182,526 research outputs found
Magnetic Fields of F-Type Stars
No full textMagnetic fields are an observable feature of many stars, with warm, F-type stars of interest in searching for the transition from the fossil fields in hot stars to dynamos in cool stars driven by convection zones. Thus, this thesis presents an observational survey of F-type stars close to the expected transition between fossil and dynamo magnetic fields. A magnetic snapshot survey of 55 targets resulted in 14 magnetic field detections, across every spectral class from F3V-F9V ranging in strength from 0.3±0.1G (36 UMa, F8V) to 8.3±0.9 G (h Dra, F8V). These results are followed up with detailed mapping using Zeeman Doppler Imaging (ZDI) of the large-scale surface magnetic fields for four of these stars, β CrB, σ Boo, θ Dra, and β Vir. On the hot side of the suspected transition zone, β CrB (A9) shows a relatively complex, but stable topology which is not common for a fossil field and is more complex than a dipole. On the cool side of the suspected transition zone, the surface magnetic field of σ Boo (F3V) shows a relatively simple field topology with a dominant dipole structure. This is the first magnetic map for an F3 star and provides an opportunity to study magnetism in a star with an outer convection zone thickness less than three per cent of the stellar radius. ZDI maps are also presented for two late F-stars, θ Dra (F8IV) and β Vir (F9V). These two late F-stars are contrasted with σ Boo, and show a more complex magnetic topology. There are differences in complexity of the magnetic field between θ Dra and β Vir, which is possibly related to an increased rotation rate for θ Dra which shows more detail due to a greater surface resolution. The ZDI maps are also used in modelling the stellar winds. While definitive evidence of the transition from fossil to dynamo field is not clear from the single-epoch magnetic map results obtained, this work suggests additional future maps obtained across different epochs will provide empirical evidence for how stellar mass, rotation and age drive the emergence of dynamo fields in stars with shallow convection zones
Data for: Nuclear genome shuffling increases recombinant protein expression in the chloroplast of Chlamydomonas reinhardtii
No full textSupplemental data for "Nuclear genome shuffling significantly increases production of chloroplast-based recombinant protein in Chlamydomonas reinhardtii" by Fields et al
Letter from M. A. Fields to W. F. Hickson
No full textLetter from M. A. Fields to W. F. Hickson, concerning dates for Washington Sectional Meeting
The Starspots and Magnetic Fields of Young Late-F Stars
No full textObservations of the magnetic activity of young solar-type stars offer insights into the early history of our Sun, its dynamo activity and planetary impacts. The warmest of solar-type stars, of F spectral type, have been shown to represent a transition from dynamo driven cool stars to fossil field dominated hot stars due to their thin convective zones, however, there are few detailed observations of the surface magnetic fields and cycles of these stars. This study thus presents multiple-epoch star spot and surface magnetic field maps of three young late-F solar-type stars, namely VXR 77A (V380 Vel, F8V, ∼27 Myr), HD 43989 (V1358 Ori, F9V, ∼26 Myr) and HIP 71933 (HD 128181, F8V, ∼15 Myr). Those images were produced using the technique of Doppler and Zeeman-Doppler Imaging using spectroscopic and spectropolarimetric data, and derived from observations made across fourteen different epochs and multiple telescopes between 2003 and 2019. The resulting star spot brightness maps and the implied underlying dynamos for two of the stars (HD 43989 and VXR 77A) are consistent with those of other solar-type stars including polar spots, but there is a persistent lack of a polar spot on the third star, HIP 71933. Differential rotation measurements performed using these images for all three stars, were found to be slightly higher than that for young G-type stars, a stellar mass dependence consistent with dynamo theory and previous observations. However, in terms of the appearance and temporal evolution of the magnetic fields observed for two of the stars, HD 43989 shows complex magnetic fields apparently evolving over a timescale of two years, but in contrast, HIP 71933 shows a more stable magnetic field configuration, with a dominant and apparently unchanging poloidal field topology over a similar timescale, that warrants further investigation to look for any potential evolution. The radial velocities measured for two of the stars (VXR 77A and HIP 71933) indicate the possibility of a binary, but this is not expected to affect the star spot and magnetic fields results due to the wide separation of any companion, if it exists. In overall terms, this study provides evidence for magnetic dynamos in warm young solar-type showing similarities to those of other young solar-type stars, but with some unusual but not unique features on HIP 71933
