Small Frequency Research Articles

Power Dispatch Capacity of a Grid-Forming Control Based on Phase Restoring Principle

The concept of grid-forming control is driving system operators to define this technology's capabilities and requirements to maintain grid stability, reliability, and the need to provide some of the services previously provided by synchronous generators. The novel control strategy, called the “Phase Restoring Principle” (PRP), was recently introduced for converter operated power systems. This article provides further insights and confirmation of the PRP grid-forming capabilities based on the response requirements from the perspective of the power system. It describes the extension of the control by supplementing PRP with active power control allowing the control to cooperate with other sources. The generalized small-signal solution of the control is derived and evidenced. Analytical deductions supported by simulative evidence of the power dispatch based on PRP are displayed in single, double, and triple converter configurations. The development of steady-state operating point and, hence, drift frequency using the principle of PRP with active power control is examined and discussed based on reference values and weighted gain selection. The enhanced PRP control structure also displays controller stability for sufficiently small drift frequencies and achieves nominal frequency with dedicated parameters.

Bayesian Inference for the Loss Models via Mixture Priors

Constructing an accurate model for insurance losses is a challenging task. Researchers have developed various methods to model insurance losses, such as composite models. Composite models combine two distributions: one for part of the data with small and high frequencies and the other for large values with low frequencies. The purpose of this article is to consider a mixture of prior distributions for exponential–Pareto and inverse-gamma–Pareto composite models. The general formulas for the posterior distribution and the Bayes estimator of the support parameter θ are derived. It is shown that the posterior distribution is a mixture of individual posterior distributions. Analytic results and Bayesian inference based on the proposed mixture prior distribution approach are provided. Simulation studies reveal that the Bayes estimator with a mixture distribution outperforms the Bayes estimator without a mixture distribution and the ML estimator regarding their accuracies. Based on the proposed method, the insurance losses from natural events, such as floods from 2000 to 2019 in the USA, are considered. As a measure of goodness-of-fit, the Bayes factor is used to choose the best-fitted model.

Self-tuning regulatory controller of cyclical disturbances using data-driven frequency estimator based on fuzzy logic

This paper proposes two learning-type regulatory controllers: adaptive fuzzy iterative learning controller (AF-ILC) and adaptive fuzzy repetitive generalized predictive controller (AFR-GPC). The proposed controllers can reject the cyclical disturbances with small range frequency variations present in many control loops of industrial processes. Moreover, they can estimate the disturbance cycle using fuzzy logic with rules based on the previous values of the integral of the absolute error between the setpoint and output. The estimated period of the disturbance cycle is sent to the regulatory controllers to define the specific control actions required to reduce the oscillations in the process output. The advantage of this technique is that adaptive controllers are automatically adjusted by a frequency estimator, which only depends on process output data. The performance levels of the developed adaptive controllers are compared in the computational simulator of a nonlinear mold level of a continuous casting process employed in the steel industry. This process counteracts the periodic oscillations in the mold level caused by bulging disturbance. The numerical results show that both AF-ILC and AFR-GPC can reduce the oscillations in the output when the disturbance frequency changes by up to 5.2% and 13%, respectively.

Tristetraprolin overexpression drives hematopoietic changes in young and middle-aged mice generating dominant mitigating effects on induced inflammation in murine models

