A coded-aperture technique allowing x-ray phase contrast imaging with conventional sources

Phase contrast imaging (PCI) solves the basic limitation of x-ray imaging, i.e., poor image contrast resulting from small absorption differences. Up to now, it has been mostly limited to synchrotron radiation facilities, due to the stringent requirements on the x-ray source and detectors, and only one technique was shown to provide PCI images with conventional sources but with limits in practical implementation. The authors propose a different approach, based on coded apertures, which provides high PCI signals with conventional sources and detectors and imposes practically no applicability limits. They expect this method to cast the basis of a widespread diffusion of PCI. (C) 2007 American Institute of Physics

Multivariate analysis of energy dispersive X-ray diffraction data for the detection of illicit drugs in border control

A system using energy dispersive X-ray diffraction has been tested to detect the presence of illicit drugs concealed within parcels typical of those which are imported into the UK via postal and courier services. The system was used to record diffraction data from calibration samples of diamorphine (heroin) and common cutting agents and a partial least squares regression model was established between diamorphine concentration and diffraction spectra. Parcels containing various crystalline and amorphous materials, including diamorphine, were then scanned to obtain multiple localised diffraction spectra and to form a hyperspectral image. The calibration model was used for the prediction of diamorphine concentration throughout the volume of parcels and enabled the presence and location of diamorphine to be determined from the visual inspection of concentration maps. This research demonstrates for the first time the potential of an EDXRD system to generate continuous hyperspectral images of real parcels from volume scanning in security applications and introduces the opportunity to explore hyperspectral image analysis in chemical and material identification. However, more work must be done to make the system ready for implementation in border control operations by bringing down the procedure time to operational requirements and by proving the system's portability

Network theory approach for data evaluation in the dynamic force spectroscopy of biomolecular interactions

Investigations of molecular bonds between single molecules and molecular complexes by the dynamic force spectroscopy are subject to large fluctuations at nanoscale and possible other aspecific binding, which mask the experimental output. Big efforts are devoted to develop methods for effective selection of the relevant experimental data, before taking the quantitative analysis of bond parameters. Here we present a methodology which is based on the application of graph theory. The force-distance curves corresponding to repeated pulling events are mapped onto their correlation network (mathematical graph). On these graphs the groups of similar curves appear as topological modules, which are identified using the spectral analysis of graphs. We demonstrate the approach by analyzing a large ensemble of the force-distance curves measured on: ssDNA-ssDNA, peptide-RNA (system from HIV1), and peptide-Au surface. Within our data sets the methodology systematically separates subgroups of curves which are related to different intermolecular interactions and to spatial arrangements in which the molecules are brought together and/or pulling speeds. This demonstrates the sensitivity of the method to the spatial degrees of freedom, suggesting potential applications in the case of large molecular complexes and situations with multiple binding sites

New models of leadership in Kent schools: final report

1. Executive Summary The overall aim of this commissioned project, led by Professor Vivienne Griffiths and Dr Andrew Lambirth at Canterbury Christ Church University, is to identify new models of leadership in Kent schools, their characteristics, benefits and challenges to schools. It builds on recent initiatives in Kent schools as set out by the Advisory Service for Kent (2009), responding to an analysis and identification of school leadership needs (ASK 2008). We were particularly asked to look at: - what schools have learnt from introducing new models of leadership - how they prepared for change - their professional needs in the run up to and during the change process - the barriers to change - the enablers. 1.1 Summary of work undertaken The study involved: a) scrutiny of available data on new models of leadership in Kent schools; b) analysis of the literature and consultation material; c) questionnaires to headteachers of federations (N=19); d) interviews with headteachers of federations (N=16). The interim report presented a description and analysis of the questionnaire responses, which dealt in particular with preparation for change and professional needs during this period of development. In this final report, analysis of the interview data is presented, together with analysis of relevant literature on new models of school leadership. 1.2 Key findings - Origins of federations often focus on the need for a link between stronger and less successful schools, as well as community needs. - Clear vision and aims are expressed, particularly by executive heads. - Federation and community school aims are usually linked to community development. - Federations are usually but not always in deprived communities. - Many federation aims included new buildings and/or a joint federation site. - All federations had joint governing bodies or were moving towards this. Benefits of federations: - Greater support for headteachers - Distributed leadership to senior and middle management - Shared curriculum, within or cross-phase - Sharing of good practice, teaching and pastoral approaches - Shared resources - Joint or semi-joint timetabling - Wider offer of subjects, especially at A-level - Joint CPD, including training for teaching assistants and trainee teachers - Improved standards, attendance and behaviour - Range of benefits to the community. Challenges: - Resistance by staff, parents and governors - Heavy workload, especially for executive heads - Need to change school cultures, especially between selective and non-selective schools - Financial pressures; not necessarily savings - Pressures to raise standards - Federations not generally recognised by Ofsted, so separate inspections. 1.3 Recommendations - Case studies and of successful federations and other new leadership models to be collected. - Dissemination of good practice at headteacher conferences and other events. - Training for executive heads, senior and middle management. - Support groups, ‘buddying’ and mentoring for executive heads and headteachers. - Training for governors, parents and other staff. - Improved communication of aims to staff, governors, parents and pupils. - Further research into the development of federations and other new models of leadership

