Addressing Computational Complexity of Electromagnetic Systems Using Parameterized Model Order Reduction

As operating frequencies increase, full wave numerical techniques such as the finite element method (FEM) become necessary for the analysis of high-frequency and microwave circuit structures. However, the FEM formulation of microwave circuits often results in very large systems of equations which are computationally expensive to solve. The objective of this thesis is to develop new parameterized model order eduction (MOR) techniques to minimize the computational complexity of microwave circuits. MOR techniques provide a mechanism to generate reduced order models from the detailed description of the original FEM formulation. The following contributions are made in this thesis: 1. The first project deals with developing a parameterized model order reduction to solve eigenvalue equations of electromagnetic structures that are discretized by using FEM. The proposed algorithm uses a multidimensional subspace method based on modified perturbation theory and singular-value decomposition to perform reduction directly on the finite element eigenvalue equations. This procedure generates parametric reduced order models that are valid over the desired parameter range without the need to redo the reduction when design parameters are changed. This provides significant computational savings when compared to previous eigenvalue MOR techniques, since a new reduced order model is not required each time a design parameter is changed. 2. Implicit moment match techniques such as the Arnoldi algorithm are often used to improve the accuracy of the reduced order model. However, the traditional Arnoldi algorithm is only applicable to first order linear systems and can not directly include arbitrary functions of frequency due to material and boundary conditions. In this work, an efficient algorithm to create parametric reduced order models of distributed electromagnetic systems that have arbitrary functions of frequency (due to material properties, boundary conditions, and delay elements) and design parameters. The proposed method is based on a multi-order Arnoldi algorithm used to implicitly calculate the moments with respect to frequency and design parameters, as well as the cross-moments. This procedure generates parametric reduced order models that are valid over the desired parameter range without the need to redo the reduction when design parameters are changed and provides more accurate reduced order systems when compared with traditional approaches such as Modified Gram Schmidt. 3. This project develops an efficient technique to calculate sensitivities of microwave structures with respect to network design parameters. The proposed algorithm uses a parametric reduced order model to solve the original network and an adjoint variable method to calculate sensitivities. Important features of the proposed method are 1) that the solution of the original network as well as sensitivities with respect to any parameter is obtained from the solution of the reduced order model, and 2) a new reduced order model is not required each time design parameters are varied

Control Loop Interactions and Their Mitigation Schemes in VSC-HVDC Systems

In line with two goals of the United Nations, i.e., providing affordable and clean energy as well as combating climate change, various converter-interfaced renewable energy sources (RESs) are being integrated into the power systems. The transfer of renewable power generated by the RESs such as offshore wind farms to remote load centers may require the use of direct current (DC) lines, which are connected to the alternating current (AC) grid via AC-DC converters. In addition to facilitating the reliable connection of RESs to the power grid, high-voltage DC (HVDC) lines may be used for the transcontinental exchange of power to transfer power over long distances. One of the major challenges in the evolution of AC systems to hybrid AC-DC systems is the control of converters. Each converter station owns various control loops that require proper tuning in their stand-alone mode of operation. Furthermore, control loops of adjacent converters may also impact one another, and as a result, there must be coordination among the control design of converters to guarantee stability and appropriate dynamic response of the entire grid. The control loop interactions among the converters worsen with increasing the size of the system and the number of converters, especially when one converter station is already in operation and re-tuning the converter's controllers is not an option. Another important aspect of future AC-DC power grids is the employment of converters built by multiple vendors, who will take part in the development of converter controllers with unique designs and know-how. These independently designed controllers will form a part of the grid control system. In this scenario, the stability of the entire system is of great importance and needs to be verified due to control loop interactions. This thesis studies both internal and external control loop interactions in voltage-sourced converters (VSCs) embedded in AC-HVDC systems. This thesis, first, studies the internal control loop interactions, where the control loops within one single converter interact with one another, and develops a method to design the individual control loops within a VSC such that the converter stability is ensured. A metric is proposed to measure interaction levels, and the impact of interactions on set-point tracking capability is also investigated. This thesis, next, considers the connections among various converters either from the AC side or the DC side and studies the external control loop interactions among the adjacent converters. Regarding the external control loop interactions caused by DC side connections, suitable system models are introduced to enable individual control design for the converters in a multi-terminal DC (MTDC)-HVDC grid. As for the AC side external control loop interactions, two scenarios are considered: 1) the converters are in the grid-following (GFL) mode of operation, and 2) the converters are in the grid-forming (GFM) mode of operation. Regarding the GFL mode of operation, the impact of control modes on the interactions is studied, and the control modes causing the highest interaction levels are identified. A novel control design framework is designed to relate the control design of each converter to the interconnected system stability. The multi-vendor issue then is considered, and the interactions are mitigated by designing individual robust controllers or by employing interaction filters. The interaction analyses are then extended to the parallel connection of GFM converters and hybrid connections of GFL and GFM converters. Stability and coupling analyses are performed among GFL and GFR converters. small-signal stability of parallel GFM converters is proved, and real-time simulations and hardware-in-the-loop-test are performed for validating the studies

