EXCHANGE REACTIONS IN METABOLISM

Recent studies from this laboratory [l, 2] on the reaction mechanism of the pentose phosphate pathway in rabbit and rat liver cells have accentuated the role of enzyme-catalyzed exchange reactions as a means by which tracer carbon is relocated in the absence of a net metabolic flux. While this is an intrinsic property of the group transferring enzymes of the pathway and is seen as a deleterious property of ¹⁴C for the mapping and quantitation of metabolic pathways, it has re-emphasized the possible usefulness of isotope exchange reactions in understanding the mechanism of action of nature's catalyst.     

Age hardening in Cu-2.5 Wt pct Ti

Age hardening in a Cu-2.5 wt pct Ti alloy has been examined as a function of aging time at 300 and 500 °C. Yield strength results exhibited a double peak in strength at each temperature,i.e., peaks at two different times. The work-hardening rate, however, increased monotonically with aging time. Slip line measurements showed that slip became coarser with aging time but remained planar. Lack of sufficient understanding of the details of the pzecipitation reactions and also of hardening mechanisms means that a convincing explanation of the double peak in strength cannot yet be made, but research needed to correct this situation was identified.     

Differential scanning tunnelling microscopy

We review the principle of differential imaging and its application to scanning tunnelling microscopy (STM). It is shown that placing a lateral dither on an STM tip at high frequency provides the means for transfering topographic information to a frequency range where noise is small. Differential STM imaging on graphite and gold is demonstrated. A simple relation between the differential image and the conventional topographic image is described.     

Case study training for seeing school through adolescents' eyes

The first of two years of training in case study activities, adapted from the program originally developed by Fritz Redl, Daniel A. Prescott, and others at the Universities of Chicago and Maryland in the 1940s, is described. Excerpts from the case study of a 16-year-old female provide examples of activities, such as: (1) identifying recurring patterns of behavior, (2) selecting a pattern of behavior for analysis by the multiple hypotheses method, and (3) summarizing the case study record. The significance of this process is that high school personnel can learn to see what adolescents are up against in and out of school.     

Molecular events including p53 and k-ras alterations in the in vitro progression of a human colorectal adenoma cell line to an adenocarcinoma

The aim of the current study was to identify genetic abnormalities in human colorectal adenoma and carcinoma derived cell lines, and to determine whether the genetic changes which occur in vitro are relevant to the in vivo situation. Loss of 1p(33-35) region was shown to be the most common chromosome 1 abnormality and loss of heterozygosity (LOH) of the DCC gene and/or adjacent sequences was detected in all adenoma derived cells as well as the carcinoma cell lines. The level of p53 protein was also investigated as increased cellular p53 protein had previously been associated with mutation of the p53 gene. A further aim was to investigate genetic changes in our in vitro model of tumour progression, where the adenoma derived PC/AA cell line has previously been converted in vitro to two distinct tumorigenic phenotypes, producing either an adenocarcinoma or a mucinous carcinoma in athymic nude mice. Progression to the adenocarcinoma phenotype was shown to involve a specific chromosome 1 rearrangement, loss of both normal copies of chromosome 18 (although DCC gene sequences were retained), loss of the remaining wild type allele of k-ras resulting in homozygosity for the k-ras codon 12 mutation and increased cellular p53 protein as detected by SDS-PAGE Western blotting. The increase in p53 protein was shown not to be due to the acquisition of a mutation in the p53 gene. Interestingly, progression of the adenoma derived PC/AA cell line to the mucinous malignant phenotype did not involve any of these molecular rearrangements, suggesting that different genetically distinct pathways are involved in colorectal carcinogenesis. These studies show that the genetic changes in our in vitro model of human colorectal tumour progression are similar to those observed in in vivo studies.     

Models for binary and multicomponent solutions a new prospectus

We have examined in detail the principal series which have been used to represent the thermodynamcs of binary systems and have concluded that in every case the higher members suffer in some important way. The best choice for a third member is based upon a series expansion of the statistical mechanical treatment of Guggenheim. An entirely new form for the fourth term is suggested for accommodating the temperature dependent part of the asymmetry.We have also determined what constitutes proper treatment of the binary terms in representing higher order systems. Not all the previous treatments have been correct in this respect.     

Input VSWR of profiled E-plane tapers

An efficient method for determining the input VSWR characteristics of waveguide E-plane tapers is presented. The taper profile is approximated by radial waveguide sections and the junction wave transfer matrices are derived applying field matching. The input reflection coefficient is easily determined using these matrices. Results computed using the present method are compared with some measured and calculated results in the literature and very good agreement is obtained.