Bidirectional Isolation Research Articles

Seismic response control of large-span suspend-dome structures using multidimensional isolation systems

Three isolation strategies have been developed for seismic response control of suspend-domes: bidirectional isolation, bidirectional isolation with additional restrainers, and three-dimensional (3D) isolation. The first and second control strategies use pendulum sliding isolation bearings (PSIBs) and shape memory alloy (SMA)-restrained PSIBs (SPSIBs), respectively, as high-position bearings to support the roof of a structure. The third strategy uses of prepressed spring bearings with additional dampers and SPSIBs with slack SMA strands to form a vertical isolation layer at the roof support and a horizontal isolation layer at the base of the substructure. This paper describes the configurations, working mechanisms, and numerical simulations of these isolation systems in detail and presents their parameter design based on the related design objectives of a prototype suspend-dome structure. In this study, an extensive numerical modeling investigation was performed on isolated and non-isolated suspend-domes to examine the feasibility and effectiveness of the seismic control systems. The results showed that the segmental 3D isolation system provides superior seismic protection performance for the target suspend-dome compared with the bidirectional isolation systems, although the former involves a complex design, modeling, and construction.

HClave: An isolated execution environment design for hypervisor runtime security

Virtualization is the cornerstone of cloud computing, but the hypervisor, the crucial software component that enables virtualization, is known to suffer from various attacks. It is challenging to secure the hypervisor due to at least two reasons. On one hand, commercial hypervisors are usually integrated into a privileged Operating System (OS), which brings in a larger attack surface. On the other hand, multiple Virtual Machines (VM) share a single hypervisor, thus a malicious VM could leverage the hypervisor as a bridge to launch “cross-VM” attacks. In this work, we propose HClave, an isolated execution environment (IEE) design for hypervisor runtime. We decouple the virtualization layer into a tiny trusted computing base (TCB), a large non-secure OS, and multiple HClave IEEs through a bidirectional isolation approach. HClave extends the nested kernel approach to deprive the traditional OS from accessing the tiny TCB’s memory and creates an IEE for hypervisor runtime. We implemented HClave based on KVM and evaluated its effectiveness and efficiency through case studies. Experimental results show that HClave can significantly improve the security of the hypervisor with reasonable runtime overhead.

Experimental verification and performance evaluation of an inertia-type bidirectional isolation system

Both horizontal and vertical ground motion can cause damage to vibration-sensitive equipment. However, most mature seismic isolation devices only isolate horizontal ground acceleration; few devices isolate both vertical and horizontal ground acceleration. In this paper, a novel inertia-type bidirectional isolation system (IBIS) is proposed that comprises independent vertical and horizontal seismic isolators. The IBIS’s vertical isolator comprises leverage apparatus with a counterweight, which provides a vertical lifting force in the static state to balance the self-weight of the isolated object, and an additional inertial force in the dynamic state, resulting in higher static but lower dynamic effective vertical stiffness. The horizontal isolator is a conventional sliding-type system comprising a sliding platform and pair of springs. The IBIS’s equations of motion are derived by using Lagrange’s equation, and the theoretical model is verified through shaking-table test results. Numerical simulation and experimental results show that the IBIS has an anti-resonance property in the vertical direction, leading to higher isolation performance under both near-fault and far-field ground acceleration. The conventional sliding-type horizontal isolator component performs well under far-field ground acceleration but may perform unsatisfactorily under near-fault ground acceleration.

Photovoltaic Energy Storage System Based on Bidirectional LLC Resonant Converter Control Technology

Bidirectional DC/DC converters are widely adopted in new energy power generation systems. Because of the low conversion efficiency and non-isolation for conventional, bidirectional DC/DC converters in the photovoltaic energy storage complementary system, this paper proposes a bidirectional isolation LLC converter topology, with compensating inductance for the energy storage system; it has excellent characteristics, such as wide input voltage range and soft switching in full-load range. First, an AC equivalent model based on the fundamental wave equivalent method is established to derive the voltage gain. Meanwhile, a small signal model is also built to design a reasonably closed-looped controller. Finally, the improved bidirectional LLC resonant converter is applied to the photovoltaic energy storage complementary system. The correctness and feasibility for the bidirectional LLC converter topology under the proposed charging and discharging control strategy of the DC bus are verified by simulation and experimental results.

