Disjoint difference families and their applications

Difference sets and their generalisations to difference families arise from the study of designs and many other applications. Here we give a brief survey of some of these applications, noting in particular the diverse definitions of difference families and the variations in priorities in constructions. We propose a definition of disjoint difference families that encompasses these variations and allows a comparison of the similarities and disparities. We then focus on two constructions of disjoint difference families arising from frequency hopping sequences and showed that they are in fact the same. We conclude with a discussion of the notion of equivalence for frequency hopping sequences and for disjoint difference families

Functional repair codes: a view from projective geometry

Storage codes are used to ensure reliable storage of data in distributed systems. Here we consider functional repair codes, where individual storage nodes that fail may be repaired efficiently and the ability to recover original data and to further repair failed nodes is preserved. There are two predominant approaches to repair codes: a coding theoretic approach and a vector space approach. We explore the relationship between the two and frame the later in terms of projective geometry. We find that many of the constructions proposed in the literature can be seen to arise from natural and well-studied geometric objects, and that this perspective gives a framework that provides opportunities for generalisations and new constructions that can lead to greater flexibility in trade-offs between various desirable properties. We also frame the cut-set bound obtained from network coding in terms of projective geometry. We explore the notion of strictly functional repair codes, for which there exist nodes that cannot be replaced exactly. Currently only one known example is given in the literature, due to Hollmann and Poh. We examine this phenomenon from a projective geometry point of view, and discuss how strict functionality can arise. Finally, we consider the issue that the view of a repair code as a collection of sets of vector/projective subspaces is recursive in nature and makes it hard to visualise what a collection of nodes looks like and how one might approach a construction. Here we provide another view of using directed graphs that gives us non-recursive criteria for determining whether a family of collections of subspaces constitutes a function, exact, or strictly functional repair code, which may be of use in searching for new codes with desirable properties

Optimum Tube Voltage for Pelvic Direct Radiography: A Phantom Study

Pelvic radiography is a frequently performed radiological examination. Its average effective dose (E) is 0.53 mSv which is comparable to the annual per caput dose from diagnostic radiology, 0.6 mSv. However, existing studies on optimum tube potential for pelvic X-rays tend to be limited to screen-film and computed radiography. The purpose of this study was to determine the tube voltage for dose-image optimisation in pelvic direct radiography (DR). Fifty-four pelvic phantom images were acquired using 50-135 kV at 5 kV increments (three images taken at each kV level) and milliampere seconds determined by automatic exposure control. The signal-to-noise ratio (SNR) and dose were measured for each image. Figure of merit (FOM) defined as the ratio of SNR2 to E was used to determine the optimum tube potential. The FOM indicates 135 kV is the optimum setting for pelvic DR. Using the European Commission tube voltage recommendation (75-90 kV) as a reference point, there was only a slight (5.56%) decrease of image quality in the femoral neck region at 135 kV. However, its E was 0.054 mSv. This appreciable dose reduction potential could be attributed to the improvement of detective quantum efficiency and image processing technology of the recent DR system

Genomic Signatures of Historical Allopatry and Ecological Divergence in an Island Lizard

Geographical variation amongcontiguouspopulations is frequently attributed to ecological divergence or historical isolation followed by secondary contact.Distinguishing between these effects is key to studies of incipient speciation and could be revealed by different genomic signatures. We used RAD-seq analyses to examine morphologically divergent populations of the endemic lizard (Gallotia galloti) from the volcanic island of Tenerife. Previous analyses have suggested ecological and historical causes to explain the morphological diversity. Analyses of 276,483 single nucleotide polymorphisms (SNPs) from>20 Mbp of the genome revealed one genetically divergent population from Anaga, a region associated with divergent mtDNA lineages in other Tenerife endemics. This population also has a high number of private alleles, and its divergence can be explained by historical isolation. Bayesian outlier analyses identified a small proportion of SNPs as candidates for selection (0.04%) which were strongly differentiated between xeric andmesic habitat types. Individual testing for specific xeric–mesic selection using an alternative approach also supported ecological divergence in a similarly small proportion of SNPs. The study indicates the roles of both historical isolation and ecological divergence in shaping genomic diversity in G. galloti.However, north–southmorphological divergence appears solely associated with the latter and likely involves a relatively small proportion of the genome

