Pulsating stars in NGC 6231 Frequency analysis and photometric mode identification near the main sequence

We used Johnson UBV photometric CCD observations to identify pulsating and other variable stars in the young open cluster NGC 6231. The multi-color information was used to classify pulsating variables, perform frequency analysis, and - where possible - to compare observed to theoretical amplitude ratios for mode identification. The data reduction was performed with standard IRAF tools. Differential light curves have been obtained by identifying a set of suitable comparison stars and the frequency analysis was then conducted on the basis of Fourier methods. Our classification of pulsating stars was based on the time scales and amplitudes of the variability with respect to the different filters and stellar parameters as calculated from published Str\"omgren and Geneva photometry. We identified 32 variable stars in the field of the cluster out of which 21 are confirmed members and twelve are newly detected variable stars. Ten stars were classified as Slowly Pulsating B (SPB) stars in NGC 6231 out of which seven are new discoveries. We also analyzed six previously reported {\beta} Cephei variables in more detail. One of them may be a hybrid {\beta} Cephei/SPB pulsator. In addition, we investigated five more previously suspected pulsators of this group which we cannot convincingly confirm. The remaining eleven variable stars are either not members of NGC 6231 or the membership status is questionable. Among them are three previously known {\delta} Scuti stars, two newly detected pulsators of this class, one new and two already known eclipsing binaries, one new SPB variable, one possible Pre-Main-Sequence (PMS) pulsator and another new variable star for which we cannot present a classification. With more than 20 main sequence pulsators of spectral type B, NGC 6231 becomes the open cluster with the largest population of such pulsating stars known.Comment: 27 pages, 35 figures, 3 Tables, accepted by A&A, abstract excessively shorted due to character limit

Post-collisional rapid exhumation and erosion during continental sedimentation: the example of the late Variscan Salvan-Dorénaz basin (Western Alps)

The Salvan-Dorénaz intramontane basin formed between ca. 308-293Ma as an asymmetric graben along crustal-scale transtensional fracture zones within the Aiguilles-Rouges crystalline massif (Western Alps) and represents a feature of the post-collisional evolution of the Variscan orogens. It contains 1.5-1.7km of continental clastic deposits which were eroded from granitic, volcanic, and metamorphic rocks. Textural and compositional immaturity of the sandstones, and the numerous lithic fragments with low chemical and physical stability suggest only short-range transport. 40Ar/39Ar analyses of detrital muscovite are interpreted to represent cooling of the crystalline basement below the respective closure temperatures. Ages from detrital muscovite range between ca. 280-330Ma. 40Ar/39Ar white mica plateau ages from granitic boulders range between 301-312Ma and suggest rapid cooling. The very short time interval recorded between the 40Ar/39Ar cooling ages and the stratigraphic age of the host sediment suggests that considerable portions of the upper crust were removed prior to the formation of the basin. Late Variscan granitic boulders document surface exposure and erosion of Late Carboniferous granites during early stages of the infilling of the basin. Therefore, unroofing of basement units, magmatic activity, and formation of the fault bounded Salvan-Dorénaz basin were acting concomitantly, and are highly suggestive of extensional tectonics. When compared with other orogens, this situation seems specific to the Variscan, especially the exclusively young ages of detrital material, however, modern analogous may exis

An evaluation of gas transfer velocity parameterizations during natural convection using DNS

Direct numerical simulations (DNS) of free surface flows driven by natural convection are used to evaluate different methods of estimating air-water gas exchange at no-wind conditions. These methods estimate the transfer velocity as a function of either the horizontal flow divergence at the surface, the turbulent kinetic energy dissipation beneath the surface, the heat flux through the surface, or the wind speed above the surface. The gas transfer is modeled via a passive scalar. The Schmidt number dependence is studied for Schmidt numbers of 7, 150 and 600. The methods using divergence, dissipation and heat flux estimate the transfer velocity well for a range of varying surface heat flux values, and domain depths. The two evaluated empirical methods using wind (in the limit of no wind) give reasonable estimates of the transfer velocity, depending however on the surface heat flux and surfactant saturation. The transfer velocity is shown to be well represented by the expression, k(s) = A (Bv)(1/4) Sc2(n), where A is a constant, B is the buoyancy flux, m is the kinematic viscosity, Sc is the Schmidt number, and the exponent n depends on the water surface characteristics. The results suggest that A = 0.39 and n approximate to 1/2 and n approximate to 2/3 for slip and no-slip boundary conditions at the surface, respectively. It is further shown that slip and no-slip boundary conditions predict the heat transfer velocity corresponding to the limits of clean and highly surfactant contaminated surfaces, respectively

