This paper proposes and implements a super-twisting sliding mode direct power control (SSM-DPC) strategy for a brushless doubly fed induction generator (BDFIG). DPC has fast and robust response under ...transient conditions; however, it suffers from active and reactive power ripples and current distortions, which degrades the quality of the output power. In contrast, vector control has good steady-state current harmonic spectra; however, it is not robust to machine parameters variations, and thus needs a phase-locked loop for synchronous coordinate transformations. The SSM-DPC strategy controls active and reactive power directly without the need of the phase-locked loop. Moreover, its transient performance is similar to DPC and its steady-state performance is the same as vector control. The proposed controller is robust to uncertainties toward parameter variations and achieves constant converter switching frequency by using space vector modulation. Simulation and experimental results of a 2 MW and 3 kW laboratory-scale BDFIG are provided and compared with those of integral sliding mode and DPC to validate the effectiveness, correctness, and the robustness of the proposed strategy.
This study investigates the spatial and temporal variations of the aridity indices to reveal the desertification vulnerability of Iraq region. Relying on temperature and precipitation data taken from ...28 meteorological stations for 31 years, the study aims to determine (1) dry land types and their delineating boundaries and (2) temporal change in aridity conditions in Iraq. Lang’s aridity (Im), De Martonne’s aridity (Am), United Nations Environmental Program (UNEP) aridity (AIu), and Erinç aridity (I
E
) indices were selected in this study because of the scarcity of the observed data. The analysis of the spatial variation of aridity indices exhibited that the arid and semi-arid regions cover about 97% of the country’s areas. As for temporal variations, it was observed that the aridity indices tend to decrease (statistically significant or not) for all stations. The cumulative sum charts (CUSUMs) were applied to detect the year on which the climate pattern of aridity indices had changed from one pattern to another. The abrupt change point was detected around year 1997 for the majority of the stations. Thus, the spatial and temporal aridity characteristics in Iraq were examined for the two periods 1980–1997 and 1998–2011 (before and after the change-point year) to observe the influence of abrupt change point on aridity phenomena. The spatial variation after 1997 was observed from semi-arid (dry sub humid) to arid (semi-arid) especially at the stations located in northern Iraq, while hyper-arid and arid climatic conditions were still dominant over southern and central Iraq. Besides, the negative temporal variations of the two periods 1980–1997 and 1998–2011 were obtained for almost every station. As a result, it was emphasized that Iraq region, like other Middle East regions, has become drier after 1997. The observed reduction in precipitation and increase in temperature for this region seem to make the situation worse in future.
This paper proposes a new reference-generation-strategy for direct torque control (DTC) of doubly fed induction generator (DFIG), under symmetrical voltage-dips. Since DTC has no current-control ...loop, it cannot prevent overcurrent during voltage-dips. The proposed method prevents overcurrent in the rotor side converter, by damping the transient-flux and modifying the references of rotor-flux and torque, during voltage dip and recovery. The analysis of DTC for DFIG is presented by a λ-i equivalent circuit, which is decomposed into forced and natural circuits. Based on the natural λ-i circuit, the method adds a transient compensation term to the rotor-flux reference, which is obtained by multiplying the stator-natural-flux with a proposed decaying-ramp function. Moreover, this method reduces the forced component of rotor-flux proportional to the grid voltage. As a result, this method adjusts the transient-flux damping time and ensures overcurrent prevention in the rotor and stator windings. The torque reference is modified to maintain the torque-angle (between rotor and stator flux vectors) constant, which results in stable control of the DFIG during grid faults. The effectiveness of the proposed method is confirmed by experimental results of a 3-kW test set-up and simulation results of a 2-MW DFIG.
The determination of optimal operation rules for water storage systems will provide a good perception on the ability of these systems to achieve their objective functions. This study aims to identify ...optimal operation policies by maximizing the annual hydropower generation of a multi-reservoir system that consists of two reservoirs with different functions in flood risk management. These reservoirs, namely, Mosul and Badush, are located in the Tigris River, Northern Iraq. The Mosul Dam was constructed to protect the cities located downstream, and the Badush Dam is building to absorb flood waves in case the Mosul Dam collapses. The particle swarm optimization model for a single reservoir (PSOS) was formulated to determine optimal operation policies during real operation time to maximize annual hydroelectric generation. PSOS was approved during these operations and developed to specify ideal operation rules for a multi-reservoir system (PSOM), which consists of two reservoirs, through three modes of annual inflows. Results of PSOS indicated its superiority during real-time operation. The annual hydropower generation was achieved by the optimal operation rules of PSOM during the three styles of inflows. These optimal policies will provide good insights into the potential of this multi-reservoir system in supplying the national electricity network with hydropower energy, which is considered environmentally friendly, in addition to achieving the original goals of its construction.
Purpose of Review
The potential of polygenic risk scores (PRS) to improve atherosclerotic cardiovascular disease (ASCVD) risk assessment and management has stoked significant interest in their ...incorporation into clinical management. The goal of this review is to apprise the readers of the latest developments and evidence of PRS readiness for clinical integration. We also discuss current limitations that must be addressed before PRS can be implemented into routine clinical practice.
Recent Findings
PRS have been shown to improve risk stratification for ASCVD and to identify patients who may derive increased benefit from primary and secondary prevention. Risk captured by PRS appears largely independent of traditional risk factors and can be ascertained at birth, prior to the development of traditional clinical risk factors. Genetic risk is modifiable through lifestyle modifications and medications.
