Experimental investigation for stability and surface properties of TiO2 and Al2O3 water-based nanofluids

Journal of Thermal Analysis and Calorimetry - Nanofluids have gained recent attention because of their potential applications in diverse engineering fields like enhancing thermal transport,...     

Microwave promoted energy-efficient N-formylation with aqueous formic acid

Microwave-induced organic reaction enhancement (‘MORE’) chemistry technique (open vessel; controlled microwave energy to stay below the boiling point of the reaction mixture) was used for the N-formylation of aliphatic and aromatic amines and amino heterocycles with aq formic acid (80%) on a multiple gram scale in a few minutes.     

Synthesis of highly condensed heterocycles using radical reactions

Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed.     

Amphoteric trap modeling of multidielectric scaled SONOS nonvolatile memory structures

We have characterized multidielectric scaled SONOS nonvolatile memory structures with the quasi-static linear voltage ramp (LVR) technique and dynamic pulse measurements. We have formulated physically-based ERASE/WRITE and retention methods with deep level amphoteric traps which capture and emit carriers to the bands in the silicon nitride film. Amphoteric trap parameters are extracted by the LVR technique. ERASE/WRITE and retention amphoteric trap model simulations agree well with the experimental dynamic pulse measurements. Experimental scaled SONOS structures have been fabricated with tunnel oxide X_OT=20 Å, nitride X_N=30 Å and blocking oxide X_OB=55 Å and demonstrated a static flatband shift of 3.6 V with ±5 V programming voltages. These structures may be used as the nonvolatile memory element in high density VLSI circuits.     

Aeroelastic flutter of a disk rotating in an unbounded acoustic medium

The linear aeroelastic stability of an unbaffled flexible disk rotating in an unbounded fluid is investigated by modeling the disk-fluid system as a rotating Kirchhoff plate coupled to the irrotational motions of a compressible inviscid fluid. A perturbed eigenvalue formulation is used to compute systematically the coupled system eigenvalues. Both a semi-analytical and a numerical method are employed to solve the fluid boundary value problem. The semi-analytical approach involves a perturbation series solution of the dual integral equations arising from the fluid boundary value problem. The numerical approach is a boundary element method based on the Hadamard finite part. Unlike previous works, it is found that a disk with zero material damping destabilizes immediately beyond its lowest critical speed. Upon the inclusion of small disk material damping, the flutter speeds become supercritical and increase with decreasing fluid density. The competing effects of radiation damping into the surrounding fluid and disk material damping control the onset of flutter at supercritical speed. The results are expected to be relevant for the design of rotating disk systems in data storage, turbomachinery and manufacturing applications.     

Stereoelectronic effects in negatively and positively (Protonated) charged species. Ab initio studies of the gauche effect in 1,4-dioxa systems

A computational study ab initio of the conformational dependence of proton affinities of 2-methoxyethoxide (MEO), dimethoxyethane (DME), and 1,4-dioxane has been carried out at the MP2/6-31+G level of theory. The results were discussed in comparison with reference systems, from simple alkoxides and ethers to anomeric moieties, in open, cyclic, and bicyclic molecules. The COCCOC species are stronger bases than the COCOC (anomeric) ones and approach regular ethers in their strength. The gauche forms in MEO and DME are altogether stronger bases than the anti forms, and anti (equatorial) protonation is preferred over gauche (axial), unless ditopic protonation is possible, like in aga-DME or cis-tetraoxadecalin. The gauche effect plays a significant role in the formation, relative stability, and reactivity of the charged species.     

Intra-annular cyclophane diamines as proton sponges: a computational study

Gas-phase proton affinities of cyclophanes containing intra-annular amino groups were calculated using density functional theory (DFT) at the B3LYP/6-31+G^∗∗//B3LYP/6-31G^∗ level. They are higher in magnitude as those for proton sponges such as 1,8-bisaminonaphthalene, however, they are slightly weaker bases than 1,8-bis(dimethylamino)naphthalene. The high basicity of the cyclophane diamines is attributed mainly to their structural flexibility, which allows them to maximize the hydrogen bond strength in the cations by achieving N-H?N linearity, while strain relief upon protonation is less important. Another contributing factor is the stabilizing interaction of the added proton with adjacent phenyl π systems of the cyclophanes. Barriers for proton transfer between the nitrogen atoms of the diamine cations are also reported.     

Photoacoustic spectroscopy of solids and surfaces

After briefly reviewing the theory and instrumentation, results from a variety of experiments carried out by the authors on the photoacoustic spectroscopy of solids and surfaces by employing an indigenous spectrometer are discussed in the light of the recent literature. Some of the important findings discussed are, phase angle spectroscopy, anomalous behaviour of monolayers, unusual frequency dependence in small cell volumes, spectra of a variety of solids including amorphous arsenic chalcogenides, photoacoustic detection of phase transitions and determination of surface areas and surface acidities of oxides. Recent developments such as piezoelectric photoacoustic spectroscopy, depth profiling and subsurface imaging are also presented. Contribution No. 124 from the Solid State and Structural Chemistry Unit.     

Itinerant electron ferromagnetism in Sr2+-, Ca2+-, and Ba2+-doped rare-earth orthocobaltites (Ln3+1−xM2+xCoO3)

Electronic and magnetic properties of Ln_1?xSr_xCoO₃ (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba²⁺ in LaCoO₃ favors itinerant electron ferromagnetism relative to Sr²⁺ while Ca²⁺ is less favorable than Sr²⁺.     

Microwave assisted synthesis of an unusual dinitro phytochemical

A novel dinitro secondary metabolite, 2-nitro-4-(2^′-nitroethenyl)phenol from a marine source, has been prepared via highly accelerated, microwave assisted, nitration reactions using mild reagents. ipso-Substitution of a carboxy group by a nitro group is discussed.