Ionization of Atoms by Slow Heavy Particles, Including Dark Matter

Atoms and molecules can become ionized during the scattering of a slow, heavy particle off a bound electron. Such an interaction involving leptophilic weakly interacting massive particles (WIMPs) is a promising possible explanation for the anomalous 9σ annual modulation in the DAMA dark matter direct detection experiment [R. Bernabei et al., Eur. Phys. J. C 73, 2648 (2013)]. We demonstrate the applicability of the Born approximation for such an interaction by showing its equivalence to the semiclassical adiabatic treatment of atomic ionization by slow-moving WIMPs. Conventional wisdom has it that the ionization probability for such a process should be exponentially small. We show, however, that due to nonanalytic, cusplike behavior of Coulomb functions close to the nucleus this suppression is removed, leading to an effective atomic structure enhancement. We also show that electron relativistic effects actually give the dominant contribution to such a process, enhancing the differential cross section by up to 1000 times.

POINT-AGAPE pixel lensing survey of M31 - Evidence for a MACHO contribution to galactic halos

The POINT-AGAPE collaboration is carrying out a search for gravitational microlensing toward M31 to reveal galactic dark matter in the form of MACHOs (Massive Astrophysical Compact Halo Objects) in the halos of the Milky Way and M31. A high-threshold analysis of 3 years of data yields 6 bright, short- duration microlensing events, which are confronted to a simulation of the observations and the analysis. The observed signal is much larger than expected from self lensing alone and we conclude, at the 95% confidence level, that at least 20% of the halo mass in the direction of M31 must be in the form of MACHOs if their average mass lies in the range 0.5-1 M-circle dot. This lower bound drops to 8% for MACHOs with masses similar to 0.01 M-circle dot. In addition, we discuss a likely binary microlensing candidate with caustic crossing. Its location, some 32' away from the centre of M31, supports our conclusion that we are detecting a MACHO signal in the direction of M31.

Infrared spectrum of an extremely cool white-dwarf star

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested(1,2) to make up much of the 'dark matter' in the halo of the Milky way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models(3-5) indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

On the parallax of WD 0346+246: a halo white dwarf candidate

We present a parallax measurement for the very cool degenerate WD 0346+246, the serendipitous discovery of which was reported by Hambly et al, We find an absolute parallax of 36 +/- 5 mas, yielding a distance estimate of 28 +/- 4pc. The resulting absolute visual magnitude of the object is M-V = 16.8 +/- 0.3, making it the second-lowest luminosity white dwarf currently known. We use the distance estimate and measured proper motion to show that the object has kinematics consistent with membership of the Galactic halo. WD 0346+246 is therefore by far the coolest and least luminous of only a handful of plausible halo white dwarf candidates. As such, the object has relevance to the ongoing debate concerning the results of microlensing experiments and the nature of any baryonic dark matter component to the Galactic halo residing in stellar remnants.

Fabrication and characterisation of high resistivity SOI substrates for monolithic high energy physics detectors

Silicon on Insulator (SOI) substrates offer a promising platform for monolithic high energy physics detectors with integrated read-out electronics and pixel diodes. This paper describes the fabrication and characterisation of specially-configured SOI substrates using improved bonded wafer ion split and grind/polish technologies. The crucial interface between the high resistivity handle silicon and the SOI buried oxide has been characterised using both pixel diodes and circular geometry MOS transistors. Pixel diode breakdown voltages were typically greater than 100V and average leakage current densities at 70 V were only 55 nA/ sq cm. MOS transistors subjected to 24 GeV proton irradiation showed an increased SOI buried oxide trapped charge of only 3.45x1011cn-2 for a dose of 2.7Mrad

Partial shoeprint retrieval using multiple point-of-interest detectors and SIFT descriptors

