Discerning the Form of the Dense Core Mass Function

We investigate the ability to discern between lognormal and powerlaw forms for the observed mass function of dense cores in star forming regions. After testing our fitting, goodness-of-fit, and model selection procedures on simulated data, we apply our analysis to 14 datasets from the literature. Whether the core mass function has a powerlaw tail or whether it follows a pure lognormal form cannot be distinguished from current data. From our simulations it is estimated that datasets from uniform surveys containing more than approximately 500 cores with a completeness limit below the peak of the mass distribution are needed to definitively discern between these two functional forms. We also conclude that the width of the core mass function may be more reliably estimated than the powerlaw index of the high mass tail and that the width may also be a more useful parameter in comparing with the stellar initial mass function to deduce the statistical evolution of dense cores into stars.Comment: 6 pages, 2 figures, accepted for publication in PAS

Academics' use of courseware materials: A survey

Learning technology has yet to enter the mainstream of higher education. The UFC-funded Teaching and Learning Technology (TLT) programme is attempting to change this by sponsoring projects concerned with courseware production and delivery. These efforts could be thwarted if the Not Invented Here syndrome prevents the use of technology-based teaching and learning materials outside the originating departments. To gain a clearer understanding of why academics have been rejecting much existing courseware, and to establish the extent of the Not Invented Here syndrome, we carried out a survey of 800 academics in eight UK universities. The survey proved to be exceptionally revealing

Magnetic inflation and stellar mass. IV. four low-mass kepler eclipsing binaries consistent with non-magnetic stellar evolutionary models

Low-mass eclipsing binaries (EBs) show systematically larger radii than model predictions for their mass, metallicity, and age. Prominent explanations for the inflation involve enhanced magnetic fields generated by rapid rotation of the star that inhibit convection and/or suppress flux from the star via starspots. However, derived masses and radii for individual EB systems often disagree in the literature. In this paper, we continue to investigate low-mass EBs observed by NASA’s Kepler spacecraft, deriving stellar masses and radii using high-quality spacebased light curves and radial velocities from high-resolution infrared spectroscopy. We report masses and radii for three Kepler EBs, two of which agree with previously published masses and radii (KIC 11922782 and KIC 9821078). For the third EB (KIC 7605600), we report new masses and show the secondary component is likely fully convective (M2 = 0.17 ± 0.01M☉ and = - ☉ + R2 0.199 0.002R 0.001 ). Combined with KIC 10935310 from Han et al., we find that the masses and radii for four low-mass Kepler EBs are consistent with modern stellar evolutionary models for M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.Published versio

Manuscript of Jonathan Swift\u27s accounts

In this document Swift lists amounts owed to him and expenses as of 8 September 1718.https://scholarworks.umt.edu/whicker/1016/thumbnail.jp

Preparation and Evaluation of Uranium Alloys Based on Burnup

Next generation fast reactor designs utilizing metallic fuel are being developed as an alternative fuel cycle option in an effort to reduce carbon emissions. Historically, oxide fuels have been the industry standard, but interest in metallic fuel systems has grown considerably due to their thermal conductivity, fissile atom density, inherent safety, and ability to reach progressively higher burnups. Chemical complexity of metallic fuel systems increase as a function of burnup from fission product ingrowth and associated fuel cladding chemical interactions (FCCI) brought on by elemental redistribution and phase formation. To date, the most extensive operational study for metallic fuel was performed at the Experimental Breeder Reactor II (EBR-II) in Idaho from the 1960’s to the early 1990’s. During its operation, thousands of U-Zr and U-Pu-Zr fuel pins with various ranges of composition, burnup, and FCCI were analyzed from post-irradiated examinations (PIE) of spent fuel. Since decommissioning EBR-II, metallic fuel chemistry and fuel cladding studies for next generation reactors have become limited due to the lack of fast neutron irradiation facilities and data to support future designs. For this purpose, an arc melting procedure was developed for surrogate U-Zr and U-Pu-Zr burnup alloys with various fission product concentrations dependent on burnup. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were used for qualitative and quantitative compositional analysis. Combined Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to determine thermal properties and phase transition temperatures. As cast alloys were implemented into diffusion couples with cladding components to determine FCCI. Targeted research aims to reach ultra-high burnups, where effects of increased burnup on fuel chemistry and FCCI must be understood to prevent eutectic formation and cladding breakdown. Data compiled in this work is compared to EBR-II for validation. Resulting data can be extrapolated to elevated burnups, yet to be studied experimentally, without the need of post-irradiated materials, thus increasing the knowledgebase to support next generation fast reactor development

