1- Introduction

2- Methods

3- Results

4- Discussion

References

Abstract 

Background: Noninvasive cardiac output assessment is important for prognostication in patients with heart failure. Electrical velocimetry (EV), an impedance cardiography technique, can be used for noninvasive cardiac output assessment. The purpose of this study was to determine the feasibility, reproducibility and accuracy of cardiac output assessment by EV in adults with congenital heart disease (CHD). Methods: Cross-sectional study of CHD patients that had simultaneous cardiac output assessment by Fick and EV (using Cardiotronic monitor, Osypka Medical). We divided the cohort into: Group 1 patients (n = 54) had hemodynamic assessment at rest only, while Group 2 patients (n = 7) had assessment both at rest and peak exercise. Results: EV cardiac output assessment was feasible in 100% of the patients. There was good correlation between Fick-derived and EV-derived cardiac index (r = 0.89, p < 0.001) in Group 1. Among 26 patients in Group 1 that underwent cardiac output assessment pre- and post-intervention, there was no difference in the strength of correlation of Fick and EV cardiac output pre- and post-intervention (p-interaction 0.244) indicating good reproducibility of the technique. There was also modest correlation between Fick-derived and EV-derived cardiac index at rest (r = 0.68, p = 0.032), and peak exercise (r = 0.62, p = 0.055), in Group 2. Conclusion: In this study, we demonstrated the feasibility and accuracy of EV cardiac output assessment in adults with CHD. We also demonstrated, for the first time, that EV cardiac output assessment was reproducible under different loading conditions, and that EV can be used for the assessment of cardiac output augmentation at peak exercise.

Introduction

Congenital heart disease (CHD) is a common and understudied cause of heart failure [1,2]. Abnormal filling pressures and cardiac output are the hallmarks of heart failure, and are responsible for heart failure-related symptoms and morbidities [3–6]. The assessment and longitudinal monitoring of hemodynamic indices such as cardiac output, is therefore important for prognostication and titration of therapy in patients with heart failure [7,8]. Cardiac catheterization is the gold standard for cardiac output assessment [9,10]. However, it is invasive, and hence not ideal for longitudinal monitoring. Doppler echocardiography provides noninvasive assessment of cardiac output using the continuity equation [11]. However Doppler stroke volume calculation is based on geometric assumptions about the anatomy of the left ventricular outflow tract; and these assumptions may not always be valid in CHD patients with complex anatomy [7,8]. There are very limited data about the feasibility and accuracy of Doppler-derived cardiac output assessment in the setting of complex CHD [7,8], and this may be one of the reasons why this technique is not routinely applied in clinical practice in the CHD population. Electrical velocimetry (EV) is an impedance cardiography technique that provides continuous assessment of stroke volume and cardiac output by measuring the maximum rate of change of impedance to peak aortic blood acceleration [12].

1- Introduction

2- Stiffness matrices for fluid and anisotropic soil layers

3- Impedances of foundations on anisotropic soil

4- Rayleigh and Love waves in anisotropic half space

5- Vertical point load applied to layered half-spaces

6- Discontinuity seismic sources

7- Derivation of PML parameters

8- Summary and conclusion

References

Abstract

In this study, we introduce and discuss features and improvements of the well-established stiffness matrix method that is used in simulation of wave propagation in layered media. More specifically, we present stiffness matrices for an acoustic layer and a vertically transverse isotropic (VTI) viscoelastic soil layer. Combining these stiffness matrices enables a straightforward technique for modeling of acousto-elastic wave propagation in layered infinite media. In addition, we propose a technique to simulate discontinuity seismic sources, which was not used earlier in the context of the stiffness matrix method. Finally, we propose a framework to derive a key parameter of the absorbing boundary domain technique Perfectly Matched Layer (PML). Numerical examples are presented in order to help understanding the features and improvements discussed in the study from the fields of geophysics and soil dynamics. It is believed that the features and improvements discussed herein will make the application of the stiffness matrix method even wider and more flexible.

