Advantages of nonuniform arrays using root-MUSIC

In this paper, we consider the Direction-Of-Arrival (DOA) estimation problem in the Nonuniform Linear Arrays (NLA) case, particularly the arrays with missing sensors. We show that the root-MUSIC algorithm can be directly applied to this case and that it can fully exploit the advantages of using an NLA instead of a Uniform Linear Array (ULA). Using theoretical analysis and simulations, we demonstrate that employing an NLA with the same number of sensors as the ULA, yields better performance. Moreover, reducing the number of sensors while keeping the same array aperture as the ULA slightly modifies the Mean Square Error (MSE). Therefore, thanks to the NLA, it is possible to maintain a good resolution while decreasing the number of sensors. We also show that root-MUSIC presents good performance and is one of the simplest high resolution methods for this type of arrays. Closed-form expressions of the estimator variance and the Cramer–Rao Bound (CRB) are derived in order to support our simulation results. In addition, the analytical expression of the CRB of the NLA to the CRB of the ULA ratio is calculated in order to show the advantages of the NLA.     

Switching times variation of power MOSFET devices after electrical stress

The switching performance of three power MOSFET devices with different oxide thicknesses is studied after several periods of electrical stress. The thickest oxide reveals a large accumulation of positive charges in the oxide bulk after small periods of stress. These charges affect the switching parameters by increasing the rise time and by decreasing the fall time. Larger periods of stress reduce the effect of positive charges by increasing the number of interface states. The threshold voltage is decreased by the effect of a positive oxide charge and increases with the appearance of interface states. All these phenomena are less observable as we reduce the oxide thickness.     

Sulfonic acid functionalised SBA-15 as catalysts for Beckmann rearrangement and esterification reaction

Hybrid inorganic–organic solid acid materials SBA-15–Ph–SO₃H were synthesized by the directly co-condensation method under the acid medium. The resulting materials perform well both in the liquid phase Beckmann rearrangement (The yield is 32.3%) and esterification reaction (The yield is 95.5%). And more, the catalysts show the different catalytic performance in these two reactions.     

Study the liquid-phase Beckmann rearrangement on the surface of SBA-15-SO<Subscript>3</Subscript>H catalyst

Hybrid inorganic–organic solid acid material SBA-15-Ph–SO₃H was synthesized by the co-condensation of tetraethoxysilane and 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane in the presence of a Poly (alkylene oxide) block copolymer under acid conditions. The catalytic activity of the obtained materials was studied in liquid-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam. The results show that there exists an obvious “Solvent effect” in this reaction system and the strong Bronsted acid is proofed again to be at the origin of the formation of ε-caprolactam. Moreover, we tentatively proposed a reaction mechanism involving a five-member ring intermediate product when toluene was used as solvent.     

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.     

Switching times variation of MOSFET devices with temperature and high-field stress

Switching times of power MOSFET devices are investigated as function of temperature and high-field stress. Measurements show that important variations are obtained on the devices turn-on time. The threshold voltage is decreasing with temperature and varies with stress, especially at low temperatures. The oxide leakage current is found to be having safe values even at high temperatures, stressing the devices does not increase the leakage current to unsafe values except for very high temperatures.     

Data Generation for Path Testing

We present two stochastic search algorithms for generating test cases that execute specified paths in a program. The two algorithms are: a simulated annealing algorithm (SA), and a genetic algorithm (GA). These algorithms are based on an optimization formulation of the path testing problem which include both integer- and real-value test cases. We empirically compare the SA and GA algorithms with each other and with a hill-climbing algorithm, Korel's algorithm (KA), for integer-value-input subject programs and compare SA and GA with each other on real-value subject programs. Our empirical work uses several subject programs with a number of paths. The results show that: (a) SA and GA are superior to KA in the number of executed paths, (b) SA tends to perform slightly better than GA in terms of the number of executed paths, and (c) GA is faster than SA; however, KA, when it succeeds in finding the solution, is the fastest.