Tristetraprolin (TTP), encoded by Zfp36 in mice, is one of the best-characterized tandem zinc-finger mRNA binding proteins involved in mRNA deadenylation and decay. TTPΔARE mice lack an AU-rich motif in the 3′-untranslated regions of TTP mRNA, leading to increased TTP mRNA stability and more TTP protein, resulting in elevated mRNA decay rates of TTP targets. We examined the effect of TTP overexpression on the hematopoietic system in both young and middle-aged mice using TTPΔARE mice and found alterations in blood cell frequencies, with loss of platelets and B220 cells and gains of eosinophils and T cells. TTPΔARE mice also have skewed primitive populations in the bone marrow, with increases in myeloid-biased hematopoietic stem cells (HSCs) but decreases in granulocyte/macrophage-biased multipotent progenitors (MPP3) in both young and middle-aged mice. Changes in the primitive cells’ frequencies were associated with transcriptional alterations in the TTP overexpression cells specific to age as well as cell type. Regardless of age, there was a consistent elevation of transcripts regulated by TNFα and TGFβ signaling pathways in both the stem and multipotent progenitor populations. HSCs with TTP overexpression had decreased reconstitution potential in murine transplants but generated hematopoietic environments that mitigated the inflammatory response to the collagen antibody-induced arthritis (CAIA) challenge, which models rheumatoid arthritis and other autoimmune disorders. This dampening of the inflammatory response was even present when there was only a small frequency of TTP overexpressing cells present in the middle-aged mice. We provide an analysis of the early hematopoietic compartments with elevated TTP expression in both young and middle-aged mice which inhibits the reconstitution potential of the HSCs but generates a hematopoietic system that provides dominant repression of induced inflammation.

Systematic Workup of Transfusion Reactions Reveals Passive Co-Reporting of Handling Errors.

Reporting of transfusion reactions is good practice and required by many guidelines. Errors in the transfusion chain can also lead to severe patient reactions and depend on active error reporting. We aimed to characterize transfusion incidents and asked whether workup of transfusion reactions may also contribute to revealing logistical errors. Transfusion medical records from 2011 to 2019 at our tertiary medical centre, as well as forensic autopsy reports, digitized sections, and court records from 1990 to 2019 were analysed. A total of 230,845 components were transfused between 2011 and 2019 at our own institution. Overall, 322 transfusion incidents were reported. Of these, 279 were from our own institution, corresponding to a frequency of 0.12% of all transfusions. The distribution of reaction types is consistent with the literature, with allergic reactions (55.9%), febrile-non-hemolytic reactions (FNHTR, 24.2%), hemolytic reactions (3.4%) and other types at smaller frequencies (<3%). Twenty-nine (10.4%) of the 279 reports revealed logistical errors, including hemoglobin above guideline threshold (4.3%), incorrect or non-performed bedside tests (3.2%), inadequate patient identification (2.5%), laboratory and issuing errors, missed product checks or failure to follow recommendations (1.1% each). Eight of 29 (27.5%) of the logistical errors were detected by serendipity during workup of incident reports. In addition, 8/932 autopsy cases under code A14 (medical treatment errors) were found to be transfusion-associated (0.9%). Systematic workup of transfusion incidents can identify previously undetected errors in the transfusion chain. Passive reporting of errors through the recording of side effects may serve as a tool to assess more closely assess the frequency and quality of handling errors in real life, and thus serve to improve patient safety.

Long-range linkage effects in adapting sexual populations

In sexual populations, closely-situated genes have linked evolutionary fates, while genes spaced far in genome are commonly thought to evolve independently due to recombination. In the case where evolution depends essentially on supply of new mutations, this assumption has been confirmed by mathematical modeling. Here I examine it in the case of pre-existing genetic variation, where mutation is not important. A haploid population with N genomes, L loci, a fixed selection coefficient, and a small initial frequency of beneficial alleles {f}_{0} is simulated by a Monte-Carlo algorithm. When the number of loci, L, is larger than a critical value of {text{4log}}^{2} left( {Nf_{0} } right), simulation demonstrates a host of linkage effects that decrease neither with the distance between loci nor the number of recombination crossovers. Due to clonal interference, the beneficial alleles become extinct at a fraction of loci 1-2mathrm{log}left(N{f}_{0}right)/{L}^{0.5}. Due to a genetic background effect, the substitution rate varies broadly between loci, with the fastest value exceeding the one-locus limit by the factor of {[{L}^{0.5}/mathrm{log}left(Nsright)]}^{0.75}. Thus, the far-situated parts of a long genome in a sexual population do not evolve as independent blocks. A potential link between these findings and the emergence of new Variants of Concern of SARS-CoV-2 is discussed.