Introduction

The stiffness matrix method is a well-developed approach for simulating wave propagation in layered media, and has been successfully applied to various problems during the last decades (e.g. [1–3] and [4]). The method describes the wave motion in a layered medium in terms of symmetric and banded matrices and with straightforward and efficient solution procedure, producing the dynamic responses simultaneously at all layer interfaces and in all directions. The method has later been extended to acoustic layers ([5,6]). The discrete version of the stiffness matrix solution, called Thin-Layer Method (TLM), has also been developed and applied to various problems ([7–9]). Recently, TLM has been combined with the so-called Perfectly Matched Layer method (PML) that enables calculation of wave motion in infinite domains [10]. Despite these extensions, there are still features and improvements of the stiffness matrix method that could advance the use of the method in theoretical and applied problems. The present study introduces and discusses some of those features, including • Vertically transverse isotropic (VTI) soil layer stiffness • Discontinuity seismic sources • Derivation of PML parameters For completeness, first we present the acoustic layer stiffness matrices in forms that can be used in offshore or fluid-soil-coupled applications (e.g. seismic wave in the ocean environment). We introduce three different formulations in terms of vertical displacement, velocity potential and pressure. Each formulation has its own advantages and disadvantages. For example, the second and third formulations make it straightforward to implement the so-called air-gun source that is used as explosive acoustic source in offshore seismic surveys. This is because the air volume injected by the air-gun is explicitly defined in the two formulations, which are shown later. On the other hand, the first formulation is more suitable for applying vertical disk load on seabed or within water column, because the disk load can be represented by a term that can be set directly in the matrix equations. It is also shown that the three solutions are interrelated such that one can be derived from the other two through relevant constitutive laws. Next, the soil stiffness matrices for the vertically transverse isotropic (VTI) layers are derived for both P-SV (in-plane) and SH (antiplane) wave modes.

Background: Rheumatoid arthritis (RA) is a complex inflammatory disease that modifies body composition. Although body mass index (BMI) is one of the clinical 48 nutrition tools widely used to assess indirectly nutritional status, it is not able to identify these body alterations. Bioelectrical Vector Analysis (BIVA) is an alternative method to assess hydration and body cell mass of patients with wasting conditions. Objective: To investigate the differences in nutrition status according to BMI groups (normal, overweight and obesity) and BIVA classification (cachectic and non-cachectic) in women with RA. Methods: Women with confirmed diagnosis of RA were included from January 2015 to June 2016. Whole-body bioelectrical impedance was measured using a tetrapolar and mono-frequency equipment. Patients were classified according to BMI as: low body weight (n=6, 2.7%), normal (n=59, 26.3%), overweight (n=88, 39.3%) and obese (n=71, 31.7%), and each 58 group was divided into BIVA groups (cachectic 51.8% and non-cachectic 48.2%). Results: A total of 224 RA patients were included, with mean age 52.7 years and 60 median disease duration of 12 years. Significant differences were found in weight, 61arm circumference, waist, hip, resistance/height, reactance/height and erythrocyte sedimentation rate among all BMI groups. However, serum albumin levels were significantly different between cachectic and non-cachectic patients independently of BMI. In all BMI categories, cachectic groups had lower reactance and phase angle than non-cachectic subjects. Conclusion: RA patients with normal or even high BMI have a significantly lower muscle component. Evaluation of body composition with BIVA in RA patients could be an option for cachexia detection.

Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by inflammation, joint pain, and destruction of the synovial membranes [1]. Life expectancy of these patients can be reduced by an average of 3 to 18 years and 80% are disabled after 20 years [2, 3]. Metabolic alterations in RA due mainly to the liberation of tumor necrosis factor alpha and interleukin-1 beta can lead to rheumatoid cachexia, which is defined as “the involuntary loss of fat free mass (FFM) with minimal or not weight loss and increase or not of fat mass (FM)” which causes muscular weakness and loss of functional capacity. Also, the mean loss of FFM, present in almost two thirds of patients with RA, is between 13 and 15%. [4]. In clinical nutrition practice, a widely-employed tool used to evaluate body mass and hence nutritional status is the body mass index (BMI). However, its main  limitation is that is not able to identify rheumatoid cachexia alterations such as loss of FFM and gain of FM [5]. Several imaging techniques have been used to analyze body composition in RA patients. Currently, the most useful tool for measuring soft tissue mass and bone mineral density is dual X-ray absorptiometry (DXA) [6, 7]. Nevertheless, DXA is not always accessible and is sensitive to the patient’s hydration status [8] and also is associated with radiation exposure [9]. Therefore, a simple tool for identifying body composition alterations as rheumatoid cachexia in outpatient settings is necessary [10].

