170 research outputs found
Implications of the Tribolium genome project for pest biology
Implications of the Tribolium genome project for pest biology The universal availability of the complete Tribolium castaneum genome sequence assembly and annotation (Richards et al., 2008) and concomitant development of the versatile Tribolium genome browser, BeetleBase (Kim et al., 2010, http://beetlebase.org/) open new realms of possibility for stored product pest control by greatly simplifying the task of connecting biology and behavior with underlying molecular mechanisms. This genome has enabled sequence similarity searches that have resulted in a flood of new discovery involving thousands of genes with important functions in digestion, osmoregulation, metamorphosis, olfaction, xenobiotic metabolism, vision, and embryonic and larval growth and development. The value of the T. castaneum genome sequence is greatly enhanced by the availability of a sophisticated functional genomic toolkit for laboratory studies of this insect. These tools include high-resolution physical and genetic maps, genomic and cDNA libraries, balancer chromosomes, and effective and reliable techniques for specific knockout of any target gene via RNA interference (RNAi). In this paper we briefly discuss just two areas of Tribolium biology research that are being revitalized by the availability of the genome sequence, namely olfaction and exoskeleton, or “smell and skin”
Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2
The recent discovery of superconductivity in iron-arsenic compounds below a
transition temperature (Tc) as high as 55K ended the monopoly of copper oxides
(cuprates) in the family of high-Tc superconductors. A critical issue in
understanding this new superconductor, as in the case of cuprates, is the
nature, in particular the symmetry and orbital dependence, of the
superconducting gap. There are conflicting experimental results, mostly from
indirect measurements of the low energy excitation gap, ranging from one gap to
two gaps, from line nodes to nodeless gap function in momentum space. Here we
report a direct observation of the superconducting gap, including its momentum,
temperature, and Fermi surface (FS) dependence in Ba0.6K0.4Fe2As2 (Tc = 37 K)
using angle-resolved photoelectron spectroscopy. We find two superconducting
gaps with different values: a large gap (~ 12 meV) on the two small hole-like
and electron-like FS sheets, and a small gap (~ 6 meV) on the large hole-like
FS. Both gaps, closing simultaneously at the bulk Tc, are nodeless and nearly
isotropic around their respective FS sheets. The isotropic pairing interactions
are strongly orbital dependent, as the ratio 2Delta/kBTc switches from weak to
strong coupling on different bands. The same and surprisingly large
superconducting gap due to strong pairing on the two small FS, which are
connected by the (pi, 0) spin-density-wave vector in the parent compound,
strongly suggests that the pairing mechanism originates from the inter-band
interactions between these two nested FS sheets.Comment: 4 figure
Photoemission study of electronic structure evolution across the metal-insulator transition of heavily B-doped diamond
We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E(F)) up to similar to 5k(B)T can be observed (k(B) is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E(F). Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E(F), can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT
Progress in QCD next-to-leading order calculations
I review progress related to the calculation of QCD jet cross sections at the
NLO accuracy. After a short introduction into the theory of NLO calculations, I
discuss two recent developments: the calculation of two- and three-jet
leptoproduction at the NLO accuracy and the extension of the dipole subtraction
method for computing NLO corrections for processes involving massive partons.Comment: 5 pages, 4 figures, LaTeX using JHEP3.cls, Invited talk at the
International Europhysics Conference on High-Energy Physics (HEP 2001
Two-dimensional universal conductance fluctuations and the electron-phonon interaction of topological surface states in Bi2Te2Se nanoribbons
The universal conductance fluctuations (UCFs), one of the most important
manifestations of mesoscopic electronic interference, have not yet been
demonstrated for the two-dimensional surface state of topological insulators
(TIs). Even if one delicately suppresses the bulk conductance by improving the
quality of TI crystals, the fluctuation of the bulk conductance still keeps
competitive and difficult to be separated from the desired UCFs of surface
carriers. Here we report on the experimental evidence of the UCFs of the
two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The
solely-B\perp-dependent UCF is achieved and its temperature dependence is
investigated. The surface transport is further revealed by weak
antilocalizations. Such survived UCFs of the topological surface states result
from the limited dephasing length of the bulk carriers in ternary crystals. The
electron-phonon interaction is addressed as a secondary source of the surface
state dephasing based on the temperature-dependent scaling behavior
Worldsheet and Spacetime Properties of p-p' System with B Field and Noncommutative Geometry
We study worldsheet and spacetime properties of the p-p' (p < p') open string
system with constant B_{ij} field viewed from the Dp' brane. The description of
this system in terms of the CFT with spin and twist fields leads us to consider
the renormal ordering procedure from the SL(2,R) invariant vacuum to the
oscillator vacuum. We compute the attendant two distinct superspace two-point
functions as well as their difference (the subtracted two-point function).
