A synchronized two-phase sinewave generator for AC metrology systemcompensations

A slave audio two-phase sinewave generator, which can be directly synchronized to a master generator, is described here. It can be used in ac metrology setups to provide additional “compensation” signals, traditionally derived with expensive multidecade inductive voltage divider networks. The generator is based on two direct digital synthesis (DDS) chips, programmed via the parallel printer PC interface; their clock is provided by a phase-locked loop circuit, which ensures frequency and phase synchronization of the DDS outputs with the master generator. The synchronization reference signal can be provided via an optical link reference channel, which avoids interference and ground loops. In its present implementation, the output voltage is V_peak =10 V, frequency range 500 Hz-4 kHz. Total harmonic distortion is contained to -65 dB, and amplitude stability is better than 500 μV/V over 24 h     

一种用于SDH 2Mb／s支路输出口的全数字锁相环

提出了一种具有极低通带宽度的二阶全数字锁相环，并采用了一些非线性的改进措施，从而使其具有一个相对较宽的牵出范围，以恢复Ｅ１支路信号的时钟。硬件实验证实，它完全可以满足ＩＴＵ－Ｔ对拌动抑制特性的要求。同时由于数字集成电路技术成熟，其集成度远远高于模拟集成电路；因而采用全数字锁相环对系统的集成有明显的益处。     

Synthesising gene clock with toggle switch and oscillator

The usefulness of a genetic clock lies in its role to stimulate a sequence of logic reactions for sequential biological circuits. A clock signal is a periodic square wave, its amplitude alternates at a steady frequency between fixed minimal and maximal levels. Transition between the minimum and the maximum is instantaneous for an ideal square wave; however, the function is unrealisable in physical bio‐systems. This research develops a new genetic clock generator based on a genetic oscillator, in which, a sine wave generator is adopted as a signal oscillator. It is shown that combination of a genetic oscillator with a toggle switch is able to generate clock signals forming an efficient way to generate a near square wave. In silico study confirms the proposed idea.Inspec keywords: genetics, oscillators, biological techniques, square‐wave generators, switchesOther keywords: toggle switch, genetic clock, logic reaction sequence, sequential biological circuits, clock signal, periodic square wave, physical biosystem, genetic clock generator, sine wave generator, signal oscillator, genetic oscillator     

Integral methodology for distribution systems reconfiguration based on optimal power flow using Benders decomposition technique

A new and efficient methodology for distribution network reconfiguration integrated with optimal power flow (OPF) based on a Benders decomposition approach is presented. The objective minimises power losses, balancing load among feeders and subject to constraints such as capacity limit of branches, minimum and maximum power limits of substations or distributed generators, minimum deviation of bus voltages and radial optimal operation of networks. A variant of the generalised Benders decomposition algorithm is applied to solve the problem. The formulation can be embedded under two stages; the first one is the master problem and is formulated as a mixed integer non-linear programming problem. This stage determines the radial topology of the distribution network. The second stage is the slave problem and is formulated as a non-linear programming problem. This stage is used to determine the feasibility of the master problem solution by means of an OPF and provides information to formulate the linear Benders cuts that connect both problems. The model is programmed in GAMS mathematical modeling language. The effectiveness of the proposal is demonstrated through two examples extracted from the specialised literature.     

A simple programmable frequency meter for low frequencies withknown nominal values

A meter which can be used to measure instantaneously the frequencies of various signals, such as power line frequencies, heart rates, and motor speeds, by only choosing the proper clock and nominal frequencies is described. The technique is based on using an up/down counter operating in the down mode only, resulting in minimum timing signals. Thus the meter is designed with a minimum number of digital integrated circuits. Two frequency meters for heart rate and power line frequency measurements are discussed. A prototype of the proposed meter is built and tested for various frequencies     

Synchronisation mechanisms of circadian rhythms in the suprachiasmatic nucleus

In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus is considered as the master circadian pacemaker. Each cell in the SCN contains an autonomous molecular clock, and the SCN is composed of multiple single-cell circadian oscillators. The fundamental question is how the individual cellular oscillators, expressing a wide range of periods, interact and assemble to create an integrated pacemaker that can govern behavioural and physiological rhythmicity and be reset by environmental light. The key is that the heterogeneous network formed by the cellular clocks within the SCN must synchronise to maintain timekeeping activity. To study the synchronisation mechanisms and the circadian rhythm generation, we propose a model based on the structural and functional heterogeneity of the SCN. The model is a heterogeneous network of circadian oscillators in which individual oscillators are self-sustained. The authors show that the dorsomedial region can smooth the periodic light?dark (LD) signal curve and affect its wave form. The authors also study the rhythmic process of the circadian oscillators under the effect of the daily LD cycle, including three courses: information afferent inputs, oscillation and information efferent outputs. The numerical simulations are also given to demonstrate the theoretical results.     

