20,908 research outputs found
Trace functions of the Parafermion vertex operator algebras
The trace functions for the Parafermion vertex operator algebra associated to
any finite dimensional simple Lie algebra \g and any positive integer are
studied and an explicit modular transformation formula of the trace functions
is obtained.Comment: 16 pages. arXiv admin note: text overlap with arXiv:1412.815
Adaptive Neural Network Feedforward Control for Dynamically Substructured Systems
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Case study and back analysis of a residential building damaged by expansive soils
This paper presents a case study of a residential house damaged by expansive soils. The field investigation revealed that the damage was most likely caused by excessive lawn watering and leaks of sewer pipe and/or stormwater pipe, which resulted in non-uniform soil moisture conditions. Three-dimensional back analysis of this distressed structure indicated that stresses were most critical at a re-entrant corner and that steel reinforcing bars in the beam in this area had yielded. The results of the back analysis also indicated that a stronger footing was required to limit differential deflection to an acceptable level and reduce stress in the footing. The case study has clearly shown that a leaking underground water pipe and/or excessive watering of a garden could cause more severe distortion to a single storey masonry veneer house than could be expected from seasonal moisture change and the deeper moisture re-distribution caused by the imposition of the house on seasonally dry reactive soil. Moreover it has been demonstrated that it would be extremely costly to design a footing for extreme, or abnormal, moisture changes
Design Guidelines for Fractional Slot Multi-Phase Modular Permanent Magnet Machines
This paper presents the design considerations for a fractional slot multi-phase modular permanent magnet (PM) machine with single-layer concentrated windings. The winding factors for various slot/pole number combinations are calculated to identify the optimal slot/pole number combinations for different phase numbers. In addition, the electromagnetic performance influenced by flux gaps (FGs), such as air-gap MMF, back-EMF, cogging torque, on-load torque and torque ripple, etc., are comprehensively investigated by using the 2-D finite element (FE) method. Several general rules with respect to the influence of FGs on multi-phase modular PM machines performance are established. The prototypes of modular PM machines are built and the finite element results are validated with experiments
Topological Nature of the Phonon Hall Effect
We provide a topological understanding on phonon Hall effect in dielectrics
with Raman spinphonon coupling. A general expression for phonon Hall
conductivity is obtained in terms of the Berry curvature of band structures. We
find a nonmonotonic behavior of phonon Hall conductivity as a function of
magnetic field. Moreover, we observe a phase transition in phonon Hall effect,
which corresponds to the sudden change of band topology, characterized by the
altering of integer Chern numbers. This can be explained by touching and
splitting of phonon bands.Comment: 12 pages, 4 figures. Detailed supplementary file is include
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Diagnosing relationships between mean state biases and El Niño shortwave feedback in CMIP5 models
The rate of damping of tropical Pacific sea surface temperature anomalies (SSTAs) associated with El Niño events by surface shortwave heat fluxes has significant biases in current coupled climate models [phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. Of 33 CMIP5 models, 16 have shortwave feedbacks that are weakly negative in comparison to observations, or even positive, resulting in a tendency of amplification of SSTAs. Two biases in the cloud response to El Niño SSTAs are identified and linked to significant mean state biases in CMIP5 models. First, cool mean SST and reduced precipitation are linked to comparatively less cloud formation in the eastern equatorial Pacific during El Niño events, driven by a weakened atmospheric ascent response. Second, a spurious reduction of cloud driven by anomalous surface relative humidity during El Niño events is present in models with more stable eastern Pacific mean atmospheric conditions and more low cloud in the mean state. Both cloud response biases contribute to a weak negative shortwave feedback or a positive shortwave feedback that amplifies El Niño SSTAs. Differences between shortwave feedback in the coupled models and the corresponding atmosphere-only models (AMIP) are also linked to mean state differences, consistent with the biases found between different coupled models. Shortwave feedback bias can still persist in AMIP, as a result of persisting weak shortwave responses to anomalous cloud and weak cloud responses to atmospheric ascent. This indicates the importance of bias in the atmosphere component to coupled model feedback and mean state biases
Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO
Following the discovery of superconductivity in an iron-based arsenide
LaO1-xFxFeAs with a superconducting transition temperature (Tc) of 26 K[1], Tc
was pushed up surprisingly to above 40 K by either applying pressure[2] or
replacing La with Sm[3], Ce[4], Nd[5] and Pr[6]. The maximum Tc has climbed to
55 K, observed in SmO1-xFxFeAs[7, 8] and SmFeAsO1-x[9]. The value of Tc was
found to increase with decreasing lattice parameters in LnFeAsO1-xFx (Ln stands
for the lanthanide elements) at an apparently optimal doping level. However,
the F- doping in GdFeAsO is particularly difficult[10,11] due to the lattice
mismatch between the Gd2O2 layers and Fe2As2 layers. Here we report observation
of superconductivity with Tc as high as 56 K by the Th4+ substitution for Gd3+
in GdFeAsO. The incorporation of relatively large Th4+ ions relaxes the lattice
mismatch, hence induces the high temperature superconductivity.Comment: 4 pages, 3 figure
Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions
Within the framework of nonequilibrium Green's functions, we investigate the
thermoelectric transport in a single molecular junction with electron-phonon
and electron-electron interactions. By transforming into a displaced phonon
basis, we are able to deal with these interactions non-perturbatively. Then, by
invoking the weak tunneling limit, we are able to calculate the
thermoelectricity. Results show that at low temperatures, resonances of the
thermoelectric figure of merit ZT occur around the sides of resonances of
electronic conductance but drops dramatically to zero at exactly these resonant
points. We find ZT can be enhanced by increasing electron-phonon coupling and
Coulomb repulsion, and an optimal enhancement is obtained when these two
interactions are competing. Our results indicate a great potential for
single-molecular-junctions as good thermoelectric devices over a wide range of
temperatures.Comment: 7+ pages, 3 figures, with updated appendix. Accepted by PR
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