Evapotranspiration: Concepts and Future Trends

Past research on evapotranspiration has provided sound theoretical knowledge and practical applications that have been validated through field measurements. Many different approaches have been used; however, when primary concepts and standard definitions are accepted, it is possible to find reasonable agreement among methods. This paper reviews such approaches, from Penman to Penman-Monteith. The standard concepts of potential evaporation (EP) and equilibrium evaporation (Ee), and the introduction of the climatic resistance (re), provide a better understanding of the role of the climate together with surface and aerodynamic resistances (rs and ra). Therefore, the concept of reference evapotranspiration (ETo), particularly the new one adopted by the Food and Agricultural Organization of the United Nations, can be better understood, as well as its limitations. Crop evapotranspiration (ETc) is related to both ETo and Ee. Crop coefficients (Kc) can be shown to have two components, αo and αc, with Kc = αoαc. The αo is a function of the climatic resistance and of the aerodynamic resistances of the crop and of the reference crop. The αc is a function of both surface and aerodynamic resistances of the crop and of the reference crop. From this analysis some ideas on future developments result that are directed toward providing compatibility between the one- and two-step calculation of ETc.     

Preparation and Properties of Cellulose Nanomaterials

Cellulose is the most abundant biomass material in nature and it is mainly extracted from natural or lignocellulosic fibers. After purification, cellulose fibers exhibit two interesting features for their further transformation into nanomaterials: a hierarchical and multi-level strcture, and a semicrystalline microstructure. Different forms of cellulose nanomaterials, resulting from a top-down deconstructing strategy (cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs)) or bottom-up strategy (bacterial cellulose (BC)) can be prepared. Multiple mechanical shearing actions applied to cellulosic fibers release more or less the nanofibrils individually. A controlled strong acid hydrolysis treatment can be applied to cellulosic fibers allowing dissolution of non-crystalline domains. Such cellulose nanomaterials have been the focus of an exponentially increasing number of works or reviews devoted to understand such materials and their applications. They have a high potential for an emerging industry. In the nanoscale, cellulose exhibits specific properties broadening the applications of this naturally occurring polymer. An overview of existing methods for the preparation of cellulose nanomaterials and their specific properties that outperform and contrast with cellulose in the microscale is proposed.     

Influence of the hydrolysis process on the biological activities of protein hydrolysates from cod (Gadus morhua) muscle

Upgrading of fish protein through limited proteolysis of by‐products and surplus of the food industry generates peptides of interest to food formulation, the animal feed industry and aquaculture. The hydrolysis process has been studied in order to investigate the role of the limiting parameters. Hydrolysates obtained under varying conditions of temperature, pH, time and enzyme concentration were tested on fibroblastic cell cultures and in gastrin radioimmunoassays. Several fractions were shown to contain biologically active peptides such as growth factors or secretagogues (gastrin and cholecystokinin). Under optimum conditions we obtained 160% stimulation of cell growth with only 25 µg ml ⁻¹ hydrolysates, and about 0.25 pg gastrin‐like peptides mg⁻¹ sample. The process of hydrolysis plays a key factor by extending the time of protein degradation in generating these molecules. © 2000 Society of Chemical Industry     

Performance enhancement of the artificial neural network–based reinforcement learning for wind turbine yaw control

The yaw angle control of a wind turbine allows maximization of the power absorbed from the wind and, thus, the increment of the system efficiency. Conventionally, classical control algorithms have been used for the yaw angle control of wind turbines. Nevertheless, in recent years, advanced control strategies have been designed and implemented for this purpose. These advanced control strategies are considered to offer improved features in comparison to classical algorithms. In this paper, an advanced yaw control strategy based on reinforcement learning (RL) is designed and verified in simulation environment. The proposed RL algorithm considers multivariable states and actions, as well as the mechanical loads due to the yaw rotation of the wind turbine nacelle and rotor. Furthermore, a particle swarm optimization (PSO) and Pareto optimal front (PoF)‐based algorithm have been developed in order to find the optimal actions that satisfy the compromise between the power gain and the mechanical loads due to the yaw rotation. Maximizing the power generation and minimizing the mechanical loads in the yaw bearings in an automatic way are the objectives of the proposed RL algorithm. The data of the matrices Q (s,a) of the RL algorithm are stored as continuous functions in an artificial neural network (ANN) avoiding any quantification problem. The NREL 5‐MW reference wind turbine has been considered for the analysis, and real wind data from Salt Lake, Utah, have been used for the validation of the designed yaw control strategy via simulations with the aeroelastic code FAST.     

