1,701 research outputs found
Guidance of the resonance energy flow in the mechanism of coupled magnetic pendulums
This paper presents a methodology of controlling the resonance energy
exchange in mechanical system consisting of two weakly coupled magnetic
pendulums interacting with the magnetic field generated by coils placed
underneath. It is shown that properly guided magnetic fields can effectively
change mechanical potentials in a way that the energy flow between the
oscillators takes the desired direction. Studies were considered by using a
specific set of descriptive functions characterizing the total excitation
level, its distribution between the pendulums, and the phase shift. The
developed control strategies are based on the observation that, in the case of
antiphase oscillation, the energy is moving from the pendulum subjected to the
repelling magnetic field, to the oscillator under the attracting field. In
contrast, during the inphase oscillations, the energy flow is reversed.
Therefore, closed-loop controller requires only the information about phase
shift, which is easily estimated from dynamic state signals through the
coherency index. Advantage of suggested control strategy is that the temporal
rate of inputs is dictated by the speed of beating, which is relatively slow
compared to the carrying oscillations
The influence of strength of hyperon-hyperon interactions on neutron star properties
An equation of state of neutron star matter with strange baryons has been
obtained. The effects of the strength of hyperon-hyperon interactions on the
equations of state constructed for the chosen parameter sets have been
analyzed. Numerous neutron star models show that the appearance of hyperons is
connected with the increasing density in neutron star interiors. The performed
calculations have indicated that the change of the hyperon-hyperon coupling
constants affects the chemical composition of a neutron star. The obtained
numerical hyperon star models exclude large population of strange baryons in
the star interior.Comment: 18 pages, 22 figures, accepted to be published in Journal of Physics
G: Nuclear and Particle Physic
The Staudinger Ligation
While the Staudinger reaction has first been described a hundred years ago in 1919, the ligation reaction became one of the most important and efficient bioconjugation techniques in the 1990s and this century. It holds the crucial characteristics for bioorthogonal chemistry: biocompatibility, selectivity, and a rapid and high-yielding turnover for a wide variety of applications. In the past years, it has been used especially in chemical biology for peptide/protein synthesis, posttranslational modifications, and DNA labeling. Furthermore, it can be used for cell-surface engineering, development of microarrays, and drug delivery systems. However, it is also possible to use the reaction in synthetic chemistry for general formation of amide bonds. In this review, the three major types, traceless and nontraceless Staudinger Ligation as well as the Staudinger phosphite reaction, are described in detail. We will further illustrate each reaction mechanism and describe characteristic substrates, intermediates, and products. In addition, not only its advantages but also stereochemical aspects, scope, and limitations, in particular side reactions, are discussed. Finally, the method is compared to other bioorthogonal labeling methods
Tryptophan metabolism and bacterial commensals prevent fungal dysbiosis in Arabidopsis roots
In nature, roots of healthy plants are colonized by multikingdom microbial communities that include bacteria, fungi, and oomycetes. A key question is how plants control the assembly of these diverse microbes in roots to maintain host–microbe homeostasis and health. Using microbiota reconstitution experiments with a set of immunocompromised Arabidopsis thaliana mutants and a multikingdom synthetic microbial community (SynCom) representative of the natural A. thaliana root microbiota, we observed that microbiota-mediated plant growth promotion was abolished in most of the tested immunocompromised mutants. Notably, more than 40% of between-genotype variation in these microbiota-induced growth differences was explained by fungal but not bacterial or oomycete load in roots. Extensive fungal overgrowth in roots and altered plant growth was evident at both vegetative and reproductive stages for a mutant impaired in the production of tryptophan-derived, specialized metabolites (cyp79b2/b3). Microbiota manipulation experiments with single- and multikingdom microbial SynComs further demonstrated that 1) the presence of fungi in the multikingdom SynCom was the direct cause of the dysbiotic phenotype in the cyp79b2/b3 mutant and 2) bacterial commensals and host tryptophan metabolism are both necessary to control fungal load, thereby promoting A. thaliana growth and survival. Our results indicate that protective activities of bacterial root commensals are as critical as the host tryptophan metabolic pathway in preventing fungal dysbiosis in the A. thaliana root endosphere
Time-Dependent Synchrotron and Compton Spectra from Jets of Microquasars
Jet models for the high-energy emission of Galactic X-ray binary sources have
regained significant interest with detailed spectral and timing studies of the
X-ray emission from microquasars, the recent detection by the HESS
collaboration of very-high-energy gamma-rays from the microquasar LS~5039, and
the earlier suggestion of jet models for ultraluminous X-ray sources observed
in many nearby galaxies. Here we study the synchrotron and Compton signatures
of time-dependent electron injection and acceleration, adiabatic and radiative
cooling, and different jet geometries in the jets of Galactic microquasars.
Synchrotron, synchrotron-self-Compton, and external-Compton radiation processes
with soft photons provided by the companion star and the accretion disk are
treated. An analytical solution is presented to the electron kinetic equation
for general power-law geometries of the jets for Compton scattering in the
Thomson regime. We pay particular attention to predictions concerning the rapid
flux and spectral variability signatures expected in a variety of scenarios,
making specific predictions concerning possible spectral hysteresis, similar to
what has been observed in several TeV blazars. Such predictions should be
testable with dedicated monitoring observations of Galactic microquasars and
ultraluminous X-ray sources using Chandra and/or XMM-Newton.Comment: Accepted for publication in ApJ; 37 manuscript pages, including 10
eps figures; uses AASTeX macro
Widespread association between the ericoid mycorrhizal fungus Rhizoscyphus ericae and a leafy liverwort in the maritime and sub-Antarctic
A recent study identified a fungal isolate from the Antarctic leafy liverwort Cephaloziella varians as the ericoid mycorrhizal associate Rhizoscyphus ericae. However, nothing is known about the wider Antarctic distribution of R. ericae in C. varians, and inoculation experiments confirming the ability of the fungus to form coils in the liverwort are lacking.
