Hop Limit Research Articles

MnO2 doping enhances energy storage performances in lead-free BiFeO3-based ceramics

BiFeO3-based ferroelectric ceramics as promising candidates for energy storage devices have attracted a great deal of interest owing to the large ferroelectric polarization and high Curie temperature. However, the Bi volatilization induced oxygen vacancy and Fe2+/Fe3+ ionic hopping limit its energy storage performances (ESP). A charge compensated method by introducing multivalent oxide is proposed to inhibit the oxygen vacancy and Fe2+/Fe3+ ionic hopping, aiming to improve dielectric breakdown strength (BDS), polarization saturation and ESP. Here, we prepared a series of MnO2-modified Bi0.83Sm0.17Fe0.95Sc0.05O3-0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3 [BSFS-BT-BMZ-x wt%MnO2] ceramics by traditional solid state sintering. It revealed that a large reversible energy storage density (Wrec) of ∼ 4.1 J/cm3 and a great efficiency (η) of ∼ 88% can be achieved at x = 2.1 ceramics. The improved ESP could be attributed mainly to the effective inhibition of Fe2+ by multi-fold valence states of Mn ions accompanying with the decreasing of oxygen vacancy and Fe3+/Fe2+ ionic hopping, leading to the refinement of grain size, and the enhancement of BDS and ferroelectric polarization. Moreover, the optimized ceramics exhibit the good frequency/thermal stability, excellent fatigue resistance and high powder density. These results demonstrate that a charge compensated method pays a route of improving ESP for dielectric ceramic capacitors.

Swarm and Location-Based QoS Routing Algorithm in MEO/LEO Double-Layered Satellite Networks

In this paper, we mainly research on the QoS (Quality of Service) routing algorithms for MEO/LEO (medium Earth orbit/low Earth orbit) double-layered satellite networks. In this type of networks, the rapidly changing network topology due to relative motion of satellites is one of the main challenges when designing an efficient routing algorithm. Specifically, the issues of high rerouting overhead and traffic routing with diverse QoS requirements remain to be resolved. This paper proposed a M-BMDP (modified bandwidth constrained minimum delay path) routing algorithm based on swarm and location for MEO/LEO double-layered satellite networks. This algorithm forms a set of LEO groups according to the footprint of MEO satellites and chooses the relative MEO satellites as its group manager. For delay sensitive traffic, the algorithm can improve the QoS as the cost of packet loss based on hop limit. And for users located in reversed crevice zone, the traffic can route through one MEO satellite to reduce the time delay. The simulation results show that the M-BMDP algorithm performs better in rerouting delay, overhead and pack loss rate compared with existing solutions.

The Hubbard model: exact constraints on spectral moments in the strong coupling limit

ABSTRACT Exact spectral moment relations are derived and presented for the low temperature, strong coupling limit of the Hubbard model, for any dimension, lattice structure and electron density. These results generate an exact, rigorous and quantitative test for proposed solutions to the Hubbard model that claim to be valid in the strong coupling, low temperature region. The test complements analyses for weak coupling and high temperatures, offering insights into the essential physics of the model, specifically the quasiparticle energy (centroid) and lifetime (width) of the spectral weight function in the infinite coupling, finite hopping limit. Numerical results are given for nearest neighbour hopping in 1, 2 and 3D.

A tunable bilayer Hubbard model in twisted WSe2.

Moiré materials with flat electronic bands provide a highly controllable quantum system for studies of strong-correlation physics and topology. In particular, angle-aligned heterobilayers of semiconducting transition metal dichalcogenides with large band offset realize the single-band Hubbard model. Introduction of a new layer degree of freedom is expected to foster richer interactions, enabling Hund's physics, interlayer exciton condensation and new superconducting pairing mechanisms to name a few. Here we report competing electronic states in twisted AB-homobilayer WSe2, which realizes a bilayer Hubbard model in the weak interlayer hopping limit for holes. By layer-polarizing holes via a perpendicular electric field, we observe a crossover from an excitonic insulator to a charge-transfer insulator at a hole density of ν = 1 (in units of moiré density), a transition from a paramagnetic to an antiferromagnetic charge-transfer insulator at ν = 2 and evidence for a layer-selective Mott insulator at 1 < ν < 2. The unique coupling of charge and spin to external electric and magnetic fields also manifests a giant magnetoelectric response. Our results establish a new solid-state simulator for the bilayer Hubbard model Hamiltonian.