Scaling theory for information networks

Networks distribute energy, materials and information to the components of a variety of natural and human-engineered systems, including organisms, brains, the Internet and microprocessors. Distribution networks enable the integrated and coordinated functioning of these systems, and they also constrain their design. The similar hierarchical branching networks observed in organisms and microprocessors are striking, given that the structure of organisms has evolved via natural selection, while microprocessors are designed by engineers. Metabolic scaling theory (MST) shows that the rate at which networks deliver energy to an organism is proportional to its mass raised to the 3/4 power. We show that computational systems are also characterized by nonlinear network scaling and use MST principles to characterize how information networks scale, focusing on how MST predicts properties of clock distribution networks in microprocessors. The MST equations are modified to account for variation in the size and density of transistors and terminal wires in microprocessors. Based on the scaling of the clock distribution network, we predict a set of trade-offs and performance properties that scale with chip size and the number of transistors. However, there are systematic deviations between power requirements on microprocessors and predictions derived directly from MST. These deviations are addressed by augmenting the model to account for decentralized flow in some microprocessor networks (e.g. in logic networks). More generally, we hypothesize a set of constraints between the size, power and performance of networked information systems including transistors on chips, hosts on the Internet and neurons in the brain.     

Intelligent controlled shunt active power filter for voltage and current harmonic compensation in microgrid system

An integrated microgrid with a novel shunt active power filter (APF) using Elman neural network (ENN) is proposed in this study. The microgrid consists of a storage system, a photovoltaic (PV) system, the shunt APF, a linear load, and a nonlinear load. Moreover, the master/slave control algorithm is adopted in the microgrid. The storage system, which is considered as the master unit, is adopted to control the active and reactive power outputs (P/Q control) in grid-connected mode and the voltage and frequency of the microgrid (V/f control) in islanded mode. Furthermore, the PV system is considered as the slave unit to implement P/Q control in both grid-connected and islanded modes. In addition, the proposed shunt APF possesses dual functions of voltage and current harmonic compensation for microgrid under voltage harmonic propagation and nonlinear load to reduce the voltage and current total harmonic distortions (THD) effectively. Additionally, an ENN controller is adopted in the proposed shunt APF to improve the transient and steady-state responses of DC-link voltage during the switching between the grid-connected mode and islanded mode. Finally, some simulation results are provided to verify the feasibility and the effectiveness of the integrated microgrid with the intelligent controlled shunt APF.     

Gigahertz Electromagnetic Structures via Direct Ink Writing for Radio‐Frequency Oscillator and Transmitter Applications

Radio‐frequency (RF) electronics, which combine passive electromagnetic devices and active transistors to generate and process gigahertz (GHz) signals, provide a critical basis of ever‐pervasive wireless networks. While transistors are best realized by top‐down fabrication, relatively larger electromagnetic passives are within the reach of printing techniques. Here, direct writing of viscoelastic silver‐nanoparticle inks is used to produce a broad array of RF passives operating up to 45 GHz. These include lumped devices such as inductors and capacitors, and wave‐based devices such as transmission lines, their resonant networks, and antennas. Moreover, to demonstrate the utility of these printed RF passive structures in active RF electronic circuits, they are combined with discrete transistors to fabricate GHz self‐sustained oscillators and synchronized oscillator arrays that provide RF references, and wireless transmitters clocked by the oscillators. This work demonstrates the synergy of direct ink writing and RF electronics for wireless applications.     

基于有限质点法的多尺度精细化分析

多尺度作为一种精细化分析的建模手段,能有效平衡结构分析中的计算效率和精度。有限质点法是一种能准确分析结构非线性行为的方法,在多种复杂行为分析中得到应用。该文利用有限质点法以质点为基本元素和显式积分的特点,基于梁、壳等低维单元的平截面假定,将多尺度连接处的质点分为主质点和从质点,集成从质点的质量、质量惯性矩阵、力、力矩等物理量至主质点,求解主质点运动方程后,由位移约束条件求得从质点位移,从而实现不同维度单元的多尺度连接。算例表明该多尺度方法对梁-壳、梁-固体及壳-固体的连接是有效的,在几何非线性及动力问题中具有良好的精度及稳定性,适合于结构复杂行为分析。     

Simulation of the Steady-State Behavior of Crystal-Controlled Oscillators Using the WATAND Computer-Aided Design Program

The WATAND computer-aided design package has been used to successfully simulate the steady-state response of crystal-controlled oscillators. The WATAND program contains a routine that allows the steady-state response of a nonlinear dynamic circuit with slow transients to be found without the lengthy and uneconomical process of integrating in the time from t = 0. Oscillators simulated were the following: an LC oscillator with discrete components; and three crystal-controlled oscillators, one with silicon integrated circuits and two with discrete components, one having an external tank. To simulate some of these oscillator circuits, some of the algorithms in WATAND had to be modified. Suggestions for further improvements in oscillator simulation are also made.     

An analytical solution based on mobility and multicriteria optimization for access selection in heterogeneous environment

Providing global connectivity with high speed and guaranteed quality at any place and any time is now becoming a reality due to the integration and co-ordination of different radio access technologies. The internetworking of existing networks with diverse characteristics has been considered attractive to meet the incredible development of interactive multimedia services and ever-growing demands of mobile users. Due to the diverse characteristics of heterogeneous networks, several challenges have to be addressed in terms of quality of service (QoS), mobility management and user preferences. To achieve this goal, an optimal network selection algorithm is needed to select the target network for maximizing the end user satisfaction. The existing works do not consider the integration of utility function with mobile terminal mobility characteristics to minimize ping-pong effects in the integrated networks. An integrated multicriteria network selection algorithm based on multiplicative utility function and residual residence time (RRT) estimation is proposed to keep the mobile users always best connected. Multiplicative weighted utility function considers network conditions, application QoS and user preferences to evaluate the available networks. In this paper, the proposed scheme is implemented with two mainstreams (pedestrian users and high-velocity users). For high-velocity users, RRT and adaptive residence time threshold are also considered to keep the probability of handover failures and unnecessary handovers within the limits. Monte-Carlo simulation results demonstrate that the proposed scheme outperforms against existing approaches.     

The study of brain networks driven by steady‐state visual evoked potentials

In this article, we investigated the brain networks during the steady‐state visual evoked potential (SSVEP) task. Two questions: (1) SSVEP‐driven network structures; and (2) the relationship between SSVEP‐driven networks and stimulus frequencies were studied from a network point of view. Method of directed transfer function was applied to brain active signals recorded from electroencephalography (EEG). The resulting connectivity matrices then were converted to graphs by applying a threshold, so that graph theoretical could be used to analyze the characteristics of SSVEP‐driven networks. The results showed that network connections exist in many scalp locations beyond occipital regions. Different from the outflow areas located mainly around the parietal areas, the inflow areas had a widely distribution pattern including the frontal, temporal, and occipital areas. Furthermore, for a wide range of thresholds, with increasing frequency (7–30 Hz), the distribution of clustering coefficient and characteristic path length presented positive and negative correlation with the three parallel flicker SSVEP subsystems, respectively. The results suggested that a specific frequency may evoke certain SSVEP components more than others, and, therefore, one may generate different evoked potentials which results in different network pattern.     

MEMS technology for timing and frequency control

An overview on the use of microelectromechanical systems (MEMS) technologies for timing and frequency control is presented. In particular, micromechanical RF filters and reference oscillators based on recently demonstrated vibrating on-chip micromechanical resonators with Q's > 10,000 at 1.5 GHz are described as an attractive solution to the increasing count of RF components (e.g., filters) expected to be needed by future multiband, multimode wireless devices. With Q's this high in on-chip abundance, such devices might also enable a paradigm shift in the design of timing and frequency control functions, where the advantages of high-Q are emphasized, rather than suppressed (e.g., due to size and cost reasons), resulting in enhanced robustness and power savings. Indeed, as vibrating RF MEMS devices are perceived more as circuit building blocks than as stand-alone devices, and as the frequency processing circuits they enable become larger and more complex, the makings of an integrated micromechanical circuit technology begin to take shape, perhaps with a functional breadth not unlike that of integrated transistor circuits. With even more aggressive three-dimensional MEMS technologies, even higher on-chip Q's are possible, such as already achieved via chip-scale atomic physics packages, which so far have achieved Q's > 10(7) using atomic cells measuring only 10 mm3 in volume and consuming just 5 mW of power, all while still allowing atomic clock Allan deviations down to 10(-11) at one hour.     

A direct digital synthesis system for acoustic wave sensors

Current designs for acoustic wave sensor system electronics are typically based on surface acoustic wave (SAW) oscillators, phase detectors, or phase-locked loops to measure changes in SAW velocity. The advantage of oscillators is a high resolution frequency output, as compared to phase detection systems which are more stable and can more easily provide amplitude information. Phase-locked loops (PLL) offer advantages of both the oscillator and phase detection systems but have the disadvantages of a fixed frequency range and the need for frequency counting circuitry. The objectives of this work were to study the performance of a direct digital synthesis (DDS) based PLL system with the advantages of a programmable frequency range, elimination of the need for frequency counting circuitry, and tolerance of large SAW sensor insertion losses. The DDS system tested had a resolution of 4 Hz and a range of 80 to 120 MHz in SAW humidity and temperature sensing applications indicating that the DDS based PLL is a practical electronic system for SAW sensors.     