Graphene-sandwich metasurface as a frequency shifter, switch, and isolator at terahertz frequencies

A graphene-sandwich metasurface for electrically controlled operation as a frequency shifter, a reciprocal switch, and a bidirectional isolator in the terahertz spectral regime was simulated using CST Microwave Studio™ 2019 software. The metasurface is a biperiodic array of identical meta-atoms, each of which comprises a silicon layer with a graphene patch on each of its two faces. The polarization-insensitive metasurface has ∼15 dB isolation loss as well as ∼15 dB extinction ratio and can be controlled to function over a wide frequency range.

A Coupled-Inductor-Based Bidirectional Circuit Breaker for DC Microgrid

DC microgrids have attracted more and more attention with its universality, high efficiency, and potential application market. However, dc fault protection is still a challenge to the development of dc microgrids. In this article, a novel bidirectional dc solid-state circuit breaker based on coupled inductor is introduced. It can realize bidirectional energy flow and bidirectional isolation and interruption of short-circuit faults with fewer components. The working principle of the topology and the working process under different conditions are described, and some properties of the novel circuit breaker are explored, including minimum fault current ramp rate and load step analysis, which provide a reference for the selection of component parameters. Finally, the feasibility and performance of the novel bidirectional circuit breaker is evaluated by simulations and experiments.

Tunable optical behavior of infrared filters with phase change material

We propose an asymmetric to quasisymmetric behavioral tunability of a structured filter operating in the mid-infrared (IR) spectral region, where the atmospheric transparency is high. The structure is designed through electromagnetic wave analysis using finite-difference time-domain computations. The behavioral tunability provides dynamic control of the optical behavior of the IR filter without geometric and structural changes and opens up a field of research area in the tunable IR devices. It is shown that optical characteristic can be switched from an optical diode (unidirectional isolator or asymmetric light transmission) to the bidirectional isolator (quasisymmetric behavior) based on the phase transition of vanadium dioxide in the entire mid-IR spectrum. The proposed structure can be fabricated with the current nano and microfabrication techniques and can be utilized in smart front IR windows for protecting delicate sensors in the IR imaging systems and IR missile seekers under strong IR laser radiation.

A Switchable Sound Tunnel by Using an Acoustic Metasurface

An acoustic metasurface (AM) is proposed to achieve a sound tunnel with switchable functionalities of asymmetric transmission and bidirectional sound isolation, which is composed of an array of steel containers filled with two inert gases, argon and xenon. Acoustic asymmetric transmission can be observed when the AM is placed vertically. The functionality of the tunnel can be switched to bidirectional sound isolation by simply rotating the AM without changing the physical structure of the device. The proposed switchable tunnel has broadband multi-functional response with a simple adjustment method, showing potential for bidirectional sound isolation and sound sensing.

Isolation Barrier Valves Installed Successfully in Deepwater Gulf of Guinea

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28453, “Egina Deepwater Development: Isolation-Barrier-Valve Case Study,” by G. Forrest, C. Morand, K. Johnson, and V. Okengwu, Halliburton, and V. Chaloupka, SPE, Total, prepared for the 2018 Offshore Technology Conference Asia, Kuala Lumpur, 20–23 March. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. A major operator manages multiple deepwater projects in the Gulf of Guinea. This paper describes one of these, a recent 44-well project. The operator required an ISO 28781-qualified bidirectional subsurface isolation barrier valve (IBV) to be installed in each well. This paper presents the results of the IBV deployment in the field. Introduction The Egina field was discovered in 2003 in Oil Mining Lease 130 located in deep water (1150–1750 m) approximately 200 km offshore Port Harcourt, Nigeria. Subsurface IBVs have become commonplace in lower-sandface-completion installations. The potential time and operational cost savings are well understood. However, industry concerns remain regarding the ability of these devices to operate reliably in demanding wellbore conditions. The primary challenges for this project were Deviated wells with horizontal drains, high dogleg severity, and azimuth changes Isolation of different reservoirs along each drain Faults Running the upper completion in sieved nonaqueous-based mud (NABM) Well-Control Philosophy and Barrier Requirements General philosophies and requirements for well control—including the overall principles for well barriers, kill methods, and project-specific needs—require the following with respect to barriers: Can be pressure-tested Location and status can be known at all times Can be re-established in a short period of time Can operate in the environment despite challenges related to pressures, temperatures, and fluids The integrity of a barrier can be verified by pressure-testing to working pressure in the direction of flow when possible. These tests can also be run in the reverse direction. After completion and tree installation, tests are conducted using available well pressure. IBV Design Update. The IBV design in question (Fig. 1) was first run in west Africa in 2008 as a result of an extensive qualification and testing program aimed at improving upon its predecessor. The new IBV improved debris tolerance to meet ISO 28781 regulatory requirements. Enhancements also included increased differential opening pressure, simplified operating and workshop-testing procedures, removal of the transit pin, and increased opening force.

