Khaje Nasir Toosi University of Technology

This paper presents a chopper-stabilized three-stage operational amplifier (OpAmp) with a unity gain bandwidth of 69 MHz and an input referred noise density of 3 nV $/\surd{Hz}$ . The proposed design achieves a stable unity gain by proposing a new pole and zero scheme with very low power consumption, drawing only 3.3 mA from a 1.8 V power supply while driving a load capacitor as large as 100pF. To achieve rail-to-rail input swing, the design uses both NMOS and PMOS differential pairs at the input and biases them in the subthreshold region to provide an identical net trans-conductance over the rail-to-rail input common mode. Furthermore, an adaptive biasing is employed and the current sources are kept ON during large signal transitions at the input, thus eliminating crossover distortion and providing a high slew rate of 40 V/ $\mu$ s at a 100 pF load capacitor. The design employs chopping at 2.5 MHz and is enhanced with a local ripple reduction loop, making the OpAmp suitable for high gain and wide bandwidth applications with less filtering required. The design also reduces the input bias current significantly from 500 nA to 1.5 nA by buffering the input and applying it to the modified bootstrap switches. The proposed OpAmp, fabricated in a 0.18 $\mu$ m CMOS process, exhibits a maximum offset of 4.5 $\mu$ V, a flicker noise corner frequency of 246 Hz, a DC gain of 146 dB, a power supply rejection ratio of 123 dB, and a common mode rejection ratio of 116 dB.

A novel approach to modeling of and integrating the state-of-charge (SOC) of a battery energy storage system (BESS) into the load frequency control (LFC) of power systems is proposed. By considering the SOC as a state variable in the statespace model of the system, a hierarchical frequency and SOC control scheme is introduced. On top of the primary frequency control (PFC), which is the lowest hierarchy level, the SOC signal is used as the input to a novel primary charge controller (PCC) to prevent the BESS from discharging/charging beyond minimum/maximum allowable ranges. In the middle level of the hierarchy, the secondary frequency control (SFC) loop is augmented to restore the system frequency to its nominal value when the PCC is active. At the top level of the hierarchy, a novel secondary charge controller (SCC) is designed to charge the BESS to its maximum allowable range so that it can continue to contribute to frequency control. System stability is studied using Popov/circle criterion. It is also shown that with multiple distributed energy storage units, following the SOC-balancing principle and by sharing SOC information among the units, only one BESS shall be equipped with the proposed primary and secondary charge controllers. Effectiveness of the proposed hierarchical control in providing fast and stable frequency response under different load and generation conditions is validated through hardware-in-the-loop (HIL) studies.

The widespread use of culverts has prompted researchers to focus on developing precise designs to prevent their failure caused by scouring at the culvert outlet. This study employed physical modelling to investigate alternation in culvert outlets under different conditions, including variations in culvert shape, blockage, and flow discharge during steady and unsteady flow conditions. Box and circular culverts were examined with 0%, 15%, and 30% blockage rates at the culvert inlet. For unsteady flow conditions, two hydrographs were generated, each with nine distinct flow discharges, while for steady flow conditions, flow rates of up to 14 l/s and 22 l/s were used. The sediment and flow conditions were carefully selected to ensure clear water throughout the experiments. According to the study results, the scour profile exhibited more growth in the circular culvert compared to the box culvert across all cases. Furthermore, an increase in flow rate led to an increase in the scour hole dimension, and the scouring increased with a rise in hydrograph stepwise. However, when the degree of blockage was increased, a strictly proportional increase in scour depth was not observed across all cases. The results and data presented in this research can be used by other researchers in addition to being used by hydraulic designers.

Researchers have recently focused on studying the flight dynamics and control of multicopters and fixed-wing aerial vehicles. However, investigating the transition phase between multicopter hover and fixed-wing cruise modes for a Dual-thrust Aerial Vehicle (DAV) is still challenging. In this paper, we develop two sets of nonlinear equations of motion for a DAV to create a multi-purpose dynamic model for designing control and transition mode scenarios. The first set considers the multicopter torque as the control input, while the second set considers the elevator torque as the control input. By analyzing three transition scenarios between multicopter hover and fixed-wing cruise flights, we observe that the best performance occurs for the third scenario in which the control system switches from multicopter control torque to elevator control torque when the multicopter thrust equals the wings’ lift. In this case, the vehicle will be protected from critical flight conditions like wing stalls while the transition will go smoothly with minimum height drop. The transition mode strategies are implemented using a model predictive controller in flight simulation. The numerical results show the dynamic behavior of the DAV in different transition scenarios from hover to cruise and vice versa, demonstrating successful altitude control and stable transitions in both phases.

