Influence Of Dynamic Changes Research Articles

Variable Power Tracking Control Strategy of Doubly Fed Induction Generators for Fast Frequency Responses

Frequency regulation and droop control of doubly fed induction generators (DFIGs) can quickly respond to frequency changes and reduce the maximum rate of frequency (MROFF) in power systems. However, due to real-time dynamic changes in the MPPT control loop, the ability to improve the lowest frequency point is limited. Therefore, this article first describes an in-depth analysis of the dynamic characteristics of the incremental power of frequency regulation with droop control using an equivalent linear model. The limitations of improving the lowest frequency point under the influence of dynamic changes in the MPPT control loop are revealed. Secondly, to address the impact of these dynamics, an improved decoupling frequency regulation (IDFR) strategy based on power tracking is proposed, aiming to increase the maximum frequency deviation (MFD) and MROCOF. Then, in order to overcome the difficulty of adjusting control coefficients in the IDFR strategy, an adaptive control coefficient tuning fuzzy control method based on frequency deviation and ROCOF was proposed to flexibly adjust control requirements under various working conditions, thereby improving the control stability and performance of the system and effectively solving the problem of control coefficient allocation. Finally, to verify the frequency regulation performance of the proposed IDFR strategy under various operating conditions, simulations were conducted based on different disturbances and wind conditions. The results show that the proposed IDFR strategy significantly improves the system MFD and MROCOF improvement ability under various conditions.

A150 DEVELOPMENT OF MIMETIC MATRICES AS INSTRUCTIVE ORGANOIDS MICROENVIRONMENT FOR THE STUDY OF COLONIC DISEASES

Abstract Background The functional complexity of the colonic epithelium is dependent on its interaction with the microenvironment involving gradients of soluble factors, extracellular matrix (ECM) proteins and stiffness. The influence of dynamic changes in the ECM has been observed in tumours, with variations in protein expression and rigidity. Their biomolecular impacts on epithelial cell behaviour are less studied due to the structural complexity of the matrix. Organoids offers a novel approach for the study of ECM biodynamics, as they require a matrix (Matrigel) to develop. Previous work showed that it is possible to grow organoids in hydrogels other than Matrigel. To evaluate the effect of matrix composition alteration on cancer initiation, we developed biofunctionalized composite hydrogels that mimic the ECM changes (chemical and physical) observed in the BmpR1a-deficient telocytes Foxl1 + (Bmpr1a△Foxl1+) mouse model of colorectal cancer (CRC) initiation. Aims The development of mimetic matrices, in association with organoids, would enable us to uncover the impact of matrix deregulation on colonic cells behaviour in pathogenesis process. Methods These hydrogels were made of alginate and 8-arm polyethylene glycol- vinyl sulfone (PEG) macromers bearing cysteine residues (CYS) and peptides. Four peptides derived from fibronectin, laminin 111, collagen I and collagen IV were used to mimic the ECM changes in the Bmpr1a△Foxl1+ colon. The grafting of CYS on alginate or peptides on PEG macromers was first characterized by thiol quantification assays. The non-grafted peptides were also analysed by uHPLC. Stiffness of the hydrogels was then determined by dynamic mechanical analysis. Finally, normal mouse organoids were seeded on hydrogels and evaluated for survival by live/dead labeling and proliferation by Alamar blue assays. Matrigel was used as a control. Results Chemical characterization revealed that CYS were grafted onto the alginate chain at around 190 μmol/g alginate. The PEG macromers were functionalized with four peptides at concentration varying from 0.25 to 1.5 mM. Rigidity of the hydrogels depends on the concentration of alginate used where lower concentration leads to soft matrix (0.5 kPa, homeostasis) and high concentration produced a stiff matrix (4 kPa, diseased). Organoids seeded in these mimetic composite hydrogels survived and proliferated in comparison to alginate alone. Conclusions Our results indicate that we can develop mimetic composite hydrogels where colon organoids can survive and thrive. This is a breakthrough model for defining the roles of ECM mechanical and biochemical stimuli in epithelial behaviour during the initiation and development of CRC. Funding Agencies CIHR

Dynamic scheduling for flexible job shop using a deep reinforcement learning approach

