Angular first-order reversal curves: an advanced method to extract magnetization reversal mechanisms and quantify magnetostatic interactions

The magnetic properties of ordered hexagonal arrays of Co nanowires (NWs) and nanotubes (NTs) with diameters of 50 nm and interwire/tube distances of 105 nm were studied using first-order reversal curves (FORCs). We report an advanced analysis of angle dependent first-order reversal curves (AFORCs), measured by changing the angle of the applied magnetic field from θ = 0° (parallel to the wire/tube axis) to 90° (perpendicular). This method allowed us to determine the magnetization reversal mode and to retrieve quantitative information on the magnetostatic interactions between NWs and between NTs. In particular, we found a sharp increase in the coercivity distribution of the NT arrays for θ > 70°, which is attributed to a transition between vortex and transverse reversal modes. Local magnetic interactions are found to prevail in the Co NT arrays, steadily increasing from θ = 0° to 90°. However, in the Co NW arrays the mean magnetic interactions decrease as θ increases, going from ones similar to local interactions to ones smaller than them.

Integrated interdisciplinary training in the radiological sciences

The radiation sciences are increasingly interdisciplinary, both from the research and the clinical perspectives. Beyond clinical and research issues, there are very real issues of communication between scientists from different disciplines. It follows that there is an increasing need for interdisciplinary training courses in the radiological sciences. Training courses are common in biomedical academic and clinical environments, but are typically targeted to scientists in specific technical fields. In the era of multidisciplinary biomedical science, there is a need for highly integrated multidisciplinary training courses that are designed for, and are useful to, scientists who are from a mix of very different academic fields and backgrounds. We briefly describe our experiences running such an integrated training course for researchers in the field of biomedical radiation microbeams, and draw some conclusions about how such interdisciplinary training courses can best function. These conclusions should be applicable to many other areas of the radiological sciences. In summary, we found that it is highly beneficial to keep the scientists from the different disciplines together. In practice, this means not segregating the training course into sections specifically for biologists and sections specifically for physicists and engineers, but rather keeping the students together to attend the same lectures and hands-on studies throughout the course. This structure added value to the learning experience not only in terms of the cross fertilization of information and ideas between scientists from the different disciplines, but also in terms of reinforcing some basic concepts for scientists in their own discipline.

Co nanostructures in ordered templates: comparative FORC analysis

A comparative study on the structural and magnetic properties of highly ordered hexagonal arrays of Co nanoholes, nanowires, nanopillars and nanotubes, with tuned pore/wire/tube diameters, is here presented. The magnetic interactions and their dependence on the geometric features of the arrays were studied using first-order reversal curves (FORCs). For all nanostructures we observe an increase of the magnetostatic interactions with the templates' pore diameter, with the higher (smaller) values found for the nanowire (nanohole) arrays. For the smallest diameters studied (35 nm), all types of arrays could be considered as almost isolated nanostructures, where local interactions prevail. In particular, both nanotube and nanohole arrays exhibit considerable local magnetostatic interactions coming from the stray fields within each void or empty core. On the other hand, the coercivity is found to decrease with diameter for the elongated nanostructures, while it increases with the pore diameter for the nanohole arrays. This behavior is associated with the magnetization reversal mechanisms present in each array. This work highlights a versatile route to tailor the size, geometrical arrangement and magnetostatic interactions of ordered arrays and demonstrates their importance for the tuning of the magnetic behavior of nanometric devices.

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays

In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm.

Tailoring the physical properties of thin nanohole arrays grown on flat anodic aluminum oxide templates

The introduction of voids in a magnetic thin-film alters the stray field distribution and enables the tailoring of the corresponding physical properties. Here we present a detailed study on thin magnetic nanohole arrays (NhAs) grown on top of hexagonally-ordered anodic aluminum oxide (AAO) substrates. We address the effect of AAO topography on the corresponding electrical and magneto-transport properties. Optimization of the AAO topography led to NhAs with improved resistance and magnetoresistance responses, while retaining their most important feature of enhanced coercivity. This opens new pathways for the growth of more complex structures on AAO substrates, a crucial aspect for their technological viability.

Domain wall dynamics in amorphous and nanocrystalline FeCoMoB microwires

We have studied the domain wall dynamics in amorphous and nanocrystalline FeCoMoB microwires. The domain wall propagation velocity has been found very fast (up to 5000 m/s) for the as-cast sample. Annealing at 575 K/1 h leads to the stress relief and sample homogenization and the domain wall velocity even increases to 5300 m/s. However, the domain wall dynamics is highly sensible to the temperature of a measurement. Annealing at 775 K/1 h leads to the appearance of the nanocrystalline structure with much higher temperature stability. The maximum domain wall velocity decreases (2800 m/s), however the domain wall dynamics is much stable with the temperature.

