Conformational studies on some nitrogen containing compounds.

Some N.M.R. techniques used in conformational analysis, the principal factors peculiar to heterocyclic conformational analysis, and the background to conformational effects in alkyl substituted hydroxylamines are reviewed. The synthesis of N-carbethoxy- and N-methyl-tetrahydro-1,2- oxazines is discussed. The mechanism of formation of N-carbethoxytetrahydro-1,2-oxazines from the condensation of 1,4 dibromo-alkanes with N-hydroxyurethan under basic conditions is found to proceed by initial attack of the oxy-anion tautomer, formed from N-hydroxyurethane, on the more reactive bromo-substituted carbon. The preferred conformations of several N-methyl-tetrahydro1,2-oxazines are deduced from their N.M.R. spectra, and a measure of the free energy difference between the equatorial and axial positions for a methyl group substituted on any one of the four ring carbon atoms is estimated. A qualitative rationalisation of the variation in free energy difference with the point of substitution is given. The N-methyl group is found to strongly prefer the equatorial position. The stereochemistry of the B/C ring junction of the alkaloid geneserine is deduced from its N.M.R. spectra, and is found to be cis. The conformational equilibrium at nitrogen in some N,N-dimethyl-hexahydropyrimidines is studied by N.M.R. For N,N-dimethyl hexahydropyrimidine and l,3,5-trimethyl-hexahydropyrimidine a free energy difference between an equatorial and axial N-methyl group of ca. 0.5 kcal./mol. is found. A new method of measuring rate constants by N.M.R. using a small digital computer is tested by studying the barriers to internal rotation in the N,N-dimethyl amides of the three pyridine carboxylic acids. The method is found to be satisfactory, and the free energies of activation for the rotational process at 25°C are 17.9 kcal./mol. for N ,N-dimethyl picolinamide, 15,9 kcal./mol. for N,N-dimethyl nicotinamide, and 16.6 kcal./mol. for N,N-dimethyl isonicotinamide. The error on these values is considered to be less than 0.1 kcal./mol

Intrathecal Opioids for Chronic Pain: A Call for Evidence

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93560/1/j.1526-4637.2012.01456.x.pd

Intrathecal Opioids for Chronic Pain: A Call for Evidence

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109561/1/pme12576.pd

Demographic characteristics of exploited tropical lutjanids: a comparative analysis

Demographic parameters from seven exploited coral reef lutjanid species were compared as a case study of the implications of intrafamily variation in life histories for multispecies harvest management. Modal lengths varied by 4 cm among four species (Lutjanus fulviflamma, L. vitta, L. carponotatus, L. adetii), which were at least 6 cm smaller than the modal lengths of the largest species (L. gibbus, Symphorus nematophorus, Aprion virescens). Modal ages, indicating ages of full selection to fishing gear, were 10 years or less for all species, but maximum ages ranged from 12 (L. gibbus) to 36 years (S. nematophorus). Each species had a unique growth pattern, with differences in length-at-age and mean asymptotic fork length (L∞), but smaller species generally grew fast during the first 1–2 years of life and larger species grew more slowly over a longer period. Total mortality rates varied among species; L. gibbus had the highest mortality and L. fulviflamma, the lowest mortality. The variability in life history strategies of these tropical lutjanids makes generalizations about lutjanid life histories difficult, but the fact that all seven had characteristics that would make them particularly vulnerable to fishing indicates that harvest of tropical lutjanids should be managed with caution

Numerical Simulations of the Transient Flow Response of a 3D, Low-Aspect-Ratio Wing to Pulsed Actuation

Numerical simulations of the natural and actuated unsteady flow over a three-dimensional low-aspect ratio wing are performed using Lattice Boltzmann method. The LBM simulations match the flow conditions and the detailed wing geometry from previous experiments, including the actuators that are installed internally along the leading edge of the wing. The present study focuses on the transient lift response to short-duration square-wave actuation, for the wing in a uniform flow at five different angles of attack. Overall, both mean and unsteady numerical results show good agreement with the experimental data, in particular at the post-stall angle of attack 19°, where the maximum lift enhancement occurs. At that angle of attack, the effects of the actuation strength and duration are investigated. In general, the lift response to a single pulse increases with increasing actuator mass-flow rate and pulse duration