Ultra-High-Resistance Pseudo-Resistors With Small Variations in a Wide Symmetrical Input Voltage Swing

This paper presents a new strategy and circuit configuration composed of serially-connected PMOS devices operating in the subthreshold region for implementing ultra-highvalue resistors required in very low-frequency active-RC filters and bio-amplifiers. Depending on the application, signal bandwidth for instance in bio-amplifiers may vary from a few mHz up to a maximum of 10 kHz. Three different resistor structures are proposed to achieve ultra-high resistance. While ranging in the order of several TY, the proposed ultra-high-resistance pseudoresistors occupy a small on-chip silicon area, which is one of the main issues in the design of analog front-end circuits in ultra-low power implantable biomedical microsystems. In addition, these ultra-high-value resistors lead to the use of a small capacitance to create a very small cut-off frequency. Therefore, the large area to implement capacitances is also considerably reduced. The proposed resistor structures have very small variations about 7% and 12% in a wide input voltage range (-0.5 V +0.5 V), thus significantly improving the total harmonic distortion of bioamplifiers and the analog front-end of the system. Simulation results of different circuits designed in a 180nm CMOS technology, are shown to demonstrate the advantages of the proposed ultra-high-resistance pseudo-resistors.

Simplifying asteroseismic analysis of solar-like oscillators

Context. The asteroseismic analysis of stellar power density spectra is often computationally expensive. The models used in the analysis may require several dozen parameters to accurately describe features in the spectra caused by the oscillation modes and surface granulation. Many of these parameters are often highly correlated, making the parameter space difficult to quickly and accurately sample. They are, however, all dependent on a much smaller set of parameters, namely the fundamental stellar properties. Aims. We aim to leverage this to develop a method for simplifying the process of sampling the model parameter space for the asteroseismic analysis of solar-like oscillators, with an emphasis on mode identification. Methods. Using a large set of previous observations, we applied principal component analysis to the sample covariance matrix to select a new basis on which to sample the model parameters. Selecting the subset of basis vectors that explains the majority of the sample variance, we then redefined the model parameter prior probability density distributions in terms of a smaller set of latent parameters. Results. We are able to reduce the dimensionality of the sampled parameter space by a factor of two to three. The number of latent parameters needed to accurately model the stellar oscillation spectra cannot be determined exactly but is likely only between four and six. Using two latent parameters, the method is able to produce models that describe the bulk features of the oscillation spectrum, while including more latent parameters allows for a frequency precision better than ≈10% of the small frequency separation for a given target. Conclusions. We find that sampling a lower-rank latent parameter space still allows for accurate mode identification and parameter estimation on solar-like oscillators over a wide range of evolutionary stages. This allows for the potential to increase the complexity of spectrum models without a corresponding increase in computational expense.

Centrifuge testing of improved monopile foundation for offshore wind turbines

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation designs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5–8 m and depths of penetration of 30–80 m. To limit monopile diameters and penetration depths, an improved monopile design: the ‘hybrid foundation’ comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the performance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments.

Oscillon spectroscopy

The sine-Gordon model in 3+1 dimensions is known to admit two oscillons of different energy and frequency but comparable lifetime. We show that the oscillon spectrum includes more spherically symmetric “states”. We identify new high-amplitude oscillons by allowing the field profile to have a number of nodes. For each number of nodes, we find 2 states with a comparable lifetime to the nodeless ones. Oscillons with nodes are, however, unstable to non-spherical perturbations and so their lifetime is significantly reduced. Interestingly, these states are seen to fragment into a collection of nodeless oscillons. The heavy nodeless oscillon is quite remarkable: despite its energy, it is stable against fragmentation. Moreover, it has considerably small oscillation frequency, meaning that it can be interpreted as a rather relativistic bound state.

