Journal articles on the topic 'Polarised-nuclei'
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Kudryavtsev, I. N., and A. P. Soznik. "Elastic intermediate-energy proton scattering by polarised nuclei." Journal of Physics G: Nuclear and Particle Physics 15, no. 9 (September 1, 1989): 1377–95. http://dx.doi.org/10.1088/0954-3899/15/9/008.
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Glättli, Hans. "Polarised nuclei for neutron science: recent applications and perspectives." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 529, no. 1-3 (August 2004): 194–98. http://dx.doi.org/10.1016/j.nima.2004.04.156.
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Lampard, GJ, HH Bolotin, AE Stuchbery, CE Doran, and AP Byrne. "Systematics of Gyromagnetic Ratios of the 21+ States in Even Ge Isotopes." Australian Journal of Physics 40, no. 2 (1987): 117. http://dx.doi.org/10.1071/ph870117.
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The relative gyromagnetic ratios of the 2t states in 70,72,74,76Ge were measured simultaneously by me ns of the thin-foil, perturbed y-r yngular distribution technique utilising the transient hyperfine field manifest t nuclei of Ge ions rapidly traversing polarised Fe. The states of interest were Coulomb excited using 75-MeV 34S projectiles incident upon natural element l Ge t rget. The present results re comp red with previously reported measurements and collective model expectations.
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Court, G. R., and W. G. Heyes. "The polarisation of 14N and 15N nuclei in polarised proton targets using irradiated ammonia." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 243, no. 1 (February 1986): 37–40. http://dx.doi.org/10.1016/0168-9002(86)90818-1.
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O’Connor, Eoin G. P., Andrew Shearer, Christian Gouiffes, and Philippe Laurent. "High Time Resolution Astronomical Polarimetry with GASP." Proceedings of the International Astronomical Union 13, S337 (September 2017): 384–85. http://dx.doi.org/10.1017/s1743921317010626.
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AbstractThe Galway Astronomical Stokes Polarimeter (GASP) is a high time resolution, full-Stokes imaging polarimeter which utilises a Fresnel rhomb prism as a beam-splitter and quarter wave retarder. The ability to perform optical photometry and polarimetry at high frame rates enables more detailed studies of a multitude of compact objects including; optical pulsars, magnetars and Active Galactic Nuclei (AGN). We present a brief discussion of the instruments’ current capabilities and hardware design. GASP is currently configured with two Electron Multiplying Charge-Coupled Devices (EMCCDs), which offer sub-millisecond frame readout speeds over a defined region of interest on the sensor. We will report results from an observational campaign at the William Herschel Telescope (WHT) in December, 2015. During this campaign GASP was used to study the Crab Pulsar, V404 Cygni and polarisation standards. As a subset of our analysis we have identified a significant contribution from the Interstellar Medium (ISM) and the interaction of a varying polarised source with the ISM, the subsequent conversion of linearly polarised light to circular, and its dependence on the angle of the source emission electric field orientation. Further to the presentation of results we will discuss future observational work, which is planned for September 2017 and subsequent improvements to increase the temporal resolution of the detectors.
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Shehu, D., G. Marsicano, J. E. Fléchon, and C. Galli. "Developmentally regulated markers of in vitro-produced preimplantation bovine embroys." Zygote 4, no. 2 (May 1996): 109–21. http://dx.doi.org/10.1017/s0967199400002987.
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SummaryExpression of various developmentally regulated markers was screened throughout the preimplantation stages of in vitro-derived bovine embryos. This was done by investigating the distribution of several nuclear, cytoplasmic and extracellular proteins by means of immunofluorescence microscopy. While lamin B appeared as a constitutive component of nuclei of all preimplantation stages, lamins A/C had a stage-related distribution. The early cleavage stage nuclei contained lamins A/C which generally disappeared in the following stages, with the possible exception of a few positive nuclei in the morula and early blastocyst stage. In the expanded blastocyst stage the nuclei of trophectoderm cells became positive while no positivity was observed in the inner cell mass cells. Starting from day 6, the appearance and/or polarised distribution of various cytoskeletal and cytoskeleton-related components such as Factin, α-catenin and E-cadherin gave an insight into the timing of events related to compaction of bovine e bryos. Compaction was correlated with the first differentiation event, i.e. the formation of trophectoderm; this is the first embryonic epithelium, characterised by cytokeratins and desmoplakin. Extracellular fibronectin was first detected in the early blastocyst stage shortly before the morphological differentiation of primitive endoderm, and in the later stages it was localised at the interface between trophectoderm and extraembryonic endoderm. Laminin and collagen IV were expressed by the endoderm cells and contributed to the extracellular matrix underlying the trophectoderm. This study is a first attempt to characterise the cells of in vitro-derived bovine embryos valid for cell line derivation.
