Dynamo models and differential rotation in late-type rapidly rotating stars

Increasing evidence is becoming available about not only the surface differential rotation of rapidly rotating cool stars but, in a small number of cases, also about temporal variations, which possibly are analogous to the solar torsional oscillations. Given the present difficulties in resolving the precise nature of such variations, due to both the short length and poor resolution of the available data, theoretical input is vital to help assess the modes of behaviour that might be expected, and will facilitate interpretation of the observations. Here we take a first step in this direction by studying the variations in the convection zones of such stars, using a two dimensional axisymmetric mean field dynamo model operating in a spherical shell in which the only nonlinearity is the action of the azimuthal component of the Lorentz force of the dynamo generated magnetic field on the stellar angular velocity. We consider three families of models with different depths of dynamo-active regions. For moderately supercritical dynamo numbers we find torsional oscillations that penetrate all the way down to the bottom of the convection zones, similar to the case of the Sun. For larger dynamo numbers we find fragmentation in some cases and sometimes there are other dynamical modes of behaviour, including quasi-periodicity and chaos. We find that the largest deviations in the angular velocity distribution caused by the Lorentz force are of the order of few percent, implying that the original assumed `background' rotation field is not strongly distorted.Comment: Astronomy and Astrophysics, in pres

Rotation periods of exoplanet host stars

The stellar rotation periods of ten exoplanet host stars have been determined using newly analysed Ca II H & K flux records from Mount Wilson Observatory and Stromgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes (APTs) at Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 \pm 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of fourteen exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature.Comment: Accepted for publication in MNRAS. 15 pages, 11 figure

Differential rotation and meridional flow on the lower zero age main sequence: Reynolds stress versus baroclinic flow

We study the variation of surface differential rotation and meridional flow along the lower part of the zero age main sequence (ZAMS). We first compute a sequence of stellar models with masses from 0.3 to 1.5 solar masses. We then construct mean field models of their outer convection zones and compute differential rotation and meridional flows by solving the Reynolds equation with transport coefficients from the second order correlation approximation. For a fixed rotation period of 2.5 d we find a strong dependence of the surface differential rotation on the effective temperature with weak surface shear for M dwarfs and very large values for F stars. The increase with effective temperature is modest below 6000 K but very steep above 6000 K. The meridional flow shows a similar variation with temperature but the increase with temperature is not quite so steep. Both the surface rotation and the meridional circulation are solar-type over the entire temperature range. We also study the dependence of differential rotation and meridional flow on the rotation period for masses. from 0.3 to 1.1 solar masses. The variation of the differential rotation with period is weak except for very rapid rotation. The meridional flow shows a systematic increase of the flow speed with the rotation rate. Numerical experiments in which either the $\Lambda$ effect is dropped in the Reynolds stress or the baroclinic term in the equation of motion is cancelled show that for effective temperatures below 6000 K the Reynolds stress is the dominant driver of differential rotation

Differential rotation on the lower main sequence

We compute the differential rotation of main sequence stars of the spectral types F, G, K, and M by solving the equation of motion and the equation of convective heat transport in a mean-field formulation. For each spectral type the rotation rate is varied to study the dependence of the surface shear on this parameter. The resulting rotation patterns are all solar-type. The horizontal shear turns out to depend strongly on the effective temperature and only weakly on the rotation rate. The meridional flow depends more strongly on the rotation rate and has different directions in the cases of very slow and very fast rotation, respectively.Comment: 4 pages, 5 figures, Astron. Nachr. 326, 265 (2005

Anastomotic complications after tracheal resection: Prognostic factors and management

