María Lovísa Ámundadóttir

Intramolecular hydrogen-bonding in aqueous carbohydrates as a cause or consequence of conformational preferences: a molecular dynamics study of cellobiose stereoisomers

It is often assumed that intramolecular hydrogen-bonding (H-bonding) exerts a significant influence on the conformational properties of aqueous (bio-)polymers. To discuss this statement, one should, however, distinguish between solvent-exposed and buried H-bonds, and between their respective roles in promoting stability (i.e., as a driving force) and specificity (for which the term steering force is introduced here). In this study, the role of solvent-exposed H-bonding in carbohydrates as a driving or steering force is probed using explicit-solvent molecular dynamics simulations with local elevation umbrella sampling in the simple context of cellobiose stereoisomers. More specifically, four β(1→4)-linked d-aldohexopyranose disaccharides are considered, which present a different stereochemisty of the potentially H-bonding groups neighboring the glycosidic linkage. Although the epimerization may largely alter the intramolecular trans-glycosidic H-bonding pattern, it is found to have only very limited influence on the Ramachandran free-energy map of the disaccharide, a loss of intramolecular H-bonding being merely compensated for by an enhancement of the interaction with the solvent molecules. This finding suggests that solvent-exposed trans-glycosidic H-bonding (and in particular the

Contrast measures for predicting perceptual effects of daylight in architectural renderings

\hbox{HO}_3^{\prime}

A human-centric approach to assess daylight in buildings for non-visual health potential, visual interest and gaze behavior

→O5 H-bond) is not the cause of the 21-helical secondary structure characteristic of cellooligosaccharides, but rather the opportunistic consequence of a sterically and stereoelectronically dictated conformational preference. In other words, for these compounds, solvent-exposed H-bonding appears to represent a minor (possibly adverse) conformational driving as well as steering force.

Modeling non-visual responses to light: unifying spectral sensitivity and temporal characteristics in a single model structure

The discovery of a novel non-rod, non-cone photoreceptor in the mammalian eye that mediates a range of ‘non-visual’ responses to light has required reexamination of how lighting needs for human health are characterised and evaluated. Existing literature provides useful information about how to quantify non-visual spectral sensitivities to light but the optimal approach is far from decided. As more is learned about the underlying biology, new approaches will continue to be published. What is currently lacking is a flexible framework to describe the non-visual spectral effectiveness of light using a common language. Without a unified description of quantities and units, much of the value of scientific publications can be lost. In this paper, we review the existing approaches by categorising the proposed quantities depending on their application. Based on this review, a unified framework is provided for use in evaluating and reporting the spectral effectiveness of light for human health. The unified framework will provide greater flexibility to model the non-visual responses to light and is adaptable to a wide range of lighting solutions of interest to researchers, designers and developers. A new visualisation tool, the SpeKtro dashboard, is available to explore the unified framework online at spektro.epfl.ch.

Integrating non-visual effects of light into lighting simulation: challenges ahead

Daylit architecture is perceived as a dynamic luminous composition, yet most existing performance metrics were designed to evaluate natural illumination for its ability to adequately illuminate a two-dimensional task surface and avoid glare-based discomfort. It may be argued that task-driven approaches based on surface illumination and glare ignore the likelihood that contrast can provide positive impacts on our visual perception of space. Advances in these metrics to accommodate climate-based sky conditions and occupant behaviour have improved our ability to evaluate task illumination and glare, yet the same attention has not been paid to evaluating positive perceptual responses to daylight. Existing studies have attempted to link subjective ratings of composition to simple global contrast metrics without reaching consensus. More advanced metrics have been developed in computational graphics and vision fields but have not been applied to studies in qualitative lighting research. This paper introduces the results from an online experiment where subject ratings of daylight composition are compared to quantitative contrast measures across a series of renderings. This paper will identify which measures correlate to subjects’ ratings of visual interest and introduces a modified contrast algorithm, which can be used as a novel prediction model for visual interest in daylit renderings.