The dynamics and control of large flexible space structures, 8

A development of the in plane open loop rotational equations of motion for the proposed Spacecraft Control Laboratory Experiment (SCOLE) in orbit configuration is presented based on an Eulerian formulation. The mast is considered to be a flexible beam connected to the (rigid) shuttle and the reflector. Frequencies and mode shapes are obtained for the mast vibrational appendage modes (assumed to be decoupled) for different boundary conditions based on continuum approaches and also preliminary results are obtained using a finite element representation of the mast reflector system. The linearized rotational in plane equation is characterized by periodic coefficients and open loop system stability can be examined with an application of the Floquet theorem. Numerical results are presented to illustrate the potential instability associated with actuator time delays even for delays which represent only a small fraction of the natural period of oscillation of the modes contained in the open loop model of the system. When plant and measurement noise effects are added to the previously designed deterministic model of the hoop column system, it is seen that both the system transient and steady state performance are degraded. Mission requirements can be satisfied by appropriate assignment of cost function weighting elements and changes in the ratio of plant noise to measurement noise

The dynamics and control of large flexible space structures, part 7

A preliminary Eulerian formulation of the in-plane dynamics of the proposed spacecraft control laboratory experiment configuration is undertaken when the mast is treated as a cantilever type beam and the reflector as a lumped mass at the end of the beam. Frequency and mode shapes are obtained for the open loop model of the beam system and the stability of closed loop control systems is analyzed by both frequency and time domain techniques. Environmental disturbances due to solar radiation pressure are incorporated into models of controlled large flexible orbiting platforms. Thermally induced deformations of simple beam and platform type structures are modelled and expressions developed for the disturbance torques resulting from the interaction of solar radiation pressure. Noise effects in the deterministic model of the hoop/column antenna system are found to cause a degradation in system performance. Appropriate changes in the ratio of plant noise to the measurement noise and/or changes in the control weighting matrix elements can improve transient and steady state performance

The dynamics and control of large flexible space structures-V

A general survey of the progress made in the areas of mathematical modelling of the system dynamics, structural analysis, development of control algorithms, and simulation of environmental disturbances is presented. The use of graph theory techniques is employed to examine the effects of inherent damping associated with LSST systems on the number and locations of the required control actuators. A mathematical model of the forces and moments induced on a flexible orbiting beam due to solar radiation pressure is developed and typical steady state open loop responses obtained for the case when rotations and vibrations are limited to occur within the orbit plane. A preliminary controls analysis based on a truncated (13 mode) finite element model of the 122m. Hoop/Column antenna indicates that a minimum of six appropriately placed actuators is required for controllability. An algorithm to evaluate the coefficients which describe coupling between the rigid rotational and flexible modes and also intramodal coupling was developed and numerical evaluation based on the finite element model of Hoop/Column system is currently in progress

Nutrient digestibility and growth performance of broiler chickens fed processed tropical sicklepod (Senna obtusifolia (L.) seed meal based - diets

The eight-week feeding trial was conducted to evaluate the nutrient digestibility and growth performance of broiler chickens fed raw or processed Senna obtusifolia seed meal (SOSM). Six experimental diets were compounded to contain 0% SOSM and 20% each of the raw, boiled, soaked, sprouted and fermented SOSM respectively. Two hundred and sixteen (216) broiler chicks were randomly allotted to six (6) dietary treatments in a randomised complete block design with three (3) replicates containing 12 chicks each. Data were collected on nutrient digestibility, feed intake, weight gain, feed conversion ratio and mortality. The result of productive performance indicated that feed intake, weight gain and feed conversion ratio were significantly (P<0.05) depressed in broiler chickens fed raw, soaked and sprouted Senna obtusifolia seed meal. However, broiler chickens fed fermented SOSM showed better (P<0.05) productive performance that was close to those fed the positive control diet (0% SOSM). The mortality rate did not reveal any particular trend. However, the low mortality rate recorded in the different treatments indicated broiler chicken can tolerate up to 20% of either raw or processed SOSM. Broiler chickens fed raw SOSM recorded lower values for dry matter (63.06%), crude protein (52.46%), ether extract (53.88%), crude fibre (30.72%) and nitrogen-free extract (46.11%) digestibility than those fed the other processed SOSM. The nutrient digestibility of broiler chickens fed fermented SOSM was significantly (P<0.05) better followed by those fed boiled Senna obtusifolia seed meal. For instance, broiler chickens fed fermented Senna obtusifolia seed meal recorded the highest crude protein and ether extract of 69.91 and 70.03% compared to the other processing methods. It can be concluded that 20% fermented SOSM can be incorporated in the diets of broiler chickens with acceptable depreciation in biological performance. Slightly lower levels of boiled SOSM can be included in the diet of broiler chickens but the levels should be ascertained in further studies

Giant Taro (Alocasia macrorrhiza) Root Meal with or without Coconut Oil Slurry as Source of Dietary Energy for Laying Hens

