Determination of bone mineral mass in vivo

Radiographic equipment incorporates two radiation sources, generating high-energy and low-energy beams. Recording equipment measures amount of radiation that has penetrated limb. Data are fed into computer that determines mass of the examined bone

Temporal fluctuations in the differential rotation of cool active stars

This paper reports positive detections of surface differential rotation on two rapidly rotating cool stars at several epochs, by using stellar surface features (both cool spots and magnetic regions) as tracers of the large scale latitudinal shear that distorts the convective envelope in this type of stars. We also report definite evidence that this differential rotation is different when estimated from cool spots or magnetic regions, and that it undergoes temporal fluctuations of potentially large amplitude on a time scale of a few years. We consider these results as further evidence that the dynamo processes operating in these stars are distributed throughout the convective zone rather than being confined at its base as in the Sun. By comparing our observations with two very simple models of the differential rotation within the convective zone, we obtain evidence that the internal rotation velocity field of the stars we investigated is not like that of the Sun, and may resemble that we expect for rapid rotators. We speculate that the changes in differential rotation result from the dynamo processes (and from the underlying magnetic cycle) that periodically converts magnetic energy into kinetic energy and vice versa. We emphasise that the technique outlined in this paper corresponds to the first practical method for investigating the large scale rotation velocity field within convective zones of cool active stars, and offers several advantages over asteroseismology for this particular purpose and this specific stellar class.Comment: 14 pages, 4 figure

Kinosternon integrum

Number of Pages: 6Integrative BiologyGeological Science

Magnetic activity on AB Doradus: Temporal evolution of starspots and differential rotation from 1988 to 1994

Surface brightness maps for the young K0 dwarf AB Doradus are reconstructed from archival data sets for epochs spanning 1988 to 1994. By using the signal-to-noise enhancement technique of Least-Squares Deconvolution, our results show a greatly increased resolution of spot features than obtained in previously published surface brightness reconstructions. These images show that for the exception of epoch 1988.96, the starspot distributions are dominated by a long-lived polar cap, and short-lived low to high latitude features. The fragmented polar cap at epoch 1988.96 could indicate a change in the nature of the dynamo in the star. For the first time we measure differential rotation for epochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). These measurements show variations on a timescale of at least one year, with the strongest surface differential rotation ever measured for AB Dor occurring in 1994.86. In conjunction with previous investigations, our results represent the first long-term analysis of the temporal evolution of differential rotation on active stars.Comment: accepted by MNRAS 18 pages 18 figure

Mashing up Visual Languages and Web Mash-ups

Research on web mashups and visual languages share an interest in human-centered computing. Both research communities are concerned with supporting programming by everyday, technically inexpert users. Visual programming environments have been a focus for both communities, and we believe that there is much to be gained by further discussion between these research communities. In this paper we explore some connections between web mashups and visual languages, and try to identify what each might be able to learn from the other. Our goal is to establish a framework for a dialog between the communities, and to promote the exchange of ideas and our respective understandings of humancentered computing.published or submitted for publicationis peer reviewe

Compressed intramolecular dispersion interactions.

The feasibility of the compression of localized virtual orbitals is explored in the context of intramolecular long-range dispersion interactions. Singular value decomposition (SVD) of coupled cluster doubles amplitudes associated with the dispersion interactions is analyzed for a number of long-chain systems, including saturated and unsaturated hydrocarbons and a silane chain. Further decomposition of the most important amplitudes obtained from these SVDs allows for the analysis of the dispersion-specific virtual orbitals that are naturally localized. Consistent with previous work on intermolecular dispersion interactions in dimers, it is found that three important geminals arise and account for the majority of dispersion interactions at the long range, even in the many body intramolecular case. Furthermore, it is shown that as few as three localized virtual orbitals per occupied orbital can be enough to capture all pairwise long-range dispersion interactions within a molecule

Rotationally Modulated X-ray Emission from T Tauri Stars

We have modelled the rotational modulation of X-ray emission from T Tauri stars assuming that they have isothermal, magnetically confined coronae. By extrapolating surface magnetograms we find that T Tauri coronae are compact and clumpy, such that rotational modulation arises from X-ray emitting regions being eclipsed as the star rotates. Emitting regions are close to the stellar surface and inhomogeneously distributed about the star. However some regions of the stellar surface, which contain wind bearing open field lines, are dark in X-rays. From simulated X-ray light curves, obtained using stellar parameters from the Chandra Orion Ultradeep Project, we calculate X-ray periods and make comparisons with optically determined rotation periods. We find that X-ray periods are typically equal to, or are half of, the optical periods. Further, we find that X-ray periods are dependent upon the stellar inclination, but that the ratio of X-ray to optical period is independent of stellar mass and radius.Comment: 10 pages, 8 figures, accepted for publication in MNRA