Terms Of Operators Research Articles

Dual interfacial engineering of a Chevrel phase electrode material for stable hydrogen evolution at 2500 mA cm−2

Constructing stable electrodes which function over long timescales at large current density is essential for the industrial realization and implementation of water electrolysis. However, rapid gas bubble detachment at large current density usually results in peeling-off of electrocatalysts and performance degradation, especially for long term operations. Here we construct a mechanically-stable, all-metal, and highly active CuMo6S8/Cu electrode by in-situ reaction between MoS2 and Cu. The Chevrel phase electrode exhibits strong binding at the electrocatalyst-support interface with weak adhesion at electrocatalyst-bubble interface, in addition to fast hydrogen evolution and charge transfer kinetics. These features facilitate the achievement of large current density of 2500 mA cm−2 at a small overpotential of 334 mV which operate stably at 2500 mA cm−2 for over 100 h. In-situ total internal reflection imaging at micrometer level and mechanical tests disclose the relationships of two interfacial forces and performance of electrocatalysts. This dual interfacial engineering strategy can be extended to construct stable and high-performance electrodes for other gas-involving reactions.

Determining the Optimal Cutting Parameters for Required Productivity for the Case of Rough External Turning of AISI 1045 Steel with Minimal Energy Consumption

One of the most important challenges for every machining shopfloor, especially a small one, is to achieve the required productivity with minimal energy consumption and engaged power. The paper presents a way to determine the optimal combination of values of cutting parameters such as depth of cut, feed rate and cutting speed from the range of their recommended values, which are usually additionally limited by the real conditions of available machines and tools. The optimal combination is the one which ensures targeted productivity and maximum energy savings at the same time. As an example, a real practice case of external rough turning of an AISI 1045 steel workpiece is presented. The selection of the optimal combination of cutting parameter values is based on a model which is developed using in situ measurements of energy consumption and engaged power in an experiment that emulates the critical operation in terms of energy consumption. The results show that optimization of cutting parameter values that enables the minimum of total energy consumption while achieving target productivity, does not necessarily enable the maximum of energy savings for a given operation. In the example from real practice shown in the paper, this optimization approach can cause higher total energy consumption by as much as 15.9% compared to the combination of parameters that ensure maximum productivity.

A Portable Servoregulation Controller to Automate CO2 Removal in Artificial Lungs.

Artificial lung (AL) systems provide respiratory support to patients with severe lung disease, but none can adapt to the changing respiratory needs of the patients. Precisely, none can automatically adjust carbon dioxide () removal from the blood in response to changes in patient activity or disease status. Because of this, all current systems limit patient comfort, activity level, and rehabilitation. A portable servoregulation controller that automatically modulates removal in ALs to meet the real-time metabolic demands of the patient is described. The controller is based on a proportional-integral-derivative (PID) based closed-loop feedback control system that modulates sweep gas (air) flow through the AL to maintain a target exhaust gas partial pressure (target or ). The presented work advances previous research by (1) using gas-side sensing that avoids complications and clotting associated with blood-based sensors, (2) incorporating all components into a portable, battery-powered package, and (3) integrating smart moisture removal from the AL to enable long term operation. The performance of the controller was tested in vitro for ∼12 h with anti-coagulated bovine blood and 5 days with distilled water. In tests with blood, the sweep gas flow was automatically adjusted by the controller rapidly (<2 min) meeting the specified tEG level when confronted with changes in inlet blood partial pressure of (p) levels at various AL blood flows. Overall, the removal from the AL showed a strong correlation with blood flow rate and blood p levels. The controller successfully operated continuously for 5 days when tested with water. This study demonstrates an important step toward ambulatory AL systems that automatically modulate removal as required by lung disease patients, thereby allowing for physiotherapy, comfort, and activity.