Introduction

Configuration of the proposed topology

Operating principle of the proposed inverter

Parameter design of passive and active components

Performance comparison with other high boost zsi topologies

Power loss analysis and efficiency comparison

Simulation and experimental results

Conclusion

References

Abstract

This paper proposes a new high boost quasi-Zsource inverter (qZSI) with combined two quasi-Z-source networks, which has a common ground between the input source and the inverter bridge. Compared with other non-coupled inductor-based (q)ZSIs, by using the same total number of passive and active components, the proposed inverter provides higher boost capability, requires smaller inductance and capacitance values at the impedance network, achieves lower voltage stress across the active switching devices, and has higher modulation index for the inverter bridge to improve the output waveform quality. Although the proposed inverter has the same voltage boost factor with the enhanced boost (quasi-)Z-source inverters (EB-ZSI and EB-qZSI), the proposed scheme has lower capacitor voltage stress than EB-ZSI and has higher efficiency than EB-qZSI. The topological configuration, operating principles, power loss analysis, and performance comparison with other high boost (q)ZSIs are presented. Finally, both simulations and experimental results are given to validate the aforementioned characteristics of the proposed topology.

Introduction

The traditional three-phase voltage source inverter (VSI) and current source inverter (CSI) are the most commonly used two kinds of pulse width modulation (PWM) inverter topologies. And, they have been widely used in many industrial applications such as uninterruptible power supply, ac motor drives, and hybrid electric vehicles [1]-[2]. However, both of them still exist some major problems. For the traditional VSI, its ac output voltage is always lower than the dc input voltage; thus, the VSI only performs a buck converter for the dc-ac power conversion. Similarly, the traditional CSI only performs a boost converter due to its ac output voltage is always greater than the original dc input voltage. For some applications where both voltage buck and boost capabilities are needed, an additional dc-dc converter will be required in VSI and CSI, which induces a two-stage power conversion, to obtain the desired ac output voltage. As a result, the volume and size of the whole system will be increased, leading to high weight, high cost and low overall efficiency[3]. To overcome the aforementioned limitations in traditional VSIs, a novel, simple and efficient design of Z-source inverter (ZSI) was firstly proposed by Peng in 2003[4], as shown in Fig. 1(a). By using the Z-source network, which consists of two inductors and two capacitors connected in an X-shape, to replace the traditional dc link in VSI, the ZSI can achieve both voltage buck and boost operating capabilities with a single-stage power conversion. In addition, both the semiconductor switches of each phase leg can be turned on simultaneously, which implies that the anti-interference ability of the inverter can be further improved, especially for the switches misgating-on caused by the electromagnetic interference noise.

In recent years, a numerous Multi-Level Inverter (MLI) topologies are proposed with reduced number of switches and control complexity. An Impedance source based MLI structure with ability of additional boost is proposed in this work. The proposed topology requires one source, one impedance network and reduced number of switches when compared to recently reported inverter literature. Due to Selfvoltage Balancing circuit (SBC), the fixed boost of 1.5 times the input and equal voltage across all the capacitors are achieved. An additional boost is obtained by placing impedance network between input source and SBC. The proposed Inverter is compared with existing topologies with respect to a number of sources, number of impedance networks, control switches, voltage balancing and boost capability. A simple level shifted based sinusoidal pulse width modulation technique is adopted for generating gate pulses. Further theoretical analysis and computer aided simulation results are validated with the experimental results.
2018 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Novel MLI topology has significant advancement in the field of power electronics, because of numerous advantages over conventional inverters. The conventional two level inverters are facing difficulty in meeting present scenario. The most popular conventional MLI structures are: Diode Clamped MLI (DCMLI), Flying Capacitor MLI (FCMLI) and Cascaded H Bridge MLI (CHMLI) [1–3]. In DCMLI, (n-1) capacitors are used as potential dividers, the voltage unbalancing across these capacitors is a serious concern. Additionally, it requires (n-1)(n-2) clamping diodes. For FCMLI, (n-1)(n-2)/2 bulky capacitors are required. In CHMLI, separate sources are required for each H Bridge and each bridge produces three levels. These H Bridges are connected in series for generating the required number of levels in output voltage where n is number of levels in output waveform. A numerous MLI topologies are proposed to address the drawbacks of conventional MLI’s. In recent years the focus is made on: Increasing the number of levels in output with asymmetrical voltage sources as reported in [4–6]. These inverters require more than one source with different voltage magnitudes. To obtain different voltages, different turn’s ratio transformers are used. The asymmetrical MLI requires DC sources with different magnitudes and switches of different rating. A few topologies are proposed by reducing the number of switches [4,7–9] and sources [10–12]. To reduce the number of input sources, series connected capacitors are used as a potential dividers. To achieve balanced voltage across all DC-link capacitors, a separate feedback circuit is used [13,14]. Inverter circuit will become complex due to this approach. With the conventional or transformer based MLI’s [15–18], in case of any shoot through or miss gating, entire circuit will get damaged. The cost and losses increases due to transformer present in the circuit. In aforementioned topologies, the maximum available voltage is limited by the input or DC link voltage. In applications like: Photovoltaic system, Electrical vehicles, Dynamic voltage restorer, etc. requires both boost and buck operations [19]. To meet this normally DC-DC converter or Z Source Inverter (ZSI) is used. If a DC-DC converter or Z Source network is integrated with MLI, then separate DC-DC converter or Z network is required across each source [20].

