Asymmetric Bridge Research Articles

Post-translational formation of strained cyclophanes in bacteria.

Cyclic peptide natural products have served as important drug molecules, with several examples used clinically. Enzymatic or chemical macrocyclization is the key transformation for constructing these chemotypes. Methods to generate new and diverse cyclic peptide scaffolds enabling the modular and predictable synthesis of peptide libraries are desirable in drug discovery platforms. Here we identify a suite of post-translational modifying enzymes from bacteria that install single or multiple strained cyclophane macrocycles. The crosslinking occurs on three-residue motifs that include tryptophan or phenylalanine to form indole- or phenyl-bridged cyclophanes. The macrocycles display restricted rotation of the aromatic ring and induce planar chirality in the asymmetric indole bridge. The biosynthetic gene clusters originate from a broad range of bacteria derived from marine, terrestrial and human microbiomes. Three-residue cyclophane-forming enzymes define a new and significant natural product family and occupy a distinct region in sequence-function space.

A Three-Phase Asymmetrical Dual-Active-Bridge Converter With Series/Parallel-Reconfigurable Output for Wide Voltage Range Applications

A three-phase asymmetrical dual active bridge (TP-ADAB) dc-dc converter with series/parallel-reconfigurable output (SPRO) is proposed for wide output range and constant peak power applications. The three outputs of the TP-ADAB converter are able to be connected in series or parallel to achieve wide output voltage range. The output voltage range, maximum output voltage/current of each power module, as well as the power rating of devices, are reduced significantly. Moreover, automatic voltage sharing in output series mode and current sharing in output parallel mode is achieved by adopting the three-phase structure. Furthermore, soft-switching of all power switches is achieved in a wide operation range. Operation principles, output characteristics, soft-switching performances, and control strategy of the proposed TP-ADAB converter are analyzed in detail. Experimental results of a 3 kW prototype are provided to verify the effectiveness and feasibility of the proposed converter.

Construction of d-f heteronuclear complexes with open-chain ether Schiff base ligand: Regulation effects of Zn(II) and Cd(II) on structures and luminescence properties

Two series of heteronuclear Zn-Ln and Cd-Ln complexes with open-chain ether Schiff base ligand (bis(5-bromine-3-methoxysalicylidene)-3-oxapentane- 1,5-diamine (H2L) and isonicotinate (IN), with composition [Zn2LnL2(OAc)(IN)](NO3)·x(CH3OH)·y(CH2Cl2) (1 Ln = Sm, x = 1, y = 0; 2 Ln = Tb, x = 0, y = 2) and {[CdLnL(IN)(OAc)(NO3)(CH3OH)]·3(CH2Cl2)}n (3 Ln = Sm; 4 Ln = Tb), have been synthesized by interfacial diffusion methods and further performed structural characterization. The structure analysis revealed that two Zn-Ln complexes are heterotrinuclear clusters and lanthanide metal ion acts as a joint bridging of two ZnL coordination units, whereas two Cd-Ln complexes are infinite one dimensional zigzag coordination polymers formed by CdLnL secondary units through asymmetric coordination bridging isonicotinate. Luminescence properties of 1–4 in the solid state and N, N-dimethylformamide (DMF) solution at room temperature were also studied. It has been found that the Sm3+ complexes 1 and 3 exhibit corresponding Sm3+ ion characteristic emission in the solid state, but the L2− ligand can’t sensitize the Tb3+ ion in complexes 2 and 4. Finally, the structures and luminescence properties of d-f heteronuclear complexes can be adjusted by selecting different transition metals such as zinc and cadmium.

Unravelling the Chemistry of the [Cu(4,7-Dichloroquinoline)2Br2]2 Dimeric Complex through Structural Analysis: A Borderline Ligand Field Case

Large dark prismatic crystals (P 1 ¯ ) consisting of closely packed centrosymmetric [Cu(4,7-dichloroquinoline)2]2Br4 binuclear units are formed when 4,7-dichloroquinoline (DCQ, C9H5NCl2) binds copper(II). Cu2+ adopts a strongly distorted square pyramidal coordination geometry, perturbed by electrostatic interactions with two axial μ–Br ligands acting as highly asymmetric bridges. It is shown that, as electronic states of ligands are higher in energy than the metal ones, antibonding orbitals bear significant ligand-like character and electronic charge is partially transferred from inner-sphere coordinated halogen atoms to copper. Overall, the title compound sits on the Hoffman’s border between main group and transition chemistry, with non-negligible contributions of the ligands to the frontier orbitals. The relative energy placement of metal and ligand states determines an internal redox process, where the metal is slightly reduced at the expense of partial oxidation of the bromide ligands. In fact, the crystal structure is partially disordered due to the substitution of some penta-coordinated Cu(II) centers with tetra-coordinated Cu(I) ions. The geometry of the complex is rationalized in terms of electrostatic-driven distortions from an ideal octahedral prototype. Implications on the reactivity of Cu(II)–quinoline complexes are discussed.

