580 research outputs found
Inelastic Diffraction and Spectroscopy of Very Weakly Bound Clusters
We study the coherent inelastic diffraction of very weakly bound two body
clusters from a material transmission grating. We show that internal
transitions of the clusters can lead to new separate peaks in the diffraction
pattern whose angular positions determine the excitation energies. Using a
quantum mechanical approach to few body scattering theory we determine the
relative peak intensities for the diffraction of the van der Waals dimers
(D_2)_2 and H_2-D_2. Based on the results for these realistic examples we
discuss the possible applications and experimental challenges of this coherent
inelastic diffraction technique.Comment: 15 pages + 5 figures. J. Phys. B (in press
“Turbulence even in a bubble”: A reflexive thematic analysis with family caregivers of people with dementia in the United Kingdom during and beyond the COVID-19 pandemic
Objective: This study aimed to understand how family caregivers of people with dementia managed changes caused by COVID-19 restrictions and how they adjusted to the lifting of restrictions. A particular focus of the study was on understanding the impact of social isolation, a reduction of social interactions, and reduced access to healthcare services.
Methods and measures: Fourteen voluntary caregivers (nine women) were interviewed using a semi-structured interview schedule.
Results: Five themes were identified based on reflexive thematic analysis: i) Outlets to cope with lockdown; ii) “Not all doom and gloom”: A silver lining amid COVID-19; iii) Optimism helps provide resilience; iv) The challenges and joys of reopening; and v) Caregiving toward a new normality.
Conclusion: The research highlighted difficulties reported by family caregivers and people with dementia during COVID-19, while also showing how such carers coped. Interviews also identified ways that family caregivers often used optimism to help navigate through lockdown and to tackle the reopening stage. Family caregivers in this study reported coping well overall, but welcomed the lifting of restrictions
Rotational quenching rate coefficients for H_2 in collisions with H_2 from 2 to 10,000 K
Rate coefficients for rotational transitions in H_2 induced by H_2 impact are
presented. Extensive quantum mechanical coupled-channel calculations based on a
recently published (H_2)_2 potential energy surface were performed. The
potential energy surface used here is presumed to be more reliable than
surfaces used in previous work. Rotational transition cross sections with
initial levels J <= 8 were computed for collision energies ranging between
0.0001 and 2.5 eV, and the corresponding rate coefficients were calculated for
the temperature range 2 < T <10,000 K. In general, agreement with earlier
calculations, which were limited to 100-6000 K, is good though discrepancies
are found at the lowest and highest temperatures. Low-density-limit cooling
functions due to para- and ortho-H_2 collisions are obtained from the
collisional rate coefficients. Implications of the new results for non-thermal
H_2 rotational distributions in molecular regions are also investigated
Ultracold collisions between two light indistinguishable diatomic molecules: elastic and rotational energy transfer in HD+HD
A close coupling quantum-mechanical calculation is performed for rotational
energy transfer in a HD+HD collision at very low energy, down to the ultracold
temperatures: K. A global six-dimensional H-H
potential energy surface is adopted from a previous work [Boothroyd {\it et
al.}, J. Chem. Phys., {\bf 116}, 666 (2002).] State-resolved integral cross
sections of different
quantum-mechanical rotational transitions in the HD
molecules and corresponding state-resolved thermal rate coefficients
have been computed. Additionally, for comparison,
H+H calculations for a few selected rotational transitions have also
been performed. The hydrogen and deuterated hydrogen molecules are treated as
rigid rotors in this work. A pronounced isotope effect is identified in the
cross sections of these collisions at low and ultracold temperatures.Comment: 9 pages, 9 figures. Accepted for publication in Physical Review
A Pre-Protostellar Core in L1551
Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have
revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively
quiescent region to the northwest of the well-known IRS 5 source. The kinetic
temperature is measured to be 9K, the total mass is ~2Msun, and the average
particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection
oriented at a position angle of 133deg. The turbulent motions are on the order
of the sound speed in the medium and contain 4% of the gravitational energy,
E_{grav}, of the core. The angular momentum vector is projected along the major
axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin
i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}|
and the virial mass is approximately equal to the total mass. L1551-MC is
gravitationally bound and in the absence of strong, ~160 microgauss, magnetic
fields will likely contract on a ~0.3 Myr time scale. The line profiles of many
molecular species suggest that the cold quiescent interior is surrounded by a
dynamic, perhaps infalling envelope which is embedded within the ambient
molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte
The spectroscopic orbit of Capella revisited
Context. Capella is among the few binary stars with two evolved giant
components. The hotter component is a chromospherically active star within the
Hertzsprung gap, while the cooler star is possibly helium-core burning. Aims.
