403 research outputs found
A randomized controlled pilot trial of classroom-based mindfulness meditation compared to an active control condition in sixth-grade children
The current study is a pilot trial to examine the effects of a nonelective, classroom-based, teacher-implemented, mindfulness meditation intervention on standard clinical measures of mental health and affect in middle school children. A total of 101 healthy sixth-grade students (55 boys, 46 girls) were randomized to either an Asian history course with daily mindfulness meditation practice (intervention group) or an African history course with a matched experiential activity (active control group). Self-reported measures included the Youth Self Report (YSR), a modified Spielberger State-Trait Anxiety Inventory, and the Cognitive and Affective Mindfulness Measure –Revised. Both groups decreased significantly on clinical syndrome subscales and affect but did not differ in the extent of their improvements. Meditators were significantly less likely to develop suicidal ideation or thoughts of self-harm than controls. These results suggest that mindfulness training may yield both unique and non-specific benefits that are shared by other novel activities
Gender Differences in Response to a School-Based Mindfulness Training Intervention for Early Adolescents
Mindfulness training has been used to improve emotional wellbeing in early adolescents. However, little is known about treatment outcome moderators, or individual differences that may differentially impact responses to treatment. The current study focused on gender as a potential moderator for affective outcomes in response to school-based mindfulness training. Sixth grade students (N = 100) were randomly assigned to either the six weeks of mindfulness meditation or the active control group as part of a history class curriculum. Participants in the mindfulness meditation group completed short mindfulness meditation sessions four to five times per week, in addition to didactic instruction (Asian history). The control group received matched experiential activity in addition to didactic instruction (African history) from the same teacher with no meditation component. Self-reported measures of emotional wellbeing/affect, mindfulness, and self-compassion were obtained at pre and post intervention. Meditators reported greater improvement in emotional wellbeing compared to those in the control group. Importantly, gender differences were detected, such that female meditators reported greater increases in positive affect compared to females in the control group, whereas male meditators and control males displayed equivalent gains. Uniquely among females but not males, increases in self-reported self-compassion were associated with improvements in affect. These findings support the efficacy of school-based mindfulness interventions, and interventions tailored to accommodate distinct developmental needs of female and male adolescents
The Effects of Dark Matter Decay and Annihilation on the High-Redshift 21 cm Background
The radiation background produced by the 21 cm spin-flip transition of
neutral hydrogen at high redshifts can be a pristine probe of fundamental
physics and cosmology. At z~30-300, the intergalactic medium (IGM) is visible
in 21 cm absorption against the cosmic microwave background (CMB), with a
strength that depends on the thermal (and ionization) history of the IGM. Here
we examine the constraints this background can place on dark matter decay and
annihilation, which could heat and ionize the IGM through the production of
high-energy particles. Using a simple model for dark matter decay, we show
that, if the decay energy is immediately injected into the IGM, the 21 cm
background can detect energy injection rates >10^{-24} eV cm^{-3} sec^{-1}. If
all the dark matter is subject to decay, this allows us to constrain dark
matter lifetimes <10^{27} sec. Such energy injection rates are much smaller
than those typically probed by the CMB power spectra. The expected brightness
temperature fluctuations at z~50 are a fraction of a mK and can vary from the
standard calculation by up to an order of magnitude, although the difference
can be significantly smaller if some of the decay products free stream to lower
redshifts. For self-annihilating dark matter, the fluctuation amplitude can
differ by a factor <2 from the standard calculation at z~50. Note also that, in
contrast to the CMB, the 21 cm probe is sensitive to both the ionization
fraction and the IGM temperature, in principle allowing better constraints on
the decay process and heating history. We also show that strong IGM heating and
ionization can lead to an enhanced H_2 abundance, which may affect the earliest
generations of stars and galaxies.Comment: submitted to Phys Rev D, 14 pages, 8 figure
Retrograde discs around one component of a binary are unstable to tilting
With hydrodynamic simulations we show that a coplanar disc around one
component of a binary can be unstable to global tilting when the disc orbits in
a retrograde direction relative to the binary. The disc experiences the largest
inclination growth relative to the binary orbit in the outermost radii of the
disc, closest to the companion. This tilt instability also occurs for test
particles. A retrograde disc is much larger than a prograde disc since it is
not tidally truncated and instead spreads outwards to the orbit of the
companion. The coplanar retrograde disc remains circular while a coplanar
prograde disc can become eccentric. We suggest that the inclination instability
is due to a disc resonance caused by the interaction of the tilt with the tidal
