Entry region of louvered fin heat exchangers

The dominant thermal resistance for most compact heat exchangers occurs on the gas side and as such an understanding of the gas side flowfield is needed before improving current designs. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. For this study, detailed flowfield measurements were made in the entry region of several louvered fin geometries whereby the louver angle, ratio of fin pitch to louver pitch, and Reynolds number were all varied. In addition to mean velocity measurements, time-resolved velocity measurements were made to quantify unsteady effects.

The results indicated larger fin pitches resulted in lower average flow angles in the louver passages and longer development lengths. Larger louver angles with a constant ratio of fin pitch to louver pitch resulted in higher average flow angles and shorter development lengths. As the Reynolds number increased, longer development lengths were required and higher average flow angles occurred as compared with a lower Reynolds number case. Time-resolved velocity measurements indicated some flow periodicity behind the fully developed louver for a range of Reynolds numbers. The Strouhal number of these fluctuations was constant for a given louver geometry, but the value increased with increasing fin pitch.     

Sensitization of ruthenium nitrosyls to visible light via direct coordination of the dye resorufin: trackable NO donors for light-triggered NO delivery to cellular targets

Three nitrosyl-dye conjugates, namely, [(Me 2bpb)Ru(NO)(Resf)] ( 1-Resf), [(Me 2bQb)Ru(NO)(Resf)] ( 2-Resf), and [((OMe) 2bQb)Ru(NO)(Resf)] ( 3-Resf) have been synthesized via direct replacement of the chloride ligand of the parent {Ru-NO} (6) nitrosyls of the type [(R 2byb)Ru(NO)(L)] with the anionic tricyclic dye resorufin (Resf). The structures of 1-Resf- 3-Resf have been determined by X-ray crystallography. The dye is coordinated to the ruthenium centers of these conjugates via the phenolato-O atom and is trans to NO. Systematic red shift of the d pi(Ru) --> pi*(NO) transition of the parent nitrosyls [(R 2byb)Ru(NO)(L)] due to changes in R and y in the equatorial tetradentate ligand R 2byb (2-) results in its eventual merge with the intense absorption band of the dye around 500 nm in 3-Resf. Unlike the UV-sensitive parent [(R 2byb)Ru(NO)(L)] nitrosyls, these dye-sensitized nitrosyls rapidly release NO when exposed to visible light (lambda >/= 465 nm). Comparison of the photochemical parameters reveals that direct coordination of the light-harvesting chromophore to the ruthenium center in the present nitrosyls results in a significantly greater extent of sensitization to visible light compared to nitrosyls with appended chromophore (linked via alkyl chains). 1-Resf has been employed as a "trackable" NO donor to promote NO-induced apoptosis in MDA-MB-231 human breast cancer cells under the control of light. The results of this work demonstrate that (a) the d pi(Ru) --> pi*(NO) transition (photoband) of {Ru-NO} (6) nitrosyls can be tuned into visible range via careful alteration of the ligand frame(s) and (b) such nitrosyls can be significantly sensitized to visible light by directly ligating a light-harvesting chromophore to the ruthenium center. The potential of these photosensitive nitrosyl-dye conjugates as (i) biological tools to study the effects of NO in cellular environments and (ii) "trackable" NO donors in photodynamic therapy of malignancies (such as skin cancer) has been discussed.     

The use of ultrathin-layer polyacrylamide gel isoelectric focusing in two-dimensional analysis of plant and fungal proteins

Although use of ultrathin polyacrylamide gel isoelectric focusing in the first dimension of two-dimensional analysis bestows a number of advantages, it has been little used by the plant science community. Nonstandardization along with problems unique to the format have probably delayed wider adoption. Relevant parameters were therefore tested in order to optimize resolution, reproducibility, economy and ease of use. Ultrathin-layer gels (200 microns in this study) used in the first dimension require a semirigid backing for support. Widely available matte-finished thin polyester film without chemical pretreatment was found to bind the gel adequately. The gel adheres to the film through all processing steps, yet, if desired, can be easily transferred to Whatman 3MM paper for special applications such as Western blotting. The ultrathin first-dimensional gels can be quickly dried on the polyester backing for convenient handling and long term storage. Strips cut from the dried gel for use in the second dimension are more easily manipulated than their tube format counterparts. The difficulty of disrupting and recovering microsamples of labeled leaf and root tissue prompted the invention of an efficient and simple communition device. An economical and efficient silver stain process is also described. This analytical technique was applied in an attempt to detect resistance gene products in different genetic backgrounds of maize. Although the ultrathin flatbed format provides as good as or better resolution than the tube gel system, the level of sensitivity was still inadequate to reveal the apparently rare resistance gene product.     

Separation and detection of a benzo[a]pyrene metabolite with capillary electrophoresis in the presence of DNA using laser-induced fluorescence

A novel approach was developed for the separation and detection of a benzo[a]pyrene B[a]P-DNA metabolite (tetrol I-1) in the presence of DNA using CE and laser induced fluorescence. Tetrol I-1 in the presence of DNA is intercalated and undergoes fluorescence quenching. Thus, an equilibrium is established between the intercalated tetrol I-1 and the uncomplexed tetrol I-1. It is only the uncomplexed tetrol that is fluorescent in the presence of DNA. The tetrol I-1 fluorescence intensities, at two concentrations of tetrol I-1 (0.005 and 0.01mg ml(-1)), were observed while varying the DNA concentration. Stern-Volmer plots were constructed of the fluorescence intensity of the uncomplexed tetrol I-1 versus DNA concentration. From the slopes of the Stern-Volmer plots quenching constants were determined. The quenching constants are essentially the same as an association constant for tetrol I-1 with DNA. The average value obtained for the association constant for the two concentrations of tetrol I-1 was 0.22+/-0.02 mg ml(-1). It was thus demonstrated that uncomplexed tetrol I-1 can be separated from DNA by CE and an association constant for tetrol I-1 bound to DNA can be obtained from the fluorescence quenching data.     

The continental component of a Pacific Marine aerosol: Identification by combined neutron activation analysis and scanning electron microscopy with X-ray analysis

The relative merits and sampling requirements of instrumental neutron activation analysis (INAA) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) analysis as applied to the continental component of marine aerosols are discussed. When correlated with air mass information, the quantitative INAA data on the concentrations of 15 major and minor elements in the continental dust fraction provides information on the geochemical type and location of the land source. Although the SEM/EDS technique provides only qualitative concentrations for 6 additional elements in the aerosol, the important feature of single particle analysis enables more nearly synoptic interpretation of aerosol composition and concentration. A combined INAA and SEM/EDS study of the aerosol samples is therefore preferred.