Stability and steady state analysis of mode lock state of medium coupled microwave oscillators

AbstractCoupled microwave oscillators could be potentially considered a good replacement for the feed network of frequency‐diverse arrays. However, previous studies showed that the stability region for a mutually weak‐coupled oscillator array in the Mode Lock State (MLS) is too small to be practical. Besides, by increasing the coupling strength or reducing the initial natural frequency of the oscillators, the current analytical methods lose their accuracy. The final steady‐state and dynamic of a non‐linear Van‐der‐Pol medium‐coupled oscillator array in the MLS is investigated. By using the Kuramoto Model results in analysing the biological cells, an alternative approach is suggested and investigated in the entrainment region for the mode‐locked microwave oscillator array. This approach is accurate even for medium‐coupled oscillator arrays, where the locking range to the beat frequency ratio is greater than 0.1. The stability of the oscillator in this region is investigated by imposing some perturbations in the form of phase noise on the initial signals. Also, the optimum initial condition to design large arrays is investigated using the analysis results. In the described initial conditions for small beat frequencies, the simulation results show that the stability region is much greater than the large beat frequency region. This capability initiates a new practical approach for implementing Frequency Diverse Arrays.

Copper-nickel electroplating of 3D-printed acrylonitrile butadiene styrene for interference and radiation shielding applications

In this study, electromagnetic and radiation shielding structures were fabricated by 3D printing acrylonitrile butadiene styrene (ABS) structures via fused filament fabrication and electroplating with copper (Cu) and nickel (Ni) metals. Prior to electroplating, the printed ABS materials were made conductive by surface electrodepositon of polypyrrole (PPy). ABS adsorbs the pyrrole monomer, which subsequently polymerizes via oxidation forming conductive PPy layer on the printed structures. The successful anchoring of PPy layer can be attributed to its hydrogen bonding and electrostatic interactions with ABS. Thermal analysis, optical, and electron microscopy equipped with energy dispersive X-ray were employed to characterize the printed shielding structures, while the interference and radiation shielding effectiveness were evaluated using a spectrum analyzer and dosimeter, respectively. The interference shielding was found to be effective at 60 ± 5 dB over relatively small frequency range. Shielding was also apparent against gamma and X-ray ionizing rays, but more significantly effective against beta rays. Furthermore, the Cu/Ni coating was able to reduce any heat-induced dimensional changes for the 3D printed ABS substrate without compromising the mechanical integrity.

Design of Flexible Multi-Band Miniature Antenna Based on Minkowski Fractal Structure and Folding Technique for Miniature Wireless Transmission System

In light of the predicament concerning the small gain and narrow frequency range of miniature antennas, this paper employs the implementation of a fractal repeating array structure and a double-layer folding antenna structure. Through these measures, the miniature antenna is endowed with a high gain and an expansive frequency range, all within its diminutive size. The paper presents an exquisite and high-gain flexible multi-band antenna, utilizing a dielectric substrate composed of the flexible material polyimide, with a thickness of merely 0.1 mm. The implementation of this flexible material bestows a feathery mass of merely 4 mg upon the antenna, enabling it to seamlessly conform to various shapes. This makes it particularly well-suited for employment within miniature wireless transmission systems and compact mobile communication devices. In an endeavor to enhance impedance matching and radiation characteristics, the Minkowski fractal structure is ingeniously incorporated as the repeating array element. This repeating array structure assumes a pivotal role and, when combined with the double-layer folding antenna structure, achieves the objective of miniaturization. Remarkably, the antenna’s dimensions measure a mere 0.04 λ0 × 0.026 λ0 (λ0 @ 2.4 GHz). The proposed antenna boasts a remarkably diminutive volume of merely 5 × 3 × 0.1 mm3, with the measured and simulated results exhibiting a striking concurrence. Both sets of results demonstrate resonance across multiple frequencies, namely, 2.4 GHz, 5.2 GHz and 5.8 GHz. Furthermore, within the effective frequency range, the antenna attains a maximum gain of 1.65 dBi and 4.37 dBi, respectively.

