Experimental quantification of natural convective heat transfer within annulus space filled with a H2O-Cu nanofluid saturated porous medium. Application to electronics cooling

This experimental study deals with cooling electronics contained in a hemispherical cavity whose cupola is maintained isothermal, being its base inclined at an angle varying from 0° (horizontal disc with the cupola oriented upwards) to 135°. The active component is a dome centered on this base. The space between the differentially heated elements of the assembly is filled with a porous medium of high porosity saturated by a water–copper nanofluid whose volume fraction varies between 0% (pure water) and 7%. The Rayleigh number based on the radius of the cupola reaches high values up to 7.29 × 10¹⁰ given the important surface heat flux generated by the device during operation. The ratio between the thermal conductivity of the solid matrix and that of the base fluid ranges between 0 (interstitial volume without porous medium) and 41.4 corresponding to the intended applications. This experimental study done with an industrial prototype at scale 1 quantifies the natural convective heat transfer via the Nusselt number determined for many configurations obtained by varying the solid-fluid thermal conductivity ratio, the inclination angle, the Rayleigh number, and the volume fraction. The study clearly shows that the cooling performance of the Cu-H₂O nanofluid degrades with its age and the number of times it has been used. Analysis of the results reproducibility also proves the irreversibility of the performance. The measured values were compared with those obtained in a recent numerical study based on the volume control method. The observed deviations taking into account the experimental uncertainty margins validate the mathematical model implemented in the numerical approach.     

SFG study of the ethanol in an acidic medium--Pt(110) interface: effects of the alcohol concentration

Ethanol in an acidic solution-Pt(110) interface was studied by SFG spectroscopy (between 1820 and 2325 cm(-1)) to explore primarily the effects of the alcohol concentration. Stretching bands of H-Pt (ca. 1970 or 2050 cm(-1)) and CO (ca. 1980 and 2040 cm(-1)) species, produced by the ethanol oxidation, were detected during the adsorption and oxidation of 0-1 mol L(-1) ethanol in a 0.1 mol L(-1) HClO(4) solution on the electrode surface. Hydrogen and CO coadsorb stably on Pt(110) between 0.05 and 0.15 V in ethanol-containing solutions. In this potential range, the blue shift of the hydrogen resonance (ca. 80 cm(-1)) reveals a weakening of the hydrogen bonding between adsorbed hydrogen and water molecules in the double layer. After the hydrogen desorption (0.15 V), the formation of compact CO islands, depending on the ethanol concentration, lifts the Pt(110) surface reconstruction. In ethanol-free solution, the surface remains reconstructed. The lower-frequency CO band is assigned to the CO species adsorbed on (1 x 2) reconstructed Pt(110) domains, having smaller local coverages, while the higher-frequency CO band is attributed to the close-packed CO species adsorbed on (1 x 1) patches. The reaction pathway forming CO(2) is less favored with increasing ethanol concentration.     

Gold(I)/Gold(III) Catalysis that Merges Oxidative Addition and π-Alkene Activation

Heteroarylation of alkenes with aryl iodides was efficiently achieved with a (MeDalphos)AuCl complex through Au^I/Au^III catalysis. The possibility to combine oxidative addition of aryl iodides and π-activation of alkenes at gold is demonstrated for the first time. The reaction is robust and general (>30 examples including internal alkenes, 5-, 6-, and 7-membered rings). It is regioselective and leads exclusively to trans addition products. The (P,N) gold complex is most efficient with electron-rich aryl substrates, which are troublesome with alternative photoredox/oxidative approaches. In addition, it provides a very unusual switch in regioselectivity from 5-exo to 6-endo cyclization between the Z and E isomers of internal alkenols.     

Chemical composition and antimicrobial activity of essential oil of Cupressus atlantica

Cupressus atlantica Gaussen, an endemic species from Morocco, is used in traditional medicine. The chemical composition of the essential oil isolated by hydrodistillation from the leaves was investigated by capillary gas chromatography and gas chromatography/mass spectrometry, and also evaluated for in vitro antimicrobial activity. Sixty-one components, representing 98.1% of the total, were detected of which fifty-seven were identified. Germacrene D (34.8%), alpha-pinene (13.6%), delta-cadinene (6.1%), alpha-phellandrene (5.5%), gamma-cadinene (5.0%), beta-caryophyllene (4.8%) and alpha-humulene (4.4%) were the predominant compounds. The oil was characterized by a relatively high amount of oxygenated monoterpenes (66.5%). The oil, screened for antimicrobial activity against both Gram-positive and Gram-negative, showed pronounced activity against all the microbes tested, except Pseudomonas, which showed resistance.     

Design and characterization of new advanced energetic biopolymers based on surface functionalized cellulosic materials

A new class of energetic biopolymers, which contain nitrate ester (O-NO₂) and nitramine (N-NO₂) as explosophoric groups, was successfully synthesized by surface modification of renewable pristine cellulose (PC) and microcrystalline cellulose (MCC) via epichlorohydrin-mediated amination followed by nitration process to produce new promising energetic aminated and nitrated cellulose and microcrystalline cellulose (APCN and AMCCN). Their structural, thermal, crystallinity and morphological features were examined and compared to those of the common cellulose nitrate. Furthermore, their energetic performances were evaluated by EXPLO5 V6.04 software. Experimental results confirm the successful chemical functionalization process to develop insensitive APCN and AMCCN with outstanding features such as nitrogen content of 15.01% and 15.39%, density of 1.692 g/cm³ and 1.708 g/cm³, and detonation velocity of 7526 m/s and 7752 m/s, respectively, which are significantly higher than those of the nitrated unmodified cellulosic biopolymers. The present investigation provides a suitable pathway to design new insensitive and energy-rich dense cellulosic biopolymers for potential application in high-performance solid propellants and composite explosives.

     

Autotandem Catalysis: Inexpensive and Green Access to Functionalized Ketones by Intermolecular Iron-Catalyzed Amidoalkynylation/Hydration Cascade Reaction via N-Acyliminium Ion Chemistry

Iron-based catalysts were applied in cascade-type reactions for the synthesis of different carbonyl compounds. The reactions proceeded by a new iron-catalyzed cascade of alkynylation/hydration by using both the σ- and π-Lewis acid properties of iron salts. The alkynylation reactions of several endo and exocyclic acetoxylactams were achieved with three different catalysts including FeCl₃ ⋅ 6H₂O, FeCl₃, and Fe(OTf)₃ showing the efficiency of σ-Lewis acidity of iron (III) salts in catalyzing the alkynylation reaction. We also demonstrated that the reaction sequence could be shortened by the direct use of hydroxylactams, leading to an environmentally friendly protocol, avoiding the need to perform unnecessary lengthy steps. A combination of the hard/soft iron Lewis acid properties was then used to implement an unprecedented tandem intermolecular alkynylation/intramolecular hydration sequence allowing expedient access to a new carbonyl structures from trivial materials.     

Transtaganolides A-D: novel metabolites from Thapsia transtagana

Four novel and unusual C-19 compounds from Thapsia transtagana, named transtaganolides A-D, have been isolated. Their structures were established by physical methods, including X-ray analysis of transtaganolides A and B. This is the first time that a 7-methoxy-4,5-dihydro-3H-oxepin-2-one ring has been found in a natural product. [structure: see text]