Using Energy Shaping and Regulation for Limit Cycle Stabilization, Generation, and Transition in Simple Locomotive Systems

Abstract This paper explores new ways to use energy shaping and regulation methods in walking systems to generate new passive-like gaits and dynamically transition between them. We recapitulate a control framework for Lagrangian hybrid systems, and show that regulating a state varying energy function is equivalent to applying energy shaping and regulating the system to a constant energy value. We then consider a simple one-dimensional hopping robot and show how energy shaping and regulation control can be used to generate and transition between nearly globally stable hopping limit cycles. The principles from this example are then applied on two canonical walking models, the spring loaded inverted pendulum (SLIP) and compass gait biped, to generate and transition between locomotive gaits. These examples show that piecewise jumps in control parameters can be used to achieve stable changes in desired gait characteristics dynamically/online.

Dynamic response of spin-2 bosons in one-dimensional optical lattices

We investigate the spin-2 chain model corresponding to the small hopping limit of the spin-2 Bose-Hubbard model using density-matrix renormalization-group and time-evolution techniques. We calculate both static correlation functions and the dynamic structure factor. The dynamic structure factor in the dimerized phase differs significantly between parameters near the SU(5)-symmetric point and those deeper in the phase where the dimerization is strong. In the former case, most of the spectral weight is concentrated in a single excitation line, while in the latter case, a broad excitation continuum shows up. For the trimerized phase, we find gapless excitations at momenta $k=\pm2\pi/3$ in agreement with previous results, although the visibility of these excitations in the dynamic spin response depends strongly on the specific parameters. We also consider parameters for specific atoms which may be relevant for future optical-lattice experiments.

A Flexible, Natural Formulation for the Network Design Problem with Vulnerability Constraints

Given a graph, a set of origin-destination (OD) pairs with communication requirements, and an integer k ≥ 2, the network design problem with vulnerability constraints (NDPVC) is to identify a subgraph with the minimum total edge costs such that, between each OD pair, there exist a hop-constrained primary path and a hop-constrained backup path after any k − 1 edges of the graph fail. Formulations exist for single-edge failures (i.e., k = 2). To solve the NDPVC for an arbitrary number of edge failures, we develop two natural formulations based on the notion of length-bounded cuts. We compare their strengths and flexibilities in solving the problem for k ≥ 3. We study different methods to separate infeasible solutions by computing length-bounded cuts of a given size. Experimental results show that, for single-edge failures, our formulation increases the number of solved benchmark instances from 61% (obtained within a two-hour limit by the best published algorithm) to more than 95%, thus increasing the number of solved instances by 1,065. Our formulation also accelerates the solution process for larger hop limits and efficiently solves the NDPVC for general k. We test our best algorithm for two to five simultaneous edge failures and investigate the impact of multiple failures on the network design.

TIME TO MODIFY OPERATING SOFTWARE (OS), DATABASES (DB) AND TCP/IP PROTOCOLS FOR DATA TRASH ELIMINATION, BASED ON USER DEFINED SHELF LIFE OF DATA

Exponentially growing data, big data, dark data and data trash are throwing excellent opportunities in the world. But associated costs and risks are also significant. “Big Garbage in, Big Garbage out” seems new phrase in computing. This paper is motivated by risk and cost stresses on non-IT firms. Literature review, from management perspective, reveals lack of world’s attention towards immortality of data in the data stores of the world and rising risks & costs. Progressive digitization calls for regular elimination of data trash and consequent avoidable costs. Existing concept of Time to Live (TTL) or hop limit is eliminating huge data in transit on the internet system in real time. Similar concepts and tools could be potential help in reduction of size of data inventory. Paper presents a rudimentary model for expansion of concept of TTL with the assistance of user defined shelf life of data.

