Local dynamic mechanical properties in model free-standing polymer thin films

High-frequency sinusoidal oscillations of a coarse-grained polymer model are used to calculate the local dynamic mechanical properties (DMPs) of free-standing polymer thin films. The storage modulus G(') and loss modulus G(") are examined as a function of position normal to the free surfaces. It is found that mechanically soft layers arise near the free surfaces of glassy thin films, and that their thickness becomes comparable to the entire film thickness as the temperature approaches the glass transition T(g). As a result, the overall stiffness of glassy thin films decreases with film thickness. It is also shown that two regions coexist in thin films just at the bulk T(g); a melt-like region (G(')G(")) in the middle of the film. Our findings on the existence of a heterogeneous distribution of DMPs in free-standing polymer thin films provide insights into recent experimental measurements of the mechanical properties of glassy polymer thin films.     

Studies with an inorganic ion-exchange membrane exhibiting selectivity for Pb(II) ions

A solid membrane electrode made with titanium arsenate as membrane material and "Araldite" as binder has been used to measure the activity of lead in the concentration range from 0.1 M to 5 x 10(-6)M. The electrode is unaffected by many cations, nitrate and acetate. The response time is 40-60 sec over the whole concentration range (in a static system) and the electrode has a working life of at least four months. The electrode can work in the pH range 2-5 and is tolerant of ethanol up to a content of 30% v v . It has been successfully used for end-point indication in potentiometric titration of lead. A membrane treated with cationic surfactant exhibits better selectivity.     

Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazones: Magnetic,E.s.r. and spectral studies

Summary Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazone (LH) with the general formulae FeLX₂ (X = Cl, Br, NO₃ or SCN) and FeLSO₄ have been prepared and characterised by elemental analysis and by magnetic measurements in the polycrystalline state in the 77–298 K range and by electronic, i.r. and e.s.r. spectra. The FeLX₂ species (X = Cl, NCS or NO₃) are square pyramidal of intermediate spin-state (S=3/2) with an⁴ A ₂ ground state. The magnetic behaviour of FeLSO₄ is commensurate with high order effects coupled with antiferromagnetic exchange interactions. FeLBr₂ is a spin-free dimer involving bromine bridging between two FeLBr₂ square pyramids. However, the low-spin species [FeL(DMF)₃]²⁺ exists in dimethylformamide solution.     

Polarographic reduction of some guanylpyrazoline nitrates and the effect of double layer structure on E1/2 values

Polarographic reduction of 4-arylhydrazono-1-guanylnitrate-3-methyl-2-pyrazoline-5-ones takes place in a single 4-electron transfer, giving a diffusion controlled irreversible wave in B.R. buffers of pH range 2.0–10.0. The reduction in these compounds takes place at the ?NH?N=C-bond. Effect of various cations, anions and solvent percentage on the reduction has been discussed. The effect of substituents and its correlation with the Hammett substituent constant (δ) have also been studied.     

High energy muon-nucleon inelastic scattering at lowq 2

The inelastic interactions of 150 GeV positive muons produced at Fermi Laboratory have been studied in nuclear emulsion. Secondary particles produced in these interactions have been identified, the energy spectra and angular distributions for pions and protons are given. The inclusive pionproduction reaction is studied and the relative shape ofp _t ² distribution is discussed. The average charged multiplicity relations are determined as a function of different parameters and are compared with the multiplicities produced in pure hadronic interactions. The integral cross sections have been measured and are compared with the first and second powers of 1/(1+q ²/m _p ² ) forσ _exp(q ²,v), the quantity commonly called the “virtualphoton-nucleon total cross section”. The values of the structure function νW ₂ are calculated for 0.02≤q ²≤0.5. The present data are compared with other muon data at the same energy.     

Lattice instability in Hf1-x Ta x V2 compounds

The temperature dependence of the electric quadrupole interaction frequency _l ^o , experienced by the¹⁸¹Ta probe occupying Hf site in the compounds Hf_1-xTa_xV₂ has been measured for x=0.06, 0.10 and 0.20 in the temperature region between 8.5 K to 296 K. The measurements show lattice transformation in all the three compounds below 120 K.     

Ammonia chemical ionization tandem mass spectrometry in structural determination of alkaloids. II. Tetraponerines from pseudomyrmecine ants

Chemical ionization tandem mass spectrometry (CI-MS/MS) of alkaloids with ammonia reagent gas and collision-activated dissociation as well as EI-MS/MS were applied to the tetraponerine alkaloids in extracts from six pseudomyrmecine ants of the genus Tetraponera. The MS/MS techniques along with gas chromatography Fourier transform infrared (GC/FTIR) spectra allowed identification in two extracts of seven of the eight known tetraponerines. The EI-MS/MS fragmentations proved diagnostic for the ring system and the CI-MS/MS patterns for the C-8 or C-9 substitution, while the Bohlmann bands in FTIR spectra were diagnostic for the C-8 or C-9 configurations. An Indian ant (T. allaborans) had T-2, T-4 and T-8, while a Chinese ant (T. binghami) had T-5, T-6, T-7 and T-8. Four other ants, T. rufonigra (India), T. penzigi (Africa), T. clypeata (Africa) and T. sp. cf. emeryi (Africa), had no tetraponerines.     

The biosynthesis of the alkaloids of croton sparsiflorus morong

Incorporation of tyrosine, dopa, dopamine, 4-hydroxyphenylpyruvic acid, (±)-, norcoclaurine-1-carboxylic acid, -norcoclaurine, -coclaurine, and -N-methylcoclaurine into N-methylcrotsparine, N-methylcrotsparinine and N-methylsparsiflorine in Croton sparsiflorus Morong has been studied. The evidence supports the direct oxidative coupling of (+)-, and (-)-N-methylcoclaurines to give N-methylcrotsparine and N-methylcrotsparinine respectively. Tracer experiment show that N-methylcrotsparine undergoes dienone-phenol rearrangement to give N-methylsparsiflorine. A double labelling experiment with (±)-N[¹⁴C]methyl[1-³H]coclaurine demonstrated that the H atom at the asymmetric centre in the 1-benzylisoquinoline precursor is retained in the bioconversion. The intermediacy of norcoclaurine-1-carboxylic acid and specific incorporation of dehydro-N-methylcoclaurinium salt into the bases have been demonstrated.