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The aim of this paper is to study the group of elliptic units of a cyclic extension
of an imaginary quadratic field
such that the degree
is a power of an odd prime
. We construct an explicit root of the usual top generator of this group, and we use it to obtain an annihilation result of the
-Sylow subgroup of the ideal class group of
Samples of graphite from a RBMK-1500 reactor at the Ignalina Nuclear Power Plant from different construction elements (stack, sleeve, and bushing) were analyzed by the instrumental neutron activation analysis (INAA) method (LVR-15 experimental reactor of the Research Centre Řež, Ltd.) using the prompt gamma activation analysis (PGAA) method (Heinz Maier-Leibnitz Zentrum) and with an inductively coupled plasma mass spectrometer (ICP-MS) (CPST, Lithuania). These measurements were performed with the aim of obtaining the missing information on the impurity distribution in the RBMK-type nuclear graphite constructions as well as for intercomparison purposes, with the results measured in the graphite sleeve samples previously obtained by INAA & GDMS (Glow Discharge Mass Spectrometry) at CEA Saclay, France, and ICP-MS (CPST, Lithuania) methods. Validation of the ICP-MS method for the nuclear graphite impurity concentration determination was proven. The experimentally obtained RBMK-1500 graphite impurity values in different graphite constructions were compared with other measurements and new limits of the possible maximal concentrations of nuclear RBMK graphite impurity concentrations were obtained.
While SrTiO3 exhibits promising electronic transport properties, its high thermal conductivity (κ) is detrimental for its use as a thermoelectric material. Here, we investigate the influence of oxygen non-stoichiometry on κ in bulk SrTiO3 ceramics. A significant reduction in κ was achieved in oxygen deficient SrTiO3−δ, owing to the presence of oxygen vacancies that act as phonon scattering centers. Upon oxidation of SrTiO3−δ, the κ of pristine SrTiO3 was recovered, suggesting that oxygen vacancies were indeed responsible for the reduction in κ. Raman spectroscopy was used as an independent tool to confirm the reduction of oxygen vacancies in SrTiO3−δ upon oxidation.
An investigation of a solar plage based on observations of UV, visible, and IR spectral lines is presented. Using model calculations, we have established distributions of the main physical parameters (temperature, density, turbulent velocity) in both plage and quiet-Sun atmospheres. Details of the models are presented and the role of magnetic pressure is discussed.
During the June 1996 campaign using the MSDP spectrograph at Pic du Midi and SUMER/CDS (JOP 12) on board SOHO, quiescent prominences were observed. We present observations and physical quantities of the June 5 prominence. Doppler shifts, temperatures and electron densities of fine structures were deduced from Hα data.
An arch-shaped prominence was observed with SUMERSOHO spectrometer on March 31–April 1, 1996. The observations were performed at three wavelengths in the Lyman continuum. Ten successive images were obtained at 41 minute time intervals. Based on the computed models of Gouttebroze-Heinzel-Vial we have determined the temperature distribution of the prominence using the intensity ratio of 876 Å and 907 Å. The observed time sequence shows that the prominence disappears by heating, i.e., ionization of hydrogen: a thermal DB. We model the heat input with the linearized MHD equations using a prescribed initial density and a broad-band spectrum of Alfvén waves and find a good qualitative agreement with observations. In the model the prominence is heated by the resonant absorption of Alfvén waves with frequencies that match the resonant condition for a particular flux tube structure that is determined by the magnetic field topology and density.
On September 21, 1996 a filament located in a region close to an enhanced network was observed with the SOHO SUMER and CDS instruments. Four Lyman lines have been detected (Lδ, Lϵ, L-6, L-7) by SUMER in the raster mode. We have corrected the spectral data for flatfield and destreching and made wavelength and absolute intensity calibrations. In all these lines we detect a central absorption and an asymmetry in the intensity of the two peaks. Preliminary NLTE computations indicate that these Lyman profiles and their absolute intensities can be reproduced with the existing models provided that we take into account a prominence-corona transition region (PCTR).
SOHO (SUMER/CDS) observed an eruptive prominence on May 1,1996, associated with a CME observed by LASCO. We investigate the physical conditions of this prominence in order to quantify velocity, temperature, and density. SUMER spectra in Si IV and O IV lines are used to obtain Doppler-shift images of the prominence. The prominence shows large-scale red and blueshifted regions, revealing a large helical structure with a global twist. In addition, fine structure analysis shows multiple components in the line profile, suggesting integration of many threads along the line-of-sight with a large dispersion of velocities (±50 km s−1).
During the September 1996 campaign of multi-wavelength observations with the SOHO (SUMER, CDS, EIT, MDI, LASCO) and Yohkoh (SXT) spacecraft, the HAO Mauna Loa Solar Observatory Chromospheric Helium Imaging Photometer and the Nobeyama radioheliograph, a filament disparition brusque (DB) associated with a Coronal Mass Ejection (CME) was observed. The timeline of this complex event, which lasted for tens of hours, shows that the CME had started before the DB of a filament, while the main “bubble” of the CME was probably launched hours after the DB from the so-called “zipper” region. All these suggest that a general reorganization of large-scale fields was taking place on the Sun, and both the DB and the CME were symptoms of this.