Abstract 20942: Non-Invasive Isolation of the Pulmonary Veins in an Animal Model

Introduction: Pulmonary vein isolation (PVI) is well established as the preferred treatment for symptomatic paroxsysmal atrial fibrillation (pAF). We introduce a novel technique in which PVI is aimed for in a pig model, by non invasive heating of the proximal ring of an implant inserted in the pulmonary veins. Hypothesis: Non-invasive heating of an implant in the PV is feasible and safe Methods: A self-expanding nitinol-based implant was positioned in the common inferior pulmonary vein of 11 pigs, using a fluoroscopy guided transatrial approach. In a second part of the experiment, implants were positioned in the superior caval vein through a transfemoral approach of another 6 animals. Ablation was performed through a contactless energytransfer from a primary extracorporal coil to a secondary heatring (HR) embedded in the proximal part of the implant. Electrophysiological properties were assessed prior to and post ablation. Histological samples were obtained after 3 months. Results: In total, eightteen PV-implants were succesfully positioned. Ablation was performed in a safe manner, without injury of adjacent structures. PVI and bidirectional block was confirmed in all PV cases, and bidirectional block in 5 of the 6 caval vein implants (entry block shown in the figure-the heatring is at the level of the white arrow). Only mild neointimal proliferation was observed 3 months post ablation. Conclusions: Non-invasive ablation using self-expanding stents in the PV is safe and feasible, bidirectional isolation can be demonstrated in almost all cases, whilst no significant neointimal formation is observed:

Zero Crosstalk Regime Direct Modulation of Mutually Coupled Nanolasers

The modulation properties of dually modulated mutually coupled nanolasers have been analysed using rate equations which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor β . Specific attention is given to zero crosstalk operating regimes where the responses of the nanolasers are independent. Such regimes may provide either bidirectional isolation where both nanolasers operate independently or unidirectional-isolation where one nanolaser is immune to the other nanolaser but not vice versa. Access to the bidirectional isolation zero-crosstalk regime is, in general, enabled by strong driving or large modulation depth of the nanolasers. Conversely, strong injection coupling and low modulation depth lead to the unidirectional isolation regime. The modulation responses of the nanolasers in both bidirectional and unidirectional isolated zero crosstalk regimes are presented. The availability of bidirectional-isolated zero crosstalk regimes is seen to offer opportunities for exploitation in photonic integrated circuits.

Complete Isolation of the Left Atrial Posterior Wall (Box Lesion) to Treat Longstanding Persistent Atrial Fibrillation.

The left atrial posterior wall has been shown to play na important role in AF pathophysiology. Evaluate the efficacy of an ablation strategy designed to completely isolate the LA posterior wall, on top of PV isolation. Methods and Results: 25 pts (72% male age 65 ± 12 years) undergoing AF ablation for persistent or long term persistent AF. Mean AF duration was 11 ± 3 months and mean LA diameter was 4.8 ± 0.4 mm. After complete PVI, a "Roof Line" was created between the top of each contralateral set of lesions and a "floor line" closed the posterior wall in a "Box" fashion, connecting the bottom of each set of contralateral lesions. After an average follow-up of 16 ± 2 months, 20 patients (80%) were free of any atrial arrhythmia recurrences (18 of whom off drugs). Five patients (20%) had sustained atypical flutter and required a new ablation procedure. All these patients had mitral isthmus dependent flutters and no electrical conduction in the PVs or posterior wall were detected. Complete LA posterior wall isolation on top of PV is associated with good outcomes in patients with persistent and long-standing persistent AF when performed using meticulous bidirectional isolation criteria and adenosine infusion. Recurrences occur predominately as perimitral flutter, without gaps in the posterior wall.

