21,237 research outputs found
Giving and Receiving Peer Advice in an Online Breast Cancer Support Group
People have access to experiential information and advice about health online. The types of advice exchanged affect the nature of online communities and potentially patient decision making. The aim of this study was to examine the ways in which peers exchange advice within an online health forum in order to better understand online groups as a resource for decision making. Messages collected over a one-month period from an online breast cancer support forum were analyzed for examples of advice exchange. The majority of the messages solicited advice through problem disclosure or requests for information and opinion. A novel form of advice solicitation—“anyone in the same boat as me”—was noted as was the use of personal experience as a form of advice giving. Women construct their advice requests to target like-minded people. The implications in terms of decision making and support are discussed
The pre-shock gas of SN1006 from HST/ACS observations
We derive the pre-shock density and scale length along the line of sight for
the collisionless shock from a deep HST image that resolves the H alpha
filament in SN1006 and updated model calculations. The very deep ACS
high-resolution image of the Balmer line filament in the northwest (NW)
quadrant shows that 0.25 < n_0 < le$ 0.4 cm-3 and that the scale along the line
of sight is about 2 x 10^{18} cm, while bright features within the filament
correspond to ripples with radii of curvature less than 1/10 that size. The
derived densities are within the broad range of earlier density estimates, and
they agree well with the ionization time scale derived from the Chandra X-ray
spectrum of a region just behind the optical filament. This provides a test for
widely used models of the X-ray emission from SNR shocks. The scale and
amplitude of the ripples are consistent with expectations for a shock
propagating though interstellar gas with ~ 20% density fluctuations on parsec
scales as expected from studies of interstellar turbulence. One bulge in the
filament corresponds to a knot of ejecta overtaking the blast wave, however.
The interaction results from the rapid deceleration of the blast wave as it
encounters an interstellar cloud.Comment: 16 pages, 6 figures, to appear in Ap
Expanding Disease Definitions in Guidelines and Expert Panel Ties to Industry:A Cross-sectional Study of Common Conditions in the United States
BACKGROUND: Financial ties between health professionals and industry may unduly influence professional judgments and some researchers have suggested that widening disease definitions may be one driver of over-diagnosis, bringing potentially unnecessary labeling and harm. We aimed to identify guidelines in which disease definitions were changed, to assess whether any proposed changes would increase the numbers of individuals considered to have the disease, whether potential harms of expanding disease definitions were investigated, and the extent of members' industry ties. METHODS AND FINDINGS: We undertook a cross-sectional study of the most recent publication between 2000 and 2013 from national and international guideline panels making decisions about definitions or diagnostic criteria for common conditions in the United States. We assessed whether proposed changes widened or narrowed disease definitions, rationales offered, mention of potential harms of those changes, and the nature and extent of disclosed ties between members and pharmaceutical or device companies. Of 16 publications on 14 common conditions, ten proposed changes widening and one narrowing definitions. For five, impact was unclear. Widening fell into three categories: creating “pre-disease”; lowering diagnostic thresholds; and proposing earlier or different diagnostic methods. Rationales included standardising diagnostic criteria and new evidence about risks for people previously considered to not have the disease. No publication included rigorous assessment of potential harms of proposed changes. Among 14 panels with disclosures, the average proportion of members with industry ties was 75%. Twelve were chaired by people with ties. For members with ties, the median number of companies to which they had ties was seven. Companies with ties to the highest proportions of members were active in the relevant therapeutic area. Limitations arise from reliance on only disclosed ties, and exclusion of conditions too broad to enable analysis of single panel publications. CONCLUSIONS: For the common conditions studied, a majority of panels proposed changes to disease definitions that increased the number of individuals considered to have the disease, none reported rigorous assessment of potential harms of that widening, and most had a majority of members disclosing financial ties to pharmaceutical companies. Please see later in the article for the Editors' Summar
Growth and instability of a laminar plume in a strongly stratified environment