Due to the influence of dynamic changes in the manufacturing environment, a single dispatching rule (SDR) cannot consistently attain better results than other rules for dynamic scheduling problems. Dynamic selection of the most appropriate rule from several SDRs based on the Deep Q-Network (DQN) offers better scheduling performance than using an individual SDR. However, the discreteness of action space caused by the DQN and the simplicity of the action as an SDR limit the selection range and restrict performance improvement. Thus, in this paper, we propose a scheduling method based on deep reinforcement learning for the dynamic flexible job-shop scheduling problem (DFJSP), aiming to minimize the mean tardiness. Firstly, a Markov decision process with composite scheduling action is provided to elaborate the flexible job-shop dynamic scheduling process and transform the DFJSP into an RL task. Subsequently, a composite scheduling action aggregated by SDRs and continuous weight variables is designed to provide a continuous rule space and SDR weight selection. Moreover, a reward function related to mean tardiness performance criteria is designed such that maximizing the cumulative reward is equivalent to minimizing the mean tardiness. Finally, a policy network with states as inputs and weights as outputs is constructed to generate the scheduling decision at each decision point. Also, the deep deterministic policy gradient (DDPG) algorithm is used to train the policy network to select the most appropriate weights at each decision point, thereby aggregating the SDRs into a better rule. Results from numerical experiments reveal that the proposed scheduling method achieves significantly better scheduling results than an SDR and the DQN-based method in dynamically changeable manufacturing environments.

Study on Obtaining Real Power Curve of Wind Turbines Using SCADA Data

The key problem to be solved in the process of wind turbine (WT) operation and maintenance is to obtain the wind turbine performance accurately. The power curve is an important indicator to evaluate the performance of wind turbines. How to model and obtain the power curve of wind turbines has always been one of the hot topics in research. This paper proposes a novel idea to get the actual power curve of wind turbines. Firstly, the basic data preprocessing algorithm is designed to process the zero value and null value in the original supervisory control and data acquisition (SCADA) data. The moving average filtering (MAF) method is employed to deal with the wind speed, the purpose of which is to consider the comprehensive result of wind on the wind turbine power in a certain period. According to the momentum theory of the ideal wind turbine and combined with the characteristics of the anemometer installation position, the deviation between the measured wind speed and the actual wind speed is approximately corrected. Here, the influence of dynamic changes in air density is also considered. Then, the Gaussian fitting algorithm is used to fit the wind-power curve. The characteristics of the power curve before and after wind speed correction are compared and analyzed. At the same time, the influence of the parameter uncertainty on the reliability of the power curve is considered and investigated. Finally, the characteristics of the power curves of four wind turbines are compared and analyzed. The research results show that among these power curves, WT3 and WT4 are the closest, WT2 is the next, and WT1 has the farthest deviation from the others. The research work provides a valuable basis for on-site performance evaluation, overhaul, and maintenance of wind turbines.

The Impact of Knowledge Management Capabilities on Innovation Performance from Dynamic Capabilities Perspective: Moderating the Role of Environmental Dynamism

As an important path to enhance the innovation performance of enterprises, knowledge management has received much attention in recent years. However, most of the existing literature on knowledge management and innovation performance is based on a static perspective, and ignores the influence of dynamic changes in the environment. This study intends to explore the relationship between dynamic knowledge management capability and innovation performance as well as examine the moderating effect of environmental dynamism. The questionnaire survey approach is used in this study and the data is collected from 253 sample enterprises in China. To estimate the proposed relationships in the theoretical model, this study adopts hierarchical Multiple Regression (MR) and Moderated Multiple Regression (MMR) methods. The results show that all dimensions of dynamic knowledge management capability have different degrees of positive influence on innovation performance. Moreover, it was also confirmed that there are different moderating effects of environmental dynamism on the relationship between the dimensions of knowledge management capability and innovation performance. This study can contribute to enriching the theoretical research of dynamic knowledge management capability and innovation performance, and offer scientific guidance for decision making to efficiently enhance the enterprise’s knowledge management level and innovation performance. Moreover, the findings can also provide valuable insights for enterprises to make use of KM capabilities to enhance innovation performance in practice.

Influence of dynamic changes of workplace on organisational culture – ADDENDUM

Influence of dynamic changes of workplace on organisational culture – ADDENDUM

Influence of dynamic changes of workplace on organisational culture

AbstractChallenged by the effects of organisational flexibility and high corporate real estate costs, organisations are increasingly seeking flexibility and operational efficiency in their office spaces. To date, the literature relating to flexible office spaces has focused mainly on their physical characteristics. The full effects of such spaces on human reactions and the corporate culture of organisations are less understood. The objective of this paper is to examine the influence of introducing activity-based working (ABW) on existing organisational culture. It was addressed from the perspective of the management of large corporate organisations. A mixed-method research that included a qualitative approach followed by a quantitative approach was adopted. The first stage included semistructured interviews with 19 large organisations who had introduced flexible layouts. The second stage involved a questionnaire survey of 32 organisations which had experienced office layout changes. Findings identify that the nature of workplace designs has a considerable impact on the corporate culture of an organisation and can be used to leverage and change its culture. Workplace designs directly influence culture by supporting the systems, symbols, engagement/motivation and behaviours of the organisation and employees. However, some differences between the perceptions of public and private organisations were identified. In conclusion, office layouts are artefacts that can either support, or change, the existing organisational culture. Therefore, the critical achievement of workspace design is to integrate the cultures, values and behaviours of organisations to meet their ultimate goals.

Clinical Associations of Preoperative and Postoperative Serum CEA and Lung Cancer Outcome.

Background: Serum carcinoembryonic antigen (CEA), a classic tumour marker, is widely used in lung cancer in clinical practice. Nevertheless, few studies have elucidated the influence of dynamic changes in CEA in the perioperative phases, as a prognostic indicator, on lung cancer prognosis. Methods: This retrospective cohort analysis included consecutive patients with stage I-III lung cancer who underwent curative resection between December 2010 and December 2014. The patients were grouped into three cohorts: group A included patients with normal preoperative CEA, group B included patients with elevated preoperative CEA but normal postoperative CEA, and group C included patients with elevated preoperative and postoperative CEA. Five-year overall survival (OS) was estimated by Kaplan-Meier analysis (log-rank test). Multivariate analyses were performed with Cox proportional hazard regression. Results: A total of 1662 patients with stage I-III lung cancer were enrolled in our study. Patients with normal preoperative CEA had 15.9 and 20.1% better 3- and 5-year OS rates than the cohort with elevated preoperative CEA (p < 0.001). Furthermore, group C had 36.0 and 26.6% lower 5-year OS rates (n = 74, 32.4%) than group A (n = 1188, 68.4%) and group B (n = 139, 59.0%) (p < 0.001). Group B had poorer OS than group A (p = 0.016). For patients with different pathological TNM stages, subgroup analyses showed that group C had the shortest OS in stages I and II (p < 0.05), and patients with a post-preoperative CEA increment had poorer OS than those without an increment (p = 0.029). Multivariate analyses suggested that group C (HR = 2.0, 95% CI, 1.5–2.7, p < 0.001) rather than the group with normalized postoperative CEA (HR = 1.2, 95% CI, 0.9–1.5, p = 0.270) was an independent prognostic factor. In subgroup analysis of adenocarcinoma (ADC), survival analyses suggested that group C predicted a worse prognosis. Multivariate analysis of ADC indicated that group C was an independent adverse prognostic factor (HR = 1.9, 95% CI, 1.4–2.7, p < 0.001). Conclusions: Combined elevated preoperative and postoperative CEA is an independent adverse prognostic factor for stage I-III lung adenocarcinoma. Additionally, routine perioperative detection of serum CEA can yield valuable prognostic information for patients after lung cancer surgery.

Models Based on Dynamic Clinicopathological Indices for Predicting Prognosis During the Perioperative Period for Patients with Colorectal Cancer.

