A bounding procedure for synthesis of prestressed systems

Optimal design of indeterminate prestressed concrete systems is stated in a nonlinear programming form. The design variables are the concrete dimensions, tendon coordinates, and prestressing force. The constraints are related to various behaviour and design requirements and the objective function represents the overall cost. On the basis of the transitivity property, a lower bound on the concrete volume is determined by solving a reduced problem. The corresponding minimum prestressing force, calculated by linear programming, is an upper bound. Similarly, a lower bound on the prestressing force is determined by assuming the maximum concrete dimensions. Based on the two bounding solutions a lower bound on the objective function is evaluated. An efficient design procedure is proposed. The best of the bounding solutions is first checked for optimality. The search is then continued, if necessary, in the reduced space of the concrete variables using a feasible directions technique. For any assumed concrete dimensions a reduced linear programming problem is solved. It is shown that the potentially critical constraints at the optimum of the latter problem can be identified a priori. The solution methodology and the efficiency of the proposed procedure are illustrated by some examples.     

A mixed approach to forecasting peak system load

Realizing that Box-Jenkins time series analysis lacks any basis in economic theory but at the same time wanting to take advantage of the excellent forecasting accuracy of the approach, in the first part of this paper the author takes the basic Box-Jenkins structure and integrates it into an econometric system. Relating Box-Jenkins parameters to economic and weather variables allows these parameters to be forecast. The forecast parameters can in turn be used in a Box-Jenkins model to provide a forecast of the series of interest. The result, for a specific example, proves to be clearly superior to a pure Box-Jenkins model.An alternative approach is suggested whereby an econometric model is estimated, the residual errors analyzed and forecast using a Box-Jenkins time series model, and then the results of both these models combined. The result, for the same example, proved to be an improvement over a simple Box-Jenkins model or the econometric model.When the two hybrid models are compared, the first model is the best, judged on forecasting accuracy. An important feature to consider when using the approaches, however, is the ease of use. On this basis, the alternative approach is best.     

Electrical transport through a single nanoscale semiconductor branch point

Semiconductor tetrapods are three-dimensional (3D) branched nanostructures, representing a new class of materials for electrical conduction. We employ the single-electron transistor approach to investigate how charge carriers migrate through single nanoscale branch points of tetrapods. We find that carriers can delocalize across the branches or localize and hop between arms depending on their coupling strength. In addition, we demonstrate a new single-electron transistor operation scheme enabled by the multiple branched arms of a tetrapod: one arm can be used as a sensitive arm-gate to control the electrical transport through the whole system.     

Planning available capacity in electrical power generation

In planning for the utilisation of available capacity, an electrical company needs to know the power requirements of the system. The load versus duration curve provides information on past demand patterns and thus forms a basis for planning future supply needs. Since electrical supply is discrete by nature, the load versus duration curve only approximates to the true supply requirements. This paper develops an algorithm for finding an optimal step function approximation to the load versus duration curve. It is based on the minimisation of a total penalty function.     

Some Aspects of Thermal and Photochemical Autoxidation

Following an outline of the pioneering work of Haber's School, emphasis is placed on a critical review of the most important recent achievements. These embrace, in the area of thermal autoxidation: the concept of critical antioxidant concentration, the multiple effects of heavy metals (including catalyst-inhibitor conversion), the development of new synergistic antioxidant combinations composed of free radical acceptor and peroxide decomposer and, finally, Denisov's direct experimental evidence for the reaction of heavy metals with molecular oxygen in organic media in support of Uri's trace metal hypothesis of the general mechanism of the initiation of autoxidation. The following recent advances in the field of photochemical autoxidation are described: photosensitized initiation by trace metals and its inhibition, the singlet oxygen hypothesis, the inadequacy of phenolic antioxidants and the reliance on UV absorbers, the importance of energy transfer in photochemical protection leading to new stabilizers. A very recent innovation which is relevant to both thermal and photochemical autoxidation is highlighted, i.e., the development of new α-dithidiketone chelates, particularly bis (stilbenedithiolate) nickel (= NiS₄C₄Ph₄or, abbreviated, NiSDT) as antioxidants which combine in a unique way the properties of free radical acceptors, peroxide decomposers and UV stabilizers. They were then found to be the most powerful antioxidants for polyethylene and polypropylene.     

