An application of the INEPT pulse sequence to the NMR assignment of halogenated marine natural products

The routine use of the INEPT pulse sequence is shown to be the method of choice for the assignment of multiplicity from ¹³C NMR spectra where no prior information about the ¹J(CH) coupling constants is available, or where these are expected to vary over a large range. This technique is illustrated using spectra obtained from polyhalogenated monoterpenes isolated from the red alga Plocamium angustum, which have ¹J(CH) values varying from 127 to 203 Hz.     

Iron plasma: Sensitivity of photoelectric cross sections to different models and general features of the Fermi-Amaldi-Modified model

Photoelectric cross sections in several atomic models are presented as a function of temperature and density. The models discussed are Thomas-Fermi (TF), Fermi-Amaldi-Modified (FAM), and Debye-Hückel-Thomas-Fermi (DHTF). We also present some systematic results for the less known FAM potential model regarding predictions for: electrostatic potentials, bound electron level energies, pressures, and branching ratios of photoelectric cross sections. The pure iron plasma which we explored had a temperature in the range of 0.2–3 keV and a density in the range of 50–1000 g/cm³. Our conclusion is that except near threshold the photoelectric cross sections per fully occupied subshell are less sensitive to changes in density and temperature, at least in the ranges of our investigation, than other factors, such as occupation numbers.     

Mass relations and neutrino oscillations in an SO(10) model

We present in detail a grand unified model based on SO(10) which naturally reproduces known fermion mass relations and mixing angles. It predicts m_νe ? m_νμ, m_ντ, and predominant ν_μ-ν_τ oscillations. Several other features of the model are analyzed in detail: construction of the Higgs potential, predictions for τ_p and sin²θ_w in a temporarily free model and a relation between the mass of the t-quark and the lifetime of the B meson.     

Axisymmetric buckling of rigidly clamped hemispherical shells

The shell is subjected to a uniform compressive surface load (either a pressure or a centrally directed load). The results of a numerical study are summarized and compared with experiments.     

Work functions and surface double layer potentials of monovalent metals from a network model

The model described in this paper uses an electronic wave function which is defined to be nonzero only along the lines connecting first nearest neighbors in the metallic lattice. The electrons are assumed to move freely along the lines between nearest neighbors. No electron-electron or electron-nucleus force is included in the model calculations (except for forces arising from the Pauli exclusion principle). The work function is defined as the amount of energy required to move an electron from a point slightly inside the crystal to a point slightly outside. The contribution of the electronic double layer is included in the calculation of the work function as well as the dependence of the double layer potential on the surface geometry. Surface states, where the electron is localized in the neighborhood of the face of the crystal, are found to have energies sufficiently above the Fermi level to eliminate the possibility that they make any contribution to the double layer potential for the case of the (100) crystal plane. Consequently, surface states have been ignored in all the calculations. The surface double layer is assumed to be caused by the presence of a finite potential barrier at the surface of the crystal. Bulk electronic wave functions can penetrate this barrier and decay exponentially outside the crystal. The only parameters required by the model are the nearest neighbor distance for the lattice and the height of the potential barrier at the surface. The former quantity is fixed by the lattice structure (body centered cubic for the alkali metals) and by the density, while the latter quantity can be adjusted to give the best agreement between the model calculations and experiment. For the alkali metals, lithium through sodium, the best value of the barrier height is about 50% of the sum of the ionization potential energy, the heat of vaporization, and the calculated Fermi level for the corresponding metal. In addition, the value of the double layer potential for sodium agrees very well with a more sophisticated calculation by Bardeen and is reasonably close to the experimental measurement.     

Cosmological constraints on heavy weakly interacting fermions

The masses and lifetimes of very heavy weakly interacting fermions which appear in many grand unified gauge models are constrained by the requirement that their decays in the hot big bang early universe should not generate excessive entropy which would dilute n_B/n_γ below its observed value.     

On the radical mechanism for photoinduced nucleation of alkane vapors

The addition of 10^?5 — 2 Torr of NO, a radical scavenger, is found to significantly quench the rate of photonucleation of nonane by NO₂ or CH₃I in a diffusion cloud chamber. This confirms a recently proposed radical mechanism for the photoinduced nucleation of these systems. The photonucleation rate of nonane induced by o-tolualdehyde (a system whose mechanism is not known) is similarly quenched by the addition of small amounts of NO, suggesting a radical mechanism. A mechanism for this system, based upon the formation of nonane radicals (resulting from hydrogen abstraction from nonane by the carbonyl molecules in the n,π* singlet or triplet state) followed by further reaction of the radicals to form low vapor pressure species, is discussed. Acetone, a system known to dissociate into radicals, is found to photoinduce nucleation of nonane when excited to the lowest singlet or triplet excited states. This adds further support to the proposed radical mechanism and suggests that acetone dissociates in its lowest singlet as well as its lowest triplet state. A theoretical model is outlined in which the production of large involatile alkanes (dimers and higher polymers) are formed from an initially produced nonane radical. These results are combined with binary nucleation theory in order to calculate the effect of these species on the rate of nucleation. These calculations indicate that low concentrations of these involatile species can indeed induce nucleation. The ability of small, photochemically produced polymers to induce nucleation is also examined and the time dependent space distribution of polymers (e.g., vinyl polymers) generated by chain transfer from a single free radical is derived. The small polymers formed in this process are analogous to the species formed in the photoinduced nucleation of alkane vapors.     

An “optical” theorem for acoustic scattering by baffled flexible surfaces

The classical optical theorem for scattering by compact obstacles is a forward scattering theorem. That is, the total cross section of the obstacle is proportional to the imaginary part of the far field directivity factor evaluated in the forward scattering direction. An analogous theorem is derived in this paper for the scattering of acoustic waves by baffled membranes and plates. In this “optical” theorem the directivity factor is evaluated in the direction of the specularly reflected wave, so that it is a reflected scattering theorem.