Improving the LDMOS Temperature Compensation Bias Circuit to Optimize Back-Off

The application of today's semiconductor transistors in high power UHF DVB-T linear amplifiers has evolved significantly by utilizing LDMOS technology. This fact provides engineers with the option to design a single transistor signal amplifier which enables output power and linearity that was unobtainable previously using bipolar junction transistors or later type first generation MOSFETS. The quiescent current stability in terms of thermal variations of the LDMOS guarantees a robust operation in any topology of DVB-T signal amplifiers. Otherwise, progressively uncontrolled heat dissipation enhancement on the LDMOS case can degrade the amplifier's crucial parameters in regards to the gain, linearity, and RF stability, resulting in dysfunctional operation or a total destruction of the unit. This paper presents one more sophisticated approach from the traditional biasing circuits used so far in LDMOS DVB-T amplifiers. It utilizes a microprocessor control technology, providing stability in topologies where IDQ must be perfectly accurate

Undiagnosed Primary Hyperparathyroidism and Recurrent Miscarriage: The First Prospective Pilot Study.

BACKGROUND: Primary hyperparathyroidism (pHPT) in pregnancy is reported to be associated with significant maternal and foetal complications and an up to threefold increase in the risk of miscarriage. However, the true incidence of pHPT in pregnancy, complete and miscarried, is unknown and there are no data on the prevalence of undiagnosed pHPT in recurrent miscarriage (RM) (≥3 consecutive miscarriages under 24-week gestation). This is the first prospective study aiming to establish the prevalence of undiagnosed pHPT in RM. METHODS: Following UK National ethics committee approval, women who had experienced 3 or more consecutive miscarriages were recruited from a nationwide RM clinic. Serum corrected calcium, phosphate, PTH and vitamin D were evaluated. Patients with raised serum calcium and/or PTH were recalled for confirmatory tests. Power calculations suggested that a minimum of 272 patients were required to demonstrate a clinically significant incidence of pHPT. RESULTS: Three hundred women were recruited, median age 35 years (range 19-42). Eleven patients had incomplete data, leaving 289 patients suitable for analysis; 50/289 patients (17%) with abnormal tests were recalled. The prevalence of vitamin D deficiency (<25 nmol/l) and insufficiency (25-75 nmol/l) was 8.7 and 67.8%, respectively. One patient was diagnosed with pHPT (0.34%) and underwent successful parathyroidectomy. CONCLUSIONS: The prevalence of undiagnosed pHPT (0.34%) in RM in this study appears to be many times greater than the 0.05% expected in this age group. The findings of this pilot study merit follow-up with a larger-scale study. Routine serum calcium estimation is not currently undertaken in RM and should be considered

Molecular and Integrative Physiological Effects of Isoflurane Anesthesia: The Paradigm of Cardiovascular Studies in Rodents using Magnetic Resonance Imaging

To-this-date, the exact molecular, cellular, and integrative physiological mechanisms of anesthesia remain largely unknown. Published evidence indicates that anesthetic effects are multifocal, and occur in a time-dependent and coordinated manner, mediated via central, and local, peripheral pathways. Their effects can be modulated by a range of variables, and their elicited end-effect on the integrative physiological response is highly variable.This review summarizes the major cellular and molecular sites of anesthetic action with a focus on the paradigm of isoflurane (ISO) – the most commonly used anesthetic nowadays – and its use in prolonged in vivo rodent studies using imaging modalities, such as Magnetic Resonance Imaging (MRI). It also presents established evidence for normal ranges of global and regional physiological cardiac function under ISO, proposes optimal, practical methodologies relevant to the use of anesthetic protocols for MRI, and outlines the beneficial effects of nitrous oxide supplementation

