Asymmetric Bridge Research Articles

Homogeneous catalytic oxidation of thymol with dinuclear Cu(II)-2-phenyl propionate-bipyridine complex

A carboxylate-bridged dinuclear copper(II) complex, [Cu2(μ2-η2:η1(ppa)2(μ2-η1:η1 (ppa)bpy)2]·ClO4·H2O (ppa (C9H9OO) = 2-phenyl propionate, bpy = 2,2′-bipyridine), was prepared and its structure was determined by X-ray diffraction analysis. The octacoordinated Cu(II) dimer complex exhibits an asymmetric conformation, with the metal centers linked by two distinct modes of the carboxylate group. These include an asymmetric chelating bridging bidentate involving two ppa ligands and a syn-syn bidentate bridging mode involving one ppa ligand. The complex was employed as a catalyst for the oxidation of thymol, demonstrating a high degree of quantitative conversion and selectivity with TBHP across a range of solvents at moderate temperatures. The homogeneous catalytic system, comprising Cu(II)-2-phenyl propionate-bipyridine, tert-butylhydroperoxide (TBHP) as oxidant, and a polar aprotic solvent (acetonitrile or acetone), demonstrated high turnover numbers (TOF) in the absence of any additives. The impact of temperature, solvent, the ratio of thymol to TBHP, different oxidants and the quantity of catalyst on the catalytic activity and product selectivity was examined. Under optimized conditions, the maximum conversion of thymol (100 %) was obtained with 100 % selectivity to thymoquinone with TBHP after 35 min at the thymol to catalyst mole ratio of 267 (TOF = 449 h−1) in acetonitrile (MeCN) at 55 °C. Based on the available evidence, this activity and selectivity to thymoquinone represent the highest reported level of performance achieved by a homogeneously copper-catalysed process.

Building Asymmetric Zn-N3 Bridge between 2D Photocatalyst and Co-catalyst for Directed Charge Transfer toward Efficient H2O2 Synthesis.

Two-dimensional (2D) polymeric semiconductors are a class of promising photocatalysts; however, it remains challenging to facilitate their interlayer charge transfer for suppressed in-plane charge recombination and thus improved quantum efficiency. Although some strategies, such as π-π stacking and van der Waals interaction, have been developed so far, directed interlayer charge transfer still cannot be achieved. Herein, we report a strategy of forming asymmetric Zn-N3 units that can bridge nitrogen (N)-doped carbon layers with polymeric carbon nitride nanosheets (C3N4-Zn-N(C)) to address this challenge. The symmetry-breaking Zn-N3 moiety, which has an asymmetric local charge distribution, enables directed interfacial charge transfer between the C3N4 photocatalyst and the N-doped carbon co-catalyst. As evidenced by femtosecond transient absorption spectroscopy, charge separation can be significantly enhanced by the interfacial asymmetric Zn-N3 bonding bridges. As a result, the designed C3N4-Zn-N(C) catalyst exhibits dramatically enhanced H2O2 photosynthesis activity, outperforming most of the reported C3N4-based catalysts. This work highlights the importance of tailoring interfacial chemical bonding channels in polymeric photocatalysts at the molecular level to achieve effective spatial charge separation.

A study of the nonlinear behaviour of the irregular Beni Haroun cable-stayed bridge to progressive seismic failure under SVGM

The progressive failure of the nonlinear irregular Cable-Stayed Bridges (CSBs) under Spatial Variability of Ground Motions (SVGM) counting seismic wave propagation, incoherence effect and site-response effect is investigated. A spectral representation method is used in order to develop a computer code. This code is used to simulate SVGM time histories to be compatible with an overall coherency function and a target response spectrum, A three-dimensional Finite Element Model (FEM) of an asymmetric bridge: the Beni Haroun cable-stayed bridge (CSB) (North Eastern Algeria) is developed in order to include the effects of the main components of SVGM on response parameters in terms of variations of absolute maximum vertical displacements and flexural moments along the deck and on height of short and tall pylons of study CSB, in particular, nonlinear bridge response quantities are examined in terms of rotational ductility demands at the ends of the short and tall piers of the bridge under all components of SVGM. The numerical results are comforted with those obtained assuming uniform seismic excitations. The analysis results reveal, among others, that the bridge responses are very sensitive to the SVGM, with site-response effects being more critical for bridge response than those of incoherence components and wave propagation. As a general trend, it is showed that the assumption of uniform excitation results in much lower ductility demands on bridges than incoherence and site SVGM components and that the latter should be considered for the seismic response assessments and progressive seismic failure studies of irregular cable-stayed bridges.

