A multistable transistor circuit

In this paper a newly proposed active element namely Dual X current conveyor differential input transconductance amplifier (DXCCDITA) is used in designing two grounded inductance (GI) simulators and a generalized immittance simulator topology which can realize floating inductor (FI), floating capacitor (FC) and floating resistor (FR) based on passive elements selected. All the designed simulators require only a single active element and minimum number of passive components one/two for implementation. The proposed simulators enjoy tunability property. None of the proposed simulators require passive component matching conditions for realization. To demonstrate the workability of the simulators they are used in design of a current mode (CM) low pass filter circuit and second order voltage mode (VM) band pass filter. The simulations are performed using 0.35μm TSMC CMOS technology parameters in Hspice program.

A physical theory of the structure of uniaxially oriented polymers is used to propose a new mechanical model that makes it possible to predict deformation processes in polymers. Polycaproamide-film fibers are used as an example to illustrate the use of the model to predict deformation and relaxation in polymers. Making optimum use of both new and traditional polymers in different sectors of industry would be impossible without proper study of their viscoelastic properties. Such studies can be performed by mathematically modeling the deformation processes which take place in these materials. In practice, an attempt is made to quantitatively predict the behavior of polymers by using various methods that involve mathematical modeling and numerical projection [1-5]. However, as is known, these methods are valid for a relatively narrow range of mechanical loads, strains, and temperatures and cannot predict certain features of the materials’ behavior. In addition, such methods do not embrace or explain all of the processes that take place in synthetic fibers and filaments because the physical features of polymers are not accounted for in the integral equations of viscoelasticity [1-12]. Thus, in this article we propose to model deformation and relaxation processes by using a nonlinear mechanical model that includes physical properties. This will make it possible to determine the mechanical characteristics of polymeric materials under conditions that correspond to different types of loading, which in turn will allow the materials’ properties to be predicted within a wide range of loads and temperatures. The supermolecular structure of oriented amorphous-crystalline polymers is variegated and complex. Thus, the polymers can be in different quasi-equilibrium states when loaded. The viscoelastic component of deformation is a subject worthy of special attention when studying the deformation of materials of the given class. In accordance with modern physics, materials may undergo viscoelastic deformation due to the rearrangement of different stable structures (clusters) which are in different states separated by energy barriers. These clusters or active conformation elements (ACEs) [13] - the nature of which is not germane to mechanical descriptions - can be in one of two stable states. The stable state in which the linear dimension is minimal - state 1 - will be referred to as being conditionally convolute and will be represented as . We will call the second stable state - state 2 - conditionally involute and will represent it as . For example, an elastic spring can either be convolute or involute. On the one hand, this element is elastic. On the other hand, it is also nonlinear. Thus, instead of using classical mechanical models in the form of Hookean springs, dampers, and combinations thereof, i.e. classical linear Maxwell elements, Kelvin-Voigt elements, etc., we are proposing to use a nonlinear model (elastic spring) which is based on energy barriers. These barriers will be represented in the form of the energy diagram shown in Fig. 1. In accordance with the proposed physical and mechanical model, an unloaded cluster can be in one of two stable states - state 1 or state 2. These states are separated by an energy gap of the width U and a barrier of the height H. A deformation

Cloud radiative kernels were built by BCC_RAD (Beijing Climate Center radiative transfer model) radiative transfer code. Then, short-term cloud feedback and its mechanisms in East Asia (0.5°S–60.5°N, 69.5°–150.5°E) were analyzed quantitatively using the kernels combined with MODIS satellite data from July 2002 to June 2018. According to the surface and monsoon types, four subregions in East Asia—the Tibetan Plateau, northwest, temperate monsoon (TM), and subtropical monsoon (SM)—were selected. The average longwave, shortwave, and net cloud feedbacks in East Asia are −0.68 ± 1.20, 1.34 ± 1.08, and 0.66 ± 0.40 W m−2 K−1 (±2σ), respectively, among which the net feedback is dominated by the positive shortwave feedback. Positive feedback in SM is the strongest of all subregions, mainly due to the contributions of nimbostratus and stratus. In East Asia, short-term feedback in spring is primarily caused by marine stratus in SM, in summer is primarily driven by deep convective cloud in TM, in autumn is mainly caused by land nimbostratus in SM, and in winter is mainly driven by land stratus in SM. Cloud feedback in East Asia is chiefly driven by decreases in mid-level and low cloud fraction owing to the changes in relative humidity, and a decrease in low cloud optical thickness due to the changes in cloud water content.

