Loop Stability Research Articles

Experimental study on a single-sided resilient composite beam–column joint

This paper presents an experimental study on a single-sided resilient composite beam–column joint, in which a nonreplaceable concrete slab and connection plate and a replaceable buckling-restrained cover plate (BRCP) are installed at the top and bottom flanges, respectively. The seismic performance and replaceability of the proposed joint were investigated considering the influence of the concrete slab. One specimen was cyclically loaded under 2 % rotation, and then the damaged core plate of the BRCP was replaced to form a new specimen that was cyclically loaded under 4 % rotation. The results showed that the neutral axis was shifted upward to the top flange, which made the damage concentrate in the core plate, and only minor damage occurred to the connection plate and concrete slab under 2 % rotation. The hysteresis curve after replacement was almost the same as that before replacement under 2 % rotation and showed full and stable loops without decrease in load capacity under 4 % rotation, implying good seismic performance and replaceability. In addition, the proposed joint was compared with a bare steel joint to examine the effects of concrete slabs. Further, a numerical model of the specimen was developed and verified by comparison with the test results to better understand the test and study the influence of connection plates. Finally, the formulas for the yield moment and initial stiffness of the joint were derived and compared with test results to verify the accuracy of the formulas. The influence of the reduction in core plate area on the joint stiffness and neutral axis position was discussed using the formulas.

Evolution of and Perspectives on Differential‐Pair‐Based CMOS Variable Gain Amplifiers With Linear‐in‐Decibel Gain Control: A Tutorial

ABSTRACTA variable gain amplifier (VGA) is an essential building block used in the automatic gain control (AGC) loop to provide a continuous, adjustable gain for the signal strength. To maintain the stability and consistency of the AGC loop, it is necessary to ensure that the gain of the VGA has an accurate dB‐linear characteristic. This tutorial provides a detailed overview of the development of dB‐linear VGAs based on differential pair structures over recent years. We categorize various VGA cells based on differential pair structures, analyze their operating principles, and explain the key features of each topology. Based on observation and extraction of the dB‐linear implementation schemes used by these VGAs, we summarize three basic methods for achieving dB‐linear gain control. We also discuss specific methods for realizing the exponential function, using a true exponential and a mathematical approximation, and present the different types of approximation functions adopted in the works described here. Considerations in regard to the tuning range, gain error, bandwidth, linearity, process‐temperature robustness, and circuit simplicity are also discussed. Finally, we draw comparisons and give perspectives for future dB‐linear VGAs.

Study on theoretical model and actual deformation of weft-knitted transfer loop based on particle constraint

Abstract In order to derive the structural properties and deformation behavior of the weft-knitted transfer fabric, a multilayer spring-mass geometric circle model with weft-knitted transfer loop is provided in conjunction with the fabric samples’ image. Eight type-value points were utilized to control the transfer loop’s morphological structure. Connections between the type-value points and the particle system were established. Non-uniform rational B spline curves and texture mapping were utilized to create the three-dimensional impression of the weft-knitted transfer loop. By measuring the offset of the type-value points in conjunction, the actual deformation of the weft-knitted transfer fabric was determined. Utilizing a cylindrical envelope box for collision detection, the possible unreasonable interpenetration phenomenon in the simulation was solved, and thus a stable weft-knitted transfer loop structure was obtained. Using Microsoft Visual Studio and C#, the deformation of the weft-knitted transfer fabric was simulated, the simulated weft-knitted transfer fabric’s deformation pattern accurately depicts the fabric’s three-dimensional structure and deformation behavior while also matching the structural characteristics of the fabric sample. The findings demonstrate that the theoretical structural model of weft-knitted transfer fabric constructed can accurately represent the loop’s structure, and the actual deformation of the simulated weft-knitted transfer fabric is consistent with the deformation characteristics of the fabric sample. Weft-knitted transfer fabric’s deformation behavior may be effectively reflected by the multilayer spring-mass geometric circle model, allowing for the modeling of the fabric’s morphology and 3D structure.

