Nitrous oxide and methane in the Atlantic Ocean between 50 degrees North and 52 degrees South: Latitudinal distribution and sea-to-air flux

We discuss nitrous oxide (N2O) and methane (CH4) distributions in 49 vertical profiles covering the upper 300 m of the water column along two 13,500 km transects between 50°N and 52°S during the Atlantic Meridional Transect (AMT) programme (AMT cruises 12 and 13). Vertical N2O profiles were amenable to analysis on the basis of common features coincident with Longhurst provinces. In contrast, CH4 showed no such pattern. The most striking feature of the latitudinal depth distributions was a well-defined “plume” of exceptionally high N2O concentrations coincident with very low levels of CH4, located between 23.5°N and 23.5°S; this feature reflects the upwelling of deep waters containing N2O derived from nitrification, as identified by an analysis of N2O, apparent oxygen utilization (AOU) and NO3-, and presumably depleted in CH4 by bacterial oxidation. Sea-to-air emissions fluxes for a region equivalent to 42% of the Atlantic Ocean surface area were in the range 0.40–0.68 Tg N2O yr-1 and 0.81–1.43 Tg CH4 yr-1. Based on contemporary estimates of the global ocean source strengths of atmospheric N2O and CH4, the Atlantic Ocean could account for 6–15% and 4–13%, respectively, of these source totals. Given that the Atlantic Ocean accounts for around 20% of the global ocean surface, on unit area basis it appears that the Atlantic may be a slightly weaker source of atmospheric N2O than other ocean regions but it could make a somewhat larger contribution to marine-derived atmospheric CH4 than previously thought

First normal stress difference and crystallization in a dense sheared granular fluid

The first normal stress difference (${\mathcal N}_1$) and the microstructure in a dense sheared granular fluid of smooth inelastic hard-disks are probed using event-driven simulations. While the anisotropy in the second moment of fluctuation velocity, which is a Burnett-order effect, is known to be the progenitor of normal stress differences in {\it dilute} granular fluids, we show here that the collisional anisotropies are responsible for the normal stress behaviour in the {\it dense} limit. As in the elastic hard-sphere fluids, ${\mathcal N}_1$ remains {\it positive} (if the stress is defined in the {\it compressive} sense) for dilute and moderately dense flows, but becomes {\it negative} above a critical density, depending on the restitution coefficient. This sign-reversal of ${\mathcal N}_1$ occurs due to the {\it microstructural} reorganization of the particles, which can be correlated with a preferred value of the {\it average} collision angle $\theta_{av}=\pi/4 \pm \pi/2$ in the direction opposing the shear. We also report on the shear-induced {\it crystal}-formation, signalling the onset of fluid-solid coexistence in dense granular fluids. Different approaches to take into account the normal stress differences are discussed in the framework of the relaxation-type rheological models.Comment: 21 pages, 13 figure

Force distribution in a scalar model for non-cohesive granular material

We study a scalar lattice model for inter-grain forces in static, non-cohesive, granular materials, obtaining two primary results. (i) The applied stress as a function of overall strain shows a power law dependence with a nontrivial exponent, which moreover varies with system geometry. (ii) Probability distributions for forces on individual grains appear Gaussian at all stages of compression, showing no evidence of exponential tails. With regard to both results, we identify correlations responsible for deviations from previously suggested theories.Comment: 16 pages, 9 figures, Submitted to PR

Role of anisotropy in the spin-dimer compound BaCuSi2O6

We present results of magnetisation and electron paramagnetic resonance experiments on the spin-dimer system BaCuSi2O6. Evidence indicates that the origin of anisotropic terms in the spin Hamiltonian is from magnetic dipolar interactions. Axial symmetry-breaking is on a very small energy scale of ~11 mK, confirming Bose Einstein condensation critical scaling over an extended temperature range in the vicinity of the quantum critical point.Comment: 4 pages, 4 figure

EGZOENCIMI U HRANI ZA RIBE S POSEBNIM OSVRTOM NA FITAZU: PREGLED

The global aquaculture industry has come under increasing pressure to optimize production efficiency while reducing environmental loadings. These new demands, which have been accompanied in certain countries by legislation, have stimulated the development of elite low output dietary formulations. Several feed manufacturers have developed diets with modified energy: protein ratios, which reduce environmental phosphorus loadings with minimum impact upon fish growth. However, problems relating to end product quality have materialized following application of these high lipid diets and it is clear that alternative strategies must be developed. In particular, there remains an urgent need to replace the expensive fishmeal component of aquafeeds. One approach might be to supplement diets with exogenous enzymes (exoenzymes) that enhance the value and utility of alternative, low grade proteins while reducing ecological impacts. This paper briefly reviews the literature relating to experimental exoenzyme aquafeeds, with specific reference to phytase.Kompletna industrija akvakulture nalazi se pod povećanim pritiskom glede optimalizacije efikasne proizvodnje, dok se u isto vrijeme smanjuju mogućnosti iskorištavanja akvatorija. Ovi, novi zahtjevi koji su u nekim zemljama povezani s legislativom, potaknuli su razvoj niskih iskorištenosti hranidbenih formulacija. Nekoliko proizvođaća razvilo je hrane s modificiranom energijom: količina bjelančevina koja smanjuje nakupljanje P a okolišu s minimalnim utjecajem na rast riba. No, problemi koji se odnose na kvalitetu gotovoga proizvoda materijalirizirani su uporabom hrana s visokim postotkom lipida i jasno je da mora biti razvijena alternativna strategija, napose stoga što ostaje urgentna potreba za zamjenu skupog ribljeg brašna kao komponente u hrani za ribe. Jedna od mogućnosti mogla bi biti dodatak egzogenih enzima (egzoenzima) koji povećavaju vrijednost i iskorištenost nisko vrijednih bjelančevina. U ovom je radu dan kratak prikaz literaturnih podataka koji se odnose na eksperimentalne hrane s egzoenzimima, s posebnim osvrtom na fitazu