Shoeprint evidence collected from crime scenes can play an important role in forensic investigations. Usually, the analysis of shoeprints is carried out manually and is based on human expertise and knowledge. As well as being error prone, such a manual process can also be time consuming; thus affecting the usability and suitability of shoeprint evidence in a court of law. Thus, an automatic system for classification and retrieval of shoeprints has the potential to be a valuable tool. This paper presents a solution for the automatic retrieval of shoeprints which is considerably more robust than existing solutions in the presence of geometric distortions such as scale, rotation and scale distortions. It addresses the issue of classifying partial shoeprints in the presence of rotation, scale and noise distortions and relies on the use of two local point-of-interest detectors whose matching scores are combined. In this work, multiscale Harris and Hessian detectors are used to select corners and blob-like structures in a scale-space representation for scale invariance, while Scale Invariant Feature Transform (SIFT) descriptor is employed to achieve rotation invariance. The proposed technique is based on combining the matching scores of the two detectors at the score level. Our evaluation has shown that it outperforms both detectors in most of our extended experiments when retrieving partial shoeprints with geometric distortions, and is clearly better than similar work published in the literature. We also demonstrate improved performance in the face of wear and tear. As matter of fact, whilst the proposed work outperforms similar algorithms in the literature, it is shown that achieving good retrieval performance is not constrained by acquiring a full print from a scene of crime as a partial print can still be used to attain comparable retrieval results to those of using the full print. This gives crime investigators more flexibility is choosing the parts of a print to search for in a database of footwear.

Characterization of x-ray lens for use in probing high energy density states of matter

By using polycapillary lenses to focus laser-produced x-ray sources to high intensities, an improvement in signal-to-noise ratio can be achieved. Here the He-alpha line emission produced by driving a titanium backlighter target is focused by a polycapillary lens and the output characterized. The x-ray spot is measured to have a peak intensity of 4.5 x 10(7) photons, with a total photon count of 8.8 x 10(8) in 0.13 +/- 0.01 mm(2). This setup is equivalent to placing the backlighter target 3 mm from the sample with a 600 mu m diameter pinhole. The polycapillary lens enables the placement of the backlighter target at a much larger distance from the sample to be studied and therefore has the ability to greatly improve the signal-to-noise ratio on detectors. We demonstrate this with two simple diffraction experiments using pyrolytic graphite and polycrystalline aluminium.

Soft matter pH sensing: from luminescent lanthanide pH switches in solution to sensing in hydrogels

The synthesis, complexation, and photophysical properties of the Eu(III)-based quinoline cyclen conjugate complex Eu1 and its permanent, noncovalent incorporation into hydrogels as sensitive, interference-free pH sensing materials for biological media are described. The Eu(III) emission in both solution and hydrogel media was switched reversibly on-off as a function of pH with a large, greater than order of magnitude enhancement in Eu(III) emission. The irreversible incorporation of Eu1 into water-permeable hydrogels was achieved using poly[methyl methacrylate-co-2-hydroxyethyl methacrylate]- based hydrogels, and the luminescent properties of the novel sensor materials, using confocal laser- scanning microscopy and steady state luminescence, were characterized and demonstrated to be retained with respect to solution behavior. Water uptake and dehydration behavior of the sensor-incorporated materials was also characterized and shown to be dependent on the material composition.

Tight junctional abnormality in multiple sclerosis white matter affects all calibres of vessel and is associated with blood-brain barrier leakage and active demyelination

Blood-brain barrier (BBB) hyperpermeability in multiple sclerosis (MS) is associated with lesion pathogenesis and has been linked to pathology in microvascular tight junctions (TJs). This study quantifies the uneven distribution of TJ pathology and its association with BBB leakage. Frozen sections from plaque and normal-appearing white matter (NAWM) in 14 cases were studied together with white matter from six neurological and five normal controls. Using single and double immunofluorescence and confocal microscopy, the TJ-associated protein zonula occludens-1 (ZO-1) was examined across lesion types and tissue categories, and in relation to fibrinogen leakage. Confocal image data sets were analysed for 2198 MS and 1062 control vessels. Significant differences in the incidence of TJ abnormalities were detected between the different lesion types in MS and between MS and control white matter. These were frequent in oil-red O (ORO)+ active plaques, affecting 42% of vessel segments, but less frequent in ORO- inactive plaques (23%), NAWM (13%), and normal (3.7%) and neurological controls (8%). A similar pattern was found irrespective of the vessel size, supporting a causal role for diffusible inflammatory mediators. In both NAWM and inactive lesions, dual labelling showed that vessels with the most TJ abnormality also showed most fibrinogen leakage. This was even more pronounced in active lesions, where 41% of vessels in the highest grade for TJ alteration showed severe leakage. It is concluded that disruption of TJs in MS, affecting both paracellular and transcellular paths, contributes to BBB leakage. TJ abnormality and BBB leakage in inactive lesions suggests either failure of TJ repair or a continuing pathological process. In NAWM, it suggests either pre-lesional change or secondary damage. Clinically inapparent TJ pathology has prognostic implications and should be considered when planning disease-modifying therapy