The effect of feeding Alocasia macrorrhiza root meal (AMRM) with or without added coconut oil slurry (COS) on egg production and egg qualities was investigated in a 20-week experiment. A control diet based on maize and 4 other diets containing 10 and 20% AMRM with or without COS were fed each to 4 replicates of 10 birds in a completely randomized design. There were no significant dietary effects on feed intake (FI) and the intake of lysine, methionine and metabolizable energy (ME). Birds fed the 20% AMRM_COS added significantly less weight during the experimental period compared to the control fed group. Body weight change (BWC) did not differ among the AMRM fed birds. Per cent hen-day and feed conversion ratio were depressed on 20% AMRM and egg weight on 10% AMRM but these depressing effects were overcome by COS addition. Egg shape index, Haugh unit and per cent shell were not affected by the diet. It is concluded that AMRM can replace 10% dietary maize without adverse effect on laying performance but 20% replacement negatively impacts on hen-day and egg weight. These adverse effects are however, overcome by treating AMRM with COS at the ratio of 9: 1. More research into higher levels of COS treated AMRM in the diet is warranted

The dynamics and control of large flexible space structures

Large, flexible orbiting systems proposed for possible use in communications, electronic orbital based mail systems, and solar energy collection are discussed. The size and low weight to area ratio of such systems indicate that system flexibility is now the main consideration in the dynamics and control problem. For such large, flexible systems, both orientation and surface shape control will often be required. A conceptual development plan of a system software capability for use in analysis of the dynamics and control of large space structures technology (LSST) systems is discussed. This concept can be subdivided into four different stages: (1) system dynamics; (2) structural dynamics; (3) application of control algorithms; and (4) simulation of environmental disturbances. Modeling the system dynamics of such systems in orbit is the most fundamental component. Solar radiation pressure effects and orbital and gravity gradient effects are discussed

Peanut contamination by Aspergillus flavus and aflatoxin B1 in granaries of villages and markets of Mali, West Africa

Peanut (Arachis hypogoea) is an important crop in Mali, West Africa. However, one of the main problems related to peanut production and commercialization is the detection of high levels of aflatoxin B1 in peanut-derived products for consumption. The objectives of this study were 1) to determine the rate of progress of Aspergillus flavus and aflatoxin B1 in granaries located in 26 villages and also in the granaries located in the corresponding 26 markets in Mali and 2) to correlate the progress of the A. flavus and aflatoxin B1 with environmental variables outside the peanut granaries. The results showed that peanuts stored and consumed in rural areas are highly contaminated by A. flavus and aflatoxin B1, with average rates of aflatoxin B1 significantly above the accepted international standards especially between the months of June and December. There was a moderate relationship (r2 = 0.58) between the aflatoxin B1 levels for two granary types, located at the villages and the corresponding granaries in the markets. The analysis of the aflatoxin B1 levels in the villages and its relation with the weather conditions outside the granaries revealed that for one village (Tiele), high relative air humidity was a contributing factor in the development of A. flavus and levels of the aflatoxin B1 in the granary. The results indicated that maximum aflatoxin B1 production occurs in presence of warm temperatures and relative humidity above 80%

Determining the electronic performance limitations in top-down fabricated Si nanowires with mean widths down to 4 nm

Silicon nanowires have been patterned with mean widths down to 4 nm using top-down lithography and dry etching. Performance-limiting scattering processes have been measured directly which provide new insight into the electronic conduction mechanisms within the nanowires. Results demonstrate a transition from 3-dimensional (3D) to 2D and then 1D as the nanowire mean widths are reduced from 12 to 4 nm. The importance of high quality surface passivation is demonstrated by a lack of significant donor deactivation, resulting in neutral impurity scattering ultimately limiting the electronic performance. The results indicate the important parameters requiring optimization when fabricating nanowires with atomic dimensions

Estimating the burden of iron deficiency among African children

Background Iron deficiency (ID) is a major public health burden in African children and accurate prevalence estimates are important for effective nutritional interventions. However, ID may be incorrectly estimated in Africa because most measures of iron status are altered by inflammation and infections such as malaria. Through the current study, we have assessed different approaches to the prediction of iron status and estimated the burden of ID in African children. Methods We assayed iron and inflammatory biomarkers in 4853 children aged 0–8 years from Kenya, Uganda, Burkina Faso, South Africa, and The Gambia. We described iron status and its relationship with age, sex, inflammation, and malaria parasitemia. We defined ID using the WHO guideline (ferritin < 12 μg/L or < 30 μg/L in the presence of inflammation in children < 5 years old or < 15 μg/L in children ≥ 5 years old). We compared this with a recently proposed gold standard, which uses regression-correction for ferritin levels based on the relationship between ferritin levels, inflammatory markers, and malaria. We further investigated the utility of other iron biomarkers in predicting ID using the inflammation and malaria regression-corrected estimate as a gold standard. Results The prevalence of ID was highest at 1 year of age and in male infants. Inflammation and malaria parasitemia were associated with all iron biomarkers, although transferrin saturation was least affected. Overall prevalence of WHO-defined ID was 34% compared to 52% using the inflammation and malaria regression-corrected estimate. This unidentified burden of ID increased with age and was highest in countries with high prevalence of inflammation and malaria, where up to a quarter of iron-deficient children were misclassified as iron replete. Transferrin saturation < 11% most closely predicted the prevalence of ID according to the regression-correction gold standard. Conclusions The prevalence of ID is underestimated in African children when defined using the WHO guidelines, especially in malaria-endemic populations, and the use of transferrin saturation may provide a more accurate approach. Further research is needed to identify the most accurate measures for determining the prevalence of ID in sub-Saharan Africa