Battery powered energy systems such as electric vehicles utilize power electronics for controlling energy flows between the battery and the load or generation, respectively. Therefore, the battery is under high frequency stress due to fast switching power electronic devices. However, most battery models throughout the literature are not able to cope with high frequency excitation. This paper proposes an easy to implement equivalent circuit model that covers aforementioned frequency regions with a series of inductors that are each connected in parallel with an ohmic resistance. This circuit is parameterized by electrochemical impedance spectroscopy (EIS) up to 100 kHz. For further regions that reach regions of megahertz a skin effect model is investigated and compared to the RL-model. It is shown that such semi-empirical models can be motivated by geometrical considerations that can be found in the literature. Moreover, the proposed model is validated by simulating the voltage response from an input current that originates from an actual back-to-back half bridge DC/DC converter. The promising results indicate that such models might be implemented in future battery energy systems to improve insights on how batteries react to perturbations such as EMI noise or high frequency current ripple.

Introduction

It is commonly accepted that lithium-ion batteries are going to be a crucial factor for the energy transition from fossil fuels towards renewable energies regarding either the necessity to buffer fluctuating feed-ins from solar and wind power plants, improving grid quality and grid stability or as one feasible energy storage for electric mobility [1,2]. Given that distributed generation is an immanent feature of renewable energies, a paradigm shift towards new forms of electrical energy networks such as microgrids [3] has been initiated and batteries are commonly seen as a self-evident part of such smaller scaled networks to guarantee uninterrupted service or increase the degree of utilization of renewable power plants [4]. One example is to equip electric cars with back-to-back battery chargers [5] instead of the nowadays widely used unidirectional vehicle battery chargers [6] so that the car’s traction battery can be used as a backup storage which is known as the concept “vehicle to grid” (V2G) [7,8]. Regardless of all the aforementioned ideas being future concepts or already commercially available, they have one vital similarity: The design of energy systems cannot be done without taking power electronics into account. In principle, power electronic devices convert a mostly arbitrary current or voltage signal into another with power switches such as field-effect transistors (FET) or insulated gate bipolar transistors (IGBT) that are turned on and off periodically, e.g. controlled by pulse-width modulation (PWM) [9]. The switching frequency is within the magnitude of several kilohertz and therefore induces highfrequency noise and current ripple as shown for a half bridge based DC/ DC converter in Fig. 1. Thus, batteries that are connected to power electronics face highfrequency excitation. Therefore, a novel model that is able to represent a battery’s high-frequency behavior with a satisfactory explanation for its elements needs to be developed. In order to achieve a model that is easy to parameterize and is potentially simple enough to be implemented in online battery monitoring systems without inducing too much computational burden [10], two well established methods for modeling and parameterizing batteries, respectively, have been chosen.

The aim of this descriptive review is to summarise the current knowledge of non-invasive bioelectrical impedance analysis (BIA) used with gynaecological surgical patients in regard to postoperative development of lymphoedema and determination of perioperative fluid balance, and as a prognostic factor in cancer mortality and a predictor of postoperative complications. The databases PubMed, MEDLINE, Scopus Web of Science, the Cochrane Library, and reference lists of selected articles were searched for relevant articles published during the period January 2008–April 2018. Only papers published in English were retrieved. Thirty-seven articles were evaluated. Where gynaecological studies were lacking, studies with a study population from neighbouring clinical fields were used instead. Studies on the clinical use of BIA with gynaecological surgical patients were divided into three categories: the postoperative development of lower limb lymphoedema (n = 7), perioperative hydration measuring (n = 3), and the BIA parameter phase angle as a prognostic factor in cancer survival and as predictive for postoperative complications (n = 6). Of these 16 studies only three used a pure gynaecological study population. Three different methods of BIA were used in these articles: single frequency-BIA, multifrequency-BIA and bioimpedance spectroscopy. BIA was found to detect lymphoedema with a sensitivity of 73% and a specificity of 84%. Studies indicated that BIA was able to detect lower limb lymphoedema at an early stage even before it became clinically detectable. During postoperative hydration measurements, an increase in extracellular fluid volume and extracellular fluid volume in relation to total body fluid volume, as well as a decrease in phase angle, were associated with higher frequencies of postoperative complications. Moreover, low values for the phase angle have been associated with increased mortality in cancer patients. However, the number of studies in this field was limited. From our review, BIA seems to be a useful tool for use in the clinical setting of the gynaecological surgical patient. The theoretical approach of using bioelectrical impedance values to measure the fluid distribution in the body compartments offers wide opportunities in the clinical setting. However, so far, all studies have set up cut-off limits within the study population, and reference values for a general population need to be defined. There are also rather few studies on a gynaecological study population. Hence, there is a need for further studies within gynaecological surgery focusing on early detection of lower limb lymphoedema, perioperative fluid balance, and postoperative complications in order to establish the value of BIA in clinical praxis.

