The effect of commercial selection on the growth, efficiency, and yield of broilers was studied using 2 University of Alberta Meat Control strains unselected since 1957 and 1978, and a commercial ...Ross 308 strain (2005). Mixed-sex chicks (n = 180 per strain) were placed into 4 replicate pens per strain, and grown on a current nutritional program to 56 d of age. Weekly front and side profile photographs of 8 birds per strain were collected. Growth rate, feed intake, and measures of feed efficiency including feed conversion ratio, residual feed intake, and residual maintenance energy requirements were characterized. A nonlinear mixed Gompertz growth model was used to predict BW and BW variation, useful for subsequent stochastic growth simulation. Dissections were conducted on 8 birds per strain semiweekly from 21 to 56 d of age to characterize allometric growth of pectoralis muscles, leg meat, abdominal fat pad, liver, gut, and heart. A novel nonlinear analysis of covariance was used to test the hypothesis that allometric growth patterns have changed as a result of commercial selection pressure. From 1957 to 2005, broiler growth increased by over 400%, with a concurrent 50% reduction in feed conversion ratio, corresponding to a compound annual rate of increase in 42 d live BW of 3.30%. Forty-two-day FCR decreased by 2.55% each year over the same 48-yr period. Pectoralis major growth potential increased, whereas abdominal fat decreased due to genetic selection pressure over the same time period. From 1957 to 2005, pectoralis minor yield at 42 d of age was 30% higher in males and 37% higher in females; pectoralis major yield increased by 79% in males and 85% in females. Over almost 50 yr of commercial quantitative genetic selection pressure, intended beneficial changes have been achieved. Unintended changes such as enhanced sexual dimorphism are likely inconsequential, though musculoskeletal, immune function, and parent stock management challenges may require additional attention in future selection programs.
Amorphous solids increase their stress as a function of an applied strain until a mechanical yield point whereupon the stress cannot increase anymore, afterward exhibiting a steady state with a ...constant mean stress. In stress-controlled experiments, the system simply breaks when pushed beyond this mean stress. The ubiquity of this phenomenon over a huge variety of amorphous solids calls for a generic theory that is free of microscopic details. Here, we offer such a theory: The mechanical yield is a thermodynamic phase transition, where yield occurs as a spinodal phenomenon. At the spinodal point, there exists a divergent correlation length that is associated with the system-spanning instabilities (also known as shear bands), which are typical to the mechanical yield. The theory, the order parameter used, and the correlation functions that exhibit the divergent correlation length are universal in nature and can be applied to any amorphous solids that undergo mechanical yield.
As the world's leading corn producer, the United States supplies more than 30% of the global corn production. Accurate and timely estimation of corn yield is therefore essential for commodity trading ...and global food security. Recently, several deep learning models have been explored for corn yield forecasting. Despite success, most existing models only provide yield estimations without quantifying the uncertainty associated with the predictions. Also, the traditional deep learning approaches typically require a large training set and are easily prone to overfitting when the number of samples in the training set is relatively small. To address these limitations, in this study, we developed a county-level corn yield prediction model based on Bayesian Neural Network (BNN) using multiple data sources that are publicly available, including time-series satellite products, sequential climate observations, soil property maps, and historical corn yield records. Using preceding years since 2001 for model training, the developed BNN model achieved an average coefficient of determination (R2) of 0.77 for late-season prediction across the U.S. Corn Belt in testing years 2010–2019, and outperformed five other state-of-the-art machine learning models. Detailed evaluation in three representative testing years demonstrated that the proposed BNN model could accurately estimate corn yield not only in normal years but also in abnormal years when extreme weather events happened. Moreover, the timeliness of the prediction was evaluated within the growing season with an R2~0.75 achieved by middle August, which is about 2 months before the harvest. We also assessed the predictive uncertainty, and more than 84% of the observed yield records were successfully enveloped in the 95% confidence interval of the predictive yield distribution. Our results also showed that the uncertainty level decreased steadily as time proceeded and stabilized around early August. Uncertainties in yield prediction were mainly induced by the observation noise and also related to the interannual and seasonal variabilities of environmental stress such as heat and water stress. This paper provides a robust framework for the within-season prediction of crop yield and highlights the need to obtain a deeper understanding of the effects of environmental stress on agricultural productivity and crop yield estimation.
•A Bayesian neural network was developed for corn yield and uncertainty estimation.•The developed model outperformed five widely used machine learning models.•The near-optimal performance was achieved 2 months before the harvest.•Predictive uncertainty could estimate the confidence level of yield prediction.•RS data noises and environmental stress increased predictive uncertainty.