Seismic response analysis of long-span and asymmetrical suspension bridges subjected to near-fault ground motion

The objective of this paper is to investigate the seismic responses of long-span and asymmetrical suspension bridges subjected to four intensity level (Small, moderate, huge, and super earthquakes) of near-fault ground motions. A typical suspension bridge located in Yunnan province of China is selected herein to study the dynamic response of long-span and asymmetrical suspension bridges. And the corresponding finite element model based on the platform of OpenSEES is established to consider the influence of velocity pulse effect, site effect, and structure-soil interaction on the seismic responses of interests e.g., tower, girder, and pile, etc., in the suspension bridge seismic analysis. Besides the near-field and far-field ground motion records are employed from the data base in Pacific Earthquake Engineering Research Center of the United States for comparison analysis. Finally numerical analysis results have suggested that the influence of near-fault effect on the response of long-span and asymmetrical suspension bridges and the different dissipation capacity of nonlinear viscous damper in various intensity levels should be paid more attention to in the seismic design of this type bridges.

Analysis of Stiffening Girder Erection Scheme of Single Tower and Single Span Asymmetric Suspension Bridge

The paper analyzes four different stiffening girder erection schemes of a single tower and single span asymmetric suspension bridge with the main span of 766m by using parameter analysis combined with finite element numerical simulation. Firstly, this paper proposes two methods to study the reasonable erection time of ground anchor suspender cables, and based on the Midas/Civil finite element software, the erection time of ground anchor suspender cables with four schemes is determined by using backward-calculation analysis method. Then the main cable deformation, cable saddle displacement, horizontal inclination of main cable, internal force of suspender cables and dynamic performance of different schemes are compared. The results show that for Scheme 3 adopted in the project, the deformation of main cable is the smallest, the change of the cable saddle displacement is more slowly, the horizontal inclination of the main cable is smaller, and the bending stiffness is larger. However, the torsional stiffness is small and the flutter stability is not as good as other schemes.

Behavior of Asymmetric Cable Stayed Bridge for Long Span

In the recent years cable stayed bridges have received more attention than any other bridges. As one of the most competitive bridge in modern times, the cable stayed bridge is ideally suitable for long span. Asymmetric cable stayed bridges are the upgrade of conventional cable stayed bridges. Analytical investigation is an important in the study of asymmetric cable stayed bridge. The response of the bridge deck under moving traffic load is very important in the analysis process. Even the slightest deflection may result in the collapse of the bridge structure. Recent reports states that the cable stayed bridges are subjected to wave like vibrations when subjected to moving loads. So the bridge must be analyzed in such a way that its deflections are well under the permissible limits. The parameters like displacements, shear forces, bending moments and percentage of reinforcements were studied in long span asymmetric cable stayed bridge. The asymmetric cable bridge was modeled using SAP2000 software.

A theoretical and experimental exploration of the seismic dynamics of multi-span bridges

A generalized reduced-order model of a multi-span continuous bridge, on flexible discrete supports, that is subjected to multi-support seismic excitation is presented. This model highlights the key non-dimensional system parameters. Real spatiotemporal ground motion time-series (from the SMART-1 array, Taiwan) are used, as an alternative to employing artificial ground motion based on some spatial incoherence kernels. Benchmark experimental test data, using the multiple support excitation rig of a four-span bridge and SMART-1 array excitation, is used to validate/calibrate the proposed reduced-order model. An operational modal analysis is conducted to obtain least-square estimates of these key dynamic parameters using a Levenberg–Marquardt algorithm. The computationally efficient reduced-order model is then employed for a parametric study that explores the effect of spatial incoherence, bridge alignment and archetypal symmetrical and asymmetrical bridge geometries. A comparison of identical and multi-support excitation cases indicate the likely range of beneficial/adverse errors in neglecting the spatiotemporal nature of ground motions in design analyses.

