Steady-state Value Research Articles

Improved charge density and stability in PDMS ferroelectrets using PDMS/PTFE composite materials

A ferroelectret is a flexible cellular polymer structure that generates electrical power under mechanical force. It behaves like a piezoelectric material in that a voltage is generated when the ferroelectret deforms. Its electrical output significantly depends on the surface charge density of the material used. Previous ferroelectrets fabricated from polydimethylsiloxane (PDMS) benefit from the soft, stretchable mechanical properties of the PDMS but the ability of this material to trap charge at its surface is poor. This paper presents approaches to enhance the surface charge density and stability of a PDMS based ferroelectret device by adding Polytetrafluoroethylene (PTFE) to the PDMS. This PDMS/PTFE composite has been evaluated when used to fabricate the ferroelectret device and when used as an additional coating the internal void surfaces of an otherwise plain PDMS ferroelectret. As the proportion of PTFE increases, the surface charge density on the void surfaces increases resulting in a corresponding increase in the piezoelectric properties of the ferroelectret. A weight ratio of PTFE powder and PDMS of 1:3 was found to achieve improved piezoelectric performance with an initial effective piezoelectric coefficient, d33e, of around 700 pC/N which decayed initially and reached a steady state value of around 365 pC/N measured after 4 months after poling. This presents a considerable improvement in performance when compared with the effective d33e of pure PDMS which has an initial value of around 110 pC/N and drops to below 8 pC/N after 4 months. The energy harvester potential of the ferroelectret was explored by cyclically compressing the PDMS/PTFE composite layer ferroelectret structure with a force of 500 N applied at 1 Hz. The output of the ferroelectret was found to charge a 10 μF capacitor to 0.12 V after 40 s. Maximum output power occurs at a load resistance of 15 MΩ, with a peak power of 4 μW. A fabricated PDMS/PTFE composite layer ferroelectret sample (weight ratio of PTFE powder and PDMS of 1:3) was also tested as a pressure sensor range from 0 to 500 N and achieved a sensitivity of 9.9 mV/N. The nonlinearity error of the proposed sensor was 1.7%.

WITHDRAWN: Gastroretentive fibrous dosage forms for prolonged delivery of sparingly soluble tyrosine kinase inhibitors. Part 3: Theoretical models of in vivo expansion, gastric residence time, and drug concentration in blood

In the present part, models are developed for in vivo expansion, gastric residence time, and drug concentration in blood after administering a slow-release, gastroretentive fibrous dosage form to dogs. The tyrosine kinase inhibitor nilotinib, which is slightly soluble in low-pH gastric fluid but practically insoluble in high-pH intestinal fluid, is used as a model drug. The models suggest that upon ingestion, the fibrous dosage form expands, is retained in the stomach for prolonged time, and releases drug into the gastric fluid at a constant rate. The released drug molecules continuously flow into the duodenum with the gastric fluid flow, and are absorbed by the blood at the same rate. The absorbed drug molecules are eliminated from the blood by the liver at a rate proportional to the drug concentration in blood. Eventually, the elimination rate and the absorption rate balance out, and the drug concentration in blood plateaus out to a steady state value. After the gastric residence time of the dosage form, drug release and drug absorption stop, and the drug concentration in blood drops to zero. By contrast, after administering an immediate-release particulate dosage form the drug particles are swept out of the stomach rapidly, and drug release and drug absorption stop much earlier. The drug concentration in blood rises and falls without attaining steady state. The gastroretentive fibrous dosage forms enable a constant drug concentration in blood for drugs that are insoluble in intestinal fluids.

100-kHz RM calcium ion NIR laser

The experimental study of the laser on RM 4p2P3/2∘ - 3d2D5/2 (λ=854.2nm) and 4p2P1/2∘ - 3d2D3/2 (λ=866.2nm) transitions in a singly ionized calcium with active medium volume of 97 cm3 has been carried out. Excitation was performed with the periodic bursts containing 200 pulses each. It is shown that the laser pulse energy enters the steady-state mode during the burst. When the frequency of pulses inside the burst equaled to 90 kHz the steady-state value of the laser energy was 59 mJ, which corresponds to the average output power of 5.3 W. The measured power ratio between lines with λ=854.2nm and λ = 866.2 nm under optimum conditions amounted to 1.7, with radiation pulse duration of 20 ns. Experimental results for lasers on atom RM-transitions operating at pulse repetition frequency f≥100 kHz are reviewed. It is demonstrated that at such f values the energy characteristics of the Ca+ laser are comparable with those of lasers on atom RM transitions of other metals. An analysis of the mechanisms preventing further increase in the average output power when the pulse repetition frequency is increased above 100 kHz is presented.