Previous genetic studies of extant planktonic foraminifera have provided evidence that the traditional, strictly morphological definition of species in these organisms underestimates their biodiversity. Here, we report the first case where this pattern is reversed. The modern (sub)tropical species plexus Globigerinoides sacculifer is characterized by large morphological variability, which has led to the proliferation of taxonomic names attributed to morphological end-members within the plexus. In order to clarify the taxonomic status of its morphotypes and to investigate the genetic connectivity among its currently partly disjunct (sub)tropical populations, we carried out a global survey of two ribosomal RNA regions (SSU and ITS-1) in all recent morphotypes of the plexus collected throughout (sub)tropical surface waters of the global ocean. Unexpectedly, we find an extremely reduced genetic variation within the plexus and no correlation between genetic and morphological divergence, suggesting taxonomical overinterpretation. The genetic homogeneity within the morphospecies is unexpected, considering its partly disjunct range in the (sub)tropical Atlantic and Indo-Pacific and its old age (early Miocene). A sequence variant in the rapidly evolving ITS-1 region indicates the existence of an exclusively Atlantic haplotype, which suggests an episode of relatively recent (last glacial) isolation, followed by subsequent resumption of unidirectional gene flow from the Indo-Pacific into the Atlantic. This is the first example in planktonic foraminifera where the morphological variability in a morphospecies exceeds its rDNA genetic variability. Such evidence for inconsistent scaling of morphological and genetic diversity in planktonic foraminifera could complicate the interpretation of evolutionary patterns in their fossil record.
Although the impact of Thompson’s work outside the UK has been recognized and pointed to many times, the ways in which Thompsonian categories and concepts, or Marxist thought from the West more broadly, was received in the countries of the former Eastern Bloc remain rather unclear. Although The Making has never been translated into Polish, Czech, or Slovak, the historians of East-Central European countries were not totally cut off from Western scholarship. Major academic institutes and universities throughout the communist bloc maintained basic contacts with colleagues in the West, and Thompson’s work was known among some local social historians. Marxism from the West in general and Thompson’s work in particular posed challenges that had to be dealt with. This paper traces the ways in which historians of Poland and Czechoslovakia responded to these challenges to the official position of Marxist orthodoxy. Taking The Making as an example, it highlights the reception (or lack thereof) of Western influences on local scholarship, and the dynamics of these encounters – whether they were affirmative or critical – in relation to the changing political landscape of East-Central European countries after World War II.
Morphological evolution in the Late Cretaceous (Maastrichtian) Contusotruncana lineage of planktonic foraminifera was studied at DSDP Sites 525 (South Atlantic) and 384 (North Atlantic). A multivariable approach was used to separate aspects of form controlled by geographical variation (size, spiral roundness of the test, percentage of kummerform specimens) from those due to changes that occurred simultaneously in geographically distant populations of the lineage (shell conicity, number of chambers in the last whorl).
A gradual increase in mean shell conicity was observed over the last 3 million years of the Cretaceous. It arose from the combination of a rapid development of highly conical shells after 68.5 Ma and a long-term trend of progressive disappearance of the ancestral morphotype. Therefore, despite the gradual change in “mean form,” the morphological evolution in the Contusotruncana lineage differs from the classical image of phyletic gradualism. The gradual increase in mean shell conicity in the lineage was accompanied by a remarkable decrease in its absolute abundance (shell accumulation rate), suggesting that the changes in shell morphology might not have been neutral with respect to natural selection. Apparently, gradual change in “mean form” of fossil lineages does not require an equally gradual development of morphological novelties. It may be caused by natural selection operating on a constant range of variation in populations living in environments without geographical barriers.
Osvald Demuth (1936–1988) studied constructive analysis from the viewpoint of the Russian school of constructive mathematics. In the course of his work he introduced various notions of effective null set which, when phrased in classical language, yield a number of major algorithmic randomness notions. In addition, he proved several results connecting constructive analysis and randomness that were rediscovered only much later.
In this paper, we trace the path that took Demuth from his constructivist roots to his deep and innovative work on the interactions between constructive analysis, algorithmic randomness, and computability theory. We will focus specifically on (i) Demuth’s work on the differentiability of Markov computable functions and his study of constructive versions of the Denjoy alternative, (ii) Demuth’s independent discovery of the main notions of algorithmic randomness, as well as the development of Demuth randomness, and (iii) the interactions of truth-table reducibility, algorithmic randomness, and semigenericity in Demuth’s work.
Large-amplitude longitudinal (LAL) prominence oscillations consist of periodic mass motions along a filament axis. The oscillations appear to be triggered by an energetic event, such as a microflare, subflare, or small C-class flare, close to one end of the filament. Observations reveal speeds of several tens to 100 km/s, periods of order 1 hr, damping times of a few periods, and displacements equal to a significant fraction of the prominence length. We have developed a theoretical model to explain the restoring force and the damping mechanism. Our model demonstrates that the main restoring force is the projected gravity in the flux tube dips where the threads oscillate. Although the period is independent of the tube length and the constantly growing mass, the motions are strongly damped by the steady accretion of mass onto the threads. We conclude that the LAL movements represent a collective oscillation of a large number of cool, dense threads moving along dipped flux tubes, triggered by a nearby energetic event. Our model yields a powerful seismological method for constraining the coronal magnetic field strength and radius of curvature at the thread locations.
On 20 August 2010 an energetic disturbance triggered damped large-amplitude longitudinal (LAL) oscillations in almost an entire filament. In the present work we analyze this periodic motion in the filament to characterize the damping and restoring mechanism of the oscillation. Our method involves placing slits along the axis of the filament at different angles with respect to the spine of the filament, finding the angle at which the oscillation is clearest, and fitting the resulting oscillation pattern to decaying sinusoidal and Bessel functions. These functions represent the equations of motion of a pendulum damped by mass accretion. With this method we determine the period and the decaying time of the oscillation. Our preliminary results support the theory presented by Luna and Karpen (2012) that the restoring force of LAL oscillations is solar gravity in the tubes where the threads oscillate, and the damping mechanism is the ongoing accumulation of mass onto the oscillating threads. Following an earlier paper, we have determined the magnitude and radius of curvature of the dipped magnetic flux tubes hosting a thread along the filament, as well as the mass accretion rate of the filament threads, via the fitted parameters.