Using direct isolation and baiting with Vaccinium macrocarpon seedlings, fungi were isolated from C. varians sampled from eight sites across a 1875-km transect through sub- and maritime Antarctica. The ability of an isolate to form coils in aseptically grown C. varians was also tested.
Fungi with 98–99% sequence identity to R. ericae internal transcribed spacer (ITS) region and partial large subunit ribosomal (r)DNA sequences were frequently isolated from C. varians at all sites sampled. The EF4/Fung5 primer set did not amplify small subunit rDNA from three of five R. ericae isolates, probably accounting for the reported absence of the fungus from C. varians in a previous study. Rhizoscyphus ericae was found to colonize aseptically-grown C. varians intracellularly, forming hyphal coils.
This study shows that the association between R. ericae and C. varians is apparently widespread in Antarctica, and confirms that R. ericae is at least in part responsible for the formation of the coils observed in rhizoids of field-collected C. varians
Analyzing the Multiwavelength Spectrum and Variability of BL Lacertae During the July 1997 Outburst
The multiwavelength spectrum of BL Lacertae during its July 1997 outburst is
analyzed in terms of different variations of the homogeneous leptonic jet model
for the production of high-energy radiation from blazars. We find that a
two-component gamma-ray spectrum, consisting of a synchrotron self-Compton and
an external Compton component, is required in order to yield an acceptable fit
to the broadband spectrum. Our analysis indicates that in BL Lac, unlike other
BL Lac objects, the broad emission line region plays an important role for the
high-energy emission. Several alternative blazar jet models are briefly
discussed. In the appendix, we describe the formalism in which the process of
Comptonization of reprocessed accretion disk photons is treated in the
previously developed blazar jet simulation code which we use.Comment: Now accepted for publication in The Astronomical Journal.
Significantly extended discussion w.r.t. original version. 3 Figures included
using epsf.sty, rotate.st
Decaying neutron propagation in the Galaxy and the Cosmic Ray anisotropy at 1 EeV
We study the cosmic ray arrival distribution expected from a source of
neutrons in the galactic center at energies around 1 EeV and compare it with
the anisotropy detected by AGASA and SUGAR. Besides the point-like signal in
the source direction produced by the direct neutrons, an extended signal due to
the protons produced in neutron decays is expected. This associated proton
signal also leads to an excess in the direction of the spiral arm. For
realistic models of the regular and random galactic magnetic fields, the
resulting anisotropy as a function of the energy is obtained. We find that for
the anisotropy to become sufficiently suppressed below E\sim 10^{17.9}eV, a
significant random magnetic field component is required, while on the other
hand, this also tends to increase the angular spread of the associated proton
signal and to reduce the excess in the spiral arm direction. The source
luminosity required in order that the right ascension anisotropy be 4% for the
AGASA angular exposure corresponds to a prediction for the point-like flux from
direct neutrons compatible with the flux detected by SUGAR. We also analyse the
distinguishing features predicted for a large statistics southern observatory.Comment: 14 pages, 6 figures, minor changes to match published versio
Steroid 21-hydroxylase is a major autoantigen involved in adult onset autoimmune Addison's disease
AbstractAn adrenal-specific protein reacting with autoantibodies in the sera of patients with adult onset Addison's disease has been purified from human adrenal glands. The protein, mol.wt. 55K, has the biochemical characteristics of steroid 21-hydroxylase and reacts on Western blots with rabbit antibodies to recombinant 21-hydroxylase. Absorption of the native human 55K adrenal protein with human adrenal autoantibodies prevented the subsequent reaction of the 55K protein with rabbit antibodies to 21-hydroxylase in Western blot analysis. In addition, human adrenal autoantibodies reacted with recombinant 21-hydroxylase expressed in yeast. These data indicate that the adrenal specific enzyme steroid 21-hydroxylase is a major autoantigen involved in adult onset autoimmune Addison's disease
Spectra and time variability of galactic black-hole X-ray sources in the low/hard state
we propose a jet model for the low/hard state of black-hole X-ray sources
which explains a) the X-ray spectra, b) the timelag spectra, c) the increase in
the amplitude (QPO and high frequency) with increasing photon energy, and d)
the narrowing of the autocorrelation function with increasing photon energy.
The model (in its simplest form) assumes that i) there is a uniform magnetic
field along the axis of the jet, ii) the electron density in the jet is
inversely proportional to distance and iii) the jet is "hotter" near its center
than at its periphery. We have performed Monte Carlo simulations of Compton
upscattering of soft photons from the accretion disk and have found power-law
high-energy spectra with photon number index in the range 1.5-2, power-law
timelags versus Fourier frequency with index ~0.8, and an increase of the rms
amplitude of the variability and a narrowing of the autocorrelation function
with photon energy as they have been observed in Cygnus X-1.Comment: 8 pages, 8 figures, accepted for publication in A&
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