LAPEL: Hop Limit Based Adaptive PIT Entry Lifetime for Vehicular Named Data Networks

Named data networking (NDN) uses the content name instead of its location within the interest message to locate the content within the network. An interest is broadcasted by the content seeking node over the wireless channel with specific content name and waits for the data message containing the actual content. The broadcast region of an interest is restricted by using the time-to-live (TTL) field of the message. Record of every pending interest is stored in the pending interest table (PIT) for a specific duration, called PIT entry lifetime (PEL). The record is purged when a node either receives the data message or the PEL expires. The size of the PIT has a significant impact on the name prefix search during the interest or data message forwarding process. Additionally, the interest and/or data message loss in the vehicular network is very frequent, which results in a significant PIT size depending on the PEL. Vanilla NDN uses the fixed PEL of $4\text{ s}$ , and the very recent work considers the constant parameters to control the PEL, which fails to reduce the PIT size. Hence, in this paper, we propose a hop limit based adaptive PEL (LAPEL) scheme, which adaptively estimates the PEL at interest forwarding vehicle. LAPEL estimates PEL based on the lower layer parameters and has no constant factor that makes it more adaptive than the previously proposed schemes. Simulation results show that LAPEL has $52\%$ less PEL, reduces $8.4\%$ the PIT size, and achieves $4.5\%$ more interest satisfaction ratio, for any simulated TTL and interest rates.

The half-filled superconducting system with on-site inter-band interactions

A two-band electronic Hamiltonian is investigated in the zero single-electron hopping limit as well as in the presence of the finite width of one of the bands. The hopping of c-electron pairs competes with the on-site pair-exchange potential, the anisotropic Kondo lattice spin-spin interaction and the local Coulomb potential in the f-band. The hopping of single electrons in c-band is also admitted in the beginning. The only interaction approximated by the mean-field method is the pair-hopping one while the remaining potentials are treated exactly what allows one to go to some extent beyond the mean-field approach. Such a handling this problem reveals significant differences between the exact and the mean-field results concerning the order parameters and the ground state energy. In this paper one addresses the case with the zero hopping of f-electron pairs in more detail, though it is possible to consider the opposite situation. It turns out that, if one admits the extremely anisotropic spin-spin interaction, i.e., the Ising component is present in the system only while the spin-flip one is neglected, the appearance of two critical temperatures and two gaps in the excitation spectrum of c-electrons at sufficiently low temperatures take place. The influence of the finite width of the conduction c-band in which the hopping of pairs takes place is investigated as well. This concerns the scenario without the Kondo lattice terms. In the end the effect of diagonal disorder is considered in a very rudimentary manner.

Extended formulations and branch-and-cut algorithms for the Black-and-White Traveling Salesman Problem

In this paper we study Integer Linear Programming models and develop branch-and-cut algorithms to solve the Black-and-White Traveling Salesman Problem (BWTSP) (Bourgeois, Laporte, & Semet, 2003) which is a variant of the well known Traveling Salesman Problem (TSP). Two strategies to model the BWTSP have been used in the literature. The problem is either modeled on the original graph as TSP using a single set of binary edge variables and with additional non-trivial hop and distance constraints between every pair of black nodes (see Ghiani, Laporte, & Semat, 2006) or as a sequence of constrained paths composed of white nodes connecting pairs of black nodes (see Muter, 2015). In this paper, we study and develop an intermediate approach based on the observation that it is sufficient to guarantee the required distance (and hop) limit of the path from a given black node to the next black node without explicitly stating which one it is. Thus, instead of stating the two constraints (after adding appropriately defined variables) for each pair of black nodes, they are stated for each black node only (that represents the source of each path). Based on this idea we develop several variants of position- and distance-dependent reformulations together with corresponding layered graph representations. Branch-and-cut algorithms are developed for all proposed formulations and empirically compared by an extensive computational study. The obtained results allow us to provide insights into individual advantages and disadvantages of the different models.

Hop-Limit Path Mapping Algorithm for Virtual Network Embedding

Virtual network (VN) mapping which deals with the allocation of network resources from the shared physical substrate to individual VNs is one of the key challenges for the application of realizing network virtualization. While a variety of state-of-the-art algorithms have attempted to address this issue from different aspects, the challenge still remains for mapping virtual link with hop count constraint. This paper presents a fast approximation path mapping algorithm to address this issue by formulating such virtual link mapping problem as a path-flow mathematical programming model, which aims to minimize the maximum link load factor. Through the use of the primal–dual method, a fully polynomial time approximation algorithm is proposed to solve this model. The experimental results show that the proposed algorithm can effectively solve the problem of path mapping with hop limit.

