27,716 research outputs found
A consistent design procedure for supercritical airfoils in free air and a wind tunnel
A computational inverse procedure for transonic airfoils in which shapes are determined supporting prescribed pressure distributions is presented. The method uses the small disturbance equation and a consistent analysis-design differencing procedure at the airfoil surface. This avoids the intermediate analysis-design-analysis iterations. The effect of any openness at the trailing edge is taken onto account by adding an effective source term in the far field. The final results from a systematic expansion procedure which models the far field for solid, ideal slotted, and free jet tunnel walls are presented along with some design results for the associated boundary conditions and those for a free flight
Chemical abundances in LMC stellar populations. II. The bar sample
This paper compares the chemical evolution of the Large Magellanic Cloud
(LMC) to that of the Milky Way (MW) and investigates the relation between the
bar and the inner disc of the LMC in the context of the formation of the bar.
We obtained high-resolution and mid signal-to-noise ratio spectra with
FLAMES/GIRAFFE at ESO/VLT and performed a detailed chemical analysis of 106 and
58 LMC field red giant stars (mostly older than 1 Gyr), located in the bar and
the disc of the LMC respectively. We measured elemental abundances for O, Mg,
Si, Ca, Ti, Na, Sc, V, Cr, Co, Ni, Cu, Y, Zr, Ba, La and Eu. We find that the
{\alpha}-element ratios [Mg/Fe] and [O/Fe] are lower in the LMC than in the MW
while the LMC has similar [Si/Fe], [Ca/Fe], and [Ti/Fe] to the MW. As for the
heavy elements, [Ba,La/Eu] exhibit a strong increase with increasing
metallicity starting from [Fe/H]=-0.8 dex, and the LMC has lower [Y+Zr/Ba+La]
ratios than the MW. Cu is almost constant over all metallicities and about 0.5
dex lower in the LMC than in the MW. The LMC bar and inner disc exhibit
differences in their [{\alpha}/Fe] (slightly larger scatter for the bar in the
metallicity range [-1,-0.5]), their Eu (the bar trend is above the disc trend
for [Fe/H] > -0.5 dex), their Y and Zr, their Na and their V (offset between
bar and disc distributions). Our results show that the chemical history of the
LMC experienced a strong contribution from type Ia supernovae as well as a
strong s-process enrichment from metal-poor AGB winds. Massive stars made a
smaller contribution to the chemical enrichment compared to the MW. The
observed differences between the bar and the disc speak in favour of an episode
of enhanced star formation a few Gyr ago, occurring in the central parts of the
LMC and leading to the formation of the bar. This is in agreement with recently
derived star formation histories.Comment: 22 pages, 20 figures; Accepted for publication in A&
Economic Feasibility of Establishing a Flax Tow or Flax Shive Pelleting Plant in North Dakota
Agribusiness,
Majorana spinors and extended Lorentz symmetry in four-dimensional theory
An extended local Lorentz symmetry in four-dimensional (4D) theory is
considered. A source of this symmetry is a group of general linear
transformations of four-component Majorana spinors GL(4,M) which is isomorphic
to GL(4,R) and is the covering of an extended Lorentz group in a 6D Minkowski
space M(3,3) including superluminal and scaling transformations. Physical
space-time is assumed to be a 4D pseudo-Riemannian manifold. To connect the
extended Lorentz symmetry in the M(3,3) space with the physical space-time, a
fiber bundle over the 4D manifold is introduced with M(3,3) as a typical fiber.
The action is constructed which is invariant with respect to both general 4D
coordinate and local GL(4,M) spinor transformations. The components of the
metric on the 6D fiber are expressed in terms of the 4D pseudo-Riemannian
metric and two extra complex fields: 4D vector and scalar ones. These extra
fields describe in the general case massive particles interacting with an extra
U(1) gauge field and weakly interacting with ordinary particles, i.e.
possessing properties of invisible (dark) matter.Comment: 24 page
Efficiently and Transparently Maintaining High SIMD Occupancy in the Presence of Wavefront Irregularity
Demand is increasing for high throughput processing of irregular streaming applications; examples of such applications from scientific and engineering domains include biological sequence alignment, network packet filtering, automated face detection, and big graph algorithms. With wide SIMD, lightweight threads, and low-cost thread-context switching, wide-SIMD architectures such as GPUs allow considerable flexibility in the way application work is assigned to threads. However, irregular applications are challenging to map efficiently onto wide SIMD because data-dependent filtering or replication of items creates an unpredictable data wavefront of items ready for further processing. Straightforward implementations of irregular applications on a wide-SIMD architecture are prone to load imbalance and reduced occupancy, while more sophisticated implementations require advanced use of parallel GPU operations to redistribute work efficiently among threads.
