3,066 research outputs found
A Bound for the Locating Chromatic Numbers of Trees
Let be a proper -coloring of a connected graph and
be an ordered partition of into the resulting
color classes. For a vertex of , the color code of with respect to
is defined to be the ordered -tuple
where
. If distinct vertices have
distinct color codes, then is called a locating coloring. The minimum
number of colors needed in a locating coloring of is the locating chromatic
number of , denoted by \Cchi_{{}_L}(G). In this paper, we study the
locating chromatic numbers of trees. We provide a counter example to a theorem
of Gary Chartrand et al. [G. Chartrand, D. Erwin, M.A. Henning, P.J. Slater, P.
Zhang, The locating-chromatic number of a graph, Bull. Inst. Combin. Appl. 36
(2002) 89-101] about the locating chromatic numbers of trees. Also, we offer a
new bound for the locating chromatic number of trees. Then, by constructing a
special family of trees, we show that this bound is best possible.Comment: 9 pages, 3 figure
On the Randic and degree distance indices of the Mycielskian of a graph
In a search for triangle-free graphs with arbitrarily large chromatic
numbers, Mycielski developed a graph transformation that transforms a graph
into a new graph which is called the Mycielskian of that graph. In this paper
we provide some sharp bounds for the Randic index of the Mycielskian graphs.
Also, we determine the degree distance index of the Mycielskian of each graph
with diameter two.Comment: just thank
Applications of Blockchain Technology beyond Cryptocurrency
Blockchain (BC), the technology behind the Bitcoin crypto-currency system, is
considered to be both alluring and critical for ensuring enhanced security and
(in some implementations, non-traceable) privacy for diverse applications in
many other domains including in the Internet of Things (IoT) eco-system.
Intensive research is currently being conducted in both academia and industry
applying the Blockchain technology in multifarious applications. Proof-of-Work
(PoW), a cryptographic puzzle, plays a vital role in ensuring BC security by
maintaining a digital ledger of transactions, which is considered to be
incorruptible. Furthermore, BC uses a changeable Public Key (PK) to record the
users' identity, which provides an extra layer of privacy. Not only in
cryptocurrency has the successful adoption of BC been implemented but also in
multifaceted non-monetary systems such as in: distributed storage systems,
proof-of-location, healthcare, decentralized voting and so forth. Recent
research articles and projects/applications were surveyed to assess the
implementation of BC for enhanced security, to identify associated challenges
and to propose solutions for BC enabled enhanced security systems
Effective interactions between inclusions in an active bath
We study effective two- and three-body interactions between non-active
colloidal inclusions in an active bath of chiral or non-chiral particles, using
Brownian Dynamics simulations within a standard, two-dimensional model of
disk-shaped inclusions and active particles. In a non-chiral active bath, we
first corroborate previous findings on effective two-body repulsion mediated
between the inclusions by elucidating the detailed non-monotonic features of
the two-body force profiles, including a primary maximum, and a secondary hump
at larger separations that was not previously reported. We then show that these
features arise directly from the formation, and sequential overlaps, of
circular layers (or 'rings') of active particles around the inclusions, as the
latter are brought to small surface separations. These rings extend to radial
distances of a few active-particle radii from the surface of inclusions, giving
the hard-core inclusions relatively thick, soft, repulsive 'shoulders', whose
multiple overlaps then enable significant (non-pairwise) three-body forces in
both non-chiral and chiral active baths. The resulting three-body forces can
even exceed the two-body forces in magnitude and display distinct repulsive and
attractive regimes at intermediate to large self-propulsion strengths. In a
chiral active bath, we show that, while active particles still tend to
accumulate at the immediate vicinity of the inclusions, they exhibit strong
depletion from the intervening region between the inclusions, and partial
depletion from relatively thick, circular, zones further away from the
inclusions. In this case, the effective, predominantly repulsive, interactions
between the inclusions turn to active, chirality-induced, depletion-type
attractions, acting over an extended range of separations.Comment: 12 pages, 14 figure
Description of clustering of inertial particles in turbulent flows via finite-time Lyapunov exponents
An asymptotic solution is derived for the motion of inertial particles
exposed to Stokes drag in an unsteady random flow. This solution provides the
finite-time Lyapunov exponents as a function of Stokes number and Lagrangian
strain- and rotation-rates autocovariances. The sum of these exponents, which
corresponds to a concentration-weighted divergence of particle velocity field,
is considered as a measure of clustering. For inertial particles dispersed in
an isotropic turbulent flow our analysis predicts maximum clustering at an
intermediate Stokes number and minimal clustering at small and large Stokes
numbers. Direct numerical simulations are performed for quantitative validation
of our analysis, showing a reasonable agreement between the two.Comment: 11 pages and 4 figure
A modal analysis of the behavior of inertial particles in turbulence
The clustering of small heavy inertial particles subjected to Stokes drag in
turbulence is known to be minimal at small and large Stokes number and
substantial at . This non-monotonic trend, which has
been shown computationally and experimentally, is yet to be explained
analytically. In this study, we obtain an analytical expression for the
Lyapunov exponents that quantitatively predicts this trend. The sum of the
exponents, which is the normalized rate of change of the signed-volume of a
small cloud of particles, is correctly predicted to be negative and positive at
small and large Stokes numbers, respectively, asymptoting to as and as , where is the
particle relaxation time and is the difference between the norm of
the rotation- and strain-rate tensors computed along the particle trajectory.
