4,951 research outputs found
Interaction of NH gas on -MoO nanostructures a DFT investigation
The structural stability, electronic properties and NH adsorption
properties of pristine, Ti, Zr and F substituted -MoO
nanostructures are successfully studied using density functional theory with
B3LYP/LanL2DZ basis set. The structural stability of -MoO
nanostructures is discussed in terms of formation energy. The electronic
properties of pristine, Ti, Zr and F incorporated -MoO
nanostructures are discussed in terms of HOMO-LUMO gap, ionization potential
and electron affinity. -MoO nanostructures can be fine-tuned with
suitable substitution impurity to improve the adsorption characteristics of
ammonia, which can be used to detect NH in a mixed environment. The present
work gives an insight into tailoring -MoO nanostructures for NH
detection.Comment: 16 pages, 20 figures, 2 table
Lattice expansion and non-collinear to collinear ferrimagnetic order in MnCrO nanoparticle
We report magnetic behaviour of MnCrO, which belongs to a special
class of spinel, known as chromite. Bulk MnCrO shows a sequence of
magnetic states, which follows paramagnetic (PM) to collinear ferrimagnetic
(FM) state below T 45 K and collinear FM state to non-collinear FM
state below T 18 K. The non-collinear spin structure has been
modified on decreasing the particle size, and magnetic transition at T
decreases in nanoparticle samples. However, ferrimagnetic order is still
dominating in nanoparticles, except the observation of superparamagnetic like
blocking and decrease of spontaneous magnetization for nanoparticle. This may,
according to the core-shell model of ferrimagnetic nanoparticle, be the surface
disorder effect of nanoparticle. The system also show the increase of T in
nanoparticle samples, which is not consistent with the core-shell model. The
analysis of the M(T) data, applying spin wave theory, has shown an unusual
Bloch exponent value 3.35 for bulk MnCrO, which decreases and
approaches to 1.5, a typical value for any standard ferromagnet, with
decreasing the particle size. MnCrO has shown a few more unusual
behaviour. For example, lattice expansion in nanoparticle samples. The present
work demonstrates the correlation between a systematic increase of lattice
parameter and the gradual decrease of B site non-collinear spin structure in
the light of magnetism of MnCrO nanoparticles
Sensing behavior of acetone vapors on TiO nanostructures --- application of density functional theory
The electronic properties of TiO nanostructure are explored using density
functional theory. The adsorption properties of acetone on TiO
nanostructure are studied in terms of adsorption energy, average energy gap
variation and Mulliken charge transfer. The density of states spectrum and the
band structure clearly reveals the adsorption of acetone on TiO
nanostructures. The variation in the energy gap and changes in the density of
charge are observed upon adsorption of acetone on n-type TiO base material.
The results of DOS spectrum reveal that the transfer of electrons takes place
between acetone vapor and TiO base material. The findings show that the
adsorption property of acetone is more favorable on TiO nanostructure.
Suitable adsorption sites of acetone on TiO nanostructure are identified at
atomistic level. From the results, it is confirmed that TiO nanostructure
can be efficiently utilized as a sensing element for the detection of acetone
vapor in a mixed environment.Comment: 13 pages, 14 figures, 3 table
Super Fibonacci Graceful Labeling of Some Special Class of Graphs
A Fibonacci graceful labeling and a super Fibonacci graceful labeling on graphs were introduced by Kathiresan and Amutha in 2006
Robust and MaxMin Optimization under Matroid and Knapsack Uncertainty Sets
Consider the following problem: given a set system (U,I) and an edge-weighted
graph G = (U, E) on the same universe U, find the set A in I such that the
Steiner tree cost with terminals A is as large as possible: "which set in I is
the most difficult to connect up?" This is an example of a max-min problem:
find the set A in I such that the value of some minimization (covering) problem
is as large as possible.
In this paper, we show that for certain covering problems which admit good
deterministic online algorithms, we can give good algorithms for max-min
optimization when the set system I is given by a p-system or q-knapsacks or
both. This result is similar to results for constrained maximization of
submodular functions. Although many natural covering problems are not even
approximately submodular, we show that one can use properties of the online
algorithm as a surrogate for submodularity.
Moreover, we give stronger connections between max-min optimization and
two-stage robust optimization, and hence give improved algorithms for robust
versions of various covering problems, for cases where the uncertainty sets are
given by p-systems and q-knapsacks.Comment: 17 pages. Preliminary version combining this paper and
http://arxiv.org/abs/0912.1045 appeared in ICALP 201
Minimum Makespan Multi-vehicle Dial-a-Ride
Dial a ride problems consist of a metric space (denoting travel time between
vertices) and a set of m objects represented as source-destination pairs, where
each object requires to be moved from its source to destination vertex. We
consider the multi-vehicle Dial a ride problem, with each vehicle having
capacity k and its own depot-vertex, where the objective is to minimize the
maximum completion time (makespan) of the vehicles. We study the "preemptive"
version of the problem, where an object may be left at intermediate vertices
and transported by more than one vehicle, while being moved from source to
destination. Our main results are an O(log^3 n)-approximation algorithm for
preemptive multi-vehicle Dial a ride, and an improved O(log t)-approximation
for its special case when there is no capacity constraint. We also show that
the approximation ratios improve by a log-factor when the underlying metric is
induced by a fixed-minor-free graph.Comment: 22 pages, 1 figure. Preliminary version appeared in ESA 200
Dial a Ride from k-forest
The k-forest problem is a common generalization of both the k-MST and the
dense--subgraph problems. Formally, given a metric space on vertices
, with demand pairs and a ``target'' ,
the goal is to find a minimum cost subgraph that connects at least demand
pairs. In this paper, we give an -approximation
algorithm for -forest, improving on the previous best ratio of
by Segev & Segev.
We then apply our algorithm for k-forest to obtain approximation algorithms
for several Dial-a-Ride problems. The basic Dial-a-Ride problem is the
following: given an point metric space with objects each with its own
source and destination, and a vehicle capable of carrying at most objects
at any time, find the minimum length tour that uses this vehicle to move each
object from its source to destination. We prove that an -approximation
algorithm for the -forest problem implies an
-approximation algorithm for Dial-a-Ride. Using our
results for -forest, we get an -
approximation algorithm for Dial-a-Ride. The only previous result known for
Dial-a-Ride was an -approximation by Charikar &
Raghavachari; our results give a different proof of a similar approximation
guarantee--in fact, when the vehicle capacity is large, we give a slight
improvement on their results.Comment: Preliminary version in Proc. European Symposium on Algorithms, 200
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