XIPE: the X-ray Imaging Polarimetry Explorer

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental Astronomy http://link.springer.com/journal/1068

Modelling the Impact of Artemisinin Combination Therapy and Long-Acting Treatments on Malaria Transmission Intensity

Lucy Okell and colleagues predict the impact on transmission outcomes of ACT as first-line treatment for uncomplicated malaria in six areas of varying transmission intensity in Tanzania

An experimental and theoretical study of the dynamics of atom-molecule scattering

In this thesis, a joint experimental and theoretical study of the dynamics of atom- molecule collisions will be presented. The focus of this study will be conducted towards the precise, quantitative theoretical description of the collision dynamics in terms of the vectors k, k', j, and j' (the incoming and outgoing relative momenta associated with the collision, and the initial and final rotational angular momentum of the target diatom respectively) that define the collision, and on the experimental measurement of these vector correlations. Chapter 1 is introductory, providing an overview of the field of reaction dynamics, and the experimental and theoretical methods that exist to treat the collisions of atoms and molecules. This work focusses on the collisions of the spherically symmetric rare gas atoms Ar and He with the open-shell heteronuclear diatomic radicals NO and OH. In particular, the fully quantum state-to-state resolved differential cross-sections for the collisions of NO(X) with Ar (reflecting the k - k' vector correlation), and the collisional cross-sections for the depolarisation of the rotational angular momenta of the NO(A) and OH(A) radicals (reflecting the j - j' vector correlation) have been determined experimentally and theoretically, and the results have been discussed and interpreted in terms of the mechanistic aspects of the collision dynamics, and the features of the potential energy surface that give rise to these. In Chapter 2, the atom-molecule systems that constitute the subject of this work will be introduced in detail. The close-coupled quantum mechanical and quasi-classical trajectory scattering calculations performed as part of this work will be discussed in greater detail, providing a greater insight into molecular scattering theory. The explicit calculation of the quantities of interest (most significantly the differential cross-section, and the tensor/depolarisation cross-sections) will be presented for the quasi-classical and quantum cases, offering the most transparent definitions of these quantities. Finally the mathematical description of the spatial probability distribution of a single vector, a pair of correlated vectors, and three correlated vectors is described in detail, including a discussion of the quantum mechanical nature of the vectors in question. Chapter 3 describes the experimental measurement of the differential cross-sections for the collisions of NO(X) with Ar. A hexapole was used to select uniquely those NO molecules in the |Ω = 0.5; j = 0.5, f> quantum state, allowing full experimental quantum state-to-state selection for the first time. A crossed molecular beam apparatus with (1+1') resonantly enhanced multi-photon ionisation detection coupled with velocity mapped ion- imaging was employed to measure the differential cross-section, and the details of the experimental set-up are provided. The accurate extraction of the true, centre of mass frame differential cross-section from the laboratory frame information yielded by the experiment is something of an involved process, and much of this Chapter will be concerned with the development of a Monte Carlo method to achieve this end. In Chapter 4, the experimental and theoretical fully quantum state-to-state resolved differential cross-sections for the collisions of NO(X) with Ar are presented, having been measured for the first time. Full resolution of the initial parity of the rotational wave- function of the NO molecule has enabled the observation of parity dependent structures within the differential cross-section, and the origin of these structures has been investi- gated, employing quasi-classical, quantum mechanical and semi-classical methods in order to elucidate the mechanism by which they arise. Chapter 5 introduces the measurement of the collisional depolarisation of the rotational angular momentum of the diatom. Rate constants for the collisional depolarisation of j were measured by monitoring the time dependence of the amplitude of Zeeman and hyperfine quantum beats in the (1+1) laser induced fluorescence decays of an ensemble of NO(A) or OH(A) radicals in the presence of a series of background pressures of a collision partner. The creation and subsequent evolution of the polarisation of j induced by the absorption of polarised laser light is described, and the magnitude of this polarisation is linked to the amplitude of the quantum beat in the laser induced fluorescence decay. The extraction of the depolarisation cross-sections from the raw experimental data is discussed, and a Monte Carlo simulation of the experiment is described to account for any additional unwanted experimental factors that may contribute to the loss of polarisation of j. A formalism is also introduced that makes use of the tensor opacities to recover spin- rotation conserving and spin-rotation changing open-shell rotational energy transfer and depolarisation cross-sections from the intrinsically closed shell quasi-classical trajectory scattering calculations. In Chapter 6, the experimentally determined collisional depolarisation cross-sections for the collisions of NO(A) with He/Ar, and of OH(A) with Ar at collision energies of 39 meV/757meV are presented along with their theoretical counterparts. The relative magnitudes of the cross-sections are rationalised in terms of the potential energy surface over which the collision takes place, and the importance of spin-rotation conserving and spin-rotation changing transitions in the depolarisation process is assessed. A detailed study of the ensemble of quasi-classical trajectories is performed to determine the character of the various atom-molecule collisions, and to identify which conditions lead to the most efficient depolarisation of j. The relative importance of the potential energy surface and the collision kinematics is also assessed at this point. The results presented in this thesis thus investigate two complementary expressions of the collision dynamics, the k - k' and j - j' vector correlations, and encompass a variety of collision partners exhibiting vastly differing collision characteristics. As such, this work serves as an illustrative overview of atom-molecule scattering dynamics, containing both experimental and theoretical reflections of the collision dynamics, and relating this information back to the fundamentals of scattering theory.This thesis is not currently available in OR

Studies of protein folding by NMR spectroscopy

This thesis describes an investigation of the folding and stability of a series of derivatives of the proteins lysozyme and α-lactalbumin which lack one or more of their four native disulphide bridges. Removal of the disulphide bridge which links the N- and C-termini from hen lysozyme results in a three-disulphide derivative (CM6,127-lysozyme). This has a profound effect on its stability against thermal denaturation, the Tm for unfolding being reduced by 25°C at pH 3.8. Calorimetric measurements performed on this three-disulphide derivative indicate that this reduction in stability may be attributed entirely to an increase in the entropy difference between the native and denatured states. Kinetic refolding studies of CM6,127-lysozyme using stopped flow optical methods and hydrogen exchange pulse labelling in conjunction with NMR and electrospray ionisation mass spectrometry (ESI-MS) suggest that this reduced stability manifests itself primarily in the α-domain of the protein. A transient intermediate populated during refolding of the unmodified protein can no longer be detected during folding of the derivative resulting in highly cooperative folding under the conditions investigated. The structure and stability of a three- and two-disulphide derivative of the homologous protein, α-lactalbumin have been investigated by NMR spectroscopy. The three-disulphide species, like its lysozyme counterpart, can adopt native structure but this is much more unstable than the intact protein. Removal of a second disulphide bridge, however, destabilises α-lactalbumin to the extent that the native state is no longer formed. Instead, in the presence of Ca2+ and high concentrations of salt, a partially structured state is induced which has some elements of tertiary structure present. Novel techniques of ESI-MS have been developed to study protein folding and stability using hydrogen exchange techniques. Applications to the investigation of cooperativity in protein folding, stability in native, partially folded and unfolded states, and the interactions of a partially folded protein with the chaperone GroEL are described.</p

Quasi-Quantum Treatment of the rotationally inelastic NO-He scattering

An analytical scaling relationship is presented that describes the collision energy dependence of rota-tionally inelastic differential cross sections and allows separation of kinematic and potential-energy effects

Praktikum iz analizne kemije

The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO spacecrafts to be launched in 2006. Located on two different orbits, the two HI instruments will provide stereographic images of solar coronal plasma and coronal mass ejections (CME) over a wide field of view (~90°), ranging from 13 to 330 solar radii (R[SUB]0[/SUB]). These observations complete the 15 R[SUB]0[/SUB] field of view of the solar corona obtained with the other SECCHI instruments (2 coronagraphs and an EUV imager). The HI instrument is a combination of 2 refractive optical systems with 2 different multi-vanes baffle system. The key challenge of the instrument design is the rejection of the solar disk light, with total straylight attenuation of the order of 10[SUP]-13[/SUP] to 10[SUP]-15[/SUP]. The optics and baffles have been specifically designed to reach the required rejection. This paper presents the SECCHI/HI opto-mechanical design, with the achieved performances. A test program has been run on one flight unit, including vacuum straylight verification test, thermo-optical performance test and co-alignment test. The results are presented and compared with the initial specifications

