Metal tin sulfides, MSnS3(M=Hf,Zr) are quasi-one-dimensional compounds that crystallize in the orthorhombic space group. First-principles density functional theory calculations were performed using ...GGA + U and HSE06 methods to analyze their structural, electronic and optical properties. It was observed that the structural and optical properties are in good agreement with available experimental results. Structural studies showed that the HfSnS3 and ZrSnS3 are quasi-one-dimensional compounds with similar lattice parameters. Electronic structure calculations reveal that both compounds are indirect band gap semiconductors with band gap values of 1.72 eV and 1.85 eV respectively. Optical properties of both materials were studied using GGA + U method. The calculations indicate that both MSnS3(M=Hf,Zr) compounds exhibit a large birefringence with a comparatively large optical anisotropy.
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•Structural, electronic, and optical properties of HfSnS3 and ZrSnS3 were investigated using density functional theory..•Electronic structure calculations indicate that both materials are wide bandgap semiconductors.•HfSnS3 and ZrSnS3 exhibit high optical anisotropy.•HfSnS3 exhibits broadband large-scale birefringence in the ultraviolet region at least of the order exhibited by ZrsnS3.
Polyether telechelics based on ethylene glycol,1,2-propylene glycol and 1,4- butylene glycol of with various molar masses and bearing at both terminals functional groups such as maleimide, ...itaconimide, nadimide and hydroxyl groups were individually examined as toughening agents for an unsaturated polyester resin (UPER). For a given telechelic, the toughening effect was evaluated at different mass ratios. The difference in toughening efficacy arose from the differential reactivity of the telechelics end groups combined with the unsaturation of the UPER with the reactive diluent, styrene. This causes a differential distribution of the polyether groups in the UPER matrices, resulting in a differential dipolar interaction of the polyether segments among themselves and with the UPER itself. The matrices cohesive strength is decided by these interactions, the possibility for which is decided by the spacing of these polyether segments in the matrix, as per the reactivity ratios between styrene-maleic complex pair and the polyether end groups. An increased inter-segmental spacing of polyether could diminish the chance for inter-segmental dipolar interactions that can stake the cohesive strength and thus the mechanical properties of the matrices. These aspects have been quantified in terms of their efficacy factors which conformed well to the strength and fracture properties of UPER blended in small proportions with the end-functionalized polyether telechelics.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper deals with a study on toughening of an unsaturated polyester resin (UPR) using maleimide end-capped oligomers of polypropylene glycol (M-PPG), polytetramethyene oxide (M-PTMO), and ...polyethylene glycol (M-PEG) of varying molecular weights. These macro bismaleimides with large spacing between the functional groups were synthesized from the corresponding polyols (hydroxy telechelics) by reaction with (4-Maleimido) benzoyl chloride (MBC). These derivatives were characterised by chemical and spectral methods. These were then blended and co-cured with a UP resin based on copoly-propylene glycol (terephthalate –maleate) and relying on maleic acid–styrene copolymerisation for curing. The impacts of the nature, concentration and molecular weight of the telechelic additive on the physical and mechanical properties of the resultant unsaturated polyester resin (UPR) blends have been examined. Addition of the telechelics improved the mechanical characteristics of the crosslinked systems significantly. The improvement in fracture properties for a telecheilc was directly correlatable to a decrease in overall crosslink density estimated exprimentally as well as theoretically. The additive’s backbone structure dictated the Tg and related properties of the blend. The properties were found to be the best for the blend toughened with M-PPG with a molecular weight 2000 g/mol, at 2.5 parts per hundred parts.The morphological features at this concentration as reflected in scanning electron microscopic analyses showed descrete poly ether particles microphase separation in the UPR matrix that acted as a crack path arrester.
Graphical Abstract
Anisotropy of optical parameters of TaTlS3 and TaTlSe3 is investigated through first principles calculations. Indirect bandgap quasi-one-dimensional semiconductors TaTlS3 and TaTlSe3 have bandgaps of ...1.15 eV and 0.84 eV, respectively. Important optical parameters are found to be strongly influenced by the radiation direction of the incident beam, as indicated by large birefringence and dichroism. Large optical anisotropy suggests promising nonlinear and linear optoelectronic applications for these materials, including wave plates, polarizers and phase-matching devices.
•Large optical anisotropy is reported for quasi 1D TaTlX3 (X = S, Se) materials•The optical properties are investigated through the DFT method using HSE06 functional•TaTlX3 exhibit large birefringence values in the energy range 1−6 eV•TaTlX3 exhibit large absorption coefficient in the visible and UV regions•Optical parameters of TaTlX3 are suitable for optoelectronic applications
Each year over 16 million older Americans undergo general anesthesia for surgery, and up to 40% develop postoperative delirium and/or cognitive dysfunction (POCD). Delirium and POCD are each ...associated with decreased quality of life, early retirement, increased 1-year mortality, and long-term cognitive decline. Multiple investigators have thus suggested that anesthesia and surgery place severe stress on the aging brain, and that patients with less ability to withstand this stress will be at increased risk for developing postoperative delirium and POCD. Delirium and POCD risk are increased in patients with lower preoperative cognitive function, yet preoperative cognitive function is not routinely assessed, and no intraoperative physiological predictors have been found that correlate with lower preoperative cognitive function. Since general anesthesia causes alpha-band (8-12 Hz) electroencephalogram (EEG) power to decrease occipitally and increase frontally (known as "anteriorization"), and anesthetic-induced frontal alpha power is reduced in older adults, we hypothesized that lower intraoperative frontal alpha power might correlate with lower preoperative cognitive function. Here, we provide evidence that such a correlation exists, suggesting that lower intraoperative frontal alpha power could be used as a physiological marker to identify older adults with lower preoperative cognitive function. Lower intraoperative frontal alpha power could thus be used to target these at-risk patients for possible therapeutic interventions to help prevent postoperative delirium and POCD, or for increased postoperative monitoring and follow-up. More generally, these results suggest that understanding interindividual differences in how the brain responds to anesthetic drugs can be used as a probe of neurocognitive function (and dysfunction), and might be a useful measure of neurocognitive function in older adults.
The relevance of focal triggers in persistent atrial fibrillation (PerAF) and long-standing persistent atrial fibrillation (LSPAF) has not been previously investigated.
We prospectively evaluated the ...prevalence and distribution of AF triggers in patients referred for catheter ablation of PerAF and LSPAF.
We analyzed consecutive patients undergoing first time AF ablation who underwent a standardized trigger protocol including cardioversion of induced or spontaneous AF and infusion of up to 20 μg of isoproterenol for 15-20 minutes either before or after pulmonary vein (PV) isolation accomplished. Triggers were defined as AF/sustained atrial tachyarrhythmia or repetitive atrial premature depolarizations.
A total of 2168 patients were included (mean age 57 ± 11 years; 1636 75% men), with 1531 patients having paroxysmal AF (PAF) (71%), 496 having PerAF (23%), and 141 having LSPAF (7%). PV triggers were found in 1398 patients with PAF (91%), 449 patients with PerAF (91%), and 129 patients with LSPAF (91%) (P = .856 for comparison across groups). Non-PV triggers were elicited in a total of 234 patients (11%), and the prevalence was similar across the different types of AF (PAF, 165 11%; PerAF, 54 11%; LSPAF, 15 11%; P = .996 for comparison across groups).
PVs are the main AF trigger site in patients with PerAF and LSPAF, with an overall prevalence similar to that found in patients with PAF. These results support the current recommendations for PV isolation as the cornerstone of catheter ablation to eliminate AF triggers in PerAF and LSPAF.
Syntactic foams based on oxazolidone‐modified epoxy resin using glass microballoons as reinforcing filler with varying densities were processed. The influence of various grades of microballoons and ...their concentration on the mechanical, thermal, thermomechanical, and flammability characteristics were investigated. The effect of temperature on the compressive strength with density was monitored in detail. By incorporating the microballoons, Tg of the syntactic foam increased from 90 °C to 115 °C. Thermal conductivity was found to decrease from (0.064 to 0.056 W/(m·K)) in conjunction with decreasing resin to filler ratio. In the case of composites filled with K25 alone, the creation of large voids due to less effective packing between the microballoons led to lower thermal conductivity. The specific heat of the different composites was in the range of 0.32 to 0.44 cal/g/°C, and the coefficient of thermal expansion was in the range of 13.2 to 17.4 × 10−6/°C with limiting oxygen index of 28% to 33%.
PbMS3 (M = Hf, Zr) are ternary sulfides with the general structure ABX3, where A is a metal, B is a transition metal and X is a chalcogen or halogen element. This work investigates the anisotropy of ...the optical and electronic properties of PbMS3, and their applicability in optoelectronic devices using first principles DFT calculations. PbHfS3 is an indirect bandgap semiconductor (1.2 eV), whereas PbZrS3 has direct bandgap (1.1 eV). The effective masses of electrons and holes exhibit strong anisotropy along the various high symmetry directions of the Brillouin zone. Important optical parameters are found to be strongly dependent on the direction of the incident radiation, best indicated by the large birefringence value. Considerable optical anisotropy suggests their promising linear and nonlinear optoelectronic applications such as polarizers, wave plates, and phase-matching elements. Small carrier effective masses, large charge recombination rates and suitable bandgap indicate the possibility of solar and photovoltaic applications.
•The anisotropy of quasi-1D PbMS3 materials are investigated using DFT.•The calculated results are in excellent agreement with the experiments.•The direct and indirect nature of the band structure is explained in detail.•PbMS3 materials exhibit good electronic and optical anisotropy.•PbMS3 materials are suitable for optoelectronic and photovoltaic applications.
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