Flexible Valve Research Articles

Murky trade waters: Regional tariff commitments and non-tariff measures in Africa

In several African regions, economic integration has successfully reduced tariff protection by freezing the opportunity to raise applied tariffs against fellow integration partners above those promised. We examine whether these regional tariff commitments have come at the expense of adverse side-effects on the prevalence of non-tariff trade barriers. Comparing the effects of applied tariff overhangs – the difference between MFN bound tariffs and effectively applied tariffs – towards all vis-à-vis African trading partners on SPS and TBT notifications of 35 African WTO members from 2001-2017, we find no general relationship between tariff overhangs and import regulation in our preferred model setting. Larger tariff overhangs specific to intra-African trade relations, however, increase the probability of SPS measures and TBT and thereby contrast with the common assumption of the former functioning as a flexible policy valve. We see the nature of Africa’s formal trade relations as an explanation for these findings. While regional tariff commitments have not only significantly moved African countries away from multilateral commitments, they have also sharply reduced their tariff policy space within Africa, thus seemingly leaving regulatory policy as one of the few legitimate options to level the playing field with the by far closest market competitors.

Results of Numerical Modeling of Blood Flow in the Internal Jugular Vein Exhibiting Different Types of Strictures.

The clinical relevance of nozzle-like strictures in upper parts of the internal jugular veins remains unclear. This study was aimed at understanding flow disturbances caused by such stenoses. Computational fluid dynamics software, COMSOL Multiphysics, was used. Two-dimensional computational domain involved stenosis at the beginning of modeled veins, and a flexible valve downstream. The material of the venous valve was considered to be hyperelastic. In the vein models with symmetric 2-leaflets valve without upstream stenosis or with minor 30% stenosis, the flow was undisturbed. In the case of major 60% and 75% upstream stenosis, centerline velocity was positioned asymmetrically, and areas of reverse flow and flow separation developed. In the 2-leaflet models with major stenosis, vortices evoking flow asymmetry were present for the entire course of the model, while the valve leaflets were distorted by asymmetric flow. Our computational fluid dynamics modeling suggests that an impaired outflow from the brain through the internal jugular veins is likely to be primarily caused by pathological strictures in their upper parts. In addition, the jugular valve pathology can be exacerbated by strictures located in the upper segments of these veins.

A lightweight flexible semi-cylindrical valve for seamless integration in soft robots based on the giant electrorheological fluid

Complete compliance of soft robots is a trending research topic. One significant aspect is the control element. In the current work, a flexible electro-rheological (ER) valve development is chosen due to the advantage of its dynamic power density, convenient electronic control mode, and no mechanical moving parts. These properties enable the ER valve to be miniaturized and easily integrated into a fluid-driven soft robot. However, the integration effect of the existing flexible ER valve configuration in soft robots is not ideal. In this study, a novel concentric semi-cylindrical flexible giant ER (GER) valve with a dual flowing direction is proposed for a soft robot to enable a larger deformation bending motion with multiple motion modes. The resulting valve has an overall volume of 50 mm3, a mass of 0.88 g, and a maximum controlling pressure of 84 kPa with a pressure change rate of 13.9, which is suitable for most soft robot applications. The pressure difference calculation method for the concentric semi-cylindrical GER valve is discussed. The effects of size, voltages, and flow rates on the valve’s static and dynamic performances, as well as the characteristics of the two pressure regulation modes, are investigated through simulations and experiments. The seamless integration and flexibility of the proposed valve are demonstrated by controlling a typical network actuator with six motion modes. Finally, a soft robot composed of two actuators is fabricated and realized the grasping of multiple everyday objects using different motion modes.

Thin-Film Heterostructures Based on Co/Ni Synthetic Antiferromagnets on Polymer Tapes: Toward Sustainable Flexible Spintronics.

Synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA-SAFs) have gained growing attention for both conventional and next-generation spin-based technologies. While the progress of PMA-SAF spintronic devices on rigid substrates has been remarkable, only few examples of flexible thin-film heterostructures are reported in the literature, all containing platinum group metals (PGMs). Systems based on Co/Ni may offer additional advantages with respect to devices containing PGMs, i.e., low damping and high spin polarization. Moreover, limiting the use of PGMs may relieve the demand for critical raw materials and reduce the environmental impact of related technologies, thus contributing to the transition toward a more sustainable future. Here, we discuss for the first time the realization of Co/Ni-based PMA-SAFs on polymer tapes and exploit it to obtain flexible giant magneto-resistive spin valves (GMR-SVs) with perpendicular magnetic anisotropy. Several combinations of buffer and capping layers (i.e., Pt, Pd, and Cu/Ta) are also investigated. High-quality flexible SAFs with a fully compensated antiferromagnetic region and SVs with a sizable GMR ratio (up to 4.4%), in line with the values reported in the literature for similar systems on rigid substrates, were obtained in all cases. However, we demonstrate that PGMs allows achieving the best results when used as a buffer layer, while Cu is the best choice as a capping layer to optimize the properties of the stacks. We justify the role of buffer and capping layers in terms of different interdiffusion mechanisms occurring at the interface between the metallic layers. These results, along with the high robustness of the samples' properties against bending (up to 180°), indicate that complex and bendable Co/Ni-based heterostructures with reduced content of PGMs can be obtained on flexible tapes, allowing for the development of novel flexible and sustainable spintronic devices for applications in many fields including wearable electronics, soft robotics, and biomedicine.

Apical Ballooning Syndrome: A Cardiac Syndrome Mimicking Acute Myocardial Infarction

Introduction: Apical ballooning syndrome, Takotsubo cardiomyopathy, or broken heart syndrome, is a rare but currently well recognized clinical entity. It occurs after severe emotional or physical stress, most often in postmenopausal women, and mimics the symptoms and signs of acute coronary syndrome, in the absence of significant coronary injury. This cardiomyopathy is rapidly and completely reversible. The exact pathophysiological mechanism of the condition remains debated; several hypotheses have been put forward, the most credible of which seems to be a sudden hyperadrenergic reaction related to stress. Objective: To report the case of a patient with clinical features of possible myocardial infarction but diagnosed as Takotsubo cardiomyopathy. Case Report: The patient was a 64-year-old woman with no cardiovascular risk factors other than age and menopause, and no particular pathological history. She was admitted on Day 3 with infarct-like chest pain, which appeared following an episode of emotional stress, associated with NYHA stage III dyspnea. On admission, the patient was pain free. The clinical examination found a conscious patient, hemodynamically and respiratory stable, apyretic. The cardiovascular examination was unremarkable. The ECG was in sinus rhythm, showing a QS aspect in the anterosepto-apical area associated with negative T waves in the inferolateral area. The biological workup showed an inflammatory syndrome, with positive troponin at 650ng/l. The thoracic echocardiography showed an aspect of hypokinetic cardiopathy at the dilated stage with severe LV dysfunction (LVEF at 38%), a thin and flexible mitral valve with restriction of the small mitral valve with moderate mitral insufficiency (SOR at 20 cm2 and RV at 19 ml), a dilated left atrium. Coronary angiography showed angiographically healthy coronary arteries, and an MRI was performed, confirming the diagnosis of Takutsbo cardiomyopathy. Discussion and Conclusion: Takotsubo cardiomyopathy is an increasingly recognized clinical entity, characterized by apical left ventricular dysfunction with chest pain, electrocardiographic changes, minimal biomarker changes, and no coronary lesions. In most cases, an episode of emotional or physical stress precedes the event. Its pathophysiological mechanism remains unknown, but high circulating catecholamines seem to be the triggering factor and the most plausible explanation for this primary acquired cardiomyopathy. It is important to be aware of this diagnosis in patients presenting with ACS because its evolution is most often spontaneously favorable.

Research on Flexible HVDC Converter Valve and VBC Redundancy Reliability Improvement

Flexible HVDC transmission play an important role in building a strong smart grid, and it is also very important to design a reliable redundant system for the converter valves and the valve-base controller (VBC). In order to improve the redundancy of the current valve control system, firstly, this paper proposed a new redundant configuration scheme for flexible HVDC converter valve and VBC. Secondly, this paper proposed a switching logic and switching time sequence for the redundant link, in order to make all VBC board hot-swappable when the HVDC system is in operation. Finally, depend on the “Baihetan-Jiangsu” HVDC project, the RTLAB-based test platform was established, which verified the correctness of the redundant system design. The test result shows that the designed scheme improves the redundant system reliability of the flexible HVDC system, and has well-referenced value.

