Rafael Vargas-Bernal

Analysis of DC Electrical Conductivity Models of Carbon Nanotube-Polymer Composites with Potential Application to Nanometric Electronic Devices

The design of nanometric electronic devices requires novel materials for improving their electrical performance from stages of design until their fabrication. Until now, several DC electrical conductivity models for composite materials have been proposed. However, these models must be valued to identify main design parameters that more efficiently control the electrical properties of the materials to be developed. In this paper, four different models used for modeling DC electrical conductivity of carbon nanotube-polymer composites are studied with the aim of obtaining a complete list of design parameters that allow guarantying to the designer an increase in electrical properties of the composite by means of carbon nanotubes.

Carbon Nanotube- and Graphene Based Devices, Circuits and Sensors for VLSI Design

With the reduction in power consumption and size chip, the electronic industry has been searching novel strategies to overcome these constraints with an optimal performance. Carbon nanotubes (CNTs) due to their extremely desirable electrical and thermal properties have been considered for their applicability in VLSI Design. CNTs are defined as sheets of graphene rolled up as hollow cylinders. They can basically be classified into two groups: single-walled (SWNTs) and multi-walled (MWNTs) as shown in Figure 1. SWNTs have one shell or wall and whose diameter ranging from 0.4 to 4 nm, while MWNTs contain several concentric shells and their diameter ranging from several nanometers to tens of nanometers.

Evolution and Expectations of Enzymatic Biosensors for Pesticides

The successful use of pesticides around the world has been due to their excellent control of pests such as insects, algaes, bacterias, viruses, rodents, or nematodes in agriculture, medicine, household, and industry. Since 9 of the 12 most dangerous and persistent organic pollutants are pesticides, therefore their qualitative and/or quantitative detection continue being one of the most strategic technological areas, given that these can be found in substances in contact with humans and other animals. The effects associated with their consumption and control, are related to human health and environmental toxicity. One of the most important contributions of the environmental chemistry is the control of pesticide residues and metabolites in food, water and soil; where plants, animal and human contacts are possible. Several methods to detect pesticides have been developed, chromatographic methods such as gas chromatography (GC) and high performance liquid chromatography (HPLC), which are coupled with mass spectrometry (MS). Although, these methods are very sensitive and reliable, they are very complex. In addition, they consume a lot of time to realize the analysis, require highly trained technicians for their use, and do not allow on-site or in-field detection. Biosensors represent an interesting technological alternative to determine the presence qualitative and quantitative of pesticides. Their operation is based through a self-contained integrated device including all subsystems required to realize the measurement and transfer of results in an electronic manner. They are a solution of lowcost, fast, high portability, and them do not require trained technicians to be used. In specific, both electrochemical as optical biosensors for pesticides, that use the enzyme immobilization by means of catalytic activity, will be studied with the aim of visualizing their evolution, advances, and perspectives in the near future. Finally, it is illustrated that research in this area might be directed with the aim of optimizing the performance desired.

Topologies based on Microfluidics of Pesticides Biosensors

The use of microfluidic systems for biosensors design is a useful strategy to reduce the size of sample to analyze in a biochemical test. In this paper, a set of topologies based on microfluidic systems are proposed with the aim of optimizing biosensors design for pesticides. The design considerations are given for each topology proposed and some characteristics in respect to their performance are established.

A Survey on the Static and Dynamic Translinear Paradigm

This chapter is devoted to review the static and dynamic translinear paradigm in the last years (2000–2011). Many papers have been written since then extending the application fields, proposing novel and new analog circuits and systems based on this principle, where MOS transistors are working in new regions of operation. These ongoing researches on translinear circuits arised of the requirements of low-power and low-voltage, which are forcing the technology at its maximum performance, and this paradigm can be an excellent solution. The chapter is presented as a summary of the advances in this field from different perspectives such as applications, circuits, and regions of operation of transistors, emphasizing the advantages and drawbacks. Also, some unsolved general trends are mentioned and research lines are described with the aim of identifying the main frame for this paradigm.

A novel magneto-impedance sensor model based on the zeros of Bessel functions

SUMMARY Nowadays, the design of magneto-impedance (MI) sensors requires the development of lumped circuit models that can be simulated through equivalent impedance circuits relied on Bessel functions. A new impedance model based on Senanis equivalent using the zeros of Bessel functions is developed in this paper. The model allows to describe the impedance as a transfer function that can be easily synthesized by means of current conveyor circuits and passive elements. The mathematical representation was verified under simulation of transfer functions involving different number of poles and zeros. Moreover, the model has been verified using SPICE simulations and measurement results from a fabricated prototype demonstrating its scope and validity. Finally, a study of finite tracking errors of CCIIs used in the implementation of magneto-impedance sensor has been realized. Copyright

Techniques to Optimize the Selectivity of a Gas Sensor

The efficient use of a gas sensor is related with its characteristics of performance and its efficient design. In this paper, a set of techniques with the aim of optimizing the selectivity of a sensor gas to a particular gas or a set of gases is presented. Gas sensors based on micro and nano technology using the principle of the change of electrical resistance are specifically analyzed. The design considerations are given for each technique proposed and some characteristics in respect to their performance are established.

