Expanding the one-dimensional CdS-CdSe composition landscape: Axially anisotropic CdS1- xSex nanorods

We report the synthesis and characterization of CdS1-xSex nanorods with axial anisotropy. These nanorods were synthesized via single injection of a mixture of trioctylphosphine sulfur and selenium precursors to a cadmium-phosphonate complex at high temperature. Transmission electron microscopy shows nanoparticle morphology changes with relative sulfur and selenium loading. When the synthetic selenium loading is between 5% and 10% of total chalcogenides, the nanorods exhibit pronounced axial anisotropy characterized by a thick head and a thin tail . The nanorods\u27 band gap red shifts with increasing selenium loading. X-ray diffraction reveals that CdS1-xSex nanorods have a wurtzite crystal structure with a certain degree of alloying. High-resolution and energy-filtered transmission electron microscopy and energy-dispersive X-ray spectroscopy confirm the head of the anisotropic nanorods is rich in selenium, whereas the tail is rich in sulfur. Time evolution and mechanistic studies confirm the nanorods form by quick growth of the CdSe-rich head, followed by slow growth of the CdS-rich tail. Metal photodeposition reactions with 575 nm irradiation, which is mostly absorbed by the CdSe-rich segment, show effective electronic communication between the nanorod head and tail segments

Controlled fabrication of colloidal semiconductor-metal hybrid heterostructures: Site selective metal photo deposition

Reliable synthesis of semiconductor-metal heterostructures would increase their availability for fundamental studies and applications in catalytic, magnetic, and opto-electronic devices. Here, we demonstrate there are three main pathways for the formation of Pt and Pd nanoparticles on CdS and CdS04Se0.6 nanorods. A thermal pathway and photochemical pathway occur when the metal precursor is heated or irradiated directly in the presence of an electron donor, leading to homogeneous nucleation and formation of freestanding metal nanoparticles. A separate photochemical pathway occurs in the presence of semiconductor nanorods, leading to exciton formation and quenching by electron trapping at surface defect sites. The localized electrons act as seeding points, leading to heterogeneous nucleation and formation of surface-bound metal nanoparticles. Careful selection of synthetic conditions allows deposition of Pt and Pd particles on CdS and CdS0.4Se0.6 nanorods with a high degree of selectivity (90-95% surface-bound obtained photochemically) over the formation of freestanding metal particles (70-94% unattached under thermal conditions). In addition, metal photo deposition occurs on specific segments of CdS0.4Se0.6 nanorods with compositional anisotropy by taking advantage of the band gap differential between different nanodomains. Irradiation at short wavelengths favors formation of Pd nanoparticles on the large band gap CdS-rich region of the nanorods (57% and 55% at 350 and 420 nm, respectively), while irradiation at longer wavelengths favors the formation of Pd nanoparticles on the small band gap CdSe-rich region of the nanorods (83% at 575 nm). The ability to tune the spatial composition of these and similar heterostructures will impact the ability to engineer and direct energy flows at the nanoscale

