11,879 research outputs found
A study of compressible turbulent boundary layers using the method of invariant modeling
Model equations for studying compressible turbulen boundary layer
Diversity and inclusion depend on effective engagement It is everyone’s business to ensure that progress is maintained
Purpose – Highlights some of the things that can be done to ensure that organizations embed diversity and inclusion.
Design/methodology/approach – Considers the need for effective engagement, the importance of performance indicators for diversity and inclusion and the key role of sharing stories. Discusses, too, how critical race theory could help to bring about improvements.
Findings – Advances the view that a transformational process that supports employees with the knowledge and sustainable skills needed to improve business performance via ethical means will form a significant part of future-proofing organizations.
Practical implications – Argues that, to achieve this organizations have to drive home the message that diversity and inclusion are everyone’s business.
Social implications – Advances the view that a unified approach to diversity and inclusion, which is embedded in the business ethics of the organization, can have a sustainable positive impact on the health and well-being of individuals, business and society.
Originality/value – Considers diversity and inclusion from diverse perspectives and draws conclusions that can help organizations to perform better in these areas
Ab initio calculation of the anomalous Hall conductivity by Wannier interpolation
The intrinsic anomalous Hall effect in ferromagnets depends on subtle
spin-orbit-induced effects in the electronic structure, and recent ab-initio
studies found that it was necessary to sample the Brillouin zone at millions of
k-points to converge the calculation. We present an efficient first-principles
approach for computing the anomalous Hall conductivity. We start out by
performing a conventional electronic-structure calculation including spin-orbit
coupling on a uniform and relatively coarse k-point mesh. From the resulting
Bloch states, maximally-localized Wannier functions are constructed which
reproduce the ab-initio states up to the Fermi level. The Hamiltonian and
position-operator matrix elements, needed to represent the energy bands and
Berry curvatures, are then set up between the Wannier orbitals. This completes
the first stage of the calculation, whereby the low-energy ab-initio problem is
transformed into an effective tight-binding form. The second stage only
involves Fourier transforms and unitary transformations of the small matrices
set up in the first stage. With these inexpensive operations, the quantities of
interest are interpolated onto a dense k-point mesh and used to evaluate the
anomalous Hall conductivity as a Brillouin zone integral. The present scheme,
which also avoids the cumbersome summation over all unoccupied states in the
Kubo formula, is applied to bcc Fe, giving excellent agreement with
conventional, less efficient first-principles calculations. Remarkably, we find
that more than 99% of the effect can be recovered by keeping a set of terms
depending only on the Hamiltonian matrix elements, not on matrix elements of
the position operator.Comment: 16 pages, 7 figure
Calculation of AGARD Wing 445.6 Flutter Using Navier-Stokes Aerodynamics
An unsteady, 3D, implicit upwind Euler/Navier-Stokes algorithm is here used to compute the flutter characteristics of Wing 445.6, the AGARD standard aeroelastic configuration for dynamic response, with a view to the discrepancy between Euler characteristics and experimental data. Attention is given to effects of fluid viscosity, structural damping, and number of structural model nodes. The flutter characteristics of the wing are determined using these unsteady generalized aerodynamic forces in a traditional V-g analysis. The V-g analysis indicates that fluid viscosity has a significant effect on the supersonic flutter boundary for this wing
Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions
In this paper we address the adequacy of various approximate methods of
including Coulomb distortion effects in (e,e') reactions by comparing to an
exact treatment using Dirac-Coulomb distorted waves. In particular, we examine
approximate methods and analyses of (e,e') reactions developed by Traini et al.