The known inclination of the orbital plane from astrometry in combination with
precise radial velocities will allow very accurate masses to be determined for
the individual Capella stars. This will constrain their evolutionary stage and
possibly the role of the active star's magnetic field on the dynamical
evolution of the binary system. Methods. We obtained a total of 438
high-resolution \'echelle spectra during the years 2007-2010 and used the
measured velocities to recompute the orbital elements. Our double-lined orbital
solution yields average residuals of 64 m/s for the cool component and 297 m/s
for the more rapidly rotating hotter component. Results. The semi-amplitude of
the cool component is smaller by 0.045 km/s than the orbit determination of
Torres et al. from data taken during 1996-1999 but more precise by a factor of
5.5, while for the hotter component it is larger by 0.580 km/s and more precise
by a factor of 3.6. This corresponds to masses of 2.573\pm0.009 M_sun and
2.488\pm0.008 M_sun for the cool and hot component, respectively. Their
relative errors of 0.34% and 0.30% are about half of the values given in Torres
et al. for a combined literature- data solution but with absolute values
different by 4% and 2% for the two components, respectively. The mass ratio of
the system is therefore q = M_A/M_B = 0.9673 \pm 0.0020. Conclusions. Our orbit
is the most precise and also likely to be the most accurate ever obtained for
Capella
Estimating and accounting for fish losses under the footrope of a survey trawl : The case of northern shelf anglerfish
Open Access via Elsevier Agreement Funding Information: We wish to thank the captain and crew of the MRV Scotia and the staff at Marine Science Scotland for their work in the data collection. A significant amount of this work was carried out as part of R.E.D.’s PhD studentship which was funded under the Natural Environment Research Council (NERC) Scottish Universities Partnership for Environmental Research (SUPER) Doctoral Training Partnership (DTP) (Grant reference no. NE/S007342/1 and website https://superdtp.st-andrews.ac.uk/). Additional funding has been provided by the University of Aberdeen and Marine Science Scotland. Funding Information: We wish to thank the captain and crew of the MRV Scotia and the staff at Marine Science Scotland for their work in the data collection. A significant amount of this work was carried out as part of R.E.D.’s PhD studentship which was funded under the Natural Environment Research Council (NERC) Scottish Universities Partnership for Environmental Research ( SUPER ) Doctoral Training Partnership ( DTP ) (Grant reference no. NE/S007342/1 and website https://superdtp.st-andrews.ac.uk/ ). Additional funding has been provided by the University of Aberdeen and Marine Science Scotland .Peer reviewedPublisher PD
NH3 in the Central 10 pc of the Galaxy I: General Morphology and Kinematic Connections Between the CND and GMCs
New VLA images of NH3 (1,1), (2,2), and (3,3) emission in the central 10
parsecs of the Galaxy trace filamentary streams of gas, several of which appear
to feed the circumnuclear disk (CND). The NH3 images have a spatial resolution
of 16.5''x14.5'' and have better spatial sampling than previous NH3
observations. The images show the ``southern streamer,'' ``50 km/s cloud,'' and
new features including a ``western streamer'', 6 parsecs in length, and a
``northern ridge'' which connects to the CND. NH3(3,3) emission is very similar
to 1.2 mm dust emission indicating that NH3 traces column density well. Ratios
of the NH3(2,2) to (1,1) line intensities give an estimate of the temperature
of the gas and indicate high temperatures close to the nucleus and CND. The new
data cover a velocity range of 270 km/s, including all velocities observed in
the CND, with a resolution of 9.8 km/s. Previous NH3 observations with higher
resolution did not cover the entire range of velocities seen in the CND. The
large-scale kinematics of the CND do not resemble a coherent ring or disk. We
see evidence for a high velocity cloud within a projected distance of 50'' (2
pc) which is only seen in NH3(3,3) and is likely to be hot. Comparison to 6 cm
continuum emission reveals that much of the NH3 emission traces the outer edges
of Sgr A East and was probably pushed outward by this expanding shell. The
connection between the northern ridge (which appears to be swept up by Sgr A
East) and the CND indicates that Sgr A East and the CND are in close proximity
to each other. Kinematic evidence for these connections is presented in this
paper, while the full kinematic analysis of the central 10 pc will be presented
in Paper II.Comment: 16 pages (containing 6 figures), 8 additional JPEG figures. Accepted
for publication in ApJ. For full resolution images, see
http://cfa-www.harvard.edu/~rmcgary/SGRA/nh3_figures.htm
Deflections in Magnet Fringe Fields
A transverse multipole expansion is derived, including the longitudinal
components necessarily present in regions of varying magnetic field profile. It
can be used for exact numerical orbit following through the fringe field
regions of magnets whose end designs introduce no extraneous components, {\it
i.e.} fields not required to be present by Maxwell's equations. Analytic
evaluations of the deflections are obtained in various approximations. Mainly
emphasized is a ``straight-line approximation'', in which particle orbits are
treated as straight lines through the fringe field regions. This approximation
leads to a readily-evaluated figure of merit, the ratio of r.m.s. end
deflection to nominal body deflection, that can be used to determine whether or
not a fringe field can be neglected. Deflections in ``critical'' cases (e.g.
near intersection regions) are analysed in the same approximation.Comment: To be published in Physical Review
The nature of the dense core population in the Pipe Nebula: A survey of NH3, CCS, and HC5N molecular line emission
Recent extinction studies of the Pipe Nebula (d=130 pc) reveal many cores
spanning a range in mass from 0.2 to 20.4 Msun. These dense cores were
identified via their high extinction and comprise a starless population in a
very early stage of development. Here we present a survey of NH3 (1,1), NH3
(2,2), CCS (2_1,1_0), and HC5N (9,8) emission toward 46 of these cores. An
atlas of the 2MASS extinction maps is also presented. In total, we detect 63%
of the cores in NH3 (1,1) 22% in NH3 (2,2), 28% in CCS, and 9% in HC5N
emission. We find the cores are associated with dense gas (~10^4 cm-3) with 9.5
< T_k < 17 K. Compared to C18O, we find the NH3 linewidths are systematically
narrower, implying that the NH3 is tracing the dense component of the gas and
that these cores are relatively quiescent. We find no correlation between core
linewidth and size. The derived properties of the Pipe cores are similar to
cores within other low-mass star-forming regions: the only differences are that
the Pipe cores have weaker NH3 emision and most show no current star formation
as evidenced by the lack of embedded infrared sources. Such weak NH3 emission
could arise due to low column densities and abundances or reduced excitation
due to relatively low core volume densities. Either alternative implies that
the cores are relatively young. Thus, the Pipe cores represent an excellent
sample of dense cores in which to study the initial conditions for star
formation and the earliest stages of core formation and evolution.Comment: 35 pages, 10 figures (excluding the appendix). For the complete
appendix contact [email protected]. Accepted for publication in ApJ
- …