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KISELEV, J. F., A. F. PRUDKOGLYAD, A. S. SHUMOVSKY, and V. I. YUKALOV. "DISCOVERY OF DICKE SUPERRADIATION BY SYSTEM OF NUCLEAR MAGNETIC MOMENTS." Modern Physics Letters B 01, no. 11n12 (February 1988): 409–16. http://dx.doi.org/10.1142/s021798498800148x.
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Spontaneous generation of the Dicke superradiation (SR) state has been found in the system of inversely polarised proton spins with “frozen” polarisation. SR is observed at the moment when the Larmor frequency crosses the resonance frequency of the passive oscillatory circuit. SR arises from incoherent maser generation of spins. The frequency of a SR generator can be retuned from several hundreds of kilohertz to hundreds of megahertz at very low temperatures. Dependence of incoherent and coherent radiation on the initial polarisation has been investigated. A radio frequency analogue of the optical SR laser is shown to be possible both for weak-amplifying and for strong-amplifying active media, depending on the factor of filling and polarisation of nuclei. SR-reverse of negative polarisation is observed in the latter case.
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Adebahr, B., M. Brienza, and R. Morganti. "Polarised structures in the radio lobes of B2 0258+35." Astronomy & Astrophysics 622 (February 2019): A209. http://dx.doi.org/10.1051/0004-6361/201833988.
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Context. The contribution of active galactic nuclei to the magnetisation of the Universe can be constrained by knowing their duty cycles, jet and magnetic field morphologies, and the physical processes dominating their interaction with the surrounding environment. Aims. The magnetic field morphology and strength of radio lobes of AGN has an influence on the mechanisms for the propagation of cosmic rays into intergalactic space. Using the source B2 0258+35 we want to investigate the interaction of its radio lobes with the surrounding environment and examine the underlying physical effects. Methods. Published H I and radio continuum data at λ21 cm were combined with newly reduced archival Westerbork Radio Synthesis Telescope polarisation data at the same wavelength to investigate the polarised emission in the radio lobes of B2 0258+35. We assumed energy equipartition between the cosmic rays and the magnetic field to calculate their pressure and investigate the physical processes leading to the detected emission. Results. We detected a unique S-shaped diffuse polarised structure. The lobes have a pressure of p = 1.95 ± 0.4 × 10−14 dyn cm−2. The calculated total magnetic field strengths are low (Beq = 1.21 ± 0.12 μG). We observe depolarisation in the northern lobe, which might originate from the H I-disc in the foreground. In addition we see an anti-correlation between the pressure and the fractional polarisation along the S-shaped structure. Therefore we consider magnetic draping and magnetic field compression as possible effects that might have created the observed S-shape. Conclusions. Our results suggest that magnetic draping can be effectively used to explain the observed polarised structures. This is likely due to the combination of a relatively low magnetic field strength, enabling super-Alfvénic motion of the rising lobes (with MA = 2.47 − 3.50), and the coherency of the surrounding magnetic field. Moreover, the draped layer tends to suppress any mixing of the material between the radio lobes and the surrounding environment, but can enhance the mixing and re-acceleration efficiencies inside the lobes, providing an explanation for the average flat spectral index observed in the lobes.
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Catoira, R., A. C. Timmers, F. Maillet, C. Galera, R. V. Penmetsa, D. Cook, J. Denarie, and C. Gough. "The HCL gene of Medicago truncatula controls Rhizobium-induced root hair curling." Development 128, no. 9 (May 1, 2001): 1507–18. http://dx.doi.org/10.1242/dev.128.9.1507.