Cost-effectiveness of intensive Vs. standard follow-up models for patients with breast cancer in Shiraz, Iran

Background: Breast cancer is the most common type of cancer amongst women throughout the world. Currently, there are various follow-up strategies implemented in Iran, which are usually dependent on clinic policies and agreement among the resident oncologists. Purpose: A cost-effectiveness analysis was performed to assess the cost-effectiveness of intensive follow-up versus standard models for early breast cancer patients in Iran. Materials and methods: This cross sectional study was performed with 382 patients each in the intensive and standard groups. Costs were identified and measured from a payer perspective, including direct medical outlay. To assess the effectiveness of the two follow-up models we used a decision tree along with indicators of detection of recurrence and metastasis, calculating expected costs and effectiveness for both cases; in addition, incremental cost-effectiveness ratios were determined. Results: The results of decision tree showed expected case detection rates of 0.137 and 0.018 and expected costs of US24,494.62 and US6,859.27, respectively, for the intensive and standard follow-up models. Tornado diagrams revealed the highest sensitivity to cost increases using the intensive follow-up model with an ICER=US148,196.2. Conclusion: Overall, the results showed that the intensive follow-up method is not cost-effective when compared to the standard model

Predicton of interface level height of stratified liquid-liquid flow using artficial neural network

In this study, artificial neural network (ANN) was used to predict the interface level height (ILH) of two immiscible liquids flowing in a horizontal pipe. A three-layer feed-forward back-propagation (FFBP) neural network was constructed and trained with experimental data of two different liquid-liquid flow systems reported in the literature. The all studied flow patterns were stratified flow (stratified smooth and stratified wavy with or without droplets at interface ). The input parameters of the ANN model were superficial velocity of phases, pipe diameter, the ratio of the lighter phase density to the heavier phase density (ρlp/ρhp) and the ratio of the lighter phase viscosity to the heavier phase viscosity (μlp/μhp), while the interface level height (ILH) of phases was its output. The Levenberg–Marquardt (LM) algorithm, the hyperbolic tangent sigmoid and the linear activation functions were used for training and developing the ANN. Optimal configuration of the ANN model was determined using minimizing the mean absolute percent error (MAPE) and mean square errors (MSE) between experimental and predicted ILH data by the ANN model. The results showed that the optimal configuration was a network with five neurons in hidden layer that was highly accurate in predicting the interface level. MAPE and correlation coefficient (R) between the experimental and predicted values were determined as 1.8% and 0.9962 for training, and 1.52% and 0.9996 for testing date sets, respectively

Correlation between flocculation and adsorption of cationic polyacrylamides on precipitated calcium carbonate

The study of each stage of the flocculation process is essential to better understand and predict flocculation mechanisms. The adsorption of cationic polyacrylamide derivatives (C-PAM) onto precipitated calcium carbonate (PCC) has been investigated systematically as a function of the C-PAM characteristics including molar mass, chain architecture, and charge density. The adsorption results show that, for C-PAM of similar molar mass, highly branched architectures reach the equilibrium faster than linear C-PAM. Similarly, the flocculation rate is higher for the branched C-PAM, which may be indicative of the predominance of the bridging mechanism. In terms of the molar mass, lower molar mass leads to lower adsorption rates and slower flocculation. Adsorption isotherms of C-PAM onto precipitated calcium carbonate could be described by the Langmuir isotherm model. The maximum amount of C-PAM that adsorbs on the particle surface as a monolayer, obtained from adsorption tests through the Langmuir isotherm linear fit, could be correlated with the structure of the aggregates, obtained from flocculation experiments. Moreover, a good correlation was obtained between the adsorption results and the kinetics of the first stage of the flocculation process dominated by particle aggregation

Ekspresija mRNA agutiju srodnog peptida i mRNA melanokortin-4 receptora u arkuatnoj jezgri za vrijeme gravidnosti i laktacije štakorica.