Selection of Micromixers for Biochemical Detection of Pesticides

The use of micromixers in a microfluidic system is basic, when two solutions necessitate to be mixed, with the aim of developing any biochemical analysis. In this article, a study of the different technologies associated with the design of micromixers is made, with the purpose of identifying which technology is the most adequate for fabricating micromixers in accordance with the parameters associated with its application. The study is exemplified with the choice of a micromixer used to detect the presence of pesticides in the product obtained of the mix between an enzyme and the solution containing possibly pesticides which is extracted of a vegetable. The presence of pesticides in vegetables is strategic to guarantee or not the complete acceptation of them by the markets and customers as secure food for its ingestion

Stress Analysis on the Folded Beams of a MEM Accelerometer

The elastic behavior of a system can be determined by the stress analysis. This knowledge is useful in order to not exceed its limit of elasticity that means, to avoid permanent deformations, which can totally modify the performance of the system. In this paper, theoretical and simulated results of the normal stress generated in the folded beams of an accelerometer, under constant acceleration, are presented. The system under analysis has a suspended mass by means of four flat beams. The analysis was realized considering a cantilever, because this element is used as beam of support. A uniformly distributed load is present on the suspension beams. In simulations, 1g (9.81 m/s2) was applied to several accelerometers with different dimensions and geometries, with the purpose of observing that the normal stress should not exceed the elastic limit of silicon.

Elemental Analysis of Rat's Femoral Neck with Experimental Diabetes by means of Scanning Electron Microscopy

Diabetes mellitus (DM) is a group of metabolic disorders, whose main characteristic is the hyperglycemia. The duration of the hyperglycemia as well as its severity, are the most important factors that establish its presence by intermediate or prolonged periods. Although, pathophysiological changes that accompany the DM are found in all body, there are specific clinical manifestations such as gradual vision loss, renal disease, and susceptibility to cardiovascular diseases. In addition, the skeleton is affected to a significant level, where a major complication is osteoporotic bone fracture. Both patients with type 1 (T1DM) and type 2 (T2DM) diabetes mellitus have a high risk to experience fracture (Vestergaard et al 2009), when its condition is compared to health individuals. Reported data suggest that patients with T1DM show a decrease in bone mineral density (BMD), which is attributed to the decrease of the bone formation during growth in children and adolescents (Hamann et al 2012). In contrast, adults with T2DM, BMD values are normal or slightly elevated; however, the risk of a fracture is high (Janghorbani et al 2007). This advises that these patients may have a poor bone quality, which cannot be estimated in conventional densitometry studies. In this paper, we use a model of experimental diabetes (ED) to evaluate macroscopically the femur; representing the part of the skeleton, in which fractures caused by the weaking of the skeleton occur more frequently. In this study, female Wistar rats were used, with 8 to 12 weeks old, and weighing 200 to 250 g. The slaughter and handling of animals was made considering the specifications outlined in the Official Mexican Standard NOM-062-ZOO-1999. Before the induction of ED, the rats were fasted for 4 hours, after this time, alloxan monohydrate (Sigma-Aldrich) was administrated intraperitoneally (180 mg/kg). Animals with blood glucose values > 150 mg/dL were considered diabetic. Rats were maintained under these conditions for 12 months before sacrifice. Prior to sacrifice, body weight and blood glucose level were recorded. The rats were sacrificed by cervical dislocation and immediately skeleton dissection was performed. To prevent damage to the bone by a chemical treatment, the bones were cleaned using beetles, Coleoptera order and Dermestidae family. Our results show that the glucose level increased significantly from 53 ± 8 in the group for non-diabetic rats to values of *234 ± 39 for the group of diabetic. *p < 0.05 student’s t-test, n = 3 ♀, two weeks after induction and kept under these conditions for 12 months. This glucose level in rats corresponds to the clinical condition of non-controlled diabetic patients. Femur macroscopic parameters such as weight, length, and diameter of the diaphysis decreased  40%,  10%, ~ 7% respectively; while the diameter of the upper and lower epiphysis increased  2%,  10%. Analysis by Scanning Electron Microscopy (SEM) shows that the group of rats with ED increased femoral neck diameter  30% resulting in widening and deformation of the head of the bone (see Figure 1A and 1B).