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The symbiotic infection of the model legume Medicago truncatula by Sinorhizobium meliloti involves marked root hair curling, a stage where entrapment of the microsymbiont occurs in a chamber from which infection thread formation is initiated within the root hair. We have genetically dissected these early symbiotic interactions using both plant and rhizobial mutants and have identified a M. truncatula gene, HCL, which controls root hair curling. S. meliloti Nod factors, which are required for the infection process, induced wild-type epidermal nodulin gene expression and root hair deformation in hcl mutants, while Nod factor induction of cortical cell division foci was reduced compared to wild-type plants. Studies of the position of nuclei and of the microtubule cytoskeleton network of hcl mutants revealed that root hair, as well as cortical cells, were activated in response to S. meliloti. However, the asymmetric microtubule network that is typical of curled root hairs, did not form in the mutants, and activated cortical cells did not become polarised and did not exhibit the microtubular cytoplasmic bridges characteristic of the pre-infection threads induced by rhizobia in M. truncatula. These data suggest that hcl mutations alter the formation of signalling centres that normally provide positional information for the reorganisation of the microtubular cytoskeleton in epidermal and cortical cells.
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Pisano, G., A. Ritacco, A. Monfardini, C. Tucker, P. A. R. Ade, A. Shitvov, A. Benoit, et al. "Development and application of metamaterial-based half-wave plates for the NIKA and NIKA2 polarimeters." Astronomy & Astrophysics 658 (January 27, 2022): A24. http://dx.doi.org/10.1051/0004-6361/202038643.
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Context. Large field-of-view imaging and polarimetry instruments operating at millimetre and sub-millimetre wavelengths are fundamental tools to understand the role of magnetic fields in channelling filament material into prestellar cores, providing unique insight in the physics of galactic star-forming regions. Among other topics, at extra-galactic scales, polarisation observations of Active Galactic Nuclei (AGNs) will allow us to constrain the possible physical conditions of the emitting plasma from the jets and/or explore the physics of dust inside supernova remnants. The kilo-pixel New IRAM KIDs Array 2 (NIKA2) camera, installed today at the Institut de Radioastronomie Millimétrique (IRAM) 30-m telescope, represents one of the best tools available to astronomers to produce simultaneous intensity and polarimetry maps over large fields at 260 GHz (1.15 mm). Aims. The polarisation measurement, in NIKA and NIKA2, is achieved by rapidly modulating the total incoming polarisation. In the end, this allows one to safely isolate the small science signal from the large, un-polarised, and strongly variable, atmospheric background. Methods. The polarisation modulation is achieved by inserting a fast rotating half-wave plate (HWP) in the optical beam. In order to allow wide field-of-view observations, the plate has to be large, with a diameter of 250 mm. The modulation of the polarised signal at 12 Hz also requires the waveplate to be sufficiently light. In addition, this key optical element has to exhibit optimal electromagnetic characteristics in terms of transmission and differential phase-shift. For this purpose, three metamaterial HWPs have been developed using the mesh-filter technology. The knowledge acquired in developing the first two single-band HWPs was used to achieve the more challenging performance requirements of the last dual-band HWP. The first and the third waveplates met the requirements for both the NIKA and NIKA2 instruments. Results. We first illustrate the design, the technical developments, the fabrication, and laboratory characterisation of the three mesh-HWPs. The deployment of two such elements in the NIKA and NIKA2 instruments at the 30-metre telescope is then described. We conclude with representative examples of astrophysical maps integrating polarimetry.
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Dunin, V., A. Gribowsky, E. Kokoulina, A. Kutov, V. Nikitin, V. Riadovikov, R. Shulyakovsky, V. Volkov, and A. Vorobiev. "Collective phenomena in hadron and nuclear interactions at high multiplicity." EPJ Web of Conferences 206 (2019): 03001. http://dx.doi.org/10.1051/epjconf/201920603001.
