22,696 research outputs found
The Social Wasps (Hymenoptera: Vespidae) of Indiana
An updated taxonomic treatment of the social wasps (Hymenoptera: Vespidae) of Indiana is made. Illustrated identification keys are provided for species of Polistes, Vespa, Vespula, and Dolichovespula. New distributional records and biological notes are provided for each species
Predicting adaptive responses - simulating occupied environments
Simulation of building performance is increasingly being used in design practice to predict comfort of occupants in finished buildings. This is an area of great uncertainty: what actions does a person take when too warm or suffering from glare; how is comfort measured; how do groups of people interact to control environmental conditions, etc? An increasing attention to model these issues is evident in current research. Two issues are covered in this paper: how comfort can be assessed and what actions occupants are likely to make to achieve and maintain a comfortable status. The former issue describes the implementation of existing codes within a computational framework. This is non-trivial as information on local air velocities, radiant temperature and air temperature and relative humidity have to be predicted as they evolve over time in response to changing environmental conditions. This paper also presents a nascent algorithm for modelling occupant behaviour with respect to operable windows. The algorithm is based on results of several field studies which show the influence of internal and external temperatures on decision making in this respect. The derivation and implementation of the algorithm is discussed, highlighting areas where further effort could be of benefit
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
Applying inspection to object-oriented software
The benefits of the object-oriented paradigmare widely cited. At the same time, inspection is deemed to be the most cost-effective means of detecting defects in software products. Why then, is there no published experience, let alone quantitative data, on the application of inspection to object-oriented systems? We describe the facilities of the object-oriented paradigm and the issues that these raise when inspecting object-oriented code. Several problems are caused by the disparity between the static code structure and its dynamic runtime behaviour. The large number of small methods in object-oriented systems can also cause problems. We then go on to describe three areas which may help mitigate problems found. Firstly, the use of various programming methods may assist in making object-oriented code easier to inspect. Secondly, improved program documentation can help the inspector understand the code which is under inspection. Finally, tool support can help the inspector to analyse the dynamic behaviour of the code. We conclude that while both the object-oriented paradigm and inspection provide excellent benefits on their own, combining the two may be a difficult exercise, requiring extensive support if it is to be successful
From a few to many electrons in quantum dots under strong magnetic fields: Properties of rotating electron molecules with multiple rings
Using the method of breaking of circular symmetry and of subsequent symmetry
restoration via projection techiques, we present calculations for the
ground-state energies and excitation spectra of N-electron parabolic quantum
dots in strong magnetic fields in the medium-size range 10 <= N <= 30. The
physical picture suggested by our calculations is that of finite rotating
electron molecules (REMs) comprising multiple rings, with the rings rotating
independently of each other. An analytic expression for the energetics of such
non-rigid multi-ring REMs is derived; it is applicable to arbitrary sizes given
the corresponding equilibrium configuration of classical point charges. We show
that the rotating electron molecules have a non-rigid (non-classical)
rotational inertia exhibiting simultaneous crystalline correlations and
liquid-like (non-rigidity) characteristics. This mixed phase appears in high
magnetic fields and contrasts with the picture of a classical rigid Wigner
crystal in the lowest Landau level.Comment: REVTEX4, 15 pages with 12 figures. Accepted for publication in
Physical Review B. To download a file with figures of higher quality, click
http://www.prism.gatech.edu/~ph274cy/ (go to publication #72
Pseudospin Magnetism in Graphene
We predict that neutral graphene bilayers are pseudospin magnets in which the
charge density-contribution from each valley and spin spontaneously shifts to
one of the two layers. The band structure of this system is characterized by a
momentum-space vortex which is responsible for unusual competition between band
and kinetic energies leading to symmetry breaking in the vortex core. We
discuss the possibility of realizing a pseudospin version of ferromagnetic
metal spintronics in graphene bilayers based on hysteresis associated with this
broken symmetry.Comment: 5 pages, 4 figures; added figure 1, modified introduction and
discussion; updated reference
Effect of Edge Roughness on Electronic Transport in Graphene Nanoribbon Channel Metal Oxide Semiconductor Field-Effect Transistors
Results of quantum mechanical simulations of the influence of edge disorder
on transport in graphene nanoribbon metal oxide semiconductor field-effect
transistors (MOSFETs) are reported. The addition of edge disorder significantly
reduces ON-state currents and increases OFF-state currents, and introduces wide
variability across devices. These effects decrease as ribbon widths increase
and as edges become smoother. However the bandgap decreases with increasing
width, thereby increasing the band-to-band tunneling mediated subthreshold
leakage current even with perfect nanoribbons. These results suggest that
without atomically precise edge control during fabrication, MOSFET performance
gains through use of graphene will be difficult to achieve.Comment: 8 pages, 5 figure
Bilayer Quantum Hall Systems at Filling Factor \nu=2: An Exact Diagonalisation Study
We present an exact diagonalisation study of bilayer quantum Hall systems at
a filling factor of two in the spherical geometry. We find the
high-Zeeman-coupling phase boundary of the broken symmetry canted
antiferromagnet is given exactly by previous Hartree-Fock mean-field theories,
but that the state's stability at weak Zeeman coupling has been qualitatively
overestimated. In the absence of interlayer tunneling, degeneracies occur
between total spin multiplets due to the Hamiltonian's invariance under
independent spin-rotations in top and bottom two-dimensional electron layers.Comment: Some remarks added in the discussion of the phase diagram, and some
typos corrected. Version to be published in Phys. Rev. Let
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