These bring us an integral (Koba-Nielsen) representation for the multiparticle
tree scattering amplitudes consisting of N-2 vectors and two tachyons. We
evaluate them explicitly for the N=3,4 cases. Several novel features are
observed which include a momentum dependent multiplicative factor to each
external vector leg and the emergence of a symplectic tensor multiplying the
polarization vectors. In the zero slope limit, the principal parts of the
amplitudes translate into a noncommutative field theory in p'+1 dimensions in
which a scalar field decaying exponentially in (p'-p) dimensions and a
noncommutative U(1) gauge field interact via the minimal coupling and a new
interaction. A large number of nearly massless states noted before are shown to
propagate in the t-channel.Comment: 41 pages, 4 figures, Latex; revised version, typos corrected, comment
on spacetime picture and eq. (5.8) improve
USp(2k) Matrix Model: Nonperturbative Approach to Orientifolds
We discuss theoretical implications of the large k USp(2k) matrix model in
zero dimension. The model appears as the matrix model of type IIB superstrings
on a large orientifold via the matrix twist operation. In the
small volume limit, the model behaves four dimensional and its T dual is
six-dimensional worldvolume theory of type I superstrings in ten spacetime
dimensions. Several theoretical considerations including the analysis on planar
diagrams, the commutativity of the projectors with supersymmetries and the
cancellation of gauge anomalies are given, providing us with the rationales for
the choice of the Lie algebra and the field content. A few classical solutions
are constructed which correspond to Dirichlet p-branes and some fluctuations
are evaluated. The particular scaling limit with matrix T duality
transformation is discussed which derives the F theory compactification on an
elliptic fibered K3.Comment: LaTeX, 29 pages, 3 figures. PostScript problems are fixe
Growth of High-Mobility Bi2Te2Se Nanoplatelets on hBN Sheets by van der Waals Epitaxy
The electrical detection of the surface states of topological insulators is
strongly impeded by the interference of bulk conduction, which commonly arises
due to pronounced doping associated with the formation of lattice defects. As
exemplified by the topological insulator Bi2Te2Se, we show that via van der
Waals epitaxial growth on thin hBN substrates the structural quality of such
nanoplatelets can be substantially improved. The surface state carrier mobility
of nanoplatelets on hBN is increased by a factor of about 3 compared to
platelets on conventional Si/SiOx substrates, which enables the observation of
well-developed Shubnikov-de Haas oscillations. We furthermore demonstrate the
possibility to effectively tune the Fermi level position in the films with the
aid of a back gate
Comparative Genomic Analysis of Chitinase and Chitinase-Like Genes in the African Malaria Mosquito (Anopheles gambiae)
Chitinase is an important enzyme responsible for chitin metabolism in a wide range of organisms including bacteria, yeasts and other fungi, nematodes and arthropods. However, current knowledge on chitinolytic enzymes, especially their structures, functions and regulation is very limited. In this study we have identified 20 chitinase and chitinase-like genes in the African malaria mosquito, Anopheles gambiae, through genome-wide searching and transcript profiling. We assigned these genes into eight different chitinase groupings (groups I–VIII). Domain analysis of their predicted proteins showed that all contained at least one catalytic domain. However, only seven (AgCht4, AgCht5-1, AgCht6, AgCht7, AgCht8, AgCht10 and AgCht23) displayed one or more chitin-binding domains. Analyses of stage- and tissue-specific gene expression revealed that most of these genes were expressed in larval stages. However, AgCht8 was mainly expressed in the pupal and adult stages. AgCht2 and AgCht12 were specifically expressed in the foregut, whereas AgCht13 was only expressed in the midgut. The high diversity and complexity of An. gambiae chitinase and chitinase-like genes suggest their diverse functions during different developmental stages and in different tissues of the insect. A comparative genomic analysis of these genes along with those present in Drosophila melanogaster, Tribolium castaneum and several other insect species led to a uniform classification and nomenclature of these genes. Our investigation also provided important information for conducting future studies on the functions of chitinase and chitinase-like genes in this important malaria vector and other species of arthropods
- …