157 research outputs found
Hierarchical Model for the Evolution of Cloud Complexes
The structure of cloud complexes appears to be well described by a "tree
structure" representation when the image is partitioned into "clouds". In this
representation, the parent-child relationships are assigned according to
containment. Based on this picture, a hierarchical model for the evolution of
Cloud Complexes, including star formation, is constructed, that follows the
mass evolution of each sub-structure by computing its mass exchange
(evaporation or condensation) with its parent and children, which depends on
the radiation density at the interphase. For the set of parameters used as a
reference model, the system produces IMFs with a maximum at too high mass (~2
M_sun) and the characteristic times for evolution seem too long. We show that
these properties can be improved by adjusting model parameters. However, the
emphasis here is to illustrate some general properties of this nonlinear model
for the star formation process. Notwithstanding the simplifications involved,
the model reveals an essential feature that will likely remain if additional
physical processes are included. That is: the detailed behavior of the system
is very sensitive to variations on the initial and external conditions,
suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs
corresponding to a variety of initial or external conditions is examined, the
slope of the IMF at high masses shows variations comparable to the range
derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap
Observation of interference between two distinct autoionizing states in dissociative photoionization of H 2
Dissociative photoionization (DPI) of randomly oriented H2 molecules has been studied using linearly polarized synchrotron radiation at selected photon energies of 31, 33, and 35 eV. Large amplitude oscillations in the photoelectron asymmetry parameter β, as a function of electron energy, have been observed. The phase of these β oscillations are in excellent agreement with the results of recent close coupling calculations [Fernández and Martín, New J. Phys. 11, 043020 (2009)]. We show that the oscillations are the signature of interferences between the 1Q1 Σu+1 and 1Q2 Πu1 doubly excited states decaying at different internuclear distances. The oscillations thus provide information about the classical paths followed by the nuclei. The presence of such oscillations is predicted to be a general phenomenon in DPIWe acknowledge NSERC, CLS, and UoW for their support. We thank Mare Nostrum BSC and CCC-UAM for allocation of computer time. Work partially supported by the MICINN Projects No. FIS2010-15127, No. ACI2008-0777, and No. CSD 2007-00010, the European MC-ITN CORINF, and the COST Action CM070
Sex‐specific alterations in whole body energetics and voluntary activity in heterozygous R163C malignant hyperthermia‐susceptible mice
Malignant hyperthermia (MH) is characterized by induction of skeletal muscle hyperthermia in response to a dysregulated increase in myoplasmic calcium. Although altered energetics play a central role in MH, MH‐susceptible humans and mouse models are often described as having no phenotype until exposure to a triggering agent. The purpose of this study was to determine the influence of the R163C ryanodine receptor 1 mutation, a common MH mutation in humans, on energy expenditure, and voluntary wheel running in mice. Energy expenditure was measured by indirect respiration calorimetry in wild‐type (WT) and heterozygous R163C (HET) mice over a range of ambient temperatures. Energy expenditure adjusted for body weight or lean mass was increased (P < .05) in male, but not female, HET mice housed at 22°C or when housed at 28°C with a running wheel. In female mice, voluntary wheel running was decreased (P < .05) in the HET vs WT animals when analyzed across ambient temperatures. The thermoneutral zone was also widened in both male and female HET mice. The results of the study show that the R163C mutations alters energetics even at temperatures that do not typically induce MH
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.
The Distance and Size of the Red Hypergiant NML Cyg from VLBA and VLA Astrometry
We have measured the annual parallax and proper motion of NML Cyg from
multiple epoch VLBA observations of the circulstellar H2O and SiO masers. The
measured parallax of NML Cyg is 0.620+/-0.047 mas, corresponding to a distance
of 1.61+/-0.12 kpc. The measured proper motion of NML Cyg is mu_x =
-1.55+/-0.42 mas/yr eastward and mu_y= -4.59+/-0.41 mas/yr northward. Both Both
the distance and proper motion are consistent with that of Cyg OB2, within
their joint uncertainty, confirming their association. Taking into
consideration molecular absorption signatures seen toward NML Cyg, we suggest
that NML Cyg lies on the far side of the Cyg OB2 association. The stellar
luminosity revised with our distance brings NML Cyg significantly below the
empirical luminosity limit for a red supergiant. Using the VLA observation the
radio photosphere and the SiO maser as a phase reference, we partially resolve
the radio photosphere of NML Cyg at 43 GHz and find its diameter is about 44
mas, suggesting an optical stellar diameter of 22 mas, if the size of radio
photosphere is 2 times the optical photosphere. Based on the position of
circumstellar SiO masers relative to the radio photosphere, we estimate the
absolute position of NML Cyg at epoch 2008.868 to be R.A. = 20h46m25.5382s +/-
0.0010s, Decl. = 40d06'59.379" +/- 0.015". The peculiar motions of NML Cyg, the
average of stars in Cyg OB2, and four other star-forming regions rules out that
an expanding "Stroemgren sphere" centered on Cyg OB2 is responsible for the
kinematics of the Cygnus X region.Comment: 15 pages, 11 figures, accepted by A&
Dust properties in M31.I.Basic properties and a discussion on age-dependent dust heating
Context. Spitzer Space Telescope observations and dust emission models are
used to discuss the distribution of dust and its characteristics in M31.
