Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2 of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2 and details of the aggregate. We find that in the motional averaging regime T2 scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2 N^{-0.44} for aggregates with d=2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2 is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times.Comment: 20 pages, 3 figures, submitted to Journal of Magnetism and Magnetic Material

`Third' Quantization of Vacuum Einstein Gravity and Free Yang-Mills Theories

Based on the algebraico-categorical (:sheaf-theoretic and sheaf cohomological) conceptual and technical machinery of Abstract Differential Geometry, a new, genuinely background spacetime manifold independent, field quantization scenario for vacuum Einstein gravity and free Yang-Mills theories is introduced. The scheme is coined `third quantization' and, although it formally appears to follow a canonical route, it is fully covariant, because it is an expressly functorial `procedure'. Various current and future Quantum Gravity research issues are discussed under the light of 3rd-quantization. A postscript gives a brief account of this author's personal encounters with Rafael Sorkin and his work.Comment: 43 pages; latest version contributed to a fest-volume celebrating Rafael Sorkin's 60th birthday (Erratum: in earlier versions I had wrongly written that the Editor for this volume is Daniele Oriti, with CUP as publisher. I apologize for the mistake.

The Fast Multipole Method (FMM) for Electromagnetic Scattering Problems

The fast multipole method (FMM) was developed by Rokhlin to solve acoustic scattering problems very efficiently. We have modified and adapted it to the second-kind-integral-equation formulation of electromagnetic scattering problems in two dimensions. The present implementation treats the exterior Dirichlet (TM) problem for two-dimensional closed conducting objects of arbitrary geometry. The FMM reduces the operation count for solving the second-kind integral equation (SKIE) from O(n3) for Gaussian elimination to O(n4/3) per conjugated-gradient iteration, where n is the number of sample points on the boundary of the scatterer. We also present a simple technique for accelerating convergence of the iterative method: complexifying k, the wavenumber. This has the effect of bounding the condition number of the discrete system; consequently, the operation count of the entire FMM (all iterations) becomes O(n4/3). We present computational results for moderate values of ka, where a is the characteristic size of the scatterer

Magnetic resonance imaging: Physics basics for the cardiologist

Magnetic resonance imaging physics can be a complex and challenging topic for the practising cardiologist. Its evolving nature and the increasing number of novel sequences used in clinical scanning have been topics of excellent reviews; however, the basic understanding of physics underlying the creation of images remains difficult for many cardiologists. In this review, we go back to the basic physics theories underpinning magnetic resonance and explain their application and use in achieving good quality cardiac imaging, whilst describing established and novel magnetic resonance sequences. By understanding these basic principles, it is anticipated that cardiologists and other health professionals will then appreciate more advanced physics manuscripts on cardiac scanning and novel sequences

CASAM: Collaborative Human-machine Annotation of Multimedia.

The CASAM multimedia annotation system implements a model of cooperative annotation between a human annotator and automated components. The aim is that they work asynchronously but together. The system focuses upon the areas where automated recognition and reasoning are most effective and the user is able to work in the areas where their unique skills are required. The system’s reasoning is influenced by the annotations provided by the user and, similarly, the user can see the system’s work and modify and, implicitly, direct it. The CASAM system interacts with the user by providing a window onto the current state of annotation, and by generating requests for information which are important for the final annotation or to constrain its reasoning. The user can modify the annotation, respond to requests and also add their own annotations. The objective is that the human annotator’s time is used more effectively and that the result is an annotation that is both of higher quality and produced more quickly. This can be especially important in circumstances where the annotator has a very restricted amount of time in which to annotate the document. In this paper we describe our prototype system. We expand upon the techniques used for automatically analysing the multimedia document, for reasoning over the annotations generated and for the generation of an effective interaction with the end-user. We also present the results of evaluations undertaken with media professionals in order to validate the approach and gain feedback to drive further research

A novel method for measuring bowel motility and velocity with dynamic magnetic resonance imaging in two and three dimensions