Occupational radiation protection should be applied to the design of treatment rooms for various radiation therapy techniques, including BNCT, where escaping particles from the beam port of the beam shaping assembly (BSA) may reach the walls or penetrate through the entrance door. The focus of the present study is to design an alternative shielding material, other than the conventional material of lead, that can be considered as the material used in the door and be able to effectively absorb the BSA neutrons which have slowed down to the thermal energy range of $$< 1$$ < 1 eV after passing through the walls and the maze of the room. To this aim, a thermal neutron shield, composed of polymer composite and polyethylene, has been simulated using the Geant4 Monte Carlo code. The neutron flux and dose values were predicted using an artificial neural network (ANN), eliminating the need for time-consuming Monte Carlo simulations in all possible suggestions. Additionally, this technique enables simultaneous optimization of the parameters involved, which is more effective than the traditional sequential and separate optimization process. The results indicated that the optimized shielding material, chosen through ANN calculations that determined the appropriate thickness and weight percent of its compositions, can decrease the dose behind the door to lower than the allowable limit for occupational exposure. The stability of ANN was tested by considering uncertainties with the Gaussian distributions of random numbers to the testing data. The results are promising as they indicate that ANNs could be used as a reliable tool for accurately predicting the dosimetric results, providing a drastically powerful alternative approach to the time-consuming Monte Carlo simulations.

Effective healthcare waste management is crucial due to the presence of disease-causing agents, necessitating effective waste management procedures to reduce potential risks. Aside from healthcare waste, this category of waste is also referred to using alternative terms such as medical waste, biomedical waste, hospital waste, and clinical waste. Proper healthcare waste management importance has increased during the coronavirus pandemic, evident from the rise in research articles. Due to the lack of comprehensive recent bibliometric research on healthcare waste management, especially post-pandemic trends, there is a need for an updated bibliometric study on this topic. This paper aims to fill the gap in research by providing an updated bibliometric study on healthcare waste management from 1995 to 2022, analyzing global research status and growth trends, as well as identifying influential journals, leading countries, sponsors, authors, and author keywords. Results showed that 97 countries have participated in the publication of 877 papers as journal articles (707, 80%), reviews (85, 10%), and conference papers (85, 10%). The top 10 major journals, produced approximately 23.6% of documents of the total numbers from which waste management and research (68, 7.7%), and waste management (38, 4.3%) are the two most productive ones. The top 10 productive countries cover 75.37% of all documents. India leads in publications, with China closely behind in second place, showing significant investment in research. Besides, the keywords COVID-19, hospital, hazardous waste, infectious waste, and knowledge had the highest number of occurrences during the studied period.

This study examines a significant accumulation of deposits on an abnormal slope in the southern Caspian Sea, which is believed to be a potential source of submarine landslides due to seismic activity in the faulting system of the northern Iranian plateau. A presumed earthquake Mw 7.7 originating from the Khazar Fault is identified as the triggering event for the landslide, and the induced landslide tsunami is simulated using the fully nonlinear and dispersive Boussinesq equations to assess the tsunami hazard along the southern coasts of the Caspian Sea. Considering the uncertainty in the dimensions of landslide, two scenarios are defined involving small and large submarine mass failures with volumes of 0.22 and 1.51 km³, respectively. The results indicate that the waves generated by the small landslide scenario reach approximately 1 m in height along the coastline, whereas waves as high as 8 m are observed during the large landslide tsunami. The tsunami waves diminish as they propagate along the coasts distant from the landslide location. However, in the case of a large probable landslide, the tsunami waves reach run-up heights of up to 4 m and inundate 300 m inland’ min the target area of the study (Anzali Port). The significant disparity between the two simulated scenarios highlights the importance of accurately estimating the potential locations and volumes of landslides, as well as the necessity of conducting further geological surveys to comprehensively evaluate tsunami hazards.

This study investigates the effects of markdown and credit policies on perishable products in a two-level supply chain. As a significant funding source, trade credit allows the retailer to receive the products from the manufacturer and pay for them later. The retailer deposits the sales payment in the bank and earns interest while paying interest after the credit’s expiration. In addition to financial concerns, if products are perishable and the demand varies over time, there will be a severe challenge for the retailer to adjust the sales and ordering policies to manage the inventory cost and revenues. Given the importance of price, the retailer examines two sales policies and chooses the more profitable one, either selling all the products at a fixed price or marking down the prices at an appropriate time to boost the demand. Assuming that demand is time-varying, this study determines the cycle length, markdown time, preservation techniques, investment, and trade credit size by considering their relationships in different decision models. Several methods are utilized in an analytical approach to solve the models and find the optimal solutions. Sensitive analyses are also conducted to evaluate the effects of the initial and marked-down price changes on the markdown time, order quantity, and sales volume.