Terraced fields with trees
No full textThe photograph is shot from a higher path, looking down into a valley with groups of structures and a village; many (fruit?) trees are in bloom, and there are terraced fields throughout the valley; steep cliffs surround the valley. The negative is black and white, and is either somewhat cloudy or the atmosphere is rainy or dusty; no number is visible
The 4-rank of for real quadratic fields F
No full text1. Introduction. Let F be a number field, and let be the ring of its integers. Several formulas for the 4-rank of are known (see [7], [5], etc.). If √{-1) ∉ F, then such formulas are related to S-ideal class groups of F and F(√(-1)), and the numbers of dyadic places in F and F(√(-1)), where S is the set of infinite dyadic places of F. In [11], the author proposes a method which can be applied to determine the 4-rank of for real quadratic fields F with 2 ∉ NF. The author also lists many real quadratic fields with the 2-Sylow subgroups of being isomorphic to ℤ/2ℤ ⊕ ℤ/2ℤ ⊕ ℤ/4ℤ. In [12], the author gives a 4-rank formula for imaginary quadratic fields F. By the formula, it is enough to compute some Legendre symbols when one wants to know 4-rank for a given imaginary quadratic field F. In the present paper, we give a similar formula for real quadratic fields F. Then we give 4-rank tables for real quadratic fields F = ℚ√d whose discriminants have at most three odd prime divisors
General, agricultural & gold fields, map of Victoria [cartographic material] /
No full textMap of Victoria showing roads, tracks, railways completed, proposed railways, railways being built, towns, stations, telegraphs, post offices and mail roads travelled. The accompanying booklet provides an index to placenames throughout Victoria. Relief shown by hachures.; Accompanying booklet entitled: References, or lists and tables of all the features delineated upon the map of Victoria / by F. Proeschel. [1860].; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-rm1043.General, agricultural and gold fields, map of VictoriaGold fields map of VictoriaGeneral, agricultural and gold fields map of Victori
Deep valley with terraced fields and a barn
No full textThe photograph is shot from a higher path, looking down into a valley of terraced fields throughout the valley and up the hillsides above it; a thatched or sod agricultural structure is on the hillside in the distance to the viewer's left; steep hillsides surround the valley, which are terraced almost to the top. The negative is black and white with no number visible
Least squares estimation of regression coefficients of singular random fields observed on a sphere
No full textWe present some results on the rate of convergence to the normal law of the least square estimates of the regression coefficient of random fields with long range dependence observed on a sphere
The Size Of The Connected Components Of Excursion Sets Of Fields
No full textThe distribution of the size of one connected component and the largest connected component of the excursion set is derived for stationary Ø 2 ; t and F fields, in the limit of high or low thresholds. This extends previous result for stationary Gaussian fields (Nosko, 1969; Adler, 1981) and for Ø 2 fields in one and two dimensions (Aronowich and Adler, 1986, 1988). An application of this is to detect regional changes in positron emission tomography images of blood flow in human brain, using the size of the largest connected component of the excursion set as a test statistic. excursion set; random fields; image analysis. ams 1991 subject classification: primary 60G15 Postal address: Bell Laboratories, Lucent Technologies, 700 Mountain Avenue, Room 2C-260, Murray Hill, NJ 07974-2070. 1 Introduction In typical activation studies of brain function with positron emission tomography (PET), a 3-D image representing the difference of the brain activity under baseline and stimulation c..
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