A wide range of cellular processes require molecular regulatory pathways to convert a graded signal into a discrete response. One prevalent switching mechanism relies on the coexistence of two stable states (bistability) caused by positive feedback regulations. Intriguingly, positive feedback is often supplemented with negative feedback, raising the question of whether and how these two types of feedback can cooperate to control discrete cellular responses. To address this issue, we formulate a canonical model of a protein–protein interaction network and analyze the dynamics of a prototypical two-component circuit. The appropriate combination of negative and positive feedback loops can bring a bistable circuit close to the oscillatory regime. Notably, sharply activated negative feedback can give rise to a bistable regime wherein two stable fixed points coexist and may collide pairwise with two saddle points. This specific type of bistability is found to allow for separate and flexible control of switch-on and switch-off events, for example (i) to combine fast and reversible transitions, (ii) to enable transient switching responses and (iii) to display tunable noise-induced transition rates. Finally, we discuss the relevance of such bistable switching behavior, and the circuit topologies considered, to specific biological processes such as adaptive metabolic responses, stochastic fate decisions and cell-cycle transitions. Taken together, our results suggest an efficient mechanism by which positive and negative feedback loops cooperate to drive the flexible and multifaceted switching behaviors arising in biological systems.

The design of low-frequency filters by means of RC feedback around active elements has long been known. The advent of the transistor has renewed interest in this field and has necessitated a more exact synthesis procedure. This is because in the classical design the active element is assumed to be an ideal voltage amplifier with infinite input impedance, zero output impedance and zero reverse transmission. The transistor satisfies the dual ideal assumptions to a considerably lesser degree than the vacuum tube. The sensitivity of the transistor parameters to temperature also requires more attention to be paid to the effect of parameter variations on the filter response. The paper extends the classical theory in several directions: 1) A synthesis procedure is developed in which the finite input and output impedances and reverse transmission of the active element are taken into account in an exact manner. 2) The freedom that exists is used to optimize the synthesis so as to permit design with a "least active" element. 3) Expressions are developed for the sensitivity of the filter to the four low-frequency active parameters and to the passive parameters. It is presumed that the design specifications include a statement of the extent of active and passive parameter variation and the tolerances on the filter response. The procedure for satisfying such specifications is an integral part of the design procedure. 4) Under the constraint of fixed source and load impedances and desired parameter insensitivity, the design achieves maximum gain. An example which includes all the above features is worked out in detail. The principal limitations of the design procedure are: 1) It is restricted to a transfer function of second degree so that if sharper cut-offs are needed, several basic sections must be used, separated by isolating stages. 2) It is best suited to achieve low-pass or moderate band-pass characteristics.

A self-reinforcing positive feedback is regarded as a critical process for maintaining alternative stable states (ASS); however, identification of ASS and quantification of positive feedbacks remain elusive in natural ecosystems. Here, we used large-scale field surveys to search for ASS and a positive feedback mechanism under a wide range of habitats on the Tibetan Plateau. Using multiple methods, we proved that three stable states exist that accompany alpine marsh degradation. Positive feedbacks between changing soil moisture and plant community composition forced the ecosystem into another stable state, and the alteration of water use efficiency (WUE) of the component species contributed to this shift. This study provides the first empirical evidence that positive feedback loops maintain ASS in the alpine marsh ecosystem on the Tibetan Plateau. Our research revealed the powerful driving role of plants in transitions between states, which may support the conservation and restoration of global alpine marsh ecosystems.

