3,756 research outputs found
The Effect of Treatment of Acidosis on Calcium Balance in Patients with Chronic Azotemic Renal Disease
Small but statistically significant negative calcium balances were found in each of eight studies in seven patients with chronic azotemic renal disease when stable metabolic acidosis was present. Only small quantities of calcium were excreted in the urine, but fecal calcium excretion equaled or exceeded dietary intake. Complete and continuous correction of acidosis by NaHCO3 therapy reduced both urinary and fecal calcium excretion and produced a daily calcium balance indistinguishable from zero.
Apparent acid retention was found throughout the studies during acidosis, despite no further reduction of the serum bicarbonate concentration. The negative calcium balances that accompanied acid retention support the suggestion that slow titration of alkaline bone salts provides an additional buffer reservoir in chronic metabolic acidosis. The treatment of metabolic acidosis prevented further calcium losses but did not induce net calcium retention. It is suggested that the normal homeostatic responses of the body to the alterations in ionized calcium and calcium distribution produced by raising the serum bicarbonate might paradoxically retard the repair of skeletal calcium deficits
Nonlinear dynamics of phase separation in thin films
We present a long-wavelength approximation to the Navier-Stokes Cahn-Hilliard
equations to describe phase separation in thin films. The equations we derive
underscore the coupled behaviour of free-surface variations and phase
separation. We introduce a repulsive substrate-film interaction potential and
analyse the resulting fourth-order equations by constructing a Lyapunov
functional, which, combined with the regularizing repulsive potential, gives
rise to a positive lower bound for the free-surface height. The value of this
lower bound depends on the parameters of the problem, a result which we compare
with numerical simulations. While the theoretical lower bound is an obstacle to
the rupture of a film that initially is everywhere of finite height, it is not
sufficiently sharp to represent accurately the parametric dependence of the
observed dips or `valleys' in free-surface height. We observe these valleys
across zones where the concentration of the binary mixture changes sharply,
indicating the formation of bubbles. Finally, we carry out numerical
simulations without the repulsive interaction, and find that the film ruptures
in finite time, while the gradient of the Cahn--Hilliard concentration develops
a singularity.Comment: 26 pages, 20 figures, PDFLaTeX with RevTeX4 macros. A thorough
analysis of the equations is presented in arXiv:0805.103
Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyFor the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parametrized model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax distance transformation and the asymmetry of the resulting probability distribution. Using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test, we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ∼1760 pc, further away than recent estimates have envisaged, and a foreground group at ∼1350 pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.Peer reviewe
Listeners’ sensitivity to syllable complexity in spontaneous speech tempo perception
Studies of speech tempo commonly use syllable or segment rate as a proxy measure for perceived tempo. While listeners’ sensitivity to syllable rate is well-established [1-4], evidence for listeners’ additional sensitivity to segment rate--that is, to syllable complexity alongside syllable rate--is as yet lacking. In [5, 6] we reported experiments that yielded no evidence for listeners’ orientation to segment rate differences between stimuli that have the same syllable rate. In these experiments, we kept syllable rate constant by equalizing phrase durations. As phrase duration is a separate temporal parameter from syllable rate, we must complement this work with experiments using less homogeneous stimulus sets. In this paper we report on an experiment that uses stimuli selected from a corpus of spontaneous British English speech. Within crucial subsets there was minimal variation in one out of syllable and segment rate, and substantial variation in the other. Stimulus duration varied independently. Listeners ranked stimuli for perceived tempo. Results suggest that faced with these more variable stimuli, listeners do orient to segment rate in ranking stimuli that have near-identical syllable rates--presumably reflecting the influence of syllable complexity. Moreover, stimulus duration emerges as a separate factor influencing listeners’ rankings, alongside f0 and intensity
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
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