Pregnancy is associated with a range of physiological adjustments to adapt the body to the demands of the growth of the fetus and subsequent lactation. It has been observed that agouti-related peptide (AGRP) and melanocortin-4 receptor (MC4R) are involved in energy homeostasis. A randomized controlled experimental study was planned to investigate the expression of AGRP and MC4R mRNAs in the stages of pregnancy and lactation in rat arcuate nucleus (ARC) of the hypothalamus. Thirty-two adult female rats were randomly divided into six groups. Pregnant rats were assigned into three groups (n = 6) of 7, 14, and 21 days of pregnancy. Two more groups were also assigned of non-suckling rats (n = 5), immediately separated from their pups after parturition, and suckling rats (n = 5), allowed to suckle five pups until day 8 (increasing milk). The sixth group consisted of four ovariectomized rats, which were assigned two weeks after surgery and served as control. Using real-time PCR, the relative expressions (compared to controls) of MC4R and AGRP mRNAs in ARC were calculated in the pregnant, suckling and non-suckling rats. Expression of AGRP mRNAs in pregnant rats on days 14 and 21 was higher than that observed in suckling and non-suckling rats (P<0.05). Expression of MC4R mRNAs in pregnant rats on days 14 and 21 was lower than that observed in suckling rats, and was higher on day 7 than that observed in both suckling and non-suckling rats (P<0.05). In conclusion, expression of AGRP in pregnancy and MC4R in lactation in ARC of rats controls energy homeostasis.Gravidnost je povezana s nizom fizioloških prilagodbi kojima tijelo odgovara zahtjevima povezanima s rastom fetusa i kasnije laktacije. Uočeno je da su agutiju srodan peptid (AGRP) i melanokortin-4 receptor (MC4R) uključeni u energetsku homeostazu. Randomiziranim kontroliranim pokusom planirano je u arkuatnoj jezgri (ARC) hipotalamusa štakorica istražiti ekspresiju mRNA AGRP i mRNA MC4R tijekom gravidnosti i laktacije. Trideset dvije odrasle štakorice nasumično su bile podijeljene u šest skupina. Gravidne su štakorice podijeljene u tri skupine (n = 6), s obzirom na 7., 14. i 21. dan gravidnosti. Još dvije skupine (n = 5) činile su nedojne štakorice koje su odvojene od svoje mladunčadi odmah nakon porođaja te dojne štakorice kojima je dozvoljeno dojenje 5 mladunaca do osmog dana rastuće laktacije. Četiri ovarijektomizirane štakorice, dva tjedna nakon operacije, dodijeljene su u 6. kontrolnu skupinu. Koristeći PCR u stvarnom vremenu, relativna ekspresija (usporedba s kontrolama) mRNA MC4R i mRNA AGRP u ARC izračunata je za gravidne, nedojne i dojne štakorice. Ekspresija mRNA AGRP kod gravidnih štakorica 14. i 21. dan bila je veća od one opažene kod dojnih i nedojnih štakorica (P<0,05). Ekspresija MC4R mRNA u gravidnih štakorica 14. i 21. dan bila je manja u odnosu na dojne štakorica i veća 7. dan u odnosu na skupine dojnih i nedojnih štakorica (P<0,05). Zaključno, ekspresija AGRP u ARC tijekom gravidnosti i MC4R u ARC tijekom laktacije kontrolira energetsku homeostazu štakorica

Promjene u RF-amidu srodnom peptidu-3 hipotalamusa i ekspresijama gena Kiss1 tijekom spermatogeneze kod štakora u uvjetima kroničnog stresa.

