Throughput analysis for cognitive radio networks with multiple primary users and imperfect spectrum sensing

In cognitive radio networks, the licensed frequency bands of the primary users (PUs) are available to the secondary user (SU) provided that they do not cause significant interference to the PUs. In this study, the authors analysed the normalised throughput of the SU with multiple PUs coexisting under any frequency division multiple access communication protocol. The authors consider a cognitive radio transmission where the frame structure consists of sensing and data transmission slots. In order to achieve the maximum normalised throughput of the SU and control the interference level to the legal PUs, the optimal frame length of the SU is found via simulation. In this context, a new analytical formula has been expressed for the achievable normalised throughput of SU with multiple PUs under prefect and imperfect spectrum sensing scenarios. Moreover, the impact of imperfect sensing, variable frame length of SU and the variable PU traffic loads, on the normalised throughput has been critically investigated. It has been shown that the analytical and simulation results are in perfect agreement. The authors analytical results are much useful to determine how to select the frame duration length subject to the parameters of cognitive radio network, such as network traffic load, achievable sensing accuracy and number of coexisting PUs

New optimal PWM strategies for a VSI induction motor drive

The applications of robust squirrel-cage induction motors in variable speed inverter drive systems have increased considerably due to the availability of easily controlled semiconductor switching devices. One problem encountered in inverter drives is the non-sinusoidal nature of the supply voltage, which results in increased motor losses and harmful torque pulsations producing undesirable speed oscillations. The latter effects are negligible at high frequency operation, due to the damping effect of the rotor and load inertia. However, torque pulsations and speed ripple may be appreciable at low frequency, wore they may result in abnormal wear of gear-teeth or torsional shaft failure. Hence, in applications where constant or precise speed control is important, eg; machine tool, antenna positioning, traction drives etc., it is essential to establish a method for determining the magnitudes of these torque pulsations and speed ripple, as a first stage in minimizing or eliminating them. When a voltage source inverter is used in such applications, pulse width modulation (PWM) techniques are usually employed, whereby the quasi square waveshape is modulated so as to minimize or eliminate the low order harmonic voltage components and thereby reduce the torque pulsations. Recent investigations have shown that total elimination of low order components does not produce optimal efficiency or torque pulsations and speed ripple. minimization. This thesis describes new PWM strategies which does not rely on complete elimination of low order harmonics, but on controlling the magnitude and phase of these components to achieve a smooth rotor motion. Initially, a mathematical model for the inverter/induction motor drive was developed, based on numerical integration of the system differential equations. The changing topology of the inverter bridge was simulated using tensor techniques. Then an analytical method, based on harmonic equivalent circuit analysis was proposed for calculating the induction motor pulsating torque components under steady-state operating conditions, in terms of stator and rotor current harmonics. The accuracy of this method was verified by comparing its results with those obtained from the mathematical model developed earlier. This provided an extremely rapid, numerically stable and efficient means for evaluating harmonic current and torque components with balanced non-sinusoidal applied voltages. This method was then used to formulate the torque performance function necessary to determine the new optimal PWM switching strategies. Throughout the work, the predicted performance was extensively validated and supported by practical results obtained from an experimental rig specifically designed to drive the machine under different PWM techniques

Advancements in understanding and addressing Alzheimer's disease: a comprehensive review