This dissertation will present strategies for addressing the performance challenges of wavefront- irregular applications on wide-SIMD architectures. These strategies are embodied in a developer framework called Mercator that (1) allows developers to map irregular applications onto GPUs ac- cording to the streaming paradigm while abstracting from low-level data movement and (2) includes generalized techniques for transparently overcoming the obstacles to high throughput presented by wavefront-irregular applications on a GPU. Mercator forms the centerpiece of this dissertation, and we present its motivation, performance model, implementation, and extensions in this work
A study of shear failures in footing
The purpose of this investigation was to conduct a model study of the basic mechanism of failure in shear of reinforced concrete footings through the use of plaster models.
Sixty-nine models were constructed and loaded to failure on a foundation of sand using various combinations of size and depth of model and column size. Load - deformation data and failure loads were recorded.
It was determined that model studies are a feasible procedure to analyse the mechanism of failure in footings. The perimeter of the loaded area was found to be the critical section in determining the ultimate shearing strength of footings rather than some arbitrary distance out from the face of the column. A dimensionless plot was developed to correlate all the data and an equation is proposed to predict ultimate loads --Abstract, page ii
Physical Bias of Galaxies From Large-Scale Hydrodynamic Simulations
We analyze a new large-scale (Mpc) numerical hydrodynamic
simulation of the popular CDM cosmological model, including in our
treatment dark matter, gas and star-formation, on the basis of standard
physical processes. The method, applied with a numerical resolution of
kpc (which is still quite coarse for following individual galaxies,
especially in dense regions), attempts to estimate where and when galaxies
form. We then compare the smoothed galaxy distribution with the smoothed mass
distribution to determine the "bias" defined as on scales large compared with the code
numerical resolution (on the basis of resolution tests given in the appendix of
this paper). We find that (holding all variables constant except the quoted
one) bias increases with decreasing scale, with increasing galactic age or
metallicity and with increasing redshift of observations. At the Mpc
fiducial comoving scale bias (for bright regions) is 1.35 at reaching to
3.6 at , both numbers being consistent with extant observations. We also
find that Mpc voids in the distribution of luminous objects are
as observed (i.e., observed voids are not an argument against CDM-like models)
and finally that the younger systems should show a colder Hubble flow than do
the early type galaxies (a testable proposition). Surprisingly, little
evolution is found in the amplitude of the smoothed galaxy-galaxy correlation
function (as a function of {\it comoving} separation). Testing this prediction
vs observations will allow a comparison between this work and that of Kauffmann
et al which is based on a different physical modelingmethod.Comment: in press, ApJ, 26 latex pages plus 7 fig
Some buffet response characteristics of a twin-vertical-tail configuration
A rigid, 1/6 size, full span model of an F-18 airplane was fitted with flexible vertical tails of two different levels of stiffness that were buffet tested in the Langley Transonic Dynamics Tunnel. Vertical tail buffet response results that were obtained over the range of angles of attack from -10 to 40 degs, and over the range of Mach numbers from 0.30 to 0.95 are presented. These results indicate the following: (1) the response occurs in the first bending mode; (2) the response increases with increasing dynamic pressure, but changes in response are not linearly proportional to the changes in dynamic pressure; (3) the response is larger at M = 0.30 than it is at the higher Mach numbers; (4) the maximum intensity of the buffeting is described as heavy to severe using an assessment criteria proposed by another investigator; and (5) the data at different dynamic pressures and for the different tails correlate reasonably well using the buffet excitation parameter derived from the dynamic analysis of buffeting
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