Tunable supercurrent through semiconductor nanowires

Nanoscale superconductor/semiconductor hybrid devices are assembled from indium arsenide semiconductor nanowires individually contacted by aluminum-based superconductor electrodes. Below 1 kelvin, the high transparency of the contacts gives rise to proximity-induced superconductivity. The nanowires form superconducting weak links operating as mesoscopic Josephson junctions with electrically tunable coupling. The supercurrent can be switched on/off by a gate voltage acting on the electron density in the nanowire. A variation in gate voltage induces universal fluctuations in the normal-state conductance, which are clearly correlated to critical current fluctuations. The alternating-current Josephson effect gives rise to Shapiro steps in the voltage-current characteristic under microwave irradiation.     

Capture of atmospheric ammonium by grassland canopies

Air pollution can cause a decline in species through acidification of the habitat. New data suggest that the decline may be due to eutrophication rather than acidification. In Western Europe, eutrophication largely results from atmospheric ammonium deposition. The amount deposited on vegetation is a function of its canopy structure. Deposition on grasslands has been underestimated, and a significant amount of the deposited ammonium appears to be assimilated by the plant canopy. These quantities are sufficient to initiate changes in the competitive relations among the plant species.     

Simulation of the effects of oxygen on food consumption and growth of Nile tilapia, Oreochromis niloticus (L.)

Fish need oxygen for aerobic generation of energy for body maintenance, locomotion, feeding and biosynthesis. The rate of oxygen uptake of most fish is limited by diffusion through the gills, and gill surface area grows at a slower rate than body mass. We hypothesize, therefore: (1) that the maximum rate of feed intake is related to the capacity to take in oxygen for processing of this feed; and (2) that the maximum rate of feed intake relative to body size decreases with increasing body size to a point where growth is zero. An oxygen limitation module based on this theory was incorporated into an existing dynamic simulation model for the Nile tilapia, Oreochromis niloticus (L.). The module calculates the maximum potential oxygen supply to the fish on the basis of Fick's law of diffusion and the allometric relationship between body weight and gill surface area. Total oxygen demand of the fish is computed as the sum of routine metabolism, feeding metabolism and energy needed for biosynthesis. In the module, the feeding rate is limited to a level where total oxygen demand does not exceed the potential supply. The model is used to simulate feeding and growth of O. niloticus. Simulation results provide strong support for the oxygen limitation theory. Hence, the model can be used for the analysis of fish growth as affected by feed amount, feed composition, as well as environmental conditions (temperature, dissolved oxygen concentration). It also explains differences in final size between fish species, and within species under different conditions.     

Effect of organic nitrogen and carbon mineralization on sediment organic matter accumulation in fish ponds

In aquaculture, ponds with high loads of organic inputs, organic matter accumulates at the bottom over time. Uneaten feed, senescent phytoplankton and faeces are the principal sources of accumulated material, but quantifications are scarce. The sedimented organic matter develops into a flocculent layer in which different processes transform the material into inorganic forms. A better understanding of factors influencing organic matter accumulation/decomposition in the sediment is needed to better understand and manage the dynamics of nitrogen in fish ponds. In this study, the rate of mineralization of organic nitrogen and the nitrogen flux between the sediment and the water column were measured. Organic matter accumulation in fish ponds was quantified, and the data were used to construct, calibrate and validate a dynamic simulation model of organic matter deposition/decomposition in fish ponds. The accumulating material consisted of dead phytoplankton, fish faeces and uneaten feed. Through model calibration, the proportion of these materials in the total accumulated organic matter was determined. In the model, gross photosynthetic rate was estimated from an empirical relationship with feed input. After calibration, the model was validated using independent data. The model simulated well the concentrations of organic carbon and nitrogen in the sediments but it may be developed further, especially by considering the effects of resuspension.     

The potential of periphyton-based culture of two Indian major carps, rohu Labeo rohita (Hamilton) and gonia Labeo gonius (Linnaeus)

The effects of periphyton, grown on bamboo substrates, on growth and production of two Indian major carps, rohu, Labeo rohita (Hamilton) and gonia, Labeo gonius (Linnaeus), were studied at the Bangladesh Agricultural University, Mymensingh. For each species, five ponds were provided with bamboo substrates and five ponds without substrate (control). Ponds were stocked at a rate of 10 000 ha^?1 in both treatments. There was no discernible difference in water quality parameters between treatments. A large number of plankton (39 genera) showed periphytic nature and colonized the bamboo substrates. Rohu grew faster, resulting in a 77% higher net production (P < 0.05) in the ponds with bamboo substrates compared with the ponds without substrate. In contrast, the growth and production of gonia did not vary significantly (P > 0.05) between the substrate and control ponds. Rohu seems to be a more suitable candidate for periphyton‐based aquaculture systems than gonia.     