Alzheimer's disease (AD) presents a multifaceted challenge in the realm of neurodegenerative disorders, affecting millions globally and posing significant burdens on patients, caregivers, and healthcare systems alike. Over a century of research has illuminated various facets of AD pathophysiology, highlighting the intricate interplay between genetic, molecular, and environmental factors in disease progression. This comprehensive review synthesized key findings from recent literature, encompassing diverse topics ranging from diagnostic challenges and emerging therapeutic approaches to caregiver support and evolving research strategies. Furthermore, it explored the complexities of AD pathogenesis, elucidating the role of amyloid-beta (Aβ) plaques, tau protein pathology, neuroinflammation, and mitochondrial dysfunction in neuronal degeneration. Therapeutic interventions for AD, both current and emerging, are critically evaluated, with a focus on pharmacological agents targeting Aβ aggregation, tau pathology, and synaptic dysfunction. Non-pharmacological strategies, including lifestyle modifications and cognitive interventions, are also explored for their potential in disease management. Finally, the review examined the landscape of AD research, highlighting ongoing efforts to elucidate disease mechanisms, identify novel therapeutic targets, and address existing gaps in prevention and treatment strategies. It emphasizes the need for collaborative endeavours among stakeholders to accelerate progress towards effective AD management and ultimately, improve outcomes for affected individuals and their families. Through its comprehensive synthesis of current knowledge and future directions, this review aims to inform clinicians, researchers, policymakers, and advocates involved in the fight against Alzheimer's disease, offering insights that may catalyse advancements in diagnosis, treatment, and care

Exploring the connection: endocrine disruptors and polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is heterogeneous endocrine disorder in females manifesting reproductive dysfunction and metabolic abnormalities. Endocrinopathy in the form of hyperandrogenism leading to alteration in clinical phenotype and fertility seen. Atherogenic dyslipidaemia and insulin resistance as a result of metabolic disturbance also encountered. Recent years, endocrine disrupting chemicals (EDCs) are widely studied and linked for their alleged role in the development of PCOS. EDCs like bisphenol A (BPA), Phthalate, methoxychlor and chlorpyrifos which are present in many industrial as well as daily use products poses risk of development of various diseases. This review discusses the role of EDCS specially BPA in the pathogenesis of PCOS with study of interest identified and extracted from databases like Pub Med and Google scholars using MeSH keywords. BPA has estrogenic property and binds to oestrogen receptors α and β. Stimulation of ovarian theca cells and dysregulation of steroid biosynthesis leads to androgen overproduction. It stimulates GnRH Pulse generator, decreasing the level of LH hence fertility is affected. BPA also interact with adipose tissue receptors and causes differentiation, lipid deposition and inhibition of adiponectin. Its serum and urinary levels are found to be elevated in PCOS patient. In animal studies, it is found that BPA exposure causes impaired folliculogenesis, insulin resistance and DNA methylation. EDC exposure, especially BPA which is an integral constituent of many industrial and daily use items may cause PCOS possibly by altering androgen synthesis, adipocyte stimulation and epigenetic modification

Flow injection analysis for the photometric determination of promethazine-HCl in pure and pharmaceutical preparation via oxidation by persulphate using Ayah 3SX3-3D solar micro photometer

The first flow injection spectrophotometric method is characterized by its speed and sensitivity which have been developed for the determination of promethazine-HCl in pure and pharmaceutical preparation. It is based on the in situ detection of colored cationic radicals formed via oxidation of the drug with sodium persulphate to pinkish-red species and the same species was determined by using homemade Ayah 3SX3-3D solar flow injection photometer. Optimum conditions were obtained by using the high intensive green light emitted diode as a source. Linear dynamic range for the absorbance versus promethazine-HCl concentration was 0-7 mmol.L-1, with the correlation coefficient (r) was 0.9904 while the percentage linearity (r2%) was 98.09%. the L.O.Q was 3.97 µg/sample, while L.O.D (S/N=3) = 0.2407µg/sample (5 µmol.L-1) from the stepwise dilution for the minimum concentration of lowest concentration in the linear dynamic range of the calibration graph. The R.S.D% at 2 mmol.L-1 promethazine-HCl is less than 1% (eight replicates) using 150 µL sample volume. Throughput 30 sample.hr-1. The method was applied successfully for the determination of promethazine-HCl in pharmaceutical preparation. By using paired t-test it was shown that there was no significant difference between the proposed method and official method and on that basis the new method can be accepted as an alternative analytical method