Teaching interdisciplinary sustainability science teamwork skills to graduate students using in-person and web-based interactions

Interdisciplinary sustainability science teamwork skills are essential for addressing the world’s most pressing and complex sustainability problems, which inherently have social, natural, and engineering science dimensions. Further, because sustainability science problems exist at global scales, interdisciplinary science teams will need to consist of international members who communicate and work together effectively. Students trained in international interdisciplinary science skills will be able to hit the ground running when they obtain jobs requiring them to tackle sustainability problems. While many universities now have sustainability science programs, few offer courses that are interdisciplinary and international in scope. In the fall semester of 2013, we piloted a course for graduate students entitled “Principles of Interdisciplinary Sustainability Research” at Michigan Technological University. This course was part of our United States National Science Foundation Partnerships in International Research and Education project on bioenergy development impacts across the Americas. In this case study, we describe the course development and implementation, share critical insights from our experience teaching the course and student learning outcomes, and give recommendations for future similar course

Model for the structure function constant for index of refraction fluctuations in Rayleigh-Benard turbulence

A model for the structure function constant associated with index of refraction fluctuations in Rayleigh-Benard turbulence is developed. The model is based upon the following assumptions: (1) the turbulence is homogeneous and isotropic at or near the mid-plane, (2) the rate of production is in balance with the rate of dissipation, (3) an inertial region exists, and (4) estimates for the rate of dissipation of temperature fluctuations and of turbulent kinetic energy can be made by assuming that the large-scale turbulence is dissipated in one eddy turnover time. From these assumptions, the dependence of the structure function on the geometry, heat flux, and the properties of the fluid is obtained. The model predicts that the normalized structure function constant is independent of the Rayleigh number. To verify the model, numerical simulations of Rayleigh-Benard turbulence were performed using two different approaches: an in-house code based on a pseudo-spectral method, and a finite volume code which employs a model for the smallest scales of the turbulence. The model was found to agree with the results of the simulations, thereby lending support for the assumptions underlying the theory.Comment: 25 pages, 10 figures, 1 tabl

Renal function and cortical blood flow during the recovery phase of acute renal failure

Renal function and cortical blood flow during the recovery phase of acute renal failure. The characteristics of the recovery process in dichromate-induced acute renal failure were determined. Rats were studied 1, 4, 7, and 14 days after the s.c. injection of either saline or potassium dichromate. In the sham-injected control animals, all values at each interval were similar. The typical pattern of acute renal failure was seen one day after dichromate injection: glomerular filtration rate (GFR) fell 80%, total renal blood flow (TRBF) was reduced 35%, the proportional flow to the outer cortex was diminished, and the urinary to plasma (U/P) inulin clearance was reduced. The early recovery phase, days 4 and 7, was characterized by: 1) a mild but significant diuresis, 2) progressive improvement in GFR and an increase in the proportional flow to the outer cortex, which actually exceeded control values, 3) a dissociation between improvement in renal function and changes in TRBF, since GFR increased progressively while TRBF remained relatively fixed, and 4) improvement in GFR that was associated with a progressive and parallel increase in absolute perfusion of the outer cortex. The present data suggest that the recovery process occurs in two stages. In the first stage, the restoration of outer cortical perfusion and renal function precedes the recovery of TRBF and tubular function, which occur during the second stage of the recovery process.Fonction rénale et débit sanguin rénal cortical au cours de la période de récupération de l'insuffisance rénale aiguë. Les caractéristiques du processus de récupération après une insuffisance rénale aiguë induite par le dichromate, ont été déterminées. Des rats ont été étudiés 1, 4, 7, et l4 jours après l'injection s.c. de dichromate de potassium ou de soluté salé. Chez les animaux contrôles, toutes les valeurs obtenues sont semblables. L'aspect typique de l'insuffisance rénale aiguë est observée un jour après l'injection de dichromate: GFR diminue de 80%, le débit sanquin rénal (TRBF) est réduit de 35%, la fraction de ce débit délivrée au cortex superficiel diminue et le U/P de l'inuline est abaissé. La phase de récupération précoce, aux jours 4 et 7, est caractérisée par: 1) une diurèse peu importante mais significativement plus grande, 2) une amélioration progressive de GFR et une augmentation de la fraction du débit délivrée au cortex superficiel, qui devient supérieure aux valeurs contrôles, 3) une dissociation entre l'amélioration de la fonction rénale indiquée par l'augmentation progressive de GFR, et TRBF qui reste relativement bas, 4) et une amélioration de GFR qui est associée à une augmentation progressive et parallèle du débit absolu de perfusion du cortex superficiel. Ces résultats suggèrent que le processus de récuparation survient en deux étapes. A la première étape, la récupération du débit cortical superficiel et de la fonction rénale précède la récupération de TRBF et de la fonction tubulaire qui constitue la deuxième étape

