Understanding the magnetic polarizability tensor

The aim of this paper is to provide new insights into the properties of the rank 2 polarizability tensor M̆ proposed by Ledger and Lionheart for describing the perturbation in the magnetic field caused by the presence of a conducting object in the eddy-current regime. In particular, we explore its connection with the magnetic polarizability tensor and the Pólya-Szegö tensor and how, by introducing new splittings of M̆, they form a family of rank 2 tensors for describing the response from different categories of conducting (permeable) objects. We include new bounds on the invariants of the Pólya-Szegö tensor and expressions for the low-frequency and high-conductivity limiting coefficients of M̆. We show, for the high-conductivity case (and for frequencies at the limit of the quasi-static approximation), that it is important to consider whether the object is simply or multiply connected but, for the low-frequency case, the coefficients are independent of the connectedness of the object. Furthermore, we explore the frequency response of the coefficients of M̆ for a range of simply and multiply connected objects

Identification of sex specific DNA regions in the snake genome using a subtractive hybridisation technique

Karyotypic studies have shown that a ZZ/ZW sex chromosome system is used by snakes, which chromosomally resembles the ZZ/ZW system used by birds. However genetic studies have shown that SOX 3; the sex determining gene in mammals and DMRT1; which is the hypothesised sex determining gene in birds, are both located on autosomal chromosomes in the snake. Therefore it has been suggested that the snake sex chromosome system is unique and has evolved independently of the bird?s system. This paper describes a subtractive hybridization method, using physical separation of biotinylated 'driver' DNA. The novel application of this technique was its use in identifying sex specific DNA regions within the genome of the Australian python; Morelia spilota imbricate. Female DNA enrichment was achieved using this technique and resulted in the identification of two non-sex specific repeating elements. The conclusion from this work is the identification of female specific DNA in snakes requires further subtractive hybridization enrichment and a more efficient screening procedure

Characterizing the shape and material properties of hidden targets from magnetic induction data

The aim of this paper is to show that, for the eddy current model, the leading order term for the perturbation in the magnetic field, due to the presence of a small conducting magnetic inclusion, can be expressed in terms of a symmetric rank 2 polarization tensor. This tensor contains information about the shape and material properties of the object and is independent of position. We apply a recently derived asymptotic formula for the perturbed magnetic field, due to the presence of a conducting inclusion, which is expressed in terms of a new class of rank 4 polarization tensors (Ammari, H., Chen, J., Chen, Z., Garnier, J. & Volkov, D. (2014) Target detection and characterization from electromagnetic induction data. J. Math. Pures Appl., 101, 54–75.) and show that their result can be written in an alternative form involving a symmetric rank 2 tensor involving 6 instead of 81 complex components in an orthonormal coordinate frame. For objects with rotational and mirror symmetries we show that the number of coefficients is still smaller. We include numerical examples to demonstrate that the new polarization tensors can be accurately computed by solving a vector-valued transmission problem by hp-finite elements and include examples to illustrate the agreement between the asymptotic formula describing the perturbed fields and the numerical predictions

The effects of climatic fluctuations and extreme events on running water ecosystems

Most research on the effects of environmental change in freshwaters has focused on incremental changes in average conditions, rather than fluctuations or extreme events such as heatwaves, cold snaps, droughts, floods or wildfires, which may have even more profound consequences. Such events are commonly predicted to increase in frequency, intensity and duration with global climate change, with many systems being exposed to conditions with no recent historical precedent. We propose a mechanistic framework for predicting potential impacts of environmental fluctuations on running water ecosystems by scaling up effects of fluctuations from individuals to entire ecosystems. This framework requires integration of four key components: effects of the environment on individual metabolism, metabolic and biomechanical constraints on fluctuating species interactions, assembly dynamics of local food webs and mapping the dynamics of the meta-community onto ecosystem function. We illustrate the framework by developing a mathematical model of environmental fluctuations on dynamically assembling food webs. We highlight (currently limited) empirical evidence for emerging insights and theoretical predictions. For example, widely supported predictions about the effects of environmental fluctuations are: high vulnerability of species with high per capita metabolic demands such as large-bodied ones at the top of food webs; simplification of food web network structure and impaired energetic transfer efficiency; reduced resilience and top-down relative to bottom-up regulation of food web and ecosystem processes. We conclude by identifying key questions and challenges that need to be addressed to develop more accurate and predictive bio-assessments of the effects of fluctuations, and implications of fluctuations for management practices in an increasingly uncertain world

