Static State Research Articles

A balanced jumping control algorithm for quadruped robots

The jumping movement of quadruped robots is crucial, so a complete set of balanced jumping algorithms is proposed in this paper due to the flaws of the current jumping algorithms. The proposed algorithm includes trajectory planning of the Center of Mass(CoM) and four jumping phases, illustrating the jumping process in detail. Tasks that a quadruped robot with the height of 0.6 m jumps up a step with the height of 0.3 m, 0.4 m, 0.5 m and 0.6 m are the research object. Optimal Parabola Trajectory of CoM(OPTC) is solved by about ten iterations based on the fastest approaching strategy before jumping. During the first phase of jumping, Ground Reaction Forces(GRFs) are precisely distributed to control six Degrees of Freedom(DoFs) based on symmetric six-dimensional spatial mechanics decoupling solution, controlling the robot to adjust itself to the best ejecting posture. The maximum displacement error is less than 0.005 m. During the second phase, full-leg ejection is implemented to eject, guaranteeing that the robot accurately tracks the OPTC after takeoff by updating proportional virtual forces. The tracking Mean Square Error(MSE) is less than 0.06. During the third phase, the flying attitude is adjusted by swinging leg theory summarized in the paper, with the maximum pitch angle less than 4.5°. Meanwhile, the theoretical landing points of feet are calculated to lead the movement of feet, ensuring a soft landing to reduce touchdown impact. The momentary landing velocities of feet are less than 0.09 m/s. During the fourth phase, the robot buffers and brakes to a static state based on the algorithm used in the first phase. Eventually, the proposed algorithms are verified through simulating experiments on Webots physical engine, and the effectiveness and feasibility are validated by the experimental results.

Observation and simulation of a heavy fog event in Qiongzhou Strait

From February 14th to February 25th, 2018, the Qiongzhou Strait, China, experienced a persistent heavy fog that was unprecedented in the past 67 years. Observations and simulation results are utilized to diagnose causes of the heavy fog event. This persistent heavy fog was closely related to the continuous occurrence of fog in various types. More fog was observed along the northern coast than the southern coast. The fog over sea lasted longer than that over land. Fog along the southern coast was more sensitive to humidity, whereas fog on the northern coast was more sensitive to wind. The wind speed on the northern coast is beneficial to the generation of advection fog. Contrastingly, the southern coast was in either a weak wind or static wind state, which was in favor of the generation of radiation fog. A low altitude inversion layer appeared before the heavy fog occurred, controlled by the warm and humid airflow in the south. When the heavy fog dissipated, the wind velocity gradually increased, controlled by the dry and cold airflow in the northeast.The variation characteristics of meteorological conditions were successfully reproduced using the WRF model. Simulated minimum visibility and sea fog area were consistent with observations. Air-sea temperature difference is of vital importance to the formation of the heav fog. The stability of atmosphere boundary layer below 150 m was sensitive to the change in sea surface temperature (SST). The higher SST led to higher boundary layer and lower stability. which further resulted in a shorter duration and smaller area of sea fog. The decrease in the SST led to the lower height of boundary layer and stronger stability, which further resulted in a longer duration and expanding area of the sea fog.

Statics and dynamics of skyrmions interacting with disorder and nanostructures

Magnetic skyrmions are topologically stable nanoscale particle-like objects that were discovered in 2009. Since that time, intense research interest has led to the identification of numerous compounds that support skyrmions over a range of conditions spanning cryogenic to room temperatures. Skyrmions can be set into motion under various types of driving, and the combination of their size, stability, and dynamics makes them ideal candidates for numerous applications. Skyrmions represent a new class of system in which the energy scales of the skyrmion-skyrmion interactions, sample disorder, temperature, and drive can compete. A growing body of work indicates that the static and dynamic states of skyrmions can be influenced strongly by pinning or disorder in the sample; thus, an understanding of such effects is essential for the eventual use of skyrmions in applications. In this article we review the current state of knowledge regarding individual skyrmions and skyrmion assemblies interacting with quenched disorder or pinning. We outline the microscopic mechanisms for skyrmion pinning, including the repulsive and attractive interactions that can arise from impurities, grain boundaries, or nanostructures. This is followed by descriptions of depinning phenomena, sliding states over disorder, the effect of pinning on the skyrmion Hall angle, the competition between thermal and pinning effects, the control of skyrmion motion using ordered potential landscapes such as one- or two-dimensional periodic asymmetric substrates, the creation of skyrmion diodes, and skyrmion ratchet effects. We highlight the distinctions arising from internal modes and the strong gyroscopic or Magnus forces that cause the dynamical states of skyrmions to differ from those of other systems with pinning. We also discuss future directions and open questions related to the pinning and dynamics in skyrmion systems.