Simulation Of The Optimum Operating Conditions For A Propylene Glycol Production Unit Using Aspen Hysys Software

Commercially, propylene glycol is produced by the direct hydrolysis of propylene oxide with water. This first-order, irreversible, exothermic reaction is performed in a glass-lined Continuous Stirred Tank Reactor (CSTR). In this study, the initiation of a CSTR was modelled from first principles and simulated using Aspen Hysys 3.2 to obtain concentration and temperature profiles. It is often very important how these profiles approximate the steady-state values. For example, when approaching a steady state the temperature may rise too high and this leads to degradation of the reactant or product, or the altitude may be unacceptable for safe operation. If either condition occurs, the system will exceed its practical stability limit. The practical stability limit represents the temperature above which it is undesirable to operate due to undesirable side reactions or equipment damage. Therefore, the best-operating conditions were obtained in terms of the flow rate of the raw material and the temperature of the reactor at 345 Kgmol/h and 82.2 °C on straight. The production of propylene glycol in the presence of an acid catalyst in an isothermal tank reactor is presented using advanced process simulation software. The effect of temperature was also calculated using the principle of energy balance on the reactor. The reactor operates optimally at a fractional conversion of 0.995 to obtain optimal values for the most important variables/parameters [reactor volume 7.92 m3, reactor length 2.83 m, reactor diameter 1.89 m, and amount of heat required for cooling per unit volume of the reactor 1205 kw].

Effects of Body Mass and Age on the Pharmacokinetics of Subcutaneous or Hyaluronidase-facilitated Subcutaneous Immunoglobulin G in Primary Immunodeficiency Diseases

PurposeTo assess the pharmacokinetics (PK) of subcutaneous immunoglobulin (SCIG) and hyaluronidase-facilitated SCIG (fSCIG) therapy across body mass index (BMI) and age categories in patients with primary immunodeficiency diseases (PIDD) previously treated with intravenous immunoglobulin (IVIG).MethodsUsing our previously published integrated population PK model based on data from eight clinical trials, simulations were conducted to examine the effects of BMI and age on serum immunoglobulin G (IgG) PK after administration of SCIG 0.15 g/kg weekly or fSCIG 0.6 g/kg every 4 weeks in patients switching from stable IVIG. Patients were assumed to have baseline IgG trough concentrations of 7 g/L (hypothetical protective threshold).ResultsMean steady-state serum IgG trough values (Cmin,ss or trough) increased with BMI and age. Mean Cmin,ss was 18% (SCIG) and 16% (fSCIG) higher in the obese than the healthy BMI group. Pediatric patients aged < 18 years had 8–22% (SCIG) and 4–20% (fSCIG) lower mean Cmin,ss values than adults, with the youngest group (2– < 6 years) having the lowest Cmin,ss. All patients across populations maintained Cmin,ss IgG concentrations of ≥ 7 g/L after switching to SCIG or fSCIG.ConclusionBoth SCIG and fSCIG successfully maintained trough values at or above the hypothetical protective threshold after switching from stable IVIG, irrespective of BMI or age. Differences in trough values between BMI groups and age groups (≤ 22%) may not warrant SCIG or fSCIG dose adjustments based on BMI or age alone; instead, the dosing paradigm should be guided by prior IVIG dose, individual IgG monitoring, and clinical findings.

