| 1. |
- Rodriguez, D., et al.
(författare)
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MATS and LaSpec : High-precision experiments using ion traps and lasers at FAIR
- 2010
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Ingår i: The European physical journal. Special topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 183, s. 1-123
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Forskningsöversikt (refereegranskat)abstract
- Nuclear ground state properties including mass, charge radii, spins and moments can be determined by applying atomic physics techniques such as Penning-trap based mass spectrometry and laser spectroscopy. The MATS and LaSpec setups at the low-energy beamline at FAIR will allow us to extend the knowledge of these properties further into the region far from stability. The mass and its inherent connection with the nuclear binding energy is a fundamental property of a nuclide, a unique ""fingerprint"". Thus, precise mass values are important for a variety of applications, ranging from nuclear-structure studies like the investigation of shell closures and the onset of deformation, tests of nuclear mass models and mass formulas, to tests of the weak interaction and of the Standard Model. The required relative accuracy ranges from 10(-5) to below 10(-8) for radionuclides, which most often have half-lives well below 1 s. Substantial progress in Penning trap mass spectrometry has made this method a prime choice for precision measurements on rare isotopes. The technique has the potential to provide high accuracy and sensitivity even for very short-lived nuclides. Furthermore, ion traps can be used for precision decay studies and offer advantages over existing methods. With MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly-charged ions) at FAIR we aim to apply several techniques to very short-lived radionuclides: High-accuracy mass measurements, in-trap conversion electron and alpha spectroscopy, and trap-assisted spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high-precision Penning trap system for mass measurements and decay studies. For the mass measurements, MATS offers both a high accuracy and a high sensitivity. A relative mass uncertainty of 10(-9) can be reached by employing highly-charged ions and a non-destructive Fourier-Transform Ion-Cyclotron-Resonance (FT-ICR) detection technique on single stored ions. This accuracy limit is important for fundamental interaction tests, but also allows for the study of the fine structure of the nuclear mass surface with unprecedented accuracy, whenever required. The use of the FT-ICR technique provides true single ion sensitivity. This is essential to access isotopes that are produced with minimum rates which are very often the most interesting ones. Instead of pushing for highest accuracy, the high charge state of the ions can also be used to reduce the storage time of the ions, hence making measurements on even shorter-lived isotopes possible. Decay studies in ion traps will become possible with MATS. Novel spectroscopic tools for in-trap high-resolution conversion-electron and charged-particle spectroscopy from carrier-free sources will be developed, aiming e. g. at the measurements of quadrupole moments and E0 strengths. With the possibility of both high-accuracy mass measurements of the shortest-lived isotopes and decay studies, the high sensitivity and accuracy potential of MATS is ideally suited for the study of very exotic nuclides that will only be produced at the FAIR facility. Laser spectroscopy of radioactive isotopes and isomers is an efficient and model-independent approach for the determination of nuclear ground and isomeric state properties. Hyperfine structures and isotope shifts in electronic transitions exhibit readily accessible information on the nuclear spin, magnetic dipole and electric quadrupole moments as well as root-mean-square charge radii. The dependencies of the hyperfine splitting and isotope shift on the nuclear moments and mean square nuclear charge radii are well known and the theoretical framework for the extraction of nuclear parameters is well established. These extracted parameters provide fundamental information on the structure of nuclei at the limits of stability. Vital information on both bulk and valence nuclear properties are derived and an exceptional sensitivity to changes in nuclear deformation is achieved. Laser spectroscopy provides the only mechanism for such studies in exotic systems and uniquely facilitates these studies in a model-independent manner. The accuracy of laser-spectroscopic-determined nuclear properties is very high. Requirements concerning production rates are moderate; collinear spectroscopy has been performed with production rates as few as 100 ions per second and laser-desorption resonance ionization mass spectroscopy (combined with beta-delayed neutron detection) has been achieved with rates of only a few atoms per second. This Technical Design Report describes a new Penning trap mass spectrometry setup as well as a number of complementary experimental devices for laser spectroscopy, which will provide a complete system with respect to the physics and isotopes that can be studied. Since MATS and LaSpec require high-quality low-energy beams, the two collaborations have a common beamline to stop the radioactive beam of in-flight produced isotopes and prepare them in a suitable way for transfer to the MATS and LaSpec setups, respectively.