First principles study of the structural, electronic, and transport properties of triarylamine-based nanowires

We investigate with state of the art density functional theory the structural, electronic, and transport properties of a class of recently synthesized nanostructures based on triarylamine derivatives. First, we consider the single molecule precursors in the gas phase and calculate their static properties, namely (i) the geometrical structure of the neutral and cationic ions, (ii) the electronic structure of the frontier molecular orbitals, and (iii) the ionization potential, hole extraction potential, and internal reorganization energy. This initial study does not evidence any direct correlation between the properties of the individual molecules and their tendency to self-assembly. Subsequently, we investigate the charge transport characteristics of the triarylamine derivatives nanowires, by using Marcus theory. For one derivative we further construct an effective Hamiltonian including intermolecular vibrations and evaluate the mobility from the Kubo formula implemented with Monte Carlo sampling. These two methods, valid respectively in the sequential hopping and polaronic band limit, give us values for the room-temperature mobility in the range 0.1-12 cm(2)/Vs. Such estimate confirms the superior transport properties of triarylamine-based nanowires, and make them an attracting materials platform for organic electronics.

Client Based System on Wireless Sensor Network for Efficient Packet Transmission

Wireless sensor networks are vulnerable to the node distributor dividend, and several distributed protocols has been transfer the data in secure .Where MD5 algorithm that implements adaptive TTL, piggybacking, and perfecting, and provides near strong consistency guarantees. Cached data items are assigned adaptive TTL values that correspond to their update rates at the data source. Expired items as well as non expired ones but meet certain criteria are grouped in validation requests to the data source, which in turn sends the cache devices the actual items that have changed, or invalidates them, based on their request rates. In DHTbased protocol can detect node distributor dividend with high security level to transfer the data. Protocol of this type initial nodes send claiming messages containing a neighbor-list along with a maximum hop limit to randomly selected neighbors then, the subsequent message transmission is regulated by a probabilistic directed technique to approximately maintain a line property through the network as well as to incur sufficient randomness for better performance on communication.

Hop constrained Steiner trees with multiple root nodes

We consider a network design problem that generalizes the hop and diameter constrained Steiner tree problem as follows: Given an edge-weighted undirected graph with two disjoint subsets representing roots and terminals, find a minimum-weight subtree that spans all the roots and terminals so that the number of hops between each relevant node and an arbitrary root does not exceed a given hop limit H. The set of relevant nodes may be equal to the set of terminals, or to the union of terminals and root nodes. This article proposes integer linear programming models utilizing one layered graph for each root node. Different possibilities to relate solutions on each of the layered graphs as well as additional strengthening inequalities are then discussed. Furthermore, theoretical comparisons between these models and to previously proposed flow- and path-based formulations are given. To solve the problem to optimality, we implement branch-and-cut algorithms for the layered graph formulations. Our computational study shows their clear advantages over previously existing approaches.

Enabling delay-tolerant communications for partially connected vehicular ad hoc networks

The packet delivery ratio and throughput in Vehicular Ad Hoc Networks (VANETs) depend on the network connectivity and degrade as the connectivity decreases. A delay-tolerant approach increases the packet delivery ratio in partially connected networks. In the previous studies, the packet lifetime and the vehicle's packet carry time are determined to maximise the packet delivery ratio in partially connected VANETs. However, IPv6 uses the hop count in the Hop Limit field instead of using seconds in the TTL field, as in IPv4. Similarly, although IPv4 packets are designed to carry the packet lifetime in seconds in the TTL field, this field is used for the hop count in practice. In this case, there is no mechanism to determine how long vehicles will carry packets in VANETs when delivering packets in a delay-tolerant fashion. In this study, we propose approaches for the delivery of IPv6 packets in a delay-tolerant fashion in partially connected networks. We also propose another method that enhances these proposed approaches and optimises the packet delivery ratio. Our analysis shows that the proposed approaches can be easily adopted for IPv6/IPv4 packets to be delivered in a delay-tolerant fashion. Additionally, we observe that our approaches increase the packet delivery ratio in partially connected VANETs and can also be used in networks where the nodes are mobile or connections get broken frequently.