Towards low-carbon papermaking wastewater treatment process based on Kriging surrogate predictive model

Papermaking wastewater contains a diverse range of organic carbon, nitrogen and other pollutants, which could lead to the emission of greenhouse gases (GHG) during biochemical treatment process. Despite the importance of decarbonizing the papermaking wastewater treatment process, the mechanisms underlying the generation of greenhouse gases remain elusive and no models currently exist to describe the process. To address this issue, this study employed benchmark simulation model No. 1 (BSM1) to simulate, the papermaking wastewater treatment process, and applied the steady-state output value of simulation to calculate the GHG emissions. Kriging surrogate model was applied to establish the emission model for GHG in the papermaking wastewater treatment process. The model provides a reference for the control and optimization of GHG emission reduction and a high accuracy was achieved with determination coefficient (R2) of above 96%. Further analysis of the parameter impact of process control on GHG emissions and the optimization effects of controllable variables contributes to the goal of reducing GHG emissions in the papermaking wastewater treatment process.

Modeling of voltage-limiting kinetics in two-layer varistor–posistor structures

PurposeThe purpose of this study is to model the dependences of the output voltage, temperature, current and electrical power dissipation of a voltage limiter based on a two-layer varistor–posistor structure on time and analysis the influence of operating modes and design parameters of such a limiter on these characteristics.Design/methodology/approachThe behavior of the limiting voltage, temperature and other parameters of the voltage limiter when an input constant overvoltage is applied is studied by the simulation method. The voltage limiter was a two-layer construction. One layer was a zinc oxide ceramic varistor. The second layer was a posistor polymer composite with a nanocarbon filler of PolySwitch technology.FindingsThe output voltage across the varistor layer decreases and reaches some fixed value related to its breakdown voltage after applying a constant overvoltage to the structure over time. The temperature of the structure increases to some steady state value, while the current decreases significantly. The amplitude of the transient current pulse increases, its duration and energy of the transient process decrease with increasing overvoltage. An increase in the internal resistance of the overvoltage source can cause a decrease in the amplitude and an increase in the duration of transient currents.Originality/valueThe ranges of values for the activation energy of conduction of the varistor layer in weak electric fields, the intensity of heat exchange between the structure under study and the environment are determined to ensure the stable operation of this structure as a voltage limiter. The results obtained make it possible to select the necessary parameters of the indicated structures to ensure the required operating modes of the voltage limiter for various applications.

A model of mass extinction accounting for the differential evolutionary response of species to a climate change

Mass extinction is a phenomenon in the history of life on Earth when a considerable number of species go extinct over a relatively short period of time. The magnitude of extinction varies between the events, the most well known are the “Big Five” when more than half of all species went extinct. There were many extinctions with a smaller magnitude too. It is widely believed that the common trigger leading to a mass extinction is a climate change such as a global warming or global cooling. There are, however, many open questions with regard to the effect and potential importance of specific factors and processes. In this paper, we develop a novel mathematical model that takes into account two factors largely overlooked in the mass extinctions literature, namely, (i) the active feedback of some taxa – in particular, vegetation – to the climate through changing the albedo of the Earth’s surface and (ii) species’ adaptive evolutionary response to a climate change. We show that whether a species goes extinct or not depends on a subtle interplay between the scale of the climate change and the rate of species’ evolutionary response. We also show that species’ response to a fast climate change can exhibit long transient dynamics (false extinction) when the species population density remain at a low value for a long time before recovering to its safe steady state value. Finally, we show that the distribution of extinction frequencies predicted by our model is generally consistent with the fossil record.

Factor substitution, long-run equilibrium, and convergence speed in the Lucas model

We study the effect of factor substitution on long-run equilibrium in the Lucas model with CES production. The long-run growth rate does not depend on the elasticity of substitution. However, there is a negative (positive) relationship between the elasticity of factor substitution and the convergence speed if the baseline ratio of physical capital to effective labor is below (above) its steady-state value.