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| 2. |
- Afanaciev, K.G., et al.
(författare)
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Investigation of the radiation hardness of GaAs sensors in an electron beam
- 2012
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- A compact and finely grained sandwich calorimeter is designed to instrument the very forward region of a detector at a future e+e- collider. The calorimeter will be exposed to low energy e+e - pairs originating from beamstrahlung, resulting in absorbed doses of about one MGy per year. GaAs pad sensors interleaved with tungsten absorber plates are considered as an option for this calorimeter. Several Cr-doped GaAs sensor prototypes were produced and irradiated with 8.5-10 MeV electrons up to a dose of 1.5 MGy. The sensor performance was measured as a function of the absorbed dose.
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| 3. |
- Anisimov, Vladimir N., et al.
(författare)
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Effects of the mitochondria-targeted antioxidant SkQ1 on lifespan of rodents
- 2011
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Ingår i: Aging. - 1945-4589 .- 1945-4589. ; 3:11, s. 1110-1119
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the mitochondria-targeted, plastoquinone-containing antioxidant SkQ1 on the lifespan of outbred mice and of three strains of inbred mice was studied. To this end, low pathogen (LP) or specific pathogen free (SPF) vivaria in St. Petersburg, Moscow, and Stockholm were used. For comparison, we also studied mole-voles and dwarf hamsters, two wild species of small rodents kept under simulated natural conditions. It was found that substitution of a LP vivarium for a conventional (non-LP) one doubled the lifespan of female outbred mice, just as SkQ1 did in a non-LP vivarium. SkQ1 prevented age-dependent disappearance of estrous cycles of outbred mice in both LP and non-LP vivaria. In the SPF vivarium in Moscow, male BALB/c mice had shorter lifespan than females, and SkQ1 increased their lifespan to the values of the females. In the females, SkQ1 retarded development of such trait of aging as heart mass increase. Male C57Bl/6 mice housed individually in the SPF vivarium in Stockholm lived as long as females. SkQ1 increased the male lifespan, the longevity of the females being unchanged. SkQ1 did not change food intake by these mice. Dwarf hamsters and mole-voles kept in outdoor cages or under simulated natural conditions lived longer if treated with SkQ1. The effect of SkQ1 on longevity of females is assumed to mainly be due to retardation of the age-linked decline of the immune system. For males under LP or SPF conditions, SkQ1 increased the lifespan, affecting also some other system(s) responsible for aging.
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| 4. |
- Valitova, Yu. N., et al.
(författare)
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Binding of sterols affects membrane functioning and sphingolipid composition in wheat roots.
- 2010
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Ingår i: Biochemistry (Moscow). - 0006-2979 .- 1608-3040. ; 75:5, s. 554-561
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Tidskriftsartikel (refereegranskat)abstract
- The present work was devoted to the exploration of the role of sterols in the functioning of membranes in root cells. Membrane characteristics and composition of the membrane lipids in the roots of wheat (Triticum aestivum L.) seedlings treated with exogenous cholesterol and antibiotic nystatin, which specifically binds with endogenous sterols, were analyzed. Cholesterol caused a fall of membrane potential, acidification of the incubation medium, decrease in potassium leakage of roots, and increase in the level of exogenous superoxide radical. Similarly to cholesterol, the application of nystatin also induced the depolarization of the plasma membrane, but in contrast with cholesterol it was accompanied by alkalinization of the incubation medium and decrease in the level of exogenous superoxide radical. Analysis of membrane lipids showed that following nystatin treatment the total sterol content in roots did not change, while the level of complex sphingolipids represented mainly by glycoceramides became higher. Using mass spectrometry with electrospray ionization (+ESI-MS) for the analysis of the glycoceramide composition, we showed that nystatin induced changes in the ratios of molecular species of glycoceramides. It was suggested that the modification of the sterol component of plasma membrane could influence membrane functioning by changing the sphingolipid composition of lipid rafts.