The Radius Distribution of Planets Around Cool Stars

We calculate an empirical, non-parametric estimate of the shape of the period-marginalized radius distribution of planets with periods less than 150 days using the small yet well-characterized sample of cool ($T_{\rm eff} <4000$K) dwarf stars in the Kepler catalog. In particular, we present and validate a new procedure, based on weighted kernel density estimation, to reconstruct the shape of the planet radius function down to radii smaller than the completeness limit of the survey at the longest periods. Under the assumption that the period distribution of planets does not change dramatically with planet radius, we show that the occurrence of planets around these stars continues to increase to below 1 $R_\oplus$, and that there is no strong evidence for a turnover in the planet radius function. In fact, we demonstrate using many iterations of simulated data that a spurious turnover may be inferred from data even when the true distribution continues to rise toward smaller radii. Finally, the sharp rise in the radius distribution below $\sim$3 $R_\oplus$ implies that a large number of planets await discovery around cool dwarfs as the sensitivities of ground-based transit surveys increase.Comment: 13 pages, 10 figures, published in Ap

A Pre-Protostellar Core in L1551. II. State of Dynamical and Chemical Evolution

Both analytic and numerical radiative transfer models applied to high spectral resolution CS and N2H+ data give insight into the evolutionary state of L1551 MC. This recently discovered pre-protostellar core in L1551 appears to be in the early stages of dynamical evolution. Line-of-sight infall velocities of >0.1km/s are needed in the outer regions of L1551 MC to adequately fit the data. This translates to an accretion rate of ~ 1e-6 Msun/yr, uncertain to within a factor of 5 owing to unknown geometry. The observed dynamics are not due to spherically symmetric gravitational collapse and are not consistent with the standard model of low-mass star formation. The widespread, fairly uniform CS line asymmetries are more consistent with planar infall. There is modest evidence for chemical depletion in the radial profiles of CS and C18O suggesting that L1551 MC is also chemically young. The models are not very sensitive to chemical evolution. L1551 MC lies within a quiescent region of L1551 and is evidence for continued star formation in this evolved cloud.Comment: 27 pages, 7 figures, ApJ accepte

Magnetic inflation and stellar mass. III. revised parameters for the component stars of NSVS 07394765

We perform a new analysis of the M-dwarf–M-dwarf eclipsing binary system NSVS 07394765 in order to investigate the reported hyper-inflated radius of one of the component stars. Our analysis is based on archival photometry from the Wide Angle Search for Planets, new photometry from the 32 cm Command Module Observatory telescope in Arizona and the 70 cm telescope at Thacher Observatory in California, and new high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrograph on the Discovery Channel Telescope. The masses and radii we measure for each component star disagree with previously reported measurements. We show that both stars are early M-type main-sequence stars without evidence for youth or hyper-inflation ( = - ☉ M M + 1 0.661 0.036 0.008 , = - ☉ M M + 2 0.608 0.028 0.003 , = - ☉ + R1 0.599 0.019 R 0.032 , = - ☉ + R2 0.625 0.027 R 0.012 ), and we update the orbital period and eclipse ephemerides for the system. We suggest that the likely cause of the initial hyper-inflated result is the use of moderate-resolution spectroscopy for precise radial velocity measurements.Published versio