2,264 research outputs found
Research Questions Guiding Selection of an Appropriate Research Method
Research objects and research outcomes are proposed to act as a guide to select a proper research method. We, however, recommend that the research question as the essential factor of the research process should guide selection. Based on this idea we here develop taxonomy of research approaches with six categories. Taxonomy is then compared with three other classifications of research methods by using the comprehensiveness, parsimony and usefulness criteria
Stellar activity as noise in exoplanet detection I. Methods and application to solar-like stars and activity cycles
The detection of exoplanets using any method is prone to confusion due to the
intrinsic variability of the host star. We investigate the effect of cool
starspots on the detectability of the exoplanets around solar-like stars using
the radial velocity method. For investigating this activity-caused "jitter" we
calculate synthetic spectra using radiative transfer, known stellar atomic and
molecular lines, different surface spot configurations, and an added planetary
signal. Here, the methods are described in detail, tested and compared to
previously published studies. The methods are also applied to investigate the
activity jitter in old and young solar-like stars, and over a solar-like
activity cycles. We find that the mean full jitter amplitude obtained from the
spot surfaces mimicking the solar activity varies during the cycle
approximately between 1 m/s and 9 m/s. With a realistic observing frequency a
Neptune mass planet on a one year orbit can be reliably recovered. On the other
hand, the recovery of an Earth mass planet on a similar orbit is not feasible
with high significance. The methods developed in this study have a great
potential for doing statistical studies of planet detectability, and also for
investigating the effect of stellar activity on recovered planetary parameters.Comment: Accepted to MNRA
Clinical findings in relation to mortality in non-tuberculous mycobacterial infections : patients with Mycobacterium avium complex have better survival than patients with other mycobacteria
We compared the clinical findings and survival in patients with Mycobacterium avium complex (MAC) and other non-tuberculous mycobacteria (NTM). A total of 167 adult non-human immunodeficiency virus (HIV) patients with at least one positive culture for NTM were included. Medical records were reviewed. The patients were categorised according to the 2007 American Thoracic Society (ATS) criteria. MAC comprised 59 % of all NTM findings. MAC patients were more often female (70 % vs. 34 %, p <0.001) and had less fatal underlying diseases (23 % vs. 47 %, p = 0.001) as compared to other NTM patients. Symptoms compatible with NTM infection had lasted for less than a year in 34 % of MAC patients but in 54 % of other NTM patients (p = 0.037). Pulmonary MAC patients had a significantly lower risk of death compared to pulmonary other NTM (hazard ratio [HR] 0.50, 95 % confidence interval [CI] 0.33-0.77, p = 0.002) or subgroup of other slowly growing NTM (HR 0.55, 95 % CI 0.31-0.99, p = 0.048) or as rapidly growing NTM (HR 0.47, 95 % CI 0.25-0.87, p = 0.02). The median survival time was 13.0 years (95 % CI 5.9-20.1) for pulmonary MAC but 4.6 years (95 % CI 3.4-5.9) for pulmonary other NTM. Serious underlying diseases (HR 3.21, 95 % CI 2.05-5.01, p <0.001) and age (HR 1.07, 95 % CI 1.04-1.09, p <0.001) were the significant predictors of mortality and female sex was a predictor of survival (HR 0.38, 95 % CI 0.24-0.59, p <0.001) in the multivariate analysis. Pulmonary MAC patients had better prognosis than pulmonary other NTM patients. The symptom onset suggests a fairly rapid disease course.Peer reviewe
Magnetic field geometry and chemical abundance distribution of the He-strong star CPD -57 3509
The magnetic field of CPD -57 3509 was recently detected in the framework of
the BOB (B fields in OB stars) collaboration. We acquired low-resolution
spectropolarimetric observations of CPD -57 3509 with FORS2 and high-resolution
UVES observations randomly distributed over a few months to search for
periodicity, to study the magnetic field geometry, and to determine the surface
distribution of silicon and helium. We also obtained supplementary photometric
observations at a timeline similar to the spectroscopic and spectropolarimetric
observations. A period of 6.36d was detected in the measurements of the mean
longitudinal magnetic field. A sinusoidal fit to our measurements allowed us to
constrain the magnetic field geometry and estimate the dipole strength in the
range of 3.9-4.5kG. Our application of the Doppler imaging technique revealed
the presence of He I spots located around the magnetic poles, with a strong
concentration at the positive pole and a weaker one around the negative pole.
