A nitrogen-based model of plankton dynamics in the oceanic mixed layer

As a first step toward the development of coupled, basin scale models of ocean circulation and biogeochemical cycling, we present a model of the annual cycles of plankton dynamics and nitrogen cycling in the oceanic mixed layer. The model is easily modified and runs in FORTRAN on a personal computer. In our initial development and exploration of the model\u27s behavior we have concentrated on modeling the annual cycle at Station S near Bermuda using seven compartments (Phytoplankton, Zooplankton, Bacteria, Nitrate, Ammonium, Dissolved organic nitrogen and Detritus). This choice of compartments and the attendant flows (fluxes or intercompartmental exchanges) permits a functional distinction between new and regenerated production. We have examined over 200 different runs and carried out sensitivity analyses. Results of model runs with detrital sinking rates of 1 and 10 meters per day are presented. In these runs, the phytoplankton biomass-specific mortality rate was varied to adjust the annual net primary production (NPP) for the mixed layer to a value equivalent to 45 gC m−2, which was calculated from the literature. Modelled cycles of zooplankton and bacterial stocks, and magnitudes of their annual production which cannot be validated due to sparse observations, are driven by the amplitude of the spring bloom and by changes in foodweb structure. Most, but not all model runs exhibit a spring bloom triggered by the winter depression of zooplankton stocks and the vernal increase in solar irradiance. The bloom is driven by nitrate entrained into the mixed layer during the wintertime deepening of the mixed layer. Following the shoaling of the pycnocline to ca 20 m, nitrate supply is limited to diffusional inputs, nitrate stocks are depleted, and regenerated production exceeds new production. The resulting cycles of new and regenerated production produce an annual cycle of the f-ratio with winter maxima approaching 0.8–0.9 and summer minima reaching ca 0.1–0.2, with annual values averaging 0.7. The model reproduces the Eppley Curve, a hyperbolic relationship of increasing f with increasing primary production. This curve is shown to be the trajectory of the production system in the f-NPP phase plane. These model runs reproduce the annual cycles of areal NPP, and average annual NPP, new production, and particulate N flux values reported in the literature. The model demonstrates that currently accepted values for these annual fluxes can be reconciled only if the f-ratio has a high annual average. At present, the annual average f-ratio is poorly quantified due to severe undersampling in fall and winter. Our model\u27s ecological structure has been successfully incorporated into the Princeton general circulation model for the North Atlantic Ocean

Seeing with sound? Exploring different characteristics of a visual-to-auditory sensory substitution device

Sensory substitution devices convert live visual images into auditory signals, for example with a web camera (to record the images), a computer (to perform the conversion) and headphones (to listen to the sounds). In a series of three experiments, the performance of one such device (‘The vOICe’) was assessed under various conditions on blindfolded sighted participants. The main task that we used involved identifying and locating objects placed on a table by holding a webcam (like a flashlight) or wearing it on the head (like a miner’s light). Identifying objects on a table was easier with a hand-held device, but locating the objects was easier with a head-mounted device. Brightness converted into loudness was less effective than the reverse contrast (dark being loud), suggesting that performance under these conditions (natural indoor lighting, novice users) is related more to the properties of the auditory signal (ie the amount of noise in it) than the cross-modal association between loudness and brightness. Individual differences in musical memory (detecting pitch changes in two sequences of notes) was related to the time taken to identify or recognise objects, but individual differences in self-reported vividness of visual imagery did not reliably predict performance across the experiments. In general, the results suggest that the auditory characteristics of the device may be more important for initial learning than visual associations

The drivers of AGN activity in galaxy clusters: AGN fraction as a function of mass and environment

We present an analysis of optical spectroscopically identified active galactic nuclei (AGN) down to a cluster magnitude of M * + 1 in a sample of six self-similar Sloan Digital Sky Survey galaxy clusters at z ~ 0.07. These clusters are specifically selected to lack significant substructure at bright limits in their central regions so that we are largely able to eliminate the local action of merging clusters on the frequency of AGN. We demonstrate that the AGN fraction increases significantly from the cluster centre to 1.5R virial , but tails off at larger radii. If only comparing the cluster core region to regions at ~2R virial , no significant variation would be found. We compute the AGN fraction by mass and show that massive galaxies (log(stellarmass) > 10.7) are host to a systematically higher fraction of AGN than lower mass galaxies at all radii from the cluster centre. We attribute this deficit of AGN in the cluster centre to the changing mix of galaxy types with radius. We use the WHAN diagnostic to separate weak AGN from 'retired' galaxies in which the main ionization mechanism comes from old stellar populations. These retired AGN are found at all radii, while the mass effect is much more pronounced: we find that massive galaxies are more likely to be in the retired class. Further, we show that our AGN have no special position inside galaxy clusters - they are neither preferentially located in the infall regions nor situated at local maxima of galaxy density as measured with ∑ 5 . However, we find that the most powerful AGN (with [O III] equivalent widths < -10 Å) reside at significant velocity offsets in the cluster, and this brings our analysis into agreement with previous work on X-ray-selected AGN. Our results suggest that if interactions with other galaxies are responsible for triggering AGN activity, the time lag between trigger and AGN enhancement must be sufficiently long to obfuscate the encounter site and wipe out the local galaxy density signal. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society

Heart failure and cognitive impairment: Challenges and opportunities

As populations age, heart failure (HF) is becoming increasingly common, and in addition to a high burden of morbidity and mortality, HF has an enormous financial impact. Though disproportionately affected by HF, the elderly are less likely to receive recommended therapies, in part because clinical trials of HF therapy have ignored outcomes of importance to this population, including impaired cognitive function (ICF). HF is associated with ICF, manifested primarily as delirium in hospitalized patients, or as mild cognitive impairment or dementia in otherwise stable outpatients. This association is likely the result of shared risk factors, as well as perfusion and rheological abnormalities that occur in patients with HF. Evidence suggests that these abnormalities may be partially reversible with standard HF therapy. The clinical consequences of ICF in HF patients are significant. Clinicians should consider becoming familiar with screening instruments for ICF, including delirium and dementia, in order to identify patients at risk of nonadherence to HF therapy and related adverse consequences. Preliminary evidence suggests that optimal HF therapy in elderly patients may preserve or even improve cognitive function, though the impact on related outcomes remains to be determined

The Tully–Fisher relation from SDSS-MaNGA: physical causes of scatter and variation at different radii

The stellar mass Tully–Fisher relation (STFR) and its scatter encode valuable information about the processes shaping galaxy evolution across cosmic time. However, we are still missing a proper quantification of the STFR slope and scatter dependence on the baryonic tracer used to quantify rotational velocity, on the velocity measurement radius and on galaxy integrated properties. We present a catalogue of stellar and ionized gas (traced by H emission) kinematic measurements for a sample of galaxies drawn from the MaNGA Galaxy Survey, providing an ideal tool for galaxy formation model calibration and for comparison with high-redshift studies. We compute the STFRs for stellar and gas rotation at 1, 1.3 and 2 effective radii (Re). The relations for both baryonic components become shallower at 2Re compared to 1Re and 1.3Re. We report a steeper STFR for the stars in the inner parts (≤1.3Re) compared to the gas. At 2Re, the relations for the two components are consistent. When accounting for covariances with integrated v/σ, scatter in the stellar and gas STFRs shows no strong correlation with: optical morphology, star formation rate surface density, tidal interaction strength or gas accretion signatures. Our results suggest that the STFR scatter is driven by an increase in stellar/gas dispersional support, from either external (mergers) or internal (feedback) processes. No correlation between STFR scatter and environment is found. Nearby Universe galaxies have their stars and gas in statistically different states of dynamical equilibrium in the inner parts (≤1.3Re), while at 2Re the two components are dynamically coupled

Business experience and start-up size: buying more lottery tickets next time around?

This paper explores the determinants of start-up size by focusing on a cohort of 6247 businesses that started trading in 2004, using a unique dataset on customer records at Barclays Bank. Quantile regressions show that prior business experience is significantly related with start-up size, as are a number of other variables such as age, education and bank account activity. Quantile treatment effects (QTE) estimates show similar results, with the effect of business experience on (log) start-up size being roughly constant across the quantiles. Prior personal business experience leads to an increase in expected start-up size of about 50%. Instrumental variable QTE estimates are even higher, although there are concerns about the validity of the instrument

The effect of minor and major mergers on the evolution of low excitation radio galaxies

We use deep, μ r lesssim 28 mag arcsec−2, r-band imaging from the Dark Energy Camera Legacy Survey to search for past, or ongoing, merger activity in a sample of 282 low-excitation radio galaxies (LERGs) at z 4σ excess of major mergers in the LERGs with M * lesssim 1011 M⊙, with 10 ± 1.5% of these active galactic nuclei involved in such large-scale interactions compared to 3.2 ± 0.4% of control galaxies. This excess of major mergers in LERGs decreases with increasing stellar mass, vanishing by M * > 1011.3 M⊙. These observations show that minor mergers do not fuel LERGs, and are consistent with typical LERGs being powered by accretion of matter from their halo. Where LERGs are associated with major mergers, these objects may evolve into more efficiently accreting active galactic nuclei as the merger progresses and more gas falls on to the central engine

Antecedents and consequences of effectuation and causation in the international new venture creation process

The selection of the entry mode in an international market is of key importance for the venture. A process-based perspective on entry mode selection can add to the International Business and International Entrepreneurship literature. Framing the international market entry as an entrepreneurial process, this paper analyzes the antecedents and consequences of causation and effectuation in the entry mode selection. For the analysis, regression-based techniques were used on a sample of 65 gazelles. The results indicate that experienced entrepreneurs tend to apply effectuation rather than causation, while uncertainty does not have a systematic influence. Entrepreneurs using causation-based international new venture creation processes tend to engage in export-type entry modes, while effectuation-based international new venture creation processes do not predetermine the entry mod

Field-Based Analytical Techniques for Aquatic Environmental Monitoring

There is a growing need for rapid and reliable but relatively low cost techniques that can be remotely deployed to provide high quality environmental data. This paper describes the use of flow injection (FI) based instrumentation for aquatic environmental monitoring. FI techniques now impact on a wide cross section of analytical chemistry activities, providing imaginative and practical solutions to challenging analytical problems and contributing to the improvement of data quality. Two specific applications are described. The first is the use of flow injection with spectrophotometric detection (FI-SPEC) for the determination of nitrogen and phosphorus species in catchments, estauries and sediments in order to investigate the impact of nutrients on water quality and provide decision support systems for catchment management. The second is the use of flow injection with chemiluminescence detectin (FI-CL) for the determination of micronutrients (particularly iron) in remote, open ocean environments. As a rate limiting nutrient, iron plays a key role in ocean productivity and climate change. The importance of 'clean' analytical protocols in order to provide high quality environmental data are also cosidere