8,803 research outputs found
Sonic boom research
A computer program for CDC 6600 is developed for the nonlinear sonic boom analysis including the asymmetric effect of lift near the vertical plane of symmetry. The program is written in FORTRAN 4 language. This program carries out the numerical integration of the nonlinear governing equations from the input data at a finite distance from the airplane configuration at a flight altitude to yield the pressure signitude at ground. The required input data and the format for the output are described. A complete program listing and a sample calculation are given
Extensions of algebraic image operators: An approach to model-based vision
Researchers extend their previous research on a highly structured and compact algebraic representation of grey-level images which can be viewed as fuzzy sets. Addition and multiplication are defined for the set of all grey-level images, which can then be described as polynomials of two variables. Utilizing this new algebraic structure, researchers devised an innovative, efficient edge detection scheme. An accurate method for deriving gradient component information from this edge detector is presented. Based upon this new edge detection system researchers developed a robust method for linear feature extraction by combining the techniques of a Hough transform and a line follower. The major advantage of this feature extractor is its general, object-independent nature. Target attributes, such as line segment lengths, intersections, angles of intersection, and endpoints are derived by the feature extraction algorithm and employed during model matching. The algebraic operators are global operations which are easily reconfigured to operate on any size or shape region. This provides a natural platform from which to pursue dynamic scene analysis. A method for optimizing the linear feature extractor which capitalizes on the spatially reconfiguration nature of the edge detector/gradient component operator is discussed
Multiple Radial Cool Molecular Filaments in NGC 1275
We have extended our previous observation (Lim et al. 2008) of NGC1275
covering a central radius of ~10kpc to the entire main body of cool molecular
gas spanning ~14kpc east and west of center. We find no new features beyond the
region previously mapped, and show that all six spatially-resolved features on
both the eastern and western sides (three on each side) comprise radially
aligned filaments. Such radial filaments can be most naturally explained by a
model in which gas deposited "upstream" in localized regions experiencing an
X-ray cooling flow subsequently free falls along the gravitational potential of
PerA, as we previously showed can explain the observed kinematics of the two
longest filaments. All the detected filaments coincide with locally bright
Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we
show that these filaments have lower star formation efficiencies than the
nearly constant value found for molecular gas in nearby normal spiral galaxies.
On the other hand, some at least equally luminous Halpha features, including a
previously identified giant HII region, show no detectable cool molecular gas
with a corresponding ratio at least a factor of ~5 lower; in the giant HII
region, essentially all the pre-existing molecular gas may have been converted
to stars. We demonstrate that all the cool molecular filaments are
gravitationally bound, and without any means of support beyond thermal pressure
should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously
the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal
shear may help delay their collapse, but more likely turbulent velocities of at
least a few tens km/s or magnetic fields with strengths of at least several
~10uG are required to support these filaments.Comment: 52 pages, 11 figures. Accepted to Ap
The Finite Basis Problem for Kiselman Monoids
In an earlier paper, the second-named author has described the identities
holding in the so-called Catalan monoids. Here we extend this description to a
certain family of Hecke--Kiselman monoids including the Kiselman monoids
. As a consequence, we conclude that the identities of
are nonfinitely based for every and exhibit a finite
identity basis for the identities of each of the monoids and
.
In the third version a question left open in the initial submission has beed
answered.Comment: 16 pages, 1 table, 1 figur
Radiation-induced magnetoresistance oscillations in two-dimensional electron systems under bichromatic irradiation
We analyze the magnetoresistance oscillations in high-mobility
two-dimensional electron systems induced by the combined driving of two
radiation fields of frequency and , based on the
balance-equation approach to magnetotransport for high-carrier-density systems
in Faraday geometry. It is shown that under bichromatic irradiation of
, most of the characterstic peak-valley pairs in the
curve of versus magnetic field in the case of monochromatic
irradiation of either or disappear, except the one around
or . oscillations
show up mainly as new peak-valley structures around other positions related to
multiple photon processes of mixing frequencies ,
, etc. Many minima of these resistance peak-valley pairs can
descend down to negative with enhancing radiation strength, indicating the
possible bichromaticzero-resistance states.Comment: 5 pages, 3 figures. Accepted for publication in Phys. Rev.
Excitation energy transfer: Study with non-Markovian dynamics
In this paper, we investigate the non-Markovian dynamics of a model to mimic
the excitation energy transfer (EET) between chromophores in photosynthesis
systems. The numerical path integral method is used. This method includes the
non-Markovian effects of the environmental affects and it does not need the
perturbation approximation in solving the dynamics of systems of interest. It
implies that the coherence helps the EET between chromophores through lasting
the transfer time rather than enhances the transfer rate of the EET. In
particular, the non-Markovian environment greatly increase the efficiency of
the EET in the photosynthesis systems.Comment: 5 pages, 5 figure
Defective hierarchical porous copper-based metal-organic frameworks synthesised via facile acid etching strategy
Introducing hierarchical pore structure to microporous materials such as
metal-organic frameworks (MOFs) can be beneficial for reactions where the rate
of reaction is limited by low rates of diffusion or high pressure drop. This
advantageous pore structure can be obtained by defect formation, mostly via
post-synthetic acid etching, which has been studied extensively on water-stable
MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a
corresponding manner by using phosphoric acid as a size-selective etching agent
and a mixture of dimethyl sulfoxide and methanol as a dilute solvent.
Interestingly, we demonstrate that the etching process which is time- and
acidity- dependent, can result in formation of defective HKUST-1 with extra
interconnected hexagonal macropores without compromising on the bulk
crystallinity. These findings suggest an intelligent scalable synthetic method
for formation of hierarchical porosity in MOFs that are prone to hydrolysis,
for improved molecular accessibility and diffusion for catalysis.Comment: 14 pages, 8 figure
Combining the Min-Conflicts and Look-Forward Heuristics to Effectively Solve A Set of Hard University Timetabling Problems
University timetabling problems (UTPs) represent a class of challenging, high-dimensional and multi-objectives combinatorial optimization problems that are commonly solved by constructive search, local search methods or their hybrids. In this paper, we proposed to combine the min-conflicts and look-forward heuristics used in local search methods to effectively solve general university timetabling problems. Our combined heuristics when augmented with the k-reset operator, and appropriate heuristic variable ordering strategy achieved impressive results on a set of challenging UTPs obtained from an international timetabling competition. A preliminary analysis of the results was given. More importantly, our search proposal shed light on effectively solving other complex or large-scale scheduling problems.published_or_final_versio
Chiral structure of the solutions of the Ginsparg-Wilson relation
We analyse the structure of solutions of the Ginsparg-Wilson relation for
lattice Dirac operator in topologically trivial gauge sector. We show that the
properties of such solutions relating to the perturbative stability of the pole
of the fermion propagator as well as to the structure of the Yukawa models
based on these solutions are solely determined by the non-local chirally
invariant part of these Dirac operators. Depending on the structure of this
part, the pole in the fermion propagator may or may not be stable under
radiative corrections. We illustrate this by explicit examples.Comment: 10 pages, Latex, no figure
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