Introduction

Postoperative recovery without complications and longterm adverse side effects is the preference of all patients and the health care providers. However, for many reasons this goal is not always achievable, but substantial measures should be taken to minimise the risks for peri- and postoperative complications and adverse side effects of the treatment. Although many risk factors for postoperative complications and long-term adverse side effects are known, there is still a need for simple methods that, perioperatively, can predict and thus make it possible to prevent or restrict the development of these unwanted qualities. During the past two decades, bioelectrical impedance analysis (BIA) has become a useful tool in clinical research. As a noninvasive method, it provides an estimation of total body fluid volume (TBV) expressed as fat-free mass (FFM). Through its geometrically based algorithm, BIA gives information on extracellular fluid volume (ECV) and intracellular fluid volume (ICV). Body composition and hydration status contain valuable information about the patients’ well-being as several medical conditions are accompanied by changes in TBV, body cell mass (BCM), fat mass (FM), FFM, ECV and ICV. In this descriptive systematic review, we aimed to summarise the contemporary evidence of use of BIA in gynaecological surgical patients in studies published between 2008 and 2018. In particular, we highlighted the use of BIA for detection and prediction of lymphoedema and its use perioperatively for prediction of postoperative recovery. Where gynaecological studies have yet to be conducted in this field, we intended to give a theoretical reasoning regarding how the BIA method could be applicable in this patient category.

Melatonin, the ‘chemical signal of darkness’, is responsible to regulate biological rhythms and different physiological processes. It is mainly produced by the pineal gland as a hormone in a rhythmic daily basis, but it may also be synthesized by other tissues, such as immune cells, under inflammatory conditions. Its abnormal circulating levels have been related to several diseases such as type 2 diabetes, Alzheimer’s disease and some types of cancer. Currently, melatonin is exclusively quantified by ELISA or radioimmunoassays, which although are very sensitive techniques and present low detection limits, usually require specialized personal and equipment, restricting the tests to a limited number of patients. To overcome such limitations, we developed a novel easy-to-use electrochemical immunosensor for rapid melatonin quantification. Anti-melatonin antibodies were immobilized into Indium tin oxide (ITO) platforms using (3- Aminopropyl)triethoxysilane (APTES), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) crosslinkers. The platforms were assayed with synthetic and biologically-present melatonin containing samples. The developed device displayed a linear response in the concentration range from 0.75 to 7.5 µmol/L and a limit of detection of 0.175 µmol/L using Electrochemical Impedance Spectroscopy (EIS) (R2=0.989) and 0.513 µmol/L using Cyclic Voltammetry (CV) (R²=0.953) for synthetic melatonin. Furthermore, the sensors exhibited a good stability and reproducibility (3.45% and 2.87% for EIS and CV, respectively, n=3), maintaining adequate response even after 30 days of assembly. On biologically-present melatonin-containing samples the device displayed a similar performance when compared to ELISA technique (deviation of 13.31%). We expect that the developed device contributes significantly to the medical area allowing precise and complete diagnosis of the diseases related to abnormal levels of melatonin.