The Decomposition Process of Melamine Formaldehyde Cores: The Key Step in the Fabrication of Ultrathin Polyelectrolyte Multilayer Capsules

Melamine formaldehyde (MF) colloidal cores were coated with polyelectrolyte multilayers. The core decomposition process at low pH was followed by confocal laser scanning microscopy (CLSM). Transient capsule swelling as a result of the osmotic pressure difference created by the decomposition of the MF resin was observed. The rate of core dissolving and the permeation of decomposition products of the MF core through the capsule walls are discussed in relation to the extent of swelling and capsule wall rupture. The core decomposition products had a diffusion coefficient of 71 μm²/s, which corresponds to a hydrodynamic diameter of ≈ 4 nm. Simultaneously with the degradation of MF polymers the hydrolysis at the melamine groups to ammeline groups occurred as was shown by infrared spectroscopy. The size and chemical composition of the reaction products did not depend on the pH. The degradation rate increased with decreasing pH.     

Evaluation of the contribution of lignin stilbene phenol units in the photoyellowing of peroxide-bleached lignin-rich pulps

In order to assess and quantify the contribution of stilbene phenols in photoreversion of bleached high-yield pulps, a method to reduce the stilbene double bond and quantify the formed diphenylethane was developed on 4-benzyloxy-3,3′-dimethoxy-4′-hydroxystilbene, as lignin monomer model, and also on a more sophisticated lignin polymer model constituted by a polystyrene framework containing 4,4′-dihydroxy-3,3′-dimethoxystilbene elements as pendent groups. The method used RhCl(PPh₃)₃ as soluble catalyst to get an efficient hydrogenation and AlCl₃ in benzene to liberate the diphenylethane from the polymer framework. For the first time a semiquantitative evaluation of the content of the stilbene phenols formed from β-1 units was given for high-yield pulps. The value of 2 p-stilbene phenols for 1000 C₉ lignin units found indicates that they are present in very small quantities after the peroxide bleaching. UV irradiation of the polystyrene model adsorbed on solid cellulose matrix had revealed an efficient stabilization after the hydrogenation treatment. This was not the case for the peroxide bleached pulp showing that the p-stilbene phenols formed from β-1 units are not the main contributors of the rapid yellowing of bleached lignin-rich pulps. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2517–2531, 1998     

Synthesis of new soluble polybenzyls by Friedel–Crafts reactions

Soluble polybenzyls were prepared by a catalytic electrophilic Friedel–Crafts type polycondensation between α,α′-dichloro-p-xylene and substituted (by an alkyl or an alkoxy side-chain) mesitylene. The influence of the length of the side-chain on the solubility of the polymer was examined. The polymers were found to be soluble in common organic solvents. Polymer characterizations were made by ¹³C nuclear magnetic resonance spectroscopy (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and elemental analysis. © 1999 Society of Chemical Industry     

Mechanical behavior of sheets prepared from sugar beet cellulose microfibrils

The mechanical behavior of films cast from sugar beet cellulose microfibrils was investigated through tensile tests. The obtaining of these microfibrils by chemical and mechanical treatments from the raw beet pulp is described. Depending on their purification level, individualization state, and moisture content, differences in tensile modulus are observed. It is found that pectins act as a binder between the cellulose microfibrils, which tends to increase the Young's modulus in dry atmosphere and to decrease it in moist conditions. The extraction of the cellulose microfibrils from the sugar beet cell wall and the obtainment of microfibril suspensions with partial individualization of the microfibrils by a mechanical treatment lead to the formation of a network of cellulose microfibrils within the film, which in turn increases the tensile modulus. Furthermore, the effect of the remaining pectins is compared with the effect of pectins previously removed and added to completely purified cellulosic microfibrils. As expected, once removed and so partly degraded, those pectins have nearly no influence on the mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1185–1194, 1997     

Styrene emulsion polymerization in the presence of a maleate-functional surfactant

Dodecylhemiester of maleic anhydride is a very good anionic stabilizer for the emulsion polymerization of styrene. Rather high solid contents may be produced. Up to about 70% of the surfactant can be grafted onto the surface of the particles. Upon floculation with calcium salt, only 3% of the surfactant is left in the washing water. © 1997 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 65: 2289–2296, 1997