A high-yield and upscalable colloidal synthesis route for the production of quaternary I2–II–IV–VI4 nanocrystals, particularly stannite Cu2+x Cd1–x SnSe4, with narrow size distribution and precisely ...controlled composition is presented. It is also shown here how the diversity of valences in the constituent elements allows an effective control of their electrical conductivity through the adjustment of the cation ratios. At the same time, while the crystallographic complexity of quaternary chalcogenides is associated with intrinsically low thermal conductivities, the reduction of the lattice dimensions to the nanoscale further reduces the materials thermal conductivity. In the specific case of the stannite crystal structure, a convenient slab distribution of the valence band maximum states permits a partial decoupling of the p-type electrical conductivity from both the Seebeck coefficient and the thermal conductivity. Combining these features, we demonstrate how an initial optimization of the nanocrystals Cd/Cu ratio allowed us to obtain low-temperature solution-processed materials with ZT values up to 0.71 at 685 K.
An appropriate way of realizing property nanoengineering in complex quaternary chalcogenide nanocrystals is presented for Cu2Cd x SnSe y (CCTSe) polypods. The pivotal role of the polarity in ...determining morphology, growth, and the polytypic branching mechanism is demonstrated. Polarity is considered to be responsible for the formation of an initial seed that takes the form of a tetrahedron with four cation-polar facets. Size and shape confinement of the intermediate pentatetrahedral seed is also attributed to polarity, as their external facets are anion-polar. The final polypod extensions also branch out as a result of a cation-polarity-driven mechanism. Aberration-corrected scanning transmission electron microscopy is used to identify stannite cation ordering, while ab initio studies are used to show the influence of cation ordering/distortion, stoichiometry, and polytypic structural change on the electronic band structure.
This paper analyzes the generation and composition of municipal solid waste in Spanish towns and cities with more than 5000 inhabitants, which altogether account for 87 % of the Spanish population. ...To do so, the total composition and generation of municipal solid waste fractions were obtained from 135 towns and cities. Homogeneity tests revealed heterogeneity in the proportions of municipal solid waste fractions from one city to another. Statistical analyses identified significant differences in the generation of glass in cities of different sizes and in the generation of all fractions depending on the hydrographic area. Finally, linear regression models and residuals analysis were applied to analyze the effect of different demographic, geographic, and socioeconomic variables on the generation of waste fractions. The conclusions show that more densely populated towns, a hydrographic area, and cities with over 50,000 inhabitants have higher waste generation rates, while certain socioeconomic variables (
people/car
) decrease that generation. Other socioeconomic variables (
foreigners
and
unemployment
) show a positive and null influence on that waste generation, respectively.
The compositional versatility of I2-II-IV-VI4 tetrahedrally-coordinated compounds allows for accommodating their functional properties to numerous technological applications. Among them, Cu2ZnSnSe4 ...is an emerging photovoltaic material and Cu2CdSnSe4 displays excellent thermoelectric properties. The third compound of this family, Cu2HgSnSe4, remains relatively unexplored. Herein, a synthetic route to produce Cu2HgSnSe4 nanoparticles with narrow size distribution and controlled composition is presented. Cu2HgSnSe4 nanoparticles were subsequently used as building blocks to produce bulk nanocrystalline materials, whose thermoelectric properties were analyzed. A very preliminary adjustment of the material composition yielded Seebeck coefficients up to 160 μV K−1, electrical conductivities close to 104 S m−1 and thermal conductivities down to 0.5 W m−1 K−1.
► Our goal in this work is to model municipal waste separation rates of the main materials collected separately in Spanish medium and large-sized cities. ► Waste separation rates of paper, glass and ...lightweight packages are analyzed. ► Those separation rates in the different cities are modeled taking their socio-economic, demographic and logistic characteristics into account. ► Several statistical regression models to manage continuous proportion data are compared. ► Significant covariates for the different separation rates are obtained from these models, and the strength of the influence of all these factors on the response variables are calculated.
Most cities are actually very concerned about the economic viability of waste management and also about the impact they may have on the environment. Economical, social and cultural factors in the population will determine the characteristics in waste and the value of the design parameters used in the calculations of a collection system. A clear understanding of these factors is fundamental to plan and to implement efficient and sustainable collecting strategies. Our goal in this work is to model municipal waste separation rates in Spanish cities with over 50,000 inhabitants taking their different socio-economic, demographic and logistic covariates into account. Several statistical regression models to manage continuous proportion data are compared, these being: Generalized linear models (GLM) with Binomial, Poisson and Gamma errors after several transformations of the data and Beta regression on the raw data. The best fits are obtained by using GLM Gamma and beta regression. Significant covariates for the different separation rates are obtained from these models, and the strength of the influence of all these factors on the response variable is calculated. All these results could be taken into account to design and to evaluate selective collection systems, and will allow us to make predictions on cities not included in this study.