Analysis of the PKR-eIF2alpha phosphorylation homology domain (PePHD) of hepatitis C virus genotype 1 in HIV-coinfected patients by ultra-deep pyrosequencing and its relationship to responses to pegylated interferon-ribavirin treatment

Chronic coinfection with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) is among the greatest challenges facing public health worldwide. In this population, the response to hepatitis C therapy by treatment with pegylated interferon plus ribavirin (PEG-IFN+RBV) is lower than in HCV-monoinfected patients, particularly in those infected by HCV genotype 1. A PKR/eIF-2α phosphorylation homology domain (PePHD) within the E2 protein has been found to interact with PKR and inhibit PKR in vitro, suggesting a possible mechanism for HCV to evade the antiviral effects of IFN. The aim of this work was to analyze the amino acid conservation in the HCV-E2-PePHD and quasispecies diversity among HCV-HIV-coinfected patients exhibiting sustained virological response, non-response, or partial response with viral relapse to PEG-IFN+RBV by ultra-deep pyrosequencing. For this purpose, HCV-E2-PePHD PCR products were generated and sequenced directly for four patients with a sustained response, seven patients with no virological response, and four patients with viral relapse before and after treatment with PEG-IFN+RBV. HCV-E2-PePHD amino acid sequences were obtained for isolates from serum collected before and during treatment (24 h, 4 weeks, and 12 weeks). Quasispecies analysis of the HCV-E2-PePHD and flanking genomic regions was performed using 454/Roche pyrosequencing, analyzing 39,364 sequence reads in total. The HCV-E2-PePHD sequence at the amino acid and nucleotide level was highly conserved among HCV genotype 1 strains, irrespective of the PEG-IFN+RBV response. This high degree of amino acid conservation and sporadic mutations in the HCV-E2-PePHD domain do not appear to be associated with treatment outcome. The HCV-E2-PePHD sequence before or during treatment cannot be used to predict reliably the outcome of treatment in patients coinfected with HCV genotype 1 and HIV.

Adenosine A2A and A2B receptor expression in neuroendocrine tumours: potential targets for therapy

The clinical management of neuroendocrine tumours is complex. Such tumours are highly vascular suggesting tumour-related angiogenesis. Adenosine, released during cellular stress, damage and hypoxia, is a major regulator of angiogenesis. Herein, we describe the expression and function of adenosine receptors (A(1), A(2A), A(2B) and A(3)) in neuroendocrine tumours. Expression of adenosine receptors was investigated in archival human neuroendocrine tumour sections and in two human tumour cell lines, BON-1 (pancreatic) and KRJ-I (intestinal). Their function, with respect to growth and chromogranin A secretion was carried out in vitro. Immunocytochemical data showed that A(2A) and A(2B) receptors were strongly expressed in 15/15 and 13/18 archival tumour sections. Staining for A(1) (4/18) and A(3) (6/18) receptors was either very weak or absent. In vitro data showed that adenosine stimulated a three- to fourfold increase in cAMP levels in BON-1 and KRJ-1 cells. The non-selective adenosine receptor agonist (adenosine-5'N-ethylcarboxamide, NECA) and the A(2A)R agonist (CGS21680) stimulated cell proliferation by up to 20-40% which was attenuated by A(2B) (PSB603 and MRS1754) and A(2A) (SCH442416) receptor selective antagonists but not by the A(1) receptor antagonist (PSB36). Adenosine and NECA stimulated a twofold increase in chromogranin A secretion in BON-1 cells. Our data suggest that neuroendocrine tumours predominantly express A(2A) and A(2B) adenosine receptors; their activation leads to increased proliferation and secretion of chromogranin A. Targeting adenosine signal pathways, specifically inhibition of A(2) receptors, may thus be a useful addition to the therapeutic management of neuroendocrine tumours.

