3,738 research outputs found
Research Synthesis
Herbert Simon’s (1956) concept of satisficing provides an intuitive explanation for the reasons why respondents to surveys sometimes adopt response strategies that can lead to a reduction in data quality. As such, the concept rapidly gained popularity among researchers after it was first introduced to the field of survey methodology by Krosnick and Alwin (1987), and it has become a widely cited buzzword linked to different forms of response error. In this article, we present the findings of a systematic review involving a content analysis of journal articles published in English-language journals between 1987 and 2015 that have drawn on the satisficing concept to evaluate survey data quality. Based on extensive searches of online databases, and an initial screening exercise to apply the study’s inclusion criteria, 141 relevant articles were identified. Guided by the theory of survey satisficing described by Krosnick (1991), the methodological features of the shortlisted articles were coded, including the indicators of satisficing analyzed, the main predictors of satisficing, and the presence of main or interaction effects on the prevalence of satisficing involving indicators of task difficulty, respondent ability, and respondent motivation. Our analysis sheds light on potential differences in the extent to which satisficing theory holds for different types of response error, and highlights a number of avenues for future research
Investigating situated cultural practices through cross-sectoral digital collaborations: policies, processes, insights
The (Belfast) Good Friday Agreement represents a major milestone in Northern Ireland's recent political history, with complex conditions allowing for formation of a ‘cross-community’ system of government enabling power sharing between parties representing Protestant/loyalist and Catholic/nationalist constituencies. This article examines the apparent flourishing of community-focused digital practices over the subsequent ‘post-conflict’ decade, galvanised by Northern Irish and EU policy initiatives armed with consolidating the peace process. Numerous digital heritage and storytelling projects have been catalysed within programmes aiming to foster social processes, community cohesion and cross-community exchange. The article outlines two projects—‘digital memory boxes’ and ‘interactive galleon’—developed during 2007–2008 within practice-led PhD enquiry conducted in collaboration with the Nerve Centre, a third-sector media education organisation. The article goes on to critically examine the processes involved in practically realising, and creatively and theoretically reconciling, community-engaged digital production in a particular socio-political context of academic-community collaboration
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
Spatially Resolving the Inner Disk of TW Hya
We present Keck Interferometer observations of TW Hya that spatially resolve
its emission at 2 micron wavelength. Analyzing these data together with
existing K-band veiling and near-infrared photometric measurements, we conclude
that the inner disk consists of optically thin, sub-micron-sized dust extending
from ~4 AU to within 0.06 AU of the central star. The inner disk edge may be
magnetospherically truncated. Even if we account for the presence of gas in the
inner disk, these small dust grains have survival times against radiation
blow-out that are orders of magnitude shorter than the age of the system,
suggesting continual replenishment through collisions of larger bodies.Comment: 11 pages, including 2 figures. Accepted by ApJ
A High Spatial Resolution Study of the λ=3 mm Continuum of Orion-KL
Recent interferometric observations have called into question the traditional
view of the Orion-KL region, which displays one of the most well-defined cases
of chemical differentiation in a star-forming region. Previous,
lower-resolution images of Orion-KL show emission signatures for oxygen-bearing
organic molecules toward the Orion Compact Ridge, and emission for
nitrogen-bearing organic molecules toward the Orion Hot Core. However, more
recent observations at higher spatial resolution indicate that the bulk of the
molecular emission is arising from many smaller, compact clumps that are
spatially distinct from the traditional Hot Core and Compact Ridge sources. It
is this type of observational information that is critical for guiding
astrochemical models, as the spatial distribution of molecules and their
relation to energetic sources will govern the chemical mechanisms at play in
star-forming regions. We have conducted millimeter imaging studies of Orion-KL
with various beam sizes using CARMA in order to investigate the continuum
structure. These \lambda;=3mm observations have synthesized beam sizes of
~0.5"-5.0". These observations reveal the complex continuum structure of this
region, which stands in sharp contrast to the previous structural models
assumed for Orion-KL based on lower spatial resolution images. The new results