Online decoupling of the time-varying longitudinal feedback loops for improved performance in Advanced Virgo Plus*

Abstract Gravitational Wave detectors require low-noise sensors combined with high-performance feedback loops to maximize the detector sensitivity in the low-frequency detection range. Some feedback loops in the detector are strongly coupled and their coupling varies over time, which is inherent to the optical configuration and the optical readout scheme used to obtain error signals for the feedback loops. This paper presents a control-based approach to deal with the time-varying interaction among three of the longitudinal degrees of freedom in the Advanced Virgo Plus detector, using the pre-existing infrastructure of the detector. An intuitive Multiple-Input Multiple-Output stability criterion is presented that illustrates how the time-varying coupling affects the stability of the feedback loops, as well as a method that identifies the coupling online and updates a decoupling matrix accordingly. Experiment results of the proposed method on the Advanced Virgo Plus detector illustrate continuous minimization of the coupling over time. Using the derived stability criterion, it is furthermore shown that the coupling is sufficiently minimized such that the interaction terms can be neglected in the control design, resulting in an improved controller performance.

Crystal Structure and Molecular Mechanism of Isocitrate Lyase from Chloroflexus aurantiacus.

Chloroflexus aurantiacus is a green, nonsulfur bacterium that employs the 3-hydroxypropionate cycle to grow, using carbon dioxide/bicarbonate as its primary carbon source. Like most bacteria, it possesses the glyoxylate cycle, facilitated by malate synthase and isocitrate lyase (ICL), allowing a "tricarboxylic acid cycle" bypass. C. aurantiacus also harbors ICL, an enzyme that catalyzes reversible isocitrate cleavage into glyoxylate and succinate. This study presents the crystal structures of C. aurantiacus-derived ICL (CaICL), in its Mg2+-bound and Mn2+ and isocitrate-bound forms, elucidating its substrate-binding mechanism and catalytic loop dynamics. CaICL forms a homotetramer and interacts with isocitrate via critical active-site residues, revealing its catalytic mechanism. The stabilization of the catalytic loop and adjacent terminal regions upon isocitrate binding underscores its functional significance. These findings advance our understanding regarding ICL enzymes, offering a basis for future investigations into their biological roles and potential applications.

Structural Prediction and Antigenic Analysis of ROP18, MIC4, and SAG1 Proteins to Improve Vaccine Design against Toxoplasma gondii: An In silico Approach.

Toxoplasmosis is a cosmopolitan infectious disease in warm-blooded mammals that poses a serious worldwide threat due to the lack of effective medications and vaccines. The purpose of this study was to design a multi-epitope vaccine using several bioinfor-matics approaches against the antigens of Toxoplasma gondii (T. gondii). Three proteins of T. gondii, including ROP18, MIC4, and SAG1, were analyzed to predict the most dominant B- and T-cell epitopes. Finally, we designed a chimeric immunogen RMS (ROP18, MIC4, and SAG1) using some domains of ROP18 (N377-E546), MIC4 (D302-G471), and SAG1 (T130-L299) linked by rigid linker A (EAAAK) A. Physicochemical prop-erties, secondary and tertiary structures, antigenicity, and allergenicity of RMS were predicted utilizing immunoinformatic tools and servers. RMS protein had 545 amino acids with a molecular weight (MW) of 58,833.46 Da and a theoretical isoelectric point (IP) of 6.47. The secondary structure of RMS protein con-tained 21.28% alpha-helix, 24.59% extended strand, and 54.13% random coil. In addition, eval-uation of antigenicity and allergenicity showed the protein to be an immunogen and non-aller-gen. The results of the Ramachandran plot indicated that 76.4%, 12.9%, and 10.7% of amino acid residues were incorporated in the favored, allowed, and outlier regions, respectively. ΔG of the best-predicted mRNA secondary structure was -593.80 kcal/mol, which indicated that a stable loop was not formed at the 5' end. Finally, the accuracy and precision of the in silico analysis must be confirmed by successful heterologous expression and experimental studies.