Summary
PRS offers a valuable way to improve early identification of actionable CVD risk. However, further work is needed before PRS can be implemented clinically.
Marijuana is the most popular drug of abuse in the United States. The association between its use and coronary artery disease has not yet been fully elucidated. This study aims to determine the ...frequency of coronary artery disease among young to middle aged adults presenting with chest pain who currently use marijuana as compared to nonusers.
In this retrospective study, 1,420 patients with chest pain or angina equivalent were studied. Only men between 18 and 40 years and women between 18 and 50 years of age without history of cardiac disease were included. All patients were queried about current or prior cannabis use and underwent coronary CT angiography. Each coronary artery on coronary CT angiography was assessed based on the CAD-RADS reporting system.
A total of 146 (10.3%) out of 1,420 patients with chest pain were identified as marijuana users. Only 6.8% of the 146 marijuana users had evidence of coronary artery disease on coronary CT angiography. In comparison, the rate was 15.0% among the 1,274 marijuana nonusers (p = 0.008). After accounting for other cardiac risk factors in a multivariate analysis, the negative association between marijuana use and coronary artery disease on coronary CT angiography diminished (p = 0.12, 95% CI 0.299-1.15). A majority of marijuana users were younger than nonusers and had a lower frequency of hypertension and diabetes than nonusers. There was no statistical difference in lipid panel values between the two groups. Only 2 out of 10 marijuana users with coronary artery disease on coronary CT angiography had hemodynamically significant stenosis.
Among younger patients being evaluated for chest pain, self-reported cannabis use conferred no additional risk of coronary artery disease as detected on coronary CT angiography.
Organic solar cell (OSC) devices suffer from low power conversion efficiency (PCE) due to deep trap states that absorb photogenerated charges, act as recombination centers, and reduce charge ...collection. To further improve the PCE, an optimized hole transport layer (HTL) must be engineered for efficient hole transport and reduced deep trap states. A hybrid HTL consisting of organic and inorganic materials was formed using a combination of CuO nanoparticles (NPs) having an average size of 50 nm and poly(3-hexylthiophene) (P3HT). The hybrid HTL was used in the fabrication and characterization of an inverted OSC device structure. In consequence, the incorporation of CuO-NPs into the P3HT resulted in an increase of 8.66% in photocurrent density. Additionally, the PCE increased from 3.77 to 4.22% while the open circuit voltage (V
oc
) was maintained. The higher hole mobility obtained for the optimum device using the charge extraction by increasing voltage (CELIV) measurement was 8.47 × 10
− 4
cm
2
V
− 1
s
− 1
. This highlights the potential of designing novel organic solar cells with inorganic nanoparticles, offering enhanced performance and efficiency.
Pulmonary hypertension is a progressive disease of various origins that is associated with right ventricular dysfunction. In the present study, the protective effect of diosgenin was investigated in ...monocrotaline-induced pulmonary hypertension in rats. Pulmonary hypertension was induced by a single subcutaneous injection of monocrotaline (60mg/kg). Diosgenin (100mg/kg) was given by oral administration once daily for 3 weeks. At the end of the experiment, mean arterial blood pressure, electrocardiography and echocardiography were recorded. Rats were then sacrificed and serum was separated for determination of total nitrate/nitrite level. Right ventricles and lungs were isolated for estimation of oxidative stress markers, tumor necrosis factor-alpha, total nitrate/nitrite and transforming growth factor-beta contents. Myeloperoxidase and caspase-3 activities in addition to endothelial and inducible nitric oxide synthase protein expression were also determined. Moreover, histological analysis of pulmonary arteries and cardiomyocyte cross-sectional area was performed. Diosgenin treatment provided a significant improvement toward preserving hemodynamic changes and alleviating oxidative stress, inflammatory and apoptotic markers induced by monocrotaline in rats. Furthermore, diosgenin therapy prevented monocrotaline-induced changes in nitric oxide production, endothelial and inducible nitric oxide synthase protein expression as well as histological analysis. These findings support the beneficial effect of diosgenin in pulmonary hypertension induced by monocrotaline in rats.
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Given rapid advancements in medical science, it is often challenging for the busy clinician to remain up-to-date on the fundamental and multifaceted aspects of preventive cardiology and maintain ...awareness of the latest guidelines applicable to cardiovascular disease (CVD) risk factors. The “American Society for Preventive Cardiology (ASPC) Top Ten CVD Risk Factors 2021 Update” is a summary document (updated yearly) regarding CVD risk factors. This “ASPC Top Ten CVD Risk Factors 2021 Update” summary document reflects the perspective of the section authors regarding ten things to know about ten sentinel CVD risk factors. It also includes quick access to sentinel references (applicable guidelines and select reviews) for each CVD risk factor section. The ten CVD risk factors include unhealthful nutrition, physical inactivity, dyslipidemia, hyperglycemia, high blood pressure, obesity, considerations of select populations (older age, race/ethnicity, and sex differences), thrombosis/smoking, kidney dysfunction and genetics/familial hypercholesterolemia. For the individual patient, other CVD risk factors may be relevant, beyond the CVD risk factors discussed here. However, it is the intent of the “ASPC Top Ten CVD Risk Factors 2021 Update” to provide a succinct overview of things to know about ten common CVD risk factors applicable to preventive cardiology.
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