A Survey Analysis of Forest Harvesting and Transportation Operations in Michigan

This paper assesses the technology involved in commercial forest harvesting and delivery operations. It investigates existing forest-based production capacity and its potential to supply the startup of large scale forest-based industries. A survey of harvesting and transportation workforce and technology was mailed to 1,130 logging firms operating in Michigan and four Wisconsin counties that adjoin Michigan’s Upper Peninsula. The response rate received was 28%. The paper details and analyses the different operational matters, conditions, equipment and transportation use reported by logging firms. The study provides technical forest products operations information and methods for assessing the capacity of logging firms and markets looking to expand their businesses

Generation of Laminar Vortex Rings by an Impulsive Body Force

It is shown that laminar vortex rings can be generated by impulsive body forces having particular spatial and temporal characteristics. The method produces vortex rings in a fluid initially at rest, and once generated, the flow field automatically satisfies the boundary conditions and is divergence-free. Numerical simulations and analytical models show that the strength of these rings can be accurately predicted by considering diffusion alone, despite the nonlinear nature of the generation process. A particularly simple model, which approximates the source of vorticity within vertical slabs, is proposed. This model predicts the ring circulation almost as accurately as a model which uses the exact geometry of the source of vorticity. It is found that when the duration of the force is less than a time scale based on the force radius and fluid viscosity, the ring circulation can be predicted accurately using an inviscid model.Comment: 37 pages, 11 figure

Numerical Solution of the Radiation Transport Equation at an Air-Water Interface for a Stratified Medium

This paper is a continuation of previous work that analytically examined the strength of radiation leaving an air-water interface. The approach here is to numerically integrate the radiation transport equation in order to capture the non-linear features of the problem, and also to include more realistic models for the thermal boundary layer. The radiation intensity of the photons emitted from the interface, relative to that of thermal radiation at the temperature of the interface, is defined here as the signal. This signal was computed for constant surface temperature and constant heat flux boundary conditions. As expected, the numerical computations show that the signal increased as the air-water temperature difference increased. The results are shown to form a hierarchy of signal strengths based on the chosen thermal stratification model. However, for both boundary conditions, the numerical results for a linear temperature profile compared very favorably with the simplified analytical linearized model over the thermal wavebands of 3–5 and 8–14 microns. In addition, the linearized model compared favorably with the most realistic models of thermal stratification

Polyacrylamide in Glycerol Solutions From an Atomistic Perspective of the Energetics, Structure, and Dynamics

All-atom molecular dynamics is used to investigate the structural, energetic, and dynamical properties of polyacrylamide (PAM) oligomers of different lengths solvated in pure glycerol, a 90:10 glycerol–water mixture, and pure water. We predict that the oligomers’ globular structure is obtained only when the modeling strategy considers the solvent as a continuous background. Meanwhile, for all-atom modeled solvents, the glycerol solutions display a strong tendency of trapping the oligomers in instantaneous elongated random coiled structures that remain locked-in over tens of nanoseconds. In pure water, the oligomers acquire considerably shorter random coiled structures of increased flexibility. The all-atom force field, generalized amber force field, is modified by including restrained electrostatic potential atomic charges for both glycerol and PAM. Three PAM oligomer lengths containing 10, 20, and 30 monomers are considered in detail by monitoring the radius of gyration, end-to-end distance, intra-potential energy, and solvent–oligomer interaction energies for decades of nanoseconds. The density and radial distribution function of glycerol solutions are calculated when modeled with the modified atomic charges, showing a very good agreement with the experimental results at temperatures around 300 K. Glycerol has multiple applications, including its use in gel formation for PAM gel electrophoresis. Our findings are relevant for the design of sensors based on microfluidics and tailored pharmaceutical buffer solutions