Comparison of Bacterial Diversity within the Coral Reef Sponge, Axinella corrugata, and the Encrusting Coral Erythropodium caribaeorum

We compared the Caribbean reef sponge, Axinella corrugata, with the Caribbean reef coral, Erythropodium caribaeorum for differences in their resident microbial communities. This cursory survey of bacterial diversity applied 16S rRNA gene sequences. Over 100 culture-independent sequences were generated from five different Axinella 16S rRNA libraries, and compared with 69 cultured isolates. The cultureindependent 16S rDNA clones displayed a higher diversity of Proteobacteria, including “uncultured” or “unknown” representatives from the Deltaproteobacteria. Arcobacterium, and Cyanobacteria were also found. We have also confirmed that Axinella sponges appeared to host specific microbial symbionts, similar to the previously identified clones termed “OSO” environmental samples. In contrast, seawater samples near Axinella were dominated by Pseudoalteromonas. Adjacent sediment samples yielded clones of Planctomycetacea, Proteobacteria, sulfate-reducing Desulfovibrio spp, and other Deltaproteobacteria. Anaerobe-like 16S rRNA sequences were detected after the oxygen supply to one Axinella sample was deliberately curtailed to assess temporal changes in the microbial community. E. caribaeorum yielded more Betaproteobacteria relative to Axinella 16S libraries, and also included the Gammaproteobacteria genus Spongiobacter. However, Axinella-derived microbes appeared phylogenetically deeper with greater sequence divergences than the coral. Overall this study indicated that marine microbial community diversity can be linked to specific source hosts and habitats

Characterising small objects in the regime between the eddy current model and wave propagation

Being able to characterise objects at low frequencies, but in situations where the modelling error in the eddy current approximation of the Maxwell system becomes large, is important for improving current metal detection technologies. Importantly, the modelling error becomes large as the frequency increases, but the accuracy of the eddy current model also depends on the object topology and on its materials, with the error being much larger for certain geome-tries compared to others of the same size and materials. Additionally, the eddy current model breaks down at much smaller frequencies for highly magnetic conducting materials compared to non-permeable objects (with similar conductivities, sizes and shapes) and, hence, characterising small magnetic objects made of permeable materials using the eddy current at typical frequencies of operation for a metal detector is not always possible. To address this, we derive a new asymptotic expansion for permeable highly conducting objects that is valid for small objects and holds not only for frequencies where the eddy current model is valid but also for situations where the eddy current modelling error becomes large and applying the eddy approximation would be invalid. The leading-order term we derive leads to new forms of object characterisations in terms of polarizability tensor object descriptions where the coefficients can be obtained from solving vectorial transmission problems. We expect these new characterisations to be important when considering objects at greater stand-off distance from the coils, which is important for safety critical applications, such as the identification of landmines, unexploded ordnance and concealed weapons. We also expect our results to be important when characterising artefacts of archaeological and forensic significance at greater depths than the eddy current model allows and to have further applications parking sensors and improving the detection of hidden, out-of-sight, metallic objects

Adjuvancy and reactogenicity of N-acetylglycosaminyl-N-acetylmuramyl-dipeptide (GMDP) orally administered just prior to trivalent influenza subunit vaccine. A double-blind placebo-controlled study in nursing home residents.