Abnormal endothelial tight junctions in active lesions and normal-appearing white matter in multiple sclerosis

Blood-brain barrier (BBB) breakdown, demonstrable in vivo by enhanced MRI is characteristic of new and expanding inflammatory lesions in relapsing remitting and chronic progressive multiple sclerosis (MS). Subtle leakage may also occur in primary progressive MS. However, the anatomical route(s) of BBB leakage have not been demonstrated. We investigated the possible involvement of interendothelial tight junctions (TJ) by examining the expression of TJ proteins (occludin and ZO-1 ) in blood vessels in active MS lesions from 8 cases of MS and in normal-appearing white (NAWM) matter from 6 cases. Blood vessels (10-50 per frozen section) were scanned using confocal laser scanning microscopy to acquire datasets for analysis. TJ abnormalities manifested as beading, interruption, absence or diffuse cytoplasmic localization of fluorescence, or separation of junctions (putative opening) were frequent (affecting 40% of vessels) in oil red-O-positive active plaques but less frequent in NAWM (15%), and in normal (

Upregulation of osteopontin and alpha B crystallin in the normal-appearing white matter of multiple sclerosis: an immunohistochemical study utilizing tissue microarrays

Tissue microarrays assembled from control and multiple sclerosis (MS) brain tissue have been used to assess the expression patterns and cellular distribution of two antigens, the proinflammatory cytokine osteopontin and the inducible heat shock protein alpha B -crystallin, which have previously been implicated in MS pathogenesis. Tissue cores were taken from paraffin-embedded donor blocks containing chronic active or chronic inactive plaques and normal-appearing white matter (NAWM) in seven MS cases, and white matter (WM) in five control cases. Expression patterns of both proteins were assessed against myelin density and microglial activation in the different tissue categories. Both proteins showed increased expression in all categories of MS tissue compared with control WM. The results indicate progressive up-regulation of expression of osteopontin with increased plaque activity, while elevation of alpha B-crystallin expression in MS tissue was independent of demyelination. In MS NAWM a significant correlation was observed between high levels of expression of osteopontin and alpha B -crystallin. Osteopontin expression was predominantly confined to astrocytes throughout MS tissues. alpha B -crystallin was expressed on astrocytes, oligodendrocytes and occasionally on demyelinated axons. Taken together, these data indicate a wider distribution of osteopontin and alpha B -crystallin in MS tissues than previously described and support their proposed role in MS pathogenesis.

The direction aftereffect is driven by adaptation of local motion detectors

The processing of motion information by the visual system can be decomposed into two general stages; point-by-point local motion extraction, followed by global motion extraction through the pooling of the local motion signals. The direction aftereVect (DAE) is a well known phenomenon in which prior adaptation to a unidirectional moving pattern results in an exaggerated perceived direction diVerence between the adapted direction and a subsequently viewed stimulus moving in a diVerent direction. The experiments in this paper sought to identify where the adaptation underlying the DAE occurs within the motion processing hierarchy. We found that the DAE exhibits interocular transfer, thus demonstrating that the underlying adapted neural mechanisms are binocularly driven and must, therefore, reside in the visual cortex. The remaining experiments measured the speed tuning of the DAE, and used the derived function to test a number of local and global models of the phenomenon. Our data provide compelling evidence that the DAE is driven by the adaptation of motion-sensitive neurons at the local-processing stage of motion encoding. This is in contrast to earlier research showing that direction repulsion, which can be viewed as a simultaneous presentation counterpart to the DAE, is a global motion process. This leads us to conclude that the DAE and direction repulsion reflect interactions between motion-sensitive neural mechanisms at different levels of the motion-processing hierarchy.