Maximal subspace averages

We consider maximal operators associated to singular averages along finite subsets Σ of the Grassmannian Gr(d,n) of d-dimensional subspaces of Rn. The well studied d=1 case corresponds to the directional maximal function with respect to arbitrary finite subsets of Gr(1,n)=Sn−1. We provide a systematic study of all cases 1≤d<n and prove essentially sharp L2(Rn) bounds for the maximal subspace averaging operator in terms of the cardinality of Σ, with no assumption on the structure of Σ. In the codimension 1 case, that is n=d+1, we prove the precise critical weak (2,2)-bound.Drawing on the analogy between maximal subspace averages and (d,n)-Nikodym maximal averages, we also formulate the appropriate maximal Nikodym conjecture for general 1<d<n by providing examples that determine the critical Lp-space for the (d,n)-Nikodym problem. Unlike the d=1 case, the maximal Kakeya and Nikodym problems are shown not to be equivalent when d>1. In this context, we prove the best possible L2(Rn)-bound for the (d,n)-Nikodym maximal function for all combinations of dimension and codimension.Our estimates rely on Fourier analytic almost orthogonality principles, combined with polynomial partitioning, but we also use spatial analysis based on the precise calculation of intersections of d-dimensional plates in Rn.

Quantitative bounds on impedance-to-impedance operators with applications to fast direct solvers for PDEs

We prove quantitative norm bounds for a family of operators involving impedance boundary conditions on convex, polygonal domains. A robust numerical construction of Helmholtz scattering solutions in variable media via the Dirichlet-to-Neumann operator involves a decomposition of the domain into a sequence of rectangles of varying scales and constructing impedance-to-impedance boundary operators on each subdomain. Our estimates in particular ensure the invertibility, with quantitative bounds in the frequency, of the merge operators required to reconstruct the original Dirichlet-to-Neumann operator in terms of these impedance-to-impedance operators of the sub-domains. A key step in our proof is to obtain Neumann and Dirichlet boundary trace estimates on solutions of the impedance problem, which are of independent interest. In addition to the variable media setting, we also construct bounds for similar merge operators in the obstacle scattering problem.

High isolation multiport integrated antenna system for cognitive radio applications

ABSTRACT A five port integrated antenna with high isolation for cognitive radio (CR) application was investigated in this study. The design approach involves both the state of operation in terms of ultra-wideband (UWB) and narrowband (NB), where the former is for sensing and the latter is for the sake of communication. The antenna in UWB state comprises an elliptical patch with a narrow cut on the top whereas four simple comb-like patterns are used to perform the task in NB range. In three of the NB antennas, Complementary Split Ring Resonators (CSRR) are used for impedance matching, in contrast to a Double Circular Ring Resonator (DCRR) in another NB antenna. In order to achieve remarkable inter port isolation, two meander lines of same electrical length are introduced between UWB and NB antennas where the first meander line (ML1) is positioned parallel and the second meander line (ML2) is tilted by an angle of 30° with respect to UWB. The potential outcome of the proposed design senses UWB spectrum from 1.9 GHz − 11.77 GHz along with seven communication tasks simultaneously in terms of single and dual band operations with remarkable gain and high isolation of <-22 dB in all ports.

Scrutinizing the Intermittency of Renewable Energy in a Long-Term Planning Model via Combining Direct Integration and Soft-Linking Methods for Colombia’s Power System

The large-scale integration of variable renewable energy sources into the energy system presents techno–economic challenges. Long–term energy system optimization models fail to adequately capture these challenges because of the low temporal resolution of these tools. This limitation has often been addressed either by direct improvements within the long–term models or by coupling them to higher resolution power system models. In this study, a combined approach is proposed to capitalize on the advantages and overcome the disadvantages of both methods. First, the temporal resolution of an energy model was enhanced by approximating the joint probability of the electricity load and the supply of intermittent sources. Second, the projected electricity mix was simulated by a power model at an hourly resolution. This framework was used to analyze mid–century deep decarbonization trajectories for Colombia, subject to future uncertainties of hydroclimatic variability and the development of the bioeconomy. The direct integration method is found to consistently reduce the overestimation of the feasible penetration of VRES. However, its impact is marginal because of its inability to assess the short–term operation of the power system in detail. When combined with the soft–linking method, the reliable operation of the power system is shown to incur an additional overhead of 12–17% investment in flexible generation capacity, 2–5% of the annual energy system cost, and a 15–27% shortfall in achieving the aspired GHG mitigation target. The results obtained by combining both methods are found to be closer to the global optimum solution than using either of these methods individually.