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| 5. |
- Christensen, Sören, 1982, et al.
(författare)
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An elementary approach to optimal stopping problems for AR(1) sequences
- 2011
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Ingår i: Sequential Analysis. - : Informa UK Limited. - 0747-4946 .- 1532-4176. ; 30:1, s. 79-93
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Tidskriftsartikel (refereegranskat)abstract
- Optimal stopping problems form a class of stochastic optimization problems that has a wide range of applications in sequential statistics and mathematical finance. Here we consider a general optimal stopping problem with discounting for autoregressive processes. Our strategy for a solution consists of two steps: First we give elementary conditions to ensure that an optimal stopping time is of threshold type. Then the resulting one-dimensional problem of finding the optimal threshold is to be solved explicitly. The second step is carried out for the case of exponentially distributed innovations. © Taylor & Francis Group, LLC.
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| 6. |
- Dumanov, E. V., et al.
(författare)
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Mixed exciton-plasmon collective elementary excitations of the Bose-Einstein condensed two-dimensional magnetoexcitons with motional dipole moments
- 2013
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 250:1, s. 115-127
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Tidskriftsartikel (refereegranskat)abstract
- The collective elementary excitations of the two-dimensional (2D) magnetoexcitons in the state of their BoseEinstein condensation (BEC) with nonzero wave vector k and inplane parallel oriented motional dipole moments are investigated in the HartreeFockBogoliubov approximation (HFBA). The breaking of the gauge symmetry is achieved using the Bogoliubov theory of quasiaverages and the KeldyshKozlovKopaev (KKK) method. The starting Hamiltonian and the Green's functions are determined using the integral two-particle operators instead of the single-particle Fermi operators. The infinite chains of equations of motion for the multioperator four- and six-particle Green-s functions are truncated following the Zubarev method and introducing a small parameter of the perturbation theory related with the lowest Landau levels (LLLs) filling factor and with the phase-space filling factor. The energy spectrum of the collective elementary excitations consists of the mixed excitonplasmon energy braches, mixed excitonplasmon quasienergy branches as well as the optical and acoustical plasmon energy branches. The exciton branches of the spectrum have gaps related with the negative values of the chemical potential and attractive interaction between the 2D megnetoexcitons with inplane, parallel oriented motional dipole moments. The slopes of the mixed excitonplasmon branches are determined by the group velocities of the moving condensed excitons in the laboratory reference frame. The acoustical and optical plasmon energy branches are gapless. Their dependence on the small wave vectors accounted from the condensate wave vector k is linear and quadratic, respectively, with saturation in the range of high values of the wave vectors.
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| 7. |
- Moskalenko, Sveatoslav A., et al.
(författare)
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Two-dimensional magnetoexciton-polariton
- 2012
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Ingår i: JOURNAL OF NANOPHOTONICS. - 1934-2608. ; 6, s. 061806-
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Tidskriftsartikel (refereegranskat)abstract
- The Hamiltonian describing the interaction of the two-dimensional (2-D) magnetoexcitons with photons propagating with arbitrary-oriented wave vectors in the three-dimensional (3-D) space is deduced. The magnetoexcitons are characterized by the numbers n(e) and n(h) of the electron and hole Landau quantizations, by circular polarization (sigma) over right arrow (M) of the holes in the p-type valence bands and by in-plane wave vectors (k) over right arrow (parallel to). The photons are characterized by the wave vectors (k) over right arrow with in-plane component (k) over right arrow (parallel to) and perpendicular component k(z), which is quantized in the case of microresonator. The interaction is governed by the conservation law of the in-plane components (k) over right arrow (parallel to)of the magnetoexcitons and photons and by the rotational symmetry around the axis perpendicular to the layer, which leads to the alignment of the magnetoexcitons under the influence of the photons with circular polarization (sigma) over right arrow (+/-)((k) over right arrow) and with probability proportional to vertical bar (sigma) over right arrow (+/-)((k) over right arrow) . (sigma) over right arrow (M)*vertical bar(2.)
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