Active vibration control and actuation of a small cantilever for applications in scanning probe instruments

Recently, the hybrid relay-reflecting intelligent surface (HRRIS) has been introduced as a spectral- and energy-efficient architecture to assist wireless communication systems. In the HRRIS, a single or few active relay elements are deployed along with a large number of passive reflecting elements, allowing it to not only reflect but also amplify the incident signals. In this work, we investigate the potential of the HRRIS in aiding the computation offloading in a single-user mobile edge computing system. The objective is to minimize the offloading latency while ensuring the secrecy of user data against a malicious eavesdropper. We develop efficient solutions to this latency minimization problem based on alternating optimization. Through numerical results, we show that the deployment of the HRRIS can result in a considerable reduction in latency. Furthermore, the latency reduction gain offered by the HRRIS is much more significant than that of the conventional reconfigurable intelligent surface (RIS).

The topic of multifunctional material systems using active or smart materials has recently gained attention in the research community. Multifunctional piezoelectric systems present the ability to combine multiple functions into a single active piezoelectric element, namely, combining sensing, actuation, or energy conversion ability with load-bearing capacity. Quantification of the bending strength of various piezoelectric materials is, therefore, critical in the development of load-bearing piezoelectric systems. Three-point bend tests are carried out on a variety of piezoelectric ceramics including soft monolithic piezoceramics (PZT-5A and PZT-5H), hard monolithic ceramics (PZT-4 and PZT-8), single-crystal piezoelectrics (PMN-PT and PMN-PZT), and commercially packaged composite devices (which contain active PZT-5A layers). A common 3-point bend test procedure is used throughout the experimental tests. The bending strengths of these materials are found using Euler-Bernoulli beam theory to be 44.9 MPa for PMN-PZT, 60.6 MPa for PMN-PT, 114.8 MPa for PZT- 5H, 123.2 MPa for PZT-4, 127.5 MPa for PZT-8, 140.4 MPa for PZT-5A, and 186.6 MPa for the commercial composite. The high strength of the commercial configuration is a result of the composite structure that allows for shear stresses on the surfaces of the piezoelectric layers, whereas the low strength of the single-crystal materials is due to their unique crystal structure, which allows for rapid propagation of cracks initiating at flaw sites. The experimental bending strength results reported, which are linear estimates without nonlinear ferroelastic considerations, are intended for use in the design of multifunctional piezoelectric systems in which the active device is subjected to bending loads.

This study describes a simple design for a single active element sinusoidal oscillator with a quadrature signal. A current conveyor transconductance amplifier (CCTA), a single resistor, and two grounded capacitors are used in the first circuit. The second circuit is improved by using a current-controlled current conveyor transconductance amplifier (CCCCTA) and two grounded capacitors without a passive resistor, which means the grounded capacitor is suitably implemented for the IC fabrication. The oscillation condition and frequency of both circuits can be controlled using the same method that concurrently adjusts the DC bias current and the resistance as well as the oscillation frequency can be independently adjusted by capacitances. The CCTA is achieved by cascading the integrated circuits (IC) AD844 and LM13700, made by Analog Devices Corporation and Texas Instruments, respectively, which are available for commercial purchase. The sinusoidal quadrature signals in the time-domain and frequency-domain can be shown with computer simulations and the results of experiments. The Monte Carlo Analysis is also utilized to examine the oscillation frequency with the influence of passive element tolerance errors. The predicted oscillation frequency has a standard variation of about 20.04 kHz, with a maximum frequency of approximately 346.89 kHz and a minimum frequency of approximately 259.09 kHz. In addition, the mean and median frequencies are 296.10 and 293.98 kHz, respectively. The results of this study indicate that computer simulation and experiment are similar to a theoretical analysis, making them suiTable for use in the teaching of electrical and electronic engineering

