118,332 research outputs found
Galois closure and Lagrangian varieties,
No full textLet X be a complex projective variety and consider the cup product morphism \psi_k from the k-th exterior product of H^{1,0} to H^{k,0}.
We use Galois closures of finite rational maps to introduce a new method for producing varieties such that \psi_k has non-trivial kernel. We then apply our result to the two-dimensional case and we construct a new family of surfaces which are Lagrangian in their Albanese variety. Moreover, we analyze these surfaces computing their Chern invariants, and proving that they are not fibred over curves of genus g ≥ 2. The topological index of these surfaces is negative and this provides a counterexample to a conjecture on Lagrangian surfaces formulated by Barja-Naranjo-Pirola
Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification
No full textIn this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics
CO2 Photoreduction at High Pressure to both Gas and Liquid Products over Titanium Dioxide
No full textThe continuous increase of CO2 emissions, which is considered a harmful greenhouse gas generated by human and natural activities, is leading to a global warming that is dangerous for all living beings. CO2 is a very stable compound and therefore recalcitrant to conversion into less harmful compounds. However, different studies were developed to find conditions for activating CO2 and converting it into useful chemicals. The photoreduction of CO2 is an intriguing process, which allows the synthesis of fuels and chemicals. Several semiconductors were proposed during the last years in order to overcome the limitations of light harvesting and limit the electron-hole recombination. In this work, we have deeply studied the mechanism of the photoreduction of CO2 in liquid phase (H2O was used as solvent), using a commercial TiO2 (EvoniK P25) photocatalyst in the presence of Na2SO3 as hole scavenger and working at different pH. Particular attention was dedicated to the influence of operating parameters on the mechanism and kinetics of the reaction. The process was carried out by means of an innovative photoreactor developed by our group [1,2] able to operate under high pressure (up to 20 bar) and, therefore, allowing to explore also unconventional temperature ranges. Through this set up we can expand the operating conditions, so overcoming the key limitation for this reaction which is related to the poor CO2 solubility in water, and increase the operating temperature, thus improving the overall kinetics and mass transfer of the process. promising productivity, as high as 102 mmol h-1 kgcat-1 for H2, 16537 mmol h-1 kgcat-1 for formaldehyde and 2954 mmol h-1 kgcat-1 for formic acid were achieved when operating at 7 bar, 80°C with 0.5 gL-1 TiO2 by tuning reaction time and pH.
References
[1] Rossetti, I.; Villa, A.; Compagnoni, M.; Prati, L.; Ramis, G.; Pirola, C.; Bianchi, C. L.; Wang, W.; Wang, D. Catal. Sci. Technol. , 5 (9), 4481–4487.
[2] I. Rossetti, A. Villa, C. Pirola, L. Prati, G. Ramis, RSC Adv. 4 (2014) 2888
Programmi di esame per la maturità classica e scientifica.
No full textNa portada: "approvati con R.D. 10 giugno 1937, n. 876"Na portada: "approvati con R.D. 10 giugno 1937, n. 876
CO2 Photoconversion to Fuels and Chemicals under High Pressure
No full textCO2 capture and storage is a fundamental research topic in order to decrease the concentration of such greenhouse gas. A new and challenging procedure is the CO2 photoreduction to alcohols and alkanes in the presence of a semiconductor.
In this research, we tested a novel concept of photoreactor developed by our group1,2 able to operate under high pressure (up to 20 bar) and to explore different temperature ranges. Unconventional operating conditions were explored through this set up, so overcoming the key limitation of CO2 solubility in water and increasing the operating temperature, to improve the overall mass transfer inside the reactor. Na2SO3 was employed as inorganic hole scavenger. Besides reactor engineering optimization, several photocatalysts were investigated in order to solve the two main limitations of semiconductor application in photocatalysis: i) the inadequate visible light absorption of the UV-active catalysts; ii) the high electron-hole recombination rate. Au/TiO2 and CuO/TiO2 with different loadings (0.1-0.5 wt.%), preparation methods (deposition/precipitation, impregnation and Flame Spray Pyrolysis), and polymorphs (anatase, rutile) were chosen as photocatalysts.
