A. Martínez

Why do cervids feed on aquatic vegetation

Consumption of aquatic plants is rare among cervids, despite the common occurrence of this form of vegetation. However, the paucity of literature reporting on this feeding behaviour suggests that Na (but also other minerals), protein, and the ubiquitous availability of aquatic vegetation may play a role in its consumption. We present results quantifying those factors that regulate the consumption of aquatic plants in the Iberian red deer. We focussed our study primarily on two questions: (i) what nutritional values are red deer seeking in the aquatic plants?; and (ii) why do red deer primarily use aquatic plants during the summer? A comparison of the seasonal variations in Na content between terrestrial vs. aquatic vegetation did not fully support the hypothesis that aquatic plants are being consumed more in summer because of any seasonal variation in Na availability. The Na content in the aquatic vegetation was adequate all the year-round; whereas, the Na content in the terrestrial vegetation was consistently deficient. However, a greater summer content of essential minerals and protein in the aquatic vegetation may be the cause for their consumption exclusively during the summer. We suggest that seasonal variations in the consumption of aquatic vegetation by cervids is primarily driven by temporal variations in the nutrient content, combined with seasonal variations in the physiological demands for these nutrients.

Avoiding Toxic Levels of Essential Minerals: A Forgotten Factor in Deer Diet Preferences

Ungulates select diets with high energy, protein, and sodium contents. However, it is scarcely known the influence of essential minerals other than Na in diet preferences. Moreover, almost no information is available about the possible influence of toxic levels of essential minerals on avoidance of certain plant species. The aim of this research was to test the relative importance of mineral content of plants in diet selection by red deer (Cervus elaphus) in an annual basis. We determined mineral, protein and ash content in 35 common Mediterranean plant species (the most common ones in the study area). These plant species were previously classified as preferred and non-preferred. We found that deer preferred plants with low contents of Ca, Mg, K, P, S, Cu, Sr and Zn. The model obtained was greatly accurate identifying the preferred plant species (91.3% of correct assignments). After a detailed analysis of these minerals (considering deficiencies and toxicity levels both in preferred and non-preferred plants) we suggest that the avoidance of excessive sulphur in diet (i.e., selection for plants with low sulphur content) seems to override the maximization for other nutrients. Low sulphur content seems to be a forgotten factor with certain relevance for explaining diet selection in deer. Recent studies in livestock support this conclusion, which is highlighted here for the first time in diet selection by a wild large herbivore. Our results suggest that future studies should also take into account the toxicity levels of minerals as potential drivers of preferences.

Seasonal variations in plant mineral content and free-choice minerals consumed by deer

The aim of this study was to assess the seasonal differences in mineral contents of plants often consumed by wild red deer located in a fenced game estate, south-eastern Spain. Forage plants were sampled throughout 1 year and analysed for macro and trace mineral concentrations. We also offered a cafeteria set of supplemented minerals to assess whether: (i) intake reflected seasonal reductions in plant content of specific minerals; or (ii) intake of mineral supplements responded to increased deer demand of minerals as a result of greater seasonal needs likely arising from lactation, antler growth or skeletal growth. Although no significant seasonal trend was found in mineral distributions of plants, our study suggested that concentrations of K, Mg, Mn, Na, P, Cu and Zn were usually low in plants available to, and consumed by, deer in the study area. In addition, Cu concentration was marginally deficient when compared with the published requirements for other subspecies of red deer. The cafeteria study showed that free-ranging deer had a strong preference for sodium compounds and zinc sulfate, a much weaker attraction to calcium iodate, and no intake in calcium phosphates, Mg and Fe. Consumption of supplemented minerals by deer was maximum in spring and summer and moderate during autumn and winter. Rather than increasing intake of minerals in response to their content in plants, deer may be responding to increased metabolic requirements during antler growth, late gestation and early lactation. Supplementation of mineral compounds is recommended, particularly in the spring–summer period, when the physiological activity is high.

Electrical Evaluation Of Welding Machines Based On The Arc Properties. Application To SMAW, GMAW And GTAW Processes

In this work, a methodology to obtain the electrical behavior of arc welding equipments is presented. The method is based on the electrical arc fundamentals and it is applied to Shielding Metal Arc Welding and to Gas Metal Arc Welding processes. For the first one, different arc points are achieved by practicing several arc lengths. For MIG process, different arc lengths are made by changing the feel wire velocity. Arc current and voltage are measured for the different arc length in both cases. Finally, a Gas Tungsten Arc Welding equipment has been used to obtain the electrical arc characteristics as a function of arc length. Different considerations about the thermal and electrical principles related to the arc behavior have been made.

