171,289 research outputs found
Substituent effects on the stereochemistry of gas-phase intracomplex nucleophilic substitutions
No full textThe mechanism and stereochemistry of the intracomplex solvolysis of proton-bound complexes [Y center dot center dot center dot H center dot center dot center dot M](+) between M = (CH3OH)-O-18 and Y = 1-arylethanol [(S)-1-(para-tolyl)ethanol (1(S)), (S)-1-(para-chlorophenyl)ethanol (2(S)), (S)-1-(meta-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (3(S)), (S)-1-(Para-alpha,alpha,alpha-trifluoromethylphenyl)-ethanol (4(S)), (R)-1-(pentafluorophenyl)ethanol (5(R)), (R)-alpha-(trifluoromethyl)benzyl alcohol (6(R)), and (R)-1-phenylethanol (7(R))] have been investigated in the gas phase (CH3F; 720 Torr) in the 25-140 degrees C temperature range. Gas-phase solvolysis of [Y center dot center dot center dot H center dot center dot center dot M](+) (Y = 2(S), 3(S), 4(S), and 7(R)) leads to extensive racemization above a characteristic temperature t(#) (e.g. at t(#) > 60 degrees C for 7(R)), whereas below that temperature the reaction displays a preferential retention of configuration. Predominant retention of configuration is instead observed in the intracomplex solvolysis of [Y center dot center dot center dot H center dot center dot center dot M](+) (Y = 1(S), 4(S), 5(R), and 6(R)) with the temperature range investigated (25 <= T <= 120 degrees C). These results indicate that the intracomplex solvolysis proceeds through the intermediacy of the relevant benzylic cations (Bz(+)), which is electrostatically coordinated to a H2O and a (CH3OH)-O-18 molecule (a pure S(N)1 mechanism). The obtained gas-phase mechanism is discussed in the light of related solution data. It is concluded that the stereochemistry of unimolecular solvolytic reactions is determined by the lifetime and the dynamics of the species involved and, if occurring in solution, by the nature and the dynamics of the solvent cage as well
Il tutto e le parti: il sistema bibliotecario di Ateneo e le (sue) biblioteche. Note storiche e appunti
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Simulation and measurement of quasi-optical multipliers
Full text linkThe lumped-element finite-difference time-domain method is used to analyze quasi-optical multipliers based on diode loaded slot antennas. The method is validated firstly for a passive microstrip-fed structure then for the diode loaded case in both small- and large-signal regimes. The diode model is separately validated using a series diode mounted on a microstrip line. Input return loss and radiation patterns show good agreement with measurements and the concept of effective conversion loss is introduced and results show reasonable agreement between measurement and simulation. A new diode arrangement is introduced where dual offset diodes are placed in the slot instead of the conventional central diode. The diode position can then act as an extra design parameter. The performance of the two structures has been compared; currently best performance is still obtained for the central-diode structure. Finally, a fully quasi-optical structure is simulated with plane-wave excitation. Central and dual-diode structures are again compared and the diode position and input plane-wave field strengths are optimized. Slot voltage distributions, radiation patterns, and effective quasi-optical conversion losses are presente
210Po in the Gessoso Solfifera Formation of Perticara Mine
No full textThe Perticara sulphur mine is a historically important mine located in the province of Rimini (Italy), known for the large crystals of sulfur that were extracted there, and for the abundance of ore. The mine was developed in the Gessoso-Solfifera Formation, a rock succession mainly formed by gypsum and limestone that is well preserved in the western Romagna Apennines area (Roveri et al., 2003). The Gessoso-Solfifera Formation comprises primary and clastic, resedimented evaporites with interbedded organic-rich shales, which were deposited during the evaporitic and post-evaporitic stages of the Messinian salinity crisis (Roveri et al., 2003). The Perticara mine was active for a few centuries until the mid-twentieth century. In 2016 the mine was re-explored by the Federazione Speleologica Regionale Emilia Romagna and starting from this data various environmental matrices (rocks, minerals, water, air) were sampled over time. Samples of natural epsomite crystals (general formula Mg(SO4)·7H2O), that extensively grow on rock walls and blocks with a fibrous habit, were collected and morphologically and chemically investigated using SEM-EDS, XRPD, ICP-AES and alpha spectrometry measurements.
Most of the fibres are of inhalable size and can be potentially adsorbed from all parts of the respiratory tract. Their solubility and the presence of significant amounts of toxic elements (As, Co, Fe, Mn, Ni, Sr, Ti, Zn) and radioactive isotope 210Po (and to a less extent 228Th) make the inhalation of these fibres potentially hazardous to human health. These preliminary results were recently published by Giordani et al. (2022). Moreover, a significant concentration of 222Rn (238U decay series), as well as CO2 and CO in the air of the mine, could play an important role in the accumulation of 210Po in epsomite, while very few amounts of 210Po were detected in the water springs and pools inside the mine or in host rocks, but further investigation is needed.
Giordani M., Meli M.A., Roselli C., Betti M., Peruzzi F., Taussi M., Valentini L., Fagiolino I. & Mattioli M. (2022) - Could soluble minerals be hazardous to human health? Evidence from fibrous epsomite. Environ. Res., 206, 112579.
Roveri M., Manzi V., Lucchi F.R. & Rogledi S. (2003) - Sedimentary and tectonic evolution of the Vena del Gesso basin (Northern Apennines, Italy): implications for the onset of the Messinian salinity crisis. Geol. Soc. Am. Bull., 115(4), 387-405
Numerical analysis of a Small Scale Polygeneration Plant with a Desiccant-Based Air Handling Unit
No full textDistributed polygeneration: desiccant-based air handling units interacting with microcogeneration systems
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