Bacterial cell-size changes resulting from altering the relative expression of Min proteins

The timing of cell division, and thus cell size in bacteria, is determined in part by the accumulation dynamics of the protein FtsZ, which forms the septal ring. FtsZ localization depends on membrane-associated Min proteins, which inhibit FtsZ binding to the cell pole membrane. Changes in the relative concentrations of Min proteins can disrupt FtsZ binding to the membrane, which in turn can delay cell division until a certain cell size is reached, in which the dynamics of Min proteins frees the cell membrane long enough to allow FtsZ ring formation. Here, we study the effect of Min proteins relative expression on the dynamics of FtsZ ring formation and cell size in individual Escherichia coli bacteria. Upon inducing overexpression of minE, cell size increases gradually to a new steady-state value. Concurrently, the time required to initiate FtsZ ring formation grows as the size approaches the new steady-state, at which point the ring formation initiates as early as before induction. These results highlight the contribution of Min proteins to cell size control, which may be partially responsible for the size fluctuations observed in bacterial populations, and may clarify how the size difference acquired during asymmetric cell division is offset.

Surface Properties of Aqueous Dispersions of Bovine Serum Albumin Fibrils

The surface properties of aqueous dispersions of worm-like fibril aggregates of bovine serum albumin (BSA) differ from those of the adsorption layers of the native protein. The dispersions of BSA fibrils are characterized by slower changes of the surface tension and dynamic surface elasticity and also have different steady-state values of the surface properties. The fourfold compression of the adsorption layer of BSA fibrils leads to noticeably higher surface pressures than those of a compressed layer of the native protein, indicating the formation of a more rigid layer structure in the former case. The spreading of BSA fibrils onto a liquid surface from a concentrated dispersion reduces the effect of surface-active admixtures on the layer properties. The dependencies of the dynamic surface elasticity on surface pressure almost coincide for the spread layers of fibrils and the native protein in the range of low surface pressures, but only the spreading of the native protein can lead to surface pressures higher than 4 mN/m. This distinction is presumably caused by the formation of stable clusters of BSA fibrils at the interface and their slow propagation along the liquid surface.

Defining the fire decay and the cooling phase of post-flashover compartment fires

The current research study discusses and characterises the fire decay and cooling phase of post-flashover compartment fires, as they are often mixed up despite their important heat transfer differences. The two phases are defined according to the fire heat release rate time-history. The fire decay represents the phase in which the fire heat release rate decreases from the ventilation- or fuel-limited steady-state value of the fully-developed phase to fire extinguishment. This phase is highly influenced by the fuel characteristics, ranging from fast decays for hydrocarbon and liquid fuels to slow decays for charring cellulosic fuels (wood). Once the fuel is consumed, the compartment volume enters the cooling phase, where the cooling in the gas-phase and solid-phase happens with significantly different modes and characteristic times. The thermal boundary conditions at the structural elements are then defined according to physical characteristics and dynamics within the compartment. The research study also underlines how the existing performance-based methodologies lack explicit definitions of the decay and cooling phases and the corresponding thermal boundary conditions for the design of fire-safe structural elements under realistic fire conditions.

Regulation of multi-area power system load frequency in presence of V2G scheme.

The integration of renewable sources (RSs) and the widespread deployment of electric vehicles (EVs) has transitioned from a luxury to a necessity in modern power systems. This results from the sharp increase in electric power demand and public awareness of switching to green energy. However, in addition to load fluctuations and changes in system parameters, these RSs and EVs negatively impact the load frequency (LF). This work presents a LF control for a modern multi-area power system incorporating photovoltaic (PV) and EV chargers. The proposed controller primarily utilizes EV chargers within modern power systems. This approach offers the advantage of using the already present components instead of introducing new ones. The proposed controller comprises the ecological optimization approach (ECO) and the integral controller (I). Both of these components are designed for autonomous vehicle-to-grid (V2G) devices. The proposed control technique is applied to a three-area power system, where the V2G scheme is located in Area-1. Variations in the load, PV power generated, and system parameters are considered to evaluate the effectiveness of the proposed (I+ECO+V2G) controller for controlling the LF. To assess the performance of the proposed I+ECO+V2G system, a comparative analysis is conducted to compare its performance with both the I+ECO system and the standard I-controller. The simulation findings demonstrate that implementing the I+ECO and the proposed I+ECO+V2G strategies results in enhanced system stability and decreased LF fluctuations compared to the conventional I-control approach. Furthermore, while comparing the I+ECO control technique to the suggested control strategy I+ECO+V2G, it was seen that the latter reaches steady state values more quickly. The results validate the robustness and effectiveness of the proposed controller in mitigating the impacts of load disturbances, uncertainties, and nonlinearities within the system. These simulations were performed using MATLAB/SIMULINK. To validate the outcomes of the simulation results, an experimental setup consisting of a real-time dSPACE DS1103 connected to another PC via QUARC pid_e data acquisition card was used. The experimental findings have substantiated the accuracy of the simulation findings about the superiority of the I+ECO+V2G methodology compared to both the I+ECO and I-control methodologies concerning system performance and LF control.

