New contention resolution schemes for WiMAX

Abstract—The use of Broadband Wireless Access (BWA) technology is increasing due to the use of Internet and multimedia applications with strict requirements of end–to–end delay and jitter, through wireless devices. The IEEE 802.16 standard, which defines the physical (PHY) and the medium access control (MAC) layers, is one of the BWA standards. Its MAC layer is centralized basis, where the Base Station (BS) is responsible for assigning the needed bandwidth for each Subscriber Station (SS), which requests bandwidth competing between all of them. The standard defines a contention resolution process to resolve the potential occurrence of collisions during the requesting process. In this paper, we propose to modify the contention resolution process to improve the network performance, including end–to–end delay and throughput

Enhancing the Vertical Resolution of Coherent Optical Receivers

The constantly increasing capacity demand in optical fiber transmission systems has driven the development of higher-order modulation to share the cost and power-consumption of optoelectronic components across many bits. However, higher-order modulation imposes challenging requirements on high-speed optoelectronic transceiver components such as on the vertical resolution of analog-to-digital and digital-to-analog converters. State-of-the-art high-speed converters limit the development of next-generation systems above 6 bit/s/Hz/pol at symbol rates beyond 100 Gbaud for Nyquist shaped channels. Ultimately, in the absence of fiber nonlinearity the upper limit on the available signal-to-noise ratio is bounded by the transceiver subsystems. Here we propose a novel optoelectronic technique to enhance the effective vertical resolution of coherent receivers through optical intensity reshaping. Finally, we show that the proposed technique to increase the effective resolution will also boost the performance of digital backpropagation used to mitigate fiber Kerr nonlinear response

MMF Design using Evolutionary Algorithms

We review the latest advances on the design of few-mode fibres guiding up to 21 polarisation modes with low differential mode delay over the C-band. suitable for long-haul transmission

Generalization Capabilities of Machine Learning-based PDM Equalization

We investigate the generalization capabilities of a novel machine learningbased receiver for recovering PDM 16-QAM symbols over unseen chromatic dispersion, Kerr nonlinear distortion, and stochastic polarization evolution

Evaluation of the Psychometric Properties of the Mental Vulnerability Questionnaire in Undergraduate Students

PURPOSE: Translate, adapt the language, and assess the psychometric properties of the Mental Vulnerability Questionnaire (MVQ) in a Portuguese population sample of young adults. DESIGN AND METHODS: A psychometric validation study was performed. The sample comprised 166 undergraduate students. Factor analysis was applied to extract three indicators. FINDINGS: The MVQ showed divergent validity with the Positive Mental Health Questionnaire (p < .001) and convergent validity with the Mental Health Inventory including five items (p < .001). Reliability was verified through the assessment of internal consistency, evidencing positive outcomes (Cronbach's α = 0.81). PRACTICE IMPLICATIONS: The MVQ shows psychometric properties enabling its adaptation to clinical practice and research, essential to an effective screening of mental vulnerability

Enabling Multimode SDM at Reduced Equalization Complexity via Optimized Elliptical Core Fibers

We identify an optimal ovality range for elliptical multimode fiber that support 45 spatial modes. These fibers significantly reduce intramode crosstalk by 11 dB over 10 km fiber length, while minimizing the group delay spread. A 32 GBd 16-QAM dual polarization transmission over a 10 km fiber with crosstalk strength as -20 dB/km demonstrates that the DSP equalization requirements at the receiver are halved with optimized elliptical core fibers compared to circular core fibers. These findings suggest that elliptical core fibers are a promising solution for enabling low-complexity multimode fiber systems

Entomological Surveillance of Behavioural Resilience and Resistance in Residual Malaria Vector Populations.

The most potent malaria vectors rely heavily upon human blood so they are vulnerable to attack with insecticide-treated nets (ITNs) and indoor residual spraying (IRS) within houses. Mosquito taxa that can avoid feeding or resting indoors, or by obtaining blood from animals, mediate a growing proportion of the dwindling transmission that persists as ITNs and IRS are scaled up. Increasing frequency of behavioural evasion traits within persisting residual vector systems usually reflect the successful suppression of the most potent and vulnerable vector taxa by IRS or ITNs, rather than their failure. Many of the commonly observed changes in mosquito behavioural patterns following intervention scale-up may well be explained by modified taxonomic composition and expression of phenotypically plastic behavioural preferences, rather than altered innate preferences of individuals or populations. Detailed review of the contemporary evidence base does not yet provide any clear-cut example of true behavioural resistance and is, therefore, consistent with the hypothesis presented. Caution should be exercised before over-interpreting most existing reports of increased frequency of behavioural traits which enable mosquitoes to evade fatal contact with insecticides: this may simply be the result of suppressing the most behaviourally vulnerable of the vector taxa that constituted the original transmission system. Mosquito taxa which have always exhibited such evasive traits may be more accurately described as behaviourally resilient, rather than resistant. Ongoing national or regional entomological monitoring surveys of physiological susceptibility to insecticides should be supplemented with biologically and epidemiologically meaningfully estimates of malaria vector population dynamics and the behavioural phenotypes that determine intervention impact, in order to design, select, evaluate and optimize the implementation of vector control measures

Comparative Analysis of Modal Dispersion in Graded-Index Multimode Fibers

In this paper, we compare the modal dispersion (MD) in standard and bend-insensitive graded-index multimode fibers (GI-MMFs and BI-MMFs). By selectively exciting 45 modes across 9 mode groups, we observed a maximum differential group delay (between mode group 9 and mode group 1) of 1.14 ns/km in BI-MMF and 2.02 ns/km in standard MMF. The reduced modal dispersion in BI-MMFs is attributed to their trench-structured index profile. Additionally, we discuss the effects of mode coupling on signal integrity and the complexities it introduces for equalization in multimode optical systems

Eliminating Malaria Vectors.

Malaria vectors which predominantly feed indoors upon humans have been locally eliminated from several settings with insecticide treated nets (ITNs), indoor residual spraying or larval source management. Recent dramatic declines of An. gambiae in east Africa with imperfect ITN coverage suggest mosquito populations can rapidly collapse when forced below realistically achievable, non-zero thresholds of density and supporting resource availability. Here we explain why insecticide-based mosquito elimination strategies are feasible, desirable and can be extended to a wider variety of species by expanding the vector control arsenal to cover a broader spectrum of the resources they need to survive. The greatest advantage of eliminating mosquitoes, rather than merely controlling them, is that this precludes local selection for behavioural or physiological resistance traits. The greatest challenges are therefore to achieve high biological coverage of targeted resources rapidly enough to prevent local emergence of resistance and to then continually exclude, monitor for and respond to re-invasion from external populations

The rise of dentine hypersensitivity and tooth wear in an ageing population

Our understanding of the aetiology of dentine hypersensitivity (DH) has changed dramatically over the past few decades. It is no longer an enigma, but other problems exist. The prevalence of DH in the world and in particular in the UK is increasing, predominately due to increases in tooth wear and the erosive dietary intake in the younger population. DH is increasingly reported in all age groups and is shown to provide clinical indication of an active erosive tooth wear. As the population ages and possibly retain teeth for longer, the likelihood of tooth wear and DH could increase. This paper describes the prevalence, aetiology, diagnosis and management of DH in relation to tooth wear, which work together through a surface phenomenon. The aim is to raise awareness of the conditions and to help inform a prevention strategy in an ageing population, which starts from younger age groups to reduce disease into older age