How much multiuser diversity is required over large-scale fading?

In multiuser diversity systems, the impact of large-scale fading on the total system performance such as link quality and system power has not been widely addressed. Considering large-scale fading, we propose an adaptive multiuser scheduling to minimize the total system power while reducing the effect of large-scale fading on the system bit error rate. The number of active users is adapted to every shadow variation, which varies slower than small-scale fading. We consider the two widely used multiuser systems (i.e., delay-tolerant, and delay-sensitive multiuser systems). Closed-form expressions for the bit error rate are derived. The selection procedure for the minimum number of users is introduced for guaranteed performance of the above multiuser systems. The impact of adaptive multiuser diversity gain on the system power and bit error rate is illustrated over large-scale fading channels by numerical results.

Impact of the number of users on error probabilities in multiuser diversity systems

Multiuser diversity gain has been investigated well in terms of a system capacity formulation in the literature. In practice, however, designs on multiuser systems with nonzero error rates require a relationship between the error rates and the number of users within a cell. Considering a best-user scheduling, where the user with the best channel condition is scheduled to transmit per scheduling interval, our focus is on the uplink. We assume that each user communicates with the base station through a single-input multiple-output channel. We derive a closed-form expression for the average BER, and analyze how the average BER goes to zero asymptotically as the number of users increases for a given SNR. Note that the analysis of average BER even in SI SO multiuser diversity systems has not been done with respect to the number of users for a given SNR. Our analysis can be applied to multiuser diversity systems with any number of antennas.

Counterphase modulation flicker photometry: phenotypic and genotypic associations

The OSCAR test, a clinical device that uses counterphase flicker photometry, is believed to be sensitive to the relative numbers of long-wavelength and middle-wavelength cones in the retina, as well as to individual variations in the spectral positions of the photopigments. As part of a population study of individual variations in perception, we obtained OSCAR settings from 1058 participants. We report the distribution characteristics for this cohort. A randomly selected subset of participants was tested twice at an interval of at least one week: the test-retest reliability (Spearman's rho) was 0.80. In a whole-genome association analysis we found a provisional association with a single nucleotide polymorphism (rs16844995). This marker is close to the gene RXRG, which encodes a nuclear receptor, retinoid X receptor γ. This nuclear receptor is already known to have a role in the differentiation of cones during the development of the eye, and we suggest that polymorphisms in or close to RXRG influence the relative probability with which long-wave and middle-wave opsin genes are expressed in human cones.

Genotypic and antimicrobial characterisation of Propionibacterium acnes isolates from surgically excised lumbar disc herniations

The anaerobic skin commensal Propionibacterium acnes is an underestimated cause of human infections and clinical conditions. Previous studies have suggested a role for the bacterium in lumbar disc herniation and infection. To further investigate this, five biopsy samples were surgically excised from each of 64 patients with lumbar disc herniation. P. acnes and other bacteria were detected by anaerobic culture, followed by biochemical and PCR-based identification. In total, 24/64 (38%) patients had evidence of P. acnes in their excised herniated disc tissue. Using recA and mAb typing methods, 52% of the isolates were type II (50% of culture-positive patients), while type IA strains accounted for 28% of isolates (42% patients). Type III (11% isolates; 21% patients) and type IB strains (9% isolates; 17% patients) were detected less frequently. The MIC values for all isolates were lowest for amoxicillin, ciprofloxacin, erythromycin, rifampicin, tetracycline, and vancomycin (≤1 mg/L). The MIC for fusidic acid was 1-2 mg/L. The MIC for trimethoprim and gentamicin was 2 to ≥4  mg/L. The demonstration that type II and III strains, which are not frequently recovered from skin, predominated within our isolate collection (63%) suggests that the role of P. acnes in lumbar disc herniation should not be readily dismissed.

Exploring diversity through ethos in initial teacher education

This paper considers whether there is value in introducing student teachers to schools of different ethos as part of their initial teacher education. A 2-year study of undergraduate post-primary student teachers at a university college in Northern Ireland reveals that encounters with schools of different ethos can help student teachers to understand differences between schools and their visions of education, as well as correcting misunderstandings and challenging stereotypes. It is argued that as a result of experiencing diverse examples of ethos, student teachers may also be helped to understand the complexity of schools as organisations and to position themselves and their professional practice within wider debates about the aims of education and schools as communities of practice. © 2008 Elsevier Ltd. All rights reserved.