Spatial resolution of drug crystallisation in the skin by X-ray micro-computed tomography

Drug crystallisation in the skin is recognised as a significant problem in topical and transdermal drug delivery. Our recent investigations provided new evidence of drug crystallisation in the skin, however, confirming the precise location of crystals remains challenging. Of note, most approaches used have required disruption of the membrane by tape stripping, with crystal detection limited to the superficial skin layers. Hence, a non-destructive method for complete spatial resolution of crystallised drug in skin is still lacking. In this communication, we report the application of X-ray micro-computed tomography (microCT) to examine drug crystallisation in mammalian skin ex vivo. Permeation studies of a saturated solution of diclofenac sodium were conducted in porcine skin; subsequently, tissue samples were scanned using microCT to generate 2D and 3D maps. A layer of drug crystals was observed on the skin surface; microCT maps also confirmed the distribution of drug crystals up to a skin depth of 0.2 – 0.3 mm. MicroCT also allowed the identification of drug crystallisation as a distinct and confirmed event in the skin and as an extension from drug crystals formed on the skin. These preliminary results confirm the potential of microCT to study this important phenomenon in topical and transdermal drug delivery

Evaluating the performance of ionic liquid coatings for mitigation of spacecraft surface charges

To reduce the impact of charging effects on satellites, cheap and lightweight conductive coatings are desirable. We mimic space-like charging environments in ultra-high vacuum (UHV) chambers during deposition of charges via the electron beam of a scanning electron microscope (SEM). We use the charge induced signatures in SEM images of a thin ionic liquid (IL) film on insulating surfaces such as glass, to assess the general performance of such coatings. In order to get a reference structure in SEM, the samples were structured by nanosphere lithography and coated with IL. The IL film (we choose BMP DCA, due to its beneficial physical properties) was applied ex situ and a thickness of 10 to 30 nm was determined by reflectometry. Such an IL film is stable under vacuum conditions. It would also only lead to additional mass of below 20 mg/m$^2$. At about 5 A/m$^2 \approx 3\cdot10^{19}$ e/(s$\cdot$m$^2$), a typical sample charging rate in SEM, imaging is possible with no noticeable contrast changes over many hours; this electron current density is already 6 orders of magnitudes higher than "worst case geosynchronous environments" of $3\cdot10^{-6}$ A/m$^2$. Measurements of the surface potential are used for further insights in the reaction of IL films to the electron beam of a SEM. Participating mechanisms such as polarization or reorientation will are discussed.Comment: Submitted to Proceedings of the 14th IAA Symposium on Small Satellites for Earth System Observatio

The Importance of Accurate X-ray Energy Spectra for Modelling Dose Deposition with Monte Carlo Techniques

X-ray Spectra are generated for a tungsten target X-ray source operating at 120 kVp for dose prediction purposes. Disparity is found between the analytical, Monte Carlo and spectroscopic method. It is shown through Thermoluminescent Dosimeter (TLD) dose measurement that the spectroscopic method is most representative of the X-ray source spectrum in use. Effects of such disparity is considered in the context of clinical radiography through human simulation. A similar disparity is also observed in a related Molybdenum target source