A Proposal for Bending Process of TRIP Steel Sheets Based on the Springback Behavior

TRIP steels, or Transformed Induced Plasticity steels, have excellent mechanical properties if compared with conventional steels. The highlighted characteristic of these steels is that they modify the microstructure with the deformation process as part of the austenite transforms to martensite, with the consequent change of the material properties. One of the main problems of TRIP steels is strong elastic recovery, or springback, after forming. In this work, the springback phenomenon is evaluated by bending tests and the influence of the variables involved in it is determined. Experimental bending forces do not agree with theoretical predictions that are proposed in the literature. In spite of the bending radius having been considered an influence factor in the process, this work demonstrates that the aforementioned factor has a minor influence, at least for TRIP 800. The factor found to affect material recovery the most was the bending angle.

Learning Chip Type Strategies in Turning Processes by Viewing with High-Speed Video Cameras

This work develops a methodology that allowed students to associate the effect of some cutting variables with chip type. For that, turning processes were carried out on two different materials since their physical and mechanical properties have a relevant influence on the chip formation. Cutting tests were run by varying the feed rate, while cutting speed and depth of cut had fixed values. These cutting conditions led to different chip geometries being obtained. Thus, it was possible to establish a chip type classification in turning operations. The methodology herein presented is based on new technologies, which raised great expectations among students, who positively considered this experience. The effect of other variables, apart from feed rate, must be theoretically analyzed in order to improve the comprenhension of the process herein involved.

Proposal of an Educational Methodology to Analyze Cutting Temperature in Turning Operations by Infrared Themography

The present work develops a learning methododology based on experiments related to the cutting temperature concept in turning processes. This proposal allows students to measure the temperature actually reached during a typical turning operation with a semi-automatic lathe. Temperature data are collected by a thermographic camera, which implies acquiring competences in this technique. The different tests involved in the practical experiment are defined for various cutting speeds and feed rates, and for a constant depth of cut. Two different materials are considered to point out the influence of turning parameters on cutting temperature.

INFLUENCE OF TURNING PARAMETERS ON CUTTING TEMPERATURE BY APPLYING THE DESIGN OF EXPERIMENTS WITH THE DEFINITION OF THE WORKPIECE MATERIAL BEHAVIOR

This paper evaluates the behavior of cutting temperature under the influence of specific cutting parameters by applying both Factorial Design and the Surface Response Methodology. Cutting speed, the feed rate and type of material were selected as input parameters to perform this study. As type of material is a non quantitative factor, it is necessary to establish a particular index to define it. Although different properties were analyzed, the average stress between the yield and strength stresses was demonstrated as the most representative property to describe material. The experimental values of temperatures during the turning process were obtained with an infrared thermography camera and experiments were designed to run the statistical analysis with commercial software. Both the Factorial Design and Surface Response methodologies showed the influence that specific values of the input parameters had on cutting temperatures. Factorial Design allowed more accurate results, but more experiments had to be carried out, while the Surface Response Methodology provided suitable information with fewer tests. A comparison was made between the experimental and some analytical results, for example those obtained by Cook, and showed a good agreement.

EVALUACIÓN DEL COMPORTAMIENTO EN ESTADOS DE CARGA DE TRACCIÓN PURA DE MATERIALES COMPUESTOS TEJIDOS HÍBRIDOS-MATRIZ VINILESTER MEDIANTE EL MÉTODO DE LOS ELEMENTOS FINITOS

Hybrid composites present a wide range of mechanical properties that cannot be obtained with a single fibers type. These characteristics are highly dependent on the orientation and configuration of each reinforcement. Thus simulation studies that predict the properties of these materials are increasingly sought in order to make the best design possible. In the present work, finite element modeling has been used to develop a methodology to determine the mechanical properties of hybrid Kevlar-carbon laminates, which are frequently applied to manufacture small vessels, starting from the characteristics of the matrix and fibers that compose them. The initially employed methodology established the hypothesis required to define the characteristics of a hybrid fabric sheet from the properties and geometry of the fibers and resin. The properties of the laminate, considered a stack of sheets, are determined with the obtained data. This method was validated by comparing the simulation values with the experimental results obtained in the tensile tests. Errors related to mechanical strength were around 5-10%, and up to 30% for deformation. Keywords: Composite, FEM, Solidworks, kevlar-carbono, vinylester

A Procedure Based on Magnetic Induction to Evaluate the Effect of Plastic Deformation by Multiaxial Stresses on TRIP Steels

As it is well-known, TRIP 800 steels modify their structure with the deformation grade. So, part of the retained austenite turns into martensite by plastic deformation. The usual techniques tried out to evaluate this transformation whether do not lead to obtain good results or the experimentation with them is very complex. In this work, a magnetic induction method is experimented and developed in order to determine the evolution of a TRIP 800 steel microstructure with the strain grade. The variables that can have influence on this kind of analysis methodology have been studied and their effects evaluated. This method has been applied to determine the induced martensite by deformation under conditions of pure shear deformation. Results point that this method allows to state that the microstructure evolution taking place in TRIP 800 steels is not proportional to the strain applied.