Multi-Physics Analysis of a Magnetorheological Valve Train with Experimental Validation

Magnetorheological (MR) fluid devices are widely used in active automotive control applications. However, MR fluid-based valve actuators are not in the limelight. This paper proposes a new flexible valve train with an MR fluid control system; the valve train can enhance the performance of internal combustion engines. A major component of this valve train is the magnetic plate block filled with MR fluid and surrounded by a magnetic coil. This plate block controls the magnetic field in this MR fluid and eventually facilitates flexible valve lifts and valve opening timings. This study overviewed the conceptual design, two-way coupled multi-physics numerical simulations, manufactured an MR valve prototype, and conducted experimental tests on a test bench to understand the real-time performance of the MR valve train. First, computer simulations were performed using a coupled magnetic and thermal multiphysics model to consider the Joule-heating effect of the magnetic coil in the MR magnetic plate block. The simulation results indicated that although the temperature of the MR fluid increased noticeably, it did not exceed the prescribed operating limits. The dimensions of the MR magnetic plate block were optimized. After computer simulations and optimization, a prototype of the proposed MR valve was fabricated and tested to understand its performance in real time. The experimental test results indicated the reliability of the proposed MR valve train in practical scenarios.

The effect of discharge areas on the operational performance of a liquid-ring vacuum pump: Numerical simulation and experimental verification

To determine the effect of discharge area on the ability of a liquid-ring vacuum pump, the inspiratory capacity and shaft power are numerically investigated for different discharge areas adjusted by the number of discharge ports at different inlet pressures. Besides, the numerical results of these key operating parameters are verified by experiments in a developed testing system with a flexible valve plate on the discharge ports. The result shows that there exists an optimal discharge area of the liquid-ring vacuum pump at each inlet pressure, and good agreements are found between the experimental data and numerical results. For a 2BEC-40 vacuum pump, the maximum isothermal compression efficiencies can reach 39.99%, 46.80%, 49.16% and 40.82% for the inlet pressures of 20 kPa, 40 kPa, 55 kPa and 70 kPa with the optimum number of discharge ports is 1, 5, 12 and 12, respectively. The results suggest that the self-adaptive adjustment of discharge areas by the valve plates is of great importance to practical applications of a liquid-ring vacuum pump.

Bending sensor based on flexible spin valve

Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive properties was revealed. Bending deformation was applied to the microobjects based on the flexible spin valves in parallel to anisotropy axes. It was revealed that during the bend the magnetoresistance changes due to the joint impact of both the change of the magnetic field projection on the film plane and the change of the magnetic properties of the ferromagnetic layers. The obtained dependences have been used in construction of bending sensor, in which the flexible spin valve microstripes were united into the Wheatstone bridge.

Bio-Design, Fabrication and Analysis of a Flexible Valve.

Fluid-driven soft robots offer many advantages over robots driven by other means in terms of universal preparation processes and high-power density ratios, but are largely limited by their inherit characteristics of rigid pressure sources, fluid control elements and complex fluid pipelines. In this paper, inspired by the principle of biofluid control and actuation, we combine simulation analysis and experimental validation to conduct a bionic design study of an efficient flexible fluid control valve with different actuation diaphragm structures. Under critical flexural load, the flexible valve undergoes a continuous flexural instability overturning process, generating a wide range of displacements. The sensitivity of the flexible valve can be improved by adjusting the diaphragm geometry parameters. The results show that the diaphragm wall thickness is positively correlated with the overturning critical pressure, and the radius of curvature is negatively correlated with the overturning critical pressure. When the wall thickness of the flexible valve maintains the same value, as the radius of curvature increases, the critical buckling load and recovery load of diaphragm overturning is a quadratic function of opposite opening, and the pressure difference converges to the minimum value at the radius of curvature R = 7.

Analysis for magnetic field disturbance of modular multilevel converter based high voltage direct current (MMC‐HVDC) converter valve

The standardised design and operational reliability enhancement of the flexible DC converter valve are impending with the construction of high shares of renewables and power electronics power system. A power frequency magnetic field calculation model able to obtain the electromagnetic disturbance at the submodule (SM) drive board during normal operation of a flexible DC converter valve is presented. Hundreds of SMs with complex structures in a converter valve tower are simplified by the equivalent to the line current to fulfil calculation accuracy requirements. In addition, a random function is employed to simulate the non-sequential switching process of the SMs. By comparing the calculated results with the measured data obtained from the SM equivalent operation experiment of 2200 V/2150 A, the validity of the calculation model is confirmed. According to the final calculations, the influence of non-sequential switching cannot be ignored when recognising the time-domain distribution features of the power frequency magnetic field of the drive board. However, engineering design can be guided only by the power frequency magnetic field intensity of the drive board calculated based on SM’s full removal in the valve tower.