Magnetic resonance imaging: the basics

Magnetic resonance imaging (MRI) is a rapidly developing field in basic applied science and clinical practice. Research efforts in this area have already been recognized with five Nobel prizes awarded to seven Nobel laureates in the past 70 years. Based on courses taught at The Johns Hopkins University, Magnetic Resonance Imaging: The Basics provides a solid introduction to this powerful technology. The book begins with a general description of the phenomenon of magnetic resonance and a brief summary of Fourier transformations in two dimensions. It examines the fundamental principles of physics for nuclear magnetic resonance (NMR) signal formation and image construction and provides a detailed explanation of the mathematical formulation of MRI. Numerous image quantitative indices are discussed, including (among others) signal, noise, signal-to-noise, contrast, and resolution. The second part of the book examines the hardware and electronics of an MRI scanner and the typical measurements and simulations of magnetic fields. It introduces NMR spectroscopy and spectral acquisition and imaging techniques employing various pulse sequences. The final section explores the advanced imaging technique of parallel imaging. Structured so that each chapter builds on the knowledge gained in the previous one, the book is enriched by numerous worked examples and problem sets with selected solutions, giving readers a firm grasp of the foundations of MRI technology

Assessment of Cellular and Organ Function and Dysfunction using Direct and Derived MRI Methodologies

Despite the tremendous growth in the field of magnetic resonance imaging (MRI) evidenced in the initial phases of its development in the early twentieth century, scientific focus has shifted in recent years toward the study of physiology and pathophysiology that span the spatial scales of the molecule, cell, tissue, and organ. Intensified research activities over the past 15 years have justified efforts toward molecular and cellular imaging, dual-modality imaging systems, real-time acquisitions, dedicated image processing techniques and applications, and the critical evaluation of their potential translational value for use in the clinic. The integrative focus on molecular-cellular-tissue-organ function and dysfunction has taken a primary role in modern, personalized medicine, and it is envisaged to continue to do so, as accumulated knowledge from basic and clinical science work continues to elucidate molecular, cellular, and physiological/pathophysiological pathways and mechanisms. In this scientific effort, MRI continues to play a critical and synergistic role from the perspectives of basic science, diagnosis, and clinical interventional/therapeutic approaches. Within the realm of the current role of MRI in modern medicine, this book summarizes state-of-the-art direct and derived MRI methodologies and approaches as applied toward the assessment of cellular and organ function and dysfunction. The contributions in this effort are not excessive but few, comprehensive, and distinguished and of high quality. The topic areas can be generalized to find applications in other scientific areas and span both brain and cardiac applications, extending interest to wider audiences

Improving the LDMOS Temperature Compensation Bias Circuit to Optimize Back-Off

The application of today's semiconductor transistors in high power UHF DVB-T linear amplifiers has evolved significantly by utilizing LDMOS technology. This fact provides engineers with the option to design a single transistor signal amplifier which enables output power and linearity that was unobtainable previously using bipolar junction transistors or later type first generation MOSFETS. The quiescent current stability in terms of thermal variations of the LDMOS guarantees a robust operation in any topology of DVB-T signal amplifiers. Otherwise, progressively uncontrolled heat dissipation enhancement on the LDMOS case can degrade the amplifier's crucial parameters in regards to the gain, linearity, and RF stability, resulting in dysfunctional operation or a total destruction of the unit. This paper presents one more sophisticated approach from the traditional biasing circuits used so far in LDMOS DVB-T amplifiers. It utilizes a microprocessor control technology, providing stability in topologies where IDQ must be perfectly accurate

Improving the LDMOS Temperature Compensation Bias Circuit to Optimize Back-Off

The application of today's semiconductor transistors in high power UHF DVB-T linear amplifiers has evolved significantly by utilizing LDMOS technology. This fact provides engineers with the option to design a single transistor signal amplifier which enables output power and linearity that was unobtainable previously using bipolar junction transistors or later type first generation MOSFETS. The quiescent current stability in terms of thermal variations of the LDMOS guarantees a robust operation in any topology of DVB-T signal amplifiers. Otherwise, progressively uncontrolled heat dissipation enhancement on the LDMOS case can degrade the amplifier's crucial parameters in regards to the gain, linearity, and RF stability, resulting in dysfunctional operation or a total destruction of the unit. This paper presents one more sophisticated approach from the traditional biasing circuits used so far in LDMOS DVB-T amplifiers. It utilizes a microprocessor control technology, providing stability in topologies where IDQ must be perfectly accurate