Forward Switching Research Articles

BOND: Flexible failure recovery in software defined networks

Failure recovery has been a hot potato in the maintenance of networks, including software defined networks (SDNs), for many years. To guarantee the network availability in SDNs, some delicate schemes and algorithms have been proposed to pre-compute and set up the backup paths for potential network failures. However, they are generally unpractical for deployment, since they ignore either the failure recovery requirements of different flows or the constrained resources (e.g., flow tables) of SDN switches.In this paper, we propose BOND, a flexible failure recovery system in SDNs. Firstly, we allocate backup rules, instead of backup paths, to forwarding switches with flows’ requirements considered. Secondly, we accelerate the failure recovery with a global hash table and precisely select backup paths to avoid potential congestions in the post-recovery network. To demonstrate the efficiency of BOND, we construct comprehensive experiments with real-world topologies. The results show that compared with Multi-Protocol Label Switching (MPLS) Fast Reroute (FRR), BOND consumes an order of magnitude less memory to achieve the same network recovery goal. Further, we implement BOND with five HUAWEI S5720 SDN switches, two Dell end hosts and a RYU controller. The prototype experiments of this real network implementation further confirm the efficiency of BOND.

Risk based Security Enforcement in Software Defined Network

Software Defined Network (SDN) paradigm provides intelligent and efficient management of different network control functions (NF) depending on changes in traffic behavior, service providers’ requirements and application context. However, the logical centralization of controllers’ functions opens up challenges towards enforcing security perimeter over the underlying network and the assets involved. In this paper, we propose a risk assessment model for pro-active secure flow control and routing of traffic in SDN. The proposed model determines threat value of different SDN entities by analyzing vulnerability and exposure with respect to Common Vulnerability Scoring System (CVSS). The risk of a given traffic is calculated as cumulative threat values of the SDN entities that guides the flow and routing control functions in generating secure flow rules for the forwarding switches. The efficacy of the proposed model is demonstrated through extensive case studies of an enterprise network.

Electric field-induced phase transition and energy storage performance of highly-textured PbZrO3 antiferroelectric films with a deposition temperature dependence

Thin PbZrO3 (PZO) antiferroelectric films with (001)-preferred orientation were deposited on SrRuO3/Ca2Nb3O10-nanosheet/Si substrates using pulsed laser deposition. Variation of the deposition temperature was found to play a key role in the control of the microstructure and strongly influence the energy storage performance of the thin film. The critical phase switching field, where the aligned antiferroelectric (AFE) domains start to transform into the ferroelectric (FE) state, decreased with increasing temperature. On the other hand, the content of the FE phase in the AFE PZO thin films increased with increasing deposition temperature. A large recoverable energy-storage density of 16.8 J/cm3 and high energy-storage efficiency of 69.2% under an electric field of 1000 kV/cm were achieved in the films deposited at 525 °C. This performance was due to the high forward switching field and backward switching field values and the low difference between these two fields. Moreover, the PZO thin films showed great charge-discharge cycling life with fatigue-free performance up to 1010 cycles and good thermal stability from room temperature to 100 °C.

Nanoscale Hydrogenography on Single Magnesium Nanoparticles.

Active plasmonics is enabling novel devices such as switchable metasurfaces for active beam steering or dynamic holography. Magnesium with its particle plasmon resonances in the visible spectral range is an ideal material for this technology. Upon hydrogenation, metallic magnesium switches reversibly into dielectric magnesium hydride (MgH2), turning the plasmonic resonances off and on. However, up until now, it has been unknown how exactly the hydrogenation process progresses in the individual plasmonic nanoparticles. Here, we introduce a new method, namely nanoscale hydrogenography, that combines near-field scattering microscopy, atomic force microscopy, and single-particle far-field spectroscopy to visualize the hydrogen absorption process in single Mg nanodisks. Using this method, we reveal that hydrogen progresses along individual single-crystalline nanocrystallites within the nanostructure. We are able to monitor the spatially resolved forward and backward switching of the phase transitions of several individual nanoparticles, demonstrating differences and similarities of that process. Our method lays the foundations for gaining a better understanding of hydrogen diffusion in metal nanoparticles and for improving future active nano-optical switching devices.