Introduction
Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infections (ALRI) in children under one year of age. In high-income countries, RSV infections cause a ...significant overload of care every winter, imposing a significant burden to the healthcare system, which has made the development of prevention strategies a major global health priority. In this context, a new bivalent RSV prefusion F protein-based vaccine (RSVpreF) has recently been approved. The objective of this study was to evaluate the cost-effectiveness of vaccinating pregnant women with the RSVpreF vaccine to prevent RSV in infants from the Spanish National Healthcare System (NHS) perspective.
Methods
A hypothetical cohort framework and a Markov-type process were used to estimate clinical outcomes, costs, quality-adjusted life years (QALY) and cost-per-QALY gained (willingness-to-pay threshold: €25,000/QALY) for newborn infants born to RSV-vaccinated versus unvaccinated mothers over an RSV season. The base case analysis was performed from the NHS perspective including direct costs (€2023) and applying a discount of 3% to future costs and outcomes. To evaluate the robustness of the model, several scenarios, and deterministic and probabilistic analyses were carried out. All the parameters and assumptions were validated by a panel of experts.
Results
The results of the study showed that year-round maternal vaccination program with 70% coverage is a dominant option compared to no intervention, resulting in direct cost savings of €1.8 million each year, with an increase of 551 QALYs. Maternal vaccination could prevent 38% of hospital admissions, 23% of emergency room visits, 19% of primary care visits, and 34% of deaths due to RSV. All scenario analyses showed consistent results, and according to the probabilistic sensitivity analysis (PSA), the probability of maternal vaccination being cost-effective versus no intervention was 99%.
Conclusions
From the Spanish NHS perspective, maternal vaccination with bivalent RSVpreF is a dominant alternative compared with a non-prevention strategy.
Nanomaterials produced from the bottom-up assembly of nanocrystals may incorporate ∼1020–1021 cm–3 not fully coordinated surface atoms, i.e., ∼1020–1021 cm–3 potential donor or acceptor states that ...can strongly affect transport properties. Therefore, to exploit the full potential of nanocrystal building blocks to produce functional nanomaterials and thin films, a proper control of their surface chemistry is required. Here, we analyze how the ligand stripping procedure influences the charge and heat transport properties of sintered PbSe nanomaterials produced from the bottom-up assembly of colloidal PbSe nanocrystals. First, we show that the removal of the native organic ligands by thermal decomposition in an inert atmosphere leaves relatively large amounts of carbon at the crystal interfaces. This carbon blocks crystal growth during consolidation and at the same time hampers charge and heat transport through the final nanomaterial. Second, we demonstrate that, by stripping ligands from the nanocrystal surface before consolidation, nanomaterials with larger crystal domains, lower porosity, and higher charge carrier concentrations are obtained, thus resulting in nanomaterials with higher electrical and thermal conductivities. In addition, the ligand displacement leaves the nanocrystal surface unprotected, facilitating oxidation and chalcogen evaporation. The influence of the ligand displacement on the nanomaterial charge transport properties is rationalized here using a two-band model based on the standard Boltzmann transport equation with the relaxation time approximation. Finally, we present an application of the produced functional nanomaterials by modeling, fabricating, and testing a simple PbSe-based thermoelectric device with a ring geometry.
ZnO nanowires (NWs) have been grown using the Chemical-Vapor-Deposition (CVD) method on two different substrates, SiO
2
and Al
2
O
3.
Striking differences have been observed between products. First, ...while only (0001) oriented NWs are found in SiO
2
grown samples,
m
plane-oriented nanostructures have been observed for alumina substrates. Second, Au catalytic interdiffusion is evidenced in NWs grown on SiO
2
, whereas for the NWs grown on alumina the Au catalytic remains at the tip. The origin of the differences in morphology and catalytic location is discussed, with the help of detailed Transmission Electron Microscopy analyses, in terms of growth mechanisms and segregation of the Au particle influenced by the substrate nature and crystallinity. Finally, we show the consequences of such effects in the photoresponse of nano-detectors based on the studied nanowires.
Substrate effects on CVD-grown ZnO nanowires have been studied, in terms of morphology and incorporation of catalytic Au, which in turn is shown to affect the NWs photoresponse.
The compositional versatility of I sub(2)-II-IV-VI sub(4 ) tetrahedrally-coordinated compounds allows for accommodating their functional properties to numerous technological applications. Among them, ...Cu sub(2)ZnSnSe sub(4) is an emerging photovoltaic material and Cu sub(2)CdSnSe sub(4) displays excellent thermoelectric properties. The third compound of this family, Cu sub(2)HgSnSe sub(4), remains relatively unexplored. Herein, a synthetic route to produce Cu sub(2)HgSnSe sub(4) nanoparticles with narrow size distribution and controlled composition is presented. Cu sub(2)HgSnSe sub(4) nanoparticles were subsequently used as building blocks to produce bulk nanocrystalline materials, whose thermoelectric properties were analyzed. A very preliminary adjustment of the material composition yielded Seebeck coefficients up to 160 mu V K super(-1), electrical conductivities close to 10 super(4) S m super(-1) and thermal conductivities down to 0.5 W m super(-1) K super(-1).
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