BackgroundRecent studies have found that clinicopathological indices, such as inflammatory and biochemical indices, play a significant role in the prognosis of colorectal cancer (CRC) patients. However, few studies have focused on the effect of dynamic changes in these indicators. In our study, we studied the influence of dynamic changes in inflammatory and biochemical indices on patient outcomes during the perioperative period.MethodsWe enrolled 551 patients from Hubei Cancer Hospital who had undergone radical resection of CRC and collected the results of laboratory examinations performed within 1 week before surgery and at the first admission after surgery. The whole population was randomly divided into the training (386) and testing (185) cohorts. We used postoperative inflammatory and biochemical indices/preoperative inflammatory and biochemical indices (ΔX) to reflect the dynamic changes. Chi-square tests, Kaplan–Meier survival analyses, and univariate and multivariate Cox regression analyses were used to evaluate the prognosis. The prediction accuracies of models for overall survival (OS) and disease-free survival (DFS) were estimated through Harrell’s concordance index (the C-index) and Brier scores. Nomograms of the prognostic models were plotted for evaluations of individualized outcomes.ResultsThe median follow-up time of the 551 patients was 35.6 (range: 1.1–73.8) months. Ultimately, the prognostic models based on age, sex, TNM stage, pathological conditions, inflammatory and biochemical indices, CEA, and CA199 were found to have exceptional performance for OS and DFS. The C-index of the nomogram for OS was 0.806 (95% CI, 0.75–0.86) in the training cohort and 0.921 (95% CI, 0.87–0.96) in the testing cohort. The C-index of the nomogram for DFS was 0.781 (95% CI, 0.74–0.82) in the training cohort and 0.835 (95% CI, 0.78–0.88) in the testing cohort.ConclusionWe successfully established a novel model based on inflammatory and biochemical indices to guide clinical decision-making for CRC.

Threats to the economic security of the state under conditions of globalization

Today, the influence of dynamic changes in geopolitical and geo-economics’ conditions requires new requirements to ensure the national security of the state and its sustainable development. One of the central places in the structure of the national security of Ukraine is its economic security, which guarantees the independence of the country, the conditions of stability and effective functioning of society. In this regard, tracking of trends in the economic sphere, detection of the main risks and threats to economic security, identification of measures dealing with reduction of their negative impact are relevant both from a scientific and practical point of view. This article considers the key threats to the economic security of the state in the context of globalization, the long-term influence of which reduces the economic security of the state, makes it vulnerable to external challenges, and significantly weakens its position on the world stage.The importance of ensuring the state economic security and counteracting the negative impact of threats that may harm it has been proved. It has been noted that ensuring of economic security is a priority of the state. The essence of economic security of the state and its importance for national security in general has been described. The current legislative documents, which identify the main real and potential threats to the national security of Ukraine at the present stage, including in the economic sphere have been considered. The interference of threats to the state economic security, which are divided according to the scope of their occurrence into internal and external, has been assessed. It has been determined that external threats are associated with adverse processes in the world economy, and internal threats are dealing with the activities of public authorities, macroeconomic and microeconomic instability of the market economy, they are stipulated to those processes that occur during economic policy. It has been noted that the current conditions for the development of the state security, due to new challenges and threats, need to improve and implement new measures to combat the negative influence of major threats to the national economic security. As a result of the study, the main measures to counter the main threats to the state economic security were identified.

Weight gain during early adulthood, trajectory of body shape and the risk of nonalcoholic fatty liver disease: A prospective cohort study among women

Background & aimsObesity is established as a major risk factor for the development of nonalcoholic fatty liver disease (NAFLD). However, the influence of dynamic changes in adiposity over the life course on NAFLD risk remains poorly understood. MethodsWe collected data from 110,054 women enrolled in the Nurses' Health Study II cohort. Early adulthood weight was ascertained at age 18 years, and weight gain since early adulthood was defined prospectively every 2 years. We used a group-based modeling approach to identify five trajectories of body shape from age 5 years up to age 50 years. NAFLD was defined by physician-confirmed diagnoses of fatty liver, after excluding excess alcohol intake and viral hepatitis, using validated approaches. ResultsWe documented 3798 NAFLD cases over a total of 20 years of follow-up. Compared to women who maintained stable weight (±2 kg), women with ≥20 kg of adulthood weight gain had the multivariable aHR of 6.96 (95% CI, 5.27–9.18), and this remained significant after further adjusting for early adulthood BMI and updated BMI (both P trend <0.0001). Compared to women with a medium-stable body shape trajectory, the multivariable aHRs for NAFLD were, 2.84 (95% CI, 2.50–3.22) for lean-marked increase, 2.60 (95% CI, 2.27–2.98) for medium-moderate increase, and 3.39 (95% CI, 2.95–3.89) for medium-marked increase. ConclusionsBoth early adulthood weight gain and lifetime body shape trajectory were significantly and independently associated with excess risk of developing NAFLD in mid-life. Maintaining both lean and stable weight throughout life may offer the greatest benefit for the prevention of NAFLD.