A domain-general monitoring account of language switching in recognition tasks: Evidence for adaptive control

Language switching experience is assumed to have an effect on domain-general control abilities in bilinguals, but previous studies on the relationship between these two variables have generated mixed results. The present study investigated the effects of bilingual experiences on the interaction between language switching and domain-general control. Thirty-two Dutch–French bilingual young adults executed a bilingual categorisation task to assess their language switching abilities and a Simon task to assess domain-general control. The results show that global response times on the Simon task were correlated to the forward switch cost (from L1 to L2); moreover, interestingly, the forward switch cost was found to be related to recent language exposure but not to the age of second language acquisition. We suggest a monitoring account of language switching to integrate the first finding with previous studies and we interpret the second finding as support for the adaptive control hypothesis.

Snap‐back free shorted‐anode super‐junction TCIGBT

A novel structure called the shorted-anode super-junction trench clustered insulated gate bipolar transistor (SA-SJ-TCIGBT) is proposed and demonstrated through numerical simulations in 1.2 kV, field-stop technology. This device is based on the SJ-TCIGBT concept. In the SA-SJ-TCIGBT structure, due to the introduction of a segmented n+-anode, the device can operate in both forward conducting mode and freewheeling diode mode without any snap back in the current–voltage characteristics. In comparison to the SJ-TCIGBT structure, the proposed device shows significant improvement in trade-off relationship between forward voltage drop and switch off energy losses. Simulation results show that 25% decrease in switching energy losses can be achieved. Moreover, the tail current is effectively reduced without any increase in the overshoot voltage. Detailed two-dimensional modelling of the structure shows that significant amount of excess electrons are extracted through the SA structure during turn-off process.

Harmonically-Driven Snapping of a Micromachined Bistable Mechanism With Ultra-Small Actuation Stroke

In this paper, we study the snapping action of a micromachined bistable mechanism harmonically driven with an ultra-small actuation stroke, which is realized through the mode amplification in a two-degrees-of-freedom (2-DOF) vibration system using an on-chip electrostatic actuator. The micromachined bistable mechanism is based on a curved beam configuration. The dynamic response of the device is theoretically predicted with the harmonic balance method. Further, to demonstrate this proposed study, a microelectromechanical systems (MEMS) prototype device is designed, fabricated, and tested. In experiments, the forward and backward state switching actions of the prototype device are realized with actuation stroke smaller than $0.4~\mu \text{m}$ , while the traveling distance between the two states is about $18~\mu \text{m}$ . To the best of our knowledge, we demonstrate for the first time the state switching of a cured beam bistable mechanism using harmonic driving in a 2-DOF vibration system. This paper has potential in applications including MEMS switches and MEMS filters. [2017-0221]

Efficient Management and Fast Handovers in Software Defined Wireless Networks Using UAVs

Compared to traditional networking, SDN has better controllability and visibility for network components, which enable better management by using the common controller. In this article, the standard architecture of SDN is enhanced to utilize UAVs as on-demand forwarding switches. The proposed approach can achieve efficient management and fast handovers by decreasing the handover latency, E2E delay, and signaling overheads. The illustrated scenarios will help in understanding the impact of existing handover approaches in the next generation wireless networks, especially the upcoming 5G, which includes small cells, UAVs, UEs, and so on. The simulation study shows that scenarios with both UAVs and small cells perform better than scenarios with only small cells. The results in this article show that the proposed SDNbased handover scenarios perform better than the existing 4G-LTE handover for UAVs.

Large deviation induced phase switch in an inertial majority-vote model.