The effects were evaluated of chronic stress and the glucocorticoid receptor antagonist (RU486) on mRNA expressions of RF-amide related peptide-3 (RFRP-3) in the dorsomedial hypothalamic nucleus (DMH) and Kiss1 in the arcuate nucleus (ARC) of male rats. Twenty-four male rats were allocated to four equal sized groups: the stress, RU486, stress/RU486, and control groups. In the stress group the rats were restrained 1 hour/day for 12 days. In the RU486 group, the rats were injected with RU486 for 12 days. In the stress/RU486 group, the rats were injected with RU486 1 hour before the stress process for 12 days. Relative expressions of RFRP-3 and Kiss1 mRNAs were determined using real-time PCR. The relative expression of RFRP-3 mRNA in the stress group was higher than that in the RU486 and control rats. The relative expression of RFRP-3 mRNA did not differ between the stress group and the stress/RU486 rats. Furthermore, the relative expressions of Kiss1 mRNA in the stress, RU486, and stress/RU486 groups were less than that of the control rats. The relative expression of Kiss1 mRNA did not differ between the stress, RU486, and stress/RU486 groups. In conclusion, dysfunction in male rat fertility caused by the chronic stress may be the result of the increase in REFP-3 and the decrease in Kiss1 mRNA expression.Istražen je učinak kroničnog stresa i antagonista glukokortikoidnog receptora (RU486) na ekspresiju mRNA RF-amidu srodnog peptida-3 (RFRP-3) u dorzomedijalnoj jezgri hipotalamusa (DMH), te na ekspresije gena Kiss1 u arkuatnom nukleusu (ARC) štakora. Dvadeset i četiri štakora bila su raspodijeljena u četiri jednake skupine: stresna skupina, RU486 skupina, stresna/RU486 skupina i kontrolna skupina. U stresnoj skupini štakori su 12 dana bili obuzdani tijekom jednog sata dnevno. U skupini RU486, štakorima je tijekom 12 dana bio primijenjivan RU486. U skupini stres/RU486, štakorima je tijekom 12 dana apliciran RU486 jedan sat prije postupka obuzdavanja. Relativne ekspresije RFRP-3 i Kiss1 mRNA određene su lančanom reakcijom polimerazom u stvarnom vremenu. Relativna ekspresija RFRP-3 mRNA u stresnoj skupini bila je veća nego u skupini RU486 i kontrolnoj skupini. Relativna ekspresija RFRP-3 mRNA nije bila različita između stresne skupine i stres/RU486 skupine. Nadalje, relativne ekspresije Kiss1 mRNA u stresnoj skupini, skupini RU486, i stresnoj skupini/RU486 bile su manje u odnosu na kontrolnu skupinu. Relativna ekspresija Kiss1 mRNA nije se razlikovala između stresne skupine, skupineRU486 i stresne skupine/RU486. Zaključno, disfunkcija plodnosti kod štakora izloženih kroničnom stresu može biti uzrokovana putem povećane ekspresije RFRP-3 i smanjene ekspresije Kiss1 mRNA

Multi-walled carbon nanotubes modified with iron oxide and silver nanoparticles (MWCNT-Fe<inf>3</inf>O<inf>4</inf>/Ag) as a novel adsorbent for determining PAEs in carbonated soft drinks using magnetic SPE-GC/MS method

The synthesis of compounds with an excellent adsorption capability plays an essential role to remove contaminants such as phthalic acid esters (PAEs) with potential carcinogenic characteristics from different food products. In this context, for the first time, a novel adsorbent (MWCNT-Fe3O4/Ag) was synthesized by using iron (magnetic agent), and silver (catalytic and surface enhancer agent) to further approach in a magnetic SPE-GC/MS method for determining of PAEs in carbonated soft drink samples. The limit of detection (LOD) and limit of quantification (LOQ) values of MSPE-GC/MS were determined in six PAEs as a range of 10.8–22.5 and 36–75 ng/L, respectively. Also, the calibration curves of PAEs were linear (R2 = 0.9981–0.9995) over the concentration level of 10.000 ng/L and the recoveries of the six PAEs were ranging from 96.60% to 109.22% with the RSDs less than 8%. Moreover, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and transmission electron microscopy analyses (TEM) were utilized to characterize the produced MWCNT-Fe3O4/Ag. Based on the findings, the surface of MWCNT is relatively uniform, which became coarser after loading with Fe3O4/Ag particles. Also, EDX spectrum showed the carbon (C), iron (Fe), oxygen (O), Ag and copper (Cu) are the main components of synthesized MWCNTs-Fe3O4/Ag. The successful adhesion of Fe3O4/Ag on the texture of MWCNTs using a co-precipitation method was confirmed by XRD and FT-IR assays. Additionally, excellent crystallinity and clear lattice nanocrystals fringes of prepared MWCNT-Fe3O4/Ag was demonstrated by TEM analysis. Based on the obtained VSM images, the prepared sorbent (MWCNT-Fe3O4/Ag) has the good magnetic performance for magnetic separation and extraction processes. It was concluded that the synthesized MWCNT-Fe3O4/Ag could be used as an efficient adsorbent for determining contaminants such as PAEs in different beverage samples. © 201