The influence of dynamic changes in lipid metabolism on survival outcomes in patients with metastatic renal cell carcinoma treated with tyrosine kinase inhibitors.

The role of lipid metabolic status in tyrosine kinase inhibitors-treated patients with metastatic renal cell carcinoma is insufficient. To analyse the influence of dynamic changes of lipid metabolism on survival outcomes in tyrosine kinase inhibitors-treated metastatic renal cell carcinoma. Serum levels of triglycerides, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol were collected, both before tyrosine kinase inhibitors therapy and at different time points of tyrosine kinase inhibitors treatment duration. Other clinicopathological and survival data were retrospectively reviewed. The clinical outcomes, including tumour response, progression-free survival and overall survival, were analysed. Kaplan-Meier survival curves were plotted and the log-rank test was used to analyse statistical significance. A total of 127 patients with metastatic renal cell carcinoma, initially treated with tyrosine kinase inhibitors as first-line systemic therapy, were included. In the whole cohort, the serum levels of triglycerides, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol fluctuated but gradually increased during tyrosine kinase inhibitors treatment. In survival analysis, the higher serum level of lipid metabolism, the longer progression-free survival was observed. In terms of overall survival, all post-treatment lipid metabolism, including the percentages of increasing change, were correlated with better survival. Further multivariate analysis showed that patients with five components of treatment-related dysfunction of lipid metabolism had superior survival to those with less than five components. However, lipid metabolism was not correlated with tumour response. Increasing parameters of lipid metabolism indicated improvement of survival in tyrosine kinase inhibitors-treated metastatic renal cell carcinoma, especially the increasing percentages.

Intensified mid-Holocene floods recorded by archeomalacological data and resilience of first farming groups of the Carpathian Basin

One of the most significant cultural transformations in European prehistory occurred in the middle of the 6th millennium BC in the heart of the Carpathian Basin. The northward expansion of Mediterranean farming groups (Starčevo-Körös-Criş cultural complex) halted and underwent a complete transformation giving rise to a new cultural group carrying an altered form of Neolithic traditions onward to Europe. This transformation is restricted to sites along a boundary found in the heart of the basin, north of which unfavorable ecological conditions hampered a long-term engagement in a Mediterranean type of agriculture. The majority of Early Neolithic Körös sites in eastern Hungary are confined to the alluvial plain of the Tisza River prone to natural biannual flooding. These wetland conditions were marginal for early farmers as it contained several elements that were hostile for herded animals and these groups were not adopted to cope with. Körös Culture pastoralists responded to these challenges posed by the new environment by complementing their diet with opportunistically exploited wild resources. This type of resilience of the first farmers seen in the alteration of traditional subsistence strategies was simply attributed to the static hostile conditions of the environment alone. Influence of dynamic changes in the hydrology has not been studied and documented so far. This paper presents a multiproxy archeomalacological approach to establish a mid-Holocene flood record in Southern Central Europe and assess the potential impacts of flood frequencies, climate change-induced higher floods on economic, societal development of the first farming groups from the heart of the Carpathian Basin. Based on our findings, intensified use of second-line subsistence resources marking resilience is coeval with intensified flooding during the second phase of cultural evolution preceding transformation. This marked transformation could have been traced regionally as well along the referred northern distribution line and is coeval with the initial phase of a minor climatic perturbation refered to as the IRD 5.b event. The southward expansion of cold waters in the North Atlantic yielded intensive cyclonic activity bringing more rain and cold weather to W Europe. In Hungary, higher continentality provided by the basin setting preserved warmer conditions. Nevertheless, increased rainfall onto the watershed of major rivers triggered heightened floods.

Power Spectra of Doppler Response Signals from Biological Objects Using Synthetic Aperture Ultrasound

The influence of dynamic change in the steering angle of incident and scattered wave beams on the spectra of the ultrasonic Doppler response is studied on the basis of the previously developed continuum model of ultrasound waves scattering in biological objects for the case, when the Doppler response signals are averaged over the period of changing the steering angle. A general expression is obtained, which combines the resultant spectrum of the power of the ultrasonic Doppler response signal from the region of interest, the spectral characteristics of the ultrasound scatterers movement, and the sensitivity function of the diagnostic synthetic aperture system. It is shown that, as compared to the Doppler response, which is a sequence of discrete values of the response signals from different steering angles, the use of averaging allows to reduce the width of the Doppler spectra without deterioration of their resolution. It is concluded that the achievement of better spatial resolution, when using the synthetic aperture method, is possible without deterioration of the spectral characteristics and, accordingly, of the accuracy of Doppler measurements of diagnostic parameters, which are determined during the ultrasound studies. The results obtained make it possible to optimize different Doppler techniques within the framework of the general synthetic aperture method.

