New generalized topologies of asymmetric modular multilevel inverter based on six-switch H-bridge

In this paper, for high and low numbers of voltage levels, two new generalized multilevel converters are introduced, which comprise a six-switch H-bridge and several switched-source units. Switched-source units consist of bidirectional and unidirectional switches along with a dc voltage source. The two proposed topologies are compared with topologies based on the six-switch H-bridge, conventional H-bridge, and some new topologies regarding the number of switches, dc voltage sources, gate drivers, and per-unit voltage block on switches. The comparison results reveal the superiority of the proposed topology with low number of voltage level (LNL) and proposed topology with high number of voltage level (HNL) regarding the per-unit voltage block and number of elements, respectively. Thus, the proposed topologies lead to reduction cost and weight of system. Furthermore, for high number of levels, HNL topology is more appropriate than LNL topology and vice versa. The performances of the proposed 15-level LNL and 61-level topologies are simulated by MATLAB, and proposed 15-level LNL topology in producing all voltage levels is validated by experimental results.     

Small-signal gate-to-drain capacitance of MOSFET as a diagnostic tool for hot-carrier induced degradation

In this paper a method for the study of hot-carrier induced charge centers in MOSFETs based on a small-signal gate-to-drain capacitance measurement is described. Numerical modeling and simulation is used to provide an understanding of the effects of spatially localized trapped carriers and interface states on this capacitance. Experimental gate-to-drain capacitance results are presented and compared with charge pumping measurements. This method is used to investigate hot-carrier degradation of n- and p-channel MOSFETs after drain avalanche hot-carrier stress conditions. It is concluded that under this stress condition the degradation of both n- and p-channel devices is due to the trapping of majority carriers and the generation of acceptor type interface states in the top half of the silicon bandgap.     

Physical characteristics modification of a SiGe-HBT semiconductor device for performance improvement in a terahertz detecting system

In order to improve the performance of a pre-designed direct conversion terahertz detector which is implemented in a 0.25 μ m-SiGe-BiCMOS process, we propose some slight modifications in the bipolar section of the SiGe device physical design. Comparison of our new proposed device and the previously reported device is done by SILVACO TCAD software simulation and we have used previous experimentally reported data to confirm our software simulations. Our proposed modifications in device structural design show a present device responsivity improvement of about 10% from 1 to 1.1 A/W while the bandwidth improvement is about 218 GHz. The minimum noise equivalent power at detector output is increased by about 14.3% and finally power consumption per pixel at the maximum responsivity is decreased by about 5%.     

Scheduling to minimize gaps and power consumption

This paper considers scheduling tasks while minimizing the power consumption of one or more processors, each of which can go to sleep at a fixed cost  $\alpha $ . There are two natural versions of this problem, both considered extensively in recent work: minimize the total power consumption (including computation time), or minimize the number of “gaps” in execution. For both versions in a multiprocessor system, we develop a polynomial-time algorithm based on sophisticated dynamic programming. In a generalization of the power-saving problem, where each task can execute in any of a specified set of time intervals, we develop a $(1+{2 \over 3} \alpha )$ -approximation, and show that dependence on $\alpha $ is necessary. In contrast, the analogous multi-interval gap scheduling problem is set-cover hard (and thus not $o(\lg n)$ -approximable), even in the special cases of just two intervals per job or just three unit intervals per job. We also prove several other hardness-of-approximation results. Finally, we give an $O(\sqrt{n})$ -approximation for maximizing throughput given a hard upper bound on the number of gaps.     

Influence of graded changes in vasomotor tone on the carotid arterial mechanics in live spontaneously hypertensive rats