In this investigation, through the use of friction stir processing (FSP), the role of vibration and FeAlCrMoNb HEA particles in modifying the microstructure and tribological performance of a novel AZ31/FeAlCrMoNb composite is appraised. The results showed that the application of vibration during FSP can be used as a successful approach for achieving applicable tribological and mechanical features through the use of FeAlCrMoNb particles. Additionally, it was discovered that the utilization of vibration leads to a conspicuous improvement in shear punch strength and hardness concerning traditional FSP that can be attributed to properly scattering the reinforcements across the Mg substrate and eliminating flaws, including the aggregation and gathering of reinforcing powders, achieved by implementing vibration during the process, resulting in enhanced SPT strength.

The bearing capacity of shallow foundations on geocell-reinforced sand (GRS) depends not only on the soil characteristics but also on the geometries and properties of geocell. The geometry characteristics of GRS comprise height, length and cell aperture size of geocell as well as the sand layer thickness engaged between footing and GRS layer. Using the design-of-experiments (DOE) method the trends of bearing capacity ratio (BCR) as a function of selected geometry parameters of geocell are systematically visualized. Furthermore, trends of BCR as a function of geocell-selected geometry parameters are analysed. To this end, the study deploys the response surface methodology (RSM) to identify several configurations of geocell by conducting only twenty-seven laboratory tests. The results show that the DOE-RSM method gives an efficient interpretation of the variable’s interaction while it lessens the number of tests. In addition, it has been found that the geocell height is the most influential parameter on BCR of footings on GRS. Moreover, an interaction between geocell aperture size and geocell height is recognised. The results are formulated and compared with the literature, resulting in good agreement.

The coordination chemistry of the organotin(IV) compounds is dominated by nitrogen and oxygen donor ligands. Some of these complexes have found prominent applications in the fields of biomedicine such as anticancer and antibacterial agents. These complexes represent important building blocks in polymer and supramolecular assembly. This review aims to summarize the recent literature on the chemistry of organotin complexes with imine and polypyridyl ligands such as bipyridine, phenanthroline and terpyridine ligands as well as oxygen donor ligands and O, N donor ligands. Given that many organotin(IV) chlorides are inexpensive, widely available, and can be easily converted to the other corresponding halides and pseudo-halides, numerous innovative ideas could be generated through application of these compounds. Polymer-containing tin moieties were also highlighted and their biological activities in combatting diseases such as cancer and inflammatory and infectious diseases were described.

This paper introduces a novel hybrid approach for predicting the rainfall-runoff (r-r) phenomenon across different data division scenarios (50%-50%, 60%-40%, and 75%-25%) within two distinct watersheds, encompassing both monthly and daily scales. Additionally, the effectiveness of this newly proposed hybrid method is evaluated in multi-step ahead prediction (MSAP) scenarios. The proposed method comprises three primary steps. Initially, to address the non-stationarity of the runoff and rainfall time series, these series are decomposed into multiple sub-time series using the wavelet (WT) decomposition method. Subsequently, in the second step, the decomposed sub-series are utilized as input data for the M5 model tree, a decision tree-based model. The M5 model tree classifies the samples of decomposed runoff and rainfall time series into distinct classes. Finally, each class is modeled using an artificial neural network (ANN). The results demonstrate the superior efficiency of the proposed WT-M5-ANN method compared to other available hybrid methods. Specifically, the calculated R² was 0.93 for the proposed WT-M5-ANN method, whereas it was 0.89 and 0.81 for the WT-ANN (WANN) and WT-M5 methods, respectively, for the Lobbs Hole Creek watershed at the daily scale.

Vortex-Induced Vibration (VIV) is a complex fluid–structure interaction in offshore structures. Traditionally, this phenomenon is considered periodic; however, many of its signals show chaotic behavior. The basic model already employed by other researchers is a rigid circular cylinder with linear springs and dampers. In this work, nonlinear snapping support is used to model nonlinearity in the system. To numerically simulate the flow, Reynolds-Averaged Navier–Stokes (RANS) equations for two-dimensional incompressible unsteady flows are applied. The degree of nonlinearity of the system can be changed by manipulating γ, which is one of the geometric properties of the spring and takes values between 0 and 1. The 0–1 test, Poincaré section, and Fast Fourier Transform are used to analyze the cylinder and lift force behavior. Also, the Hilbert transform is applied to the signals, and the phase shift between displacement and lift force is obtained. The results show that the system behavior consists of branches: branch I and branch II. The large amplitudes occur in branch II. It is found that chaos emerges at the beginning of branch II, regardless of the value of γ. By raising the γ value, the span of branch II becomes more expansive, and its first point is placed at lower reduced velocities. Also, the wake dynamics becomes more regular at the end of branch I and more irregular at the beginning of branch II with the increase in γ. When the cylinder displacement signal is chaotic, the lift force behavior is also chaotic, but not vice versa.