Transformation of the enterprise cost in conditions of knowledge economics formation

Deep changes in the information society are determined by the growth of the role of knowledge and information as resources, which are characterized by the ability to quickly lose their relevance, inexhaustibility, and in the case of exceptional uniqueness – high cost. The actualization of this trend is due to the emergence of the knowledge economy. The issues of formation, evaluation and management of value of an enterprise are of considerable interest among Ukrainian and foreign researchers. However, a number of aspects need clarification, in particular, the problems of transforming the structure of the market value of a company and new approaches to managing the value of enterprises. The purpose of the article is to substantiate the process of transformation of theoretical approaches and methodological tools for estimating the value of an enterprise under the influence of dynamic changes in the economic environment, taking into account Ukrainian conditions and the development of methodological recommendations for assessing the value of an enterprise. The research is based on the general scientific methods of cognizing economic phenomena and processes, as well as special research methods (economic-mathematical, statistical analysis, expert estimation and forecasting methods). The article examines approaches to the valuation of a company, which are based on two groups of principles – based on factors of production that generate income, and based on market behavior in the context of knowledge economy. Under the influence of the changing external environment, innovative transformations within the enterprise, a significant increase in business activity is necessary. The solution to this problem is impossible without upgrading the methods and mechanisms of this development, changing its priorities, market institutions, relations between subjects of economic activity, the base of resources. Conclusions. The transformation of the value of the enterprise is one of the key factors for improving the efficiency of economic activity, it depends on its stable operation, dynamic development, the position of the enterprise in the market, and other. Under such conditions, in the process of management of value of an enterprise, it is effective to apply a systematic approach, which is subordinated to the general goal of enterprise development and determines the expediency of management decisions depending on the situation that occurs under the influence of the internal and external environment of the enterprise.

Research on regenerative braking control strategy of plug-in hybrid electric vehicle considering CVT ratio rate of change

At present, the regenerative braking control strategies for hybrid electric vehicles equipped with continuously variable transmission (CVT) mainly focus on improving the regenerative braking efficiency. But the influence of dynamic change of the CVT ratio is not considered with regard to the intended braking effect. For a CVT ratio control strategy based on steady-state optimal efficiency, the performance of motor-only braking and engine/motor combined braking modes are analyzed. The analysis of these modes shows that actual braking strength deviates from that required during the dynamic braking process. After analyzing the dynamic characteristics of a transmission system, a CVT ratio control strategy based on the limitations of the ratio rate of change is proposed, with the use of a discrete exhaustive optimization method. The simulation results show that, under a variety of braking conditions, the proposed regenerative braking control strategy can make the actual braking strength follow the requirements and recover more braking energy.

ゼロサプレス型BDDを用いた動的生産プランニングの統合的解候補表現のための解法

Dynamic changes as machine breakdowns make current production plan infeasible and inaccurate. The influence of dynamic changes spread to whole production planning that consists of several domains such as process planning, production scheduling and so on. In this study, solution space in the production planning is defined as comprehensive. We have applied Zero-Suppressed Binary Decision Diagrams (ZDDs) for the representation of solution candidates that satisfy constraints between such domains so for. In dynamic production planning problems, manufacturing achievements and dynamic changes may make solution space change. In this paper, we define such events as constraints for ZDDs and propose an approach to update the ZDD to deal with the events. Moreover,we propose a genetic algorithm (GA) to find solutions in the ZDD. Experimental results demonstrate that the proposed approach to address such event with ZDDs and the GA are effriciently used to solve the dynamic production planning problem.

Effects of elastic modulus change in helical tubes under the influence of dynamic changes in curvature and torsion.