Strain in epitaxial MnSi films on Si(111) in the thick film limit studied by polarization-dependent extended x-ray absorption fine structure

We report a study of the strain state of epitaxial MnSi films on Si(111) substrates in the thick film limit (100-500~\AA) as a function of film thickness using polarization-dependent extended x-ray absorption fine structure (EXAFS). All films investigated are phase-pure and of high quality with a sharp interface between MnSi and Si. The investigated MnSi films are in a thickness regime where the magnetic transition temperature $T_\mathrm{c}$ assumes a thickness-independent enhanced value of $\geq$43~K as compared with that of bulk MnSi, where $T_\mathrm{c} \approx 29~{\rm K}$. A detailed refinement of the EXAFS data reveals that the Mn positions are unchanged, whereas the Si positions vary along the out-of-plane [111]-direction, alternating in orientation from unit cell to unit cell. Thus, for thick MnSi films, the unit cell volume is essentially that of bulk MnSi --- except in the vicinity of the interface with the Si substrate (thin film limit). In view of the enhanced magnetic transition temperature we conclude that the mere presence of the interface, and its specific characteristics, strongly affects the magnetic properties of the entire MnSi film, even far from the interface. Our analysis provides invaluable information about the local strain at the MnSi/Si(111) interface. The presented methodology of polarization dependent EXAFS can also be employed to investigate the local structure of other interesting interfaces.Comment: 11 pages, 10 figure

Sensitive X-ray Detectors Synthesised from CsPbBr3

The materials used in detection of high energy photons are of primary importance in the construction of efficient, cost effective and sensitive detectors. Current research into Perovskites for solar cell technology has stimulated interest in their potential alternative uses, one of which is in direct photon conversion radiation detectors, owed primarily to their high-Z elemental composition twinned with exceptional charge carrier transport properties. Here, the Perovskite CsPbBr 3 has been synthesised through solution growth. The raw CsPbBr 3 was a granular powder which was formed into disks of 8 mm diameter and 1-2 mm thickness by two methods: 1). the powders were pressed into pellets using a hydraulic press or 2). sealed in a quartz ampoule under vacuum and then melted and quenched to form a polycrystalline solid which was cut to size. Metallic contacts were deposited on the front and back faces to permit charge collection. The results from the pressed devices are promising, particularly given that the production method is cost effective, repeatable and scalable. The solid-from-melt devices show similar performance but further development is required to optimise the production method

High resolution characterisation of microstructural evolution in Rbx_{x}Fe2−y_{2-y}Se2_{2} crystals on annealing

The superconducting and magnetic properties of phase-separated A$_x$Fe$_{2-y}$Se$_2$ compounds are known to depend on post-growth heat treatments and cooling profiles. This paper focusses on the evolution of microstructure on annealing, and how this influences the superconducting properties of Rb$_x$Fe$_2-y$Se$_2$ crystals. We find that the minority phase in the as-grown crystal has increased unit cell anisotropy (c/a ratio), reduced Rb content and increased Fe content compared to the matrix. The microstructure is rather complex, with two-phase mesoscopic plate-shaped features aligned along {113} habit planes. The minority phase are strongly facetted on the {113} planes, which we have shown to be driven by minimising the volume strain energy introduced as a result of the phase transformation. Annealing at 488K results in coarsening of the mesoscopic plate-shaped features and the formation of a third distinct phase. The subtle differences in structure and chemistry of the minority phase(s) in the crystals are thought to be responsible for changes in the superconducting transition temperature. In addition, scanning photoemission microscopy has clearly shown that the electronic structure of the minority phase has a higher occupied density of states of the low binding energy Fe3d orbitals, characteristic of crystals that exhibit superconductivity. This demonstrates a clear correlation between the Fe-vacancy-free phase with high c/a ratio and the electronic structure characteristics of the superconducting phase.Comment: 6 figures v2 is exactly the same as v1. The typesetting errors in the abstract have been correcte