Author Correction: Nearly all the sky is covered by Lyman-α emission around high-redshift galaxies.

Change history: In this Letter, author M. Akhlaghi should be associated with affiliation (2) rather than (3). This error has been corrected online.

Nearly all the sky is covered by Lyman-α emission around high-redshift galaxies.

Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-α transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 104 kelvin) gas in and around galaxies, especially at cosmological redshifts greater than about 1.6 at which the spectral line becomes observable from the ground. Tracing cosmic hydrogen through its Lyman-α emission has been a long-standing goal of observational astrophysics1-3, but the extremely low surface brightness of the spatially extended emission is a formidable obstacle. A new window into circumgalactic environments was recently opened by the discovery of ubiquitous extended Lyman-α emission from hydrogen around high-redshift galaxies4,5. Such measurements were previously limited to especially favourable systems6-8 or to the use of massive statistical averaging9,10 because of the faintness of this emission. Here we report observations of low-surface-brightness Lyman-α emission surrounding faint galaxies at redshifts between 3 and 6. We find that the projected sky coverage approaches 100 per cent. The corresponding rate of incidence (the mean number of Lyman-α emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high-column-density absorbers frequently detected in the spectra of distant quasars11-14. This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected in emission.

Algorithms for dairy barn design: maternity and milking areas.

This paper presents a series of algorithms for dairy barn design. The aim of the study was to develop algorithms for the design of new barn areas that can added to the main barn areas (resting, feeding, and exercise) to complement barn layout. More specifically, we developed design and dimensioning schemes to incorporate the maternity area and the milking area (holding pen and milking parlor) into dairy barns. Each algorithm requires input design parameters related to the characteristics of the areas considered. The output of the algorithms provides layout solutions for the maternity and milking areas and the overall dimensions of both areas, which enables the user to assess the possibility of incorporating maternity and milking into a dairy barn composed of resting, exercise, and feeding areas. The algorithms presented in this paper allow for space optimization by using the values defined for the design parameters considered.

Algorithms for dairy barn design: resting, feeding, and exercise.

This study presents a series of algorithms designed to assist farmers and other decision-makers in the design of dairy cattle housing. Four algorithms have been developed, each for a different basic design (2 rows head-to-head, 2 rows head-to-wall, 3 rows, or rows perpendicular to feed alley). Each algorithm requires input of herd size and various other parameters (e.g., free-stall width), depending on the design; the output gives barn layout and overall size, thus facilitating comparison of designs in terms of financial cost and animal welfare. Although these algorithms have been developed primarily for small family farms in Galicia (northwest Spain) with herd sizes of up to 250, they could be useful for herds of any size, because herd size is an input parameter. We consider that these algorithms are useful tools for dairy farm planning, and they can be readily incorporated into personal computer applications, greatly facilitating their application.

History of urethral catheters and their balloons: drainage, anchorage, dilation, and hemostasis.

Male urethral catheterization, as practiced in early Greece, was made possible by a sound knowledge of anatomy. It has been preserved by written tradition and advanced by the development of new materials. Balloon dilation, conceived and practiced more than 160 years ago by urologists, has undergone a similar cycle. Some useful ideas, once conceived, have been forgotten and have surfaced again, decades, sometimes centuries, later as new inventions.