Linear frequency tuning of SAW resonators

Frequency tuning in SAW (surface acoustic wave) resonator-stabilized oscillators is normally accomplished via utilization of a voltage-controlled phase shifter. The design of abrupt junction varactor diode-inductor networks which employ impedance transformation techniques to obtain linear frequency tuning of two-port SAW resonators is reported. The approach is similar to that previously developed for linear tuning of bulk wave, quartz crystal resonators. This technique uses varactor diode parallel inductance to provide a linear reactance versus voltage network, which is effectively connected in series with the resonator motional impedance in order to tune the effective resonator center frequency. Typical tuning ranges are significantly larger than those achievable using the phase shifter approach, and are on the order of 400 ppm for the 320-MHz resonator used.     

A reconfigurable high-frequency phase-locked loop

Reconfigurable phase-locked loops (PLLs) present the advantage of fast-frequency acquisition combined with narrow-noise bandwidth, since their parameters can be dynamically adjusted. High-frequency PLLs are generally implemented by means of analog circuits which are not easily reconfigured during operation. However, the five-port technique allows the discrimination of the phase difference between two microwave signals using a mixed circuit. In this paper the design of a PLL comprising a five-port based phase detector is presented. This system benefits from the phase-detector digital circuit to carry out the loop filtering. Simulation results for different conditions of noise and frequency acquisition are shown. We also present measurement results to confirm the simulations.     

The effect of individual variation on the structure and function of interaction networks in harvester ants

Social insects exhibit coordinated behaviour without central control. Local interactions among individuals determine their behaviour and regulate the activity of the colony. Harvester ants are recruited for outside work, using networks of brief antennal contacts, in the nest chamber closest to the nest exit: the entrance chamber. Here, we combine empirical observations, image analysis and computer simulations to investigate the structure and function of the interaction network in the entrance chamber. Ant interactions were distributed heterogeneously in the chamber, with an interaction hot-spot at the entrance leading further into the nest. The distribution of the total interactions per ant followed a right-skewed distribution, indicating the presence of highly connected individuals. Numbers of ant encounters observed positively correlated with the duration of observation. Individuals varied in interaction frequency, even after accounting for the duration of observation. An ant''s interaction frequency was explained by its path shape and location within the entrance chamber. Computer simulations demonstrate that variation among individuals in connectivity accelerates information flow to an extent equivalent to an increase in the total number of interactions. Individual variation in connectivity, arising from variation among ants in location and spatial behaviour, creates interaction centres, which may expedite information flow.     

Living on the edge of chaos: minimally nonlinear models of genetic regulatory dynamics

Linearized catalytic reaction equations (modelling, for example, the dynamics of genetic regulatory networks), under the constraint that expression levels, i.e. molecular concentrations of nucleic material, are positive, exhibit non-trivial dynamical properties, which depend on the average connectivity of the reaction network. In these systems, an inflation of the edge of chaos and multi-stability have been demonstrated to exist. The positivity constraint introduces a nonlinearity, which makes chaotic dynamics possible. Despite the simplicity of such minimally nonlinear systems, their basic properties allow us to understand the fundamental dynamical properties of complex biological reaction networks. We analyse the Lyapunov spectrum, determine the probability of finding stationary oscillating solutions, demonstrate the effect of the nonlinearity on the effective in- and out-degree of the active interaction network, and study how the frequency distributions of oscillatory modes of such a system depend on the average connectivity.     

Genetic redundancy strengthens the circadian clock leading to a narrow entrainment range

Circadian clocks are internal timekeepers present in almost all organisms. Driven by a genetic network of highly conserved structure, they generate self-sustained oscillations that entrain to periodic external signals such as the 24 h light–dark cycle. Vertebrates possess multiple, functionally overlapping homologues of the core clock genes. Furthermore, vertebrate clocks entrain to a range of periods three times as narrow as that of other organisms. We asked whether genetic redundancies play a role in governing entrainment properties and analysed locomotor activity rhythms of genetically modified mice lacking one set of clock homologues. Exposing them to non-24 h light–dark cycles, we found that the mutant mice have a wider entrainment range than the wild types. Spectral analysis furthermore revealed nonlinear phenomena of periodically forced self-sustained oscillators for which the entrainment range relates inversely to oscillator amplitude. Using the forced oscillator model to explain the observed differences in entrainment range between mutant and wild-type mice, we sought to quantify the overall oscillator amplitude of their clocks from the activity rhythms and found that mutant mice have weaker circadian clocks than wild types. Our results suggest that genetic redundancy strengthens the circadian clock leading to a narrow entrainment range in vertebrates.