We theoretically study noise-induced phase switch phenomena in an inertial majority-vote (IMV) model introduced in a recent paper [Chen et al., Phys. Rev. E 95, 042304 (2017)]. The IMV model generates a strong hysteresis behavior as the noise intensity f goes forward and backward, a main characteristic of a first-order phase transition, in contrast to a second-order phase transition in the original MV model. Using the Wentzel-Kramers-Brillouin approximation for the master equation, we reduce the problem to finding the zero-energy trajectories in an effective Hamiltonian system, and the mean switching time depends exponentially on the associated action and the number of particles N. Within the hysteresis region, we find that the actions, along the optimal forward switching path from the ordered phase (OP) to disordered phase (DP) and its backward path show distinct variation trends with f, and intersect at f = fc that determines the coexisting line of the OP and DP. This results in a nonmonotonic dependence of the mean switching time between two symmetric OPs on f, with a minimum at fc for sufficiently large N. Finally, the theoretical results are validated by Monte Carlo simulations.

Switching dynamics of single and coupled VO2-based oscillators as elements of neural networks

In the present paper, we report on the switching dynamics of both single and coupled VO2-based oscillators, with resistive and capacitive coupling, and explore the capability of their application in oscillatory neural networks. Based on these results, we further select an adequate SPICE model to describe the modes of operation of coupled oscillator circuits. Physical mechanisms influencing the time of forward and reverse electrical switching, that determine the applicability limits of the proposed model, are identified. For the resistive coupling, it is shown that synchronization takes place at a certain value of the coupling resistance, though it is unstable and a synchronization failure occurs periodically. For the capacitive coupling, two synchronization modes, with weak and strong coupling, are found. The transition between these modes is accompanied by chaotic oscillations. A decrease in the width of the spectrum harmonics in the weak-coupling mode, and its increase in the strong-coupling one, is detected. The dependences of frequencies and phase differences of the coupled oscillatory circuits on the coupling capacitance are found. Examples of operation of coupled VO2 oscillators as a central pattern generator are demonstrated.

Conducting-insulating transition in adiabatic memristive networks.

The development of neuromorphic systems based on memristive elements-resistors with memory-requires a fundamental understanding of their collective dynamics when organized in networks. Here, we study an experimentally inspired model of two-dimensional disordered memristive networks subject to a slowly ramped voltage and show that they undergo a discontinuous transition in the conductivity for sufficiently high values of memory, as quantified by the memristive ON-OFF ratio. We investigate the consequences of this transition for the memristive current-voltage characteristics both through simulation and theory, and demonstrate the role of current-voltage duality in relating forward and reverse switching processes. Our work sheds considerable light on the statistical properties of memristive networks that are presently studied both for unconventional computing and as models of neural networks.

Schottky behavior of reduced graphene oxide at various operating temperatures

Demand of portability has been a growing trend due to the thirst of catching up with the latest evolution of technology. This scenario has urged power supply designers to develop devices that are relatively smaller, faster and having a higher percentage of efficiency. In contrast, smaller devices tend to experience overwhelming heat dissipation which can be hazardous to the devices. A Schottky diode is a semiconductor diode which has a relatively low forward voltage drop and fast switching action. Despite having low voltage drop, Schottky devices are extremely sensitive to elevated temperature owing to high leakage at reverse bias region. The leakages are due to low energy barrier which is susceptible to thermal runaway when a nominal amount of heat is applied. This paper presents the study of Schottky behaviour of reduced graphene oxide (RGO) at various operating temperature. RGO has superior electronic and thermal properties as well as high carrier mobility. Graphene was obtained by chemical exfoliation of graphene oxide, which is a reduction method. Through spray-coating, the RGO is deposited onto a trench-structured Schottky base to form a Schottky diode. Electrical characterization has been carried out at different range of temperature; ranging from 25 °C to 125 °C. Result shows that overall, the device has the same range voltage drop around 1V in all five different temperatures and is also considered to have a significantly low leakage current. Furthermore it also shows a unique current-voltage (I-V) pattern in which the impedance tangent increases from 25 °C to 50 °C but as the temperature gets higher, the impedance approaches the characteristics of a room temperature.