Metabolically Healthy Obesity: Epidemiology, Criteria, and Implications in Chronic Kidney Disease.

The increasing prevalence of obesity is a worldwide health concern. Although obesity primarily affects the development of cardiometabolic disorders, it has also been closely linked to chronic kidney disease (CKD). However, potential causal relationships between obesity and CKD remain unclear, as obesity and CKD share a number of common risk factors. Accordingly, the risk of incident CKD in obese people without metabolic abnormalities, also called “metabolically healthy obesity” (MHO), has been a matter of interest. Recent investigations found that MHO was related to increased risk of incident CKD; however, the conclusions were based primarily on the static state. According to previous publications, approximately one-half of people initially identified as MHO became metabolically unhealthy, while one-tenth reduced their body weight to normal range while remaining metabolically healthy. It is essential to consider these transitions in obese-metabolic health status when analyzing obesity-related outcomes. This review discusses research on obesity and metabolic health in patients with CKD. Furthermore, we summarize recent reports on the implications of obesity and metabolic health in CKD and discuss the possible mechanisms of their relationship with CKD.

Testing the weak cosmic censorship conjecture in the massive gravitational theories

In this paper, based on the new version of the gedanken experiments proposed by Sorce and Wald, we examine the weak cosmic censorship in the process of accreting matter fields for nearly extremal static charged black holes in the massive gravitational theories coupled to a Maxwell field. In the investigation, we assume that the black hole is perturbed by some matter fields satisfied null energy condition and ultimately settles down to a static state in the asymptotic future. Moreover, we also treat the cosmological constant, the graviton mass, and the coupling constants as variables, and they can be affected by the physical process. Then, after applying the Noether charge method, we derive the first-order and second-order perturbation inequalities of the perturbation matter fields. As a result, we find that the nearly extremal black hole cannot be destroyed under the second-order approximation of perturbation. This result implies that the weak cosmic censorship conjecture is satisfied in the gravitational theories with massive graviton.

Realistic compact stars in conformal teleparallel gravity

Abstract We explore an interior solution of a physically symmetric vierbein with two unknown functions in conformal teleparallel gravity. The field equations can be described in a closed system for a particular form of the metric potentials and an appropriate anisotropic function. As a result, we find a new set of configurations consistent with observed pulsars. In particular, the boundary conditions for the interior spacetime are used for the Schwarzschild spacetime to constrain the conformal field with a unit value through the surface of a compact object. Furthermore, we apply the present model to the pulsar 4U 1608−52 with an approximate radius R = 9.52 ± 0.15 km and mass $M= 1.74 \pm 0.14\, \mathrm{M}_{\odot }$. To analyze the stability, we also study the causality conditions and the adiabatic index by assuming the Tolman–Oppenheimer–Volkoff equation, an adiabatic index, and the static state. Moreover, the consistency of the model under consideration with other pulsars is investigated.

The Influence of Deuterium Isotope Effects on Structural Rearrangements, Ensemble Equilibria, and Hydrogen Bonding in Protic Ionic Liquids.

We report strong isotope effects for the protic ionic liquid triethylammonium methanesulfonate [TEA][OMs] by means of deuterium solid-state NMR spectroscopy covering broad temperature ranges from 65 K to 313 K. Both isotopically labelled PILs differ in non-deuterated and fully deuterated ethyl groups of the triethyl ammonium cations. The N-D bond of both cations is used as sensitive probe for hydrogen bonding and structural ordering. The 2 H NMR line shape analysis provides the deuteron quadrupole coupling constants and the characteristics of a broad heterogeneous phase with simultaneously present static and mobile states indicating plastic crystal behavior. The temperatures where both states are equally populated differ by about 80 K for the two PILs, showing that deuteration of the ethyl groups in the trialkylammonium cations tremendously shifts the equilibrium towards the static state. In addition, it leads to a significant less cooperative transition, associated with a significantly reduced standard molar transition entropy.

