27,662 research outputs found
Origin of conductivity cross over in entangled multi-walled carbon nanotube network filled by iron
A realistic transport model showing the interplay of the hopping transport
between the outer shells of iron filled entangled multi-walled carbon nanotubes
(MWNT) and the diffusive transport through the inner part of the tubes, as a
function of the filling percentage, is developed. This model is based on
low-temperature electrical resistivity and magneto-resistance (MR)
measurements. The conductivity at low temperatures showed a crossover from
Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions
(3D) between the neighboring tubes as the iron weight percentage is increased
from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly
dependent on temperature as well as magnetic field and shows both positive and
negative signs, which are discussed in terms of wave function shrinkage and
quantum interference effects, respectively. A further increase of the iron
percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D
weak localization (WL). This change is ascribed to the formation of long iron
nanowires at the core of the nanotubes, which yields a long dephasing length
(e.g. 30 nm) at the lowest measured temperature. Although the overall transport
in this network is described by a 3D WL model, the weak temperature dependence
of inelastic scattering length expressed as L_phi ~T^-0.3 suggests the
possibility for the presence of one-dimensional channels in the network due to
the formation of long Fe nanowires inside the tubes, which might introduce an
alignment in the random structure.Comment: 29 pages,10 figures, 2 tables, submitted to Phys. Rev.
Influence of complex configurations on properties of pygmy dipole resonance in neutron-rich Ca isotopes
Starting from the quasiparticle random phase approximation based on the
Skyrme interaction SLy5, we study the effects of phonon-phonon coupling~(PPC)
on the low-energy electric dipole response in Ca. Using the same set
of parameters we describe available experimental data for Ca and
give prediction for Ca. The inclusion of the PPC results in the
formation of low-energy states. There is an impact of the PPC effect on
low-energy ~strength of Ca. The PPC effect on the electric
dipole polarizability is discussed. We predict a strong increase of the summed
~strength below 10MeV, with increasing neutron number from Ca till
Ca.Comment: 11 pages, 10 figure
Structure of low-lying quadrupole states in nuclei near 132Sn
The properties of the low-lying 2^+ states in the even-even nuclei around
132Sn are studied within the quasiparticle random phase approximation. Starting
from a Skyrme interaction in the particle-hole channel and a density-dependent
zero-range interaction in the particle-particle channel, we use the finite rank
separable approach in our investigation. It is found that the fourth 2^+ state
in 132Te could be a good candidate for a mixed-symmetry state.Comment: 6 pages, 2 figures, proceedings of International Conference on
Nuclear Structure and Related Topics (NSRT09), June 2009, JINR, Dubna, Russi
Effect of the green-emitting CaF2:Ce3+,Tb3+ phosphor particles’ size on color rendering index and color quality scale of the in-cup packaging multichip white LEDs
In this paper, we investigate the effect of the green-emitting CaF2:Ce (3+), Tb (3+) phosphor particle's size on the color rendering index (CRI) and the color quality scale (CQS) of the in-cup packaging multichip white LEDs (MCW-LEDs). For this purpose, 7000K and 8500K in-cup packaging MCW-LEDs is simulated by the commercial software Light Tools. Moreover, scattering process in the phosphor layers is investigated by using Mie Theory with Mat Lab software. Finally, the research results show that the green-emitting CaF2: Ce (3+), Tb (3+) phosphor's size crucially influences on the CRI and CQS. From that point of view, CaF2: Ce (3+), Tb (3+) can be proposed as a potential practical direction for manufacturing the in-cup packaging phosphor WLEDs.Web of Science13235134
Dynamics of horizontal-like maps in higher dimension
We study the regularity of the Green currents and of the equilibrium measure
associated to a horizontal-like map in C^k, under a natural assumption on the
dynamical degrees. We estimate the speed of convergence towards the Green
currents, the decay of correlations for the equilibrium measure and the
Lyapounov exponents. We show in particular that the equilibrium measure is
hyperbolic. We also show that the Green currents are the unique invariant
vertical and horizontal positive closed currents. The results apply, in
particular, to Henon-like maps, to regular polynomial automorphisms of C^k and
to their small pertubations.Comment: Dedicated to Professor Gennadi Henkin on the occasion of his 65th
birthday, 37 pages, to appear in Advances in Mat
The Higgs Sector on a Two-Sheeted Space Time
We present a general formalism based on the framework of non-commutative
geometry, suitable to the study the standard model of electroweak interactions,
as well as that of more general gauge theories. Left- and right-handed chiral
fields are assigned to two different sheets of space-time (a discretized
version of Kaluza-Klein theory). Scalar Higgs fields find themselves treated on
the same footing as the gauge fields, resulting in spontaneous symmetry
breaking in a natural and predictable way. We first apply the formalism to the
Standard Model, where one can predict the Higgs mass and the top Yukawa
coupling. We then study the left-right symmetric model, where we show that this
framework imposes constraints on the type and coefficients of terms appearing
in the Higgs potential.Comment: 24 pages, uses revtex
Using Extensive Reading to Improve First Year Students Learner Autonomy
Extensive Reading (ER) has been a hot topic among the scholars all over the world due to the benefits it brings to studentsrsquo study. It is often argued to improve learner autonomy, vocabulary learning, writing, attitude towards reading and so forth. This paper reviews the literature relevant to the above issues and indicates the challenges of implementing Extensive Reading into the language classrooms
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