Efficiency of magnetic coupled boost DC‐DC converters mainly dedicated to renewable energy systems: influence of the coupling factor

This paper presents a specific analysis of an individual basic magnetically coupled direct current‐to‐direct current (DC–DC) converter specially designed for integration in a distributed architecture of renewable energy generators for smart grid applications. In such distributed architecture dedicated for renewable energy, parallel high‐voltage DC presents many advantages over the classical centralized one. We show that in such setup, high voltage can be advantageously produced using a specific magnetically coupled boost converter, and we point out the influence of the coupling factor, generally considered equal to one, on the overall performance of the converter and on the global energy efficiency of the installation. In this study, the generalized concepts of system energy parameters of DC–DC converters are introduced and applied to the transient analysis. Consequently, the operation of a magnetic coupled DC–DC converter with a recovery stage is modeled. The simulation results are compared with those of the behavioral study, deduced from the model pointing out the large influence of the coupling factor value on the global behavior and mainly on the value of the recovery voltage, in all the various parts of the switching cycle. The renewable energy generator operating parameters, such as current and voltage values, can then be predicted in a more useful way to compute new similar DC–DC converter systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Prediction of gas barrier properties of high polymers

This paper studies the correlation of polymer structure and morphology and gas permeability. A scale of numerical values based on polymer cohesive energy density and fractional free volume has been devised to predict permeability and also to estimate diffusion and solubility properties.     

Piecewise monotone filtering in discrete-time with smallobservation noise

A discrete-time model for filtering with small observation noise is considered. A piecewise linear observation function is considered with two intervals of monotonicity. A sequential quadratic variation test is found to detect intervals of linearity of the observation function. Diffusion approximations to certain discrete processes are made to estimate the mean times for reaching a decision and the error probabilities     

Exceptionally High Dielectric Constant in Ceramic Pr2CuO4

The pristine layered cuprate Pr₂CuO₄ samples of >95% density were fabricated as thin disks. The samples, analyzed by X‐ray diffraction and Scanning electron microscopy, showed clean T′‐type phase with Rietveld refined lattice parameters a = b = 3.95805(±5) Å and c = 12.2262(±5) Å. The measured dielectric properties of the Pr₂CuO₄ ceramics, in the temperature range ?100°C–150°C and frequencies (ν) 0.1 Hz–1 MHz, showed extremely high ε_r′ > 10⁴ (above ?30°C), and dissipation (tan δ = ε_r′′/ε_r′) between 0.1 and 5 (for 500 Hz ≤ ν ≤ 1 MHz, and ?100 ≤ T ≤ 150°C). The ac conductivity of Pr₂CuO₄ ceramics ranged between 10^?6 and 10^?3 Scm^?1 for the measured frequencies and temperatures, and showed frequency‐dependent double power law behavior akin to a modified Jonscher's power law.     

Detection of traps induced and activated by high field stress in an N-channel VDMOSFET transistor using current deep level transient spectroscopy (CDLTS)

Commercial VDMOSFETs transistors were subjected to positive and negative high field stress. A new model of current deep level transient spectroscopy (CDLTS) characterization is adopted in a research of defects induced and activated by electrical stress. This model is based on pulse width scan instead of classical temperature scan. The band gap is scanned by varying the pulse base level. Positive and negative high field stresses were applied for different periods ranging from 30 to 120 min. After each stress period, activation energies and capture cross sections of detected traps were estimated. Different defects were detected and we have distinguished the doping levels and interface states from deep levels located in the forbidden band gap.     

La motivation à l'accomplissement et l'auto-évaluation des performances en relation avec le rendement scolaire.

32 overachieving and 33 underachieving secondary school students, equated for IQ range were required to perform a series of school and nonschool tasks and to evaluate their own achievement on these tasks. Self-evaluation scores were then correlated with Ss' school achievement. Underachievers were self-critical, inconsistent in their answers, and had difficulty in accurate self-evaluation, indicating a low interiorization of high standards of performance in the tasks required. Results confirm the importance of the cognitive mechanisms controlling a task as motivating factors determining academic achievement. It is proposed that these mechanisms, when studied through self-evaluation, might supplement the theory of achievement motivation in explaining the lack of motivation observed in underachievers. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Compression of the upper cervical spinal cord causing symptoms of brainstem compromise. A case report

STUDY DESIGN: A case is reported in which a flexion-induced compression of the upper cervical spinal cord caused symptoms of brainstem compromise in the absence of radiographic evidence of osseous instability. OBJECTIVES: A 41-year-old woman developed postoperative cervical instability with flexion-induced neurologic symptoms referable to the brainstem. The instability was caused by direct compression at the third cervical vertebral body, which in turn was caused by differential movements between the neuraxis and skeletal elements in the upper cervical spine. SUMMARY OF BACKGROUND DATA: Pathologic processes at the craniocervical junction may cause brainstem compromise with neurologic symptoms. The mechanism of brainstem involvement is usually either vertebrobasilar insufficiency or direct mechanical compression. In cases where the brainstem is compressed by skeletal elements, the compressing osseous structures usually are the walls of the foramen magnum or the odontoid process, or, less frequently, the atlas or axis vertebrae. Symptoms of brainstem dysfunction caused by dynamic compression at the level of the third cervical vertebra in the absence of hindbrain herniation are unusual and, to the best of the authors' knowledge, have not been described previously. METHODS: The patient underwent initial examination, evaluation, and periodic follow-up examination with magnetic resonance imaging from the time of her first visit until 26 months after the surgical treatment. The patient experienced postsurgical instability with dynamic compression by the C3 vertebral body, which caused brainstem compromise. Surgical treatment consisted of decompressive C3 corpectomy and fusion of C2 to C6, supplemented by anterior fixation. RESULTS: After undergoing surgical decompression of C3, reconstruction, and anterior internal fixation of C2 to C6, the patient had dramatic neurologic improvement. Diplopia, paresthesia, and nystagmus disappeared immediately after surgery. Swallowing difficulties, hoarseness, and vertigo improved gradually. At follow-up examination 26 months after surgery, the patient was asymptomatic. Magnetic resonance imaging showed good position of the construct, with no evidence of compression of the spinal cord or brainstem. CONCLUSIONS: Instability of the cervical spine may result in symptoms of brainstem dysfunction, even in the absence of hindbrain herniation. This instability is explained by the differential movement between the bony structures and neuraxis in the upper cervical region. Diagnosis and adequate management of this instability alleviates the neurologic symptoms and prevents possible hazardous complications.