Diet and gut health in residents of a retirement village

Background: New Zealand has an aging population with increasing demand for long-term aged care residential facilities. Irritable bowel syndrome (IBS) is a common functional gastrointestinal (GI) symptoms affecting 10 – 15% of the Western population. Restriction of a group of fermentable carbohydrates (FODMAPs) has been shown to significantly improve GI symptoms in patients with IBS. Currently there are no New Zealand data on the frequency and nature of GI symptoms and FODMAP intake of long-term aged care residents. Objectives: The overarching aim of this study is to assess the number of residents in a residential care facility who are suffering from IBS-like symptoms, particularly residents with diarrhoea or incontinence and to understand whether FODMAP intake is associated with IBS symptoms. Specific objectives are as follows: - To describe the frequency of GI symptoms in rest home (RH), hospital level care (H) and free-living (FL) residents of a retirement village. - To determine the nature and quantity of commonly consumed high FODMAP foods by RH and H residents. - To assess individual FODMAP intake of RH and H residents. - To investigate any associations between FODMAP intake and IBS symptoms in RH and H residents. Design: One hundred and sixteen eligible RH and H residents and 133 eligible FL, or independent residents living in a retirement village were invited to take part in the study. The Gastrointestinal Symptom Rating Score questionnaire modified for patients with IBS (GSRS-IBS) with six additional questions looking at upper GI symptoms was used and differences in responses between gender and level of care were compared. Dietary FODMAP intake was assessed for 30 RH or H residents with highest total GSRS-IBS score (symptomatic group) and 30 age, sex, and level of care matched asymptomatic residents with low total GSRS-IBS score. Comparisons were made between symptomatic and asymptomatic groups for macronutrient, micronutrient and FODMAP intakes. A simple regression analysis was conducted to determine the relationship between total FODMAP intake and GSRS-IBS score. Results: 74 (64%) RH and H residents and 51 (38%) FL residents completed the GI symptom questionnaire. Just over half of RH and H residents reported perceived discomfort of bloating-related and upper GI-related symptoms while most common symptoms reported by FL residents were diarrhoea-related (59%) and bloating-related (57%) discomforts. However, no significant differences were observed by gender or level of care for individual or total GI symptom scores. Dietary analysis was completed in 27 symptomatic and 27 asymptomatic RH and H residents who had all three main meals at the facility during data collection. A large quantity of lactose (16g/d consumed on average) from milk and milk products contributed to the total FODMAP intake. Wheat-based products, dried fruit, and homemade soups (containing onion, other high FODMAP vegetables and flour) contributed to high oligosaccharide intake, prunes, canned fruit, mushroom, onion and corn contributed to high polyol intake and fruit salad, orange juice and apple based dishes contributed towards fructose in excess of glucose intake. There were no significant differences in nutrient intake between the symptomatic and asymptomatic groups and there was no significant relationship between FODMAP intake and total GSRS-IBS score. Conclusion: This novel study has produced data on GI symptoms and FODMAP intake in older adults living in a retirement village in New Zealand. A larger study with a bigger sample size and residents from multiple facilities across New Zealand is required to produce more representative data

Critical regions of RC primary elements detailed in according to provisions rules for curvature ductility: comparisons and numerical analyses

In moment resisting frames beams and columns are designed for flexural, axial, and shear actions due to vertical and horizontal loads. Special proportioning and detailing requirements are applied in these elements for making them capable of resisting against severe earthquakes without significant loss of strength beyond the flexural elastic limit, and avoiding brittle failure (shear mechanisms). As known, the required flexural inelastic excursions (expressed by the local ductility demand) depend on the dissipative capacity of the structure. The flexural ductility significantly increases with the transverse reinforcement amount provided to confine section core and to prevent buckling of compressed longitudinal bars. In this paper detailing provisions adopted by some seismic codes are compared. At first, the codes provisions to be applied within critical regions of RC primary frames sections are discussed and compared as a function of the curvature ductility demand. Then, non-linear monotonic moment-curvature analyses are performed on fiber sections of columns and beams, and by taking into account the confinement effects on concrete core as well. The numerical investigations are carried out for comparing the available curvature ductility with the expected one applying the provisions mentioned by the seismic codes

Adjusting for Ascertainment Bias in Meta-Analysis of Penetrance for Cancer Risk

Multi-gene panel testing allows efficient detection of pathogenic variants in cancer susceptibility genes including moderate-risk genes such as ATM and PALB2. A growing number of studies examine the risk of breast cancer (BC) conferred by pathogenic variants of such genes. A meta-analysis combining the reported risk estimates can provide an overall age-specific risk of developing BC, i.e., penetrance for a gene. However, estimates reported by case-control studies often suffer from ascertainment bias. Currently there are no methods available to adjust for such ascertainment bias in this setting. We consider a Bayesian random-effects meta-analysis method that can synthesize different types of risk measures and extend it to incorporate studies with ascertainment bias. This is achieved by introducing a bias term in the model and assigning appropriate priors. We validate the method through a simulation study and apply it to estimate BC penetrance for carriers of pathogenic variants of ATM and PALB2 genes. Our simulations show that the proposed method results in more accurate and precise penetrance estimates compared to when no adjustment is made for ascertainment bias or when such biased studies are discarded from the analysis. The estimated overall BC risk for individuals with pathogenic variants in (1) ATM is 5.77% (3.22%-9.67%) by age 50 and 26.13% (20.31%-32.94%) by age 80; (2) PALB2 is 12.99% (6.48%-22.23%) by age 50 and 44.69% (34.40%-55.80%) by age 80. The proposed method allows for meta-analyses to include studies with ascertainment bias resulting in a larger number of studies included and thereby more robust estimates.Comment: 36 pages. arXiv admin note: text overlap with arXiv:2304.0191

Comparisons of Codal Detailing Rules for Curvature Ductility and Numerical Investigations