Together with GALEX FUV, NUV, and SDSS images we studied the age dependence of
the dust heating process. Methods.Spitzer IRAC/MIPS maps of M31 were matched
together and compared to dust emission models allowing to constrain the dust
mass, the intensity of the mean radiation field, the abundance of Polycyclic
Aromatic Hydrocarbons (PAH) particles. The total infrared emission (TIR) was
analyzed in function of UV and Optical colors and compared to predictions of
models which consider the age-dependent dust heating. Results. We demonstrate
that cold-dust component emission dominates the infrared spectral energy
distribution of M31. The mean intensity of the radiation field heating the dust
is low (typically U<2, where U=1 is the value in the solar surrounding). Due to
the lack of submillimetric measurements the dust mass (M_{dust}) is only weakly
constrained by the infrared spectrum. We show that across the spiral-ring
structure of M31 a fraction >3% of the total dust mass is in PAHs. UV and
optical colors are correlated to (TIR/FUV) ratios in \sim 670 pc-sized regions
overall the disk of M31, although deviating from the IRX-beta relationship for
starburst galaxies. We derived that in 83% of the regions analyzed across the
10kpc ring more than 50% of the energy absorbed by the dust is rediated at
\lambda > 4000 \AA and that dust in M31 appears mainly heated by populations a
few Gyr old even across the star-forming ring. The attenuation is varying
radially peaking near 10kpc and decreasing faster in the inner regions of M31
than in the outer regions. We finally derived the attenuation map of M31 at
6"/px resolution (\sim 100 pc/px along the plane of M31).[abridged]Comment: 21 pages, 18 figures, accepted for publication in A&A. Only low
resolution images included, full resolution images will be avaiable in the
journal electronic version. Fig.14 and Fig.17 will be avaiable via CD
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
CHANDRA/VLA Follow-up of TeV J2032+4131, the Only Unidentified TeV Gamma-ray Source
The HEGRA Cherenkov telescope array group recently reported a steady and
extended unidentified TeV gamma-ray source lying at the outskirts of Cygnus
OB2. This is the most massive stellar association known in the Galaxy,
estimated to contain ~2600 OB type members alone. It has been previously argued
that the large scale shocks and turbulence induced by the multiple interacting
supersonic winds from the many young stars in such associations may play a role
in accelerating Galactic cosmic rays. Indeed, Cyg OB2 also coincides with the
non-variable MeV-GeV range unidentified EGRET source, 3EG 2033+4118. We report
on the near-simultaneous follow-up observations of the extended TeV source
region with the CHANDRA X-ray Observatory and the Very Large Array (VLA) radio
telescope obtained in order to explore this possibility. Analysis of the CO,
HI, and IRAS 100 micron emissions shows that the TeV source region coincides
with an outlying sub-group of powerful OB stars which have evacuated or
destroyed much of the ambient atomic, molecular and dust material, and which
may be related to the very high-energy emissions. An interesting SNR-like
structure is also revealed near the TeV source region in the CO, HI and radio
emission maps. Applying a numerical simulation which accurately tracks the
radio to gamma-ray emission from primary hadrons as well as primary and
secondary e+/-, we find that the broadband spectrum of the TeV source region
favors a predominantly nucleonic - rather than electronic - origin of the
high-energy flux, though deeper X-ray and radio observations are needed to
confirm this. A very reasonable, ~0.1%, conversion efficiency of Cyg OB2's
extreme stellar wind mechanical luminosity to nucleonic acceleration to ~PeV
(10^15 eV) energies is sufficient to explain the multifrequency emissions.Comment: ApJ accepte
Synchrony and Physiological Arousal Increase Cohesion and Cooperation in Large Naturalistic Groups
Separate research streams have identified synchrony and arousal as two factors that might contribute to the effects of human rituals on social cohesion and cooperation. But no research has manipulated these variables in the field to investigate their causal – and potentially interactive – effects on prosocial behaviour. Across four experimental sessions involving large samples of strangers, we manipulated the synchronous and physiologically arousing affordances of a group marching task within a sports stadium. We observed participants’ subsequent movement, grouping, and cooperation via a camera hidden in the stadium’s roof. Synchrony and arousal both showed main effects, predicting larger groups, tighter clustering, and more cooperative behaviour in a free-rider dilemma. However, synchrony and arousal interacted on measures of clustering and cooperation: such that synchrony only encouraged closer clustering — and encouraged greater cooperation—when paired with physiological arousal. The research has implications for understanding the nature and co-occurrence of synchrony and physiological arousal in rituals around the world. It also represents the first use of real-time spatial tracking as a precise and naturalistic method of simulating collective rituals
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/
- …