P2Y purinergic receptor signaling in oral squamous cell carcinoma cell lines and its role in proliferation and cisplatin-mediated apoptosis

Treatment of advanced stage oral squamous cell carcinoma (OSCC) often involves the use of chemotherapeutic agents, such as cisplatin. However, its use often results in therapeutic failure due to chemoresistance. This study focused on a class of purinergic receptors, namely P2Y, which are activated via interaction with extracellular nucleotides. The functional effects of P2Y receptor activation in OSCC cell lines as well as the signaling pathways involved were investigated. The expression of P2Y2 receptors in histological sections of OSCC was studied due to its association with cancer. Activation of MAPK pathways via extracellular nucleotides were studied in OSCC cell lines, along with downstream effects such as proliferation and cisplatin-mediated apoptosis. Immunohistochemical staining of OSCC tissue samples showed loss of P2Y2 expression as the disease progressed. Western blotting identified different MAPK signaling pathways were activated by extracellular nucleotides. Bromodeoxyuridine proliferation assays showed increased cellular proliferation in the OSCC cell lines H400 (p < 0.001) and SAS (p < 0.001) after 24 h treatment with ATP. However, the ability of extracellular nucleotides to activate multiple P2Y receptor subtypes may indicate the involvement of other subtypes aside from P2Y2. Cisplatin-mediated apoptosis was enhanced in SAS cells co-treated with ATP (p < 0.001), while H376 (p < 0.001) showed reduction in the number of apoptotic cells and no significant changes were observed in H103. This study concluded that extracellular nucleotide on OSCC cell lines with different characterizations had varied downstream effects, which suggests the use of targeted therapy to specific individuals

Broadcast-enhanced key predistribution schemes

We present a formalisation of a category of schemes that we refer to as broadcast-enhanced key predistribution schemes (BEKPSs). These schemes are suitable for networks with access to a trusted base station and an authenticated broadcast channel. We demonstrate that the access to these extra resources allows for the creation of BEKPSs with advantages over key predistribution schemes such as flexibility and more efficient revocation. There are many possible ways to implement BEKPSs, and we propose a framework for describing and analysing them. In their paper “From Key Predistribution to Key Redistribution,” Cichoń et al. [2010] propose a scheme for “redistributing” keys to a wireless sensor network using a broadcast channel after an initial key predistribution. We classify this as a BEKPS and analyse it in that context. We provide simpler proofs of some results from their paper, give a precise analysis of the resilience of their scheme, and discuss possible modifications. We then study two scenarios where BEKPSs may be particularly desirable and propose a suitable family of BEKPSs for each case. We demonstrate that they are practical and efficient to implement, and our analysis shows their effectiveness in achieving suitable trade-offs between the conflicting priorities in resource-constrained networks

Using the surface profiles of modern ice masses to inform palaeo-glacier reconstructions

Morphometric study of modern ice masses is useful because many reconstructions of glaciers traditionally draw on their shape for guidance Here we analyse data derived from the surface profiles of 200 modern ice masses-valley glaciers icefields ice caps and ice sheets with length scales from 10(0) to 10(3) km-from different parts of the world Four profile attributes are investigated relief span and two parameters C* and C that result from using Nye s (1952) theoretical parabola as a profile descriptor C* and C respectively measure each profile s aspect ratio and steepness and are found to decrease in size and variability with span This dependence quantifies the competing influences of unconstrained spreading behaviour of ice flow and bed topography on the profile shape of ice masses which becomes more parabolic as span Increases (with C* and C tending to low values of 2 5-3 3 m(1/2)) The same data reveal coherent minimum bounds in C* and C for modern ice masses that we develop into two new methods of palaeo glacier reconstruction In the first method glacial limits are known from moraines and the bounds are used to constrain the lowest palaeo ice surface consistent with modern profiles We give an example of applying this method over a three-dimensional glacial landscape in Kamchatka In the second method we test the plausibility of existing reconstructions by comparing their C* and C against the modern minimum bounds Of the 86 published palaeo ice masses that we put to this test 88% are found to be plausible The search for other morphometric constraints will help us formalise glacier reconstructions and reduce their uncertainty and subjectiveness (C) 2010 Elsevier Ltd All rights reserve