2,495 research outputs found
Ultra-low carrier concentration and surface dominant transport in Sb-doped Bi2Se3 topological insulator nanoribbons
A topological insulator is a new state of matter, possessing gapless
spin-locking surface states across the bulk band gap which has created new
opportunities from novel electronics to energy conversion. However, the large
concentration of bulk residual carriers has been a major challenge for
revealing the property of the topological surface state via electron transport
measurement. Here we report surface state dominated transport in Sb-doped
Bi2Se3 nanoribbons with very low bulk electron concentrations. In the
nanoribbons with sub-10nm thickness protected by a ZnO layer, we demonstrate
complete control of their top and bottom surfaces near the Dirac point,
achieving the lowest carrier concentration of 2x10^11/cm2 reported in
three-dimensional (3D) topological insulators. The Sb-doped Bi2Se3
nanostructures provide an attractive materials platform to study fundamental
physics in topological insulators, as well as future applications.Comment: 5 pages, 4 figures, 1 tabl
Ambipolar Field Effect in Topological Insulator Nanoplates of (BixSb1-x)2Te3
Topological insulators represent a new state of quantum matter attractive to
both fundamental physics and technological applications such as spintronics and
quantum information processing. In a topological insulator, the bulk energy gap
is traversed by spin-momentum locked surface states forming an odd number of
surface bands that possesses unique electronic properties. However, transport
measurements have often been dominated by residual bulk carriers from crystal
defects or environmental doping which mask the topological surface
contribution. Here we demonstrate (BixSb1-x)2Te3 as a tunable topological
insulator system to manipulate bulk conductivity by varying the Bi/Sb
composition ratio. (BixSb1-x)2Te3 ternary compounds are confirmed as
topological insulators for the entire composition range by angle resolved
photoemission spectroscopy (ARPES) measurements and ab initio calculations.
Additionally, we observe a clear ambipolar gating effect similar to that
observed in graphene using nanoplates of (BixSb1-x)2Te3 in
field-effect-transistor (FET) devices. The manipulation of carrier type and
concentration in topological insulator nanostructures demonstrated in this
study paves the way for implementation of topological insulators in
nanoelectronics and spintronics.Comment: 7 pages, 4 figure
Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators
Three-dimensional (3D) topological insulators (TI) are novel quantum
materials with insulating bulk and topologically protected metallic surfaces
with Dirac-like band structure. The spin-helical Dirac surface states are
expected to host exotic topological quantum effects and find applications in
spintronics and quantum computation. The experimental realization of these
ideas requires fabrication of versatile devices based on bulk-insulating TIs
with tunable surface states. The main challenge facing the current TI materials
exemplified by Bi2Se3 and Bi2Te3 is the significant bulk conduction, which
remains unsolved despite extensive efforts involving nanostructuring, chemical
doping and electrical gating. Here we report a novel approach for engineering
the band structure of TIs by molecular beam epitaxy (MBE) growth of
(Bi1-xSbx)2Te3 ternary compounds. Angle-resolved photoemission spectroscopy
(ARPES) and transport measurements show that the topological surface states
exist over the entire composition range of (Bi1-xSbx)2Te3 (x = 0 to 1),
indicating the robustness of bulk Z2 topology. Most remarkably, the systematic
band engineering leads to ideal TIs with truly insulating bulk and tunable
surface state across the Dirac point that behave like one quarter of graphene.
