Synthesis of double C-glycoside analogue of sTn

A sTn double C-glycoside, sTn analogue 2, was synthesized using samarium chemistry developed in our laboratory. Complications in the oxidation reaction affording aldehyde acceptor were overcome by double protection of amide and the use of a room-temperature ionic liquid as solvent. Studies are underway to conjugate the sTn double C-glycoside hapten 2 to KLH carrier protein for biological evaluation as a vaccine.     

Solid-phase chemoenzymatic synthesis of C-sialosides

The chemoenzymatic regioselective acylation of Neu5Ac followed by SmI2-mediated C-glycosylation on a solid support is described for five C-glycosides. This method should facilitate the construction of combinatorial libraries of inhibitors of neuraminidase activity and hemagglutinin interaction as potential antiviral agents.     

Chemoenzymatic synthesis of heparan sulfate tetrasaccharide from a N-acetyl-α-d-glucosamine-O-methylglycoside acceptor

Heparan sulfate tetrasaccharide 2 was efficiently prepared in seven steps through chemoenzymatic synthesis. A monosaccharide 5, N-acetyl-α-d-glucosamine- O-methylglycoside (GlcNAc-OMe), was successfully used as an acceptor in a heparosan synthase (pmHS2)-catalyzed glycosylation reaction. This avoided the multi-step synthesis of a more complex disaccharide acceptor 3, greatly simplifying the route to tetrasaccharide target 2. This approach provides a critical tetrasaccharide intermediate for subsequent chemoenzymatic transformation to fondaparinux and its analogues.     

Natural Convection Inside an Inclined Wavy Enclosure Filled with a Porous Medium

The Darcy flow model with the Boussinesq approximation is used to investigate numerically the natural convection inside an inclined wavy cavity filled with a porous medium. Finite Element Method is used to discretize the governing differential equations with non-staggered variable arrangement. Results are presented for and , where ϕ, Ra, A and λ correspond to the cavity inclination angle, Rayleigh number, aspect ratio and surface waviness parameter, respectively. Stream and isotherm lines representing the corresponding flow and thermal fields, and local and average Nusselt numbers distribution expressing the rate of heat transfer are determined and shown on graphs and tables. A good agreement is observed between the present results and those known from the open literature. The flow and thermal structures found to be highly dependent on surface waviness for inclination angles less than 45°, especially for high Rayleigh numbers.     

Free Convection in Spherical Annular Sectors Filled with a Porous Medium

Calculated free convection flows and heat transfer are presented for concentric spherical annular sectors, filled with a porous medium. Two isothermal walls and an adiabatic radial wall at the sector angle define the sectors. The governing equations (in the stream function and temperature formulation) are solved numerically using ADI (alternative direction implicit) finite-difference method. Over the range of geometric parameters examined, the obtained results for spherical annuli and low Rayleigh number Ra. As Ra increases, multicellular flows develop for small values of the aspect ratio parameter . In addition, analytical solutions of the governing equations were obtained for small values of Ra (1) and it was shown that these solutions agree well with those obtained numerically. Significant differences in the local heat transfer rates on the inner and outer walls of the spherical annuli were observed from these solutions.     

Numerical comparison of conjugate and non-conjugate natural convection for internally heated semi-circular pools

In this numerical investigation, a detailed comparison of the conjugate and non-conjugate natural convection within a semi-cylindrical cavity has been presented. The cavity is assumed to be filled with a fluid containing uniformly distributed internal heating sources. The bottom circular wall of the cavity is taken to be thick with finite conductive properties, while the top wall is considered to be isothermal. The Navier–Stokes and energy equations are solved numerically by using the SIMPLER algorithm. A Rayleigh number range from 3.2×10⁶ to 3.2×10¹¹ has been investigated and the effects of solid-to-fluid conductivity ratios of 1.0, 5.0 and 23.0 have been analysed. The present numerical results for a semi-circular cavity with entirely isothermal walls are compared with known results from the open literature. It was found that these results for the non-conjugate problem are in very good agreement. The present results for a conjugate cavity show a remarkable difference from the non-conjugate analysis. The average Nusselt number for the solid–fluid interface shows a decrease while the top wall average Nu number has increased. It has been concluded that these effects increase for a system with a low solid-to-fluid conductivity ratio. It is evident from the present conjugate results that the assumption of isothermal enclosing walls gives somewhat different results when the walls are thick and the solid-to-fluid conductivity ratio is small.     

Heat transfer characteristics of internally heated liquid pools at high Rayleigh numbers

Detailed numerical analysis is presented for buoyancy driven flow of a Newtonian fluid contained in a square enclosure for high Rayleigh (Ra) numbers. Natural convection is due to internal heating sources, which are assumed to be uniformly distributed within the enclosure. All walls of the cavity are maintained at constant temperature. Flow and heat transfer characteristics are investigated for a Ra number range of 10⁷ to 10¹² while Prandtl (Pr) number is taken to be 7.0. Governing equations (in primitive variables) are discretised using control volume technique based on staggered grid formulation. These equations are solved using SIMPLER algorithm of Patankar. Flow and heat transfer characteristics, streamlines, isotherms and average wall Nusselt (Nu) number, are presented for whole range of Ra number considered. Finally, present results for average wall Nu numbers are compared with experimental observations obtained from open literature. It is concluded that both results are in very good agreement, which confirmed the accuracy of the scaling used for present investigation. Received on 15 November 1999     

Buoyancy-driven flow in an enclosure containing time periodic internal sources

A computational study is carried out to investigate the effect of the sinusoidally driven heat source on the fluid flow and heat transfer within a two-dimensional square cavity. The cavity, which has solid walls of constant temperature, is filled with a fluid including uniformly distributed internal heat source. In addition, the effects of the different periods of the sinusoidally driving heat source on heat transfer are investigated and presented as figures.