Dynamic behavior of reciprocating-plate columns

The unsteady-state behaviour of a reciprocating plate column in which adjacent plates move out of phase with each other has been studied experimentally by determining responses to step changes. The one-dimensional, two-parameter model developed, leading to a system of differential equations with time-dependent coefficients, was simplified to allow parameter estimation in the Laplace domain. Special features of the experimental technique for obtaining instantaneous values of the tracer concentration which closely approximate to the average for a column cross section are described; the limitations of parameter estimation in the Laplace domain are discussed.     

Blue-green algae: their excretion of iron-selective chelators enables them to dominate other algae

During blue-green algal blooms, other algae can be completely suppressed. This ability of blue-green algae to suppress other algae may be determined by the abailability of iron. Iron deprivation induces the production of hydroxamate chelators, which appear to be the agent suppressing other algae.     

Spontaneous mutagenesis of a plant potyvirus genome after insertion of a foreign gene

The RNA genome of tobacco etch potyvirus (TEV) was engineered to express bacterial beta-glucuronidase (GUS) fused to the virus helper component proteinase (HC-Pro). It was shown previously that prolonged periods (approximately 1 month) of TEV-GUS propagation in plants resulted in the appearance of spontaneous deletion variants. Nine deletion mutants were identified by nucleotide sequence analysis of 40 cDNA clones obtained after polymerase chain reaction amplification. The mutants were missing between 1,741 and 2,074 nucleotides from TEV-GUS, including the sequences coding for most of GUS and the N-terminal region of HC-Pro. This region of HC-Pro contains determinants involved in helper component activity during aphid transmission, as well as a highly conserved series of cysteine residues. The deletion variants were shown to replicate and move systemically without the aid of a helper virus. Infectious viruses harboring the two largest HC-Pro deletions (termed TEV-2del and TEV-7del) were reconstructed by subcloning the corresponding mutated regions into full-length DNA copies of the TEV genome. Characterization of these and additional variants derived by site-directed mutagenesis demonstrated that deletion of sequences coding for the HC-Pro N-terminal domain had a negative effect on accumulation of viral RNA and coat protein. The TEV-2del variant possessed an aphid-nontransmissible phenotype that could be rescued partially by prefeeding of aphids on active HC-Pro from another potyvirus. These data suggest that the N-terminal domain of HC-Pro or its coding sequence enhances virus replication or genome expression but does not provide an activity essential for these processes. The function of this domain, as well as a proposed deletion mechanism involving nonhomologous recombination, is discussed.     

Arterial fasciocutaneous vascular territories of the lower leg

The purpose of this study was to analyze the fasciocutaneous arterial circulation of the lower extremity to provide a quantitative guide to design reliable fasciocutaneous flaps. Thirty-one fresh cadaver limbs were studied using the techniques of dissection of latex injected specimens, selective ink injections, and barium latex radiographs. Fasciocutaneous perforator locations were recorded according to fascial septum of origin and distance relative to bony landmarks between the knee and the ankle. Selective ink injections of the trifurcation vessels identified four anterior tibial, three peroneal, and three posterior tibial fasciocutaneous territories. Although perforator site locations were randomly distributed along the trifurcation vessel within any vascular territory, the separate cutaneous regions that make up the fasciocutaneous territories occur in predictable locations with a measurable standard deviation. The transverse section radiographs confirmed the transverse dimensions of the vascular territories. Additionally, the summation of any two vascular territories calculated from the anatomical data conforms to the clinically observed 2.5:1 to 3:1 length-to-width ratios for fasciocutaneous flap viability as reported by Ponten and by Barclay et al. This study provides a quantitative anatomical framework using primary fasciocutaneous vascular territories to design potentially reliable fasciocutaneous flaps in the lower extremity.