Effects of ocean biology on the penetrative radiation in a coupled climate model

The influence of phytoplankton on the seasonal cycle and the mean global climate is investigated in a fully coupled climate model. The control experiment uses a fixed attenuation depth for shortwave radiation, while the attenuation depth in the experiment with biology is derived from phytoplankton concentrations simulated with a marine biogeochemical model coupled online to the ocean model. Some of the changes in the upper ocean are similar to the results from previous studies that did not use interactive atmospheres, for example, amplification of the seasonal cycle; warming in upwelling regions, such as the equatorial Pacific and the Arabian Sea; and reduction in sea ice cover in the high latitudes. In addition, positive feedbacks within the climate system cause a global shift of the seasonal cycle. The onset of spring is about 2 weeks earlier, which results in a more realistic representation of the seasons. Feedback mechanisms, such as increased wind stress and changes in the shortwave radiation, lead to significant warming in the midlatitudes in summer and to seasonal modifications of the overall warming in the equatorial Pacific. Temperature changes also occur over land where they are sometimes even larger than over the ocean. In the equatorial Pacific, the strength of interannual SST variability is reduced by about 10%–15% and phase locking to the annual cycle is improved. The ENSO spectral peak is broader than in the experiment without biology and the dominant ENSO period is increased to around 5 yr. Also the skewness of ENSO variability is slightly improved. All of these changes lead to the conclusion that the influence of marine biology on the radiative budget of the upper ocean should be considered in detailed simulations of the earth’s climate

What causes the spread of model projections of ocean dynamic sea-level change in response to greenhouse gas forcing?

Sea levels of different atmosphere-ocean general circulation models (AOGCMs) respond to climate change forcing in different ways, representing a crucial uncertainty in climate change research. We isolate the role of the ocean dynamics in setting the spatial pattern of dynamic sea-level (zeta) change by forcing several AOGCMs with prescribed identical heat, momentum (wind) and freshwater flux perturbations. This method produces a zeta projection spread comparable in magnitude to the spread that results from greenhouse gas forcing, indicating that the differences in ocean model formulation are the cause, rather than diversity in surface flux change. The heat flux change drives most of the global pattern of zeta change, while the momentum and water flux changes cause locally confined features. North Atlantic heat uptake causes large temperature and salinity driven density changes, altering local ocean transport and zeta. The spread between AOGCMs here is caused largely by differences in their regional transport adjustment, which redistributes heat that was already in the ocean prior to perturbation. The geographic details of the zeta change in the North Atlantic are diverse across models, but the underlying dynamic change is similar. In contrast, the heat absorbed by the Southern Ocean does not strongly alter the vertically coherent circulation. The Arctic zeta change is dissimilar across models, owing to differences in passive heat uptake and circulation change. Only the Arctic is strongly affected by nonlinear interactions between the three air-sea flux changes, and these are model specific.Peer reviewe

Natural and Vaccine-Mediated Immunity to Salmonella Typhimurium is Impaired by the Helminth Nippostrongylus brasiliensis

The impact of exposure to multiple pathogens concurrently or consecutively on immune function is unclear. Here, immune responses induced by combinations of the bacterium Salmonella Typhimurium (STm) and the helminth Nippostrongylus brasiliensis (Nb), which causes a murine hookworm infection and an experimental porin protein vaccine against STm, were examined. Mice infected with both STm and Nb induced similar numbers of Th1 and Th2 lymphocytes compared with singly infected mice, as determined by flow cytometry, although lower levels of secreted Th2, but not Th1 cytokines were detected by ELISA after re-stimulation of splenocytes. Furthermore, the density of FoxP3+ T cells in the T zone of co-infected mice was lower compared to mice that only received Nb, but was greater than those that received STm. This reflected the intermediate levels of IL-10 detected from splenocytes. Co-infection compromised clearance of both pathogens, with worms still detectable in mice weeks after they were cleared in the control group. Despite altered control of bacterial and helminth colonization in co-infected mice, robust extrafollicular Th1 and Th2-reflecting immunoglobulin-switching profiles were detected, with IgG2a, IgG1 and IgE plasma cells all detected in parallel. Whilst extrafollicular antibody responses were maintained in the first weeks after co-infection, the GC response was less than that in mice infected with Nb only. Nb infection resulted in some abrogation of the longer-term development of anti-STm IgG responses. This suggested that prior Nb infection may modulate the induction of protective antibody responses to vaccination. To assess this we immunized mice with porins, which confer protection in an antibody-dependent manner, before challenging with STm. Mice that had resolved a Nb infection prior to immunization induced less anti-porin IgG and had compromised protection against infection. These findings demonstrate that co-infection can radically alter the development of protective immunity during natural infection and in response to immunization

Signatures of Selection for Environmental Adaptation and Zebu × Taurine Hybrid Fitness in East African Shorthorn Zebu