This work demonstrates a new route to achieving intrinsic quantum transport of
the topological surface states and designing conceptually new TI devices with
well-established semiconductor technology.Comment: Minor changes in title, text and figures. Supplementary information
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Effects of molecular association on mutual diffusion : a study of hydrogen bonding in dilute solutions
Author name used in this publication: T. C. ChanVersion of RecordPublishe
Identification and Behavioral Evaluation of Sex Pheromone Components of the Chinese Pine Caterpillar Moth, Dendrolimus tabulaeformis
Background: The Chinese pine caterpillar moth, Dendrolimus tabulaeformis Tsai and Liu (Lepidoptera: Lasiocampidae) is the most important defoliator of coniferous trees in northern China. Outbreaks occur over enormous areas and often lead to the death of forests during 2–3 successive years of defoliation. The sex pheromone of D. tabulaeformis was investigated to define its chemistry and behavioral activity. Methodology/Principal Findings: Sex pheromone was collected from calling female D. tabulaeformis by headspace solid phase microextraction (SPME) and by solvent extraction of pheromone glands. Extracts were analyzed by coupled gas chromatography/mass spectrometry (GC-MS) and coupled GC-electroantennographic detection (GC-EAD), using antennae from male moths. Five components from the extracts elicited antennal responses. These compounds were identified by a combination of retention indices, electron impact mass spectral matches, and derivatization as (Z)-5-dodecenyl acetate (Z5-12:OAc), (Z)-5-dodecenyl alcohol (Z5-12:OH), (5Z,7E)-5,7-dodecadien-1-yl acetate (Z5,E7-12:OAc), (5Z,7E)-5,7-dodecadien-1-yl propionate (Z5,E7-12:OPr), and (5Z,7E)-5,7-dodecadien-1-ol (Z5,E7-12:OH). Behavioral assays showed that male D. tabulaeformis strongly discriminated against incomplete and aberrant blend ratios. The correct ratio of Z5,E7-12:OAc, Z5,E7-12:OH, and Z5,E7-12:OPr was essential for optimal upwind flight and source contact. The two monoenes, Z5-12:OAc and Z5-12:OH, alone or binary mixtures, had no effect on behavioral responses when added to the optimal threecomponen
Study on Microcystis aeruginosa growth in incubator experiments by combination of Logistic and Monod functions
A combination of Logistic and Monod functions was proposed in this paper to study Microcystis aeruginosa growth in incubator experiments. This enables the Microcystis aeruginosa growth dynamics to be better described in incubator experiments and its parameters to be calculated more accurately. This method was justified by the data from the experiment and applied to study the effect of prometryn on Microcystis aeruginosa growth. In the experiment, a different concentrations of prometryn (0, 50, 100 and 200 μg·L−1) were added to the culture medium; the algal cell density, concentrations of orthophosphate (PO43−-P) and ammonia nitrogen (NH4+-N) were measured. The results show that Microcystis aeruginosa growth with time can be well described using the Logistic function. The maximum algae densities of Microcystis aeruginosa corresponding to the four prometryn concentrations are 11.7 × 106, 8.1 × 106, 5.6 × 106and 3.0 × 106cells·mL−1, respectively. The derived formula for the specific growth rate, growth rate and inhibition rate using Logistic function agreed reasonably well with the measured data. It was found that variations of consumed nutrients concentrations (PO43−-P and NH4+-N) can also be well described by the Logistic function. A function that describes the relationship between algal densities and consumed nutrient (PO43−-P and NH4+-N) concentrations is also derived from the Logistic function. Combination of Monod and Logistic functions can better describe relationship between specific growth rates and nutrients concentrations compared to the use of Monod function alone. In general, the half saturation coefficient, Kcfor PO43−-P (4.74 × 10−4, 1.99 × 10−3, 5.54 × 10−3and 3.87 × 10−2mg·L−1) and Kcfor NH4+-N (1.80 × 10−3, 5.84 × 10−3, 5.23 × 10−3and 1.06 × 10−2mg·L−1) in Monod function increase with increasing prometryn concentrations, which indicates that the affinity of algae growth to PO43−-P and NH4+-N decrease with increasing prometryn concentrations. In addition, relationships between nutrients concentrations and time can be derived by combining of Monod and Logistic functions, which agree well with the measured data. It is concluded that the combined application of Monod and Logistic functions provides a promising and more robust method of studying algal growth in incubator experiments
A suite of web applications to streamline the interdisciplinary collaboration in secondary data analyses
BACKGROUND: We describe a system of web applications designed to streamline the interdisciplinary collaboration in outcomes research. DESCRIPTION: The outcomes research process can be described as a set of three interrelated phases: design and selection of data sources, analysis, and output. Each of these phases has inherent challenges that can be addressed by a group of five web applications developed by our group. QuestForm allows for the formulation of relevant and well-structured outcomes research questions; Research Manager facilitates the project management and electronic file exchange among researchers; Analysis Charts facilitate the communication of complex statistical techniques to clinicians with varying previous levels of statistical knowledge; Literature Matrices improve the efficiency of literature reviews. An outcomes research question is used to illustrate the use of the system. CONCLUSIONS: The system presents an alternative to streamline the interdisciplinary collaboration of clinicians, statisticians, programmers, and graduate students
