Visualizing, rather than deriving Russell-Saunders terms : a classroom activity with quantum numbers

A one hour classroom activity is presented, aimed at consolidating the concepts of microstates and Russell-Saunders energy terms in transition metal atoms and coordination complexes. The unconventional approach, based on logic and intuition rather than rigorous mathematics, is designed to stimulate discussion and enhance familiarity with quantum numbers in classes of Chemistry undergraduate students

Urban Evolution: The Role of Water

The structure, function, and services of urban ecosystems evolve over time scales from seconds to centuries as Earth’s population grows, infrastructure ages, and sociopolitical values alter them. In order to systematically study changes over time, the concept of “urban evolution” was proposed. It allows urban planning, management, and restoration to move beyond reactive management to predictive management based on past observations of consistent patterns. Here, we define and review a glossary of core concepts for studying urban evolution, which includes the mechanisms of urban selective pressure and urban adaptation. Urban selective pressure is an environmental or societal driver contributing to urban adaptation. Urban adaptation is thesequential process by which an urban structure, function, or services becomes more fitted to its changing environment or human choices. The role of water is vital to driving urban evolution as demonstrated by historical changes in drainage, sewage flows, hydrologic pulses, and long-term chemistry. In the current paper, we show how hydrologic traits evolve across successive generations of urban ecosystems via shifts in selective pressures and adaptations over time. We explore multiple empirical examples including evolving: (1) urban drainage from stream burial to stormwater management; (2) sewage flows and water quality in response to wastewater treatment; (3) amplification of hydrologic pulses due to the interaction between urbanization and climate variability; and (4) salinization and alkalinization of fresh water due to human inputs and accelerated weathering. Finally, we propose a new conceptual model for the evolution of urban waters from the Industrial Revolution to the present day based on empirical trends and historical information. Ultimately, we propose that water itself is a critical driver of urban evolution that forces urban adaptation, which transforms the structure, function, and services of urban landscapes, waterways, and civilizations over time

The JCMT Gould Belt Survey: a quantitative comparison between SCUBA-2 data reduction methods

Performing ground-based submillimetre observations is a difficult task as the measurements are subject to absorption and emission from water vapour in the Earth's atmosphere and time variation in weather and instrument stability. Removing these features and other artefacts from the data is a vital process which affects the characteristics of the recovered astronomical structure we seek to study. In this paper, we explore two data reduction methods for data taken with the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) at the James Clerk Maxwell Telescope (JCMT). The JCMT Legacy Reduction 1 (JCMT LR1) and The Gould Belt Legacy Survey Legacy Release 1 (GBS LR1) reduction both use the same software (starlink) but differ in their choice of data reduction parameters. We find that the JCMT LR1 reduction is suitable for determining whether or not compact emission is present in a given region and the GBS LR1 reduction is tuned in a robust way to uncover more extended emission, which better serves more in-depth physical analyses of star-forming regions. Using the GBS LR1 method, we find that compact sources are recovered well, even at a peak brightness of only three times the noise, whereas the reconstruction of larger objects requires much care when drawing boundaries around the expected astronomical signal in the data reduction process. Incorrect boundaries can lead to false structure identification or it can cause structure to be missed. In the JCMT LR1 reduction, the extent of the true structure of objects larger than a point source is never fully recovered

Identification of C 25 highly branched isoprenoid (HBI) alkenes in diatoms of the genus Rhizosolenia in polar and sub-polar marine phytoplankton.

We report the identification of a range of C25 highly branched isoprenoid (HBI) alkenes and certain sterols in filtered phytoplankton samples obtained from western Svalbard (Arctic) and near South Georgia (South Atlantic, sub-Antarctic) in 2016 and 2014, respectively. The C25 HBIs contained 3–5 double bonds and had structures identified previously from analysis of laboratory diatom cultures. The same HBIs were also identified in individual diatom taxa isolated from the mixed assemblages and with reasonably similar distributions. Thus, C25 HBIs were identified in Rhizosolenia setigera isolated from western Svalbard near-surface waters, while the same HBIs were also found in R. polydactyla f. polydactyla and R. hebetata f. semispina picked from seawater collected from a site in the South Atlantic. The main sterol composition was slightly different between the two locations, with cholesta-5,24-dien-3β-ol (desmosterol) identified as one of the major components in the sample from West Svalbard, consistent with the diatom assemblage being dominated by R. setigera. In contrast, the major sterol in the South Atlantic sample was cholesta-5,22-dien-3β-ol (22-dehydrocholesterol), likely reflecting the relatively high proportion of the genus Pseudo-nitzschia. For both locations, the suite of HBIs included a tri-unsaturated isomer (HBI III; 6Z-2,6,10,14-tetramethyl-9-(3'-methylpent-4-enylidene)-pentadec-6-ene), proposed in previous studies as a potential proxy measure of pelagic sea ice-edge conditions, and thus, a counterpart to the mono- and di-unsaturated HBIs IP25 and IPSO25, which have been used as seasonal sea ice proxies in the Arctic and Antarctic, respectively. HBI III has been reported previously in sediments from West Svalbard and we report here its occurrence in a small number of surface sediments from the South Atlantic. For both regions, HBI III was present as one of the major HBIs in sediments, which contrasts the HBI distributions in the filtered phytoplankton samples, where HBIs with four and five double bonds were the major components. Differences in HBI distributions between phytoplankton and sediment samples may potentially be due to the presence of other (unanalysed) diatoms in the filtered water samples, seasonal/annual variability in the production of HBIs by a range of diatoms, differential degradation of HBIs between sources and sediments, or a combination of these. Interestingly, we did not detect any C30 HBIs in the water samples, picked cells or sediments from either location, despite earlier reports of these lipids in laboratory cultures of R. setigera. This study represents the first source identification of certain C25 HBI lipids under in situ pelagic conditions

The JCMT Gould Belt survey: Dense core clusters in Orion B

The James Clerk Maxwell Telescope Gould Belt Legacy Survey obtained SCUBA-2 observations of dense cores within three sub-regions of OrionB: LDN1622, NGC2023/2024, and NGC2068/2071, all of which contain clusters of cores. We present an analysis of the clustering properties of these cores, including the two-point correlation function and Cartwright’s Q parameter. We identify individual clusters of dense cores across all three regions using a minimal spanning tree technique, and find that in each cluster, the most massive cores tend to be centrally located. We also apply the independent M–Σ technique and find a strong correlation between core mass and the local surface density of cores. These two lines of evidence jointly suggest that some amount of mass segregation in clusters has happened already at the dense core stage

THE JCMT GOULD BELT SURVEY: DENSE CORE CLUSTERS IN ORION A

The Orion A molecular cloud is one of the most well-studied nearby star-forming regions, and includes regions of both highly clustered and more dispersed star formation across its full extent. Here, we analyze dense, star-forming cores identified in the 850 and 450 μm SCUBA-2 maps from the JCMT Gould Belt Legacy Survey. We identify dense cores in a uniform manner across the Orion A cloud and analyze their clustering properties. Using two independent lines of analysis, we find evidence that clusters of dense cores tend to be mass segregated, suggesting that stellar clusters may have some amount of primordial mass segregation already imprinted in them at an early stage. We also demonstrate that the dense core clusters have a tendency to be elongated, perhaps indicating a formation mechanism linked to the filamentary structure within molecular clouds

Radiative capture of protons by deuterons

The differential cross section for radiative capture of protons by deuterons is calculated using different realistic NN interactions. We compare our results with the available experimental data below $E_x = 20 MeV$. Excellent agreement is found when taking into account meson exchange currents, dipole and quadrupole contributions, and the full initial state interaction. There is only a small difference between the magnitudes of the cross sections for the different potentials considered. The angular distributions, however, are practically potential independent.Comment: 4 pages (twocolumn), 4 postscript figures included, submitted for publication, revised versio

A novel tri-unsaturated highly branched isoprenoid (HBI) alkene from the marine diatom Navicula salinicola

A novel tri-unsaturated C25 highly branched isoprenoid (HBI) alkene has been identified in a laboratory culture of the diatom Navicula salinicola and its structure determined using a combination of NMR spectroscopy and gas chromatography–mass spectrometry (GC–MS). This represents the first report of a C25 HBI in a marine diatom from the Navicula genus, although a different tri-unsaturated C25 HBI has been reported previously in the freshwater species N. sclesvicensis and unspecified HBIs have been identified in the brackish N. phyllepta. The newly characterised HBI contains a relatively unusual conjugated diene sub-unit, a structural feature only previously reported in some HBIs biosynthesised by a further marine diatom, Haslea ostrearia

Do pelagic grazers benefit from sea ice? Insights from the Antarctic sea ice proxy IPSO25

Sea ice affects primary production in polar regions in multiple ways. It can dampen water column productivity by reducing light or nutrient supply, provide a habitat for ice algae and condition the marginal ice zone (MIZ) for phytoplankton blooms on its seasonal retreat. The relative importance of three different carbon sources (sea ice derived, sea ice conditioned, non-sea-ice associated) for the polar food web is not well understood, partly due to the lack of methods that enable their unambiguous distinction. Here we analysed two highly branched isoprenoid (HBI) biomarkers to trace sea-ice-derived and sea-ice-conditioned carbon in Antarctic krill (<i>Euphausia superba</i>) and relate their concentrations to the grazers' body reserves, growth and recruitment. During our sampling in January–February 2003, the proxy for sea ice diatoms (a di-unsaturated HBI termed IPSO₂₅, <i>δ</i>¹³C  =  −12.5 ± 3.3 ‰) occurred in open waters of the western Scotia Sea, where seasonal ice retreat was slow. In suspended matter from surface waters, IPSO₂₅ was present at a few stations close to the ice edge, but in krill the marker was widespread. Even at stations that had been ice-free for several weeks, IPSO₂₅ was found in krill stomachs, suggesting that they gathered the ice-derived algae from below the upper mixed layer. Peak abundances of the proxy for MIZ diatoms (a tri-unsaturated HBI termed HBI III, <i>δ</i>¹³C  =  −42.2 ± 2.4 ‰) occurred in regions of fast sea ice retreat and persistent salinity-driven stratification in the eastern Scotia Sea. Krill sampled in the area defined by the ice edge bloom likewise contained high amounts of HBI III. As indicators for the grazer's performance we used the mass–length ratio, size of digestive gland and growth rate for krill, and recruitment for the biomass-dominant calanoid copepods <i>Calanoides acutus</i> and <i>Calanus propinquus</i>. These indices consistently point to blooms in the MIZ as an important feeding ground for pelagic grazers. Even though ice-conditioned blooms are of much shorter duration than blooms downstream of the permanently sea-ice-free South Georgia, they enabled fast growth and offspring development. Our study shows two rarely considered ways that pelagic grazers may benefit from sea ice: firstly, after their release from sea ice, suspended or sinking ice algae can supplement the grazers' diet if phytoplankton concentrations are low. Secondly, conditioning effects of seasonal sea ice can promote pelagic primary production and therefore food availability in spring and summer