Rehabilitation of steel structures using innovative brace members equipped with YSPD damper

Earthquakes are serious risks to human life and infrastructure. An earthquake's influence on human life and its socioeconomic consequences highlight the need to investigate and create the most efficient and easily adaptable ways to minimize losses. The basic concept of different control mechanisms used for protecting structures from the destructive impacts of earthquakes is to dissipate the energy efficiently, therefore ensuring that the structure remains undamaged or sustains minimum damage. To achieve this purpose, the passive control mechanism is a particularly suitable and reliable technology as it doesn't rely on external power to actively dissipate energy. The present study proposes using a passive energy dissipation device called the Yielding Shear Panel Device (YSPD) for strengthening the current steel structures. The YSPD consists of a square hollow section (SHS) that houses a diaphragm plate. The fundamental concept of the YSPD involves harnessing the lateral deformation of a steel plate to absorb and disperse the seismic energy. The Bouc-Wen-Baber Noori (BWBN) material has been used for simulating the hysteresis force-deformation relationship of YSPDs by pinching. YSPDs are simulated as spring components that connect between the beam and the V-brace. A nonlinear time history dynamic analysis was performed to assess the alteration in the structural capacity with the setting up of YSPDs. The performance of the tested structure was assessed considering story drift, story displacement, story shear, column shear, and YSPD hysteresis loops. The results indicated that YSPD installation has improved the structure's capacity. However, the use of dampers resulted in significant drift in all stories, a reduction in total floor displacement, and a decrease in the shear force of the stories. However, the results demonstrated that the YSPD dampers effectively absorbed energy and exhibited stable hysteresis loops.

Assessment of ASYST and RELAP5 for predicting stability and limit cycles of a low-pressure natural circulation loop with flashing instability

Two thermal hydraulics system codes, ASYST VER3 and RELAP5 MOD3.3, are assessed for their prediction of stability and limit cycles of low-pressure natural circulation with potential flashing instability. The benchmark conditions are from a nearly five-meter-tall water loop whose experiments have generated a published dataset covering both stability and limit-cycle oscillations. These conditions are simulated by a model of the entire system, and the target asymptotic behaviors are approached through sufficiently long transients under prescribed operational settings. ASYST is found not conservative for stability prediction, in the sense that the unstable operational range is underpredicted with discrepancy mainly in the high-subcooling stability boundary. Qualitative flow changes across the island of instability are however simulated satisfactorily, and for conditions correctly predicted as unstable, reasonable prediction is achieved for the oscillation period, time-averaged flow rate, and peak flow rate. Further comparison against experimental void fraction confirms that ASYST simulates physical two-phase behaviors in the limit cycles. RELAP5 predicts a much more stable system whose island of instability is significantly smaller than that of reality. Its simulated flow oscillations also noticeably deviate from the typical patterns of flashing instability, resembling sinusoidal waves following periods different from the experimental measurement. Underprediction of flashing and overproduction of subcooled boiling are identified as potential major defects in RELAP5, which calls for future model calibration and further investigation. In general, the current assessment contributes to the awareness of potential uncertainties when adopting ASYST and RELAP5 for predicting flashing instability and its induced transients.

Optimal balance of organic detritus and feed for fish growth and water quality improvement through regulating nutrients cycling

In order to explore the effects of different feed composition on the nutrient level and microbial loop structure in aquaculture ponds, a field simulation experiment in aquaculture ponds was conducted by adding different proportions (0%, 20%, 40% and 60%) of bagasse to fish feed for combined feeding. The addition of bagasse significantly reduced the levels of various forms of nitrogen and phosphorus in the water, especially with the addition of 60% bagasse. In the treatments without addition and with 20% bagasse added, nitrogen and phosphorus levels remained relatively high, which should be attributed to the decomposition of feed and the release of sediment, ultimately stimulating the abundant reproduction of algae. Bacterial growth was limited due to insufficient supply of organic carbon, and the growth of fish relied more on the components of the feed. With the addition of 60% bagasse, the high organic carbon and low nitrogen and phosphorus levels could not support the growth of phytoplankton, bacteria, and zooplankton. It is inferred that organic carbon may be more degraded into carbon dioxide, ultimately limiting the growth of fish. Adding 40% bagasse achieved a balanced level of carbon, nitrogen, and phosphorus, establishing a healthy and stable microbial loop structure (including phytoplankton, bacteria, and zooplankton). Most nutrients were converted into plankton, which then became natural food for fish, ensuring complete nutrient utilization. This is beneficial for both water quality improvement and fish reproduction. Therefore, adding a moderate proportion of bagasse to the feed can maximize the effects of water quality improvement, fish reproduction, and even the quality of fish meat.

Hydrogen modified dislocation loop types and shapes in irradiated iron

Dislocation loops are one type of irradiation defects that severely degrade the mechanical properties of nuclear materials. In this study, we found that hydrogen atoms in irradiation environment significantly modify the loop properties including loop types and shapes during in-situ hydrogen irradiation. <100> loops have been energetically stable from 300 °C in H+ irradiated iron whereas the stability of <100> loops is delayed until 500 °C in Fe+ irradiated iron. Meanwhile, both <100> loops and 1/2<111> loops exhibit polygonal shapes with sharp corners at 400 °C after H+ irradiation, similar to loops predicted at 900 °C without hydrogen. Our results highlight the importance of considering the hydrogen effects in dislocation loop evolution and stability.

Numerical study of steel beam to reinforce concrete column (RCC) connection with through-plate and buckling-restrained steel plates

This study examines the behavior and failure mechanisms of steel beam-to-reinforced concrete column connections with through-plate and buckling-restrained steel plates (BRSPs) configurations. These connections are critical components in composite steel and concrete structures, playing a vital role in force transfer and resistance to various loads, especially dynamic loads such as earthquakes. The primary objective of this study is to analyze the hysteresis behavior of these connections under cyclic loading using numerical analyses. Parametric models with varying BRSP thicknesses, ranging from 5 to 25 mm, were used to investigate their impact on hysteresis behavior and load-bearing capacity. The effects of different BRSP thicknesses on stress distribution and failure mechanisms were analyzed. The results from the parametric studies show that increasing the thickness of BRSPs improves the stress distribution in the beam-to-column connections. This improvement includes reduced stress concentration and enhanced uniformity of stress distribution, which can lead to reduced localized failures and increased overall connection stability. Numerical simulations indicate that the use of BRSPs (with a thickness of 15 and 17 mm) results in wider and more stable hysteresis loops, reflecting increased energy absorption capacity and improved deformation behavior of the connections under cyclic loading. The findings show that BRSPs can reduce failure concentration, increase flexural resistance, and prevent buckling in steel beams. These results underscore the importance of using BRSPs to enhance structural performance and mitigate potential failures under severe loading conditions.

A comparative experimental and numerical study on the shear and flexural mechanism of an innovative butterfly-damper

In this paper, the behavior of an innovative metallic damper made of butterfly plates (with shear or flexural mechanisms) to improve the behavior of the CBF system is considered. These dampers can provide similar seismic resistant properties but concentrate most damage in the damper region during a seismic event. This has considerable practical utility in the construction industry and can allow quick replacement of these dampers (instead of replacing braces) after damage without impacting the serviceability of the building. To consider the behavior of the proposed dampers, experimental and numerical as well as parametrical studies were carried out. Experimental results indicated that both shear and flexural dampers pertain to stable hysteresis loops although the flexural damper showed a better ultimate rotation. However, experimental and numerical results revealed that the shear damper's ultimate strength, stiffness, and energy dissipating capacity reached >3.58, 4.59, and 14.56 times greater than flexural dampers. Results indicated that the response of the dampers is related to the slenderness and that the allowable slenderness was suggested for the design of the dampers.