The incidence of stent late restenosis is high (Zwart et al., 2010, "Coronary Stent Thrombosis in the Current Era: Challenges and Opportunities for Treatment," Curr. Treat. Options Cardiovasc. Med., 12(1), pp. 46-57) despite the extensive use of stents, and is most prevalent at the proximal and distal ends of the stent. Elastic modulus change in stented coronary arteries subject to the motion of the myocardium is not studied extensively. It is our objective to understand and reveal the mechanism by which changes in elastic modulus and geometry contribute to the generation of nonphysiological wall shear stress (WSS). Such adverse hemodynamic conditions could have an effect on the onset of restenosis. Three-dimensional (3D), spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries and fluid structure interaction (FSI) were carried out for a helical artery with physiologically relevant flow parameters. To study the effect of coronary artery (CA) geometry change on stent elastic modulus mismatch, models where the curvature, torsion and both curvature and torsion change were examined. The elastic modulus is increased by a factor of two, five, and ten in the stented section for all three modes of motion. The changes in elastic modulus and arterial geometry cause critical variations in the local pressure and velocity gradients and secondary flow patterns. The pressure gradient change is 47%, with respect to the unstented baseline when the elastic modulus is increased to 10. The corresponding WSS change is 15.4%. We demonstrate that these changes are attributed to the production of vorticity (vorticity flux) caused by the wall movement and elastic modulus discontinuity. The changes in curvature dominate torsion changes in terms of the effects to local hemodynamics. The elastic modulus discontinuities along with the dynamic change in geometry affected the secondary flow patterns and vorticity flux, which in turn affects the WSS.

THE SENSITIVITY OF VASCULAR ENDOTHELIUM AND ITS PREDICTORS IN PATIENTS WITH CARDIOVASCULAR PATHOLOGY

Aim.To estimate the role of endogenous metabolic factors in formation of vascular endothelium reactivity in patients with different genesis cardiovascular regulation disorders.Materials and methods.The research included 30 patients with ischemic heart disease (IHD) with stable form of exertional angina (EA) of II–III severity class, 30 patients with I–II stage and 1st–2nd degree essential hypertension (EH), and 15 clinically healthy volunteers. We researched the signs of functional state of vascular endothelium before and after occlusion test. The parameters investigated included: adhesion of thrombocytes, spontaneous aggregation, prostacyclin activity of blood plasma, levels of antithrombine-III, of von Willebrand factor, contents of malonic aldehyde, of nitrites, of endothelin-1, of membrane-connected haemoglobin, of methaemoglobin in erythrocytes, activity of angiotensineconverting enzyme, level of sorption on the membrane of erythrocytes of nucleotides. Research of hemorheology was performed by viscosimetry method.Results.In healthy volunteers high probability of endothelium sensitivity to transverse strain decrease (in 82%) was determined and 25% increase of activity of peroxide oxidation of lipids. In patients with exertional angina influence of dynamic changes of blood flow on endothelium occurred by 2% decrease of viscosity and more than 120% increase of production von Willebrand factor (in 87%). It was concluded that as higher the production of prostacyclin in response to mechanic stimuli (more than 50%) is, the higher is probability of blood flow dynamic changes influence on endothelium. In patients with essential hypertension 30% increase of level of antithrombine-III in 100% of cases caused increase of sensibility of vascular endothelium to transverse strain.Conclusion.The most significant factors linked with sensibility of endothelium of vascular wall to dynamic blood flow changes in examined groups of patients were determined. In patients with exertional angina vascular reaction was mostly linked with rheological qualities and adhesive-aggregation characteristics of blood. In patients with essential hypertension the sensitivity of vascular endothelium was implied to be concordant with anticoagulant activity of blood plasma.

Effects of stent length, transition length and overexpansion in stented coronary arteries

In this work, we study the effect of stent length, stent transition length and stent overexpansion under the influence of dynamic changes in curvature and torsion. It is our objective to understand the influence of these three parameters on local hemodynamics. Three-dimensional, spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries and fluid structure interaction were carried out for a simplified coronary artery with physiologically relevant flow parameters. A model with moving deformable walls with an elastic modulus change of five in the stented section is used as the baseline control case. From the local hemodynamics and wall shear stress changes, it can be concluded that the smaller stent length that adequately covers the lesion site, higher transition length and lower overexpansion of the stented section would lead to improved flow conditions in the stented artery.