Guest Editorial

Multimedia Tools and Applications -     

Robust estimators under semi‐parametric partly linear autoregression: Asymptotic behaviour and bandwidth selection

Abstract. In this article, under a semi‐parametric partly linear autoregression model, a family of robust estimators for the autoregression parameter and the autoregression function is studied. The proposed estimators are based on a three‐step procedure, in which robust regression estimators and robust smoothing techniques are combined. Asymptotic results on the autoregression estimators are derived. Besides combining robust procedures with M‐smoothers, predicted values for the series and detection residuals, which allow to detect anomalous data, are introduced. Robust cross‐validation methods to select the smoothing parameter are presented as an alternative to the classical ones, which are sensitive to outlying observations. A Monte Carlo study is conducted to compare the performance of the proposed criteria. Finally, the asymptotic distribution of the autoregression parameter estimator is stated uniformly over the smoothing parameter.     

Influence of fat source and sorghum grain treatment on performance and digestibilities of high yielding dairy cows

Forty-eight lactating Holstein cows averaging 81 d in milk were allotted to eight blocks based on milk yield during the 14-d pretreatment period and randomly assigned to six treatment groups in a 2 x 3 factorial arrangement of treatments for 64 d. Factors were type of sorghum grain processing [dry-rolled vs. steam-flaked; fed at 34% of dry matter (DM) in a total mixed ration (TMR) based on alfalfa] and type of supplemental fat (2.5% of DM as cottonseed oil, tallow, or prilled fatty acids). Compared with dry-rolled sorghum, steam-flaked sorghum did not affect milk yield, fat percentage, or fat yield but did increase milk protein percentage, body weight gains, and estimated net energy for lactation (22%). Fat source did not affect lactational response, but, compared with tallow, prilled fatty acids tended to decrease DM intake. Steam-flaked sorghum, compared with dry-rolled sorghum, increased digestibilities of DM, organic matter, crude protein, and starch, regardless of fat source. The TMR containing prilled fat had lower digestibilities of DM and organic matter than did TMR containing cottonseed oil or tallow; and TMR containing prilled fat had lower digestibilities of crude protein and total fatty acids than did TMR containing tallow. This study showed that steam-flaking of sorghum grain increased milk protein content, body weight gains, and estimated net energy for lactation, regardless of dietary fat source.     

Identification of the flavonoid fraction in saffron spice by LC/DAD/MS/MS: Comparative study of samples from different geographical origins

The flavonoid fraction in saffron spice has been analysed, for the first time, by LC-DAD-MS/MS ESI and five kaempferol derivatives have been found. Compounds such as kaempferol-3-sophoroside, kaempferol-3-sophoroside-7-glucoside and kaempferol-3,7,4′-triglucoside were tentatively identified, whereas other compounds, such as kaempferol tetrahexoside and kaempferol-3-dihexoside were detected. Saffron samples from different geographical origins were clearly separated by their kaempferol 3-sophoroside contents that were able to explain 100% of the variance when a discriminant test was carried out.     

Some implications of nanoscience in food dispersion formulations containing phospholipids as emulsifiers

This contribution is concerned with phospholipid films in relation to food dispersions such as emulsions and foams. Structural, morphological and surface rheological characteristics of dipalmitoyl phosphatidylcholine (DPPC) and dioleoyl phosphatidylcholine (DOPC) monolayers were determined at the air–water interface at 20 °C and at pH 5, 7, and 9, by means of surface pressure (π)–area (A) isotherms coupled with Brewster angle microscopy (BAM), atomic force microscopy (AFM) and surface dilatational and shear rheometry. From the π–A isotherms it was deduced that DPPC monolayers show structural polymorphism at the air–water interface. DOPC monolayers formed a liquid-expanded (LE) structure under all experimental conditions, a consequence of the weak molecular interactions due to the double bond in the hydrocarbon chain. Electrostatic interactions between film-forming components influence the monolayer structure. BAM and AFM images corroborate, at a microscopic and at nanoscopic level respectively, the structural polymorphism deduced from the π–A isotherm for DPPC monolayers as a function of surface pressure and the pH of the aqueous phase. However, the homogeneous morphology of DOPC monolayers at a microscopic level, as observed by BAM, shows structural heterogeneity at a nanoscopic level when observed by AFM. The relative monolayer thickness increases with surface pressure and is a maximum at the collapse point, especially for DPPC monolayers. The results confirm that the interfacial rheological characteristic measured under dilatation and shear conditions are very dependent on the structural characteristics and morphology of the phospholipids (DPPC and DOPC) monolayers.     

Dietary corn germ containing phytic acid prevents pork meat lipid oxidation while maintaining normal animal growth performance

The effects of dietary defatted corn germ meal (DCGM) containing phytic acid (PA) on pig health during development and on its Longissimus dorsi m. (LD) lipid oxidative stability has been evaluated. Rations of DCGM were prepared at the level of substitution of 0%, 10%, 20% and 40% and offered to twenty four animals of Landrace x Large White crossbreds throughout 25 days before slaughtering. Animals were sacrificed at an average weight of 91.24 kg (±0.950) and samples for meat lipid oxidation analysis were taken after seven days under refrigeration at 3 °C. Animals fed with DCGM did not show any significant difference, in comparison to the control, in carcass characteristics, such as cold carcass weight, backfat depth, muscle depth, lean meat percentage and carcass dress yielding (p  0.05). Finally, no difference in meat proximate chemical composition was detected solely arising from lipid oxidation since LD from DCGM-treated pigs revealed an inhibition of 63.0%.     

A Planning Model for the Fuerte-Carrizo Irrigation System, Mexico

A methodology is presented for planning the operation of the Fuerte-Carrizo irrigation system in northwest Mexico. The system has two storage dams, two irrigation districts, and water transfer capabilities between both dams. The methodology uses a combination of linear programming (LP) and simulation. The LP model maximizes the net return of the farmers, subject to restrictions of the system, availability of water and land, and water transfer relationships. The simulation model is programmed as a microcomputer interactive package simulating the performance of the system. The methodology has proven to be a useful tool to assist those responsible for the operation of the irrigation system.     

A simple genetic algorithm for the design of reinforced concrete beams

We present an optimization model for the design of rectangular reinforced concrete beams subject to a specified set of constraints. Our model is more realistic than previously published models because it minimizes the cost of the beam on strength design procedures, while also considering the costs of concrete, steel and shuttering. Thus our method leads to very practical designs. As there is an infinite number of possible beam dimensions and reinforcement ratios that yield the same moment of resistance, an efficient search technique is preferred over the more traditional iterative methods. We employ a simple genetic algorithm as the search engine, and we compare our results with those obtained via geometric programming. Since the adjustment of parameters in a genetic algorithm (e.g., population size, crossover and mutation rates, and maximum number of generations) is a significant problem for any application, we present our own methodology to deal with this problem. A prototype of this system is currently being tested in México, in order to evaluate its potential as a reliable design tool for real world applications.