ObjectiveWe sought to identify risk factors for anastomotic complications after tracheal resection and to describe the management of these patients.MethodsThis was a single-institution, retrospective review of 901 patients who underwent tracheal resection.ResultsThe indications for tracheal resection were postintubation tracheal stenosis in 589 patients, tumor in 208, idiopathic laryngotracheal stenosis in 83, and tracheoesophageal fistula in 21. Anastomotic complications occurred in 81 patients (9%). Eleven patients (1%) died after operation, 6 of anastomotic complications and 5 of other causes (odds ratio 13.0, P = .0001 for risk of death after anastomotic complication). At the end of treatment, 853 patients (95%) had a good result, whereas 37 patients (4%) had an airway maintained by tracheostomy or T-tube. The treatments of patients with an anastomotic complication were as follows: multiple dilations (n = 2), temporary tracheostomy (n = 7), temporary T-tube (n = 16), permanent tracheostomy (n = 14), permanent T-tube (n = 20), and reoperation (n = 16). Stepwise multivariable analysis revealed the following predictors of anastomotic complications: reoperation (odds ratio 3.03, 95% confidence interval 1.69-5.43, P = .002), diabetes (odds ratio 3.32, 95% confidence interval 1.76-6.26, P = .002), lengthy (≥4 cm) resections (odds ratio 2.01, 95% confidence interval 1.21-3.35, P = .007), laryngotracheal resection (odds ratio 1.80, 95% confidence interval 1.07-3.01, P = .03), age 17 years or younger (odds ratio 2.26, 95% confidence interval 1.09-4.68, P = .03), and need for tracheostomy before operation (odds ratio 1.79, 95% confidence interval 1.03-3.14, P = .04).ConclusionsTracheal resection is usually successful and has a low mortality. Anastomotic complications are uncommon, and important risk factors are reoperation, diabetes, lengthy resections, laryngotracheal resections, young age (pediatric patients), and the need for tracheostomy before operation

Omentum is highly effective in the management of complex cardiothoracic surgical problems

AbstractObjectives: Vascularized, pedicled tissue flaps are often used for cardiothoracic surgical problems complicated by factors that adversely affect healing, such as previous irradiation, established infection, or steroid use. We reviewed our experience with use of the omentum in these situations to provide a yardstick against which results with other vascularized flaps (specifically muscle flaps) could be compared. Methods: A retrospective review was undertaken of 85 consecutive patients in whom omentum was used in the chest. In 47 patients (group I), use of omentum was prophylactic to aid in the healing of closures or anastomoses considered to be at high risk for failure. In 32 patients (group II), omentum was used in the treatment of problems complicated by established infection. In 6 patients (group III), omentum was used for coverage of prosthetic chest wall replacements after extensive chest wall resection. Results: Overall, omental transposition was successful in its prophylactic or therapeutic purpose in 88% of these difficult cases (75/85). Success with omentum was achieved for 89% of patients (42/47) in group I, 91% of patients (29/32) in group II, and 67% of patients (4/6) in group III. Three patients (3.5%) had complications of omental mobilization. Four patients (4.7%) died after the operation as a result of failure of the omentum to manage the problem for which it was used. Conclusions: Results with omental transposition compare favorably with published series of similarly challenging cases managed with muscle transposition. Complications of omental mobilization are rare. We believe that its unique properties render the omentum an excellent choice of vascularized pedicle in the management of the most complex cardiothoracic surgical problems.J Thorac Cardiovasc Surg 2003;125:526-3

Local models of stellar convection: Reynolds stresses and turbulent heat transport

We study stellar convection using a local three-dimensional MHD model, with which we investigate the influence of rotation and large-scale magnetic fields on the turbulent momentum and heat transport. The former is studied by computing the Reynolds stresses, the latter by calculating the correlation of velocity and temperature fluctuations, both as functions of rotation and latitude. We find that the horisontal correlation, Q_(theta phi), capable of generating horisontal differential rotation, is mostly negative in the southern hemisphere for Coriolis numbers exceeding unity, corresponding to equatorward flux of angular momentum in accordance with solar observations. The radial component Q_(r phi) is negative for slow and intermediate rotation indicating inward transport of angular momentum, while for rapid rotation, the transport occurs outwards. Parametrisation in terms of the mean-field Lambda-effect shows qualitative agreement with the turbulence model of Kichatinov & R\"udiger (1993) for the horisontal part H \propto Q_(theta phi)/cos(theta), whereas for the vertical part, V \propto Q_(r phi)/sin(theta), agreement only for intermediate rotation exists. The Lambda-coefficients become suppressed in the limit of rapid rotation, this rotational quenching being stronger for the V component than for H. We find that the stresses are enhanced by the presence of the magnetic field for field strengths up to and above the equipartition value, without significant quenching. Concerning the turbulent heat transport, our calculations show that the transport in the radial direction is most efficient at the equatorial regions, obtains a minimum at midlatitudes, and shows a slight increase towards the poles. The latitudinal heat transport does not show a systematic trend as function of latitude or rotation.Comment: 26 pages, 20 figures, final published version. For a version with higher resolution figures, see http://cc.oulu.fi/~pkapyla/publ.htm

