Radio Spectrum Management for Tetherless Communications

For any new radio technology, spectrum management is an essential part of the development process, to identify the best frequency band for operation of the system. This has to take account of the many other users and applications of the radio spectrum, so that systems neither cause, nor receive, harmful interference from other radio systems. It is a process that is sometimes considered to be unnecessarily restrictive and slow; however, that is because it is often a difficult balancing act between the technical, commercial and political pressures on the (finite) radio spectrum. This paper describes the underlying principles and processes of radio spectrum management, explaining the relationships between the organisations which are responsible for spectrum management at the national, regional and international levels. It also describes the current work on the identification of frequency bands for the new tetherless communications technologies, and in particular the 2.4 and 5 GHz bands. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ability of 16 priority PAHs to be directly cytotoxic to a cell line from the rainbow trout gill

Sixteen polycyclic aromatic hydrocarbons (PAHs) were screened for their ability to be directly cytotoxic to a cell line from the rainbow trout gill, RTgill-W1. Exposure times of 2 h or less were sufficient for direct cytotoxicity to be detected, which appeared to be caused by a common mechanism, the general perturbation of membranes. This was judged by the similarity of results obtained for three fluorescent indicator dyes, alamar Blue, 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) and neutral red. Among the 16 PAHs tested, just two- and three-ring PAHs were found to be directly cytotoxic. These were naphthalene approximately = acenaphthylene approximately = acenaphthene > fluorene approximately = phenanthrene. The results suggest that water solubility and lipophilicity are the critical properties determining the direct cytotoxicity of PAHs and that they do so by influencing PAH accumulation in membranes. Only naphthalene was effective at concentrations well below its water solubility limit. Therefore, direct cytotoxicity is likely to be most environmentally relevant only with naphthalene.     

Wild-type but not mutant p53 activates the hepatocyte growth factor/scatter factor promoter

p53 transactivates the expression of a variety of genes by binding to specific DNA sequences within the promoter. We have investigated the ability of wild-type p53 and a non-DNA binding p53 mutant to activate the hepatocyte growth factor/scatter factor (HGF/SF) promoter using chloramphenicol acetyltransferase reporter constructs. We also used deletion sequences of the HGF/SF promoter to identify which regions, if any, were responsible for p53 binding. Our results show that wild-type but not mutant p53 activates the HGF/SF promoter when using -3000 and -755 bp upstream of the HGF/SF gene. This activation is lost when promoter sequences covering -365 and -239 bp are used. Analysis of the DNA sequence between -365 and -755 bp shows one putative p53 half-site with 80% homology to the consensus sequence and another half-site 3 bases downstream of this with 100% homology to the consensus sequence. In contrast to previously identified p53 binding DNA sequences, the downstream half-site is inverted. We propose that the HGF/SF promoter can be activated by wild-type p53 in vivo and that this could be as a result of a novel form of sequence-specific DNA binding.     

Errors in dynamic force measurement

Loadcells for materials testing machines are calibrated statically by comparison with a transfer standard, traceable to the National Physical Laboratory. There is evidence to suggest that, under certain conditions, this static calibration may be insufficient for dynamic testing. The possibility of an error being generated by the inertia of the mass between the loadcell and the specimen is discussed and the results of experiments to measure this error are presented. For the case chosen it is shown that the inertia error may be predicted by calculation. Errors may also arise from the method of dynamic force measurement. The conventional DVM and the analogue peak hold voltmeter are widely used but are subject to errors in a practical machine situation due to their method of operation. Bandwidth limitations are also illustrated for a number of instruments with different sampling rates. A better, although more expensive and complicated solution is to digitise the signal and to use some form of spectral analysis such as the Fast Fourier Transform or the Cross Correlation Integral. The theory for the latter is presented and its merits discussed.     

Methods for determining the depth of near-surface defects

In previous work by the authors,^(1,6) it was demonstrated that the presence of near-surface defects could be detected reliably, even though the defect echo was contained within the near-surface echo. The algorithm consists of examining the variation in the composite (near-surface plus defect) response after it has been deconvolved from a near-surface response known to be defect-free. This paper presents two algorithms that have been developed subsequent to the work presented in ref. (6) for estimating thedepth of a near-surface defect, given that its presence has already been detected. One algorithm uses complex frequency domain techniques, and the other uses time domain analysis. Both procedures operate on the surface-plus-defect signal, using reference signals containing surface-only and defect-only responses. The defect signal is extracted from the composite signal. Defect depth is then computed from the time difference between the centers of the front-surface and extracted defect responses. A mean absolute depth error of 0.015 in. was obtained by applying the algorithms to experimental data containing depths from 0.020 to 0.130 in. below the near-surface.     

Correlations for wall and particle shape effects on fixed bed bulk voidage

Correlations have been derived, by both geometrical arguments and empirical treatment of data, for the bulk void fraction in a fixed bed. The void fraction has been correlated as a function of particle-to-tube diameter ratio for packings of spheres and equilateral solid cylinders. Prediction of void fraction for equilateral hollow cylinders can be made from the solid cylinder correlation, provided a correction factor is included that allows for internal voidage and interpenetration of packings.     

Choline acetyltransferase (ChAT) immunoreactivity in paraffin sections of normal and diseased intestines

There is increasing interest in localizing nerves in the intestine, especially specific populations of nerves. At present, the usual histochemical marker for cholinergic nerves in tissue sections is acetylcholinesterase activity. However, such techniques are applicable only to frozen sections and have uncertain specificity. Choline acetyltransferase (ChAT) is also present in cholinergic nerves, and we therefore aimed to establish a paraffin section immunocytochemical technique using an anti-ChAT antibody. Monoclonal anti-choline acetyltransferase (1.B3.9B3) and a biotin-streptavidin detection system were used to study the distribution of ChAT immunoreactivity (ChAT IR) in paraffin-embedded normal and diseased gastrointestinal tracts from both rats and humans. Optimal staining was seen after 6-24 hr of fixation in neutral buffered formalin and overnight incubation in 1 microgram/ml of 1.B3.9B3, with a similar distribution to that seen in frozen sections. In the rat diaphragm (used as a positive control), axons and motor endplates were ChAT IR. Proportions of ganglion cells and nerve fibers in the intramural plexi of both human and rat gastrointestinal tracts were also ChAT IR, as well as extrinsic nerve bundles in aganglionic segments of Hirschsprung's disease. Mucosal cholinergic nerves, however, were not visualized. In addition, non-neuronal cells such as endothelium, epithelium, and inflammatory cells were ChAT IR. We were able to localize ChAT to nerves in formalin-fixed, paraffin-embedded sections. The presence of ChAT IR in non-neuronal cells indicates that this method should be used in conjunction with other antibodies. Nevertheless, it proves to be a useful technique for studying cholinergic neuronal distinction in normal tissues and pathological disorders.