In moment resisting frame structures special detailing rules are applied to critical regions of primary columns and beams to ensure adequate curvature ductility. This is necessary for dissipating earthquake energy through hysteretical behavior of critical regions where inelastic flexural excursions occur. In this paper codal detailing rules for designing longitudinal and transverse reinforcement of primary elements as function of curvature ductility are assessed. Four seismic codes are considered: Italian code, New Zealand code, Eurocode 8 and American code. Non-linear monotonic moment-curvature analyses are performed on some sections of columns and beams detailed in according to the considered codal provisions. In the analyses the confinement effects within the concrete core have been taken into account as well. The paper concludes comparing the measured curvature ductility of the studied sections with the expected one by the codal pro- visions within the critical regions

Selective Alcohol Dehydrogenation and Hydrogenolysis with Semiconductor-Metal Photocatalysts: Toward Solar-to-Chemical Energy Conversion of Biomass-Relevant Substrates

Photocatalytic conversion of biomass is a potentially transformative concept in renewable energy. Dehydrogenation and hydrogenolysis of biomass-derived alcohols can produce renewable fuels such as H 2 and hydrocarbons, respectively. We have successfully used semiconductor-metal heterostructures for sunlight-driven dehydrogenation and hydrogenolysis of benzyl alcohol. The heterostructure composition dictates activity, product distribution, and turnovers. A few metal (M = Pt, Pd) islands on the semiconductor (SC) surface significantly enhance activity and selectivity and also greatly stabilize the SC against photoinduced etching and degradation. Under selected conditions, CdS-Pt favors dehydrogenation (H 2) over hydrogenolysis (toluene) 8:1, whereas CdS 0.4Se 0.6-Pd favors hydrogenolysis over dehydrogenation 3:1. Photochemically generated, surface-adsorbed hydrogen is useful in tandem catalysis, for example, via transfer hydrogenation. We expect this work will lead to new paradigms for sunlight-driven conversions of biomass-relevant substrates

Axial composition gradients and phase segregation regulate the aspect ratio of Cu2ZnSnS4 nanorods

Cu2ZnSnS4 (CZTS) is a promising material for solar energy conversion, but synthesis of phase-pure, anisotropic CZTS nanocrystals remains a challenge. We demonstrate that the initial concentration (loading) of cationic precursors has a dramatic effect on the morphology (aspect ratio) and composition (internal architecture) of hexagonal wurtzite CZTS nanorods. Our experiments strongly indicate that Cu is the most reactive of the metal cations; Zn is next, and Sn is the least reactive. Using this reactivity series, we are able to purposely fine-tune the morphology (dots versus rods) and degree of axial phase segregation of CZTS nanocrystals. These results will improve our ability to fabricate CZTS nanostructures for photovoltaics and photocatalysis

Molecular level control of nanoscale composition and morphology: Toward photocatalytic nanocomposites for solar-to-chemical energy conversion of biomass

Understanding the factors influencing nanocrystal formation is a challenge yet to be realized. In comparison to the large number of studies on nanocrystal synthesis and their applications, the number of studies on the effect of the precursor chemistry on nanocrystal composition and shape remains low. Although photochemical fabrication of metal-semiconductor nano-heterostructures is reported in literature, control over the free particle formation and the site of metal deposition have not been achieved. Moreover, utilization of metal- semiconductor nano-heterostructures in photocatalytic reactions other than water splitting is hardly explored. In this thesis, we studied the effect of chalcogenide precursor reactivity on the composition, morphology and the axial anisotropy of cadmium-chalcogenide nanocrystals. We also investigated the influence of the irradiation wavelength in synthesizing metal-semiconductor nano-heterostructures. Finally, we showed that metal semiconductor nano-heterostructures can be used as a photocatalyst for alcohol dehydrogenation reactions. We explored the pathways for the formation of Pt and Pd nanoparticles on CdS and CdS0.4Se0.6 nanorods. This study revealed that the wavelength of irradiation is critical to control free-standing vs. bound metal (Pt and Pd) nanoparticles to semiconductor. Additionally, we observed that metal photodeposition occurs on specific segments of axially anisotropic, compositionally graded CdS0.4Se0.6 nanorods due to the band-gap differential between their nano-domains. We used semiconductor-metal heterostructures for sunlight-driven dehydrogenation and hydrogenolysis of benzyl alcohol. Heterostructure composition dictates activity (turnovers) and product distribution. A few metal (Pt, Pd) islands on the semiconductor surface significantly enhance activity and selectivity and also greatly stabilize the semiconductor against photoinduced etching and degradation.</p