Revisión del género <i>Venustoraphidia</i> Aspöck & Aspöck, 1968 de la Península Ibérica (Insecta, Raphidioptera)

To date, this genus was represented by only two species from Europe: Venustoraphidia nigricollis (Albarda, 1891), known from Central and Eastern Europe, and its vicariant Venustoraphidia renate (Aspock & Aspock, 1974), known from the Peloponnese. The genus is new to the Iberian Peninsula fauna, where it is represented by a third and new vicariant species of V. nigricollis on the other side of the Mediterranean: Venustoraphidia conviventibus n. sp. We record all the bibliographical references related to Venustoraphidia genus, and known data on the external morphology, genitalia, biology, juvenile stages, phaenology and distribution of the two previously known species. A key for the identification of the aforementioned species, including the new species present in the Iberian Peninsula is provided. Finally, a brief bio-geographical analysis is performed on the distribution of these three species based on paleo-climatic elements and the presumptive bi-directional isolation to the east/west of central European elements, leaving isolated populations in the Peloponnese Peninsula, on the other side of the Corinthian Isthmus, and in the Iberian Peninsula, beyond the Pyrenees.

A Bidirectional Dual-Frequency Retrodirective Array for Full-Duplex Communication Applications

A bidirectional dual-frequency retrodirective array is presented, which uses intermediate frequency (IF) phase conjugation as the design concept. The proposed array has the ability of working at two different interrogating frequencies. For each interrogating signal, the frequency is converted to the other. This array contains the attractive features of simultaneously achieving bidirectional dual-frequency retrodirectivity and high isolation between the receiving and retransmitting signals. It is suitable for a full-duplex communication system. The proposed array is fabricated and demonstrated. Monostatic and bistatic measurements have been done to validate the performance of the system.

A wavelength selective bidirectional isolator for access optical networks

A wavelength selective bidirectional optical isolator is proposed. Being different from conventional isolators, a well-designed wave plate is employed and works together with the Faraday rotator. Different wavelengths thus experience different phase retardation so that wavelength-dependent polarization states are obtained for bidirectional beams. As an example, a (1.49 μm, 1.31 μm) wavelength selective isolator is proposed, which means only 1.49 μm light can propagate along one-direction while the opposite wave is just for 1.31 μm light. Over 60 dB optical isolation is obtained by selecting suitable wave plate thickness and orientation. This interesting isolator may have promising applications in access optical networks.

A Liquid Crystal Tunable Wavelength-Interleaved Isolator With Flat Spectral Response

A liquid crystal tunable bidirectional isolator is proposed. A wave plate is employed to realize a wavelength interleaving function. If it works as a full wave plate, the corresponding light only may pass along a specific direction while the opposite way is isolated. However, for wavelengths that the light experiences a half wave plate, the isolator's passing direction is reversed. A liquid crystal cell is utilized to tune the isolator so that both the isolated wavelength and direction could be reconfigured. A 100-GHz channel-interleaved tunable bidirectional isolator is demonstrated with 30 dB isolation in both directions. The spectral response at ITU grids are further flattened by using a wave plate stacking technique.

Complete antral encirclement is not required for pulmonary vein isolation

Complete circumferential antral ablation may not be necessary for successful pulmonary vein (PV) isolation in patients with paroxysmal atrial fibrillation (AF). We examined the feasibility of a noncircumferential approach limited to segments of the antra required for PV-atrial conduction. During ablation for paroxysmal AF, each PV antrum was divided into six segments, and ablation was sequentially targeted to antral segments with the earliest activity until bidirectional isolation was achieved. Ablation at the ostium was avoided. Patients requiring complete circumferential ablation (circumferential group) were compared with those undergoing incomplete antral ablation (noncircumferential group) with respect to freedom from symptomatic atrial arrhythmia, procedure, and ablation times. Ninety-nine patients underwent ablation with successful isolation of PVs (n = 37 circumferential; n = 62 noncircumferential). There were no significant differences in age, gender, AF duration, or LA size. Procedure time (202 ± 45 vs. 185 ± 47 minutes; P = .06) and ablation time (51 ± 15 vs. 41 ± 14 minutes; P = .004) were shorter in the noncircumferential group. During follow-up (12 ± 6 months), freedom from symptomatic recurrence was 73% in both groups (P = .97), with organized atrial tachycardia being more common in the circumferential group (P = .06). In 22 patients undergoing repeat study, PV reconnection was demonstrated in 82% and 81% of PVs in each group. Reconnection in the noncircumferential group occurred in previously ablated segments in 10 (77%) of 13 cases. Noncircumferential antral ablation achieves similar success rates with shorter procedure and ablation times than circumferential ablation. Greater attention should be focused on producing permanent lesions rather than on completing antral encirclement after isolation is achieved.

