5,112 research outputs found
Doping Effect of Nano-Diamond on Superconductivity and Flux Pinning in MgB2
Doping effect of diamond nanoparticles on the superconducting properties of
MgB2 bulk material has been studied. It is found that the superconducting
transition temperature Tc of MgB2 is suppressed by the diamond-doping, however,
the irreversibility field Hirr and the critical current density Jc are
systematically enhanced. Microstructural analysis shows that the diamond-doped
MgB2 superconductor consists of tightly-packed MgB2 nano-grains (~50-100 nm)
with highly-dispersed and uniformly-distributed diamond nanoparticles (~10-20
nm) inside the grains. High density of dislocations and diamond nanoparticles
may take the responsibility for the enhanced flux pinning in the diamond-doped
MgB2.Comment: 16 pages, 6 figure
Revisiting the B {\to} {\pi} {\rho}, {\pi} {\omega} Decays in the Perturbative QCD Approach Beyond the Leading Order
We calculate the branching ratios and CP asymmetries of the ,
decays in the perturbative QCD factorization approach up to the
next-to-leading-order contributions. We find that the next-to-leading-order
contributions can interfere with the leading-order part constructively or
destructively for different decay modes. Our numerical results have a much
better agreement with current available data than previous leading-order
calculations, e.g., the next-to-leading-order corrections enhance the
branching ratios by a factor 2.5, which is helpful
to narrow the gaps between theoretic predictions and experimental data. We also
update the direct CP-violation parameters, the mixing-induced CP-violation
parameters of these modes, which show a better agreement with experimental data
than many of the other approaches.Comment: 23 pages, 4 figures, 4 table
Spectra of Baryons Containing Two Heavy Quarks in Potential Model
In this work, we employ the effective vertices for interaction between
diquarks (scalar or axial-vector) and gluon where the form factors are derived
in terms of the B-S equation, to obtain the potential for baryons including a
light quark and a heavy diquark. The concerned phenomenological parameters are
obtained by fitting data of mesons instead of the heavy quarkonia.
The operator ordering problem in quantum mechanics is discussed. Our numerical
results indicate that the mass splitting between and
is very small and it is consistent with the heavy quark effective
theory (HQET).Comment: 16 page
Secret Symmetries in AdS/CFT
We discuss special quantum group (secret) symmetries of the integrable system
associated to the AdS/CFT correspondence. These symmetries have by now been
observed in a variety of forms, including the spectral problem, the boundary
scattering problem, n-point amplitudes, the pure-spinor formulation and quantum
affine deformations.Comment: 20 pages, pdfLaTeX; Submitted to the Proceedings of the Nordita
program `Exact Results in Gauge-String Dualities'; Based on the talk
presented by A.T., Nordita, 15 February 201
Record Maximum Oscillation Frequency in C-face Epitaxial Graphene Transistors
The maximum oscillation frequency (fmax) quantifies the practical upper bound
for useful circuit operation. We report here an fmax of 70 GHz in transistors
using epitaxial graphene grown on the C-face of SiC. This is a significant
improvement over Si-face epitaxial graphene used in the prior high frequency
transistor studies, exemplifying the superior electronics potential of C-face
epitaxial graphene. Careful transistor design using a high {\kappa} dielectric
T-gate and self-aligned contacts, further contributed to the record-breaking
fmax
T-Bet and Eomes Regulate the Balance between the Effector/Central Memory T Cells versus Memory Stem Like T Cells
Memory T cells are composed of effector, central, and memory stem cells. Previous studies have implicated that both T-bet and Eomes are involved in the generation of effector and central memory CD8 T cells. The exact role of these transcription factors in shaping the memory T cell pool is not well understood, particularly with memory stem T cells. Here, we demonstrate that both T-bet or Eomes are required for elimination of established tumors by adoptively transferred CD8 T cells. We also examined the role of T-bet and Eomes in the generation of tumor-specific memory T cell subsets upon adoptive transfer. We showed that combined T-bet and Eomes deficiency resulted in a severe reduction in the number of effector/central memory T cells but an increase in the percentage of CD62LhighCD44low Sca-1+ T cells which were similar to the phenotype of memory stem T cells. Despite preserving large numbers of phenotypic memory stem T cells, the lack of both of T-bet and Eomes resulted in a profound defect in antitumor memory responses, suggesting T-bet and Eomes are crucial for the antitumor function of these memory T cells. Our study establishes that T-bet and Eomes cooperate to promote the phenotype of effector/central memory CD8 T cell versus that of memory stem like T cells. © 2013 Li et al
Transcript-indexed ATAC-seq for precision immune profiling.