Introduction

Melatonin (N-acetyl-5-methoxy tryptamine) is an indoleamine present in most biological interfaces. In several species, melatonin plays important roles as a hormone and it is believed that its biological signaling is one of the oldest existing in nature.1 In humans, melatonin biosynthesis is rhythmically active in the pineal gland. Some other tissues, which includes the retina and gastrointestinal tract, may also synthesize melatonin in a rhythmic manner. 2 Melatonin may also be synthesized on demand by macrophages, lymphocytes and microglia when activated by pathogens or abiotic injuries.2-4 . Under normal conditions its maximum concentration in human plasma is about 50-200 pg/mL (0.22-0.86 nmol/L) during the night and lower than 2.0 pg/mL (8.6 pmol/L) at daylight, 5-7 which is in accordance with one of its major functions: translating environmental darkness to adjust endogenous physiology. Excretion of melatonin in the urine is also a pivotal marker of melatonin bioavailability. It is noteworthy to mention that melatonin can also be found in human saliva at concentrations ten times lower than in plasma, which highlights the possibility for the development of non-invasive and sensitive methods for detection of the indoleamine in different biological fluids. The idea that melatonin is only linked to the circadian rhythms or seasonal behavior was long challenged by the scientific community. In the last decades, intense efforts have been spent in understanding the influence of this hormone in other actions and physiological systems3,8-10 . For example, studies have shown that melatonin presents a very important role on the organization of the immune response11 . In this case, the hormone derived from the pineal gland is ceased but is locally produced by defense cells and acts locally, as regulator of the immune response. Also, under inflammatory frames, nocturnal pineal melatonin suppression favors the mounting of inflammation by allowing the rolling and adherence of leukocytes as well as its vascular permeability.

The electrochemical phenomenon of corrosion is a global source of deterioration of reinforced 35 concrete structures. In environments lacking chloride ions (chlorides), low-carbon steel reinforcing bars (rebar) embedded within concrete form a passive film due to the high pH (ca. 13 to 13.5) of the concrete pore solution and are generally not expected to exhibit any significant corrosion activity during the designed service life of a structure. However, external chloride ions, which originate from sources such as ocean saltwater or deicing salts placed on roadways, can permeate porous concrete cover layers and depassivate the steel rebar after a critical threshold of local chloride concentration has been reached at the rebar surface [1, 2]. After depassivation, corrosion activity of the steel rebar readily increases. As the volume of corrosion products is greater than the sum of the reactant volumes, internal expansion of these products causes concrete cracking [3], subsequently increasing the chloride solution permeability of the concrete 45 [4, 5] and reducing the mechanical performance of the composite [6, 7]. Premature replacement of damaged structures and associated mass consumption of additional construction materials is undesirable due in part to the high energy demands required for concrete production [8]. Because reinforced concrete degradation is dependent on the cracked state of the 49 composite matrix, research of novel crack-resistant construction materials has gained popularity in recent decades [9, 10]. In particular, hybrid fiber-reinforced concrete (HyFRC) is a candidate to reduce corrosion-induced cracking damage due to the mechanical toughening provided by the inclusion of different types of short (e.g., 8-mm to 60-mm long), discontinuous 53 fibers dispersed throughout its cementitious matrix [11, 12]. A crack-resistant concrete such as HyFRC is further advantageous considering that a primary functional purpose of reinforced concrete is to resist mechanical loads, requiring any new implemented construction material to be damage-tolerant against not only corrosion-induced cracking but also structural loading [13, 14]. An increase in the time to corrosion initiation was observed for reinforced HyFRC (i.e., HyFRC composite with embedded steel rebar) compared to reinforced concrete after subjecting samples to flexural stress [15, 16]. While a lower corrosion current density icorr of reinforced HyFRC was also measured compared to reinforced concrete, indicating favorable durability performance after active corrosion had begun, electrochemical characteristics of samples were limited to corrosion potential, polarization resistance, and corrosion current density based on assumed Stern-Geary coefficients. Several corrosion-related studies with different types of fiber reinforced concrete have utilized similar techniques [17-20], making detailed information from certain other electrochemical tests, such as Tafel polarization and electrochemical impedance 66 spectroscopy (EIS), rarely available for fiber-reinforced concrete composites.