TEMPERATURE DISTRIBUTION ANALYSIS IN PARALLEL PLATE TREATMENT CHAMBER FOR PULSED ELECTRIC FIELD PROCESSING: NUMERICAL STUDY

Studies on temperature distribution in parallel plate treatment chambers are limited due to its design which is more prone to arcing, thus, neglecting its use in continuous processing. Therefore, this study discusses the temperature distribution due to Joule heating in a parallel plate treatment chamber acting in continuous mode. The numerical results predict that at a slow flow rate (i.e., 0.0234 cm3/s), the fluid flow near the chamber wall is in a static state (0 cm/s), thus, increasing its residence time and resulting in receiving more pulses. In this situation, the temperature increased dramatically from 25 °C (inlet temperature) to approximately 58 °C, i.e., 132 % increment. On the other hand, a slight increase in temperature (i.e., < 27 °C) is predicted by numerical simulation at a higher flow rate (i.e., 0.138 cm3/s) at the same location (near the chamber wall). This less rise is due to the low residence time which causes the liquid to quickly leave the treatment area, thus, getting less pulse. The temperature soar in this condition is very low which is approximately 8 % of the inlet temperature. From the results obtained, flow rate control helps to reduce the temperature rise, thus, keeping the temperature at ambient temperature or slightly above the ambient and at the same time reducing the risk of the treated media from experiencing adverse effects on its physical attributes as a result of high temperatures.

A New Large Scale SVM for Classification of Imbalanced Evolving Streams

Classification from imbalanced evolving streams possesses a combined challenge of class imbalance and concept drift (CI-CD). However, the state of imbalance is dynamic, a kind of virtual concept drift. The imbalanced distributions and concept drift hinder the online learner’s performance as a combined or individual problem. A weighted hybrid online oversampling approach,”weighted online oversampling large scale support vector machine (WOOLASVM),” is proposed in this work to address this combined problem. The WOOLASVM is an SVM active learning approach with new boundary weighing strategies such as (i) dynamically oversampling the current boundary and (ii) dynamic weighing of the cost parameter of the SVM objective function. Thus at any time step, WOOLASVM maintains balanced class distributions so that the CI-CD problem does not hinder the online learner performance. Over extensive experiments on synthetic and real-world streams with the static and dynamic state of imbalance, the WOOLASVM exhibits better online classification performances than other state-of-the-art methods.

Epithelial to mesenchymal transition (EMT) of feto-maternal reproductive tissues generates inflammation: a detrimental factor for preterm birth

Human pregnancy is a delicate and complex process where multiorgan interactions between two independent systems, the mother, and her fetus, maintain pregnancy. Intercellular interactions that can define homeostasis at the various cellular level between the two systems allow uninterrupted fetal growth and development until delivery. Interactions are needed for tissue remodeling during pregnancy at both fetal and maternal tissue layers. One of the mechanisms that help tissue remodeling is via cellular transitions where epithelial cells undergo a cyclic transition from epithelial to mesenchymal (EMT) and back from mesenchymal to epithelial (MET). Two major pregnancy-associated tissue systems that use EMT, and MET are the fetal membrane (amniochorion) amnion epithelial layer and cervical epithelial cells and will be reviewed here. EMT is often associated with localized inflammation, and it is a well-balanced process to facilitate tissue remodeling. Cyclic transition processes are important because a terminal state or the static state of EMT can cause accumulation of proinflammatory mesenchymal cells in the matrix regions of these tissues and increase localized inflammation that can cause tissue damage. Interactions that determine homeostasis are often controlled by both endocrine and paracrine mediators. Pregnancy maintenance hormone progesterone and its receptors are critical for maintaining the balance between EMT and MET. Increased intrauterine oxidative stress at term can force a static (terminal) EMT and increase inflammation that are physiologic processes that destabilize homeostasis that maintain pregnancy to promote labor and delivery of the fetus. However, conditions that can produce an untimely increase in EMT and inflammation can be pathologic. These tissue damages are often associated with adverse pregnancy complications such as preterm prelabor rupture of the membranes (pPROM) and spontaneous preterm birth (PTB). Therefore, an understanding of the biomolecular processes that maintain cyclic EMT-MET is critical to reducing the risk of pPROM and PTB. Extracellular vesicles (exosomes of 40-160 nm) that can carry various cargo are involved in cellular transitions as paracrine mediators. Exosomes can carry a variety of biomolecules as cargo. Studies specifically using exosomes from cells undergone EMT can carry a pro-inflammatory cargo and in a paracrine fashion can modify the neighboring tissue environment to cause enhancement of uterine inflammation.