Hydrology and the functioning of seasonal wetland aquaculture–agriculture systems (Fingerponds) at the shores of Lake Victoria, Kenya

Experimental seasonal wetland-based integrated aquaculture–agriculture systems called ‘Fingerponds’ were established at two sites (Nyangera and Kusa villages) at the shores of Lake Victoria in Kenya to enhance the wetland fishery potential. This paper examines the hydrological characteristics of Fingerponds. In Fingerponds’ design, the water supply is un-regulated and the water balance is maintained by natural losses and gains. At the beginning of the season, flood events are critically important for the initial water supply to the ponds. During their functional period (which lasted for about 6 months into the dry season after flood recession), precipitation accounted for nearly 90% of the total water gains while seepage and evaporation contributed an average of 30–70% of the losses, respectively. Seasonal pond water budgets indicated that the losses outweighed the gains leading to a progressive decline of water depth during the dry season. A prediction of the effect of pond volume and weather conditions on the functional period for fish production was carried out using a dynamic simulation model. The results indicated that the culture period can be extended by 2.5 months by deepening the ponds to an average depth of 1.5 m: this would increase the overall fish harvest. Drier weather accelerated losses and shortened the culture period by 1–2 months.     

Parameterization and calibration of a model to simulate effects of feeding level and feed composition on growth of Oreochromis niloticus (L.) and Oncorhynchus mykiss (Walbaum)

A dynamic model to simulate growth of the African catfish. Clarias gariepinus (Burchell), was parameterized and calibrated for Nile tilapia. Oreochromis niloticus (L.), and rainbow trout, Oncorhynchus mykiss (Walbaum). The model predicts fish weight and fat percentage from the amount and composition of the feed and water temperature. The major factor determining the efficiency of feed conversion is the proportion of energy provided by protein oxidation, which is positively related to the protein feeding level and the protein/energy ratio of the feed. The model predicted fresh weight of the herbivorous Oreochromis niloticus in independent experimental data with a mean deviation of -2.1% (range -23% to +37%) of observed values (fish weights 10-40 g), For the carnivorous Oncorhynchus mykiss, this value was 4.8% (range -21% to +24%, 50-800 g), Options for further improvement of the model are discussed. We conclude that the structure of the model applies to a broad range of fish species and feeding schedules, provided that both feed and fish are characterized by a set of specific parameters.     

Optimization and kinetics of in vitro stimulation of carp (Cyprinus carpio L.) leukocytes

The optimization of a leukocyte stimulation microassay with carp (Cyprinus carpio L.) leukocytes is described. Leukocytes were isolated from the thymus, anterior kidney, spleen, mid-kidney and peripheral blood.Leukocyte cultures were stimulated with PHA-P, LPS (Escherichia coli 055: B5) PWM, ConA and PPD from Mycobacterium fortuitum. The optimum incubation temperature for leukocyte cultures differed depending on the mitogen used. The optimum incubation period was 3.5 days for leukocyte cultures derived from lymphoid organs and 4.5 days for peripheral blood lymphocyte cultures. Leukocytes from various organ sources showed similar reactivity patterns to stimulation in vitro by different mitogens. The results of these mitogen stimulations did not present sufficient arguments in favour of compartmentation.     

Effect of exercise on activation of the p38 mitogen-activated protein kinase pathway, c-Jun NH2 terminal kinase, and heat shock protein 27 in equine skeletal muscle

OBJECTIVE: To investigate the effects of exercise on activation of mitogen-activated protein kinase (MAPK) signaling proteins in horses. ANIMALS: 6 young trained Standardbred geldings. PROCEDURE: Horses performed a 20-minute bout of exercise on a treadmill at 80% of maximal heart rate. Muscle biopsy specimens were obtained from the vastus lateralis and pectoralis descendens muscles before and after exercise. Amount of expression and intracellular location of phosphospecific MAPK pathway intermediates were determined by use of western blotting and immunofluorescence staining. RESULTS: Exercise resulted in a significant increase in phosphorylation of p38 pathway intermediates, c-Jun NH2 terminal kinase (JNK), and heat shock protein 27 (HSP27) in the vastus lateralis muscle, whereas no significant changes were found in phosphorylation of extracellular regulated kinase. In the pectoralis descendens muscle, phosphorylation of p38 and HSP27 was significantly increased after exercise. Immunohistochemical analysis revealed fiber-type- specific locations of phosphorylated JNK in type 2a/b intermediate and 2b fibers and phosphorylated p38 in type 1 fibers. Phosphorylated HSP27 was strongly increased after exercise in type 1 and 2a fibers. CONCLUSIONS AND CLINICAL RELEVANCE: The p38 pathway and JNK are activated in the vastus lateralis muscle after a single 20-minute bout of submaximal exercise in trained horses. Phosphorylation of HSP27 as detected in the study reported here is most likely induced through the p38 signaling pathway.