A new approach to demonstrate the exothermic behavior of textiles by using a thermal manikin: Correction methods of manikin model

In high humidity environments, certain textile fibers, such as wool, viscose, cotton, and polyester, demonstrate a tendency for exothermic heat generation. Utilizing a comprehensive thermal manikin model, this study sought to examine the intricate heat flux patterns across the manikin's torso post an 1800-s transition under fluctuating humidity levels, ranging from 35% to 80%. Initial findings highlighted a dichotomy: some segments exhibited a marked decrease in heat, subsequently recovering, whereas others showed a rapid escalation. Notably, to maintain a skin temperature of 35 °C on the manikin, there was a transient heat reduction in select segments, emphasizing the pivotal role textiles play in ensuring thermal comfort during transient conditions. The research incorporated two distinct data correction methodologies: the first calibrated heat flux measurements based on steady-state values pre and post humidity alteration, and the second drew upon a consistent reference segment, such as the head, which remained unaffected by the fabric. Intriguingly, these heat flux behaviors correlate directly with a fabric's moisture buffering capability, with wool emerging as the most adept, showcasing a buffering efficiency 26%, 45%, and 96% superior to viscose, cotton, and polyester, respectively. Furthermore, the microclimate—a critical layer between garment and skin—plays a determinant role, with wool's microclimate witnessing a sharp 58% surge when external humidity reached 80% after the stipulated transition period. This investigation highlights the unique thermal insulation properties of wool in varying humidity contexts, providing a strong basis for future scholarly investigations into the intricate thermal characteristics of textiles.

Climate policy, financial frictions, and transition risk

We study climate and macroprudential policies in an economy with financial frictions. Using a dynamic stochastic general equilibrium model featuring both a pollution market failure and a market failure in the financial sector, we explore transition risk – whether ambitious climate policy can lead to macroeconomic instability. It can, but the risk can be alleviated through macroprudential policies – taxes or subsidies on banks' assets. Then, we explore efficient climate and macroprudential policy in the long run and over business cycles. The presence of financial frictions affects the steady-state value and dynamic properties of the efficient carbon tax.

Fabrication and characterization of a two-dimensional individually addressable electrowetting microlens array.

We demonstrate a two-dimensional, individually tunable electrowetting microlens array fabricated using standard microfabrication techniques. Each lens in our array has a large range of focal tunability from -1.7 mm to -∞ in the diverging regime, which we verify experimentally from 0 to 75 V for a device coated in Parylene C. Additionally, each lens can be actuated to within 1% of their steady-state value within 1.5 ms. To justify the use of our device in a phase-sensitive optical system, we measure the wavefront of a beam passing through the center of a single lens in our device over the actuation range and show that these devices have a surface quality comparable to static microlens arrays. The large range of tunability, fast response time, and excellent surface quality of these devices open the door to potential applications in compact optical imaging systems, transmissive wavefront shaping, and beam steering.

A CRITIC-TOPSIS and optimized nonlinear grey prediction model: A comparative convergence analysis of marine economic resilience

