1,036 research outputs found
Numerical thermo-mechanical stress analysis for HVDC cables
Calculating the current rating of paper insulated HVDC cables under low ambient temperatures can require additional mechanical considerations. Under rapid cable heating or cooling processes, an extremely high mechanical stress or a rapid pressure drop can develop due to the strong impregnant thermal expansion or contraction respectively. This may cause plastic deformation of the sheath or the creation of voids. This paper demonstrates the importance of this thermo-mechanical constraint through the application of finite element modelling techniques which permit a coupling of the thermal and mechanical properties within the cable. The results show that the FEA technique can be fully applied to analyze the internal thermo-mechanical stress distribution of the cable and calculate the resulting mechanical stress-limited rating, which provides an alternative to an analytical method previously developed by the same author
Blow up criterion for compressible nematic liquid crystal flows in dimension three
In this paper, we consider the short time strong solution to a simplified
hydrodynamic flow modeling the compressible, nematic liquid crystal materials
in dimension three. We establish a criterion for possible breakdown of such
solutions at finite time in terms of the temporal integral of both the maximum
norm of the deformation tensor of velocity gradient and the square of maximum
norm of gradient of liquid crystal director field.Comment: 22 page
Calculating transition dipole moments of phosphorescent emitters for efficient organic light-emitting diodes
The out-coupling of light from an organic light-emitting diode, and thus its efficiency, strongly depends on the orientation of the transition dipole moment (TDM) of the emitting molecules with respect to the substrate surface. Despite the importance of this quantity, theoretical investigations of the direction of the TDM of phosphorescent emitters based on iridium(iii) complexes remain limited. One challenge is to find an appropriate level of theory able to accurately predict the direction of the TDM. Here, we report relativistic time-dependent density functional theory (TDDFT) calculations of the TDM, emission energies and lifetimes for both the ground-state (S0) and triplet (T1) excited-state geometries of fac-tris(2-phenylpyridyl)iridium(iii) (Ir(ppy)3), using the two-component zero-order regular approximation (ZORA) or including spin-orbit coupling (SOC) perturbatively using the simpler one-component (scalar) formulation. We show that the one- and two-component approaches give similar emission energies and overall radiative lifetimes for each individual geometry. Use of the S0 geometry leads to two of the excited triplet substates being degenerate, with the degeneracy lifted for the T1 geometry, with the latter matching experiment. Two-component calculations using the T1 geometry give results for the direction of the TDM more consistent with experiment than calculations using the S0 geometry. Finally, we show that adding a dielectric medium does not affect the direction of TDM significantly, but leads to better agreement with the experimentally measured radiative lifetime.Mohammad Babazadeh, Paul L. Burn and David M. Huan
Spin Structure of the Pion in a Light-Cone Representation
The spin structure of the pion is discussed by transforming the wave function
for the pion in the naive quark model into a light-cone representation. It is
shown that there are higher helicity () states in
the full light-cone wave function for the pion besides the ordinary helicity
() component wave functions as a consequence from
the Melosh rotation relating spin states in light-front dynamics and those in
instant-form dynamics. Some low energy properties of the pion, such as the
electromagnetic form factor, the charged mean square radius, and the weak decay
constant, could be interrelated in this representation with reasonable
parameters.Comment: 15 Latex pages, 2 figures upon reques
Pion-photon and photon-pion transition form factors in light-cone formalism
We derive the minimal Fock-state expansions of the pion and the photon wave
functions in light-cone formalism, then we calculate the pion-photon and the
photon-pion transition form factors of and
processes by employing these
quark-antiquark wave functions of the pion and the photon. We find that our
calculation for the transition form factor
agrees with the experimental data at low and moderately high energy scale.
Moreover, the physical differences and inherent connections between the
transition form factors of and have been illustrated, which indicate that these
two physical processes are intrinsically related. In addition, we also discuss
the form factor and the decay width at .Comment: 20 pages, 2 figure
Novel hybrid vesicles co-assembled from a cationic lipid and PAAc-g-mPEG with pH-triggered transmembrane channels for controlled drug release
This work presents an important example of novel hybrid vesicles with pH-triggered transmembrane channels prepared by co-assembly of poly(acrylic acid)-g-poly(monomethoxy ethylene glycol) (PAAc-g-mPEG) with a cationic lipid, didodecyldimethylammonium bromide (DDAB), via electrostatic interaction for effective doxorubicin (DOX) release
Axial vector form factor of nucleons in a light-cone diquark model
The nucleon axial vector form factor is investigated in a light-cone quark
spectator diquark model, in which Melosh rotations are applied to both the
quark and vector diquark. It is found that this model gives a very good
description of available experimental data and the results have very little
dependence on the parameters of the model. The relation between the nucleon
axial constant and the anomalous magnetic moment of nucleons is also discussed.Comment: 8 pages, Revtex4, 1 figure, version to be published in Phys. Rev.
Lepton Polarization and Forward-Backward Asymmetries in b -> s tau+ tau-
We study the spin polarizations of both tau leptons in the decay b -> s tau+
tau-. In addition to the polarization asymmetries involving a single tau, we
construct asymmetries for the case where both polarizations are simultaneously
measured. We also study forward-backward asymmetries with polarized tau's. We
find that a large number of asymmetries are predicted to be large, >~ 10%. This
permits the measurement of all Wilson coefficients and the b-quark mass, thus
allowing the standard model (SM) to be exhaustively tested. Furthermore, there
are many unique signals for the presence of new physics. For example,
asymmetries involving triple-product correlations are predicted to be tiny
within the SM, O(10^{-2}). Their observation would be a clear signal of new
physics.Comment: 21 pages, LaTeX, 4 figures (included). Paper somewhat reorganized,
references greatly expanded, conclusions unchange
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