Neutron-neutron final state interactions in the reaction H(d, pp)2n

The reaction ²H(d, pp)2n has been studied at a bombarding energy of 12 MeV, detecting the two protons in coincidence at angles of ±20° as well as +20° and −15°. In both cases, a narrow band was observed in a three-dimensional plot of the yield versus the energies of the two detected protons. E1 and E2, with most of the yield concentrated in the area where E1 ≈ E2. This suggests a two-step sequential process of the type d + d → (2p) + (2n) → p + p + n + n. In a missing mass plot for the third, undetected “particle” a pronounced, narrow peak appears at low relative energies in the (nn) system.     

Modeling sound transmission through the pulmonary system and chest with application to diagnosis of a collapsed lung

A theoretical and experimental study was undertaken to examine the feasibility of using audible-frequency vibro-acoustic waves for diagnosis of pneumothorax, a collapsed lung. The hypothesis was that the acoustic response of the chest to external excitation would change with this condition. In experimental canine studies, external acoustic energy was introduced into the trachea via an endotracheal tube. For the control (nonpneumothorax) state, it is hypothesized that sound waves primarily travel through the airways, couple to the lung parenchyma, and then are transmitted directly to the chest wall. In contradistinction, when a pneumothorax is present the intervening air presents an added barrier to efficient acoustic energy transfer. Theoretical models of sound transmission through the pulmonary system and chest region to the chest wall surface are developed to more clearly understand the mechanisms of intensity loss when a pneumothorax is present, relative to a baseline case. These models predict significant decreases in acoustic transmission strength when a pneumothorax is present, in qualitative agreement with experimental measurements. Development of the models, their extension via finite element analysis, and comparisons with experimental canine studies are reviewed.     

Quantum mechanics: a new tool for engineering thermodynamics

Computational quantum mechanics is leading to new, theoretically based methods for the prediction of thermodynamic properties and phase behavior of interest to engineers. Three such methods we have been working on are reviewed here. In the most direct and computational intensive form, computational quantum mechanics is used to obtain information on the multidimensional potential energy surface between molecules, which is then used in computer simulation to predict thermodynamic properties and phase equilibria. At present, this method is limited to the study of small molecules due to the computational resources available. The second method is much less computationally intensive and provides a way to improve group-contribution methods by introducing corrections based on the charge and dipole moment of each functional group that is unique to the molecule in which it appears. The final method we consider is based on the polarizable continuum model, in which the free energy of transferring a molecule from an ideal gas to a liquid solution is computed, leading directly to values of activity coefficients and phase equilibrium calculations.     

Urinary phenylethylamine excretion: gas chromatographic assay with electron-capture detection of the pentafluorobenzoyl derivative

Phenylethylamine was extracted into n-hexane from alkaline urine saturated with sodium chloride, and back-extracted into dilute acid. The extract was freeze-dried and the residue converted to a pentafluorobenzoyl derivative for analysis by gas chromatography on a column of OV-225 with electron-capture detection. Quantification was achieved by adding an internal standard of tolylethylamine to each sample prior to extraction. Output values in normal subjects and in some patients with phenylketonuria and hyperphenylalaninaemia were in agreement with those in some other recent reports.     

Storage and separation of CO2 and CH4 in silicalite, C168 schwarzite, and IRMOF-1: a comparative study from Monte Carlo simulation

Storage of pure CO2 and CH4 and separation of their binary mixture in three different classes of nanostructured adsorbents--silicalite, C168 schwarzite, and IRMOF-1--have been compared at room temperature using atomistic simulation. CH4 is represented as a spherical Lennard-Jones molecule, and CO2 is represented as a rigid linear molecule with a quadrupole moment. For pure component adsorption, CO2 is preferentially adsorbed than CH4 in all the three adsorbents over the pressure range under this study, except in C168 schwarzite at high pressures. The simulated adsorption isotherms and isosteric heats match closely with available experimental data. A dual-site Langmuir-Freundlich equation is used to fit the isotherms satisfactorily. Compared to silicalite and C168 schwarzite, the gravimetric adsorption capacity of pure CH4 and CO2 separately in IRMOF-1 is substantially larger. This implies that IRMOF-1 might be a potential storage medium for CH4 and CO2. For adsorption from an equimolar binary mixture, CO2 is preferentially adsorbed in all three adsorbents. Predictions of mixture adsorption with the ideal-adsorbed solution theory on the basis of only pure component adsorption agree well with simulation results. Though IRMOF-1 has a significantly higher adsorption capacity than silicalite and C168 schwarzite, the adsorption selectivity of CO2 over CH4 is found to be similar in all three adsorbents.     

Electron-electron and spin-orbit interactions in armchair graphene ribbons

The effects of intrinsic spin-orbit and Coulomb interactions on low-energy properties of finite width graphene armchair ribbons are studied by means of a Dirac Hamiltonian. It is shown that metallic states subsist in the presence of intrinsic spin-orbit interactions as spin-filtered edge states, in contrast with the insulating behavior predicted for graphene planes. A charge-gap opens due to Coulomb interactions in neutral ribbons, that vanishes as Delta approximately 1/W, with a gapless spin sector. Weak intrinsic spin-orbit interactions do not change the insulating behavior. Explicit expressions for the width-dependent gap and various correlation functions are presented.