Characterization of fresh and spent samples was carried out by traditional techniques (XRD, BET, TEM, UV) combined with specific in situ analysis (DRIFTS).
The operating conditions (pressure, temperature, pH, irradiation power) and photocatalysts have been varied allowing the investigation of the whole process several possible applications of this reactor. In particular focusing on the maximization of gas (H2 and CH4) and liquid (CH3OH, HCHO, HCOOH) products.
Keywords: CO2 photoconversion, gold photocatalysts, copper oxide photocatalysts, high pressure photocatalysis.
References
(1) Rossetti, I.; Villa, A.; Pirola, C.; Prati, L.; Ramis, G. A Novel High-Pressure Photoreactor for CO2 Photoconversion to Fuels. RSC Adv. 2014, 4 (55), 28883–28885.
(2) Rossetti, I.; Villa, A.; Compagnoni, M.; Prati, L.; Ramis, G.; Pirola, C.; Bianchi, C. L.; Wang, W.; Wang, D. CO2 Photoconversion to Fuels under High Pressure: Effect of TiO2 Phase and of Unconventional Reaction Conditions. Catal. Sci. Technol. 2015, 5, 4481–4487
CO2 photoreduction at high pressure to both gas and liquid products over titanium dioxide: the effect of unconventional reaction conditions
No full textThe photoreduction of CO2 is an intriguing process, which allows the synthesis of fuels and chemicals. One of the limitations for CO2 photoreduction in the liquid phase is its low solubility in water. Several studies have been proposed during the last years in order to enhance the photocatalysts performance and improve the phototreactors for this purpose (1, 2). This point has been here addressed by designing a fully innovative concept of pressurized photoreactor, allowing operation up to 20 bar and applied for the first time to improve the productivity of this very challenging process (3-5). The photoreduction of CO2 in the liquid phase was performed using the commercial TiO2 (Evonink P25) in the presence of Na2SO3 as a hole scavenger. The different reaction parameters (temperature, working pressure, pH) and various catalysts have been considered for investigation of productivity and selectivity in the gas and liquid phase.
The expected and formed products in liquid phase in the constant pressure and temperature and in the course of reaction time were formic acid and formaldehyde, respectively. Moreover, for longer reaction time, gas phase products formed (H2 and CO with no trace of methanol or methane) after accumulation of significant amount of organic compounds in the liquid phase. The formation of gas products takes place within two parallel reaction pathway: i) CO2 photoreduction into formic acid which may further photoreduce to formaldehyde and finally evolve into CO/CO2+H2 (photoreforming), ii) enhancing the CO2 dissolution in the water by addition of a base with formation of carbonates (pH= 12-14) resulted in the reduction of carbonates to formaldehyde and consequently formed CO/CO2+H2 in the gas phase through photoreforming.
In order to improve visible light absorption and increase the lifetime of the photogenerated charges, Au was loaded on TiO2 (0.1-0.5 wt%) by a deposition-precipitation method. Methanol and methane were the main products in liquid and gas phase, respectively, demonstrating the higher reactivity of catalyst in the present of Au. Increasing the Au loading from 0.1wt% to 0.2 wt% improved the productivity toward methanol and methane in liquid and gas phase, respectively. However, further increasing in metal loading negatively affected the Au dispersion and catalyst surface area and resulted in lower H2 productivity. Furthermore, testing parameters, such as temperature and pressure directly affected the products formation. Increasing the pressure favored the liquid products accumulation was detrimental for H2/CH4 productivity. On the other hand, increasing the temperature, decreased the CO2 solubility in the water, but enhanced the kinetics and mass transfer leading to the formation of H2/CH4.
Acknowledgements: Fondazione Cariplo (grant 2016-0858 “UP – Unconventional Photoreactors”) is gratefully acknowledged.
References:
(1) Yamashita H., Fujii Y., Ichihashi Y., Zhang S.G., Ikeue K., Park D.R., Koyano K., Tatsumi T., Anpo M., 1998, Catalysis Today, 45, 221.