using a high energy approximation of the distorted waves and phase shifts due
to Lenz and Rosenfelder. This approximation has been used in the separation of
longitudinal and transverse structure functions in a number of (e,e')
experiments including the newly published 208Pb(e,e') data from Saclay. We find
that the assumptions used by Traini and others are not valid for typical (e,e')
experiments on medium and heavy nuclei, and hence the extracted structure
functions based on this formalism are not reliable. We describe an improved
approximation which is also based on the high energy approximation of Lenz and
Rosenfelder and the analyses of Knoll and compare our results to the Saclay
data. At each step of our analyses we compare our approximate results to the
exact distorted wave results and can therefore quantify the errors made by our
approximations. We find that for light nuclei, we can get an excellent
treatment of Coulomb distortion effects on (e,e') reactions just by using a
good approximation to the distorted waves, but for medium and heavy nuclei
simple additional ad hoc factors need to be included. We describe an explicit
procedure for using our approximate analyses to extract so-called longitudinal
and transverse structure functions from (e,e') reactions in the quasielastic
region.Comment: 30 pages, 8 figures, 16 reference
Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri
We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK
Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting
from these observations show that SiO masers form a highly elliptical ring of
emission approximately 58 x 32 mas with an axial ratio of 1.8:1. The major axis
of this elliptical distribution is oriented at position angle of ~59 deg. The
line-of-sight velocity structure of the SiO masers has an apparent axis of
symmetry consistent with the elongation axis of the maser distribution.
Relative to the assumed stellar velocity of 35 km/s, the blue- and red-shifted
masers were found to lie to the northwest and southeast of this symmetry axis
respectively. This velocity structure suggests a NW-SE rotation of the SiO
maser shell with an equatorial velocity, which we determine to be ~3.6 km/s.
Such a NW-SE rotation is in agreement with a circumstellar envelope geometry
invoked to explain previous water and OH maser observations. In this geometry,
water and OH masers are preferentially created in a region of enhanced density
along the NE-SW equator orthogonal to the rotation/polar axis suggested by the
SiO maser velocities.Comment: 17 Pages, 4 figures (2 color); accepted for publication in Ap
Inherent noise can facilitate coherence in collective swarm motion
Among the most striking aspects of the movement of many animal groups are their sudden coherent changes in direction. Recent observations of locusts and starlings have shown that this directional switching is an intrinsic property of their motion. Similar direction switches are seen in self-propelled particle and other models of group motion. Comprehending the factors that determine such switches is key to understanding the movement of these groups. Here, we adopt a coarse-grained approach to the study of directional switching in a self-propelled particle model assuming an underlying one-dimensional Fokker–Planck equation for the mean velocity of the particles. We continue with this assumption in analyzing experimental data on locusts and use a similar systematic Fokker–Planck equation coefficient estimation approach to extract the relevant information for the assumed Fokker–Planck equation underlying that experimental data. In the experiment itself the motion of groups of 5 to 100 locust nymphs was investigated in a homogeneous laboratory environment, helping us to establish the intrinsic dynamics of locust marching bands. We determine the mean time between direction switches as a function of group density for the experimental data and the self-propelled particle model. This systematic approach allows us to identify key differences between the experimental data and the model, revealing that individual locusts appear to increase the randomness of their movements in response to a loss of alignment by the group. We give a quantitative description of how locusts use noise to maintain swarm alignment. We discuss further how properties of individual animal behavior, inferred by using the Fokker–Planck equation coefficient estimation approach, can be implemented in the self-propelled particle model to replicate qualitatively the group level dynamics seen in the experimental data
Search for Intrinsic Excitations in 152Sm
The 685 keV excitation energy of the first excited 0+ state in 152Sm makes it
an attractive candidate to explore expected two-phonon excitations at low
energy. Multiple-step Coulomb excitation and inelastic neutron scattering
studies of 152Sm are used to probe the E2 collectivity of excited 0+ states in
this "soft" nucleus and the results are compared with model predictions. No
candidates for two-phonon K=0+ quadrupole vibrational states are found. A 2+,
K=2 state with strong E2 decay to the first excited K=0+ band and a probable 3+
band member are established.Comment: 4 pages, 6 figures, accepted for publication as a Rapid Communication
in Physical Review
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