Australian dry-land crop producers farm in regions with highly variable climate and soils. Farmers have responded to the pressures of rising costs by pioneering and adapting new technologies to ...narrow the gap between actual and water-limited yield. With yields reaching a plateau in many of the developed world’s cropping areas, it is possible that Australia’s leading farmers have similarly closed the exploitable yield gap and require technological breakthroughs to sustainably push the production frontier to new and higher levels. To assess the potential for Australian farmers to continue closing the yield gap, and possibly increase water-limited yield, the long-term farm production records of individual wheat fields of three leading farmers in South East Australia were used to ascertain the applicability of modelling to develop new and innovative practices. The cropping systems simulator APSIM was used to establish the attainable simulated yield based on the farmers’ chosen management inputs for wheat crops over a period of 16–20 years. A strong relationship (r2=0.89, RMSD=508kgha−1) was found between actual and simulated yields. This relationship indicates that yield-reducing factors not simulated by APSIM (weeds, disease etc.) were largely controlled on these farms and confirms APSIM’s suitability for this analysis. Over the 16–20 year study period, the average yield gaps on the three farms ranged from 480 to 770kgha−1; representing between 74 and 82% of their water-limited yield potential. For these leading farmers, the yield gap is only small and unlikely to be economically exploitable under current management practices. Consequently, three tactical management innovations with potential to improve farm wheat yield and reduce risk were evaluated. One innovation investigated whether farmers practicing no-till crop establishment, who were able to control weeds prior to sowing, could benefit from sowing current cultivars earlier than present-day practice. It was found that leading farmers are already sowing at the optimum time and sowing earlier would not increase yield because of greater risk of frost damage. Two other innovations were found to have practical application. The first used Yield Prophet® to assist farmers decide when to apply in-crop nitrogen fertiliser based on a more complete understanding of nitrogen and water requirements of crops in variable growing seasons. The second innovation involved sowing slow maturing wheat cultivars earlier than current practice but only in years with adequate stored soil water and early season rainfall. Both innovations were found to increase grain yield and reduce risk of over- or under-application of nitrogen fertiliser. Investigation of strategic and tactical management options to increase yield using simulation modelling for subsequent evaluation in the field has the potential to keep Australian farmers at the forefront of innovations in crop production.
Arbuscular mycorrhizal fungi (AMF) are ubiquitous in agroecosystems and often stated to be critical for crop yield and agroecosystem sustainability. However, should farmers modify management to ...enhance the abundance and diversity of AMF? We address this question with a focus on field experiments that manipulated colonisation by indigenous AMF and report crop yield, or investigated community structure and diversity of AMF. We find that the literature presents an overly optimistic view of the importance of AMF in crop yield due, in part, to flawed methodology in field experiments. A small body of rigorous research only sometimes reports a positive impact of high colonisation on crop yield, even under phosphorus limitation. We suggest that studies vary due to the interaction of environment and genotype (crop and mycorrhizal fungal). We also find that the literature can be overly pessimistic about the impact of some common agricultural practices on mycorrhizal fungal communities and that interactions between AMF and soil microbes are complex and poorly understood. We provide a template for future field experiments and a list of research priorities, including phosphorus-efficient agroecosystems. However, we conclude that management of AMF by farmers will not be warranted until benefits are demonstrated at the field scale under prescribed agronomic management.
Cemented paste backfill (CPB), an engineered mix consisting typically of tailings, cement and water, has become a regularly used structural material in most mines worldwide. The performance of the ...CPB structure is dependent both on the quality of each constituent and the rheological behavior of fresh CPB during placement into mined-out voids. A connection between the backfill's rheological behavior and the structural changes governing thixotropy and structural breakdown can provide a better understanding of the different yield stress-viscosity results. In this study, the mineral admixture effect on rheological properties of fresh CPB slurry is studied by considering a combined assessment of time dependency and thixotropy. A total of three mineral admixtures such as fly ash (FA), granulated blast furnace slag (Slag) and silica fume (SF) were used for the preparation of CPB material. The rheological parameters, mainly yield stress and plastic viscosity, were examined by the Bingham model. Results indicate that the thixotropy of fresh CPB decreases with FA dosage, while the addition of Slag and SF gives lower thixotropy values at early ages, and a higher rate of thixotropy acquisition at a later age. A partial replacement of cement with FA leads to an increase in the static deformability and significant improvement in fluidity of CPB, and a plot of thixotropy versus plastic viscosity results in a linear correlation between them. Moreover, the addition of slag particles reduces the yield stress and plastic viscosity of CPB, while SF-containing CPB exhibits improved yield stress and lower plastic viscosity. Plotting thixotropy versus plastic viscosity generates a poor linear relation for SF- and Slag-containing CPB slurries. The findings of this study will be useful in the lucrative design, efficient operation and safe production of early-age CPB material.