Experimental studies of laminar plumes descending under gravity into stably stratified environments have shown the existence of a critical injection velocity beyond which the plume exhibits a bifurcation to a coiling instability in three dimensions or a sinuous instability in a Hele-Shaw flow. In addition, flow visualization has shown that, prior to the onset of the instability, a stable base flow is established in which the plume penetrates to a depth significantly smaller than the neutral buoyancy depth. Moreover, the fresh water that is viscously entrained by the plume recirculates within a ‘conduit’ whose boundary with the background stratification appears sharp. Beyond the bifurcation, the buckling plume takes the form of a travelling wave of varying amplitude, confined within the conduit, which disappears at the penetration depth. To determine the mechanisms underlying these complex phenomena, which take place at a strikingly low Reynolds number but a high Schmidt number, we study here a two-dimensional arrangement, as it is perhaps the simplest system which possesses all the key experimental features. Through a combination of numerical and analytical approaches, a scaling law is found for the plume’s penetration depth within the base flow (i.e. the flow where the instability is either absent or artificially suppressed), and the horizontal cross-stream velocity and concentration profile outside the plume are determined from an asymptotic analysis of a simplified model. Direct numerical simulations show that, with increasing flow rate, a sinuous global mode is destabilized giving rise to the self-sustained oscillations as in the experiment. The sinuous instability is shown to be a consequence of the baroclinic generation of vorticity, due to the strong horizontal gradients at the edge of the conduit, a mechanism that is relevant even at very low Reynolds numbers. Despite the strength of this instability, the penetration depth is not significantly affected by it, instead being determined by the properties of the plume in the vicinity of the source. This scenario is confirmed by a local stability analysis. A finite region of local absolute instability is found near the source for sinuous modes prior to the onset of the global instability. Sufficiently far from the source the flow is locally stable. Near the onset of the global instability, varicose modes are also found to be locally, but only convectively, unstable
Mixing by Swimming Algae
In this fluid dynamics video, we demonstrate the microscale mixing
enhancement of passive tracer particles in suspensions of swimming microalgae,
Chlamydomonas reinhardtii. These biflagellated, single-celled eukaryotes (10
micron diameter) swim with a "breaststroke" pulling motion of their flagella at
speeds of about 100 microns/s and exhibit heterogeneous trajectory shapes.
Fluorescent tracer particles (2 micron diameter) allowed us to quantify the
enhanced mixing caused by the swimmers, which is relevant to suspension feeding
and biogenic mixing. Without swimmers present, tracer particles diffuse slowly
due solely to Brownian motion. As the swimmer concentration is increased, the
probability density functions (PDFs) of tracer displacements develop strong
exponential tails, and the Gaussian core broadens. High-speed imaging (500 Hz)
of tracer-swimmer interactions demonstrates the importance of flagellar beating
in creating oscillatory flows that exceed Brownian motion out to about 5 cell
radii from the swimmers. Finally, we also show evidence of possible cooperative
motion and synchronization between swimming algal cells.Comment: 1 page, APS-DFD 2009 Gallery of Fluid Motio
Longitudinal and Transverse Zeeman Ladders in the Ising-Like Chain Antiferromagnet BaCo2V2O8
We explore the spin dynamics emerging from the N\'eel phase of the chain
compound antiferromagnet BaCo2V2O8. Our inelastic neutron scattering study
reveals unconventional discrete spin excitations, so called Zeeman ladders,
understood in terms of spinon confinement, due to the interchain attractive
linear potential. These excitations consist in two interlaced series of modes,
respectively with transverse and longitudinal polarization. The latter have no
classical counterpart and are related to the zero-point fluctuations that
weaken the ordered moment in weakly coupled quantum chains. Our analysis
reveals that BaCo2V2O8, with moderate Ising anisotropy and sizable interchain
interactions, remarkably fulfills the conditions necessary for the observation
of these longitudinal excitations.Comment: 5 pages, 4 figures, 2 additional pages of supplemental material with
2 figures; Journal ref. added; 1 page erratum added at the end with 1 figur
X-Ray Emission from M32: X-Ray Binaries or a micro-AGN?
We have analysed archival {\it ROSAT} PSPC data for M32 in order to study the
x-ray emission from this nearest elliptical galaxy. We fit spectra from three
long exposures with Raymond-Smith, thermal bremsstrahlung, and power-law
models. All models give excellent fits. The thermal fits have kT4 keV,
the Raymond-Smith iron abundance is Solar, the power-law
fit has =1.60.1, and all fits have consistent with the
Galactic column. The source is centered on M32 to an accuracy of 9, and
unresolved at 27 FWHM (90 pc). M32 is x-ray variable by a factor of
3--5 on timescales of a decade down to minutes, with evidence for a possible
period of 1.3 days.
There are two plausible interpretations for these results: 1) Emission due to
low-mass x-ray binaries; 2) Emission due to accretion onto a massive central
black hole. Both of these possibilities are supported by arguments based on
previous studies of M32 and other old stellar systems; the {\it ROSAT} PSPC
data do not allow us to unambiguously choose between them. Observations with
the {\it ROSAT} HRI and with {\it ASCA} are required to determine which of
these two very different physical models is correct.Comment: 9 pages, 5 PostScript figures, uses AASTeX style files, Accepted for
publication in Astrophysical Journal Letter
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