field of the binary. This model is applicable to Be/X-ray binaries in which the
Be star disc may be retrograde relative to the binary orbit if there was a
sufficiently strong kick from the supernova that formed the neutron star
companion. The accretion on to the neutron star and the resulting X-ray
outbursts are weaker in the retrograde case compared to the prograde case.Comment: 6 pages, 3 figures, accepted for publication in MNRA
Generalized Warped Disk Equations
The manner in which warps in accretion disks evolve depends on the magnitude of the viscosity. ... See full text for complete abstract
The Effects of UV Continuum and Lyman alpha Radiation on the Chemical Equilibrium of T Tauri Disks
We show in this Letter that the spectral details of the FUV radiation fields
have a large impact on the chemistry of protoplanetary disks surrounding T
Tauri stars. We show that the strength of a realistic stellar FUV field is
significantly lower than typically assumed in chemical calculations and that
the radiation field is dominated by strong line emission, most notably Lyman
alpha radiation. The effects of the strong Lyman alpha emission on the chemical
equilibrium in protoplanetary disks has previously been unrecognized. We
discuss the impact of this radiation on molecular observations in the context
of a radiative transfer model that includes both direct attenuation and
scattering. In particular, Lyman alpha radiation will directly dissociate water
vapor and may contribute to the observed enhancements of CN/HCN in disks.Comment: 14 pages, 4 figures, accepted by ApJ Letter
Rate coefficients for rovibrational transitions in H_2 due to collisions with He
We present quantum mechanical and quasiclassical trajectory calculations of
cross sections for rovibrational transitions in ortho- and para-H_2 induced by
collisions with He atoms. Cross sections were obtained for kinetic energies
between 10^-4 and 3 eV, and the corresponding rate coefficients were calculated
for the temperature range 100<T<4000 K. Comparisons are made with previous
calculations.Comment: 21 pages, 2 figures, AAS, eps
Circumbinary disk evolution in the presence of an outer companion star
We consider a hierarchical triple system consisting of an inner eccentric
binary with an outer companion. A highly misaligned circumbinary disk around
the inner binary is subject to two competing effects: (i) nodal precession
about the inner binary eccentricity vector that leads to an increase in
misalignment (polar alignment) and (ii) Kozai-Lidov (KL) oscillations of
eccentricity and inclination driven by the outer companion that leads to a
reduction in the misalignment. The outcome depends upon the ratio of the
timescales of these effects. If the inner binary torque dominates, then the
disk aligns to a polar orientation. If the outer companion torque dominates,
then the disk undergoes KL oscillations. In that case, the highly eccentric and
misaligned disk is disrupted and accreted by the inner binary, while some mass
is transferred to the outer companion. However, when the torques are similar,
the outer parts of the circumbinary disk can undergo large eccentricity
oscillations while the inclination remains close to the polar orientation. The
range of initial disk inclinations that evolve to a polar orientation is
smaller in the presence of the outer companion. Disk breaking is also more
likely, at least temporarily, during the polar alignment process. The stellar
orbits in HD 98800 have parameters such that polar alignment of the
circumbinary disk is expected. In the absence of the gas, solid particles are
unstable at much smaller radii than the gas disk inner tidal truncation radius
because KL driven eccentricity leads to close encounters with the binary.Comment: Accepted for publication in ApJ
Molecules in the Circumstellar Disk Orbiting BP Piscium
BP Psc is a puzzling late-type, emission-line field star with large infrared
excess. The star is encircled and enshrouded by a nearly edge-on, dust
circumstellar disk, and displays an extensive jet system similar to those
associated with pre-main sequence (pre-MS) stars. We conducted a mm-wave
molecular line survey of BP Psc with the 30 m telescope of the Institut de
Radio Astronomie Millimetrique (IRAM). We detected lines of 12CO and 13CO and,
possibly, very weak emission from HCO+ and CN; HCN, H2CO, and SiO are not
detected. The CO line profiles of BP Psc are well fit by a model invoking a
disk in Keplerian rotation. The mimumum disk gas mass, inferred from the 12CO
line intensity and 13CO/12CO line ratio, is ~0.1 Jupiter masses. The weakness
of HCO+ and CN (relative to 13CO) stands in sharp contrast to the strong HCO+
and CN emission that characterizes most low-mass, pre-main sequence stars that
have been the subjects of molecular emission-line surveys, and is suggestive of
a very low level of X-ray-induced molecular ionization within the BP Psc disk.
These results lend some support to the notion that BP Psc is an evolved star
whose circumstellar disk has its origins in a catastrophic interaction with a
close companion.Comment: 6 pages, 4 figures; to appear in Astronomy & Astrophysic
Astrochemistry in the Early Universe: Collisional Rates for H on H2
We present preliminary results of a full quantum calculation of state to state cross sections for H on H2. These cross sections are calculated for v=0,4 j=0,15 for energies up to 3.0 eV. The cross sections are calculated on the BKMP2 potential surface (Boothroyd et al. 1996) with the ABC scattering code (Skouteris et al. 2000)
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