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Multiparticle production is described in the language of quarks and gluons. In the experiment the real hadrons are registered. For transfer from quarks and gluons to observed hadrons, various phenomenological models are used. In order to describe the high multiplicity region, we have developed a gluon dominance model. It represents a convolution of two stages. First stage is described by QCD. For second one (hadronisation), the phenomenological model is used. The description of topological cross sections in p $ \bar p $ collisions within of our model testifies that in hadron collisions the mechanism of hadronisation is being replaced by the recombination one. At that point, gluons play an active role in the multiparticle production process, and valence quarks are passive. They stay in the leading particles, and only the gluon splitting is responsible for the region of high multiplicity. The model with inclusion of intermediate quark charged topologies describes topological cross sections in annihilation. We observe the significant growth of a scaled variance of number of neutral pions with increasing of the total multiplicity at U-70 accelerator at IHEP (Protvino). The following experiment with 3.5 A GeV deuteron, lithium and carbon beams of the Nuclotron (JINR, Dubna) falling at a carbon target is carried out at the NIS-GIBS setup. The noticeable excess yield of soft photons(pT < 50 MeV/c) is observed. The existing models based on Monte Carlo simulation and theoretical estimations predict a lower yield. Our Collaboration plans to study excess of soft photon yield and other phenomena at the SPD (Spin Physics Detector) setup at JINR, Dubna with polarised beams of proton and light nuclei up to 25 GeV.
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Pötzl, F. M., A. P. Lobanov, E. Ros, J. L. Gómez, G. Bruni, U. Bach, A. Fuentes, et al. "Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron." Astronomy & Astrophysics 648 (April 2021): A82. http://dx.doi.org/10.1051/0004-6361/202039493.
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Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. Methods. We observed the flat spectrum radio quasar 3C 345 at 1.6 GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Results. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300 μas angular resolution, corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest (u, v)-distances of 1.1 × 1012 K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be > 11 to explain the high brightness temperatures.
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Grosset, L., D. Rouan, F. Marin, D. Gratadour, E. Lagadec, S. Hunziker, M. Montargès, et al. "High angular resolution polarimetric imaging of the nucleus of NGC 1068." Astronomy & Astrophysics 648 (April 2021): A42. http://dx.doi.org/10.1051/0004-6361/202038260.
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Context. Polarisation is a decisive method to study the inner region of active galactic nuclei (AGNs) since, unlike classical imaging, it is not affected by contrast issues. When coupled with high angular resolution (HAR), polarisation can help to disentangle the location of the different polarising mechanisms and then give insight into the physics taking place in the core of AGNs. Aims. We obtained a new data set of HAR polarimetric images of the archetypal Seyfert 2 nucleus of NGC 1068 observed with SPHERE/VLT. We aim in this paper to present the polarisation maps and to spatially separate the location of the polarising mechanisms, thereby deriving constraints on the organisation of the dust material in the inner region of this AGN. Methods. With four new narrow-band images between the visible and the near-infrared combined with older broad-band observations, we studied the wavelength dependence of the polarisation properties from 0.7 to 2.2 μm of three selected regions within the inner 2″ surrounding the central engine. We then compared these measurements to radiative transfer simulations of scattering and dichroic absorption processes, using the Monte Carlo code MontAGN. Results. We establish a detailed table of the relative importance of the polarising mechanism as a function of aperture and wavelength. We are able to separate the dominant polarising mechanisms in the three regions of the ionisation cone, the extended envelope of the torus, and the very central bright source of the AGN. Thus, we estimate the contribution of the different polarisation mechanisms to the observed polarisation flux in these regions. Dichroic absorption is estimated to be responsible for about 99% of the polarised flux coming from the photo-centre. However, this contribution would only be restricted to this location because the double-scattering process would be the most important contributor to polarisation in the equatorial plane of the AGN and single scattering is dominant in the polar outflow bi-cone. Conclusions. Even though results are in good agreement with larger apertures measurements, the variety of situations with different mechanisms at play highlights the importance of spatial resolution for the interpretation of polarisation measurements. We also refine the estimation of the integrated optical depth in the visible of the obscuring structure to a range of 20−100, constraining the geometry of the inner region of this AGN.
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Lico, R., J. Liu, M. Giroletti, M. Orienti, J. L. Gómez, B. G. Piner, N. R. MacDonald, F. D’Ammando, and A. Fuentes. "A parsec-scale wobbling jet in the high-synchrotron peaked blazar PG 1553+113." Astronomy & Astrophysics 634 (February 2020): A87. http://dx.doi.org/10.1051/0004-6361/201936564.
