Thermo-mechanical response of Al 6061 with and without equal channel angular pressing (ECAP)

The thermo-mechanical responses of Al 6061 before and after equal channel angular pressing (ECAP) at different strain rates and temperatures were measured. Al 6061 was solution heat treated before ECAP pressing at room temperature and subjected to up to three passes. After pressing, the billets were aged at 100 °C for 2 days. An as-received Al 6061-T651 was studied similarly to investigate the differences between processed and non-processed specimens. The responses of ECAP material were determined at −30, 22, 125 and 250 °C, and at strain rates from 10⁻⁵ to 2530 s⁻¹; the 6061-T651 specimens were subjected to uniaxial compressive loading at −31, 22, 85, 150, 230 and 315 °C, and strain rates ranging from 10⁻⁵ to 2200 s⁻¹. It was found that, the ECAP process increases the strength versus the T651 condition. Additionally, the Al 6061 ECAP is not sensitive to strain rate at room and lower temperatures, but the sensitivity increases as the number of passes and/or temperature are increased and this is the same for the non-processed material. Increasing the number of passes increases the flow stress at room and lower temperatures, has almost no effect at 125 °C and decreases at 250 °C. For both materials, the dynamic flow stress is higher than the stress at quasi-static strain rates even when the quasi-static strain rate regime is insensitive to strain rate. The Al 6061 has strong texture after one pass but steadily increases as the number of passes are increased. This is the first study that reports on the thermo-mechanical responses of ECAP and non-ECAP Al 6061 at such a wide range of strain rates, including dynamic, and temperatures.     

An Unexpected Synthesis of Novel Oxygen-Bridged 1,5-Benzothiazepine Derivatives and their Reductive Five-Membered-Ring Opening

Summary.  A convenient procedure is reported for the preparation of benzofuro-annelated 2-phenyl-1,5-benzothiazepine derivatives by oxidative cyclocondensation of phenolic β-diketones with o-aminothiophenol in DMSO. The regiochemistry of these compounds is proven by HMBC signals and the existence of a five-bond ¹⁹F,¹³C-2 coupling. Surprisingly, treatment with LiAlH₄ at room temperature led to a double reduction under opening of the five-membered ring. Refluxing such solutions with a higher amount of LiAlH₄ gave rise to a further reduced derivative possessing the trans-configuration. All structures (regio- and stereochemistry) were assigned on the basis of NMR spectroscopic data. Received November 22, 1999. Accepted December 21, 1999     

First principles study and comparison of vibrational and thermodynamic properties of XBi(X= In,Ga, B,Al)

In the present work, vibrational and thermodynamic properties of XBi(X = B, Al, Ga, In) compounds are compared and investigated. The calculation is carried out using density functional theory(DFT) within the generalized gradient approximation(GGA) in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory(DFPT) as implemented in Quantum ESPRESSO(QE) code. Thermodynamic properties involving phonon density of states(DOS) and specific heat at constant volume are investigated using quasiharmonic approximation(QHA) package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm~(-1), 150 cm~(-1), 300 cm~(-1), and 150 cm~(-1), respectively. For all compounds,the three acoustic modes near the gamma point have a linear behavior. C_V is a function of T~3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected.     

Anti-Inflammatory CeO2 Nanoparticles Prevented Cytotoxicity Due to Exogenous Nitric Oxide Donors via Induction Rather Than Inhibition of Superoxide/Nitric Oxide in HUVE Cells

The mechanism behind the cytoprotective potential of cerium oxide nanoparticles (CeO₂ NPs) against cytotoxic nitric oxide (NO) donors and H₂O₂ is still not clear. Synthesized and characterized CeO₂ NPs significantly ameliorated the lipopolysaccharide (LPS)-induced cytokines IL-1β and TNF-α. The main goal of this study was to determine the capacities of NPs regarding signaling effects that could have occurred due to reactive oxygen species (ROS) and/or NO, since NP-induced ROS/NO did not lead to toxicity in HUVE cells. Concentrations that induced 50% cell death (i.e., IC50s) of two NO donors (DETA-NO; 1250 ± 110 µM and sodium nitroprusside (SNP); 950 ± 89 µM) along with the IC50 of H₂O₂ (120 ± 7 µM) were utilized to evaluate cytoprotective potential and its underlying mechanism. We determined total ROS (as a collective marker of hydrogen peroxide, superoxide radical (O₂^•−), hydroxyl radical, etc.) by DCFH-DA and used a O₂^•− specific probe DHE to decipher prominent ROS. The findings revealed that signaling effects mediated mainly by O₂^•− and/or NO are responsible for the amelioration of toxicity by CeO₂ NPs at 100 µg/mL. The unaltered effect on mitochondrial membrane potential (MMP) due to NP exposure and, again, CeO₂ NPs-mediated recovery in the loss of MMP due to exogenous NO donors and H₂O₂ suggested that NP-mediated O₂^•− production might be extra-mitochondrial. Data on activated glutathione reductase (GR) and unaffected glutathione peroxidase (GPx) activities partially explain the mechanism behind the NP-induced gain in GSH and persistent cytoplasmic ROS. The promoted antioxidant capacity due to non-cytotoxic ROS and/or NO production, rather than inhibition, by CeO₂ NP treatment may allow cells to develop the capacity to tolerate exogenously induced toxicity.     

Selective detection of carboxylic acids, ureas and phenols and semiquantitative determination of citric acid by capillary solid-state spot-tests

Solid-state spot-tests for the selective detection of carboxylic acids, ureas and phenols have been developed. Mixtures of p-dimethylaminobenzaldehyde with N-methylurea and of p-dimethylaminobenzaldehyde with phthalic acid are used as reagents. Based on these tests a semiquantitative determination of citric acid is also developed. These tests utilize three properties of the coloured boundary: colour, length and direction of movement. Our work on capillary solid-state spot-tests,(1) has now been extended to some further organic compounds.     

Studies on the nef reaction induced by organic bases

Studies of the Nef reaction in the presence of primary, secondary and tertiary amines have been described. A convenient synthesis of N-substituted pyrroles and 3,6-dimethyl-4-hydrazinocarbonyl-5-(4-amino-3-nitrophenyl)-pyridazine 16 has been developed.     

Novasomes as Nano-Vesicular Carriers to Enhance Topical Delivery of Fluconazole: A New Approach to Treat Fungal Infections

The occurrence of fungal infections has increased over the past two decades. It is observed that superficial fungal infections are treated by conventional dosage forms, which are incapable of treating deep infections due to the barrier activity possessed by the stratum corneum of the skin. This is why the need for a topical preparation with advanced penetration techniques has arisen. This research aimed to encapsulate fluconazole (FLZ) in a novasome in order to improve the topical delivery. The novasomes were prepared using the ethanol injection technique and characterized for percent entrapment efficiency (EE), particle size (PS), zeta potential (ZP), drug release, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and antifungal activity. The FN7 formulation with 94.45% EE, 110 nm PS and −24 ZP proved to be the best formulation. The FN7 formulation showed a 96% release of FLZ in 8 h. FTIR showed the compatibility of FLZ with excipients and DSC studies confirmed the thermal stability of FLZ in the developed formulation. The FN7 formulation showed superior inhibition of the growth of Candida albicans compared to the FLZ suspension using a resazurin reduction assay, suggesting high efficacy in inhibiting fungal growth.     

Structure and Magnetic Properties of a New Lattice System of the Heterometallic Decanuclear Ce<Subscript>6</Subscript>Mn<Subscript>4</Subscript> Aggregate

In this paper, we present a mixed valence f–d Ce₆Mn ₄ ^III compound having formula [Ce ₆ ^IV Mn ₄ ^III (μ₄-O)₄ (μ₃-O)₄(O₂C^tBu)₁₂(ea)₄(OAc)₄]·H₂O (1), which is obtained by the reaction of hydrated lanthanide nitrate, pivalic acid, and ethanolamine in MeCN as a solvent. The single crystal X-ray diffraction analysis demonstrates that the central core consists of an octahedron with four triangular pyramids added to four related faces or as an octahedron encapsulated in a tetragon. The fitting of magnetization data using the anisotropic model gives D = 2.13 cm^–1 and g = 1.97 (D is the axial zero-field splitting parameter).