Numerical simulation of arc stabilizing cycle in vacuum arc remelting of titanium alloy

Through utilizing numerical simulation methods, the flow state of the molten pool during the vacuum self-consumption melting process of titanium alloy was analyzed. The influence of the stable arc cycle on the shape of the molten pool, dendrite arm spacing, surface quality, and shrinkage cavity was examined. The results showed that without an external magnetic field, the molten pool for smelting a Φ720 mm specification titanium alloy ingot is dominated by self-inductance magnetic force, leading to a downward flow in the central part of the melt. A mere 0.5 G stray magnetic field can result in Ekman pumping, causing an upward secondary flow in the core to counteract it. At an externally added magnetic field strength of 50 G, choosing a 10 s-20 s cycle can achieve a relatively stable double loop flow pattern. The shape of its molten pool, dendrite arm spacing, and contact ratio all reach optimal performance, thus verifying the possibility and feasibility of the double loop flow, and the macroscopic segregation of the simulated ingots essentially matches the experimental results, aiming to provide references for selecting parameters in actual production.

Robustness Improved Method for Deadbeat Predictive Current Control of PMLSM with Segmented Stators

Permanent magnet linear synchronous motors (PMLSMs) with stator segmented structures are widely used in the design of high-power propulsion systems. However, due to the inherent delay and segmented structure of the systems, there are parameter disturbances in the inductance and flux linkage of the motors. This makes the deadbeat predictive current control (DPCC) algorithm for a current loop less robust in the control system, leading to a decrease in control performance. Compensation methods such as compensation by observer and online estimation of parameters, are problematic to apply in practice due to the difficulty of parameter adjustment and the high complexity of the algorithm. In this paper, a robustness-improved incremental DPCC (RII-DPCC) method—which uses incremental DPCC (I-DPCC) to eliminate flux linkage parameters—is proposed. The stability of the current loop was evaluated through zero-pole analysis of the discrete transfer function. Current feedforward was introduced to improve the stability of I-DPCC. The inductance stability range of I-DPCC was increased from 0.8–1.25 times to 0–2 times the actual value, and the theoretical stability range was increased more than 4 times, effectively improving the robustness of the predictive model to flux linkage and inductance parameters. Finally, the effectiveness of the proposed method was verified through numerical simulation and experiment.

Experimentally Demonstrating Indefinite Causal Order Algorithms to Solve the Generalized Deutsch's Problem

AbstractDeutsch's algorithm is the first quantum algorithm to demonstrate an advantage over classical algorithms. Here, Deutsch's problem is generalized to functions and a quantum algorithm with an indefinite causal order is proposed to solve this problem. The algorithm not only reduces the number of queries to the black box by half compared to the classical algorithm, but also significantly decreases the complexity of the quantum circuit and the number of required quantum gates compared to the generalized Deutsch's algorithm. The algorithm is experimentally demonstrated in a stable Sagnac loop interferometer with a common path, which overcomes the obstacles of both phase instability and low fidelity of the Mach–Zehnder interferometer. The experimental results show both ultrahigh and robust success probabilities . This study opens a path toward solving practical problems with indefinite cause‐order quantum circuits.

Quantitative Effects of the Loop Region on Topology, Thermodynamics, and Cation Binding of DNA G-quadruplexes.

The thermal stability of G-quadruplexes is important for their biological roles. G-quadruplexes are stable in the presence of cations such as K+ and Na+ because these cations coordinate in the G-quartet of four guanine bases. It is well known that the number of G-quartets and the configuration of the guanine bases affect the binding affinity of the cation. Recently, structures formed in the loop regions connecting the guanine stretches have attracted significant attention, because the loop region affects G-quadruplex properties, such as topology, thermal stability, and interactions with proteins and small molecules. Considering these effects, the loop region can also affect the binding affinity of the cations. Here, we designed a series of G-quadruplex-forming DNA sequences that contain a hairpin in a loop region and investigated the effects of the sequence and structure of the loop region on the cation binding affinity as well as the thermal stability of the G-quadruplex as a whole. First, structural analysis of the DNA sequences showed that the hairpin at the loop plays a key role in determining G4 topology (strand orientation). Second, in the case of the G-quadruplexes with the hairpin-forming loop region, it was found that a longer loop length led to a higher thermodynamic stability of the G-quadruplex as well as higher cation binding affinity. In contrast, an unstructured loop region did not lead to such effects. Interestingly, the cation binding affinity was correlated to the thermodynamic stability of the hairpin structure at the loop region. It was quantitatively demonstrated that the stable loop region stabilized the whole G-quadruplex structure, which induced higher cation binding affinity. These systematic and quantitative results showed that the loop region is one of the determinants of cation binding and expanded the possibilities of drug development targeting G4s by stabilizing the loop region.