Static state power smoothing and transient power quality enhancement of a DC microgrid based on multi-function SMES/battery distributed hybrid energy storage system

Using hybrid energy storage system (HESS) to solve the issues of power regulation and fault protection of DC microgrids has attracted extensive attention. To realize multiple functions of power flow control and power quality enhancement of the DC microgrid, a concept of distributed HESS based on superconducting magnetic energy storage (SMES) and battery energy storage (BES) is introduced in this paper. A SMES-based energy-storage-composited DC transformer (ESDCT) is designed to interconnect the low-voltage DC microgrid into a medium-voltage DC power system. It is with the functions of DC voltage transformation, and grid fault isolation. The BES is selected to regulate the unstable output power of the LVDC microgrid caused by renewable energy generators and load variations. The modeling of the SMES-based ESDCT and the cooperative control of the BES and SMES is analyzed. Finally, the performance of the SMES/BES distributed HESS is verified via a simulation, and the feasibility of the proposed SMES-based ESDCT is demonstrated via a scaled-down experiment.

Data-driven based multi-objective combustion optimization covering static and dynamic states

In order to reduce pollutant emissions and improve energy efficiency under the working conditions of static and dynamic states in the coal-fired power plants, data-driven based multi-objective combustion optimization (MOCO), which is around the implementation of air flow adjustment, is proposed to consider NOx emissions and boiler efficiency simultaneously. The strategy of combining kernel extreme learning machine (KELM) model with multi-objective evolutionary algorithm based on decomposition (MOEA/D) is presented to regulate the air distribution mode under static state. The double optimization is proposed to control the air flow under dynamic state. The first optimization is to employ auto-regressive moving-average with exogenous inputs (ARMAX) model and particle swarm optimization algorithm to optimize the parameters of PI controller. The second optimization is to use ARMAX models and tendentious guidance MOEA/D (TG-MOEA/D) to optimize the setpoint of air flow. The experiments showed that the KELM + MOEA/D strategy could further improve the effect of MOCO under static state, and the double optimization had decreased NOx emissions by an average of 12.18 % with keeping the boiler efficiency at a desired level under dynamic state. Moreover, data-driven based MOCO owns a high real-time performance, so that it is suitable for online application.

Analysis of two-phase flow in non-inertial coordinate using combination of three-fluid model and drift flux model

After the Fukushima accident, to increase the safety of nuclear power plants, work began on Floating Nuclear Power Plants with the construction of the power plant floats above 100 m eliminate the risk of earthquakes and tsunamis. The study investigated integration of three-fluid model and Drift Flux model, to analyze different two-phase flow regimes in a vertical channel under ocean motions. By upgrading the model, an attempt has been made to include the additional forces caused by ocean movements in momentum equations so that it can be used in the thermal-hydraulic analysis of two-phase flow in non-inertial coordinate the simulation results with the presented method converge well with the simulation results of the RELAP5 mod 3.2 code and experimental results. Compared to static state, under rolling motion, void fraction and Critical Heat Flux (CHF) vary periodically with time. The amplitude oscillation of CHF changes with increasing maximum angle in rolling motion and also with increasing acceleration amplitude in heaving motion.

Analysis on the discharge characteristics and spreading behavior of an ex-vessel core melt in the SMART

The aim of this research is to analyze the characteristics of a core melt discharged from the reactor vessel and the spreading behavior the core melt in the reactor cavity of the SMART. First, a severe accident sequence under conservative conditions is simulated by the MELCOR code to obtain the conditions for an analysis of the spreading behavior and coolability of the ex-vessel melt. Second, the spreading behavior and coolability of the ex-vessel melt are analyzed by the MELTSPREAD code. The level, temperature, and pressure of the water in the cavity as well as the temperature, mass, composition, and discharge velocity of the melt were utilized to construct the ex-vessel analysis. The melt spread only to part of the cavity, and that the height of the corium in a static state was less than 25 cm. The characteristics of a small modular reactor on the spreading behavior and coolability of melt were analyzed. In the SMART, the amount of melt discharged into the cavity is relatively small and the area of the cavity is sufficiently large when compared to a high-power pressurized water reactor. It was found that the coolability of an ex-vessel core melt can be sufficiently secured.

Copper Phthalocyanine Improving Nonaqueous Catalysis of Pseudomonas cepaciaLipase for Ester Synthesis.

The nonaqueous catalysis of lipases is significant for synthesis of high pure esters, but they usually behave low catalytic activity due to denaturation and aggregation of enzyme protein in organic phases. To improve the nonaqueous catalysis, the inexpensive copper phthalocyanine was taken as a new carrier on which Pseudomonas cepacia lipase was immobilized by physical absorption, and used for synthesis of hexyl acetate, an important flavor, via transesterification of hexanol and vinyl acetate. Results showed that the desired loading was 10mg lipase immobilized on 10mg copper phthalocyanine powder. When the immobilized lipase was employed in the reaction system consisted of 1.5 mL hexanol and 1.5 mL vinyl acetate at 37℃ and 160rpm, the conversion was five fold of that catalyzed by native lipase after 1h, and reached 99.0% after 8h. Undergoing six times of 8-h reuses, the immobilized lipase had an activity attenuation rate 1.22% h- 1, lower than 1.77% h- 1 of native lipase, which meant that the immobilized lipase was more stable. Even at the room temperature and the static state without shaking or stirring, the immobilized lipase could bring conversion 42.8% after 10h and the native lipase gave 20.1%. Obviously, the immobilized lipase is an available biocatalyst in organic phase and has great potential in food industry.

A Dynamical Compact Model of Diffusive and Drift Memristors for Neuromorphic Computing (Adv. Electron. Mater. 8/2022)

Neuromorphic Computing Different from memory applications where only the static ending states are used, neuromorphic computing with memristors utilizes their dynamical switching process itself, which calls for a comprehensive dynamical memristor model. Such a model shown here can reproduce the long-term memory of drift memristors and the short-term plasticity of diffusive memristors. It captures quasi-static and dynamic characteristics of these devices, demonstrating a good agreement with the experimental data. More details can be found in article number 2100696 by J. Joshua Yang and co-workers.

Einstein static universe and its stability in generalized Rastall gravity

The Einstein static (ES) state is a good candidate for describing the very early universe in terms of a regular cosmological model in which the Big Bang singularity is avoided. In the present study we propose an ES solution in the framework of generalized Rastall gravity (GRG), a modified version of original Rastall theory in which the coupling parameter is allowed to vary with respect to the spacetime coordinates. Introducing an ansatz for the Rastall parameter, existence and the corresponding stability of the solutions are investigated. We show that the GRG is capable of describing a stable singularity-free state for the universe. The problem of transition from an ES to an inflationary state is also addressed. We find that a time variation of the equation of state parameter from values lying in the range |w|<1/3 to the value w=−1/3 can give rise to such a phase transition. The vector and tensor perturbations around the ES solution are studied, as well. In the case of GRG, the vector perturbations remain frozen, nevertheless, the tenor perturbations can grow in such a way that the ES solution remains stable provided the ratio of Rastall gravitational constant to the Einsteinian one always exceeds a minimum value for each tensor mode.

Characteristics of Gut Microbial Profiles of Offshore Workers and Its Associations With Diet.