The strength of marine economic resilience (MER) determines whether a region can maintain its original development path or fall into stagnation in the face of economic shock, which is an important starting point for promoting marine economic sustainable development. We discuss the connotation and propose a logical framework for MER, which is estimated by CRITIC-TOPSIS method from 2006 to 2019 based on three dimensions (country, region, province). Furthermore, the temporal evolution trend and regional disparities are accessed by Dagum Gini coefficient. Results reveal that MER has shown a significant upward trend, and it is undergoing gradient change in China, and unfortunately, the specific performance is in the imbalance, and lack of coordination of MER in the southern marine economic circle is the most prominent. Foreseeably, the novel fractional nonlinear grey model with double optimization (DOFNGBM(1,1)) combining Grey wolf optimization (GWO) algorithm is proposed and its performance is examined. Ulteriorly, as predicted by DOFNGBM(1,1) and presented by σ convergence and β convergence models, based on the cross-comparison between in-sample and out-of-sample, significant findings indicate that weak convergence of China’s MER indicates that coastal areas with a low level have faster improvement rates, and MER in China will present different ways of growing delightedly. Comparatively, considering the driving factors of marine economic resilience, all of them are proven to be conducive to raising the steady-state value of MER to a higher level, despite the regional heterogeneity of their effects. Purposefully, it implies that diversified development and synergistic cooperation can improve the endogenous power of marine economic resilience.

Dynamic characteristics of refrigerant and lubricant in R290 rolling piston compressor of low-temperature air to water heat pump (LT-AWHP) during defrosting cycle

The dynamic characteristics of refrigerant and lubricant in R290 rolling piston compressor used in LT-AWHP (ambient temperature (ta) of 7 ∼ −30 °C) are not clear at present. In this study, the changing characteristics of suction and discharge pressure and temperature, physical properties of oil sump (temperature, viscosity, solubility) and oil sump liquid level in the high pressure shell double-cylinder rolling piston compressor during defrosting cycle (steady state→ defrosting→ steady state) were experimentally researched in a R290 LT-AWHP with the rated power consumption of 1.9 kW using PAG40 and POE68 lubricants at ta of −12 and −20 °C. The results show that, the defrosting time and the change rule of oil sump physical properties are different when completely miscible oil and partially miscible oil used, but the defrosting time (about 3 – 5 min) is less than that of the R290 air to air heat pump (about 8 min). After defrosting, the fluid in the upside of compressor shell remains liquid and gas mixture for a long time, which would decrease total heating performance of the heat pump. After defrosting, oil sump viscosity is lower than the steady state value for a long time after discharge pressure is stabilized again. Within a period after the four-way valve reversing, the oil sump liquid level drops a lot, which may result in metal wear for insufficient oil supply on the side of sliding vane. This research would promote the improvement of defrosting process and provide guidance for the lubricant selection of R290 LT-AWHP.

Voltage Stability Control of Boost Converter Using Linear Quadratic Integrator

This paper proposes an optimal control design to regulate output voltage of DC/DC boost converter. Linear Quadratic Integrator (LQI) was designed by determining Q and R weighting matrices in order to minimize error output voltage on several disturbance scenarios. The state-space average model of the boost converter is generated using MATLAB/Simulink, while the controller gain is obtained using LQI function on MATLAB/M-file. We also conduct simple hardware experiment using Arduino board as the main controller. The simulation results for the two test scenarios, namely changing input condition and changing load condition show an IAE value was less than 0.2. In the hardware experiment result, the steady-state error value was less than 9.5% for the both test scenarios.

A Stress-State-Dependent Sliding Wear Model for Micro-Scale Contacts

Abstract Wear is a complex phenomenon taking place as two bodies in relative motion are brought into contact with each other. There are many different types of wear, for example, sliding, fretting, surface fatigue, and combinations thereof. Wear occurs over a wide range of scales, and it largely depends on the mechanical properties of the material. For instance, at the micro-scale, sliding wear is the result of material detachment that occurs due to fracture. An accurate numerical simulation of sliding wear requires a robust and efficient solver, based on a realistic fracture mechanics model that can handle large deformations. In the present work, a fully coupled thermo-mechanical and meshfree approach, based on the momentum-consistent smoothed particle Galerkin (MC-SPG) method, is adapted and employed to predict wear of colliding asperities. The MC-SPG-based approach is used to study how plastic deformation, thermal response, and wear are influenced by the variation of the vertical overlap between colliding spherical asperities. The findings demonstrate a critical overlap value where the wear mechanism transitions from plastic deformation to brittle fracture. In addition, the results reveal a linear relationship between the average temperature and the increasing overlap size, up until the critical overlap value. Beyond this critical point, the average temperature reaches a steady-state value.