Real‐time resilient microgrid power management based on multi‐agent systems with price forecast

AbstractMicrogrids have emerged to diversify conventional electric generation using small‐scale distributed generation. Large efforts have been put into designing control strategies to optimise the power schedules of microgrids, however, verification that such control systems also are reliable in terms of stability during normal operation and fault conditions is needed. This study presents a hierarchical distributed control system that fulfils these conditions for an AC microgrid. The stability maintained by proposed controller, considering the large signal model, is analysed with the use of Lyapunov's direct method. Resilient control distribution is achieved by the implementation of suitable forecast models and fault‐tolerance mechanisms to avoid single points of failure. The resilience of the control system is verified with the use of graph theory. The stable and resilient operation of the proposed control system is tested by a real‐time microgrid model implemented with an OPAL‐RT real‐time simulator, combined with a communication network built with Raspberry Pis, testing the control system presented under normal and faulty conditions. Simulation results show a stable operation in terms of voltage and frequency in both conditions, resilient operation is shown for the faulty condition case. Additionally, cost minimisation performance is included to validate optimal power management capabilities.

CFT approach to constraint operators for (β-deformed) hermitian one-matrix models

Since the (β-deformed) hermitian one-matrix models can be represented as the integrated conformal field theory (CFT) expectation values, we construct the operators in terms of the generators of the Heisenberg algebra such that the constraints can be derived by inserting the constructed operators into the integrated expectation values. We also obtain the second order total derivative operators associating with the derived constraint operators and analyze their properties. We explore the intrinsic connection between the derived constraint operators and W-representations of some matrix models. For the Gaussian hermitian one-matrix model in the external field and β-deformed N×N complex matrix model, we investigate the superintegrability and derive the corresponding character expansions from their W-representations. Moreover a conjectured formula for the averages of Jack polynomials in the literature is proved.

Novel Anolyte Redox Active Organic Molecules for Redox Flow Battery Applications

Non-aqueous redox flow batteries (NARFBs) offer several advantages over traditional aqueous electrolyte-based redox flow batteries, such as higher cell voltage, potentially higher energy density, and flexible operating temperatures. However, the current aqueous chemistries use toxic metals such as Vanadium and Chromium and highly acidic and oxidative acid mixtures. The efforts to develop metal-ligand based chemistries to tap the benefits of NARFBs have met with mixed success and only V(acac)3 based symmetric NARFBs have shown potential for long term operations. Even so, the solubility of V(acac)3 in non-aqueous solvents is low to compete with their aqueous counterpart. Moreover, modification of V(acac)3 to enhance the solubility has resulted in poor redox cyclability. As a result, recent research trends have shifted from the development of Metal-ligand complexes to small redox-active organic molecules (ROMs), which could provide higher solubility. However, due to the developing field, a few ROMs have been reported as stable electron donors and acceptors in their oxidized and reduced states. Therefore, we have focused on developing highly soluble anolyte materials with stable redox states. This presentation will discuss the design principle, synthesis, and electrochemical analysis of novel anolyte ROMs. The additional information about the kinetics, bulk electrolysis, and the performance in the full cell will also be discussed.

Development of a Piezoresistive Pressure Sensor Using an in-House Pulsewave Simulator to Ensure Detection of Full Pulse Waveform on Diverse Populations

