Asymptotic normality and parameter change test for bivariate Poisson INGARCH models

In this paper, we consider the problem of testing for a parameter change in bivariate Poisson integer-valued GARCH(1, 1) models, constructed via a trivariate reduction method of independent Poisson variables. We verify that the conditional maximum-likelihood estimator of the model parameters is asymptotically normal. Then, based on these results, we construct CMLE- and residual-based CUSUM tests and derive that their limiting null distributions are a function of independent Brownian bridges. A simulation study and real data analysis are conducted for illustration.     

Molten Salt Assisted Self‐Assembly: Synthesis of Mesoporous LiCoO2 and LiMn2O4 Thin Films and Investigation of Electrocatalytic Water Oxidation Performance of Lithium Cobaltate

Mesoporous thin films of transition metal lithiates (TML) belong to an important group of materials for the advancement of electrochemical systems. This study demonstrates a simple one pot method to synthesize the first examples of mesoporous LiCoO₂ and LiMn₂O₄ thin films. Molten salt assisted self‐assembly can be used to establish an easy route to produce mesoporous TML thin films. The salts (LiNO₃ and [Co(H₂O)₆](NO₃)₂ or [Mn(H₂O)₄](NO₃)₂) and two surfactants (10‐lauryl ether and cethyltrimethylammonium bromide (CTAB) or cethyltrimethylammonium nitrate (CTAN)) form stable liquid crystalline mesophases. The charged surfactant is needed for the assembly of the necessary amount of salt in the hydrophilic domains of the mesophase, which produces stable metal lithiate pore‐walls upon calcination. The films have a large pore size with a high surface area that can be increased up to 82 m² g^?1. The method described can be adopted to synthesize other metal oxides and metal lithiates. The mesoporous thin films of LiCoO₂ show promising performance as water oxidation catalysts under pH 7 and 14 conditions. The electrodes, prepared using CTAN as the cosurfactant, display the lowest overpotentials in the literature among other LiCoO₂ systems, as low as 376 mV at 10 mA cm^–2 and 282 mV at 1 mA cm^–2.     

The effectiveness of pair programming: A meta-analysis

Several experiments on the effects of pair versus solo programming have been reported in the literature. We present a meta-analysis of these studies. The analysis shows a small significant positive overall effect of pair programming on quality, a medium significant positive overall effect on duration, and a medium significant negative overall effect on effort. However, between-study variance is significant, and there are signs of publication bias among published studies on pair programming. A more detailed examination of the evidence suggests that pair programming is faster than solo programming when programming task complexity is low and yields code solutions of higher quality when task complexity is high. The higher quality for complex tasks comes at a price of considerably greater effort, while the reduced completion time for the simpler tasks comes at a price of noticeably lower quality. We conclude that greater attention should be given to moderating factors on the effects of pair programming.     

A systematic review of quasi-experiments in software engineering

Background:Experiments in which study units are assigned to experimental groups nonrandomly are called quasi-experiments. They allow investigations of cause–effect relations in settings in which randomization is inappropriate, impractical, or too costly.Problem outline:The procedure by which the nonrandom assignments are made might result in selection bias and other related internal validity problems. Selection bias is a systematic (not happening by chance) pre-experimental difference between the groups that could influence the results. By detecting the cause of the selection bias, and designing and analyzing the experiments accordingly, the effect of the bias may be reduced or eliminated.Research method:To investigate how quasi-experiments are performed in software engineering (SE), we conducted a systematic review of the experiments published in nine major SE journals and three conference proceedings in the decade 1993–2002.Results:Among the 113 experiments detected, 35% were quasi-experiments. In addition to field experiments, we found several applications for quasi-experiments in SE. However, there seems to be little awareness of the precise nature of quasi-experiments and the potential for selection bias in them. The term “quasi-experiment” was used in only 10% of the articles reporting quasi-experiments; only half of the quasi-experiments measured a pretest score to control for selection bias, and only 8% reported a threat of selection bias. On average, larger effect sizes were seen in randomized than in quasi-experiments, which might be due to selection bias in the quasi-experiments.Conclusion:We conclude that quasi-experimentation is useful in many settings in SE, but their design and analysis must be improved (in ways described in this paper), to ensure that inferences made from this kind of experiment are valid.     

A mathematical model of the heat and fluid flows in direct-chill casting of aluminum sheet ingots and billets

A finite-element method model for the time-dependent heat and fluid flows that develop during direct-chill (DC) semicontinuous casting of aluminium ingots is presented. Thermal convection and turbulence are included in the model formulation and, in the mushy zone, the momentum equations are modified with a Darcy-type source term dependent on the liquid fraction. The boundary conditions involve calculations of the air gap along the mold wall as well as the heat transfer to the falling water film with forced convection, nucleate boiling, and film boiling. The mold wall and the starting block are included in the computational domain. In the start-up period of the casting, the ingot domain expands over the starting-block level. The numerical method applies a fractional-step method for the dynamic Navier-Stokes equations and the “streamline upwind Petrov-Galerkin” (SUPG) method for mixed diffusion and convection in the momentum and energy equations. The modeling of the start-up period of the casting is demonstrated and compared to temperature measurements in an AA1050 200×600 mm sheet ingot.     

