Numerical Simulation of Turbulent Flow and Heat Transfer in a Three-Dimensional Channel Coupled with Flow Through Porous Structures

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.     

Statics and dynamics of 2D colloidal crystals in a random pinning potential

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.     

Fast Biosynthesis of GFP Molecules: A Single‐Molecule Fluorescence Study

It's not easy being green : Real‐time visualization of labeled ribosomes and de novo synthesized green fluorescent protein molecules using single‐molecule‐sensitive fluorescence microscopy demonstrates that the mutant GFPem is produced with a characteristic time of five minutes. Fluorescence of the fastest GFP molecules appears within one minute (see picture).

     

Structural,electronic, and magnetoresponsive properties of triangular lanthanide clusters and their free‐standing nitrides

The molecular and electronic structures, stabilities, bonding features, and magnetoresponsive properties of three‐membered [c‐Ln₃]^+/0/? (Ln = La, Ce, Pr, Nd, Gd, Lu) and heterocyclic six‐membered [c‐Ln₃E₃]^q (Ln = La, Ce, Pr, Nd, Gd, Lu; E = C, N; q = 0 or 1) rings have been investigated by means of electronic structure calculation methods at the DFT level. The [c‐Ln₃]^+/0/? clusters are predicted to be bound with respect to dissociation to their constituent atoms, the estimated binding energies ranging from 45.8 to 2056.4 kJ/mol. The [c‐Ln₃] rings capture easily a planar three‐coordinated nitrogen atom at the center or above the center of the ring yielding the lanthanide nitride clusters [c‐Ln₃(μ₃‐N)] adopting a planar geometry, except [c‐La₃(μ₃‐N)] which exhibits pyramidal geometry. The [c‐Ln₃(μ₃‐N)] clusters are predicted to be bound, with respect to dissociation to N (⁴S) atom and [c‐Ln₃] clusters in their ground states, the binding energies ranging from 53.9 to 257.9 kcal/mol. The six‐membered [c‐Ln₃E₃]^q rings are predicted to be bound with respect to dissociation to LnE^q monomers in their ground states with dissociation energies in the range of 173.8 to 318.0 kcal/mol. Calculation of the NICS_zz‐scan curves of the clusters predicted a “hermaphrodic” magnetic response of the [c‐Ln₃]^+/0/? and heterocyclic six‐membered [c‐Ln₃E₃]^q rings, manifested by the coexistence of successive diatropic (aromatic) and paratropic (antiaromatic) zones. The [c‐La₃]^+/0/? and [c‐Lu₃]^? are predicted to be weakly antiaromatic, the [c‐Lu₃]^0/+, [c‐Lu₃C₃]⁺, and [c‐Lu₃N₃] double (σ+π) aromatic, and the [c‐Gd₃C₃] and [c‐Gd₃N₃]⁺ rings (σ+δ)‐aromatic systems. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Distributed multicast address management in the global Internet

We describe a distributed architecture for managing multicast addresses in the global Internet. A multicast address space partitioning scheme is proposed, based on the unicast host address and a per-host address management entity. By noting that port numbers are an integral part of end-to-end multicast addressing we present a single, unified solution to the two problems of dynamic multicast address management and port resolution. We then present a framework for the evaluation of multicast address management schemes, and use it to compare our design with three approaches, as well as a random allocation strategy. The criteria used for the evaluation are blocking probability and consistency, address acquisition delay, the load on address management entities, robustness against failures, and processing and communications overhead. With the distributed scheme the probability of blocking for address acquisition is reduced by several orders of magnitude, to insignificant levels, while consistency is maintained. At the same time, the address acquisition delay is reduced to a minimum by serving the request within the host itself. It is also shown that the scheme generates much less control traffic, is more robust against failures, and puts much less load on address management entities as compared with the other three schemes. The random allocation strategy is shown to be attractive primarily due to its simplicity, although it does have several drawbacks stemming from its lack of consistency (addresses may be allocated more than once)     

Synthesis of esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone

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.     

Studies toward diazonamide A: initial synthetic forays directed toward the originally proposed structure

A brief introduction into the chemistry of diazonamide A (1) is followed by first-generation sequences to access the originally proposed structure for this unusual marine natural product. These explorations identified a route capable of delivering a model compound possessing the complete heteroaromatic core of the natural product, highlighting in the process several unanticipated synthetic challenges which led both to new methodology as well as an improved synthetic plan that was successfully applied to fully functionalized intermediates.     

Studies toward diazonamide A: development of a hetero-pinacol macrocyclization cascade for the construction of the bis-macrocyclic framework of the originally proposed structure

In this article, we describe further studies toward the originally proposed structure of diazonamide A (1). After confronting a number of failures in synthesizing the heterocyclic core of that structure, success was finally realized through the development of a novel hetero-pinacol-based macrocyclization cascade sequence. Subsequent elaboration led to an advanced compound bearing both of the 12-membered rings of the target molecule. In addition, preliminary biological studies with intermediates and simplified analogues obtained via the developed sequences are also described.     

Interactions of complementary PEGylated liposomes and characterization of the resulting aggregates

The interaction of complementary liposomes bearing both recognizable and protective ligands at their external surface has been investigated. Aggregation of hydrogenated phosphatidyl choline/cholesterol (2:1 molar ratio) based liposomes was mediated by the molecular recognition of the complementary phosphate and guanidinium groups incorporated in separate unilamellar liposomes. The phosphate group was incorporated in the bilayer employing dihexadecyl phosphate, while the guanidinium moiety was introduced in the membrane through the incorporation of various guanidinium lipids. For the latter, anchoring ability and primarily introduction of a spacer group between their lipophilic part and the guanidinium group was found to affect the ability for molecular recognition. Also, poly(ethylene glycol) (PEG) introduced in both types of liposomes at various concentrations and up to 15% with respect to cholesterol modifies the interaction effectiveness and morphology of the obtained aggregates. Interaction of these complementary liposomes leads to large precipitating aggregates or fused liposomes, as shown by phase contrast microscopy and dynamic light scattering. Specifically, fusion of liposomes takes place under a nonleaking process involving lipid mixing, as demonstrated by calcein entrapment and resonance energy transfer experiments. Calorimetric parameters also correlate with the processes of aggregation and fusion. The interactions of non-PEGylated liposomes involve exothermic processes of higher enthalpic content than those of the PEGylated counterparts.