T cells create vast amounts of diversity in the genes that encode their T cell receptors (TCRs), which enables individual clones to recognize specific peptide-major histocompatibility complex (MHC) ligands. Here we combined sequencing of the TCR-encoding genes with assay for transposase-accessible chromatin with sequencing (ATAC-seq) analysis at the single-cell level to provide information on the TCR specificity and epigenomic state of individual T cells. By using this approach, termed transcript-indexed ATAC-seq (T-ATAC-seq), we identified epigenomic signatures in immortalized leukemic T cells, primary human T cells from healthy volunteers and primary leukemic T cells from patient samples. In peripheral blood CD4+ T cells from healthy individuals, we identified cis and trans regulators of naive and memory T cell states and found substantial heterogeneity in surface-marker-defined T cell populations. In patients with a leukemic form of cutaneous T cell lymphoma, T-ATAC-seq enabled identification of leukemic and nonleukemic regulatory pathways in T cells from the same individual by allowing separation of the signals that arose from the malignant clone from the background T cell noise. Thus, T-ATAC-seq is a new tool that enables analysis of epigenomic landscapes in clonal T cells and should be valuable for studies of T cell malignancy, immunity and immunotherapy
Prospects for Improving the Intrinsic and Extrinsic Properties of Magnesium Diboride Superconducting Strands
The magnetic and transport properties of magnesium diboride films represent
performance goals yet to be attained by powder-processed bulk samples and
conductors. Such performance limits are still out of the reach of even the best
magnesium diboride magnet wire. In discussing the present status and prospects
for improving the performance of powder-based wire we focus attention on (1)
the intrinsic (intragrain) superconducting properties of magnesium diboride,
Hc2 and flux pinning, (2) factors that control the efficiency with which
current is transported from grain-to-grain in the conductor, an extrinsic
(intergrain) property. With regard to Item-(1), the role of dopants in Hc2
enhancement is discussed and examples presented. On the other hand their roles
in increasing Jc, both via Hc2 enhancement as well as direct
fluxoid/pining-center interaction, are discussed and a comprehensive survey of
Hc2 dopants and flux-pinning additives is presented. Current transport through
the powder-processed wire (an extrinsic property) is partially blocked by the
inherent granularity of the material itself and the chemical or other
properties of the intergrain surfaces. These and other such results indicate
that in many cases less than 15% of the conductor's cross sectional area is
able to carry transport current. It is pointed out that densification in
association with the elimination of grain-boundary blocking phases would yield
five-to ten-fold increases in Jc in relevant regimes, enabling the performance
of magnesium diboride in selected applications to compete with that of Nb-Sn
Waveguide-integrated terahertz-frequency quantum cascade lasers for detection of trace-gas species
We demonstrate high-performance THz QCLs lasing at 2.2, 2.53, 3.5 and 4.7 THz, which target absorption lines of water, methane, hydroxyl and atomic oxygen respectively. Reliable single-mode targeting of gas species is obtained through the use of a photonic lattice design. A highly reproducible micro-machined waveguide block yields narrow beam-divergence and enables future integration of a complete THz heterodyne system including local-oscillator, mixer, and feed-horn
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