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81.
For the development of novel endocannabinoid templates with potential resistance to hydrolytic and oxidative metabolism, we are targeting the bis-allylic carbons of the arachidonoyl skeleton. Toward this end, we recently disclosed the synthesis and preliminary biological data for the (13S)-methyl-anandamide. We report now the total synthesis of the (10S)- and (10R)-methyl-counterparts. Our synthetic approach is stereospecific, efficient, and provides the analogs without the need for resolution. Peptide coupling, P-2 nickel partial hydrogenation, and cis-selective Wittig olefination are the key steps. 相似文献
82.
Guang Yang Bernhard Weigand Alexandros Terzis Kilian Weishaupt Rainer Helmig 《Transport in Porous Media》2018,122(1):145-167
This study investigates numerically the turbulent flow and heat transfer characteristics of a T-junction mixing, where a porous media flow is vertically discharged in a 3D fully developed channel flow. The fluid equations for the porous medium are solved in a pore structure level using an Speziale, Sarkar and Gatski turbulence model and validated with open literature data. Overall, two types of porous structures, consisted of square pores, are investigated over a wide range of Reynolds numbers: an in-line and a staggered pore structure arrangement. The flow patterns, including the reattachment length in the channel, the velocity field inside the porous medium as well as the fluctuation velocity at the interface, are found to be strongly affected by the velocity ratio between the transversely interacting flow streams. In addition, the heat transfer examination of the flow domain reveals that the temperature distribution in the porous structure is more uniform for the staggered array. The local heat transfer distributions inside the porous structure are also studied, and the general heat transfer rates are correlated in terms of area-averaged Nusselt number accounting for the effects of Reynolds number, velocity ratio as well as the geometrical arrangement of the porous structures. 相似文献
83.
Application of an aerosol shock tube to the measurement of diesel ignition delay times 总被引:1,自引:0,他引:1
D.R. Haylett P.P. Lappas D.F. Davidson R.K. Hanson 《Proceedings of the Combustion Institute》2009,32(1):477-484
Shock tube ignition delay times were measured for DF-2 diesel/21% O2/argon mixtures at pressures from 2.3 to 8.0 atm, equivalence ratios from 0.3 to 1.35, and temperatures from 900 to 1300 K using a new experimental flow facility, an aerosol shock tube. The aerosol shock tube combines conventional shock tube methodology with aerosol loading of fuel-oxidizer mixtures. Significant efforts have been made to ensure that the aerosol mixtures were spatially uniform, that the incident shock wave was well-behaved, and that the post-shock conditions and mixture fractions were accurately determined. The nebulizer-generated, narrow, micron-sized aerosol size distribution permitted rapid evaporation of the fuel mixture and enabled separation of the diesel fuel evaporation and diffusion processes that occurred behind the incident shock wave from the chemical ignition processes that occurred behind the higher temperature and pressure reflected shock wave. This rapid evaporation technique enables the study of a wide range of low-vapor-pressure practical fuels and fuel surrogates without the complication of fuel cracking that can occur with heated experimental facilities. These diesel ignition delay measurements extend the temperature and pressure range of earlier flow reactor studies, provide evidence for NTC behavior in diesel fuel ignition delay times at lower temperatures, and provide an accurate data base for the development and comparison of kinetic mechanisms for diesel fuel and surrogate mixtures. Representative comparisons with several single-component diesel surrogate models are also given. 相似文献
84.
We report the first experimental study of a model system of a two-dimensional colloidal crystal in a random pinning potential. The colloidal crystal consists of monodispersed charged polystyrene microspheres suspended in deionized aqueous media and confined near a rough charged surface. It is found that the static orientational correlation function g6(r) decays exponentially for intermediate and strong pinning, in agreement with theories. The driven depinning is dominated by thermally activated creep motion along 1D-like channels between regions with short-range order. A coexistence model is proposed for describing the observations. 相似文献
85.
Andrew J. Peel Alexandros Terzopoulos Rajesh B. Jethwa Dipanjana Choudhury Hao-Che Niu Andrew D. Bond Jonathan Slaughter Dominic S. Wright 《Chemical science》2022,13(18):5398
Methods for measuring enantiomeric excess (ee) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which is reacted with the mixture of enantiomers under investigation. However, these CDAs have almost exclusively been based on carbon frameworks, which are generally costly and/or difficult to prepare. In this work, a methodology based on the readily prepared inorganic cyclodiphosph(iii)azane CDA ClP(μ-NtBu)2POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be highly effective in the measurement of ee’s of chiral amines, involving in situ reaction of the chiral amines (R*NH2) with the P–Cl bond of the CDA followed by quaternization of the phosphorus framework with methyl iodide. This results in sharp 31P NMR signals with distinct chemical shift differences between the diastereomers that are formed, which can be used to obtain the ee directly by integration. Spectroscopic, X-ray structural and DFT studies suggest that the NMR chemical shift differences between diastereomers is steric in origin, with the sharpness of these signals resulting from conformational locking of the bornyl group relative to the P2N2 ring induced by the presence of the P(v)-bonded amino group (R*NH). This study showcases cheap inorganic phosphazane CDAs as simple alternatives to organic variants for the rapid determination of ee.The simple inorganic cyclodiphosph(iii)azane chiral derivatisation agent ClP(μ-tBuN)2POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of ee’s of chiral amines using 31P NMR spectroscopy. 相似文献
86.
Nonlinear Dynamics - Contact–impact events frequently occur between solid contact interfaces in complex dynamic mechanical systems and engineering applications. Impact force models are used... 相似文献
87.
88.
L. Cristofolini A. Lappas K. Prassides K. Vavekis M. Buchgeister 《Hyperfine Interactions》1997,104(1-4):61-66
The zero‐field μ+SR technique is employed to study the magnetic properties of the non‐superconducting borocarbides Sm1-xLuxNi2B2C (x=0.0,\ 0.2) and NdPt1.5Au0.6B2C. Coherent ordering of the Sm electronic moments appears below TN=9.86(3) and 4.15(3) K for the x=0.0 and 0.2 compositions, respectively. No long range order of the Nd3+ moments is found in NdPt1.5Au0.6B2C down to 80 mK. Freezing of the electronic moments into a spin‐glass state occurs at Tf\approx 1.2 K. A stretched exponential decay of the μ+ spin polarisation is observed above Tf with the exponent \beta smoothly decreasing on approaching Tf from above, reminiscent of the behaviour in other spin glasses.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
A. Lappas K. Prassides A. Amato R. Feyerherm F. N. Gygax A. Schenck 《Hyperfine Interactions》1994,86(1):555-560
We report a muon spin relaxation study of the magnetic properties of the La1.2Tb0.8CuO4 phase with the T* structure. Random magnetic order is revealed between 280 and 170 K by the zero field data. A spontaneous muon precession then appears below 170 K, arising from antiferromagnetic long range order of the Cu2+ spins. Evidence exists below 20 K for ordering of the Tb3+ ions. We find that the T* phase adopts the same magnetic structure as the (T/O) phase La2CuO4. 相似文献
90.
The esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone were prepared by reaction of urea with the esters of 2-hydroxy-2-phosphinylethanal in acidic medium. The ir, 1H nmr and 31P nmr spectral data of the products are reported. All the isolated products had cis configuration. The stereochemistry of their formation is discussed. 相似文献