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 $t$-frameproof codes ($t$-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 $\bar{t}$-separable code ($\bar{t}$-SSC) is introduced to improve such a scheme based on a binary $t$-FPC. A binary $\bar{t}$-SSC has the same traceability as a binary $t$-FPC but has more codewords than a binary $t$-FPC. A composition construction for binary $\bar{t}$-SSCs from $q$-ary $\bar{t}$-SSCs is described, which stimulates the research on $q$-ary $\bar{t}$-SSCs with short length. Several infinite series of optimal $q$-ary $\bar{2}$-SSCs of length $2$ are derived from the fact that a $q$-ary $\bar{2}$-SSC of length $2$ is equivalent to a $q$-ary $\bar{2}$-separable code of length $2$. Combinatorial properties of $q$-ary $\bar{2}$-SSCs of length $3$ are investigated, and a construction for $q$-ary $\bar{2}$-SSCs of length $3$ is provided. These $\bar{2}$-SSCs of length $3$ have more than $12.5\%$ codewords than $2$-FPCs of length $3$ 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