44,039 research outputs found
Nuclear modification factor in intermediate-energy heavy-ion collisions
The transverse momentum dependent nuclear modification factors (NMF), namely
, is investigated for protons produced in Au + Au at 1 GeV within
the framework of the isospin-dependent quantum molecular dynamics (IQMD) model.
It is found that the radial collective motion during the expansion stage
affects the NMF at low transverse momentum a lot. By fitting the transverse
mass spectra of protons with the distribution function from the Blast-Wave
model, the magnitude of radial flow can be extracted. After removing the
contribution from radial flow, the can be regarded as a thermal one
and is found to keep unitary at transverse momentum lower than 0.6 GeV/c and
enhance at higher transverse momentum, which can be attributed to Cronin
effect.Comment: 8 pages, 5 figures; aceepted by Physics Letters
Resonant States in the Electronic Structure of the High Performance Thermoelectrics AgPb_{2+m}$ ; The Role of Ag-Sb Microstructures
Ab initio electronic structure calculations based on gradient corrected
density functional theory were performed on a class of novel quaternary
compounds AgPb_{2+m}$, which were found to be excellent high
temperature thermoelctrics with large figure of merit ZT ~2.2 at 800K. We find
that resonant states appear near the top of the valence and bottom of the
conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be
understood in terms of modified Te-Ag(Sb) bonds. Electronic structure near the
gap depends sensitively on the microstructural arrangements of Ag-Sb atoms,
suggesting that large ZT values may originate from the nature of these ordering
arrangements.Comment: Accepted in Physical Review Letter
The evolution of interfacial transition zone in alkali-activated fly ash-slag concrete
This paper investigates the mechanisms of microstructure evolution of interfacial transition zone (ITZ) in alkali-activated fly ash-slag (AAFS) concrete using scanning electron microscope. Results indicate that the formation of original ITZ depends on the so-called “wall effect”, leading to a deficit of large grains and a higher effective alkaline activator/precursor ratio compared to paste matrix. The alkaline reaction process is correspondingly accelerated, which promotes the formation of low Ca C-(N)-A-S-H gels and reduces the porosity in the ITZ. Afterwards, the high Ca C-(N)-A-S-H gels are generated due to the release of more Ca from slag, resulting in the continuous refinement of pores. The C-(N)-A-S-H gels with rich Si and Al are then produced at 7 d, attributing to the species diffusion from paste matrix to ITZ. Consequently, a compact and dense microstructure is formed in the ITZ at 28 d, which would be beneficial to the long-term performance of concrete
Scattering of plasmons at the intersection of two metallic nanotubes: Implications for tunnelling
We study theoretically the plasmon scattering at the intersection of two
metallic carbon nanotubes. We demonstrate that for a small angle of crossing,
, the transmission coefficient is an oscillatory function of
, where is the interaction parameter of the Luttinger
liquid in an individual nanotube. We calculate the tunnel density of states,
, as a function of energy, , and distance, , from the
intersection. In contrast to a single nanotube, we find that, in the geometry
of crossed nanotubes, conventional "rapid" oscillations in due
to the plasmon scattering acquire an aperiodic "slow-breathing" envelope which
has nodes.Comment: 4 pages, 2 figures (revised version
Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays
According to the heavy-quark flavour symmetry, the transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays and , we perform a
phenomenological study of transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate transition form factors from
to . It is found that, although being consistent with
each other within error bars, the central values of our results for form factors at , , are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table
- …