The physical structure of urban settlements has become increasingly vulnerable to hazards following the growing trends of natural hazards, including earthquakes. The concept of resilience has gained momentum to facilitate better planning and response to such hazards. This research seeks to develop a conceptual spatial framework considering different phases of disaster risk management to evaluate urban physical resilience. Twenty indicators that define urban structure are identified and included in an Interpretive Structural Modeling—Analytic Network Process (ISM-ANP) hybrid model for analysis. The model and the indicator weights are adjusted using statistical and optimization techniques. District 4 of Tehran has been selected as the study area, and the proposed evaluation framework is applied to several zones with different physical urban structures. According to the results, the most important indicators of urban structure are the Robustness of Buildings, Street Width, Building Density, and Aspect Ratio. Sensitivity analysis and scenario-making are performed to explore the desired state of urban physical resilience for each zone. The results of the case study indicate moderate levels of urban physical resilience. The study provides more clear and practical insights into the concept of resilience to help urban planners and decision-makers improve urban physical resilience.

This article introduces a method for the adaptive control of a six-dimensional (6D) hyperchaotic system using a multi-input multi-output (MIMO) approach, leveraging the deep deterministic policy gradient (DDPG) algorithm. The states and tracking errors of the hyperchaotic system are amalgamated to form an input image signal. This signal is then processed by a deep convolutional neural network (CNN) to extract profound features. Subsequently, the DDPG determines the coefficients of the proportional–integral–derivative (PID) controller based on the features discerned from the CNN. The proposed approach exhibits robustness to uncertainties and varying initial conditions, attributed to the DDPG’s ability to learn from the input image signal and adaptively adjust control policies and PID coefficients. The results demonstrate that the proposed adaptive PID controller, integrated with DDPG and CNN, surpasses conventional controllers in terms of synchronization accuracy and response speed. The paper presents the following: a 6D hyperchaotic system’s dynamic model, a CNN-based DDPG’s structure, and how it performs and compares to traditional methods. Then, it summarizes the main findings.

Objective To assess the impact of self-medication on the transmission dynamics of COVID-19 across different age groups, examine the interplay of vaccination and self-medication in disease spread, and identify the age group most prone to self-medication. Methods We developed an age-structured compartmentalized epidemiological model to track the early dynamics of COVID-19. Age-structured data from the Government of Gauteng, encompassing the reported cumulative number of cases and daily confirmed cases, were used to calibrate the model through a Markov Chain Monte Carlo (MCMC) framework. Subsequently, uncertainty and sensitivity analyses were conducted on the model parameters. Results We found that self-medication is predominant among the age group 15-64 (74.52%), followed by the age group 0-14 (34.02%), and then the age group 65+ (11.41%). The mean values of the basic reproduction number, the size of the first epidemic peak (the highest magnitude of the disease), and the time of the first epidemic peak (when the first highest magnitude occurs) are 4.16499, 241,715 cases, and 190.376 days, respectively. Moreover, we observed that self-medication among individuals aged 15-64 results in the highest spreading rate of COVID-19 at the onset of the outbreak and has the greatest impact on the first epidemic peak and its timing. Conclusion Studies aiming to understand the dynamics of diseases in areas prone to self-medication should account for this practice. There is a need for a campaign against COVID-19-related self-medication, specifically targeting the active population (ages 15-64).

This paper compares two methods for retrofitting an existing hospital concrete structure to improve its seismic performance: internal and external retrofitting. Internal retrofitting involves adding chevron braces, reinforcing shear walls with Fibre-reinforced plastic coating, and wrapping the walls, columns, and beams using steel jackets. External retrofitting uses two braced exterior steel frames connected to the concrete building using dampers. The paper also proposes a new design objective for hospital structures that ensures immediate occupancy performance level under earthquake hazard level-1 and prevents collapse under higher ground motion intensity. The paper evaluates the base structure, the two retrofitting schemes, and the proposed design method using pushover and nonlinear dynamic analyses under 20 selected earthquake records. The paper then compares the probabilistic seismic risk models using fragility curves. The results show that external retrofitting is more effective and economical than internal retrofitting and that the proposed design objective can significantly reduce the seismic risk of hospital structures.