Biaxial strain sensing using a Pd/Co-based perpendicular flexible spin valve

We fabricated a Pd/Co-based spin valve structure, which has in-plane (IP) free and out-of-plane (OOP) fixed layers, on a flexible substrate. By applying %-order biaxial tensile strain to the substrate, a spin reorientation transition from IP to OOP occurs in the free layer, resulting in a drastic change in the shape of the magnetoresistance curve. This change is reversible with increasing and decreasing strain. We suggest that our system could be utilized as an in-plane “direction-independent” strain sensor and as a pressure detector.

Manipulation of Magnetic Properties and Magnetoresistance in Co/Cu/γ′-Fe4N/Mica Flexible Spin Valves via External Mechanical Strains

The strain-tailored magnetic and electronic transport properties in flexible spin valves (SPVs) have attracted attention due to their practical applications in flexible spintronic devices. Here, magnetic and spin-dependent electronic transport properties of Co/Cu/γ′-Fe4N/mica flexible SPVs are investigated. The strain-induced change ratio of magnetoresistance (MR) is 49% in Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(11.0 nm) flexible SPVs. The magnetic properties of Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(7.9 nm) flexible SPVs show mechanical stability at bending strains. The magnetic properties of flexible SPVs did not deteriorate after 100 times of bending and 60 h of bending. As the Co layer thickness decreases from 7.2 to 2.4 nm, the sign of MR changes from negative to positive. A negative MR appears due to the opposite scattering spin asymmetry coefficients between Co/Cu and γ′-Fe4N/Cu interfaces. A positive MR arises from the same scattering spin asymmetry coefficients at Co/Cu and γ′-Fe4N/Cu interfaces or magnetization misalignments between Co and γ′-Fe4N layers. Additionally, the MR is a combination of an anisotropy magnetoresistance and a giant magnetoresistance effect, which has been confirmed by MR–H curves with different measurement configurations (Hin-plane∥I, Hin-plane⊥I and Hout-of-plane⊥I) and M–H curves. The M–H curves show that the magnetization of γ′-Fe4N reverses before that of the Co layer.

Numerical simulation of multi-physical field coupling of a piezoelectric pump with flexible valve at an optimal working point

A piezoelectric pump with flexible valve was proposed for living cells transmission to avoid the cell damage caused by valve material during transmitting process. However, the dynamic switching characteristics of the flexible valve coupled with the flow field directly affected both the flow field inside the pump chamber and the output performance of the pump. At the same time, the output performance of the piezoelectric pump mainly took the optimal working point as a standard. Therefore, the electric-solid-liquid multi-physical field coupling finite element model of the piezoelectric pump with flexible valve based on dynamic mesh was established to study the dynamic characteristics of the valve and the transient flow characteristics of the flow field under the optimal working point. The calculation results of the flow rate show that the output flow rate of the pump is 6.19 g/min at the optimal working point (200 VPP, 10 Hz). The error is 8.94 % compared with the experimental flow rate, which verifies the accuracy of the calculation model. The results of this paper can provide a reference for multi-physical field coupling calculation and optimization design of valve-based piezoelectric pumps with different structures.

A Lightweight Flexible Semi-Cylindrical Valve for Seamless Integration in Soft Robots Based on the Giant Electrorheological Fluid

A Lightweight Flexible Semi-Cylindrical Valve for Seamless Integration in Soft Robots Based on the Giant Electrorheological Fluid

Design and Analysis of a Novel Composited Electromagnetic Linear Actuator

Electromagnetic linear actuators, as key executive components, have a vital impact on the performance of fully flexible variable valve trains. Considering that the conventional moving coil electromagnetic linear actuator (MCELA) has the disadvantages of low force density and a lack of end-passive self-holding ability, a novel composited electromagnetic linear actuator (CELA) is proposed by combining the performance advantages of MCELA and moving iron electromagnetic linear actuator (MIELA) in this work. Firstly, the structure and magnetic circuit design scheme of the proposed actuator are introduced and the finite element simulation model is established. The magnetic field distribution and force characteristics of the actuators are assessed by finite element simulation. Secondly, the construction of the prototype of the actuator is outlined, based on which the feasibility of the design scheme and the steady-state performance of the actuator are verified. Finally, the coordinated control strategy is proposed to realize the multi motion coordination control of the actuator. The research results show that the maximum starting force of the CELA with the end-passive self-holding ability is 574.92 N while the holding force can approach 229.25 N. Moreover, the CELA is proven to have excellent dynamic characteristics and control precision under different motion modes and to have an improved adaptability to the complex working conditions of internal combustion engines.