Spanning the Saint Lawrence

The recently opened Samuel De Champlain Bridge is an iconic gateway to Montreal. Its signature structure, an asymmetrical cable-stayed bridge, features a 240 m long main span over the Saint Lawrenc...

A dimeric oxidovanadium(V) complex derived from a hydrazonate ligand with an unusual asymmetrically bridged μ-(oxido)μ-(H2O){oxidovanadium(V)}2 core

The binuclear oxidovanadium(V) complex [{VO(L)}2(μ-O)(μ-H2O)]∙2CH3CN (1), where L2– is the dianion of the Schiff base 2-salicylaldehyde-2-hydroxybenzoylhydrazone, were prepared and characterized by elemental analysis, FTIR, 1H, 13C and 51V NMR. Furthermore, the crystal structure of the compound 1 was determined by single crystal X-ray diffractometry revealing a distorted octahedral O5N-coordination geometry around the V(V) acceptor centers. The vanadium ions are connected by the μ-O2– and the μ-H2O asymmetric bridges located in the edge between the two octahedrons which keeps a distance of 3.194 Å between the two vanadium centers. Crystal data for C32H28N6O10V2 (M =758.48 g/mol): orthorhombic, space group P212121 (no. 19), a = 12.9655(8) Å, b = 14.1902(9) Å, c = 18.4379(10) Å, V = 3392.3(4) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.616 mm-1, Dcalc = 1.485 g/cm3, 18803 reflections measured (3.622° ≤ 2Θ ≤ 56.704°), 8263 unique (Rint = 0.0473, Rsigma = 0.1020) which were used in all calculations. The final R1 was 0.0509 (I > 2σ(I)) and wR2 was 0.1531 (all data). The (VO)2(μ-O)(μ-H2O) core in compound 1 represents a rare case and few examples of similar type have been structurally characterized.

TECHNICAL AND ENERGY INDICATORS OF MEAN POWER AUTONOMOUS SYNCHRONOUS GENERATOR

The energy performance improving of the exciter by switching on the zero diodes and capacitors leads to asignificant change in the harmonic composition of the excitation voltage. The study investigates the harmoniccomposition of the excitation voltage of synchronous generators with asymmetrical bridge exciters using the unitsof forced capacitive switching. To determine the harmonic composition of the excitation voltage, we decompose theexperimental curve into a Fourier series and expressions for calculating the harmonic components. The results ofthe spectral analysis indicate that the excitation voltage at the rated mode of the generator contains a significant thirdharmonic, which is 66 percent of the amplitude of the first harmonic. The significant value of the third harmonic isdue to the large angles of control of the exciter thyristor in the nominal mode of operation of the synchronousgenerator. Due to the significant third harmonic, the secondary winding of the rectifier transformer must beconnected to a triangle. The presence of even harmonics is caused by the voltage asymmetry with respect to theabscissa.A non-symmetrical bridge exciter with a forced capacitance switching unit for a synchronous generator hasbeen developed, which provides improved energy performance during its nominal operation. The scheme of controlof the bridge asymmetrical exciter of the synchronous generator with the node of forced capacitive switching for therated mode of operation, as well as in the mode of the field suppression at short circuits of the stator windings hasbeen described.The comparative estimation of the suppression modes of the field at a short circuit of the windings of thegenerator stator with the possible mode of inverting the exciter and using the node of forced capacitive switchinghas been carried out. Experimental studies have confirmed the calculated dependences of the modes of the magneticfield suppression. The analysis of experimental dependencies shows that the units of forced capacitive switchingprovide a higher speed of the field suppression modes, regardless of the presence and magnitude of the supply ofvoltage the exciter.

Signal Generation for Switched Reluctance Motors using Parallel Genetic Algorithms

Switched reluctance motors (SRM) are an inherent part in robotics and automation systems where energy and cost efficiency is required. This motor type has no windings and permanent magnets on the rotor which results in a simple and robust structure. However, SRMs require a complex electronic control system to generate a specified number of voltage pulses for each motor phase. This paper presents the signal generation of multiple phases using only one current sensor in an asymmetric half bridge (AHB). In addition to maintain the predetermined phase voltages, sufficient current measurement windows and a minimal current ripple for the individual phases are further optimization criteria for signal generation. The generation of a state vector which controls the individual semiconductor for each motor phase to achieve a required phase voltage and simultaneously fulfill the multi-objective optimization criteria is challenging. Due to the vast number of possible solutions, a genetic algorithm (GA) was used to find state combinations that are suitable for the formulated optimization criteria. The results were discussed and recommendations about the genotype representation and the used genetic operators were given. Interested readers will find detailed information about the software technical implementation using the Global Optimization Toolbox from MATLAB.

