Effect of silicon thickness on the degradation mechanisms of sequential laterally solidified polycrystalline silicon TFTs during hot-carrier stress

We have investigated bias stress-induced aging effects in polycrystalline silicon thin-film transistors (poly-Si TFTs), as a function of the active layer thickness. Two aging mechanisms were identified: hot-carrier injection in the gate insulator and deep-state generation in the active "body." Hot-carrier injection was found dominant in devices having very thin (30 nm) or thick (100 nm) active layers. Deep-state generation dominated in devices having intermediate active layer thickness (50 nm). The fully depleted aspect of ultrathin active-layer devices, as well as their relative immunity to substantial degradation under bias stress, favor the implementation of thin active layer for the fabrication of high-performance and high-reliability poly-Si TFTs.     

Reactive power consumption in photovoltaic inverters: a novel configuration for voltage regulation in low‐voltage radial feeders with no need for central control

High photovoltaic (PV) system generation in low‐voltage feeders can cause voltage rise especially in low demand conditions. The conventional way of coping with voltage violation is disconnection of the PV systems or curtailment of the generated power. To address this issue, a novel configuration for voltage management in a radial feeder via regulated reactive power capability in PV inverters is presented. The novelty of the proposed configuration is based on the fact that all the PV inverters with the ability to consume reactive power are involved in voltage regulation without being centrally controlled. In order to apply the configuration, a reference voltage is initially estimated for each PV system, and the PV inverters are calibrated accordingly. These settings depend on the feeder topology and can be calculated by the distribution network operator with a simple power flow modelling tool. Finally, this paper presents a sensitivity analysis in order to examine how reactive power consumption in a single inverter influences PV penetration and inverter sizing at various PV topologies along the feeder. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrochemical promotion of the CO2 hydrogenation reaction using thin Rh, Pt and Cu films in a monolithic reactor at atmospheric pressure

A monolithic electropromoted reactor (MEPR) with up to 22 thin Rh/YSZ/Pt or Cu/TiO₂/YSZ/Au plate cells was used to investigate the hydrogenation of CO₂ at atmospheric pressure and temperatures 220–380 °C. The Rh/YSZ/Pt cells lead to CO and CH₄ formation and the open-circuit selectivity to CH₄ is less than 5%. Both positive and negative applied potentials enhance significantly the total hydrogenation rate but the selectivity to CH₄ remains below 12%. The Cu/TiO₂/YSZ/Au cells produce CO, CH₄ and C₂H₄ with selectivities to CH₄ and C₂H₄ up to 80% and 2%. Both positive and negative applied potential significantly enhance the hydrogenation rate and the selectivity to C₂H₄. It was found that the addition of small (0.5 kPa) amounts of CH₃OH in the feed has a pronounced promotional effect on the reaction rate and selectivity of the Cu/TiO₂/YSZ/Au cells. The selective reduction of CO₂ to CH₄ starts at 220 °C (vs 320 °C in absence of CH₃OH) with near 100% CH₄ selectivity at open-circuit and under polarization conditions at temperatures 220–380 °C. The results show the possibility of direct CO₂ conversion to useful products in a MEPR via electrochemical promotion at atmospheric pressure.     

A hierarchical method to integrated solvent and process design of physical CO2 absorption using the SAFT‐γ Mie approach

Molecular‐level decisions are increasingly recognized as an integral part of process design. Finding the optimal process performance requires the integrated optimization of process and solvent chemical structure, leading to a challenging mixed‐integer nonlinear programming (MINLP) problem. The formulation of such problems when using a group contribution version of the statistical associating fluid theory, SAFT‐γ Mie, to predict the physical properties of the relevant mixtures reliably over process conditions is presented. To solve the challenging MINLP, a novel hierarchical methodology for integrated process and solvent design (hierarchical optimization) is presented. Reduced models of the process units are developed and used to generate a set of initial guesses for the MINLP solution. The methodology is applied to the design of a physical absorption process to separate carbon dioxide from methane, using a broad selection of ethers as the molecular design space. The solvents with best process performance are found to be poly(oxymethylene)dimethylethers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3249–3269, 2015     

The Adhesion Properties of Mortars in Relation with Microstructure

The interaction between masonry units and mortar is a crucial factor for the quality of a wall. The most important factor is the adhesion between bricks and mortar in order to construct a masonry wall with adequate strength, good impermeability, and durability. In this work mortars were produced with various cement/lime/aggregates ratio. The adhesion properties of the mortars with clay bricks were tested with a simplified tensile/tear testing measurement. In order to investigate the adhesion properties in relation with microstructure the mortars were characterized with X-ray diffraction and were further investigated with scanning electron microscopy and stereoscopy. It was found that adhesion is favored by the formation of a Si–Al matrix with a low Ca content in the brick/mortar interface and the formation of fine Ca–Al–Si phases which can penetrate into the brick.     

Dielectric charging in silicon nitride films for MEMS capacitive switches: Effect of film thickness and deposition conditions

The paper presents a systematic investigation of the dielectric charging and discharging process in silicon nitride thin films for RF-MEMS capacitive switches. The SiN films were deposited with high frequency (HF) and low frequency (LF) PECVD method and with different thicknesses. Metal–Insulator–Metal capacitors have been chosen as test structures while the Charge/Discharge Current Transient method has been used to monitor the current transients. The investigation reveals that in LF material the stored charge increases with the film thickness while in HF one it is not affected by the film thickness. The dependence of stored charge on electric field intensity was found to follow a Poole–Frenkel like law. Finally, both the relaxation time and the stored charge were found to increase with the electric field intensity.     

Bone-derived growth factor release from poly(alpha-hydroxy acid) implants in vitro

Matrix proteins were extracted from bovine cortical bone and polymer implant discs (13 mm x 2 mm composed of 50:50 poly DL-lactide-co-glycolide; mol. wt. approximately 9000) prepared by compression moulding granules with lyophilized bone matrix extracts (BMX) 10.1 (w/w). BMX-containing polymers were cultured for 5 wk in either serum-free Dulbecco's modification of Eagle's medium (DMEM) or phosphate buffer, and growth factor activity released into the media assayed by its ability to stimulate the proliferation of murine fibroblast BALB/c/3T3 cells. Approximately 60-75% of the biological activity was released during the first week of culture; however, less than half of the growth factor units originally incorporated into the implants retained biological activity. Scanning electron microscopy revealed the development of significant internal porosity by week 2; the size of the channels, pores and surface openings suggested they were of the right order for bone ingrowth. These preliminary findings suggest that poly(alpha-hydroxy acid) polymers containing bone-derived growth factors could have potential for stimulating osseous regeneration in vivo.     

Numerical model of heat transfer in the rabbit eye exposed to 60-GHz millimeter wave radiation

A numerical model of the anterior chamber of the rabbit eye is presented. The model takes into account both the fluid dynamics of the aqueous humor and the realistic boundary conditions at the interface of the cornea with the environment. The model is used to determine the temperature distribution and velocity field under 60-GHz millimeter wave radiation. The maximum predicted temperature (45.8 (°) C for an incident power density of 475 mW/cm(2)) is in good agreement with experimental results. Moreover, the model shows that there is a value for the incident power density (about 100 mW/cm(2)) for which the direction of aqueous humor flow due to buoyancy is inverted, because of the inversion of the temperature gradient in the anterior chamber of the eye. This phenomenon has already been reported from experimental observations and can be numerically studied, if aqueous humor fluid dynamics are taken into account in the heat-transfer model.     

Dimming/brightening in Athens: Trends in Sunshine Duration, Cloud Cover and Reference Evapotranspiration

Evidence of global dimming/brightening is mainly based upon few measurements of solar radiation. A need for more research supported and extended with the use of other climatic variables, such as sunshine duration, recorded for a longer time period and successfully used as a proxy for solar radiation over the past 80 years, has already been urged. Thus, in this study, residual sunshine duration series computed after removal of the cloudiness-related variability, from daily sunshine duration and cloudiness data measured at the National Observatory of Athens are used for highlighting global dimming or brightening periods in Athens, during the period 1951–2001. Furthermore, the consistency of trends in radiation records and their implications for the hydrological cycle and especially the trends in reference evapotranspiration are examined, during the period 1951–2001. The analysis focuses on the seasonal decadal variations, determines and explains the causes of the seasonal trends from the inter-annual and decadal variability of the sunshine duration during the last half past century, with a special emphasis in detecting possible sub-periods in Athens. The signs of trends in the modeled annual and seasonal reference evapotranspiration are estimated, according to the indicated global dimming/brightening periods.     

Investigating customer satisfaction dimensions with service quality of online auctions: an empirical investigation of e-Bay

Over the recent years, C2C (consumer-to-consumer) electronic market has increased rapidly, and has become the most active segment of e-markets today. Despite the growth and popularity of online auctions and especially of e-Bay, which has been considered to be one of the most profitable e-commerce companies, the online auction environment is risky and transactions are complex due to the fact that buyer and seller do not know each other and they are not familiar. Although many studies have examined the impact of e-service quality on customer satisfaction in B2C (business-to-consumer) or B2B (business-to-business) commerce, the literature is insufficient in the case of C2C commerce. However, a number of authors have conducted research in C2C and particularly in e-Bay but in all of the cases, data source from e-Bay’s feedback system was employed in order to investigate service quality issues. Nevertheless, in this study a field research was conducted in order to collect the necessary data and thus reducing possible bias. The purpose of this paper is to examine some determinants of satisfaction with service quality dimensions in the online auction environment. More specifically, this paper is examining the case of e-Bay, in order to have a better understanding of buyers’ satisfaction in this risky environment. The paper’s aim is accomplished through an empirical investigation of a sample of 2,099 buyers of e-Bay, examining buyers’ expectation and perception levels towards service quality of e-Bay. Gap analysis was first employed in order to identify users’ disconfirmation dimensions in the online auction market place. Some research hypotheses are formulated to find out whether these dimensions have a positive disconfirmation. In most of the cases a positive disconfirmation is tracked down. Secondly, factor analysis was utilized to identify broad determinants of e-Bay service quality. The pool of the initial items deduced to four factors. These factors are, to a degree, differentiated in the Greek environment from factors found in other studies. A second round of research hypotheses are formulated again to find out whether those factors are related to the users’ disconfirmation dimensions. Finally, a new theoretical model is proposed based on the above mentioned hypotheses.