Seasonality of Conceptions Under Varying Conditions in a Rhesus Macaque Breeding Colony

Rhesus macaques (Macaca mulatta) are well documented as seasonal breeders. Despite this, little is known about what factors influence seasonal reproduction in rhesus. It has been proposed that rhesus are relaxed income breeders (Brockman and van Schaik, 2005), which means they respond to changes in photoperiod but endogenous cues can allow deviations from photoperiod-timed seasonality. This study presents the results of a natural experiment on the influence of different housing conditions (featuring different levels of environmental exposure) on the seasonal pattern of reproduction in rhesus. Once the number of attempts was controlled for, rhesus did not exhibit a seasonal distribution in their conceptions regardless of their level of exposure to environmental cues. This indicates that no conceptual model as of yet has adequately assessed the variation in seasonal reproduction in rhesus macaques

Reconceptualise a dynamic framework of the learning constructs in higher education

This paper reconceptualised the interrelated learning constructs in higher education based on the Dynamic Systems Theory (DST). The university students' learning experience before, during and post the Emergency Online Learning (EOL) was investigated to explore the dynamic changes among the learning constructs in higher education. A case study of a Chinese university was conducted, and one hundred and ninety-three university students participated in the questionnaire. The data collected from this empirical research identify different hierarchical constructs of the conceptualised learning environment and reconceptualise the period of system reformation influenced by the EOL. The key findings include the identifications of the attractors and repellors framed by the DST and the impact on the changes in the learning constructs. The results of this paper contribute to further understanding of the university constructs' changes to better plan and support students' active learning in higher education

Terrestrial laser scanning to reconstruct branch architecture from harvested branches

Quantifying whole branch architecture is critical to understanding tree function, for example, branch surface area controls woody gas exchange. Yet, due to measurement difficulty, branch architecture of small diameter branches (e.g. <10 cm ø) is either modelled, subsampled or ignored. Methods that use Terrestrial Laser Scanning (TLS) are now being widely applied to analyse tree and plot level tree architecture; however, resolving small diameter branches in-situ remains a challenge. Currently, it is suggested accurate reconstruction of small diameter branches can only be achieved by harvest and measurement in controlled conditions. Here we present a new TLS workflow for rapid and accurate reconstruction of complete branch architecture from harvested branches. The workflow sets out scan configuration, post processing (including a novel reectance filter) and fitting of Quantitative Structure Models (QSM) to reconstruct topologically coherent branch models. This is demonstrated on 595 branches (scanned indoors to negate the impact of wind) and compared with 65 branches that were manually measured (i.e. with measuring tape and callipers). Comparison of a suite of morphological and topological traits reveals a good agreement between TLS derived metrics and manual measurements where RMSE (%RMSE) for total branch length = 0.7 m (10%), volume = 0.09 litres (43%), surface area = 0.04 m2 (26%) and N tips = 6.4 (35%). Scanning was faster and invariant to branch size compared with manual measurements which required significantly more personnel time. We recommend measuring a subsample of tip-widths to constrain the QSM taper function as the TLS workflow tends to overestimate tip-width. The workflow presented here allows for a rapid characterisation of branch architecture from harvested branches. Increasing the number of branches analysed (e.g. many branches from a single tree or branches from many species globally) could allow for a comprehensive analysis of the “missing link" between the leaves and larger diameter branches

New insights into large tropical tree mass and structure from direct harvest and terrestrial lidar