The composition of gut microbiota is not a static state in humans but fluctuates in response to changes in environments, diet, and lifestyle factors. Here, we explored differences in gut microbiota between populations worked offshore and onshore and further studied microbiota-associated variables in offshore workers (OFWs). We investigated the gut microbiota of 168 healthy subjects (offshore: 145 and onshore: 23) using 16S rRNA sequencing. Our results indicated that the marine environment caused significant changes in intestinal microbial structure, which was mainly reflected in the increase in bacterial diversity, changes in composition, and the emergence of more specific bacteria in OFWs. In addition, characteristics of gut microbiota in OFWs were further explored, and the genus Holdemanella was considered a potential contributor to the stable state of health. Besides, some dietary factors, namely, duck, mutton, dairy products, and algae vegetables were identified as the gut microbial covariates in the OFWs cohort and were positively correlated with the genus Holdemanella. This suggests the positive intervention of diet on Holdemanella. Our data highlight, for the first time to our knowledge, that the marine geographical environment plays an important role in shaping the gut mycobiome composition. And diet could be considered as the targeted intervention that alters the composition of the microbiome to improve host health.

(Invited) On the Structural and Mechanistic Studies of PGM-Free Oer Catalysts for PEM Electrolyzer

Low temperature water electrolysis represents a critical technology for green hydrogen production. Low temperature electrolysis can be operated using either proton exchange or alkaline membrane electrolyte. Compared to alkaline electrolyzer, proton exchange membrane (PEM) electrolyzer offers advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential.Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the PGM materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve, however, adds a significant cost to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost. These materials are known to be applicable in the alkaline electrolyte but not in acid due to dissolution. Since the traditional porous carbon cannot be used as the support under the oxidative potential during OER, their stand-alone conductivity represents another critical consideration.Argonne National Laboratory has recently designed and prepared a new class of PGM-free OER catalyst for PEM electrolyzer. The new catalysts are consisted of highly porous yet stable transition metal oxide derived from the metal-organic-frameworks (MOFs).Two catalyst series, ANL-Cat-A and ANL-Cat-B, were developed and investigated. The OER catalyst activity and durability were first measured by rotating disk electrode (RDE) method and in half-cell in the acidic media. Very promising OER activities were achieved. The catalyst durability was also measured through the multiple potential cycling from the voltage of 1.2 V to 2.0 V (vs. RHE) in the acidic electrolyte. Both ANL catalysts demonstrated promising activity and durability in the acidic medium. These PGM-free OER catalysts were also integrated into the membrane electrode assemblies and tested in PEM water electrolyzer under operating condition (60 °C to 80 °C and ambient pressure). Several MEAs demonstrated promising OER current density of 2000 mA/cm2 at 2.2 V iR-corrected .Extensive structural characterizations were carried out, both in static state and under the reaction condition using various tools such as high resolution electron microscopy and in situ X-ray absorption spectroscopy. Interesting correlation between the structure and property relationship was found. Computational modeling was also performed to understand the fundamental mechanism behind electron conductivity and the acid tolerance behind this new class of OER catalysts. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Numerical investigation on flow and heat transfer characteristics of U-shaped channels with side-wall column ribs

For improving the cooling performance of U-shaped channels in the blade mid-chord region both in static and rotating states, this paper introduces the column rib spoiler structure on the side wall, putting forward the arrangement of column ribs along the radial direction in sequenced and staggered ways, as well as the vertical and inclined column ribs. The flow and cooling characteristics of this new channel (AR = 1:1) with different column rib structures and arrangements are studied in detail, considering rotational numbers varying from 0 to 0.4 at a typical Reynolds number of 10,000. The enhanced heat transfer mechanism of vertical and inclined column ribs in both arrangement modes and the coupling mechanism combined with the rotation effect are emphatically analyzed. The cooling performance of the two channels is compared in many aspects and the optimized size and layout of side-wall column ribs are obtained. Results show that the cooling method proposed can significantly improve the cooling effect of the U-shaped channel by 37.9% and 41.6% in the static state and rotating state, respectively. This study will provide important reference data for the development of high-efficient mid-chord cooling technology in gas turbine blades.