The East African Shorthorn Zebu (EASZ) cattle are ancient hybrid between Asian zebu × African taurine cattle preferred by local farmers due to their adaptability to the African environment. The genetic controls of these adaptabilities are not clearly understood yet. Here, we genotyped 92 EASZ samples from Kenya (KEASZ) with more than 770,000 SNPs and sequenced the genome of a pool of 10 KEASZ. We observe an even admixed autosomal zebu × taurine genomic structure in the population. A total of 101 and 165 candidate regions of positive selection, based on genome-wide SNP analyses (meta-SS, Rsb, iHS, and ΔAF) and pooled heterozygosity (Hp) full genome sequence analysis, are identified, in which 35 regions are shared between them. A total of 142 functional variants, one novel, have been detected within these regions, in which 30 and 26 were classified as of zebu and African taurine origins, respectively. High density genome-wide SNP analysis of zebu × taurine admixed cattle populations from Uganda and Nigeria show that 25 of these regions are shared between KEASZ and Uganda cattle, and seven regions are shared across the KEASZ, Uganda, and Nigeria cattle. The identification of common candidate regions allows us to fine map 18 regions. These regions intersect with genes and QTL associated with reproduction and environmental stress (e.g., immunity and heat stress) suggesting that the genome of the zebu × taurine admixed cattle has been uniquely selected to maximize hybrid fitness both in terms of reproduction and survivability

Enhanced Iterative-Deepening Search

Iterative-deepening searches mimic a breadth-first node expansion with a series of depth-first searches that operate with successively extended search horizons. They have been proposed as a simple way to reduce the space complexity of best-first searches like A* from exponential to linear in the search depth. But her

Sub-newton monopropellant thrusters for small spacecraft propulsion

This thesis documents the design and testing of a sub-newton High Test Peroxide (HTP) monopropellant thruster architecture, suitable for micro and nanosatellite applications. The main goals were to demonstrate that a thruster targeting a 0.1 N thrust level could achieve a high performance, and to investigate the fundamental processes governing its operation. The thruster design exhibited high thermal performance using 87.5 %wt. HTP, with chamber temperatures in excess of 600 °C, corresponding to characteristic velocity efficiencies approaching 0.963 ± 0.004 (1𝜎). These values are similar to equivalent larger-thrust systems. The thruster was also tested with 98.0 %wt. HTP, with temperatures approaching 800 °C. These results represent some of the highest performance of an HTP monopropellant system, and is a first at sub-newton thrust levels. The experimental results were collected by direct measurement of the internal fluid conditions, something not previously achieved on a thruster of this scale. This was made possible by the novel application of conventional metal additive manufacturing techniques, permitting the inclusion of integrated instrumentation standpipes and other complex ancillary geometry. The manufacturing process also enabled the production of a large number of different catalyst bed designs for use in one of the most extensive experimental studies on the impact of the catalyst bed geometry. The geometry was parametrically defined by the catalyst bed loading and aspect ratio, with respective values ranging from 1.48 kg.m-2.s-1 to 64.8 kg.m-2.s-1 and 0.33 to 6. The baseline thruster design, with a nominal bed loading of 10 kg.m-2. s-1 and an aspect ratio of 2, had the highest demonstrated performance. However, data analysis suggested that lower catalyst bed loadings and aspect ratios, i.e. shorter and wider beds, should be more optimal over a blowdown range. The study provided data towards validating a simplified pseudo-physical front model of the catalyst bed. This model describes the phase transition between the cool liquid/multiphase and the hot gas regimes. The phase change front was found to be axially close to the complete decomposition front, representing the maximum temperature in the bed. The catalyst bed flooding condition was used to relate the fundamental reactivity of the catalyst bed to the pseudo-physical front model. It was proposed that the reactivity can be used to size a bed with minimal experimental testing, through the Damköhler number: the estimated liquid-phase decomposition rate was greater than the rate of forced propellant diffusion for nominal catalyst bed operation. The pressure roughness phenomenon was also investigated using spectral analysis. These results were used to justify the proposed local oscillatory diffusion process in the catalyst bed. This is responsible for the pressure roughness, as well as the localised choking in the upstream liquid/multiphase regime that causes high pressure drop over this region. An extensive study on microinjectors was also conducted. This is a field of limited published research. The study characterised the performance of Poiseuille-type microbore tube and Venturitype orifice plate injectors. Poiseuille injectors demonstrated stable performance while orifice injectors were challenging to manufacture and prone to blocking. ‘Chugging’ flow instabilities were also captured, and it is proposed that the onset of this condition is tied to the inertia of the propellant flow through the injector. This, along with the minimum critical flow rate for the Venturi cavitation phenomenon, suggests that the Poiseuille microinjectors are a more robust architecture and better suited to sub-newton monopropellant thrusters

Heuristic search in one and two player games

With the continuing price-performance improvement of small computers there is growing interest in looking again at some of the heuristic techniques developed for problemsolving and planning programs, to see if they can be enhanced or replaced by more algorithmic methods. The application of raw computing power, while and anathema to some, often provides better answers than is possible by reasoning or analogy. Thus brute force techniques form a good basis against which to compare more sophisticated methods designed to mirror the human deductive process. One source of extra computing power comes through the use of parallel processing on a multicomputer, an so this aspect is also covered here. Here we review the development of heuristic algorithms for application in singleagent and adversary games. We provide a detailed study of iterative deepening A * and its many variants, and show howe ective various enhancements, including the use of refutation lines and a transposition table, can be. For adversary games a full review of improved versions of the alpha-beta algorithm (e.g. Principal Variation Search) i