Deformation, shape transformations, and stability of elastic rod loops within spherical confinement

Mechanical insight into the packing of slender objects within confinement is essential for understanding how polymers, filaments, or wires organize and rearrange in limited space. Here we combine theoretical modeling, numerical optimization, and experimental studies to reveal spherical packing behavior of thin elastic rod loops of homogeneous or inhomogeneous stiffness. Across varying loop lengths, a rich array of configurations including circle, saddle, figure-eight, and more intricate patterns are identified. A theoretical framework rooted in the local equilibrium of force and moment is proposed for the rod loop deformation, facilitating the determination of internal and contact forces experienced by the rods during deformation. For the confined homogeneous rod loops, their stable and metastable configurations are well described using proposed Euler rotation curves, which offer a concise and effective approach for configuration prediction. Moreover, formulated analysis on the stability and critical force for homogeneous rod loops on great circles of the spherical confinement are performed. For inhomogeneous rod loops with two segments of differing stiffness, the stiffer segment exhibits less deviation from the great circle, while the softer segment undergoes more pronounced deformation. These findings not only enhance our understanding of buckling and post-buckling phenomena but also offer insights into filament patterning within confining environments.

A 0.055 mm2 Total Area Triple-Loop Wideband Fractional-N All-Digital Phase-Locked Loop Architecture for 1.9–6.1 GHz Frequency Tuning

This paper presents a wideband fractional-N all-digital phase-locked loop (WBPLL) architecture featuring a triple-loop configuration capable of tuning frequencies from 1.9 to 6.1 GHz. The first and second loops, automatic frequency control (AFC) and counter-assisted phase-locked loop (CAPLL), respectively, perform coarse locking, while the third loop employs a digital sub-sampling architecture without a frequency divider for fine locking. In this third loop, fractional-N frequency synthesis is achieved using a delta-sigma modulator (DSM) and digital-to-time converter (DTC). To minimize area, digital modules such as counters, comparators, and differentiators used in the AFC and CAPLL loops are reused. Furthermore, a moving average filter (MAF) is employed to reduce the frequency overlap ratio of the digitally controlled oscillator (DCO) between the second and third loops, ensuring stable loop switching. The total power consumption of the WBPLL varies with the frequency range, consuming between 8.8 mW at the WBPLL minimum output frequency of 1.9 GHz and 12.8 mW at the WBPLL maximum output frequency of 6.1 GHz, all at a 1.0 V supply. Implemented in a 28 nm CMOS process, the WBPLL occupies an area of 0.055 mm2.

Multi-zero pole dynamically compensated LDO with low quiescent current

This paper presents an LDO design tailored to the various power domains of CPUs. In contemporary CPU designs, different functional modules typically necessitate distinct voltage levels, thus requiring a flexible and adjustable power management approach. An LDO with an internally compensated super source follower (SSF) and a multi-zero-pole compensated loop stability is proposed. The SSF is used to reduce the output impedance of the LDO, enhancing its carry-under-load capability. The loop is then transformed into a multi-zero-pole system through Miller compensation, feed-forward compensation, and zero-pole tracking compensation techniques, enabling the LDO to achieve stability and reliability under different loads. The LDO proposed in this study was designed using a 110 nm CMOS process. The LDO can operate within a temperature range of −40–150 °C, with a low quiescent current of 57 μA. The power supply rejection ratio of the circuit is −22 dB at 1 MHz. When the load current jumps from 5 mA to 300 mA within 40 μs, the output voltage experiences an undershoot of 271 mV, an overshoot of 174 mV, and a maximum adjustment time of 100 μs. The load regulation is 0.00267 mV/mA, and the line regulation is 1 mV/V.

On the stability of Markov feedback loops of a microsystem

On the stability of Markov feedback loops of a microsystem