indicate that the spatial scaling previously used in determination of molecular
abundances for this region are in need of complete revision. Here we present
the results of the continuum observations, discuss the sizes and structures of
the detected sources, and suggest an observational strategy for determining the
proper spatial scaling to accurately determine molecular abundances in the
Orion-KL region.Comment: 20 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Properties of the Bare Nucleus of Comet 96P/Machholz 1
We observed comet 96P/Machholz 1 on a total of nine nights before and after perihelion during its 2017/2018 apparition. Both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96P an object of great interest. Our observations show no evidence of a detectable dust coma, implying that we are observing a bare nucleus at distances ranging from 2.3 to 3.8 au. Based on this assumption, we calculated its color and found average values of g'–r' = 0.50 ± 0.04, r'–i' = 0.17 ± 0.03, and i'–z' = 0.06 ± 0.04. These are notably more blue than those of the nuclei of other Jupiter-family and long-period comets. Furthermore, assuming a bare nucleus, we found an equivalent nuclear radius of 3.4 ± 0.2 km with an axial ratio of at least 1.6 ± 0.1. The lightcurve clearly displays one large peak, one broad flat peak, and two distinct troughs, with a clear asymmetry that suggests that the shape of the nucleus deviates from that of a simple triaxial ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear rotation period to 4.10 ± 0.03 hr and 4.096 ± 0.002 hr before and after perihelion, respectively. Within the uncertainties, 96P's rotation period does not appear to have changed throughout the apparition, and we conclude a maximum possible change in rotation period of 130 s. The observed properties were compared to those of comet 322P and interstellar object 1I/'Oumuamua in an attempt to study the effects of close perihelion passages on cometary surfaces and their internal structure and the potential interstellar origin of 96P
A Machine Learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves
A fundamental challenge for wide-field imaging surveys is obtaining follow-up
spectroscopic observations: there are > photometrically cataloged
sources, yet modern spectroscopic surveys are limited to ~few x targets.
As we approach the Large Synoptic Survey Telescope (LSST) era, new algorithmic
solutions are required to cope with the data deluge. Here we report the
development of a machine-learning framework capable of inferring fundamental
stellar parameters (Teff, log g, and [Fe/H]) using photometric-brightness
variations and color alone. A training set is constructed from a systematic
spectroscopic survey of variables with Hectospec/MMT. In sum, the training set
includes ~9000 spectra, for which stellar parameters are measured using the
SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest
algorithm to perform a non-parametric regression that predicts Teff, log g, and
[Fe/H] from photometric time-domain observations. Our final, optimized model
produces a cross-validated root-mean-square error (RMSE) of 165 K, 0.39 dex,
and 0.33 dex for Teff, log g, and [Fe/H], respectively. Examining the subset of
sources for which the SSPP measurements are most reliable, the RMSE reduces to
125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable
via low-resolution spectroscopy. For variable stars this represents a ~12-20%
improvement in RMSE relative to models trained with single-epoch photometric
colors. As an application of our method, we estimate stellar parameters for
~54,000 known variables. We argue that this method may convert photometric
time-domain surveys into pseudo-spectrographic engines, enabling the
construction of extremely detailed maps of the Milky Way, its structure, and
history
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
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Integrated motivational interviewing and cognitive behavioural therapy for people with psychosis and comorbid substance misuse: randomised controlled trial
Objectives
To evaluate the effectiveness of integrated motivational interviewing and cognitive behaviour therapy in addition to standard care for patients with psychosis and a co-morbid substance use problem.
Design
Two-centre, open, rater-blind randomised controlled trial
Setting
UK Secondary Care
Participants
327 patients with clinical diagnoses of schizophrenia, schizophreniform or schizoaffective disorder and DSM-IV diagnoses of drug and/or alcohol dependence or abuse
Interventions
Participants were randomly allocated to integrated motivational interviewing and cognitive behaviour therapy or standard care. Therapy has two phases. Phase one – “motivation building” – concerns engaging the patient, then exploring and resolving ambivalence for change in substance use. Phase two –“Action” – supports and facilitates change using cognitive behavioural approaches. Up to 26 therapy sessions were delivered over one year.
