Search

The present study investigates convective heat/mass transfer and flow characteristics inside rotating disks. The rotating disks are simulated on the commonly used 3.5 ? hard disk drives (HDD). The experiments are conducted for the various hub heights of 5, 10 and 15 mm in a single rotating disk and 4, 6 and 8 mm in co-rotating disks and for the various rotating Reynolds numbers of 5.53 × 10 4, 8.53 × 10 4 and 1.13 × 10 5. To accommodate the general operating conditions of HDD, the experiments are also conducted with an obstruction of rectangular cross-section in the space, which simulates a read-write head arm. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using laser Doppler anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by disk rotation. The results of a single rotating disk show that the heat transfer on the rotating disk is enhanced considerably according to the reduction of the hub height and the increase of the rotating Reynolds number. The head arm inserted in the cavity between the rotating disk and the cover enhances uniformity of the heat/mass transfer on the disk due to the deficit of the momentum in the average flow despite the enhancement of the tangential component of fluctuation velocity. The heat/mass transfer rates on the co-rotating disks have very low values near the hub in the inner region of the solid-body rotation and increase rapidly toward the outer region. The change of heat/mass transfer for various hub heights is negligible.

The present study is conducted to investigate the local heatmass transfer characteristics on the shroud with blade tip clearances. The relative motion between blade and shroud is neglected, and four-bladed linear cascade is used in this study. naphthalene sublimation method is employed to determine the detailed local heatmass transfer coefficients on the surface of shroud. The tip clearance is changed from 0.66t to 2.85t of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the high pressure side due to the high pressure difference. Therefore, the heatmass transfer characteristics of the shroud are changed significantly from those with endwall. A first, high heatmass transfer occurs along the profile of blade a the pressure side due to the entrance effect and acceleration of the gap flow. Then, the heatmass transfer coefficients on the shroud increase along the suction side of the blade because tip leakage vortices are generated and interact with the main flow. The results show that the heatmass transfer characteristics are changed largely with the gap distance between the tip of turbine blade and the shroud.

We present the complete nucleotide sequence of recP, a locus required for high-efficiency recombination of chromosomal DNA during genetic transformation in Streptococcus pneumoniae. The sequence was determined by using plasmid DNA templates and synthetic oligonucleotide primers. The locus contained a single large open reading frame, ORF1, of 1,968 base pairs (bp). ORF1 is included within the recP locus previously mapped genetically and accounts for 94% of its extent. The predicted molecular weight of the largest polypeptide encoded within ORF1, 71,662, coincided with that measured previously (72,000) for the product of in vitro transcription-translation of the cloned recP locus. A Shine-Dalgarno sequence (AGAAAGGA; delta G = -17 kcal [ca. -71.1 kJ]) lay 6 bp upstream of ORF1. A sequence (TTGcat-17 bp-TATAAT) similar to the E. coli sigma-70 promoter consensus was located 52 bp upstream of ORF1. This putative promoter overlapped a structure consisting of two perfect inverted 10-bp repeats and a loop of 8 bp.

A 225-base-pair fragment of a recombination gene was identified by insertion-duplication mutagenesis and used as a radioactive probe to clone the corresponding rec locus from Streptococcus pneumoniae in Escherichia coli plasmid vectors. Attempts to clone large pieces of this locus were unsuccessful, but small pieces of DNA from this region were cloned in the E. coli transcriptional terminator vectors pKK232-8 and pJDC9. The extent of the rec region, 2.1 to 2.2 kilobases, was defined by determining the competence phenotype of insertion mutations constructed in vitro. A deletion of the rec locus showed it to be necessary for chromosomal integration but not for plasmid establishment. A plasmid carrying the entire locus encoded a 72-kilodalton polypeptide in a cell-free E. coli transcription-translation system.