1,693 research outputs found
Nature of eclipsing pulsars
We present a model for pulsar radio eclipses in some binary systems, and test
this model for PSRs B1957+20 and J2051-0827. We suggest that in these binaries
the companion stars are degenerate dwarfs with strong surface magnetic fields.
The magnetospheres of these stars are permanently infused by the relativistic
particles of the pulsar wind. We argue that the radio waves emitted by the
pulsar split into the eigenmodes of the electron-positron plasma as they enter
the companion's magnetosphere and are then strongly damped due to cyclotron
resonance with the ambient plasma particles. Our model explains in a natural
way the anomalous duration and behavior of radio eclipses observed in such
systems. In particular, it provides stable, continuous, and frequency-dependent
eclipses, in agreement with the observations. We predict a significant
variation of linear polarization both at eclipse ingress and egress. In this
paper we also suggest several possible mechanisms of generation of the optical
and -ray emission observed from these binary systems.Comment: 12 pages, 5 figures, submitted to Ap
Conserved Amino Acids in Each Subunit of the Heteroligomeric tRNA m\u3csup\u3e1\u3c/sup\u3eA58 Mtase from \u3cem\u3eSaccharomyces cerevisiae\u3c/em\u3e Contribute to tRNA Binding
In Saccharomyces cerevisiae, a two-subunit methyltransferase (Mtase) encoded by the essential genes TRM6 and TRM61 is responsible for the formation of 1-methyladenosine, a modified nucleoside found at position 58 in tRNA that is critical for the stability of . The crystal structure of the homotetrameric m1A58 tRNA Mtase from Mycobacterium tuberculosis, TrmI, has been solved and was used as a template to build a model of the yeast m1A58 tRNA Mtase heterotetramer. We altered amino acids in TRM6 and TRM61 that were predicted to be important for the stability of the heteroligomer based on this model. Yeast strains expressing trm6 and trm61 mutants exhibited growth phenotypes indicative of reduced m1A formation. In addition, recombinant mutant enzymes had reduced in vitro Mtase activity. We demonstrate that the mutations introduced do not prevent heteroligomer formation and do not disrupt binding of the cofactor S-adenosyl-l-methionine. Instead, amino acid substitutions in either Trm6p or Trm61p destroy the ability of the yeast m1A58 tRNA Mtase to bind , indicating that each subunit contributes to tRNA binding and suggesting a structural alteration of the substrate-binding pocket occurs when these mutations are present
Syntactic Complexity of R- and J-Trivial Regular Languages
The syntactic complexity of a regular language is the cardinality of its
syntactic semigroup. The syntactic complexity of a subclass of the class of
regular languages is the maximal syntactic complexity of languages in that
class, taken as a function of the state complexity n of these languages. We
study the syntactic complexity of R- and J-trivial regular languages, and prove
that n! and floor of [e(n-1)!] are tight upper bounds for these languages,
respectively. We also prove that 2^{n-1} is the tight upper bound on the state
complexity of reversal of J-trivial regular languages.Comment: 17 pages, 5 figures, 1 tabl
Non-planar Feynman integrals, Mellin-Barnes representations, multiple sums
The construction of Mellin-Barnes (MB) representations for non-planar Feynman
diagrams and the summation of multiple series derived from general MB
representations are discussed. A basic version of a new package AMBREv.3.0 is
supplemented. The ultimate goal of this project is the automatic evaluation of
MB representations for multiloop scalar and tensor Feynman integrals through
infinite sums, preferably with analytic solutions. We shortly describe a
strategy of further algebraic summation.Comment: Contribution to the proceedings of the Loops and Legs 2014 conferenc
The Paleohistory of Circumpolar Arctic Colonization
We have attempted to show that the circumpolar arctic zone was colonized from different regions of Eurasia. This penetration took place at different stages according to the evolution of palaeogeographical conditions during the last glacial phase and the early part of the Holocene
On the nucleon-nucleon interaction leading to a standing wave instability in symmetric nuclear matter
We examine a recently proposed nucleon-nucleon interaction, claimed by its
authors both realistic and leading to a standing wave instability in symmetric
nuclear matter. Contrary to these claims, we find that this interaction leads
to a serious overbinding of 4He, 16O and 40Ca nuclei when the Hartree-Fock
method is properly applied. The resulting nuclear densities contradict the
experimental data and all realistic Hartree-Fock results.Comment: 4 pages, 1 figur
Lipophilicity of bacteriochlorin-based photosensitizers as a determinant for PDT optimization through the modulation of the inflammatory mediators
Photodynamic therapy (PDT) augments the host antitumor immune response, but the role of the PDT effect on the tumor microenvironment in dependence on the type of photosensitizer and/or therapeutic protocols has not been clearly elucidated. We employed three bacteriochlorins (F2BOH, F2BMet and Cl2BHep) of different polarity that absorb near-infrared light (NIR) and generated a large amount of reactive oxygen species (ROS) to compare the PDT efficacy after various drug-to-light intervals: 15 min. (V-PDT), 3h (E-PDT) and 72h (C-PDT). We also performed the analysis of the molecular mechanisms of PDT crucial for the generation of the long-lasting antitumor immune response. PDT-induced damage affected the integrity of the host tissue and developed acute (protocol-dependent) local inflammation, which in turn led to the infiltration of neutrophils and macrophages. In order to further confirm this hypothesis, a number of proteins in the plasma of PDT-treated mice were identified. Among a wide range of cytokines (IL-6, IL-10, IL-13, IL-15, TNF-α, GM-CSF), chemokines (KC, MCP-1, MIP1α, MIP1β, MIP2) and growth factors (VEGF) released after PDT, an important role was assigned to IL-6. PDT protocols optimized for studied bacteriochlorins led to a significant increase in the survival rate of BALB/c mice bearing CT26 tumors, but each photosensitizer (PS) was more or less potent, depending on the applied DLI (15 min, 3 h or 72 h). Hydrophilic (F2BOH) and amphiphilic (F2BMet) PSs were equally effective in V-PDT (>80 cure rate). F2BMet was the most efficient in E-PDT (DLI = 3h), leading to a cure of 65 % of the animals. Finally, the most powerful PS in the C-PDT (DLI = 72 h) regimen turned out to be the most hydrophobic compound (Cl2BHep), allowing 100 % of treated animals to be cured at a light dose of only 45 J/cm2
Ferromagnetic fluid as a model of social impact
The paper proposes a new model of spin dynamics which can be treated as a
model of sociological coupling between individuals. Our approach takes into
account two different human features: gregariousness and individuality. We will
show how they affect a psychological distance between individuals and how the
distance changes the opinion formation in a social group. Apart from its
sociological aplications the model displays the variety of other interesting
phenomena like self-organizing ferromagnetic state or a second order phase
transition and can be studied from different points of view, e.g. as a model of
ferromagnetic fluid, complex evolving network or multiplicative random process.Comment: 8 pages, 5 figure
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