Flexible and skin mountable wearable health monitoring devices have gained much attention in recent years due to their non-invasive approach to continuous monitoring of weak human physiological signals. In general, ultra-sensitive pressure sensors can be categorized by the operation mechanism into piezoresistive, capacitive, triboelectric, and piezoelectric sensors. Specifically, piezoresistive sensors has drawn much attention because of their fast response, broad detection range, simple structure, and relative simplicity of the signal measuring system. Despite the success of the past efforts in acquiring the full pulse waveform of the human heartbeat, their signal acquisition requires utilization of unwearable measuring equipment. In this study, the central research objective will be to do finite element analysis to optimize the design, and then to fabricate, test and finally verify wearability of the full system (including the signal acquisition portion) on the wrist. A piezoresistive pressure sensor capable of precise monitoring of arterial pulse waveform allows detection of not only the pulse but also possible irregularities in its waveform that can be potentially the harbingers of various medical conditions. Modeling of the sensor’s micro-features showed micro-features with the shape of a pyramid, size of 100 μm, angle of 50-60 degrees and spatial configuration of 1 per 300 μm realizes high sensitivity and signal level (1 mA for pulse waveform detection from the wrist). This helps to eliminate the dependability of the sensor response read-out on complex and unportable measuring devices such as sourcemeters. Furthermore, fabrication of the conductive micro-patterned sensor has been accomplished by the standard micro-fabrication techniques including photolithography and wet etching. Methods such as electrospinning, bipolar exfoliation of graphene and electrostatic spray deposition were used to ensure long term stable conductivity and operation of the device. After the fabrication, this piezoresistive sensor was fully calibrated and characterized by a developed pulse waveform simulator to ensure viability of the system to detect the full pulse waveform from the wrist with various amplitudes of excitation signal (accounting for diverse human population with different pulse strengths). The detailed results will be discussed during the presentation.

Effect of Carbonate Anions on the Stability of Quaternary Ammonium Groups for Aemfcs

Anion-exchange membrane fuel cells (AEMFCs) have been attracting significant attention as a promising green and effective technology for energy conversion, suitable for both automotive and stationary applications. AEMFCs operate in an alkaline environment and thus allow the use of non-precious metal electrocatalysts from a wide selection of materials, as well as lower cost anion-exchange membranes (AEMs). In spite of the significant progress recently achieved, the commercial development of AEMFCs is hampered by both AEM degradation and the carbonation processes. The chemical decomposition of the AEMs during fuel cell operation is still considered as the main challenge that needs to be addressed. The combination of high pH environment and high current densities in the AEMFCs results in hydroxide anions with limited solvation, becoming extremely reactive towards positively charged quaternary ammonium (QA) salts. This decomposition leads to detrimental reduction in anion conductivity and therefore in fuel cell performance. Understanding the carbonation process is also critical to allow AEMFCs to operate with ambient air. Hydroxide anions created in the oxygen reduction reaction react with CO2 even at low concentrations, to form bi/carbonates ions. The lower diffusion coefficients and ionic mobility of CO3 -2 and HCO3 - increases resistivity and reduces power output.In this study we experimentally show for the first time the effect of carbonation on the degradation processes of the AEM. The experimental results are compared to modeling by MD. This study provides insights into the carbonation effect on cation stability in alkaline systems, which has significant implications for the final stability of AEMs resulting in long term operation of AEMFCs under real ambient air conditions.

Renormalizable extension of the Abelian Higgs-Kibble model with a dimension-six operator

A deformation of the Abelian Higgs Kibble model induced by a dimension 6 derivative operator is studied. A novel differential equation is established fixing the dependence of the vertex functional on the coupling $z$ of the dim.6 operator in terms of amplitudes at $z = 0$ (those of the power-counting renormalizable Higgs-Kibble model). The latter equation holds in a formalism where the physical mode is described by a gauge-invariant field. The functional identities of the theory in this formalism are studied. In particular we show that the Slavnov-Taylor identities separately hold true at each order in the number of internal propagators of the gauge-invariant scalar. Despite being non-power-counting renormalizable, the model at $z \neq 0$ depends on a finite number of physical parameters.

ПЕРЕРАСПРЕДЕЛЕНИЕ КАРБИДНОЙ ФАЗЫ И АТОМОВ УГЛЕРОДА В ДИФФЕРЕНЦИРОВАННО ЗАКАЛЕННЫХ РЕЛЬСАХ ПРИ УЛЬТРАДЛИТЕЛЬНОЙЭКСПЛУАТАЦИИ

The methods of scanning, transmission electron microscopy were used to study the redistribution of carbide phases and carbon atoms in the cross section of the head at distances of 0, 2, 10 mm from the surface along the rounding radius of the fillet and along the central axis of 100-meter differentially hardened rails after extremely long term operation (rassed tonnage with 2013 1770 million gross tons).