In contrast, high concentration Si III spots are located close to the magnetic
equator. Further, our analysis of the spectral variability of CPD -57 3509 on
short time scales indicates distinct changes in shape and position of line
profiles possibly caused by the presence of beta Cep-like pulsations. A small
periodic variability in line with the changes of the magnetic field strength is
clearly seen in the photometric data.Comment: 11 pages, 5 tables, 7 figures, accepted for publication in MNRA
Observational study of the association of first insulin type in uncontrolled type 2 diabetes with macrovascular and microvascular disease
<p>Aims: To compare the risk of vascular disease, HbA1c and weight change, between first prescribed insulins in people with type 2 diabetes.</p>
<p>Methods: People included in THIN United Kingdom primary care record database who began insulin (2000–2007) after poor control on oral glucose-lowering agents (OGLD) were grouped by the number of OGLDs in their treatment regimen immediately before starting insulin (n = 3,485). Within OGLD group, Cox regression compared macrovascular (all-cause mortality, myocardial infarction, acute coronary syndrome and stroke) and microvascular disease (peripheral neuropathy, nephropathy, and retinopathy) between insulin type (basal, pre-mix or Neutral Protamine Hagedorn, NPH) while ANCOVAs compared haemoglobin A1c (HbA1c) and weight change.</p>
<p>Results: Mean follow-up was 3.6 years. Rates of incident macrovascular events were similar when basal insulin was compared to pre-mix or NPH, adjusted hazard ratio versus basal: pre-mix 1.08 (95% CI 0.73, 1.59); NPH 1.00 (0.63, 1.58) after two OGLDs, and pre-mix 0.97 (0.46, 2.02); NPH 0.77 (0.32, 1.86) after three OGLDs. An increased risk of microvascular disease in NPH versus basal after 3 OGLDs, adjusted hazard ratio1.87 (1.04, 3.36), was not seen after two agents or in comparisons of basal and pre-mix. At one year, after two OGLDs, weight increase was less with basal compared with pre-mix. After three OGLDs, mean HbA1c had reduced less in basal versus pre-mix or NPH at 6–8 and at 9–11 months, and versus pre-mix at 12–14 months.</p>
<p>Conclusion: We found no difference in the risk of macrovascular events between first insulins in the medium term when started during poor glycaemia control. The increased risk of microvascular events with NPH warrants further study. In certain groups, first use of basal insulin was associated with less gain in weight and decrease in HbA1c compared to other insulins.</p>
New Insights into Properties of Large-N Holographic Thermal QCD at Finite Gauge Coupling at (the Non-Conformal/Next-to) Leading Order in N
In the context of [1]'s string theoretic dual of large-N thermal QCD-like
theories at finite gauge/string coupling (as part of the `MQGP' limit of [2]),
we discuss the following. First, up to LO in N, using the results of [3], we
show that the local T^3 of [2] is the T^2-invariant sLag of [3] in a resolved
conifold. This, together with the results of [4], shows that for a
(predominantly resolved or deformed) resolved warped deformed conifold, the
local T^3 of [2] in the MQGP limit, is the T^2-invariant sLag of [3] justifying
the construction of the delocalized SYZ type IIA mirror of the type IIB
background of [1]. Then, using the prescription of [5], we obtain the
temperature dependence of the thermal (and electrical) conductivity working up
to leading order in N (the number of D3-branes), and upon comparison with [6]
show that the results mimic a 1+1-dimensional Luttinger liquid with impurities.
Further, including sub-leading non-conformal terms in the metric determined by
M (the number of fractional D-branes = the number of colors = 3 in the IR after
the end of a Seiberg duality cascade), by looking at respectively the scalar,
vector and tensor modes of metric perturbations and using [7]'s prescription of
constructing appropriate gauge-invariant perturbations, we obtain respectively
the speed of sound, the diffusion constant and the shear viscosity \eta (and
\eta/s) including the non-conformal O((g_s M^2) (g_s N_f)/N<<1)-corrections,
N_f being the number of flavor D7-branes.Comment: 1+75 pages, LaTeX; Some corrections in Tc-related calculations,
results unchange
Extreme Technicolor & The Walking Critical Temperature
We map the phase diagram of gauge theories of fundamental interactions in the
flavor-temperature plane using chiral perturbation theory to estimate the
relation between the pion decaying constant and the critical temperature above
which chiral symmetry is restored. We then investigate the impact of our
results on models of dynamical electroweak symmetry breaking and therefore on
the electroweak early universe phase transition.Comment: RevTeX, 18 pages, 3 figure
Recommended from our members
Turbulent structure and scaling of the inertial subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar
The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the maximum wavelengths that belong to the inertial subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the inertial subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced decoupled structure identified from the vertical velocity skewness. However, on many occasions, combining the analysis of the inertial subrange and vertical velocity statistics suggests higher decoupling height than expected from the skewness profiles. Our results show that investigation of the length scales related to the inertial subrange significantly complements the analysis of the vertical velocity statistics and enables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.Peer reviewe
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