<title>Intracavity laser spectroscopy using dispersive and dynamic resonators</title>

Introduction. Recently, photovoltaic (PV) systems are increasingly favored for converting solar energy into electricity. PV power systems have successfully evolved from small, standalone installations to large-scale, grid-connected systems. When the nonlinear loads are connected to a grid-tied PV system, the power quality can deteriorate due to the active power supplied by the PV array, there’s a noticeable decline in the quality of power delivered to consumers. Its combination with the shunt active power filter (SAPF) enhances system efficiency. Consequently, this integrated system is adept at not only powering local loads but also at compensating for reactive power and filtering out harmonic currents from the main grid. The novelty of the work describes how an operation of a small scale PV system connected to the low voltage distribution system, and nonlinear load can be achieved, the investigation aims to analyze the system’s behavior and elucidate the advantages of employing various control algorithms. These proposed algorithms are designed to ensure a unity power factor for the utility grid while prioritizing high convergence speed and robustness against load power fluctuations across different levels of solar irradiation affecting the PV modules. The purpose of this work is to enhance the dynamic performance of the SAPF by cooperatively using a self-tuning filter (STF) based instantaneous active and reactive power method (PQ) with a novel predictive current control, enhance the system resilience, ensure optimal management of the total active power between the PV system, the electrical network and the non-linear load by integrating the functionalities of the SAPF under different levels of solar irradiation and maintain the DC-link capacitor voltage constant. Methods. A novel predictive current controller is designed to generate the switching signals piloted the three phase source voltage inverter, also a novel algorithm of instantaneous active and reactive power is developed, based on STF, to extract accurately the harmonic reference under non ideal grid voltage, also the perturb and observe algorithm is used to extract, under step change of solar irradiation, the maximum power point tracking of the PV module and the PI controller is used to maintain constant the DC-link capacitor voltage of the SAPF. Results. The efficacy of the proposed system is primarily centered on the grid side, and the performance evaluation of the control system is conducted using the STF based PQ algorithm and predictive current control. In addition, comprehensive testing encompasses all modes of operation, including scenarios involving distorted voltage sources, step changes in solar radiation, and variations in nonlinear loads. Results highlight superior performance in both transient and stable states, affirming the robustness and effectiveness of the proposed controllers. Practical value. The total harmonic distortion value of the grid current for all tests respects the IEEE Standard 519-1992. References 21, tables 7, figures 25.

This paper presents the second-order current-mode filter with 4 input currents and single output current. Five filter responses, namely High-pass (HP), Low-pass (LP), Band-pass (BP), Band-reject (BR) and All-pass (AP) filters are achieved. The pole frequency and quality factor are tuned by input bias current called electronic control. It has high output impedance which is able cascading in the current-mode filter and driving load without buffering devices. The filter uses only single active element namely current controlled current differencing transconductance amplifier (CCCDTA) and 2 grounded capacitors which is ideal for monolithic integrated circuit implementation. The filter was proved by Pspice simulation using BJT technology. The results are agreed with theoretical prediction.

This paper presents a voltage-mode biquadratic filter performing completely standard functions: low-pass, high-pass, band-pass, band-reject and all-pass functions, based on single voltage differencing transconductance amplifier (VDTA). The proposed filter has three input voltage and a single output voltage. The features of the circuit are that; the quality factor and natural frequency can be tuned independently; the circuit description is very simple, consisting of merely one VDTA, one resistor and two capacitors; the pole frequency can be electronically adjusted. Additionally, each function response can be selected by suitably selecting input signals with digital method; the double input voltage is not required. Using only single active element, the proposed circuit is very suitable to further develop into an integrated circuit. The PSPICE simulation results are depicted. The given results agree well with the theoretical anticipation.

A new CMOS dual-X second generation current conveyor (DXCCII) with an FDNR circuit application