Linear composition-dependent phase transition behavior and energy storage performance of tetragonal PLZST antiferroelectric ceramics

The composition dependent dielectric, ferroelectric and energy storage properties of tetragonal lead lanthanum zirconate stannate titanate (PLZST) antiferroelectric ceramics were systematically studied in this paper. Two sets of simple linear scaling relations were established for the forward switching field EAFE-FE, the backward switching field EFE-AFE and recoverable energy density Wre. As Zr content increases (Ti fixed), EAFE-FE, EFE-AFE, Wre decreases linearly, while the stored energy density Wst declines first and then increases. In addition, decreasing Ti content (Zr fixed) leads to linear increments in all of EAFE-FE, EFE-AFE, Wre and Wst. These results not only reveal the superiority of PLZST with lower Zr and lower Ti contents for energy storage capacitors, but also provide a fast way to design PLZST ceramics with specific energy storage properties. Our work may also be very helpful for better understanding the mechanism of phase transition behaviors of antiferroelectric materials.

A chaotic self-oscillating sunlight-driven polymer actuator.

Nature provides much inspiration for the design of materials capable of motion upon exposure to external stimuli, and many examples of such active systems have been created in the laboratory. However, to achieve continuous motion driven by an unchanging, constant stimulus has proven extremely challenging. Here we describe a liquid crystalline polymer film doped with a visible light responsive fluorinated azobenzene capable of continuous chaotic oscillatory motion when exposed to ambient sunlight in air. The presence of simultaneous illumination by blue and green light is necessary for the oscillating behaviour to occur, suggesting that the dynamics of continuous forward and backward switching are causing the observed effect. Our work constitutes an important step towards the realization of autonomous, persistently self-propelling machines and self-cleaning surfaces powered by sunlight.

Effect of Language Switching On the Response Latency in the Cued Picture-Naming Paradigm among Hindi Dominant and Balanced Bilinguals

Language dominance has long been considered an important factor in determining the processing time associated with language switching. It is evident that when an unbalanced bilingual switch from ones non-dominant to dominant language (backward switching), s/he requires more reaction time in comparison to when s/he switches from dominant language to non-dominant language (forward switching). In this study, the researcher examined the effects of language dominance and switching on the response time in the cued picture-naming paradigm. Results indicate that the overall response time required by balanced bilingual is less than that of Hindi dominant bilinguals. It was also found that, Hindi dominant required more reaction time in backward switching in comparison to forward switching. For balanced bilinguals, the difference between forward and backward switching was not found to be significant. The results of this study have been discussed in light of the concept of ‘reactive inhibition’ of the Inhibitory Control Model (ICM).

Power saving mechanism with network coding in the bottleneck zone of multimedia sensor networks

Power consumption is one of the most important issues for the lifetime of a wireless sensor network (WSN). Specifically, the lifetime of a WSN depends on the power consumption of the nodes in the bottleneck zone near each sink node, where all sensing data is collected via the nodes in the bottleneck. However, these nodes’ energy is depleted very quickly because of the heavy traffic imposed on them. Therefore, in this paper, we propose a power saving mechanism using network coding and duty cycling in the bottleneck zone of WSNs to prolong the lifetime of WSNs. We propose duty cycling, packet forwarding, and role switching schemes for nodes in the bottleneck zone. In our proposed approach, the packet forwarding in the coder nodes employs random linear network coding to enhance energy efficiency and reliability in the bottleneck zone. We evaluate the performance to show that the proposed protocol outperforms the conventional system in terms of the lifetime of WSNs, without reducing the reliability of packet delivery in the bottleneck zone. In a grid topology network, the lifetime achieved with the proposed protocol is doubled or tripled compared with the conventional system.

