15,407 research outputs found
Flight test techniques for wake-vortex minimization studies
Flight test techniques developed for use in a study of wake turbulence and used recently in flight studies of wake minimization methods are discussed. Flow visualization was developed as a technique for qualitatively assessing minimization methods and is required in flight test procedures for making quantitative measurements. The quantitative techniques are the measurement of the upset dynamics of an aircraft encountering the wake and the measurement of the wake velocity profiles. Descriptions of the instrumentation and the data reduction and correlation methods are given
Current Approaches to HR Strategies: Inside-Out vs. Outside-In
In an effort to determine the best practices with regard to Human Resource (HR) strategies, we conducted interviews with HR executives knowledgeable about their HR strategies from 20 companies, and gathered archival materials such as the HR strategy documents from 9 of the companies. We found that the content, process, and evaluation of the HR strategies can each be classified as focusing primarily on the HR function, the people of the firm, or the business. We provide some examples of ways that firms can move from an HR focused to a business-focused HR strategy
Towards electron transport measurements in chemically modified graphene: The effect of a solvent
Chemical functionalization of graphene modifies the local electron density of
the carbon atoms and hence electron transport. Measuring these changes allows
for a closer understanding of the chemical interaction and the influence of
functionalization on the graphene lattice. However, not only chemistry, in this
case diazonium chemistry, has an effect on the electron transport. Latter is
also influenced by defects and dopants resulting from different processing
steps. Here, we show that solvents used in the chemical reaction process change
the transport properties. In more detail, the investigated combination of
isopropanol and heating treatment reduces the doping concentration and
significantly increases the mobility of graphene. Furthermore, the isopropanol
treatment alone increases the concentration of dopants and introduces an
asymmetry between electron and hole transport which might be difficult to
distinguish from the effect of functionalization. The results shown in this
work demand a closer look on the influence of solvents used for chemical
modification in order to understand their influence
Extended two-level quantum dissipative system from bosonization of the elliptic spin-1/2 Kondo model
We study the elliptic spin-1/2 Kondo model (spin-1/2 fermions in one
dimension with fully anisotropic contact interactions with a magnetic impurity)
in the light of mappings to bosonic systems using the fermion-boson
correspondence and associated unitary transformations. We show that for fixed
fermion number, the bosonic system describes a two-level quantum dissipative
system with two noninteracting copies of infinitely-degenerate upper and lower
levels. In addition to the standard tunnelling transitions, and the transitions
driven by the dissipative coupling, there are also bath-mediated transitions
between the upper and lower states which simultaneously effect shifts in the
horizontal degeneracy label. We speculate that these systems could provide new
examples of continuous time quantum random walks, which are exactly solvable.Comment: 7 pages, 1 figur
Exact enumeration of Hamiltonian circuits, walks, and chains in two and three dimensions
We present an algorithm for enumerating exactly the number of Hamiltonian
chains on regular lattices in low dimensions. By definition, these are sets of
k disjoint paths whose union visits each lattice vertex exactly once. The
well-known Hamiltonian circuits and walks appear as the special cases k=0 and
k=1 respectively. In two dimensions, we enumerate chains on L x L square
lattices up to L=12, walks up to L=17, and circuits up to L=20. Some results
for three dimensions are also given. Using our data we extract several
quantities of physical interest
Simulations of energetic beam deposition: from picoseconds to seconds
We present a new method for simulating crystal growth by energetic beam
deposition. The method combines a Kinetic Monte-Carlo simulation for the
thermal surface diffusion with a small scale molecular dynamics simulation of
every single deposition event. We have implemented the method using the
effective medium theory as a model potential for the atomic interactions, and
present simulations for Ag/Ag(111) and Pt/Pt(111) for incoming energies up to
35 eV. The method is capable of following the growth of several monolayers at
realistic growth rates of 1 monolayer per second, correctly accounting for both
energy-induced atomic mobility and thermal surface diffusion. We find that the
energy influences island and step densities and can induce layer-by-layer
growth. We find an optimal energy for layer-by-layer growth (25 eV for Ag),
which correlates with where the net impact-induced downward interlayer
transport is at a maximum. A high step density is needed for energy induced
layer-by-layer growth, hence the effect dies away at increased temperatures,
where thermal surface diffusion reduces the step density. As part of the
development of the method, we present molecular dynamics simulations of single
atom-surface collisions on flat parts of the surface and near straight steps,
we identify microscopic mechanisms by which the energy influences the growth,
and we discuss the nature of the energy-induced atomic mobility
Topological defects in lattice models and affine Temperley-Lieb algebra
This paper is the first in a series where we attempt to define defects in
critical lattice models that give rise to conformal field theory topological
defects in the continuum limit. We focus mostly on models based on the
Temperley-Lieb algebra, with future applications to restricted solid-on-solid
(also called anyonic chains) models, as well as non-unitary models like
percolation or self-avoiding walks. Our approach is essentially algebraic and
focusses on the defects from two points of view: the "crossed channel" where
the defect is seen as an operator acting on the Hilbert space of the models,
and the "direct channel" where it corresponds to a modification of the basic
Hamiltonian with some sort of impurity. Algebraic characterizations and
constructions are proposed in both points of view. In the crossed channel, this
leads us to new results about the center of the affine Temperley-Lieb algebra;
in particular we find there a special subalgebra with non-negative integer
structure constants that are interpreted as fusion rules of defects. In the
direct channel, meanwhile, this leads to the introduction of fusion products
and fusion quotients, with interesting mathematical properties that allow to
describe representations content of the lattice model with a defect, and to
describe its spectrum.Comment: 41
Low-loss photonic crystal fibers for transmission systems and their dispersion properties
We report on a single-mode photonic crystal fiber with attenuation and
effective area at 1550 nm of 0.48 dB/km and 130 square-micron, respectively.
This is, to our knowledge, the lowest loss reported for a PCF not made from VAD
prepared silica and at the same time the largest effective area for a low-loss
(< 1 dB/km) PCF. We briefly discuss the future applications of PCFs for data
transmission and show for the first time, both numerically and experimentally,
how the group velocity dispersion is related to the mode field diameterComment: 5 pages including 3 figures + 1 table. Accepted for Opt. Expres
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