(2) Anpo M., Yamashita H., Ichihashi Y., EharaS., 1995, J. Electroanal. Chem, 396, 21.
(3) Rossetti I., Villa A., Pirola C., Pratia L., Ramis G., 2014, RSC Adv, 4, 28883.
(4) Rossetti I., Villa A., Compagnoni M., Prati L., Ramis G., Pirola C., et al., 2015, Catal. Sci. Technol, 5, 4481.
(5) Galli F., Compagnoni M., Vitali D., Pirola C., Bianchi C.L., Villa A., Prati L., Rossetti I., 2016, App Catal B: Environmental, 200, 386
Microwave Measurements Part I: Linear Measurements
No full textAn Overview of the most relevant issues concerning RF and microwave linear measurements is presented. Vector Network Analyzer foremost used instrumentation for this kind of measures is describe
Dietary polyphenols and their effects on cell biochemistry and pathophysiology
No full textPolyphenols, occurring in fruit and vegetables, wine, tea, extra virgin olive oil, chocolate, and other cocoa products, have been demonstrated to exert beneficial effects in a large array of disease states, including cancer, cardiovascular disease, and neurodegenerative disorders. Many of the biological effects of polyphenols have been attributed to their antioxidant properties, either through their reducing capacities per se or through their possible influences on intracellular redox status. As such, polyphenols may protect cell constituents against oxidative damage and have been reported to limit the risk of various degenerative diseases associated with oxidative stress, including cardiovascular diseases, type 2 diabetes, and cancer. However, accumulating evidence suggests that the classical hydrogen-donating antioxidant activity is unlikely to be the sole explanation for their cellular effects in vivo. Indeed, it has recently become clear that, in complex biological systems, polyphenols are able to exhibit several additional properties which are yet poorly understood. It is evident that polyphenols are potent bioactive molecules and a clear understanding of their precise mechanisms of action as either antioxidants or modulators of cell signaling is crucial to the evaluation of their potential as chemopreventive or anticancer agents and inhibitors of neurodegeneration
Azo spojevi pirola i fenilarsinskih kiselina
No full textU želji da ispitamo bakteriostazu i kemoterapeutska svojstva azo spojeva pirola i fenilarsinisikih kiselina na tripanozome i rekurens, priredili smo nekoliko novih spojeva iz navedene grupe. Priređeni su: 5-oksi-2-metil-3-karbetokis-pirol-(4 azo 4)-fenilarsinska kisellina - (1) (I), 5-oksi-2-metil-3-karbetoksi-pirol-(4 azo 4')-oksi-(3)-fenilarsinska kiselina-(1) (l), 5-oksi-2-metil-3-karbetoksi-pirol-(4 azo 4')-amino - (4) - difenilarinska kiselina(1,1') (IIl). Navedeni spojevi načinjeni su tako, da su diazotirane odgovarajuće fenilarsinske kiseline i vezane na 5-oksi-2-metil-3- karbetoksi-pirol
Biogas upgrading by physical water washing in a micro-pilot absorption column conducted at low temperature and pressure
No full textThe European Energy Policy has currently two main goals to reach: to minimize exposure to volatility of fossil fuel prices and to reduce of greenhouse gas (GHG) emissions. To reach these targets a practical way, among the others is represented by the biogas production by anaerobic digestion (Bonoli et al., 2014) (AD) and its upgrading to biomethane. In this work the absorption of CO2is studied using a column working at atmospheric pressure and low temperature (599%) and a stream of methane (>99.9 %) in order to reproduce a typical raw biogas composition, i.e. molar fraction of methane of about 0.6. The internal temperature was monitored by a thermocouple and the inlet and outlet flow of biogas (G) was measured using a mass flowmeter while the water flow rate (L) was monitored using a magnetic induction flowmeter. The compositions were determined using a 3000A micro-Gas Chromatograph Agilent, previously calibrated. The temperature was varied between 6.5 and 20 °C and the water flow rate between about 0.5 and 5 L/h. The composition of the gas exiting the micro-pilot plant was monitored every 5 minutes until the stationary condition
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