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Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans the biological, physical, and social sciences.
Abstract An investigation has been made of the measurement of degree of swelling of vulcanizates and the estimation of υ τ , the volume fraction of polymer in a vulcanizate swollen to equilibrium. Methods have been established for dealing with a volatile swelling liquid, allowing for small percentages of nonpolymer in…
The application of autoradiography to the measurement of volume diffusion is limited because of the difficulty in interpreting the effects of the energy of the radiations, the scattering and absorption properties of the specimen and other complicating factors. A general method of interpretation is described in which t…
This paper is a brief review of the physical and chemical methods of strengthening glass, in particular that due to the large for small ion exchange resulting from treatment in molten salt at temperatures below the annealing range for the glass. Abrasion of treated glass is shown to reduce markedly the strength of exp…
The infrared spectra of highly crystalline samples of cellulose containing the lattice types I, II, and III were compared with one another and with the spectrum of amorphous cellulose in the 850–1500 cm.−1 region. The spectra of cellulose II and of amorphous cellulose showed interesting similarities at 1420, 893–897,…
A new infrared ratio, α1372 cm. −1/α2900 cm. −1, is proposed for measuring crystallinity in cellulosic materials. The advantage of this ratio over others which have been used is that it can be applied to both celluloses I and II and, therefore, to samples containing a mixed lattice. Two series of samples, encompassing…
CONTENTS I. Introduction 233 II. Peculiarities of the electrochemical behaviour of metals in narrow gaps and crevices 234 III. Change in steady-state potentials at sites to which access of electrolyte is impeded 235 IV. Change in nature of corrosion medium in gaps 236 V. Formation of macrocells of crevice–open surface…
Observations have been made of the two-photon excitation of an electron from the valence to the conduction band in CdS (${E}_{g}=2.5$ eV) using a pulsed ruby laser ($\ensuremath{\hbar}\ensuremath{\omega}=1.78$ eV). The radiative recombination emission from exciton and impurity levels subsequent to the simultaneous abs…
Measurements of the oscillatory magnetoresistance of a high-quality graphite single crystal were made for all angles $\ensuremath{\theta}$ between the magnetic field and the $c$ axis, for magnetic fields up to 24 kG, and for temperatures from 1.22 to 4.22\ifmmode^\circ\else\textdegree\fi{}K. The results were analyzed…
The lattice thermal conductivity of a number of semiconductors including InSb, GaAs, GaSb, CdTe, and CdS has been measured between 1.7 and 300\ifmmode^\circ\else\textdegree\fi{}K. This, together with previous work on Si and Ge, is used to investigate the validity of the relaxation time expressions for scattering of ph…
The conductivity and the Hall and Seebeck coefficients of reduced and doped strontium titanate were measured over the temperature range 4.2-300\ifmmode^\circ\else\textdegree\fi{}K. An average effective mass of about 10 ${m}_{0}$ was deduced from these experiments. This value agrees well with the results of a recent en…
Abstract 9‐Allylcarbazole, 9‐Δ 3 ‐butenylcarbazole, 9‐Δ 4 ‐pentenylcarbazole and 9‐Δ 5 −hexenylcarbazole were synthesized and their polymerization with Z IEGLER ‐N ATTA catalyst systems studied. 9‐Allylcarbazole could not be polymerized and 9‐Δ 3 ‐butenylcarbazole could only be polymerized with extreme difficulty. How…
Abstract The molecular structure of polyethylene oxide (PEO), (—CH 2 CH 2 O‐) n , was studied by the X‐ray diffraction and infrared absorption spectroscopic methods. The X‐ray diffraction data were observed for the highly oriented PEO samples and were analyzed by use of the method of FOURIER transform of the helix pro…
A quantitative description of the capillary hysteresis properties of a porous material is developed through bivariate distribution density function ƒ(α, β), where α and β are wetting and drying potentials. This is formally equivalent to the independent domain theory of Poulovassilis. The similarity hypothesis (implyin…
Measurement of transmitted phonon drag across 10 ohm cm $p$-type silicon indicates a phonon mean free path of the relevant thermal phonons which varies from about 80 \ensuremath{\mu} at 77\ifmmode^\circ\else\textdegree\fi{}K to 12 \ensuremath{\mu} at 250\ifmmode^\circ\else\textdegree\fi{}K. The values depend on the me…
A measurement of the quantum efficiency of silicon has been carried out over the photon energy range from 4.9 to 21.2 eV by measuring the photoresponse of silicon surface-barrier photodiodes. The quantum efficiency increases from 2.0 at $h\ensuremath{\nu}=4.9$ eV to approximately 3 at $h\ensuremath{\nu}=6$ eV; between…
The absolute reflection spectrum of type IIa diamond was measured at room temperature from 4 to 30 eV and analyzed by dispersion techniques to obtain the optical parameters. Structure observed in the dielectric constant near 7, 12, 16, 20, and 24 eV was attributed to interband transitions at critical points in the joi…
Allotropes of lanthanum, cerium, praseodymium, and neodymiumc have been observed at elevated pressures with an x-ray diffraction camera which incorporates a diamondanvil, high-pressure cell. In each case a high-pressure modification was observed which has a face-centered cubic structure. At room temperature the unit c…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT17-Azasteroids. I1Sumanas Rakhit and Marcel GutCite this: J. Org. Chem. 1964, 29, 4, 859–862Publication Date (Print):April 1, 1964Publication History Published online1 May 2002Published inissue 1 April 1964https://pubs.acs.org/doi/10.1021/jo01027a022https://doi.org/10.1021/j…
Pyrenoids of 6 diatoms, Acnanthes minutissima, Cyclotella meneghiniania, Cymbella affinis, Gomphonema parvulum, Nitzschia sp., and Surirella ovalis, were examined comparatively with the electron microscope. All except those of G. parvulum were membrane-limited. The pyrenoid membrane forms a ridge around the pyrenoid o…