13,279 research outputs found
New Volleyballenes: Y20C60, La20C60, and Lu20C60
New stable Volleyballenes Y20C60, La20C60, and Lu20C60 molecular clusters
have been proposed using first-principles density functional theory studies. In
conjunction with recent findings for the scandium system, these findings
establish Volleyballene M20C60 molecules as a stable general class of fullerene
family. All M20C60 (M=Y, La, and Lu) molecules have Th point group symmetries
and relatively large HOMO-LUMO gaps
Lower bounds for algebraic connectivity of graphs in terms of matching number or edge covering number
In this paper we characterize the unique graph whose algebraic connectivity
is minimum among all connected graphs with given order and fixed matching
number or edge covering number, and present two lower bounds for the algebraic
connectivity in terms of the matching number or edge covering number.Comment: arXiv admin note: substantial text overlap with arXiv:1310.853
On capacity of wireless ad hoc networks with MIMO MMSE receivers
Widely adopted at home, business places, and hot spots, wireless ad-hoc
networks are expected to provide broadband services parallel to their wired
counterparts in near future. To address this need, MIMO techniques, which are
capable of offering several-fold increase in capacity, hold significant
promise. Most previous work on capacity analysis of ad-hoc networks is based on
an implicit assumption that each node has only one antenna. Core to the
analysis therein is the characterization of a geometric area, referred to as
the exclusion region, which quantizes the amount of spatial resource occupied
by a link. When multiple antennas are deployed at each node, however, multiple
links can transmit in the vicinity of each other simultaneously, as
interference can now be suppressed by spatial signal processing. As such, a
link no longer exclusively occupies a geometric area, making the concept of
"exclusion region" not applicable any more. In this paper, we investigate
link-layer throughput capacity of MIMO ad-hoc networks. In contrast to previous
work, the amount of spatial resource occupied by each link is characterized by
the actual interference it imposes on other links. To calculate the link-layer
capacity, we first derive the probability distribution of post-detection SINR
at a receiver. The result is then used to calculate the number of active links
and the corresponding data rates that can be sustained within an area. Our
analysis will serve as a guideline for the design of medium access protocols
for MIMO ad-hoc networks. To the best of knowledge, this paper is the first
attempt to characterize the capacity of MIMO ad-hoc networks by considering the
actual PHY-layer signal and interference model
Strongly Separable Codes
Binary -frameproof codes (-FPCs) are used in multimedia fingerprinting
schemes where the identification of authorized users taking part in the
averaging collusion attack is required. In this paper, a binary strongly
-separable code (-SSC) is introduced to improve such a scheme
based on a binary -FPC. A binary -SSC has the same traceability as
a binary -FPC but has more codewords than a binary -FPC. A composition
construction for binary -SSCs from -ary -SSCs is
described, which stimulates the research on -ary -SSCs with short
length. Several infinite series of optimal -ary -SSCs of length
are derived from the fact that a -ary -SSC of length is
equivalent to a -ary -separable code of length . Combinatorial
properties of -ary -SSCs of length are investigated, and a
construction for -ary -SSCs of length is provided. These
-SSCs of length have more than codewords than -FPCs of
length could have.Comment: 11 pages, submitted to Designs, Codes and Cryptography. arXiv admin
note: text overlap with arXiv:1411.684
Solutions to the modified Korteweg-de Vries equation
This is a continuation of Ref.[1](arXiv:nlin.SI/0603008). In the present
paper we review solutions to the modified Korteweg-de Vries equation in terms
of Wronskians. The Wronskian entry vector needs to satisfy a matrix
differential equation set which contains complex operation. This is different
from the case of the Korteweg-de Vries equation. We introduce an auxiliary
matrix to deal with the complex operation and then we are able to give complete
solution expressions for the matrix differential equation set. The obtained
solutions to the modified Korteweg-de Vries equation can simply be categorized
by two types: solitons and breathers, together with their limit cases. Besides,
we give rational solutions to the modified Korteweg-de Vries equation in
Wromskian form. This is derived with the help of the Galilean transformed
modified Korteweg-de Vries equation. Finally, typical dynamics of the obtained
solutions is analyzed and illustrated. We list out the obtained solutions and
