99 research outputs found
TeV gamma-rays and neutrinos from photo-disintegration of nuclei in Cygnus OB2
TeV gamma-rays may provide significant information about high energy
astrophysical accelerators. Such gamma-rays can result from the
photo-de-excitation of PeV nuclei after their parents have undergone
photo-disintegration in an environment of ultraviolet photons. This process is
proposed as a candidate explanation of the recently discovered HEGRA source at
the edge of the Cygnus OB2 association. The Lyman-alpha background is provided
by the rich O and B stellar environment. It is found that (1) the HEGRA flux
can be obtained if there is efficient acceleration at the source of lower
energy nuclei; (2) the requirement that the Lorentz-boosted ultraviolet photons
can excite the Giant Dipole resonance implies a strong suppression of the
gamma-ray spectrum compared to an E_\gamma^{-2} behavior at energies \alt 1 TeV
(some of these energies will be probed by the upcoming GLAST mission); (3) a
TeV neutrino counterpart from neutron decay following helium
photo-disintegration will be observed at IceCube only if a major proportion of
the kinetic energy budget of the Cygnus OB2 association is expended in
accelerating nuclei.Comment: To be published in Phys. Rev.
Fifty Years of IMF Variation: The Intermediate-Mass Stars
I track the history of star count estimates of the Milky Way field star and
open cluster IMFs, concentrating on the neglected mass range from 1 to 15
M. The prevalent belief in a universal IMF appears to be without
basis for this mass range. Two recent estimates of the field star IMF using
different methods and samples give values of the average logarithmic slope
between -1.7 and -2.1 in the mass range 1.1 to 4 M. Two
older estimates between 2 and 15 M disagree severely; the field IMF
in this range is essentially unknown from star counts. Variations in
among open cluster IMFs in this mass range have not decreased despite numerous
detailed studies, even for studies using homogeneous data and reduction
procedures and including only clusters with a significant mass range. These
cluster variations \textit{might} be due to the combined effects of sampling,
systematic errors, stellar evolution uncertainties, dynamical evolution, and
unresolved binaries. If so, then the cluster data are consistent with a
universal IMF, but are also consistent with sizeable variations. The cluster
data do not allow an estimate of an average IMF or because the average
depends on the choice of weighting procedure and other effects. If the spread
in cluster IMFs is in excess of the effects listed above, real IMF variations
must occur that do not depend much on physical conditions explored so far. The
complexity of the star formation process seen in observations and simulations
suggests that large realization-to-realization differences might be expected,
in which case an individual cluster IMF would be in part the product of
evolutionary contingency in star formation, and the function of interest is the
probability distribution of IMF parameters.Comment: 18 pages, including 4 figures: invited talk presented at the
conference on "IMF@50: The Stellar Initial Mass Function Fifty Years Later"
held at Abbazia di Spineto, Siena, Italy, May 2004; to be published by Kluwer
Academic Publishers, edited by E. Corbelli, F. Palla, and H. Zinnecke
Searches for the Shell Swept up by the Stellar Wind from Cyg OB2
We investigated the kinematics of ionized gas in an extended (20 degrees by
15 degrees) region containing the X-ray Superbubble in Cygnus with the aim of
finding the shell swept up by a strong wind from Cyg OB2. H-alpha observations
were carried out with high angular and spectral resolutions using a Fabry-Perot
interferometer attached to the 125-cm telescope at the Crimean Observatory of
the Sternberg Astronomical Institute. We detected high-velocity gas motions,
which could result from the expansion of the hypothetical shell at a velocity
of 25-50 km/s. Given the number of OB stars increased by Knoedlseder (2000) by
an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough
[Lw ~= (1-2)x10^39 erg/s] to produce a shell comparable in size to the X-ray
Superbubble and to a giant system of optical filaments. Based on our
measurements and on X-ray and infrared observations, we discuss possible
observational manifestations of the shell swept up by the wind.Comment: 14 pages, Astronomy Letter
The mediating role of shared flow and perceived emotional synchrony on compassion for others in a mindful-dancing program
While there is a growing understanding of the relationship between mindfulness and compassion, this largely relates to the form of mindfulness employed in first-generation mindfulness-based interventions such as Mindfulness-Based Stress Reduction. Consequently, there is limited knowledge of the relationship between mindfulness and compassion in respect of the type of mindfulness employed in second-generation mindfulness-based interventions (SG-MBIs), including those that employ the principle of working harmoniously as a “secular sangha.” Understanding this relationship is important because research indicates that perceived emotional synchrony (PES) and shared flow—that often arise during participation in harmonized group contemplative activities—can enhance outcomes relating to compassion, subjective well-being, and group identity fusion. This pilot study analyzed the effects of participation in a mindful-dancing SG-MBI on compassion and investigated the mediating role of shared flow and PES. A total of 130 participants were enrolled into the study that followed a quasi-experimental design with an intervention and control group. Results confirmed the salutary effect of participating in a collective mindful-dancing program, and demonstrated that shared flow and PES fully meditated the effects of collective mindfulness on the kindness and common humanity dimensions of compassion. Further research is warranted to explore whether collective mindfulness approaches, such as mindful dancing, may be a means of enhancing compassion and subjective well-being outcomes due to the mediating role of PES and shared flow.N/
Interspecific Proteomic Comparisons Reveal Ash Phloem Genes Potentially Involved in Constitutive Resistance to the Emerald Ash Borer
The emerald ash borer (Agrilus planipennis) is an invasive wood-boring beetle that has killed millions of ash trees since its accidental introduction to North America. All North American ash species (Fraxinus spp.) that emerald ash borer has encountered so far are susceptible, while an Asian species, Manchurian ash (F. mandshurica), which shares an evolutionary history with emerald ash borer, is resistant. Phylogenetic evidence places North American black ash (F. nigra) and Manchurian ash in the same clade and section, yet black ash is highly susceptible to the emerald ash borer. This contrast provides an opportunity to compare the genetic traits of the two species and identify those with a potential role in defense/resistance. We used Difference Gel Electrophoresis (DIGE) to compare the phloem proteomes of resistant Manchurian to susceptible black, green, and white ash. Differentially expressed proteins associated with the resistant Manchurian ash when compared to the susceptible ash species were identified using nano-LC-MS/MS and putative identities assigned. Proteomic differences were strongly associated with the phylogenetic relationships among the four species. Proteins identified in Manchurian ash potentially associated with its resistance to emerald ash borer include a PR-10 protein, an aspartic protease, a phenylcoumaran benzylic ether reductase (PCBER), and a thylakoid-bound ascorbate peroxidase. Discovery of resistance-related proteins in Asian species will inform approaches in which resistance genes can be introgressed into North American ash species. The generation of resistant North American ash genotypes can be used in forest ecosystem restoration and urban plantings following the wake of the emerald ash borer invasion
Photoelectron and threshold photoelectron valence spectra of pyridine
The pyridine molecule has been examined by the means of photoelectron and threshold photoelectron spectroscopies. Ionization energies were determined for both outer and inner valence orbitals and new adiabatic values were also resolved. Vibronic structure associated with several states was assigned mainly to be due to C-C stretches and ring bends. Additionally a Rydberg state converging to 7b2 state was ascribed. The data shown here are in a good agreement with previous results and brings some new insights into the electronic structure of this biologically and astrochemically relevant and important molecule
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