943 research outputs found
The infection biology of pig-associated Salmonella
Through the use of an establishe dline of porcine intestinal epithelial cells, known as IPEC-1, this in vitro work examines the initial adhesion, invasion and persistence abilities of different Salmonella serovars and phage types, including multiresistant and monophasic S. typhimurium DT193 isolates. The resultant innate immune response of the porcine cells to the isolates is assessed through determination of interleukin (IL)-6 and IL-8 concentrations present in cell culture supernatants
Restoration Of Dual-Frequency Signals With Nonlinear Propagation In Fibers With Positive Group-Velocity Dispersion
It is shown experimentally and theoretically that a sinusoidally modulated pulse evolves with time into a train of dark soliton-like pulses and then returns to its initial sinusoidal shape on propagation through a nonlinear single-mode fiber with positive group velocity dispersion. The experimental results are in agreement with predictions from the nonlinear Schrodinger equation
Observation of a Modulational Instability in Bose-Einstein condensates
We observe the breakup dynamics of an elongated cloud of condensed Rb
atoms placed in an optical waveguide. The number of localized spatial
components observed in the breakup is compared with the number of solitons
predicted by a plane-wave stability analysis of the nonpolynomial nonlinear
Schr\"odinger equation, an effective one-dimensional approximation of the
Gross-Pitaevskii equation for cigar-shaped condensates. It is shown that the
numbers predicted from the fastest growing sidebands are consistent with the
experimental data, suggesting that modulational instability is the key
underlying physical mechanism driving the breakup.Comment: 6 pages, 5 figure
Ultrafast All-Optical Switching In Semiconductor Nonlinear Directional-Couplers At Half The Band-Gap
Efficient ultrafast all-optical switching in nonlinear directional couplers made of AlGaAs and AlGaAs/GaAs quantum wells near half the band gap is reported. The switching is limited by multiphoton absorption which is dominated by three-photon absorption in this spectral range. The three-photon absorption in the quantum well nonlinear directional coupler is stronger than that of bulk AlGaAs. Autocorrelations of the output pulses in the bar and cross states confirm pulse breakup through nonlinear coupling, and illustrate the effects of multiphoton absorption. All sets of experimental data are fitted well by a theoretical model
Farmers' willingness to pay for a village poultry vaccine service in Ethiopia: prospect for enhancing rural livelihoods
This research examines farmers’ willingness to pay for village poultry vaccine programmes using data from 400 household heads from two districts in Ethiopia, Horro and Jarso. The study applied a contingent valuation method to elicit farmers’ willingness to pay for village poultry vaccine services. Two hypothetical vaccine programmes were designed for Newcastle disease and Gumboro disease. Both parametric and non-parametric approaches were employed in data analysis. The results show that farmers recognise the benefits of the vaccine programme and that many would be willing to pay for it. Results from non-parametric estimates produced households’ mean willingness to pay Ethiopian Birr (ETB) 80 up to ETB 87 per year based on vaccine programme type. This demonstrates the potential and prospect of reducing the impact of infectious poultry diseases and enhancing rural livelihoods through village poultry. Exponential probit analysis revealed that farmers’ willingness to pay for village poultry vaccine service is influenced by age, education level, and region of respondents. Younger and more-educated farmers were more likely to pay for village poultry vaccine services and farmers from Horro, a relatively food secure and educated area, were more likely to pay than those from the less food secure Jarso district
Late Holocene palynology and palaeovegetation of tephra-bearing mires at Papamoa and Waihi Beach, western Bay of Plenty, North Island, New Zealand.
The vegetation history of two mires associated with Holocene dunes near the western Bay of Plenty coast, North Island, New Zealand, is deduced from pollen analysis of two cores. Correlation of airfall tephra layers in the peats, and radiocarbon dates, indicate that the mires at Papamoa and Waihi Beach are c. 4600 and c. 2900 conventional radiocarbon years old, respectively. Tephras used to constrain the chronology of the pollen record include Rotomahana (1886 AD), Kaharoa (700 yr B.P.), Taupo (Unit Y; 1850 yr B.P.), Whakaipo (Unit V; 2700 yr B.P.), Stent (Unit Q; 4000 yr B.P.), Hinemaiaia (Unit K; 4600 yr B.P.), and reworked Whakatane (c. 4800 yr B.P.) at Papamoa, and Kaharoa and Taupo at Waihi Beach. Peat accumulation rates at Papamoa from 4600 - 1850 yr B.P. range from 0.94 to 2.64 mm/yr (mean 1.37 mm/yr). At Waihi Beach, from 2900 yr B.P. - present day, they range from 0.11 to 0.21 mm/yr (mean 0.20 mm/yr). Peat accumulation at both sites was slowest from 1850 to 700 yr B.P., suggesting a drier overall climate during this interval. At both sites, the earliest organic sediments, which are underlain by marine or estuarine sands, yield pollen spectra indicating salt marsh or estuarine environments. Coastal vegetation communities declined at both sites, as sea level gradually fell or the coast prograded, and were eventually superseded by a low moor bog at Papamoa, and a mesotrophic swamp forest at Waihi Beach. These differences, and the marked variation in peat accumulation rates, probably reflect local hydrology and are unlikely to have been climatically controlled. The main regional vegetation during this period was mixed northern conifer-angiosperm forest. Kauri (Agathis australis) formed a minor component of these forests, but populations of this tree have apparently not expanded during the late Holocene at these sites, which are near its present southern limit. Occasional shortlived forest disturbances are detectable in these records, in particular immediately following the deposition of Taupo Tephra. However, evidence for forest clearance during the human era is blurred by the downward dislocation of modern adventi ve pollen at these sites, preventing the clear differentiation of the Polynesian and European eras
A Human Development Framework for CO2 Reductions
Although developing countries are called to participate in CO2 emission
reduction efforts to avoid dangerous climate change, the implications of
proposed reduction schemes in human development standards of developing
countries remain a matter of debate. We show the existence of a positive and
time-dependent correlation between the Human Development Index (HDI) and per
capita CO2 emissions from fossil fuel combustion. Employing this empirical
relation, extrapolating the HDI, and using three population scenarios, the
cumulative CO2 emissions necessary for developing countries to achieve
particular HDI thresholds are assessed following a Development As Usual
approach (DAU). If current demographic and development trends are maintained,
we estimate that by 2050 around 85% of the world's population will live in
countries with high HDI (above 0.8). In particular, 300Gt of cumulative CO2
emissions between 2000 and 2050 are estimated to be necessary for the
development of 104 developing countries in the year 2000. This value represents
between 20% to 30% of previously calculated CO2 budgets limiting global warming
to 2{\deg}C. These constraints and results are incorporated into a CO2
reduction framework involving four domains of climate action for individual
countries. The framework reserves a fair emission path for developing countries
to proceed with their development by indexing country-dependent reduction rates
proportional to the HDI in order to preserve the 2{\deg}C target after a
particular development threshold is reached. Under this approach, global
cumulative emissions by 2050 are estimated to range from 850 up to 1100Gt of
CO2. These values are within the uncertainty range of emissions to limit global
temperatures to 2{\deg}C.Comment: 14 pages, 7 figures, 1 tabl
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