Increasingly, dynamic magnetic resonance imaging (MRI) has potential as a noninvasive and accessible tool for diagnosing and monitoring gastrointestinal motility in healthy and diseased bowel. However, current MRI methods of measuring bowel motility have limitations: requiring bowel preparation or long acquisition times; providing mainly surrogate measures of motion; and estimating bowel-wall movement in just two dimensions. In this proof-of-concept study we apply a method that provides a quantitative measure of motion within the bowel, in both two and three dimensions, using existing, vendor-implemented MRI pulse sequences with minimal bowel preparation. This method uses a minimised cost function to fit linear vectors in the spatial and temporal domains. It is sensitised to the spatial scale of the bowel and aims to address issues relating to the low signal-to-noise in high-temporal resolution dynamic MRI scans, previously compensated for by performing thick-slice (10-mm) two-dimensional (2D) coronal scans. We applied both 2D and three-dimensional (3D) scanning protocols in two healthy volunteers. For 2D scanning, analysis yielded bi-modal velocity peaks, with a mean antegrade motion of 5.5 mm/s and an additional peak at similar to 9 mm/s corresponding to longitudinal peristalsis, as supported by intraoperative data from the literature. Furthermore, 3D scans indicated a mean forward motion of 4.7 mm/s, and degrees of antegrade and retrograde motion were also established. These measures show promise for the noninvasive assessment of bowel motility, and have the potential to be tuned to particular regions of interest and behaviours within the bowel.Radiolog

The occurrence of Rhynchophorus ferrugineus in Greece and Cyprus and the risk against the native greek palm tree Phoenix theophrasti

Ο κόκκινος ρυγχωτός κάνθαρος των φοινικοειδο')ν, Rhynchophorus ferrugineus (Coleoptera: Curculionidae), είναι ο σημαντικότερος εχθρός των φοινικσειδών παγκοσμίως. Την τελευταία δεκαετία εισέβαλε στις Μεσογειακές χώρες προκαλώντας σοβαρές ζημιές σε καλλιέργειες χουρμαδιάς καθώς και σε καλλωπιστικά φοινινοειδή. Το R. ferrugineus βρέθηκε για πρώτη φορά στην Ελλάδα το Νοέμβριο 2005 στη Χερσόνησο (Νομός Ηρακλείου, Κρήτη) επί Phoenix canariensis και για πρώτη φορά στην Κύπρο στη Λεμεσό τον Αύγουστο 2006 επίσης επί Ρ. canariensis. Εν συνεχεία το R. ferrugineus βρέθηκε στην Ελλάδα, προσβάλλοντας κατά κανόνα P. canariensis, σε Ρόδο (Σεπτέμβριος 2006), Ωρωπό και Βλληνικό Αττικής (Δεκέμβριος 2006). Στην Κύπρο βρέθηκε επίσης τον Οκτώβριο 2006 σε Λάρνακα, Αμμόχωστο και Πάφο, Σε πειραματική δοκιμή στο εργαστήριο, στο Μπενάκειο Φυτοπαθολογικό Ινστιτούτο, διαπιστό)θηκε ότι το R. ferrugineus μπορεί να προσβάλλει και να καταστρέψει και το ιθαγενές είδος φοίνικα Phoenix theophrasti.The red palm weevil (RPW), Rhynchophorus ferrugineus (Coleopiera: Curculionidae), is the most important pest of palm trees in the world. In the last decade R. ferrugineus has invaded the Mediterranean basin where it causes severe damage in date palm cultivations as well as in ornamental palm trees. R. ferrugineus has been found for first time in Greece in Hersonissos (Heraklion district, Crete) infesting Phoenix canariensis, on November 11th, 2005 and for first time in Cyprus in Limassol district on August 20th, 2006, infesting also P. canariensis. Afterwards, R. ferrugineus has been found in Rhodos island, Greece, on 15/9/2006 and in Oropos and Ellinikon (Attiki district, Greece) on 5/12/2006 and 27/12/2006 respectively, infesting mainly P. canariensis. In Cyprus it has also been found in October 2006 in Larnaca, Famagusta and Paphos districts. In laboratory experimentation the susceptibility of the native Greek palm tree Phoenix theophrasti in R. ferrugineus was proved