A large portion of the terrestrial vegetation carbon stock is stored in the above-ground biomass (AGB) of tropical forests, but the exact amount remains uncertain, partly owing to the lack of measurements. To date, accessible peer-reviewed data are available for just 10 large tropical trees in the Amazon that have been harvested and directly measured entirely via weighing. Here, we harvested four large tropical rainforest trees (stem diameter: 0.6–1.2 m, height: 30–46 m, AGB: 3960–18 584 kg) in intact old-growth forest in East Amazonia, and measured above-ground green mass, moisture content and woody tissue density. We first present rare ecological insights provided by these data, including unsystematic intra-tree variations in density, with both height and radius. We also found the majority of AGB was usually found in the crown, but varied from 42 to 62%. We then compare non-destructive approaches for estimating the AGB of these trees, using both classical allometry and new lidar-based methods. Terrestrial lidar point clouds were collected pre-harvest, on which we fitted cylinders to model woody structure, enabling retrieval of volume-derived AGB. Estimates from this approach were more accurate than allometric counterparts (mean tree-scale relative error: 3% versus 15%), and error decreased when up-scaling to the cumulative AGB of the four trees (1% versus 15%). Furthermore, while allometric error increased fourfold with tree size over the diameter range, lidar error remained constant. This suggests error in these lidar-derived estimates is random and additive. Were these results transferable across forest scenes, terrestrial lidar methods would reduce uncertainty in stand-scale AGB estimates, and therefore advance our understanding of the role of tropical forests in the global carbon cycle

Star formation in 30 Doradus

Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.Comment: 15 pages, 12 figures. Accepted for publication in The Astrophysical Journa

The Luminosity, Mass, and Age Distributions of Compact Star Clusters in M83 Based on HST/WFC3 Observations

The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope has been used to obtain multi-band images of the nearby spiral galaxy M83. These new observations are the deepest and highest resolution images ever taken of a grand-design spiral, particularly in the near ultraviolet, and allow us to better differentiate compact star clusters from individual stars and to measure the luminosities of even faint clusters in the U band. We find that the luminosity function for clusters outside of the very crowded starburst nucleus can be approximated by a power law, dN/dL \propto L^{alpha}, with alpha = -2.04 +/- 0.08, down to M_V ~ -5.5. We test the sensitivity of the luminosity function to different selection techniques, filters, binning, and aperture correction determinations, and find that none of these contribute significantly to uncertainties in alpha. We estimate ages and masses for the clusters by comparing their measured UBVI,Halpha colors with predictions from single stellar population models. The age distribution of the clusters can be approximated by a power-law, dN/dt propto t^{gamma}, with gamma=-0.9 +/- 0.2, for M > few x 10^3 Msun and t < 4x10^8 yr. This indicates that clusters are disrupted quickly, with ~80-90% disrupted each decade in age over this time. The mass function of clusters over the same M-t range is a power law, dN/dM propto M^{beta}, with beta=-1.94 +/- 0.16, and does not have bends or show curvature at either high or low masses. Therefore, we do not find evidence for a physical upper mass limit, M_C, or for the earlier disruption of lower mass clusters when compared with higher mass clusters, i.e. mass-dependent disruption. We briefly discuss these implications for the formation and disruption of the clusters.Comment: 36 pages, 13 figures, 1 table; accepted for publication in the Astrophysical Journa

Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83

We use new WFC3 observations of the nearby grand design spiral galaxy M83 to develop two independent methods for estimating the ages of young star clusters. The first method uses the physical extent and morphology of Halpha emission to estimate the ages of clusters younger than tau ~10 Myr. It is based on the simple premise that the gas in very young (tau < few Myr) clusters is largely coincident with the cluster stars, is in a small, ring-like structure surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The second method is based on an observed relation between pixel-to-pixel flux variations within clusters and their ages. This method relies on the fact that the brightest individual stars in a cluster are most prominent at ages around 10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older than about 100 Myr. These two methods are the basis for a new morphological classification system which can be used to estimate the ages of star clusters based on their appearance. We compare previous age estimates of clusters in M83 determined from fitting UBVI Halpha measurements using predictions from stellar evolutionary models with our new morphological categories and find good agreement at the ~95% level. The scatter within categories is ~0.1 dex in log tau for young clusters (10 Myr) clusters. A by-product of this study is the identification of 22 "single-star" HII regions in M83, with central stars having ages ~4 Myr.Comment: 33 pages, 10 figures, 3 tables; published in March Ap

Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure