Aerospace composite cured by quickstep and autoclave processing techniques: Evaluation and comparison of reaction progress

Quickstep is relatively a new technique for aerospace composite processing. Thermoset resins (prepregs) have been frequently designed by autoclave method requiring low ramp rate curing of 2–3 K min−1. However, ramp rate up to 15 K min−1 has been achieved via Quickstep processing. This technique allows alteration in chemo-rheology of resin system and so influences the reaction progress. In this attempt, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) were used to monitor the cure progress of 977-2A epoxy resin and carbon fiber reinforced composite. The curing reaction progress of 977-2A epoxy/carbon fiber was considered for the first time by comparing Quickstep processing and autoclave method. According to DSC results, the reaction progress in Quickstep technique was comparable to that of autoclave curing. Moreover, DMTA of Quickstep cured samples showed increase in glass transition temperature (Tg) due to increased cross-linking density at greater hold time (upper cure temperature). FTIR was used to monitor the conversion of representative functional groups versus applied Quickstep and autoclave curing steps. The structural analysis depicted that the Quickstep curing path for 977-2A resin was different than the autoclave curing; however the final cross-linked structure was similar to that of autoclave cured samples

Examining folic acid intake: a cross-sectional study of pregnancy-related practices

Background: Folic acid supplementation during the periconceptional period is critical in preventing neural tube defects (NTDs) in the developing fetus. In Pakistan, a profound lack of awareness is seen regarding preventable pregnancy-related illnesses and the consequential high maternal and fetal mortality and morbidity rates. However, data from the surveys in the region of Sindh lacks inquiries regarding the baseline characteristics of the surveyed participants. Therefore, this study endeavoured to address this gap. Methods: Between October 2022 and April 2023, a cross-sectional study was conducted at two major tertiary care hospitals in Hyderabad and Jamshoro, Pakistan. A total of 374 participants, chosen by non-probability consecutive sampling, comprised the sample size. The association of demographic variables and knowledge, attitude, and practice of consumption of folic acid during pregnancy was determined using the χ2 test. A p value of less than 0.5 was considered statistically significant. Results: The mean age of the participants was 26.4±5.7 years. A total of 199 (53.20%) participants were literate, compared to 175 (46.79%) participants who were illiterate. Literate women fared better than illiterate women in all the metrics with a p-value of <0.001 and a Pearson correlation coefficient (r) of >0.7. Moreover, folic acid was consumed by only 38% of pregnant women during the periconceptional period. Conclusions: A substantial lack of knowledge regarding folic acid was found in the surveyed sample, significantly more marked in the illiterate faction. Additionally, the practice was rather unsatisfactory. However, the attitude remained encouraging

Probing charge trapping sites in M–N–C electrocatalysts via time-resolved transient absorption spectroscopy

Among non-platinum group metal (non-PGM) electrocatalysts for the oxygen reduction reaction (ORR), the class of metal-decorated nitrogen-doped carbon (M–N–C) materials is most promising. The active site is generally accepted to be a metal coordinated with nitrogen within the carbon lattice and/or nanoparticles. But confusion remains around the catalytic mechanisms. Better and more fundamental insights into these materials allow the design of more efficient M–N–C catalysts. In this study, we report the first direct observation of charge-trapping sites induced by metal decoration in M–N–C electrocatalysts using ultrafast time-resolved transient absorption spectroscopy. Ultrafast time-resolved spectroscopy has long been used for molecular characterization and to study photocatalysts, but its application to probe the intrinsic properties of electrocatalysts can be extended to all materials. Such sites have been associated with modulated charge distribution and enhancement of electron transfer efficiency during catalytic processes. Our study not only provides new insights into the electronic behavior of M–N–C materials but also establishes ultrafast spectroscopy as a powerful tool to study charge dynamics in electrocatalysts broadly, paving the way for more informed and efficient catalyst design

Prophylactic mesh placement for the prevention of incisional hernia in high-risk patients after abdominal surgery: A systematic review and meta-analysis

Background and objectives: In high-risk populations, the efficacy of mesh placement in incisional hernia (IH) prevention after elective abdominal surgeries has been supported by many published studies. This meta-analysis aimed at providing comprehensive and updated clinical implications of prophylactic mesh placement (PMP) for the prevention of IH as compared to primary suture closure (PSC).Materials and methods: PubMed, Science Direct, Cochrane, and Google Scholar were systematically searched until March 3, 2020, for studies comparing the efficacy of PMP to PSC in abdominal surgeries. The main outcome of interest was the incidence of IH at different follow-up durations. All statistical analyses were carried out using Review Manager version 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, 2014) and Stata 11.0 (Stata Corporation LP, College Station, TX). The data were pooled using the random-effects model, and odds ratio (OR) and weighted mean differences (WMD) were calculated with the corresponding 95% confidence interval (CI).Results: A total of 3,330 were identified initially and after duplicate removal and exclusion based on title and abstract, 26 studies comprising 3,000 patients, were included. The incidence of IH was significantly reduced for PMP at follow-up periods of one year (OR= 0.16 [0.05, 0.51]; p=0.002; I2=77%), two years (OR= 0.23 [0.12, 0.45]; p\u3c0.0001; I2=68%), three years (OR= 0.30 [0.16, 0.59]; p=0.0004; I2= 52%), and five years (OR=0.15 [0.03, 0.85]; p=0.03; I2=87%). However, PMP was associated with an increased risk of seroma (OR=1.67 [1.10, 2.55]; p= 0.02; I2=19%) and chronic wound pain (OR=1.71 [1.03, 2.83]; p= 0.04; I2= 0%). No significant difference between the PMP and PSC groups was noted for postoperative hematoma (OR= 1.04 [0.43, 2.50]; p=0.92; I2=0%), surgical site infection (OR=1.09 [0.78, 1.52]; p= 0.62; I2=12%), wound dehiscence (OR=0.69 [0.30, 1.62]; p=0.40; I2= 0%), gastrointestinal complications (OR= 1.40 [0.76, 2.58]; p=0.28; I2= 0%), length of hospital stay (WMD= -0.49 [-1.45, 0.48]; p=0.32; I2=0%), and operating time (WMD=9.18 [-7.17, 25.54]; p= 0.27; I2=80%).Conclusions: PMP has been effective in reducing the rate of IH in the high-risk population at all time intervals, but it is associated with an increased risk of seroma and chronic wound pain. The benefits of mesh largely outweigh the risk, and it is linked with positive outcomes in high-risk patients

Empirical investigation to explore potential gains from the amalgamation of Phase Changing Materials (PCMs) and wood shavings

The reduction of gained heat, heat peak shifting and the mitigation of air temperature fluctuations are some desirable properties that are sought after in any thermal insulation system. It cannot be overstated that these factors, in addition to others, govern the performance of such systems thus their effect on indoor ambient conditions. The effect of such systems extends also to Heating, Ventilation and Air-conditioning (HVAC) systems that are set up to operate optimally in certain conditions. Where literature shows that PCMs and natural materials such as wood-shavings can provide efficient passive insulation for buildings, it is evident that such approaches utilise methods that are of a degree of intricacy which requires specialist knowledge and complex techniques, such as micro-encapsulation for instance. With technical and economic aspects in mind, an amalgam of PCM and wood-shavings has been created for the purpose of being utilised as a feasible thermal insulation. The amalgamation was performed in the simplest of methods, through submerging the wood shavings in PCM. An experimental procedure was devised to test the thermal performance of the amalgam and compare this to the performance of the same un-amalgamated materials. Comparative analysis revealed that no significant thermal gains would be expected from such amalgamation. However, significant reduction in the total weight of the insulation system would be achieved that, in this case, shown to be up to 20.94%. Thus, further reducing possible strains on structural elements due to the application of insulation on buildings. This can be especially beneficial in vernacular architectural approaches where considerably large amounts and thicknesses of insulations are used. In addition, cost reduction could be attained as wood shavings are significantly cheaper compared to the cost of PCMs

Untangling the effects of octahedral rotation and ionic displacements on the electronic structure of BiFeO3

This article was originally published in Physical Review B. The version of record is available at: https://doi.org/10.1103/PhysRevB.104.035159The electronic structure and related properties of perovskites ABO3 are strongly affected by even small modifications in their crystalline structure. In the case of BiFeO3, variations in the octahedral rotations and ionic displacements lead to significant changes in the band gap. This effect can possibly explain the wide range of values (2.5–3.1 eV) reported in the literature, obtained from samples of varied structural qualities, including polycrystalline films, epitaxial films grown by pulsed-laser deposition and molecular beam epitaxy, nanowires, nanotubes, and bulk single crystals. Using hybrid density-functional calculations, we investigate the dependence of the electronic structure on the crystal lattice distortions of the ferroelectric-antiferromagnetic BiFeO3, disentangling the effects of the ferroelectric ionic displacements and the antiferrodistortive octahedral rotations on the band gap and the band-edge positions. The band gap is shown to vary from 3.39 eV for the rhombohedral ground-state (R3c) structure down to 1.58 eV for the perfect cubic (Pm¯3m) structure, with changes in the conduction band being much more prominent than in the valence band. The gap varies linearly with the ferroelectric ionic displacements, but nonlinearly with the octahedral rotations around the pseudocubic [111]c axis, and this is explained in terms of the different interactions between Bi 6s,6p, Fe 3d, and O 2p bands. We argue that such large variation of the band gap with structural changes may well explain the large scattering of the reported values, especially if significant deviations from the equilibrium crystal structure are found near domain boundaries, extended defects, or grain boundaries in polycrystalline films.This work was supported by the NSF Early Career Award Grant No. DMR-1652994, the Extreme Science and Engineering Discovery Environment (XSEDE) supported by National Science Foundation Grant No. ACI-1053575, and the Information Technologies (IT) resources at the University of Delaware