Characterizing Nature and Participant Experience in Studies of Nature Exposure for Positive Mental Health: An Integrative Review

A growing number of studies demonstrate significant associations between nature experiences and positive mental health outcomes (e.g., improved mood, decreased stress). However, implementation of this research by practitioners in fields such as urban design or public health has been limited. One reason for this is that it remains unclear what elements of nature and types of participant experience are consistently associated with mental health benefits. As a result, decision-makers who aim to enhance mental health in cities have little guidance about which elements of nature and types of experiences in natural areas may lead to positive mental health outcomes. We reviewed 30 studies with 41 distinct exposures in nature that elicited positive mental health benefits and characterized the elements of nature found at these sites, as well as aspects of participants’ experience. Elements of natural areas considered include: forest, managed grass, and water as dominant land cover types, specific water features (e.g., small ponds, fountains) and built features (e.g., trails, paths). The majority of the studies we reviewed assessed the experiences of individuals (vs. in groups) participating in walks during warmer seasons. Most studies did not describe the “nature of the nature” associated with positive mental health outcomes. We contacted authors and used Google Earth imagery to reconstruct the specific natural elements, landscape typology, and site adjacencies present in past studies. We recommend specific ways researchers could better and more transparently document important elements of nature and participant experience in study design and reporting that will enhance the planning and design relevance of their work

Clinical Team Response to the Impact of COVID-19 on Diabetes Self-Management: Findings From a Qualitative Study

The aims of this study were to explore providers’ perceptions of how COVID-19 affected patients’ psychological wellbeing and diabetes self-care and discover how providers responded to sustain and improve patients’ psychological health and diabetes management during the pandemic. Twenty-four semi-structured interviews were completed with primary care providers (n=14) and endocrine specialty clinicians (n=10) across sixteen clinics in North Carolina. Interview topics included: (1) current glucose monitoring approaches and diabetes management strategies for people with diabetes (2) barriers and unintended consequences encountered with respect to diabetes self-management, and (3) innovative strategies developed to overcome barriers. Interview transcripts were coded using qualitative analysis software and analyzed to identify cross-cutting themes and differences between participants. Primary care providers and endocrine specialty clinicians reported that people with diabetes experienced increased mental health symptoms, increased financial challenges and positive and negative changes in self-care routines due to COVID-19. To offer support, primary care providers and endocrine specialty providers focused discussions on lifestyle management and utilized telemedicine to connect with patients. Additionally, endocrine specialty clinicians helped patients access financial assistance programs. Findings indicate that people with diabetes experienced unique challenges to self-management during the pandemic and providers responded with targeted support strategies. Future research should explore the effectiveness of these provider interventions as the pandemic continues to evolve

Efficient and accurate extraction of in vivo calcium signals from microendoscopic video data

In vivo calcium imaging through microendoscopic lenses enables imaging of previously inaccessible neuronal populations deep within the brains of freely moving animals. However, it is computationally challenging to extract single-neuronal activity from microendoscopic data, because of the very large background fluctuations and high spatial overlaps intrinsic to this recording modality. Here, we describe a new constrained matrix factorization approach to accurately separate the background and then demix and denoise the neuronal signals of interest. We compared the proposed method against previous independent components analysis and constrained nonnegative matrix factorization approaches. On both simulated and experimental data recorded from mice, our method substantially improved the quality of extracted cellular signals and detected more well-isolated neural signals, especially in noisy data regimes. These advances can in turn significantly enhance the statistical power of downstream analyses, and ultimately improve scientific conclusions derived from microendoscopic data