Uniformity and diversity in religious education in Northern Ireland

This paper considers the tension that can exist in the aims of religious education between the desire to encourage open-minded, critical thinking through exposure to diverse traditions, ideas and cultures and the encouragement, overt or otherwise, into uniformity whereby learners take on the values of a particular tradition, culture or ideology (say of a religion, family or school). The particular situation of teaching religious education to post-primary school pupils in Northern Ireland is considered, and evidence cited to suggest that the Northern Ireland Core Syllabus in Religious Education has tried to impose a particular non-denominational Christian uniformity on pupils and teachers through its use of religious language. This has contributed to a culture of 'avoidance' in relation to the teaching of broad Christian diversity. The article concludes that there is a need for an ongoing and meaningful dialogue to discover what kind of balance between uniformity and diversity is best in teaching religious education in Northern Ireland, and notes that this also requires the reassessment of fundamental issues such as the aims of education and the relationship between secular and religious values in publicly funded schools. © 2004 Christian Education.

Improving signal reliability for indoor off–body communications using spatial diversity at the base station

In this paper, we investigate the potential improvement in signal reliability for indoor off-body communications when using spatial diversity at the base station. In particular, we utilize two hypothetical indoor base stations operating at 5.8 GHz each featuring four antennas which are spaced at either half- or one-wavelength apart. Three on-body locations are considered along with four types of user movement. The cross-correlation between the received signal envelopes observed at each base station antenna element was calculated and found to be always less than 0.5. Selection, maximal ratio, and equal gain combining of the received signal has shown that the greatest improvement is obtained when the user is mobile, with a maximum diversity gain of 11.34 dB achievable when using a four branch receiver. To model the fading envelope obtained at the output of the virtual combiners, we use diversity specific, theoretical probability density functions for multi-branch receivers operating in Nakagami-m fading channels. It is shown that these equations provide an excellent fit to the measured channel data.

Small–scale fading characteristics of diversity combining schemes used for body–to–body communications within an urban environment at 2.45 GHz

In this paper, an analysis of spatial diversity and small-scale fading characteristics for body-to-bodycommunications is presented. The measurements were made at 2.45 GHz in an urban environment with uncontrolled pedestrian and vehicular traffic. The virtual array of four distributed receive antennas where situated on the centralchest, central waist, left waist and left wrist of the user’s body. Combining of the received signal measured at each ofthe antennas in the virtual array has shown that an average diversity gain of up to 11.8 dB can be achieved when usingfour distributed antennas and a maximal ratio combining scheme. To model the small-scale fading characteristics obtained at the output of the virtual combiners, we use diversity specific, theoretical probability density functions for multi-branch receivers operating in Nakagami-m fading channels. It is shown that these equations provide an excellent fit to the measured channel data.

Wave action modifies the effects of consumer diversity and warming on algal assemblages

To understand the consequences of biodiversity loss, it is necessary to test how biodiversity-ecosystem functioning relationships may vary with predicted environmental change. In particular, our understanding will be advanced by studies addressing the interactive effects of multiple stressors on the role of biodiversity across trophic levels. Predicted increases in wave disturbance and ocean warming, together with climate-driven range shifts of key consumer species, are likely to have profound impacts on the dynamics of coastal marine communities. We tested whether wave action and temperature modified the effects of gastropod grazer diversity (Patella vulgata, Littorina littorea and Gibbula umbilicalis) on algal assemblages in experimental rock pools. The presence or absence of L. littorea appeared to drive changes in microalgal and macroalgal biomass and macroalgal assemblage structure. Macroalgal biomass also decreased with increasing grazer species richness, but only when wave action was enhanced. Further, independently of grazer diversity, wave action and temperature had interactive effects on macroalgal assemblage structure. Warming also led to a reversal of grazer-macroalgal interaction strengths from negative to positive, but only when there was no wave action. Our results show that hydrodynamic disturbance can exacerbate the effects of changing consumer diversity, and may also disrupt the influence of other environmental stressors on key consumer-resource interactions. These findings suggest that the combined effects of anticipated abiotic and biotic change on the functioning of coastal marine ecosystems, although difficult to predict, may be substantial.