No abstract

Alginate is a polysaccharide with the property of forming hydrogels, which is economic production, zero toxicity, and biocompatibility. In the agro-industry, alginate is used as a super absorbent polymer, coating seeds, fruits, and vegetables and as a carrier of bacteria and fungi as plant-growth promoters and biocontrol. The latter has a high impact on agriculture since the implementation of microorganisms in a polymer matrix improves soil quality; plant nutrition, and is functional as a preventive measure for the appearance of phytopathogenic. Additionally, it minimizes losses of foods due to wrong post-harvest handling. In this review, we provide an overview of physicochemical properties of alginate, some methods for preparation and modification of capsules and coatings, to finally describe its application in agro-industry as a matrix of plant-growth-promoting microorganisms, its effectiveness in cultivation and post-harvest, and its effect on the environment, as well as the prospects for future agro-industrial applications.

Photothermal techniques allow the detection of characteristics of material without invading it. Researchers have developed hardware for some specific Phase and Amplitude detection (Lock-In Function) applications, eliminating space and unnecessary electronic functions, among others. This work shows the development of a Digital Lock-In Amplifier based on a Field Programmable Gate Array (FPGA) for low-frequency applications. This system allows selecting and generating the appropriated frequency depending on the kind of experiment or material studied. The results show good frequency stability in the order of 1.0 × 10−9 Hz, which is considered good linearity and repeatability response for the most common Laboratory Amplitude and Phase Shift detection devices, with a low error and standard deviation.

The rise in renewable energy has increased the use of DC/AC converters, which transform the direct current to alternating current. These devices, generally called inverters, are mainly used as an interface between clean energy and the grid. It is estimated that 21% of the global electricity generation capacity from renewable sources is supplied by photovoltaic systems. In these systems, a transformer to ensure grid isolation is used. Nevertheless, the transformer makes the system expensive, heavy, bulky and reduces its efficiency. Therefore, transformerless schemes are used to eliminate the mentioned disadvantages. One of the main drawbacks of transformerless topologies is the presence of a leakage current between the physical earth of the grid and the parasitic capacitances of the photovoltaic module terminals. The leakage current depends on the value of the parasitic capacitances of the panel and the common-mode voltage. At the same time, the common-mode voltage depends on the modulation strategy used. Therefore, by the manipulation of the modulation technique, is accomplished a decrease in the leakage current. However, the connection standards for photovoltaic inverters establish a maximum total harmonic distortion of 5%. In this paper an analysis of the common-mode voltage and its influence on the value of the leakage current is described. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. A comparative table with the most important aspects of each converter is shown based on number of components, modes of operation, type of modulation strategy used, and the leakage current value obtained. It is important to mention that analyzed topologies present a variation of the leakage current between 0 to 180 mA. Finally, the trends, problems, and researches on transformerless grid-connected PV systems are discussed.

The present manuscript focuses on reviewing the optical techniques proposed to monitor milk quality in dairy farms to increase productivity and reduce costs. As is well known, the quality is linked to the fat and protein concentration; in addition, this issue is crucial to maintaining a healthy herd and preventing illnesses such as mastitis and ketosis. Usually, the quality of the milk is carried out with invasive methods employing chemical reagents that increase the time analysis. As a solution, several spectroscopy optical methods have been proposed, here, the benefits such as non-invasive measurement, online implementation, rapid estimation, and cost-effective execution. The most attractive optical methods to estimate fat and protein in cow’s milk are compared and discussed considering their performance. The analysis is divided considering the wavelength operation (ultraviolet, visible, and infrared). Moreover, the weaknesses and strengths of the methods are fully analyzed. Finally, we provide the trends and a recent technique based on spectroscopy in the visible wavelength.