1. The contribution of vasomotor tone to the increased stiffness of carotid arteries in living spontaneously hypertensive rats (SHR) is largely unknown. Whether a reduced vascular tone is associated with an increase or a decrease in arterial stiffness in vivo remains to be determined. The goal of the present investigation was to show that a decrease in vascular tone is associated with a decrease in arterial stiffness, independent of the structural composition of the arterial wall. 2. New high resolution echo-tracking techniques were used to evaluate pulsatile changes of carotid blood pressure and diameter following transient and graded changes of vasomotor tone produced by the dihydropyridine derivative, isradipine. Treatment for 8 weeks was given to groups of SHR rats either with a low (0.6 kg day-1) or a high (2.6 mg kg-1 day-1) dose. Another SHR group received an acute dose of 2.6 mg kg-1 day-1. Results were compared to those of placebo-treated Wystar-Kyoto (WKY) and SHR rats. Whatever the dosage, acute or chronic calcium blockade caused a decrease in blood pressure which was maximal 1 h after administration and disappeared after the 16th h. Carotid arterial thickness and the composition of the arterial wall was determined from histomorphometry. 3. In placebo-treated SHR, the inverse relationship relating blood pressure to carotid arterial distensibility was significantly shifted toward higher values of blood pressure compared to the curve of normotensive placebo-treated WKY rats. The curve of SHR receiving chronically a non antihypertensive (0.6 mg kg-1 day-1) isradipine dose prolonged that of placebo-treated SHR toward lower values of blood pressure, so that carotid distensibility was significantly higher than in WKY for the same diameter and blood pressure level (145 mmHg). With administration of a chronic antihypertensive dose (2.6 mg kg-1 day-1) causing a significant decrease in arterial function. Acute antihypertensive calcium blockade with a single isradipine dose (2.6 mg kg-1 day-1) caused a similar shift in the pressure-distensibility curve toward the WKY curve although the histomorphometric composition of the arterial wall differed significantly from that of chronically treated animals. 4. The study provides evidence that, in living SHR submitted to calcium blockade, (i) a low dose of isradipine causing no substantial antihypertensive effect is associated with a significant elevation of carotid arterial distensibility for the same pressure and diameter as normotensive controls, and (ii) an acute or chronic dose causing a substantial antihypertensive effect is associated with a transient shift of the SHR distensibility-pressure curve toward a physiological arterial function, increasing carotid distensibility for the same pressure and diameter as WKY controls. Since such findings were observed independently of the histomorphometric composition of the arterial wall, they imply that the transient decrease in arterial stiffness produced by calcium blockade should involve specific changes in the connections between arterial smooth muscle and extracellular matrix.     

Determination of optical properties of amorphous Ta2O5 films deposited by spin- and dip-coating methods

The optical properties of amorphous Ta₂O₅ films prepared by the sol-gel dip- and spin-coating deposition technique and dried at 60°C have been investigated. Refractive index, extinction coefficient and optical energy gap have been calculated from optical transmission measurements using the Swanepoel method. The films of similar thickness deposited by the two methods were compared. It is shown that the optical properties are dependent on the deposition methods. The energy band gap of the Ta₂O₅ films is 3.75 ± 0.12 eV and is independent of the coating methods.     

Heat treatment effects on the optical properties of Sol–gel Ta2O5 thin films

In this work optical properties of Ta₂O₅ thin films with respect to heat treatment temperature were investigated. Ta₂O₅ thin films were prepared by sol–gel process using dip-coated method with a constant speed of 107 mm/min. Optical properties have been calculated from optical transmission measurements as a function of heat treatment temperature. The refractive indices and absorption coefficients were affected by heat treatment. The refractive index at λ=550 nm increased from 1.84 to 2.04 and absorption coefficient increased from 241 to 5668 cm⁻¹ when heat treatment temperature increased from 100°C to 500°C. The thickness of the film decreased from 272 to 190 nm and their optical band gap decreased from 3.68±0.09 eV to 3.51±0.08 eV for the film heated from 100°C to 500°C.     

Synthesis and characterization of nanocrystalline CdZnO thin films prepared by sol-gel dip-coating process

Nanocrystalline Cd_xZn_1 − xO thin films with different Cd volume ratios in solution (x = 0, 0.25, 0.50, 0.75 and 1) have been deposited on glass substrate by sol-gel dip-coating method. The as-deposited films were subjected to drying and annealing temperatures of 275 °C and 450 °C in air, respectively. The prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy and dc-electrical measurements. The results show that the samples are polycrystalline and the crystallinity of the films enhanced with x. The average grain size is in the range of 20-53 nm. The atomic percent of Cd:Zn was found to be 9.50:1.04, 6.20:3.77 and 4.42:6.61 for x = 0.75, 0.50 and 0.25, respectively. It was observed that the transmittance and the band gap decreased as x increased. All the films exhibit n-type electrical conductivity. The resistivity (ρ) and mobility (μ) are in the range of 3.3 × 10² − 3.4 × 10^− 3 Ω cm, and 1.5 − 45 cm² V^− 1 s^− 1 respectively. The electron density lies between 1.26 × 10¹⁶ and 0.2 × 10²⁰ cm^− 3.     

Optimal online pricing with network externalities

We study the optimal pricing strategy for profit maximization in presence of network externalities where a decision to buy a product depends on the price offered to the buyer and also on the set of her friends who have already bought that product. We model the network influences by a weighted graph where the utility of each buyer is the sum of her initial value on the product, and the linearly additive influence from her friends. We assume that the buyers arrive online and the seller should offer a price to each buyer when she enters the market. We also take into account the manufacturing cost. In this paper, we first assume that the monopolist defines a unique price for the product and commits to it for all buyers. In this case, we present an FPTAS algorithm that approximates the optimal price with a high probability. We also prove that finding the optimum price is NP-hard. Second, we consider a market with positive network externalities and assume that the monopolist could offer a private price to each customer. We prove that this problem is also hard to approximate for linear influences. On the positive side, we present a polynomial time algorithm for the problem when influences are symmetric. At last, we show that the seller has more ability to extract influences with price discrimination.