Optimized prestressing by linear programming

The problem of optimizing the prestressing force and the tendon configuration for an indeterminate prestressed structure with prescribed cross-sectional dimensions is formulated in linear programming form, The structure is subjected to multiple load conditions and constraints are related to the structural behaviour and to the tendon configuration. It is shown that the number of behaviour constraints at each point in the structure can be reduced, as they represent parallel hyperplanes in the design space. Necessary conditions for feasible solutions are derived. The method based on transformation of the design variables, is suitable for beams, frames, grids and plates. Its application is illustrated for the case of a prestressed bridge.     

Locking of thin plate/shell elements

Often, finite element solutions of thin plate/shell elements become very stiff and the displacement field solutions diverge from those predicted by Kirchhoff's theory. This phenomenon is known as the locking phenomenon. A theoretical fomulation demonstrating its existence is developed, and results of finite element analysis of a single element and mesh are discussed. This leads to a sufficient and necessary criterion which must be satisfied to avoid the locking phenomenon.     

Directional causality in the demand for electrical energy in the United States

The majority of the studies on the demand for electrical energy have been done with single-equation models. In this paper it is demonstrated that not only is the quantity of electrical energy demanded a function of price, but price is related causally to quantity in the residential sector. The significance of this is that it is not sufficient to estimate single-equation models. Since bidirectional causality cannot be statistically rejected, any estimation of the demand for electrical energy must be done in a system of simultaneous equations to avoid specification errors and the associated problems.     

Effect of polysaccharide charge on formation and properties of biopolymer nanoparticles created by heat treatment of β-lactoglobulin–pectin complexes

Biopolymer nanoparticles can be formed by heating globular protein/polysaccharide mixtures above the thermal denaturation temperature of the protein under pH conditions where the two biopolymers are weakly electrically attracted to each other. In this study, the influence of polysaccharide linear charge density on the formation and properties of these biopolymer nanoparticles was examined. Mixed solutions of globular proteins (β-lactoglobulin) and anionic polysaccharides (high and low methoxyl pectin) were prepared. Micro-electrophoresis, dynamic light scattering, turbidity and atomic force microscopy (AFM) measurements were used to determine the influence of protein-to-polysaccharide mass ratio (r), solution pH, and heat treatment on biopolymer particle formation. Biopolymer nanoparticles (d < 500 nm) could be formed by heating protein–polysaccharide complexes at 83 °C for 15 min at pH 4.75 and r = 2:1 in the absence of added salt. The biopolymer particles formed were then subjected to pH and salt adjustment to determine their stability. The pH stability was greater for β-lactoglobulin-HMP complexes than for β-lactoglobulin-LMP complexes. The addition of 200 mM sodium chloride to heated complexes greatly improved the pH stability of HMP complexes, but decreased the pH stability of LMP complexes. The biopolymer particles formed consisted primarily of β-lactoglobulin, which was probably surrounded by a pectin coating at low pH values. AFM measurements indicated that the biopolymer nanoparticles formed were spheroid in shape. These biopolymer particles may be useful as delivery systems or fat mimetics.     

Using Exploratory Scenarios in Planning Practice

Abstract

Problem, research strategy, and findings: Despite growing interest by practitioners in using exploratory scenarios within urban planning practice, there are few detailed guidelines for how to do this. Through the discussion of five case examples, we illustrate different approaches to linking exploratory scenarios to different planning contexts. We conclude by observing that to directly inform a plan, regardless of the specific approach taken, exploratory scenarios in urban planning must incorporate stakeholder values and not only rely on expert judgment and analysis.

Takeaway for practice: Exploratory scenarios are effective for analyzing uncertainty within a planning process. However, exploratory scenarios can be incorporated into planning practice in different ways, ranging from workshops among experts that aim to cultivate general learning to complex projects that result in highly detailed scenarios and recommendations for plans. Practitioners can draw on the cases we present to inspire planning methods for particular projects, taking into account specific contexts and goals.