A Novel BiFeO3–BaTiO3–BaZrO3 Lead‐Free Relaxor Ferroelectric Ceramic with Low‐Hysteresis and Frequency‐Insensitive Large Strains

A novel (0.67−x)BiFeO3–0.33BaTiO3–xBaZrO3 lead‐free relaxor ferroelectric ceramic was developed by a solid‐state reaction method. Measurements of temperature‐dependent dielectric permittivity and the polarization/strain hysteresis loops demonstrated an obvious evolution of dielectric relaxor behavior at room temperature (RT) from nonergodic to ergodic states. A significantly enhanced electrostrain of ~0.37% at 7 kV/mm with a relatively small hysteresis of ~39% and a low‐frequency sensitivity was found at x = 0.04, showing large potential for actuator applications. This was basically attributed to a rapid response of forward and backward switching between ergodic and ferroelectric phases owing to similar free energies and large local random fields.

Jointly optimized QoS-aware virtualization and routing in software defined networks

Software Defined Networks (SDNs) have been recognized as the next-generation networking paradigm that decouples the network control plane from the data forwarding plane. A logically centralized controller is responsible for all the control decisions and communication among the forwarding switches. However, current traffic engineering techniques and state-of-the-art routing algorithms do not effectively use the merits of SDNs, such as global centralized visibility, control and data plane decoupling, network management simplification and great computation capability. In this paper, a multi-tenancy management framework is proposed to enable the jointly optimized design of quality-of-services (QoSs)-aware virtualization and routing by tenant isolation and prioritization as well as flow allocation, fulfilling QoS requirements of tenants’ applications. Specifically, a fine-grained network virtualization is first proposed to isolate and prioritize tenants through the design of network and switch hypervisors. Furthermore, a QoS-aware dynamic flow allocation is proposed to enable optimal flow routes selection upon the given network slicing with QoS provisioning. Finally, an adaptive feedback management tool, called QoS-aware Virtualization-enabled Routing (QVR), is proposed to combine virtualization with flow allocation and supports reliable and efficient transmissions with regards of time-varying QoS requirements, network topologies, and traffic statistics. Simulations confirm that QVR achieves much less shared edges, congestion latency, and traffic delay for multiple tenants, thus facilitating virtualization-enabled traffic engineering for multi-tenancy SDNs.

Families of Forward Converters Suitable for Wide Input Voltage Range Applications

A topology approach is proposed to derive forward converters suitable for wide voltage range applications. A unified forward switching cell concept from the core principle of forward conversion is proposed with three cells given, named as forward positive cell, forward negative cell, and forward composite cell. All cells consist of active switch, diode, transformer, and comprehensive demagnetizing voltage source. By utilizing different subcircuit to balance the voltage of the comprehensive demagnetizing voltage source, various types of forward switching cells, including RCD type, active-clamping type, LCDD type, flyback-integrated type, and independent-circuit type, are deduced from the traditional forward converters with topology derivation rules given. Families of forward converters, including existing ones and novel ones, are constructed as examples. The forward converters built in such a way illustrates features such as recycle of leakage and magnetizing energy, low voltage stress on devices, etc. The proposed method is extended to flyback converter family to further justify the feasibility. An input-series interleaved RCD forward converter and an active-clamping forward converter are analyzed in detail and verified with experimental results.

The Computer Interlocking Software System Reliability Test Based on the Monte Carlo

The railway switch failure prediction for railway signal equipment maintenance plays an important role. The paper put forward railway switch failure prediction algorithm based on least squares support vector machine, and chose five characteristic indexes composed of railway switch failure prediction models characteristic input vectors. It reduces the dimension of input vectors, shorten the least squares support vector machine training time, and use a pruning algorithm to accelerate the computing speed maintaining a good regression performance at the same time. The experiment proved that railway switch failure prediction algorithm has strong self-learning ability and higher prediction accuracy based on least squares support vector machine. And it can accelerate the speed of switch failure prediction and improve the accuracy and reliability of railway switch failure prediction.