominal pain and jaundice, it is already advanced at the time of detection, thus making a cure difficult. When gallbladder cancer is suspected, enhanced CT is carried out. Multidetector computed tomography (MDCT), in particular — one of the methods of enhanced CT — is useful for decision of surgical criteria, because MDCT shows findings such as localization and extension of the tumor, and the presence or absence of remote metastasis. Procedures such as magnetic resonance imaging, endoscopic ultrasonography, bile duct biopsy, and cholangioscopy should be carried out taking into account indications for these procedures in individual patients. However, direct biliary tract imaging is necessary for making a precise diagnosis of the horizontal extension of bile duct cancer
Flowcharts for the management of biliary tract and ampullary carcinomas
No strategies for the diagnosis and treatment of biliary tract carcinoma have been clearly described. We developed flowcharts for the diagnosis and treatment of biliary tract carcinoma on the basis of the best clinical evidence. Risk factors for bile duct carcinoma are a dilated type of pancreaticobiliary maljunction (PBM) and primary sclerosing cholangitis. A nondilated type of PBM is a risk factor for gallbladder carcinoma. Symptoms that may indicate biliary tract carcinoma are jaundice and pain in the upper right area of the abdomen. The first step of diagnosis is to carry out blood biochemistry tests and ultrasonography (US) of the abdomen. The second step of diagnosis is to find the local extension of the carcinoma by means of computed tomography (CT), magnetic resonance imaging (MRI), magnetic resonance cholangiopancreatography (MRCP), percutaneous transhepatic cholangiography (PTC), and endoscopic retrograde cholangiopancreatography (ERCP). Because resection is the only way to completely cure biliary tract carcinoma, the indications for resection are determined first. In patients with resectable disease, the indications for biliary drainage or portal vein embolization (PVE) are checked. In those with nonresectable disease, biliary stenting, chemotherapy, radiotherapy, and/or best supportive care is selected
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