1,721,060 research outputs found
Preparation and physico-chemical characterization of ordered large-pore silica films for membranes applications
No full textContributo orale su invito
Coups d’état and defense spending : a counterfactual analysis
Full text linkWe explore how institutional set-ups, in particular changes in political institutions through coups d’état, can affect the way military expenditures are determined. We use a counterfactual approach, the synthetic control method, and compare the evolution of the military burden for 40 countries affected by coups with the evolution of a synthetic counterfactual that replicates the initial conditions and the potential outcomes of the countries of interest before exposure to coups. Our case studies suggest that successful coups result in a large increase in the military burden. However, when no effects or a decrease in the defense burden are found, it is often the consequence of a democratization process triggered by the coup. These results are in keeping with recent theoretical developments on the bargaining power of the military in authoritarian regimes. Failed coups, by contrast, produce a smaller, and mostly positive, effect on the military burden, possibly as a result of the incumbent’s strategy to avert further challenges to the stability of the regime by buying off the military
Highly porous silica glasses and aerogels mase easy: The hypersaline route
No full textThrough the addition of inorganic salts as porogens during an alcohol-based sol-gel process high surface area silica glasses and aerogels with varying pore sizes are synthesized. In the presence of ZnCl2 and CaCl2 respectively, tetraethyl orthosilicate (TEOS) dissolved in ethanol hydrolyzes also in the absence of any acid or base catalysts, eventually forming high surface area monolithic silica networks. The porosity can be controlled by the gel ageing step as well as the salt nature. Two different gel drying conditions were investigated, i.e., room temperature (RT) air drying at ambient pressure and supercritical (sc) CO2 drying. While a reference solution which only contains ethanol and TEOS does not gel at all, the addition of ZnCl2 leads to mesoporous aerogels with high surface areas of 1400 m2 g−1 after sc CO2 drying. Interestingly, the utilization of CaCl2 however, produces aerogel-like materials of high porosity for both drying methods under preservation of the nano-and macroscopic features. Thereby, it is shown that inorganic salts can influence the structure formation during the sol-gel process where the type of salt controls the framework connectivity/stability and tunes the porosity towards smaller pore sizes than usually obtained. At the same time, the herein presented hypersaline aerogel-synthesis is very simple, fast and in the case of CaCl2 drying can even be performed in ai
One-step Synthesis of Magnetic Chitosan Polymer Composite Films
Full text linkIn this study, a magnetic iron oxide–chitosan composite film is synthesized by one-step method and thoroughly investigated in order to better understand its inorganic/organic properties. A deep physico-chemical characterization of the magnetic films has been performed. In particular, the material composition was evaluated by means of XRD and ATR-FTIR spectroscopy, whereas the thermal stability and the subsequent inorganic phase transitions involving iron oxide species were followed by TGA analyses carried out at different experimental conditions (i.e. inert and oxidative atmosphere). The magnetic properties of the films were tested at the bulk and at the surface level, performing respectively magnetization hysteresis curve and magnetic force microscopy (MFM) surface mapping. Results indicate that the synthesized material can be prepared through a very simple synthetic procedure and suggests that it can be successfully applied for instance to environmental applications, such as the adsorption of contaminants from solid and liquid media thanks to its pronounced magnetic properties, which favour its recover.Fil: Cesano, Federico . Universita Di Torino; ItaliaFil: Fenoglio, Gaia . Universita Di Torino; ItaliaFil: Carlos, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación y Desarrollo En Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue; ArgentinaFil: Nisticò, Roberto. Universita Di Torino; Itali
New branched flower-like Ag nanostructures for SERS analysis
No full textIn this work, metallic silver flower-like and aerogel-like nanostructures deposited onto hydrophobic dielectric substrates (HF-treated Si and PDMS) showed interesting potentialities as solid SERS substrates aimed to high sensitive molecular detection and quantitation. In detail, the nanostructures were incubated in 4-MBA solutions at 10−2 M – 10−9 M concentrations. The quantitative analysis confirmed a monotonic increase of the SERS signal intensity as a function of the 4-MBA concentration, following a Langmuir model, thus suggesting a chemisorption phenomenon. The best homogeneity and adhesion strength in liquid media of Ag nanostructures to the solid substrates were reached for the flower-like systems and the aerogel-like ones compared to traditional polyhedral nanostructures (taken as reference substrate), thus making them extremely appealing as a solution for the development of SERS-based sensors
Military in politics and budgetary allocations
Full text linkThis paper investigates the effect of military involvement in politics on budgetary allocations for defence. We employ a variety of econometric models, including pooled OLS and panel data with fixed effects and control for other known determinants of military spending. To deal with endogeneity issues, we also use an IV methodology and find that a higher degree of military involvement in policy-making increases the probability that the military obtain a larger share of output
The Effect of Parental Job Loss on Child School Dropout: Evidence from the Occupied Palestinian Territories.
No full textWe study the effect of parental job loss on child school dropout in developing countries. We focus on Palestinian households living in the Occupied Palestinian Territories and having the household head employed in Israel during the Second Intifada (2000-2006). We exploit quarterly variation in conflict intensity across districts in the OPT to instrument for Palestinian workers' job loss in Israel. Our 2SLS results show that parental job loss increases child school dropout probability by 9 percentage points. The effect varies with child and household characteristics. We provide evidence that the effect operates through the job loss-induced reduction in household income
Salts as structure-directing agents: The hypersaline chemistry of aerogels
No full textBased on recent investigations, the use of inorganic salts is a new powerful route for obtaining high surface area mesoporous materiaIs in a facile one-step approach, also called “salt-templating”.
Here, high surface area aerogels were synthesized adding simple inorganic water soluble salts as pore forming agents during the sol-gel process. The model oxide precursor (i.e.,TEOS for silica) hydrolyses in the presence of a salt, e.g. ZnCl2, without using any acid/base catalysts, forming the silica network and producing monoliths with high surface area. The porosity can be controlled by the gel-ageing step (the less the time, the higher the porosity). Two different gel-drying conditions were investigated: room temperature (RT) air drying and CO2 supercritical drying. Supercritically dried silica aerogels reach the impressive BET surface area value of ca. 1400 m2 g-1, but also the simple air-drying procedure produces highly porous monoliths with BET surface areas in the range of 700-800 m2 g-1, thanks to the stabilizing salting-in effect of zinc ions (according to Hofmeister series).
Compared to standard sol-gel processes, the herein presented synthesis is extremely simple: it only consists of dissolution of both oxidic precursors and inorganic salts in the selected solvent (i.e. ethanol), gel formation induced by solvent evaporation, salt removal through simple washing with water/ethanol. This way, no organic templates need to be employed and the overall approach is highly efficient and sustainable. In this regard, the salt-templating solution could principally be recovered for following syntheses afterwards, thus reducing by-products. Moreover, the synthesis of highly porous monoliths by RT air drying is of high interest since no special equipment is required, it simplifies the standard procedure and gives access to advanced materials at low cost
Sol-gel chemistry, templating and spin-coating deposition: A combined approach to control in a simple way the porosity of inorganic thin films/coatings
Full text linkPorous materials are powerful functional devices that can find applications in many fields, from nanotechnology to biomedicine, from catalysis to membrane separation. In general, porous materials can be processed in various forms, but a rising interest is growing around inorganic thin films and coatings, due to the increased number of applications based on their use. Among the different strategies proposed till now for preparing inorganic porous thin layers/coatings, a simple and versatile route consists in the combined use of sol-gel chemistry, templating, and spin-coating deposition. Therefore, in order to provide a helpful toolbox for users, an extended discussion around the physico-chemical principles behind each of these steps is here reported, also highlighting the advantages and disadvantages of each procedure, together with critical points
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