Analysis of Midpoint Current Characteristics for Novel Six-Phase N+2 Power Converter in Different Working Condition

In this paper, a novel N+2 power converter is introduced and be applied to a six-phase switched reluctance motor (SRM) drive system. Compared with six-phase asymmetric half bridge (AHB) converter, the number of power devices required by this N+2 converter is greatly reduced, while the independence and controllability of each phase can be ensured. However, in N+2 converters, the two midpoint switches are also important components and working at much higher switching frequency than phase switches. The value of the midpoint current directly affects the heating problem of these midpoint switches then affects the reliability of the N+2 converter. Hence, different operate modes of multi-phase excitation state of N+2 converter are enumerated to obtain the relation between the midpoint current and phase currents. Then the characteristics of the midpoint current under different control parameters were obtained through MATLAB-Simulink, and the parameter optimization rules for reducing the amplitude of midpoint current are summarized. In addition, the characteristics of midpoint current in several typical fault states are also summarized. Finally, the simulation results are verified by experiments.

Investigating asymmetric spatial butterfly-shaped steel arch bridges: a case study

Jiusha Bridge in Hangzhou city, China, is an asymmetric spatial butterfly-shaped steel arch bridge. The bridge deck and steel arch rib form a half-through structure at one end and a through structure at the other. The bridge sits on a soft soil foundation with poor thrust resistance; therefore, different force transmission structures adopted at the asymmetric ends to balance the large arch thrust during internal force transmission of the structure were researched. The mechanical behaviour of the asymmetric steel arch bridge under dead load and live load was compared with that of a symmetric half-through and through steel arch bridge. Subsequently, a full-bridge finite-element (FE) model was established in order to adjust the stiffness contribution of the middle arch and side arches to the bridge, optimise the hanger forces in the finished bridge state and analyse the bridge's stress, stiffness, stability and dynamic characteristics. The stresses in some key members and joints were calculated by means of a refined FE model consisting of beam elements, truss elements and plate elements. Some of the special construction technologies used on Jiusha Bridge are also briefly discussed.

Low-Cost Drive for Switched Reluctance Machine Using Piezoelectric Actuators

Contemporary power electronics designs are based on stationary placement of power switches. Inability to change the terminal connections causes increase in number of switches, corresponding components, and driver circuits. Moreover, most fault tolerant realizations require additional switches (redundancy approach). Hence, the motivation behind this paper is to engineer a solution which can allow for a dynamic circuit topology, thereby alleviating the size, cost, and complexity issues associated with current technology. Dynamic circuit topology refers to a technology that enables making or breaking a connection without disrupting the circuit functionality. This idea embarks a novel set of possibilities such as replacing vulnerable components for increased fault tolerance, multiplexing components to change circuit behavior, and multiplexing circuits between multiple loads. In this paper, electromechanical actuation using piezoelectric materials has been explored for dynamic relocation of one asymmetric bridge to all the phases of a switched reluctance machine, reducing the number of semiconductor switches by a factor of 4. The presented concept can generate new opportunities such as reduced part converter topologies, which can in turn introduce substantial saving in development cost and the required footprint.

Novel Current Profile of Switched Reluctance Machines for Torque Density Enhancement in Low-Speed Applications

In this article, a current profiling technique is proposed for the torque density enhancement in switched reluctance machines (SRMs). The novel current profile is initially developed from the harmonic current injection method and is then modified into a unipolar waveform to allow the application of an asymmetric bridge inverter. It is found that, neglecting the magnetic saturation, the optimal current profile for the maximum torque per ampere operation in an SRM is close to a pulse with high-order harmonics. However, an optimized current with relatively low-order harmonics can provide better performance in the practical situation. Based on the analytical and the finite element results, the proposed method is proved to be able to enhance the torque density by 20% at the light load condition and by 15% at the rated condition compared with the conventional SRM excitation. Also, the large torque ripple and core loss in SRMs are suppressed and the efficiency is improved. More importantly, unlike many other current profiling techniques, the proposed current profile has fixed parameters and is easily adaptable to different machine specifications. The effectiveness of the proposed method is verified by both the finite-element analyses and the experiments.