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•Effect of mineral admixtures on flow properties of fresh cemented paste backfill is investigated.•The addition of fly ash and granulated blast furnace slag improves the fluidity of cemented paste backfill.•A partial replacement of cement with silica fume results in higher yield stress and lower plastic viscosity.•A linear relationship exists between thixotropy and the corresponding plastic viscosity for samples containing fly ash.
Yield stress materials are ubiquitous, yet the best way to obtain the value of the yield stress for any given material has been the subject of considerable debate. Here we compare different methods ...of measuring the yield stress with conventional rheometers that have been used in the literature on a variety of materials. The main conclusion is that, at least for well-behaved (non-thixotropic) materials, the differences between the various methods are significant; on the other hand, the scaling of the measured yield stress with the volume fraction of dispersed phase shows the same dependence independently of the way in which the yield stress is obtained experimentally. The measured yield strain is similarly found to depend on the method employed. The yield stress values obtained for a simple (non-thixotropic) yield stress fluid are only similar for Herschel–Bulkley fits and stress-strain curves obtained from oscillatory measurements. Stress-strain curves with a continuous imposed stress or strain rate differ significantly, as do oscillatory measurements of the crossover between G′ and G″ or the point where G′ starts to differ significantly from its linear response value. The intersection of the G′ and G″ curves as a function of strain consistently give the highest value of the yield stress and yield strain. In addition, many of these criteria necessitate some arbitrary definition of a crossover point. Similar conclusions apply for a class of thixotropic yield stress materials, with the stress-strain curve from the oscillatory data giving the dynamic yield stress and the Herschel–Bulkley fit either the static or dynamic yield stress, depending on how the measurement is carried out.
Linear models are commonly used to describe the early structural build-up of cement-based materials. However, some studies have shown that there exists a faster non-linear phase before the linear ...phase. In this study, a simple non-linear thixotropy model is presented to describe the structural build-up process. It was quantified using static yield stress and storage modulus, which are measured through the stress growth protocol and small amplitude oscillatory shear (SAOS) tests, respectively. The effect of pre-shear, rest condition and viscosity modifying admixtures (nanoclay and diutan gum) on the build-up behavior are studied. The results showed distinctly different trends between static yield stress and storage modulus. This may be attributed to the two different structures of fresh cement pastes, i.e. floc structures and C-S-H structures, measured by the stress growth protocol and SAOS test, respectively.
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Bioprinting technologies have tremendous potential for advancing regenerative medicine due to the precise spatial control over depositing a printable biomaterial, or bioink. Despite ...the growing interest in bioprinting, the field is challenged with developing biomaterials for extrusion-based bioprinting. The paradigm of contemporary bioink studies relies on trial-and-error methods for discovering printable biomaterials, which has little practical use for others who endeavor to develop bioinks. There is pressing need to follow the precedent set by a few pioneering studies that have attempted to standardize bioink characterizations for determining the properties that define printability. Here, we developed a pentenoate-functionalized hyaluronic acid hydrogel (PHA) into a printable bioink and used three recommended, quantitative rheological assessments to characterize the printability: 1) yield stress, 2) viscosity, and 3) storage modulus recovery. The most important characteristic is the yield stress; we found a yield stress upper limit of ∼1000 Pa for PHA. Measuring the viscosity was advantageous for determining shear-thinning behavior, which aided in extruding highly viscous PHA through a nozzle. Post-printing recovery is required to maintain shape fidelity and we found storage modulus recoveries above ∼85% were sufficient for PHA. Two formulations had superior printability (i.e., 1.5 MDa PHA − 4 wt%, and 1 MDa PHA − 8 wt%), and increasing cell concentrations in PHA up to 9 × 106 cells/mL had minimal effects on the printability. Even so, other factors such as sterilization and peptide modifications to enhance bioactivity may influence printability, highlighting the need for investigators to consider such factors when developing new bioinks.
Bioprinting has potential for regenerating damaged tissues; however, there are a limited number of printable biomaterials, and developing new bioinks is challenging because the required material physical properties for extrusion-based printing are not yet known. Most new bioinks are developed by trial-and-error, which is neither efficient nor comparable across materials. There is a need for the field to begin utilizing standard methods proposed by a few pioneering studies to characterize new bioinks. Therefore, we have developed the printability of a hyaluronic acid based-hydrogel and characterized the material with three quantitative rheological tests. The current work impacts the bioprinting field by demonstrating and encouraging the use of universal bioink characterizations and by providing printability windows to advance new bioink development.
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