Fade depth scaling with channel bandwidth

The dependence of small-scale fading on bandwidth is quantified experimentally in the 3.1–10.6 GHz band for indoor channels. The fade depth converges to 4 dB at 1 GHz bandwidth, with little reduction for further increase in bandwidth. A simple yet accurate empirical fade depth model is developed, enabling convenient evaluation of the link budget for a channel with given bandwidth

A COMPUTER PROGRAM FOR THE KINETIC ANALYSIS OF A LINK-SEGMENT MODEL

The computer program LINK has been created to aid the biomechanics instructor in the teaching and demonstration of kinetic analysis of a knee joint link-segment model. Written in the BASIC computer programming language, this program is designed to be a step-by-step demonstration tool complete with geometric diagrams, discussion of pertinent terms, and mastery tests. Input values are based upon anthropometric measurements, force values recorded from an isokinetic dynamometer (Cybex), and corresponding knee angles. Preset values may be selected for demonstration, or the user may input hisher own data. The output is calculated values of force, torque, and power (for the knee joint angles utilized). Specific geometry for these calculations are based upon the anthropometric measures. This computer program is written to be used with all IBM compatible microcomputers

Linking priorities for training, research and policy on ageing in sub-Saharan Africa

This forum raises for debate the issues of training, research and policy on ageing in sub-Saharan Africa. The obstacles to a seamless linkage between these areas are discussed. The forum concludes with recommendations to overcome the obstacles, for consideration by all individuals involved in ageing and health on the sub-continent

What is the excess risk of infertility in women after genital chlamydia infection? A systematic review of the evidence

Methods: Twelve databases were searched, limited to peer-reviewed literature published from January 1970 to September 2007. Conference abstracts and reference lists from reviews published since 2000 and from key articles were hand-searched. Studies were selected for review if they met the following criteria: (1) the study population comprised women of child-bearing age (defined as 15–45 years) and incorporated a comparison group of women documented as "chlamydia negative"; (2) the study outcomes included either infertility or successful pregnancy; and (3) the study design was one of the following: cohort, randomised controlled trial, "before and after" study, screening trial and systematic review. Studies were excluded if they described genital infections that either did not include Chlamydia trachomatis or described genital chlamydial co-infection, in which no data were available for C trachomatis infection alone. Results: 3349 studies were identified by the search. One study satisfied the inclusion criteria, a longitudinal investigation measuring pregnancy rates in adolescent women with and without current chlamydial infection at baseline. That study reported no significant difference in subsequent pregnancy rates; however, it had serious methodological limitations, which restricted its conclusions. Conclusions: This systematic review demonstrates the absence of valid evidence on the attributable risk of post-infective tubal factor infertility after genital chlamydial infection. The findings contribute empirical data to the growing debate surrounding previous assumptions about the natural history of chlamydial infection in women

Expression of connexins in human preimplantation embryos in vitro

Intercellular communication via gap junctions is required to coordinate developmental processes in the mammalian embryo. We have investigated if the connexin (Cx) isoforms known to form gap junctions in rodent preimplantation embryos are also expressed in human embryos, with the aim of identifying species differences in communication patterns in early development. Using a combination of polyA PCR and immunocytochemistry we have assessed the expression of Cx26, Cx31, Cx32, Cx40, Cx43 and Cx45 which are thought to be important in early rodent embryos. The results demonstrate that Cx31 and Cx43 are the main connexin isoforms expressed in human preimplantation embryos and that these isoforms are co-expressed in the blastocyst. Cx45 protein is expressed in the blastocyst but the protein may be translated from a generally low level of transcripts: which could only be detected in the PN to 4-cell embryos. Interestingly, Cx40, which is expressed by the extravillous trophoblast in the early human placenta, was not found to be expressed in the blastocyst trophectoderm from which this tissue develops. All of the connexin isoforms in human preimplantation embryos are also found in rodents pointing to a common regulation of these connexins in development of rodent and human early embryos and perhaps other species

Area summation in human vision at and above detection threshold

The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world's structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating