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The ability of microramps to control shock - boundary layer interaction at the vicinity of an axisymmetric compression corner was investigated computationally in a Mach 4 flow. A cylinder/flare model with a flare angle of 25° was chosen for this study. Height (h) of the microramp device was 22% of the undisturbed boundary layer thickness (δ) obtained at the compression corner location. A single array of these microramps with an inter-device spacing of 7.5h was placed at three different streamwise locations viz. 5δ, 10δ and 15δ (22.7h, 45.41h and 68.12h in terms of the device height) upstream of the corner and the variations in the flowfield characteristics were observed. These devices modified the separation bubble structure noticeably by producing alternate upwash and downwash regions in the boundary layer. Variations in the separation bubble’s length and height were observed along the spanwise (circumferential) direction due to these devices.
Pollinator declines coupled with increasing demand for insect pollinated crops have the potential to cause future pollinator shortages for our most nutritious and valuable crops. Ensuring adequate crop pollination may necessitate a shift in pollination management, from one that primarily relies on the managed European honeybee (Apis mellifera L.) to one that integrates alternative pollinators. While a growing body of scientific evidence supports significant contributions made by naturally occurring, native bees for crop pollination, translating research to practice requires buy-in from growers. The intention of agricultural extension is to address grower needs and concerns; however, few studies have assessed grower knowledge, perceptions and attitudes about native pollinators. Here we present findings from questionnaire-based surveys of over 600 apple growers in New York State and Pennsylvania, coupled with ecological data from bee surveys. This hybrid sociological and biological survey allows us to compare grower knowledge and perceptions to an actual pollinator census. While up to 93% of respondents highly valued importance of native bees, 20% growers did not know how much native bees actually contribute to their orchard pollination. Despite the uncertainty, a majority of growers were open to relying on native bees (up to 60% in NY and 67% in PA) and to making low-cost changes to their farm's management that would benefit native pollinators (up to 68 in NY and 85% in PA). Growers consistently underestimated bee diversity, but their estimates corresponded to major bee groups identifiable by lay persons, indicating accurate local knowledge about native bees. Grower reliance on honeybees increased with farm size; because native bee abundance did not measurably decrease with farm size, renting honeybees may be motivated by risk avoidance rather than grower perception of lower native bee activity. Demonstrated effectiveness of native pollinators and clear guidelines for their management were the most important factors influencing grower decision to actively manage orchards for native bees. Our results highlight a pressing need for an active and research-based extension program to support diversification of pollination strategies in the region.
In the present study, unsteady MHD boundary layer flow of a rotating Walters’-B fluid (viscoelastic fluid) over an infinite vertical porous plate embedded in a uniform porous medium with fluctuating wall temperature and concentration taking Hall and ion-slip effects into consideration is discussed. The MHD flow in the rotating fluid system is induced due to the non-torsional oscillations of the plate in its own plane and the buoyancy forces arises from temperature and concentration differences in field of gravity. The partial differential equations governing the fluid motion are solved analytically by using regular perturbation and variable separable methods by assuming very small viscoelastic parameter. Solution for velocity field in the case when natural frequency due to rotation and Hall current is equals to the frequency of oscillations i.e. in the case of resonance is also obtained. In order to note the influences of various system parameters and to discuss the important flow characteristics, the numerical results for fluid velocity in the non-resonance case, temperature and species concentration are computed and depicted graphically versus boundary layer parameter whereas skin friction, Nusselt number and Sherwood number at the plate are computed and presented in tabular form. An interesting observation recorded that there arises flow reversal in the primary flow direction due to high rotation. When natural frequency is greater than the frequency of oscillations the fluid velocity in the primary flow direction is maximum at the plate whereas incase when natural frequency is smaller than the frequency of oscillations, it is maximum in the neighborhood of the plate.
This research article addresses the effect of fillers on the high-temperature corrosion behavior of AISI 347 weld joints. Multi-pass pulsed current gas tungsten arc welding was carried out on 6.67 mm thick plates of AISI 347 using three different fillers namely ER347, ER2553, and ERNiCrMo-3. The fusion zone microstructures of AISI 347 employing ER2553 and ERNiCrMo-3 exhibited columnar and dendritic grain growth; whereas vermicular delta ferrite was observed at the fusion zone of ER347 welds. Tensile studies showed that the weld employing ERNiCrMo-3 exhibited better tensile strength than the parent metal. High-temperature corrosion studies were carried out on the fusion zones by exposing the coupons to an aggressive, synthetic molten-salt incinerator environment containing 40% Na2SO4–40% K2SO4–10% NaCl–10% KCl at 650 °C for 50 cycles. The studies attested that the fusion zone employing ERNiCrMo-3 exhibited better corrosion resistance than the other two fillers used in the study. Spallation of oxides was witnessed due to the dissolution of Cr2O3 in the ER347 and ER2553 fusion zones. The hot corroded samples were characterized using surface analytical techniques.