Inheritance Pattern of Huntington’s Disease, a Multiplayer Game

Evolutionary game theory (EGT) is one of several major developments of game theory. EGTcovers ecology and population genetics, among other fields in biology. Most studies in EGTwere on a two-player game but non-linearities in biology often occur that need to be considered.Huntington's disease (HD), named after the person who wrote the first detailed description ofthe disease in 1872, is a neurodegenerative disease that is inherited. This is a case in populationgenetics, which follows the inheritance pattern called the dominant lethal. In this study, wepresented this disease as a multiplayer game among the alleles of the HD gene. We utilizedGokhale and Traulsen’s model, wherein a payoff matrix for a four-player game was reducedinto a payoff matrix for a two-player game. Depending on the fitness values of each genotype,we have determined that populations consisting of both Huntington and normal alleles mayconverge to either a purely Huntington, a purely normal, or a mixed composition where bothtypes of genes coexist. If the normal genotype produces more surviving offspring than the othergenotypes, then even if a small frequency of normal alleles is injected into a purely Huntingtonpopulation, the population will be replaced by the normal genotype over time. Such a result wasobtained using replicator dynamics and analysis of the stability of equilibrium points. Similaranalyses on other genotypes were provided in relation to the inheritance pattern of HD.

Experimental and Simulation Studies of Micro-Swing Arc Welding Process for X80M Pipeline

Pipe girth welds are prone to incomplete fusion problems in the automatic welding process of long-distance pipelines, which is often related to temperature inhomogeneity in the weld bead. The narrow gap and micro-swing welding technique was applied in pipeline construction to improve welding quality. The manuscript provides a detailed investigation of the micro-swing welding technique with a combination of welding experiments and numerical simulation. A swing welding strategy was proposed according to the actual welding condition in pipeline construction to study the formation mechanism of weld joints. The swing width grew to 1.25–1.35 times from the 3 to 6 o’clock position in the same filling layer. It also increased with filling layers, and filling layer 5 had the biggest swing width, almost two times that of filling layer 2. “Middle concave” morphology appeared at the 3 o’clock position, which could effectively avoid the occurrence of incomplete fusion, while “hump” morphology may appear at the 6 o’clock position, and incomplete fusion defects occurred if the next pass failed to eliminate the influence of the “hump”. The temperature field presented an obvious “sawtooth” shape at small swing frequencies, which could cause temperature inhomogeneity. It could be effectively eliminated when swing frequency reached over 5 Hz.

Stochastic dynamics and first passage analysis of iced transmission lines via path integration method

The mechanism of stochastic factors in wind load on iced transmission line galloping has attracted widespread attention. In this paper, the random part of wind load is simulated by Gaussian white noise, and a galloping model of the iced transmission line excited by stochastic wind is established. The path integration method based on the Gauss–Legendre formula and short-time approximation is used to solve the steady-state probability density function of the system and the evolution of the transient probability density. The resonance response of the system is considered when the fluctuating wind acts. Meanwhile, through path integration, the stability of galloping motion is evaluated based on the first passage theory. Comparing with the Monte Carlo simulation, the effectiveness of the proposed method is verified. It turns out that the large external excitation intensity and the small natural frequency are not conducive to the stability of iced transmission line galloping.

Looking to block out noise? Try metamaterials

The small frequency ranges of acoustic metamaterial absorbers is an advantage in commercial sound blocking applications.

Discrete Dynamics of Warhead Modulation on Covalent Inhibition of Oxyr: A QM/MM Study.

The bacterial transcriptional factor OxyR, a peroxide sensor conserved in bacterial virulence pathways, has the capability to exhibit exceptional reactivity toward hydrogen peroxide (H2O2). H2O2 is essential for oxidizing cysteine thiolates to maintain cellular redox homeostasis and is dispensable for bacterial growth that can potentially mitigate drug resistance, thus underlining OxyR as a valuable target. We employ quantum mechanics/molecular mechanics (QM/MM) umbrella sampling (US) simulations at the DFTB3/MM level of theory and propose a reaction mechanism with four potential covalent inhibitors. The potential of mean force reveals the direct role of intrinsic reactivity of inhibitors, for instance, benzothiophenes and modified experimental inhibitors with methyl oxo-enoate warhead-activated carbonyl samples in the first step of reaction, which shed light on the significance of proton transfer indispensable for full inhibition, whereas the nitrile inhibitor undergoes a stepwise mechanism with a small proton-transfer energy barrier and lower imaginary frequencies that materialize instantly after nucleophilic attack. To unveil the molecular determinants of respective binding affinities, transition states along the reaction path are optimized and characterized with B3LYP 6-31+G(d,p). Furthermore, the post-simulation analysis indicates the catalytic triad (His130/Cys199/Thr129), thermodynamically favored for inhibition, which restricts water molecules from acting as the potential source of protonation/deprotonation. This study thus serves as a preamble to add variation in the proposed structures and unveils the impact of functional groups lying in warheads that modulate the kinetics of proton transfer, which will certainly aid to design more selective and efficient irreversible inhibitors of OxyR.

A Developed Jerk Sensor for Seismic Vibration Measurements: Modeling, Simulation and Experimental Verification

Acceleration-based sensors are widely used in indicating the severity of damage caused to structural buildings during dynamic events. The force rate of change is of interest when investigating the effect of seismic waves on structural elements, and hence the calculation of the jerk is necessary. For most sensors, the technique used for measuring the jerk (m/s3) is based on differentiating the time–acceleration signal. However, this technique is prone to errors especially in small amplitude and low frequency signals, and is deemed not suitable when online feedback is required. Here, we show that direct measurement of the jerk can be achieved using a metal cantilever and a gyroscope. In addition, we focus on the development of the jerk sensor for seismic vibrations. The adopted methodology optimized the dimensions of an austenitic stainless steel cantilever and enhanced the performance in terms of sensitivity and the jerk measurable range. We found, after several analytical and FE analyses, that an L-35 cantilever model with dimensions 35 × 20 × 0.5 (mm3) and a natural frequency of 139 (Hz) has a remarkable performance for seismic measurements. Our theoretical and experimental results show that the L-35 jerk sensor has a constant sensitivity value of 0.05 ((deg/s)/(G/s)) with ±2% error in the seismic frequency bandwidth of 0.1~40 (Hz) and for amplitudes in between 0.1 and 2 (G). Furthermore, the theoretical and experimental calibration curves show linear trends with a high correlation factor of 0.99 and 0.98, respectively. These findings demonstrate the enhanced sensitivity of the jerk sensor, which surpasses previously reported sensitivities in the literature.

Dynamic analysis of a free vibrating cantilever beam

This paper has as subject a theoretical, numerical and experimental study of the behavior of a 1.5 meters long and cross section of 0.02 meters wide and high beam. The main objective was to analyze a structure, in this case it was a cantilever steel beam, to establish the possible solutions that best define the behavior of this structure, to obtain the results and to prove the veracity of the results obtained by means of an experimental analysis method. In this sense, essential theoretical foundations were used for the understanding and realization of the mathematical formulations of this project, in order to obtain the analytical results of the vibration modes of the beam and respective natural frequencies. To complement the analysis of the beam behavior, the finite element method procedure was applied using the ansys software to obtain more accurate results. The results obtained for the beam from these two methodologies include bending modes among the first 10 degrees of freedom. To validate the study done previously a physical model of the beam was used for the experimental test, for this it was defined that the equipment for measuring the resonance frequencies would be a digital stroboscope, enabling the measurement of only 8 vibration modes due to its small frequency range.