Analysis of signal to noise ratio in coronagraph observations of coronal mass ejections

We establish a baseline signal-to-noise ratio (SNR) requirement for the European Space Agency (ESA)-funded Solar Coronagraph for OPErations (SCOPE) instrument in its field of view of 2.5–30 solar radii based on existing observations by the Solar and Heliospheric Observatory (SOHO). Using automatic detection of coronal mass ejections (CMEs), we anaylse the impacts when SNR deviates significantly from our previously established baseline. For our analysis, SNR values are estimated from observations made by the C3 coronagraph on the Solar and Heliospheric Observatory (SOHO) spacecraft for a number of different CMEs. Additionally, we generate a series of artificial coronagraph images, each consisting of a modelled coronal background and a CME, the latter simulated using the graduated cylindrical shell (GCS) model together with the SCRaytrace code available in the Interactive Data Language (IDL) SolarSoft library. Images are created with CME SNR levels between 0.5 and 10 at the outer edge of the field of view (FOV), generated by adding Poisson noise, and velocities between 700 km s−1 and 2800 km s−1. The images are analysed for the detectability of the CME above the noise with the automatic CME detection tool CACTus. We find in the analysed C3 images that CMEs near the outer edge of the field of view are typically 2% of the total brightness and have an SNR between 1 and 4 at their leading edge. An SNR of 4 is defined as the baseline SNR for SCOPE. The automated detection of CMEs in our simulated images by CACTus succeeded well down to SNR = 1 and for CME velocities up to 1400 km s−1. At lower SNR and higher velocity of ≥ 2100 km s−1 the detection started to break down. For SCOPE, the results from the two approaches confirm that the initial design goal of SNR = 4 would, if achieved, deliver a comparable performance to established data used in operations today, with a more compact instrument design, and a margin in SNR before existing automatic detection produces significant false positives

The glaciated valley landsystem of Morsárjökull, southeast Iceland

A 1:4470 map of the Morsárjökull foreland, southern Iceland shows the spatial distribution of post Little Ice Age glacial sediment–landform associations pertaining to the operation of a typical active temperate outlet glacier of the south Vatnajökull ice cap. The map depicts an exemplar for the debris-charged glaciated valley landsystem, with characteristics further indicative of ‘uncovered alpine glaciers’, such as the uneven distribution of moraine volume, the localized appearance of a fluted subglacial bed and within-valley lateral moraine asymmetry. Such glaciers are characterized by strong glacier-climate coupling, because temporally and spatially sporadic rock avalanche-type medial moraines can only locally retard ablation. This morainic debris also has a short residence time in the glacier system due to its strong coupling with the proglacial fluvial system and resulting in efficient sediment transfer. Areas of more substantial latero-frontal moraine document phases of rock slope failure onto the snout and the passage of the debris to the ice margin

Heliospheric Images of the Solar Wind at Earth

During relatively quiet solar conditions throughout the spring and summer of 2007, the SECCHI HI2 white-light telescope on the STEREO B solar-orbiting spacecraft observed a succession of wave fronts sweeping past Earth.We have compared these heliospheric images with in situ plasma and magnetic field measurements obtained by near-Earth spacecraft, and we have found a near perfect association between the occurrence of these waves and the arrival of density enhancements at the leading edges of high-speed solar wind streams. Virtually all of the strong corotating interaction regions are accompanied by large-scale waves, and the low-density regions between them lack such waves. Because the Sun was dominated by long-lived coronal holes and recurrent solar wind streams during this interval, there is little doubt that we have been observing the compression regions that are formed at low latitude as solar rotation causes the high-speed wind from coronal holes to run into lower speed wind ahead of it