Plant breeding makes genetic gains over years, so growing newer varieties generally provides greater benefits than growing older ones. However, in low-altitude districts of Nepal, a few rice varieties covered 75% of the rice area and were more than 20 years old (first paper in this series). We test here if this slow rate of adoption of new varieties could be accelerated using a participatory method, Informal Research and Development (IRD), where packets of seeds of new rice varieties are widely distributed to many farmers. From 2008 to 2011, over 117 000 IRD packets were distributed in 18 districts of the Nepal Terai, including over 70 000 of three released varieties from a client-oriented breeding (COB) programme in Nepal. The IRD significantly increased the adoption of the three COB varieties. The benefits obtained by farmers in a single growing season equal the costs of IRD, if for every 75 kits distributed an additional 1 ha is grown. This assumes that the new varieties produce a 10% increase in yield (lower than that evidenced in their release proposals). On an average, fewer than three IRD kits were distributed for each hectare of a new variety grown by farmers in 2011. Furthermore, the effectiveness of IRD could be increased 1.2 to 2.7 fold (depending on the COB variety) if the IRD distribution were to be restricted to the region where the variety was most accepted. The best comparison of IRD with extension by the conventional system was their popularity compared with similar-aged varieties that had been promoted in the two systems. The adoption of three COB varieties was about twicethat of three varieties from the National Rice Research Programme (NRRP) that were closest in release date to the COB varieties. Unlike cost effectiveness assessed by hectares grown per IRD kit distributed, this comparison can only indicate efficacy because, as well as extension method, many factors influenced the adoption rates of the COB and NRRP varieties. The costs of IRD are small, both relative to the cost of breeding new varieties and to the benefits gained; so it is one of the simplest and most cost-effective interventions to increase agricultural productivity.
Farmers who continue to grow old and obsolete varieties do not gain the benefits they could get from growing newer ones. Given the potential large scale of these foregone benefits, relatively few studies have examined the age of varieties that farmers grow. In three surveys, members of over 3300 households were interviewed to find the rice varieties they grew in 2008 and 2011 in 18 districts in the Terai, the low-altitude region of Nepal. This provided the first description of detailed geographical patterns of adoption of rice varieties and their ages that were repeated over time. There were large differences between district and individual varieties that showed specific geographical patterns of adoption. Such detailed knowledge on spatial diversity of varieties is invaluable for planning extension activities and developing breeding programmes, and cheaper ways than household surveys of collecting this information are discussed. Some of the factors considered important in determining this complex pattern of adoption were seed availability, growing environments that differed from east to west and the continued popularity of varieties once they had established markets. Rice diversity was low because a small number of rice varieties occupied large areas. In 2011, nine varieties covered at least 75% of the total rice area in western districts, just four in central districts and eight in eastern districts. Of these, most were released before 1995 resulting in a high average age of the predominant varieties – they always had an average age of over 20 years no matter which region or year was considered. Even though there were some large changes in varietal composition from 2008 to 2011, the average age of the predominant varieties remained almost the same. In a second paper in this series, we examine how these very low varietal replacement rates, that reduce yields and increase risk to farmers, can be accelerated using a participatory research for development approach called Informal Research and Development (IRD) (Joshi et al., 2012).
The permutability property of Bäcklund transformations of solutions (of soliton equations), as discussed at the end of the previous chapter, forms one of the main sources of integrable partial difference equations (P∆Es) on the two-dimensional space–time lattice. In this chapter we study these equations in their own right, i.e. ignore their origin, and no longer assume that the dependent variable is a solution of any previously given PDE. In particular, we will consider the “integrability” of these P∆Es.
In general terms the concept of integrability is associated with regularity, solvability and amenability to exact and explicit treatments. These notions will have different mathematical meanings in different contexts, and it is indeed an open problem to give a universal definition of integrability. There are many characteristics associated with integrability, such as the existence of a Lax pair, compatibility structures such as Bäcklund transforms and hierarchies of compatible equations, good behavior of solutions with respect to singularities, regularity with regard to growth properties and complexity of solutions. These aspects of integrability are reflected in various different approaches in constructing and solving P∆Es, such as the τ -function approach of Hirota and the Kyoto school, symmetry methods and inverse methods such as “direct linearization”, some of which will be discussed in later chapters. Many of these features can be posed as definitions of integrability, but they are often restricted to specific classes of integrable systems. It is remarkable that if any two different definitions of integrability can be applied to some joint set of equations, they agree on which equations should be called integrable.
The presence of free parameters in the equations (namely the Bäcklund parameters λ and μ, which we will now reinterpret as lattice parameters) will play a crucial role in the development of the theory in this chapter. Furthermore, as we will see later, the parameters render the P∆Es very rich: since they can be seen to represent the widths of the underlying lattice grid they allow us to recover, through continuum limits, a great wealth of other equations, semi-continuous (i.e. differential-difference type) as well as fully continuous (i.e. partial differential type) ones. The interplay between the discrete and continuous structures will prove to be one of the emerging features of the integrable systems that we study.