On the mean and variance of the writhe of random polygons

We here address two problems concerning the writhe of random polygons. First, we study the behavior of the mean writhe as a function length. Second, we study the variance of the writhe. Suppose that we are dealing with a set of random polygons with the same length and knot type, which could be the model of some circular DNA with the same topological property. In general, a simple way of detecting chirality of this knot type is to compute the mean writhe of the polygons; if the mean writhe is non-zero then the knot is chiral. How accurate is this method? For example, if for a specific knot type K the mean writhe decreased to zero as the length of the polygons increased, then this method would be limited in the case of long polygons. Furthermore, we conjecture that the sign of the mean writhe is a topological invariant of chiral knots. This sign appears to be the same as that of an "ideal" conformation of the knot. We provide numerical evidence to support these claims, and we propose a new nomenclature of knots based on the sign of their expected writhes. This nomenclature can be of particular interest to applied scientists. The second part of our study focuses on the variance of the writhe, a problem that has not received much attention in the past. In this case, we focused on the equilateral random polygons. We give numerical as well as analytical evidence to show that the variance of the writhe of equilateral random polygons (of length n) behaves as a linear function of the length of the equilateral random polygon.

Preparation and magnetic properties of cylindrical NiFe films and antidot arrays

Continuous NiFe (Permalloy) cylindrical films and arrays of cylindrical NiFe antidots 7 nm thick have been prepared by sputtering onto cylindrical aluminum wires and onto wires anodized to form a porous anodic alumina layer. The antidots are arranged in a close-packed pattern determined by the hexagonal pore arrangement in the porous alumina, with period 103 nm and diameter 42 nm. Hysteresis loops were measured at different angles with respect to the cylinder axis and indicate an easy plane normal to the radius of the wire. The antidots enhance the coercivity compared to the continuous cylindrical film.

A performance analysis of echographic ultrasonic techniques for non-invasive temperature estimation in hyperthermia range using phantoms with scatterers

Optimization of efficiency in hyperthermia requires a precise and non-invasive estimation of internal distribution of temperature. Although there are several research trends for ultrasonic temperature estimation, efficient equipments for its use in the clinical practice are not still available. The main objective of this work was to research about the limitations and potential improvements of previously reported signal processing options in order to identify research efforts to facilitate their future clinical use as a thermal estimator. In this document, we have a critical analysis of potential performance of previous ultrasonic research trends for temperature estimation inside materials, using different processing techniques proposed in frequency, time and phase domains. It was carried out in phantom with scatterers, assessing at their specific applicability, linearity and limitations in hyperthermia range. Three complementary evaluation indexes: technique robustness, Mat-lab processing time and temperature resolution, with specific application protocols, were defined and employed for a comparative quantification of the behavior of the techniques. The average increment per degrees C and mm was identified for each technique (3 KHz/ degrees C in the frequency analysis, 0.02 rad/ degrees C in the phase domain, while increments in the time domain of only 1.6 ns/ degrees C were found). Their linearity with temperature rising was measured using linear and quadratic regressions and they were correlated with the obtained data. New improvements in time and frequency signal processing in order to reveal the potential thermal and spatial resolutions of these techniques are proposed and their subsequent improved estimation results are shown for simulated and measured A-scans registers. As an example of these processing novelties, an excellent potential resolution of 0.12 degrees C into hyperthermia range, with near-to-linear frequency dependence, could be achieved. Specifically defined "numerical" and physical multi-scatter phantoms are described, which mimic ultrasound velocity in tissues of about 1560 m/s @ 35 degrees C and have a quasi-uniform internal scattering structure designed to assure standard signal patterns adequate for processing comparisons in the same time and sound velocity conditions for all the techniques analyzed, and to obtain easily repeatable multi-pulse echo-patterns. A perfect lineal dependence (100% of correlation coefficient) between the unitary average increment measured by each technique and temperature rising was observed while working with simulated A-scan registers, where all the parameters are under an accurate control. Nevertheless a very small quadratic tendency appeared in the results obtained from experimental echo registers, which are more similar to a real tissues case. It would be an interesting future work to analyze the behavior of these techniques in real tissues in order to confirm or reject this light quadratic tendency. Finally, new methods were detailed and applied in order to precisely quantify the advantages of each estimation technique; their respective intrinsic limitations were also underlined.

Duplex ultrasound evaluation for dialysis access selection and maintenance: a practical guide

Detailed case directed history and examination is the mainstay of dialysis access modality selection, ie site and type of access, as well as for maintenance of dialysis access for longevity. As a logical step following history and physical examination, duplex ultrasound evaluation (DUE) is the most cost effective and non-invasive screening tool for evaluation for access placement and for assessment of an established access. Pre-operative vascular mapping allows selection of the optimal dialysis access modality and site. In established accesses, duplex ultrasound testing will diagnose the majority of vascular access complications and direct proper surgical or interventional radiology management. This review outlines a practical decision-making algorithm using DUE for choosing and managing the dialysis access.