Positron lifetime measurements on CdTe 0.15% Zn-doped by weight are presented, trapping to monovacancy defects is observed. At low temperatures, localization at shallow binding energy positron traps dominates. To aid defect identification density functional theory, calculated positron lifetimes and momentum distributions are obtained using relaxed geometry configurations of the monovacancy defects and the Te antisite. These calculations provide evidence that combined positron lifetime and coincidence Doppler spectroscopy measurements have the capability to identify neutral or negative charge states of the monovacancies, the Te antisite, A-centers, and divacancy defects in CdTe.
Polymethylpentene (PMP) possesses high mechanical, thermal and chemical stability coupled with high conductivity and ionic selectivity which is used for autoclavable medical and laboratory equipment. The Positron annihilation Lifetime (PAL) measurements were performed at temperatures from 300 K down to 165 K (1st cooling run), from 175 K up to 425 K (1st heating run), and from 425 K to 165 K (2nd cooling run) under vacuum. The temperature dependence of the free volume and its contents, which were deduced from the ortho‐ positronium (o ‐Ps) lifetime, exhibited a little change between the cooling and heating runs, so that the behavior appears to be reversible. The variation of the free volume with temperature reflects the glass transition temperature of PMP at about 300 K. Based on the free volume theory of Cohen‐Turnbull, the ionic conductivity σ is correlated with the mean hole volume Vh·. A linear relation between ln(σT0.5) and 1/Vh was observed and the critical hole volume was also estimated to be around 811.9 Å3. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Smart parking lots are smart places capable of supporting both parking and charging services for electric vehicles (EVs). In order to manage EV charging, the parking lot local controller (PLLC) requires data exchange with EV charging stations (EVCSs) through communication infrastructures. However, data losses and communication delays are unavoidable and may significantly degrade the system performance. This work aims to investigate the underlying communication networks for remote monitoring of EVCSs in a smart campus parking lot. The communication network consists of two subnetworks: parking area network (PAN) and campus area network (CAN). PAN covers communication among EVs, charging stations and PLLC, while CAN enables dedicated communication between PLLCs and a global controller of the university. As one of the major obstacles in EV system is the lack of unified communication architecture to integrate EVCS in the power grid, we develope communication models for the in-vehicle system and EVC-Ss based on logical node concept of IEC 61850 standard. Furthermore, we implement network models for EVCSs using OPNET modeler. Different communication technologies and configurations are considered in modeling and simulations, and end-to-end delay is evaluated and discussed.
A method for measurement of lip incompetence is described. Electromyographic techniques were used to obtain relaxation of the muscles of the lip and of a jaw elevator muscle. Standardized photographs were taken of the subject's profile, from which lip separation and face height were measured. Variation was found in successive measurements of lip posture, some of which appeared to depend upon mandibular posture. With the teeth in occlusion, lip separation was reduced. Active maintenance of lip contact by the subject was often associated with a reduction in lower face height, which may have been a direct consequence of the lip muscle activity, or of jaw elevator activity facilitating the lip closure.
The positron annihilation lifetime (PAL) technique was used to investigate the yield and lifetime of positronium (Ps) in three different samples of per‐fluorinated sulfonic acid/polytetrafluoroethylene (PTFE) proton exchange membranes. The high probability of Ps formation enables the study of the hole volume size by the PAL technique and explains the mechanism of both methanol permeation and proton conductivity of the membranes in relation to the relative humidity (RH). The influence of various membrane parameters, including water uptake, proton conductivity, and mechanical properties, was studied. The concentration of water molecules and SO3−–H3O+groups is correlated with the ion exchange capacity (IEC) of the membranes where higher IEC leads to high absorbance of water. The proton conductivity is enhanced by increasing the IEC value of the membrane. The activation energies of decomposition temperature for the F‐950 membrane are the lowest (Eb = 2.856 and 1.030 eV for the 1st and 2nd decomposition peaks, respectively, implying that the membrane with high IEC is thermally less stable. With increasing the IEC of the membranes, the concentration of the water molecules/SO3 group increases. In addition, the proton conductivity of the membrane is positively influenced by increasing water content at high RH. The fact that the variations in hole volume size and both methanol permeability and proton conductivity are highly dependent on RH suggests that hole volume size plays an important role in many parameters of hydrated perfluorinated sulfonic acid/PTFE proton exchange membranes. The outcomes data were introduced and interpreted appropriately with a theoretical model and compared with the literature.
Free volume plays a key role on transport in proton exchange membranes (PEMs), including ionic conduction, species permeation, and diffusion. Positron annihilation lifetime spectroscopy and electrochemical impedance spectroscopy are used to characterize the pore size distribution and ionic conductivity of synthesized PEMs from polysulfone/polyphenylsulfone multiblock copolymers with different degrees of sulfonation (SPES). The experimental data are combined with a bundle-of-tubes model at the cluster-network scale to examine water uptake and proton conduction. The results show that the free pore size changes little with temperature in agreement with the good thermo-mechanical properties of SPES. However, the free volume is significantly lower than that of Nafion®, leading to lower ionic conductivity. This is explained by the reduction of the bulk space available for proton transfer where the activation free energy is lower, as well as an increase in the tortuosity of the ionic network.
The photovoltaic performance of Cu(In1-x,Gax)Se2 (CIGS) materials is commonly assumed to be degraded by the presence of vacancy-related defects. However, experimental identification of specific vacancy defects remains challenging. In this work we report positron lifetime measurements on CIGS crystals with x = 0, and x = 0.05, saturation trapping to two dominant vacancy defect types, in both types of crystal, is observed and found to be independent of temperature between 15–300 K. Atomic superposition method calculations of the positron lifetimes for a range of vacancy defects in CIS and CGS are reported. The calculated lifetimes support the assignment of the first experimental lifetime component to monovacancy or divacancy defects, and the second to trivacancies, or possibly the large In-Se divacancy. Further, the calculated positron parameters obtained here provide evidence that positron annihilation spectroscopy has the capability to identify specific vacancy-related defects in the Cu(In1-x,Gax)Se2 chalcogenides.
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