General meta-model based co-simulations applied to mechanical systems

A fully functional meta-model co-simulation environment that supports integration of many different simulation tool specific models into a co-simulation is described in this paper.The continuously increasing performance of modern computer systems has a large influence on simulation technologies. It results in more and more detailed simulation models. Different simulation models typically focus on different parts (sub-systems) of the complete system, e.g., the gearbox of a car, the driveline, or even a single bearing inside the gearbox. To fully understand the complete system it is necessary to investigate several or all parts simultaneously. This is especially true for transient (dynamic) simulation models with several interconnected parts. One solution for a more complete and accurate system analysis is to couple different simulation models into one coherent simulation, also called a co-simulation. This also allows existing simulation models to be reused and preserves the investment in these models.Existing co-simulation applications are often capable of interconnecting two specific simulators where a unique interface between these tools is defined. However, a more general solution is needed to make co-simulation modelling applicable for a wider range of tools. Any such solution must also be numerically stable and easy to use in order to be functional for a larger group of people.The presented approach for mechanical system co-simulations is based upon a general framework for co-simulation and meta-modelling [9]. Several tool specific simulation models can be integrated and connected by means of a meta-model. A platform independent, centralised, meta-model simulator is presented that executes and monitors the co-simulation. All simulation tools that participate in the co-simulation implement a single, well defined, external interface that is based on a numerically stable method for force/moment interaction.     

Regional energy system optimization – Potential for a regional heat market

Energy supply companies and industrial plants are likely to face new situations due to, for example, the introduction of new energy legislation, increased fuel prices and increased environmental awareness. These new prerequisites provide companies with new challenges but also new possibilities from which to benefit. Increased energy efficiency within companies and increased cooperation between different operators are two alternatives to meet the new conditions. A region characterized by a high density of energy-intensive processes is used in this study to find the economic potential of connecting three industrial plants and four energy companies, within three local district heating systems, to a regional heat market, in which different operators provide heat to a joint district heating grid. Also, different investment alternatives are studied. The results show that the economical potential for a heat market amounts to between 5 and 26 million EUR/year with payback times ranging from two to eleven years. However, the investment costs and the net benefit for the total system need to be allotted to the different operators, as they benefit economically to different extents from the introduction of a heat market. It is also shown that the emissions of CO₂ from the joint system would decrease compared to separate operation of the systems. However, the valuation of CO₂ emissions from electricity production is important as the difference of emitted CO₂ between the accounting methods exceeds 650 kton/year for some scenarios.     

The effect of irrigation level and harvest mechanization on virgin olive oil quality in a traditional rain‐fed ‘Souri’ olive orchard converted to irrigation

BACKGROUND: Olive trees are generally grown under rain‐fed conditions. Since yield response to application of water in the growing season may be considerable, irrigation is increasingly introduced to existing, mature orchards. An additional feature of modernization of olive cultivation is mechanical harvesting. To investigate the effect of irrigation level on the quality of virgin olive oil (VOO) produced from cv. Souri, six regimes, ranging from deficit to excess, were applied to trees in a mature, traditional orchard as it was converted to irrigation. Furthermore, in order to investigate the effect of damage incurred during harvest, oil quality of hand‐picked fruit was compared to that of mechanically harvested olives. RESULTS: Data were collected from two consecutive growing seasons. Increased irrigation quantity increased the free acidity level of the oil and decreased the total phenol content of VOO, while the peroxide level of the oil was not affected. Oil of hand‐picked fruits had lower free acidity, higher polyphenol content and slightly lower peroxide level compared to the oil of mechanically harvested olives. CONCLUSION: Fruits from irrigated trees demonstrated an apparent sensitivity to mechanical wounding that subsequently led to increased free acidity, increased peroxide level and decreased total phenol content in oil. Management of irrigated orchards including method and timing of harvest and oil extraction techniques should consider these results in order to optimize production of high‐quality oil. Copyright © 2008 Society of Chemical Industry     

Tracking airborne Legionella and Legionella pneumophila at a biological treatment plant

Biological treatment plants are frequently used to degrade organic substances in wastewater from wood refinement processes. Aeration ponds in such plants provide an optimal growth environment for many microorganisms, including Legionella species. To investigate whether legionellae could be dispersed as aerosols from the ponds and transported by the wind, the wetted-wall cyclone SASS 2000(PLUS) and the impactors MAS-100 and STA-204 were used to collect air samples directly above, upwind, and downwind of aeration ponds during a 4-month period. Computational fluid dynamics was used a priori to estimate the aerosol paths and to determine suitable air-sampling locations. Several Legionella species, including Legionella pneumophila, were identified in air samples at the biological treatment plant using microbiological and molecular methods. L. pneumophila was identified up to distances of 200 m downwind from the ponds, but, in general, not upwind nor outside the predicted aerosol paths. The highest concentration level of viable legionellae was identified directly above the aeration ponds (3300 CFU/m3). This level decreased as the distance from the aeration ponds increased. Molecular typing indicated that a single clone of L. pneumophila was dispersed from the ponds during the period of the study. Thus, our study demonstrated that aerosols generated at aeration ponds of biological treatment facilities may contain L. pneumophila, which then can be transported by the wind to the surroundings. The methods used in this study may be generically applied to trace biological aerosols that may pose a challenge to environmental occupational health.