Atmospheric input of nitrogen and phosphorus to the Southeast Mediterranean: Sources, fluxes, and possible impact

Estimates of the sources and wet deposition fluxes of inorganic nutrients (PO43-, NO3-, NO2-, NH4+) have been made using a long-term wet atmospheric deposition measurement at three sites along the Mediterranean coast of Israel. The nutrient composition in rainwater indicated a dominant anthropogenic source for NO, and NH: and a continental, natural, and anthropogenic, rock/soil source for PO43-. The calculated long-term dissolved inorganic N (IN) and inorganic P (IP) fluxes were 0.28 and 0.009 g m(-2) yr(-1) to the coastal zone and estimated as 0.24 and 0.008 g m(-2) yr(-1) to the Southeast (SE) Mediterranean, with a possible increasing pattern of the annual dissolved IN fluxes. Concentration of total and seawater leachable LP (LIP) from dust was examined on 20 Whatman 41 filters collected during 1996. The mean total IP concentration in dust was 0.13 +/- 0.11% (geomean = 0.09%), with a mean of 387 +/- 205 mu g IP per g of dust leached by seawater. LIP from dust varies between 6 and 85% (mean of 38%) of the dry total IF. Dust of desert-type (Saharan) events exhibited lower LIP solubility in seawater (similar to 25%, median) than air masses of European origin (similar to 45%, median). The calculated ratio of wet deposition to total (wet and dry) deposition here of 0.2 showed the importance of dry deposition of P in the SE Mediterranean basin compared to atmospheric inputs into the northwestern basin. The total IP and seawater LIP fluxes from dry deposition were estimated as 0.04 and 0.01 g m(-2) yr(-1), respectively. Atmospheric inputs of bioavailable N and P represent an imbalanced contribution to the new production of 8-20 and 4-11%, respectively, and reinforce the unusual N: P ratios (similar to 27) and possible P limitation in the SE Mediterranean

Hydrodynamic propulsion of human sperm

The detailed fluid mechanics of sperm propulsion are fundamental to our understanding of reproduction. In this paper, we aim to model a human sperm swimming in a microscope slide chamber. We model the sperm itself by a distribution of regularized stokeslets over an ellipsoidal sperm head and along an infinitesimally thin flagellum. The slide chamber walls are modelled as parallel plates, also discretized by a distribution of regularized stokeslets. The sperm flagellar motion, used in our model, is obtained by digital microscopy of human sperm swimming in slide chambers. We compare the results of our simulation with previous numerical studies of flagellar propulsion, and compare our computations of sperm kinematics with those of the actual sperm measured by digital microscopy. We find that there is an excellent quantitative match of transverse and angular velocities between our simulations and experimental measurements of sperm. We also find a good qualitative match of longitudinal velocities and computed tracks with those measured in our experiment. Our computations of average sperm power consumption fall within the range obtained by other authors. We use the hydrodynamic model, and a prototype flagellar motion derived from experiment, as a predictive tool, and investigate how sperm kinematics are affected by changes to head morphology, as human sperm have large variability in head size and shape. Results are shown which indicate the increase in predicted straight-line velocity of the sperm as the head width is reduced and the increase in lateral movement as the head length is reduced. Predicted power consumption, however, shows a minimum close to the normal head aspect ratio

A cleaner burning biomass-fuelled cookstove intervention to prevent pneumonia in children under 5 years old in rural Malawi (the Cooking and Pneumonia Study): a cluster randomised controlled trial

Medical Research Council, UK Department for International Development, and Wellcome Trust

The failed liberalisation of Algeria and the international context: a legacy of stable authoritarianism

The paper attempts to challenge the somewhat marginal role of international factors in the study of transitions to democracy. Theoretical and practical difficulties in proving causal mechanisms between international variables and domestic outcomes can be overcome by defining the international dimension in terms of Western dominance of world politics and by identifying Western actions towards democratising countries. The paper focuses on the case of Algeria, where international factors are key in explaining the initial process of democratisation and its following demise. In particular, the paper argues that direct Western policies, the pressures of the international system and external shocks influence the internal distribution of power and resources, which underpins the different strategies of all domestic actors. The paper concludes that analysis based purely on domestic factors cannot explain the process of democratisation and that international variables must be taken into more serious account and much more detailed

Stokes Number Effects on Deposition in Particle‐Laden Turbulent Pipe Flows

The ability to predict particle dispersion, interaction, and deposition in turbulent pipes is of value in improving the transport and process efficiency of high concentration particulate flows. In this work, the settling and deposition behavior of suspensions of dense particles in a cylindrical pipe has been studied using direct numerical simulation coupled with Lagrangian particle tracking, with the influence of Stokes number on deposition behavior examined. From the analysis performed, it can be concluded that particle deposition is sensitive to Stokes number. In particular, the dispersion function and mean vertical displacement of the particles are demonstrated to decrease considerably faster with time at the higher Stokes number. Particle migration towards the lower wall regions of the pipe also shows the formation of a solid bed of these particles, whilst over the same time period only dune-like structures are produced at the lower Stokes number. Further analysis of the particle dynamics confirms these findings and generates insight into the particle dynamics within the deposition regions

Excavation at Aguas Buenas, Robinson Crusoe Island, Chile, of a gunpowder magazine and the supposed campsite of Alexander Selkirk, together with an account of early navigational dividers

Excavations were undertaken of a ruined building at Aguas Buenas, identified as an 18th-century Spanish gunpowder magazine. Evidence was also found for the campsite of an early European occupant of the island. A case is made that this was Alexander Selkirk, a castaway here from 1704 to 1709. Selkirk was the model for Defoe’s Robinson Crusoe. A detailed discussion is given of a fragment of copper alloy identifi ed as being from a pair of navigational dividers