Asymmetric bridge structure based on NiFe bimetallic sites for optimizing nitrate reduction reaction

Asymmetric bridge structure based on NiFe bimetallic sites for optimizing nitrate reduction reaction

Improved Reduced Switch Converter Topology for Torque Ripple Reduction in Four-Phase Switched Reluctance Motor Under Dynamic Loading

In this paper, simulation, and performance comparison of a switched reluctance motor (SRM) for a classical asymmetric bridge converter and an improved reduced switch converter topology are provided. In an improved converter, switches are shared by adjacent phases, and one diode is connected in series with each phase winding to avoid reversal of current. Double-phase magnetization is adopted for the analysis of both converter topologies. The performance of both converter topologies are demonstrated using a proportional plus integral (PI) based hysteresis current controller and dynamic load on a 7.5 kW, 8/6 pole, 4- phase SRM. Improved reduced switch converter topology uses half the number of switches as compared to the classical asymmetric bridge converter. According to the simulation results, an improved converter offers superior starting and average torque with less speed settling time. An improved converter reduces the most serious problem of torque ripple in SRM by 50% compared to the classical topology. The reduced switches lower the winding losses and improve the efficiency of the drive system.

Stereoisomeric Homo‐ and Hetero‐Binuclear Iridium(III) Complexes with 3‐Oxidopicolinate Bridging Ligand and Their Application in OLEDs

AbstractThe small and simple 3‐hydroxypyridine‐2‐carboxylic acid (Hpic‐OH) is explored as asymmetric bridging ligand for the synthesis of neutral binuclear cyclometalated iridium(III) complexes. Once fully deprotonated the picO2– ligand can act as ancillary ligand toward two iridium centers adopting both the N^O– and O^O– chelation modes. To tune the energy of the excited states within such binuclear complexes, the 2‐(2,4‐difluorophenyl)pyridine (Hdfppy) and the 2‐phenylbenzothiazole (Hpbtz) are used as cyclometalating ligands to respectively obtain both blue‐ or orange‐emissive homo‐cyclometalated complexes (BB and YY, with formula [Ir(dfppy)2]2(picO) and [Ir(pbtz)2]2(picO), respectively). Moreover, for the first time, short‐bridged hetero‐cyclometalated binuclear complexes are also obtained (BY and YB, with formula [Ir(dfppy)2](picO)[Ir(pbtz)2] and [Ir(pbtz)2](picO)[Ir(dfppy)2]). Depending on the reciprocal arrangement of the cyclometalating ligands on the two sides of the small picolinate bridge, two couples of diastereoisomers are obtained and efficiently separated, as proved by combined NMR and DFT studies. The reported binuclear complexes are highly emissive with photoluminescence quantum yields (PLQYs) up to 67%, which are comparable to those of their mononuclear analogues (B and Y). Due to the full reversibility of their redox processes, all the complexes are also tested in solution‐processed organic light‐emitting diodes, providing unique OLEDs based on hetero‐binuclear cyclometalated iridium(III) complexes.

Optimization of cable-stayed force for asymmetric single tower cable-stayed bridge formation based on improved particle swarm algorithm

PurposeThis paper aims to optimize cable-stayed force in asymmetric one-tower cable-stayed bridge formation using an improved particle swarm algorithm. It compares results with the traditional unconstrained minimum bending energy method.Design/methodology/approachThis paper proposes an improved particle swarm algorithm to optimize cable-stayed force in bridge formation. It formulates a quadratic programming mathematical model considering the sum of bending energies of the main girder and bridge tower as the objective function. Constraints include displacements, stresses, cable-stayed force, and uniformity. The algorithm is applied to optimize the formation of an asymmetrical single-tower cable-stayed bridge, combining it with the finite element method.FindingsThe study’s findings reveal significant improvements over the minimum bending energy method. Results show that the structural displacement and internal force are within constraints, the maximum bending moment of the main girder decreases, resulting in smoother linear shape and more even internal force distribution. Additionally, the tower top offset decreases, and the bending moment change at the tower-beam junction is reduced. Moreover, diagonal cable force and cable force increase uniformly with cable length growth.Originality/valueThe improved particle swarm algorithm offers simplicity, effectiveness, and practicality in optimizing bridge-forming cable-staying force. It eliminates the need for arbitrary manual cable adjustments seen in traditional methods and effectively addresses the optimization challenge in asymmetric cable-stayed bridges.

An asymmetrical quadruple active bridge series resonant DC–DC converter for modular solid‐state transformers

AbstractThe DC–DC conversion stage of a three‐stage solid‐state transformer is the most challenging due to the combination of high power, medium voltage, and medium frequency. This combination also causes most of the losses in the DC–DC stage. To address this issue, a new asymmetrical quadruple active bridge series resonant DC–DC converter (AQAB‐SRC) has been proposed as a building block for solid‐state transformers. The converter achieves soft switching of all switches throughout the operating range by extending and using the half‐cycle continuous conduction mode control strategy. It also has fewer high‐frequency transformers compared to other converters, as more bridges are connected to the same multi‐winding transformer. The optimal design of AQAB‐SRC has been analyzed theoretically, and simulation and lab‐scale experimental results have been obtained to validate the feasibility and validity of the proposed topology.

Study on the Closing Sequence of Asymmetric High Pier Multi-Span Continuous Rigid Frame Bridge

In order to study the influence of different closing schemes on the non-symmetrical high-pier multi-span continuous rigid frame bridge, this paper uses Midas/Civil finite element software to simulate the vertical displacement of main beam, stress of main beam, horizontal displacement of pier top and bending moment of pier bottom under four different closing schemes. The results show that the vertical displacement of the main beam is small when scheme 3 is adopted. The stress of the main beam and the bending moment of the bottom of the pier are smaller after adopting the scheme 4 closing scheme. The maximum horizontal displacement of the top pier is smaller after the closure of scheme 1 and Scheme 3. After comprehensive consideration, it is suggested that the closure of Hegou Bridge should be carried out in scheme 4.

Influence of wind barrier on aerodynamic characteristics of vehicle on railway–highway combined bridge

Wind barriers with different parameters will change the aerodynamic force of the car on the bridge as well as the stability of the vehicle–bridge system, affecting the vehicle’s safety and comfort. A numerical simulation test was conducted on the bridge-deck with three different air permeability wind barriers under three distinct vehicles of varying sizes and wind directions, with a large-span road–rail asymmetric cable-stayed bridge serving as the engineering foundation. The results show that the roll force of the bridge is proportional to the width of the body and inversely related to the height of the train. The roll force of a vehicle is inversely proportional to its height and width. The type of vehicle and the properties of the bridge deck exert minimal influence on the stability of the bridge when a single vehicle is positioned upstream. When a single vehicle is situated downstream, the tri-component force coefficient of the bridge undergoes significant changes, and the vehicle’s impact on the bridge’s stability becomes more pronounced. When the bridge deck’s ventilation rate is at 50%, the drag coefficient of the bridge deck doubles compared to that of a bare bridge deck, and the wind pressure coefficient of the vehicle surface on the bridge approaches zero. In scenarios involving two vehicles, the shielding effect caused by the vehicles positioned upstream and downstream results in a substantial shift in the aerodynamic forces acting on the two vehicles. This increases the wake width of the bridge and generates a visible vortex in the wake.

Analysis and Implementation of a Switched Reluctance Generator in Connection with the Three-Phase Power Grid and Proposal of an Anti-Islanding Strategy

This paper presents a dynamics study of the Switched Reluctance Generator (SRG) dynamics when connected to a three-phase AC power grid. A mathematical model that includes magnetic saturation is used to represent the SRG, which is driven by an asymmetric half bridge converter. Output generated voltage is smoothed with a shunt capacitor leading to a DC link voltage. This voltage is regulated using a PI compensator that controls the magnetizing angle of the generator phases. It is shown that putting a freewheeling stage between the magnetizing and the demagnetizing states per phase, allows the best use for a better usage of the mechanical power in electromechanical conversion process. Injection of active power in the grid is performed by two PI compensators that determine the modulation indexes to each sinusoidal PWM modulators that drive the three phases of the converter. This work also proposes the implementation of an islanding detection method for distributed generation (DG) systems. This method is based on voltage and frequency parameters detection. It proved to be robust and useful to detect the islanding under different load conditions and the output of the power grid.