BSE Case Associated with Prion Protein Gene Mutation
Bovine spongiform encephalopathy (BSE) is a transmissible spongiform encephalopathy (TSE) of cattle and was first detected in 1986 in the United Kingdom. It is the most likely cause of variant Creutzfeldt-Jakob disease (CJD) in humans. The origin of BSE remains an enigma. Here we report an H-type BSE case associated with the novel mutation E211K within the prion protein gene (Prnp). Sequence analysis revealed that the animal with H-type BSE was heterozygous at Prnp nucleotides 631 through 633. An identical pathogenic mutation at the homologous codon position (E200K) in the human Prnp has been described as the most common cause of genetic CJD. This finding represents the first report of a confirmed case of BSE with a potential pathogenic mutation within the bovine Prnp gene. A recent epidemiological study revealed that the K211 allele was not detected in 6062 cattle from commercial beef processing plants and 42 cattle breeds, indicating an extremely low prevalence of the E211K variant (less than 1 in 2000) in cattle
Performance analysis of MIMO-SESS with Alamouti scheme over Rayleigh fading channels
Las unidades fraseológicas han estado presentes en los repertorios desde los comienzos
de la lexicografía. Y no solamente en los diccionarios generales, sino también en las
catalogaciones especializadas, tanto de naturaleza monolingüe como bilingüe. No
obstante, siempre ha existido dificultad terminológica para la categorización de los
diferentes fenómenos del discurso repetido. Si bien esto no ha sido un inconveniente
para que se hayan publicado numerosas compilaciones, sobre todo de refranes en un
principio, ya que en la actualidad, fundamentalmente, gracias al auge de los estudios
teóricos sobre fraseología, han proliferado otras obras (algunas aplicadas a la
glosodidáctica, dada su importancia hoy en día) en las que se da cabida con mayor
frecuencia a enunciados de valor específico y a locuciones; en unas ocasiones,
ahondando en el origen que les dio entidad y, en otras, estableciendo etiquetados
precisos que hasta el momento solían estar ausentes, pero con la finalidad, al fin y al
cabo, de desentrañar el sentido, dada la escasa deducibilidad que presentan estas
secuencias fijadas por la simple suma de sus elementos constitutivos. Un análisis de
estos repertorios a través de los siglos, es, por tanto, el objetivo de este trabajo.Since the beginning of lexicography, phraseological units have been included in
repertoires; not only in general dictionaries, but also in monolingual and bilingual
specialized catalogues. However, there have always been terminological difficulties for
classifying various phenomena of repeated speech. Although this has not been
inconvenient for publishing many compilations of sayings, especially at the beginning,
because nowadays they frequently include utterances with precise value and idioms,
mainly due to the rise of theoretical studies on phraseology (some applied to ASL
Linguistics, given its importance today). In them, sometimes, the origin of the
phraseological unit is included and, in others, accurate labels that were absent before are
determined in order, finally and ultimately, to unravel the meaning, given the reduced
deductibility that these sequences present from the simple sum of their constituent
elements. The objective of this work is, therefore, an analysis of these repertories
throughout the centuries
Detection of Hepatocyte Growth Factor (HGF) Ligand-c-MET Receptor Activation in Formalin-Fixed Paraffin Embedded Specimens by a Novel Proximity Assay
Aberrant activation of membrane receptors frequently occurs in human carcinomas. Detection of phosphorylated receptors is commonly used as an indicator of receptor activation in formalin-fixed paraffin embedded (FFPE) tumor specimens. FFPE is a standard method of specimen preparation used in the histological analysis of solid tumors. Due to variability in FFPE preparations and the labile nature of protein phosphorylation, measurements of phospho-proteins are unreliable and create ambiguities in clinical interpretation. Here, we describe an alternative, novel approach to measure receptor activation by detecting and quantifying ligand-receptor complexes in FFPE specimens. We used hepatocyte growth factor (HGF)-c-MET as our model ligand-receptor system. HGF is the only known ligand of the c-MET tyrosine kinase receptor and HGF binding triggers c-MET phosphorylation. Novel antibody proximity-based assays were developed and used to detect and quantify total c-MET, total HGF, and HGF-c-MET ligand-receptor interactions in FFPE cell line and tumor tissue. In glioma cells, autocrine activation of c-MET by HGF-c-MET increased basal levels of c-MET phosphorylation at tyrosine (Tyr) 1003. Furthermore, HGF-c-MET activation in glioma cell lines was verified by Surface Protein-Protein Interaction by Crosslinking ELISA (SPPICE) assay in corresponding soluble cell lysates. Finally, we profiled levels o
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