Pablo Martínez-Torres

The cos²θ angular dependence of the effective thermal conductivity of composites with aligned anisotropic fillers has been theoretically predicted, but never experimentally validated for multiple orientation angles θ. Here, we validate this angular law by measuring the thermal conductivity of ferrofluids loaded with graphitized carbon nanofibers of volume concentrations up to 1.3% and five orientations (θ = 0°, 30°, 45°, 60°, 90°) with respect to a 200-G magnetic field. Using the thermal-wave-resonator-cavity technique, we find a three-fold enhancement of the thermal conductivity along the direction parallel to the aligned fibers. Lower enhancements with respect to the random orientation configuration are observed for other directions of two types of fibers. For all cases, the measured thermal conductivity follows a cos²θ angular dependence, which provides its first complete multi-angle experimental validation for predicting the thermal conductivity of oriented filler composites. These results can thus be useful to develop particulate composites for adaptive thermal management.

Ultrasonic fatigue at an operating frequency of 20 kHz was conducted on thermally treated clay bricks at 500, 750, and 1000 °C with a holding time of 5 h, using a three-point bending setup to assess their fatigue endurance. A Vickers hardness test was also performed on small clay squares thermally treated at the same temperatures, showing increased hardness values. X-ray diffraction (XRD) analysis was also performed, revealing temperature-induced changes in the clay chemical composition. Specifically, the illite transformation into spinel at 1000 °C contributed to a significant increase in hardness and, consequently, a diminution in fatigue life. A finite element simulation under different applied loads was performed to evaluate the von Mises stress behavior of the clay brick. Considering the change in mechanical properties, such as bulk density, at various temperatures. The simulation results show a corresponding behavior with the values of the Vickers hardness. This study provides a perspective on the relationship between ultrasonic fatigue, Vickers hardness, and thermal treatment.

We present the design of the mechanical structure of the mini Beam-Beam detector, a subsystem of the Multi-Purpose Detector, soon to enter into operation at the Nuclotron based Ion Collider fAcility of the Joint Institute for Nuclear Research. The miniBeBe detector was designed and is currently being developed by the Mexican team of the NICA Collaboration to contribute to the level-zero trigger of the Time of Flight Detector. The mechanical structure meets the requirements of minimizing the material budget and be free of ferromagnetic materials, without compromising its robustness. The design also allows for easy module replacement for maintenance and overall removal at the end of the first stage of the experiment, without affecting the rest of the subsystems, to leave room for the installation of the Inner Tracking System. In addition, a Finite Element Method analysis of the mechanical components under load was performed. Based on this analysis, it was determined that the design meets the space constraints within the Multi-Purpose Detector, as well as a deformation of less than 1 mm with overall stress of less than 2 MPa, such that no material used in the design is at risk of mechanical failure during operation. The heat transfer analysis of the cooling system revealed that the temperature of the cooling plate is maintained within a range of 19.00°C to 21.41°C, which is sufficient to ensure that the silicon photomultipliers operate below a temperature of 25.00°C, thereby optimizing their functionality.