Results 1 - 10 of 553943
Results 1 - 10 of 553943. Search took: 0.154 seconds
|Sort by: date | relevance|
[en] Early infarcts are hard to diagnose on non-contrast head CT. Dual-energy CT (DECT) may potentially increase infarct differentiation. The optimal DECT settings for differentiation were identified and evaluated. One hundred and twenty-five consecutive patients who presented with suspected acute ischemic stroke (AIS) and underwent non-contrast DECT and subsequent DWI were retrospectively identified. The DWI was used as reference standard. First, virtual monochromatic images (VMI) of 25 patients were reconstructed from 40 to 140 keV and scored by two readers for acute infarct. Sensitivity, specificity, positive, and negative predictive values for infarct detection were compared and a subset of VMI energies were selected. Next, for a separate larger cohort of 100 suspected AIS patients, conventional non-contrast CT (NCT) and selected VMI were scored by two readers for the presence and location of infarct. The same statistics for infarct detection were calculated. Infarct location match was compared per vascular territory. Subgroup analyses were dichotomized by time from last-seen-well to CT imaging. A total of 80–90 keV VMI were marginally more sensitive (36.3–37.3%) than NCT (32.4%; p > 0.680), with marginally higher specificity (92.2–94.4 vs 91.1%; p > 0.509) for infarct detection. Location match was superior for VMI compared with NCT (28.7–27.4 vs 19.5%; p < 0.010). Within 4.5 h from last-seen-well, 80 keV VMI more accurately detected infarct (58.0 vs 54.0%) and localized infarcts (27.1 vs 11.9%; p = 0.004) than NCT, whereas after 4.5 h, 90 keV VMI was more accurate (69.3 vs 66.3%). Non-contrast 80–90 keV VMI best differentiates normal from infarcted brain parenchyma.
[en] The development of new cathode materials with high capacity, good stability, and high safety is important for the future improvement of Li batteries. LiFeBO is considered to be a type of promising electrode materials for Li-ion batteries due to its low cost, high theoretical capacity of 220 mAh/g (about 30% larger than that of LiFePO), low toxicity, and small volume change of 2% during the Li reversible extraction/insertion process. However, its electronic conductivity and rate performance still need further improvement. To optimize the performance of the LiFeBO, Mn, Cr, and Ni doping at Fe site have been studied experimentally, while the effect of minor addition of 3d transition metals on the electronic structure of LiFeBO is rarely investigated. Thus, density functional theory calculations corrected by on-site Coulomb interactions have been conducted to study the crystal structure and electronic property of the LiFeMBO (M = Mn, Co, and Ni) electrode systems. The results indicate that the coordination geometry about Fe in LiFeBO is a distorted trigonal bipyramid with a distortion which can be attributed to a Jahn-Teller effect. The band gap energy of LiFeBO is calculated to be 3.40 eV, which is in reasonable agreement with the previously computed values. The doping at Fe site with Mn cannot reduce the distortion of Jahn-Teller effect, whereas Co doping intensifies Jahn-Teller distortion of the FeO trigonal bipyramid in LiFeBO. Ni substitution is predicted to be able to introduce impurity levels, and the Jahn-Teller distortion degree of the trigonal bipyramid decreased from 11.9 of the FeO to 8.7% of the NiO. Thus, Ni doping is expected to increase stability and the electronic conductivity of the LiFeBO structure.
[en] Herein, the optically induced operation of ZnO-based laser structures is reported, fabricated with plasma-assisted molecular beam epitaxy (PA-MBE) on native ZnO substrate. ZnMgO is used both to confine the optical mode within ZnO waveguide and to form quantum barriers of ZnO quantum wells. The resonator of these devices is defined by reactive ion etching (RIE) with a chlorine/argon plasma. The lowest laser threshold is measured to be approximately 0.4 MW cm at room temperature when excited via the third harmonic of a YAG:Nd (355 nm). It is observed that the mode spacing depends on both the resonator length and the excitation power density, which is explained by introducing plasmonic corrections to the waveguide refractive index. (© 2020 Wiley‐VCH GmbH)
[en] Optical absorption and emission spectra are the important quantifiable properties for CuI as a promising optoelectronic material. Previous research on the sputter deposition of CuI focuses on room-temperature growth. Herein, the effect of growth temperature on the selected optical features of sputtered CuI thin films is investigated. An enhanced visible light transparency and a steeper absorption edge are achieved for CuI thin films by optimizing the growth temperature. The PL intensity ratio of free exciton to defect-related emission increases with increasing substrate temperature. These results suggest a strategy of growth temperature optimization for the enhanced absorption and emission of CuI for advanced optoelectronic applications. (© 2020 Wiley‐VCH GmbH)
[en] In carbonate electrolytes, the organic-inorganic solid electrolyte interphase (SEI) formed on the Li-metal anode surface is strongly bonded to Li and experiences the same volume change as Li, thus it undergoes continuous cracking/reformation during plating/stripping cycles. Here, an inorganic-rich SEI is designed on a Li-metal surface to reduce its bonding energy with Li metal by dissolving 4m concentrated LiNO in dimethyl sulfoxide (DMSO) as an additive for a fluoroethylene-carbonate (FEC)-based electrolyte. Due to the aggregate structure of NO ions and their participation in the primary Li solvation sheath, abundant LiO, LiN, and LiNO grains are formed in the resulting SEI, in addition to the uniform LiF distribution from the reduction of PF ions. The weak bonding of the SEI (high interface energy) to Li can effectively promote Li diffusion along the SEI/Li interface and prevent Li dendrite penetration into the SEI. As a result, our designed carbonate electrolyte enables a Li anode to achieve a high Li plating/stripping Coulombic efficiency of 99.55 % (1 mA cm, 1.0 mAh cm) and the electrolyte also enables a Li||LiNiCoMnO (NMC811) full cell (2.5 mAh cm) to retain 75 % of its initial capacity after 200 cycles with an outstanding CE of 99.83 %. (© 2020 Wiley‐VCH GmbH)
[en] Underachieved capacity and low voltage plateau is ubiquitous in conventional aqueous magnesium ion full batteries. Such limitations originate from the electrochemistry and the low carrier-hosting ((de)intercalation) potential of electrode materials. Herein, via a strategy of enhancing the electrochemistry through carrier-hosting potential compensation, high-energy Mg/Na hybrid batteries are achieved. A MgVCr(PO) (MVCP) cathode is coupled with FeVO (FVO) anode in a new aqueous/organic hybrid electrolyte, giving reliable high-voltage operation. This operation enables more sufficient (de)intercalation of hybrid carriers (Mg/Na), thereby enhancing the reversible capacity remarkably (233.4 mA h g at 0.5 A g, 92.7 Wh k g, that is, ≥1.75‐fold higher than those in conventional aqueous electrolytes). The relatively high Na-hosting potential of the electrodes compensates for the low Mg-hosting potential and widens/elevates the discharge plateau of the full battery up to 1.50 V. Mechanism study further reveals an unusual phase transformation of FVO to FeV and the low-lattice-strain pseudocapacitive (de)intercalation chemistry of MVCP. (© 2020 Wiley‐VCH GmbH)
[en] The government of India is promoting the electric vehicle industry to reduce the import dependence on crude oil and natural gas and to achieve ecological benefits. Electric vehicle projects are forging ahead due to the proactive policies of the government. The lithium-ion battery is an essential component of an electric vehicle. The lithium-ion battery is also used in the energy storage device and the communication sector. Presently, lithium-ion battery cells are not produced in India. Indian demand for lithium-ion cells are entirely met by import. However, battery packs are assembled in India with imported battery cells by a few units. (author)
[en] The aim of this work was to study photon and electron dose distributions in a phantom filled with water using the Monte Carlo Geant4 tool for electron energies ranging from 1 to 21 MeV and for photon energies ranging from 1.25 MeV to 25 MeV, corresponding to conventional radiotherapy Linac energies. The results of the Geant4 calculations were validated based on the relevant experimental data previously published. The results obtained were fitted and analytical models of dose distributions were developed for gamma radiation and electrons. For each of these models, one-dimensional (including dose depth profiles as a function of the depth inside the phantom) and two-dimensional (including the dose distribution as a function of depth and lateral position inside the phantom) dose distributions have been considered. Results are presented for photons and electrons of various energies. The coefficient of determination R illustrates an excellent match between the developed analytical model and the Geant4 results. It is demonstrated that the analytical models developed in the present study can be applied in various fields such as those used for calibration applications and radiation therapy. It is concluded that the analytical models developed allow for quick, easy and reliable clinical dose estimates and offer promising alternatives to the standard tools and methods used in radiotherapy for treatment planning.
[en] Compounds belonging to the series PbSbxTe1-x and Pb1-xSbxTe ( x = 0.1, 0.3, 0.5) were prepared in the nanostructured form by employing high-energy ball-milling and subsequent hot-pressing. The amphoteric property of antimony was utilized to substitute lead and tellurium in the compounds having the formula PbSbxTe1-x and Pb1-xSbxTe to make them p and n. All the compositions were evaluated for their figure of merit (ZT) and power factor after ascertaining their Seebeck coefficient, electrical and thermal conductivities. These compositions exhibited very high Seebeck coefficient both in low- and room-temperature regimes. Thermoelectric generator modules were constructed using combinations of n- and p-type PbSbTe and the voltage developed was measured and compared with the calculated values, and they are found to be in good agreement. Different combinations of p- and n-types from the series were tested, and the best among them were identified. (author)
[en] The dislocations are the deep level defects with a negative impact on the multi-crystalline silicon (mc-Si) solar cells. Though potential mechanisms of dislocation formation on the silicon ingot have been studied, few investigations consider the effect of LED hydrogenation on dislocation clusters. In this study, we have explored the influence of hydrogenation on the dislocation clusters of large-area (244.34±0.05 cm2) mc-Si solar cells using the high-intensity infrared LED source. However, applying normal cooling measure to hydrogenation will trigger the instability of the hydrogenation improvement effect due to residual thermal stress, so we proposed an appropriate rapid cooling measure (RCM) followed by hydrogenation and achieved optimized results. The results indicated that electrical properties, minority carrier lifetime, current density, power density and external quantum efficiency were enhanced through LED hydrogenation and RCM, and the degradation of mc-Si solar cells also was significantly suppressed. To estimate the content of dislocations after LED hydrogenation and RCM, we applied the X-ray diffraction techniques to calculate the dislocation density using the full-width at half maximum of the rocking curve at (111), (220), (311), (400) and (331) reflections. The dislocation density of mc-Si PERC solar cells was decreased by 0.12 x 108 cm-2 (±0.02 x 108 cm-2) after LED hydrogenation and RCM. Meanwhile, photoluminescence images also illustrated that LED hydrogenation passivated dislocation clusters as well as impurities and defects gathered by dislocations. Therefore, LED hydrogenation of dislocation clusters is an effective measure to improve the performance of dislocation-containing mc-Si solar cells. (author)