957 research outputs found
The 35S U5 snRNP is generated from the activated spliceosome during In vitro splicing
Primary gene transcripts of eukaryotes contain introns, which are removed during processing by splicing machinery. Biochemical studies In vitro have identified a specific pathway in which introns are recognised and spliced out. This occurs by progressive formation of spliceosomal complexes designated as E, A, B, and C. The composition and structure of these spliceosomal conformations have been characterised in many detail. In contrast, transitions between the complexes and the intermediates of these reactions are currently less clear. We have previously isolated a novel 35S U5 snRNP from HeLa nuclear extracts. The protein composition of this particle differed from the canonical 20S U5 snRNPs but was remarkably similar to the activated B* spliceosomes. Based on this observation we have proposed a hypothesis that 35S U5 snRNPs represent a dissociation product of the spliceosome after both transesterification reactions are completed. Here we provide experimental evidence that 35S U5 snRNPs are generated from the activated B* spliceosomes during In vitro splicing
Spin-transfer mechanism of ferromagnetism in polymerized fullerenes: calculations
A mechanism of the high temperature ferromagnetism in polymerized fullerenes
is suggested. It is assumed that some of the C molecules in the crystal
become magnetically active due to spin and charge transfer from the
paramagnetic impurities (atoms or groups), such as hydrogen, fluorine, hydroxyl
group OH, amino group NH, or methyl group CH, dispersed in the
fullerene matrix. The exchange interaction between the spins localized on the
magnetically active fullerenes is evaluated using \textit{ab initio}
calculations. The nearest neighbour and next nearest neighbour exchange
interaction is found to be in the range eV, that is, high enough
to account for the room temperature ferromagnetism.Comment: typos corrected, 8 pages, 3 figures, LaTe
Surface photometry of new nearby dwarf galaxies
We present CCD surface photometry of 16 nearby dwarf galaxies, many of which
were only recently discovered. Our sample comprises both isolated galaxies and
galaxies that are members of nearby galaxy groups. The observations were
obtained in the Johnson B and V bands (and in some cases in Kron-Cousins I). We
derive surface brightness profiles, total magnitudes, and integrated colors.
For the 11 galaxies in our sample with distance estimates the absolute B
magnitudes lie in the range of -10>Mb>-13. The central surface brightness
ranges from 22.5 to 27.0 mag/sq.arcsec. Most of the dwarf galaxies show
exponential light profiles with or without a central light depression.
Integrated radial color gradients, where present, appear to indicate a more
centrally concentrated younger population and a more extended older population.Comment: accepted by A&
Tidal dwarfs in the M81 group: the second generation?
We derive quantitative star formation histories of the four suspected tidal
dwarf galaxies in the M81 group, HolmbergIX, BK3N, Arp-loop (A0952+69), and
Garland, using Hubble Space Telescope/Wide Field Planetary Camera2 images in
F606W and F814W obtained as part of a Snapshot survey of dwarf galaxies in the
Local Universe. We consider the spatial distribution and ages of resolved
stellar populations in these dwarf irregular galaxies. We use synthetic
color-magnitude diagrams to derive the ages of the major star formation
episodes, star formation rates, and approximate metallicity ranges. All the
galaxies show evidence of continuous star formation between about 20 and 200
Myr ago with star formation rates in the range 7.5*10^(-3)- 7.6*10^(-4)
M(sun)/yr. The metallicity of the detected stars spans a wide range, and have
lower than solar abundance. A possible scenario is that all four dwarf galaxies
were formed from material in the metal-poor outer part of the giant spiral
galaxy M81 after the tidal interaction between M81, M82, and NGC3077 about 200
Myr ago. While we do not directly detect pronounced old stellar populations,
the photometric limits of our data are such that the presence of such a
population is not entirely ruled out
Localized States at Zigzag Edges of Multilayer Graphene and Graphite Steps
We report the existence of zero energy surface states localized at zigzag
edges of -layer graphene. Working within the tight-binding approximation,
and using the simplest nearest-neighbor model, we derive the analytic solution
for the wavefunctions of these peculiar surface states. It is shown that zero
energy edge states in multilayer graphene can be divided into three families:
(i) states living only on a single plane, equivalent to surface states in
monolayer graphene; (ii) states with finite amplitude over the two last, or the
two first layers of the stack, equivalent to surface states in bilayer
graphene; (iii) states with finite amplitude over three consecutive layers.