By 2004, more than 485 suction anchors had been installed at over 50 different sites (Andersen et al., 2005). Most of these anchors are in clay, but some are in sand or layered soil. Examples of skirted foundations in sand are the offshore platforms at the Draupner E and Sleipner T sites in the North Sea (Tjelta, 1995). Recently there has arisen a salient trend in the construction of modern wind turbines with a slender design and more than 100 m in tower height; the natural frequencies of these rather novel structures are close to 0.2 Hz. Fig. 1 compares the average water depths for wind farms that are currently in the design phase. The transition to deeper water increases the span between the turbine superstructure and the seabed. Coupled with greater environmental loading from the highermagnitude wind and waves, the move to deeper water increases the moments applied to the foundations. While monopiles are attractive solutions for developers and designers alike, the increased water depth requires larger diameters with stiffer cross-sections. The monopiles used to date consists of a stiff pile of diameter of 4–6 m and embedment depths ranging from 20 to 30 m. In 2008, Ibsen reported the performance of a bucket foundation installed in Frederikshavn, Denmark as an attractive alternative foundation which can be used to increase the moment capacity (Ibsen, 2008). The bucket foundation, also referred to as “suction caisson”, is a large cylindrical monopod foundation, typically made of steel (Fig. 2) which has the potential to be a cost effective option in certain soil conditions. A bucket foundation typically requires less steel compared to a monopile, but fabrication costs are slightly higher due to the complicated lid structure (Table 1). However, the total cost, steel and fabrication, of a bucket foundation is likely to be less than of a monopile. Typical loading conditions for an offshore bucket foundation are illustrated schematically in Table 2. The loads are shown to be acting at the interface level between the foundation and the turbine shaft. An axial load of approximately 264 t act at this point. This foundation is an upside-down bucket made of steel with diameter D, skirt length d and skirt wall thickness t. A standard realscale foundation for a 5 MW wind turbine has D = 12–18 m, t ≈ 30 mm and embedment ratio ranging between 0.5 and 1. Motion of a bucket foundation will induce forces transmitted through the foundation-soil contact elements into the underlying deformable ground, which produce cyclic strains in terms of displacements and rotation of the foundation. Under a moderate to high amplitude of cyclic loading, most soils change stiffness and damping. In order to study the long-term performance and the uncertainties related to the dynamic response of these structures, the soil stiffness due to these cyclic strains must be taken into consideration. The current codes of practice (API, ISO and DNV) for the design of offshore foundations provide limited guidance for predicting changes in the foundation stiffness and the resulting changes in damping, which are important design drivers for serviceability limit state (SLS) and fatigue limit state (FLS) requirements.

Performance-Based Seismic Design (PBSD) approach embraces explicit assessment of the response of structural components with target building performance objectives. As shallow foundation exhibits inelastic behavior at the interface of the soil-foundation system upon excessive load, realistic assessment of cyclic inelastic rocking response of foundation is recommended [1,2]. Two mechanisms of nonlinearity take place between the soil and foundation; geometric nonlinearity (i.e. rocking response) and material nonlinearity (i.e. yielding of soil). The rocking response of shallow foundations has been one of the key research areas that has gained interest in recent years. Various experimental studies, such as a large-scale shaking table test of a bridge column [3], a small-scale shaking table test of a 3-storey building [4] and a centrifuge modelling of rocking-isolated inelastic RC bridge piers [5], have captured the rocking of the shallow foundation and found that this behavior reduces the residual drift and seismic demand of the structure. However, rocking shallow foundation may also experience large differential settlement during excessive cyclic loads which mainly result from yielding of near-field soil. On this basis, rocking of the foundation and yielding of soil should be carefully analyzed in the PBSD of shallow foundations [4,5]. There exists literature which provides guideline on modelling of shallow foundations. For example, ASCE 41-13 [6] provides a component action table with modelling parameters and acceptance criteria for nonlinear and linear analysis of shallow foundations. The values in the component action tables for nonlinear analysis procedures are based on the analysis of rocking shallow foundation, which was observed from experimental model tests. For the linear analysis procedure, the empirical coefficient, m-factor, is revised to reflect the allowable rotation of the rocking foundation from the nonlinear analysis procedure [7]. Unlike ASCE 41-06 [8] where rocking foundation and yielding at the soil-foundation interface are uncoupled and checked separately, ASCE 41-13 [6] considers the coupled behavior of foundation rocking and yielding of the soil. This approach is more realistic as the failure of the foundation is governed by stiffness degradation and yielding of the soil [9]. Kutter et al. [7] provided a rationale for the revisions made in ASCE 41-13 for rocking shallow foundation and validated these revisions with extensive experimental results [7,10]. The numerical modelling of dynamic soil-structure interaction (SSI) between an inelastic soil domain and a structural model for shallow foundation is a complicated task. The model entails an infinite soil domain, interface property between the structural foundation and soil, and verification and benchmark analysis. The Finite Element (FE) analysis is a rigorous method which is able to model the infinite soil domain with an arbitrary geometry and diverse soil layers. However, special measures should be taken to accurately model the boundaries of the numerical model. The scattered waves from a structure should be dissipated or absorbed at the boundaries in order to avoid the wave reflection. This means that the numerical domain should be large enough to avoid the negative effects of the reflected wave to the structural responses.