Dual Sliding Mode with PI Controller Based Switched Reluctance Motor Drive

In this paper, a Dual Sliding Mode with Proportional Integral (DSM-PI) controlled Switched Reluctance Motor drive circuit is proposed with closed loop speed control. An asymmetric half bridge converter is used to drive SRM which is fed by a front-end circuit. The dual sliding mode PI controller is utilized for better time response. With variable proportional and integral gains in DSM-PI controller the error generation value is altered with faster values making the speed of the motor to settle faster with reduced ripple and disturbances. The topology is modelled in MATLAB/Simulink environment and the simulation results on a three-phase 6/4 SRM are presented.

An Active Boost Power Converter for Improving the Performance of Switched Reluctance Generators in DC Generating Systems

In this article, an active boost power converter is proposed for switched reluctance generators (SRGs) that support low-voltage dc loads or dc microgrids. In the proposed converter, a front-end circuit is added to a conventional asymmetric half bridge power converter. With the front-end circuit, excitation voltage and demagnetization voltage can be regulated flexibly to improve the system efficiency and increase the maximum output power under constant phase current constraints. Then a multiloop control strategy is developed to control the power converter. The multiloop controller contains a power controller and a boost voltage controller. The power controller is designed to control SRG over the entire operating range. The boost voltage controller is designed to control the front-end circuit. Two strategies are compared for the boost voltage control: voltage hysteresis control strategy and power flow control strategy. Comparing with voltage hysteresis control, proposed power flow control shows improvements in minimizing output voltage ripple and is suggested for the proposed converter. In the end, simulation and experimental results are given to verify the feasibility of the proposed power converter and control strategy. Comparisons between the proposed converter and the conventional converter are also given for evaluation.

Incorporation of Ni2+, Co2+, and Selenocysteine into the Auxiliary Fe-S Cluster of the Radical SAM Enzyme HydG.

The radical SAM enzyme HydG generates CO- and CN--containing Fe complexes that are involved in the bioassembly of the [FeFe] hydrogenase active cofactor, the H-cluster. HydG contains a unique 5Fe-4S cluster in which the fifth "dangler" Fe and the coordinating cysteine molecule have both been shown to be essential for its function. Here, we demonstrate that this dangler Fe can be replaced with Ni2+ or Co2+ and that the cysteine can be replaced with selenocysteine. The resulting HydG variants were characterized by electron paramagnetic resonance and X-ray absorption spectroscopy, as well as subjected to a Tyr cleavage assay. Both Ni2+ and Co2+ are shown to be exchange-coupled to the 4Fe-4S cluster, and selenocysteine substitution does not alter the electronic structure significantly. XAS data provide details of the coordination environments near the Ni, Co, and Se atoms and support a close interaction of the dangler metal with the FeS cluster via an asymmetric SeCys bridge. Finally, while we were unable to observe the formation of novel organometallic species for the Ni2+ and Co2+ variants, the selenocysteine variant retains the activity of wild type HydG in forming [Fe(CO)x(CN)y] species. Our results provide more insights into the unique auxiliary cluster in HydG and expand the scope of artificially generated Fe-S clusters with heteroatoms.

Phase Current Digital Analysis of Power Converter for Freewheeling Diode Fault Diagnosis on Switched Reluctance Motor Drive

Power converter is critical but prone to be failure in switched reluctance motor (SRM) drives. The open- and short-circuit fault characteristics of freewheeling diode in asymmetric bridge power converter are analyzed in details. Based on logic judgment, four online fault diagnostic methods with digital phase current analysis of power converter are proposed in this paper. The fault features are extracted by analyzing the relationship between chopping signal and the current information from some special positions. The four fault diagnostic methods are carried out according to the current obtained by detecting dc bus current and the lower freewheeling bus current, the chopped bus current, the upper excitation bus current and lower freewheeling bus current, the lower excitation bus current, and dc bus current, respectively. Comparisons between the four diagnostic methods are conducted. Simulations and experiments on a 12/8 SRM validate the effectiveness of the proposed methods.