Main outcomes
The primary outcome was death from any cause or admission to hospital in the 12 months after therapy. Secondary outcomes were frequency and amount of substance use (Timeline Followback), readiness to change, perceived negative consequences of use, psychotic symptom ratings, number and duration of relapses, global assessment of functioning and deliberate self harm, at 12 and 24 months, with additional Timeline Followback assessments at 6 and 18 months. Analysis was by intention-to-treat with robust treatment effect estimates.
Results
327 participants were randomised. 326 (99.7%) were assessed on the primary outcome, 246 (75.2%) on main secondary outcomes at 24 months. Regarding the primary outcome, there was no beneficial treatment effect on hospital admissions/ death during follow-up, with 20.2% (33/163) of controls and 23.3% (38/163) of the therapy group deceased or admitted (adjusted odds-ratio 1.16; P= 0.579; 95% confidence interval 0.68 to 1.99). For secondary outcomes there was no treatment effect on frequency of substance use or perceived negative consequences, but a statistically significant effect of therapy on amount used per substance-using day (adjusted odds-ratios: (a) for main substance 1.50; P=0.016; 1.08 to 2.09, (b) all substances 1.48; P=0.017; 1.07 to 2.05). There was a statistically significant treatment effect on readiness to change use at 12 months (adjusted odds-ratio 2.05; P=0.004; 1.26 to 3.31), not maintained at 24 months. There were no treatment effects on assessed clinical outcomes.
Conclusions
Integrated motivational interviewing and cognitive behaviour therapy for people with psychosis and substance misuse does not improve outcome in terms of hospitalisation, symptom outcomes or functioning. It does result in a reduction in amount of substance use which is maintained over the year’s follow up.
Trial registration
Current Controlled Trials: ISRCTN1440448
Inside-Out Evacuation of Transitional Protoplanetary Disks by the Magneto-Rotational Instability
How do T Tauri disks accrete? The magneto-rotational instability (MRI)
supplies one means, but protoplanetary disk gas is typically too poorly ionized
to be magnetically active. Here we show that the MRI can, in fact, explain
observed accretion rates for the sub-class of T Tauri disks known as
transitional systems. Transitional disks are swept clean of dust inside rim
radii of ~10 AU. Stellar coronal X-rays ionize material in the disk rim,
activating the MRI there. Gas flows from the rim to the star, at a rate limited
by the depth to which X-rays ionize the rim wall. The wider the rim, the larger
the surface area that the rim wall exposes to X-rays, and the greater the
accretion rate. Interior to the rim, the MRI continues to transport gas; the
MRI is sustained even at the disk midplane by super-keV X-rays that Compton
scatter down from the disk surface. Accretion is therefore steady inside the
rim. Blown out by radiation pressure, dust largely fails to accrete with gas.
Contrary to what is usually assumed, ambipolar diffusion, not Ohmic
dissipation, limits how much gas is MRI-active. We infer values for the
transport parameter alpha on the order of 0.01 for GM Aur, TW Hyd, and DM Tau.
Because the MRI can only afflict a finite radial column of gas at the rim, disk
properties inside the rim are insensitive to those outside. Thus our picture
provides one robust setting for planet-disk interaction: a protoplanet interior
to the rim will interact with gas whose density, temperature, and transport
properties are definite and decoupled from uncertain initial conditions. Our
study also supplies half the answer to how disks dissipate: the inner disk
drains from the inside out by the MRI, while the outer disk photoevaporates by
stellar ultraviolet radiation.Comment: Accepted to Nature Physics June 7, 2007. The manuscript for
publication is embargoed per Nature policy. This arxiv.org version contains
more technical details and discussion, and is distributed with permission
from the editors. 10 pages, 4 figure
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