In distribution systems, High Impedance Faults (HIFs) occur due to downed live conductors connected to a high impedance ground surface or unbroken conductor touching leaning tree. This contact restricts the current value between 0 and 75 A depending on the high impedance surface [1]. The conventional relays are incapable of detecting currents with these low magnitudes. In this context, fallen live conductors pose a threat to humans and their property. HIFs in distribution systems often generate fires and cause loss of power supply to consumers. Therefore, HIF detection has now become a big issue for power utilities. In this work, a 11 kV system is chosen because a huge number of HIFs come with supply voltages of 15 kV or less, with the difficulty faced in HIF detection being worse at lower voltages. The difficulty is less severe above 15 kV, but HIFs can occur at these voltages as well [1]. The HIF phenomena and detection methods are comprehensively documented in [2]. The method proposed in [3] measures and analyzes the harmonic content to understand what extent this is useful in HIF detection. Another method based on the concept of fractal geometry analyzes chaotic properties of fault current [4]. The primary problem with these methods is setting a threshold, which affects the performance of the detection method. A reliable detection scheme using time-frequency analysis for feature extraction is in [5,6]. Time-frequency analysis is highly sensitive to a non-stationary signal and shows good performance in all the detection criteria. However, the time consumed during the computations raises a question about the utilization of this method in protection applications. The Wavelet Transform (WT) method is capable of processing the signal by analyzing low- and high-frequency components. A method based on WT detects HIF using wavelet decomposed coefficient of a voltage signal [7,8]. Both voltage and current signal features are extracted using wavelet packet transform for detection and discrimination of HIF [9]. The standard deviation of detail and approximation coefficient of level 3 [10] and level 7 [11] of db4 mother wavelet is used for the detection process. In addition to WT feature extraction, Principal Component Analysis (PCA), Bayes classifier [12,13] and fuzzy inference system [14] are used for classification into HIF and non-HIF. WT provides a better resolution in signal processing. However, high computational burden, high sampling rate and memory space requirements restrict the use of this method in protection applications. In [15], the amplitude and phase information of HIF current signal is proposed. Mathematical Morphology (MM) [16,17] was recently employed in HIF detection and the method needs an enhancement.

In ancient times, thunder, lightning and electric fish [1] were the natural phenomena related to electricity. They were treated as myths, but not as energy until the discovery of electrostatic phenomena by Thales of Miletus in 640–540 BCE [2,3]. Much later in 1752, B. Franklin discovered electricity [4], and in 1820 H.C. Örsted revealed electromagnetism [5]. Since then, a series of great discoveries on the principles of electricity and magnetism has been achieved by Volta, Coulomb, Gauß, Henry, Faraday and others, leading to many inventions such as batteries (1800), generators (1831), electric motors (1831), telegraphs (1837) and telephones (1876), to name just a few. In the early 19th century electricity has been established as a scientific discipline, and in the late 19th century the greatest progress has been witnessed in electrical engineering [6]. In 1882, the first power grid, which was a direct-current (DC) distribution system invented by T. Edison, was set up in New York to provide 110 V DC power supplying over 1000 bulbs in a short distance. At that time, the problem was how to transfer energy at a low loss from power plants to customers over a long distance through transmission lines [7]. It is now well known that electricity must be transmitted at high voltages and in the form of alternating current (AC), because DC voltage could not be increased or decreased by DC systems at that time [8]. In 1885, L. Gaulard and J.D. Gibbs developed a device named transformer, which can increase or decrease the electrical voltage of AC systems. Thereafter, G. Westinghouse applied transformers in AC distribution systems to transmit electricity efficiently over long distances, which has promoted the development of electrical engineering [5]. Transformers played a vital rôle in electricity transmission, especially in energy conversion between different voltages. Transformers can, however, only increase or decrease AC voltage (AC-AC) at the same frequency. Moreover, energy loss in transformers, magnetic radiations, huge volume and high cost of copper limited their wider use [9]. In practical applications, electric energy was expected to be converted from one form to another, for instance, between AC and DC, or just to different voltages or frequencies, or some combinations of those — demands that cannot be fully met by transformers. Therefore, novel techniques were required to solve those problems. With the development of semiconductor switches, power electronics has come into being [10]. Power electronics refers to electric power, electronics and control systems. Electric power deals with static and rotating power equipment for generation, transmission and distribution of electric power; while electronics is concerned with solid-state semiconductor power devices and circuits together with control systems for power conversion specified to meet the desired control objectives. Power electronics is one of the main technologies to realise energy conversion with high efficiency. It is known that about 70% of electric energy is converted by power electronics devices before it reaches the consumer. Nowadays, power electronics has become a fundamental technology critical for the development of energy conservation, especially for renewable energy [11]. The history of power electronics is linked to the breakthrough and the evolution of power-semiconductor devices.