BI-DIRECTIONAL SCALABLE SOLID-STATE CIRCUIT BREAKERS FOR HYBRID-ELECTRIC VEHICLES

Power electronics in hybrid-electric military ground vehicles require fast fault isolation, and benefit additionally from bi-directional fault isolation. To prevent system damage or failure, maximum fault current interrupt speeds in tens to hundreds of microseconds are necessary. While inherently providing bi-directional fault isolation, mechanical contactors and circuit breakers do not provide adequate actuation speeds, and suffer severe degradation during repeated fault isolation. Instead, it is desired to use a scalable array of solid-state devices as a solid-state circuit breaker (SSCB) having a collectively low conduction loss to provide large current handling capability and fast transition speed for current interruption. Although, both silicon-carbide (SiC) JFET and SiC MOSFET devices having high breakdown voltages and low drain-to-source resistances have been developed, neither device structure alone is capable of reverse blocking at full voltage. Limitations exist for using a dual common-source structure for either device type. Small-scale SSCB experiments were conducted using 0.03 cm2 normally-on SiC VJFETs. Based on results of these tests, a normally-on VJFET device modification is made, and a proposed symmetric SiC JFET is considered for this application.

Pulmonary vein isolation predicts freedom from arrhythmia after circumferential antral ablation for paroxysmal atrial fibrillation

The aims of this observational study were to evaluate (i) the feasibility of obtaining bidirectional pulmonary vein (PV) isolation by means of circumferential radiofrequency ablation of the antral aspect of the PV ostium; (ii) whether the electrophysiological demonstration of bidirectional PV isolation predicts freedom from atrial tachyarrhythmia recurrence after ablation in patients with paroxysmal atrial fibrillation. The study group comprised 28 patients affected by frequent recurrences of paroxysmal atrial fibrillation refractory to antiarrhythmic drugs, who underwent transcatheter ablation of the PVs by means of a non-fluoroscopic navigation system. Radiofrequency pulses were delivered in a point-by-point fashion at the antral aspect of the ostium of each vein presenting distal PV potentials. After ablation of each PV, bidirectional isolation was tested by means of a basket catheter. No antiarrhythmic drugs were prescribed on discharge. Outpatient visits, 24-h electrocardiographic Holter monitoring, and continuous 7-day digital electrocardiogram were scheduled at 3, 6, and 12 months. A distal potential was detected in 101/123 (82%) mapped PVs. Bidirectional isolation was obtained in 81/101 (80%) PVs; bidirectional isolation of all targeted PVs was obtained in 17 (61%) patients. After a mean follow-up of 12.2 +/- 4.2 months, clinical success was observed in 15 (53%) patients. On multivariate analysis, only bidirectional isolation of all targeted PVs predicted the clinical success of ablation (P < 0.003; hazard ratio 7.504; confidence interval 1.943-28.990). Circumferential antral ablation achieves bidirectional isolation in 80% of PVs. Bidirectional isolation of all PVs is essential to curing patients with paroxysmal atrial fibrillation.

Wavelength-interleaving bidirectional circulators

We report a wavelength-interleaving bidirectional circulator, in which the even and odd ITU channels circulate in opposite handedness. Demonstrated three-port bidirectional isolation ranges from 45 dB for single-pass to 90 dB for dual-pass over the entire C-band with low loss, large flat-top bandwidth, low PDL, and good temperature stability. This new device technology is an enabler for bidirectional optical networks and opens up a range of possibilities for bidirectional fiber devices: isolators, circulators, add-drops, cross-connects, and uni- to bidirectional optical network interfaces.