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Context. The detection of quasi-periodic variability in active galactic nuclei in general, and in blazars in particular, is key to our understanding of the origin and nature of these objects as well as their cosmological evolution. PG 1553+113 is the first blazar showing an approximately two-year quasi-periodic pattern in its γ-ray light curve, which is also revealed at optical frequencies. Aims. Such quasi-periodicity might have a geometrical origin, possibly related to the precessing nature of the jet, or could be intrinsic to the source and related to pulsational accretion flow instabilities. In this work we investigate and characterise the high-resolution radio emission properties of PG 1553+113 on parsec scales in order to differentiate between these different physical scenarios. Methods. We monitored the source with the very long baseline array (VLBA) at 15, 24, and 43 GHz during an entire cycle of γ-ray activity in the period 2015–2017, with a cadence of about 2 months, both in total and polarised intensity. We constrained the jet position angle across the different observing epochs by investigating the total intensity ridge lines. Results. We find a core-dominated source with a limb-brightened jet structure extending for ∼1.5 mas in the northeast direction whose position angle varies in time in the range ∼40°−60°. No clear periodic pattern can be recognized in the VLBA light curves during 2015–2017 or in the 15 GHz Owens Valley Radio Observatory light curve during the period 2008–2018. The core region polarisation percentage varies in the range ∼1−4%, and the polarisation angle varies from being roughly parallel to roughly transverse to the jet axis. We estimate a rotation measure value in the core region of ∼−1.0 ± 0.4 × 104 rad m−2. The brightness temperature (TB) is found to decrease as the frequency increases with an intrinsic value of ∼1.5 × 1010 K and the estimated Doppler factor is ∼1.4. Conclusions. Although the jet wobbling motion indicates that geometrical effects can produce an enhanced emission through the Doppler boosting modulation, additional mechanisms are required in order to account for the quasi-periodic variability patterns observed in γ rays. The intrinsic TB value indicates that the total energy in the core region is dominated by the magnetic field.
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Prior, Christopher, and Konstantinos N. Gourgouliatos. "Observational signatures of magnetic field structure in relativistic AGN jets." Astronomy & Astrophysics 622 (February 2019): A122. http://dx.doi.org/10.1051/0004-6361/201834469.
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Context. Active galactic nuclei (AGN) launch highly energetic jets sometimes outshining their host galaxy. These jets are collimated outflows that have been accelerated near a supermassive black hole located at the centre of the galaxy. Their, virtually indispensable, energy reservoir is either due to gravitational energy released from accretion or due to the extraction of kinetic energy from the rotating supermassive black hole itself. In order to channel part of this energy to the jet, though, the presence of magnetic fields is necessary. The extent to which these magnetic fields survive in the jet further from the launching region is under debate. Nevertheless, observations of polarised emission and Faraday rotation measure confirm the existence of large scale magnetic fields in jets. Aims. Various models describing the origin of the magnetic fields in AGN jets lead to different predictions about the large scale structure of the magnetic field. In this paper we study the observational signatures of different magnetic field configurations that may exist in AGN jets in order to asses what kind of information regarding the field structure can be obtained from radio emission, and what would be missed. Methods. We explore three families of magnetic field configurations. First, a force-free helical magnetic field corresponding to a dynamically relaxed field in the rest frame of the jet. Second, a magnetic field with a co-axial cable structure arising from the Biermann-battery effect at the accretion disk. Third, a braided magnetic field that could be generated by turbulent motion at the accretion disk. We evaluate the intensity of synchrotron emission, the intrinsic polarization profile and the Faraday rotation measure arising from these fields. We assume that the jet consists of a relativistic spine where the radiation originates from and a sheath containing thermalised electrons responsible for the Faraday screening. We evaluate these values for a range of viewing angles and Lorentz factors. We account for Gaussian beaming that smooths the observed profile. Results. Radio emission distributions from the jets with dominant large-scale helical fields show asymmetry across their width. The Faraday rotation asymmetry is the same for fields with opposing chirality (handedness). For jets which are tilted towards the observer the synchrotron emission and fractional polarization can distinguish the field’s chirality. When viewed either side-on or at a Blazar type angle only the fractional polarization can make this distinction. Further this distinction can only be made if the direction of the jet propagation velocity is known, along with the location of the jet’s origin. The complex structure of the braided field is found not to be observable due to a combination of line of sight integration and limited resolution of observation. This raises the possibility that, even if asymmetric radio emission signatures are present, the true structure of the field may still be obscure.
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GLATTLI, H. "Polarised nuclei for neutron science: recent applications and perspectives." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, May 2004. http://dx.doi.org/10.1016/s0168-9002(04)00894-0.
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