All the colours of the rainbow.

Our perception of colour has always been a source of fascination, so it's little wonder that studies of the phenomenon date back hundreds of years. What, though, can modern scientists learn from medieval literature — and how do we go about it

Beyond scattering and absorption: Perceptual un-mixing of translucent liquids

Is perception of translucence based on estimations of scattering and absorption of light or on statistical pseudocues associated with familiar materials? We compared perceptual performance with real and computer-generated stimuli. Real stimuli were glasses of milky tea. Milk predominantly scatters light and tea absorbs it, but since the tea absorbs less as the milk concentration increases, the effects of milkiness and strength on scattering and absorption are not independent. Conversely, computer-generated stimuli were glasses of “milky tea” in which absorption and scattering were independently manipulated. Observers judged tea concentrations regardless of milk concentrations, or vice versa. Maximum-likelihood conjoint measurement was used to estimate the contributions of each physical component—concentrations of milk and tea, or amounts of scattering and absorption—to perceived milkiness or tea strength. Separability of the two physical dimensions was better for real than for computer-generated teas, suggesting that interactions between scattering and absorption were correctly accounted for in perceptual unmixing, but unmixing was always imperfect. Since the real and rendered stimuli represent different physical processes and therefore differ in their image statistics, perceptual judgments with these stimuli allowed us to identify particular pseudocues (presumably learned with real stimuli) that explain judgments with both stimulus sets

Color-coordinate system from a 13th-century account of rainbows.

We present a new analysis of Robert Grosseteste’s account of color in his treatise De iride (On the Rainbow), dating from the early 13th century. The work explores color within the 3D framework set out in Grosseteste’s De colore [see J. Opt. Soc. Am. A 29, A346 (2012)], but now links the axes of variation to observable properties of rainbows. We combine a modern understanding of the physics of rainbows and of human color perception to resolve the linguistic ambiguities of the medieval text and to interpret Grosseteste’s key terms

All the colours of the rainbow

Our perception of colour has always been a source of fascination, so it's little wonder that studies of the phenomenon date back hundreds of years. What, though, can modern scientists learn from medieval literature — and how do we go about it

Dickite from sandstones in Northern England and Northern Wales

RESP-

Does slow and steady win the race? Investigating feedback processes in giant molecular clouds

We investigate the effects of gradual heating on the evolution of turbulent molecular clouds of mass $2\times 10^6$ M$_\odot$ and virial parameters ranging between $0.7-1.2$. This gradual heating represents the energy output from processes such as winds from massive stars or feedback from High Mass X-ray binaries (HMXBs), contrasting the impulsive energy injection from supernovae (SNe). For stars with a mass high enough that their lifetime is shorter than the life of the cloud, we include a SN feedback prescription. Including both effects, we investigate the interplay between slow and fast forms of feedback and their effectiveness at triggering/suppressing star formation. We find that SN feedback can carve low density chimneys in the gas, offering a path of least resistance for the energy to escape. Once this occurs the more stable, but less energetic, gradual feedback is able to keep the chimneys open. By funneling the hot destructive gas away from the centre of the cloud, chimneys can have a positive effect on both the efficiency and duration of star formation. Moreover, the critical factor is the number of high mass stars and SNe (and any subsequent HMXBs) active within the free-fall time of each cloud. This can vary from cloud to cloud due to the stochasticity of SN delay times and in HMXB formation. However, the defining factor in our simulations is the efficiency of the cooling, which can alter the Jeans mass required for sink particle formation, along with the number of massive stars in the cloud.Comment: 35 pages, 46 figures, accepted for publication in MNRA