Flexible Magnetoreceptor with Tunable Intrinsic Logic for On‐Skin Touchless Human‐Machine Interfaces

AbstractArtificial magnetoception is a new and yet to be explored path for humans to interact with the surroundings. This technology is enabled by thin film magnetic field sensors embedded in a soft and flexible format to constitute magnetosensitive electronic skins (e‐skins). Being limited by the sensitivity to in‐plane magnetic fields, magnetosensitive e‐skins are restricted to basic proximity and angle sensing and are not used as switches or logic elements of interactive wearable electronics. Here, a novel magnetoreceptive platform for on‐skin touchless interactive electronics based on flexible spin valve switches with sensitivity to out‐of‐plane magnetic fields is demonstrated. The technology relies on all‐metal Co/Pd‐based spin valves with a synthetic antiferromagnet possessing perpendicular magnetic anisotropy. The flexible magnetoreceptors act as logic elements, namely momentary and permanent (latching) switches. The switches maintain their performance even upon bending to a radius of less than 3.5 mm and withstand repetitive bending for hundreds of cycles. Here, flexible switches are integrated in on‐skin interactive electronics and their performance as touchless human‐machine interfaces is demonstrated, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances. This technology offers qualitatively new functionalities for electronic skins and paves the way towards full‐fledged on‐skin touchless interactive electronics.

Research on a Piezoelectric Pump with Flexible Valves

Imitating the structure of the venous valve and its characteristics of passive opening and closing with changes in heart pressure, a piezoelectric pump with flexible valves (PPFV) was designed. Firstly, the structure and the working principle of the PPFV were introduced. Then, the flexible valve, the main functional component of the pump, was analyzed theoretically. Finally, an experimental prototype was manufactured and its performance was tested. The research proves that the PPFV can achieve a smooth transition between valved and valveless by only changing the driving signal of the piezoelectric (PZT) vibrator. The results demonstrate that when the driving voltage is 100 V and the frequency is 25 Hz, the experimental flow rate of the PPFV is about 119.61 mL/min, and the output pressure is about 6.16 kPa. This kind of pump can realize the reciprocal conversion of a large flow rate, high output pressure, and a small flow rate, low output pressure under the electronic control signal. Therefore, it can be utilized for fluid transport and pressure transmission at both the macro-level and the micro-level, which belongs to the macro–micro combined component.

A low frequency driven piezoelectric pump with flexible valve

A low frequency driven piezoelectric pump with flexible valve (LDPPFV) is presented. LDPPFV is able to achieve precise flow control by adjusting driving voltage or driving frequency. The flexible valve has high elasticity and low stiffness, which can effectively reduce the reverse leakage of the check valve and realize the low frequency (<5 Hz) drive of the piezoelectric pump. The prototype of LDPPFV is designed and manufactured. The frequency and voltage characteristics of LDPPFV under different external loads are investigated. Experimental results indicate that with the increase of the thickness of the flexible valve, the optimal frequency of LDPPFV increases, but the flow rate decreases. Under no external load, the maximum flow rate of 18.10 ml/min is achieved at 4.5 Hz. Under external loads of 0/1/3 kPa, the output flow rate of LDPPFV has a good linear relationship with driving frequency and voltage. Least square method is used to fit the flow rate and the driving parameters. The linear correlation coefficients R2 are all above 0.980.

Random vibration analysis of an offshore flexible direct current converter valve

With the rapid development of the direct-current grid technology and construction, the flexible direct-current transmission technology has been widely used in many aspects, such as long-distance large-capacity power transmissions, offshore platforms and island power supplies. The offshore flexible direct current converter valve will encounter a variety of unfavorable loads during the marine transportation and the long-term operation on the sea. The safety requirements of the offshore flexible direct current converter valve are higher as a result. Based on the structural characteristics of the converter valve, the converter valve is calculated by finite element method. Under two working conditions of the marine transportation and the long-term operation on the sea, this paper carries out modal analysis and random vibration analysis of the converter valve tower respectively. This paper gives the unfavorable position of the force from the calculation results, and provides a reference for the design and selection of the flexible direct current converter valve to meet the needs of the offshore converter station’s construction.