Multilayer graphene edge states are shown to be robust to the inclusion of the
next nearest-neighbor interlayer hopping. We generalize the edge state solution
to the case of graphite steps with zigzag edges, and show that edge states
measured through scanning tunneling microscopy and spectroscopy of graphite
steps belong to family (i) or (ii) mentioned above, depending on the way the
top layer is cut.Comment: 6 pages, 4 figure
Higher Fano manifolds
In this paper we address Fano manifolds with positive higher Chern characters. They are expected to enjoy stronger versions of several of the nice properties of Fano manifolds. For instance, they should be covered by higher dimensional rational varieties, and families of higher Fano manifolds over higher dimensional bases should admit meromorphic sections (modulo the Brauer obstruction). Aiming at finding new examples of higher Fano manifolds, we investigate positivity of higher Chern characters of rational homogeneous spaces. We determine which rational homogeneous spaces of Picard rank have positive second Chern character, and show that the only rational homogeneous spaces of Picard rank having positive second and third Chern characters are projective spaces and quadric hypersurfaces. We also classify Fano manifolds of large index having positive second and third Chern characters. We conclude by discussing conjectural characterizations of projective spaces and complete intersections in terms of these higher Fano conditions
Endocrine Disorders Associated with Medicinal Products: Approaches to Preclinical Safety Assessment
The endocrine system coordinates almost all organs and other systems in vertebrates. In particular, it regulates such important biological functions as metabolism, development, reproduction, and behaviour. To date, a significant amount of information has accumulated on endocrine disorders associated with chemical compounds (endocrine disruptors) used in various fields of human activity. The aim of this study was to evaluate the possibility of preclinical risk assessment for the endocrine function disorders attributable to new medicinal products. Endocrine disruptors are associated with a wide range of adverse events, including developmental problems arising from functional abnormalities of the endocrine system. Endocrine disorders caused by endocrine-disrupting chemicals are characterised by a long latency period between exposure and manifestation of a dysfunction; a nonlinear dose–response relationship; and a linear correlation of damage severity to exposure timing and duration. The chemicals influence the endocrine system through multiple mechanisms, the main of which being the interaction with cellular receptors sensitive to certain hormones and the influence on gene expression, intracellular signalling, and hormone transport, etc. This paper discusses the possibility of using hormone levels as indicators of endocrine disruption and presents the literature and authors’ own data on normal levels of relevant hormones in the blood of animals. An analysis of animal blood hormone levels in preclinical programmes will provide an opportunity to evaluate potential iatrogenic risks
Interaction Between Superconducting and Ferromagnetic Order Parameters in Graphite-Sulfur Composites
The superconductivity of graphite-sulfur composites is highly anisotropic and
associated with the graphite planes. The superconducting state coexists with
the ferromagnetism of pure graphite, and a continuous crossover from
superconducting to ferromagnetic-like behavior could be achieved by increasing
the magnetic field or the temperature. The angular dependence of the magnetic
moment m(alpha) provides evidence for an interaction between the ferromagnetic
and the superconducting order parameters.Comment: 11 pages, 4 figures, to be published in Phys. Rev.
Circular Economy and Environmental Safety in a New Social Reality
The problem of ensuring environmental safety in our country in the conditions of increasing macroeconomic instability and risks in the sphere of national and world economy puts on the agenda the need to move to a new model of social and economic development - "circular economy"or "closed-loop economy". This model makes it possible to minimize the external negative effects on the part of economic entities and their impact on the environment and, conversely, the consequences of man-made externalities in the environment on the human. In this regard, the analysis and assessment of such a relationship between the economy and the environment, as well as the identification and assessment of these externalities, make it possible to formulate a number of recommendations to strengthen environmental safety and transition to a qualitatively new type of sustainable development. © Published under licence by IOP Publishing Ltd
«Green Economy», Nuclear Energy and "Natural Capitalism": Dialectics of Development
The article reveals the content of the concepts of "green economy"and "natural capitalism", the history of their appearance in science and the modern semantic context. The role of the idea of coevolution of the modern biosphere and the processes of transformation of traditional biogeocenoses into anthropobiogeocenoses with a decisive human influence in them is revealed. The risks of nuclear energy development and the state of the "green economy"are compared. The necessity of a more active formation of a new type of economy - an ecological economy that meets the tasks of reproduction of the natural environment is put forward and justified. The initial step on this path should be the adoption of the "Environmental Code"of the Russian Federation and the humanitarian reformatting of the thinking of the person based on ecological culture and ecological consciousness. © Published under licence by IOP Publishing Ltd
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