Cut-free sequent-style systems for a logic associated to involutive Stone algebras

Abstract In [4, 5], it was introduced a logic (called Six) associated to a class of algebraic structures known as involutive Stone algebras. This class of algebras, denoted by S, was considered by the first time in [6] as a tool for the study of certain problems connected to the theory of finite-valued Łukasiewicz–Moisil algebras. In fact, Six is the logic that preserves degrees of truth with respect to the class S. Among other things, it was proved that Six is a 6-valued logic that is a Logic of Formal Inconsistency (LFI ); moreover, it is possible to define a consistency operator in terms of the original set of connectives. A Gentzen-style system (which does not enjoy the cut-elimination property) for Six was given. Besides, in [5], it was shown that Six is matrix logic that is determined by a finite number of matrices; more precisely, four matrices. However, this result was further sharpened in [17], proving that just one of these four matrices determine Six, i.e. Six can be determined by a single 6-element logic matrix. In this work, taking advantage of this last result, we apply a method due to Avron, Ben-Naim and Konikowska [3] to present different Gentzen systems for Six enjoying the cut-elimination property. This allows us to draw some conclusions about the method as well as to propose additional tools for the streamlining process. Finally, we present a decision procedure for Six based in one of these systems.

Pseudo-differential operators with isotropic symbols, Wick and anti-Wick operators, and hypoellipticity

We study the link between Ψdos and Wick operators via the Bargmann transform. We deduce a formula for the symbol of the Wick operator in terms of the short-time Fourier transform of the Weyl symbol. This gives characterizations of Wick symbols of Ψdos of Shubin type and of infinite order, and results on composition. We prove a series expansion of Wick operators in terms of anti-Wick operators which leads to a sharp Gårding inequality and transition of hypoellipticity between Wick and Shubin symbols. Finally we show continuity results for anti-Wick operators, and estimates for the Wick symbols of anti-Wick operators.

Enhanced bifunctional aspects of oxygen vacancy rich cation substituted MnCo2O4 intercalated with g-C3N4 as an oxygen evolution and supercapacitor electrode

Rational design of electrocatalyst for oxygen evolution reaction (OER) to efficiently evolve oxygen molecules with low overpotential and electrode material disclosing high power density for supercapacitor remains a challenge. Pristine g-C3N4, MnCo2O4/g-C3N4 and cation modified MnCo2O4 intercalated with g-C3N4 (Mn0·4Ni0·6Co2O4/g-C3N4) were prepared and investigated its efficacy towards catalyzing OER. Mn0.4Ni0.6Co2O4/g-C3N4 electrocatalyst exhibits a low overpotential of 320 mV @ current density of 10 mA/cm2 and a small Tafel slope of 75.2 mV/dec. It follows simultaneous evolution of oxygen from oxyhydroxide species during the electrocatalytic performance. The same electrocatalyst also reveals excellent stability during its long term operation. Simultaneously, the same material discloses elevated specific capacitance of 1987.2 F/g at 1 A/g and a maximum retention of capacitance even after its cycling for 8000 cycles than pristine g-C3N4 and MnCo2O4/g-C3N4 composite. This observation greatly insists that Mn0·4Ni0·6Co2O4/g-C3N4 composite can be employed as an electrode material for high performance supercapacitors due to its excellent capacitance and outstanding cycling stability.

Evaluation of the optimization effect of a combined constructed wetland with micro-polluted water sources

The research aimed to evaluate the eight-years purification performance of a large-scale combined constructed wetland (CW) improving micro-polluted water, to analyze problems occurring during long term operation and their causes, as well as to propose measures and suggestions for further optimization. The results shows that the average removal rates (RRs) of permanganate index (CODMn), ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) were 4.39 % ± 12.64 %, 41.57 % ± 16.36 %, 32.61 % ± 23.36 % and 47.05 % ± 20.39 % during 2013–2020, respectively. Compared with other similar constructed wetlands, the removal rate of each pollution indicator was relatively low. The deep purification zone exhibited the best performance due to the long hydraulic retention time (HRT); the pretreatment zone had low capacity in removal of CODMn and TN; the emergent plant zone was significantly affected by the plant arrangement; the purification performance of submerged plant zone in the first three years was inefficient due to the difficult restore of submerged plants. The average RRs for CODMn, NH4+-N, TN, and TP after the optimization engineering were 2.54 ± 14.76 %, 39.62 ± 18.47 %, 31.86 ± 22.19 %, and 46.06 ± 21.02 %, respectively, indicating that the overall purification performance was not improved significantly. The analysis shows that influent concentrations, temperature, HRT and design of combined processes were key factors influencing the purification performance of CW. In the future, it is necessary to take targeted measures for the above key factors to improve the water quantity and quality assurance rate of drinking water sources, to ensure the drinking water health and safety.