their corresponding basic Wronskian vectors in the conclusion part.Comment: 37 pages and 11 figures. We added some comments and references in the
new versio
Two-Dimensional Scandium Carbide Monolayer and its Nanotubes
A two-dimensional scandium carbide monolayer with a Sc3C10 primitive cell
(Sc3C10 sheet) has been identified using first-principles density functional
theory. In the Sc3C10 sheet, there is a similar basic structure to the one in
the Volleyballene Sc20C60, the Sc8C10 subunit, in which two connected carbon
pentagons are surrounded by one scandium octagon. The hybridization between Sc
d orbitals and C s-p orbitals is crucial for stabilizing the Sc3C10 sheet. Ab
initio molecular dynamics simulations demonstrate that this Sc3C10 sheet is
exceptionally stable. In addition, a series of stable ScC nanotubes have been
obtained by rolling up this Sc3C10 sheet. All nanotubes studied have been found
to be metallic
Riding on the Primary: A New Spectrum Sharing Paradigm for Wireless-Powered IoT Devices
In this paper, a new spectrum sharing model referred to as riding on the
primary (ROP) is proposed for wireless-powered IoT devices with ambient
backscatter communication capabilities. The key idea of ROP is that the
secondary transmitter harvests energy from the primary signal, then modulates
its information bits to the primary signal, and reflects the modulated signal
to the secondary receiver without violating the primary system's interference
requirement. Compared with the conventional spectrum sharing model, the
secondary system in the proposed ROP not only utilizes the spectrum of the
primary system but also takes advantage of the primary signal to harvest energy
and to carry its information. In this paper, we investigate the performance of
such a spectrum sharing system under fading channels. To be specific, we
maximize the ergodic capacity of the secondary system by jointly optimizing the
transmit power of the primary signal and the reflection coefficient of the
secondary ambient backscatter. Different (ideal/practical) energy consumption
models, different (peak/average) transmit power constraints, different types
(fixed/dynamically adjustable) reflection coefficient, different primary
system's interference requirements (rate/outage) are considered. Optimal power
allocation and reflection coefficient are obtained for each scenario.Comment: Submitted to IEEE Trans. Wireless Communication
Sc20C60: A Volleyballene
Since the discovery of the fullerene C60, many very interesting structures
have been proposed, such as Ti8C12, Au20, Au32, Au42, TM@Sin, Eu@Si20, B80, and
B_{40}^{-/0}. Here, an exceptionally stable hollow cage containing 20 scandiums
and 60 carbons was identified. This Sc20C60 molecular cluster has a Th point
group symmetry and a volleyball-like shape, that we refer to below as
Volleyballene. Electronic structure analysis shows that the formation of
delocalized {\pi} bonds between Sc atoms and neighboring five-membered carbon
rings is crucial for stabilizing the cage structure. A relatively large
HOMO-LUMO gap was found. The results of vibrational frequency analysis and
molecular dynamics simulations also demonstrate that this Volleyballene
molecule is exceptionally stable
Topological Superconductors in Correlated Chern Insulators
In this paper, we realize a topological superconductor (TSC) in correlated
topological insulator - the interacting spinful Haldane model. We consider the
electrons on the Haldane model with on-site negative-U interaction and then
study its properties by mean field theory and random-phase-approximation (RPA)
approach. We found that in the intermediate interaction region, the ground
state becomes a TSC with the Chern number 2. We also study its edge states and
the zero modes of the pi-flux.Comment: 13 pages, 14 figure
Optimal path of diffusion over the saddle point and fusion of massive nuclei
Diffusion of a particle passing over the saddle point of a two-dimensional
quadratic potential is studied via a set of coupled Langevin equations and the
expression for the passing probability is obtained exactly. The passing
probability is found to be strongly influenced by the off-diagonal components
of inertia and friction tensors. If the system undergoes the optimal path to
pass over the saddle point by taking an appropriate direction of initial
velocity into account, which departs from the potential valley and has minimum
dissipation, the passing probability should be enhanced. Application to fusion
of massive nuclei, we show that there exists the optimal injecting choice for
the deformable target and projectile nuclei, namely, the intermediate
deformation between spherical and extremely deformed ones which enables the
fusion probability to reach its maximum.Comment: 7 pages, 9 figures, 18 conferenc
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