Additionally, the trajectory crossing is predicted only in hyperbolic flows
where for sufficiently inertial particles with a that scales with
. Following the onset of crossovers, a transition from clustering
to dispersion is predicted correctly. We show these behaviors are not unique to
three-dimensional isotropic turbulence and can be reproduced closely by a
one-dimensional mono-harmonic flow, which appears as a fundamental canonical
problem in the study of particle clustering. Analysis of this one-dimensional
canonical flow shows that the rate of clustering, quantified as the product of
the Lyapunov exponent and particle relaxation time, is bounded by ,
behaving with extreme nonlinearity in the hyperbolic flows and always remaining
positive in the elliptic flows. These findings, which are stemmed from our
analysis, are corroborated by the direct numerical simulations.Comment: full article, 16 figure
Stable Stair-Climbing of a Quadruped Robot
Synthesizing a stable gait that enables a quadruped robot to climb stairs is
the focus of this paper. To this end, first a stable transition from initial to
desired configuration is made based on the minimum number of steps and maximum
use of the leg workspace to prepare the robot for the movement. Next, swing leg
and body trajectories are planned for a successful stair- climbing gait.
Afterwards, a stable spinning gait is proposed to change the orientation of the
body. We simulate our gait planning algorithms on a model of quadruped robot.
The results show that the robot is able to climb up stairs, rotate about its
yaw axis, and climb down stairs while its stability is guaranteed.Comment: Proceeding of the 2013 RSI/ISM International Conference on Robotics
and Mechatronics, February 13-15, 2013, Tehran, Ira
A Lagrangian Decomposition Algorithm for Robust Green Transportation Location Problem
In this paper, a green transportation location problem is considered with
uncertain demand parameter. Increasing robustness influences the number of
trucks for sending goods and products, and consequently, makes the air
pollution enhance. In this paper, two green approaches are introduced which
demand is the main uncertain parameter in both. These approaches are addressed
to provide a trade-off between using available trucks and buying new hybrid
trucks for evaluating total costs besides air pollution. Due to growing
complexity, a Lagrangian decomposition algorithm is applied to find a tight
lower bound for each approach. In this propounded algorithm, the main model is
decomposed into master and subproblems to speed up convergence with a tight
gap. Finally, the suggested algorithm is compared with commercial solver
regarding total cost and computational time. Due to computational results for
the proposed approach, the Lagrangian decomposition algorithm is provided a
close lower bound in less time against commercial solver
On the Design of Universal LDPC Codes
Low-density parity-check (LDPC) coding for a multitude of equal-capacity
channels is studied. First, based on numerous observations, a conjecture is
stated that when the belief propagation decoder converges on a set of
equal-capacity channels, it would also converge on any convex combination of
those channels. Then, it is proved that when the stability condition is
satisfied for a number of channels, it is also satisfied for any channel in
their convex hull. For the purpose of code design, a method is proposed which
can decompose every symmetric channel with capacity C into a set of
identical-capacity basis channels. We expect codes that work on the basis
channels to be suitable for any channel with capacity C. Such codes are found
and in comparison with existing LDPC codes that are designed for specific
channels, our codes obtain considerable coding gains when used across a
multitude of channels.Comment: 5 pages, 2 figures, To appear in Proc. IEEE International Symposium
on Information Theory (ISIT 2008), Toronto, Canada, July 200
Novel method for planar microstrip antenna matching impedance
Because all microstrip antennas have to be matched to the standard generator
impedance or load, the input impedance matching method for antenna is
particularly important. In this paper a new methodology in achieving matching
impedance of a planar microstrip antenna for wireless application is described.
The method is based on embedding an Interdigital capacitor. The fine results
obtained by using a microstrip Interdigital capacitor for matching antenna
impedance led to an efficient method to improve array antenna performance. In
fact, a substantial saving on the whole surfaces as well as enhancement of the
gain, the directivity and the power radiated was achieved.Comment: Submitted to Journal of Telecommunications, see
http://sites.google.com/site/journaloftelecommunications/volume-2-issue-2-may-201
- β¦