A Mathematical Visit to Hanoi

This article, written in September 1978, is appearing after several unexpected publication delays. In the meantime a sequence of events in Southeast Asia — the Chinese invasion, the exodus of refugees, the war in Cambodia — is inevitably having an impact on Vietnam’s pace of economic recovery from the War and level of technological development. In any case, this article obviously cannot address the political and economic issues that have come into focus in the past year.     

Second virial coefficient of amylose acetate

The second virial coefficients of amylose acetate fractions have been determined at different temperatures and have been analyzed according to recent theories of second virial coefficient.     

A microcomputer-controlled microcalorimeter calibration circuit

Summary A Microcomputer-Controlled Microcalorimeter Calibration Circuit 3. Enthalpies of Solution of Linear and Cyclic Alkanes in Glacial Acetic Acid The molar enthalpy of solution ofn-alkanes and cycloalkanes has been studied in an isoperibol calorimeter at 25.0 °C. Reasoning from a purely volumetric effect of intrusion of solute molecules into an associated solvent, we might expect compact cycloalkane molecules to disturb the solvent structure less than linear alkanes and to have a smaller exothermic enthalpy of solution than then-alkanes. That is not the case, evidently, as the cyclic compounds mix with aH _s that is exothermic in the same degree as their linear counterparts. These results are discussed in terms of a model in which each alkane molecule occupies a cavity in the structured solvent that is large with respect to itself. Enthalpy of solution of saturated alkanes in glacial acetic acid does not depend on the geometry of the alkane for the two homologous series studied thus far.     

The Extractive-Spectrophotometric Determination of Iron(III) As a Mixed-Ligand Complex with N-Hydroxy-N,N′DI-p-Tolyl-p-Toluamidine and Thiocyanate

The extractive-photometric determination or iron(III) as a mixed-ligand complex with N -hydroxy-N, N′ -di-p -tolyl-p -toluamidine (HDTTA) and thiocyanate is described. The orange-red Waterinsoluble 1:1:2 (metal: HDTTA: SCN^?) ternary complex formed in 0.1–0.6 M hydrochloric acid solutions is quantitatively extractable into benzene. The wavelength of maximum absorption, molar absorptivity and sensitivity of the colour system are 460nm, 12000 l. mole^?1 cm^?1 and 0.0046 μg Fe/cm ²respectively. The influence or foreign ions on the determination of iron has been studied. This method has also been applied to determine the iron content of several alloys.     

Electronic structure and conformational study of thiobiurets

Quantum mechanical calculations at all valence complete neglect of differential overlap (CNDO/2) and self-consistent charge extend Huckel (SCC-EH) and the Pi electron Pariser-Parr-Pople with limited configuration interaction (PPP-LCI) levels of approximation have been accomplished for monothiobiuret and dithiobiuret. From the calculated results, a discussion of the electronic structure, photoelectron and electronic spectra and the conformational stability are given. The electronic and¹H nmr spectra are also reported. A trans-cis-CONHCS-structure is found to be the stable conformation for monothiobiuret consistent with other evidences.     

Poly (1,3-[2-methoxy-4-hydroxy-5-acetylphenylene] butylene) (HMAP-BG) as a polymeric ligand

Poly(1,3[2-methoxy-4-hydroxy-5-acetylphenylene]butylene) was prepared by Friedel-Craft polycondensation of 2-hydroxy, 4-methoxyacetophenone and 1,4-butane-diol in presence of poiyphosphoric acid catalyst. The polymer samples were characterized by IR spectra, TGA and their M_n determined by nonaqueous titration. Viscosity measurents in DMSO showed that solutions exhibited normal behaviour. Polymers were complexed with Cu(II), Ni(II), Mn(II), Co(II) and Zn(II) and characterized. Chelation and ion exchange properties were also studied by employing the batch equilibrium method.     

Abrupt dissolution of polydiacetylenes

Polydiacetylenes, where R?? (CH₂)_3,4OCONHCH₂COO(CH₂)_1,3CH₃ dissolve almost instantaneously within a narrow range of temperature (ca. 3°C). The enthalpy of dissolution of these polymers is determined by differential scanning calorimetry to be 25–46kJ/mole of the repeat unit. The abruptness of dissolution is due to breaking of intramolecular H bonds, which appears to be a cooperative phenomenon. Supporting infrared evidence is cited.     

Rocket borne instrumentation for the measurement of electron density—height profile in the ionosphere

The present paper describes the construction and working of a high frequency capacitance rocket payload for the measurement of electron concentration in the ionosphere, designed and fabricated mostly with indigenous components. This payload was flight-tested in the first and second Indian Centaure test rocket launched on 26-2-1969 and 7-12-1969 from Thumba Equatorial Rocket Launching Station. The paper also presents the calibration procedures and some of the preliminary results obtained from the first flight to show the capabilities of the instrument.