Energy efficient network design tool for green IP/Ethernet networks

An innovative energy-efficient network design algorithm and a tool to lower the network power consumption are proposed. The goal is an energy efficient network that carries its rated communication load while meeting the QoS requirements by using the minimum set of nodes and links. QoS metrics include hop limit, bandwidth limit reliability and stability. The proposed algorithm addresses the set-covered problem. To discover the optimum network configuration efficiently, we propose a network configuration generation algorithm that utilizes DAPDNA-2, a parallel data flow type reconfigurable processer. The processor automatically produces the node/link set in n-digit binary form where links are modeled as “1” for power on and “0” for power off; it also confirms that the QoS requirements are satisfied. Evaluation results show that DAPDNA-2 is 2-orders faster than the conventional sequential method running on a Pentium-4 processor. Prototype Gigabit Layer-2 switches having remote link power on/off and traffic monitoring functions are developed. Using these switches, we successfully demonstrate an energy efficient IP/Ethernet network. The evaluation results show that network power savings of up to 30% can be realized under the NFSNET topology model. The proposed algorithm and power efficient network architecture can be applied to realize the future green network.

Transfer behavior of quantum states between atoms in photonic crystal coupled cavities

In this article, we discuss the one-excitation dynamics of a quantum system consisting of two two-level atoms each interacting with one of two coupled single-mode cavities via spontaneous emission. When the atoms and cavities are tuned into resonance, a wide variety of time-evolution behaviors can be realized by modulating the atom-cavity coupling strength $g$ and the cavity-cavity hopping strength $\ensuremath{\lambda}$. The dynamics is solved rigorously via the eigenproblem of an ordinary coupled linear system and simple analytical solutions are derived at several extreme situations of $g$ and $\ensuremath{\lambda}$. In the large hopping limit where $g\ensuremath{\ll}\ensuremath{\lambda}$, the behavior of the system is the linear superposition of a fast and slow periodic oscillation. The quantum state transfers from one atom to the other atom accompanied with weak excitation of the cavity mode. In the large coupling limit where $g\ensuremath{\gg}\ensuremath{\lambda}$, the time-evolution behavior of the system is characterized by the usual slowly varying carrier envelope superimposed upon a fast and violent oscillation. At a certain instant, the energy is fully transferred from the one quantum subsystem to the other. When the two interaction strengths are comparable in magnitude, the dynamics acts as a continuous pulse having irregular frequency and line shape of peaks and valleys, and the complicated time-evolution behaviors are ascribed to the violent competition between all the one-excitation quantum states. The coupled quantum system of atoms and cavities makes a good model to study cavity quantum electrodynamics with great freedoms of many-body interaction.

Optimal multicast route packing

This paper considers the hop-constrained multicast route packing problem with a bandwidth reservation to build QoS-guaranteed multicast routing trees with a minimum installation cost. Given a set of multicast sessions, each of which has a hop limit constraint and a bandwidth requirement, the problem is to determine the set of multicast routing trees in an arc-capacitated network with the objective of minimizing the cost. For the problem, we propose a branch-and-cut-and-price algorithm, which can be viewed as a branch-and-bound method incorporating both the strong cutting plane algorithm and the column generation method. We implemented and tested the proposed algorithm on randomly generated problem instances with sizes up to 30 nodes, 570 arcs, and 10 multicast sessions. The test results show that the algorithm can obtain the optimal solution to practically sized problem instances within a reasonable time limit in most cases.

Discrete breathers in nonlinear Schrödinger hypercubic lattices with arbitrary power nonlinearity

We study two specific features of onsite breathers in Nonlinear Schrödinger systems on d -dimensional cubic lattices with arbitrary power nonlinearity (i.e., arbitrary nonlinear exponent, n ): their wavefunctions and energies close to the anti-continuum limit–small hopping limit–and their excitation thresholds. Exact results are systematically compared to the predictions of the so-called exponential ansatz (EA) and to the solution of the single nonlinear impurity model (SNI), where all nonlinearities of the lattice but the central one, where the breather is located, have been removed. In 1D, the exponential ansatz is more accurate than the SNI solution close to the anti-continuum limit, while the opposite result holds in higher dimensions. The excitation thresholds predicted by the SNI solution are in excellent agreement with the exact results but cannot be obtained analytically except in 1D. An EA approach to the SNI problem provides an approximate analytical solution that is asymptotically exact as n tends to infinity. But the EA result degrades as the dimension, d , increases. This is in contrast to the exact SNI solution which improves as n and/or d increase. Finally, in our investigation of the SNI problem we also prove a conjecture by Bustamante and Molina [C.A. Bustamante, M.I. Molina, Phys. Rev. B 62 (23) (2000) 15287] that the limiting value of the bound state energy is universal when n tends to infinity.