One hundred and fifty-three nursing home residents received 0, 5, 25 or 50 mg N-acetylglucosaminyl-N-acetylmuramyl-dipeptide (GMDP) orally, and trivalent influenza subunit vaccine intramuscularly. One day after intervention, there was a strong increase of total leucocytes, monocytes and neutrophils in the groups receiving 25 or 50 mg GMDP. A GMDP dose dependent increase in systemic, but not in local, vaccine side-effects was observed. No significant differences in post-vaccination haemagglutination inhibiting serum antibody titres were observed between the four groups, indicating that oral administration of GMDP together with influenza vaccination, does not lead to a higher vaccine efficacy

D'atri spaces of type k and related classes of geometries concerning jacobi operators

In this article we continue the study of the geometry of $k$-D'Atri spaces, $$ $\leq n-1$ ($n$ denotes the dimension of the manifold)$,$ began by the second author. It is known that $k$-D'Atri spaces, $k\geq 1,$ are related to properties of Jacobi operators $R_{v}$ along geodesics, since she has shown that ${\operatorname{tr}}R_{v}$, ${\operatorname{tr}}R_{v}^{2}$ are invariant under the geodesic flow for any unit tangent vector $v$. Here, assuming that the Riemannian manifold is a D'Atri space, we prove in our main result that ${\operatorname{tr}}R_{v}^{3}$ is also invariant under the geodesic flow if $k\geq 3$. In addition, other properties of Jacobi operators related to the Ledger conditions are obtained and they are used to give applications to Iwasawa type spaces. In the class of D'Atri spaces of Iwasawa type, we show two different characterizations of the symmetric spaces of noncompact type: they are exactly the $\frak{C}$-spaces and on the other hand they are $k$ -D'Atri spaces for some $k\geq 3.$ In the last case, they are $k$-D'Atri for all $k=1,...,n-1$ as well. In particular, Damek-Ricci spaces that are $k$-D'Atri for some $k\geq 3$ are symmetric. Finally, we characterize $k$-D'Atri spaces for all $k=1,...,n-1$ as the $\frak{SC}$-spaces (geodesic symmetries preserve the principal curvatures of small geodesic spheres). Moreover, applying this result in the case of 4% -dimensional homogeneous spaces we prove that the properties of being a D'Atri (1-D'Atri) space, or a 3-D'Atri space, are equivalent to the property of being a $k$-D'Atri space for all $k=1,2,3$.Comment: 19 pages. This paper substitute the previous one where one Theorem has been deleted and one section has been adde

Prehistory of Transit Searches

Nowadays the more powerful method to detect extrasolar planets is the transit method. We review the planet transits which were anticipated, searched, and the first ones which were observed all through history. Indeed transits of planets in front of their star were first investigated and studied in the solar system. The first observations of sunspots were sometimes mistaken for transits of unknown planets. The first scientific observation and study of a transit in the solar system was the observation of Mercury transit by Pierre Gassendi in 1631. Because observations of Venus transits could give a way to determine the distance Sun-Earth, transits of Venus were overwhelmingly observed. Some objects which actually do not exist were searched by their hypothetical transits on the Sun, as some examples a Venus satellite and an infra-mercurial planet. We evoke the possibly first use of the hypothesis of an exoplanet transit to explain some periodic variations of the luminosity of a star, namely the star Algol, during the eighteen century. Then we review the predictions of detection of exoplanets by their transits, those predictions being sometimes ancient, and made by astronomers as well as popular science writers. However, these very interesting predictions were never published in peer-reviewed journals specialized in astronomical discoveries and results. A possible transit of the planet beta Pic b was observed in 1981. Shall we see another transit expected for the same planet during 2018? Today, some studies of transits which are connected to hypothetical extraterrestrial civilisations are published in astronomical refereed journals. Some studies which would be classified not long ago as science fiction are now considered as scientific ones.Comment: Submiited to Handbook of Exoplanets (Springer