Asymmetrical Sc coordination-induced bridging structure and surface relaxation for boosting H2O2 photoactivation in Fenton-like catalysis

A single-atom of the transition metal scandium is introduced into the g-C3N4/MoSe2 heterojunction interfaces to form a single-atom bridging structure (Se–Sc–N) for H2O2 activation in a photo-Fenton-like system.

A quick demagnetization approach for low torque ripple in three‐phase switched reluctance motor drive system for electric vehicle applications

SummaryElectric vehicles (EVs) have gained a forward approach for achieving the low carbon economy and green transportation. Switched reluctance (SR) motor‐based propulsion mechanisms have been popularly used for EVs due to the wide speed range capability. The conventional phase current regulation technique does not give the satisfactory reduction of torque ripple in SR motor drive, particularly for automotive applications. To overcome the issue, a frontend boost converter (FEBC) is proposed to realize the quick excitation and demagnetization. Initially, the problems associated with the conventional asymmetric half bridge converter are investigated at various levels of phase current. The various operating modes of proposed drive system with FEBC are explained in detail. The proposed FEBC has the significant benefit of being able to provide variable boosting voltages based on the dynamic behavior of the SR motor. The phase voltages are increased during the fast magnetization and demagnetization modes due to the inclusion of FEBC, and hence, quick magnetization and demagnetization have been achieved. The proposed FEBC drive system has been simulated through the Matlab Simulink toolbox. The experimental results are also carried out in order to validate the simulation results.

Research on the Mechanical Performance of a Mountainous Long-Span Steel Truss Arch Bridge with High and Low Arch Seats

The Loushui River Bridge is a mountainous long-span steel truss arch bridge with high and low arch seats. The design and construction of the bridge follow the principle of minimizing environmental damage and promoting sustainable development. In this article, the mechanical performance of this bridge is investigated experimentally and numerically at both the construction and operation stages. A series of validated finite element models were established for linear and nonlinear analyses by introducing geometric imperfections, geometric nonlinearities, and material nonlinearities. Then, several optimized models based on different types of design are compared with the original structure. The results indicate that the stability of the asymmetric bridge met the design requirements in both the construction and operation stages. However, the lateral stability and stiffness of the asymmetric bridge are weak due to the wind hazard that occurred in its mountain ravine. The out-of-plane instability from the short half-arch is the dominant failure mode, and the weakest area is where the arch ribs intersect with the bridge deck. It can be solved by adding more cross bracings without affecting the clearance above the bridge deck or by improving the material intensity of the arch.

Cell polarity: How to build an asymmetric bridge

A new study provides key insights into planar cell polarity (PCP) establishment through the discovery of molecular asymmetries in the homotypic adhesive interactions of the PCP cadherin, Flamingo, resulting in the formation of asymmetric, intercellular bridges.

Wind field characteristics of asymmetric bridge deck for a road-rail same-story bridge

The purpose of this study is to investigate the flow field characteristics of the road-rail same-story asymmetric bridge deck and the influence of the asymmetric arrangement of the bridge deck on the flow field of the main girders. Numerical simulation tests were conducted on this bridge to analyze the distribution characteristics of the flow field near the main girder, as well as the aerodynamic characteristics of the railway bridge deck and highway bridge deck under different wind speeds and directions. The results indicate that the wind speed has less influence on the flow field distribution and aerodynamic characteristics of the road-rail same-story asymmetric bridge deck, but the incoming flow direction has a significant impact on its flow field characteristics. Compared to the railway bridge deck, during the reattachment position of the airflow, the highway bridge deck moves toward the windward side, and the volume of the separation bubble has been reduced, thus improving the effect on the negative pressure area of the railway bridge deck. The road-rail same-story asymmetric bridge deck has different aerodynamic interference characteristics for different wind speeds and different wind directions.

Design and Development of Cascaded Current Control in DC Motor Variable Speed Drive using dSPACE

Even today, DC motors are still used in variety of applications, including home appliances, transportation, as well as industrial crane and rolling machine. However, achieving precise speed and torque control in DC drives at industry level could be challenging, as instability and reduced efficiency remains at large. This project focuses on developing a cascaded control system for a Separately Excited Brushed DC motor using dSPACE platform. The cascaded control system, designed using MATLAB Simulink, incorporates a proportional-integral (PI) controller at the speed loop and a Hysteresis controller at the current loop to improve robustness and dynamic performance. The experimental setup utilizes the dSPACE 1104 platform, an asymmetric bridge converter board, gate driver, and electrical load. Speed measurement is done using an incremental encoder, while current is measured using the ACS712 current sensor. The drive system was tested in alternate low and high speed cycle on various load level to test for stability, robustness and dynamic performance. The proposed control system was compared with PI-closed-loop control and open-loop control determine the best drive performance. Experimental results showed significant improvement in term of transient response and ripple reduction of speed and current for proposed cascaded current control over the closed-loop design.

Investigation of reasonable shock absorption of asymmetric long-span suspension bridges considering force differences

Compared with conventional suspension bridges, asymmetric long-span suspension bridges exhibit significant differences in the forces of key members on different sides under earthquake action, due to their uneven mass and stiffness distributions. In this study, the seismic response characteristics of an asymmetric long-span suspension bridge were analyzed using the Guangdong Xijiang Special Bridge as a case study. The shock absorption laws of the asymmetric parameter combinations of the viscous dampers for each control target were investigated. Accordingly, a response surface model for each control objective was established based on the response surface method. The objective function was constructed based on the principle of reducing the differences in multi-target seismic responses on different sides. Finally, a particle swarm optimization algorithm is used to determine the optimal combination of parameters for the viscous dampers on both sides. The results show that the seismic response of the members on the higher-mass side is more evident for an asymmetric long-span suspension bridge under earthquake action. Members on the smaller-mass side have a better shock absorption effect. After optimization using the proposed method, the average optimization magnitude of each control objective reached 23.1%, compared with the traditional symmetric parameters. The optimal combination of the asymmetric parameters of the viscous dampers on both sides can equalize the full-bridge forces and improve the shock-absorption effect of the dampers. The proposed method has a referable meaning for shock absorption control of asymmetric structures.

RELACJA FORMY I KONSTRUKCJI W MOSTACH PYLONOWYCH SANTIAGO CALATRAVY

One of the most common bridge solutions is suspended structures, among which the work of Santiago Calatrava stands out. The article analyzes the realized asymmetric pylon bridges designed by the architect, with cables on diagonal supports. The research aims to evaluate the pylons in terms of the relationship between the obtained architectural form and the proportions of the diagrams of the main forces. Compliance of the obtained forms with intuitive methods of preliminary design of the structure by architects was examined. The article can be a starting material for interdisciplinary research on optimizing the amount of material.

Improved Shape-Finding Method and Parametric Study for Designing Asymmetric Suspension Bridges in Mountainous Terrain

The suspension bridges in mountainous areas are commonly designed with asymmetrical overall layouts to match the terrain and construction under limited space. However, the effects and influences of the asymmetry parameters on the bridge performance have yet to be thoroughly investigated. To address this gap, based on a real-world suspension bridge with a main span length of 700 m, this paper first presents an improved shape-finding method that can fully consider the components of hanger forces in each construction step. In the iterative process, the shape of the cable is determined based on the equilibrium equations, and the hanger forces are calculated through the nonlinear finite element analysis. After deciding the bridge’s initial state, the asymmetry parameters’ effects are carefully investigated through finite element analysis under the static and seismic conditions. Results show that the side-to-span ratio of the main cable and the tower’s stiffness can affect the horizontally constrained stiffness, resulting in distinct bridge behavior. Moreover, reasonably designing the dampers between the tower and the girder can be beneficial in minimizing the longitudinal displacement and controlling the tower’s moment under the seismic situations.