Long term operation of the radiation-hard Hall probes system and the path toward a high performance hybrid magnetic field sensor

The paper reports a systematic assessment of the radiation-hard Hall probes (RHP) magnetic diagnostic system of the JET tokamak, which is based on InSb semiconductor thin films, and describes the path that lead to the proposal of an innovative magnetic probe concept. A relevant account of RHP operation during the recent deuterium–tritium experimental campaign is also provided, showing correct operation under ITER-like intense neutron flux. The period considered for the systematic assessment of the RHP system ranges from October 2009 to March 2021, during which the machine produced more than 19 000 pulses. The RHP system consists of six three-dimensional Hall probes, which have built-in recalibration capability, thanks to the presence of microsolenoids that produce a local known field during a tailored automatic pre-pulse calibration sequence, that can also be initiated manually. During pulses, the microsolenoids can also be used as inductive sensors as their signals are recorded as well. Moreover, the system provides temperature measurements at the location of the probes, which are continuously recorded too. The assessment demonstrates accurate long-term operation of the RHP system. All the diagnostic channels reliably provide pre-pulse calibration data and pulse signals and the original sensitivities of the Hall sensors are preserved. Integration considerations and a data fusion analysis lead to the proposal of a high performance, compact, broadband, hybrid field probe, consisting of the combination of an inductive coil and a Hall sensor, to be manufactured by means of the coil technology developed for ITER or an alternative concept with improved radiation-hardness. The hybrid probe is expected to deliver the advantages of both inductive and Hall sensing technologies, essentially in the same package size of a single ITER magnetic discrete probe. In particular, it would solve the problem of the drift of the integrator for long lasting burning plasma discharges. The signals produced by the coil and the Hall sensor, processed by means of a Luenberger–Kalman observer, provide a magnetic field measurement which is non-drifting and low-noise. For these reasons, the hybrid probe has been proposed as the potential primary magnetic diagnostic sensor for future burning plasma experiments and demonstration fusion power plants.

Convergence of parallel overlapping domain decomposition methods for the Helmholtz equation

We analyse parallel overlapping Schwarz domain decomposition methods for the Helmholtz equation, where the exchange of information between subdomains is achieved using first-order absorbing (impedance) transmission conditions, together with a partition of unity. We provide a novel analysis of this method at the PDE level (without discretization). First, we formulate the method as a fixed point iteration, and show (in dimensions 1, 2, 3) that it is well-defined in a tensor product of appropriate local function spaces, each with L^2 impedance boundary data. We then obtain a bound on the norm of the fixed point operator in terms of the local norms of certain impedance-to-impedance maps arising from local interactions between subdomains. These bounds provide conditions under which (some power of) the fixed point operator is a contraction. In 2-d, for rectangular domains and strip-wise domain decompositions (with each subdomain only overlapping its immediate neighbours), we present two techniques for verifying the assumptions on the impedance-to-impedance maps that ensure power contractivity of the fixed point operator. The first is through semiclassical analysis, which gives rigorous estimates valid as the frequency tends to infinity. At least for a model case with two subdomains, these results verify the required assumptions for sufficiently large overlap. For more realistic domain decompositions, we directly compute the norms of the impedance-to-impedance maps by solving certain canonical (local) eigenvalue problems. We give numerical experiments that illustrate the theory. These also show that the iterative method remains convergent and/or provides a good preconditioner in cases not covered by the theory, including for general domain decompositions, such as those obtained via automatic graph-partitioning software.